Hello, I need help. I would like to know how to solve the following question, what Geometry/Physics you need to know for it.
Hello, I need help. I would like to know how to solve the following question, what Geometry/Physics you need to know for it.
A satellite is launched into a circular orbit around a planet with negligible radius in a direction tangent to the orbit at a distance R, and another satellite is launched with half the velocity of the first one. What is the minimum distance between the planet and the satellite during the orbit, in terms of R? <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/173.66.142.5|173.66.142.5]] ([[User talk:173.66.142.5|talk]]) 23:17, 29 April 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
A satellite is launched into a circular orbit around a planet with negligible radius in a direction tangent to the orbit at a distance R, and another satellite is launched with half the velocity of the first one. What is the minimum distance between the planet and the satellite during the orbit, in terms of R? <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/173.66.142.5|173.66.142.5]] ([[User talk:173.66.142.5|talk]]) 23:17, 29 April 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
== [[Hedge]] plants ==
I haven't found this in our article, but what causes a tree/shrub to be suitable as a plant for a hedge. a} I had read before that trees that you trim the top off die. Why isn't that happening when I trim e.g. a birch to be a hedge. b) Would fig trees work and could you still get figs from them if it were trimmed to be a hedge? [[Special:Contributions/76.97.245.5|76.97.245.5]] ([[User talk:76.97.245.5|talk]]) 23:47, 29 April 2009 (UTC)
Revision as of 23:47, 29 April 2009
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Ok; the idea of global warming is consistant with it being a natural process all we do as humans is speed up that process...
Has there been thought on the idea of creating a large volcanic eruption which would place large amounts of what ever into the atmosphere and thus help cool the earth...Simlar effect in Victorian times when global temp was reduced due to an eruption. The Year Without a Summer 1800 and something? To control this even would be extremly difficult of course but would it work? —Preceding unsigned comment added by 214.13.113.138 (talk) 08:41, 22 April 2009 (UTC)[reply]
Or maybe there could be a way to divert an asteroid (nuclear blasts?) so it falls into Earth, the impact of which will result in blocking out of the sun like it's frickin dinosaur extinction time. That might also achieve your goal.—Preceding unsigned comment added by 94.27.153.3 (talk) 10:00, 22 April 2009 (UTC)[reply]
I am afraid that your second method is just silly. Life on Earth would not exist without sunlight and furthermore, the impact of an asteroid on the Earth's surface would result in many deaths. --PST10:10, 22 April 2009 (UTC)[reply]
First, what do you mean by "natural process"? "Natural" like in "without human intervention"? We have caused this by releasing greenhouse gases into the atmosphere that disturbed the balance, and now the system is "readjusting", so the mean temperature will rise until a new equilibrium in energy received/energy lost is reached. It is true that in the past "natural" warmings occured (over thousands of years), but as far as we know nothing even roughly comparable to the situation today ever happened (warming the planet in centuries or even decades). We are to blame! Now coming to the question: What makes you think that we are able to trigger a volcanic eruption? I don't say it is impossible, but at least nothing like this has been tried before (for good reasons, I'd think), so it would at least be a really uncontrollable, dangerous experiment. But now to the main caveat: You are confusing climate change with the actual weather. Climate is something that happens on the scale of several years, but the cooling you mentioned mainly affected a single year and then quickly (in climate scales) disappeared. To the contrary, a much discussed theory is that vulcanic eruptions in the past could have triggered massive climate changes which added to or even caused mass extinctions, because many lifeforms could not adapt fast enough to the changing world. This is because vulcanos also emit greenhouse gases, and large vulcanos can put an awful lot of them into the atmosphere in a short time. So in summary: I think it would be a real bad idea to try something we don't understand (vulcanic eruptions) to cure something we don't understand (the climate). TheMaster17 (talk) 10:08, 22 April 2009 (UTC)[reply]
To the second question with the meteor: I hope this is irony, because the answer has to be nearly the same: we have no idea how to divert an asteroid, because of very many practical problems on the way. And even if we could, we would bring an incalculable element into an already incalculable situation. TheMaster17 (talk) 10:17, 22 April 2009 (UTC)[reply]
(Reply to both PST and TheMaster) I could be wrong, but it looks to me like those two anons are unrelated. I'm pretty sure 94 was trying to be sarcastic indicating that the first idea was likely to be very difficult to achieve and to have serious side effect and so was (almost?) as silly as the second idea which I guess he/she hoped the OP could more easily see as an idea which would never work. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
Well, of course the Earth has warmed and cooled before, but the current process is, as far as we know, different in that a) it's primarily driven by greenhouse gases (instead of them acting as a feedback to amplify an otherwise triggered warming trend) and b) it's a lot faster that anything we have seen before. So calling it "a natural process" that we "only speed up" is a very arguable position. What cools the Earth after a large volcanic eruption are aerosols, mostly sulfur-aerosols in the atmosphere. We have indeed injected a large number of those via industrial processes, and they have masked the early warming trend. Warming only became very notable when Europe and the US installed scrubbers to reduce acid rain and other negative effects of sulfur emissions. There also have been some proposals to actively introduce aerosols to reduce the warming. However, there are serious technical challenges and ecological side effects - and, since it's a global problem, it will be very hard to find a politically acceptable solution. Just imagine Mexico emitting large aerosol clouds that rain out as acid rain over Yosemite National Park, or emissions in Germany causing respiratory diseases in Poland and the Czech Republic. A final problem is that CO2 accumulates over a long time, while aerosols have a short atmospheric lifetime. So to counteract the effect of inreasing CO2 concentration, one would need ever-increasing aerosol emissions. There is some discussion at Mitigation of global warming. --Stephan Schulz (talk) 10:23, 22 April 2009 (UTC)[reply]
I think your point b is pretty worthless. Saying that the temperature is changing faster then anything we have ever seen before completely ignores the fact that written human history runs for thousands of years, and thermometers that operate independent of air pressure have only been around for 400 years tops. And do we have documents showing a daily temperature record for hundereds or thousands of locations so that we have a basis of comparison? I would say we don't have anything like that until the 19th century. So saying we have never seen anything like this before does not mention that we had our eyes closed the other 23 hours of the day. 65.121.141.34 (talk) 13:06, 22 April 2009 (UTC)[reply]
We don't have human recorded measurements but we do have quite good estimates of previous temperatures from ice core samples for example. Take a look at temperature record for more detail. We may have closed our eyes for the other 23 hours, fortunately there were cameras recording the 23 hours while our eyes were closed which we can now review. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
In fact, the icecore registers the temperature at the place where the evaporation happened, not the place where the snow fell. Since there is a lot og mixing between one and the other, The ice core turn out to be an excellent proxy for the past global average temperatures. Dauto (talk) 19:42, 22 April 2009 (UTC)[reply]
But temperature changes exist all over the planet, not just at one location. If anything, the temps at the poles vary more than on the rest of the planet, so any global temp changes would be well-preserved in ice cores. Thus, Antarctic ice cores are a good indication of the global temperature. Also, we can go back a few thousand years by looking at tree rings. Rapidly warming weather would favor some trees and hurt others, and the tree rings from those years would reflect that. StuRat (talk) 14:36, 22 April 2009 (UTC)[reply]
But things other then temperature can have a big impact on tree rings, like drought or flooding or fire. Is there a way to differentiate? 65.121.141.34 (talk) 15:11, 22 April 2009 (UTC)[reply]
Yes, but not perfectly. The general idea is that drought and flooding are local effects that last a small number of years. By looking at tree rings over wide geographic areas and over longer time periods you get plot a general trend. See Dendroclimatology. APL (talk) 15:56, 22 April 2009 (UTC)[reply]
Yes, it's only useful for relatively recent history. I've read articles about attempts to use it to go back farther than 1000 years, but never spectacularly far back. 2 or 3 thousand at the absolute most. Still just a drop in the bucket compared to geologic time periods. APL (talk) 20:21, 23 April 2009 (UTC)[reply]
from the temperature record article,
"However, coverage of these proxies (tree rings and ice cores) is sparse: even the best proxy records contain far fewer observations than the worst periods of the observational record. Also, problems exist in connecting the proxies (e.g. tree ring width) to the variable of interest (e.g. temperature)." I am not saying global warming does not exist, I am just saying that the evidence supplied is less conclusive then most people are lead to believe. 65.121.141.34 (talk) 16:15, 22 April 2009 (UTC)[reply]
I'm not sure what you are saying. Are you saying you don't believe global warming is happening or are you saying that because the record of the past is less accurate than the present there is a possibility that something like what is happening now might have happened before and therefore it cold be natural and not man made? By the way the Paleocene–Eocene Thermal Maximum only 55 million years ago looks like it had spikes of 3°C increases in less than a thousand years so there is a possibility that it was as bad as is happening now so that would bolster the second point of view if that is what you are saying. Dmcq (talk) 16:42, 22 April 2009 (UTC)[reply]
I am saying that there are holes in the theory that are not addressed well and thus it is not the scientific fact it is often purported to be. 65.121.141.34 (talk) 16:51, 22 April 2009 (UTC)[reply]
There may be holes in the theory, but your atempts here fall in the naive category. Denial isn't a scientifically acceptable alternative. Dauto (talk) 19:45, 22 April 2009 (UTC)[reply]
Yes, indeed. Scientist are humans like anybody else and can be partial. But we are not talking about a handfull of scientists. We are talking about the whole world wide community of climatologists. What you are proposing is a conspiracy involving the vast majority of the climatologists of the world. Unless you have some strong evidence to suport that idea, I think I am going to file it as an irrational conspiracy theory. Besides, what is the motivation behind that conspiracy? There isn't more money to be made just by supporting global warming theory. Dauto (talk) 00:16, 24 April 2009 (UTC)[reply]
Just because coverage is more sparse doesn't mean that it is inadequate. The question is, would we detect the current rise from the ice core? If we would, then the fact that the record is more sparse is largely irrelevant. Our excellent modern observation is good because we can see more carefully what is going on, it doesn't mean it's necessary to detect massive global warming Nil Einne (talk) 03:50, 23 April 2009 (UTC)[reply]
These kinds of ideas are what is increasingly being called "Plan B" amongst climatologists. If it's truly too late to stop emitting CO2 - or if we can't get international agreement - or if the 'runaway' scenario has truly kicked in - is there anything we can do to make the planet cooler and thus circumvent the worst of the danger? Well, volcano's definitely aren't it because they are actually a major contributor of greenhouse gasses. While the smoke from the ash plume would reduce temperatures for days, weeks, months or even perhaps a year or two - the CO2 it emits will still be in the upper atmosphere in 10,000 years time. So that particular trick certainly won't work. But there are other possibilities. It's known that the contrails from the exhausts of high altitude airliners is reflecting heat away from the earth to a small degree (it was noted that after the 9/11 attacks when all North American aircraft were grounded - the temperature shot up a couple of degrees!). So maybe we could make some more big white clouds up there and block sunlight that way? The really big problem with all "Plan B" approaches is that we really don't understand the complicated inner-workings of the whole planet to know whether one of these "cunning plans" would actually do more harm than good. For example - if we reflect away sunlight to make the earth cooler, plants that use sunlight to perform photosynthesis would do less well - this might result in disasterous world-wide crop failures - and since plants consume CO2 and output oxygen during photosynthesis - we might easily make MORE CO2 than we do now! In fact, it's hard (or perhaps, impossible) to imagine any kind of "Plan B" that might not have disasterous consequences. Worse still, these things have to be world-wide events - we're modifying the atmosphere for the entire planet - and you really can't go around doing that kind of thing without (at least) the agreement of all of the major governments of the world. While we may ultimately have no choice but to attempt something that wreckless - it would have to be a last-ditch effort when we know for 100% sure that we're doomed if we don't do it. But there are LOTS of "Plan B" ideas out there...covering large areas of the ocean with white foam polystyrene beads to make it reflect sunlight away...launching massive sun-screens into earth orbit to block sunlight...there are MANY choices! SteveBaker (talk) 19:19, 22 April 2009 (UTC)[reply]
As for aerosols such as sulfur dioxide, a better alternative is to launch them up to the stratosphere, where it doesn't interact with our weather. As for warming/cooling being part of a natural cycle, yes there has been a period of warming since the Younger Dryas, but that warming is no longer a part of the trend seen today. As for rapid climate change in the past, some of those events may have been caused by methane clathrate collapses (which are starting to occur today), but now instead of 3C of warming in several centuries (under 1,000 years), it could be 3C in several decades (less than 100 years). ~AH1(TCU)23:05, 22 April 2009 (UTC)[reply]
An ocean fertilization project has just failed - the algae bloom produced was just eaten by animals, which released most of the Carbon back into the atmosphere via their metabolic processes. [2] --Stephan Schulz (talk) 14:52, 23 April 2009 (UTC)[reply]
And see Law of unintended consequences. Intentional geoengineering in an attempt to offset our unintentional geoengineering that results from burning gigatons of fossil fuels is pretty scary. One should carefully review the history of previous engineering disasters, then scale up the risk to a global level. Engineering disasters occur when smart people get together and only anticipate some of the relevant consequences of their actions. See also Superiority (short story) and Wonder weapons. Technology can do some wonderful things, but it doesn't always deliver exactly the desired wonderful thing on the desired schedule. Technology develops best when people approach it incrementally, learning from their mistakes as they go. Humans cannot even write error-free software on the first attempt (or even after years of debugging by teams of skilled professionals). We don't have access to a "test planet" where we can try various geoengineering schemes to see how they will work, and to verify our models. --Teratornis (talk) 23:31, 24 April 2009 (UTC)[reply]
Ok stupid idea or not..i wasnt actully suggesting doing it i asked a THEORETICAL question of WOULD IT WORK? IE planet gets colder glaciers reform gulf stream stays blah blah blah....sure why not blow up the world divert astaeroids...Guess i need to solve the problem and argue about who is to blame NOT what i wanted suppose we could stick with recycle your fairy liquid bottles rock on the scientists! —Preceding unsigned comment added by 214.13.113.138 (talk) 07:26, 26 April 2009 (UTC)[reply]
People have already discussed why it may not work and the potential catastrophic side effects which could easily be worse then what you're trying to solve. There's not much more to say. As has already been mentioned there are a lot more ideas which are at least aren't quite as extreme which are being studied although even these already have many many difficulties and potential failings. No one bothers to study ideas which are so insane and inpractical that they aren't worth considering so you're not going to get much better then what has already been said. Also, I don't know of anyone who is arguing over who is to blame, except the denialists. Most people are arguing over how best to resolve it concentrating on things that are actually potentially possible. Nil Einne (talk) 01:53, 29 April 2009 (UTC)[reply]
B cell activation
Hi everyone just I have a couple of quick questions - Would I be correct in saying that B cells don't have to be activated by a helper T cell before they can produce antibodies? If they don't need helper T cells to activate them how are they activated in the absence of helper T cells - does another type of cell activate them into producing antibodies/forming plasma cells etc. or can they can activate themselves? If they can activate themselves (I don't know if they can or not)then wouldn't that render the helper T cell uneccessary in this sense? (I realise helper T cells probably have other functions aside from activating B cells.) Sorry if my questions are badly worded and thanks in advance to all who help! —Preceding unsigned comment added by 92.21.237.143 (talk) 11:21, 22 April 2009 (UTC)[reply]
"Some textbooks state that electricity within wires flows at nearly (or even exactly) the speed of light,[1] which can give the impression that electrons themselves move almost instantly through a circuit. The electrons in a typical wire actually move at a drift velocity on the order of centimeters per hour[2] (much slower than a snail). The random thermal motions of the electrons are much faster than this, but still much slower than light, and with no tendency to occur in any particular direction. It is the electrical signal that travels almost at the speed of light. The information that a light switch has been turned on propagates to the bulb very quickly, but the charge carriers move slowly.[citation needed]"
Wow, misconceptions are everywhere, including the Speed of electricity article and most of the things on the web that discuss this. When somebody asks for the "speed of electricity", what they usually mean is something like "If I switch on a light, how quickly does the signal travel from switch to light", or "if I send a signal along a wire, how quickly does it reach the receiver". To answer these questions requires cable theory. The answer you get depends greatly on the conductivity, boundary impedance, and capacitance of the wire, but it is always far slower than the speed of light. This article, for example, calculates the speed of signal transmission for a telegraph cable across the Atlantic -- a very fast carrier -- and gets a result of about 2x106 m/sec, or about 1/10000 of the speed of light. In other words, very fast in human terms (two seconds to cross the Atlantic), but very slow compared to light. The wires in your home are typically hundreds or thousands of times slower. For computer equipment, conduction speeds along wires are often an important design factor. Looie496 (talk) 18:21, 22 April 2009 (UTC)[reply]
The calculation for transatlantic cables may have been accurate in the days of the telegraph, but is not even close when most telephone cables are considered. Up until the mid-70s, transatlantic telephony used either satellite or copper cable. Satellite experienced noticeable delay, and cable did not. We can therefore estimate that the round-trip time was less than 100ms. Therefore for the signal to cross the atlantic, we can estimate a time of 50ms maximum, which is a speed of about 1x108 m/s, or about 1/3 the speed of light. --Phil Holmes (talk) 09:12, 23 April 2009 (UTC)[reply]
In a physics lab, we would send pulses down 200' coax cables and measure velocities of 2/3 c. Of course the pulse got smeared some and there are other issues to consider, but Looie's assertion that most wiring would be many orders of magnitude less than c seems unlikely to me too. Dragons flight (talk) 09:36, 23 April 2009 (UTC)[reply]
The way to imagine this (crudely) is to imagine an almost frictionless 200' long garden hose and some half-inch ball-bearings. If you stretch out the hose on level ground and roll a ball-bearing down the length of it - it might take 30 seconds to pop out of the other end. But if you fill the hosepipe full of ball bearings from end to end then if you try to push one ball in at one end - then another one pops out of the other end almost instantaneously. So even though the individual balls move fairly slowly - the time between stuffing one in one end and a DIFFERENT ball popping out of the other is quite short. The hose is a wire, the balls are electrons. The electrons move incredibly slowly - like watching the minute hand move on an analog clock. But when you push an electron into one end of the wire - a different one pops out the other end with a delay that's about equal to the speed of light. SteveBaker (talk) 19:06, 22 April 2009 (UTC)[reply]
Neat! Thanks for answers. The one I understand the best is from SteveBaker. That one I grasp the best and it makes sense on how the "speed of electricity" happens. --LordGorval (talk) 21:15, 22 April 2009 (UTC)[reply]
wikipedia article on E.D.T.A.[ethylene diamine tetra acetic acid]
in the above article,Uses in Medicine,Last entry is Use in Thalassemia Major to remove excess iron.Pl.indicate the reference of source i.e journal etc.thanks —Preceding unsigned comment added by 117.198.195.147 (talk) 12:59, 22 April 2009 (UTC)[reply]
Well to be fair to the OP, if our article says something (and it does "This therapy is used to treat the complication of repeated blood transfusions, which used in cases of severe thalassaemia") then it should be referenced (which it isn't). However that should be dealt with on the article talk page (which I've copied it to), not here Nil Einne (talk) 13:42, 22 April 2009 (UTC)[reply]
Yes, I know all challenged claims require a citation and are subject to removal if none is provided - but I got the impression that the anon was also interested in the veracity of the statement apart from just the quality of Wikipedia. Wisdom89(T / C)14:53, 22 April 2009 (UTC)[reply]
How to insulate an old home ?
My current house was built in the 1920s (I know, that's not old by European standards). The windows have all been replaced with triple-pane insulated windows. Now the problem is the walls. They are cold all winter long and hot all summer long. I don't believe there's any insulation at all (other than the bricks and wood of which the house is constructed, which offer minimal insulation value). The obvious answer is blown-in insulation. However, the wiring in the walls is sub-par and gets warm now. If it was buried under layers of insulation it might get hot enough the cause a fire. So, is there any way to insulate the walls, short of ripping all the walls apart to replace the wiring ? One thought we had was to disconnect the existing wiring, leave it in place, and install exterior mounted wiring to replace the wall wiring. This would then allow for blown-in wall insulation. Is this idea feasible ? Has anyone done this ? Any other ideas ? StuRat (talk) 14:11, 22 April 2009 (UTC)[reply]
Those sound like some possibilities. Do you know how much of an insulation value (R-factor) the thermal wallpaper provides ? StuRat (talk) 20:11, 22 April 2009 (UTC)[reply]
If your wiring is getting hot, you should definitely replace it. (5-10% of all deadly house fires in the U.S. involve electrical causes[4]) Wiring from that era probably has degraded insulation (mine certainly did) but more importantly as code standards and appliance usage have changed, the system may not be laid out to properly handle the much higher electrical loads we now use leading to overheating of the wires. Rmhermen (talk) 16:02, 22 April 2009 (UTC)[reply]
It should definitely be rewired to start with. The old wiring can usually be used to pull through the new wiring; it certainly won't mean ripping any walls apart, and your house will be a lot safer.--Shantavira|feed me15:59, 22 April 2009 (UTC)[reply]
My thoughts too exactly. The insulation on ancient wiring can quite easily crumble and cause a fire, never mind the possibility of shocks. Do it now before it does you in. Dmcq (talk) 16:07, 22 April 2009 (UTC)[reply]
When you do get to the insulation I think your idea of blow in is best to start with. The problem with having thin insulation trying to do the whole job is with any bits which have to stick through may tend to get condensation at times, but they can be good supplementing the main business. Dmcq (talk) 16:18, 22 April 2009 (UTC)[reply]
To do a good job of blowing in insulation, you will need to make holes in the plaster or wallboard anyway, and patch and paint as part of the job. Therefore, the incremental cost of putting the new wiring inside the walls rather than outside the walls is much lower: the incremental cost is mostly in the wall repair. Depending on where you live, you may want to make the walls thicker to hold more insulation. This involves removing the plaster or wallboard and adding studs another set of studs, which should be offset from the existing studs. Of course, with the walls open you are no longer restricted to blown insulation. -Arch dude (talk) 20:13, 22 April 2009 (UTC)[reply]
Everyone seems to think new wires can be pulled through the walls using the old wiring. I'm far more skeptical that thin, 90 year old wires with deteriorating insulation wouldn't just break. Also, the builders may well have attached the wiring to studs using staples. And the walls are made of wet plaster, so the thought of tearing them open is horrifying. What about my idea of leaving the old wiring in place, disconnecting it, and putting new surface mounted wiring in place ? Has anyone done this ? StuRat (talk) 20:08, 22 April 2009 (UTC)[reply]
In addition to the fragility, a 90 year old home with the original wires would likely have knob and tube wiring instead of free-floating Romex-style power cable. (Applicable words from the article "Currently the United States NEC forbids use of loose, blown-in, or expanding foam insulation over K&T wiring. This is because K&T is designed to let heat dissipate to the surrounding air.") -- 128.104.112.117 (talk) 22:29, 22 April 2009 (UTC)[reply]
There are ways of "snaking" wire through walls without pulling on the existing wire (which being metal should not have gotten any weaker - if it has it is an even greater fire hazard) Another problem with knob and tube (which was less common already by the 20s) is that some insurers refuse to write policies for houses that still use it. Rmhermen (talk) 00:49, 23 April 2009 (UTC)[reply]
My house is also of that period, but the previous owner did a major renovation. Where the original double brick walls are still in place, they are now lined with another layer of wall of standard frame construction, which allowed space for insulation and new wiring. All wiring and plumbing in the house was replaced. That's the sort of job you'd need to do things properly, but as you can imagine, it can be awfully expensive. I think you need to talk to a renovation contractor (or rather, several of them) to talk about what is possible and what it might cost. --Anonymous, 23:23:23 UTC, April 22, 2009.
Hi there, I've been revising Dynamics for a few days now and come across this question, and I'm not too sure where to go for the final part.
Two particles of masses m1 and m2 move under their mutual gravitational attraction. Show from first principles that the quantity is constant, where r is the position vector of one particle relative to the other and M = m1 +m2 .
The particles are released from rest a long way apart, and fall towards each other. Show that the position of their centre of gravity is fixed, and that when they are a distance r apart their relative speed is .
When the particles are a distance a apart, They are given equal and opposite impulses, each of magnitude I , and each perpendicular to the direction of motion. Show that subsequently , where ω is the angular speed of either particle relative to the centre of mass and µ is the reduced mass of the system.
Show further that the minimum separation, d, of the two particles in the subsequent
motion satisfies .
That's all okay until I get to the minimum separation bit, at which point I get a bit confused - could anyone let me know how to go about finishing this part of the question please? Thanks! :) Otherlobby17 (talk) 14:44, 22 April 2009 (UTC)[reply]
It is possible to rearrange the angular momentum as an Effective Radial Potential. This is a "pseudo"-potential energy field. When added to the gravitational potential, there is a minimum of potential energy (this is the optimal radius for stable circular orbit); and another point at even lower radius, where effective potential is equal to the gravitational potential at infinite radius (this is the minimum separation for the scenario you described). This derivation is detailed in Marion & Thornton's dynamics textbook. I will try to dig out my notes on the subject. Nimur (talk) 15:56, 22 April 2009 (UTC)[reply]
No need - here's Effective potential (which should probably be renamed to something less general, like "Effective potential due to angular momentum"). To find the minimum separation, just locate the point where initial energy equals the potential energy. The particle can go no further (so it is at the minimum radius) unless new energy is added from another source. Nimur (talk) 16:00, 22 April 2009 (UTC)[reply]
While the effective potential idea works, it is not the simplest way to solve that problem. Before the Impulses, the system had both energy and angular momentum equal to zero. The Impuses transfer energy and angular momentum given by the formulae:
and both are conserved thereafter.
At the point of minimun separation, the velocity has no radial component
, and
which gives us energy and anguloar momentum
Solving the system of equations we get from this it is easy to show that
Adverts for toilet cleaning products always boast about how they kill "99.99% of all germs" in the toilet (in the UK, at least). Now, correct me if I'm wrong, but people don't go around licking toilet bowls regularly, do they? Exactly what would be the problem with germs inside a toilet? Is this just more advertising BS designed to sell products to ignorant consumers, or do germs inside a toilet pose a genuine threat of which I'm ignorant? Vimescarrot (talk) 14:50, 22 April 2009 (UTC)[reply]
I am reminded of a study on household germ contamination I read. They found that the most contaminated places in most houses were the cloth or scrubber used to clean kitchen surfaces, and the chopping board; the latter having some particularly nasty germs. The head of the study was quoted as saying "In the average house if I was forced to lick either the toilet seat or the chopping board, I'd choose the toilet seat every time". DJ Clayworth (talk) 15:43, 22 April 2009 (UTC)[reply]
And I would answer that he obviously does not know what he is even doing with this study. Just because you find bacteria on a surface, does not mean that anybody will become sick from licking it. I, as a biologist with training in immunology, would rather stick with Vimescarrot's explanation: Nobody eats out of the toilet, but everybody prepares food on kitchen surfaces. To what germs will our body be more resistent? And the problem, in reality, is the other way round: By cleaning all those bacteria which normally live there, you pave the way for bacteria that normally cannot grow there (because the "normal bacteria" outcompete them) and which could be "real" pathogens (meaning they can really make you sick, because your body has no immunity for them). There are few surfaces, in a hospital for example, that really need to be sterile. Most other things are perfectly "healthy" in everyday live even when they are covered with germs, unless your immunesystem is severely compromised. TheMaster17 (talk) 16:02, 22 April 2009 (UTC)[reply]
So microwaving my dishcloths to kill the germs on them is a bad idea? What about the fact that my mother wipes bloodstained hands on a cloth meant for drying hands that have just been washed? =p Vimescarrot (talk) 17:44, 22 April 2009 (UTC)[reply]
The chopping board may be a special case. The expert may have been concerned about getting germs from raw poultry. I wonder how he'd feel about a dry counter top? (compared to a dry toilet seat) APL (talk) 17:46, 22 April 2009 (UTC)[reply]
The stuff inside the toilet bowl can contribute to foul smelling odors. Also, doesn't flushing release a small aerosol of bacteria in to the air above the toilet? I remember reading that somewhere, I'm sure someone will prove me wrong. Livewireo (talk) 18:05, 22 April 2009 (UTC)[reply]
The dishcloth one always gets me. Is that measured before you place it in hot water (to get it wet ready to wipe a side), just after and before using to clean or after cleaning? I guess my point is - the circumstances will matter as much to the number of bacteria as the place you are measuring. I would expect that the reason for most people to want rid of germs from toilet seats is that they A) sit on them with a part of their body they otherwise only wash daily (or potentially less) compared to touching something with your hands (which would be washed numerous times a day by most). Also toilets are a place where people go to get rid of their 'waste' so they associate them with being dirty/unhygienic as a result it'd make perfect sense for a marketing/branding dept to make a point about their product killing germs there. After all that it still matters whether the bacteria is harmful or not. Numbers alone are a bit of a con in comparison to the type of bacteria? ny156uk (talk) 19:11, 22 April 2009 (UTC)[reply]
It's true that in the UK these adverts make us feel like we are surrounded by monsters, and that we should get rid of them before it's too late. However, if they wanted to be honest, they'd say "kill 99.99% of germs (99.9999999% of those being harmless)". Laurent (talk) 19:28, 22 April 2009 (UTC)[reply]
There's no such thing as a harmless germ. A germ is defined as a microorganism that can cause disease. A harmless bacteria is not a germ. APL (talk) 20:12, 23 April 2009 (UTC)[reply]
Toilet bowls normally contain far more "germs" than toilet seats. And they can be harmful to you if someone else in your household has a communicable disease which you don't want to catch. They also look and smell bad when you get ugly growths on the sides of the bowl. It's true that you aren't likely to be exposed to those germs though, with exceptions for pets or small children which happily drink from and play in the toilet bowls. However, nothing fancy is needed to kill those germs, bleach will do the job, although you need to scrub the bowl to get the bleach on all the microbes. Bleach in a thick gel would be even better, as that can stick to the sides of the bowl long enough to kill whatever needs killing. Many toilet bowl cleaners are just that, bleach in a thick gel in a bottle with an angled neck for ease of delivery. Note, however, that bleach and other cleansers may be worse for the children and pets than the original germs were, so keep them out of the bathroom during cleaning. StuRat (talk) 19:45, 22 April 2009 (UTC)[reply]
Products that kill "99.99%" of germs are likely to leave behind ones that are now more resistant to the antibiotic spray, creating what are sometimes called "superbugs". Also, humans don't usually drink from a toilet bowl, but a pet dog might. Another thing, MythBusters confirmed that flushing the toilet brings a small number of the fecal germs up into the air, thus landing on other items such as your toothbrush (in very detectable amounts, even if placed in enclosed containers). ~AH1(TCU)22:48, 22 April 2009 (UTC)[reply]
Such products are not antibiotics and thus there is minimal risk of inducing the formation of resistant strains of anything - Disinfectants such as benzalkonium chloride generally do not produce tolerance. Wisdom89(T / C)22:56, 22 April 2009 (UTC)[reply]
I've noted much more guarded language from advertisers of these products of late - one I noticed a couple of evenings ago said "Kills up to 99% of known germs that may do you harm"...which is pretty much saying "It might kill some bacteria"! The word "germ" is carefully vague - is this bacteria? fungi? viruses? The advertiser's favorite get-out-clause "up to" is a good one. If there are some really virulent bugs, then 1% of them will plenty enough to harm you. Evidently it only kills "known" germs (known by whom?) - and it might only kill the ones that would do me harm...what about my pets or whatever? SteveBaker (talk) 00:08, 23 April 2009 (UTC)[reply]
Are you really serious about microwaving a dishcloth to kill bacteria? What makes you think that this will work? As far as I know, microwaves only really heat water, and most spores of bacteria are water poor, plus they have a small volume, are very damage resistant and repair capable. I would assume microwaving for a long time will reduce the number of viable bacteria, but kitchen microwaving is not capable of sterilizing something. My main argument stays the same: For 99.99999999... % of time that life on earth existed, there were no artificial antibiotics and no really sterile surfaces. Even considering that we have changed the rules lately (moving around the globe faster and changing the patterns of germs that can infect us, by changing the environment we live in), I'm totally fine with my immunesystem coping with the "usual" suspects like bacteria dwelling in my home, the soil, the food, the water or whatever I encounter on a regular basis. I think cleaning your home from 99.99% of bacteria on a regular basis does more harm than good, because you disturb the established pattern of microorganisms and so create a situation where really nasty things can creep into your home, that in addition are new to your immunesystem. I'm not saying that you shouldn't clean your home, but trying to keep it near-sterile every week is really overdoing it, without a clear justification why those things you try to eradicate should not peacefully coexist with you. TheMaster17 (talk) 08:12, 23 April 2009 (UTC)[reply]
I would assume that the idea is to heat the water in a damp dishcloth to boiling point (or so) and to keep it there long enough to sterilise it. But I'd be pretty surprised if that actually worked. If you merely warm it up to a nice comfy body-heat, you may actually be encouraging the bacteria to multiply. I strongly agree that an overly sensitive person can do more harm than good. Continually killing only 99% of bacteria simply encourages the remaining 1% to evolve to the point where you can't kill them that way. Better to reserve that killing capability until you actually need it for something. Also, it's been well documented that children NEED exposure to a wide variety of bacteria in order to develop immune responses to them. Children who are born into families of "neat freaks" get sick far more often than those of people with a more relaxed attitude to cleanliness. So, keep things clean - yes. Pay a heck of a lot of attention to places where you prepare chicken and such - but otherwise, chill out. We are able to withstand most of what the bacteria can throw at us without even noticing that we're doing it - and when we do get sick, modern medicine is there to help. Of course different rules come into play if you're actually immuno-compromised in some way (eg with AIDS or something). SteveBaker (talk) 11:53, 23 April 2009 (UTC)[reply]
A news report (this isn't it but it makes reference to it) recently recommended 2 minutes of microwaving as a way to sterilise dishcloths. MyhtBuster actually confirmed that there is no discernible difference between a toothbrush stored near a toilet in the bathroom and one stored in a seperate room, so I'm not sure which episode you saw...Anyway, thanks for this info, guys. :) Vimescarrot (talk) 18:05, 23 April 2009 (UTC)[reply]
I was surprised by that too, because I remembered reading often that microwaving was reported as being an insufficient treatment for reducing pathogens. (e.g. in reheating leftover hamburger.) This is the study you were referring to, I think [5] If you want something really germy forget toilets and cutting boards, women's handbags tested as being really icky on the outside. 76.97.245.5 (talk) 18:29, 24 April 2009 (UTC)[reply]
And then there are the handles on the doors of "restrooms" that are used by people who've had their hands up their arses or all over their family jewels (or whatever the equivalent term for the female variety is) and don't wash. Telephone mouthpieces too. -- JackofOz (talk) 20:59, 25 April 2009 (UTC)[reply]
No. White vinegar is distilled, and is basically pure, dilute acetic acid. White wine vinegar is vinegar made from white wine, and it retains some of the complex flavors associated with wine. IMO, white vinegar is not very useful for cooking due to its simple flavor (but can be useful for cleaning coffeemakers, etc.), while white wine vinegar is quite useful for sauces, vinaigrettes, etc. -- Coneslayer (talk) 17:05, 22 April 2009 (UTC)[reply]
White (distilled) vinegar can be used for cooking, but would be used in pickling or acidifying something (like the water used to cook poached eggs) when you don't want to add any additional flavors. I wouldn't use distilled vinegar in something like a vinaigrette or sauerbraten, where the flavor of the vinegar is a major component of the dish. -- 128.104.112.117 (talk) 22:23, 22 April 2009 (UTC)[reply]
I think I am probably just not trying the right search terms, but where can I learn more about the tendency of some birds to collect (e.g. steal) shiny things and other man made objects for use in their nests? I'd like to know more about which birds do this and what types of things they go after. Dragons flight (talk) 23:38, 22 April 2009 (UTC)[reply]
Magpies hoard food; that behavior is well documented. I know magpies are also said to steal and hoard shiny objects, but I'm not sure there is any rigorous scientific study of that. If they do that at all, I guess it must be an extension of the food hoarding behavior. Now the bowerbird that Steve mentioned is a different story altogether. In bowerbirds, collecting colorful objects is a part of a (pretty damn impressive) courtship ritual. --Dr Dima (talk) 05:14, 23 April 2009 (UTC)[reply]
@Phil I ran out of google patience for a scientific study on magpies stealing, [6]. But if you get a chance to look inside a nest you can usually see some "evidence". If you do have magpies nesting nearby you could also leave a small piece of chrome plated metal out. (OR: The biggest thing I've seen one make off with was a make up mirror. The one's I encountered didn't go for aluminum foil but would take paper chewing gum wrappers that were aluminum coated.) The members of the crow family (which include Magpies and Jackdaws) have been found to be quite bright and they do get bored and play. The Kremlin used to have trouble with some crows claw-scating down their dome and peeling the gold off the roof. 76.97.245.5 (talk) 18:02, 24 April 2009 (UTC)[reply]
April 23
NRPG ?
NRPG. I'm uncertain as to what it means, and don't know where it is located in the CNS. Possibly called the Nucleus reticularis paragigantoceullaris, it definately excites the Raphe magnus and is involved in opiod modulation of pain transmission. Is that what its called and am I correct in assuming its next to the gigantocellular nucleus. Any help would be most appreciated, many thanks MedicRoo (talk) 01:15, 23 April 2009 (UTC)[reply]
Googling informs me that it's located in the ventrolateral part of the medulla oblongata, and that your speculations are correct. Looie496 (talk) 16:51, 23 April 2009 (UTC)[reply]
Light through optical centre
Imagine that a light ray passes towards the direction of the optical centre of a convex lens.
when the light ray strikes the lens from air, it is not normally incident. So, it must be bent towards the normal at that point. It means that it will not pass through the optical centre. Even if it does, as it emerges out of the lens, it is not normally incident on the glass-air boundary. So it will be shifted away from the normal. It means that the light ray will emerge parallel to the incident ray. But the wiki article says that it will not get deviated. Please Explain with diagrams--harish (talk) 01:28, 23 April 2009 (UTC)[reply]
You didn't say what article you're talking about, but in any case, the ray will only emerge parallel to the incident ray if the angles of bending are exactly opposite when it enters and leaves the glass, which will only happen if the glass surfaces are parallel on both sides. For a convex lens as shown in the figure, the two sides of the glass are not parallel. Looie496 (talk) 02:46, 23 April 2009 (UTC)[reply]
The two surfaces are papallel at the center of the lens which seems to be the point of the question, though that is not entirely clear to me. Dauto (talk) 04:22, 23 April 2009 (UTC)[reply]
The image is poorly drawn. The upper and lower rays are shown changing direction by refraction at both lens surfaces, as occurs with a lens of real thickness, while the purported central ray is unreal as the OP noticed. To be consistent with the thin lens approximation, the rays should change direction only at the center line of the lens (and in that case the central ray can arguably be drawn as it is). Cuddlyable3 (talk) 00:08, 24 April 2009 (UTC)[reply]
So, the total answer is that the ray will experience a little bit of deviation if it is not along the principal axis. Right?--harish (talk) 01:11, 24 April 2009 (UTC)[reply]
I heard of the news today that medical research has shown that the use of Bonjela and similar over-the-counter treatments contain salts which could cause liver and/or brain damage in children under the age of 16. I'm curious in knowing which chemicals in Bonjela cause these side effects, and why the risk of damage to adults doesn't exist. Is it due to a more developed blood-brain barrier or maybe a metabolic deficiency that disappears over the age of 16? I can't find much reason why the same salts wouldn't cause toxic effects in adults. Regards, --—Cyclonenim | Chat 07:08, 23 April 2009 (UTC)[reply]
Bonjela contains similar ingredients to aspirin, whose use is strongly correlated with Reye's syndrome in small children. That article itself mentions that the cause really is unknown, and my quick search of google scholar shows that this is still a very active area of research with little concrete evidence on any reason for the link, although the link itself is very firmly established for at least injested pills. Someguy1221 (talk) 07:41, 23 April 2009 (UTC)[reply]
Bonjela is amazing. I found it far more effective in treating mouth sores than comparable U.S. products. I have bought it from a London chemist at astronomical shipping charges after the tube bought in Britain ran out. Are they reformulationg it somehow to correct the problem but maintain the effectiveness? Edison (talk) 19:09, 23 April 2009 (UTC)[reply]
There was some iodine-compound stuff my friend managed to bring back from Sweden I think, and it's insane, you apply it and ulcer never comes back. Shame it's banned for whatever reason in the UK. Bonjela is the next best thing for us over 16s :) Regards, --—Cyclonenim | Chat 14:04, 24 April 2009 (UTC)[reply]
Oh, and to answer your question, they've just made packaging more obvious that under 16s shouldn't be using it, just like aspirin. Bonjela Teething Gel doesn't contain the salicylates, and therefore can still be used on chilren from 2 months to 16 years. Regards, --—Cyclonenim | Chat 14:05, 24 April 2009 (UTC)[reply]
What could a super-large telescope array see?
I understand that the resolution or amount of detail that can be seen by telescopes, both optical and radio wave, increases with their width. And that very wide telescopes can be simulated by joining up two or more widely-spaced telescopes in an array. I know such arrays have been formed of radio telescopes at least. I'm not sure if optical telescopes have been linked like this yet, or if that is something for future technology.
My question is, if you had a very long baseline for two or more telescopes, such as one telescope being on earth and another on the moon or even on Neptune or Pluto, would the amount of detail be enough to see planets orbiting stars, or even see some surface detail on those planets? And is there any theorectical limit to the length of the baseline? 89.242.82.4 (talk) 10:56, 23 April 2009 (UTC)[reply]
What becomes tricky on very large scales is the speed-of-light limitations in the communications path between telescopes. Also, no matter how far apart you put your telescopes, their light-gathering abilities don't get any better - so imaging very dim objects doesn't really improve. SteveBaker (talk) 11:42, 23 April 2009 (UTC)[reply]
(ec) The technique is a type of astronomical interferometry called aperture synthesis. It's been done for a long time in radio astronomy; Very Long Baseline Interferometry can link radio telescopes across the entire face of the Earth. High-precision atomic clocks allow radio astronomers to synchronize and combine radio signals from widely separated telescopes.
The problem is quite a bit more difficult at optical wavelengths. Because radio waves are typically a million times (or more) longer than visible and near-infrared light waves, the problem of 'lining up' the data from multiple radio telescopes is correspondingly much easier than it would be for a similar array of optical telescopes. (On the plus side, the much-shorter optical wavelengths mean that comparable resolution can be obtained with a much smaller baseline size.)
Nevertheless, a substantial number of optical interferometers now exist: List of astronomical interferometers at visible and infrared wavelengths. One of the largest is the CHARA array in California; its six telescopes are linked optically through a series of vacuum-filled pipes to generate a 330-meter (1100-foot) baseline. Together, they can resolve features down to 0.0005 arcseconds (0.5 milliarcseconds) — in 2007 they generated images of the surface of the star Altair, 17 light years away.
The twin 10-meter Keck telescopes in Hawaii can be linked optically to generate a very sensitive nulling interferometer with an 85-meter baseline. In that configuration, they are aimed at a star and configured so that the light from that star is optically cancelled-out between the two telescopes. Off-center light – as from an extrasolar planet – doesn't get cancelled out. In principle, the planet should become visible once it's no longer drowned out by the glare of its star.
Off the top of my head, I don't think there's any upper limit imposed by physics on the size of an interferometer array. The real bounds are the limitations of engineering. For an optical interferometer to work, you need to know and maintain the relative positions of the components with a precision of less than one micron (smaller than the wavelength of the light you're collecting). It's painstaking but possible to do when you've got a group of telescopes all together on the same mountain; it's a nightmare to manage if you want to put the telescopes further apart. Proposals exist for space-based optical interferometers as well, though as far as I know none are currently under construction. TenOfAllTrades(talk) 12:10, 23 April 2009 (UTC)[reply]
I don't want to spoil your wonderful answer, Ten, but I have to say that "vacuum-filled" made me do a double-take. Deor (talk) 13:08, 23 April 2009 (UTC)[reply]
Ha! Yes, I winced a bit when I typed it, too. I figured the minor scientific blasphemy could be excused for the sake of clarity of meaning. (When I was drafting the post, my original response described the system as being linked by 'vacuum tubes' — precisely correct, but horribly confusing to anyone who read the phrase as meaning the electronic device rather than simple empty pipes. I also toyed around with 'evacuated' tubes, but that leaves one shaking one's head at the obvious necessity to remove people from the light path.) TenOfAllTrades(talk) 19:47, 23 April 2009 (UTC)[reply]
I think too much is made of these kinds of "minor blasphemies". The meaning is perfectly clear in context and the phrase is entirely useful. Language is just language - it doesn't have to reflect precisely the deep-down scientific truth - so long as everyone is clear about what is meant by it. SteveBaker (talk) 03:34, 24 April 2009 (UTC)[reply]
The only limit imposed by physics on the size of those arrays that I am aware of is the coherence length of the radiation. This length is proportional to the square of the wavelength, so it becomes an increasingly harder problem to deal with as the wavelength beeing used becomes smaller. The coherence length is also inversely proportional to the bandwidth so it is possible to get arbitrarily large length simply by using arbitrarily narrow bandwidths. There is no free lunch though. An arbitrarily narrow bandwidth makes the source arbitrarily dim and hard to see. There's a trade off here that is taken into consideration when deciding how large to build an telescope array. Dauto (talk) 18:04, 23 April 2009 (UTC)[reply]
So if you did have an array consisting of optical telescopes on the earth and the moon, or at equivalent distances on satelites, and assuming the engineering problems were overcome, then would you be able to see any surface detail on planets orbitting stars? The baseline distance would be far greater than that of current arrays. Is there any formula that relates array width to resolution? 89.241.44.96 (talk) 10:10, 25 April 2009 (UTC)[reply]
Does it seem like perpetual black night? Or might it even be whiteness, or nothingness? The blind spot on the eye is more like nothingness or whiteness rather than blackness, with the brain seeming to fill in what is there from the surrounding image. See http://www.colorcube.com/illusions/blndspot.htm As there are various causes of blindness, so the subjective experience may differ. 89.242.82.4 (talk) 11:07, 23 April 2009 (UTC)[reply]
For people who have been utterly blind since conception, whole areas of the brain related to vision don't develop so I doubt there would be any sense of 'blackness' - just no vision sense at all. That's impossible for a sighted person to even imagine and discussing what that means with a blind-since-birth person results in no common terms of reference. They can't explain what it's like to not have a sense that they never had. Can you explain to a dolphin what it's like to have no echolocation sense? Or to a fish, how it feels to have no lateral-line electrical sense? I don't think so. People who have become blind after being sighted will doubtless have a different sense of what it's like. SteveBaker (talk) 11:40, 23 April 2009 (UTC)[reply]
I once heard someone saying (I am not blind) that a completely blind person can see just as much with their eyes as I can see with my knees. That makes it pretty clear for me... -M —Preceding unsigned comment added by 195.67.112.146 (talk) 12:21, 23 April 2009 (UTC)[reply]
There is a phenomenon in perception (I'm blanking on the name right now, but it's related to change blindness and inattentional blindness) where the mind subtracts out a constant stimulus. It still may be registering at the sensory nerves, but after a while it is no longer perceived consciously. You've probably experienced this yourself. If there's a humming fan, after awhile it no longer registers, but when it turns off you can "hear" the silence. Likewise with scents - after a short period in a strongly scented room, you no longer can smell anything "off", but leave and reenter and the smell hits you. I would imagine the same would happen with a blind person. Immediately after becoming totally blind they might register a strong white/strong black perception. But after a while with that constant stimulus, the brain would ignore the signals coming from the optic nerves completely, and they wouldn't "see" anything at all. -- 128.104.112.117 (talk) 14:38, 23 April 2009 (UTC)[reply]
I have a blind friend who experiences different colours depending on the circumstances he is in, particularly when talking to certain individuals. I generate a blue/green colour. Normally he is not aware of any colour because he is not 'looking' but concentrating with his other senses. Richard Avery (talk) 14:54, 23 April 2009 (UTC)[reply]
I'd bet that too - otherwise how could he know that this 'color' is blue and not pink? If you'd never seen blue or pink they be just arbitary labels. Assuming Nil Einne is right (and it seems very likely) then this is just a case of synaesthesia - which is a rather well-known phenomenon, even in sighted people. SteveBaker (talk) 20:05, 23 April 2009 (UTC)[reply]
I linked this article before, but you might find it interesting in this regard. [8] It illustrates that even when a blind person regains sight the brain is having trouble interpreting what it is "seeing". 76.97.245.5 (talk) 17:22, 24 April 2009 (UTC)[reply]
Why do people collect things / derive satisfaction from completing sets of objects?
I am well aware of hoarding, but I'm interested in the more mundane and widespread human compulsion to collect things. I know we're not the only animal to do this, but I'm having a hard time seeing the evolutionary value of such a finely honed desire to accumulate things.
I'm sure there are occasional cases where an impressive collection of _____ resulted in the acquisition of a mate, but I doubt that that was the conscious goal of the collection to begin with.
So... why do (most) humans feel a need and derive satisfaction from collecting things? What is it about a complete set that soothes the mind? Oftentimes these objects serve no use other than to occupy space (and please the collector...)
61.189.63.224 (talk) 13:00, 23 April 2009 (UTC)[reply]
Not all human desires/traits are linked (clear or otherwise) to an evolutionary reason. We could speculate that things that are collectable have their roots in effort/time/reward. It takes time and effort to get a complete set of something, so the satisfcation is the reward. If you receive a complete set instantly it wouldn't have your emotional journey attached to it. I'm not sure that everything needs to have an evoluntionnary reason for existence. 194.221.133.226 (talk) 13:52, 23 April 2009 (UTC)[reply]
Just a guess: In prehistoric times collecting nuts and berries (food) may, on occasions, have made a difference between survival or not. Equally, gathering bits of timber (fire) and heaps of rock fragments (defense / tools) may have given some hominids an advantage in survival. Collecting stamps, beer coasters or Van Goghs could be just a sublimation of this. --Cookatoo.ergo.ZooM (talk) 14:23, 23 April 2009 (UTC)[reply]
Is it possible that it's a learned behavior planted in our heads by society? How many times in your life have you heard the phrase "collect all six" (or whatever quantity)? Is the drive to collect a set universal in all cultures, or only in capitalistic societies? 168.9.120.8 (talk) 14:29, 23 April 2009 (UTC)[reply]
Also note that extreme cases of "collecting" are considered compulsive hoarding and are classified by many psychologists as a personality disorder. In extreme cases, it can be linked to a variety of more serious conditions such as addiction, delusion, and obsessive-compulsive personality disorder. Viewed from this perspective, "collecting" may be seen as a disorder, rather than an vestigial evolutionary habit - but of course it depends on the severity and how much it interferes with other activities. Nimur (talk) 15:42, 23 April 2009 (UTC)[reply]
There is obviously value in an evolved tendency to collect stuff like food or sticks for a fire - but as the OP points out - we may get highly obsessed with having one of every kind of postage stamp released by Tibet - yet have no interest in collecting 400 almost identical postage stamps from Tibet. That's a totally different behavior. We would have no evolutionary advantage to collecting one of every kind of berry from the bushes near our caves - yet that's what we do with postage stamps. My guess is that it has more to do with tool use. When going hunting - you need one knife, one axe, one spear, one bow, etc - it's important not to leave without your complete "set" of tools - and it does you no good to have six knives with you if you forgot your spear. But that's a really wild guess...I bet the real answer is REALLY interesting! SteveBaker (talk) 16:29, 23 April 2009 (UTC)[reply]
It could just be a self-fulfilling thing. We collect things that are valuable, complete sets are often deemed more valuable than the sum of their parts, so we collect complete sets. There doesn't need to be a reason for complete sets to be considered valuable, they are because they are. It's like fiat currency. It has no inherent value, but because everyone thinks it has value, it does have value. --Tango (talk) 16:48, 23 April 2009 (UTC)[reply]
This same compulsion may be the cause of some Wikipedia editors creating stub articles about every highway exit, or other things that can be linked by succession boxes. The same satisfaction may accrue as when someone pops yet another US state quarter into an album. Edison (talk) 19:04, 23 April 2009 (UTC)[reply]
I have over 300 toy MINI Coopers...but I don't think they're valuable (well, except maybe one or two of them). It's not a matter of value...there is some deep obsessive streak in many people. Why we have that is hard to say - but it's clearly not the hope of monetary reward. SteveBaker (talk) 20:05, 23 April 2009 (UTC)[reply]
Collecting things isn't a particularly human trait. Just a couple of non-food examples: Bowerbirds collect all sort of decorative material to attract mates. Magpie nests often feature collections of lost glasses, spoons and assorted shiny objects. (Oops already mentioned in a post a bit higher up :-) Birds roosting on rocky ground steal pebbles they consider attractive from neighboring nests. Octopus vulgaris uses shells and other collected items to protect it's eggs. Hermit crab are well known for their skills in decorating their shells with all sort of debris and anemones. Domestic cats and dogs are sometimes found to have a hiding spot for socks, gloves, hair ties or shoelaces that they "collected". 76.97.245.5 (talk) 17:06, 24 April 2009 (UTC)[reply]
The O.P. wrote: "I doubt that that was the conscious goal of the collection to begin with." In fact most adaptive behaviors do not result from conscious goal-formation. For example, most of the time when one human feels sexually attracted to another human, the cause of attraction is rarely a consciously felt desire to create offspring. In many encounters, perhaps even most, one or both partners have a consciously felt desire to thwart procreation. Quite clearly, in the ancestral environment it was not necessary to consciously desire children - it was only necessary for people to desire sex, and then be willing to love and care for the products.
As I pointed out before though - simply collecting a large number of food items in order to survive the winter isn't the kind of behavior our OP is interested in. The question is about the tendency for people to want complete collections containing one (and typically, only one) of every representative of some kind of set. You would not want a thousand very similar empty coke cans on a shelf in your garage - but there are people who try to have one of every variation on the coke can from 1950 or whatever. Someone who had a thousand empty coke cans with no particular 'meaning' to them would be labelled kinda crazy. Someone who had a collection of every different can Coke ever made would be considered somewhat amazing - but not really crazy. That's clearly nothing like the same behavior. We can easily understand the evolutionary drive to acquire large amounts of 'stuff' - but where did the drive to collect just one of each different 'something' to make a set come from? It's hard to guess. SteveBaker (talk) 00:22, 25 April 2009 (UTC)[reply]
Also as I suspect some contributors can such as SB attest to, collecting 300 Tibetian stamps, wikipedia highway articles, US state quarters, beer coasters or toy Mini Coopers, doesn't generally help to attract mates. Nil Einne (talk) 20:08, 25 April 2009 (UTC)[reply]
I have a collection of about 2,500 LPs, many of which I still play frequently (partly because I have some rarities that have not yet made it to CD transfer, and partly because I prefer the sound of LPs, even on crappy equipment such as I have). My collection includes some LPs that I played once, and never again. It also includes some LPs that I never played at all. These include the start of the complete set of Haydn symphonies (he wrote over 100 of them). A complete set occupies about 50 LPs. I acquired about half of them, then the company that produced them went bust or something. Although I've never played any of them (well, maybe just a couple), I've always been deeply, profoundly dissatisfied at owning only half the set. I've often asked myself: since I'm not that interested in Haydn, why did I start collecting his symphonies to begin with? I still have no answer to that. All I know is that my life would be immeasurably richer if I owned a complete set of unplayed Haydn symphonies rather than half a set of unplayed Haydn symphonies. Go figure. -- JackofOz (talk) 20:52, 25 April 2009 (UTC)[reply]
You might like to try Brain food, section 3.10 seems to have a few words about dietary brain enhancers. Most foods purported to assist brain function are of dubious value, but there's no accounting for placebos. Richard Avery (talk) 14:49, 23 April 2009 (UTC)[reply]
Wodehouse in the Jeeves account (early 20th century) was reflecting a common belief. Fish had been considered "brain food" way back in the 19th century, and nutrition books in the 21st century still claim it is "brain food," with some dissent that it is not particularly a brain food. See Google book search:[9]. Edison (talk) 19:01, 23 April 2009 (UTC)[reply]
Sugar enhances brain function over the short term by enhancing arousal, if you don't eat too much. Over the long term, I'm not aware of any solid evidence for foods whose value for the brain is different from their value for the body in general. You'll find vast numbers of claims all over the place, but solid evidence is sorely lacking. Looie496 (talk) 16:44, 23 April 2009 (UTC)[reply]
Grace Slick of Jeffersen Airplane in the song "White Rabbit" urges us to "Feed your head". It is not clear with what, but the audience at Woodstock seemed to know what she meant. Peace. Cuddlyable3 (talk) 19:25, 23 April 2009 (UTC)[reply]
Whilst not conlusive, there is a lot of evidence in support of the theory too. See [10], [11], plus many more in support on PubMed. The topic is still under heavy debate, but most articles seem to confirm the effect of n-3 fatty acids on the brain. Regards, --—Cyclonenim | Chat 23:36, 23 April 2009 (UTC)[reply]
Many infant formulas are fortified with DHA (Docosahexaenoic acid) as DHA is used in metabolic pathways in the production of phospholipids found in the brain. It is also of rather high concentration in natural mother's milk. Primary natural source of DHA? Fish oil. Jeeves may have been on to something. --Jayron32.talk.contribs00:45, 24 April 2009 (UTC)[reply]
In case you're not kidding, let me say that I only add my name after I add the resolved flag to show that it's my opinion, based on the original poster's comments, that this question is now fully resolved. If you were kidding, then sorry to be such a nuisance. StuRat (talk) 07:48, 24 April 2009 (UTC)[reply]
Minimum amount of fuel to circumnavigate the globe
If you were limited to travelling only by propulsive transport (ie no bikes, swimming, hangliding etc) what is the minimum amount of fuel that you would have to use? And presuming that different vehicles will use more/less efficient fuel etc, what's the least amount of CO2 you'd emit doing it? If anyone has any thoughts that'd be great. 86.8.176.85 (talk) 19:18, 23 April 2009 (UTC)[reply]
Well, assuming you aren't going to let us use yachts or sailing ships or hot air balloons of any kind - the Virgin Atlantic GlobalFlyer circumnavigated on about 10,000kg of JP4 jet fuel. That was a solo flight in one of the most efficient planes imaginable - so it's probably about the best you can do in a plane. Concorde needed about sixty times as much fuel (and consequently, six refuelling stops) to do the same thing. Doing the trip in a boat ought to be a lot more efficient...especially if you can cheat and use sails. SteveBaker (talk) 19:57, 23 April 2009 (UTC)[reply]
If you don't count the fuel you use in the 1st 10 minutes, a satellite really can go around thousands of times while using no fuel. Otherwise, I would say That a helium balloon would do pretty well. 65.121.141.34 (talk) 20:29, 23 April 2009 (UTC)[reply]
The trouble with a helium balloon is that you do actually need to consume helium and ballast on those long flights because you have to 'steer' by rising up and dropping down into the wind currents that happen to be going in the direction you want to go. Doing a round-the-world trip on helium alone would be really tough! There are various hybrids of helium balloons and solar-heated hot-air (a "rozier"), for example. A rozier was the first balloon to circumnavigate the world - but it needed a lot of propane still - certainly less than the GlobalFlyer thing...but I suspect our OP won't let us use balloons. I love the satellite idea though - that's great! SteveBaker (talk) 20:38, 23 April 2009 (UTC)[reply]
As always, this sort of thing comes down to clearly defining some ambiguous criteria. As noted above, how strict is "propulsive"? Sailpower seems rather obviously against the spirit of what you've requested, but consider these less-obvious problems:
GlobalFlyer flew west-to-east to benefit from the jet stream, a non-propulsive ~150 kph boost
Satellites, considering launch propulsion, launch from west-to-east to benefit from the Earth's rotational velocity, a non-propulsive ~1500 kph boost.
Ships of various forms often exploit ocean currents, non-propulsive ~5 kt boosts.
Additionally, why disallow bikes or swimming? Humans require fuel and a decent CO2 estimate could be made.
For some specifics, the S9G reactor used in Virginia-class submarines has a design lifetime of 33 years and an estimated reactor mass of 360 kg.[12] The USS Triton required two months to circumnavigate the globe (the first submerged circumnavigation). The Virginia would "use" 1.8 kg of reactor mass over that time frame, with effectively no CO2 emissions associated with propulsion. — Lomn21:15, 23 April 2009 (UTC)[reply]
To be complete, I'd argue you also have to amortize some cost for the radioactive nuclear vessel and other stuff that, upon decommissioning, has to be trucked somewhere to be buried and monitored for the next 10,000 years. Tempshill (talk) 22:15, 23 April 2009 (UTC)[reply]
A Cessna 150 cruising at 198 km/h consuming 23 L/hr of Avgas should be able to fly a 36 787 559km circumnavigation consuming 4 273 302 L. I wonder whether the OP wants such an abstract calculation or practical information?
The good news is that thousands of Cessnas have been produced so they are readily available, not too difficult to fly and you have room for a passenger. The bad good news is that the standard aeroplane needs a LOT of refuelling stops, about every 600km. Arranging that on land would need international negotiations and almost certainly demand a longer route. Over the oceans....well, if you are in no rush you could beg "friendly" aircraft carrier captains to let you land and fill up. Cuddlyable3 (talk) 23:44, 23 April 2009 (UTC)[reply]
You might want to check your decimal point – the circumference of the Earth is roughly 36 thousand kilometers, not 36 million. That would make a much more reasonable four thousand liters of fuel. Cheers! TenOfAllTrades(talk) 01:50, 24 April 2009 (UTC)[reply]
Eeek! I'm not sure I'd want to contemplate landing (or taking off for that matter) from an aircraft carrier in a Cessna 150! It's a seriously scarey business in something like and F18 that's designed for the job. The lack of an arrester cable hook would mean you'd either have to pull off some impressively short landings or smack into the crash netting each time. The relative fragility of the landing gear would demand really smooth seas when you did it - and I honestly wouldn't want to be in a Cessna that's hooked up to a modern deck catapult for the take-off run! If you have to stick to land-based routes, you'll be taking some considerable detours...but still, I think you could do it using marginally less gas than the Virgin Atlantic GlobalFlyer - so perhaps this is still the best solution so far in terms of fuel efficiency. SteveBaker (talk) 03:30, 24 April 2009 (UTC)[reply]
The stall speed of a Cessna 150 is only 42 knots, minimum ground roll for landing is 450', 1075' for takeoff. Remember, the carrier would be travelling at least 25 and as much as 35 knots into the wind. No problem, no arresting gear or catapult required, it would be loads of fun, though a pitching flight deck might make it a little more interesting.—eric05:36, 24 April 2009 (UTC)[reply]
I don't remember which one, but in one edition of Microsoft Flight Simulator, landing some manner of Cessna on an aircraft carrier was one of the built-in "adventures". Who knows how accurate it was modeled. I'm not sure you'd be able to find carriers that carried the right fuel, though. (Maybe for helicopters?) APL (talk) 13:38, 24 April 2009 (UTC)[reply]
Well, the largest carrier on the planet is probably the Nimitz - it's entire deck is 1100' long - so your 1075' minimum take-off run would require you start at one end of the deck and you'd 'unstick' about 30' from the end...well, 30' minus the length of the plane - maybe you'd have three feet to spare. Yikes! But recall that the flight deck of a carrier doesn't work like that. The landing and take-off areas are both much shorter than the total length of the deck because the thing is designed to have planes landing and taking off simultaneously. Also, not many carriers are the size of the Nimitz - most are more like 800 feet long - and then you're flat out of luck for your take-off run. Worse still - the minimum take-off run you're quoting for a Cessna assumes a near-minimum take-off weight...and since we're nowhere near the next airfield - you're definitely going to be needing a full fuel load! As for steaming into the wind at 25 to 35 knots...yeah - it can definitely do that - but the turbulance that causes at the front and back end of the deck would flip a little cessna around like a dry leaf in the fall! You're going to need very light winds and a very, very calm ocean and the biggest aircraft carrier in the world to stand a chance in hell of doing that! (Maybe if we put a huge conveyor belt onto the carrier deck and landed on that?) ;-) SteveBaker (talk) 13:48, 24 April 2009 (UTC)[reply]
If your airplane needs 50 knots airflow over the wings to fly, which is very close to the requirements of our Cessna 150, a takeoff into a headwind of only 5 knots (which is 10 percent of the takeoff speed) will reduce the length of the takeoff run by approximately 19 percent over what would otherwise be required with no wind. A headwind of 25 knots (50 percent of the takeoff speed) will reduce the ground run by 75 percent. Eichenberger, J. A. (2003). Your Pilot's License. p. 183.
I've never been on the flight deck of a carrier, so can't speak to how much turbulence there would be.
Sorry, but typed in the distance for landing over a 50' obstacle rather than the short field takeoff distance, it's actually 735'[13]. As to takeoff weight, the distance quoted is for a 1600 lb. aircraft, 22.5 gal. fuel (max is 38 gal.), 340 lbs. for pilot and passengers and 76 lbs. for baggage. From the flight manual, 1600 lbs, sea level, 59°, 20 knot headwind, ground roll: 305'. No worries.—eric16:47, 24 April 2009 (UTC)[reply]
According to [14] which links to [15] and says "Cessna O-1B Birddog in the colors of the South Vietnamese Air Force. This aircraft was landed onboard USS Midway during the fall of Saigon in 1975, by a pilot who had never before landed on an aircraft", this was the only case of a Cessna landing on a aircraft carrier. I don't know how that compares to a 150 Nil Einne (talk) 15:57, 25 April 2009 (UTC)[reply]
The original questioner mentioned bicycles. Since you can't circumnavigate on a bike, the questioner must be thinking about switching vehicles. You could arrange your trip so that the last leg of the trip was made on a small, fuel efficient scooter carried on your original vehicle. I'm not saying it would be a safe thing to do, but you could cover about sixty degrees of longitude by scootering across Africa sticking reasonably close to the equator.
But then again, if you're going to take it to that ridiculous level, you might as well go all the way and procure some sort of solar car.APL (talk) 02:24, 24 April 2009 (UTC)[reply]
And if you're not in a hurry - or under any cost limitations - then a solar boat would not be out of the question so you don't have to worry about putting the car on a boat in order to get it across the wetter bits of the planet. The point is that if you have no time or budget constraints, you could use a series of electric cars and boats with batteries charged from solar panels - lined up waiting at each port of call along the way. But truly, a yacht makes more sense...plenty of people have sailed around the world using nothing more than the wind and a technology that's been around for thousands of years - it's a very do-able thing. This is one of those questions where you have to keep excluding the obvious, practical answers in order to get the answer the OP wanted - and that just gets silly! The proper answer is: zero...unless you're in a hurry or trying to do it within a particular budget. SteveBaker (talk) 03:30, 24 April 2009 (UTC)[reply]
Wow, thanks for ll these great answers guys. In answer to your musings, I'd be fine with any vehicle as long as it is powered by more than human energy, although I guess I'm more interested in fuel-burning methods. I like the ideas of a nuclear submarine and a solar car, though. I'd be fine with vehicle changes, and I'm interested in both hard numbers answers and "well, if you put a flux capacitor on a jetpack, then..." sort of answers too. Thanks, again, you've all been great. 86.8.176.85 (talk) 03:25, 24 April 2009 (UTC)[reply]
LAMP is Lutheran Association of Missionaries and Pilots. They fly donated planes across the oceans for Christian mission work, including providing planes for medical flights in third world countries. I read of one such plane which was flown from California to Hawaii enroute to Asia. It was a single engine small plane with extra fuel tanks, making a near-suicidal long duration over-water flight. When it contacted Honolulu air control, it was give priority for landing over larger commercial craft. They routinely do what are, basically, Charles Lindbergh flights.Edison (talk) 05:36, 24 April 2009 (UTC)[reply]
If you are not in a hurry, you could sit where you are and wait for plate tectonics to take you at least part of the way around in a few hundred million years. Best to position yourself as far as possible from a subduction zone, however. A somewhat faster option, but also not guaranteed to work, and probably not something you could survive, would be to seal yourself into a Drifter (floating device) and release yourself into the ocean. I'm pretty sure that some of these devices have circumnavigated the globe. Neither option requires any fuel for propulsion, but if you wanted to survive a circumnavigation in a drifter, you would probably need to pack enough food to last for several years, along with enough clothing to handle whatever climate regions you drifted through. --Teratornis (talk) 22:56, 24 April 2009 (UTC)[reply]
Nobody, except at the very beginning, said anything about latitude. If you start far enough south, you can go around many times, using this for propulsion, without needing to refuel until after several times around the world. And there's even a place where they have the fuel that you'd need to go around the world that way! Nyttend (talk) 12:50, 26 April 2009 (UTC)[reply]
Among the vertebrates, as far as I know, cats (but not lions), fennecs, and some snakes have vertical slit pupil; and goats have horizontal slit pupil. Frogs and toads have a variety of pupil shapes. Most others have a round pupil. Of the invertebrates, cephalopods have some pretty interesting eyes. A slit pupil is associated with eyes that have multifocal optics [17]. In addition to the slit pupil, cats also have a non-circular high-resolution region of the retina (not a true fovea AFAIR). This region is shaped like a lance-head or a distorted diamond, elongated horizontally, perpendicular to the pupil slit orientation. --Dr Dima (talk) 01:08, 24 April 2009 (UTC)[reply]
current procedure terminology - has it changed over the years?
I am currently researching a cancer case for a deceased fire fighter from 1970. His family is adamant that he died due to colon cancer, the death certificate states diverticular disease.
With the CPT, is it possible that in 1970 diverticual disease was the term used to describe colon cancer? I had another file from the 70's that stated a person passed due to lymphosarcoma, this turned out to be what was later referred to as non-Hodgkin's lymphoma.
I have looked for a history of the terminalology with out success.
I'm just Googling, but the first result if you google "diverticular disease" "colon cancer" states that the two diseases can have very similar symptoms and can be mistaken for each other, for what it's worth. Tempshill (talk) 22:18, 23 April 2009 (UTC)[reply]
Diverticular disease, particularly diverticulitis complicated by intestinal perforation and peritonitis, could be quickly fatal. Colon cancer might be present in such a situation but might not be listed as the proximate cause of death (either because the person filling out the form was unaware, or just not thinking of it). Death certificates are notoriously unreliable in this way. --Scray (talk) 02:05, 24 April 2009 (UTC)[reply]
As someone in medical school in the year you cited, I can assure you that colon cancer and diverticulitis were just as clearly distinguished by doctors and the CPT codes then as now. However, I agree entirely that causes of death listed on death certificates are not always entirely reliable. I remember being surprised as a covering intern the first time a patient died and the unit clerk handed me the death certificate to fill out-- it needed to be done right away so the body could be released to the funeral home. I had not been involved in the care of the patient and could have put down "hiccups" and no one else had to approve it. There are two common potentials for error: (1) a doctor available to pronounce the patient dead and fill out the certificate may not have known much about the patient, or (2) may have arbitrarily selected one of the patient's problems as the "cause of death" even though other conditions may have been present and contributed to it. People with diabetes often die of heart attacks, but a death certificate may not list the diabetes even though the heart attack may not have happened without it. alteripse (talk) 18:23, 28 April 2009 (UTC)[reply]
April 24
Blowing bubbles
Why do the children's toys that you dip into soapy water to blow bubbles with have all those vanes on them? How is this design better than just a plain plastic loop? Dismas|(talk)00:04, 24 April 2009 (UTC)[reply]
The vanes (those grooves along the edge is what I assume you are refering to) hold extra soap, which is fed into the bubble blowing area after you blow a bubble. With a plain plastic hoop, you'd only get one or two bubbles before having to reload; the vanes allow for more bubbles to be blown on a single dip. As a father of a three-year old, I have must first-hand knowledge in this field of study... --Jayron32.talk.contribs00:39, 24 April 2009 (UTC)[reply]
I couldn't find any information specifically about the function of the globose nucleus. From "Color Atlas of Neuroscience", Greenstein, p. 202: "The spinocerebellum exerts control over axial musculature through the efferent outputs from the vermian cortex and the fastigial nucleus. It controls limb movements through outputs to the globose and emboliform nuclei." Other texts provide similar information. Axl¤[Talk]08:40, 25 April 2009 (UTC)[reply]
Water consumption while dehydrated
From the dehydration article: "It is wise to slowly drink liquids when dehydrated." I've heard that advice all my life but never really understood why. Also, how come most poisonous product labels advise: "if ingested, do not induce vomiting." I figure vomiting would be a good idea and all if you just swallowed something poisonous? TravisAF (talk) 02:41, 24 April 2009 (UTC)[reply]
Once someone starts re-hydrating, the risk is in rapid fluid shifts (since the dehydration won't get any worse). So there's generally no rush to the re-hydration, but overdoing it can cause electrolyte imbalances. Regarding your second question, it's a bad idea to induce vomiting for caustic substances like drain cleaners, because they can cause significant damage on the way up - better to let a poison control center advise on how to treat. --Scray (talk) 03:05, 24 April 2009 (UTC)[reply]
Another concern about induced vomiting is the risk of aspiration of vomitus into the lungs. Some toxins will be absorbed much more rapidly from the lungs than they would from the stomach, other nasties – like the caustics Scray mentions – are apt to do much more severe damage to the delicate tissues of the lung (compared to the relatively tough lining of the stomach). Inflammation of the lungs or trachea (caused by even small amounts of aspirated vomitus) may close airways and make a bad situation much worse. TenOfAllTrades(talk) 03:30, 24 April 2009 (UTC)[reply]
For more on the electrolyte-imbalance thing, see water intoxication. It can kill. --Anonymous, 03:59 UTC, April 24, 2009.
Indeed, if you are drinking water, rather than specially designed re-hydration fluids, you could get into serious trouble. Anything more than very mild dehydration should be treated with proper salts, not plain water. (Rule of thumb: If you can drink the re-hydration stuff without it being so disgusting it makes you gag, then you need it.) --Tango (talk) 10:30, 24 April 2009 (UTC)[reply]
It might be worth pointing out that "dehydration" goes way beyond just being thirsty. I've frequently come back from a desert hike or bike ride and slugged down a half gallon of water or Gatorade without ill effect. You have to be gallons down before you get into really serious concerns about rehydrating in the right way. Looie496 (talk) 19:00, 24 April 2009 (UTC)[reply]
Indeed, half a gallon wouldn't generally be enough to cause a problem. I think not eating properly can increase the risk - it's all about the balance between water and salt, if you aren't getting enough salt in your diet (NB: the required amount of salt is very low - this is not an excuse to put loads of salt on your chips!), even a small amount of water could be too much. When you've been on these hikes, etc., you have probably been eating high energy food like chocolate - the milk chocolate wrapper I've just looked at says it has 200mg of sodium per 100g, the RDA (according to Wikipedia) being about 1500mg, this is a good example of how much salt there is in many of the foods we eat. --Tango (talk) 19:56, 24 April 2009 (UTC)[reply]
Lost in the woods
If i became lost in the woods, why would i not just eat grass and leaves until i found my way? It seems obvious to me to eat them if i was starving. EVAUNIT-66603:38, 24 April 2009 (UTC)[reply]
The question is why you can't survive on grass and any old leaves: after all, some animals are happy with that sort of diet (and there are some leaves we do eat, such as lettuce). The main difference is that humans can't digest cellulose, which tends to be a large constituent of various kinds of plant material. Also, some leaves may be toxic, as Scray points out. However, we do have a long list of plants with edible leaves, with some cautions at the top. --Anonymous, 04:04 UTC, April 24, 2009.
You won't be able to get much nutrition from grass as was explained above. Dehydration should be bigger concern anyways. Dauto (talk) 04:29, 24 April 2009 (UTC)[reply]
If you get lost in the woods, you may want to remember that an average adult should survive some hours without shelter, some days without water, and some weeks without food. (YMMV: weather and your starting physical condition will greatly affect these estimates. If you are in the snow or in the desert, adjust accordingly.) "OMG! I NEED TO EAT RIGHT NOW!!!" should not be your first concern, even when you start to feel a bit peckish. First worry about sleeping out of rain, wind, hot sunlight, and night frost. Later think about clean water. 88.114.222.252 (talk) 12:44, 24 April 2009 (UTC)[reply]
There we go again. What's up with that? That's the second time I see someone on these pages talking about people not being able to survive more than a few hours without shelter. That's only true on the most extreme conditions. I would worry first about water if I got lost in a forest. Dauto (talk) 17:44, 24 April 2009 (UTC)[reply]
What woods, when and where? As noted above the human digestive system is ill adapted to gain much nutrition from grass. However, most forests will provide nuts and berries which you could very well live on for a while. You'd have to know what grows where and when locally. Many plant buds and some flowers are also edible and contain more energy than leaves. The problem would also be that gathering all those would be taking time you might spend better on finding the next road or river. (Most flowing water ends up at/near human habitation downstream sooner or later.) 76.97.245.5 (talk) 15:55, 24 April 2009 (UTC)[reply]
If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --131.188.3.21 (talk) 13:32, 26 April 2009 (UTC)[reply]
To clarify, most fish can only survive in one environment or the other, but there are some, such as salmon, which can handle either fresh- or salt-water. StuRat (talk) 07:38, 24 April 2009 (UTC)[reply]
"exact" is a tough thing here...the earth isn't a billiard ballapparently, it is...see below! But the numbers from the Earth article that TravisAF quotes above are pretty reasonable. The standard for the shape of the earth that is most commonly used in exacting applications is called 'WGS-84' or World Geodetic System from the World Geophysical Survey of 1984. The values it gives are the best "mean sea level" description of the shape available - and I presume that the numbers above are from that definition. However, if you stretched a piece of string around the circumpherence of the planet then measured it - the answer would not be exactly that given above - and the result would vary depending on where you measured it - and probably on where the sun and moon were at the time because shape of the earth is affected by tides. It's probably also worth mentioning that the surface of the earth is like a fractal - so a precise measurement even at a particular moment in time and a particular direction over the planet is going to suffer from the Coastline paradox (see also: How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension).
"The earth isn't a billiard ball". From the above figures the earth's circumference varies by only a few parts in a thousand. Are billiard balls that accurately spherical? And the bumps in the earth are less than one part in a thousand. Are billiard balls smoother than that? DJ Clayworth (talk) 15:09, 24 April 2009 (UTC)[reply]
From Earth: "Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls." Dragons flight (talk) 15:16, 24 April 2009 (UTC)[reply]
Wow! That's a cool observation. But - an 0.17% tolerance means that when we say the circumpherence is 40,041.47 km - we're overstating the precision by a couple of orders of magnitude! SteveBaker (talk) 19:39, 24 April 2009 (UTC)[reply]
Of course, the number is almost exactly 40,000 kilometers because that was the original definition of the kilometer; it was defined as 1/10000 the distance between the north pole and the equator along a meridian of longitude; which would be 1/4th of a circumference. But you all knew that... --Jayron32.talk.contribs21:27, 24 April 2009 (UTC)[reply]
This reminds me of a study that I think appeared in the Journal of Irreproducible Results, where the authors tried to determine whether Nebraska (or maybe it was Kansas?) was indeed "as flat as a pancake". The conclusion was that it was very much flatter than a pancake. If it were only as flat as a pancake, there would be miles-deep canyons all over the place. Or something like that. --Trovatore (talk) 21:32, 24 April 2009 (UTC)[reply]
The above discussion correctly notes that the Earth is smoother than a billiard ball, but it's not quite round enough. Discussion here. --Sean22:46, 24 April 2009 (UTC)[reply]
Yes - the poles are considerably squashed compared to the equator. The problem here is that we're presented with numbers that are accurate to 10 meters! Even with (proportionately) billiard-ball smoothness - that's way too much precision. Having just one mountain or valley along your chosen "circle" will throw off your measurement of the circumpherence by vastly more than 10 meters! That number can only be the result of a specification for the idealised shape of the earth - per WGS-84's ruling on the matter. SteveBaker (talk) 00:06, 25 April 2009 (UTC)[reply]
Smoothness and roundness are similar. The way I think about it is as a "power spectrum". Using a spherical harmonic breakdown (such as the set of WGS-84 coefficients), you can actually see how much "energy" is contained at each "frequency" (really, it's not energy, because it's a geometric description, but "frequency" is a moderately reasonable word - the spherical harmonics functions map well as spatial frequencies, albeit not sinusoidal frequency). And I'm sure you could find some way to represent mass-distribution as gravitational potential energy too, so "energy spectrum" is not really such a bad terminology after all). Anyway, the point is, Earth's deviation from perfect sphere is evident at the lower-order terms of the spherical harmonic decomposition, and its roughness is evident from the magnitudes of the higher-order terms. With sufficient number of terms, (impractical and unwieldy, but definitely possible), every topographic feature could also be described. The magnitudes of those coefficients would be REALLY small (in the same way that a band-limited radio-signal has zero spectral power at "infinitely high" frequencies). Nimur (talk) 14:47, 27 April 2009 (UTC)[reply]
Name
What's the name given to a situation when you hear something going on in a dream, then you wake up to hear it going on in the real world? 58.165.23.195 (talk) 07:14, 24 April 2009 (UTC)[reply]
You might be thinking of something paranormal, such as precognition or premonition. Or you might have fallen asleep with the television on.
Sounds more like he's asking about a real-world sound making it into a dream (very possible) and then waking up with the sound still there. Nothing paranormal about it. :) -- Aeluwas (talk) 08:49, 24 April 2009 (UTC)[reply]
Forgive me if I missed it, but I think I skimmed all the relevant pages on Wikipedia and didn't see anything. I've been wondering lately how the earliest links were drawn between proteins and genes. Many genetic mutations were connected to visible phenotypes long before the central dogma was developed. Was the connection with a particular protein made for any of these mutations? How were the chemical functions of the earliest studied proteins identified? Thank you. Someguy1221 (talk) 07:44, 24 April 2009 (UTC)[reply]
The current theory from my biology book is that RNA was a molecule which dabbled in several roles of the cell. It did things which we think of proteins doing--regulating the rates of reactions, and they were involved in metabolic pathways and they even stored "blueprints" for other RNA molecules (because remember, RNA can be transcribed off of another RNA strand--that is how RNA viruses do their thing, theey call it "the RNA directed synthesis of new RNA".
Also don't over hype the difference between RNA and DNA. The difference is only an oxygen on the sugar backbone. All that "difference" does is help the molecule be more stable. DNA can last several years, RNA can last only about 45 minutes on its own, without being sequestered from common reagent molecules.
The difference between RNA and protein, is well, that RNA is an acid. Both molecules owe their properties to organic chemistry. Both RNA (in the rna world) and current proteins had the same exact functional groups. However, proteins generally were more effecient, could fold better, and were recycleable.
In a way, your question could be answered that evolution took place and RNA simply became excinct because it is a fierce job market inside the cell, and well, RNA's job got sent overseas and only a few vestigial pathways still utilize RNA as a reactant in reactions today. Some even in your own cells!JameKelly (talk) 08:49, 24 April 2009 (UTC)[reply]
That answer seems a bit off topic to me... I certainly could be wrong, but the way I read the question, the OP is interested in the first example of a gene (i.e. the DNA sequence) being causally related to the protein it codes for. I think the answer you are looking for is found in the biochemistry article, which discusses the discovery and characterization of proteins. The first instance of a gene being linked to the enzyme it produces (from Biochemistry): "In 1958, George Beadle and Edward Tatum received the Nobel Prize for work in fungi showing that one gene produces one enzyme" (for research performed in the 1940's). The History of biochemistry article, which should be a good resource, is focused more on the 1800's and is surprisingly sparse on the advances of the 20th century. --- Medical geneticist (talk) 11:11, 24 April 2009 (UTC)[reply]
In addition (since the OP is interested in mutations & phenotypes) -- Archibald Garrod is widely acclaimed as the first to postulate that an inherited disorder could be due to deficiency of a particular enzyme, as in the case of alkaptonuria. However, although he made the connection in the early 1900's, the actual enzymatic deficiency was first demonstrated in 1958 and the gene mutations weren't described until 1996! In terms of the discovery of genetic mutations that cause disease, it's hard to ascribe a "first" for many things since many discoveries are made in parallel. There is a nice timeline at the National Human Genome Research Institute (http://www.genome.gov/25019887) that shows the progress from Beadle & Tatum's "one gene one enzyme" theory in 1941, the discovery of the double helix structure in 1953, discovery of the genetic code in the 1960's, development of DNA sequencing in the 1970's, to the first human disease gene Huntingtin being mapped in 1983 and cloned in 1993. Genes that are defective in chronic granulomatous disease, Duchenne muscular dystrophy, and retinoblastoma were all mapped and characterized in the 1980s-1990's, with many more following after that and still continuing today. --- Medical geneticist (talk) 13:12, 24 April 2009 (UTC)[reply]
Differential Capacitive sensors
Well i want to be very frank. I am a first year undergraduate Electrical Engg student. For joining one of my professors for a summer time project, he gave me a paper something to do with "Switched Capacitor Dual Slope Capacitance to Digital Converter For Differential Capacitive sensors". Unfortunately, being just a first year, i haven't the faintest inkling what these terms mean, except the term capacitor! I have tried searching on Google and wiki, but the sites only give highly technical information way above my head. However, i am determined to understand this topic. So can someone please explain me what the above mentioned terms are, in a down to earth, layman manner, so that a person with just basic electrical knowledge would catch the point ? Or perhaps suggest a link which does so? I am dearly in need of help !!Rkr1991 (talk) 10:13, 24 April 2009 (UTC)[reply]
Well, I'm no expert - but we can try to break up that turgid title into manageable bites:
Switched capacitor -- OK so we're going to use a switch to choose one of two or more capacitors.
Dual slope -- So the graph of some function is going to have two straight-line slopes. Probably because the slope changes when you switch from one capacitor to the other.
Capacitance to Digital convertor -- sounds like an analog to digital convertor that measures capacitance instead of voltage.
Differential Capacitive sensor -- well, whenever something is 'differential' you're either measuring the rate at which something changes or the difference between two things - this 'convertor' is clearly a 'sensor'.
So I guess (and I'm no expert either!) that this is a project to build a gizmo that measures some aspect of the capacitance of something using a computer. How it's gonna work is by somehow switching capacitors on and off. I think I'd start by searching on "Capacitance to Digital convertor" to understand how capacitance is measured digitally.
I agree that this does sound a little tough for a first year project - but that's the point of doing things like this with experts in the field. So talk to your professor. He's there to teach you - and if you don't understand what the heck this thing is - it's because (I presume) he has not yet taught you about it. That's his fault, not yours. So make every effort to read as much as you can - then go to him and ask for an explanation and a break-down of the project into bite-sized pieces.
Hopefully others here will be able to explain this in more detail.
(ec) A dual-slope analog to digital converter (ADC) is a specific type of ADC commonly used in digital multimeters. It is described in our article integrating ADC which is an alternative name for it. It is more accurate than a single-slope ADC because it lets through a greater number of clock pulses but is slower to update as a result. The "switched capacitor" bit of the title is probably referring to changes of range, which are achieved sometimes by switching the value of the integrating capacitor and sometimes by switching the value of an offset voltage or current. The "for differential capacitive sensors" is probably referring to the type of input that is being measured. Many transducers (eg displacement detector) are essentially capacitors and the quantity being measured physically moves one of the plates causing the capacitance to change. The requirement of the measuring system is thus to measure the capacitance, either absolute, or the difference between the transducer and a reference capacitor (hence differential). Of course, some of that is guesswork; for a more specific answer you will need to provide a link to the paper you are reading, or at least some of the details (author, exact title, journal, date etc) and hope someone here has access to it. SpinningSpark13:17, 24 April 2009 (UTC)[reply]
Learning something new requires juggling some number of unfamiliar concepts in short term memory. With time and effort, you can push concepts into your long term memory - once you have done that, you have "learned." When learning is difficult, that means you are encountering too many unfamiliar concepts at once to fit into your short term memory. This happens readily because short term memory is very limited - most people can only manipulate between four and seven "chunks" of information that way. Short term memory seems to work like a FIFO queue - if the unfamiliar chunks keep coming, they push earlier chunks out, and you lose them. Your emotional brain responds by generating emotions of anxiety and frustration. Long term memory, in contrast, is seemingly unlimited. As long as your brain continues to work, you can apparently just keep pushing more knowledge into your long term memory. The problem is that chunks can only move from short term memory into long term memory at a slow rate. Because short term memory is very limited, and long term memories can be slow to form, humans hit on a trick, thousands of years ago, to augment memory: writing. When you are trying to learn something that overwhelms your short term memory, you should immediately start writing. For example, read the paper you are trying to understand, but don't worry about understanding it right away. Instead, do this:
Make a list of all the terms in the paper you don't understand yet.
For each term, try searching the Web and so on, and write whatever you find that might relate to it.
Keep coming back each day, re-read the paper, review your list of terms, and see if you notice anything you missed before.
Look up all the references that the paper cites, read them, and see if any of them shed further light on your list of terms.
Identify your conceptual sticking points. You will figure out some terms sooner than others. When you figure something out, move it to the bottom of your notes. Keep the unknown items at the top.
Look for clues about the interrelatedness of terms. Probably every jargon term in the paper relates to the other jargon terms in various ways. The paper is not just a stream of consciousness list of random terms. You want to understand not only what each term means in isolation, but why the author used them all together. Sometimes you can understand the relationship between two items before you fully understand the items. See: ontology.
Show your notes to some experts, and ask them to comment. They may suggest introductory references you can read, or they may point out errors in your thinking. For example, you might have listed a particular concept more than once, because maybe the paper refers to it by synonyms. In that case, your problem got simpler, because instead of two concepts to learn, you find you only have to learn one.
I couldn't find the exact link on the net, but here are its details : Novel Switched-Capacitor Dual Slope Capacitance to Digital Converter for Differential Capacitive Sensors by, Boby George, Member, IEEE and V Jagadeesh Kumar, member, IEEE. I hope someone would be able to find the exact paper, and then explain what exactly is the problem being approached, and the principle used in this case. I would like to add that it is not my professor's fault for not teaching this. I, being free in the coming summer, approached him for doing some extra work, and he has offered to take me in his research team as an assistant, if i can tell him what i understood from this.(He is one of the authors of this paper.) Thanks in advance for all the help.Rkr1991 (talk) 06:33, 25 April 2009 (UTC)[reply]
I would also like to thank 2 particular users - SpinningSpark and SteveBaker, who have both helped me out on numerous questions. Thanks for your time guys ! And thanks to Teratornis too...Rkr1991 (talk) 07:13, 25 April 2009 (UTC)[reply]
No, I can't find it either, but I did find this and wonder if the paper you have is a pre-print of the published paper with a different title. Sorry, I don't have a current subscription to IEEE Explore so cannot read it, and it doesn't have an abstract. You might want to take a look at this book though, which you can preview in google books. SpinningSpark12:38, 25 April 2009 (UTC)[reply]
Eggplant is in the nightshade family which contains toxic substances. Hair loss may be an effect of poisoning from ingesting unripe/inedible parts of the plant or an allergic reaction. As our article notes aubergines are high in nicotine, which can cause hair loss through constriction of blood flow to the follicles and accelerated cell aging. That is for prolonged exposure and high quantities, though. I doubt the average person would regularly eat 9 kgs of eggplants. That would signify a highly deficient diet that would cause many other health effects. High doses of caffeine can also cause hair loss, while low doses actually stimulate hair growth. This page [[18]] recommends eggplant leaves as a remedy for hair loss, but I'd rate that one under "people will try anything". 76.97.245.5 (talk) 15:14, 24 April 2009 (UTC)[reply]
"Female" DNA
Google doesn't lie ... so there is "male DNA" and "female DNA" (the question for "male Cellulose" and "female proteins" (the shapely ones) comes later...). Question: When "female DNA" is found at a crime scene, does that mean that no Y-chromosome genes were found in this sample or was there another test done ? (because X-Chromosomes are found in males and females). Does "The blood in the car showed female DNA" actually mean "in the blood we found no Y-chromosome genes but lots of other genes and human markers, so it must be the blood of a woman/female" ? Thanks --83.141.221.231 (talk) 14:38, 24 April 2009 (UTC)[reply]
I don't know the answer but most likely the absence of Y specific markers would indicate "female". Of course if the woman had AIS then the test would be misleading. And any test that relies on the absence of a marker is prone to contamination from other sources. David D.(Talk)14:42, 24 April 2009 (UTC)[reply]
Another possible way to confirm a "female" sample would to look at a lot of polymorphic markers on the X chromosome. A male would have only one in every case (hemizygous for X) but a female would be heterozygous for many of the markers. David D.(Talk)14:48, 24 April 2009 (UTC)[reply]
What would you see in the latter case? Female: More bands than usual (male)? Could you conclude from the complexity of the pattern whether the blood was from 1, 2, more women? In the meantime, I found the (a) (SRY-F + SRY-R) and (b) (PABX-F + PABX-R) Primer-pair approach. A male should give 2 bands, a female one band, a mix (of blood) of 2 females should give 2 diff. (PABX-F + PABX-R) results. --83.141.221.231 (talk) 15:06, 24 April 2009 (UTC)[reply]
You could not detect such a difference with PCR. It could be done using antibody pulldown, probably directed at lysine methylation on histones. In males the X sequences would far less represented than in females. But to be pedantic, what if a male had Kleinfelter's Syndrome (XXY)? Such a male would have half his X sequences silenced. And besides, the sensitivity would be problematic at a forensic level. David D.(Talk)00:58, 26 April 2009 (UTC)[reply]
You're all overthinking this. "We found female DNA" = "We did a karyotype and the sex chromosomes were 'XX"". "We found male DNA" = "We did a karyotype and the sex chromosomes were "XY". Depending on the circumstances, it may not even be as complicated as that....e.g. we found male DNA in the sperm specimen. - Nunh-huh01:12, 26 April 2009 (UTC)[reply]
Looks like you can differentially label the X and Y, so don't need a full karyotype.[19] That would also solve rare genetic combinations and multiple contributors, since it seems to allow counting of the chromosomes in whole cells. In other ideas, there are non-genetic ways to identify the sex of a biological sample, so "high levels of PSA" would mean the sample's DNA is probably male (though surprising-to-me high rate of false-positive), whereas DNA from a sample that also has high levels of various pregnancy horomones is from a female. Going the other way, if the biological sample is sperm, I can guarantee it contains DNA from a male. DMacks (talk) 07:24, 26 April 2009 (UTC)[reply]
Canis lilliputia and canis brobdingnag
What happens when a female St. Bernard/Wolfhound/Great Dane is impregnated by a male Chihuahua/Yorkshire Terrier/Toy Poodle? And what happens in the reverse situation? I assume this never happens naturally but would have to be by insemination (please correct me if I'm wrong). I imagine a very smalle female dog would have more trouble than the reverse situation, but is such a pregnancy viable? Are there any examples of such dogs carrying to term? And for the reverse, I imagine this might either kill the tiny female or, as the pup grows too big, her body will reject through a miscarriage? Or does it work that a female can carry and the combination of genes still results in a very small dog despite the large male breed? I've always wondered about this.--70.19.69.27 (talk) 21:42, 24 April 2009 (UTC)[reply]
Thank you for that link Deor. Extremely unsatisfying answers based on sheer speculation but that may be because the answers are simply unknown.--70.19.69.27 (talk) 03:37, 25 April 2009 (UTC)[reply]
I'm gonna take a stab in the dark and guess that this has to do with sorbitol, a sweetener that's often used in chewing gum and the excessive consumption of which can cause extreme weight loss due to its laxative effect. How much counts as excessive is probably going to vary from person to person, but frankly, it's not that hard to tell when you've eaten too much of it, what with the diarrhea and all. -- Captain Disdain (talk) 01:51, 25 April 2009 (UTC)[reply]
With another stab in the dark, chewing gum provides pretty much no nutrients; therefore it isn't 'necessary'; therefore it is "excessive consumption". That's taking a very extreme view that "excessive" means anything more than is necessary for life. DJ Clayworth (talk) 14:16, 27 April 2009 (UTC)[reply]
In the true spirit of modern "psychobabble", it's only too much if it is negatively interfering with other areas of your lifestyle. This tautological statement doesn't convey a lot of information, but it's used to describe a lot of addiction-spectrum conditions without making normative claims, moral pronouncements, or legal advice. Nimur (talk) 14:52, 27 April 2009 (UTC)[reply]
Line spectrum question
Doubly ionized lithium Li2+ (Z = 3) and triply ionized beryllium Be3+ (Z = 4) each emit a line spectrum. For a certain series of lines in the lithium spectrum, the shortest wavelength is 365.1 nm. For the same series of lines in the beryllium spectrum, what is the shortest wavelength?
I'm not entirely sure, but since 365.1nm is in the visible light spectrum that means it's in the Balmer series? Therefore you have to use the equation, 1/wavelength=R(1/2^2-1/n^2), and then solve for n. But when I solve for n I get 55.79 which doesn't make sense since it should be an integer. Also when I solve for n, I'm not sure where to plug that in. I'm thinking I need the equation, 1/wavelength=1.097x10^7(Z^2)(1/nf^2-1/ni^2), but I'm not entirely sure. Also I don't know which n I solved for in the original equation. 69.69.75.22 (talk) 00:08, 25 April 2009 (UTC)[reply]
You used the equation for Hydrogen. The correct equation is 1/wavelength=R(Z^2/2^2-Z^2/n^2) for a balmer series line. See Rydberg formula. The Z=1 for hydrogen, which is where you went wrong. The more general equation is needed for all other elements. --Jayron32.talk.contribs00:38, 25 April 2009 (UTC)[reply]
Forget about ni and nf. get the Rydelberg equation for the Lithium and devide by the Rydelberg equation for the beryllium. The mistery factor cancels out. Dauto (talk) 03:21, 25 April 2009 (UTC)[reply]
I need clarification on this issue. I know for endothermic solution reactions, solubility increases with temperature. Conceptually this makes sense dH is positive therefore Energy in the form of higher temperature must be invested to make this reaction happen. Secondly, Le Chatelier's principle also supports this.
Now, for exothermic reactions, Le Chatelier's principle suggests that solubility decreases with temperature since "heat" is a product here so the system will shift to reduce heat/temperature. However from a thermodynamics standpoint (dG=dH - TdS) such a reaction will be very spontaneous since dH is negative and T increases therefore the "-TdS" term becomes more negative and the overall dG is negative. Intuitively, I am slightly leaning more towards the Thermodynamics implication thinking that this scenario might be a limitation in the scope of Le Chatelier's principle.
Please explain the apparent paradox assuming there's one. I understand physics without nearly as much effort as I have to spend on rectifying chemistry!
P.S. I will try to incorporate whatever feedback this question generates into the paragraph here since I imagine that is where the information is best suited, correct?
Le Chatelier's principle is correct. To use Gibbs free energy as you've done you must assume an isobaric and isothermic process. Since the reaction is exothermic, the only way the process can also be isothermic is if the excess heat is being absorbed by the surroundings. As heat leaves the system, the change in its entropy must be negative (dS<0) throughing a wrench in your reasoning. Dauto (talk) 04:08, 25 April 2009 (UTC)[reply]
Indeed, to explain a little more; the Gibbs equation is a state function; so all values are as measured at any instant in time. It's not dTdS, its TdS, which means that the entropy value is not dependent on changes of temperature; it is dependent on absolute temperature at any point. It has nothing to do with whether the solution is heating up or cooling down, only with what the temperature is at the point where you are measuring the values. --Jayron32.talk.contribs04:30, 25 April 2009 (UTC)[reply]
Thanks for the answers. I realized I was trying to derive one from the other, but I didn't realize what I was asking. I was so stuck thinking that I just didn't see something, but the straightforward answers I have received today were very helpful and rock solid; this enabled me to reevaluate what I was seeking to find, and in hindsight I was trying to derive one from the other, which I can't so I can rest easy now and move on to the next subject. Thank you again, JameKelly (talk) 12:11, 25 April 2009 (UTC)[reply]
will 1,3,5-trimethoxybenzene react with hydrochloric acid? (Or even base?!)
I suspect it reacts with sulfuric acid, if I have my unknown correct. I didn't manage to complete an HCl or NaHCO3 reactivity test in lab however ... would the H+ attach to the ether oxygens, whereupon there is some weird nucleophilic substitution and the alkyl groups fall off (probably with some nucleophile at the end to stabilise the leaving group) and resonance stabilisation stabilises the former ether oxygen...? Or what? Why else would sulfuric acid attack 1,3,5-trimethoxybenzene? Surely it's not a strong enough electrophile (well, perhaps without the presence of SO3) to attack benzene bonds? John Riemann Soong (talk) 05:57, 25 April 2009 (UTC)[reply]
You may get some chlorine-for-methoxy substitution, but probably not in high yields, and you may also get a mixture of mono-, di-, and tri- chloro products. A low enough pH will protonate the oxygen, which will make methanol as a decent leaving group. The chlorine is likely just a good enough nucleophile to substitute here. --Jayron32.talk.contribs17:19, 25 April 2009 (UTC)[reply]
Yup, protonation of an ether oxygen is pretty good bet. But then I'd think more ikely to hydrolyze (I assume your "sulfuric acid" is a few-molar aqueous solution?). the Me-O side of this ether than the O-Ar side. Once you're at an oxonium, SN2 nucleophilic attack on the methyl seems easier than first going to an even less stable structure like aryl carbocation (SN1...can't do SN2 on an sp2 center). DMacks (talk) 07:01, 26 April 2009 (UTC)[reply]
I'm trying to find out why it would react with sulfuric acid (the bottle / lab manual said "concentrated"), but not 5% HCl ... I guess it was just the acidity of the solution? John Riemann Soong (talk) 08:00, 26 April 2009 (UTC)[reply]
Doesn't your textbook/lab-manual tell you what sorts of functional groups give a positive test for each of your qualitative analysis methods? Is conc. sulfuric a test for ethers or for aromatics? Your text (if it's any good) or other class materials would explain why/how each one behaves under the various test conditions. What exactly makes this test "positive" (something dissolves, precipitates, changes color, releases a gas, catches fire, ...)? DMacks (talk) 06:31, 27 April 2009 (UTC)[reply]
My lab manual only explains how to do the test. We're supposed to test for "solubility", but a reaction or color change counts as a positive for solubility. I thought ethers were fairly inert actually, and so were aromatic compounds, in the absence of metal catalysts. John Riemann Soong (talk) 18:12, 27 April 2009 (UTC)[reply]
If the remainder of the solution isn't very volatile, and you aren't concerned with keeping it sterile, you can just leave the solution exposed to the air until the water evaporates. This could be done, for example, to create sea salt from sea water. StuRat (talk) 20:43, 25 April 2009 (UTC)[reply]
The blast radius of a nuclear bomb is a few miles, so let's be generous and say that 100 square miles would be affected. The area of Antarctica is about 5,000,000 square miles. That's 50,000 bombs - more than the U.S. and Russia have combined. That's not taking into consideration the fact that the ice can be quite thick, so one bomb probably wouldn't melt all of it in its assigned sector. Clarityfiend (talk) 09:39, 25 April 2009 (UTC)[reply]
(After edit conflict; another big number) Well, a typical nuclear test can create a crater hundreds of metres across, but that is still very small compared to the size of a whole continent. So let's crunch some numbers. Antarctica article says area of Antartica is 14 million km2 and 98% of the continent is covered by ice with an average depth of 1.6 km. So that is about 22 million km3 of ice. That has a mass of about 22 x 1018 kg. For simplicity, let's assume this is all just on the point of melting (so we ignore the heat required to warn it up to 0oC). Water (data page) says latent heat of fusion of ice is about 6 kJ/mol. 1 mole of ice has a mass of about 18 grammes, so 22 x 1018 kg is about 1.2 x 1021 moles, which will require about 7.2 x 1024 J of heat to melt it. One megaton is 4.184 x 1015 J, so 7.2 x 1024 J is about 1.7 x 109 Mt. The most powerful hydrogen bomb ever tested had an energy yield of 50 Mt. So to melt all the ice covering Antarctica, you would need at least 35 million hydrogen bombs, even if all if the bombs' energy was released as heat energy and absorbed by the ice. Gandalf61 (talk) 09:47, 25 April 2009 (UTC)[reply]
Agreed. By an independent calculation based on very similar assumptions I got an estimate of 50 million bombs. You could probably achieve the same effect with much less energy by painting the ice black and letting the sun do the work. --Heron (talk) 11:44, 25 April 2009 (UTC)[reply]
The first few bombs might result in dark dust falling on the rest of the ice, so it might not be necessary to paint it all, just use a few nukes. --Tango (talk) 14:51, 25 April 2009 (UTC)[reply]
I don't see where the dark material would come from - you're mostly blowing up kilometers-thick ice - what's going to get chucked up into the air will be water-vapor. Even dark dust would get tossed into the upper atmosphere. That would tend to block the sun - making the continent colder - and reducing the amount of melting. That's been a notable effect of large volcanoes and such. It's hard to predict - so it's far from obvious which effect wins. SteveBaker (talk) 15:39, 25 April 2009 (UTC)[reply]
Drop the bomb on a bit with thinner ice so you expose the ground underneath. I seem to recall using bombs to spread dark dust over ice to make it melt being proposed in the context of terraforming Mars - perhaps it wouldn't work so well on Earth, with a thicker atmosphere to hold onto the dust. --Tango (talk) 16:22, 25 April 2009 (UTC)[reply]
Nuclear weapons are very powerful against human-sized targets. But not geographical-sized targets. You could easily make a large area uninhabitable for humans with exceptionally "dirty" hydrogen bombs. But melting, totally destroying it, no. No more than you could crack the planet in half with nukes. --98.217.14.211 (talk) 17:31, 25 April 2009 (UTC)[reply]
Nukes alone would not do it, but there might be another way. If we were to find a large asteroid (or more), we could use nuclear pulse propulsion on it, and direct it towards Antarctica. It wouldn't be very easy with our current technological level, but I think it can be done. 69.69.75.22 (talk) 17:50, 25 April 2009 (UTC)[reply]
Yes, that might work. Antarctica wouldn't be an easy target, though. Most asteroids are in the plane of the solar system so for them to hit Antarctica it would need to be a "glancing blow". There wouldn't be much margin for error (too much one way, you miss Antarctica and hit something else, too far the other way and you miss the Earth entirely) and it would have to travel through more atmosphere, so more of it would burn up before impact so you would need to start with a larger asteroid (which means more nukes, or whatever else you use, would be needed to propel it). --Tango (talk) 18:57, 25 April 2009 (UTC)[reply]
It would be easier if you pick an asteroid with more or less the right orbit to start with. You need an earth-crossing asteroid with a highly inclined orbit, preferably eccentric as well. 1866 Sisyphus fits the bill but might be a little too big - it would be the dinosaurs all over again. I recommend 2102 Tantalus as a candidate missile. SpinningSpark22:35, 25 April 2009 (UTC)[reply]
Exploding a nuke directly over Antarctica probably wouldn't melt the continent, but exploding a few in the most vulnerable areas to subglacial seepage (which would undermine parts of the ice shelf) might do the trick. For example, Pine Island Bay in West Antarctica, and the Totten and Cook glaciers/ice shelves in East Antarctica. ~AH1(TCU)01:33, 26 April 2009 (UTC)[reply]
What's more, Antarctica is a continent — a ton of explosions would melt the ice cap at a particular location, but you couldn't melt the continent any easier than you could melt land anywhere else. Nyttend (talk) 12:42, 26 April 2009 (UTC)[reply]
That's a good point. We interpreted the question as "melt the ice cap that covers Antarctica", but that isn't actually what the OP asked. --Tango (talk) 21:23, 26 April 2009 (UTC)[reply]
There is something I really don't understand. The North American Plate includes both continental and oceanic crust. Therefore, I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust). But there is no convergent boundary within the North American Plate! Where is my mistake? Where is going the oceanic crust? Enherdhrin (talk) 10:48, 25 April 2009 (UTC)[reply]
PS : sorry for my english.
The oceanic crust in the Atlantic isn't subducting; it's just pushing North America farther westward as it's created at the Mid-Atlantic Ridge. The subduction is taking place on the other side of the continent, as the westward-moving continental crust overrides the Pacific Plate. Deor (talk) 13:15, 25 April 2009 (UTC)[reply]
The explanation above is correct. I'm curious about that statement: "I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust)." I don't understand your logic. There is no subduction zone on the east side of the northamerican continental crust, And yet, the continental crust is much older than the oceanic crust right next to it. I don't understand why you would think that's a contradiction. I isn't. Dauto (talk) 14:01, 25 April 2009 (UTC)[reply]
New oceanic crust is always being created at the Mid-Atlantic ridge, so the North American Plate always gets bigger, but the land area stays the same. The crust near the ridge at a certain distance is always of a certain age, but the crust closer to the continental shelf gets older and older, as does the land itself (discounting any newer orogenies). The expansion of the plate does not present a contradiction because plates are always being subsided somewhere else. ~AH1(TCU)01:19, 26 April 2009 (UTC)[reply]
The North American Plate is growing; the "continental" portion of it stays about the same size, and the "oceanic" portion is being added to at the Mid Atlantic Ridge. This is not a problem, since other plates, especially the Pacific Plate, are actually shrinking as they are being subducted under several plates, including the North American Plate. Crust creation and subduction is a zero-sum game, but not per plate, only over the whole earth. The individual plates are shrinking and/or growing based on what is happening at the plate boundaries.--Jayron32.talk.contribs01:33, 26 April 2009 (UTC)[reply]
@Deor : thanks for your reply. @Dauto : AH1 and Jayron32 have perfectly analysed my mistake : I falsely assumed that the size of the North American was fixed. Thanks to all of you for your explanations.Enherdhrin (talk) 11:30, 26 April 2009 (UTC)[reply]
Male/female ratio
Seeing as both the birth and death rates are higher in males than in females, which gender is more prevalent in the world: male or female? 58.165.23.195 (talk) 13:42, 25 April 2009 (UTC)[reply]
All your questions are answered at human sex ratio. In short, more boys are born than girls (105:100), possibly an evolutionary method to balance out the ratio, although sex-selective abortion and female infanticide heavily skew the numbers in some countries. But demonstrating precisely what you said, the male:female ratio gets considerably skewed the other way in older and older populations. In some countries, the ratio amongst people over 65 is 70:100 or worse. Someguy1221 (talk) 13:54, 25 April 2009 (UTC)[reply]
I recall reading once that males are more likely to die in the womb but the ratio at birth was as you say, something like 105:100. This surprised me at the time and no explaination was offered. I presume most likely there's something going on earlier then is being detected here, e.g. females less likely to be implanted, male sperm more successful in fertilising ova (which entails a whole lot of possibile reasons), more male sperm etc. Alternatively sex selective abortion is more widespread then people realise. The book was a rather old sociology book so there may be more info available now. Nil Einne (talk) 19:48, 25 April 2009 (UTC)[reply]
Social Science/Sociological Question: What is the difference between Modernity and the Enlightenment?
Modernity and the Enlightenment are majoratively written about as two seperate entities, although they share similar features and are sometimes interlinked as one and the same. Please can someone identify what the features are that distinguish between the two? —Preceding unsigned comment added by Sheepdisease (talk • contribs) 14:42, 25 April 2009 (UTC)[reply]
The Enlightenment is a period; Modernity is a state of mind. Enlightenment leads to Modernity. Such is a very crude way to think about it but it mostly works. Both terms are rather vague (esp. modernity, which basically stands for whatever one wants it to). --98.217.14.211 (talk) 17:36, 25 April 2009 (UTC)[reply]
Storage of medicines
I've seen it many times that on the packaging of medicine it says "store at room temperature." I wonder why they don't say "store at a temperature below X °C/°F" instead. I think most medicines are not harmed by low temperature. (I can't imagine all over-the-counter medicines are transported in heated trucks during the winter months. Short-term exposure to low temperature must be OK for most of them.) What are some mechanisms by which medicines will go bad when stored at low temperature? (I can think of one: some components of a mixture crystallize out and settle at the bottom of the container, thereby changing the composition of the mixture.) --173.49.78.81 (talk) 15:40, 25 April 2009 (UTC)[reply]
They may just say that to clarify that they don't need to be refrigerated. If there was a maximum temperature (that wasn't so high as to be unnecessary to warn against) that they could be stored at, I think it would say so. --Tango (talk) 16:51, 25 April 2009 (UTC)[reply]
Also, need to target the lowest common denominator of consumer, who doesn't know what the actual numerical temperature is. So "room temp", "cool, dry place", "refrigerate" are clear and are good enough descriptions for safe and enough storage to have the expiration date be reasonable. Also, no reason to confuse people into storing stuff in the fridge "just to be sure I don't exceed this temperature" (people don't know how close they need to be or how long and how much too hot is bad...what the hell is a "degree"?). Yes, I have a jaded view of the typical consumer:( Some (and many more, more recently) do actually also specify a maximum temperature. One problem with fridge isn't the low temp, but that the low temp leads to condensation, and water can lead to pills losing structural integrity and also major chemical changes for things that need to be stored "dry" as well (a good Slow News Day evening news topic is how bad it is to store medicines in the cabinet next to a steamy hot shower). DMacks (talk) 18:59, 25 April 2009 (UTC)[reply]
In the case of dry meds, generally the colder they are stored the longer they will last. In the case of liquid meds, it may be important to avoid freezing, so the colder you can store them, without risking freezing, the better. As to why the manufacturers don't include such info; it simply wouldn't increase their profits to do so. First, they'd have to spend lots of money to determine how long their med lasts at various temps. Then they would also lose money if people are able to use old meds which otherwise would have been tossed out and replaced with new meds. So, they do the bare minimum and give some relatively short period for which they know the meds will last at room temps, and call it good enough. StuRat (talk) 20:34, 25 April 2009 (UTC)[reply]
I guess the next question is: Why don't countries impose laws on drugs companies requiring them to include such information? Probably because the benefit would be minimal and it isn't worth annoying people with extra red-tape. --Tango (talk) 23:40, 25 April 2009 (UTC)[reply]
From my past experience working within the Pharmacological Industry (*see disclaimer below) - Governments (via Regulatory Bodies like the FDA (US), MHRA (UK) etc) do expend considerable resources on determining and specifying exactly what information drugs companies should and must include on/in their products' packaging and information leaflets. Similarly, every drugs company expends considerable resources on complying:
Because if they don't they face potentially onerous penalties (even if no harm results - I know of one company forced into closure because it failed to properly maintain documentation proving its compliance with manufacturing regulations);
Because they don't want to hurt profits by actually harming their customers;
And because, believe it or not, most Pharma Industry people are decent human beings with consciences who genuinely want to provide the best and safest medications they can.
This leads me to conclude that such basic information as storage instructions, that has been scrutinised and worked on by both Regulators and Manufacturers, is likely to be about as appropriate as it can be. (Assuming a legitimate source - counterfeiting drugs and their packaging is a major global industry.)
(*Disclaimer: I was employed by a contracting company to administer facilities maintenance at a drug manufacturing/packaging/distribution site, but no longer have any connection with, or have any reason to doctor spin for, "Big Pharma.") 87.81.230.195 (talk) 19:45, 26 April 2009 (UTC)[reply]
I believe that the drug companies are complying with the regulations - and that this means that their storage instructions are safe. However, the US Army (who maintain LARGE supplies of drugs in storage in case of urgent need) tested a bunch of drugs and found that the "use-by" dates on almost all of the medication they had was too conservative by orders of magnitude. They had been tossing out expensive drugs by the truckload because they were past their expiry dates - when in fact, they would have been both safe and effective for years afterwards. It's possible that the drug companies are being deliberately over-cautious in order to avoid any risk whatever - but it's also possible that either they want to make money by giving their product an unnecessarily short shelf-life - or that they simply don't bother to test them for long enough to find out when they finally do start to degrade. There is also a fine line for them to tread if a drug would last longer if kept under ideal conditions but degrade rapidly at room temperature or whatever. Do they put the shorter room-temperature number on the label on the grounds that people are too stupid to keep the drugs properly cool/dry/whatever - or do they put a longer duration and hope that people pay attention to the storage instructions? SteveBaker (talk) 13:07, 29 April 2009 (UTC)[reply]
Expansion of the universe
Is it true that the universe is expanding at an increasing rate? Meaning it's expanding faster now than it did billions of years ago? Also this statement found on the article, Metric expansion of space confuses me. It says, "The metric expansion leads naturally to recession speeds which exceed the "speed of light" c". What does "recession speeds" mean? 69.69.75.22 (talk) 17:44, 25 April 2009 (UTC)[reply]
Yes, current observations support an accelerating expansion. Recession speed means the speed at which two objects are moving apart (usually with us as one of those objects). We observe distant galaxies which have redshifts corresponding to them moving away from us faster than the speed of light. For normal motion, that is impossible, but since it is the universe itself expanding, rather than just objects moving through space, that rule doesn't apply. --Tango (talk) 18:53, 25 April 2009 (UTC)[reply]
To clarify: Those galaxies were not receding from us faster than the speed of light when the light we now observe was emitted. And, as best as we currently can determine, the universe's expansion first slowed down, and then sped up again. So if you asked "billions of years ago", you have to be specific. Current thinking is that gravity pulls the universe together, but dark energy pushes it apart. When the universe was smaller, gravity was the dominant force, slowing the expansion down. However, the universe still grew past the threshold where dark energy overtook gravity as the most significant large-scale force. --Stephan Schulz (talk) 23:46, 25 April 2009 (UTC)[reply]
Actually most of them were receding faster than c when they emitted the light we now observe. Recession speeds have mostly been decreasing since the big bang, so if they're larger than c now they were even larger in the past when the light was emitted. (There has been a slight increase recently, but only slight—the predicted exponential expansion is still in the future.) In the diagram on the right, the red line is light emitted by the yellow object (a distant quasar) and detected 12–13 billion years later by the brown object (Earth). Cosmological time is measured vertically from the cone's apex to its base, and distance is measured circularly around the cone (as shown by the orange line). The "recession speed" is the change in that distance over time. It can increase faster than c = 300,000 km/sec, but there's no direct connection between that and the speed of light, which is a local limitation on the angle that these lines can be tilted from the vertical. It's kind of hard to see in this image (easier in the top-down view), but the distance between us and the light increased at first, which means that the distance between us and the quasar was increasing faster than c then (and still is—the speed is around 2c now and was around 3c then). -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
Just by the way, any observations of increased redshift in objects that already have an enormously large redshift would not indicate an accelerating expansion, because those objects are seen as they were farther in the past to begin with. Therefore, the acceleration would have to have been determined by other sources. ~AH1(TCU)01:04, 26 April 2009 (UTC)[reply]
The expansion affects the light in transit, so redshifts do contain information about the expansion after the light was emitted. Specifically what the redshift tells you is a(now)/a(then), and what you want to know is a''(t). If you measured the redshift of the cosmic microwave background for a long time (i.e. keeping "then" fixed while varying "now"), then an acceleration in the redshift would be direct evidence for accelerating expansion happening now. But we haven't been doing astronomy nearly long enough for that—the predicted rate of acceleration is about 0.3% per billion years per billion years. A better technique is to look at many objects at different redshifts, which amounts to varying "then" while keeping "now" fixed. The first actual evidence for accelerating expansion came from redshift measurements of type Ia supernovas out to z≈1, which is several billion years back, enough to see a (somewhat noisy) trend. -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
acid
I went to the store but they only had 5% vinegar for sale remainder is water. Does anyone know a simple way that I can concentrate the vinegar I get from to store to 25%? Wikivanda199 (talk) 18:27, 25 April 2009 (UTC)[reply]
Acetic acid (the key ingredient in vinegar) boils at a slightly higher temperature than water (118C) and the combination doesn't form an azeotrope, so distillation should work. Boil the vinegar and more water will evaporate than acetic acids so what you end up with should be a higher concentration of acetic acid than you started with. Keep boiling it until you reach the desired concentration. --Tango (talk) 18:50, 25 April 2009 (UTC)[reply]
Many chemical supply companies will sell "glacial" acetic acid, which is about as concentrated as you can get. You can order some of that and dilute it down to 25% also. --Jayron32.talk.contribs18:56, 25 April 2009 (UTC)[reply]
Check also gardening, cleaning-products, and photo-lab suppliers (not sure what concentration is sold for stop bath)--lots of strong (and reasonably priced) chemicals. Googling around, apparently there are some vinegars that are much higher acid concentration than normal. DMacks (talk) 19:15, 25 April 2009 (UTC)[reply]
I've never seen it elsewhere, but a local East Asian food shop sells 5x concentrated white vinegar. (Strangely, it's from Germany. I think it's called "Essig Essenz". There's a warning on the label in big, bold letters "DILUTE BEFORE USING".) You might be able to get it at a specialty shop, or order it online. -- 75.42.235.205 (talk) 19:49, 25 April 2009 (UTC)[reply]
"Essig-Essenz" is commonly available in German supermarkets. It's sold as a food item with other vinegars, but is used for both food and non-food applications, in particular cleaning of tiles, or anything that suffers from lime build-up and can stand acid. For consumption, it is very boring and without real flavor if diluted with water, but it can be diluted with other fluids, in particular wine, to make e.g. interesting salad dressings. --Stephan Schulz (talk) 08:41, 26 April 2009 (UTC)[reply]
Ebay.com has a number of suppliers under "acetic acid". You can also look under "vinegar", but there are so many things under that category you should limit the search to "everything else." (that would include food). —Preceding unsigned comment added by 98.21.107.30 (talk) 21:15, 25 April 2009 (UTC)[reply]
Well if you had 25% vinegar and wanted to get down to 5%, you would just add water. So what you want is to add negative water. What is negative water? Well, for one thing, it could be water owed. So maybe you could buy the appropriate amount of distilled water on your credit card or borrow it from a friend and so on with your slips. I haven't worked out all the specifics however mathematically I believe my reasoning is correct. Let us know the results. 79.122.60.88 (talk) 12:48, 26 April 2009 (UTC)[reply]
That sounds like something out of an adventure game. I remember one that had a packet of "Instant something-or-other" with the instructions "Just add nothing!", so you had to add the contents of an empty bottle to it. You idea is much the same, just taken to a greater extreme. --Tango (talk) 21:17, 26 April 2009 (UTC)[reply]
How about adding NaOH or KOH as you have acetic acid in your diluted vinegar, and then evaporate all the liquid...you'll have solid sodium (or potassium) acetate left. Add to it an equivalent amount of hydrochloric acid having (at least) the desired concentration of acetic acid you want. Now you've got acetic acid and salt at whatever concentration the acid was. Distill it if you don't want to have any salt present--don't have to worry about being careful to separate the acetic acid from the water (which is pretty hard unless you have a good still from what I hear). DMacks (talk) 21:46, 26 April 2009 (UTC)[reply]
April 26
radical addition of alkynes
There are two (pencil and paper) subsyntheses I would like to make (well the reason I'm adding halogens is that I'm trying to attach the products onto an aryl group later, but that's not the issue). Can I check that the following ideas are valid:
first synthesis
First synthesis: I know alkene reactivity > alkyne reactivity, but would it be possible to use acid-catalysed hydration of just the alkene bond? If I set the temperature low enough, it would be possible to get a major product where I just added to the alkene bond but not the alkyne bond, right?
In addition, how would I design the reaction so I can "stop" at the alkene stage, and not do a double-hydrobromination? (My textbook says you can stop it for normal Marvkovnikov addition, without commentary on radical addition, such that you don't form geminal halides, but I have no idea how you would detect the optimal formation of your alkene product such that you could stop the reaction on time.)
In addition, does the overall idea of radical (anti-Markovnikov) addition of Br to an alkyne bond work? Are radical stability effects magnified such that the formation of 2-bromo product is limited? I assume that the radical addition for alkenes is much faster than the carbocation formation step, hence why the radical effect dominates, but is a radical on an sp-carbon going to be more unstable than say a radical on a secondary sp2 carbon? John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
second synthesis
Second synthesis: Assuming the validity of radical addition to an alkyne, this second synthesis seems to imply I would get a cis-product as well as a trans-product. I only want the trans-product. Is it possible to design a reaction that favours the formation of trans-product? (The formation of diastereomers isn't important for my first synthesis.) John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
Enhancement by implants
More and more often I would find a third arm or an implanted wlan interface to my computer very useful. Being in a hurry very often, I would greatly appreciate a way to put on my socks while continue to operate the keyboard, just as an example. Or to make a phone call, talking silently via some future-style nerve-reading interface while listening to some slow talking time-sucker on the normal phone.
I know this is far from practice, at least for otherwise healthy people (and thus this is not asking for medical advice), but what is the state of art for such enhancements? (Well, I know I could buy a headset for a start ...) 93.132.137.0 (talk) 11:45, 26 April 2009 (UTC)[reply]
Well - perhaps not as far as you think. If you'd be prepared to use your real hands for putting on your socks on, there is a guy who has demonstrated typing by thought alone ([20]). See Brain-computer interface for example. At present, it's rather slow (eight characters per minute!) - but it's getting there. There are plans to sell a starwars-themed toy that lets you control the motion of a ball moving up and down a tube by thought alone: [21]. So it's certainly possible. SteveBaker (talk) 14:54, 26 April 2009 (UTC)[reply]
The thing that has real prospects is "add-ons" to replace things that are missing, such as an amputated limb. The big problem with wholly new things like a third arm is that you don't have any brain circuitry to manage them. There are some tricks that potentially could be used to reconfigure brain circuitry that has other functions, but none of them are likely to come into play very soon. Looie496 (talk) 16:47, 26 April 2009 (UTC)[reply]
The strange thing is that when I try to put on my socks while brushing my teeth and wanting to do even more in parallel (but not attempting for certainty of failure) I really feel like I could handle a third or forth arm. After all, I frequently pick up things with my feet. (Maybe I was a spider in some previous life.) As for the links from Steve Baker (thanks!), they made me realize I won't need any extra limbs implanted when there is/would be the possibility to steer some detached actuators instead --- a kind of real-science telekinesis. 93.132.137.0 (talk) 22:04, 26 April 2009 (UTC)[reply]
Earthrise on the Moon
Earthrise, today's featured picture at Commons
Today's featured picture at Commons has the following caption: "Taken by Apollo 8 crewmember Bill Anders on December 24, 1968, showing the Earth seemingly rising above the lunar surface. Note that this phenomenon is only visible from someone in orbit around the Moon. Because of the Moon's synchronous rotation about the Earth (i.e., the same side of the Moon is always facing the Earth), no Earthrise can be visible from the surface of the Moon." I can understand this very well. However, would you always see the exact same scene? Would Earth appear to be basically a circle in the sky that doesn't move? Or would it move somewhat because the Moon isn't always precise-to-the-millimetre facing the same way? Just curious...Nyttend (talk) 12:55, 26 April 2009 (UTC)[reply]
It would appear as the Moon does from Earth, just larger -- that is, it would exhibit phases as well as size changes due to orbital eccentricities and the libration that allows us to see more than half the Moon. — Lomn12:59, 26 April 2009 (UTC)[reply]
From the perspective of someone standing on the surface of the moon, the earth would stay in more or less the exact same place in the sky, hour by hour, day by day, year by year (it would move a little because the moon 'librates' - see image at right) - but as the long lunar day progresses from dawn to dusk to night, the earth would go through phases - just as the moon appears to go through phases from earth. SteveBaker (talk) 14:45, 26 April 2009 (UTC)[reply]
I haven't seen anything written about this, but the Earth would almost certainly have to move slightly, because the Moon's orbit is slightly elliptical rather than circular, and in addition is perturbed by the Sun. Looie496 (talk) 16:37, 26 April 2009 (UTC)[reply]
Also of course you would see evolving cloud patterns on the surface and a complete rotation every ~25 hours. It would be a lot more dynamic than the view we have of the Moon. -- BenRG (talk) 18:46, 26 April 2009 (UTC)[reply]
Googling on "libration in longitude", I found a page at demonstrations.wolfram.com that says the extent of this libration is 6°. Since the Earth's visual diameter as soon from the Moon is about 2°, it follows that there are parts of the Moon -- ones that we see roughly edge-on from the Earth's surface -- where you could indeed see the Earth rise. It would never come very high above the horizon, and later it would turn around and set in practically the same place, the whole cycle taking about a month. --Anonymous, 21:25 UTC, April 26, 2009.
This "almost stationary" earth phenomenon was a critical element of Apollo's lunar surface S-band communications antennae, which where directional and set up to point to one spot in the sky (towards Earth). Nimur (talk) 15:09, 27 April 2009 (UTC)[reply]
Yes, but the Apollo missions each spent only a few days on the lunar surface. Given that the earth would make its apparent motion over an entire month, the amount of motion over a few days might well be little enough to make the assumption that it's stationary be a viable one. SteveBaker (talk) 12:41, 28 April 2009 (UTC)[reply]
A new article on an interesting supernova. I'm an astronomy amateur and would therefore appreciate review of the text by someone with a little more experience. Thanks, —Anonymous DissidentTalk13:32, 26 April 2009 (UTC)[reply]
One of the missing info would be, is it in the Milky Way, in what galaxy, what distance? How fast did it rise and dim, to what magnitude (visible for whom?). All that theoretic stuff that now is in the article would just be a chapter. --Ayacop (talk) 18:20, 26 April 2009 (UTC)[reply]
I'm fairly sure I know the answer to this - but I need some evidence. At my local car club, we restore a lot of rusty old wrecks. Getting rid of rust is obviously important - but what I want to know is whether rust spreads because the rusty metal traps water and salt better than smooth metal - or whether it's because the existing rust is acting chemically as some kind of catalyst for reaction. It's obvious that rust starts as a little spot and then grows - it's just a question of what that mechanism is. I'm pretty sure it's not a chemical effect - but there is a big argument about it that needs resolving.
I think iron rust spreads because it's flaky. It exposes the material below to further rusting. (This is from something that I read about why iron and steel rust but aluminum doesn't. Catalysis was not mentioned.) --173.49.78.81 (talk) 15:38, 26 April 2009 (UTC)[reply]
As I understand it (which may not be very far), rusting is an example of electrochemicalcorrosion and any initial defect in the protective paint layer forms an anode with a current formed through the water (which is why salt water is so destructive because of its high conductivity). This link has some further explanation [22] which you may find useful. BTW both chloride and sulphate commonly act as catalysts in rusting. Mikenorton (talk) 19:00, 26 April 2009 (UTC)[reply]
I agree - rust is electrochemical, so it will induce local static voltage in the electrically connected metal. Because the rust is a worse conductor than the "pure" iron (or steel/alloy), it has some resistivity and the voltage does not equalize; current flows; and this current encourages the further rusting. (Those electrons have to go somewhere - and they go to the oxidation reaction, encourage it, and move along to the next spot). You can weld on some extra metal like Zinc to preferentially absorb that current, but I've never heard of this being used on a land vehicle (I'm no auto-body expert though). Anyway, I think this is neither mechanical (flaking) nor catalytic because the existing rust is actively participating in the electrochemical reaction throughout the entire connected surface. Nimur (talk) 15:14, 27 April 2009 (UTC)[reply]
On high-speed tallow candles
The Dictionary of Misinformation(a trivia book dedicated to debunking common misconceptions), in a section about the claims that a botfly can fly at 800 mph, says that "a tallow candle will penetrate a board at such a velocity". Is this true? I recall the Mythbusters refuting a similar proposition about a straw penetrating through a tree trunk in a hurricane(about 300 mph wind speed), but 800 mph is more than twice that, so I'm not sure how to extrapolate from that to the presumably softer candle. 69.224.37.48 (talk) 18:38, 26 April 2009 (UTC)[reply]
The Botfly thing has been debunked over and over (Here, for example) - one good reason being that it would have to consume more than it's own weight in food every few minutes in order to be able to produce that much energy.
But I wouldn't be quite so quick to dismiss the idea of the candle going through a board at 800mph. It's not the hardness of the candle that matters so much as the mass. When any object hits any other object and is stopped - all of the kinetic energy that the moving object had has to go somewhere. A candle weighs...I dunno...0.1kg let's say. At 800mph - 350 ms-1 it's going about a third of the muzzle velocity of a 50cal bullet with about three times the mass. But kinetic energy is proporitional to the SQUARE of the velocity - so it's going to deliver only about a third of the 'punch' of a modern 50cal bullet. However, the target is a "board" - perhaps just a half inch of wood. I've seen karate people smash "boards" with their open hands. I think that an 800mph candle would go through a "board" like a knife through butter!
The Mythbusters did point out that a straw couldn't go through a tree trunk - but they did get them to penetrate a fair way into the trunk (a tree trunk is a lot thicker than a board) - and they found that a heavier projectile would do considerably more damage. A candle weighs maybe 50 times more than a straw, we're talking about it going almost three times faster - so perhaps 450 times more energy - and through a 1/2" board rather than an 8" tree...I think that's no problem at all!
It would probably be seriously deformed (unless you shaped it to be very aerodynamic), but it is very difficult to stop something that is moving that fast - unless it had to travel a long distance through the air, I'm pretty sure it would make it in some form or other and, as Steve says, all that really matters is the mass, what form that mass is in is pretty much irrelevant. --Tango (talk) 22:54, 26 April 2009 (UTC)[reply]
Besides - the original "thought experiment" didn't say there was air - we may therefore assume the whole thing happen in a vacuum. At any rate, it's pretty much specified that the candle hits the board at 800mph...who knows how? SteveBaker (talk) 02:49, 27 April 2009 (UTC)[reply]
The board is toast. Same as if the board moving 800 mph in vacuum hit a stationary candle. Same as if foam space shuttle insulation hit a carbon fiber wing surface at several hundred miles per hour. Edison (talk) 04:42, 27 April 2009 (UTC)[reply]
I'm confused - the tallow candle is propelled to high velocity by some external energy source? Is it possible that they are using the (archaic) usage of "candle" to mean "rocket"? (This seems unlikely since they call it a "tallow candle", but a modern hybrid fuel rocket can work on paraffin with pretty good combustion). Is the idea that at 800 mph, even something as soft as tallow can penetrate a solid object? I'm also thinking that the flame exit velocity of a regular candle could actually be close to 800 mph (transsonic at high temperatures) in a very local sense; but I don't see how this convective flow would penetrate a board at 800 mph (unless the board is not combusting but is acting as a rocket nozzle or venturi tube... in that case, the flame gases could easily exit at 800 mph if confined to a small hole. Nimur (talk) 15:28, 27 April 2009 (UTC)[reply]
Does it have to be recognizable as a candle after it hits the board? I think you would have a demolished board, and little bits of candle everywhere. —Preceding unsigned comment added by 65.121.141.34 (talk) 20:01, 27 April 2009 (UTC)[reply]
To clarify, all the book says on this subject is the clause I quoted above, with no indication of how you'd accelerate the candle to that speed. I get the impression that it's supposed to remain intact while cleanly punching a hole through the board, but everything shattering into bits seems more likely. 69.224.37.48 (talk) 23:57, 27 April 2009 (UTC)[reply]
If a candle were attached to a rocket fired in space and accelerated to 800 mph (357 meters/sec), then detached from the rocket and made to strike a board, the board would become splinters and the candle would probably liquify or vaporize, or at least be smashed to small fragments. If it were in a stable axial trajectory, it might just blast a circular hole throught the board about the diameter of the candle, like a jet airliner smashing into the Pentagon at several hundred miles per hour. If you tried firing a candle from a gun, it might turn to melted tallow. It is low in density, and would decelerate quickly in air. It might be possible to accelerate it to 800 mph with a discarding sabot and high pressure air in a long tube, such as Mythbusters used to accelerate frozen chickens to smash into airplane windshields. The board should then be fairly close to the muzzle. Definitely do not try this at home. (But if you do I would like to see the video.) Edison (talk) 00:45, 28 April 2009 (UTC)[reply]
I've seen a demonstration (real-life, not on TV) of a soft tallow candle fired through boards. I don't know at what speed but it was definitely subsonic. It was fired from a home-made rifle! Dbfirs16:24, 28 April 2009 (UTC)[reply]
Battery Disposal
I decided to so some spring cleaning this weekend and my project turned up a ton of alkaline batteries. I raed on my the website for my community waste disposal agency that batteries manufactuerd after 1996 don't have lead in them and can be disposed of safely with regular garbage. Thing is, I have no idea how old these batteries are: no dates! are there any indicators I can look for to indicate lead safety? Thanks --Shaggorama (talk) 20:38, 26 April 2009 (UTC)[reply]
I have no idea about procedures in MD, but in the EU every supermarket provides receptacles for spent batteries. They all (I believe) contain heavy metals which is bad for the ears, not to mention refuse dumps :) --Cookatoo.ergo.ZooM (talk) 22:19, 26 April 2009 (UTC)[reply]
You could buy a modern, non-lead battery and weigh it. Then weigh the old batteries. If any of the old batteries are heavier, they probably contain lead. This is not a certain test, of course. It would be best to dispose of all the old batteries as if they; contained lead. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 18:08, 27 April 2009 (UTC)[reply]
If the batteries actually are labelled as "alkaline batteries" as you say, then they're pretty much guaranteed not to be lead-based - see alkaline battery. Lead-based batteries are, additionally, quite uncommon as small household batteries even pre-1996; and they generally are clearly labelled even going back into the 1980s. The danger of lead isn't a particularly new discovery. ~ mazcat|c13:14, 28 April 2009 (UTC)[reply]
Alkaline batteries usually contained cadmium -- not good for landfill. Large modern rechargeable torches often have sealed lead-acid batteries, again, not good for landfill. It would be good to try to find a recycling facility if possible. Dbfirs16:33, 28 April 2009 (UTC)[reply]
Indeed, Dbfirs does have a good general point though - even in the case of alkaline batteries, there's a possibility of mercury being used in small amounts, and that's no more pleasant than lead or cadmium. As a general rule it's always best to recycle batteries if practical - lead is not the only dangerous heavy metal involved. ~ mazcat|c19:31, 28 April 2009 (UTC)[reply]
Best is a matter of opinion. You must explain to use what you define as being "best" to get an answer there. As for most durable (and ignoring the astroturf answer), tall festuca is popular for high-traffic areas that require durable grass. There are many types, so it is usually possible to find a type that grows in most areas that have sunshine. -- kainaw™23:25, 26 April 2009 (UTC)[reply]
Hi. This is from a question that didn't really get answered last time, but hopefullt this is answerable. Let's say you have a depression in the land, and water is starting to fill it. I want a general formula that calculates the amount of time needed for water to completely fill the depression. I know parameters such as the average and maximum depth of the area, the elevation at which the water is coming, the area of land filled, the length that the water initially needs to travel in order to meet the lowest point, whether the depression is dry or already has water in it, etc. Would I need any other information such as the salinity of the water, the temperature, the curvature of the Earth, the density of the rock, the air pressure in the depression, the wind direction and speed, etc? Does the formula, d = t2(a/2) (where d is distance, t is time, and a is acceleration (9.98 m/s)) be related to this formula? Thanks. ~AH1(TCU)22:39, 26 April 2009 (UTC)[reply]
Surely all the information you need is the volume to be filled and the rate at which the water is flowing in? Divide one by the other and you have your answer. --Tango (talk) 22:49, 26 April 2009 (UTC)[reply]
Perhaps, but I need to calculate the rate at which the water is filling in, from parameters such as the depth of the depression using a type of formula. So, how do I do this? ~AH1(TCU)22:53, 26 April 2009 (UTC)[reply]
If the water is falling in from above the depression, then Tango is entirely correct: flow rate and volume are the only necessary parameters. If you add in drainage, you may need to move up to a differential equation, but even then, salinity and all that should be irrelevant. — Lomn01:14, 27 April 2009 (UTC)[reply]
The rate the water is filling it in is something you need to measure, you can't calculate it without far more information that it is reasonable to have (assuming you are talking about a real world situation, rather than some idealised one). You need to measure the cross sectional area of the river that is filling it in and how fast it is moving, multiply those together and you get the amount of water filling the depression per unit time. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
If you want to know the depth of water as a function of time then you're going to need to learn some calculus. You need an equation describing the shape of the depression - then you're going to calculate the integral of that function - and this new function can then be evaluated to figure the rate of filling. SteveBaker (talk) 02:43, 27 April 2009 (UTC)[reply]
Don't ignore the flow of water through the soil into the aquifer. Newton-Raphson matrix methods might help in providing non-determinate solutions.Edison (talk) 04:39, 27 April 2009 (UTC)[reply]
Yes, if there is significant drainage then it gets more complicated. The drainage will depend on how filled it is already so you will, as Lomn says, need a differential equation. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
The Earth's magnetic field is certainly strong enough to have a noticeable repulsion: all you have to do is point an opposing magnetic pole and you will be repelled. That's how a compass works: it's a lightweight magnet, and if you flip it around, you can notice it being repelled from the "wrong" way and attracted towards pointing North. Levitation is hard because most of us are on the "side" of the earth as considering it a bar magnet, so the field is relatively weak and is substantially parallel to the surface. At the poles, the field is stronger and pointed perpendicular to the surface. However, the field is still really weak (0.6 gauss according to the article) and a gauss is a pretty small field, so you'd need something pretty light to be able to levitate well. DMacks (talk) 07:28, 27 April 2009 (UTC)[reply]
As well as being quite weak, the Earth's magnetic field is approximately uniform over distances of the order of a few metres. The force that turns a compass needle is a torque, which is present even in a uniform magetic field, because the forces on the two poles of the compass needle are opposite in direction. However, to produce a net force on a magnetised object you need to have a non-uniform magnetic field, to make the forces on the two ends of the object also different in magnitude. The Earth's magnetic field is so close to uniform that the net force on any reasonably sized magnetised object will be minute.
You do get a net force on a current carrier moving through a uniform magnetic field. 0.6 gauss is 60 microteslas, so a wire that is perpendicular to this strength of field will experience a force of 6x10-5 N per metre per amp - so to get a measurable force you need either a very long wire and/or a very large current. However, stronger magnetic fields produce bigger effects - this NewScientist item says that a field of 17 teslas can levitate a frog ! Gandalf61 (talk) 12:24, 27 April 2009 (UTC)[reply]
Very small and charged items like electrons and some light ions do get trapped by Earth's magnetic fields, and can be "repelled", "trapped", "resonated", and a variety of other interesting magnetic-field related motions. Take a look at the Van Allen radiation belt article. Those electrons and ions, under gravity, would get pulled into the lower ionosphere; under thermal motion, they would blow into space pretty fast; but they get trapped in the magnetic field and pulled into an "equilibrium" distance, complete with fun bouncing helical orbits that look nothing like your classic Newtonian gravitational elliptic orbits! Nimur (talk) 15:34, 27 April 2009 (UTC)[reply]
Hi,
Can you tell me What is a steam table?.How to calculate the value of enthalpy,using steam table for a given value of pressure and temperature?.Please reply if you are having any idea about this, plz share with me.... —Preceding unsigned comment added by Smenonp (talk • contribs) 12:04, 27 April 2009 (UTC)[reply]
Steam table redirects to the Water data page steam table. If you don't understand enthalpy, there is an article on that also. Basically the idea is that the enthalpy of vaporization is not constant - it actually depends on the temperature of the source water. To really understand this, you have to realize that while the "boiling point" of water is the phase transition point, in reality there is an equilibrium reaction between water and its vapor at any temperature. The steam table will tell you the values you need to calculate the parameters of that vaporization reaction. Nimur (talk) 15:38, 27 April 2009 (UTC)[reply]
Chameleons Changing Colors As Camouflage?
I have a question regarding our article on List of common misconceptions, specifically whether or not chameleons change their color to match their surroundings as a form of camouflage. Our article currently states:
"Chameleons do not change color to match their surroundings. They are naturally camouflaged and, although they can change their skin color into a variety of different colors, these changes are caused by temperature or interaction with predators or other Chameleons.[1]".
Another editor is disputing this here [23]. The video [24] he cites appears to be legit to my eyes, but maybe this is a video of an anole and not a chameleon.
well, the video is not a legitimate source. it could easily be photoshopped (and probably is—doesn't look natural at all). by contrast, the source against it comes from a major university. Wikipedia has long guidelines about what is a reliable source, about how "original research" is not allowed, etc. --98.217.14.211 (talk) 14:08, 27 April 2009 (UTC)[reply]
Hmm, but the chameleon article itself states, with two (possibly less credible, but still) citations:
"Recent research indicates that they do not only change their color for reasons of camouflage, but also use colour changes as a method of communication, including to make themselves more attractive to potential mates." -- Aeluwas (talk) 14:22, 27 April 2009 (UTC)[reply]
The issue here is having good citations and reading what they actually say. If it can be cited effectively, great. If not, then no. In those cases, citation #1 is about communication, not camouflage ("Overall, our results suggest that the evolution of the ability to exhibit striking changes in colour evolved as a strategy to facilitate social signalling and not, as popularly believed, camouflage."). Citation #2 specifically says it is not about camouflage ("Chameleons can produce a wide range of colors and patterns on their skin, but they do this primarily to express mood, not to blend in with different environments."). So I'd say that the distillation of these sources that claims they are camouflage PLUS expression rather than expression and NOT camouflage is incorrect (certainly not what the sources say). --98.217.14.211 (talk) 14:28, 27 April 2009 (UTC)[reply]
I knew that was going to bite me in the ass. ;) I was very close to adding a "I haven't had time to check the citations" part, but I omitted it. -- Aeluwas (talk) 16:34, 27 April 2009 (UTC)[reply]
That video looks like it was intentionally made to show off a cool match moving technique. (The super-shaky camera is common in these sorts of clips. Subtly is apparently not the goal.) APL (talk) 16:30, 27 April 2009 (UTC)[reply]
The video is not a good source, but the statement in the list of misconceptions seems to be wrong according to sources that are good, such as this recent PLOS paper. It looks like a case of confusion. Apparently there are arguments that color changes are used for more than just camouflage, and that the other functions may have been most important in driving the evolution of the capability. But there doesn't seem to be any dispute about the claim that color changes do have a camouflage ("crypsis") function. Looie496 (talk) 16:53, 27 April 2009 (UTC)[reply]
This is OR: But when I lived in Kenya as a kid in the late 1960's, I caught a baby chameleon and kept it as a pet for several months before my parents made me let it go. They certainly do change color in an effort to match their surroundings - but it takes them maybe 30 seconds to complete the change (maybe adults are faster), the range of colors they can produce isn't all that great and they certainly can't reproduce patterns in the background. However, they certainly DO change through shades of green, brown, reddish brown and grey. Obviously, if you are a kid and have one of these things as a pet - you're going to try to make it do crazy color changes - and it really can't. If you sit it on a bright red sheet of paper, then after maybe half a minute, you have a reddish-brown chameleon because that's the closest it can come. If you put it on a sheet of yellow paper - you get a kind of greenish brown because mine couldn't turn yellow at all...but if you put it on a sheet of dark green paper, it'll make a reasonably good match for it. It's not going to completely vanish - but the match is good enough in 'real world' situations that the animal might encounter. Attempts to make it match spots and stripes produced a greyish-brown chameleon no matter what. It was cool to have this thing sit on your finger so you could carry it around the room looking for flies and watch that AMAZING tongue shoot out...that's by far the most impressive thing they do. SteveBaker (talk) 18:36, 27 April 2009 (UTC)[reply]
It sounds like the claim in the article that color change does not match background as camo is bogus and original research, rather than adding that some other factors in addition to background matching/camo produce color change as well. I have certainly watched a chamelion change color to match the background, and background matching is widely accepted as a survival mechanism. If it changes color to indicate temp, that would make it a great thermometer, but would be an implausible evolutionary way to enhance survival. As a reality check, what do other encyclopedias such as Britannica say? Wiki editors often go off on a crusade as True Believers in a viewpoint not widely shared in a particular field, hanging their prejudices on one reference and ignoring many others with other conclusions. Edison (talk) 15:09, 28 April 2009 (UTC)[reply]
I added a contrary ref: "Others state that chameleons can change their color in milliseconds for camouflage as well as social signalling.[2]National Geographic quotes an expert on chameleon color change, Christopher Raxworthy, associate curator of herpetology at the American Museum of Natural History, to the effect that they match the background to survive, but they also color change as a social signalling mechanism: ""Most of the time, chameleons are behaving as highly cryptic animals trying to avoid detection from predators." So the only "misconception" would be that they 'only color change for camouflage, and that's a pretty trivial one. If scientists disagree, then it should not be on a list of "common misconceptions" at all. — Preceding unsigned comment added by Edison (talk • contribs)
They change color in MILLISECONDS! I find that hard to swallow. The pet chameleon that I owned took a good 30 seconds to do it. Perhaps adult animals are faster - perhaps there are sub-species differences - but I strongly doubt it. There are animals out there that can change color that fast (cuttlefish for example) - but I never saw my chameleon do that. It's certainly possible that they could also change color to reflect mood or mating status or something - but most of the time it's certainly camoflage. These are slow-moving animals with plenty of enemies - this is their only defense! I strongly suspect that the nay-sayers are trying to make the poor critter do something it's unable to do - like match patterns or colors that it's simply unable to do...or perhaps they are buying into the "changing in milliseconds" idea and not waiting the 30 seconds that my chameleon took...or possibly they have been looking at some particular sub-species that doesn't do it. My chameleon came from a tree outside our apartment on the outskirts of Nairobi, Kenya...who knows what chameleons from other places do? I know for 100% sure that my chameleon could match reasonable backgrounds like tree bark or leaves or reddish dirt if given time. When you're an 12 year old kid with a pet chameleon - that's pretty much their only party trick (they don't obey "sit", "down" or "roll over" - and they have a whole different take on the game of "fetch"!) - so everyone who comes to your house gets to see it! Actually - I know my mother has this on video - but unfortunately, that's 8mm cine film and it's currently on the other side of the planet - so I can't easily produce it! SteveBaker (talk) 23:17, 28 April 2009 (UTC)[reply]
If they can really change color in milliseconds I suggest making computer monitors out of chameleon leather. APL (talk) 13:02, 29 April 2009 (UTC)[reply]
What's so special about swine flu?
There is something I don't quite understand about this current swine flu panic we are having right now. I'm not trying to be flippant, but I don't really get what the big deal is. Every year influenza kills hundreds of thousands of people, every year new varieties of flu start spreading. I don't get why this particular one is getting so much attention? Is it deadlier than all those other varieties? Is it much more contagious? Belisarius (talk) 14:59, 27 April 2009 (UTC)[reply]
This outbreak is getting attention because of the possibility that it could become a pandemic. See swine flu. The H1N1 strain of flu is a subtype of Influenza A that descended from the virus that caused the "Spanish" influenza pandemic of 1918-1919 that "infected one third of the world's population (or ≈500 million persons at that time) and caused ≈50 million deaths." Sounds pretty important to me. --- Medical geneticist (talk) 15:27, 27 April 2009 (UTC)[reply]
But, so, why? Why is this influenza so much more dangerous than the gazillion other types of influenza out there? You know, the diseases that hundreds of millions of people contract every year, the diseases that kill hundreds of thousands of people annually? Belisarius (talk) 15:51, 27 April 2009 (UTC)[reply]
I was going to ask the same question here. I would love to see statistics on how many people die of the flu each year in Mexico. I feel like the media just happen to be jumping on this one more than other years. -- MacAddct1984(talk • contribs)16:09, 27 April 2009 (UTC)[reply]
You are asserting that human influenza is a petty illness, and for a heathy adult it's almost always non-lethal. The problems start arising when you are dealing with a group of individuals with a weaker immune system, such as the young children, ill or elderly population. You'll notice that over 1000 cases of swine flu have been reported during this pandemic, but comparatively few deaths (about 1:10, maybe just over/under). When flu infects individuals with compromised immune systems, it can cause some serious, and potentially lethal, consequences (whether it is human, bird of swine flu). Regards, --—Cyclonenim | Chat 16:13, 27 April 2009 (UTC)[reply]
We weren't asserting that it was a petty illness, on the contrary, we were saying that it is a big deal, but did not seem any worse than any other year, when thousands die each year from influenza. But I guess the fact that it's a new illness is the problem and there is currently no easy vaccine. -- MacAddct1984(talk • contribs)16:40, 27 April 2009 (UTC)[reply]
Sorry, upon rereading (where I added the below comment) I realised I misunderstood the original question, but forgot to strike. Will do so now. Regards, --—Cyclonenim | Chat 16:45, 27 April 2009 (UTC)[reply]
I realised that I probably didn't answer the question. The reason that this has so much more attention is that it has the potential to go wildly out of control. With human influenza, we have flu jabs which we can provide to the immune-compromised individuals and hopefully keep them alive through tough times like winter. With a new strain of swine flu, one which we have essentially no vaccination for, all of those immune-compromised individuals are at risk of catching the disease, meaning it can spread much, much faster and therefore kill more people. See the Spanish flu, for example, which mutated and killed thousands and thousands of people because there was no vaccination. The same problem can occur now if we don't have a vaccination, although a vaccine may be created quicker than back then. Regards, --—Cyclonenim | Chat 16:17, 27 April 2009 (UTC)[reply]
There are two things special about this outbreak. First, the genetic structure of the strain is quite different from other flu variants. Secondly, there are reports from Mexico that many of the people most seriously affected are in the 25-45 age range, a group that normally is the least affected by flu. However, more recent reports make it unclear to what extent the original reports are correct. Looie496 (talk) 16:41, 27 April 2009 (UTC)[reply]
The picture to the right compares the death rates (per 100 000) of the spanish flu with the death rates of more common flus. Notice the 'bump' around 30 year old people. Dauto (talk) 18:05, 27 April 2009 (UTC)[reply]
It's of note that this is not the first Swine flu pandemic fear—there was one in 1976 as well that didn't turn into a pandemic. The fear is, as noted, that it is related to the 1918 strain, which was much more deadly than the normal ones floating around in "flu season." --98.217.14.211 (talk) 02:08, 28 April 2009 (UTC)[reply]
To embellish a bit upon what Looie said above: Any disease that can take a perfectly healthy adult and cripple and/or kill them is scary, and when that disease is transmitted via air with no known cure it is triply scary. Add to that the fact that, unlike with the SARS and Bird flu scares of recent years, this disease has manifested itself strongly in a large population center/transportation hub relatively early in the outbreak, leading to the cases now being reported on 3 continents. Add all that with today's Twitter-minded society (and resulting hysteria), and you get a big deal in the media.
It will probably end up being nothing bigger than SARS and the bird flu--already it seems that subsequent cases outside of Mexico are less virulent (although it might be a bit too early to draw that conclusion), and though it seems to have a death rate ~1%, there may be untold numbers more who never got sick enough to go to the hospital (and thus be counted as a suspected case). Also, lets not forget how much medical care has improved since 1918.-RunningOnBrains02:46, 28 April 2009 (UTC)[reply]
The 1918-1919 flu did not mostly kill the elderly or those with weak immune systems. It killed healthy 19 -25 year olds, since their robust immune systems overreacted and the consequences of that compromised lung function. Edison (talk) 15:05, 28 April 2009 (UTC)[reply]
I have a problem of drooling while I sleep. Usually when I wake up, I find my pillow wet from my saliva. At any normal time my mouth has excess saliva. Is there a cure for this? What basically is the problem? Thanks. —Preceding unsigned comment added by 116.71.46.207 (talk) 15:02, 27 April 2009 (UTC)[reply]
If it is really bad, you could consult your doctor on whether you have a mouth condition that might be causing excessive salivation. If it is only moderate, you could try a mild diuretic before going to sleep, such as drinking tea. Looie496 (talk) 16:37, 27 April 2009 (UTC)[reply]
[comment removed - suggesting a specific OTC drug (which I don't think it actually intended to reduce salivation but just does so as a side effect) is unquestionably medical advice and is inappropriate for the reference desk --Tango (talk) 18:22, 27 April 2009 (UTC)][reply]
Mouth breathing certainly isn't the only way you end up drooling in your sleep, but mouth breathers do tend to drool in their sleep more frequently. I'd guess everybody does it sometimes, whether they're aware of it or not. The explanation for it is pretty simple: when you're asleep, you don't swallow saliva as often as you do when you're awake, and your mouth tends to go slack. If your head is in a certain position, gravity takes care of the rest; in itself, this is a really common and everyday thing. The excessive saliva may or may not be another story; if that concerns you, OP, you should probably talk to a doctor. -- Captain Disdain (talk) 20:14, 27 April 2009 (UTC)[reply]
Try swallowing your spit during the day, and closing your mouth when you sleep. I find that by the time I'm hours into sleep my saliva tends to evaporate away anyway (leaving my mouth dry). Also, It's been found that napping causes more drooling than regular sleeping. ~AH1(TCU)00:04, 28 April 2009 (UTC)[reply]
Looking at this again, I see that I probably didn't get what you were asking. The arcuate fibers are a set of connections -- the set of nerve fibers connecting the two brain areas I mentioned. Looie496 (talk) 19:44, 27 April 2009 (UTC)[reply]
I think the original question was about the arcuate fibers, not arcuate fasciculus. Please do not confuse between the two. The original question refers to the fact that the arcuate fibers article, in its present form, contains little more than just links to the three following articles: Internal arcuate fibers, Anterior external arcuate fibers, and Posterior external arcuate fibers. Now, from what I've read, all these fibers are formed by axons of neurons in nucleus gracilis and nucleus cuneatus of medulla oblongata. While medulla oblongata is generally associated with basic autonomous functions, the two aforementioned nuclei are thought to be mainly somatosensory. Lesioning experiments in cats and rodents show mostly propioceptive and somatosensory deficits following lesions to nucleus gracilis and nucleus cuneatus. So, I would say that the overarching function is delivering somatosensory information to various brain areas. You will have to do more reading to know the details. You will also have to do some research to find out if arcuate fibers in humans are implicated in some additional functions; they very well may be. Hope this helps. --Dr Dima (talk) 19:50, 27 April 2009 (UTC)[reply]
Right Hand Rule and Help with Magnetism
I do not get how to use the right hand rule at all...is there a way to find direction of a field, direction of velocity of a charged particle, or direction of force without using it?
Or
Could someone help me with a sample problem so i can better understand it??
"If a negativley charged particle were moving downward along the right edge of this page, which way would the mangetic field be oriented so that the particle would initially be deflected to the left?"
and
"Three particeles are moving in a uniform magnetic field. Each initially have a velociety pointing to the right. One goes into a circle that is clockwise, two goes straight, three goes in a larger circle that is counterclockwise. One and three have the same velociety and magnitude of electric charge. What can be said about the charges and masses of these particles?"
These are obviously homework problems, but I have about 40 problems like these and help with these two would definatley help me grasp the concept that I am trying to learn. —Preceding unsigned comment added by 70.129.227.81 (talk) 18:05, 27 April 2009 (UTC)[reply]
There are two different right-hand rules in magnetism as you can see in those pictures. The first one is used to find the direction of the magnetic field produced by a current. The second one is used to find the direction of the magnetic force on a (positive) charge moving with velocity 'v' (revert direction for a negative charge). I hope these pictures help. Dauto (talk) 18:38, 27 April 2009 (UTC)[reply]
OK, for those problems you will make use of the second rule which relates the direction of three physical quantities -- Velocity, Magnetic Field and Force, as indicated on the picture. The problems always give you information about two of those directions and you use the picture to help you find the direction of the third quantity in order to answer the question. Your first problem, for instance, gives the direction of the velocity (downward the page) and the direction of the force (towards the left) and asks about the orientation of the magnetic field. Keep in mind that for a negative charge the direction of the force will be the opposite of the one shown in the picture. Put your open right hand in the air with the thumb away from the other fingers in such a way that your thumb points towards the direction of the velocity and the palm (for a positive charge) or the back of your hand (for a negative charge) points towards the direction of the force. Your mid finger will be pointing towards the direction of the magnetic field. Dauto (talk) 20:30, 27 April 2009 (UTC)[reply]
In physics or electrical engineering exams it is funny to see students moving their right hands around with orthogonal thumb and digits trying to line them up with the illustrations on the exam for particle movement and magnetic field. It looks sort of like they are throwing down Gang signal#Hand signs for the Latin Kings. The illustration attached to the response is unhelpful to the OP since it shows all the fingers held straight. See also the illustration from Right hand rule, which unfortunately also has problems. Edison (talk) 14:48, 28 April 2009 (UTC)[reply]
There seem to be many different right-hand rules. This one is closer to the rule I learned. (The hand shape is the same as in your image but the labels are permuted.) That straight-palm version is as good as any other; there are still three distinguishable axes, and it looks less silly in public. You can use a left-hand rule, for that matter, if you assign the labels appropriately. And here's yet another variation. Pick one that you like and learn it. But whatever you do, don't learn two. -- BenRG (talk) 21:32, 28 April 2009 (UTC)[reply]
That straight-palm version makes a lot of sense now that I look at it. Your fingers show the direction of the parallel field lines, your thumb shows the current in the wire, and the force is in the direction you would push with your hand. I endorse that one. -- BenRG (talk) 21:47, 28 April 2009 (UTC)[reply]
I used to have a cartoon for the magnetic field around a wire using a student reading aloud from a physics textbook: "as you face the direction of current flow (had a vector pointing forward along the spine), magnetic field moves through the book from the front front cover to the back cover" and a caption "Moral: you won't get physics if you don't look in your textbook." Well, you get the idea. I know, {{global}}. DMacks (talk) 21:41, 28 April 2009 (UTC)[reply]
Measuring the temp of the Sun
Reading through the Sun article reveals a lot of information about the temperatures of various parts of the Sun. How are these temps measured? How about measure the temp of the core of the earth? Are these considered actual measurements (no one has taken a thermometer to either) or are they just theoretical calculations? Thanks. Anythingapplied (talk) 19:50, 27 April 2009 (UTC)[reply]
They are theoretical calculations. I wouldn't use the word Just. Those models (specially the one for the sun core) are very solid and thrustworthy models, and have been confirmed by indirect observations. Dauto (talk) 20:34, 27 April 2009 (UTC)[reply]
(ec)These are not direct measurements. The usual approach involves either analytic or numerical models of the star or planet interior. The models are calibrated using seismology (Earth) / helioseismology (Sun) data and - in the case of the Sun at least - the light that the Sun emits at different wavelengths. Different wavelengths (different photon energies) can escape from different depths: more energetic photons usually come from deeper within the Sun as they usually have smaller absorption and scattering cross-sections; but be warned that this is by no means always the case. Matching observed spectra to the models makes it possible to infer temperature distributions with higher reliability. So these are indirect measurements. --Dr Dima (talk) 20:43, 27 April 2009 (UTC)[reply]
It is funny now to read analyses by 19th century scientists trying to account for the high temperature of the sun and the extreme age of the sun, in terms of chemical reactions (the reactants would have been used up by then) or cooling from an initial high temperature. Early measurements of the sun's tempereature did not equal todays. In 1876, astronomers determined the sun was at 1354 to 2000 degrees Centigrade(p18).By 1907, the estimate was up to "12,000 to 15,000 Fahrenheit(6600 to 8300 C) . By 1907 the best explanation seems to be not nuclear fusion, but that the sun was contracting 220 feet per year (supposedly adequate to account for its continued constant heat output for 24 million years), although presciently they referred to the relatively newly known power of radium to continue giving off heat for a very long time, at least a baby step toward the modern nuclear explanation. The 1907 estimate was actually a bit high, if it was supposed to be the surface, today estimated at 5778K (5504C) per the Sun article. Edison (talk) 00:25, 28 April 2009 (UTC
The sound that sports arena spotlights make when switched on
In movies when large spotlights are turned on (e.g. at a football sports arena) there is an accompanying sound, sort of like a shutter being closed. What is the cause of this? ----SeansPotato Business22:57, 27 April 2009 (UTC)[reply]
Flood lights involve a high power electrical arc. That heats the gas inside the light and will cause it to expand, creating a sound in exactly the same way thunder is produced. (The arc continues to exist after that, but since the gas is already hot there is no further sound.) I expect, but I'm not 100% sure (this is just personal deduction, rather than something I've read in a reliable source), that that is the characteristic sound of flood lights turning on. --Tango (talk) 23:19, 27 April 2009 (UTC)[reply]
It might also be enhanced for dramatic effect. In the actual site, the sound of lights being turned on would likely be drowned out by background noise such as air handling equipment, traffic on the street outside, and airplanes flying over. See Foley (filmmaking)Edison (talk) 00:19, 28 April 2009 (UTC)[reply]
There is also a loud sound when floodlights are turned on at a movie studio sound stage. Normally, the sound is not heard in the actual movie ("Lights, camera, action.") But it can be heard in a scene in the movie "Singing In the Rain" which shows the floodlights being turned on. It is the sound of heavy duty relays, called "contactors", actuating. The moving part of each relay slaps against the electromagnet. Contactors are used so that only light wiring is needed to connect the floodlights to a control panel. Heavy wiring for the floodlights themselves goes directly from the building electrical service entrance to the floodlights. This reduces long runs of heavy wiring and the need for heavy switches in the control panel. Big electrical machinery, such as at steel plants, also uses this method. Undoubtedly it is the same at sports stadiums. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 02:57, 28 April 2009 (UTC)[reply]
In a movie, every sound you hear is intentionally placed on the soundtrack in post-production, unless it is a low budget documentary. In more modern stage lighting, the control is electronic and is not simply relays closing in full voltage. In vintage lighting, knife switches on a lighting board were used along with banks of rheostats as dimmers, again not always with noisy relays. Movies would have the luxury of turning on the lights without distracting the audience. In sports venues the clunking of relays would not be heard over the murmer of fans (of both sorts). Edison (talk) 14:40, 28 April 2009 (UTC)[reply]
April 28
Microgravity and Moon missions
Astronauts in orbit around the Earth experience microgravity because they are in free fall--there are lots of explanations of this phenomena out there. But what gravitational effects did the Apollo astronauts experience while they were in transit to the Moon, since they weren't in orbit anymore? 128.103.197.57 (talk) 00:11, 28 April 2009 (UTC)[reply]
In earth orbit, in moon orbit, or in a trajectory between the earth and moon or between the earth and another planet, for all the recent talk of "microgravity" the astronauts and everything in and near their craft are essentially weightless, in free fall. They are literally falling. Only when the craft is spinning or is accelerated by rockets are they other than weightless. Food or liquid released in midair stays there, affected only perhaps by air currents of static charges. Anyone can put on his/her pants two legs at a time with ease (as one astronaut demonstrated). There is no "up" or "down." Edison (talk) 00:17, 28 April 2009 (UTC)[reply]
Some astronauts vomit because of the weightlessness. How many of them undergo that? Wouldn't it be a good idea to use sailors as astronauts?—Preceding unsigned comment added by 98.21.107.234 (talk) 00:37, 28 April 2009 (UTC)[reply]
I suppose that's why astronauts undergo training, and those who manage not to vomit in training, or learn to control their reactions, are those that actually get a ticket to orbit. --Ouro (blah blah) 06:20, 28 April 2009 (UTC)[reply]
Apparently, about half of astronauts suffer from Space adaptation syndrome (space sickness), but it doesn't last too long so it is usually just accepted as part of life in space. I'm not sure if being used to dealing with motion sickness would actually help, our article doesn't say if any particular people are more susceptible than others. --Tango (talk) 12:13, 28 April 2009 (UTC)[reply]
Spaceships don't normally rock back and forth like boats (with one exception). Throw in the fact that the sailors would have to have a lot of advanced education and training, and it would seem to be an impractical idea. Clarityfiend (talk) 18:40, 28 April 2009 (UTC)[reply]
The Apollo astronauts did not follow a straight-line course to the moon. So I am pretty sure that you'll find that the answer is that the astronauts were in freefall any time they weren't accelerating.
Consider this thought experiment : If the Apollo capsule was stationary with its engines off halfway between the Earth and the Moon, would the astronauts feel Earth's gravity? No. Because the capsule would fall. With nothing holding it up the capsule would fall like a broken elevator. When you're falling you don't feel gravity. APL (talk) 14:07, 28 April 2009 (UTC)[reply]
It goes without saying that if their engines were not turned on and there is no air or ground or other form of drag or thrust forces on their spacecraft then there could only be free-fall. Since that was the case for most of the trip - they were in zero g most of the time. However, whenever they turned the engines on - there would be acceleration - and therefore some kind of pull that they would feel just like gravity. The term "free fall" is really better than "zero-g" - any time you're falling freely you're not going to feel the force of whatever gravity there is. It is a common misconception that the people on the International Space Station are "in zero g" just because they are out in space. But that's not the reason - it's because they are falling freely. If they tried to hover over one spot on the earth at their present altitude (which would require some seriously impressive engines) - they'd feel gravity almost as strongly as we do. SteveBaker (talk) 23:00, 28 April 2009 (UTC)[reply]
Often I'll talk with a dog owner who claims their particular breed of dog has "hair" instead of "fur". Is this a bunch of nonsense? Our fur article says that "fur" means "the hair of a nonhuman mammal". I think the distinction these dog owners are trying to make is that their dog's breed doesn't shed, or doesn't shed as much, as dog breeds that have "fur". Nonsense or truth? Tempshill (talk) 02:26, 28 April 2009 (UTC)[reply]
Well, the distinction between "hair" and "fur" is pretty arbitrary (making humans the special case has nothing to do with biology). What they probably mean is that the fur in question more resembles human hair than it does other dog furs. --98.217.14.211 (talk) 02:37, 28 April 2009 (UTC)[reply]
Hair IMHO refers collectively or individually to strands that are relatively long and can be directed (combed) individually. Fur is always a collective word for relatively short strands that trap air that can keep one warm. Cuddlyable3 (talk) 12:51, 28 April 2009 (UTC)[reply]
the sun's surface
Given that the sun consists of gas, I'd expect it to look like a density gradient rather than suddenly becoming opaque at a well-defined sphere. What changes at that level? —Tamfang (talk) 06:21, 28 April 2009 (UTC)[reply]
There is no level. As I said in a response to an earlier post today, photons of different energies escape, on average, from different depths. For any photon, the deeper within the Sun it was emitted, the lower is its probability of escape. For a photon of a given energy, there is formally a certain depth from which the probability of escape is exp(-1); probability of escape from deeper layers is smaller, and probability of escape from less deep layers is higher. That particular depth is the depth where the Sun becomes "opaque" for that particular energy of a photon. The important thing is that that depth is different for different photon energies. X-ray photons escape from deeper layers than visible-light photons, and photons at the centers of spectral lines usually escape from shallower layers than continuum photons. If you need more detail, please see Opacity (optics). --Dr Dima (talk) 07:53, 28 April 2009 (UTC)[reply]
You are correct, there is no well defined surface of the sun. The corona extends a long way out from what we would usually consider the surface, it just gets more and more tenuous. The same is true of the Earth's atmosphere, the exosphere doesn't have a well-defined top. --Tango (talk) 12:08, 28 April 2009 (UTC)[reply]
Skeptics are saying the homo floresiensis are homo sapiens ("us") with the serious disorder microcephaly. Given that microcephaly happens to us tragically often, could it be it is an "obsolete" and ancestral trait we share with homo floriensis, and it is blocked from appearing in humans unless the genes that now prevent it are disabled or missing, or (or perhaps the same thing)the genes that caused it are allowed to be expressed? Let me try to say what I mean again:The hobbits do have microcephaly, but it's not a disorder? For us, it's a disorder?Thanks, Rich (talk) 07:14, 28 April 2009 (UTC)[reply]
I think basically the question is unanswerable. How could anybody know if microcephaly would have been seen as an disorder in these hominids, if we don't know what was their "normal" state? It all depends on the basic question: Were these people Homo sapiens or where they something different? As long is this is not answered, you cannot derive anything about deviation from any "norm". TheMaster17 (talk) 08:48, 28 April 2009 (UTC)[reply]
I don't understand why whether they were homo sapiens or not is the basic question. It seems to me that whether they were diseased or not is at least as basic. After all, if they weren't homo sapiens, they might be a diseased form of some other hominid. In addition, if we find further remains, perhaps of a fetus, we might figure out if the small brains were normal to them. And in us, maybe geneticists will find a large ensemble of unused and perhaps degraded genes that code for the development of microcephalic but potentially "thrivable" offspring. Thank you for your comments.Rich (talk) 09:15, 28 April 2009 (UTC)[reply]
I think you misunderstood what I wanted to express: The presence of a disorder can only be stated if the normal state is known. So only when we know what kind of hominids these people were, can we say anything about disorders. There is no alternative to this approach I could think of, because every other method to infer "disorders" of some kind are just speculation and extrapolation from known hominids. And how would you, to mention your example, infer from a fetus what the "normal" state would be in an adult? Human fetusses are far from finished when you look at body proportions, and as long as you don't know what kind of hominids you are looking at, you cannot safely transfer any proportion of growth (even when you know the species, this may not be possible, as growth patterns have changed during hominid evolution). I think I didn't get your last point: What would an unexpressed gene in humans tell you about the unknown kind of hominid on Flores? (btw: There is no such thing as a degraded gene. Genes change all the time, and these changes are what enables evolution, allowing changes in the function of the geneproduct.) It is not possible to infer a function from a genomic sequence, just to make an educated guess at the parts that the product would have. So finding a gene (or the remnants of a once-active gene) would never tell you that it would cause microcephaly in humans. TheMaster17 (talk) 09:47, 28 April 2009 (UTC)[reply]
The Nova documentary I just finished watching on this very topic said (with convincing detail) that the microcephaly theory is busted and it's pretty clear now that they were indeed a separate species. Small bones in the Hobbit's hands are a close match for apes and are quite different from those in later hominids. Also, most of their anatomy is very close indeed to "Lucy" - another early hominid specimin. Conclusion was that the Hobbits were simply a parallel thread of evolution - an almost completely separate species (far more separate than, for example, the Neanderthals). Still around on their idyllic island until maybe 18,000 years ago - probably wiped out by a volcanic eruption. SteveBaker (talk) 02:30, 29 April 2009 (UTC)[reply]
Also, why is it so hard to get a proper high-resolution computer image of a *real* skew-T diagram? Isn't this supposed to be like, public domain information? John Riemann Soong (talk) 07:59, 28 April 2009 (UTC)[reply]
I'm guessing that while the information ON the diagram may be in the public domain, the weird triangular graph paper it's drawn onto belongs to some graph-paper printing company who's copyright you'd be violating if you posted a blank sheet of the stuff online and at useful resolutions. You can get free graph paper in PDF form here (A very useful site that should be in every working scientist's bookmark folder!) - but not with all of the shading and peripheral annotations in the JPEG image you linked to. Still, since it's an emergency - perhaps something there will suffice for your needs. SteveBaker (talk) 12:30, 28 April 2009 (UTC)[reply]
No. But if applied to a product as a novel part of its design (artistic or functional) then yes. The graph on a graph paper is not IMO novel. Cuddlyable3 (talk) 12:43, 28 April 2009 (UTC)[reply]
Cured??? Most viral illnesses are self-limited and don't need to be "cured". For the common viral illnesses everyone is familiar with (the "common cold", the "flu", "viral gastroenteritis" etc.) we treat the symptoms and let the immune system do the rest. There are very few modern medicines that directly kill a virus or interfere with the mechanisms of viral entry into the host cell, replication, or dissemination. Far fewer than 100. Probably 10-20 at best (at least in widespread use). The antiviral drug article has a useful summary of some of the approaches. --- Medical geneticist (talk) 13:52, 28 April 2009 (UTC)[reply]
(multiple ec) In the strictest sense: none. Medicine does not cure a disease, it only treats the disease so that the body itself can cope with it better. Another problem is in numbering virusses: They mutate very fast, so would you count every different strain as a new kind of virus? Or only broader groups, like influenza? So it depends on the perspective. Have a look at viral disease, but this list is far from complete, as stated. In what context do you want to know this "number"? Concerning the previous answer to this topic: what is "killing a virus"? It's as meaningful as "killing a shoe", because virusses are not considered to be living by most if not all current definitions. TheMaster17 (talk) 13:59, 28 April 2009 (UTC)[reply]
I can just judge from what I know: In my studies of biology, I never met any biologist who considered virusses to be lifeforms. Every definition of life I know excludes virusses, because they always lack central properties of life: homeostasis, response to stimuli, growth and/or undergoing cellular division, a metabolism of their own. For sure it is possible to speculate about some form of "non-cellular life", i.e. some other kind of physical system which shows all characteristics of life. But this only blurs the everyday meaning of the word life: life as we know it on earth. And in this sense, a virus is "just" a very complex transportation device for nucleic acids. Without the machinery of a living cell it is only sitting around, slowly degrading. TheMaster17 (talk) 14:44, 28 April 2009 (UTC)[reply]
Medical geneticist, I could guess that you meant it colloquial, but as the initial question had some rather blurry words and concepts, I wanted to make clear that a virus is not living, and that many other misconceptions follow from this original one. A blurry answer to a blurry question usually helps nobody ;-). TheMaster17 (talk) 14:50, 28 April 2009 (UTC)[reply]
Viruses are not individually living any more than toenail clippings are, but they are clearly part of life in a holistic sense. They certainly require other living beings to aid them in most of their life processes, but they aren't "non-living" either. So, are my toenail clippings living? Well, no. But are they entirely outside of the concept of "life". No on that either, since they would not exist without life. The convenience of classifying something as living or not is arbitrary; even deciding what constitutes an individual organism can be tricky (see Lichen). So the question is more Is a virus an organism No, it probably isn't. But it still part of "life". --Jayron32.talk.contribs01:43, 29 April 2009 (UTC)[reply]
Jayron, I don't agree with your definition of life, but I can understand that some people like the idea of "the entire earth constituting a living being", then that is what you are running into when you follow this line of thought. I'm perfectly fine with calling my toenail clippings dead and never living: Just because they were built by living cells, they are not anymore living than for example the skeleton that corals built or the slime that snails excrete. Whatever you do with your toenail clippings, they will never have a metabolism or be able to divide and grow on their own. But we are getting rather off-topic. TheMaster17 (talk) 06:54, 29 April 2009 (UTC)[reply]
Viruses are much closer to living organisms than toenail clippings are. No matter where you put a toenail clipping, it will not cause another toenail clipping to be generated.
The distinction about whether viruses reproduce "on their own" is specious. Do we reproduce on our own? Viruses (some of them at least) have clearly functional machinery adapted to parasitizing cells and thereby reproducing themselves. They do need the cells to do it, but so what? The cells are prey. Lots of organisms can't reproduce without a specific parasitic host.
It's also not true that viruses (some of them at least) don't respond to stimuli — they attach to specific surface features of cells, and respond by inserting their genetic material.
The main distinction, which is true, is that they don't have a metabolism. If you think that makes them "not life", then fine, that's your definition and you're welcome to it. But I think you can see how others might reasonably disagree. --Trovatore (talk) 07:49, 29 April 2009 (UTC)[reply]
(unindent) I think we are really getting into a philosophical discussion here: What is "on its own" (so basically, what constitutes "self")? What is "reacting to stimuli" (Is a lock reacting to stimuli when it opens the door after I have turned the key? Basically this is the way that insertion mechanisms in virusses work.)? If you want, we can talk about this on my talk page, but for the starting question, this is off-topic. But you are totally right that I can see how others can reasonably disagree: This is really muddy water and many generations of very bright people have discussed this, and all depends on very personal definitions of cause and effect. TheMaster17 (talk) 08:31, 29 April 2009 (UTC)[reply]
The purpose and use are extremely important. You need to think about biological and chemical hazards, radiation safety, and protocols for any animal work - among a slew of other things. Wisdom89(T / C)19:32, 28 April 2009 (UTC)[reply]
An easy place to check for local regulations is your local City Hall, if such a thing exists where you live. There are permits needed for places that serve food, places that handle food ... there are possibly permits for places that handle such-and-such types of chemicals or animals or nuclear fusion reactors or whatever it is you're planning to conduct research on. Tempshill (talk) 00:50, 29 April 2009 (UTC)[reply]
Wearing Black on a hot day
People keep telling me to wear lighter colors when it's hot. None of them seem to know precisely why they think this is a good idea.
I don't think it is quite that simple. Light colours reflect heat better so they stop you getting warmed up, however they are worse at radiating heat, so they stop you cooling down. There are desert tribes that traditionally wear black, and they probably know what they're doing when it comes to staying cool. Dark colours can also help protect your eyes from the bright sunlight (I've seen it suggested that you wear black paint/soot/whatever under your eyes in bright sunlight if you don't have any sunglasses). I think it is more important to wear lose fitting clothing that covers most of your body (exposed skin is at risk of sunburn, etc.). An unbuttoned shirt worn over a t-shirt is supposed to work well. --Tango (talk) 19:31, 28 April 2009 (UTC)[reply]
As a long-time desert dweller, I can tell you from experience that in a hot sun, light is a lot better than dark -- the heat absorption of dark clothes is the dominant factor. If it's hot because you're in the jungle, it might not make much of a difference. Looie496 (talk) 20:09, 28 April 2009 (UTC)[reply]
As a camper, one of the luxery items you can buy are shower bags. They are entirely black, you fill them up with water and leave them in the sun and they warm up. Then you hang them from a tree and have a warm shower. If it weren't black it probably would get much hotter than the ground around it, but the can get quite warm. Anythingapplied (talk) 20:33, 28 April 2009 (UTC)[reply]
You need to read "Why Do Bedouins Wear Black Robes in Hot Deserts?" by Taylor, Finch, Shkolnik and Borut, Nature283, 373-375 (24 January 1980). That's a subscription-only link, but there's a summary in the Guardian here. To summarise, white garments let more radiation in while black ones absorb more, so the effects almost balance out. --Heron (talk) 21:08, 28 April 2009 (UTC)[reply]
The simple answer is that the color black absorbs light (that's why its black.), the energy from that absorbed light is transformed into heat. Therefore, on a sunny day, a black object will be noticeably warmer than a similar white object.
As mentioned above, the situation with clothing is complex because so many additional factors go into it, including how the clothes "breath", how much sun penetrates the cloth and hits your skin, etc.
If I had to theorize, I'd bet that a cloth that was black on the inside and white on the outside might keep you coolest, but that's just a wild guess. APL (talk) 21:25, 28 April 2009 (UTC)[reply]
The question is largely to do with whether the heat is conducted into your body (because the air temperature is above body heat) or radiated into your body (from the sun). If the heat is in the air itself - then no amount of light-colored clothing will help you to avoid that - and the light colored cloth reflects heat that your body is trying to radiate back in again - so black clothing would be cooler. However, if the heat is coming from the rays of the sun - then reflecting them away is a big win compared to the downside of a reduction in the amount of heat your body can radiate. Hence - (although I'm slightly hesitant of my conclusion) it ought to be better to wear dark clothing in the shade - and when the air temperature is above body heat - and you're better off with light clothing in sunlight and when the air temperature is below body heat.
Furthermore - let's examine the whole premise of this. Do Bedouins really wear black out in the desert? Sure, we're all leaping to that conclusion - but is it actually true? Let's take a look at the WikiCommons photos in Category:Bedouins [27] - and the first few pages of photos from a Google/Images search on "Bedouin" - a rough count says that about two thirds of those photos are of people wearing light colored clothing - with only a third or so in black or other dark colors (there are some judgment calls to be made on blue, green and striped clothing - also white headgear with black robes - so it's not a "Black and white" question!). Perhaps these people are aware of the kinds of distinctions I describe. If you're planning to spend the day in the shade of your tent on a hot day - wear black - if you're out on your camel doing whatever it is you do - wear white. If you're in your honking great SUV - crank up the A/C and wear a hawaiian shirt? SteveBaker (talk) 22:44, 28 April 2009 (UTC)[reply]
Well to be fair it was in Nature. Also if you look more carefully at the category, most of the black and white images show dark coloured clothing. These are likely I expect to be the older images (in general) so it's possible Bendouin clothing colour choice has changed over the past 100 years or so particularly since anyone there is obviously interacting enough with the outside community to be photographed. (It's also quite ORry.) None of this of course means the reason they choose black coloured clothing has anything to do with whether it keeps them cooler Nil Einne (talk) 02:20, 29 April 2009 (UTC)[reply]
That doesn't work - oxygen and air pressure are also minimal necessities and without them, starvation and dehydration are not a problem! SteveBaker (talk) 02:26, 29 April 2009 (UTC)[reply]
It may literally be hotter if you're taking fluid from the center of the cup instead of sipping at the surface. Do you still notice the effect if your stir the drink well right before you take your sip? APL (talk) 21:27, 28 April 2009 (UTC)[reply]
"Taste hotter"?
Anyway, another reason might be partial cooling of the liquid as it passes your lips on its way to the tongue, rather than being channeled straight to your tongue through a straw. ~Amatulić (talk) 22:04, 28 April 2009 (UTC)[reply]
Indeed and I would expect the initial contact (surface) area when your sipping to be larger then when you're drinking from a straw Nil Einne (talk) 02:25, 29 April 2009 (UTC)[reply]
You'd expect the straw to allow for extra cooling of the liquid - so my bet is with User:APL - try placing the end of the straw as close to the surface and as near to the edge of the container as possible. That's where you'd be sipping liquid from if you weren't using a straw - not the middle/bottom of the cup where it's undoubtedly hotter. SteveBaker (talk) 22:28, 28 April 2009 (UTC)[reply]
I don't see why it would though. The liquid doesn't stay in the straw for long. A straw has a low heat capacity and quickly heats up and is surrounded by an insulator (air). Your lips have a large heat capacity and are better conductors. Of course either way it may or may not be enough to make a significant difference Nil Einne (talk) 02:25, 29 April 2009 (UTC)[reply]
This is my theory, and it depends on how you drink from the cup. If you "slurp" from the edge of the cup like I think many people do, you may actually be drinking the hot liquid at a slow rate, and you're sucking quite a bit of air into the mouth in the process. The air flow causes both convective(?) and evaporative cooling of the hot liquid right before it gets into your mouth. Compare this with drinking through a straw, you may be drinking at a faster rate in the latter case. A plastic straw is not a good conductor of heat and there's little convective and no evaporative cooling as the hot liquid is sucked into your mouth. (There's another mechanism I can think of that contributes to the difference, which would be more significant if you're drinking from a relatively empty cup and/or if the cup is a good conductor of heat.) --98.114.146.142 (talk) 04:52, 29 April 2009 (UTC)[reply]
Is it possible to sniff blood from the nose into the eyes during a nosebleed?
In my experience, most medical people say it is impossible to bleed from the eyes. Many online posts from the general public on the subject though suggest that if fluid can drain from the eye into the nose, when you cry or with an allergy for example, surely it could also go the other way, resulting in the blood from the nose being secreted from the tear duct.
There is a duct or channel from the eye to the nasal cavity that allows for drainage of tears. After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist.
Because that duct exists (and I have seen some people hold their nose and manage to force air up into them and out the eyelids), it would be possible to force a blood through those ducts, if you have a noseful of blood to start with. ~Amatulić (talk) 22:02, 28 April 2009 (UTC)[reply]
PCR is performed on a nasal swab to detect Influenza A (Swine flu falls within this category) or Influenza B. The turnaround time in a good clinical lab should be within 8-12 hours, or 24 hours at the longest. If positive, the lab should reflex to type the specimen. That probably takes another few days, but they wouldn't wait to initiate therapy if the PCR was positive. The PCR-based assays are very sensitive (95-99%) and specific (90-99%). With the second typing assay on all PCR positives you'd end up with very few false positives. The rapid antigen screens that are sometimes used would be less reliable and give significantly higher false positives. --- Medical geneticist (talk) 21:09, 28 April 2009 (UTC)[reply]
Agree, but would add that Electrospray ionization mass spectrometry is accurate, much faster than conventional analysis of PCR products, can provide results in under 3 hours, and the sample processing rate is about 1 specimen per minute (PMID 17534439). Amazing - though the hardware isn't available in many places at this point. --Scray (talk) 01:26, 29 April 2009 (UTC)[reply]
Sorry for the jargon. What I should have written was: If the PCR is positive for Influenza A, The "reflex response" from the lab should be to perform an additional test to determine the specific subtype. --- Medical geneticist (talk) 16:49, 29 April 2009 (UTC)[reply]
Elastic Potential energy
If you apply stress pass the point where the potential energy growth is linear, will you get less energy back, or does it just mean you're applying less energy to store the energy? 99.227.94.24 (talk) 21:14, 28 April 2009 (UTC)[reply]
If you applied less energy than was stored, that would involve energy appearing from nowhere, so that can't be happening. When you go past the elastic limit of an object it permanently deforms, which uses up energy, that is why you get less back. --Tango (talk) 21:56, 28 April 2009 (UTC)[reply]
Sorry about that, I was referring to the growth in energy in graphs. Probably should have made that clearer. But that answers the question anyhow. 99.227.94.24 (talk) 23:16, 28 April 2009 (UTC)[reply]
Electrodynamic potential energy
How can electrodynamic potential energy be liberated? When a electric motor spins, is it turning electrodynamic potential energy in to mechanical energy? 99.227.94.24 (talk) 23:55, 28 April 2009 (UTC)[reply]
Electrodynamic potential energy is a term I am unfamiliar with, but it sounds like the energy stored by electrically charged particles which are in the presence of other electrically charged particles. If I have two electrons which are being held stationary near each other, the repulsive force between them implies that there is a potential energy generated by their proximity. Anything which causes these electrons to go from a stationary state into one of motion away from each other will convert that potential energy into kinetic energy. --Jayron32.talk.contribs01:31, 29 April 2009 (UTC)[reply]
Apparently, electrodynamic potential energy is the same as magnetic potential energy. The power supply to the motor creates a current in the motor windings. The entire circuit consisting of the power supply and the windings induces a magnetic field, which contains magnetic potential energy. The magnetic field exerts a force on the rotor. As the rotor moves, energy is transferred from the magnetic field to the rotor, which gains kinetic energy. So the answer to the question appears to be "yes". --Heron (talk) 09:35, 29 April 2009 (UTC)[reply]
But the whole setup is in a steady state: as long as the motor keeps getting power it will keep producing useful work, but the energy stored in the electromagnetic field won't change. The energy source that's ultimately being depleted in exchange for the work is probably chemical or nuclear or hydroelectric or wind or solar. Only if you powered the motor by a capacitor would you really be converting stored-up electromagnetic field energy into work. -- BenRG (talk) 18:55, 29 April 2009 (UTC)[reply]
I'm not sure if that's it. This is a popular children's toy. It's a flat sheet of plastic with ridges and an image on it. The viewing angle affects what is seen on the plastic. -- penubag (talk) 01:52, 29 April 2009 (UTC)[reply]
EC = edit conflict (though this'll get confusing if a bunch of us try answering at the same time, and then get a notice that someone else has saved an edited version of the content since it was loaded = edit conflict). --Scray (talk) 03:22, 29 April 2009 (UTC)[reply]
Usually someone will mention an edit conflict because they haven't bothered to read the new replies (or if they have, haven't modified their reply) which could already address what they are discussing or may help clarify some uncertainty or whatever. In this specific case I started to reply but couldn't quite remember the name so had to search. I also got distracted by something else. By the time I found what I was looking for, you had replied but I didn't bother to consider your latest reply and modify you post hence I mentioned an edit conflict (if I did I probably wouldn't have bothered to mention holograms since I was a bit uncertain from your first post but your reply sounds precisely like lenticular printing) Nil Einne (talk) 23:40, 29 April 2009 (UTC)[reply]
if a small legal (chemical)analytical lab got a "DEA number" for handling chemicals of concern,
would every one in the lab(exept for janitors,guards,etc.)also need a "DEA number" to handle the chemicals? —Preceding unsigned comment added by 66.237.50.35 (talk) 04:18, 29 April 2009 (UTC)[reply]
Youtube video: Take a bottle of Mountain Dew, pour out all but about one quarter inch, put a very small amount of baking soda in, pour a bit of hydrogen peroxide in and shake, and it glows brightly. What's going on here? Is this just fake? If not, how does it work? Does it have to be this soda? Or is it carbolic acid that's needed or soemthing else in soda?--70.19.69.27 (talk) 04:41, 29 April 2009 (UTC)[reply]
Well, 99% of YouTube 'science' videos are faked - but this one could just maybe be real. Our Hydrogen Peroxide article says:
"Hydrogen peroxide is used with phenyl oxalate ester and an appropriate dye in glow sticks as an oxidizing agent. It reacts with the ester to form an unstable CO2 dimer which excites the dye to an excited state; the dye emits a photon (light) when it spontaneously relaxes back to the ground state."
Is there any "phenyl oxalate ester" in Mountain Dew? The amount of dubious chemicals they put in that stuff...anything is possible! But perhaps something else in the soda has a similar effect and is creating an artificial "glow stick"?
Another possibility (assuming the video is indeed a fake) is that I believe that Hydrogen Peroxide glows nicely in UV light - so perhaps they have a UV lamp illuminating the 'set' when they do the experiment. The baking soda makes it froth up nicely, the Hydrogen Peroxide makes it glow and the bright food coloring in the Mountain Dew gives it the vibrant color. That's a guess though.
There are a ton of youtube videos of this, all with lots of "it's a fake" comments. Either external light projected, which diffuses due to the cloudiness of the Dew or (more commonly suggested) another chemical is added (maybe glowstick material itself). DMacks (talk) 05:57, 29 April 2009 (UTC)[reply]
Yes - well, it wouldn't surprise me - as I said, there is this worrying trend that about 99% of so-called science videos on YouTube are faked. Most of the people who actually figure out the fake then go on to post fakes of their own instead of properly debunking the original video. Sad...very sad. I daren't ask how many kids are encouraged to play around with hydrogen peroxide in an effort to reproduce this. Anyway there are lots of videos where people try the exact same trick and it doesn't work - and just a couple which show someone adding contents of the inner tube from a glow-stick into the 'dew' and only then getting the same results. Since we know that hydrogen peroxide is one ingredient of a glow stick - then adding the 'missing' phenyl oxalate ester from a glow stick would indeed produce the effect we're seeing in the videos. So this is 'busted'. SteveBaker (talk) 12:51, 29 April 2009 (UTC)[reply]
Chlorine is more electronegative than Nitrogen, so why doesn't it form hydrogen bonds? Is it because Cl has a larger atomic radius? Thanks. —Preceding unsigned comment added by 116.71.62.233 (talk) 07:43, 29 April 2009 (UTC)[reply]
Maybe I'm mis-understanding your question or the types of structures you're considering, but given that electronegativity means (casually) "holds its electrons tightly", it seems pretty intuitive that the more tightly an atom holds its valance electrons, the less likely/stable it would be to share them with an adjacent hydrogen atom. DMacks (talk) 07:49, 29 April 2009 (UTC)[reply]
And the answer from DMacks was: Because it is too electronegative to share an electron with a hydrogen. Have a look at electronegativity. The high electronegativity is one way to explain while certain elements "prefer" to make ionic bonds. TheMaster17 (talk) 08:47, 29 April 2009 (UTC)[reply]
I have to correct myself. I misunderstood what was a hydrogen bond in english. I thought it meant "covalent bond", but as a colleague of mine pointed out, it means the partially covalent binding that hydrogen can built to any electronegative atom (like the bond between the O in one water molecule to the H of another). I'm no chemist, but in my chemical training I was told that all partially negative atoms can form this kind of bound state with a hydrogen under the right conditions, so I would think that chlorine is perfectly fit to do so. Hmm, I'm suprised that DMacks as a chemist obviously also mixed up the terms. TheMaster17 (talk) 09:17, 29 April 2009 (UTC)[reply]
There are several inter-related effects involved, so depending on what you are comparing and unless you feel like really examining every detail, easiest to pick one that casually explains that one particular example. A more formal explanation (as always for (semi)covalent bonding) is whether your valence electrons are in n=2 or n>2, how many you have, and what your nuclear charge is, and these are observed as electronic effects such as polarizeability, electronegativity, bonding atomic-orbital overlap, atomic radius. They all correlate, but not really possible to pick any one as "the cause" of every example of any given effect. Electronegativity is a one of several good "rules of thumb" for patterns of hydrogen-bonding. Atomic radius as such is another that correlates with H-bonding, but seems poorer as a primary cause (per question as asked): electrons further out are less tightly held (further from the positive nucleus), so they should be more able to reach out and bond. It's virtually all really just back-rationalization of observations and the real reason is "because that's how it is", so we pick something that explains certain cases satisfactorily:( DMacks (talk) 13:36, 29 April 2009 (UTC)[reply]
Yes, but that's not what hydrogen bonding means - a hydrogen bond is (usually) a temporary intramolecular bond formed between polar molecules. Our hydrogen bond article says that hydrogen bonding occurs in compounds in which hydrogen is bonded to oxygen, nitrogen or fluorine. These elements have electronegativiies of 3.04, 3.44 and 3.98 respectively on the Pauling scale. The electronegativity of chlorine is 3.16, in between nitrogen and oxygen - so asking why hydrogen bonding does not occur in chlorine compounds such as HCl is a good question (and one to which I don't know the answer). Gandalf61 (talk) 13:30, 29 April 2009 (UTC)[reply]
N, O and F are all period-2 elements; Cl is in period-3, and is thus much more massive than the other three, which causes inter-molecular forces to be unstable because the tiny hydrogen nucleus cannot hold a Cl atom in place (note this is just my ad-hoc explanation which may or may not reflect reality, the real reason the bond is not stable could be determined by calculating the energies of the quantum-mechanical wavefunction). Truthforitsownsake (talk) 13:41, 29 April 2009 (UTC)[reply]
That doesn't make sense. A heavier atom moves more slowly making it easier to be bond to. That's the oposite of what you said. I think the mass of the atom plays no role here, but the size of the atom (clorine is about twice as big as a fluorine, for instance) may be important. Dauto (talk) 16:28, 29 April 2009 (UTC)[reply]
I think I still didn't get it: Chlorine is really unable to form hydrogen bonds, though it is strongly electronegative? What happens in organic compounds were chlorine sits at the border of the molecule, in contact to water as solvent? Doesn't it form even weak hydrogen bonds with the solvent molecules (as N,O and F would do in this situation)? This would be a fact to remember for me. TheMaster17 (talk) 14:12, 29 April 2009 (UTC)[reply]
(EC) This depends on your definition of "at risk". It seems the virus is able to be transmitted from human to human, so you can catch it without getting anywhere near pigs. But the prerequisite for this is that the other person is infected, and at the moment, the outbreaks are local and rather small in all countries except mexico (and the situation there is far from clear because a normal influenza is also circulating). TheMaster17 (talk) 08:54, 29 April 2009 (UTC)[reply]
Another important fact is that most people (outside of mexico at least) seem to get better rather quick. Why there seems to be such a contrast between mexico and the rest of the affected countries is a mystery, at least to me, at the moment. TheMaster17 (talk) 09:02, 29 April 2009 (UTC)[reply]
I don't find this puzzling at all. I have high confidence in the Mexican government's ability to count the bodies of the dead (that's the numerator). The denominator (the number of people in Mexico who've had this flu) is another matter entirely - Mexico city is absolutely huge, and the health care system is overwhelmed. As a result, one would expect an under-estimate of the denominator, giving a falsely high death rate. --Scray (talk) 11:22, 29 April 2009 (UTC)[reply]
And as the mexican administration had to correct even the number of deaths from the new H1N1 type A strain today, it seems they are unable to get any number correct. All calculations done so far are false. Now the new mystery (and also the real mystery in the past) to me is the complete naivness of the WHO. They have sparked significant panics all over the civilized world (you should hear what they are teaching here in germany at the schools: according to one teacher, the "new flu" is worse than the black death from medieval times...), because they obiously did not expect that the mass media would twist every word and number they release. But scientifically speaking, there is nothing near an EPIdemic ongoing at the moment, with the exception that the situation in mexico is unclear. So to use the word "possible PANdemic" in this connection is unfounded: Every year we have a "possible pandemic of flu", if the new yearly strains should acquire the required characteristics. TheMaster17 (talk) 12:04, 29 April 2009 (UTC)[reply]
There are really three versions of this kind of disease:
Swine Flu that only pigs get that can't be passed to humans - which has probably been around in various strains for millions of years - just like bird flu, cat flu and flu varieties for most other species on the planet.
Swine Flu that mutated so that humans could catch it from pigs but could not pass it on to other humans - perhaps it's been around for a while - it's hard to tell because people don't usually live in very close proximity to pigs, so not many people catch it.
Swine Flu that's mutated AGAIN so it can be passed between humans.
All of the concern with Bird Flu a few years ago was because that virus had just taken the step from (1) to (2) in countries where people habitually allow their chickens and ducks to wander through their houses. At stage (2), the disease is easily controlled - don't go near birds and you won't catch it - but the concern is that it's now only one mutation step away from the super-dangerous stage (3) when it can pass like wildfire from person to person.
So the huge concern is that Swine Flu appears to be in stage (3) right now. Worse still, many new diseases are much more lethal than older strains. That's because the virus cannot spread from a dead victim, hence, over time, diseases evolve to be less lethal so that they can spread more easily. A disease that's so mild that you don't even take a day off work spreads VERY easily. Hence there is significant evolutionary pressure on diseases that spread by coughs and sneezes to become gentler. Brand new diseases such as Swine Flu have not yet evolved that gentler nature - so for the first year or so, they can be very dangerous.
However, as others have pointed out - we know how many people have died (around 100 so far) - but we have no idea how many were infected and survived - possibly without any symptoms at all. If only 200 people were infected but 100 died - then with a 50% mortality rate, this would be a deeply scary disease. If a million people were infected but 100 died - then this is not much worse than a typical flu season and there is really no reason to panic. We still don't know where we are along that scale - so we're taking reasonable precautions until we know for sure.
This disease was certainly passed from a pig to a human sometime in the past when it was in stage (2) - but now that it's mutated into stage (3) - which must have happened inside a human - it's just a regular human disease and you're far more likely to catch it from another person than from a pig because the pigs can only have type (1) and (2) of the virus. To get type (3) they'd have to catch it from an infected human - and that's really unlikely! You need to be much more concerned about catching it from another person than catching it from a pig.
So in areas where the disease is rampant - avoid crowds - stay away from sick people - wash hands regularly, keep your hands away from your eyes, nose and mouth where possible (unless you've just washed them carefully). If you get flu-like symptoms, stay away from other people and call a doctor. However, those measures are far from 100% effective - the virus can hang around for quite a while on non-biological surfaces and people show no symptoms until they've had the disease in their bodies for many days...so these safety measures are only improving your odds.
No lower than for a person in a non-Muslim country that doesn't go near pigs. I would expect that cooking pork makes it safe to eat - it does with most diseases and I haven't seen any health warnings telling people not to eat pork. That this flu originally came from pigs is pretty much irrelevant at this point. It can pass from human to human - that's going to be by far the most common way people catch it from now on. --Tango (talk) 12:50, 29 April 2009 (UTC)[reply]
I think you've misunderstood. The disease came from pigs originally but now it's carried by humans.
For now any country that's not Mexico is pretty safe. However, it's entirely possible for someone infected to get on a plane and fly to any other country of the world and start a new outbreak. He would not have to bring a pig with him.
I'm not sure we can say how likely that is, we're not experts, and even the experts are still working on it. APL (talk) 12:53, 29 April 2009 (UTC)[reply]
Yes - that's well worth emphasizing - we have enough economic and societal problems as it is without people suddenly abandoning eating pork for absolutely no good reason! Flu is spread through respiratory processes - coughing and sneezing. Dead pigs do neither - they are perfectly safe. But as I said before - you're never going to catch THIS strain of swine flu from a pig anyway - even in the exceedingly unlikely event that it's coughing an sneezing all over you. The evolutionary step that enabled this disease to spread from human to human happened inside a human - not inside a pig. If a pig ever did catch this strain, they'd be getting it from the farmer! Really: right now, the only things to avoid is other people with symptoms - and (arguably) people who visited Mexico during the last couple of weeks. SteveBaker (talk) 13:17, 29 April 2009 (UTC)[reply]
Forget the "swine" part of it. Once it goes human-to-human the original vector does not matter. It's just "a flu", one that humans at the moment have no native resistance to. --140.247.251.93 (talk) 20:16, 29 April 2009 (UTC)[reply]
Of course they have "native resistance". While few people have had the opportunity to develop immunity, most human bodies are well equipped to fight (resist) such an illness. We can see this by the fact that the overwhelming majority of people who have had the illness have recovered. You may find it useful to read the World Health Organisation's FAQ, with particular note on the safety of pork products, and the fact that most infected people have merely displayed standrad flu symptoms and have recovered without medical treatment. Gwinva (talk) 22:33, 29 April 2009 (UTC)[reply]
What warning level does the WHO have to raise the alert to (already at 5 out of 6) for it not to appear rude to wear a mask when dealing with the public all day? Edison (talk) 23:24, 29 April 2009 (UTC)[reply]
firing an SCR
Hi, I am doing a project on controlled rectifiers. At some point, I have the output of an op-amp (+11v) to fire an scr. The gate current required to fire it is nearly 100uA. I believe the opamp isnt able to provide that much of current. Any idea what device to use to increase the opamp output current ? 218.248.80.114 (talk) 20:45, 29 April 2009 (UTC)[reply]
Calling all electronics design experts! Steve Baker? 100 microamps sounds like a minimal demand on an op amp. Most of the old ones I used could carry tens of milliamps. Which op amp? Which SCR? I have some in the basement if I could find them, but using data sheets is more of an approved "engineering" approach. [30] has a test circuit to make sure the device has not been accidentally fried (all too common in labs). Edison (talk) 23:16, 29 April 2009 (UTC)[reply]
1918 Spanish flu mortality
Can someone make sense of the following figures for me:
An estimated one third of the world's population (or ≈500 million persons) were infected and had clinically apparent illnesses during the 1918–1919 influenza pandemic. The disease was exceptionally severe. Case-fatality rates were >2.5%, compared to <0.1% in other influenza pandemics. Total deaths were estimated at ≈50 million and were arguably as high as 100 million.
Perhaps the numbers are including people killed by things like famine caused by the Spanish flu that might kill people who were not infected? 65.121.141.34 (talk) 20:54, 29 April 2009 (UTC)[reply]
which I read, suggests that it is not true. The 50-100 million figure does include deaths due to influenza, pneumonia, bronchitis, phthisis cased by the infection, but not secondary effects like famine etc. Anyone have easy access to the sources cited for the >2.5% estimate ? Abecedare (talk) 21:10, 29 April 2009 (UTC)[reply]
People surviving once and being re-infected again later - possibly mutiple times - before dying of it, may skew the results slightly. Vimescarrot (talk) 21:24, 29 April 2009 (UTC)[reply]
True, but each person would have to be infected 4-8 times, in order to make the numbers work. Seems unlikely, especially since infection by the (common) flu virus is supposed to provide temporary immunity. Abecedare (talk) 22:10, 29 April 2009 (UTC)[reply]
"had clinically apparent illnesses" - perhaps the mortality rate is computed using a figure for all infected, not just cases of "clinically apparent illness". But I don't know how they would estimate that. Rmhermen (talk) 21:58, 29 April 2009 (UTC)[reply]
The world population in 1918 was around 1.5Bn. So even assuming that everyone was "infected", 50-100million deaths would imply 3.3-6.7% mortality. Still significantly higher 2.5% ! Abecedare (talk) 22:10, 29 April 2009 (UTC)[reply]
our article indicates that morbidity and mortality rate estimates vary greatly. Not surprising, when there's mathematical disagreement within one source as quoted above! Gwinva (talk) 23:02, 29 April 2009 (UTC)[reply]
effects of caffeine
Hopefully this question doesn't overstep the mark and creep into asking medical advice - which I know cannot be issued by wikipedians. If this question is unacceptable I am very sorry. The article on caffeine says its half life is approx 4.9 hrs in healthy adults. I am a healthy adult and my question is why don't the effects last that long? - as presumably you should still be feeling half of 'buzz' you originally got 4.9 hours after you ingested it. After a less than 2 hours I seem to be back to normal. This is the case for many other people I know as well. Is there any reason why people stop feeling the effects before the caffeine has even had a half life? I don't consume caffeine excessively, 2 cups of tea a day at most so I wouldn't say I have a high tolerance to caffeine. Many thanks and I hope someone can shed some light on the subject! —Preceding unsigned comment added by 92.16.11.107 (talk) 21:33, 29 April 2009 (UTC)[reply]
I would expect that the half-life is not necessarily a reliable indicator of the amount of time it will 'noticeably' have an affect on the body when asking a person. For instance many people will wake up the morning after a night of drinking and feel perfectly fine, but if tested they may well still be over the limit. What they 'feel' is 'normal' but what they are is still showing the effects of alcohol consumption. Hopefully someone will be able to clarify for you though, would be interesting to know ny156uk (talk) 22:36, 29 April 2009 (UTC)[reply]
The "half-life" probably refers to the detectable amount in your system. That isn't the same as the amount bound to receptors and due to weakening action potential that again doesn't equate the same effect. 76.97.245.5 (talk) 23:41, 29 April 2009 (UTC)[reply]
Hello, I need help. I would like to know how to solve the following question, what Geometry/Physics you need to know for it.
A satellite is launched into a circular orbit around a planet with negligible radius in a direction tangent to the orbit at a distance R, and another satellite is launched with half the velocity of the first one. What is the minimum distance between the planet and the satellite during the orbit, in terms of R? —Preceding unsigned comment added by 173.66.142.5 (talk) 23:17, 29 April 2009 (UTC)[reply]
I haven't found this in our article, but what causes a tree/shrub to be suitable as a plant for a hedge. a} I had read before that trees that you trim the top off die. Why isn't that happening when I trim e.g. a birch to be a hedge. b) Would fig trees work and could you still get figs from them if it were trimmed to be a hedge? 76.97.245.5 (talk) 23:47, 29 April 2009 (UTC)[reply]
Resolved
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