Wikipedia:Reference desk/Science

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November 14

Bismuth-213

When the isotope bismuth-213 emits an alpha particle, what new element results? what if it emits a beta particle? Thanks!!

You're gonna have to make this homework question less obvious if you want it answered. Consider: Bismuth is element 83, yours has a mass of 213, find out how many neutrons and protons it has, then subtract the number of neutrons and protons in an alpha particle, and recalculate the element number of the result. Repeat for a beta particle. Tuckerekcut 01:03, 14 November 2006 (UTC)

Elementary! --Light current 01:07, 14 November 2006 (UTC)

By the way, bismuth-213 is a ficticious isotope. --Bowlhover 01:11, 14 November 2006 (UTC)

So is the question a trick?--Light current 01:33, 14 November 2006 (UTC)

What do you mean, it is fictitious? According to Isotopes of bismuth, it has a half-life of around 46 minutes. — Knowledge Seeker দ 03:13, 14 November 2006 (UTC)

I wonder why the article Bismuth doesnt link to Isotopes of Bismuth?--Light current 03:27, 14 November 2006 (UTC)

It does, at the bottom of the element box, on the right side. StuRat 04:24, 14 November 2006 (UTC)

I've been very careless lately; I looked at the list of 3 isotopes in the Bismuth article, and assumed that they were the only ones. I don't think I saw the "isotopes of bismuth" link. --Bowlhover 04:34, 14 November 2006 (UTC)

Isotopes never really become "fictitious", they just become more and more unstable. You might say oxygen-24 is the heaviest isotope of oxygen, but my colleague Calem Hoffman is writing a paper on oxygen-25. It's unbound to neutron decay, so its lifetime is so short that its energy has a large range because of the uncertainty principle between energy and time. Still, it's a legitimate state that has objective reality. —Keenan Pepper 06:08, 14 November 2006 (UTC)

Yes, but O-9999 is still rather fictitious. StuRat 06:43, 14 November 2006 (UTC)

Maybe on Earth, but what about inside a neutron star? —Keenan Pepper 21:39, 14 November 2006 (UTC)

I wouldn't think even the most stable atoms would stay intact in such an environment. StuRat 02:55, 15 November 2006 (UTC)

A neutron star is by definition a star made entirely of neutrons! 8-)--Light current 03:04, 15 November 2006 (UTC)

How naïve! —Keenan Pepper 05:54, 15 November 2006 (UTC)

Only the central part of a neutron star is made up entirely of neutrons, not all the star, AFAIK. However, that depends to a significant extent on how you define a surface of a star (not a trivial task). Anyway, I don't think that you would find O-9999 at any depth inside a neutron star; rather, just a "soup" of neutrons, protons and electrons. However, if a catastrophic event involving a neutron star would happen (for example, a collapse to a black hole if the mass exceeds the limit, or collision with another star / black hole), some of the matter will be ejected. Most of it would still be neutrons I suppose, at least for an hour or two (neutron, when left alone, has a lifetime of about 15 minutes; it can be longer if it still has other particles to strongly interact with). Then maybe there is a chance to find something like a highly excited O-9999 nucleus, namely, a nucleus of a stable Oxygen isotope with a cloud of neutrons around it. --Dr_Dima.

irradiated food

When food is irradiated with gamma rays from a cobalt-60 source, does the food become radioactive? why is this?

Probably the easiest way to explain this is to think of atoms as tiny bombs. Radioactive atoms are bombs which are liable to blow up at any moment, whereas most atoms are relatively stable unless hit in exactly the right place and with exactly the right amount of energy. So consider Co-60 a insidious bomb. When this bomb explodes, it sends a shard of shrapnel hurling through space. Chances are, that shrapnel will never hit anything (space is actually pretty empty), but a very small percentage of the time, the shard will hit something. When the shard does hit something, a few things can happen: most of the time, everything probaly just snaps back into place, no harm done. Sometimes, however, a molecule will get knocked out of whack. If, by some wild chance, that molecule happens to be DNA, and that part of the DNA happened to have two cysteine residues next to each other, then the DNA will end up pretty messed up at that point, and if this dimer in the DNA happens to cause a mutation, and if that mutation happens to be bad (you see where this is going), then death or some other pathology can result (please note that death and pathologies can result from a lot of other molecular bombardment mishaps, but this is a popular one). This is how the radiation kills whatever is in the food. However, very rarely, the bomb shard hits another molecule in such a way that that molecule becomes "armed" up to blow up itself. The reason irradiation doesn't tend to make other things radioactive is because this secondary "explosion" is very unlikely in the first place, and exposure is limited in such a way to decrease this possibility even furthur, ensuring that irradiated food is no more radioactive than, say, brazil nuts (actually, probably much less so...).Tuckerekcut 00:53, 14 November 2006 (UTC)

No. Gamma rays are high energy light. It doesn't change atomic structures. It can change chemical bonds and that kills bacteria but to be radioactive the atomic structure changes. Usually, neutron radiation is required to make something radioactive IIRC. --Tbeatty 03:01, 14 November 2006 (UTC)

Gamma_rays#Uses has some similiar info -- Wikicheng 04:47, 14 November 2006 (UTC)

My bad, I probably shouldn't try to answer chem problems in the future, I didn't even look up the decay process for Co 60.Tuckerekcut 12:28, 14 November 2006 (UTC)

See Induced gamma emission, however, for info on how gamma rays can make some substances temporarily radioactive. Rmhermen 15:42, 14 November 2006 (UTC)

Atoms

Can you tell me how many types of atoms can you expect to find in a pure sample of any element?

Depends on your definition of "pure", and "type", which element you're talking about, and where you got your sample from.

In the real world, most samples of elements, no matter how pure, contain very small traces of contaminants. Ignoring that, for the moment, most elements come in more than one isotope, though the number varies greatly between the different elements. Gold, for instance, has only one stable isotope, whereas tin has 10. --Robert Merkel 03:26, 14 November 2006 (UTC)

A have a feeling this is a high school chem question. In which case, the answer is 1. "pure sample" of any one element means it contains only atoms of that one element. --`/aksha 03:49, 14 November 2006 (UTC)

Right. In high school you learn that a sample of each chemical element consists of atoms of only one type (namely, atoms of that chemical element). If you are preparing for a chemistry exam, follow `/aksha's advice. In college or university you learn that atoms of a chemical element are actually not all alike. the electric charge of the nucleus of all the atoms of a given chemical element is the same, and the chemical properties of all the atoms of that chemical element are very, very similar. However, the number of neutrons in the nucleus of an atom need not be the same, look at isotopes in Wiki.

Another year passes, and you learn that the protons and the neutrons in the nucleus may be arranged in different quantum states. Again, even in a single-element single-isotope sample not all atoms are the same. You open Wiki, and here it is, an article on nuclear isomers.

A few months go by, and you suddenly learn that when you put a magnet to your sample, for elements/isotopes with net electron and/or nuclear magnetic moment, some atoms have higher energy than the others. Again, even in single-element single-isotope single-nuclear-isomer sample not all atoms are the same. Fascinating, as Spock used to say. Wait, there is more.

Now you take a basic plasma science course. You heat up your atoms to a few thousand Kelvin or more, and - surprise surprise - again, not all atoms are the same. Some have excited electrons in them, some have lost one or more electrons altogether and became positive atomic ions. Now you have a variety of atoms in your single-element single-isotope single-nuclear-isomer sample! The punchline is simple. If you want good grades at school, know what the teacher expects you to say. If you want to succeed in science, read books and talk to scientists. And, using Wiki ref desk also helps ;-) --Dr_Dima

Molecule

How many atoms are there in one molecule of H3PO4 ? and how many atoms of each element are there in this molecule?

See chemical formula for a description of what the formula above means, from which you can figure out the answer to your question. --Robert Merkel 03:28, 14 November 2006 (UTC)

3 hydrogen atoms, 1 phosphorous atom, and 4 oxygen atoms. (you should go read chemical formula anyway, this isn't meant to be a place for homework questions). --`/aksha 03:43, 14 November 2006 (UTC)

Then don't encourage the behavour by answering homework questions. --BluePlatypus 07:35, 14 November 2006 (UTC)

Are there Infinite Possible Futures? or just a lot?

A piece of semi-spiritual philosophy hold "We live in a universe of infinite possibilities". But is this actually true, according to our best guesses of the laws of physics? Are there an infinite number of states this galaxy could be in 10 minutes from now? or just some arbitrarily large yet finite number? --Alecmconroy 03:57, 14 November 2006 (UTC)

In 10 minutes it will be in one state. Therefore, the answer is 1.  :) --Tbeatty 04:30, 14 November 2006 (UTC)

Nice answer. If I may interpret, Tbeatty means it all depends on what kind of "possibilities" you're talking about. For more information, I recommend Norman Swartz's book The Concept of Physical Law, specifically the chapter Potentialities, available online free of charge. —Keenan Pepper 06:18, 14 November 2006 (UTC)

Also see many-worlds interpretation. --Wooty  Woot? | contribs 06:36, 14 November 2006 (UTC)

Since there are a finite number of particles in the universe we inhabit, I would say that the number of possible futures is finite. However, there may be an infinite number of universes... Clarityfiend 07:55, 14 November 2006 (UTC)

There are, however, apparently an infinite number of possible positions and momenta for each particle, unless space is quantized. So the answer, really, is that we just don't know. -- SCZenz 16:17, 14 November 2006 (UTC)

Earliest sound recording (possibly pre-Edison)

Is anyone familiar with any attempts to record sound prior to Edison's famous 1877 invention of the phonograph? Our article on Sound recording and reproduction says "the first practical sound recording and reproduction device ..."

The reason I ask is this: Talk:Frédéric_Chopin#The_First_Recording_Ever. It was posted by a new user earlier today, and you can see my answer to him there. While I know quite a bit about Chopin, I know less about early attempts at sound recording. Is what this user suggests even possible? (You can tell from my reply what I think.) Yet perhaps there were attempts to record sound before Edison which we haven't covered in Wikipedia. Thanks! Antandrus (talk) 04:44, 14 November 2006 (UTC)

The code for the cd is XOHA CDO10491. Most likely, XOHA stands for 'hoax' and O10491 for 1 April 1991. DirkvdM 09:58, 14 November 2006 (UTC)

There is a good article about it here (scroll down until you see "hoax"). --Kainaw ^(talk) 14:03, 14 November 2006 (UTC)

No one before Thomas Edison is known to have even made the attempt to record and play back sound. Scott built the phonautograph whcih had all the elements needed to record sound: a diaphragm to respond to sound waves, a stylus to record them, and a smoked glass plate to receive the tracing. But obviously you could not operate a playback stylus from the smoked glass. In theory, such a smoked glass tracing could have been photographically copied and used to etch a playable record. The technology to practically do that did not exist in the 1860's. That was the basis of the Chopin recording hoax. Yet there exist a few pre-Edison sound wave tracings, by Scott, and from 1868 by the physiologist Donders (Donders, F. C. (1868/1969).On the speed of mental processes. Acta Psychologica, 30, 412-431.) These are clear black and white photo reproductions of words and phrases recorded by Donders with a phonautograph while doing reaction time experiments. I know of no one having done the obvious task of translating these phonautograph traces to wave files. There would be a need for equalization of different parts of the frequency spectrum, and perhaps controlling for geometric distortions but I would expect some sound could be recovered. Ideally, the phonautograph would be modelled and its resonant frequencies and distortions "subtracted out" in the reproduction, but it would be cool to hear at least a raw playback of the tracings. Edison 14:37, 14 November 2006 (UTC)

What does it mean when your Monocytes decrease..

What does it mean when your Monocytes decrease..

A decrease in monocytes could mean you are immunocompromised. A more detailed explanation would depend on the context. Rockpocket 06:33, 14 November 2006 (UTC)

It's not particularly meaningful to look at monocyte percentage as an isolated number, because (obviously), if something (like a bacterial infection) increases your neutrophil count, your monocyte % will decrease, and that won't really mean anything, it's just the result of the increase in polys, which is the significant thing. The WBC differential count provides the greatest amount of information when it is looked at as a pattern, in terms of both changes over time, and the relative quantities of the various cells. A low monocyte count in isolation isn't usually particularly significant - though of course if this occurs in a clinical situation, it should be reviewed by the clinician and clarified by him or her with the patient. - Nunh-huh 07:21, 14 November 2006 (UTC)

Compromised? Makes it sound like your immune system was paid-off for a back door. X [Mac Davis] (DESK|How's my driving?) 17:14, 14 November 2006 (UTC)

Naming a Diels-Alder product

I am attempting to name of the following product of a Diels-Alder reaction: [1]. I have found the name of a similar molecule[2], but cannot determine exactly how to translate the change from O to N. Thank you in advance; any help is greatly appreciated.

--ChunkySoup 07:03, 14 November 2006 (UTC)

the dienophile in the similar compound is maleic anhydride, which leads to a succinic anhydride derivative. the dienophile in your DA reaction is methyl maleimide, which leads to a succinimide derivative. Xcomradex 08:05, 14 November 2006 (UTC)

Chemical Abstracts names it as cis-3a,4,9,9a-tetrahydro-2-methyl-4,9[1',2']-benzeno-1H-benz[f]isoindole-1,3(2H)-dione and lists as an alternate name cis-9,10-dihydro-N-methyl-9,10-ethanoanthracene-11,12-dicarboximide. --Ed (Edgar181) 19:10, 14 November 2006 (UTC)

microalgal bioreactors

hello, ive been doing some research and i cant find anything on microalgal bioreactors. i need to know what a microalgal bioreactor is, what its used for, whats its uses and its effects on the surrounding envionment? And who uses microalgal bioreactors such as organisations etc...

thanks heaps guys, graham

Have you read Biochemical engineering? It's primarily composed to material related to bioreactors. I'm only familiar with tissue-related bioreactors, but I'd assume a microalgal one would be used to grow algae, with primary uses by whomever would be studying algae. I don't think the reactor has an effect on the surrounding environment, since it's designed to be a completely in-vitro system. 16:27, 14 November 2006 (UTC)

alternating magnet

Is there a permanent magnet that alternates its poles withut any supply of energy

It is not likely that you'll find one. If this exists, all you need to do is to wind a coil of wire around it. The changing magnetic field would produce alternating current without spending any energy ! -- Wikicheng 11:07, 14 November 2006 (UTC)

Erm, not quite. You need a power source. There won't be any alternating current if you don't put any current in the wire to start with. You can't get energy from nothing. - Mgm|^(talk) 11:17, 14 November 2006 (UTC)

A changing magnetic field passing through a wire creates electrical current. You don't need to put current in the wire to get it going. You can try it yourself. Attach the ends of a coil to a volt meter and wave a magnet back and forth past all the coil. You'll see the volt meter bounce. --Kainaw ^(talk) 14:00, 14 November 2006 (UTC)

Also, the alignment and re-alignment of the magnetic dipoles would need energy. Frankchn 11:10, 14 November 2006 (UTC)

Well, if we get a permanent magnet which changes it's polarity without using any energy (wow !), the we can get AC from the magnet by simply winding a coil of wire around it ? If effect, such a magnet does not exist.-- Wikicheng 13:15, 14 November 2006 (UTC)

But wait! That means that if the earth were surrounded by a giant coil of wire, then every time it flipped its magnetic pole (every few million years) it would generate a half cycle of electricity. Cool! 14:42, 14 November 2006 (UTC)Edison

Yes but the frequency would be rather low beacuse the flipping actually seems to take thousands of years. THe induced voltage would therefore be very low. 8-)--Light current 16:23, 14 November 2006 (UTC)

I didn't know that earth flips its magnetic poles (albeit once in a million years). I am assuming that the change would not be instantaneous but would be gradual. So does it mean that in the middle of this cycle, there will be a period when there are no North and South poles ?(because the N pole is slowly becoming S pole and vice versa) -- Wikicheng 11:32, 15 November 2006 (UTC)

To some degree yes (though the other non-magnetic sets of poles would still exist in their same location, see e.g. North pole), but it's not as if the Earth's magnetic field is as simple as that of a bar magnet. It fluctuates quite a bit and during the course of a flip (if I recall correctly), it's sort of a general weaking of the polar poles compared to fluctuations all over the Earth and eventually the magnetic poles re-establish themselves, potentially reversed. That is a very simplified version of the story, of course. digfarenough (talk) 20:34, 15 November 2006 (UTC)

Good info. Geomagnetic_reversal has more details. Thanks -- Wikicheng 04:50, 16 November 2006 (UTC)

organ transplantation

What are the sources available for organ transplantation?Are such sources effective?Are they ethical?How may the government improve its healthy system to make organ transplantation more effective?—Preceding unsigned comment added by 210.195.36.143 (talk • contribs)

This is a too broad a question for a full treatment here. You might like to start at organ transplantation and see some of the many links from there.--Shantavira 11:50, 14 November 2006 (UTC)

Why would organ transplantation be unethical unless you "stole" the organ, or got it from the black market? Unless you believed one should leave God's creatures how they were born. X [Mac Davis] (DESK|How's my driving?) 17:12, 14 November 2006 (UTC)

I believe they were asking if the sources were ethical. On top of stolen organs, some question the ethics of paying for organs, for example. Skittle 22:36, 14 November 2006 (UTC)

Anomalous compounds/substances

What are the examples of such compound which show anomalous behaviour?

Why do water show anomalous behaviour?Explain in short.

maheshwor

See our articles on physics and chemistry of water and hydrogen bonding. Gandalf61 13:25, 14 November 2006 (UTC)

In short, anomaly. The fact that water expands as it freezes might be considered an anomaly.--Shantavira 13:27, 14 November 2006 (UTC)

Which types of painkillers does caffeine enhance?

The caffeine article mentions, in the "effects" section, that caffeine is sometimes used in conjunction with painkillers; I've heard elsewhere that caffeine enhances the action of analgesics. My question is, which classes of analgesics does caffeine enhance? Does it affect NSAIDs, narcotics, gabapentin, and/or local anesthetics? Thanks. -- Creidieki 13:42, 14 November 2006 (UTC)

Caffeine is matabolized by cytochrome P450, and thus may potentiate any other drug which is metabolized through this pathway. You'll have to be more specific for the other compounds (these things you have listed are grouped by mechanism of action, not mechanism of catabolism), but I will tell you that gabapentin isn't even metabolized in the body (and get this: the bigger a dose you take, the less of it is bioavailable, isn't that weird?), so it is not contraindicated with caffeine. However, there are other interactions (because a certain isoform of cytochrome p450, CYP2A6, is slightly inhibited by gabapentoin) in your list. Gabapentoin should not be taken with naproxen (an NSAID), hydrocodone or morphine (these are narcotics), unless your doctor specifically is aware of the interplay between these drugs (its, um, complicated, and needs vigilant monitoring). Gabapentoin has other contraindications too, but not, as far as I remember (which is not very far), in the drug classes listed above. This is not medical advice, see your physician if this question is anything but hypothetical, mixing drugs can have potentially lethal effects. Tuckerekcut 19:28, 14 November 2006 (UTC)

Thank you for your response; I've been bouncing around between physicians a bit. I'll corner one of them about some questions I have now. -- Creidieki 21:20, 14 November 2006 (UTC)

Some unorganized, general info...Excedrin & other brands of headache medicine contain acetaminophen, aspirin & caffeine -- which apparently provides "significantly superior efficacy and speed of onset compared with" ibuprofin. Codeine is often given with caffeine, according to this site, but it's not clear that it helps with the opiate effects or the acetaminophen that often accompanies it. This paper suggests that caffeine consumption increases headache risk. According to this paper, "acute, but not long term, caffeine intake reduced neuropathic pain state in nerve-injured rats, but only at very high doses." -- Scientizzle 19:41, 14 November 2006 (UTC)

The last abstract I linked to explains "The potential hyperalgesic effect of chronic A(1) adenosine receptor blockade [by caffeine] may have been compensated for by an antinociceptive effect of caffeine through antagonism of A(2A) receptors and tolerance development." Drugs that work through adenosine receptor systems may be particularly affected by caffeine. -- Scientizzle 19:45, 14 November 2006 (UTC)

An innovative application of laser?

Hi all! Could you help me out and give me a really innovative thing you could/would like to do with lasers? Thanks in advance. PS: This aint for school. And I need it as fast as possible.--202.88.231.147 14:11, 14 November 2006 (UTC)

Use a laser to levitate an object. Edison 14:43, 14 November 2006 (UTC)

I heard on the radio yesterday that the only reason supermarkets still put plastic wrap onto cucumbers is that the label doesn't stick to the cucumber properly. So I'd laser-etch the label info (including the barcode) into the skin of the cucumber. Hopefully some tweaking of the laser frequency and power could produce a mark that noticeably changes the colour of the cucumber skin (ideally bleaches it white) without really damaging the skin (affecting its shelf life and customer acceptability). As cucumbers are mostly eaten in little slices, the mark shouldn't be off-putting to the final consumer. -- Finlay McWalter | Talk 14:48, 14 November 2006 (UTC)

Believe it or don't it's been done! I read a blurb about laser-etched food items a few years ago; sorry, no link.

Atlant 18:50, 14 November 2006 (UTC)

A means of propulsion for spacecraft. A powerful stationary laser in Earth orbit aims a laser at the spacecraft. The beam then reflects off the craft, accelerating it away from the laser. StuRat 15:01, 14 November 2006 (UTC)

Make three lasers: red, blue, and green. Each one will be fine-tuned to a specific frequency. Use them to project HD television on a screen. Then, make the screen out of three fibers: red, blue, and green. When meshed together, they will appear to be nearly black. But, the fibers are made so that they reflect one and only one frequency of light - the one the lasers produce. So, when all 3 lasers hit the fabric, it produces crisp and clear white light. When they don't, it is black - even in a completely lit room. So, you can have super-mega-huge projection television without having to shut off all the lights. --Kainaw ^(talk) 15:07, 14 November 2006 (UTC)

It's not precisely related, but this might interest you: Tunable crystals] 16:14, 14 November 2006 (UTC)

Optical computers 16:14, 14 November 2006 (UTC)

Burn a marriage proposal to your loved-one onto the surface of the Moon? --Kurt Shaped Box 20:48, 14 November 2006 (UTC)

Sinc the current best focussed lasers produce a spot one mile wide at the moons surface, the power density would probably not be enough to boil a cup of tea!--Light current 21:43, 14 November 2006 (UTC)

What if you cranked it up to 11? ;) --Kurt Shaped Box 21:53, 14 November 2006 (UTC)

I think the problem is one of the atmosphere tending to defocus the beam due to turbulence; so the power is a secondary issue-- Its how fine you can focus it on the moons surface. --Light current 22:00, 14 November 2006 (UTC)

Wouldn't a wide beam be the most suitable choice for carving a message into the moon anyway? If you wanted to be able to see it from earth, this is... --Kurt Shaped Box 22:54, 14 November 2006 (UTC)

No because as I said before you cant get enough power per sq cm to actually burn anything!--Light current 23:07, 14 November 2006 (UTC)

Could George W. Bush? --Kurt Shaped Box 01:02, 15 November 2006 (UTC)

Yes, if you give him a blowtorch and a rocket to get to the Moon. And a $9.99 laser pointer to apply to the freshly burnt surface, as it must be an "application of laser" after all. --Dr_Dima.

Could you set a soapbox on fire with a laser?Edison 15:24, 15 November 2006 (UTC)

Yes, but that's arson. --Dr_Dima.

That's just great. The first grafitti on the Moon. Speaking of which, does anybody actually "own" or have any legal rights to any part of our neighbor (somebody who could sue you for defacing his or her property)? Clarityfiend 00:32, 15 November 2006 (UTC)

The Outer Space Treaty says that the Moon or anywhere else outside earth can't be claimed by any particular country. Until there is actually an attempt to economically exploit some extraterrestrial body, however, it's really not an issue. --Robert Merkel 00:39, 15 November 2006 (UTC)

the liver

To whom this may concern, I tried to get a clear copy of your "view from below" the liver and I am unable to. It down loads fuzzy and prints illegible. Is there any possible way that you can send me a clear copy or fix the one on the page so that it is more functioning. As a user of your site I am always excited to see all your wonderfull illustrations but when they are unreadable, it is frustrating. I am a homeschooler doing a unit on the digestive system with my two children so this particular illustraion would be wonderful to have since it labels all the liver parts.

Thank you in advance for your help. With much appreciation Christine Blamire

My email:(removed)

Those images from Grey's anatomy are kind of hard to read and fuzzy. Does it look different on the internet to you? X [Mac Davis] (DESK|How's my driving?) 17:10, 14 November 2006 (UTC)

I had some free time, so I emailed her a response, which I've included below:

Hi! I'm Creidieki (please excuse the weird name), and I'm one of the volunteers answering questions at Wikipedia's Reference desk.

I should note first that we don't usually reply via email. In general, putting your email in a public place on Wikipedia is an easy way for spammers and other impolite folk to find it. We've hidden your email address on the page. For the reference desk, you should check back at the same reference desk page you asked on to see answers to your question.

It looked like you hadn't realized that, so I thought I'd send you an email; other people may also respond to your question on the reference desk, and you should look for those responses over the next several days, at http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#the_liver . (Or you could go to Wikipedia, type "Wikipedia:Reference desk" into the search box, go to "science", and then scroll down to find your question).

Anyway, on to answering your question. Wikipedia is a free encyclopedia, which means a couple of things. It's put together by volunteers, and we only accept material that can be freely redistributed (under a license called the GFDL). That's really good, because it means that schools and universities and people can use Wikipedia's material under very generous terms. Unfortunately, it's also difficult to find trained medical illustrators who want to draw complicated diagrams for free. It looks like the liver picture you were asking about was scanned from a 1917 book copy of Grey's Anatomy; it's probably accurate, but we're not going to be able to find a better copy of that specific diagram for you.

So, if you want a good image of the liver, you're probably going to have to look elsewhere. I searched google for a bit, and came up with a few candidates for better images. Frankly, I have no idea how authoritative these images are; all I can say is that they claim to be diagrams of the liver. You may want to go to a local library and see if they have an updated copy of Grey's Anatomy, or other similar books.

http://www.ariess.com/s-crina/liver-anatomy.htm -- claims to use Grey's Anatomy as a source.

http://medicalcenter.osu.edu/patientcare/healthinformation/otherhealthtopics/LiverBiliaryPancreaticDis4540/TheLiverAnatomyandFunctio4542/ -- from a university medical center.

I hope those two links help. Again, you should check at the reference desk for other answers.

-- Creidieki 17:29, 14 November 2006 (UTC)

THe image in question is a plate from an old (out of copyright) edition of Gray's Anatomy. You can get a bigger version of the same image here. -- Finlay McWalter | Talk 17:35, 14 November 2006 (UTC)

Tai Chi hand postures

What is the meaning (purpose) of the hands in the closing posture of Yang style Tai Chi. Right fist in palm of left hand or left fist in palm of right hand. Thank You Mike Woodside

It's a salute. It's typically found at the end of wushu sets, though its origin probably predates competitive kung fu.

If I understand you correctly, you are basically covering your fist with the other hand (usually the left covering the right). I was taught that this is symbollically "covering your weapon" and saying that you mean no harm, although since your fist is still there, it means that you will defend yourself as necessary. We use it as a sign of respect at the beginning and end of class and forms (Shaolin Wushu Kung Fu). At least that's what we were told, I have no idea if it is correct. But it sounds reasonable. --Bennybp 01:45, 15 November 2006 (UTC)

Kashi

According to this article, Kashi products cause "excessive gas". Is there any truth to this (perhaps from the ingredients) or is this edit vandalism? | AndonicO ^{Talk | Sign Here} 19:44, 14 November 2006 (UTC)

The claim seems somewhat unlikely given the ingredients, and after having eaten Kashri cereals I've never noticed any untoward effects. A radical change of diet may initially cause extra gas as the flora adapts to it; perhaps that is the origin of the complaint, but then it is not specific to Kashri. The anon's IP address has no history of vandalism and is assigned to the Detroit Medical Center, but the statement is depreciative of a commercial product, completely unsourced, and in this form ("may") unfalsifiable. Altogether I've found it best to remove this claim.  --Lambiam^Talk 20:28, 14 November 2006 (UTC)

There might be a basis for the claim in that high fiber foods can cause gas, and Kashi cereals tend to have a higher dietary fiber content than more mainstream cereals.--Mabris 21:24, 14 November 2006 (UTC)

Natural logarithm units

When taking the natural log of a number in a given unit, would the result be in the same unit? That is, would the following statement be true?

$\ln \left(10m\right)\approx 2.3m$

My thinking is that it would be false, as:

$\ln \left(10m\right)=\ln \left(10\right)+\ln \left(m\right)\neq 2.3m{\mbox{ in general}}$

Any comments would be appreciated. --132.194.13.121 20:24, 14 November 2006 (UTC)

Mathematical functions do not change units. Taking the log of a number is no different than multiplying by a constant. For example: 10 * 10m = 100m. Your example of proving it wrong would be: 10 * 10m = 10 * 10 + 10 * m. That makes no sense, just as ln(m) makes no sense. --Kainaw ^(talk) 20:31, 14 November 2006 (UTC)

Thanks for the reply, although I think you might be mistaken here. Mathematical functions frequently change units, provided they are not linear functions. As an example, consider (10m)² = 100m². I believe a simplified version of the 'correct' answer here is that the natural log function results in a unitless number. Comments? --132.194.13.121 20:40, 14 November 2006 (UTC)

The issue here is that the natural logarithm only takes unitless numbers as arguments. Thus physical quantities that involve natural logs of numbers with units always have some "scale" in the argument to cancel out the units. Otherwise there would be exactly the problem you describe. -- SCZenz 20:42, 14 November 2006 (UTC)

(after edit conflict) A more appropriate spot for this question is the Mathematics reference desk, but in any case the statement is false. If 0 < m < 1/10, ln(10m) < 0, while 2.3m > 0. When you graph ln(10m) against m you get a curve that has the same shape as the green curve in the article Logarithm, whereas graphing 2.3m gives a straight line. There must be a relationship between the "2.3" in the question and the fact that ln(10) = 2.302585..., so someone may have mistakenly thought that log(a×b) = log(a) × b for the case a = 10.  --Lambiam^Talk 20:44, 14 November 2006 (UTC)

I think m is supposed to be a unit here, perhaps meters. -- SCZenz 20:47, 14 November 2006 (UTC)

(after another edit conflict) Now I understand the question, the "m" is supposed to be metres, and not a variable. Then indeed ln(10m) is meaningless. (By convention, units are not set in italics.)  --Lambiam^Talk 20:51, 14 November 2006 (UTC)

Thanks for all the responses. This came up in a Chem lab project measuring vapor pressures at various temperatures. (Hence the post in the Science desk.) When this is done, a plot of lnP vs. 1/T yields a straight line, the slope of which is of interest. Now, the average slope of this plot would be m = Δ(lnP) / Δ(1/T). So in this sense the unit for pressure isn't important as it is subtracted out as I showed above. In other words, what SCZenz said above. Sorry for the confusion Lambiam - I did mention "When taking the natural log of a number in a given unit". --132.194.13.121 21:03, 14 November 2006 (UTC)

Right, the slope will be independent of the "scale" (i.e. unit) of pressure being used in the argument, so it often isn't specified. -- SCZenz 21:06, 14 November 2006 (UTC)

If you treat the log of a unit as an unspecified constant, then they should all cancel out at the end. By itself, ln(10 m) is meaningless, but ln(10 m) – ln(5 m) = ln(10) + ln(m) – ln(5) – ln(m) = ln(10) – ln(5) = ln(2) = 0.693. It works out that way because the difference of the logs is the log of the ratio, which is dimensionless. If you end up with the log of a unit in your final answer, that means you made a mistake. —Keenan Pepper 21:15, 14 November 2006 (UTC)

THe log of a number is the power to which you raise the base to get that number. Does a power have units? 8-)--Light current 21:48, 14 November 2006 (UTC)

Answer : NO!--Light current 22:09, 14 November 2006 (UTC)

For instance consider the problem of changing nepers into dBs. THe bases are different but the net difference between the two units is only one of multiplication by a certain constant that relates the two bases (base e and base 10 -- cant remember what it is and too lazy to work it out). Is this comment relavant?--Light current 21:54, 14 November 2006 (UTC)

I think the best answer is there is a unit ln(P) where P is in pascals, but there is no special name for this unit. Indeed, I can't think of any unit with a special name that is the result of taking the natural or common logarithm of a quantity expressed in some other unit. --Gerry Ashton 02:41, 15 November 2006 (UTC)

Sorry, that doesn't work either. In dimensional algebra, the numbers are conceptually multiplied by their units of measure. Thus 2 m × 3 m = 6 m²: you're just multiplying the 2, the 3, and the two instances of "meters" all together. In fact it works just like 2m × 3m = 6m² where m is a mathematical variable instead of being meters. But if it was meaningful to take ln(20 Pa), you would get ln(20) + ln(Pa), not ln(20) times anything. It simply is a fact that taking the logarithm is something you can only do with a pure, dimensionless number.

What may confuse the issue is that something like "pressure in pascals" is a dimensionless number, and so it's safe to take its logarithm if you want. Think of the word "in" here as indicating division. You are dividing the actual pressure, 20 Pa, by the unit Pa to get the pure number 20. So as soon as you work with something like "pressure in pascals" or "length in meters", you are using dimensionless numbers.

--Anonymous, 07:05 UTC, November 15.

Logarithmic scales always have an implicit reference value - the value of the underlying that corresponds to a value of 0 on the logarithmic scale. For example:

• The reference value for the decibel scale (in the acoustics definition) is 20 µPa.
• The reference value for the decibel watt scale is 1 W.
• The reference value for the pH scale is 1 mol/litre.
• The reference value for the Krumbein scale of grain size is 1mm.

By assigning a value of ln(10) to "ln(10m)" you are implicitly using a reference value of 1m. If you use a different reference value, you add or subtract a constant amount from the values in the logarithmic scale. Gandalf61 13:02, 15 November 2006 (UTC)

Strictly, one should only take logs of a dimensionless scalar, so in the original question you shouldn't really ever have ended up with an expression like $d\ln(p)/d(1/T)$ because you're taking logs of a dimensional quantity. It's algebraically equivalent to $d\ln(p/p_{0})/d(1/T)$ (with $p_{0}$ constant), which is a valid expression because here you're taking a log of a dimensionless quantity. Given that this equivalence holds regardless of the value of the reference value $p_{0}$, it's convenient to simply write $\ln(p)$ as a lazy shorthand, provided that you interpret it as "$\ln(p/p_{0})$, for some $p_{0}$ which had better turn out to cancel out or otherwise something has definitely gone wrong". Arbitrary username 00:24, 17 November 2006 (UTC)

Saltwater

What chemicals are in saltwater?

Salt, and water. Philc _T^E_C^I 23:16, 14 November 2006 (UTC)

Perhaps you mean seawater? Vespine 23:18, 14 November 2006 (UTC)

(edcon)

Plus a few other things probably. Sea water--Light current 23:19, 14 November 2006 (UTC)

Heck, even saltwater itself would tell you. DMacks 23:22, 14 November 2006 (UTC)

November 15

physiology

I used to use a program called body works 4.0 to learn about human body, anatomy, etc.

I see this software, even the newest version, is outdated. Does anyone have any recommendations for an easily accessible program geared towards physiology / anatomy?

Outdated how ? Does it show the "proper places to do bleedings" ? :-) StuRat 02:42, 15 November 2006 (UTC)

Bicarbonate vs. Hydrogen Carbonate

I'm doing my science homework and I've been learning about Polyatomic Ions in class and now we're practicing writing formulas and nomenclature. I had to write a formula for Hydrogen Carbonate. I know that there is some controversy weather or not it is the same as Bicarbonate. I thought that the formula for Bicarbonate was HCO₃ and that Hydrogen Carbonate would be H₂CO₃. If anyone knows the answer, this would be very helpful. Thank You -- Jesusfreak 01:51, 15 November 2006 (UTC)

The prefix 'Bi' is sometimes (always?) used to indicate the presence of hydrogen as in sodium bicarbonate (NaHCO₃??)

Ahh! look what I found!

The bicarbonate ion is a polyatomic anion with the empirical formula HCO3− and a molecular mass of 61.02 daltons; it consists of one central carbon atom surrounded by three identical oxygen atoms in a trigonal planar arrangement, with a hydrogen atom attached to one of the oxygens. The bicarbonate ion carries a negative one formal charge and is the conjugate base of carbonic acid, H2CO3; it is the conjugate acid of CO32−, the carbonate ion.

So hydrogen carbonate is bicarbonate!

--Light current 02:12, 15 November 2006 (UTC)

H₂CO₃ is carbonic acid, and it is unstable with respect to loss of carbon dioxide: CO₂ + H₂O ⇌ H₂CO₃. The equilibrium lies heavily away from carbonic acid. Xcomradex 02:29, 15 November 2006 (UTC)

Is that why my lager is fizzy?--Light current 02:31, 15 November 2006 (UTC)

Yes, bicarbonate and hydrogen carbonate are synonymous (HCO₃⁻). In fact, I believe hydrogen carbonate is the IUPAC recommended term (so, for instance, sodium hydrogen carbonate instead of sodium bicarbonate), which is logical: using bi- to indicate the hydrogen is not intuitive. It’s more awkward, though, and in practice the bicarbonate terminology seems to be well-entrenched. — Knowledge Seeker দ 03:31, 15 November 2006 (UTC)

Um, this may be out-of-date terminology for all I know, but I think "hydrogen carbonate" is H2CO3. "Carbonic acid" is hydrogen carbonate dissolved in water. The pure substance, with no water to make it dissociate, is not particularly an acid. --Trovatore 03:40, 15 November 2006 (UTC)

The orinal question was about ions, not full compounds. You're correct that H₂CO₃ would be "hydrogen carbonate", but it would not be "a hydrogen carbonate ion". DMacks 03:47, 15 November 2006 (UTC)

Well just to quote from our page again,

The bicarbonate ion is a polyatomic anion with the empirical formula HCO3

carbonic acid,(is) H2CO3

Seems pretty clear to me! And Im no chemist!--Light current 03:57, 15 November 2006 (UTC)

But it doesn't mention hydrogen carbonate. Our hydrogen carbonate was a redirect to bicarbonate; this seems to have been the clamorous error of some idiot user who calls himself Trovatore. What was he thinking? I guess we'll never know. Anyway, I've redirected it to carbonic acid; I think this is more correct, though technically speaking the pure substance H2CO3 (which, I think, can't exist at standard temperature and pressure, but can exist under other conditions) should be called hydrogen carbonate rather than carbonic acid. --Trovatore 04:34, 15 November 2006 (UTC)

i think it should point to bicarbonate, since someone is far more likely to be wondering about sodium hydrogen carbonate etc than something else. my two cents. Xcomradex 05:15, 15 November 2006 (UTC)

Not a good excuse for inaccuracy, in my view. But if you like, you could make a disambig page. --Trovatore 05:23, 15 November 2006 (UTC)

sounds too much like hard work ;-) --Xcomradex 07:04, 15 November 2006 (UTC)

Meh, who cares where it points, as long as it's clear from that page which one that page is talking about. And provides a route to "the other one". I just added a dablink for that last bit. DMacks 20:39, 15 November 2006 (UTC)

I restored the redirect target to bicarbonate. I have never seen hydrogen carbonate refer to carbonic acid, though if someone has a good source I would like to see it. There is plenty of documentation that hydrogen carbonate refers to the same ion as bicarbonate. See, for instance, this answers.com search (in particular, the Columbia University Press encyclopedia), another search, our own nomenclature articles (see point five), and a PubChem search (and the PubChem listing. — Knowledge Seeker দ 22:07, 15 November 2006 (UTC)

Well what do you think the formula is for carbonic acid?--Light current 00:39, 18 November 2006 (UTC)

I think the formula is H₂CO₃, which should be apparent if you read the article to which you linked. — Knowledge Seeker দ 03:53, 18 November 2006 (UTC)

Exoskeletons

I'd like to bone up on exoskeletons...why exactly can't they grow, leading animals to shed the old before growing a new one ? Mammal bones can grow, including the skull, which is pretty much a portion of exoskeleton. Is there some inherent reason why other animals with full exoskeletons can't do this, or have they just failed to evolve that ability ? StuRat 02:32, 15 November 2006 (UTC)

"This structure makes cuticle extremely strong, as well as highly effective at keeping the spider from drying out, but the material does have one serious drawback. While it's flexible enough for movement, it can't expand like human bones and tissue -- in other words, it can't grow. In order to increase its size, the spider has to form a new, larger cuticle exoskeleton and shed its old one (this is called molting)." Got it from http://science.howstuffworks.com/spider1.htm Hope that helps! (too lazy to sign in) User:Sifaka 152.3.72.50 03:15, 15 November 2006 (UTC)

Thanks, but that only says THAT it doesn't grow, not WHY. StuRat 04:41, 15 November 2006 (UTC)

If you look at this site http://www.cals.ncsu.edu/course/ent425/tutorial/integ.html it has a nice diagram of the exoskeleton cellular layers. The outermost and exposed layers that form the hard inflexible parts of the exoskeleton called sclerites are formed from individual protein molecules that are linked together by quinone compounds. This is a pretty exothermic reaction so these are very stable bonds that are forming and are energetically difficult to reverse. However that isn't enough to explain it. First of all since the sclerites are not composed of living cells and they are on the outside of the insect exposed to air, modifying them, which would take place in an aqueous environment by appropriate enzymes would be difficult. If the insect were to dissolve portions of the whole cuticle at once, it will lose water quickly and open itself to disease vectors. One could imagine an insect sloughing off pieces of its exoskeleton at a time. Human skin which has a similar pattern of layering, but is different in that dead cells take the place of the cuticle. These cells are sloughed off rather quickly and allow a human to grow. An insects exoskeleton can't slough off in tiny pieces like human skin because it is one big interconnected mass. Instead it has to get rid of the whole thing and harden a whole new layer that is big enough for it. That is why newly shed insects are very soft to the touch. Their cuticle hasn't hardened yet. Procuticle has some more information with lots of jargon. Ecdysis, the scientific term, describes the cellular actions behind molting. That is about the best I can do without consulting an entomologist. Sifaka ^talk 05:04, 15 November 2006 (UTC)

Random guess time! Your skeleton is inside you, therefore your bones can grow by adding layers on. For an exoskeleton to grow, the dry outer layer which is not in contact with the useful fleshy parts of the animal would have to have another layer laid down. This is rather hard to arrange. It's possible that I'm in fact saying what Sifaka is saying ("...they are on the outside of the insect exposed to air..."). Skittle 21:15, 15 November 2006 (UTC)

Endoskeletons are remodeled by osteoclasts and osteoblasts continuously breaking down and reforming bone, on both (all) surfaces. These are active beneath the periosteum, the thin membrane covering bones. It is difficult for me to imagine how such an environment could be maintained on the exterior surface of an animal. — Knowledge Seeker দ 22:26, 15 November 2006 (UTC)

I can picture a series of overlapping plates, like roofing tiles, which grow at one end, like fingernails. When needed, a new plate could also grow between two existing plates, to fill in a gap. The advantage of being able to avoid shedding, and the vulnerability that entails, would seem to make this method preferable. So why doesn't it happen ? StuRat 01:10, 16 November 2006 (UTC)

You mean kind of like (fish) scales? I have a feeling it's probably related to the complexity of the organism, since there really aren't any animals larger than insects (which, admittedly, can get pretty darn big) that have exoskeletons. With such a relatively tiny volume, the exoskeleton is competitive with an endoskeleton, whereas larger animals require an endoskeleton. I'm not a biologist, so I can't really say why, though. Virog^{It's not}_{my fault!} 04:08, 16 November 2006 (UTC)

Don't snakes have exoskeletons ? And aren't some of them huge, like an anaconda ? StuRat 07:11, 16 November 2006 (UTC)

No, snakes are vertebrates, which among other things, means they have a spinal column and therefore an endoskeleton. — Knowledge Seeker দ 07:15, 16 November 2006 (UTC) See [3] for a photograph of a snake skeleton, or a Google Images search for more. — Knowledge Seeker দ 07:18, 16 November 2006 (UTC)

It's probably the difference between monocoque and truss structures. 16:39, 16 November 2006 (UTC)

Non-Standard Sleeping Pattern Name

Is there a name for the patter of sleeping 12 hours, staying active for 24 hours, sleeping for 12, and so forth? If so... what is it? Thanks in advance ^^ kaiti-sicle 02:43, 15 November 2006 (UTC)

Well, 12 on/12 off isn't a normal diurnal variation or circadian rhythm, but at least the terms may point you to an answer. Marine life has a 12 hour tidal rhythm, but people shouldn't :). - Nunh-huh 05:52, 15 November 2006 (UTC)

I don't think enough people could follow that schedule that there is a name for it. Many biological rhythms are close to 24 hours. Even when external cues are removed, the drift of rhythm is smaller that that. The system you describe would shift sleep alternately between day and night. In the 1970s, some medical or surgical residencies required every-other-night call, which was essentially 36 hours awake, followed by 8-10 asleep, for 1-3 years with occasional breaks. It was grueling. Currently, residency rules mandate going home after being at work for 24 hours, and people may then sleep for 12 hours, but do not then stay awake another 24 hours-- it is a stressful, unnatural rhythm that cannot be sustained. alteripse 11:45, 15 November 2006 (UTC)

Just a slight nitpick: current residency rules mandate going home after 30 hours, it's just that no new patients can be started in the last 6 hours.Tuckerekcut 15:29, 15 November 2006 (UTC)

I would think that every time an exhausted resident makes a mistake that kills somebody, the hospital would be sued for millions, and this idiotic practice would end. Why doesn't this happen ? StuRat 18:32, 15 November 2006 (UTC)

The issue is complex. For one, rarely can clear-cut situations like that be determined. Also, there are several barriers to reduce the number of resident work-hours. For instance, suddenly curtailing work hours leaves hospitals and programs short of workers; there will not be enough doctors to handle the work (in fact, even the recent restrictions have led to some busier hospital services, which can also lead to mistakes). Another is that with duty hour restrictions, residents will not gain enough experience. Given the choice between longer hours or an extra year of residency, many residents would choose the former. And finally, many doctors believe that physicians have to be “tough” to deal with the stresses they will face and they should get used to a grueling lifestyle. Of course, there are many reasons to limit hours as well—I am not expressing an opinion here. — Knowledge Seeker দ 22:32, 15 November 2006 (UTC)

Two minor additions. The current restrictions did result from a lawsuit over an avoidable death in NYC about 15 years ago. The other significant safety drawback of shorter shifts not mentioned by knowledgeseeker is that reduced continuity incurs an increased patient risk: it will take longer for the new resident to recognize changing status of an acutely ill patient, each sign-out involves a synopsis of the clinical information, and there is often a difference in the level of mental energy exerted on patients signed out to you who have already had their initial plans and evaluation formulated by the last shift. These are very real safety trade-offs to balance against optimized alertness. The typical replacements for residents when work hours are shortened but the patient load must be handled are nurse practitioners who cost more and work shorter shifts. alteripse 23:06, 15 November 2006 (UTC)

The second argument is reasonable, although I picture somebody working for 30 hours straight to be a much higher risk than a new doctor. The first argument, that hospitals won't have enough doctors, is not sound. They will merely need to hire more (and possibly pay more), if the hours of each are kept down. I'm not aware of any absolute shortage of doctors, at least in the US, so it's just an issue of the hospitals being unwilling to pay them adequately for their time. Of course, any change would need to be phased in, to allow for hiring new doctors, but that's not an argument to refuse to make the change at all. StuRat 01:01, 16 November 2006 (UTC)

Hospital practices continue to evolve in attempts to improve patient safety. My points above were not intended to justify "no change", but to illustrate the multiple dimensions of what might initially seem a simple problem. I mentioned nurse practitioners as substitutes for house staff, but the other solution, as you suggested, is much more expensive doctors who have already completed their residencies-- called hospitalists, which can cost as much as 5x what a residents costs. And of course the cost of hospital care takes another upward jump... alteripse 01:13, 16 November 2006 (UTC)

Its actually called Wikipedia addiction 8-)--Light current 20:04, 15 November 2006 (UTC)

Thanks for the info. I was curious because I have a tendency to fall back on that pattern; not consistently but for weeks at a time. kaiti-sicle 02:55, 16 November 2006 (UTC)

Acids

Why do all acids contain hydrogen?--Light current 04:01, 15 November 2006 (UTC)

They don't, although many of them do. The definition of a Lewis acid is a compound that likes to collect a pair of electrons. A better known non-hydrogen containing one is Aluminum trichloride. Electrophiles are by definition Lewis acids.

"Lewis Acids All species have a vacant orbital and/or an available LUMO (Lowest unoccupied molecular orbital)
 and all species with full or partial positive charge behave as Lewis Acids.
 Lewis Acid behaviour is found amongst:

    • Metal cations
    • Electrophiles (attacking Lewis acids)
    • Electrofuges (Lewis Acid leaving groups
    • Lewis acid "ligands" around and anionic centre (H+ and R+)
    • Classic electron deficient species such as boron trifluoride, BF3
    • Cationic spectator counter ions
    • Electron deficient pi-systems which take part in multicentre interactions
" 

Stolen from http://www.meta-synthesis.com/webbook/12_lab/lab.html

Some of the above are kind of complicated if you haven't taken organic chemistry yet. The short answer is many acids have hydrogen because the corresponding thing the hydrogen is attached to is perfectly happy replacing the hydrogen bond which it has to share with the hydrogen with a pair of electrons that it gets to keep for itself.

152.3.72.50 04:07, 15 November 2006 (UTC)

P4reformatted the block quote above. --ColinFine 04:44, 15 November 2006 (UTC)

One reason that many acids (for some definition of "acid" that is more restrictive than the Lewis definition) contain active hydrogen is because that essentially is the standard more-restrictive definition. See Acid#Definitions of acids and bases for more definition info. It began as a descriptor of materials that had a common property...only later was is ascribed to "has active hydrogen". DMacks 06:04, 15 November 2006 (UTC)

High specific heat of water relating to exothermic reaction (simpler question on paragraph 3)

Because water has a high specific heat will an exothermic reaction such as, heat escaping to the atmosphere after heating or more specifically to a calorimeter, progress slowly compared to the progression of the endothermic reaction taken place during the actual heating. If yes would a measurment of heat capacity be calculated wrong if temperature is measured before exothermic reaction is complete? or would it not matter when you measure the water during the exothermic reaction. 69.150.209.13 05:31, 15 November 2006 (UTC)

Um, what reactions are you talking about? Transfer of heat, by itself, isn't a chemical reaction at all; it's neither exothermic nor endothermic. If you're trying to measure the heat capacity of water by adding a known amount of heat energy and then measuring the temperature, you should do so immediately. If you wait until all the heat escapes and the water is back to its original temperature, you'll get a heat capacity of infinity, which is obviously wrong. —Keenan Pepper 06:41, 15 November 2006 (UTC)

During a chemistry lab, we were told to get the heat capacity of a calorimeter. By heating one beaker of 50mL of water and leaving another 50mL in a styrophome cup. Then to measure both temperature: cool (22 C) hot (42 C) - my results. Then we were told to mix the water. the temperature of the new warm water was 35 C. The hot water seemed to lost only 7 degrees. amd the cool seemed to gain whole 13 degrees. Ideally it was said the heat transfer is supposed to be moderatly equal. I do not understand why I got these reuslts. I apologize for my errors in the first question. I wanted to make it simpler but made it more complex 69.150.209.13 08:24, 15 November 2006 (UTC)

That doesn't sound that far off. Did you use a fancy digital thermometer or a regular liquid thermometer? Probably the 22 and 42 measurements happened to be a little low and the 35 to be a little high. —Keenan Pepper 15:56, 15 November 2006 (UTC)

Was the transfer done such that the cold water was added to the warm water in the beaker? If that's the case, it could be that the beaker was warmer than the water, and was still transferring heat to the water when the cold water was added.--Mabris 16:46, 15 November 2006 (UTC)

The beaker wouldn't have to be warmer. Assuming the beaker was 42°C as well, the system would a temperature that can be concluded from making the calculations on 32°C water, 42°C water and a 42°C beaker. 35°C seems very plausible in that scenario. TERdON 02:40, 18 November 2006 (UTC)

Hydrocarbon fuel cells with proton-conducting electrolytes

This question is about fuel cells that run on hydrocarbon fuel rather than H₂. If the electrolyte conducts O²⁻ ions, I can write down the half-reactions and everything makes sense, but if the electrolyte conducts protons, I'm not sure what goes on. Is CO₂ formed at the anode? If so, it seems like some electrons are wasted, because carbon is oxidized and oxygen is reduced at the same place, and the electrons from that redox couple don't flow through the circuit. Is that accurate? —Keenan Pepper 05:53, 15 November 2006 (UTC)

The applicable half-reactions are in the article Direct-methanol fuel cell. The electrolyte conducts protons, C is oxidized at the anode (producing CO₂ as you had guessed) but the reduction of the oxygen occurs at the cathode. --Mabris 17:06, 15 November 2006 (UTC)

Oh, I see where I went wrong. I had the hydrocarbon reacting with O₂ at the anode, but really it reacts with water and makes more protons and electrons, so the total number of electrons is the same no matter the electrolyte. Thanks! —Keenan Pepper 21:09, 15 November 2006 (UTC)

redox potential

Generally NAD is said to be having more negative redox potential than FAD.......and also NAD is capable of donating electrons to FAD but not in a reverse manner ie from FAD to NAD in normal conditions...My question is in what conditions FAD can donate elecctrons to NAD?{i know one example of this kind that is formation of acteyl Coa from pyruvate.here FAD accepts electrons and donates them to NAD...enzyme acting here is pyruvate dehudrogenase complex. how is this possible?)--hima 09:19, 15 November 2006 (UTC)

Since FAD is covalently bound to a protein the amino acid side chains can signifiantly change the chemical environment. This context is the critical factor. David D. (Talk) 12:20, 15 November 2006 (UTC)

The energy to overcome this reaction which seems to work against the redox potentials comes from the oxidization of the Coenzyme A to acetyl-CoA and CO₂. The pyruvate dehydrogenase coordinates the reaction to make this thermodynamically feasible.--Mabris 16:53, 15 November 2006 (UTC)

thx for ur answers....there is even one more issue in this case..that is FAD here is first of all a co-factor for the enzyme....and so as a co-factor it accepts electrons inorder to regenerate lipomide..an enzyme in this multienzyme complex..and transfers them to NAD inorder to release more amount of energy...--203.109.89.230 09:31, 16 November 2006 (UTC)

Watts in terms of volts - equation please

What's the equation linking Watts and volts? I have a feeling it's W=IV^2 or something like that. Thanks, --86.146.247.51 12:10, 15 November 2006 (UTC)

P = IV —Preceding unsigned comment added by 138.29.51.251 (talk • contribs)

Power (in watts) = Voltage (in volts) x Current (in amps), i.e., P = VI. You can substitute in Ohms Law (V = IR) to get other variations on this. (edit conflict)--jjron 12:17, 15 November 2006 (UTC)

See electric power. Gandalf61 12:20, 15 November 2006 (UTC)

Thanks everyone.86.146.247.51 12:22, 15 November 2006 (UTC)

Power=Current times voltage =Current squared times resistance=Voltage squared divided by resistance assuming direct current or alternating current with unity power factor (resistive load). If the circuit contains inductance or capacitance, then consult power factor. Edison 15:32, 15 November 2006 (UTC)

I know I'm being an annoying pedant, but can we be physicists and say potential difference, not voltage!? Englishnerd 22:25, 15 November 2006 (UTC)

Alessandro Volta would be weeping in his grave hearing you say that. Vespine 23:24, 15 November 2006 (UTC)

I dont know, can you? But if you want to be pedantic you should say electrical potential difference to distinguish from other sorts of potential.--Light current 04:35, 16 November 2006 (UTC)

Ah, Touché! Englishnerd 18:40, 16 November 2006 (UTC)

Sam Ting. Edison 05:36, 16 November 2006 (UTC)

Who was Sam Ting and what did he discover in the field of electricity? (I'm joking! :P 192.168.1.1 6:55pm, 16 November 2006 (PST)

Magnetism

I recently had a question on a test for MRI. The question was "What is not a characteristic of a magnet? The answers where a. attracts, b. holds iron, c. dipoles, d. resistive. I need to know if a characteristic of a magnet is that it holds iron? I was confused because I answered resistive. But after looking up resistive in the dictionary (which is a term used normally when talking about electronics) I found that resistive can also mean repel..I think the question was worded badly. Can anyone share some insight?

I'd say the most probable answer is d. All the others are certainly characteristic of a magnet, but only d is questionable. And when the word resistive is used in science, it can safely be assumed (at least I would) to refer to electrical resistance, which isn't characteristic of a magnet. –Mysid☎ 14:07, 15 November 2006 (UTC)

Superconducting magnets are often used for NMR, right? It's definitely D. —Keenan Pepper 15:39, 15 November 2006 (UTC)

• Surely there are non-ferrous magnets around... I'm having doubts about B. - Mgm|^(talk) 09:26, 16 November 2006 (UTC)

When we studied physics, we knew only about ferrous magnets. Assuming that the text book is yet to be updated, d would be the most suitable answer.--Wikicheng 13:04, 16 November 2006 (UTC)

Is 'none of the above' a suitable answer? Most contemporary MRI machines are electromagnets, meaning that they utilize magnetic fields produced by electricity circling through coiled wires. If the wires are electrically resistive, this means that you have to continuously pump more electricity into the wires (coils) to sustain the magnetic field. This is a 'resistive' electromagnet. Most, but not all, contemporary electromagnetic MRI machines are superconducting, meaning that the wire used for the coils has an electrical resistance that approaches zero when the wire is at certain temperatures. These are akin to perpetual-motion machines in that once the electricity is in the coil, you can disconnect if from the power source and the electricity will just keep circling, indefinitely, as long as the wire remains superconducting. Tgilk (talk) 14:18, 12 September 2009 (UTC)

low tech derusting and plating

I've heard there was a way to clean and plate iron such as found in old hammer heads by leaving them in molasses and then putting them in some kind of electrolyte with copper pennies. How this work and what would the setup be? 71.100.6.152 17:13, 15 November 2006 (UTC)

I'd use quick-hard instead of the molases, and you can electroplate things at home with reasonable materials - sulfuric acid (WEAR KITCHEN RUBBER GLOVES BE NEAR RUNNING WATER HAVE A SAFETY MASK OR GOGGLES), copper, distilled water, CuSO4, wires and a battery. More info for home electro-platers findable at [4]. READ THE SAFETY NOTES BEFORE ATTEMPTING ANYTHING AND HAVE COMPOTENT PROFESSIONAL SUPERVISION. JBKramer 17:43, 15 November 2006 (UTC)

Would that [be] quick-hard lime? [(To replace the molasses?)] 71.100.6.152 18:36, 15 November 2006 (UTC)

No, it works only on metal. It is a hardening agent. JBKramer 19:19, 15 November 2006 (UTC)

In our area the stores no longer carry battery acid of any other form of sulphuric acid and the one feed store that carries copper sulphate charges way too much. Is there a process whereby we can use other materials instead? 71.100.6.152 01:28, 16 November 2006 (UTC)

See also Phosphoric acid#Rust removal (aka "Naval Jelly"). In a pinch, maybe Coca Cola or Pepsi Cola would do, given enough time as they both contain some small amount of phosphoric acid.

Atlant 17:51, 16 November 2006 (UTC)

Okay. Found some battery acid today and some copper sulfate at about $4 per lb of acid and $8 per lb of sulphate. This should be enough to do the hammer heads although I like what I have now read about using phosphoric acid and then oil or paint. All I need to know is how to setup the electrolyte bath and the right voltage and current to use. I don't want to turn this into a hobby but just to get an idea of how its done and do a few parts to be sure I know what I'm doing. 71.100.6.152 00:51, 17 November 2006 (UTC)

nuts and bolts

I have a 'guiness book of records' type question - is this ok?

What is the largest nut? On a swing bridge I have observed hex nuts appox 2ft diameter, 1ft depth and approx 1ft bolt diameter - does anyone know of much larger nut and bolt combinations. Thank you.

If you're looking for the biggest nutter, you may well have come to the right place. :) DirkvdM 09:13, 16 November 2006 (UTC)

This nut/bolt combo looks roughly the same size as yours, and it used to build the Grand Coulee Dam. Laïka 15:28, 16 November 2006 (UTC)

Thanks, but the nuts I mentioned are at least twice the size of those (and therfore 8 times the weight) - I doubt anyone, even a professional weightlifter could carry one. Unfortunately I don't have a picture of one - anyone else got anything?

Its not the nut thats the problem, its the size and weight of the spanner (wrench) to turn it. This I think may be the limiting factor--Light current 16:04, 16 November 2006 (UTC)

Interesting - in the case of the bridge I mentioned the nuts/bolts shouldn't be under extreme load since they merely affix the bridge deck to the bit that rotates underneath - so they probably aren't that tight. This leads to the 'worlds biggest spanner' question...

how to test out reactolite (photochromic) spectacle lenses?

i just bought a pair of prescription specs with reactolite lenses - but after 8 hours of use i haven't noticed them go dark! this included walking around outside in a cloudy uk november day for several hours, and staring up at my kitchen fluorescent lamp for a few minutes. neither of them had any noticeable darkening affect!

how can i test if they are working and be sure they're ok once and for all? obviously its a bit difficult finding bright sunshine in the uk in november.86.31.114.97 20:12, 15 November 2006 (UTC)

A flashlight might do the trick. I suspect there is not too much difference in luminescence between a cloudy day and a fluorescent lamp. --HappyCamper 20:14, 15 November 2006 (UTC)

These types of glasses only change color when exposed to certain frequencies of light. I suspect that light filtered through clouds is just not bright enough and light from a bulb or fluorescent lamp doesn't contain the right frequencies (ie why would you want your glass to go dark inside a building?). You could try a full spectrum bulb or just wait for a sunny day to test them. --Cody.Pope 21:14, 15 November 2006 (UTC)

You need real UV light, since I have a pair. Usually the stores that sell them have a little display that has UV light. Failing that, the local donut shop has a counterfeit money detector... --Zeizmic 21:21, 15 November 2006 (UTC)

Also, I just found a website that says the lenses need a 'break-in' period, before they will work as desired. --Cody.Pope 21:23, 15 November 2006 (UTC)

Also that means you have to buy donuts! 8-)--Light current 16:12, 16 November 2006 (UTC)

What if you don't have a gallbladder?

About a year ago, I had my gallbladder removed because of gallstones. The gallbladder is one of those body parts that you can live without just fine, but I'm curious about how the body changes to accomodate the lack of one. I haven't found any answers to that, either online or in the articles on gallbladder, liver, and bile. Basically, the gallbladder stores bile from the liver and then releases it into the small intestine when it is needed. Where does the bile go if you don't have a gallbladder? Does it get stored in the liver, or does it get released directly into the small intestine? —Cswrye 21:25, 15 November 2006 (UTC)

I think you should ask the surgeon who removed it what they did with the connecting pipes - that should give you the answer..

I thought the gall bladder made bile -which we dont need.--Light current 22:08, 15 November 2006 (UTC)

The gallbladder is connected to the main bile duct, which also connects the liver to the small intestine. In a normal person, most bile gets diverted into the gallbladder, but bile can also pass directly through the duct into the small intestine. Without a gallbladder, the only place that bile can go is into the small intestine, but I don't know if the liver compensates for the lack of a gallbladder by storing bile in its place instead of releasing it into the bile duct. If so, I wonder if that puts any extra strain on the liver. If it doesn't, I wonder what the intestine does with all that extra bile. —Cswrye 22:32, 15 November 2006 (UTC)

After the gall bladder is removed, the liver still makes bile and secretes it into the small intestine via the common duct. Bile emulsifies fats so that dietary fats can be digested by enzymes and transported into the blood or lymph system. Gallstones are usually made of cholesterol, which is a component of bile. [5] I'm assuming that liver stores the bile, I mean, it stores so many other things as well. Chickenflicker 23:04, 15 November 2006 (UTC)

Aha! I found this article: Bile canaliculus. A Bile canaliculus is a "thin tube that collects bile secreted by hepatocytes", hepatocytes being liver cells. They "merge and form bile ductules, which eventually become [the] common hepatic duct Note that they are also called biliary canaliculi, which are defined as "any of the intercellular channels between liver cells" [6]. Chickenflicker 23:04, 15 November 2006 (UTC)

Humans do not currently have a need to store bile (the only role of the gallbladder). When the gallbladder is removed, you are essentially losing a side branch of an otherwise straight tube. The straight tube (common bile duct) still exists. Bile flows from the liver through the bile duct to the small intestine. The only difference after removal is that it doesn't spend time in the gallbladder before entering the small intestine. Also, the liver does not store bile. InvictaHOG 23:29, 15 November 2006 (UTC)

I disagree. Bile is needed to digest fats, and the gallbladder helps to regulate the release of bile to match the consumption of fats. Without it, you probably aren't as able to digest fat. This could cause diarrhea, if you have a high fat diet. If so, I suggest reducing your fat intake to a level that the small continuos flow of bile can handle. Of course, a low fat diet is also a good recommendation for everyone, at least low animal fats. Fish and vegetable fats may actually be beneficial. StuRat 00:25, 16 November 2006 (UTC)

My mum had hers removed after some complications involving gall stones and even since she has found she has to live on a very low fat diet to avoid feeling ill. Plugwash 00:50, 16 November 2006 (UTC)

Removal of the gallbladder does not destroy the ability to produce bile, just the ability to store it. After a cholecystectomy, one may feel ill after ingesting meals high in fat, but moderately fatty meals should be perfectly fine. It is only when a large amount of bile is needed, more than can be produced and excreted over a short period of time by the liver, that discomfort is likely to occur. It's like if you replaced the hot water heater in your home with a much smaller one. It would be okay to take a quick shower, but things would get uncomfortable if you try to have a long soak. Tuckerekcut 01:28, 16 November 2006 (UTC)

In high school, while dissecting a frog, I poked the gall bladder with a scalpel, and it squirted the full load into my eye. I haven't been normal since. Edison 05:39, 16 November 2006 (UTC)

Thanks everyone! This has actually been very informative. I never could get a satisfying answer from my doctor, who just insisted that it wasn't a big deal. Losing a gallbladder really isn't that bad, but I figured that it had to affect something. —Cswrye 06:29, 16 November 2006 (UTC)

Making magnets

Rently, I purchased a pair of magnets (I think that they were made of neodymyum or something that sounded like that) which were gold plated, from [[7]] and I was wondering, how do they make them if they are so magnetic? If they use machines, which they probably do, are the machines' "hands" or grabbers or whatevers made out of plastic so the magnets don't stick to them? How do they manufacture them without them sticking to the machinery and ruining it? Thanks for your answers. Ilikefood 21:37, 15 November 2006 (UTC)

Per Magnet , permanent magnets are made with the magnetic field from an electromagnet or a solenoid, although stroking a ferromagnetic material with a magnet will magnetize it somewhat, as will vibrating it in the presence of a magnetic field. Some magnets are heated above the curie point before magnetizing. Edison 22:34, 15 November 2006 (UTC)

rare earth magnets (like yours) are manufactured by machining the sintered material before it is magnetic, then gold plating them to seal out the atmosphere. the final step of the process is to magnetise them. an overview[8] --Xcomradex 22:50, 15 November 2006 (UTC)

I just want to say that this is a great question!! I read it 1st and kinda thought it's a pretty silly question, then I double take and go well hang on, you've got a point, how DO they do it?! Something I didn't know that never even occured to me. Thank you:). Vespine 23:12, 15 November 2006 (UTC)

remembering of course, there is a whole bunch of non-magnetic materials that can be used in place of steel. eg. copper, silver, aluminum, lead, magnesium, platinum and tungsten are not magnetic, nor are most ceramics, glasses etc. you can even get non-magnetic steels, eg[9]. Xcomradex 00:15, 16 November 2006 (UTC)

At the NHMFL, they use beryllium copper tools instead of steel ones to avoid accidents. —Keenan Pepper 01:54, 16 November 2006 (UTC)

Thanks. Ilikefood 22:06, 16 November 2006 (UTC)

Cellulose found in paper

What type of cellulose is found in paper? If it is just plain "cellulose", where/how would I find its refractive index? Chickenflicker 22:49, 15 November 2006 (UTC)

Well, the plain cellulose article does say Cellulose is the major constituent of paper, so that's one, as far as refractive index goes? As for refractive index, that's a good one! No idea... having a look at [list of indices of refraction] I'd put it somewhere around glycerol, around 1.4, but that's just a guess, more then water 1.3, less then glass 1.5. Vespine 23:05, 15 November 2006 (UTC)

A google search for "cellulose refractive index" turns up some stuff around 1.5 - however the amount of water absorbed alters the value - lowering it according to one source?

Yeah, I've been trying Google, but all of the "celluloses" that I found seemed to be synthetically made, rather than just cellulose from plants and such. This is actually an extention of my question "why does grease turn paper clear," since I haven't been able to find a clear answer, after asking: http://answers.google.com, the Ref. Desk [10], my chemistry teacher, and an organic chemistry teacher at UMD. --Chickenflicker 01:26, 16 November 2006 (UTC)

Your refractive index line of reasoning is valid. According to the info one can find at The TexLoc Closet (textile related) site, the refractive index of different celluloses varies from 1.47 to 1.54. Water is 1.33. Plasticsusa.com gives the values for celluloses as 1.46 to 1.51. At Refraction Index of Various Substances for 3D modelers (important if you are programming for PovRay or the like) the RI for Glycerin is given as 1.473, and for various oils it is 1.47-1.54. Thus, pure cotton cellulose paper should be quite transparent when oiled, depending on your oil selection, but in the case of commonly used modern papers, the transparency and colour of would be influenced by non-cellulose ingredients, such as rosin, starch or gelatin applied during sizing, fillers (such as CaCO₃, other chalky materials, dyes and pigments), and whitener such as TiO₂ (with a refractive index of 2.4, and an pretty efficient opacifier)). Seejyb 11:26, 16 November 2006 (UTC)

A very helpful response. =) Thanks! Chickenflicker 05:36, 17 November 2006 (UTC)

HOW DO BOATS STAY AFLOAT?

I would like to know how ships stay afloat without sinking?

thank you,

Isa Abdullah

The weight of the water displaced equals the weight of the boat. Or, if it floats your boat, you can think of the air below the waterline not pushing down as hard as the water below the boat is pushing up. See buoyancy. StuRat 00:15, 16 November 2006 (UTC)

I think you mean the weight of the water displaced by the hull of the boat is equal to or in excess of the weight of the boat and what it contains. Hence a boat made of many tons of steel can float in water because it displaces (by occupying space where water would otherwise be) more water than all of that steel, the cargo, the crew, the air, everything that the ship is made of, contains, or has on it. Robovski 04:35, 16 November 2006 (UTC)

I ignored the weight of air, as that's quite insignificant compared to the weight of water. I am including the weight of the cargo, crew, and anything else in the boat, of course. I disagree, however, that the weight of the water displaced can exceed the weight of the boat, et all. If this was the case, the boat would float higher in the water until the weights were equal. StuRat 07:01, 16 November 2006 (UTC)

I've always found the above standard answers don't quite clarify it very well for people who don't get it. 'Displacement' refers not really to water being moved or something (although in a sense it is) but to the volume of the boat below the waterline. The amount of water that would have been there has to be heavier than the boat itself (plus the air, cargo and crew and what have you). The material of the boat itself may be heavier than water (per volume!), but it forms only the outer layer. Inside it is air, which is negligible in weight. But it does add to the volume. The central term here is density, which is mass ('weight') per volume. The thing to keep in mind is that you have to divide the mass of the boat (plus contents) as a whole by the volume below the waterline. If the boat floats than that is equal to the density of water (1 kg/l). You could say that to the water it is as if there is water there because the average density is the same. If you add weight to the boat, the volume below the waterline will have to increase too, to keep the mass/weight balance equal, so the boat sinks a little, so the boat 'sinks' a little to compensate. I hope that made it a little clearer. Please say if there's something you don't get yet, so we can come up with a better answer (and add it to the buoyancy article). DirkvdM 09:38, 16 November 2006 (UTC)

Here is another version. I'll try to explain why anything floats. Hope it doesn't add to the confusion :-). When a body is put in water, it displaces some water. It also loses some weight. (If you measure the weight of a 1 kg stone immersed in water, it would weigh less than 1 kg). The weight it loses is equal to the weight of the water displaced. Suppose you have a steel ball which weighs 1 kg in air. When you immerse it in water, it displaces some water. Suppose that the weight of the water it displaces is 250 g and hence the ball loses 250 g. Now the apparent weight of the ball (the weight when it is in water) would be 750 g. Let us say that you make the ball hollow, but without altering its weight. Now if you put it in water, you'll find that it displaces more water. Let us say 400 g of water is displaced. Now the ball loses 400g and apparent weight of the ball would be 600g. Suppose you increase the size of the hollow such that the weight of the water it displaces is 1 kg. Now when you put it in water, the weight it loses is 1 kg. that would mean that the apparent weight would be zero. This is when the ball starts floating.--Wikicheng 13:26, 16 November 2006 (UTC)

---

Here's a somewhat related gedanken. Say you have a perfect cube submerged in a tank of inviscid fluid that's resting on the bottom of the tank (which is perfectly flat). The density of the cube is less than that of the fluid. Does the cube float? Virog^{It's not}_{my fault!} 08:50, 17 November 2006 (UTC)

Suppose the volume of the cube is V. When it is fully submerged, it will displace the fluid of volume V. You mentioned that the density of the cube is less than that of the fluid. That means that the fluid displaced will weigh more than the cube, which means that the cube has lost more weight. It should experience an upward force equal to the that of the additional weight it has lost. It will raise to the surface and will float. -- Wikicheng 09:48, 17 November 2006 (UTC)

Have you tried looking at the forces on the cube? Merely looking at displacement won't necessarily answer the question: since the cube is resting at the bottom of the tank, there's no fluid pressure on that lower surface, which is necessary for causing buoyancy. It's an unstable equilibrium. Virog^{It's not}_{my fault!} 18:01, 17 November 2006 (UTC)

For another example, one which is perhaps easier to intuit (am I using the word right?), imagine a suction cup stuck at the bottom of a filled bathtub. The suction cup can stay at the bottom even if it is less dense than water overall. --71.244.101.6 18:21, 18 November 2006 (UTC)

November 16

electric bike

I am working on a project to build an electric bike similar to the one being sold by Golden Motors (China)that uses a brushless DC motor/generator inside a front wheel hub. It costs $175 plus about $60 for shipping to where I live but I think I can do a better job for less money and learn alot about motors and generators along the way in addition to having a lot of fun. Any design or construction tips or suggestions about where to buy magnets etc.? 71.100.6.152 01:50, 16 November 2006 (UTC)

That kit is remarkably cheap, in my view. I very much doubt that you'll be able to build something cheaper. Better, perhaps, but not cheaper. Regardless, I'm almost certain you won't be able to build an electric motor that's competitive with factory-built ones. -Robert Merkel 05:01, 16 November 2006 (UTC)

Mother Earth News had plans in the 1970's for electrifying a bicycle with a 12 volt starter motor from a car. The kit price sounds reasonable. Edison 05:42, 16 November 2006 (UTC)

Yes, very reasonable but it won't help me learn anything about building various types of practical DC brushless motors unless I try to take it apart. 71.100.6.152 11:02, 16 November 2006 (UTC)

I liked looking at the products, and we actually have something on this: Brushless DC electric motor, which is a very interesting read. Looks like China has an advantage here, since these motors must be hand-wound, and use custom circuit boards. It would be difficult to do it yourself, but you could take apart hard-drive and fan motors to see how they work. People are doing this for electric model airplanes. --Zeizmic 13:52, 16 November 2006 (UTC)

Yes I've taken a broken fan motor apart to see how it worked and read about modelers using 58x CD drive motors in model airplanes. In fact after one shattered a CD and busted the drive I thought about using it for something like that myself but I wanted something with enough power to get me up a hill on a bike (which is hard sometimes with a ull load of groceries) as well as using it to charge the battery coming down hill as well as break the decent. I don't theink the motor from China is going to have the power I want. All I really need are coils, magnets, Hall effect switch and a battery right? 71.100.6.152 15:46, 16 November 2006 (UTC)

energy

what criteria must be met before energy can be conserved?

First sentence of Conservation of energy? --Wirbelwindヴィルヴェルヴィント (talk) 02:11, 16 November 2006 (UTC)

But maybe you're talking about energy conservation ? StuRat 06:56, 16 November 2006 (UTC)

Conservation laws arise from continuous symmetries. Specifically, energy is conserved if physical laws are invariant with respect to translation in time. See Noether's theorem. Gandalf61 11:54, 16 November 2006 (UTC)

The big rip, explained for a layman?

Recently someone posted a link to the big rip in a discussion about the universe. I have to say I didn't really understand that article, especially this sentence: "...this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point gets ever closer. When the size of the observable universe is smaller than any particular structure, then no interaction between the furthest parts of the structure can occur" If the edge of the universe is moving away (from us?) at the speed of light, how can it "get ever closer" ? As best I understand it, while the physical objects like stars and galaxies are, in fact, moving away from each other in the macroscopic universe; per the Big Rip theory whatever invisible stuff makes up the fabric of the universe is shrinking, and so while that shrinking can't be perceived or measured (?) in the macroscopic universe, at a quantum level it is still affecting the macroscopic universe. Is that correct? What is that "stuff" that is shrinking, anyway, and how does it relate to other theories of matter and existence, like string theory? What would be some other articles to read? 192.168.1.1 6:59pm, 15 November 2006 (PST)

The key term there is "observable" - while the actual universe is getting bigger, the area that we can see is getting smaller. There is no "shrinking" in the classical sense, other than the amount of stuff we can see is shrinking. Another article that was not listed under the See also section would be cosmic inflation, though that might be a bit difficult to read. Virog^{It's not}_{my fault!} 03:08, 16 November 2006 (UTC)

It's good to know we've got about 20 billion years before the end of time. --Cody.Pope 05:12, 16 November 2006 (UTC)

It is confusingly phrased and should probably be corrected. Here is my explanation: If you have climbed a tower, the horizon is far away; then as you go down the horizon gets closer and closer. This movement of the horizon is not a real movement, and the horizon is not real but only a virtual thing. The edge of the observable universe is like a horizon, it is also virtual. To someone who is (with respect to us) at that edge, there is nothing remarkable there. But we are at the edge of her observable universe. This edge is very similar to the event horizon of a black hole. In fact, you might say we are living in the non-black part of a black hole turned inside out (just like haggis is a sheep turned inside out). Everything beyond the edge is black: nothing, not even light, can escape from there to us. While space rushes out, the blackness moves in. The edge is where space rushes out at the speed of light.  --Lambiam^Talk 08:29, 16 November 2006 (UTC)

induction heaters

I was surprised to find that there are three types of induction heaters. One appears to use a coil with high frequency (20khz) alternating current flowing through it to heat a "core" of magnetic material placed inside the coil and the second appears to heat non-magnetic but electrical conductive materical that has been formed into a closed single turn secondary coil around a closed core with a primary coil and the third is magnetic material inserted between the ends of an open core. Can anyone tell me how each of these induction based heaters work, if there any other types of induction heaters and if is there a working circuit diagram for each type of coil anywhere? I've only found a few homemade coils on You Tube and other places but no circuit diagrams or details of how they work. 71.100.6.152 11:33, 16 November 2006 (UTC)

Have you already read our Induction heating article? (I know it's a bit sparse.) What points do you need more info on?

Atlant 18:00, 16 November 2006 (UTC)

Well a complete circuit diagram and parts list would be nice for one homemade unit I've seen at You Tube. 71.100.6.152 23:23, 16 November 2006 (UTC)

PLC

hi,can you please give me some information about different methods of communication in a programmable logic controller with an input device such as computers i am sepecifically after some information with the use of following devices →twisted cable →co-axial →fibre optics please reply me with the use of these devices in PLCs including there advantages and disadvantages olus their use in industry.

Essentially, the various physical layers and communications protocols just provide varying trade-offs between cost, distance, speed, reliability, configurability, and the like. Roughly speaking, ranked in order of increasing cost, you might find:

1. Twisted pair (whether point-to-point or multidrop)
2. Coaxial cable (point-to-point or multidrop)
3. Fiber optics (always point-to-point)

A PLC easily generates twisted-pair, coax, and light-emitting diode-driven-fiber protocols. It'll cost you some serious money to generate long-haul, laser drive fiber protocols.

After reading all that (and the referenced articles), do you have a more-specific question?

Atlant 18:06, 16 November 2006 (UTC)

RPM

How many rpms would a fan blade have to spin at to generate wavelengths of visible light? And is it possible, or would ho-hum-trillion rpms be too much for any physical structure to tolerate?--172.134.127.134 15:47, 16 November 2006 (UTC)

(My area is way lower frequency phenomena, but I will have a go at it. Those skilled at fields and waves please correct any misstatements.) First determine why a spinning fan blade would generate electromagnetic waves at any frequency. Do they have magnets attached?(careful, they will fly off when you least expect it). Or are the blades electrically charged? If it had 2 blades with opposite electric charge on them or opposite magnetic polarity, it would be a rotating dipole. It would generate an alternating field as it rotated. The wavelength is so short that the rotating fan blade could be submicroscopic and still be an efficient radiator. Electromagnetic spectrum says the longest wavelength (lowest frequency) of visible light is 700 nm (red, right next to infrared in wavelength). To get frequency, divide the speed of light by the wavelength: frequency=c/wavelength = (3*10^8 m/s)/(700*10^-9 m)=4.28 *10^14 Hz. Multiply by 60 to get revolutions per minute: 2.57 * 10^16 rpm, or 25,700,000,000,000,000 rpm. It would have to be down at the atomic or molecular level to not fly apart from the radial forces. The article Micropower tells how researchers are actually fabricating tiny high speed turbines and generators out of etched silicon wafers, using technology derived from integrated circuit construction. They have built a generator 10 mm wide which spins at 100,000 rpm, with higher speeds in the works, but this is many orders of magnitude larger and slower than what your fan based optical generator would require. Edison 17:21, 16 November 2006 (UTC)

If f is the frequency and r the length of a blade (the radius of the fan), the tip moves at a speed v = 2πfr. Since v < c, r < c/(2πf). Using f = c/λ (see Edison's reply), this means r < λ/(2π) ≤ 700/6.28 nm = 111 nm. This is truly a nano engine.  --Lambiam^Talk 18:37, 16 November 2006 (UTC)

<joke>The fan will be generating visible light far earlier than that, when its motor catches on fire at such a high RPM. </joke> 22:39, 16 November 2006 (UTC)

Eyeglass prescription

Is the following idea obsessive-compulsive or is it sound? I can't tell.

I have a new prescription for my very first pair of eyeglasses:

		Sphere	Cylinder	Axis
Distance Vision	oculus dexter	+0.25	-0.75	180
	oculus sinister	-0.25	-1.00	010

They say you should renew the prescription every 2 years, and my insurance only pays up to $340 CAD once every 2 years, so basically I will be wearing these for quite a while. So I want to make sure they are 100% physically accurate to my eyeball needs.

As such, I am very tempted to go to a totally different optometrist and actually pay the money for a 2nd prescription, just to compare with the first one and "make sure" it's 100% accurate. Theoretically the two prescriptions would be exactly the same, although something tells me they probably wouldn't be.

Any thoughts or knowledge on this matter? --Sonjaaa 16:05, 16 November 2006 (UTC)

Yes - from personal experience - once your eyesight settles down (mine got worse up to the age of about 16 and hasn't changed much since then - might be something to do with puberty and adult head shape?) the prescription won't change much - on repeated eyesight tests (at the same and different opticians over 5 years)I got roughly the same every time - but it does differ from time to time - by a very small amount - I assumed this was due to experimental error - and the human body is not a rigid thing - so mabye the perfect presciption varies from day to day. More noticably I noticed a very big difference with lenses made to the same prescription from different manufacturers. In the UK the eyetest is cheap but the glasses are expensive so it's not a big problem to get your eyes tested again. —The preceding unsigned comment was added by 87.102.1.174 (talk • contribs) 18:51, November 16, 2006 (UTC).

(insert usual disclaimer about this not being medical advice... if you die because of what I wrote, you can't sue me from the grave, etc etc...)

As someone who has been wearing glasses since the age of six, I can tell you that "accurate prescription" is very loosely defined. Your eyes work better and worse in different circumstances, you'll find that you see worse when you're tired, at the end of a long day, if you've spent a long time in front of a screen, in bad lighting conditions (dusk, especially), etc. So there is no one "true" prescription for you.

Second, the major cost in changing prescriptions is the frame, not the lens (at least, that's been my experience in Europe, although I imagine in holds true in Canada as well). So once you get a frame, you can change the lenses without having to buy a new frame. So even if you feel your first prescription is 'off', you can always try it out for awhile before deciding whether you want to change it. Do make sure to enquire as to the cost of frame+lenses or just lenses at your optician's before going down this road. Note that there are several different kinds of lenses (plastic, glass, coated plastic...), your optician will explain the differences, advantags and disadvantages to you.

With a weak prescription like yours (1 diopter is nothing!), your eyesight is still very good, and the difference that + or - 0.25 or 0.5 in either direction will do is minimal, you will barely notice it. I don't think it's worth getting fussed up about, especially taking into consideration the variability of your eyesight (as mentioned above).

There is the added factor that, for a given eye, there is a choice to slightly (usually by + or - 0.25) over- or under-correct your sight. This is a decision best left to your eye doctor, I know nothing of the subject, but different methodologies used by different doctors may account for a discrepancy in different prescriptions given by them (in addition to the natural variability). Next time you may wish to talk to your doctor about this, and try out different lens strengths slightly above and below what (s)he recommended, to see what the effects are.

So, in conclusion, my advice to you is: go with that prescription, and live with it for a few months. See how you feel using your glasses - do you find yourself squinting a lot, do your eyes feel very tired after long stretches of different activities (eg computer use)? If you drive or cycle (or similar), can you read the roadsigns far enough ahead (this one is usually a good test of your eyesight) for you to feel safe? Most of all, though, do you feel comfortable with your eyesight? Take all this feedback back to your doctor next time you see him/her and discuss it. But, to be honest, with your eyes (my glasses are around -6.0, I'm blind as a mole without them!) there isn't much that can go wrong.

Hope this helps! — QuantumEleven 16:46, 16 November 2006 (UTC)

With the above disclaimers: I am not an eye doctor, but I have worn glasses for many years and I once slept in a Holiday Inn Express (reference to U.S. tv commercial). The sphere correction is minimal, but you have a stronger cylinder prescription to correct astigmatism. Without the glasses if you look at a vertical line and a horizontal line, you will likely notice one of them appears better focussed than the other. With the corrective lenses, they should both appear sharp. But you may find it takes a few days to get used to corrected vision; your brain is accustomed to the size distortion in the vertical versus the horizontal direction, so when you step off the curb (kerb?) and look down, there may be a moment of disorientation. Edison 17:31, 16 November 2006 (UTC)

Optometrists also "balance" your prescription needs between good near-focus and good far-focus. I discovered this when I complained to my optometrist that the correction I'd gotten from his last several sets of glasses wasn't very good. He then gave me a prescription that was purely aimed at correcting my distance vision (and damn my ability to use it for near vision) and the correction was remarkably better, but of course I have to take the glasses off a lot more to work up close. So be sure to tell your optometrist what your specific goals are.

And yes, they sometimes get it blatantly wrong or you gave a conflicting set of "better"/"worse" answers. This happened to me at least once.

Atlant 18:13, 16 November 2006 (UTC)

I went for a second opinion and got these results:

New Prescription		Sphere	Cylinder	Axis
Distance Vision	oculus dexter	+0.50	-0.75	180
	oculus sinister	+0.50	-0.75	015

The sphere for left eye is quite different!! --Sonjaaa 22:23, 16 November 2006 (UTC)

Acarids

How come I can't find any information on acarids , acaridans on Wikipedia? Is it because they have another name? Keria 16:29, 16 November 2006 (UTC)

Is this it? Acarina If so, then somebody should create redirects to help ppl find it more easily. --Sonjaaa 16:38, 16 November 2006 (UTC)

Thank you very much - my dictionary gave me acarid as translation but it doesn't seem to be the usual term. Keria 16:41, 16 November 2006 (UTC)

It might not be the most common term, but it's not an unreasonable term to expect to work (many dictionaries, including wiktionary, have one or both names). So acarid, acarids, acaridan, and acaridans are now all redirects to Acarina. -- Finlay McWalter | Talk 19:01, 16 November 2006 (UTC)

Prothrombin time

Most articles trace the first description of the prothrombin time, discovered by Dr Armand Quick of Milwaukee, to a 1935 paper in J Biol Chem. I recently discovered that this reference does not in fact exist (as JBC is now available fulltext for free back to 1905). How could this have happened? JFW | T@lk 16:33, 16 November 2006 (UTC)

There certainly seems to be many references to that article, but there is another one of the same time with a similar title
Quick AJ, Stanley-Brown M, Bancroft FW. A study of the coagulation defect in hemophilia and in jaundice. Am J Med Sc 1935;190:501
It is odd that two nearly identical articles (at least judging by their titles) would be published the same year in two different journals.--Mabris 16:59, 16 November 2006 (UTC)

I suspect that it was a simple mistake (somebody knew they had read the article, but got the name of the journal wrong). However, since the journal was not available for free for people to verify this ref, they just took it on faith and replicated the error. This is a problem with sources that aren't readily available for free. Wikipedia should try to keep uses of such refs to a minimum, because of just this problem. StuRat 19:02, 16 November 2006 (UTC)

I am shocked, SHOCKED I say, that generations of scientists would cite a paper without having actually read it. Edison 22:56, 16 November 2006 (UTC)

Future geography

I've seen maps of the Earth's original landmass, Pangaea, and its evolution as plate tectonics cause it to morph into the continents of the present day. Have geologists predicted what the Earth is going to look like in another several million years? Maps, predictions, or other opinions would be greatly appreciated. --Naferius 17:31, 16 November 2006 (UTC)

At Continental drift there is a link [11] which shows the continents, past and future. Edison 17:34, 16 November 2006 (UTC)

However, note that Pangaea is not the original land mass, as the supercontinent cycle has repeated itself many times over the Earth's history, causing various continents to join, then break apart again. We can trace back through the last several cycles. StuRat 18:47, 16 November 2006 (UTC)

Since the continents are destined to jam together again, and maybe break apart at different places, we can only go so many (hundred) million years in the future. --Zeizmic 21:38, 16 November 2006 (UTC)

Diabeties

Can people get diabeties from eating meals too far apart? For example having breakfast at the normal time but then not eating until late afternoon?

--213.106.15.82 19:23, 16 November 2006 (UTC)

I don't think that could cause diabetes, but could make the symptoms worse if you are diabetic or pre-diabetic/hypoglycemic. A large number of small meals is typically recommended for such people, to keep their blood sugar as constant as possible. StuRat 19:38, 16 November 2006 (UTC)

No. No. alteripse 21:11, 16 November 2006 (UTC)

I have never heard of a direct causal mechanism for diabetes being meal timing. There may be some indirect effect wherein meal timing gives rise to greater caloric intake, thus it leads to weight gain and precipitates the onset of type II diabetes. So maybe, in an indirect way, but I can't think of a direct pathway. --TeaDrinker 21:38, 16 November 2006 (UTC)

I have heard that continual eating especially sweet things can increase chances of deleloping diabetes becuase of the constant demand for insulin by the digestive system. Also drinking too much tea turns you into a raving TeaDrinker! 8-)--Light current 23:23, 16 November 2006 (UTC)

for psychiatrists

What happens if a person who doesn't have any psychotic dissorder like schizophrenia starts taking neuroleptics and antipsychotics? does that person have a risk of actually developing schizophrenia if without taking that medicine that person was not destined to have the illnes develop ever at all?.

do other psychiatric medicines like antidepresants and axiety/epileptia pills like rivotril also have the posibility of triggering schizophrenia or any other dissorder like bipolar dissorder or multiple personality or whatever?.

Miscellaneous side effects without beneficial effect. No. No. alteripse 21:10, 16 November 2006 (UTC)

I don't believe antipsychotics will cause a disorder like schizophrenia in a normal person, but it is definitely not considered safe for a person without a disorder to take any drugs which alter brain chemistry, especially long term. Taking medication or recreational drugs which create imbalances in brain chemistry (seratonin, dopamine)may make changes which are irreversible. This is a field which is still activley being researched. Vespine 22:10, 16 November 2006 (UTC)

If you read carefully the patient leaflets on these mind altering drugs, you will see that some of the side effects they can cause are actually the same as the condition for which they have been prescribed! THis also applies to some other types of drugs in my experience.--Light current 23:20, 16 November 2006 (UTC)

As a chemist (not psychiatrist) the answer is yes (or they may cause another mental illness that would not develope without the drug use.) The effects may or may not be permanent. Other possible side effects are mental retardation (for the period of use) and unknown long term effects - the only way to find out is try it.

Meals for humans

Is the human body designed to require feeding 3 or 4 times a day. Or do we do it just to stop ourselves feeling hungry?--Light current 23:29, 16 November 2006 (UTC)

I do recall that we are supposed to eat about six "snack-like meals" a day instead of three big meals... Cbrown1023 00:15, 17 November 2006 (UTC)

It is recommended to eat little bits, more often, throughout the day, rather than a whole lot in just three meals. --Russoc4 00:24, 17 November 2006 (UTC)

From Human Evolution: "Early hominoids, like apes, were essentially plant eaters (fruit, leaves, roots), their diet only occasionally supplemented by meat (often from scavenging)." We evolved from chimpanzee-like animals that generally ate several times during the day, and this is thus the best way to feed ourselves today. Dar-Ape 00:33, 17 November 2006 (UTC)

science fair project

what type of trees make money? where are the trees located? email biwniambi <AT> aol.com

money is made of cotton... see Banknote#Materials_used_for_banknotes. Cbrown1023 00:14, 17 November 2006 (UTC)

November 17

Displacement of the Universe

When an object expands, it displaces something already there. If our universe is expanding, what is it displacing?

Is the universe an object? Melchoir 00:27, 17 November 2006 (UTC)