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July 10

Elevation of the Cajon Pass in San Bernardino County, CA

Wikipedia states the summit elevation to be 4190 Ft and the coordinates to be 34deg 18.7 & 117Deg 28.5.. Google Earth shows this location to be right at the CA 138 junction, and the elevation at 3111 ft.

Is the Wikipedia article incorrect, or is Google Earth just a fun toy, not to be used for data?

Other search hits verify the 4190 elevation! —Preceding unsigned comment added by Chipscom (talk • contribs) 02:35, 10 July 2010 (UTC)[reply]

I think you can trust the elevations shown in Google Earth, although sometimes the surface features are drawn at the wrong spot because of incorrect handling of the satellite photos -- for example you can sometimes see rivers flowing along the walls of canyons, which looks pretty weird. But it is less reliable about putting labels at the right places. Looie496 (talk) 05:02, 10 July 2010 (UTC)[reply]

The reason for rivers flowing up the sides of canyons in Google Earth is that the source elevation data is sampled as some regular interval (say, every 50 meters). If the bottom of a 50m wide canyon is at (say) 15m above sea level - and there are vertical cliffs either side of the canyon bottom that rise to 65m above sea level. The regular 50m sampling might say something like 65m,65m,15m,65m,65m - but the Google Earth software can't tell from those elevation numbers whether there is a 45 degree slope slope from 65m down to 15m and back up again (a V-shaped valley) - or whether there is a vertical cliff-face somewhere between one 50m sample point and the next (a U-shaped valley, perhaps). If the river happens to run somewhere other than through the dead-center of the 50m-wide canyon then the software has no way to know whether it actually runs along the top of the cliff, the bottom of the cliff - or whether there is a 45 degree slope with a river running along halfway up it on a narrow ledge. Now, you and I both know that rivers almost always run along the bottoms of canyons - not the tops or the sides - but remember that Google Earth doesn't necessarily know that there is a river there - all there is to represent it are some pixels in a photograph. A typical muddy river is really hard for software to pick out from the similarly colored dirt that's nearby - especially if there are overhanging trees, rocks and white-water in the river, etc. So the software makes a guess at how to draw the slope - and the river ends up flowing along a 45 degree slope! Looking like a really good place to go water skiing without a boat! (An old joke amongst people like me who have to actually solve these kinds of problems for a living!) SteveBaker (talk) 07:13, 10 July 2010 (UTC)[reply]

Well, no doubt that's part of the story, but from looking at the actual pattern of errors, I suspect a more important factor is that the satellite photos are often taken at an angle, and the software has problems in shifting points correctly to compensate for differences in ground elevation. In other words, my impression is that the software projects the photos onto a flat surface and then warps the surface according to the topographic data, rather than taking the theoretically correct approach of warping the surface first and then projecting the satellite photos onto the warped surface. Looie496 (talk) 16:50, 10 July 2010 (UTC)[reply]

I doubt that. The process of 'orthorectification' (which fixes those problems) is well understood and there is a mountain of free/OpenSourced software produced by various US government agencies that can perform that task. It's really unlikely that Google would be getting that wrong given how easy it is to fix. I work in this very area of computer graphics technology - and the 'sloping rivers' problem is well known - even when orthorectification has been optimally performed. The bottom line is that the terrain photography is almost always provided at a much higher resolution than the elevation data. In effect, the imagery 'samples' the elevation data to determine how it should be drawn - and the Nyquist sampling limit isn't close to being met. So you get all sorts of weird-looking artifacts as a result. SteveBaker (talk) 04:19, 11 July 2010 (UTC)[reply]

The AAA Road Atlas, 1996 edition, shows on its Los Angeles area map that after the route 138 interchange as you go north on I-15, the road turns right, then more sharply right, and then left in the space of a few miles, and Cajon Pass is marked near the end of the left turn, with an elevation of 4,190 feet. Nearby is Summit Lookout, 4,260 feet.

The National Geographic Road Atlas, 1999 edition, shows a pass symbol at very nearly the same place on the road, but labeled Cajon Summit, 4,259 feet. The American Map Road Atlas, 2006 edition, appears to have used maps from the same source and agrees with this.

The Rand McNally Road Atlas, 2001 edition, renders the road differently, showing a left turn between the two right turns. But it puts the pass symbol in the same place and labels it Cajon Pass, 4,260 feet. Unlike the others, this one also marks the pass on its main Southern California map, but this time the label is Cajon Summit and the elevation is given as 4,257 feet! (The location looks farther south, too, nearer the route 138 interchange, but I assume that's due to the limitations of the map scale.)

In view of all this I am inclined to believe that the AAA atlas has it right with 4,190 feet, while the others are confusing locations on and just off the Interstate, and that the elevation that was found in Google Maps is probably the elevation of the route 138 interchange, not the pass.

--Anonymous, 05:40 UTC, July 10, 2010.

Some old US maps used a different measure of a 'foot' called a 'survey foot' - but I don't think the difference is enough to account for this much error. SteveBaker (talk) 07:13, 10 July 2010 (UTC)[reply]

That's a red herring; it's only different by a couple of parts per million. See Foot (length)#Survey foot. --Anonymous, 11:40 UTC, July 13, 2010.

I've adjusted the coordinates a bit in the article. Anonymous, can you confirm that they now match the location shown in the atlases? Deor (talk) 12:07, 10 July 2010 (UTC)[reply]

Sorry, I only just now got back to this and have now viewed the area in Google Maps for the first time. It seems clear to me that all of the road atlases are showing the elevation of the high point on I-15; after all, they are road atlases. They aren't interested in the exact location of the saddle point of the pass as a landform, or the location of the high point on a minor road like 138 or on the railway. Further, I see from Google Maps that the northbound and southbound lanes of I-15 are widely separated in that area. I now think this accounts both for the different shape of the road in the Rand McNally vs. the other road atlases, and also the difference in elevation between the road atlases. From Google Maps it appears that the high point in the southbound lanes is about 34.34954,-117.44664, right next to the lookout parking lot. This must be at about elevation 4,257 to 4,260 feet. But in the northbound lanes the high point would be about 34.35193,-117.43861 and at a lower elevation, maybe the 4,190 feet although from the contour lines it looks a bit higher. Note where the article says "Some maps may show the Cajon Pass as a feature on SR 138, which crosses I-15 south of the summit between West Cajon Valley and Summit Valley. The highest point on I-15 between Los Angeles and Victorville is thus sometimes identified as Cajon Summit. However, the entire area, including Cajon Summit, is often called Cajon Pass"; I think this explains the terminological confusion. --Anonymous, 11:40 UTC, July 13, 2010.

Now I'm really confused. The USGS topographic map of the region, which one would expect to be definitive, has the label "Cajon Pass" at a point on California State Route 138 (34°19′32″N 117°25′43″W / 34.3255°N 117.4286°W), at what looks to be an altitude of only a little over 3,800 feet. Perhaps this whole thread should be copied to the article's talk page, so that those interested in the article can work out the best-sourced location and altitude to include in it. Deor (talk) 16:59, 10 July 2010 (UTC)[reply]

As far as I can tell, the railroad tracks occupy the pass's lowest high point (if that makes sense), while the road winds along somewhat higher slopes. The U.S. Geological Survey Geographic Names Information System: Cajon Pass page gives an elevation of 3835 feet, but the GNIS database is not always to be trusted, especially with elevation. This page, about the railroad tracks, says that the pass "crests the summit at 3872 feet", but also that in 1972 the Santa Fe Railway decided to "reconstruct the summit of Cajon Pass". The "summit was lowered by 50 feet to 3822 feet". The section of track is known as the "Big Cut". Pfly (talk) 17:11, 11 July 2010 (UTC)[reply]

Also I just discovered that the article, Cajon Pass, puts its location at 34.349,-117.447, which according to USGS topo maps is not Cajon Pass but "Cajon Summit": USGS topographic map of article coords. Interstate 15 doesn't cross Cajon Pass. Perhaps the confusion arises from the assumption that it does? Perhaps it is common to say I-15 crosses Cajon Pass, but to be precise, the pass is about a mile southeast of I-15.Pfly (talk) 17:20, 11 July 2010 (UTC)[reply]

submitting an article for review.

I have tried numerous times to submit an article for review but I can not seem to get it to post. I have reviewed the process on many of the pages available and just can't figure out what I am doing wrong. I have several articles I could submit. I am currently taking online courses towards the acquistion of my Masters Degree in the Science of Higher Education. Each term I am required to submit a course project, all of which I have received an A grade on. I am more than willing to submit these papers to Wiki, however, I must first figure out how to do so. If I could get some assistance, it would be great. Thank you in advance for your help and I hope to get a reply soon. My new term just started and I have a little bit of extra time at the present. Once the term gets into full swing I will not be able to do any extracurriular activities such as submission of articles for Wiki. So the sooner you can reply, the better. —Preceding unsigned comment added by Patter lake (talk • contribs) 02:41, 10 July 2010 (UTC)[reply]

Questions about Wikipedia itself are best directed to the Wikipedia Help Desk - where I'm sure they'll be happy to help you. SteveBaker (talk) 03:50, 10 July 2010 (UTC)[reply]

Try following the instructions on WP:PR --Chemicalinterest (talk) 12:40, 11 July 2010 (UTC)[reply]

Night sky on Mars

I've been wondering what the night sky looks like on Mars. My hypothesis is that all the constellations would look the same as here, but that since the axial tilt of Mars is different from that of Earth, the North Star isn't directly above the Martian North Pole, and therefore there is some other point in the Martian Northern Hemisphere about which the stars appear to rotate. Can anyone confirm or deny? +An gr 13:11, 10 July 2010 (UTC)[reply]

Celestia is a good tool to find the night sky on other planets. I'm not sure about the exact axial tilt, but even on Earth, precession plays a role in which star becomes the North Star more than any variations in tilt (22-24°). As for the planets on Mars, they would have different positions across the constellations and different brightnesses than seen on Earth. ~A H 1^(TCU) 14:25, 10 July 2010 (UTC)[reply]

I should have checked the links before posting. I meant: since Polaris isn't the North Star on Mars, there is some other point in the Martian Northern Hemisphere about which the stars appear to rotate. Likewise the apparent point of rotation in Earth's Southern Hemisphere is different from that in Mars's Southern Hemisphere. I suppose not only the planets but also the Sun would have different positions across the constellations, so that the Martian Zodiac would be different from ours. +An gr 14:55, 10 July 2010 (UTC)[reply]

Well, for the Southern hemisphere of earth, there is no southern "pole star" that's visible to the naked eye. The two stars Acrux and Gacrux in the Southern cross constellation are the closest thing we have - but they aren't as exact as Polaris is for the Northern hemisphere. SteveBaker (talk) 15:08, 10 July 2010 (UTC)[reply]

Okay, but this isn't answering my question. Am I correct in thinking that the constellations would look the same on Mars as on Earth but that their point of apparent rotation would be different? And here's a related question: would the smaller circumference of Mars play a role in the appearance of the night sky? +An gr 15:20, 10 July 2010 (UTC)[reply]

Yes, the constellations would look the same on Mars as they do on Earth, at least with the naked eye (astronomers could take very precise measurements and see very small differences). The point in the sky that they rotate around would be different, although there is no actual (visible) star at that point(see here). Mars' axial tilt is actually quite similar to Earth's (25.2 compared to 23.5, see here, but points in a different direction.

24.150.18.30 (talk) 15:39, 10 July 2010 (UTC)[reply]

The reduced diameter of Mars would result in the horizon being closer - which might allow you to see more stars closer to the horizon than here on Earth - but aside from that, the only noticable difference would be the point about which the stars rotate. Constellations would look essentially identical. Earth and Mars are very close together compared to the distance to even the nearest stars. Even out as far as Pluto, you'd need some rather precise measurements with a big telescope to see a measurable difference. SteveBaker (talk) 04:12, 11 July 2010 (UTC)[reply]

According to Astronomy on Mars, "The orientation of Mars's axis is such that its north celestial pole is in Cygnus at R.A. 21h 10m 42s Decl. +52° 53.0′. The top two stars in the Northern Cross, Sadr and Deneb, point to the north celestial pole of Mars. The pole is about halfway between Deneb and Alpha Cephei." The article also mentions that the Martian north celestial pole lies only a few degrees from the Milky Way, which therefore is always visible. Looie496 (talk) 16:40, 10 July 2010 (UTC)[reply]

As for the Zodiac question, this is determined by the planet's orbital plane. As it says in the Mars article under "inclination", the orbital plane of Mars is only 1.85° different from that of the Earth (which we call the ecliptic). So the Sun's path through the constellations would be almost the same as we see here. --Anonymous, 17:01 UTC, July 10, 2010.

One more thing worth noting: All the modern photos from Mars show a hazy pink sky. The sky itself is blue there (product of the atmosphere), but it gets very dusty and windy so there is always a haze, ~~and that will make nighttime viewing a bit problematic. However, I haven't read up on this too much so this may be completely oversimplistic~~. SamuelRiv (talk) 19:20, 10 July 2010 (UTC) EDIT from article Extraterrestrial skies: "The sky is thus rather bright during the daytime and stars are not visible" SamuelRiv (talk) 16:31, 11 July 2010 (UTC)[reply]

Thanks to everyone for the informative answers and especially to Looie496 for directing my attention to Astronomy on Mars, a topic I never imagined we would have an article on. That and Extraterrestrial skies are going to make interesting reading I think. (Next we need an article on Astrology on Mars!) +An gr 20:45, 10 July 2010 (UTC)[reply]

WP:WHAAOE (nearly). CS Miller (talk) 21:35, 10 July 2010 (UTC)[reply]

Hollow core concrete slabs

How are hollow core concrete slabs manufactured? —Preceding unsigned comment added by 113.199.149.217 (talk) 14:59, 10 July 2010 (UTC)[reply]

I you're referring to the things in the picture - they just pour concrete into molds. SteveBaker (talk) 15:04, 10 July 2010 (UTC)[reply]

those are blocks not slabs.. eg I think these are meant http://www.concretec.ae/products/Home_Img/DSC00703_2_26_200802_39_164071250.JPG

According to Hollow-core slab they are extruded.

eg http://www.mabeton.com/products3.htm

For more info try google books and search for "concrete extrusion slab hollow" or similar eg [1] 87.102.85.197 (talk) 15:41, 10 July 2010 (UTC)[reply]

Actually youtube is very useful here eg http://www.youtube.com/watch?v=wEDPtSK1RLw&feature=related there are several videos showing hollow core slab manufacturing from a variety of manufacturers and sources.87.102.85.197 (talk) 18:02, 10 July 2010 (UTC)[reply]

I know those things as besa blocks, however googling it seems like this might not be as common a name for them as I assumed, might be an Australian thing.. Vespine (talk) 00:59, 12 July 2010 (UTC)[reply]

According to Concrete masonry unit you are right, but the spelling is different.Sf5xeplus (talk) 01:21, 12 July 2010 (UTC)[reply]

Funny! I wasn't sure of the spelling, i don't think i've ever had to write it before, so i googled besa blocks and it had more then enough results to convince me that I had the right spelling. :) Vespine (talk) 05:56, 12 July 2010 (UTC)[reply]

DRI and RDA intake

What are the DRI and RDA intake for carbohydrate, protein, total fat, saturated fat, fiber, sodium and calcium? —Preceding unsigned comment added by 74.14.117.187 (talk) 15:12, 10 July 2010 (UTC)[reply]

You can find the Reference Daily Intake at Reference Daily Intake which are based on RDA.

The DRI's can be found at Dietary Reference Intake

The figures are for specific conditions (age sex), for the general picture try the external links in those articles. 87.102.85.197 (talk) 15:45, 10 July 2010 (UTC)[reply]

Recharging the unrechargeable Issue

Of course, rechargeable batteries are meant to be recharged, but others are dry cell, the type we use once and then simply throw them away. Is it possible that all, cells, even those not build to be recharged, i.e. the ones we use-up and then throw away can be somehow recharged ? Of course it's implausible, but some one thinks it can be done → http://shopping.rediff.com/product/maxis-green-magic-alkaline-battery-charger/10471140 Check it out, boys... Jon Ascton (talk) 18:10, 10 July 2010 (UTC)[reply]

Non-rechargeable batteries drop their available voltage with further use, regardless of how long they are charged for. Furthermore, there is a risk of explosion if they are recharged unsuitably, so I'd advise against it. Regards, --—Cyclonenim | Chat 18:40, 10 July 2010 (UTC)[reply]

All reactions are reversible, but there are many examples were the reverse reaction is not feasible. Recharging alkaline batteries is one such case. When the cell discharges zinc is converted to zinc ions; to recharge one would usually reverse the potential to re-deposit zinc. However since the cell is alkaline the anode reaction is this:

Zn + 4OH^- > Zn(OH)₄^2- + 2e^-    (A)

The problem is that the zincate ion (Zn(OH)₄^2-) is negatively charged (unlike normal Zn²⁺ ions), so when the 'anode' is made negative in an attempt to recharge the zincate ion actually moves away from the 'anode' rather than moving towards as it would be if it where Zn²⁺. This means that the alternative reaction which is basically electrolosis of water occurs:

H₂O + e- > 1/2H₂ + OH^-    (B)

H₂ is hydrogen gas - production of this increases the pressure inside the cell hence the warning "Do not attempt to recharge, Danger of leak or explosion" , usually the battery does not explode since there is a pressure releasing valve built in - instead the high pressure can force out the electrolyte which is corrosive and caustic Potassium hydroxide which can damage people and electrical equipment.

The hydrogen produced may be able to reduce zincate to zinc in fact this isn't likely - not a strong enough reductant - but there is no guarantee that this will happen at the electrode - which means that it may not be available to the battery:

H₂ + Zn(OH)₄^2- > Zn + 2OH^- + 2H₂O    (C)

Similar but less problematic processes happen at the cathode, which can also result in the production of oxygen gas.

That's why attempting to recharge alkaline batteries is neither realistic nor a good idea.

(How they work) Devices that attempt to recharge non-rechargable alkaline batteries use on-off pulses of electricity: The on pulse causes reaction B. During the off pulse reaction C can occur which should prevent build up of pressure.87.102.85.197 (talk) 18:54, 10 July 2010 (UTC)[reply]

I remember hearing that those chargers can only be used for about 5 times before the voltage drops so low it is essentially useless. --Chemicalinterest (talk) 20:33, 10 July 2010 (UTC)[reply]

Medically pure tin

How can I make pure tin? I want to make it convert into the alpha form and pewter does not convert. --Chemicalinterest (talk) 20:31, 10 July 2010 (UTC)[reply]

Possibilities:

a. Electroplate from a tin(II) solution

b. Electrorefine a tin solder.

If you decide to try either of these further advice could be given depending on what you're working from.87.102.85.197 (talk) 20:46, 10 July 2010 (UTC)[reply]

Out of curiosity, isn't a tin(II) solution going to have cation impurities anyway, some of which will inevitably deposit on electroplating? I suppose on could set up two cathode-anode structures, with one tin terminal on each attracting all things with higher electronegativity and all things with lower, respectively, right? Or how would one purify, say, from a tin can? SamuelRiv (talk) 16:35, 11 July 2010 (UTC)[reply]

(from a solution of the metal ions) the deposition of more electropositive metals can be avoided by using a deposition voltage lower than their deposition voltage see Standard electrode potential (data page) - so a solution of tin(II) can be deposited to tin in the precense of Fe(ii) etc.

Conversely less electropositive metals (eg Ag+) can be deposited out first, using the method above.

Electrorefining (ie starting from metal) is more complex since the net reaction is metal > metal (accross electrodes) and technically EMF=0 (excluding effects due to impurities) .. in practice it also works, there's a good introduction here [2] 178.78.64.206 (talk) 18:49, 11 July 2010 (UTC)[reply]

(Separating tin from iron using electrorefining I think will be tricky though).178.78.64.206 (talk) 19:22, 11 July 2010 (UTC)[reply]

Stoichiometry

How many mL of 0.3M KMnO₄ is required to titrate 0.02 moles of sodium oxalate.

Isn't the answer 100 mL?--478jjjz (talk) 20:47, 10 July 2010 (UTC)[reply]

Have you got the reaction? It's given at [3] 1 mole permanganate reacts with 2.5 moles of oxalate.

From Sodium oxalate:

5H₂C₂O₄ + 2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 10CO₂ + 8H₂O

87.102.85.197 (talk) 20:50, 10 July 2010 (UTC)[reply]

I have

Na₂C₂O₄ + 2KMnO₄ → 2 NaMnO₄ + K₂C₂O₄

--478jjjz (talk) 20:56, 10 July 2010 (UTC)[reply]

Reduction to manganate(VI) is right for alkaline conditions. But your equation is wrong - the oxalate needs to be oxidised, and the permanganate reduced.87.102.85.197 (talk) 20:59, 10 July 2010 (UTC)[reply]

My instructor has given the following answer

[0.02 x (2/5) /0.3] x 1000 = 26.67 mL

He doesn't explain a diddly-squat, so I am baffled.

I am supposed to use 16 H⁺ + 2 MnO₄⁻ + 5 C₂O₄^2-→ 2 Mn²⁺ + 8 H₂O + 10 CO₂

, but I don't understand why.--478jjjz (talk) 21:18, 10 July 2010 (UTC)[reply]

That's the reaction: Permanganate is reduced to manganese 2+ ions, and oxalate is oxidised to carbon dioxide

These are called redox reactions. Didn't you get a class about them? There's an introduction here http://www.chemtutor.com/redox.htm I think you need to understand anout redox reactions first - then you'll understand the equation you were given.87.102.85.197 (talk) 21:26, 10 July 2010 (UTC)[reply]

This was on a lab quiz in the 1st semester of my general chemistry course. Redox reactions will be studied in detail in the next semester. The lab manual was written by my college professors who cover the topics in a different order than my acutal textbook. The lab manual keeps jumping back and forth in terms of the topics covered in the textbook.--478jjjz (talk) 21:31, 10 July 2010 (UTC)[reply]

It appears that 87's reaction works for this example. If there is 0.02 moles of oxalate, and the ratio of oxalate to permanganate is 5·2, then there needs to be 0.02 · 2 ÷ 5 moles of permanganate, or 0.008M. The concentration is 0.3M per liter and there is 0.008M; divide 0.3 ÷ 0.008 = 37.5. 1000 mL in a liter ÷ 37.5 = 26.66(repeating). The last problem could also be a proportion; 0.3M over 0.008M = 1000 ml over ??? ml. Hope this helps. --Chemicalinterest (talk) 22:20, 10 July 2010 (UTC)[reply]

Molniya orbit

Does this table make sense? Within a range of 500 to 39,900 km above the Earth, 1.5 to 10.0 km/s?--Email4mobile (talk) 15:20, 11 July 2010 (UTC)[reply]

It doesn't make sense, actually. Some of these orbital speeds are calculated with respect to the tangential speed at the surface of the Earth (8km/s), and some are calculated with respect to a stationary frame. I'll have to fix this. SamuelRiv (talk) 17:09, 11 July 2010 (UTC)[reply]

Aircraft tails

If the vertical stabilizers on an aircraft are tilted outward (e.g. Lockheed Martin F-22 Raptor) or inward (e.g. Lockheed Have Blue), does this make any difference in maneuverability or drag? Also, is there a name for this tilt? --The High Fin Sperm Whale 20:50, 10 July 2010 (UTC)[reply]

That would be the dihedral of the vertical stabilizer(s). This certainly impacts drag, lift, and maneuverability, especially because the rudder or rudders serve as elevators) as well. The exact parameters are complex, of course, because the airframe and the rest of the aircraft dynamics are all interconnected. Nimur (talk) 16:25, 11 July 2010 (UTC)[reply]

Following on that, as one gets to very steeply angled vertical stabilizers it becomes possible to discard the elevators entirely, leading to ruddervators which combine the function of rudder and elevator in the same control surfaces. TenOfAllTrades(talk) 16:32, 11 July 2010 (UTC)[reply]

So I'm assuming that tails that point out from the centre are more maneuverable since they are used on many fighter aircraft (e.g. McDonnell Douglas F/A-18 Hornet, Lockheed Martin F-22 Raptor, Lockheed Martin F-35 Lightning II)? --The High Fin Sperm Whale 16:35, 11 July 2010 (UTC)[reply]

They also reduce the radar signature of the aircraft by avoiding the right angle between the horizontal and vertical fins that acts like a corner reflector for the radar. But I'm not sure whether that is the dominant reason for using them. When you have a computer flying the plane, it's easy to have the software decode simple left/right and up/down commands from the pilot into the complicated mix of flapperons (aileron/flaps) and ruddervators needed to make the plane do that. In the past, when those controls were essentially connected directly to the joystick with cables and push-rods, the various control surfaces had to map onto the pilot's inputs directly and simply. SteveBaker (talk) 16:58, 11 July 2010 (UTC)[reply]

This page discusses several examples, and the reasoning behind them. Canted vertical stabilizers were first added to military aircraft in the 1960s to reduce radar cross-section (the SR-71 spy plane may be the first example, with its unique inward-canted tails), more recent aircraft also definitely take advantage of the canted stabilizers to increase manoeuverability and performance. (The link I provided discusses some of the specific benefits in the F-18, as one example.) As SteveBaker notes, the advent of fully fly-by-wire craft made it much easier for aircraft designers to take advantage of 'non-traditional' control surface orientation and placement. TenOfAllTrades(talk) 17:19, 11 July 2010 (UTC)[reply]

How does it affect the areodynamics if an airplane's tail is canted inward (Lockheed SR-71 Blackbird and Lockheed Have Blue)? --The High Fin Sperm Whale 21:26, 11 July 2010 (UTC)[reply]

Diatomaceous earth

I have just produced a very large image of diatomaceous earth, a powdery rock made up of the skeletons of dead diatoms. Does anyone know much about diatoms and can help identify some of the classes of diatoms present in this sample? - Zephyris _Talk 21:59, 10 July 2010 (UTC)[reply]

Probably they are deformed and compacted so much that they are unrecognizable. --Chemicalinterest (talk) 12:36, 11 July 2010 (UTC)[reply]

They probably aren't too compressed/distorted (the rock has not been greatly compacted as you can tell its the low density and absorbency), and there are definately fairly complete shells (look, for example, at the centre bottom). I'm sure some general level of classification would be possible... - Zephyris _Talk 14:40, 11 July 2010 (UTC)[reply]

July 11

Ground connection

Why do some electrical devices have plugs with three "sticks" (don't know their names) instead of two? I heard that the third one is a connection to the ground. If so, 1) why include this, and 2) how would the current go to the ground? Thanks. 74.15.137.192 (talk) 00:53, 11 July 2010 (UTC)[reply]

The Ground pin or prong, also known as the Earth, is indeed a connection to the ground/Earth. 1) Appliances designed for such systems have internal connections between their external cases or other touchable components (if conducting) and the Earth pin on their power plug so that if a fault develops in the appliance making such parts live, there will be a lowest-resistance path for the electrical current to pass harmlessly to Earth rather than taking the only somewhat higher-resistance path via the appliance's user, electrocuting them in the process. 2) Power supply circuits using this system include connections between the Earth socket (which takes the Earth pin) and the ground, often but not necessarily utilising existing good Earth connections such as metal water-supply pipes that pass through the ground.

Not all appliances used with 3-pin plugs necessarily have an Earth connection: table lamps, for example, often use cables or flexes with only two internal wires, one for the Live and one for the Neutral; in this case the Earth pin has no electrical function, but on most modern 3-pin sockets, it is still necessary for pushing aside the internal shrouds that otherwise block off the other two socket holes to prevent such things as small children poking sharp objects into them, and to discourage irresponsible adults attempting to insert flex wires without using a plug. 87.81.230.195 (talk) 01:32, 11 July 2010 (UTC)[reply]

I'm guessing '87 is from the UK. Here in the US, there aren't shrouds in the socket to be pushed aside by the third pin. There are far too many two-pin devices still being made to allow that possibility. Fortunately, 110v is a lot less dangerous than 240v. But you're right otherwise. Devices with plastic cases can't really become dangerous even if an internal wire breaks loose - so two pins is enough. Devices with metal cases or exposed metal parts can potentially become live in the event of some kind of internal fault - and internally connecting all of the metal parts to the earth wire provides both an efficient way to route the current away - and a way to rapidly trip an earth leakage circuit breaker to make everything safe. SteveBaker (talk) 04:04, 11 July 2010 (UTC)[reply]

Indeed: I'm afraid I subconsciously subsumed North American systems under the subset "not modern" :-) . 87.81.230.195 (talk) 22:48, 12 July 2010 (UTC)[reply]

The goal of the earth-wire is not to reroute the current from the user but to make sure that ther are a path for the current that has low enough resistance to blow the fuse. The resistance in the earth-wire are often large enough that the the voltage-drop makes the remaining potential of the casing still lethal but since the current is so high the fuse will interrupt the current fast.

If we assume zero source impedance and earthing impedance and the same thickness of the live wire and the earth wire then the case would get half the live potential, 115 V for a 230 V 1 phase system, this is still lethal but the fuse will interrupt it in less than 200 ms in most cases.--Gr8xoz (talk) 10:09, 15 July 2010 (UTC)[reply]

But what prevents the current from always flowing to the earth? 74.15.137.192 (talk) 09:39, 11 July 2010 (UTC)[reply]

Most of the components are isolated from contact with the ground to prevent this from happening. They are either physically kept away, or are insulated by wrapping them in plastic or some other nonconductive material. This is why (among other reasons) wires are usually coated in plastic. Staecker (talk) 10:21, 11 July 2010 (UTC)[reply]

Yes: to clarify a little further, the Earth pin is connected (via a third wire inside the cable) only to parts of the appliance that should not be live, but may become live if a fault inside the appliance occurs. 87.81.230.195 (talk) 16:42, 11 July 2010 (UTC)[reply]

Indeed, if you pull apart a device with a 3 pin plug and carefully trace the earth wire, you'll find that it doesn't connect to anything at all besides the metal parts of the case of the machine. When the gizmo is functioning normally, the earth wire simply isn't connected and no electricity flows along it. Where it comes into play is if someone yanks hard on the power cord or drops the device or something - at that point, either the live or neutral wire could come loose and touch one of the metal parts of the case. If you're holding it at the time, you're going to get a powerful - and possibly lethal - electric shock. This is so dangerous that we have that earth wire there as a "just in case" measure. So if the live wire should come loose, the current won't flow through your body because the earth wire is a "shorter" path (less resistance) to ground than your flesh. But when the machine is working perfectly - the earth wire doesn't do anything at all! You could disconnect it and the machine would continue to work perfectly well (but please don't because that's dangerous!)...of course none of this is an absolute guarantee - it could be that you dropped an electrical device and that it broke such that the earth wire became disconnected AND the live wire ended up touching the case. But it is generally assumed that such 'double fault' conditions are sufficiently rare as to be of little concern. Personally, if I drop an electrical device, I'll first unplug it at the wall before picking it up and checking it for obvious damage. SteveBaker (talk) 16:51, 11 July 2010 (UTC)[reply]

Okay that makes a lot of sense, thanks for the explanation. 74.15.137.192 (talk) 22:49, 11 July 2010 (UTC)[reply]

Relevant to this discussion is Appliance classes. Appliances with an earth plug are called Class 1, appliances without an earth plug are called class 2 or "double insulated" which means they are designed in such a way that no internal fault can cause the chassis to become live, typically this means a housing entirely made of plastic. Vespine (talk) 00:52, 12 July 2010 (UTC)[reply]

Quantum mechanics, psychology, and free will

Up until now, I thought that neuroscientists were generally in favor of hard determinism (I know philosophy falls outside their field) because of Libet's experiment on conscious decision-making, but I came across this: Excitatory postsynaptic potential#Miniature EPSPs

See what it says about the quantal nature of synaptic activity.

Wouldn't that hold relevance to the article on Free Will? I don't see anything there mentioned about it. That is, couldn't miniature EPSPs provide a basis for free-will?

And one more thing: Are there any other interesting experiments or research which involve quantum mechanics and psychology? Aside from EPSPs, apparently IPSPs are probabilistic also? So, are there miniature IPSPs too? ☯ Zenwhat (talk) 05:01, 11 July 2010 (UTC)[reply]

(1) Speaking as a neuroscientist, I can tell you that neuroscientists are generally materialists, but don't care very much whether the world is deterministic at the subatomic level. Only a small fraction of neuroscientists know about the Libet experiments in any detail, and of the ones that do, attitudes are mixed.

(2) The "quanta" that are involved in synaptic release have absolutely nothing to do with quantum mechanics. They are subcellular structures that are large enough to be visible in an electron microscope -- they are called quanta because they come in discrete packets, called synaptic vesicles. They are orders of magnitude too large for quantum mechanical phenomena to come into play.

(3) I don't believe there have been any experiments that involve quantum mechanics and neuroscience or psychology. A few people in the "physics of consciousness" camp have suggested ideas for experiments, but I'm not aware of any having been conducted. You might look at our article on quantum mind for further pointers. (I think it's ridiculous myself.) Looie496 (talk) 06:12, 11 July 2010 (UTC)[reply]

I'll add (from a different perspective) that random phenomena is a bad direction in which to start searching for free will. free will is not random (in fact, there is no decent analytical definition of what free will means, and so there is no possibility of testing for or measuring it). when a scientist uses a random model to study human/cognitive behavior it's not because he necessarily thinks there is or isn't anything random about human/cognitive behavior, it's only because human/cognitive behavior is too subtle and complex to be handled accurately using a deterministic model under current empirical limitations. --Ludwigs2 07:10, 11 July 2010 (UTC)[reply]

Modern mainstream physics does not describe a "free will" in any shape or form. A system may exhibit a pronounced quantum-mechanical behavior if it is small enough. This usually has no effect on a large scale (indeed, you do not need to know the rotational and vibrational state of every molecule to estimate the thermodynamic properties of the air in the room; knowing pressure and temperature is enough to get a very accurate prediction). On a large (macroscopic) scale a system may exhibit a "deterministically chaotic" behavior, which simply means that to predict the system behavior on a long enough time scale the initial conditions must be known with impossible accuracy (imagine a nitrogen molecule released in a vessel of oxygen gas; no amount of accuracy will help you predict the nitrogen molecule location a minute later). Alternatively, a large system may have a "deterministic" behavior proper (for example, a deep enough attractor state for the probability of escape to be negligible over the longest relevant time scale; put your lab notebook in the desk drawer in the evening and you will find it there the next morning). Finally, a macroscopic system may (by chance or by feat of engineering) reflect in its macroscopic state a state of a much smaller, quantum-mechanical system it is brought into interaction with. When this happens deliberately it is called "a measurement"; when this happens by chance it may be referred to as "a butterfly effect". Note that nothing I described above has anything even remotely to do with a free will. Neuroscience, on the other hand, has something to say about the free will. It has been shown repeatedly that the brain prepares for an action (or for a particular decision) before the decision is consciously taken or the action is is consciously initiated. Some human data are summarized in the Neuroscience of free will article, with due caveats. There are also some monkey electrophysiology + behavior data reported by several groups on a few different tasks, all pointing to the same thing. However, again, this does not imply that there is no free will; rather, this implies that the brain is indeed involved in the early stages of decision-making :) . Indeed, when we decide to turn our head to attend to a particular stimulus, the brain must have already compared its relative importance to the other stimuli for us. And when we speak with other people, we do not consciously prepare every word we say, yet we say what we want and do not spew random nonsense. The unconscious decision precedes the conscious one, but it is still our decision and not Erwin Schrödinger's. It is still a free will, or at least it feels like a free will, so at least some people assume it is; and our entire moral system (and the entire criminal justice system, too) are based on this assumption. On the other hand, as Ludwigs2 said above, any sufficiently complicated but ultimately chaotic system is indistinguishable from a system with a free will; at least not at the Turing test level. Yet no-one seriously blames a computer's free will for coming down with a Blue Screen of Death or mucking up its own file-system at the worst possible moment. A very compelling scientific evidence against the existence of the human free will would necessarily lead to abolition of the notion of crime or responsibility for one's actions; and the human civilization will need to adjust accordingly (as it has adjusted to the fact that the Earth is round, or that the sky does not separate the waters above from the waters below). I personally do not see this forthcoming anytime soon. --Dr Dima (talk) 08:30, 11 July 2010 (UTC)[reply]

I would just like to point out, as a philosophical thing, that there is no recourse in the probabilistic for free will. Showing something is not classically deterministic does not give the individual agent any freedom. Doing what you do because of a cosmic dice rolling is not free will in any sense. It is still deterministic, just with the dice as the determiner. Free will is a complicated and quite fuzzy concept, one rooted more in moral questions than physical ones, and looking for a physical analogy for it has been, so far as I have been able to see, quite fruitless. The world is, as far as anyone can tell, ultimately mechanistic, even if some of that mechanism is, at a very low level, inherently probabilistic. (I would contrast this with things that are "apparently probabilistic," like shuffling a deck of cards, which appears randomly determined only because we aren't tracking all of the initial conditions and variables involved. The quantum level is truly probabilistic so far as we know—the information required to understand it in a deterministic way just simply does not exist, according to reigning thought on these things.) At the levels of complexity one is talking about, speaking of the world, or the human brain, in strictly deterministic terms is not always the most sensible way for coming to terms with moral problems, that much I agree. But searching relentlessly for some tiny part that might be somehow outside the rest of the physical system seems to me quite pointless on the face of it, and probabilistic functions are no less determined, even if their outcome cannot be predicted ahead of time. --Mr.98 (talk) 12:30, 11 July 2010 (UTC)[reply]

I concur with the point of view that free will is not random. Therefore deterministic models of human mind are likely better models to explain our perceived free will. Dauto (talk) 13:21, 11 July 2010 (UTC)[reply]

I somewhat disagree (but not with your conclusion). Randomness does not equate to what most people think of as "free will". When you roll a dice - does the dice have "free will" to decide what number will come up? No! It's just obeying the laws of physics. That doesn't stop it from coming up with different numbers each time you roll it - and it doesn't mean that there aren't 'weighted' dice that come up with a '6' more often than the other numbers.

There are undoubtedly random effects going on here - between quantum effects, external 'noise' sources impinging on the neural network and chaos theory effects, there are plenty of reasons to believe in randomness in the brain. The brain is a massively parallel, asynchronous machine, without timing interlocks of any kind. Which means that (in computing terms) it's going to be super-sensitively dependent on internal timing and 'race-conditions'. To try to put that into concrete terms: Suppose someone asks you a question that doesn't have an automatically "right" answer. One part of your brain starts assembling data that would result in a "Yes" answer and another part is coming up with other information that would produce a "No" - then differences in speed between those two parts (which could depend on anything from what you ate for breakfast to the phase of the moon!) might cause you to answer the question differently each time you are asked. That might make it 'seem' like you were making a 'free choice' - when in fact, it was essentially just a random fluctuation.

However, I don't see how any of those things results in an assumption of "free will". After all, we can plug random number sources and timing weirdnesses just like this into any 100% deterministic computer and have the result of a question be somewhat randomly determined - and we certainly wouldn't say that was "free will"! I have had plenty of programs that I've written that have "race-conditions" that I hadn't noticed that would cause the program to behave differently each time I ran it. In software, we'd generally call those "bugs". Some programmers use the specific term "heisenbug" to describe them because any attempt to pin the bug down causes it to behave differently!

So I definitely don't hold with the idea of "free will" - that smacks of something highly non-scientific, verging into matters of "the soul" and all manner of other metaphysical bullshit. However, that's not because of a lack of randomness - it's because the brain is just another computing machine (albeit a somewhat flaky one) - and it has to obey the exact same laws of physics as the laptop on your desk or that rock over there.

SteveBaker (talk) 16:40, 11 July 2010 (UTC)[reply]

I fully agree that free will has nothing to do with randomness -- the idea that it does is an artifact of most people's intuitive dualism. And I also agree with Steve that there is a lot of randomness in the human mind at the macroscopic level -- and not just the human mind. I've studied the behavior of rats running on a T-maze, where on every trial they have a choice of going right or left, with no motivation to choose one direction over the other. The rats have a pretty strong natural tendency to alternate, choosing the opposite direction from the previous trial, but there are lots of exceptions, and it is extremely difficult to find any deterministic pattern in them. It even goes beyond mammals: Paul Grobstein has studied decision-making in frogs, and found that their choices seem to contain a large component of unpredictable randomness. Why does this happen? Nobody really knows -- my guess is that it happens because operant conditioning requires a basic mechanism for randomizing behavior as a starting point for learning. In other words, you can't find novel solutions to problems if you can't start out by experimenting randomly. Looie496 (talk) 17:08, 11 July 2010 (UTC)[reply]

I would just point out, to both Steve and Looie, that there are two different (among many) definitions of "randomness" here. One is like dice—they are only random in the sense that our model of them and their conditions is insufficiently complicated enough to calculate the outcome, but with a sufficiently omniscient model of the initial conditions and the rolling mechanism, you could hypothetically calculate out what the next roll would be at "classical" (non-quantum) scales. It is only "random" in the sense that it is complex. The other is a quantum definition, where the information to predict the end-state simply is not there. The probabilistic nature of quantum effects is, as far as our theory tells us, utterly and irreconcilably random. It is not random because it is complex—in fact, it is quite simple, by comparison. But knowing all of the initial conditions will not tell you whether a given atom of a given radioactive element will decay at a particular point in time. From a philosophical point of view I would consider those to be quite different. A decision-making process that is "random" because it is a complex mixture of variables and conditions is not quite the same thing as one that is "random" in the sense that it is non-deterministic. Now I do agree that in both cases, as I said before, there is no way that I can see to turn either of those forms of randomness into something like "free will," which I do agree with you is not a scientific concept anyway. --Mr.98 (talk) 18:36, 11 July 2010 (UTC)[reply]

Yes, I'm aware of the difference between randomness and pseudorandomness. But where brain function is concerned, they both have the same consequences. (Quantum randomness is relevant because of the so-called Butterfly effect, which amplifies tiny perturbations into large differences, and is sure to operate strongly in a system with the powerful positive feedback loops that the brain has.) Looie496 (talk) 23:15, 11 July 2010 (UTC)[reply]

You do realize, however, that the usual (philosophical) understanding of 'free will' sees both determinism and randomness as a lack of free will, right? determinism signifies a lack of free will because it violates the 'free' aspect; randomness signifies a lack of free will because it violates the 'will' aspect. free will implies that you can make an exercise of will (which implies focus and function) which is not predetermined by material conditions. Altruism is often pointed to as an example of free will (and suffers the same philosophical critiques as free will). --Ludwigs2 23:34, 11 July 2010 (UTC)[reply]

Note that free will is often (implicitely) invoked in certain discussions, e.g. when you need to assume that the experimentor has the free will to choose the setting of his measurement apparatus in an arbitrary way. 't Hooft (who still believes that local deterministic models are feasible) has recently commented on this issue. Count Iblis (talk) 00:18, 12 July 2010 (UTC)[reply]

Condition with monologuing, stream-of-consciousness speech

Is there a psychiatric or neurological condition characterized by extreme talkativeness (e.g., a monologue that may go on for 15 minutes or more), stream-of-consciousness-like speech in which a particular theme is carried for maybe 15 seconds, followed by another, tangentially-related theme, and so forth, and attention to irrelevant detail (such as giving the home addresses of persons whose names come up)? Thanks in advance for your attention. 70.50.64.16 (talk) 06:00, 11 July 2010 (UTC)[reply]

Williams Syndrome can look a lot like that. So can some forms of mental retardation or autism. Looie496 (talk) 06:20, 11 July 2010 (UTC)[reply]

We can give direction if you're looking for an answer to a random question. If you are asking for a real person please consult a medical doctor. --mboverload @ 06:45, 11 July 2010 (UTC)[reply]

talkativeness is a symptom of many different psychological conditions (as well as being part of the spectrum of normal behavior). In and of itself it is not indicative of anything without a proper differential diagnosis. if it's behavior that in some way interferes with the person's life, they should consult a therapist. --Ludwigs2 07:00, 11 July 2010 (UTC)[reply]

The symptoms you describe, I believe, are called Pressure of speech. This is not a diagnosis, this is the answer to your direct question. We can not and do not provide diagnoses. If you suspect that someone you know exhibits these symptoms, please consult a specialist. --Dr Dima (talk) 08:45, 11 July 2010 (UTC)[reply]

Stumbled upon Tachylalia. Consult a specialist. --Ouro (blah blah) 10:23, 11 July 2010 (UTC)[reply]

These conditions may also be seen in Asperger's Syndrome, monomania, and a "verbal" form of hypergraphia. ~A H 1^(TCU) 14:39, 11 July 2010 (UTC)[reply]

I have Asperger's and I have a definite tendency to "monologue" which I try (but fail) to notice and curtail. But in my experience, 'aspies' don't randomly change the subject every 15 seconds - instead tending to drill down in more and more detail in the same obsessive subject for as long as you let them...and if you happen to catch one of their 'pet' subjects, 15 minutes would barely be enough to get started! In my case (and, in most others I've seen), simply interrupting the person and telling them to please stop talking is a good thing...and it shouldn't offend them. I'd prefer the momentary annoyance of not being able to finish that extended thought - to the realization that I've monopolized the conversation and upset everyone within earshot. Of course if you're interested in every possible detail of how a 1963 Mini Cooper works, how it was designed and which Monte Carlo rallies it won - please feel free to ask and I'll be more than happy to give you a two hour dissertation! It's also not just speech...people who frequent these Reference Desk pages will surely have noticed how my posts are much longer and (arguably) overly-detailed than those of normal people. SteveBaker (talk) 15:50, 11 July 2010 (UTC)[reply]

Do not assume that a psychiatric or neurological diagnosis is necessary if talkativeness can be explained by simple enthusiasm or nervousness. A self-absorbed actor met a lady and told her about his career, talking for an hour non-stop about his theatrical successes. Eventually he ended by saying "Sorry I've been speaking only about me and I would rather hear about you. Tell me, how did you like my latest play?". Cuddlyable3 (talk) 21:57, 11 July 2010 (UTC)[reply]

Resonating chimney creates infrasound in breeze?

When its quiet at night I can often hear or feel an unpleasant very low-pitched noise in one particular room. That room has a chimney that has been closed up, nearly. The total length of the chimney must be about 25 feet. I cannot detect where it is coming from, only guess. Perhaps the chimney is resonating like an organ-pipe or like blowing across the top of a bottle.

What frequency of sound would a 25ft long organ pipe make? Would the frequency of sound of it in bottle mode be similar? Thanks 92.15.3.130 (talk) 11:35, 11 July 2010 (UTC)[reply]

The first harmonic frequency would be 11hz. Slightly lower actually, once you include the diameter (and harmonics at the odd multiples of this). See Acoustic resonance. That said I've never heard of it happening with a chimney, although I have with caves. I'm pretty sure you'd need some fast wind, a regular breeze probably wouldn't work. (But I'm not really sure.) Ariel. (talk) 12:38, 11 July 2010 (UTC)[reply]

The formula given in the article suggests about 11Hz, with harmonics at 33hz, 55hz, etc. Assuming the loudness of the harmonics decrease as the Hz rises, and that the unhearable 11Hz modulates the higher harmonics, it may well explain what I've been hearing. 92.15.3.130 (talk) 16:44, 11 July 2010 (UTC)[reply]

My next question is - how would the subjective loudness or energy (not the same thing) of the various tones compare? Would the noise I could barely hear be accompanied by more powerful infrasound at 11Hz? 92.15.3.130 (talk) 16:49, 11 July 2010 (UTC)[reply]

Perhaps a house with windows open in the summer could act like a very low frequency whistle. Maybe this might explain The Hum. 92.28.255.202 (talk) 10:08, 12 July 2010 (UTC)[reply]

Anecdotally, when I used to live in St Andrews there was one high-walled, open-ended alley I regularly walked through where I could, often at night but rarely during the (noisier) day, just hear a very, very low sound, on both the pitch and volume thresholds of audibility. After some deliberate observations I determined that this was not related to the sometimes similar low growling sounds of aircraft active at RAF Leuchars several miles away, and concluded that it was probably an 'organ-pipe effect' caused by wind and the alley's physical characteristics. Until I consciously noticed the sound, I often felt uneasy around the alley, and I have read speculations that some "haunting" experiences may be triggered by infrasound. 87.81.230.195 (talk) 22:42, 12 July 2010 (UTC)[reply]

Parkinson's disease differences from chronic alcoholism

How are the symptoms and diagnosis of these two differentiated? Thanks 92.15.3.130 (talk) 11:43, 11 July 2010 (UTC)[reply]

You may be interested in Parkinson's disease#Diagnosis and Long-term effects of alcohol. The tremor experienced by people with Parkinson's disease is different and usually more severe than that in alcoholism. The Parkinson's disease article describes it very well; the alcoholism article not quite so well. Regards, --—Cyclonenim | Chat 12:40, 11 July 2010 (UTC)[reply]

As for the temors experienced in alcohol withdrawl, see delirium tremens. ~A H 1^(TCU) 14:37, 11 July 2010 (UTC)[reply]

Typically in Parkinson's the symptoms originate on one side of the body and worsen and remain worse on that side even after symptoms begin to affect both sides of the body. This is NOT seen in alcoholism induced tremors. Secondly Bradykinesia- slowing of voluntary motion is a hallmark of Parkinson's. This is not seen in Alcoholism. Finally significant improvement with levodopa, is seen in Parkinson's. A careful history and simple CNS examination can distinguish the two. Hope this helps.--Fragrantforever 04:49, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Where is the 2nd dimension?

I was watching this video, http://www.youtube.com/watch?v=UnURElCzGc0 with Carl Sagan explaining the fourth dimension to laymans using the second dimension as an analogy.

I showed it to my friend and he was a bit skeptical. He says that we strictly live in a 3D universe, and he gave a rather convincing argument for it that had me stumped. Rather than paraphrase what he said, I'll just quote him directly so I don't lose any of his arguments.

"Yea, the 1D-2D bullshit. The guy in this video tells you: IMAGINE, that there is a flatland. Okay? Why do you want me to imagine? Isn't there a 2D realm already? He asks you to ignore the height of the square and just try to pretend it doesn't exist.

So, what is he doing now? He is asking you to ignore reality (which is the only thing that exists)and recall a non existing "idea". You see, in our universe, squares don't really exist. Lines don't exist either. Lines, squares circles, and all 2D shapes are all just perfect ideas. They don't exist in our universe. You can draw a line and it can seem to be perfect, but, after you zoom in you will see imperfect and rough edges. You can use laser sharp cutting and it will be perfect this time. But, you zoom in more, still, it's not perfect. You will never ever reach a perfect line.

When you talk about a square, you KNOW you're talking about something that's so perfect that it doens't exist. And when you build a square building, no matter how accurate, you're just immitating the absolute idea of a square. Something your brain had imagined one day and you're trying to achieve it. So, it's WRONG to think that there is 1D, and then comes 2D, then our 3D. Because, all that exists in the universe is 3D. The other "D's" are philosophical ideas. And so is the 4th dimension. The 4th dimension is a "clever" approach to apply perfect ideas to try to imagine how the 4th dimension "would" look like. But, it's not more real than you imagining what would have happened if we lived in a cube planet. You can derive euqations to try to understand how gravity would be like? how the earth orbit would be like? But, that's all just on paper.

People who use the (2D-3D) (3D-4D) analogy try to convince you that there IS a fourth dimension and that you are to it as a 2D realm to 3D one!!!

FUCK! Did we approve 2D realm as a reality now? Didn't we just agree it's just our imagination?

I believe other dimensions are just "other scenarios" of the same 3D universe. This is all I can approve. Because it's a general rule that can be applied on lines and squares, and on our universe too.

2D is a realm of infinite scenarios of 1D. 3D is a realm of infinite scenarios of 2D. and 4D is a realm for infinite scenarios of 3D, and there it stops. And, since there is no 1D or 2D, then it's only 3D with different scenarios and that's ALL."

I thought about what he was saying, and it made sense. There are no true 2D objects except those we think of in our heads or exist in abstraction. Or are there? Could it be that all objects have a projection in 2D but we can't see it because we only see and experience the universe in 3D? ScienceApe (talk) 14:33, 11 July 2010 (UTC)[reply]

Your friend obviously lacks imagination. What Sagan is asking you to do is to IMAGINE a 2D world. Not that there is a 2D world - just use your imagination. The problem he is trying to solve is to explain how a fourth spatial dimension might work. That's difficult because our brains are not well-equipped to imagine a 4D world (and here we're talking strictly about four SPATIAL dimensions - we're not talking about 4D as in three spatial dimensions plus time. To try to help our imaginations along - to understand (at least at some level) what an 'extra' dimension would be like, it's easier to imagine that we're 2D beings in a 2D universe - then to imagine how the 'extra' third dimension would appear to such beings. Most people have no trouble whatever imagining 2D - there have been at least a couple of fictional stories written about 2D universes..."Flatland" (which I, personally, think is a pretty terrible book) and "Planiverse" which makes it onto my personal "top 20" bookshelf.

So, we have to imagine creatures whose whole existance lies on the surface of (let us say) a sheet of paper. Now we know this 2D universe doesn't really exist (and according to some of the appendices of Planiverse, cannot exist as a meaningful thing because chemical reactions would be impossible in 2D)...but this is just a thought experiment. So these 2D creatures would look to us like drawings on a page.

This is easy to imagine. Think about the PacMan game. It is set in a 2D world. The 'walls' of the maze have no height. PacMan is a circle with a mouth, not a sphere. The ghosts are just 2D shapes. When PacMan is caught between two walls with a ghost coming towards him from both directions, he can't put on a James Bond jetpack and move out of the screen to avoid them...he's trapped in a 2D world. Now - that's not hard to understand is it? So the question is, if we go to PacMan and tell him that there really is a third dimension - and that he could escape the ghosts easily by moving "up" and out of the screen...or tunneling "down" under them. This would be a very tough concept for his tiny 2D brain to imagine.

Just as it's hard to imagine (for us) escaping out of a doorless, windowless jail cell with solid walls, roof and floor by moving in the 4th dimension...stepping "up", going past the walls and then back "down" again. Unfortunately, we don't even have good words for "up", and "down" in the 4th dimension...which makes even discussing this problem tricky! Suppose we make some words: Norf and Souf (like North and South) to describe directions in the 4th dimension. We have cell walls to the north, south, east, west, and floors above and below...but the stupid 3D prison cell designers forgot to build walls to the Norf and Souf! So as 4D beings, we walk out of the cell by moving Norf - then a little to the East - then back Souf again! It's just as easy for them as if the jailer forgot to build North and South side walls for our cell!

This is hard to imagine - but let's do the analogous thing in PacMan-land: PacMan is stuck in a square jail cell - encompassed by four typical pacman game walls to the North, South, East and West. But nobody built a floor or ceiling to his jail. But if a 3D being like you or me were imprisoned in pacman-land, we could simply step over those pathetic 2D walls by moving "up" - then east then back "down" again.

The analogy here makes it much easier to imagine those "Norf" and "Souf" directions - which our poor little brains simply can't grasp - by imagining how pacman has problems understanding "up" and "down".

What's worse about your friend's rhetoric is that he claims that 4D is the most you could have...but one of the leading scientific theories that we have to explain how our 'for-real' universe works (string theory) requires there to be somewhere between 15 and 26 actual 'for-real' spatial dimensions! It is quite possible (and some would say, almost certain) that we really do live in a 26D universe!

But it does require an effort of imagination and a degree of patience to follow Sagan's explanation - and I guess some people are simply incapable of doing that - which is sad. Anyway, if this interests you (and I surely hope YOUR imagination is up to it) - then grab a copy of Planiverse and prepare to have your brain stretched!

SteveBaker (talk) 15:18, 11 July 2010 (UTC)[reply]

for a person who laughed at the idea of sound waves being represented in a physical form for the lack of proof ( Steve Baker) possesses quite a vivid imagination to assume we live in a 26D universe!!! where did the proof come for this 26D universe steve? or do you ask for proof only when it suits you? Most of us could argue that the argument of the OP's friend is perfectly sane... and would suit most scientific minds.... My suggestion is to continuously think out of the box and not to ridicule or laugh at what appears to be fantastic today for lack of proof like how Steve Baker dramatically did using quite a few profanities in the thread about representing physical matter in the form of sound waves.--Fragrantforever 16:27, 11 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Fragrantforever: see Bosonic string theory. – Clockwork Soul 16:56, 11 July 2010 (UTC)[reply]

The "proof" of dimensions is a mathematical construct, thus all theorems associated with them are perfectly correct. The application of those dimensions to the physical world is something that simply works, and works well, thus we see three dimensions around us, referred to as 3D, and it corresponds pretty much exactly with the mathematical form (and for reference, we get another hint on Earth where the pull of gravity marks the z-axis and the surface of the earth is x-y). As physics expands, we find that we can make time into a fourth dimension, with a major difference in metric, and again still fit the dimension model just as easily as we did with space. Note that all proofs still hold, once we fit reality so well to the math. When Steve refers to the possibility of a 10D or 26D universe, that refers to a specific framework of particle physics that is still debatable, but if the clues fall into place, then through the same mathematical theorems we will understand that there are 6 or 22 more "hidden" dimensions that only the borderline-possible fundamental particles see, but we here on Earth still only see four. SamuelRiv (talk) 16:59, 11 July 2010 (UTC)[reply]

Really this is a generic know-nothing argument that can be used against any scientific discovery since Copernicus. Of course the Earth isn't moving—isn't it obvious? You know what it's like to be in a moving vehicle. Of course matter isn't made of atoms; have you ever seen an atom? Have you ever seen a new species arise? And so on. The evidence supporting modern science is very subtle. If it weren't, it wouldn't be modern science, because the ancients would have discovered it already. Nevertheless, the evidence is there, and in such overwhelming quantities that you can't help being persuaded by it once you've found it. Incidentally, the three-dimensionality of space isn't obvious either. The experience of space is so immediate and unconscious that it took a long time for anyone to realize that one could associate the number 3 with it. A possible response to this argument would be to say "I don't believe that space is three-dimensional. Can you convince me?" and then see if he can do it without asking you to imagine two-dimensional space. -- BenRG (talk) 18:38, 11 July 2010 (UTC)[reply]

The OP's friend expresses an objection to the elements (point, line, sphere,..) of Euclidean geometry that Buckminster Fuller made in his book "Synergetics". It is correct that none of those primitive elements can be physically realized in the real world of atomic particles. However that does not invalidate the use of orthogonal dimensions to make 3 independent measurements that together uniquely locate a real object in space. The friend is confusing construction with analysis. Sagan (a consummate explicator) demonstrates removal of information about a dimension in order to prepare a thought experiment about how we might perceive information on a 4th dimension. The hypercube model can be interpreted as being the history of a cube whose size changes during a span of time where time is posited as the 4th dimension. The friend's closing statements about "scenarios" such as "2D is a realm of infinite scenarios of 1D" would be better understood in terms of calculus, thus "a 2D area can be differentiated into infinitely many lines". Again, this is all about analysis not real construction. Cuddlyable3 (talk) 21:40, 11 July 2010 (UTC)[reply]

This is turning out to be a very interesting and enlightening thread. But what I dont understand is that some people quote the Bosonic string theory and refer to tachyons and invoke the idea of 26D when they are on this thread and on an another thread laugh at the idea of tachyons and possibility of travelling faster than the speed of light. If you beleive the Bosonic String Theory to be true and beleive Tachyons exist, then you should beleive that it is ( atleast experimentally) possible to travel faster than light. How can you invoke parts of such theories when it suits you and reject parts of it when it doesnt? My arguement is, all these are hypotheses with limited proof only in lab settings, if we start demaning proof for every theory we would never proceed anywhere. The reason why I raised my objection was we were discussing several weeks ago, if physcial form can be transmitted as sound waves - a very knowledgeble person ridiculed and rubbished this idea for the lack of proof. But now truns around and talks about tachyons and 26D. Shudnt we have a moderation in our demand for scientific proof? The beauty of science ( I Repeat) is that what seems too fantastic to be true today could be a very well accepted fact in a few years or months. --Fragrantforever 04:22, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

... or what seems too fantastic can very well be laughed at as the silly imaginings of science-fantasy writers when a proper theory is found that has experimental verification. Faster than light, parallel universes, more than three dimensions (allow 4 for space-time), wormholes, transmission of matter by sound waves or light waves or "transporters" etc all fall into the fantastic category (IMHO). We are fascinated by the concepts, discuss the theories, develop the mathematics, but we don't know whether we are talking about fantasy or reality until we have experimental evidence. Dbfirs 06:57, 12 July 2010 (UTC)[reply]

The 26-dimensional bosonic string theory is unrealistic for several reasons, but it can still be useful to study unrealistic theories because they can give insight into more realistic theories that are more difficult to solve. Note that "tachyon" doesn't mean what you think it means. In field theory (and string theory, I believe), the speed of information propagation is always c, regardless of the nature of the particle. Tachyons in field theory are formally analogous to classical faster-than-light particles in a certain way, but they don't propagate faster than light. Also, tachyons aren't automatically fatal to a theory. They make the vacuum unstable, but there might still be a different, stable vacuum. In fact, this is exactly what happens in the Standard Model; the fundamental Higgs field is tachyonic. What is fatal is when there's no such stable state, which is the case in bosonic string theory, I think. -- BenRG (talk) 09:15, 12 July 2010 (UTC)[reply]

Actually, tachyon condensation says "the fate of the closed string tachyon in the 26-dimensional bosonic string theory remains unknown", which seems to imply that the tachyon might not be fatal to the bosonic string theory after all. I have no idea. -- BenRG (talk) 09:20, 12 July 2010 (UTC)[reply]

ScienceApe: your friend's argument is stupid because cubes don't "exist" either -- so by his/her argument, neither does the 3rd dimension. 63.17.82.101 (talk) 09:52, 14 July 2010 (UTC)[reply]

Surprised no one's mentioned the Möbius strip. 67.243.7.245 (talk) 01:30, 19 July 2010 (UTC)[reply]

fluorescent light

how to disposing of long fluorescent light bulbs without breaking them —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 19:49, 11 July 2010 (UTC)[reply]

In Norway, shops that sell electronic articles are required to accept them and dispose them free. That's useful if you happen to be Norwegian. Cuddlyable3 (talk) 20:55, 11 July 2010 (UTC)[reply]

That relates to a similar situation with the Waste Electrical and Electronic Equipment Directive, which only applies in the European Union.Sf5xeplus (talk) 22:03, 11 July 2010 (UTC)[reply]

Ask the organization that collects garbage where you are. In my case, they used to be collected as ordinary garbage but now I have to keep the things until the next annual "Environment Day" or take them to an inconvenient "household hazardous waste" site. --Anonymous, 21:35 UTC, July 11, 2010.

Where are you located? What country? At least near where I live, Ikea takes them. Ariel. (talk) 22:08, 11 July 2010 (UTC)[reply]

I live in the US and dispose of them in the regular trash (sorry green people). --Chemicalinterest (talk) 01:13, 12 July 2010 (UTC)[reply]

Here in Spain, they are often disposed of in the normal glass recycling bins. That's what my local council told me to do last time I asked them (not that I trust them to know the answer, but I couldn't be bothered to look it up). Modern domestic flourescent tubes are nowhere near as toxic as the early models in any case, but correct (and actual) disposal procedures will vary from place to place. Physchim62 (talk) 01:45, 12 July 2010 (UTC)[reply]

Common 4 foot fluorescent tubes sell for about $1.60 retail in the U.S., and cost the merchant about $1.50 to $2 a piece to recycle in bulk [4]. This is more than the merchant's profit on selling a new one, so the merchant has a substantial net loss if he sell a fluorescent tube and accepts the old one for recycling. If he accepts one for recycling that you bought elsewhere, the loss is naturally greater. Some merchants accept them for "recycling," then smash them in the dumpster (to prevent kids taking them out and smashing them somewhere else). The compact fluorescent bulbs are cheaper to recycle. Some good-hearted people have gotten the recycling bug to the extent that they want to recycle common incandescent light, which is nonsense. Edison (talk) 02:16, 12 July 2010 (UTC)[reply]

That depends what you recycle them as! Here in Spain, the glass is collected separately, but not recycled as glass, just crushed and used as hard-core for roads. It cuts down on the amount of landfill (and makes for safer recycling of other waste), but is much cheaper than trying to do "glass-to-glass" recycling, which requires separation of colours and glass types. Physchim62 (talk) 02:34, 12 July 2010 (UTC)[reply]

Fluorescent tubes contains mercury and most incandescent light contains lead, that is the reason they should be treated separately. The amount of glass is insignificant so recycling it has limited utility. I would be very surprised if it is legal to dispose them in glass recycling bins in Spain as it is part of EU. I do not know about US regulation but they should not be smashed in the dumpster and any regulation that give merchants economic incitements in doing so without proper control is clearly flawed.--Gr8xoz (talk) 09:17, 15 July 2010 (UTC)[reply]

Tetramethrin

Are there any known cases of toxicity in humans from tetramethrin? Unlikely given the minute quantities we're exposed to and I'm not even sure if anything in our bodies reacts to it as it's used in wasp killers, but I'm curious if it does present effects in humans. Regards, --—Cyclonenim | Chat 22:39, 11 July 2010 (UTC)[reply]

According to the references at the bottom of the tetramethrin article: [5] and [6], these chemicals are really very safe. They don't absorb through the skin, absorption through the lungs is slightly more of a concern, but the chemical is metabolised quickly by mammals. They had to feed rats an entire gram of the stuff per kilo of bodyweight to get an effect - scaled up to human body size, that would require you to eat a hell of a lot over a short timespan to suffer a risk that way. I don't think you have to worry - and probably the best precaution is to avoid breathing too much of it over a short period of time. SteveBaker (talk) 22:52, 11 July 2010 (UTC)[reply]

The safety data lists it as irritating to eyes, skin, and respiratory systems, but the LD50's (lethal doses) are very high. Looie496 (talk) 23:04, 11 July 2010 (UTC)[reply]

Up to 1990, when the last WHO review was carried out, there were no reported cases of poisoning or adverse effects in humans [7]. Pyrethoid insecticides are known for having very low toxicity for mammals: they can be substantially more toxic to birds, reptiles and fish, which leads to some environmental concerns. Physchim62 (talk) 23:15, 11 July 2010 (UTC)[reply]

Remember though that measures like LD50 are generally talking about acute toxicity. Long-term effects are much slipperier and harder to measure. In the first PDF link given by Steve, we read that a committee at EPA reviewed the carcinogenicity data of pyrethrins in animals and decided thatthey showed carcinogenicity, but they were unable to classify pyrethrins into a carcinogenicity group until some of the tissue specimens [...] were re-read.

Now, my general sense is that if you wanted to avoid everything with even this much hint of cancer-causing, you'd have a tough time in this world. Still, it's a note of caution; I wouldn't be reckless with the stuff. --Trovatore (talk) 03:52, 12 July 2010 (UTC)[reply]

Thanks guys, pretty useful stuff. Regards, --—Cyclonenim | Chat 09:19, 12 July 2010 (UTC)[reply]

Electric stove

My understanding is that an electric stove is essentially a big resistor. If so, will you get electrocuted if you touched the stove while it's on (because of the current running through it)? 74.15.137.192 (talk) 23:04, 11 July 2010 (UTC)[reply]

No. The 'elements' of the cooker are insulated. --Tagishsimon (talk) 23:06, 11 July 2010 (UTC)[reply]

It's usually a Nichrome wire (or coil) inside a ceramic tube. See Heating element. But it's not always like that, inside a toaster, or a space heater for example it's not always insulated. Ariel. (talk) 00:44, 12 July 2010 (UTC)[reply]

Blow dryers have bare nichrome wire. I dissolve it in hydrochloric acid to get nickel and chromium compounds. --Chemicalinterest (talk) 01:12, 12 July 2010 (UTC)[reply]

If you touch a metal spoon to a hot stove element and touch the handle of the oven door with your other hand you DO feel the electric current. I tried it! —Preceding unsigned comment added by 142.104.215.119 (talk) 01:36, 12 July 2010 (UTC)[reply]

That is surprising. There may be faulty insulation. I do not advise passing electric current through your body as an electrical test in the manner you describe. Edison (talk) 02:08, 12 July 2010 (UTC)[reply]

In India, at least such elements (as we call 'em here, like a heater's main coil etc) are never insulated. Newspapers are filled with numerous accidents, sometimes even "accidents", when the heater kept on the window-sill fell down in full bathtub and the bather gets electrocuted. Of course, the bather is mostly a newly-wed bride... Jon Ascton (talk) 04:55, 12 July 2010 (UTC)[reply]

The ones on top of the stove (range) are always insulated - otherwise any metal pot would short them. If an insulated heater fell in water it would still be bad - the insulation is only for the external parts, the internal wiring, switch, etc, are never fully insulated. Ariel. (talk) 05:45, 12 July 2010 (UTC)[reply]

Note your's "always" and mine "never" ! That's huge difference in safety-standards, between us ! Kipling was right - "East is east, and West is west / And never twain shall meet..." Jon Ascton (talk) 06:13, 12 July 2010 (UTC)[reply]

No, you are talking about different types of heating element. Both are common in both countries. In the UK it is illegal to fit uninsulated heaters in a bathroom, but this doesn't stop people using them there and sometimes electrocuting themselves (or their brides?).Dbfirs 06:30, 12 July 2010 (UTC)[reply]

An uninsulated stove-top element wouldn't just be dangerous, it would be nearly unusable. Besides which, hot nichrome is a bit delicate, even expecting you to put a non-conducting pot directly on the element would be essentially the same as selling a stove that didn't work for more than a few days. APL (talk) 16:19, 12 July 2010 (UTC)[reply]

Are you suggesting that the newly wed brides are murdered, or that they are killing themselves, or that they have poor safety habits? --Sean 19:44, 12 July 2010 (UTC)[reply]

July 12

Potable water caulking

Is anyone aware of a commercial product that's marketed or made for sealing potable water systems. In other words, it can come into contact with drinking water without risks? Obviously plumbing solder does this, but is there anything that's applied like a caulking? Even better if it can both metal and plastics, and withstand heat (up to 100 C)? Shadowjams (talk) 00:18, 12 July 2010 (UTC)[reply]

Wouldn't most silicone based caulks work fine for that? Here's one[8]. I think if you look you will find lots of them. Ariel. (talk) 00:44, 12 July 2010 (UTC)[reply]

Some silicone caulks contain additives which may leach into water on prolonged (or high-temperature) contact. Kitchen and bathroom silicone caulking may contain antifungal agents (to discourage mildew). Products marked as meeting ANSI/NSF Standard 61 (for potable water contact) are a good bet. (Dow Corning's 732 and 748 sealants meet these standards: [9].) Here's a searchable index of NSF-certified products. TenOfAllTrades(talk) 02:03, 12 July 2010 (UTC)[reply]

Thank you, that's perfect. I just hope I can find them. Shadowjams (talk) 02:57, 12 July 2010 (UTC)[reply]

They should be available at most decent sized home improvement stores. I am not sure what your location is, but in the US, places like Lowes or Home Depot should carry some of those. Googlemeister (talk) 13:27, 12 July 2010 (UTC)[reply]

Symptoms of vasular dementia

Several years before he was diagnosed with vascular dementia, my grandfather had difficulty controlling the movement of his hands; we thought that it was perhaps Parkinson's disease, but (for reasons that I don't remember, as I was only a child then) the doctors eventually decided that it wasn't. Can vascular dementia cause symptoms like those of Parkinson's? I've read the vascular dementia article and some things I found online, but nothing I've seen talks about it. By the way, please don't think that I'm asking for medical advice; my grandfather died in 2006. 71.79.87.249 (talk) 02:01, 12 July 2010 (UTC)[reply]

Many people dont realise the difference between Parkinsonism and Parkinsons disease. Parkinsonism refers to any condition that causes a combination of the movement abnormalities seen in Parkinson's disease — such as tremors, slow movement, impaired speech or muscle stiffness resulting from the loss of dopamine containing nerve cells (neurons). Not everyone who has parkinsonism has Parkinson's disease.

In the case of your Granddad, I THINK you are refering to a condition, what we doctors, call Lewy Body Dementia, which shares characteristics with both Alzheimer's disease and Parkinson's disease. Like Alzheimer's, it causes confusion. Like Parkinson's, it can result in rigid muscles, slowed movement and tremors.

But the most striking symptom of Lewy body dementia may be its visual hallucinations, which can be one of the first signs of the disorder. Hallucinations may range from abstract shapes or colors to conversations with deceased loved ones.

Apart from Lewy Body Dementia which I briefly explained earlier, other causes of parkinsonism include:

Stroke
Encephalitis, Progressive supranuclear palsy,
Multiple system atrophy, Corticobasal degeneration, Certain medications, such as some antipsychotics and metoclopramide
Head trauma, isolated or repeated, such as injuries sustained in boxing.--Fragrantforever 06:07, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

You might like to take a look at our article on Parkinson's disease, which describes the many different signs that a doctor would look for if s/he suspected Parkinson's in a patient. To add to FF's comment above, not all tremor in old people is parkinsonianism: parkinsonianism is quite distinctive to a doctor, although not necessarily to family members. Because Parkinson's disease is fairly well known among the general public and associated with "shaking hands", it is obvious to ask the question "does Granddad have Parkinson's, look how his hands are shaking", but the answer isn't always "yes". Physchim62 (talk) 11:32, 12 July 2010 (UTC)[reply]

The "vascular" in "vascular dementia" means that the problem is caused by an impairment of blood supply to the brain. The "dementia" part means that the problem has damaged parts of the brain involved in memory and cognition. Normally damage to those parts of the brain won't in itself cause tremor, but the vascular issues can easily extend to other parts of the brain such as the cerebellum and basal ganglia where damage can produce tremor. In other words, vascular dementia shouldn't cause tremor in itself, but the vascular problems that cause the dementia can also independently cause tremor. Looie496 (talk) 16:06, 12 July 2010 (UTC)[reply]

Simple circuit to charge my bike light batteries to supply my lights

I would like to charge a battery (possibly lead acid or possibly just a number of NiCds in a battery-pack) from my bike dynamo and in turn use those batteries to power rear and front lights arranged from LEDs. Can the simple circuit, suggested by Katie, 6 years old, from Sussex, do what I want? I only own a soldering iron and solder, so I don't want to use a PCB if I can avoid. There are some complicated designs out there for powering LED bike lights, but they would be very expensive and time consuming to build, considering I'd only produce one.

Notice that the lights are two-deep in series and then in parallel - if the forward voltage drop on the LEDs is 3.2-3.6v, should that be fine? I'd sooner not use a resistor, since I figure that just wasted energy.

Also, is the ammeter really necessary? It was just there in the design I copied with no explanation. --78.148.136.27 (talk) 03:08, 12 July 2010 (UTC)[reply]

(EC) As it turns out I'm somewhat interested in a similar thing although decided to go with a 18650 li-ion rechargable li-ion battery flashlight. But in the same vein I do like to understand what I'm buying so I have some knowledge of LEDs. Am I right you are planning to use an array of 5mm LEDs or something similar? Have you consider using one or more high powered LEDs like an Cree XP-G or XP-E or even a Cree MC-E or SSC P7 or heck if you really want a bright like may be a SST-50 or even a SST-90 (although I'm not sure if you really want to be generating 30W+ for the light) or something of that sort? This [10] may be helpful. You may want to work out what sort of brightness you want (have you seen the output of a power LED?) and have some idea of what sort of beam profile you want (do you want it to throw a lot? Do you want it mostly flood?) Depending on what you use the heatsinked LED it self may bost around US$8-$15 shipped (well not if you want a SST-50 let alone a SST-90), a constant current driver of some sort (for your usage either a linear regulator or buck) from a place like DealExtreme or Kaidomain or Lightake would cost about US$3-US$5 or so shipped. This does have a PCB, but I don't exactly understand you aversion. If you get a already solder PCB you may need to do some touchup soldering particularly if it's from something like DX/LT/KD but it's not like you need to assemble everything from scratch. In fact depending on your set-up and how good your board is you the soldering may only involve wiring the LED to the driver and then the power supply. You will need to consider heat-sinking and probably water proofing. If you do want to use an array of LEDs you may still want to consider some sort of driver, again probably either a linear regulator or some sort of buck (see e.g. [11]). You could try direct driving and/or a simple resistor but of course this will mean the output will vary depending on battery charge and also is likely to be a lot more fiddly. The power supply I admit is not something I'm that familiar with particularly since you want a dynamo/battery set up but I presume it's something that's largely seperate. BTW, while you may be able to get some decent advice here, may I suggest a more specialised forum like [12] (be aware people in CPF in general may sometimes be a bit snobbish or have fairly extreme recommendations/ideas) [13] [14] and maybe [15]. Nil Einne (talk) 03:35, 12 July 2010 (UTC)[reply]

P.S. A constant current regulator which at best would likely have an efficiency of 90% may seem like a waste. But consider what I mentioned about maintaining a constant output. Also consider that if you overdrive the LEDs other then reducing life (potentially fairly drasticly) you don't necessarily get much more light output, on other words your efficiency isn't exactly improving. In any case, if you do choose a power LED, direct driving under you setup is probably not possible. Also if you are worried about efficiency, the efficiency of the LED clearly matters too, in such a case the XP-G driven at a lowish current may be a good bet as it's fairly efficient although you may also want to consider how this affects the pricing, complexity of the design and beam profile. Of course an XM-L would probably be even better but that probably won't be widely available until the end of the year. Nil Einne (talk) 04:02, 12 July 2010 (UTC)[reply]

Hey, thanks for your suggestions. I've moved my query to candlepowerforums and I seem to be getting good help - there's already a fair few people that have been addressing similar problems for some time. I've ultimately decided to power two XP-G LEDs and recharge a single NiCd while moving and use the NiCd to power some 5 mm lights while stationary.

I didn't want a PCB because I don't own the equipment to prepare one. What's the cheapest option? Any way to make my own circuit without having to eat away copper with acid?

Also, do you know why power LEDs are so frequently mounted on strange ninja stars?

Here is my present design (two other designs cobbled together). I don't understand it for the most part, but the designers of the other two circuits are very helpful!

I'm actually trying to modify the design to make it something that I can comprehend. Can you explain the highlighted region? Apparently, it boosts the power at moderate speeds, though I really don't see how. If anything, it should just slow current flow since it's flowing into a a capacitor rather than through the circuit. R1 looks like it compromises the rectifier. 92.25.105.88 (talk) 23:09, 13 July 2010 (UTC)[reply]

free GIS software that can do orthorectification?

(am putting this on the Science desk because I think that the type of people who use and understand GIS would be more prevalent here than on Computing)

Could someone please recommend a free GIS application that can handle orthorectification? I've got some maps with slight scanning distortions that I need to rectify and I can't pony up for a private license of ArcGIS :-) 218.25.32.210 (talk) 03:20, 12 July 2010 (UTC)[reply]

Question on 3D TVs

We were planning to buy a 3D TV and Samsung has launched the latest 3D LED TV which seems mouthwatering. My question is, will such 3D TVs show all programmes in 3 dimension or will it show only SELECTIVE/ special programmes which have to be shot with a 3D camera? Meaning to say will tennis balls and footballs appear to jump into our living room irrespective of whether the programme is shot in 3D or not?--Fragrantforever 04:28, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Only selective. Keep in mind there are no 3D tv shows being broadcast, but you can get 3D movies. Ariel. (talk) 04:45, 12 July 2010 (UTC)[reply]

In the UK, the FIFA World Cup and Wimbledon were shown in 3D, certainly on Sky and, IIRC, on Freeview HD. See 3D_TV#3D_Channels for further details. CS Miller (talk) 08:42, 12 July 2010 (UTC)[reply]

Thanks Ariel, so the TV doesnt convert 2D programmes into 3D? --Fragrantforever 05:02, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

No. The camera only records the image in 2D. You can't convert 2D into 3D (there are fake things movie studios do to make it look 3D, but it's not automatic). --mboverload @ 05:06, 12 July 2010 (UTC)[reply]

The TV cameras have to take two pictures for each frame of video - one for the left eye and one for the right. So this definitely requires special efforts on behalf of the TV companies. There are a couple of movies that were made right before the 3D boom which were "converted" to 3D at some vast expense using clever computer technologies - but from what I understand, the result 3D experience was kinda pathetic.

There are much bigger problems with 3D though. A co-worker friend of mine bought a 3D TV to watch the World Cup on - and reported bad headaches after watching the first game.

There are many problems with using 3D technology for real-world footage. In a computer-generated movie (ToyStory/Shrek/etc), the graphics system can keep everything in perfect focus from zero feet out to infinity feet from the 'camera'. In real world photography, they can't do that. The Director has to decide at which distance the camera will be focussed and things that are closer or further than that are blurry. When you see things in 2D, your brain somehow realizes that it's looking at a moving picture on a 2D screen and that your eyes should focus on the plane of the screen to get everything correctly focussed. But in a 3D situation, you're being tricked into seeing the at all sorts of distances depending on the 3D cues in the movie. But when you do that, your eyes are not focussing properly because the blurriness was 'built into' the image when it was filmed. This is likely the cause of the headaches my co-worker felt. It is hoped that producers and cameramen will learn to minimize this effect - but it's far from certain that they'll ever be able to get this 100% right.

Also, in order to produce 3D, two pictures have to be generated by the TV - some do that by halving the frame rate (resulting in somewhat jerky pictures) - others do it by halving the horizontal resolution of the screen (resulting in blurrier images than your TV would normally produce). So there is always some loss of quality when going to 3D.

Of course everyone watching the TV has to wear the special 3D glasses. My friend reports that this is OK when everyone in the family sits down to watch something...but when the TV is on for just one person - and the others are reading or playing with the computer or something - and only glance at the TV once in a while, the double-imaging you get without the glasses is really annoying/distracting. (He also had one of his three pairs break when someone sat on them...they cost him $75 to replace).

So this is very definitely a "try before you buy" thing. You need to find someone who already has one of these - and watch at least a selection of 3D programs before you commit to spending a small fortune on one of these gizmos. If you can't do that - then at least be sure that the store you buy it from will take it back and return your money within 30 days if you decide you can't stand it.

It's also a gamble at this point. Will a lot of people find the downsides to be something they can't live with? If so, then 3D TV will die because the additional cost of broadcasting in 3D will not be cost-effective unless most families have the equipment to view them. It's bad enough that they have to broadcast a separate Hi-Def signal as well as a regular TV picture. To have to broadcast in 3D AS WELL will be painful when the initial novelty wears off.

SteveBaker (talk) 14:49, 12 July 2010 (UTC)[reply]

Another issue with 3d television and movies that doesn't seem widely understood is that the 3d effect only works properly if you keep your head upright. If you like to watch movies laying on your side, or even with your head at an angle leaning on your date, the 3d effect will be broken for you. I think this accounts for a good percentage of the headaches and "it doesn't work for me". (Though it's also true that some people have a very poor sense stereoscopy.) APL (talk) 16:13, 12 July 2010 (UTC)[reply]

Yeah - I didn't think to mention that - but you're right. If your head leans over to one side, the image will start to flicker "vertically" for you and the 3D illusion will gradually diminish. Also it's not just that some people have poor sense of stereoscopy - it's that 5% of people don't have it at all! (See Stereoblindness) SteveBaker (talk) 14:55, 14 July 2010 (UTC)[reply]

Thanks everyone for such interesting and informative answers. Fragrantforever 06:24, 13 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Gulf of Mexico Oil Spill

I understand the ecological brouhaha that Greenpeace and other champions cryout loud. But what I dont understand is, BP is a company which has agreed to explore the ocean surface to extract crude and supply the US Govt so that the crude can be used for its use. No company, in its right bearings, would deliberately sabotage itself and burst the pipes and kill its own staff to cause such a catastrophic oil spill. People argue, BP had subcontracted the operations of the rig to a third party who didnt maintain strict quality and good standards which resulted in this tragedy.

My question is moral issues aside, when a company agrees to undertake such difficult scientific procedure, like extracting crude from below the ocean floor, cant they have a clause in the contract which protects them from such unforseen calamities? Because everyone seems happy to blame the organisation while very little seems to be the focus on actually sitting together and using technology to solve this issue. ( Im not supporting BP here but was annoyed to see Obama's repeated press and tv statements blaming BP and offering nothing constructive as a viable option).

The reason why I ask this Question is, if hypothetically speaking the new cap fails to stop the flow and oil ccontinues to gush out, how long are we going to indulge in sabre rattling?--Fragrantforever 05:14, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

That's a political question and not appropriate for this Reference desk. Looie496 (talk) 05:25, 12 July 2010 (UTC)[reply]

It might make a good question for the humanities or misc desk, though - it's a basic problem with laissez faire - who pays for incidental damages that go beyond the ability of the one who caused it? And who is paying for damage to the Commons? --Stephan Schulz (talk) 09:29, 12 July 2010 (UTC)[reply]

You make it sound like BP was forced into extracting oil from the surface of the ocean; I'll throw you a hint: they weren't. They explored for the best locations containing the most oil, and either bought the drilling rights from another company or applied to the U.S. authorities for the right to drill there. They weren't forced into anything, they went into it for profit.

I do agree that disproportionate blame has been placed on BP given the regulations in the U.S. allowed for BP to do exactly what they did. They didn't break the law, and this could have happened to any oil-drilling company. Oh, yeah, and Transocean is an American company that is now owned by BP. I think morally that the company actually responsible for the disaster should cough up the funds, but of course, legally, the way it works is that the backbone company coughs up.

To answer your last question, the answer would be "until it's fixed". They're very confident the new 80,000 barrel cap will work, and they're confident the leak will stop completely by August, but if it doesn't then they'll just have to spend more and more on R&D, and on clean up and compensation. Eventually, if the matter is not solved, their worth will have dropped so low that a takeover is likely. There is speculation already that Exxon are looking at a buyout, and there is speculation that the British government would intervene should a takeover occur (because, unlike Cadbury, this is serious and if the UK loses BP, they're going to face serious consequences with pensions). As I say, though, that's just newspaper speculation.

In future, I'd go to the miscellaneous desk as this isn't really a science question. Regards, --—Cyclonenim | Chat 09:34, 12 July 2010 (UTC)[reply]

As a minor point of clarification, BP are not meaningfully a 'UK company' and the UK government itself does not own any BP shares (although both were the case some some years ago). BP is a multinational company and from our article "Around 40% of BP shares are held by UK shareholders, and 39% in the USA. BP's UK dividends represent approximately one-seventh of all dividend payments in the UK and form the basis of many pension schemes." Presumably their fractional share of US dividend payments will be somewhat less because the US economy is larger, but nonetheless BP's financial woes resulting from the accident will be not much less of a headache for the US as for the UK (as well as for the owners of those other 21% of their shares). 87.81.230.195 (talk) 22:14, 12 July 2010 (UTC)[reply]

As a minor point to the above, BP no longer pays dividends. Googlemeister (talk) 13:01, 13 July 2010 (UTC)[reply]

Indeed in terms of holding BP responsible, a lot of people have criticised the requirement for BP to pay the wages for all people affected by the moratorium (indeed I think it may go further then wages), BP themselves initially seemed to make a noise then I guess realised they weren't going to win that war so gave up. It is an odd thing because the moratorium is government imposed and while in response to the recent disaster, BP isn't responsible (okay as lobbyists they may be partially responsible but that's a bit far) for whatever shortcomings in US regulations and enforcement allows companies to operate faulty drilling sites which this disaster seem to have highlighted which have resulted in the moratorium. BTW Transocean is not owned by BP. The well that failed was built by Transocean but under lease to BP however. Transocean have a rather complicated history with a variety of mergers, acquisitions etc. They are listed in the NYSE and SIX and their headquarters is in Switzerland (was in the Cayman Islands for a while). Nil Einne (talk) 16:17, 12 July 2010 (UTC)[reply]

Thanks everyone for the answers... Im still new to Wikipedia and had by mistake posted this question here. I was replying to a few threads here on the science desk and instead of posting this in the Misc Section had inadvertently left this q here. My apologies. Only after posting I realised the folly but dint know how to shift the question to the Misc desk hence left this here.--Fragrantforever 09:45, 12 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Doesn't matter now, probably since the question is established on this desk, it won't be moved. --Chemicalinterest (talk) 11:01, 12 July 2010 (UTC)[reply]

The problem with insulating the oil companies from blame is that removes the incentive for them to take all necessary safety precautions - these companies need to understand that an oil spill of this magnitude is probably going to bankrupt them. Ideally, that should make them focus on well safety to a greater degree than they have been in the past. As it happens, there is a 'cap' of (I believe) just 15 million dollars on the direct liability of an oil company for an accident like this - although they could be sued for much more. BP agreed to waive that and are already several billions of dollars in the hole.

As for the time it's going to take, I should point out that:

The 1979 Ixtoc I oil spill in the Gulf of Mexico took 9 months to shut off - and it was in only 160 feet of water (versus 5,000 in this case).
The Exxon Valdez oil spill dumped just one tanker-load of oil onto the coastline in the Gulf of Alaska - yet the best efforts of their large cleanup crew was able to remove just 4% of the oil from the beaches for each year they worked on it.
20 years after the Exxon Valdez disaster, an ecological survey said that it would take an additional 30 years for the ocean ecology in the area to recover.

So, since this leak is harder to get at than Ixtoc and spilled VASTLY more oil than the Exxon Valdez, the very best we should expect is for it to take more than 9 months to cap the well, more than 25 years to clean up the beaches and wetlands - and at least 50 years for the marine habitat to recover. But those are likely to be under-estimates if history is to be believed. SteveBaker (talk) 14:29, 12 July 2010 (UTC)[reply]

Not if history is to be believed Steve, if the people who did the ecological survey are to be believed. It has been my experience (having lived in effected areas of Alaska) that these ecologists are not frauds necessarily, but the do seem to have an inherent bias against oil production. Googlemeister (talk) 16:14, 12 July 2010 (UTC)[reply]

That's fairly irrelevant if they do their work properly. Do you have any evidence to the contrary? --Stephan Schulz (talk) 16:21, 12 July 2010 (UTC)[reply]

The burden of proof would be on them, not me. It is their paper and their hypothesis after all. Googlemeister (talk) 19:52, 12 July 2010 (UTC)[reply]

There's a legal concept: torts. Guess what? One might be liable for the extended damages caused by one's accidents. Look it up. To repeat: "torts." I realize it's terribly obscure and no one has ever heard of it, hardly, and for some reason Obama et al. are suggesting it applies to BP. Crazy newfangled liberal idea! 63.17.82.101 (talk) 10:03, 14 July 2010 (UTC)[reply]

Is it Normal, guys ?

A few question above someone's placed a question about an electronic circuit and given a link to it. What I find interesting and well...disturbing is the fact that the person is a six years old child ! I can't even imagine an Indian kid asking such question, they can't even wipe their noses properly at this age ! I doubt even if a high school passed out actually understands it fully ! What I want to know is this : Is it considered normal (by you wiseguys in West), or it is just once in while like Siamese twins! How do people view this trait in kids, especially the rightwing folks... Jon Ascton (talk) 06:02, 12 July 2010 (UTC)[reply]

Just because it says 6yr on it, doesn't mean it actually is. 6 year olds can certainly copy a drawing like that, but don't think they could create the circuit on their own. Ariel. (talk) 06:12, 12 July 2010 (UTC)[reply]

In the UK, a child of six-year old wouldn't understand circuits. You might get a very, very basic knowledge (where the cells go, where the light bulb will go) at Primary education (say between 8-11) but the only real understanding of circuits comes during GCSE education, ages 15-16. This is then reinforced at A-level education if you choose to study electronics. I very much doubt a six-year old could have designed a circuit of this complexity. Regards, --—Cyclonenim | Chat 09:26, 12 July 2010 (UTC)[reply]

Haha! Sorry about that; it was just my quirky sense of humour - I put "Katie, 6 yr" since I noticed that it looked like something a child had drawn and sent in. I should try to find an open-source program for drawing circuits. :D 92.28.80.71 (talk) 09:54, 12 July 2010 (UTC)[reply]

You could try something like Eagle. It's not open source but it does work on more than just Windows (thought you might be on a Linux system). Dismas|^(talk) 10:30, 12 July 2010 (UTC)[reply]

I could understand circuits (like oscillators, timers, and light-sensing circuits (cover the photo cell and the streetlight turns on.)) when I was about 10 years old, but not 6 unless you have some very special training and high IQ. P.S. When I was around 10 or 11, I designed and built a circuit that would make noise if you left a door open. So much for Cyclonenim's understanding. --Chemicalinterest (talk) 10:56, 12 July 2010 (UTC)[reply]

Yeah - I think 6 years old would be a hell of a stretch. My father owned a TV repair shop and did aircraft radio and radar work on the side. I remember that he had me playing with flashlight bulbs, switches and batteries before I went to primary school - so that would be at about age 5 or 6. I had a reasonable understanding of series and parallel circuits and concepts like when you have the lights in series they don't glow as brightly - but there is no way I could have made the diagram that '92 drew. At age 8, I became fascinated with relays and I built a little game using relays and light bulbs. Each player had a button and a light bulb. When you turned the machine on, a large capacitor (scavenged from an old TV set) would charge up over several seconds, causing a relay to suddenly trip and turn on a third light marked "GO!" - then the two players had to push their buttons as fast as possible. The first person to do so lit up their light and prevented their opponent's light from turning on - so the person with the fastest reaction time won. The "GO" light discharged the capacitor, untripped the relays and started the whole machine running again. It took me weeks of fiddling around to get it all to work right - and it certainly involved a lot of trial and error because I didn't have the math to figure out capacitor time constants and such. My father kept the gizmo in his office in a plexiglass case with my photo in it for several decades. He brought it to show everyone at my wedding reception "as a warning for my wife" - and it was still working then. But sadly, I don't know what eventually became of it. SteveBaker (talk) 14:12, 12 July 2010 (UTC)[reply]

Is it normal? No. Do I think the person can't be six? No. There are six billion people on this world. At least one of them has to be smart enough to figure that sort of stuff out at age 6. I've heard of (extraordinarily smart) people doing algebra at 4. If I remember from physics, all you need is algebra to calculate how everything in your simple circuit should work. Falconus^{p t c} 15:22, 12 July 2010 (UTC)[reply]

What's wrong with you Westerners. My parents taught me serial v. parallel around the age of six. I became especially interested in electricity at tha age of 8 after I picked up a book about it, and constructed my own galvanic cells and electroplating devices. (Didn't really understand the Nernst equation at the time though...redox potentials at the age of 10). Now if I had been shown those books at a younger age, maybe I could have drawn circuit diagrams at the age of six. I remember drawing blueprints for an especially large castle (I still <3 castles) at the age of six for a school project, and that's much harder than drawing a circuit diagram. John Riemann Soong (talk) 16:18, 12 July 2010 (UTC)[reply]

Oh interest and motivation are such more important than intelligence at this age. To this day, the foundation of my science knowledge started with the Magic School Bus and books on science and technology I picked out of my elementary school library. They actually contain a lot of info, which will lead you to learn how to draw a circuit diagram. The teaching method of the teacher is more important than the ability of the student. When I was in third grade in AMERICA, our teacher had us build telegraph circuits.... we had to know how an electromagnet worked. How to prevent short circuits. Things like switches and path of least resistance. For a third grader, trying not to mix up the receiver and transmitter citcuits took some thinking.

Then, when we wanted to hook everyone one of us (all 23) into a single telegraph network, we had to think hard how to do it. To me that's harder than figuring out that current*potential difference = power. Okay our teacher helped us a little, but we were in fucking third grade. Don't insult the ability of grade school children. John Riemann Soong (talk) 16:28, 12 July 2010 (UTC)[reply]

Just because education doesn't teach it doesn't mean a child couldn't learn it at that age. We have the Internet nowadays, as well as other sources. For example, I learned the basic times table at age three. There are also plenty of recorded cases of extraordinary mathematical or scientific talent in young children. Some preteens and teenagers have even been shown to be able to perform calculations that regular adults fail to complete. Never underestimate nerd power (what, no article?!). ~A H 1^(TCU) 00:57, 13 July 2010 (UTC)[reply]

omniverse

Does the omniverse exist? —Preceding unsigned comment added by 220.253.104.38 (talk) 09:36, 12 July 2010 (UTC)[reply]

That rather depends on what you mean by "exist". As a self-consistent concept, it certainly exists in the same sense as the empty set, aleph null, democracy and Luke Skywalker exist. However, I don't think I would put it on the same plane of existence as the can of Diet Coke that I just drank, or the chair on which I am sitting. Gandalf61 (talk) 09:51, 12 July 2010 (UTC)[reply]

Maybe. We don't know. It's very likely that we cannot possibly know. The Many-worlds interpretation of quantum mechanics is (I believe) gaining traction as an explanation for some of the wierder things we observe here in our universe - but it is a smaller concept than the omniverse because it doesn't include universes where the laws of physics are different. However, we probably can't formulate an experiment to prove the existence of a multiverse either. But we've figured out some pretty weird stuff over the years - it's not impossible that we might some day know the answer. Mind you, the concept of the existence of a can of Diet Coke that you just drank is philosophically tricky too! SteveBaker (talk) 13:45, 12 July 2010 (UTC)[reply]

Indeed ! But maybe that Diet Coke still exists in some parallel universe in which I decided to have a coffee instead. Gandalf61 (talk) 13:53, 12 July 2010 (UTC)[reply]

Actually the many worlds interpretation would not include an omniverse. Many worlds only describes universes with the same physical laws. Also, the diet coke/coffee thing is incorrect. The many worlds only splits when there is a non-deterministic quantum event. Deterministic events do not split. And it's extremely rare for a quantum event to influence the macro world (unless the brain is a quantum device - which would be very interesting if true, but I have not heard anything like that). Ariel. (talk) 14:41, 12 July 2010 (UTC)[reply]

Roger Penrose believes there is an intimate connection between quantum physics and conciousness - see The Emperor's New Mind. One possible explanation of free will is that it is a manifestation of quantum wave-function collapse at a macroscopic level. On the other hand, maybe I don't have free will at all, in which case I drank Diet Coke in every possible universe, and my Diet Coke now has even less existence than I thought ! Gandalf61 (talk) 16:07, 12 July 2010 (UTC)[reply]

I believe it exists, simply because any formally describable structure can be simulated using a computer. In our own universe described by the Standard model Lagrangian, there will always be a finite probability for some civilization to do exactly the right kind of computer simulation that gives rise to virtual observers living in a universe described by any other Lagrangian. You can think of this other Lagrangian as an effective Lagrangian implemented by the computer. Count Iblis (talk) 14:18, 12 July 2010 (UTC)[reply]

Simulation hypothesis. SteveBaker (talk) 02:25, 13 July 2010 (UTC)[reply]

Where the hell is Metadata?

Why this time I get no Metadata?

Example of a photo which failed to fetch *metadata* Also example of an actual Nikon Coolpix L20 production

Jon Ascton (talk) 10:25, 12 July 2010 (UTC)[reply]

Some images have image metadata (data about the data), stored in a format like EXIF. And some don't. -- Finlay McWalter • Talk 10:33, 12 July 2010 (UTC)[reply]

I know that. All images taken by me have meta, this is the sole exception, why ?

Probably it was striped by whatever software you used to crop it. APL (talk) 15:35, 12 July 2010 (Utc)

When I change a photo, even just to crop it, the meta data is stripped by my software (Canon Zoom, in my case) as soon as I save the changed version.. Bielle (talk) 16:11, 12 July 2010 (UTC)[reply]

Usually to keep the metadata after editing, you'd have to upload the unedited version first to Wikipedia or Commons, then use an editing software that doesn't remove it and make the edit there. ~A H 1^(TCU) 00:51, 13 July 2010 (UTC)[reply]

Is it a Fraud, a Cheap marketing stunt?

Please look carefully at this site. They are telling us these pictures have been taken with a Nikon Coolpix L20, a point-and-shoot thing ! Is it possible, you can see an actual Nikon Coolpix shot (taken by myself in above question ) and make a comparison of quality. Jon Ascton (talk) 12:16, 12 July 2010 (UTC)[reply]

Looks fine to me. Quite a lot of photographic quality depends on the photographer's skill and his knowledge of his equipment; I'd say the equipment itself is a secondary concern at best. Alternately, why do you expect the photos weren't taken with the camera in question? — Lomn 13:42, 12 July 2010 (UTC)[reply]

What I say is that the pics on the link given above seem clearly taken with a digital SLR, ask any expert

It's been reduced to 400 pixels wide - I don't see how you could tell: take a look at http://commons.wikimedia.org/wiki/Category:Taken_with_Nikon_Coolpix_L20 178.78.64.206 (talk) 14:03, 12 July 2010 (UTC)[reply]

Probably what you're seeing is the lighting. Your photograph is horribly lit with the camera's built-in flash. The pictures on that web page are all using either natural sunlight or studio lighting.

Good quality lighting is a major factor in giving photos a "professional look". It is a major part of a photographer's art, but amateurs barely even consider it. It is far more important than the quality of the camera. APL (talk) 15:46, 12 July 2010 (UTC)[reply]

Is there a way to hack into the camera's firmware to allow you to manually set frameshutter speeds? John Riemann Soong (talk) 15:58, 12 July 2010 (UTC)[reply]

You can with several Canon cameras: [16] Regards, --—Cyclonenim

| Chat 17:21, 12 July 2010 (UTC)[reply]

ooh before I buy any Canons from eBay...which ones? John Riemann Soong (talk) 19:00, 12 July 2010 (UTC)\[reply]

List of cameras supporting a raw format, specifically the Cannon's saying that they require CHDK firmware. Basically, all of the Powershot models. I recently put it on my camera, and, while it's certainly useful for giving you more functionality with your camera, I'm not sure I'd describe it as "turning it into a super camera". The sensor's still the same size, and the lens doesn't change; those physical parameters are largely what limits the camera's picture taking ability. I'm also not sure what you mean by "frameshutter speeds". If you just mean Shutter speed, then most of the Powershots are capable of manually setting shutter speed anyway, thought eh CHDK may create a larger range of available shutter speeds. Buddy431 (talk) 20:26, 12 July 2010 (UTC)[reply]

Yep. If you could hack your camera and get great low-light shots photographers wouldn't be spending $1800 on a single lens. --mboverload @ 03:52, 13 July 2010 (UTC)[reply]

And having a large quantity of light makes it possible to take crisp pictures with small-sensor cameras (like a point-and-shoot). Indoors, it becomes necessary to lower the shutter speed (risking blur), raise the ISO (increasing graininess), or turn on the flash (which, with a point-and-shoot flash, will create garish highlights, and make everything look like it has a drop shadow). I have a point-and-shoot, and an aversion to flash, so I have a whole lot of blurry, grainy pictures. But they look good as thumbnails! Paul (Stansifer) 17:50, 12 July 2010 (UTC)[reply]

It's too bad they don't make the full-size originals available -- that would make it easy to tell. As is, the only indication that this is a small-sensor camera is the "indoors in poor light" portrait: the subject's hair displays the loss of detail typical of the noise-reduction algorithms used by these cameras. --Carnildo (talk) 01:01, 14 July 2010 (UTC)[reply]

For what it's worth, even at 400 pixels wide, you can see at least one major optical flaw: the Vignetting is terrible. Look especially at "outdoors 2" -- the corners are noticeably darker than the center. Personally, none of the SLR lenses I've owned have ever had vignetting this bad; I'd probably return the lens if it did. Certainly believable it's a point-and-shoot. 128.12.174.253 (talk) 07:28, 14 July 2010 (UTC)[reply]

Octopus eye

Can octopuses see colors? Thanks. --Mudupie (talk) 10:29, 12 July 2010 (UTC)[reply]

Octopus#sensation says that some can, and some can't. -- Finlay McWalter • Talk 10:32, 12 July 2010 (UTC)[reply]

It's more likely that they can see colours than that they can understand the strategy and tactics of a football team! Physchim62 (talk) 12:37, 12 July 2010 (UTC)[reply]

The evidence is that Paul is attracted to flags with horizontal stripes in them - and octupii are known for being attracted to horizontal lines from prior studies - so that's no surprise. Now all we have to explain is why countries that have lots of horizontal stripes in their national flags are better at soccer than those that don't (except the USA who are crap at soccer despite their obvious vexillological advantages). SteveBaker (talk) 13:37, 12 July 2010 (UTC)[reply]

Well then why did England only manage a tie? Googlemeister (talk) 16:08, 12 July 2010 (UTC)[reply]

Have you seen our flag? Please pay attention. SteveBaker (talk) 01:43, 13 July 2010 (UTC)[reply]

Maybe the Brits need to hire an octopus to play goal. Then when he goes down on one knee to try and stop a kick, he'll still have 7 arms left. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:10, 13 July 2010 (UTC)[reply]

But the US has won the last 44 football championships! And they play 33% more than the Canadians! — Lomn 13:45, 12 July 2010 (UTC)[reply]

That's not football, as it uses neither feet nor a proper ball. It's the girly version of Rugby. --Stephan Schulz (talk) 14:19, 12 July 2010 (UTC)[reply]

Outside of actual warfare, American football is likely the most brutal sport on earth. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:09, 13 July 2010 (UTC)[reply]

It's called football because it's played on foot rather than horseback. And historically soccer, or Association Football is the more correct British name. See: Names for association football. Football alone actually refers to Rugby (or used to anyway). Ariel. (talk) 14:47, 12 July 2010 (UTC)[reply]

New rule: no one is allowed to use the name "football" because it just leads to fighting. From now on we have soccer, rugby, and gridiron. The word "football" is banned. Also, none of those sports should be called girly by fans of any of the others. There—no more fighting, we can all be friends now. 24.68.50.170 (talk) 09:11, 13 July 2010 (UTC)[reply]

What should we call Aussie rules football and Canadian football? Googlemeister (talk) 12:59, 13 July 2010 (UTC)[reply]

We have an article on the Manly United Football Club. So, all that seems to be required is to find a suburb called Girly which is home to the Girly Rugby Team. --Cookatoo.ergo.ZooM (talk) 22:47, 13 July 2010 (UTC)[reply]

I don't understand the "Quantum" in Quantum Mechanics

Despite all the definitions I looked up, and all the explanations, I still don't understand Quantum. In the notes on the Intro to Quantum Mechanics, it states

"The word "quantum" comes from the Latin word for "how much" (as does "quantity"). Something that is "quantized", like the energy of Planck's harmonic oscillators, can only take specific values. For example, in most countries money is effectively quantized, with the "quantum of money" being the lowest-value coin in circulation. "Mechanics" is the branch of science that deals with the action of forces on objects, and so "quantum mechanics" is the form of mechanics that deals with objects for which particular properties are quantized. "

But I still don't understand. Why not call in Quantity Mechanics? What's the difference? 148.168.127.10 (talk) 16:44, 12 July 2010 (UTC)[reply]

Why do you say you don't understand it? A quantized thing can only take on certain values. Saying something has a "quantity" does not imply any such thing. Friday (talk) 16:53, 12 July 2010 (UTC)[reply]

Because I don't understand it! When you say certain values, what do you mean? If I have five apples, that's a quantity. If I were only allowed to have five apples, would that be quantum? 148.168.127.10 (talk) 17:09, 12 July 2010 (UTC)[reply]

If by some bizarre twist of physics, a person could only have 3 or 5 or 9 apples but not 4 or 6.5 or 12, we might say that the number of apples is quantized. And we might call this field Quantum Appleology or some silly thing like that. Friday (talk) 17:23, 12 July 2010 (UTC)[reply]

So when we say light is quantized, that means it can only be a certain frequency to eject an electron from a material right? But that's not true, that's the minimum frequency isn't it. It can be more. So if applies were quantized, then that means 5 apples would be the minimum I can have, but I can have more. Is this correct? 148.168.127.10 (talk) 17:32, 12 July 2010 (UTC)[reply]

No, Light is said to be quantized because it comes in a whole number of photons. A pulse of light can have one photon or one trillion photons, but it can not have one and a half photons.

This can seem obvious now, but since it's not observable on a human scale it was once very controversial. APL (talk) 18:12, 12 July 2010 (UTC)[reply]

So as long as the quantity is in whole numbers, then it's quantized? So it doesn't matter how many apples I have, if I can only have whole apples, then it's quantized? 148.168.127.10 (talk) 18:32, 12 July 2010 (UTC)[reply]

Pretty much. A quantity can either be 'continuous' or 'quantized'. "Quantized" could refer to quantities that are restricted to any 'discrete set', but in practice it's usually integers. The opposite is 'continuous' quantities which are not restricted to any particular set. APL (talk) 18:50, 12 July 2010 (UTC)[reply]

It's worth again stressing that it is contrast to continuous values. In the initial instances where it was applied — energy and light — that is a big deal. Energy and light come in little chunks. This is fairly counterintuitive if you deal with either of them. At the level in which quanta of energy or light actually matter, the physical laws get somewhat strange. This is why it has its own field of mechanics associated with it. --Mr.98 (talk) 18:58, 12 July 2010 (UTC)[reply]

What does discrete set mean? I heard it before, and I have an idea of what it means, but could you clarify? 148.168.127.10 (talk) 19:54, 12 July 2010 (UTC)[reply]

A set of points in a topological space is a discrete set if each of its points is isolated. Informally, for any point in the set, you can draw a small circle around it that contains no other points in the set. In the real number line (with the usual topology) the set of integers is a discrete set, but the set of rational numbers is not. Gandalf61 (talk) 13:01, 13 July 2010 (UTC)[reply]

I think the key here is the phrase "quantum of money being the lowest-value coin". Therefore, quantum mechanics deals with the smallest things: that thing which cannot become any smaller. That's the essence of quantum mechanics: mechanics which occur at the smallest size possible, if you like.--TammyMoet (talk) 17:19, 12 July 2010 (UTC)[reply]

I'm not sure I would put it like that. Molecular vibration is quantized for example, and an entire molecule is kind of "big". Friday (talk) 17:26, 12 July 2010 (UTC)[reply]

Historically, the term "quantum" comes from "quantized." It specifically was the name given to the lowest unit of energy, a definitional thing. "Quantum mechanics" refers to mechanics which takes place at or around the scale in which one cares about individual "quanta" of energy. If they had named it the "Quantong" or the "Kwantog" or the "Querty" or the "Energon" we'd call it a different name. The term "quantum" predates its usage for the lowest quantity of energy, mind you—it is a generic term for "something that has a quantity." It had been used in different contexts in physics as early as the 1870s, though it was its use in the term "light-quantum" in the early 20th century that gave it its more common meaning. --Mr.98 (talk) 18:53, 12 July 2010 (UTC)[reply]

Had Herr Planck bothered to ask, I would have suggested "discrete mechanics", since it gets the "quantized" idea across in common language, and it describes the world at a scale that is very "discreet". :) --Sean 20:09, 12 July 2010 (UTC)[reply]

Ja, but if Nature is discreet, how will we unravel her secrets, eh? --Mr.98 (talk) 20:56, 12 July 2010 (UTC)[reply]

This simple experiment was done just over 100 years ago and found how electric charges are quantised as whole multiples of the charge of the electron. Cuddlyable3 (talk) 20:54, 12 July 2010 (UTC)[reply]

Temperature Fluctuations at the Equator

I was doing an online quiz recently and one of the questions was "In which months is it hottest on the equator?" The answer given was March and September. Is that correct? Why would it be warmer at the equinoxes than at the solstices? Rojomoke (talk) 17:11, 12 July 2010 (UTC)[reply]

(Unless I've got this completely backwards...) The solstices are when the sun is the farthest North or South of the equator it could go (23 deg, corresponding to the Tropics of Cancer and Capricorn). The equinoxes are when the sun is directly over the equator. Of these two months, one of them will be when the earth is physically closer to the sun because of its elliptical orbit, so all other things being equal only one of these is "the" hottest months. Zunaid 18:12, 12 July 2010 (UTC)[reply]

The sun is closest to earth in December. Googlemeister (talk) 19:50, 12 July 2010 (UTC)[reply]

January, actually. --Sean 20:18, 12 July 2010 (UTC)[reply]

Note also that the hottest month tends to lag a bit behind the month of most direct sunlight, so I'd think April or October is more likely. But yes, at the equator, "hottest" should be tied to the equinoxes rather than the solstices. — Lomn 18:17, 12 July 2010 (UTC)[reply]

In the northern hemisphere, the hottest month is usually July while the coldest is usually January. So for the equator, ignoring apsis, the hottest months should be April and October, as stated above. ~A H 1^(TCU) 00:47, 13 July 2010 (UTC)[reply]

Insects repairing themselves

I have heard or read that insects (and maybe all arthropods) have little or no ability to repair damaged tissues, such that if you whack a flying housefly with your hand, even though you didn't squish it, the damage is sure to be mortal, as you have probably cracked its skin someplace. True? Comet Tuttle (talk) 17:37, 12 July 2010 (UTC)[reply]

Fascinating question. Well not all arthropods anyway : shrimp (and similar) for instance have the ability to heal - they molt their exoskeleton - and can grow back arms that have been bitten off. Don't know about insects.77.86.10.49 (talk) 18:36, 12 July 2010 (UTC)[reply]

A fascinating and delicious example of this is that you can break the claw from a live stone crab and then return it to the sea and it will just regrow a bigger one with little ill effect. --Sean 20:26, 12 July 2010 (UTC)[reply]

Here's a quote from a recent paper, PMID 15269788: "Over a half century ago, Wigglesworth demonstrated that the large hemipteran insect Rhodnius prolixus has a robust wound healing response (Wigglesworth 1937). He characterized the response by light microscopy and described the proliferation and spreading of epidermal cells and the accumulation of blood cells (hemocytes) at the wound site. Since this pioneering work, only a few follow-up studies have appeared (Lai-Fook 1966, 1968). There has been little work on other insects aside from a number of studies of wound healing during imaginal disc and leg regeneration (Reinhardt et al. 1977; Truby 1985; Bryant and Fraser 1988) and the recent discoveries that Drosophila embryos undergo a scarless wound healing process involving actin cable formation and filopodial extension (Kiehart et al. 2000; Wood et al. 2002) and that wounded adult cells activate the Jun N-terminal kinase (JNK) signaling pathway (Ramet et al. 2002; see below)."

Thank you, anonymous editor. Looks like what I heard was close to the opposite of true. Comet Tuttle (talk) 00:13, 13 July 2010 (UTC)[reply]

Oops, that was me. Looie496 (talk) 04:04, 13 July 2010 (UTC)[reply]

Insects to not experience inflammation, so the whole Wound healing cascade does not happen for them. Here's an article that is partially about that. I read a better one a while ago, but can't find it. Basically insects can repair some damage, but not as much as vertebrates. Ariel. (talk) 05:50, 13 July 2010 (UTC)[reply]

How about spiders? Can they actually regenerate their legs? Yaknow like when someone picks one up in a tissue to throw it outside and a leg comes off somehow and then comments 'Oh, it'll grow back - they can shed their legs to escape predators like lizards do with their tails'. Folk wisdom? --Kurt Shaped Box (talk) 06:14, 13 July 2010 (UTC)[reply]

They can regenerate legs when they moult, but it takes a couple of cycles to regenerate a full sized one. The legs don't directly grow back like in a lizard or starfish though. Also, I can't find any mention of this in wikipedia. Not under Moult, and not in Regeneration (biology) Ariel. (talk) 06:55, 13 July 2010 (UTC)[reply]

I have heard of lizards regrowing tails, but did not know they could regrow legs. Neat! Googlemeister (talk) 12:58, 13 July 2010 (UTC)[reply]

Erm, uh. Sorry, that not what I meant. Lizards don't regenerate legs, just tails (but see [17]) - salamanders can though. Thanks for catching that. I should have written: The legs don't directly grow back like how a lizard or starfish can regenerate certain limbs. Ariel. (talk) 13:25, 13 July 2010 (UTC)[reply]

harnessing infinite?

Okay so I've been reading a lot about this stuff, searching for the answer to this question but nothing seems to address it. Pretend I'm five years old, please.

I understand that black holes are not only possible but extremely evident that they exist. But there's a mathematical freak out when you get to the center of the black hole called the singularity. Apparently this singularity thing drives scientists crazy cause we don't have any form of logic to explain what's going on, mathematical or otherwise, and to add insult to injury they keep finding more and more of these things.

Using the same logic that got them to black holes, scientist figure there could be a thing opposite of a black hole, coincidently called the white hole, which holds the same singularity as its sister. This one's weird because although it is indeed POSSIBLE scientist agree its not really likely to happen in nature.

I went on to learn that worm holes are actually a product of a pair of a black hole and a white hole. So, as long as you can survive the singularity (which you can't) you can go THROUGH the black hole and come out of the white hole.

This got me thinking (Thinking! I know. Dangerous, right?)

So, all these wise guys say that white holes are entirely possible, but they don't occur in nature. Well! I mean, coca-cola doesn't happen in nature but we make it anyways, right? And after the scare with the particle accelerator and the possibility of it sparking a black hole, I was all like, "Crap! We can MAKE them??" So, okay, if we can make a black hole can't the same be true for the white ones? Like if we were some how able to make some gadget that will stop just before the singularity, is it possible for this same gadget to have a function in which it reverses what the singularity does and create a white hole from a black one?

After having posed that question to myself, I considered the consequences of such a feat. Imagine a weapon of infinite energy or a fuel plant with the same infinite energy.

Also, while reading about this stuff, I found that Relativity suggests that once inside the event horizon time and space switch roles in that the path you are going in is inescapable like trying to avoid next Thursday. But they never addressed the properties of TIME inside the event horizon. So again, I dealt with the dangers of thinking and thought, "Hey! Wait a minute!" Can a guy with a time machine INSIDE the event horizon escape the black hole? —Preceding unsigned comment added by 65.3.131.144 (talk) 18:10, 12 July 2010 (UTC)[reply]

TLDR. If you want a proper answer ask a straight-up question; don't tell a long rambling story. Short answer: NO. Long answer: anything is possible in science fiction; if we were to consider such technology as causality-violating time machines to be possible then certainly gadgets that stop "just short of the singularity" and "turn black holes into white holes" can also be imagined. And no, black holes don't contain inifinite energy because they don't contain infinite mass. Zunaid 18:23, 12 July 2010 (UTC)[reply]

"TLDR" is rude as hell. The OP did break it up into paragraphs but they didn't get the formatting right so it wasn't clear. If it is too long for you to read and take seriously, just don't read it. Nobody is forcing you to. --Mr.98 (talk) 18:49, 12 July 2010 (UTC)[reply]

It's important to keep in mind that the workings of the singularity are somewhat mysterious. The "mathematical freak out" you mention is, as I understand it, considered by most to be an assertion that the current theory must be wrong (or, more likely, incomplete) in some way. As for whether we can make things that don't occur in nature, in principle, yes, indeed we can. (For example, a nuclear fission explosion can basically not occur in nature, at all, even though the principles on which it is based are utterly natural.) But in the case of black holes/white holes, I don't know enough of the details. If you introduce time travel, I think you end up going outside of the realm of what science can say. It would depend entirely on the assumption of the nature of the time travel if one was to make any sense of how it might hypothetically operate inside of a black hole. --Mr.98 (talk) 18:49, 12 July 2010 (UTC)[reply]

When modeling black holes in general relativity there is a singularity, meaning a place where general relativity breaks down and can't make predictions. That doesn't drive physicists crazy, it just means that we don't know (yet) what would be there. This is normal in science; there are always things that we don't know. White holes are not a source of infinite energy–they would have a finite mass/energy. It's not clear what difference there would be between a black hole and a white hole in a quantum gravity theory. In general relativity, black holes can be created but not destroyed, while white holes can be destroyed but not created. In quantum gravity, though, it appears that "black" holes evaporate after being created, which destroys them. There may be no distinction between black and white holes in reality. -- BenRG (talk) 19:26, 12 July 2010 (UTC)[reply]

The thing about the singularity at the center of a black hole is that it's safely cloaked by the event horizon. We can't know (much) about what goes on inside the event horizon - basically we know the mass, the amount of spin and the electrical charge on the black hole. So we can't ever actually know what happens inside. Maybe some unknown force at super-small distances stops the decline into a true singularity? Maybe temporal distortions inside the black hole mean that it can never actually reach that infinitely small dot - or that it'll take an infinite amount of time to actually get there. The actual result doesn't matter in any practical terms - the event horizon guarantees that nothing inside the hole can affect us out here (except for the mass, charge and spin which are all independent of whether there is an actual singularity or not). SteveBaker (talk) 22:10, 12 July 2010 (UTC)[reply]

I can't believe that no one's linked to the awesome cosmic censorship hypothesis yet. Sometimes, I think that physics gets all the fun stuff. Paul (Stansifer) 03:22, 13 July 2010 (UTC)[reply]

Moreover, from the point of view of an outside observer it takes an infinite amount of time for anything to fall into the black hole (In other words, nothing ever really falls into a black hole), So sendding a gadget down the whole to change its nature is not feasible. Dauto (talk) 12:27, 13 July 2010 (UTC)[reply]

Rorschach test in job interviews

On Talk:Rorschach test/disclosure, someone made the claim that the Rorschach test is used in "job enterviews." What kind of a job would include a Rorschach test as part of its interview? The Hero of This Nation (talk) 18:13, 12 July 2010 (UTC)[reply]

I don't know about Rorschach in particular, but there are jobs which require psychological evaluations involved. Even quite menial jobs often have "personality assessment" as part of the application/interview process (I worked retail once for a major chain and they required me to do a multiple-choice psych form, I guess to make sure I wouldn't steal or something... it was fairly hogwash). Jobs that have high security components (like working at a nuclear power plant) probably require more in-depth evaluations. Again, I don't know about Rorschach tests specifically, but that is where I would be looking for more information. Of course, the specifics of the interview process for such jobs are likely not disclosed widely, as knowing ahead of time how they worked would probably jeopardize the purpose of such a test. --Mr.98 (talk) 18:39, 12 July 2010 (UTC)[reply]

For jobs that include psychological tests as part of the screening process, are the tests administered by trained psychologists? Is psychological testing regulated (in the U.S. or elsewhere) to ensure that only qualified people administer such tests? The Hero of This Nation (talk) 15:41, 13 July 2010 (UTC)[reply]

1) Possibly, 2) No. Psychological treatment i.e, psychiatry is regulated but tests used by employers are often called "personality tests" which are unregulated. DISCUS[18] is an example I encountered that consists of a PC program that puts multiple-choice questions on screen and spits out a report about what kind of job the testee is fit for. It seems the company qualifies anyone who buys their program by a short course (I have pages from the course and they are psychobabble.) There was a move by a Norwegian standards organisation to certify personality tests that ruled out DISCUS as undocumented. Cuddlyable3 (talk) 20:23, 13 July 2010 (UTC)[reply]

Is anyone here a doctor

Is anyone here a doctor? I'm sorry but not being or related to any real doctors most of what I know about the internal workings of the medical profession comes from medical TV shows ;) IN shows like House or General Hospital or Scrubs, etc., etc., the only clear division between what a doctor can and cannot do is whether they specialise in afiield of surgery or medicine. Other than that it seems an immunologist can be an emergency room doctor, a plastic surgeon can be a ("real") sergeon and a doctor of any specialty can be a GP. Is this correct? thanks —Preceding unsigned comment added by 68.76.146.113 (talk) 18:23, 12 July 2010 (UTC)[reply]

At least in the United States and the UK that's not the case. In the US one must be board certified, which is a test that one meets the standards for a specialty. Someone with that certification can function as that specialist (outwith the tutelage of a certified specialist). Template:Medical specialties boards lists many of the specific boards that certify specialists for different areas. That doesn't list general practice (is that what "family practice" means?). General practice is a specialty in the UK at least - details are here. -- Finlay McWalter • Talk 18:42, 12 July 2010 (UTC)[reply]

I'm going to call ^{[citation needed]} on Finlay McWalter's phrase "In the US one must be board certified". I don't think this is a must. There are plenty of pediatricians, for example, who are not board certified, and plenty who are. Comet Tuttle (talk) 20:42, 12 July 2010 (UTC)[reply]

(edit conflict)I'm fairly sure you're wrong on that. Board certification exists to certify particular specialties, but in the U.S. there is no legal requirement that you be board certified to practice in a particular field. A plastic surgeon could legally change professions to neurosurgeon without any additional training or certification. Granted, malpractice insurance rates would skyrocket, and you'd probably have to set up your own practice (since most hospitals would reject that sort of career move), but an M.D. is legally allowed to practice in any field of medicine. —ShadowRanger ^(talk|stalk) 20:44, 12 July 2010 (UTC)[reply]

In addition to denial of payment by many insurers, denial of admitting privileges by many hospitals, and denial of coverage by insurers, there are prohibitions against misrepresenting one's credentials, such that if a plastic surgeon said, "I am a neurosurgeon" (particularly in print or other durable material), then a variety of sanctions could be invited, both legal (fraud?) and professional (e.g. sanction by the physician's board in that state). It is true that a person trained as a plastic surgeon could practice neurosurgery - but only if the patient is foolish enough to sign up for a person who doesn't even profess the requisite credentials. -- Scray (talk) 03:22, 13 July 2010 (UTC)[reply]

This section on GPs in the U.S. is pretty clear, and relevant to some of the comments above - the training of GPs in the UK is much more formalized than it has been in the U.S.; in contrast, Family Practice is a clearly-defined specialty. -- Scray (talk) 03:29, 13 July 2010 (UTC)[reply]

Also, in the U.S. a physician might complete a residency and be board-certified in Internal medicine, then pursue fellowship and sub-specialty board certification in nephrology. These certifications are through the ABIM. At one time, these certifications were lifelong, but around 1990 the system for renewal of certification was instituted, requiring testing and completion of training modules every 10 years (both in the specialty and in the sub-specialty) in order to represent one self as a specialist (or sub-specialist) in the respective discipline. It is not enough to know whether the doctors has been certified, one needs to know whether they are certified (though the importance of this might be secondary in some situations where practitioners are not numerous). -- Scray (talk) 03:37, 13 July 2010 (UTC)[reply]

I wouldnt take the TV Shows very seriously. Real life "doctoring" is much more interesting and rewarding than TV shows( Im speaking personally here). And it isnt so dramatic, we dont cry or fight at the drop of a hat and we literally dont sit and hold hands with every single patient, either. As a specialist in Emergency and Trauma Care, I see my share of busy whirlwind days and very quiet peaceful days - today is one such day;)) About your question as to how an immunologist can treat a patient in the ER or how a plastic surgeon can give GP advice, ofcourse we do it. And no one gets arrested or thrown in jail for that. Im authorised to see a walk in OPD patient ( If Im on OPD duty on that day) who might be suffering from a medical condition or surgical condition which doesnt relate directly to my specialisation. But in these days of heightened judicial activism and lawyers and patients waiting to pounce on a doctor for any small slip, normally doctors have become wary and play it safe. It ultimately boils down to what you personally choose. Medicine is an ocean and an art, a good surgeon can also be a good physican and a good gynecologist. Even though you choose to specialise in one particular field, you have to go through a vigorous rotating internship where you have to work in dirrerent wards, psychiatry, oncology, dematology and path labs and so on. So any doctor who takes his work seriously would definitely know much more than the mere basics of other specialities too. This is what they show in TV soaps albeit in a dramtic way. Usually doctors wouldnt go beyond their specilisation and give unwanted advice in other specialities only because there wudnt be much spare time to indulge in such luxuries. A specilist is always tied up with his/ her commitments and would only give advice if a specific request emanates from a friend/ another specialist. ( what we call internal referral). Another glaring error in TV "doctor" shows is that, they show doctors mixing their personal and professional lifes. In most cases, this isnt true. Even the best looking ( and most sought after) doctor would rather experiment outside his work environs. We do have patients who try and hit on us. We mostly ignore it with a smile. After all we are also responsible "thinking" humans who have loving families back home and unlike TV shows people dont drop their trousers at the drop of a hat.Fragrantforever 04:58, 13 July 2010 (UTC)

Dentistry works the same way -- specialty boards are basically a prank for specialty organizations to collect money. It's a cheap (er, expensive) trick that specialists use when they promote themselves as 'board-certified.' DRosenbach ^{(Talk | Contribs)} 03:00, 14 July 2010 (UTC)[reply]

My water heater

Referring back to [19], I finally looked and found it is a State 510E. No web address, of course, since the concept didn't exist yet.Vchimpanzee · talk · contributions · 19:36, 12 July 2010 (UTC)[reply]

If you simply google 'state 510e water heater' (without quotes), the first several hits include forums discussing the appliance, in which you may find useful information. 87.81.230.195 (talk) 22:54, 12 July 2010 (UTC)[reply]

July 13

The bends and pressure

When somebody enters an area with higher of lower pressure, does the pressure inside her/his body change as well? 74.15.137.192 (talk) 03:01, 13 July 2010 (UTC)[reply]

Unless this is a trick question, i think the answer would obviously be yes. That's why you don't cave in or blow apart, up to a point. It's when you can no longer equalize the pressure with your environment that one of those two things might happen. Vespine (talk) 05:10, 13 July 2010 (UTC)[reply]

This subject is complicated, so if you want more details please ask. The pressure changes somewhat. In a liquid and a solid pressure has little effect, but in a gas pressure presses the atoms closer together. Note: this is only an approximation. So if a person goes into an area of lower pressure nothing much happens to the liquid that makes up the body. Officially the pressure is lower, but practically speaking there is no change. Except for the air in the lungs - but that air equalizes with the air outside. There is one caveat, at lower pressure liquids boil easier (vapor pressure). So in a low pressure environment the liquid might try to boil. When a liquid boils the pressure goes up, which will try to stretch the blood vessels (for example). But the blood vessels refuse to stretch (somewhat), which will result in a higher pressure inside the blood vessels than in the air outside. Which is why I said somewhat - the pressure is lower, except if it's low enough to cause water to boil, in which case the body will prevent it, and will end up with a higher pressure than outside. Another change with pressure is gas solubility. Gases dissolve in water (like seltzer), the higher the pressure, the more they dissolve. Going from regular pressure to vacuum, there is little change. But at high pressure a lot of gas might be dissolved in the blood. If a person goes to an area of lower pressure, that gas will come out, and it's too much pressure for the blood vessels to prevent. Ariel. (talk) 06:09, 13 July 2010 (UTC)[reply]

iPhone 4 antenna

So it's largely confirmed that bridging the lower left gap on the new iPhone reduces the cellular signal strength by around 20db, but as an electronics engineering student 20db seems to be a lot to me, especially after spending a lot of work building a 12dbi UHF antenna. Will changing the geometry of the antenna really cause such a substantial drop in antenna gain, or is there another reason behind it (interaction with the human body/ with WiFi)? --antilived^{T | C | G} 03:25, 13 July 2010 (UTC)[reply]

[20] and [21] (see all blog entries)--mboverload @ 03:55, 13 July 2010 (UTC)[reply]

Yes I already know that the antenna gets detuned due to the hand bridging the gap, but I'm wondering will a detuned antenna really drop the signal by 20dB (that's a 100-fold reduction in RF power), or is there some other factor too? --antilived^{T | C | G} 04:20, 13 July 2010 (UTC)[reply]

The iPhone4's antenna wraps around the case with a small gap. When you bridge the gap, you're effectively shorting out the antenna completely. If you have one, then at this point, your best bet is probably to buy a soft case for the phone. SteveBaker (talk) 14:43, 14 July 2010 (UTC)[reply]

Electrophoresis

Hi, A while ago an idea occurred to me about separating ions in an aqueous solution, but I wasn't sure if it would work or what would happen and haven't found much information since then either so I thought I'd ask here. Basically what I was thinking was, if you had a ionic solution - say salt water - and if you applied an electric field, then the +ve ions would move in the direction of the field and the -ve ions would move opposite to the field, until that movement created an equal and opposite field. So in the brine, if put two parallel metal plates on either side of the solution (insulated from it of course) and applied a voltage across them, then the Na and Cl ions would move slightly towards -ve and +ve plates respectively. Now if you put a solid partition down the middle of the set up and removed the field, you'd have a one solution with a slight excess of sodium ions and a another with a slight excess of chlorine ions.

My questions are: would it work at all? And if so, what would the properties of the created solutions be? After looking up on google and wikipedia I eventually found "electrophoresis" which seems to be what I'm thinking about, and seems to indicate that it would work; but beyond that, I can't find any more useful info - mostly just stuff about seperating DNA and whatnot, leaving my second question unanswered. The kind of stuff I'm wondering is, for example, what would happen if you tried to evaporate the water? Would the ions evaporate too? Or what if you dipped a positively charged plate into the solution with excess chlorine? Would the excess ionic chlorine then lose electrons and turn into chlorine gas??

202.37.61.14 (talk) 03:48, 13 July 2010 (UTC)[reply]

Are you certain they would actually move? Because water is also ionic, and the H and OH groups should also separate, but obviously they don't. I think you need energy input to separate the ions, an electric field is not enough (unless you were somehow taking energy from it, in which case it would do the same as electrolysis). Ariel. (talk) 06:36, 13 July 2010 (UTC)[reply]

I wouldn't bet money that they would move, but I can't see why they wouldn't - the energy input would come from the transient (displacement) current that would flow when you introduce the field, in the same way as energy is stored in a capacitor even though, once you've charged it, no current flows and no energy is transferred. As for the water, I suppose it would also move, but I'm assuming that it would only rotate, with most of the movement happening with the ions (since I guess it'd take less energy to move the ions than break the covalent bonds of the water, in same as that when you perform the electrolysis of brine it's the salt rather than the water that comes apart). 202.37.61.14 (talk) 07:29, 13 July 2010 (UTC)[reply]

If you pass a current through the cell rather than just apply an electric field, you end up with a brine cell used in the chloralkali process. This makes sodium hydroxide and chlorine gas. Brammers (talk/c) 07:37, 13 July 2010 (UTC)[reply]

Yeah, I know, but I wasn't talking about electrolysis; in fact the whole notion entered my head when I wondered what would happen if you could avoid the oxidation and reduction that happens in electrolysis. 202.37.61.14 (talk) 10:26, 13 July 2010 (UTC)[reply]

202.37 is correct as far as what we're describing here is, effectively, a capacitor, with an (insulated) bag of saltwater acting as the dielectric between the plates. Now, what happens when you apply an electric field across our bag of saltwater? The saltwater solution will become polarized, arranging itself (as the original question notes) opposite the appplied field. How does that come about? There are a few possibilities. 1) The sodium and chloride ions can migrate to generate a charge gradient across the solution. 2) The water molecules can ionize, generate a large pool of free hydrogen/hydronium and hydroxide ions which can migrate. (The very small population of these ions naturally present near neutral pH is also able to migrate.) 3) The water molecules orient themselves so that their existing dipoles align. 4) The molecules in solution become individually polarized — induced dipoles are generated by distortions to each molecule's (or atom's) electron cloud.

In practice, (4) is a very fast process, and (3) is quite quick too. (1) requires movement of ions over distances which are large (for molecules) and would be rather slow. I suspect it also has a heavy entropy penalty, and so is thermodynamically less favorable. (2) requires ionization of water and is probably quite energetically costly — so also unlikely to make a significant contribution unless the 'cheaper' processes have been exhausted. While I haven't done the math, my gut instinct here is that induced dipole formation and dipole orientation will be responsible for the vast majority of the polarization of the sample, and you won't see significant ion migration and separation until you get very close to the breakdown voltage of the dielectric. TenOfAllTrades(talk) 13:45, 13 July 2010 (UTC)[reply]

A very tiny amount of charge separation will prolly occur. This is because separating as much as 0.000000000000001 mol of Na+ and Cl- (probably smaller) over that distance will result in a HUMONGOUS field that will cancel out the previous field.

Now, that sort of charge separation is so unstable, so with lots of mutual Na+ repulsion and mutual Cl- repulsion, Na+ stops becoming an inert counterion and becomes Lewis acidic, generating a proton gradient, which will travel over to the chloride-dense side. Meanwhile at that density, the chloride ions will actually start to become basic. Part of this is due to Coulombic forces, part of this is due to the entropy considerations (so much charge separation ==> lots of water ordering). You'll end up making HCl and NaOH, or possibly NaOH, Cl2 and H2.

Bear in mind when you separate DNA, you aren't just moving the negative part of the DNA... the counterions travel with them. John Riemann Soong (talk) 15:11, 13 July 2010 (UTC)[reply]

help

I am creating a page on my school from where I graduated 3 years ago. I have all the required data needed but do not have a website of reference since the school itself does not have one. Can I still continue with my article?— Preceding unsigned comment added by Nepalsk (talk • contribs)

The best place for this question would be at the Help Desk. They answer questions about how to edit Wikipedia there. This is the Reference Desk where we answer questions about things outside of Wikipedia. Dismas|^(talk) 05:48, 13 July 2010 (UTC)[reply]

Have a read of Creating a new page. There are thousands of schools in the world, do they all really need a encyclopedia article about them? If the school in question doesn't have a website, and you are struggling to find any references, it could be that the school is simply not notable enough to warrant its own article. Why should the school have a page? Don't take it personally but if the only answer you can think of is because you graduated from it, I'm not sure that's a valid enough reason. Vespine (talk) 05:52, 13 July 2010 (UTC)[reply]

If you were in the UK, you'd be able to find Ofsted reports on the school online, as well as potential menions in local history books if it's been around a while. Is there an equivalent of Ofsted reports available in the country in question? That would ensure at least some sources. 86.164.57.20 (talk) 14:00, 13 July 2010 (UTC)[reply]

You should read our guideline: Wikipedia:Notability (high schools) which lays out the rules for writing articles about schools - and contrary to what User:Vespine said, we do generally accept articles about high schools without being too concerned about notability. SteveBaker (talk) 14:39, 14 July 2010 (UTC)[reply]

Is HGH a precursor to testosterone?

My friend says HGH is a precursor to testosterone. I did a search online and I can't find anyplace that says that. Is it? —Preceding unsigned comment added by 76.169.33.234 (talk) 06:18, 13 July 2010 (UTC)[reply]

It doesn't seem to be. The picture I linked shows that it starts from cholesterol. The article on HGH does mention that the production of HGH is stimulated by androgens (like testosterone), but not the reverse. Ariel. (talk) 06:31, 13 July 2010 (UTC)[reply]

No, HGH is not a precursor to testosterone. HGH is a polypeptide (well, actually a group of related polypeptides). Testosterone is a steroid, derived from cholesterol. Axl ¤ [Talk] 10:22, 13 July 2010 (UTC)[reply]

Can you 'boil' heat water by compressing it?

A gas heats up when compressed. I assume the same happens with a liquid. Now I know water is hardly compressible, so a huge lever would be needed, so to say, but it seems to me that that should be possible. But how far can you heat it up? What happens when it gets to the boiling point? It can't boil in the normal sense because it can't evaporate. This article says it forms a solid at 100 C (= 212 F). But is this practically feasible, with relatively everyday materials? What sorts of pressures would be involved? Several articles I found mention 'diamond anvil cell techniques', but how far could this be taken with a normal strong container, say a diving cylinder? DirkvdM (talk) 08:26, 13 July 2010 (UTC)[reply]

Have you come across a kitchen appliance called a pressure cooker? It cooks food in water in a heated sealed "cooker", taking advantage of the fact that the pressure of the steam raises the boiling point of the water. HiLo48 (talk) 09:00, 13 July 2010 (UTC)[reply]

On a side note, I can remember going to a science museum when I was a child, where they had a demonstration of the changing boiling point of liquids with pressure, in which a glass of water was sealed inside a chamber and an hydraulic system was rigged up so that when you pulled a knob the pressure in the chamber dropped dramatically, causing the water boil; so the opposite is certainly true - you can boil water by decompressing it, so to speak. 202.37.61.14 (talk) 10:14, 13 July 2010 (UTC)[reply]

(After edit conflict with Dr Dima below)

Yeah, I thoght about those two, but they're fundamentally different.

In a pressure cooker the pressure is the result of the heat. What I want is the reverse, produce heat as a result of pressure.
The goal is not to boil (evaporate) the water, but to heat it up. My mistake, I shouldn't have used the word 'boil'. Which is why I changed it into 'heat'.

But what I really want to know is if this can be done 'at home', or at least with simple materials, outside a laboratory environment and certainly not using diamonds. DirkvdM (talk) 10:49, 13 July 2010 (UTC)[reply]

Thermodynamics is not all intuitive. This is a great example. You can bring liquids to "boil" (I'll explain the quotes in a minute) both by compression and by expansion. -- 1 -- . Let us first consider expansion. Expansion is easy: drop the pressure below the vapor pressure for the given temperature of the liquid, and the liquid will start to boil. This is what 202.37.61.14 just described. If you keep pressure and temperature constant, the liquid will all boil out. If you do not keep temperature constant (do not provide heat source) but keep the pressure constant, the liquid will cool as it boils, and eventually stop boiling. This will happen when the vapor pressure -- as a function of temperature -- drops enough to match the value of the pressure that you maintain. If the pressure is maintained below the solid-liquid-gas triple-point pressure, the liquid will turn into mixture of solid (ice) and gas (vapor). -- 2 -- . Let us now consider compression. Compression is more tricky. As the OP said, liquid is heated when compressed. When the heat can escape, the compressed liquid will eventually turn into solid. However, when the heat produced has nowhere to escape, you end up raising both the temperature of the liquid (that is, the vapor pressure) and the boiling point (that is, the vapor pressure needed for the vapor bubbles to form). This competition is decided by a number of factors. The most important one is how you compress. If you compress gently (isentropically), the heating is weaker than when you compress violently (by a shock wave). I do not know if you can produce a liquid-gas mixture by sending a shock wave through water (no rarefaction, just shock); but you can definitely bring the water above the liquid-gas critical point. Above the critical point you cannot tell the liquid from the gas, so "boiling" has no meaning. If you allow the liquid to isentropically expand after the shock and to return to the original pressure, its temperature will end up higher than the initial one, and it may well boil. Finally, an extremely strong shock will turn liquid into plasma, which is essentially an extremely hot gas (so hot that some or all electrons leave the atoms and become free). So yes, you can turn the liquid into gas by either expanding it or compressing it; but you need to know how to compress or how to expand. --Dr Dima (talk) 10:29, 13 July 2010 (UTC)[reply]

Ah yes, I should have also mentioned that the heat is not allowed to escape (although that is somewhat inherent to the question), so a diving cylinder is inside a thermos flask, so to say.

And again, apologies about the use of the word 'boil', because that is not what I'm after. (Note, though, that I also put it between quotes, for just that reason). I want a rise in temperature, but by a considerable amount, not just a few degrees.

What I was thinking about is a gradual build-up of the pressure. But as I understand your last bit (which I don't fully), that is really about a shock wave. I was thinking more about something like cranking up the pressure by hand, with a lever.

Also, I was assuming there is no air in the container, just water. However, a small amount of air would be unavoidable in practise, and since that is (relatively) highly compressible, it would affect the process considerably, I suppose. But wouldn't it at some point be 'absorbed' by the water? So here's an added question. How much would all this be affected by any air in the container? DirkvdM (talk) 10:49, 13 July 2010 (UTC)[reply]

For not too large pressures, you can calculate this using the heat capacity and the coefficient of thermal expansion as follows. Since in this process no heat is exchanged with the environment, the entropy stays constant (assuming you compress it slowly). The differential of the entropy in terms of dT and dP can always be formally expressed as:

dS=\left({\frac {\partial S}{\partial T}}\right)_{P}dT+\left({\frac {\partial S}{\partial P}}\right)_{T}dP\,

If we put dS = 0 and solve for the ratio dT/dP, you get the partial derivative (dT/dP)_S which tells you by how much the temperature will rise per unit pressure increase. However, using the above expression, you will get an expression involving the entropy. The coefficient of dT can be expressed in terms of the heat capacity a constant pressure:

\left({\frac {\partial S}{\partial T}}\right)_{P}={\frac {C_{P}}{T}}

To simplify the other coefficient, consider the fundamental thermodynamic relation

dE=TdS-PdV

You can read this as T being the partial derivative of E w.r.t. S at constant V and minus P being the partial derivative of E w.r.t. V at constant S. The second derivative of E w.r.t. S and V can be evaluated by differentiating w.r.t. S at constant V first and then by differentiating w.r.t. V at constant S, or the other way around. The equality of the two ways of evaluating the second derivative yields that the derivative of T w.r.t. V at constant S is the same as the minus the derivative of P w.r.t. S at constant V.

Now, we want an identity involving the derivative of S w.r.t P at constant T. We can find that by partially integrating both terms in the fundamtal thermodynamic relation

dE=TdS-PdV=d(TS)-SdT-d(PV)+VdP

So, we have

dG=-SdT+VdP

where G = E - T S + P V is the Gibbs free energy.

And then the symmetry of the second derivatives of G yields that

\left({\frac {\partial S}{\partial P}}\right)_{T}=-\left({\frac {\partial V}{\partial T}}\right)_{P}

We can thus express this in terms of the thermal expansion coefficient

$\alpha ={\frac {1}{V}}\left({\frac {\partial V}{\partial T}}\right)_{P}$

Putting everything together, you find that

$\left({\frac {\partial T}{\partial P}}\right)_{S}={\frac {VT\alpha }{C_{P}}}={\frac {T\alpha }{\rho c_{P}}}$

where lowercase c_P is the specific heat capacity per unit mass and rho is the density.

Count Iblis (talk) 15:26, 13 July 2010 (UTC)[reply]

At 25 °C and 1 bar, you find that this is approximately 1.48 *10^(-3) K/bar. So, you can see that you need to raise the pressure to thousands of bars to get just a few degrees of temperature increase. You can't then use the above linear formual anymore, of course, as the density and expansion coefficients will change. But it is still a good order of magnitude estimate. Count Iblis (talk) 16:03, 13 July 2010 (UTC)[reply]

Ah, thanks. I don't follow most of your first post (largely because I don't know what the symbols stand for), but the linear equation at 25 C is within my grasp. :) To increase the temperature just one C (or K), to 26 C, would require about 700 bar. That's 70 million Pa. Which is 70 million kg/m*s². For 1 l = 1 kg of water that would mean .... excuse my continued ignorance, but how do I translate this into energy? And does that become more or less as the pressure and temperature increase? The density barely changes, and I assume there is hardly any thermal expansion and I further assume the two are inversely related. Or something. That's about as far as I get. Help! DirkvdM (talk) 17:23, 13 July 2010 (UTC)[reply]

You can use the fundamental thermodynamic relation

dE = T dS - P dV

and use that dS = 0. Put differently, because this is an adiabatic process, the work done on the system is the change in internal energy. It is convenient to express dV in terms of dP and dS:

dV=\left({\frac {\partial V}{\partial S}}\right)_{P}dS+\left({\frac {\partial V}{\partial P}}\right)_{S}dP

If you substitute this in the fundamental thermodynamic relation and then put dS = 0, you find that the energy change is:

dE_{\text{adiabatic}}=-P\left({\frac {\partial V}{\partial P}}\right)_{S}dP=PV\beta _{S}dP

where

\beta _{S}

is the isentropic compressibility. Now this can be expressed in terms of the isothermal compressibility and the heat capacity ratio, as derived in the article relations between heat capacities:

\beta _{S}=\beta _{T}{\frac {c_{V}}{c_{P}}}\,

You can easily find the isothermal compressibility in tables. As explained in the same article, the specific heat capacity at constant volume can be expressed as:

c_{V}=c_{P}-{\frac {\alpha ^{2}T}{\rho \beta _{T}}}

So, we have:

\beta _{S}=\beta _{T}-{\frac {\alpha ^{2}T}{\rho c_{P}}}\,

All the quantities in this equation can be easily found. If we approximate things by assuming that

\beta _{S}

stays constant as the pressure is increased (this should not be too bad an approximation), then integrating the equation for dE_{adiabatic} gives for the energy increase per unit mass:

\Delta E_{\text{adiabatic}}={\frac {\beta _{S}\Delta \left(P^{2}\right)}{2\rho }}

So, it is proportional to the change in the square of the pressure. But you can compute things precisely by doing a numerical integration using tabulated values for the thermal expansion coeffcient, the isothermal compressibility and the density, if you also consider the equation for the temperature change derived above.

Count Iblis (talk) 03:18, 14 July 2010 (UTC)[reply]

With only my half forgotten secondary school physics and math, I'm hanging on by my fingernails here. :) In the first equation, the change in energy, which is the energy one has to put in, is related to T, P and V, being temperature, pressure and volume, and S, which I now understand stands for mass, which indeed does not change, so dS=0. So in the second equation the first part after the equal-sign is 0, so it says the acutal change in volume is the change in volume per change in pressure times the actual change in pressure. That makes sense to me. But after that, I don't follow.

So let me skip to the final formula. Rho is density, which is mass per volume. For water, that is 1 kg/m³.

\beta _{S}

is the isentropic compressibility. The compressibility article mentions this for water at 25 C (although I don't know if that's isentropic - I barely even know what that means): 4,6 * 10^-10 m²/N = 4,6 * 10^-10 m*s²/kg. For 1 C temperature change we found above that that requires a pressure change of 7 * 10⁸ Pa = 7 * 10⁸ kg/(m*s²). Fill all that in in the formula and we get

(4,6 * 10^-10 m*s²/kg * (7 * 10⁸ kg/(m*s²)²)) / (2 * 1 kg/m³) =

(4,6 * 7²)/2 * 10^16-10 ((m*s²/kg * kg²)/(m²/s⁴)) / (kg/m³) =

113 * 10⁶ m²/s²

Hold on, I should have ended up with kg*m²/s². My head is spinning slightly. I can't even read my own equations anymore. :) Where did I go wrong? DirkvdM (talk) 10:49, 14 July 2010 (UTC)[reply]

I find 1130 J/kg. The pressure is 700 bar = 7*10^7 Pa and the density is approximately 10^3 kg/m^3 (more precisely 997 kg/m^3). The cpompressibility is the isothermal compressibility, but the correction term you need to subtract to compute the isentropic compressibility would change it by a few percent and the value for the compressibility isn't that accurate to start with.Count Iblis (talk) 16:24, 14 July 2010 (UTC)[reply]

Nitroglycrine

What is the safest and most practical method to make Nitroglycrine ? —Preceding unsigned comment added by Jon Ascton (talk • contribs) 10:41, 13 July 2010 (UTC)[reply]

This may come across as sarcastic, but the best way is not to make it. It is a highly dangerous explosive formed by a reaction between highly dangerous acids and glycerin. Just the heat of the reaction, if uncontrolled could explode it sending you flying. C-4 is a much better explosive, if you drop it on the floor it won't blow up. It needs a detonator like lead azide or mercury fulminate to detonate it. Gunpowder is also useful. Armstrong's mixture is a highly sensitive explosive made from easily obtainable materials. CuO-Al thermite is a low explosive, but it is difficult to ignite. --Chemicalinterest (talk) 10:51, 13 July 2010 (UTC)[reply]

Not those established users doing tests again, I hope. Hopefully not a fight about renaming titles. --Chemicalinterest (talk) 10:52, 13 July 2010 (UTC)[reply]

I've signed the post Nil Einne (talk) 11:12, 13 July 2010 (UTC)[reply]

Ok, then tell us how to make C-4....

(EC) Have you looked at Nitroglycerine#Manufacturing? It covers the industrial angle. I don't think it's common for people to produce it for fun, because of the obvious risks. The Bojinka plot evidentally used nitroglycerine but I don't think it's a particular common explosive of choice for terrorists and such either. Nil Einne (talk) 11:19, 13 July 2010 (UTC)[reply]

Nitroglycerin is easy to make. All you need is college-level chemistry. From there, find some idiots to test your procedures at different temperature levels until you get it to work without exploding. Then, if you have and IQ over 10, which would mean that you aren't stupid enough to waste your time trying to make a weak explosive like nitroglycerin when there are much stronger explosives that are much safer to make, you will soak paper in the nitroglycerin and roll them up to make dynamite. -- kainaw ™ 12:04, 13 July 2010 (UTC)[reply]

Hey, wait man. Didya say "weak"? I thought NG was the strongest xp around, bigger than RDX etc...

My chemistry book states that CL-20 is the strongest chemical explosive. --Chemicalinterest (talk) 12:53, 14 July 2010 (UTC)[reply]

What makes you assume he wants a strong explosive? He just says he wants to know the safest and most pracical method to make nitroglycerine. He doesn't say why, which could be loads of reasons (although I think we can rule out homework).

Btw, speaking of questions we are nog supposed to answer, medical questions are among them. Questions about good ways to blow yourself up seem to be ok, though.

Here's my answer: out in some wasteland, from a safe distance. Maybe build a robot first. :) DirkvdM (talk) 14:06, 13 July 2010 (UTC)[reply]

FYI, dynamite isn't paper soaked in nitroglycerin, but some filler/stabilizer like sawdust or diatomaceous earth soaked in it and then stuffed into a paper tube. --Sean 15:00, 13 July 2010 (UTC)[reply]

Really? I thought it was agarose gel soaked in nitroglycerine. John Riemann Soong (talk) 15:05, 13 July 2010 (UTC)[reply]

That might be an alternative absorbent that serves the same role in its manufacture. I was just pointing out that a stick of dynamite isn't a rolled-up tube of nitroglycerine-soaked paper, as it might appear. --Sean 15:31, 13 July 2010 (UTC)[reply]

Several ways to make it; see dynamite. --Chemicalinterest (talk) 15:36, 13 July 2010 (UTC)[reply]

black swallowtails

i had a black swallowtail chrysalis we found in the garden and it was alive when we found it , it was wiggling, but after i kept it in a tupperware on the porch all winter and put a few drips of water on it every few days it never hatched. so we ripped it open and it was dead. what did i do wrong????? we also ad some other catterpillars, like wooly bears, inchworms, and black swallowtails and they died too. are we cursed or what?????--98.221.179.18 (talk) 12:21, 13 July 2010 (UTC)[reply]

Speaking from having tried this with various (UK) species of butterflies and moths over a decade or so as a child/youth, it's harder than most people realise: caterpillars and pupae often need very specific foodstuffs (including the actual age and condition of the plants) and environmental conditions (like temperature and humidity) to develop to maturity, and it's not easy finding out just what these are in each case, although hobby organisations of Lepidopterists may be able to give useful advice. Try and track one down via your local library or by searching the internet.

A general aim should be to try to reproduce their ideal conditions as closely as possible, which in the case of pupae may include burying them under a light layer of soil or pinning them up by the silk pad attached to their cremaster so as to hang down from it as they would normally, depending on the usual habits of the species concerned. It's usually better to build or obtain dedicated boxes or tanks (empty aquaria are useful) rather than using small ad hoc containers - there used to be specialist companies selling such entomological equipment; I don't know if any still operate, but if they do you could consult their catalogues to see what sort of housing has been designed. Chrysalises need to be able to breath but usually do not need to be kept artificially moistened (hence, probably, your problem with that pupa), and some benefit by being placed under gentle warmth to simulate sunshine - I remember successfully hatching a large proportion of Small tortoiseshell pupae close to maturity (when you can see the wing colours through the shell) by placing them on paper on the bottom of a large (dry) fish tank under a couple of incandescent light bulbs.

A further difficulty is that many caterpillars and chrysalises are already diseased or parasitised when you find them. Bear in mind that in the wild most never make it to maturity for these and other reasons (like being predated by birds, which you can prevent) - otherwise we'd be up to our necks in the adults! Also, young caterpillars in particular often need very delicate handling - a common ploy is to pick them up gently on the tip of a small artist's brush rather than touching them directly.

Watching the development of butterflies and moths is certainly fascinating. so persevere! One warning, though, make sure you're not interfering with any locally or nationally rare species, which may well be illegal and probably bad for the species - pupils at the prep school (i.e. aged 7-11) associated with my senior school (11-18) in Kent once inadvertantly but significantly reduced the population of a rare British fritillary before older naturalists caught on. 87.81.230.195 (talk) 16:03, 13 July 2010 (UTC)[reply]

Equation

I saw this equation posted on a forum: ${\frac {\mathrm {d{\overline {L_{CM}}}} }{\mathrm {d} t}}\mid _{S}={\frac {\mathrm {d} {\overline {L_{CM}}}}{\mathrm {d} t}}\mid _{S'}+{\overline {\omega }}\times {\overline {L_{CM}}}$ .It looks like it has something to do with angular momentum, but I've never seen it before. Can someone expain what it means? 74.15.137.192 (talk) 14:07, 13 July 2010 (UTC)[reply]

It looks like it is something to do with relating angular momentum at different points. If would help if you linked to the forum so we can see it in context. We need to know what the variables mean if we're going to give a definitive answer (I'm just guessing at the moment based on commonly used variable names. --Tango (talk) 14:16, 13 July 2010 (UTC)[reply]

(ec) What Tango said. dL_CM/dt is the time rate of change of the angular momentum vector. ω is generally an angular velocity (rate of rotation), but in the above equation it's a vector quantity (in order for it to be crossed with the L vector). We'd be better able to put the equation in context if you provided a link to the relevant discussion. TenOfAllTrades(talk) 14:23, 13 July 2010 (UTC)[reply]

Angular velocity as a vector means the magnitude is the usual rate of rotation and the direction is the axis of rotation. --Tango (talk) 15:55, 13 July 2010 (UTC)[reply]

Ah, of course. My coffee hadn't kicked in yet! I'm still not certain exactly how the formula given would/should be applied, however. It looks like it might be the change in angular momentum when you apply a torque to a rotating body around some axis other than its original axis of rotation, but context would, again, be very helpful. TenOfAllTrades(talk) 16:24, 13 July 2010 (UTC)[reply]

Unfortunately there wasn't really any context to it. Someone just posted it as his 'favorite equation', if that makes any sense. Personally, it doesn't make much sense to me, because if the angular momentum and the angular velocity happen to be parallel, then the second term just become zero. 74.15.137.192 (talk) 17:29, 13 July 2010 (UTC)[reply]

If ω is the angular velocity of the reference frame s, the equation looks like it could be the torque on CM in the rotating frame. 198.103.39.129 (talk) 18:02, 13 July 2010 (UTC)[reply]

Elevated heart rate

Is it dangerous or unhealthy to have a slightly elevated heart rate for a short period of time (a couple months) from a diet medication such as phentermine in a healthy adult? —Preceding unsigned comment added by 76.169.33.234 (talk) 14:36, 13 July 2010 (UTC)[reply]

That's going to depend on what constitutes 'slightly', what the resting heart rate is, what other medications are being taken, what other conditions or genetic susceptibilities that the patient has, and a host of other factors. Our article on phentermine lists some of the common side effects, as well as providing links to more extensive information. TenOfAllTrades(talk) 14:53, 13 July 2010 (UTC)[reply]

(e.c.) I'm not sure we can answer questions like that. It's not a diagnosis, but answering you wrong would be bad, so it would be irresponsible to try. You can look up tachycardia though, which is the medical term for that, and has some pretty serious effects listed there - but it depends on how fast you mean by slightly. Ariel. (talk) 14:55, 13 July 2010 (UTC)[reply]

It's not diagnosis, but it is prognosis, which is the other thing we aren't allowed to do when asked medical questions. Therefore, we cannot answer this question. A doctor, or possibly a pharmacist, needs to be consulted. --Tango (talk) 15:56, 13 July 2010 (UTC)[reply]

A doctor should certainly be able to answer you. Vimescarrot (talk) 15:47, 13 July 2010 (UTC)[reply]

I understand your concern about answering the question, but I'm not taking it, I was just wondering. Of course I would talk to a doctor and get a prescription first, its just I am wondering if it is dangerous even before I go see a doctor. What if no other medications are being taken, no heart problems at all with me or any family members, and with 10-20 beats per minute increase. Also I am 22 years old and need to lose about 10-15 pounds so I am not obese. Thanks again —Preceding unsigned comment added by 76.169.33.234 (talk) 17:02, 13 July 2010 (UTC)[reply]

It isn't that people here don't want to help... it's just that what you are asking is not within the realm of what RD volunteers are capable of answering in a responsible manner. You have been given some appropriate links in the first few responses but you asked a yes/no question and, as indicated by TenOfAllTrades, there are many nuances that make it a much more complicated answer than you are hoping for. Sorry. --- Medical geneticist (talk) 17:30, 13 July 2010 (UTC)[reply]

OK, got it. As for the other factors, I was just asking in general... I did get an answer from someplace else. Thank you to everyone for the help :-) —Preceding unsigned comment added by 76.169.33.234 (talk) 02:50, 14 July 2010 (UTC)[reply]

I dont see any risk in giving general medical info as long as we are not giving medical advice. Phentermine is an amphetamine-like prescription medication used to suppress appetite. It can help weight loss by decreasing your hunger or making you feel full longer. Phentermine may be recommended if you're significantly overweight — not if you want to lose just a few pounds. Phentermine is one of the most commonly prescribed weight-loss medications, but it does have some potentially serious drawbacks. Raised BP, Nervousness and Constipation are very common. Heart rate is not a fixed number but a range which can change with age and other factors. Even for two people in the same age group, the heart rate could be different due to other factors. You havent mentioned your age or what your heart rate is. This drug, being a prescription drug, has to be prescribed to you by your doctor and Im sure he will check your heart rate, BP and other vitals. A slight increase or even a persistent increase Im sure would be recorded by him/ her and it would be appropriate that you address this issue of occasional or persistent tachycardia with your consultant. Fragrantforever 04:34, 14 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

Stretching tapes

why do cling films and some kind of surgical and other tapes need to be stretched in order to self-adher properly? It doesn't seem to be just geometry tension and pressure but I am struggling to work out the exact adhesive mechanism/ --BozMo talk 16:29, 13 July 2010 (UTC)[reply]

This may not be correct, but think of the adhesive as many tiny parallel poles covered with adhesive on the sides and nonsticky on the bottoms, where they are exposed. They are mounted on the flexible backing. When the backing is stretched, it breaks down the parallel arrangement, allowing the sticky sides to come in contact with what it is adhering to. --Chemicalinterest (talk) 12:56, 14 July 2010 (UTC)[reply]

Dark matter

Here I don't see why they think there is dark matter here. All I see is a dark ring, but dark matter does not interact with light. Is there some gravitational lensing here or something? --The High Fin Sperm Whale 17:28, 13 July 2010 (UTC)[reply]

Yes, lensing. It's mentioned in the accompanying press release. --Sean 17:45, 13 July 2010 (UTC)[reply]

Gravitation

Two bodies of equal mass 1 kg are placed 1 kilometre apart in free space.Only force acting between them is gravitational force.How to find time after which the bodies will meet —Preceding unsigned comment added by 59.92.2.26 (talk) 17:59, 13 July 2010 (UTC)[reply]

This looks like a homework question. Have you looked at the articles Newton's laws of motion and Newton's law of universal gravitation? You don't mention how large the bodies are. ~~If they are each a kilometer in diameter they are touching before you start!~~ Cuddlyable3 (talk) 18:10, 13 July 2010 (UTC)[reply]

Also important is initial velocities. If the bodies are stationary to begin with you will get very different answers than if they are moving relative to one another. --Jayron32 23:49, 13 July 2010 (UTC)[reply]

I was kind of wondering that also. How would you get them positioned perfectly still, with no initial force in any direction? Very hard to do - almost impossible, I'd say. In effect, the question is postulating God doing it, because He can do anything. But even the most finely tuned machine is liable to have some variation in it. Maybe the teacher is hoping they won't ask that question. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:10, 14 July 2010 (UTC)[reply]

They could have been placed at the specified distance in space by being tethered on a string of negligible mass which was vaporized by a laser at t=0. Certainly no initial velocity should be supposed. And what, pray tell, is "Inertial force?" The size is an interesting question. For textbook purposes, I would assume a very small radius for each mass.How would the answer vary if the objects 1 km apart were each spheres of uniform density of radius 1 mm versus 10000 km?Edison (talk) 04:42, 14 July 2010 (UTC)[reply]

See Free-fall time, for small bodies this gives 96 years in the first case, for the second case it depends on the masses.--Patrick (talk) 06:09, 14 July 2010 (UTC)[reply]

Food preparation, handling of (fish) meat

Dear Wikipedia

I am surrounded by chefs and food at my workplace. Since I was employed, I've doubled my knowledge of food, fish in particular, and how to prepare it. I present to you now, or rather I ask advice on, a certain number of axioms. If anyone could please provide the scientific answers to why a chef might be inclined to do so and so, I would be most thankful. I'd hate to run around cooking and telling others to cook, without knowing the underlying scientific principles.

1) Why does meat have to rest after being cooked? Say for instance a beef is fried on pan for 6-7 minutes, then placed in the oven for 15-20 minutes, it should 'rest' (ie lie idle on a plate) approximately 10 minutes. The matter is not how long, but for what reason.

2) Is the sugary content of a meat an indication of whether or not it is good for frying on a pan? I understand to some degree the principles of the maillard reaction, but this question came up when dealing with fish: Some fish (which?) do not contain as much sugar as other, and are less subject to being fried. Haddock comes to mind as a fantastic frying fish, ditto Coalfish, whereas Trout... would that work at all?

3) Red fish filets/pieces (salmon, trout etc) can't lie flesh to flesh with white fish. Any reason?

4) To eat raw (red) meat is practically unheard of. Still whale is offered as part of our sushi. Can ordinary land-mammal meat be eaten in the same manner?

5) Some fish, especially the 'looser' ones like Cod, can not be sliced into too small pieces before being fried. This will see them fall apart, more or less. Why? Also, Haddock has a far higher tolerance, sticking more easily together during heating. What is the difference between the meat of the haddock and cod?

Thank you in advance for your time and answers :) 88.90.16.109 (talk) 18:00, 13 July 2010 (UTC)[reply]

On #4—I don't think it's that unheard of, just not common in American cuisine. See for example steak tartar, yukhoe, other things in Category:Raw beef dishes, Carpaccio, etc. I don't know what the limitations are health-wise in terms of quality, types of animals, etc., or why fish is more common than land animals in this regard (assuming there is reason other than custom). --Mr.98 (talk) 18:15, 13 July 2010 (UTC)[reply]

I would assume that this is mostly about health. It is much more common for parasites and infections to move from one mammal to another mammal than it is for them to move from a fish to a mammal. In general, the more similar the physiology and environment of two species, then also the more likely that they can share parasites / infections. In some cases the risk might be historical than current, but cultural taboos against raw meat persist. For example, trichinella is very rare in the United States today (~25 cases / year), and yet my grandmother still insists that all pork must be thoroughly blackened for safety. Dragons flight (talk) 19:14, 13 July 2010 (UTC)[reply]

on 1: It has to do with the meat juices, which under the heat will be drawn to the surface and ultimately evaporate. If you allow the meat to cool slightly before it is eaten, these juices will make their way back towards the centre of the meat and thus the meat becomes more juicy. 2: Pan-fried trout, which is what I think you're talking about, is delicious, but it usually is fried with the skin still on. 3: never heard of it. With 4, Mr 98 is quite right that red meat can be eaten raw: in these dishes it is usually either cut extremely thinly or pulverised so that an acid (lemon juice) will "cook" the meat. I don't advise eating pork or chicken in this manner, although lamb is delicious as a Carpaccio. 5: both fish have meat which falls into thick slices naturally, though cod is thicker. --TammyMoet (talk) 19:17, 13 July 2010 (UTC)[reply]

(ec) To #1, 'resting' meat serves two purposes. First, it is supposed to allow for the meat to reabsorb some of its juices before you start hacking away at it with a carving knife. Second (and most important) it provides for more even cooking. In the cooking process that you describe above, a piece of meat is pan fried/seared rapidly for a few minutes to create a tasty, browned crust on the exterior. It is then oven roasted for a period of time — several minutes up to a few hours, depending on size.

Thicker pieces of meat require more cooking time, as it takes longer for the externally applied heat to reach the center of the cut. Even then, remember that the temperature isn't uniform all the way; there will be a temperature gradient through the meat. The outside will be hottest (as it is directly exposed to the hot air in the oven), while the center of the meat will be coolest. At the moment that you take the meat out of the oven, it might well be 'medium' at the surface, but 'rare' at its core. During the ten to twenty minutes (or even more!) of 'resting', the hotter outer layers of the meat will have the chance to transfer some of their heat to the inner parts, while they themselves cool off a bit. The result is that the meat comes to a more uniform temperature – and degree of doneness – throughout. TenOfAllTrades(talk) 19:29, 13 July 2010 (UTC)[reply]

For #2, are you referring to pan-frying or immersion frying? Trout and salmon are rarely deep-fried, but it's not due to the sugar content - it's the fat. Both are very fatty fish and the addition of oily batter just makes it even fattier. Deep-fried salmon also tastes more muted, as if the neutral cooking oil was wiping out the flavour of the fish oil. There may also be problems with poor adhesion of the batter to oilier fish. Matt Deres (talk) 14:38, 14 July 2010 (UTC)[reply]

Cat vision

I've read the article Cat, and have learnt that cats don't see red. I'm after more detail, though, and I know their sight is more acute than humans. What frequency ranges do they typically see? I do have a reason for asking this besides curiosity :) --TammyMoet (talk) 18:10, 13 July 2010 (UTC)[reply]

This article The Spectral Sensitivity of Dark- and Light-adapted Cat Retinal Ganglion Cells answers your question. Cuddlyable3 (talk) 18:17, 13 July 2010 (UTC)[reply]

Cool thanks! Wish I could understand it! Joking aside, how does this 510nm peak sensitivity compare with human vision? Does it mean they can see what we know as ultra-violet? --TammyMoet (talk) 19:09, 13 July 2010 (UTC)[reply]

Compare to: File:Cone-fundamentals-with-srgb-spectrum.png. 510nm is green with a tinge of blue. Ariel. (talk) 19:36, 13 July 2010 (UTC)[reply]

Note that the peak sensitivity is the frequency/wavelength at which the sensitivity is highest, not the highest frequency/wavelength at which there is any sensitivity. What the article abstract appears to say is that cats have cones similar to human S and M cones, but there's also evidence of a third cone type in between those (peaking around 520 nm), which was only active in dark (scotopic) conditions. They also have rods similar to human rods, which peak around 500 nm but aren't shown on the image that Ariel linked. That would mean they have color vision similar to a human protanope ("red-blind") in the daytime, but might also have some nighttime color discrimination (unlike humans). -- BenRG (talk) 20:30, 13 July 2010 (UTC)[reply]

There is a difference between not being able to see red and not being able to distinguish red from other colours. As far as I can tell (I can't understand the paper Cuddlyable links to much more than you can), cats can see roughly the same range of wavelengths are we can, but they have slightly different abilities to distinguish certain wavelengths and combinations of wavelengths (for example, humans can't distinguish between yellow light and a combination of red and green light, cat's might be able to, I'm not sure of the details). --Tango (talk) 21:10, 13 July 2010 (UTC)[reply]

The deal is with how many different kinds of color receptor they have. Being sensitive to red - and being able to distinguish red from (say) green are two very different things. Humans have three kinds of color receptor - which are most sensitive to red, green and blue respectively. When we see pure yellow light, both the red and green receptors respond (although less strongly than they do to red and green) - so we can see yellow light, but we can't tell whether it really is yellow (like a yellow sodium street lamp) or whether it's a mixture of red and green (like a picture of a yellow sodium street light displayed on a TV screen). We think TV pictures look realistic because they show pretty much all the colors we can see - but in truth, they aren't.

Cat's only have two kinds of color receptors - one sees green and the other violet-ish blue. That means that to a cat, red and green look exactly the same. Red and yellow things don't look black (like, for example, infra-red looks to us) - they look green. They may be able to distinguish shades of violet, blue and cyan better than we do (it's hard to tell) - but they are useless at distinguishing orange, yellow and red from green. It's more or less true to say that they are red/green color-blind.

By contrast, (weirdly) goldfish have amazing color vision - with many more color receptors than us. There are species of shrimp with even better still - some have as many as 14 different color receptors - and for them, the yellow "color" put out by a computer screen would look violently different from the yellow put out by a sodium lamp. Not just a little bit different...consider how much different a frequency that's midway between red and blue (ie, green) looks from a mixture of red+blue to us. For a goldfish, those two kinds of yellow (red+green and halfway-between-red-and-green) probably look as different as magenta (red+blue) and green (halfway between red and blue) looks to us!

It is widely believed that the reason we are able to see shades of red/yellow/orange/green is because we've evolved to eat fruit - and the difference between an unripe and a ripe fruit is typically some change in color between red (ripe) and green (unripe). Cats are carnivores - and whether that poor little mouse is spurting red, yellow or green blood is of very little concern to them!

SteveBaker (talk) 14:31, 14 July 2010 (UTC)[reply]

Pressure of Deepwater Horizon Oil Leak

The Deepwater Horizon Oil Leak is about 1500 m below sea level. At that level, the absolute pressure is about 1.52e7 Pa. Does anyone know what is the pressure of the oil leak? I wonder how the leak is able to overcome the absolute pressure at that level.Inkan1969 (talk) 18:59, 13 July 2010 (UTC)[reply]

The pressure is 4,400psia (absolute psi). Source: [22] (search for "Pressure Data Within BOP"). Ariel. (talk) 19:32, 13 July 2010 (UTC)[reply]

That is roughly 3e7 Pa. Googlemeister (talk) 19:50, 13 July 2010 (UTC)[reply]

You might like the photo of the pressure gauge they are using: [23]. Ariel. (talk) 19:53, 13 July 2010 (UTC)[reply]

Thanks for the picture and the number, Ariel. The picture doesn't correspond to your number though; it reads only 250 psi. Anyway, I see now that the leak can overcome the absolute water pressure as its own pressure is double the value. Inkan1969 (talk) 19:58, 13 July 2010 (UTC)[reply]

It's low because the pipe is open. Once they seal it the pressure will rise. I linked it to show the pressure range they are expecting. Ariel. (talk) 21:08, 13 July 2010 (UTC)[reply]

If you follow Ariel's link, you'll see that the pressure at the end of the pipe is only ~2250 psi (15.5 MPa), i.e. only slightly above the pressure of the ambient sea water (at least prior to the capping exercises). This isn't surprising since the flow has been largely unconstrained, so there is no reason for a high pressure to accumulate. One can predict the flow rate from the pressure difference and vice versa. If a 50 cm diameter pipe is belching 50000 barrels a day, then that's less than 1 mph in flow velocity and requires only about 100 Pa of overpressure at the exit. That's actually hardly anything. If it were accessible, a single man with a stout piece of plywood could temporarily block that off. However, that's not the real issue. The oil is being forced out of the ground by the partial weight of the Earth above the oil pocket, and if you attempt to block it, the pressure at the well head will rapidly build. Ariel's link also shows this very well, indicating a pressure in the well bore of 4400 psi, nearly double that of the ambient water. And if one tried to close all of the openings through which oil is currently escaping or being collected, you'd have to be able to resist at least that much pressure and possibly even significantly higher pressures. Dragons flight (talk) 20:19, 13 July 2010 (UTC)[reply]

The leak is 5000' below the surface of the water - but the oil reservoir is 18,000' below that! So the oil is being pushed down on by 18,000 feet of solid rock - creating pressure many times that of the water at 5,000 feet - but when the pipeline between the reservoir and ocean meet, the oil will expand outwards until the pressures are equalized - which is why the pressure gauge is reading so low. However, when the well is capped, the pipe will have to withstand the full pressure of 18,000 feet of rock...and that's the big concern here. If the pipe was weakened or cracked by all the torment it's been through - then capping it could cause it to break in a big way and allow this incredible oil pressure to force it's way out though cracks and fissures in the rock at the sea floor - resulting in a much greater problem. It's frustrating that the process to cap this thing is so slow - but not making matters worse than they already are is a prime concern here. SteveBaker (talk) 13:56, 14 July 2010 (UTC)[reply]

How do you know that most of the weight of the rock above isn't transferred to the rock substrate on either side of the pocket? I have been deep in the earth in a gold mine and in a cave, and in neither case was I under any pressure at all from the many meters of rock and dirt overhead. So it may be incorrect to assume that a pocket of oil 18000 feet below the surface is pressurized by the weight of all the rock. Rock is very good at transferring weight around a void. It is not necessarily a plastic fluid like mud, which would tend to fill voids. If we take the density of rock to be about three times that of water, then the pressure from 18000 feet of rock would be about 24000 pounds per square inch, or 3 times the pressure from a column of water of 18000 feet. How thick would the steel well casing and cap of an ordinary oil well have to be to contain it? Edison (talk) 18:17, 14 July 2010 (UTC)[reply]

Arch

Why is an inverted caternary the ideal shape for an arch? 74.15.137.192 (talk) 19:16, 13 July 2010 (UTC)[reply]

Have you read our article about inverted catenary arches? It is far from clear that an inverted catenary is "ideal" for arches. — Lomn 19:55, 13 July 2010 (UTC)[reply]

"Hooke discovered that the catenary is the ideal curve for an arch of uniform density and thickness which supports only its own weight."? 74.15.137.192 (talk) 01:56, 14 July 2010 (UTC)[reply]

You have to define "ideal" (Greatest enclosed space? Most pleasing to the eye? Greatest supported load for a given span?) If you keep reading in the inverted catenary arch article to see what "ideal" means in this case: "the [unloaded inverted caternary] arch endures almost pure compression, in which no significant bending moment occurs inside the material. If the arch is made of individual elements (e.g., stones) whose contacting surfaces are perpendicular to the curve of the arch, no significant shear [e.g. slipping] forces are present at these contacting surfaces." The Mathematics Reference Desk might be able to assist you in setting up the appropriate equations to demonstrate this is the case, if you are so interested. -- 174.24.195.56 (talk) 02:48, 14 July 2010 (UTC)[reply]

"Which supports only its own weight" strongly suggests, to me at least, that it's not "ideal" for practical purposes. — Lomn 13:59, 14 July 2010 (UTC)[reply]

animal feelings

do animals like horses ever get bored? some people say that certain expressions show boredom but others say that theyre not like humans and dont get bored. im stuck!!! —Preceding unsigned comment added by 98.221.179.18 (talk) 20:57, 13 July 2010 (UTC)[reply]

It's a difficult question. Animals certainly have feelings of some kind, but it's hard to say to what extent they are comparable to human feelings. It's a matter of definition, really. Animals kept in captivity in conditions where they have very little stimulation often end up going round and round in circles, which could easily be interpreted as boredom. --Tango (talk) 21:03, 13 July 2010 (UTC)[reply]

My two year old runs around in circles, and loves it. Staecker (talk) 22:24, 13 July 2010 (UTC)[reply]

We can measure levels of anxiety, brain activity, and things like that in animals. Animals without certain types of stimulation can get quite listless and their health can suffer. Some animals (e.g. fish in a tank) don't seem to care very much. You might find Temple Grandin's book Animals in Translation particularly interesting along these lines. --Mr.98 (talk) 21:06, 13 July 2010 (UTC)[reply]

I think it also depends on the intelligence of the animal. I'm fairly sure a chimpanzee or orangutan can get bored, but something like a slug most likely can't. --The High Fin Sperm Whale 21:25, 13 July 2010 (UTC)[reply]

If you've ever been to a zoo where they have panthers in too-small cages, and they pace relentlessly, it's pretty evident that they're not happy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:05, 13 July 2010 (UTC)[reply]

If you've ever had a dog such as a border collie or Australian shepherd, the answer would be more clear. They need a lot of mental stimulation otherwise they start to act out. Dismas|^(talk) 23:20, 13 July 2010 (UTC)[reply]

Animals can certainly display neurological and behavioral problems from a lack of mental stimulation. Whether you can call this "boredom" is perhaps debatable, but the Wikipedia article on Stereotypy#In animals describes some common symptoms in animals from what can be described as "extreme boredom". --Jayron32 23:47, 13 July 2010 (UTC)[reply]

Domesticated animals of many kinds show behavior that's symptomatic of lack of stimulation (which I guess is "boredom"). Dogs chase their tails, parrots pull out their feathers, zoo and farm animals exhibit repetitive behavior, humans get cabin fever. All of these things "go away" when the animal has some kind of stimulation. It's pretty clear though that animals with smaller brains and less active life-styles don't have these problems. Many hunters (like maybe crocodiles) can stay perfectly still for days without evident problems. I suspect the deal is that some animals have evolved to lay in wait - or to conserve energy by staying dormant, where others are 'wired' to use every spare moment of their day productively. This evolutionary trait is what allows some to sit around and do nothing whatever without "getting bored" while the others are likely to suffer mental issues if prevented from doing what their brain chemistry is frantically trying to make them do. SteveBaker (talk) 13:19, 14 July 2010 (UTC)[reply]

most of the animals I see in the zoo appear very bored and unwell.Fragrantforever 04:24, 14 July 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

And don't let's forget parrots who are very prone to get bored and behave abnormally[24] if not stimulated or kept with a partner. 86.4.183.90 (talk) 07:14, 14 July 2010 (UTC)[reply]

The above answers dealing with caged animals pacing in circles: can someone PLEASE correct the ignorance evident in the explanations for this common phenomenon? 63.17.82.101 (talk) 10:30, 14 July 2010 (UTC)[reply]

Well, you could correct it. What, specifically, do you think is incorrect in the explanations? What evidence do you have for that claim? We're all about dispelling ignorance around here! SteveBaker (talk) 13:41, 14 July 2010 (UTC)[reply]

Yes, horses can get bored. It can result in the problem behavior called cribbing. --Sean 18:56, 14 July 2010 (UTC)[reply]

July 14

diving

How is it like diving 600 feet underwater? what kind of marine life is down there? Are there coral reefs, sea slugs, moray eels, stonefish, or dolphins? I'd go scuba diving now if i could.--Diver62 (talk) 00:06, 14 July 2010 (UTC)[reply]

Me, too. You picked an interesting depth because the Photic zone goes down to a maximum of around 200 meters, or around 660 feet — below this, it is very very dark, and photosynthesis cannot occur; bioluminescence is essentially the only light available. So, in addition to the fact you're an technical diver at this point because of the crushing pressure, you're going to be carrying around a lot of flashlight gear. Comet Tuttle (talk) 00:26, 14 July 2010 (UTC)[reply]

did u ever go diving before? i'm just a highschool teen and i'm interested in going for cetology and marine biology in college. i also want to go diving as a profesional and be diver in caverns and wrecks. do u have similiar interests? i even wrote a 6-page short story of my future life of diving in the red sea. the beautiful creation of God underwater, diving in a cavern, almost killed by an octopus, and losing our air and rope. it is also about wreck diving and finding treasures and seeing squid crushing fish in the window of a sunken ship. that's my type of life! —Preceding unsigned comment added by Diver62 (talk • contribs) 00:59, 14 July 2010 (UTC)[reply]

Erm, is there a reason in particular why you bolded this post? Falconus^{p t c} 03:36, 14 July 2010 (UTC)[reply]

It looks accidental (he opened the bold but did not close it), I removed it. Ariel. (talk) 04:24, 14 July 2010 (UTC)[reply]

List of diver training organizations is for you. PADI and NAUI are the leading organizations of dive instructors. However, do not expect to be threatened in any way by octopuses, which are shy. Comet Tuttle (talk) 05:35, 14 July 2010 (UTC)[reply]

I've seen on the internet of an octopus taking someone's underwater camera from them and swimming away with it. I just wrote it in the story for excitement, even though it may not be true. I like octopuses and dolphins especially.I also like police, detectives, and karate. Even though I want to do karate, I don't do it. I'll hopefully do it when I'm grownup. —Preceding unsigned comment added by Diver62 (talk • contribs) 11:12, 14 July 2010 (UTC)[reply]

Can people withstand the water pressure at 600ft? That is about 20 atmospheres, or 300 psi roughly. Googlemeister (talk) 13:07, 14 July 2010 (UTC)[reply]

People have dived 1,083 feet being the record on scuba gear! Isn't that amazing! All that pressure is upon you in such a deep, dark,area full of lantern-fish! —Preceding unsigned comment added by Diver62 (talk • contribs) 15:19, 14 July 2010 (UTC)[reply]

That is amazing! They must have spent weeks decompressing. Googlemeister (talk) 15:22, 14 July 2010 (UTC)[reply]

Trevor Jackson dived 600 feet and explored a ship wreck. That is a deep dive and maybe the deepest I would dive. there is also a danger of the bends, nitrogen narcosis, oxygen toxity, and related troubles down there i wouldn't ever want to deal with. —Preceding unsigned comment added by Diver62 (talk • contribs) 15:34, 14 July 2010 (UTC)[reply]

High pressure nervous syndrome, considered "a limiting factor in future deep diving". The effects "become significant at depths exceeding 1,000 feet." -- 110.49.193.34 (talk) 15:41, 14 July 2010 (UTC)[reply]

Sheck Exley is one of the ONLY EIGHT people in the history of technical scuba diving to go below 800 feet. —Preceding unsigned comment added by Diver62 (talk • contribs) 15:42, 14 July 2010 (UTC)[reply]

Actually, high pressure nervous sydrome starts occuring at 500 feet. —Preceding unsigned comment added by Diver62 (talk • contribs) 15:47, 14 July 2010 (UTC)[reply]

Worth noting is that those really deep dives are interesting as technical accomplishments, rather than as exploration or entertainment. Under those pressures, one incurs tremendous amounts of time in decompression (up to twelve hours) at multiple depths and with multiple gas mixtures, in exchange for at most a few minutes of bottom time. It's also an extraordinarily risky pursuit — of the nine people (all men) who have made dives to at least 800 feet, at least three have subsequently been killed in diving mishaps. Even 600-foot dives are quite risky, costly, and time-consuming.

Truth be told, if you're just hoping to see interesting underwater sights – including coral reefs, sea slugs, moray eels, stonefish, or dolphins – you're probably better off staying within a hundred feet of the surface. You save all the technical mucking about and can spend hours exploring the sea. TenOfAllTrades(talk) 15:55, 14 July 2010 (UTC)[reply]

I would have said 30 feet. It's nice and bright. Comet Tuttle (talk) 18:10, 14 July 2010 (UTC)[reply]

Sure thing. That is a good point you brought out. I like to see all the paraphernalia of the sea, but also like to explore the caves, caverns, shipwrecks, and just go deep for the fun of it. I might even be a police diver someday, since i like police,or live in a submarine. Whatever God has for my life is the best thing, and that's what i'll do. —Preceding unsigned comment added by Diver62 (talk • contribs) 16:39, 14 July 2010 (UTC)[reply]

hummers

did the US used hummers in war years ago because i dont see anything about it in your site —Preceding unsigned comment added by 98.221.179.18 (talk) 00:21, 14 July 2010 (UTC)[reply]

sorry, i accidentally snet too many messages

--98.221.179.18 (talk) 00:23, 14 July 2010 (UTC)[reply]

No worries; I deleted the extras. See High Mobility Multipurpose Wheeled Vehicle for the military Humvee. Hummer is our article about the consumer car brand. Comet Tuttle (talk) 00:28, 14 July 2010 (UTC)[reply]

poor bees

around the hottest time of the summer, the bumble bees start acting very wierd. they stay on the plants at night and dont fly back to their nests. sometimes they dont eat too. then the other day i saw about 7 of them lying dead in the stones by our house. are they dehydrated perhaps???? or tired?? i cant find an answer anywhere else. thanks for answering--98.221.179.18 (talk) 00:59, 14 July 2010 (UTC)[reply]

Contact your local university. Maybe they would be interesting in analyzing one of the dead ones. I doubt they would be dehydrated unless there were no flowers. Tired is unlikely too. Is it possible it's mating season, and you are seeing the dead drones, and the new queens who didn't make a hive? Ariel. (talk) 09:19, 14 July 2010 (UTC)[reply]

"carpenter bees"

we have these bees that are like bumblebees but theyre much bigger like three times the size and they have shiny black abdomens, not furry like bumblebees. we thouught they are carpenter bees but they gather pollen like other bees and i never see them chew wood. most books say they are carpenter bees but i dont think so. are they queen bees of some sort??? then there's some very, very tiny bumblebees that are half the normal size of a bee. i dont know!!!!--98.221.179.18 (talk) 01:03, 14 July 2010 (UTC)[reply]

Carpenter bees do collect pollen and nectar, and they fit the description; so your "big bumblebees" are probably carpenter bees indeed. You need to find where they make their tunnels in order to see or hear them "chew wood" (they can't digest wood, really, AFAIK. They just burrow in it). It is much easier to find wasps that gnaw on wood than carpenter bees that do this. The reason, I am guessing, is that the carpenter bees have no interest in openly advertising the location of their largely defenseless larvae and of the food supply, whereas wasps gnaw on wood to build their nests elsewhere. --Dr Dima (talk) 01:58, 14 July 2010 (UTC)[reply]

it is mating season for bees but i thought the drones cant fly. and i dont know why they dont go to the flowers we have in abundance in our garden instead of dying--98.221.179.18 (talk) 10:57, 14 July 2010 (UTC)[reply]

Of course drones can fly. That's pretty much the whole evolutionary point of having them :) . In most social bees the drones are basically flying insemination devices. Carpenter bees are not really social, so drones also protect the tunnels, at least in some species. --Dr Dima (talk) 11:17, 14 July 2010 (UTC)[reply]

ink

i want to make some homemade ink for a big crow feather i have but i dont know how. can anyone help--98.221.179.18 (talk) 01:08, 14 July 2010 (UTC)[reply]

Do you have any historical museums or that kind of thing in your area? I wouldn't be surprised if they know someone who knows how to make ink. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:19, 14 July 2010 (UTC)[reply]

Per the rubric at the top of the page, google tends to be a good first stop for this sort of question. --Tagishsimon (talk) 01:27, 14 July 2010 (UTC)[reply]

We also have an article on Iron gall ink. --Dr Dima (talk) 02:06, 14 July 2010 (UTC)[reply]

India Ink is also an option, for those who can't find oak galls. -- 174.24.195.56 (talk) 02:27, 14 July 2010 (UTC)[reply]

Call a Judaica shop, they often sell (or know where to get) ink for quills, because scribes use it. You can also order it online. Ariel. (talk) 07:03, 14 July 2010 (UTC)[reply]

The simplest ink you can make would be from 'lamp black' - the fine-grained carbon that's deposited onto a surface from a smokey candle or some other kind of yellow-burning flame - mixed with a small amount of either water or alcohol (alcohol would help it dry faster on the page). Since you're going 'retro' here, you'll presumably be writing by the light of a tallow candle or an oil lamp...so this stuff will be easy to find! The mixture would probably be ground together in a pestle and mortar to ensure that the result is a smooth liquid. This stuff is bad for your lungs - and you should probably wear a face-mask while you're collecting the dry ingredient (although it should be safe once you've mixed in some liquid to stop the dust flying into the air). I wouldn't make a large batch of the stuff (at least not to start with) because it will settle out from the liquid and have to be re-ground when you need it again. This kind of ink is inconvenient, and doesn't produce great results...but that's why we now have ballpoint pens! SteveBaker (talk) 13:05, 14 July 2010 (UTC)[reply]

"One great beauty of lampblack, especially for ink-making, is that it is extremely fine in grain, and does not need to be made finer by grinding. It may be used just as it is found deposited on the cold surface of metal or earthenware, and needs only to be mixed with a little gum water to make a black ink corresponding to what we call India ink." -- The Materials and Techniques of Medieval Painting, Daniel V. Thompson, Dover Books. You'll need to stir it again before using it, is all. Gum arabic is commonly found in art shops next to the watercolours, by the way. 213.122.25.117 (talk) 14:06, 14 July 2010 (UTC)[reply]

Resistor calculation

I would like to power some LEDs while stationary on my bike and here is part of a circuit that I hope might work. I'm trying to calculate what resistor, if any, is needed between the battery and the LEDs. I don't know yet, whether I want it before or after the transistor.

My LED's have a max rated forward voltage of 3.8 V (and normal forward voltage of 3.3 V) and each needs 20 mA (I'm not certain whether I want eight LEDs or even more, but assuming it's eight, that's 160 mA total) and I need to use a PNP transistor but I don't know which one; is there a difference? I read somewhere that 0.7 V is a typical loss over a t ransistor? My battery is 4.8 V, consisting of 4 NiCd cells.

Is the answer 1.875 ohms? In which case the LEDs in parallel can just be treated like a single component, carrying 160 mA? —Preceding unsigned comment added by 92.25.105.88 (talk) 01:26, 14 July 2010 (UTC)[reply]

The circuit you show won't work because the pnp transistor needs a current flowing between its base and the negative rail. Frankly, I don't see the need for a transistor there at all; you're turning on and off with a SPST switch. You're right that you can treat the LEDs as being in parallel, but you run the risk of uneven lighting because you can't guarantee that their characteristics are matched when the same voltage is across them, Some may be brighter or dimmer than others. If each of the eight LEDS actually does drop 3.3 V at 20 mA, and your battery actually is 4.8 V, then a single resistor of (4.8 − 3.3) / 0.16 = 9.35 (use 9.1 or 10) ohms would do the trick - you'd be dissipating 1.5 x 0.16 = 0.24 watts in it (a bit close to the maximum rating for some small resistors). Personally, if space wasn't a problem, I'd use one 75 ohm resistor in series with each LED. That would likely lead to more uniform brightness if the LEDs weren't perfectly matched and reduce the dissipation in each resistor to a negligible wattage. --RexxS (talk) 02:12, 14 July 2010 (UTC)[reply]

Even the diode D5 is not needed. Remove the transistor and the diode D5, reverse the polarity of the batteries such that the positive terminal connects to the anode and the negative terminal connects to the cathode. See the article LED if you need details. The article says that a typical voltage drop is about 2V for a red LED. In this case, you can even put two LEDs and a suitable resistor in series and use four such combinations in parallel. This will bring down the current. -- WikiCheng | Talk 05:12, 14 July 2010 (UTC)[reply]

Refer to the circuit diagram shown

File:For wikipedia.JPG

Resistor calculations

. With this, assuming the voltage across each LED is 2V, the voltage across each resistor would be 4.8 - 2 * 2 = 0.8. If you need a current of 20 mA (0.02 A), then you will need to use the resistor of value 0.8 / 0.02 = 40 ohms. It will consume about 0.8 * 0.02 = 0.016 W and hence a 47 ohm quarter watt resistor would do.

If you use a single LED instead of two, then the calculations would change. The current through each resistor will increase and hence you may need a resistor of higher wattage. WikiCheng | Talk 10:47, 14 July 2010 (UTC)[reply]

Here is the full circuit. I corrected the batteries (thanks!!) but the D5 diode and the T1 transistor are needed. The idea behind the SPST switch is that I can switch off the circuit when the bike is parked/locked up, so I don't drain the batteries. When on the road, I want the transistor to switch on the LEDs when I stop at lights. Does the transistor work, now that the orientation of the batteries has changed (just a careless mistake)?

The LEDs which I'm looking at buying (taking into account their brightness) have a forward voltage of 3.3 V but can tolerate a max of 3.8. I don't want to use a resistor to bring the voltage down to 3.3 V because the LEDs will quickly loose full brightness as the batteries drain. This way, each battery has to loose 0.15 V (=at least a few minutes?) before the brightness starts to decrease. 89.243.130.113 (talk) 10:56, 14 July 2010 (UTC)[reply]

Ok, so what you want to do is monitor the voltage across the two series LEDs 'XPG' and switch on the other LEDs when it drops below a certain voltage? The thing you have to realise is that semiconductor junctions have an approximately exponential relationship between voltage and current, so you cannot simply apply a voltage to them and expect to be able to predict the current. You always need a current limiting mechanism (usually a resistor), particularly as the junctions have a negative temperature coefficient of voltage - which means as they get hotter, they pass more current and get even hotter. You will always need some series resistance. Looking at your full diagram, when the alternator is stopped, you are clamping the battery with the E-B junction of the transistor and the two 'XPG' junctions. There's no limit to the current, so you will need a resistor in series with the base of the transistor. That will have to be calculated from a knowledge of the forward drop of the LEDs marked 'XPG' and the fact that to turn on the transistor fully, you should plan to have a B-E current of 16 mA, about one-tenth of the C-E current (160 mA). Then you still need to limit the current through your LEDs 1–8 to 20 mA each. A fully saturated power transistor can drop as little as 0.2 V (look for VCE_sat in the data sheet). That would give a voltage of about 4.6 V at the collector, so the resistor(s) have to now drop about 1.3 V while passing the current (160 mA for one or 20 mA for eight individual ones). That gives a single resistor of 8.2 ohms or eight individual series resistors of 63 ohms. I'd prefer the latter, to allow for individual variations in the LEDs 1–8. I suspect you're also trying to use the transistor to provide a constant current as the battery voltage reduces, but you really don't have enough voltage headroom to do that with simple circuitry, although FET-based ICs that provide constant current are available with relatively low voltage drops, but that would make it a lot more complex and expensive. However, you are using NiCd batteries which have a low internal resistance and a remarkably small voltage drop as they discharge, so that would compensate to some extent for your fears of the light dimming as the batteries discharge. Finally, I should warn that you're clamping the LEDs 'XPG' to about 0.7 V above the charging voltage of the batteries – please ensure this will give the results you want, or again use a resistor in series with diode D5 to limit the charging current to the NiCds if the voltage across the 'XPG' LEDs should be more than that when the alternator is running. --RexxS (talk) 14:20, 14 July 2010 (UTC)[reply]

This is my modified circuit but I'm pretty confused. My understanding is that when the bike is in motion, the 6 V will charge the batteries (1.4 V are needed to fully charge each NiCd cell so if I put a resistor there, I prevent them from fully charging and reaching 4.8 V?) I don't know how to figure what current will pass through the batteries relative to the LEDs.

When stationary, the potential difference that normally exists between the emitter and the base reverses from <-0.7 to +4.8 and current flows through the emitter to the base and collector but to return to the batteries from the base, it must pass through the XP-G LEDs which have a forward voltage of 3.0 V and therefore wont allow a current to pass? How will any current be able to pass through the base? Surely the LEDs themselves offer plenty of resistance to only 4.8V? --Seans Potato Business 20:07, 14 July 2010 (UTC)[reply]

Ideas for scientific imagery

I am considering some post grad studies, specifically a new course offered at a local art university entitled "Visualizing Science and Art". To be accepted by the institute, a portfolio and an admission test is required. I possess adequate (?) skills in computing and graphics, but am widely illiterate in scientific disciplines beyond the level of secondary education. Fortunately, some tests indicate that, given time, dedication and curiosity, one can learn new tricks in advanced canine years.
So, the question: Can you suggest some (maybe six to eight) "smallish" projects for this portfolio, preferably from different disciplines, where I could test my skills, both at researching and visualising scientific ideas?
Of course, images / short movies will be made available to the WP and can be linked to relevant articles if expert editors deem them to be constructive didactic tools. Feel free to post to my talk-page, if required.
Thank you. --Cookatoo.ergo.ZooM (talk) 09:01, 14 July 2010 (UTC)[reply]

Go to American Scientist and look through their current and past issues, paying special attention to the column called "Sightings". It's devoted to scientific visualizations, and many of the articles and images are online. If you know how to use Google to find what you want, do a site search for "sightings" and/or "visualizations". There is enough material there to keep you busy for years. Good luck. Viriditas (talk) 12:29, 14 July 2010 (UTC)[reply]

Fractal graphics are impressive and can be created surprisingly simply, see Mandelbrot set. There are unlimited possibilities in the field of Fractal art, see this gallery. Cuddlyable3 (talk) 14:30, 14 July 2010 (UTC)[reply]

The obvious one to me would be wildlife photography. Sow about finding a species article on here that can be found where you live but is currently very short and lacks images and trying to improve it? You could also look at some microscopic stuff - try looking at this site for some ideas. There are also some cool books filled with scientific pictures of varying scales - similar to the power of ten video. I can't remember what they are called but maybe someone else can. Smartse (talk) 14:34, 14 July 2010 (UTC)[reply]

I guess the question we should ask you is, what type of scientific visualization are you hoping to generate? Is it photographs and photo-like images (microscope images, computed tomography, astrophotography, etc.)? Is it quantitative information (for numerical data presented effectively and honestly, see Edward Tufte's gold-standard works, especially The Visual Display of Quantitative Information)? Is it processes, project outlines, or flowcharts? Is it diagrams or explanatory illustrations? Is your target audience scientific specialists, university students, the general public, or high schoolers? Do you have some examples of what type of work you're considering? Finally, what access do you have to original data/material which might guide your chioces? TenOfAllTrades(talk) 18:25, 14 July 2010 (UTC)[reply]

Phone connectors in the UK

I know that phones in the UK have a different type connectors than those in the US, but form factors aside, are the two interfaces electrically compatible? Also, do the phones in the UK have different handset connectors than those in the US? Will a headset amplifier made for US phones work with a UK phone, assuming no connector issues? —Preceding unsigned comment added by 173.49.10.26 (talk) 11:14, 14 July 2010 (UTC)[reply]

Exoplanetary systems in Sagittarius

How many stars in Sagittarius are known to have planets? (The Wikipedia article says 16 and 19, so that needs to be fixed) Also, where can I find a list of these particular stars? Finally, is it true that "Sagittarius has more planetary host stars than any other constellation"? Viriditas (talk) 12:10, 14 July 2010 (UTC)[reply]

1. regarding 16 vs 19. "Number of stars known to have planets" is a (usually increasing) function of time, so it simply needs a date and a reference. 2. Regarding "more planetary hosts". Sagittarius is a constellation, that is, a group of stars that look close for the Earth-based observer but are not necessarily close to each-other (indeed, distance from Earth to different stars in the same constellation is often very different). The farther is the star from Earth, the harder it is to detect a planet orbiting it. Besides, we do not even know how many stars there are in the Sagittarius. This being said, it is indeed possible that Sagittarius houses more Milky Way stars (and therefore maybe more stars with planets) than any other constellation. That is because the center of the Milky Way galaxy (our galaxy) happens for the Earth-based observer to lie within the bounds of Sagittarius constellation. Does this help? --Dr Dima (talk) 21:31, 14 July 2010 (UTC)[reply]

Head massagers: How do they work?

Lately, more and more of my friends have been buying head massagers (like the ones seen here: http://www.rolostore.com/images/medium/kk_headm.jpg). I've noticed that these things have interesting, differing and sometimes hilarious effects on people. For instance a friend of mine is immune to the effects, another finds them overly tickelish and yet another just becomes totally relaxed. I myself get goosebumps. What could explain the effect of these simple devices? —Preceding unsigned comment added by 137.224.252.10 (talk) 12:13, 14 July 2010 (UTC)[reply]

They obviously don't have any meaningful effect but reflect the expectation of the purchaser. Different strokes for different folks, but they all pay. 86.4.183.90 (talk) 13:28, 14 July 2010 (UTC)[reply]

Not a good answer in my opinion, 86.4. People have varying degrees of sensitivity to stimulation. Complete OR, but I had no expectations when one of those devices was used on me, and the experience was quite noticeable. 10draftsdeep (talk) 20:03, 14 July 2010 (UTC)[reply]

Methyl 1 d - muscle growth drug

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. TenOfAllTrades(talk) 13:30, 14 July 2010 (UTC)[reply]

Metadiscussion moved to the talk page. TenOfAllTrades(talk) 15:21, 14 July 2010 (UTC)[reply]

watermellon

removing a bit o' trolling

whenever I eat watermellon I am struck by the fact that it resembles flesh somewhat. has anyone tried implanting it to see what happens? what does the body have to say about it? —Preceding unsigned comment added by 92.224.207.86 (talk) 13:26, 14 July 2010 (UTC)[reply]

Not being rude, but are you being serious? I seriously doubt anyone has tried, if they did something similar to transplant rejection would probably occur. Smartse (talk) 14:22, 14 July 2010 (UTC)[reply]

(EC) Doctors don't randomly implant tissues into people to see what would happen. That would be very, very unethical and most likely, illegal. In any case, as watermelon flesh is 92% water, and most of the rest seems to be sugar, it would be very surprising indeed if the human body was able to use watermelon flesh for anything (other then eating it). Googlemeister (talk) 14:24, 14 July 2010 (UTC)[reply]

Sepsis? It's a vegetable. What's it supposed to accomplish in an animal, other than to either putrefy or be absorbed by the body? Acroterion _(talk) 14:26, 14 July 2010 (UTC)[reply]

I implanted some in my mouth, and then my stomach, and lo, it was good. --Mr.98 (talk) 14:41, 14 July 2010 (UTC)[reply]

OP here. Guys, in case it wasn't clear, I'm not a doctor. I was just curious. 92.230.234.245 (talk) 14:57, 14 July 2010 (UTC)[reply]

I apologize for mocking you, by the way, below. Wikipedia has a rule against that. I'm not laughing at you, I'm laughing near you. 213.122.25.117 (talk) 15:21, 14 July 2010 (UTC)[reply]

whenever I eat jelly I am struck by the fact that it resembles vitreous humour somewhat. has anyone tried gouging out someones eyes and replacing it with jelly to see what happens? —Preceding unsigned comment added by 92.19.107.38 (talk) 15:04, 14 July 2010 (UTC)[reply]

Whenever I eat human flesh, I am struck by the fact that it resembles watermelon. Has anyone tried grafting arms and legs onto a watermelon to see what happens? 213.122.25.117 (talk) 15:14, 14 July 2010 (UTC)[reply]

This is such a funny question :D --Chemicalinterest (talk) 15:18, 14 July 2010 (UTC)[reply]

Funny? it is sad that this passes for humour - no, not vitreous humour, just young schoolkid humour. 86.4.183.90 (talk) 18:57, 14 July 2010 (UTC)[reply]

As a serious response to what seems to have been a serious question, watermelon will likely cause a foreign body reaction that would initiate a granuloma. Because watermelon is very soft and easily compressible, it would not fit into the category of space-maintaining graft material, such as calcium sulfate, silicon dioxide or allograft/xenograft bone particles such as would be used in a bone graft. In fact, calcium sulfate is not very firm and resorbs quite quickly (few weeks) and so is also not good if one would like to maintain space. Everything I've said above applied primarily to intraoral grafting and can be found in any advanced-level dentistry text. DRosenbach ^{(Talk | Contribs)} 15:18, 14 July 2010 (UTC)[reply]

This topic was covered in Rugrats (Episode: The Inside Story) Hemoroid Agastordoff (talk) 16:26, 14 July 2010 (UTC) [reply]

Cold Skin

I notice that the skin on the backs of my arms (where the triceps are) is noticeably colder than other places on my body. Why is that? It doesn't matter if I have had a workout and my metabolism is elevated, or if I am otherwise fairly warm, the backs of the arms always feel cool. Hemoroid Agastordoff (talk) 16:36, 14 July 2010 (UTC)[reply]

I think because they get a lot of air which helps the sweat to evaporate and cools them. --Chemicalinterest (talk) 18:14, 14 July 2010 (UTC)[reply]

birds

why are baby birds less scared of humans than the adult birds????? there is a mockingbird and it has about three babies hidden around our yard. the adults fly away at first sight of humans, but the babies even let us pick them up. some people say the parents teach the baby birds to be scared --98.221.179.18 (talk) 17:42, 14 July 2010 (UTC)[reply]

~~1. You're not supposed to pick up baby birds. The parents may abandon them because they will smell different after coming into contact with your skin.~~ 2. Our fear article is about humans, but it notes that although a capacity to fear seems to be part of human nature, "people develop specific fears as a result of learning". Human babies fear nothing, either; it's through learning that they develop fear. Comet Tuttle (talk) 18:07, 14 July 2010 (UTC)[reply]

Are we sure 1. is because they smell different? As a general rule, most birds have a poor sense of smell except in scavenger species. Googlemeister (talk) 18:50, 14 July 2010 (UTC)[reply]

This site says my claim #1 is a total urban myth! My apologies! Pick 'em up, toss 'em back into the nest, etc. Comet Tuttle (talk) 19:08, 14 July 2010 (UTC)[reply]

Moving them is a problem. Just touching them is usually ok. I still wouldn't advise doing it without a good reason - you may interfere with the bird's usual development even if it isn't abandoned. The adult won't feed it while you are holding it, for instance, so it may not get as much food as it would otherwise get. --Tango (talk) 20:59, 14 July 2010 (UTC)[reply]

What use would fear be to a baby bird? It can't escape or defend itself in any case. Looie496 (talk) 19:29, 14 July 2010 (UTC)[reply]

It could make an alarm call. --Tango (talk) 20:59, 14 July 2010 (UTC)[reply]

thats what it did around my house. the baby called an alarm because a cat was near and the mother attacked the cat, pecking its head and tail--Horseluv10 (talk) 21:36, 14 July 2010 (UTC)[reply]

Osteochondritis and related conditions

We have articles on Osteochondritis and Osteochondrosis as well as Osteochondritis dissecans. The first two aren't linked.

What is the relationship between these conditions and which, if any, are subtypes of the others or entirely different conditions?

FT2 ^{(Talk | email)} 18:50, 14 July 2010 (UTC)[reply]

Caveat: I am not an expert on these topics, but have a reasonable layman's grasp of medical terminology and etymology.

The word root "osteochondro-" means "bone and cartilage".
The suffix "-osis" just means "condition", but usually a diseased condition of some kind.
"-itis" means "inflammation", which is just one kind of pathological condition.
"Dissecans" means "dissected" or "split".

So putting all that together:

"Osteochondrosis" is any disease of the bone and cartilage.
"Osteochondritis" is when the bone and/or cartilage are inflamed, and kind of osteochondrosis.
"Osteochondritis dissecans" is a condition of the bone and cartilage where there is inflammation and where the bone and/or cartilage has split. It is a kind of osteochondritis, and therefore also a kind of osteochondrosis.

Medical terminology does not always match the things described, as many usages evolve past their roots, but reading osteochondritis dissecans indicates that the above is correct: "[[Osteochondritis dissecans]] is a type of osteochondrosis in which a lesion has formed within the cartilage layer itself, giving rise to secondary inflammation.". --Sean 19:09, 14 July 2010 (UTC)[reply]

IV

when people are fed interveinously, do they get hungry--Horseluv10 (talk) 20:25, 14 July 2010 (UTC)[reply]

I'm not sure. People are only fed by IV if their digestive system is not working (people that are just in a coma are fed by a tube into the stomach, rather than into a vein), so it may depend on what is wrong with their digestive system. You can't get stomach contractions if the muscles around the stomach don't work, for example. --Tango (talk) 20:56, 14 July 2010 (UTC)[reply]

@@ Line 670: / Line 670: @@
 do animals like horses ever get bored? some people say that certain expressions show boredom but others say that theyre not like humans and dont get bored. im stuck!!!  <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/98.221.179.18|98.221.179.18]] ([[User talk:98.221.179.18|talk]]) 20:57, 13 July 2010 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
-:It's a difficult question. Animals certainly have feelings of some kind, but it's hard to say to what extent they are comparable to human feelings. It's a matter of definition, really. Animals kept in <br />
+:It's a difficult question. Animals certainly have feelings of some kind, but it's hard to say to what extent they are comparable to human feelings. It's a matter of definition, really. Animals kept in captivity in conditions where they have very little stimulation often end up going round and round in circles, which could easily be interpreted as boredom. --[[User:Tango|Tango]] ([[User talk:Tango|talk]]) 21:03, 13 July 2010 (UTC)
-captivity in conditions where they have very little stimulation often end up going round and round in circles, which could easily be interpreted as boredom. --[[User:Tango|Tango]] ([[User talk:Tango|talk]]) 21:03, 13 July 2010 (UTC)
 ::My two year old runs around in circles, and loves it. [[User:Staecker|Staecker]] ([[User talk:Staecker|talk]]) 22:24, 13 July 2010 (UTC)
 :We can measure levels of anxiety, brain activity, and things like that in animals. Animals without certain types of stimulation can get quite listless and their health can suffer. Some animals (e.g. fish in a tank) don't seem to care very much. You might find [[Temple Grandin]]'s book ''[[Animals in Translation]]'' particularly interesting along these lines. --[[User:Mr.98|Mr.98]] ([[User talk:Mr.98|talk]]) 21:06, 13 July 2010 (UTC)
@@ Line 683: / Line 682: @@
 :::Animals can certainly display neurological and behavioral problems from a lack of mental stimulation.  Whether you can call this "boredom" is perhaps debatable, but the Wikipedia article on [[Stereotypy#In animals]] describes some common symptoms in animals from what can be described as "extreme boredom".  --[[User:Jayron32|<font style="color:#000099">Jayron</font>]]'''''[[User talk:Jayron32|<font style="color:#009900">32</font>]]''''' 23:47, 13 July 2010 (UTC)
-::::Domesticated animals of many kinds show behavior that's symptomatic of lack of stimulation (which I guess is "boredom").  Dogs chase their tails, parrots pull out their feathers, zoo and farm animals exhibit repetitive behavior, humans get [[cabin fever]].  All of these things "go away" when the animal has some kind of stimulation.  It's pretty clear though that animals with smaller brains and less active life-styles don't have these problems.  Many hunters (like maybe crocodiles) can stay perfectly still for days without evident problems.  I suspect the deal is that some animals have '''evolved''' to lay in wait - or to conserve energy by staying dormant, where others are 'wired' to use every spare moment of their day productively.  This evolutionary trait is what allows some to sit around and do nothing whatever without "getting bored" while the others are likely to suffer mental issues if prevented from doing what their brain chemistry is frantically trying to make them do. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 13:19, 14 July 2010 (UTC)
+::::Domesticated animals of many kinds show behavior that's symptomatic of lack of stimulation (which I guess is "boredom").  Dogs chase their tails, parrots pull out their feathers, zoo and farm animals exhibit repetitive behavior, humans get [[cabin fever]].  All of these things "go away" when the animal has some kind of stimulation.  It's pretty clear though that animals with smaller brains and less active life-styles don't have these problems.  Many hunters (like maybe crocodiles) can stay perfectly still for days without evident problems.  I suspect the deal is that some animals have evolved to lay in wait - or to conserve energy by staying dormant, where others are 'wired' to use every spare moment of their day productively.  This evolutionary trait is what allows some to sit around and do nothing whatever without "getting bored" while the others are likely to suffer mental issues if prevented from doing what their brain chemistry is frantically trying to make them do. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 13:19, 14 July 2010 (UTC)
-'''u wrote that animals evolve. they dont. they were all created by God in 6 days :)--[[User:Horseluv10|Horseluv10]] ([[User talk:Horseluv10|talk]]) 22:03, 14 July 2010 (UTC)'''
 most of the animals I see in the zoo appear very bored and unwell.Fragrantforever 04:24, 14 July 2010 (UTC)  <small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Fragrantforever|Fragrantforever]] ([[User talk:Fragrantforever|talk]] • [[Special:Contributions/Fragrantforever|contribs]]) </span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->