Wikipedia:Reference desk/Archives/Science/2010 April 14

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April 14

Pressure

What is the general direction of a low pressure center as it moves across the US? Lamb99 (talk) 00:58, 14 April 2010 (UTC)

The trade winds in the US blow from west to east. As a side note weather forecasts in the US are more accurate further from the west coast because of this. Ariel. (talk) 02:44, 14 April 2010 (UTC)

They are called westerlies. The trade winds go from east to west and are over the tropics. Dauto (talk) 03:01, 14 April 2010 (UTC)

The term Ariel was trying to think of was prevailing winds. The trade winds and the westerlies are two instances of prevailing winds. --Anonymous, 05:15 UTC, April 14, 2010.

Hmm, and the map in those articles makes it look as though the trade winds do blow in the US. I've added a comment to the trade winds talk page. --Anonymous, 05:40 UTC, April 14, 2010.

Strong low pressure systems over the US can also travel northward due to ridging within its warm sector, southward due to cold Arctic air, or even retrograde westward in a counter-clockwise loop. We've seen all three of those this year, satellite archives here. ~AH1^(TCU) 23:42, 14 April 2010 (UTC)

Research influenced by funding source

I frequently read about research studies sponsored by companies or industries with a special interest, in which the conclusions of the study invariably support the position of the sponsor. A recent example that comes to mind is the FDA's 2008 finding that bisphenol A in plastics is perfectly safe, citing chemical industry studies while ignoring independent research that reached other conclusions.

What is this phenomenon called, where the conclusions of a study are pre-biased according to the sponsor's interests? I thought there might be an article on it somewhere, but all I can find is one sentence in Selection bias#Related issues. ~Amatulić (talk) 05:28, 14 April 2010 (UTC)

In general, that type of thing is called a conflict of interest. Note that the lab may do everything legit, but the company hiring them can still twist the results, by suppressing info found contrary to their business interests and highly publicizing info helpful to their business. To do this, they require the lab to sign a nondisclosure agreement before they are funded, which states that any info learned belongs to the funding company, and the lab has no right to release it independently. The same company might fund many studies at several labs, and pick and choose to find those that support their position. StuRat (talk) 05:36, 14 April 2010 (UTC)

As someone from the other side of the pond, I find it astonishing how often government decisions are the result of influence by commericial interests, rather than the public good. 89.242.91.98 (talk) 09:38, 14 April 2010 (UTC)

Are you sure it doesn't happen there, too ? StuRat (talk) 14:50, 15 April 2010 (UTC)

Research has shown that people are unaware of the factors that affect their decisions. I recommend Influence: Science and Practice for everyone. To the point, even if everything is on the up and up researchers will still be affected by their sponsors, but they may genuinely deny it. It's human nature. Imagine Reason (talk) 14:21, 14 April 2010 (UTC)

I detect a conspiracy, since your link is now a redlink. :-) StuRat (talk) 14:49, 15 April 2010 (UTC)

The specific question of the FDA (and other agencies) is often referred to as regulatory capture. --Mr.98 (talk) 14:33, 14 April 2010 (UTC)

Interesting replies, but not quite what I'm looking for. Doing some googling, the correct term appears to be "funding bias". Since such an article doesn't exist on Wikipedia, maybe I'll write one sometime.

I found some academic papers using this term, although the most accessible is this economist's blog article, which uses more specific terms "funding outcome bias" and "funding publication bias":

Anders Sandberg (2007-01-14). "Supping with the Devil". OvercomingBias.

Also, this paper on funding bias related to health effects on cell phone use doesn't any term to describe the phenomenon, although it refers to another paper that uses the term "sponsorship bias". ~Amatulić (talk) 18:20, 14 April 2010 (UTC)

Another source of bias is coming to a conclusion prior to examining the data, then using data evidence to support that pre-stated conclusion. This method is technically not science. ~AH1^(TCU) 23:48, 14 April 2010 (UTC)

I agree that approaching a study with a bias can be a problem, but not if it's a double-blind study with only objective measures. In such a scenario, there's no method by which the researchers can bias the data to support a given conclusion. Say they have a cholesterol lowering drug (or that this is what they want to conclude). If they take blind blood samples, send them to a lab for cholesterol counts, administer the drug, then repeat the blood tests, there's no opportunity for them to mess with the data. Any subjective measures, on the other hand, like determining if an anti-acne med works by "counting and classifying the severity of pimples" would likely fall prey to such bias. Also, if the researchers have the opportunity to throw out "bad data", this process can be highly subjective. StuRat (talk) 14:58, 15 April 2010 (UTC)

Metal in the microwave?

The microwave in my house has a metal rack in it, in the chamber where the food cooks. How does this work without doing damage? I've brushed my hand on the rack after the microwave had been running for ten minutes or so, and it was hot, but not nearly so hot as a spoon I left in the microwave for two or three minutes. Is this some special kind of metal? Please explain! 71.104.119.240 (talk) 05:54, 14 April 2010 (UTC)

I found patent #4455467 which talks about it. It seems that the rack is designed to try to hide in the cold spots of the microwave, but also that the rack is simply large enough to absorb the heat. Ariel. (talk) 09:11, 14 April 2010 (UTC)

Thank you! I wouldn't have thought that it was safer to put a big rack in the microwave than a spoon or a bit of foil, but I guess it makes sense that smaller items can't absorb the heat. (I guess that explains why I've known a few spoons to survive microwave cooking, whereas a thin foil wrapper on a stick of butter bursts into flame immediately - according to my roommate who tried to melt the butter with the wrapper on.) 71.104.119.240 (talk) 07:56, 15 April 2010 (UTC)

IIT QUESTION

A LARGE FLASK FITTED WITH A STOP COCK IS EVACUATED AND WEIGHED, ITS MASS WAS FOUND TO BE 134.57gm. IT IS THEN FILLED TO A PRESSURE OF 735mm AND THEN RE-WEIGHED , ITS MASS IS FOUND TO BE 137.456gm THE FLASK IS THEN FILLED WITH WATER AND WEIGHED AGAIN, ITS MASS IS NOW 1067.9gm. ASSUMING IT IS AN IDEAL GAS CALCULATE MOLECULAR MASS OF GAS.

    FORMULAE THAT COULD BE USED IS OF A REAL GAS EQUATION i.e :-
    
                    PV=RnT
         where:- P = PRESSURE
                 V = VOLUME
                 R = CONSTANT[0.0821]
                 n = NO. OF MOLES
                 T = TEMPERATURE
—Preceding unsigned comment added by 122.173.31.193 (talk) 06:17, 14 April 2010 (UTC) 

Please don't use all caps. StuRat (talk) 06:20, 14 April 2010 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.:StuRat (talk) 06:20, 14 April 2010 (UTC)

As a hint, you're given the pressure, you can get the volume from the amount of water and the density of water, and you've probably been told the temperature (or can assume room temperature). You can now solve for the number of moles. With this and the mass of the gas, you can calculate the molecular (molar) mass. Good luck. -- 140.142.20.229 (talk) 20:43, 14 April 2010 (UTC)

Even harmonics in Electrical power lines

It is generally said that only ODD harmonics are present in electrical supplyand odd harmonics are only dealt with -- My question is "Why EVEN harmonics are not present OR why it is not a problematic issue? —Preceding unsigned comment added by 170.38.136.2 (talk) 06:21, 14 April 2010 (UTC)

That's not a generally true statement. Harmonics are typically caused by some type of distortion; certain types of distortion favor amplification of even or odd harmonics. For example, see Triangle wave vs. Square wave to compare the frequency spectra. If your distortion caused the time-domain waveform to look more like a triangle wave (rising and falling during non-negligible periods), you would see more energy in odd harmonics. In general, a signal distorted by an arbitrary, general nonlinear distorting system will spread its energy to many frequencies, including even-harmonic, odd-harmonic, and non-harmonic frequencies. Nimur (talk) 15:35, 14 April 2010 (UTC)

Two answers. First, practically all non-linear loads - the things that induce waveform distortion - do it symmetrically (as a bridge rectifier does), thus all distortion is odd-order. Second, any substantial source of even-order distortion (like a one-way diode shorting the unfuzed line) will cause DC in the line. The grid wasn't designed to feed DC, and numerous client transformers plugged into the grid were not designed to be fed DC... the system goes berserk and then either the culprit disconnects from the grid or it will be tracked quite soon. NVO (talk) 09:23, 15 April 2010 (UTC)

Gravity, friction and mass II

Would you please explain what is conflict in my logic based on my understanding of the laws of physics between statement number 1 and statement number 2. I suspect my knowledge of physics is flawed and I would welcome guidance.

Statement 1.

Two bodies(say a sphere) of identical size and shape are dropped at the same time from the same height. One sphere is filled with lead and the other sphere is filled with feathers. Both spheres will hit the ground at the same time.

Statement 2.

The same two spheres are each placed on identical skateboards and set off at the same time down an identical slope. The sphere filled with lead will pass the sphere filled with feathers.

If gravity is a constant accelerating force what is the explanation for the outcome of statement number 2 ?

Thank you.

86.12.198.101 (talk) 08:42, 14 April 2010 (UTC)

You seem to have asked the samed question here yesterday, and you got several very detailed responses (see Wikipedia:Reference desk/Science#Gravity, friction_and_mass. above). Do you have a follow-up question ? Gandalf61 (talk) 08:54, 14 April 2010 (UTC)

To summarise briefly (just in case you missed the answer in the detail of the discussion), resistances will have an effect, but even if you ignore all resistance, skateboard wheels carry energy proportional to the square of speed, and this energy comes from gravity through the loss in height. A lighter sphere will have less energy to lose, so a bigger proportion will go to the wheels and less will be available for linear speed.

If the spheres were sliding down a frictionless slope with no air resistance, then they would slide at the same speed. Dbfirs 19:27, 14 April 2010 (UTC)

Memory

Today, I realized that it is easier for me to remember the name of a person if I say it out loud at least once with focused attention, rather than simply writing it down and forgetting about it. Is there something to this in the recall process, or is it simply an idiosyncrasy? Why would I be able to better recall a name spoken out loud rather than recalling a note with the name written on it? Viriditas (talk) 09:31, 14 April 2010 (UTC)

I don't know of a name for what you're describing, but I'd say it's not an idiosyncrasy. It's a common suggestion that if you want to remember the names of the people you meet, you want to address them by their names in your conversations with them. Apparently saying their names aloud helps you remember their names. A related phenomenon I've observed is that if you don't know how to pronounce a word or name, it's very difficult to remember it. So vocalizing a word seems to play a role in helping you recall it. --98.114.98.221 (talk) 11:21, 14 April 2010 (UTC)

This is often called Salience (neuroscience) --Digrpat (talk) 14:46, 14 April 2010 (UTC)

Salience, yes, thank you. That was the word I was looking for. Viriditas (talk) 20:36, 14 April 2010 (UTC)

It might be that vocalizing the name develops procedural memory of the name, as opposed to declarative memory. Paul (Stansifer) 17:55, 14 April 2010 (UTC)

Interesting. But, isn't learning a name and saying it more of a declarative memory task? And isn't writing down a name, regardless of the information, a procedural task? I don't think about much when I'm writing, I just do it. Viriditas (talk) 20:36, 14 April 2010 (UTC)

about science

how to study science more easily?  (Unsigned comment added by Sharook (talk • contribs) 15:36, 14 April 2010 (UTC))

It usually helps to have a solid grasp of basic mathematics; depending on how quantitative your scienctific inquiries are, math generally helps. Are you looking for references to books or websites, or do you want some practical study tips? Nimur (talk) 15:38, 14 April 2010 (UTC)

It is "easier" with a gifted instructor who cares whether you learn, and with a good textbook. It is "easier" to become skilled at the math portion of science if you do lots of well chosen problem sets, and that process seems to work best in a group setting, where each contributes. It is also "easier" though not easy, if the learning is as experiential as possible, with good labs and demonstrations. In "bad" labs the emphasis is all on achieving results which are "correct" with a degree of precision greater than the equipment and time provided readily allows, leading to a temptation to "drylab" or fudge results. Edison (talk) 16:11, 14 April 2010 (UTC)

I think it helps if you understand WHY some technique or formula is important rather than learning it 'cold'. It also helps immensely if you choose to learn just because you love the subject. I don't know how old you are - but I was really turned on to science through The Feynman Lectures on Physics (a set of three text-books) which are intended for kids in their final year or two of high school or their first year or two of college. Feynman was the consummate scientist. If you need inspiration, find any biography of him (there are MANY) and be amazed by how he treated subjects as diverse as how to pick up women in bars, how to eradicate ants from his kitchen and how to travel to Tuva with a scientific viewpoint - and had fun doing it. SteveBaker (talk) 18:11, 14 April 2010 (UTC)

Practicing with more scientific experiments can also make science more interesting. ~AH1^(TCU) 23:30, 14 April 2010 (UTC)

May I respectfully remind everyone that not all science is math-based and one needs no more love of math qua math than love of words qua words for most sciences: both are simply useful tools and in many sciences the math is learned long after the initial flame of interest is kindled. I think the key event is seeing how a scientific explanation of something enhances your understanding of it in a way that makes it seem the best way to make sense of it, and leaving you wanting to know more and more things that way. Mine was started by reading Isaac Asimov's World of Carbon at about 13. alteripse (talk) 02:40, 15 April 2010 (UTC)

The only science is physics! Chemistry is just wet physics. Biology is just hydrocarbon-contaminated chemistry. Sociology is just primate biology. The humanities are just sociology for the imprecise. Nimur (talk) 05:47, 15 April 2010 (UTC)

Ob. XKCD: [1] SteveBaker (talk) 13:31, 15 April 2010 (UTC)

This argument is so sophomoric that it makes me nostalgic for college but I'll play another round for the sake of old times. You have the hierarchy inverted. The true intellectual challenge is to scientifically examine systems of more and more complexity, so those who investigate higher order systems deserve more respect than those who stick to math problems. Even more impressive are those who can apply multiple levels of analysis to high-order problems. For example the scientific investigation of diabetes ranges from math, physics, and electronics, to the psychological and social sciences and part of the challenge is to have the wisdom to decide at what level one might best find a solution. Sort of makes a mathematician seem pretty one-dimensional, and a physicist not much better, doesnt it? alteripse (talk) 01:13, 16 April 2010 (UTC)

I think anyone who confines their interest to any one narrow area of study is pretty one-dimensional, but polymaths seems to be rarer these days. Dbfirs 07:08, 16 April 2010 (UTC)

how does the nitrate reduction test work in microbiology?

I'm really really annoyed at my TAs because they seem to avoid organic chemistry explanations like the plague ... they say they can't help me with explaining why one test gives what colour and by what mechanism. OMG. So ... I was hoping someone here could tell me. Supposedly Zn(0) acts like a catalyst(?), but I'm a bit suspicious of people using this term. I rather suspect the zinc actually gets consumed. John Riemann Soong (talk) 16:25, 14 April 2010 (UTC)

We're talking about the nitrate reductase test? DMacks (talk) 17:32, 14 April 2010 (UTC)

Here's a fuller explanation than we have in the article. The test is to see if bacteria have the capability of respiring using NO₃^- in the absence of oxygen. The bacteria are grown in tubes containing media containing NO₃^-. The test to see if they are capable of such reduction is a specific test for NO₂^-. NO₂^- turns reddish purple in the presence of N, N dimethyl-1-naphthylamine and sulfanilic acid. If the bacteria have reduced NO₃^- to NO₂^-, and no further, the color change will be apparent. But if there is no color change, the bacteria may be incapable of NO₃^- reduction, or they may have reduced NO₃^- to NO₂^-, and then further reduced the NO₂^- to N₂ or other intermediates. So we distinguish between these two possibilities by adding zinc to the colorless media. Under acidic conditions, zinc catalyzes the reduction of NO₃^- to NO₂^-. So if there is NO₃^- present in the colorless media, adding zinc will produce the color change and indicate that the bacteria incubated in that medium were incapable of NO₃^- reduction. If addition of the zinc to the colorless media does not produce a color change, it means that NO₃^- is not present, and that therefore the bacteria incubated in that tube were capable of NO₃^- reduction. - Nunh-huh 00:33, 15 April 2010 (UTC)

Thanks! I kinda knew some of that already. What I am really interested in is the organic chemistry of it and the mechanism by which zinc "catalyses" the reduction. What even supplies the electrons? What gets oxidised in the reaction? Are we using metallic zinc, or the Lewis acid catalyst Zn2+? How many steps and intermediates does the reaction go through? It seemed to me that a sulfonic acid was quite oxidised already. Does the napthylamine become a nitro compound and become an aromatic dye? John Riemann Soong (talk) 00:56, 15 April 2010 (UTC)

OK, I currently suspect the napthylamine becomes an amino-napthoquinone, which shows up as red. Can anyone confirm my suspicion? Thanks. John Riemann Soong (talk) 00:58, 15 April 2010 (UTC)

I dunno about the red part of the test, but I'll make what I think is a reasonable guess about the zinc part.

We've got metallic zinc and acidic aqueous solution, right? Two things spring to mind:

• First, metal + acid → salt + hydrogen, so Zn + 2HX → ZnX₂ + H₂.

• Secondly, dissolving metal reductions, such as the Clemmensen reduction. See also the various uses of zinc/acid for the reduction of nitro compounds.

Have a quick read of nitrate reductase test, nitrate reductase, nitrite reductase, nitrate and nitrite just to check the answer isn't there.

There's plenty of info I found with Google, such as Fluka's Nitrate Reduction Test. The detailed description says the red ppt is Prontosil and that Zn powder catalyses the reduction of nitrate to nitrite. I would've thought there'd be plenty of discussion in textbooks and/or the literature on the mechanisms of such simple reactions as [NO₃]⁻ + Zn → [NO₂]⁻. Try electron transfer for starters, or maybe Anal. Chem. (1986) 58, 1590–1591.

Ben (talk) 11:45, 15 April 2010 (UTC)

Thanks so much! I just wanted to update the article as well as improve my own chemical understanding. I'm familiar with the Clemmensen reduction but in that reduction the product is I believe zinc oxide and the fully-reduced (former) ketone/aldehyde. And Zinc here is really a stochiometric reactant and not a true catalyst, right? So Zn2+ acting like a Lewis acid template? The problem is that I can't really see what happens to the nitro group that "activates" the reaction. John Riemann Soong (talk) 15:47, 16 April 2010 (UTC)

Using earwax to test purity of water

I remember, as a child, being told on a wilderness survival course that you could test the purity of water by putting earwax in it. If the wax floated, the water was contaminated; if it sank, it was safe to drink. We were solemnly told not to clean our ears out in the week before a wilderness trip, and to always have a cotton bud in our survival kit.

Is there any scientific logic behind this? To me it now seems plainly wrong. I can see that certain things - salt, for example - would affect the density of the water. But there must surely be all sorts of bacteria which could contaminate water without affecting its ability to support earwax, never mind the obvious flaw that however pure your water was to begin with, it's now got earwax in! --OpenToppedBus - Talk to the driver 16:41, 14 April 2010 (UTC)

Seems entirely bogus to me. As you say - there are a wide variety of factors that could affect the density of the water (not least, temperature) that wouldn't affect your health - and contaminants at the level of a few parts per million that could kill you that would have an utterly negligable effect on density. There is no way this could work. I suspect this was a variety of snipe hunt to persuade kids not to wash their ears before the trip. SteveBaker (talk) 17:58, 14 April 2010 (UTC)

I agree that it sounds silly. Perhaps the logic behind it has to do with the amount of air dissolved in the water. Water with no air in it would be denser, I believe, perhaps causing the Q-tip to float, and this would indicate a lack of plant life, and also wouldn't support many types of animal life, some of which may be harmful to human health. So that may be where the idea came from. However, drinking water just because earwax floats in it is a really bad idea. Just assume it's unsafe and boil it or decontaminate it via another approved method. StuRat (talk) 18:48, 14 April 2010 (UTC)

wielding

what are the sparks from wielding? are they super heated metal filings? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 17:06, 14 April 2010 (UTC)

Yes, they are little burning pieces of metal. By the way, that's 'welding'. Hope this helps, --The High Fin Sperm Whale 17:56, 14 April 2010 (UTC)

I have "wielded" (as in firearms) and "welded" (as in metals with electric arc). The two processes were very different. Edison (talk) 03:33, 18 April 2010 (UTC)

decarboxylation and reduction of pyruvate

Why do these steps in fermentation not yield ATP? I imagine a dicarbonyl is quite electronically strained given the repulsion between the two carbonyl carbons. Furthermore, the reduction of acetaldehyde into ethanol AFAIK is exothermic. John Riemann Soong (talk) 17:32, 14 April 2010 (UTC)

"This tape will self-destruct in five seconds"

What kinds of technologies exist that can make a message self-destruct after it has been heard? Hemoroid Agastordoff (talk) 18:31, 14 April 2010 (UTC)

If it's on computer, just erasing all copies would do the trick. The usual self-destructing casette tape shown on spy shows appears to start a small fire when the tape completes. This would be easy to do in the tape recorder, by ejecting it into a fireproof compartment containing something like match heads, striking them, and having the plastic cassette case catch fire from that. Making the tape itself self-destruct, without help from the player, would require some fancier engineering, and would also destroy the player and maybe set the house on fire. A more realistic way to blank out the tape quickly might be to subject it to a strong electro-magnet. StuRat (talk) 18:37, 14 April 2010 (UTC)

With computers it actually gets trickier unless you are talking about extremely specialized technology. There are a lot of places in a computer's memory that information can reside, and in theory it wouldn't be too hard to hijack a message-delivering program that was trying to delete itself (deny the program the permissions to delete itself, for example). --Mr.98 (talk) 18:46, 14 April 2010 (UTC)

The ultimate form of this is quantum cryptography, where, in theory, the message is physically destroyed (the quantum state is changed) upon observation. This means that no matter what one might want to do with the original version of the message, it is technically gone. --Mr.98 (talk) 18:46, 14 April 2010 (UTC)

Old fashioned way might be to make the tape of a flammable plastic and tight wrap white phosphorous into the tape five second further down the spool than the message. You would have to wrap it un an inert atmosphere but exposed to air when the tape ran on the P would start burning and set off the tape. Or on an iPod record Captain Beaky and His Band immediately after the message forcing the listener involuntarily to smash the iPod up into small pieces... --BozMo talk 19:07, 14 April 2010 (UTC)

If the listener can be trusted to destroy the tape, it could just end "Please destroy this tape within five seconds". If the listener can't be trusted, then it becomes a Digital Rights Management problem of a sort, and there's no secure way to do it because of the analog hole: that is, the listeners could just be recording the audio with a different tape recorder onto a non-self-destructing tape. In that case BozMo's solution is really the only thing that works, although I would suggest "I'm Sad the Goat Just Died Today" by The Frogs, which is so astonishingly unmusical that the destination recorder might shred the tape in protest. Or, if you're working with video, I once saw a DVD player break down thirty minutes into Max Hell Frog Warrior. Paul (Stansifer) 21:03, 14 April 2010 (UTC)

They actually did that (the first thing) in one episode. Phelps played the tape while on a rooftop and instead of the usual self-destruct notice it ended with "Please dispose of this tape in the usual manner". There was a chimney next to him and he dropped it into that to incinerate it. --Anonymous, 21:55 UTC, April 14, 2010.

I picture it dropping safely into a pile of cold ashes, only to be retrieved by the enemy, thus blowing the whole plan. StuRat (talk) 22:17, 14 April 2010 (UTC)

Fortunately, that didn't happen: we saw the puff of smoke as it was consumed. No doubt the head office, although short of white-phosphorus-equipped tapes, had sufficient resources to locate a building where not only was there a place on the roof to conceal the tape, but also a chimney that led directly to an apparatus where the fire was always burning. I mean, anything else would hardly be credible, would it? --Anon, 04:24 UTC, April 15, 2010.

A message on some edible paper provides an easy way to dispose of it. StuRat (talk) 22:19, 14 April 2010 (UTC)

It would be pretty easy to make a special kind of USB key that would run a display program when inserted into a computer and then destroy itself. Looie496 (talk) 01:28, 15 April 2010 (UTC)

A powerful little permanent magnet glued inside the Craig tape recorder after the playback head and before the tape reached the takeup reel would erase it just after it was played. No puff of smoke required. A degaussing coil could be installed under the takeup reel with AC imposed on it when erasing of the reel is desired. That would require a powerful inverter and be far more failure prone than the magnet option. The recording could be on specially made magnetic tape with a nitrate backing (like old movie film) rather than modern plastic. Then a small ignition source like a piece of resistance wire briefly energized would cause the reel of tape to burst into flame, taking the recorder and anything flammable near it with (do not try this at home). If it were recorded on a shellac disc or a wax cylinder it would be easily smashed, melted or burned. If it were recorded on a steel wire from a wire recorder, current could be passed through the wire heating it above its Curie point, thereby erasing it. Edison (talk) 01:41, 15 April 2010 (UTC)

Listen very carefully. I shall say this only once. Cuddlyable3 (talk) 17:44, 15 April 2010 (UTC)

The problem with most of the above solutions involving destroying the tape after it finished playing have some problems: it only takes effect after the tape completely finished playing. So stopping it half a second before the end and rewinding it makes it usable again. A better solution would be to insert an eraser magnet (like what is used when you record a message) right after the place of the reading head. So the message is being erased while it is playing. --131.188.3.21 (talk) 21:44, 17 April 2010 (UTC)

Your statement is clearly incorrect. Please read posts before responding. A magnet which erased the tape immediately after each segment of it played would not allow playback. Edison (talk) 03:29, 18 April 2010 (UTC)

... but it would erase (continuously) a fraction of a second after playback. It could be implemented just by reversing the positions (and connections) of the record and playback heads in a conventional cassette player. I agree that this is not the "Mission Impossible" style of self-destruct, but it satisfies the general query. It does require modified cassette recorders. Dbfirs 16:10, 18 April 2010 (UTC)

Physics - Safer Car

2004 Ford Crown Victoria - Police Interceptor (16 mpg) does not have Crumple zones.

Does that mean it is safer for me to drive in that?

Weight - 4157 lbs for a Sedan (Dinosaur Car aka Traditional Sedan)

Frontal Driver Rating - 5/5 Frontal Passenger Rating - 5/5 Side Driver Rating - 4/5 Rollover 2 Wheel Drive Rating - 5/5

--

2004 Chevrolet Impala (20 mpg) - I think has Crumple zones.

Frontal Driver Rating - 5/5 Frontal Passenger Rating - 5/5 Side Driver Rating - 4/5 Rollover 2 Wheel Drive Rating - 4/5

Just wondering which car to buy from the Police car Auction.

Weight - 3446 lbs

--

A little more information regarding the Crown Victoria which I don't understand whether is a liability or advantage during a crash:

As one of the few remaining passenger cars with body-on-frame construction (that's why it doesn't have Crumple Zones?), it is rugged, and enables repairs after minor accidents without the need to straighten the chassis – an important benefit for a car frequently used by police forces for PIT maneuvers, a maneuver in which the back left or back right corner of a fleeing vehicle is gently pushed with the front left or front right corner of the chase vehicle, disrupting tire adhesion on the fleeing vehicle with the goal of causing the fleeing vehicle to rotate and decelerate.

--

I would like to have bought the Safest Car on the market right now, which is Lexus 2010 with all the new electronic safety features that take it one step towards driver-less cars. Or the Ford Taurus 2010 which has the most of the new electronic features safety features. But I am not able to afford a brand new car, let alone a "Luxury Car" such as the Lexus.

I don't need all the space afforded by the car. But because on the road there are Pick-up Trucks/SUVs/Sport Utility vehicles it makes it necessary to buy a heavier car. But I don't think buying a Pick up truck is safer, because it is more prone to roll-overs. It will be mostly only 1 person using the car i.e. no passengers or luggage.

I think people who buy very small cars - Smart Cars/Honda Fit for a higher mpg are foolish, as they will suffer severe injuries or even death if they crash with the big vehicles mentioned above (or even for that matter a mid-size vehicle like Corolla).

Since I don't have a blank cheque to pay for Gas like Police departments, I am considering 2004 Chevrolet Impala vs. 2004 Ford Crown Victoria. These are cars that are part of most police fleet, with Crown Victoria having a 80% market share.

The Crown Victoria sedan 16 mpg has a lower mpg than a Dodge Caravan SUV which is 18 mpg.

--33rogers (talk) 19:10, 14 April 2010 (UTC)

Well, in the UK the Lexus's selling point is that they combine luxury car features with family car prices. When I was buying a new car a couple of years ago, it was a little (say 15%) dearer than Toyota or Honda, but lots (say 30%) cheaper than BMW or Audi. So don't write it off. Lexus have been producing cars for some time so why not look for a used model? --TammyMoet (talk) 19:22, 14 April 2010 (UTC)

Read Driver-less_cars#Driver-assistance section, then you will see that all new safety features only the "Luxury Cars" of 2009/2010 have them, with the exception being the Taurus.--33rogers (talk) 19:37, 14 April 2010 (UTC)

Crumple Zones are a safety feature. All else being equal, you want them in your car. Of course, they make the car harder to repair after an accident, but If I have to have unrepairable damage, I'd rather it be to my car's frame and not to my own. APL (talk) 19:25, 14 April 2010 (UTC)

If nothing else changed, a car with crumple zones would be safer, in general. However, the Crown Vic is a larger car, which also gives you more distance, and thus time, to decelerate the passengers during a crash, as well as the more mass working to push smaller cars out of the way in an accident. So, which car is actually safer, I can't say. I suggest looking up the safety stats for each. StuRat (talk) 19:31, 14 April 2010 (UTC)

Just thinking, Would it be easier to maneuver a mid-size car like the Chev Impala, to prevent a crash in the first place? Should that be also a factor to consider in the decision making process? --33rogers (talk) 19:42, 14 April 2010 (UTC)

Yes, all things being equal, a smaller car will have a smaller turning radius, and otherwise be more maneuverable. However, safety features like anti-lock brakes and traction control may have a greater effect than vehicle size. StuRat (talk) 20:19, 14 April 2010 (UTC)

Regarding Crumple Zones, my theory is this: a car with crumple zone will absorb more impact of the forces in a crash? Whereas the other car Crown Vic, which has no crumple zone, will be deflecting most of the crash force impact to the other car, thus being more safer? --33rogers (talk) 19:46, 14 April 2010 (UTC)

No - folding crumple zones transfer the energy into the car - thus, away from the passengers. The car has the distance of the crumple zone in order to slow down...It's like having a few feet of brakes before the collision. Vimescarrot (talk) 19:52, 14 April 2010 (UTC)

Agreed. StuRat (talk) 20:19, 14 April 2010 (UTC)

Rogers, the physics don't work that way. You really don't want a rigid collision. Any sort of "deflection" would result in the car suddenly going one way and passengers going a different way. You want to ease into those direction changes, and crumpling is a way to do that. APL (talk) 05:05, 15 April 2010 (UTC)

Note also that cars are not solely designed to maximise the safety of the occupants; they are also designed to minimise, as far as practicable, damage/injuries to what the car hits, especially pedestrians. Crumple zones to some extent (though body shape to a larger one) can reduce an impact sufficiently to, sometimes, reduce the effect of a collision to injury from what otherwise might have been death. 87.81.230.195 (talk) 12:15, 15 April 2010 (UTC)

I don't see any of these answers noting that the police car must be able to purposely collide with another vehicle without crumpling. For example, you must be able to do a PIT maneuver without the front of the car collapsing into your front wheel. Therefore, crumple zones are removed. -- kainaw™ 13:19, 15 April 2010 (UTC)

The part of a car that is responsible for the most accidents is the nut behind the wheel. Cuddlyable3 (talk) 17:47, 15 April 2010 (UTC)

Ah yes, there's also a nut loose on my keyboard that sometimes causes similar problems. :-) StuRat (talk) 02:21, 17 April 2010 (UTC)

Flashing of white tail by alarmed animals

I disturbed a Muntjac deer by the side of the road, and as it ran away it raised its short tail showing a very visible white 'signal', just as a rabbit would. When it stopped with a lowered tail it almost disapeared as the colour of its fur matched that of the floor of the wood, and if I had not seen it moving earlier I would never have noticed it.

What is the evolutionary purpose of the white tail signal? It would make it much easier for a predator (or hunter) to see it and follow it, so more likely to be eaten. How could it have evolved? I'm not sure it would even help the relatives of the alarmed animal (and hence pass on those genes even if the target animal was killed) as its running away ought to be enough to tell them to be alert. 78.149.114.89 (talk) 19:44, 14 April 2010 (UTC)

May be there was a young fawn near by that you did not notice because you had your attention atracted to the white tail? 169.139.217.79 (talk) 19:49, 14 April 2010 (UTC)

I think the idea is this:

1) The predator starts to chase they prey.

2) The prey, knowing it has been spotted, raises the tail, as there's no point in hiding now.

3) The predator fixates on the easy to see tail during the chase.

4) The prey then lowers the tail, while changing direction, stopping or otherwise hiding it's position.

5) Had the predator been tracking some other part of the prey, it might have kept it in sight, but, having tracked the tail, which is no longer visible, it loses sight of the prey animal long enough for it to escape.

From the deer's behavior, it sounds like you got the standard anti-predator treatment, which seemed to work properly. As far as the deer is concerned, it just saved itself from being eaten by you. StuRat (talk) 19:55, 14 April 2010 (UTC)

This is common in many animals - not the 'broken wing' behavior certain birds use to draw predators away from their nests. the evolutionary advantage is that a predator has a much lower chance of catching an animal that is alert to its presence, so any animal that is aware of the predator and can attract its attention lowers the risks to nearby (unaware) prey animals at minimal risk to itself. --Ludwigs2 20:17, 14 April 2010 (UTC)

I'm not sure I would have seen it running away without its raised tail, so that knocks out the logical sequences suggested above. 78.149.114.89 (talk) 22:30, 14 April 2010 (UTC)

Not really, that just means you aren't as good of a predator (at least as far as eyesight goes) as the deer thought you were. StuRat (talk) 00:32, 15 April 2010 (UTC)

Mainly because he was not a predator (he wasn't hunting was he?), but the deer didn't know that. 169.139.217.77 (talk) 01:20, 15 April 2010 (UTC)

I'd swear I saw a documentary that referred to the deer's tail, and similar markings in other species, as "follow-me" markings. They said that the purpose was to keep the herd moving together—to alert the other deer, and make it easier for them to follow the leader. I am unable to find a reference for this explanation at this time. -- Coneslayer (talk) 12:31, 15 April 2010 (UTC)

They might well use it for other purposes like that, but, in this case, intentionally raising the tail when it thinks it's been spotted by a predator shows it's using the tail to help it escape. StuRat (talk) 14:42, 15 April 2010 (UTC)

A deer is not clever enough to do the reasoning you have described. Its just an instinct. See anthropomorphism and anthropomorphic fallacy. Although I'm not sure that either of those terms is the correct one to mean giving animals the same thoughts and feelings as humans, like Walt Disney. 78.151.110.54 (talk) 14:18, 16 April 2010 (UTC)

It's painful to write about animal behavior in a way that doesn't use words we normally apply to humans. We just don't have words to describe it. Instead of "it thinks" we should say "impulses travel from neuron to neuron in it's brain, recognizing the pattern of predator pursuit and causing a predetermined instinctual set of signals to be sent to the appropriate muscles in it's tail" ? If you wish, please rewrite my entire 5 steps that way. I have better things to do. StuRat (talk) 02:14, 17 April 2010 (UTC)

No need, Stu. Your statements were accurate except perhaps that "instinctively" should replace "intentionally". The anthropomorphism was in the mind of the reader. Dbfirs 19:13, 18 April 2010 (UTC)

Cryptorchidism in patients with 5-Alpha-Reductase Deficiency. [?]

I have several questions concerning people with 5-Alpha-Reductase Deficiency. The wikipedia article says that (in childhood) they are often raised as girls because their external genitals are indistinguishable from those of natal females. At puberty, however, they are identified as boys due to —among other sex characteristics— their clitorises growing into (very small) penises and their testes descending.

My first question deals with the location of said testes in a post-pubertal man with 5aRD: How far below his abdomen are said testes located (vis-á-vis a typical, adult man)? I've tried finding images of people with 5aRD —both men and children— but thus far have come up fruitless.

Also, are patients with 5aRD more likely to develop testicular torsion, cancer, and other maladies as a result of this condition? Or is there some other factor that I'm failing to take into consideration?

May these individuals be benefitting from the action of superficial veins (notably, the Great Sapphenous Vein) providing blood to their testes cooler than arterial or deep-vein blood? Has anybody looked into this? Where may one find articles and pictures of this fascinating condition? Pine (talk) 20:48, 14 April 2010 (UTC)

I moved this question to Talk:5-alpha-reductase deficiency. Check there for the answer. alteripse (talk) 02:08, 15 April 2010 (UTC)

Cat and dog repeller

Does anyone know of any way to repel cats and dogs (and even deer) from moving vehicles on a 50 kilometres per hour (31 mph) or less road? I've seen so many cats, dogs, and deer hit on this road, I'm wondering if there's something I can affix to my car to give the little critters a fighting chance. Thanks. Viriditas (talk) 20:58, 14 April 2010 (UTC)

Do you mean to lessen the blow if you hit them, or to make it less likely they'll get hit at all? If it's the second i'm not sure there's much you could do yourself, but protective fencing would help, also more 'openess' would probably help too - I find that mostly it's animals coming out of bushes and straight onto the road is a common cause (though Pheasants do seem to be constantly suicidal no matter what you do to try stop it). ny156uk (talk) 21:53, 14 April 2010 (UTC)

Yes, I often run down peasants pheasants. StuRat (talk) 22:00, 14 April 2010 (UTC)

Those big spotlights on the roof, like on a redneck's truck, would probably give them more warning at night. However, you might cause traffic accidents and they might be illegal. StuRat (talk) 21:58, 14 April 2010 (UTC)

You could also make more noise, say by keeping the windows down and radio on. But, again, this would annoy the neighbors. Perhaps a sound that only cats and dogs could hear would be in order. StuRat (talk) 22:02, 14 April 2010 (UTC)

They make lots of products similar to these specifically for deer. I've heard some town councils in areas with deer/car problems encourage people to install them. Beach drifter (talk) 23:03, 14 April 2010 (UTC)

a little explanation Beach drifter (talk) 23:04, 14 April 2010 (UTC)

(Edit Conflict) In my experience (with deer, badgers, etc. in the New Forest, other Hampshire and Southern English locales, and in Scotland), the best way to minimize/avoid impacts is to drive slowly and very carefully, keep a constant lookout, and slow down or stop whenever necessary. Animals tend not to understand, or rapidly get accustomed to, traffic noises both usual and unusual, and extra noise-making mechanisms would be extremely irksome for local human inhabitants, should there be any in earshot. Deer in particular are apt to be dazzled by lights and and freeze (hence the illegal hunting method of lamping), and also react unpredictably to traffic, sometimes leaping into a vehicle's path at the last second; cats are also prone to this. Of course, driver caution is enhanced in the New Forest because within its boundaries all animals (including the numerous free-roaming ponies and cattle) have automatic right of way and it is a fineable offense to hit one whatever the circumstances.

Within ten miles of my own house, in the Forest of Bere, I have had at times to slow down or stop for mice, weasels, partridges, owls (who like sitting on the median line), rabbits, (domestic) cats, fox cubs (adults tend to get out of the way) badgers, deer, and what appeared to be a juvenile puma (duly reported to the Big Cats in Britain Society - what, no Wiki article?). 87.81.230.195 (talk) 23:08, 14 April 2010 (UTC)

Just as a side comment: a few years ago I drove on U.S. Route 191 in southeastern Utah at dusk. A national park ranger had described the route as "Deer Alley", and so it was. The road was festooned with signs and they were fully justified by the number of deer nearby. I was particularly taken by the signs that said WATCH FOR DEER IN YOUR LANE — deer in someone else's lane obviously being someone else's problem! --Anonymous, 04:27 UTC, April 15, 2010.

I'm sure the deer will signal before changing lanes. :-) StuRat (talk) 14:35, 15 April 2010 (UTC)

Bear locomotion

While bears run... how do they land with their feet? heel first or toes/front part first? --Belchman (talk) 21:47, 14 April 2010 (UTC)

I watched some bear movie clips on YouTube - it looks to me like their claws/toes hit the ground before the heel. But there are a lot of species of bear out there. Anyway - you can watch bear videos just as easily as I can...so tag! You're it! SteveBaker (talk) 04:06, 15 April 2010 (UTC)

Mastering crystallography

Within a week, I need to master crystallography, with emphasis on X-ray crystallography, because my 4th year biochem final exam will be heavily based on crystallography. The exam will test concepts as well as applications like doing some simple calculations involving space groups, coordinates, etc. Will it be possible to master the topic within that time frame? My plan is to read the book "X-ray crystallography made crystal clear" twice while taking notes. But I found that some pages are hard to understand due to heavy mathematics. For someone like me with only Calculus 1 and 2 background to fully understand crystallography, what other better, more easily-accessible resources or webpages are there to help you master crystallography? Thanks. —Preceding unsigned comment added by 142.58.132.157 (talk) 21:55, 14 April 2010 (UTC)

See Main Page - Online Dictionary of Crystallography. -- Wavelength (talk) 23:09, 14 April 2010 (UTC)

Wikipedia has articles on X-ray crystallography and Crystallography. Cuddlyable3 (talk) 17:15, 15 April 2010 (UTC)

doctors dont wear gloves

why dont doctors dont wear gloves? example http://www.youtube.com/watch?v=NMxqzZW2Z8c&feature=channel

they never do —Preceding unsigned comment added by Jonny12350 (talk • contribs) 22:32, 14 April 2010 (UTC)

The naive thought is that bare hands are always dirty and gloved hands are always sterile. But it's not always like that. Obviously a gloved hand can be dirty if it has touched something dirty. Similarly, hands can stay relatively sterile if they are washed properly and don't come into contact with anything after cleaning. An ungloved hand also can better feel nuances that a gloved hand could miss, which might be important for certain types of examination. OK maybe not for proctology exams.

Gloves also have another purpose, to protect doctors from contagions. However, a gloved hand can still be rubbed in the eyes, spreading disease to the doctor, just like bare hands. So it may come down to the only advantage of gloves being that they serve to remind the doctor not to touch his hands to anything he shouldn't. Instead, maybe a few shock treatments would make that lesson permanent. :-) StuRat (talk) 23:02, 14 April 2010 (UTC)

Wearing gloves is in most cases offers only a source of false security for the real purpose intended because they are not replaced at the appropriate time. Have you not seen restaurant workers continue to wear their gloves to protect their hands from soil when dumping trash or even cleaning the rest room? Washing hands is therefore the preferred method since one will do it more likely than replacing gloves to keep their own hands clean. 71.100.8.49 (talk) 22:53, 14 April 2010 (UTC)

Further, doctors always wash their hands upon entering any room, and after touching just about anything. Beach drifter (talk) 22:57, 14 April 2010 (UTC)

I have a disgusting story about rubber gloves. There was a janitor at a hospital who was apparently mentally retarded. They made him wear gloves when tossing out the garbage, some of which was medical waste. He then went to the cafeteria, with his gloves still on, and handled all the food at the salad bar, such as eggs, looking for "just the right one". In his mind, since he was wearing gloves, his hands were clean, so it was OK to touch the food. He was reprimanded. StuRat (talk) 00:29, 15 April 2010 (UTC)

The premise is false. Doctors always wear gloves when there is a requirement for sterility. Looie496 (talk) 01:23, 15 April 2010 (UTC)

First up, wearing gloves does not provide sterility unless the gloves are sterilised. The huge majority are not. Asking why doctors don't wear gloves is like asking why policemen don't smile. The truth is some of them do and some don't. It depends on a wide variety of circumstances and a wide variety of attitudes. There is a widespread belief within the UK National Health Service that doctors are among the worst observers of hygiene and prevention of cross-infection procedures. Never mind the hands, watch out for the tie! Richard Avery (talk) 07:31, 15 April 2010 (UTC)

hi OP here. all of you are answering about sterility that was never my question. im talking about protecting the doctors from contagions. like hepatitis c ect. if hes not wearing gloves when contacting blood wont he catch it ? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 10:14, 15 April 2010 (UTC)

He's not contacting blood (except with the end of the needle, which he'll not subsequently touch directly), he's only contacting skin which he's already sterilised (though primarily to avoid pushing skin bacteria in with the needle). Few contagions are easily (if at all) passed on by casual unlesioned skin-to-skin contact. 87.81.230.195 (talk) 12:05, 15 April 2010 (UTC)

NOT TRUE WHEN HE PUTs a swab on the site afterwards he touches blood iv even had minor surgical things done on me where the doctor got plenty of blood on him and didnt wear gloves sry caps —Preceding unsigned comment added by Jonny12350 (talk • contribs) 13:34, 15 April 2010 (UTC)

There aren't many diseases you can catch merely by getting someone's blood on your hands (an exception would be if you had a cut or hangnail). In general, you must then touch your hands to a mucous membrane, such as the eyes, for the contagion to gain entry into your body. However, you can do this whether you have gloves on or not. After contacting potentially contagious blood, the hands should then be sterilized, or the gloves removed. There is a problem with removing gloves, though, that it's easy to spread the blood from them onto something else while doing so. So, while the gloves do provide some protection in the case of minor cuts on the hands, they also have this drawback. StuRat (talk) 14:32, 15 April 2010 (UTC)

It is likely the medical/sanitary equivalent of security theater, that is it isn't a marked increase in sanitation when you wear the gloves; but the gloves make the customer/patient/even the doctor feel better about their own sanitation. Washing properly, and avoiding contacting problem areas afterwards, is likely the best method; but as a customer/patient, you don't see the washing go on, so you have no evidence that it happened. You can see the gloves, so you can get a better sense of security in seeing them, even if they are no actual proof of them improving sanitation in any way. --Jayron32 15:02, 15 April 2010 (UTC)

yes but if you have an even tiny micro tear on your hand (there seem to be alot near the fingernails) couldent he get infected with hep c  ? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 18:30, 15 April 2010 (UTC)

Possible, but unlikely. The reduction in the ability to feel through the gloves could also make other accidentally exposure, like the doctor cutting himself with a scalpel, more likely. StuRat (talk) 18:34, 15 April 2010 (UTC)

Fractals and the structure of the brain

Is there an article or reference for any coverage or discussion of fractal based structure of the brain. As I recall by using certain chemical procedures to process the tissues of the brain a network structure is revealed that mimics either fractal analysis of blood flow through healthy or through cancerous tissue. 71.100.8.49 (talk) 22:48, 14 April 2010 (UTC)

A Google Scholar search for "fractal structure of the brain" finds a number of things, including PMID 14642486 and PMID 16112737. Looie496 (talk) 01:21, 15 April 2010 (UTC)

Birds riding thermals

Why is it that some bird species can use thermals to go really high up into the sky whilst other birds appear to be completely unable? I've seen hawks and gulls riding thermals but I don't think that I've ever seen something like a pigeon, or a duck, or a starling doing the same. —Preceding unsigned comment added by 95.148.104.4 (talk) 22:52, 14 April 2010 (UTC)

Birds like hawks, vultures, pelicans, and so on have much larger wings to take advantage of rising air current, and also have a need to be spending time high in the sky, that is how they find food. A pigeon has neither the wing area nor the desire or need to soar. Beach drifter (talk) 22:59, 14 April 2010 (UTC)

Also, large birds can't fly by flapping alone, that uses too much energy when you're that big. StuRat (talk) 23:04, 14 April 2010 (UTC)

The peregrine falcon, a large bird, can use thermals to get to high altitudes then dive down by taking advantage of their weight and gravity at extremely high speeds to catch prey. ~AH1^(TCU) 23:26, 14 April 2010 (UTC)

A couple of years ago I saw a flock of geese rising on a thermal. I've only seen it the one time, and it must have been a hell of a thermal, because geese normally have to work pretty hard just to stay in the air. Looie496 (talk) 01:17, 15 April 2010 (UTC)

Birds are evolved to do what they need to do to survive in whatever environment they inhabit...look at an albatross File:Albatross shape.png and compare to a sailplane File:Dg800.jpg - both are designed to glide, take advantage of thermals - and guess what? They both have long, skinny wings. Compare a hummingbird File:Archilochus-alexandri-002-edit.jpg to a helicopter File:Indian air force dhruv helicopter j4042 arp.jpg - the wings are about half the length of the body in both cases. A Perigrine Falcon folds its' wings back for speed in a dive File:PeregrineFalconSilhouettes.svg - not unlike a swing-wing Panavia Tornado File:TornadoGR1 27Sqn RAF Mildenhall 1988.jpeg that retracts its wings for high speed flight. The point being that you don't build a jet fighter with long spindly wings - and falcons didn't evolve long spindly wings either. They simply aren't evolved to glide - they don't need to...and albatrosses don't need speed. SteveBaker (talk) 03:53, 15 April 2010 (UTC)

See wing loading. Hawks, eagles and such have low wing loading and can soar, but don't go very fast (peregrine falcons aside, who close their wings when they stoop from a height). Ducks, on the other hand, fly very fast and efficiently due to their smaller, low-drag, highly-loaded wings. The penalty is that they descend rapidly when they stop flapping - watch a duck land alight and see how steeply they descend. An efficient glide ratio is necessary for soaring, as the rising air must exceed the bird's descent rate. Acroterion _(talk) 17:07, 15 April 2010 (UTC)

How do gulls manage both soaring and fast, flapping flight, as a matter of interest? I read somewhere the other week that a Herring Gull can pull 40mph+ in still air (say, if pursuing a duck or a puffin with intent to kill/steal food) and probably a lot more with the wind behind it - yet the HG can also soar for hours, seemingly effortlessly on thermals and ridge lift, keeping an eye out for food. They seem to have the best of both worlds - but why? --Kurt Shaped Box (talk) 17:38, 15 April 2010 (UTC)

They're just at the transition in size where they can do a bit of both, but probably not either as well as a hummingbird hovers (by flapping) or a albatross hovers (by soaring on thermals). StuRat (talk) 18:50, 15 April 2010 (UTC)

Gulls do seem to be wonderfully 'mid-range', general-purpose creatures, in terms of their adaptations and abilities - they don't exactly excel at any one thing but they can fly, glide, swim, run, hunt and scavenge with reasonable aptitude, eat a huge range of foodstuffs - both animal and vegetable, they can generally defend themselves against any predator fast enough to catch them and generally move too fast for any predator strong enough to overpower them. They're also quite intelligent and resourceful, as it goes - and they live a long time, with a fairly consistent reproductive rate. I think that this is probably one of the winning formulas, in terms of the success of a species. --Kurt Shaped Box (talk) 20:47, 15 April 2010 (UTC)

Reading all that, one might actually get the impression that you like gulls. :-) StuRat (talk) 19:31, 16 April 2010 (UTC)

One other advantage to gulls, they are able to live either with, or without, people. Not all species can. StuRat (talk) 19:42, 16 April 2010 (UTC)

I do admire the gulls for their toughness and adaptability, FWIW - but mainly, I just think that they look cool and have a lot of character. I think that the key to survival on the Planet of The Humans is probably not to be too fussy about food or habitat - and to always maintain a healthy mistrust of people, albeit not to the extent of constant fear (which could get in the way of feeding opportunities), whilst having little-to-no economic value as meat/skin/other biological products or as a pet. --Kurt Shaped Box (talk) 21:33, 16 April 2010 (UTC)

Note that there are also several other methods of gaining lift similar to "riding on thermals". In one, instead of vertically rising columns of heated air, there is a horizontally moving "river of air". This can happen in a mountain pass, for example. The birds use this fast moving air to gain speed, then trade this horizontal speed for altitude, once they leave it. Once at altitude they do their scanning for prey. When they lose enough height, they go back into the "river of air" for another boost. StuRat (talk) 18:57, 15 April 2010 (UTC)

Birds riding the jet stream ?

Can any birds do this, or is it just too fast, too high, and too cold for them ? StuRat (talk) 18:59, 15 April 2010 (UTC)

Andean condors are occassionally seen at extreme altitudes of about 30,000 ft which might brush the lower end of the jet stream, but they are not at the same latitude as the jet stream. Even if they could use it, would they want to? They would have a really hard time getting back to their previous location. Googlemeister (talk) 20:29, 15 April 2010 (UTC)

If the jet stream is headed in the direction they wish to migrate, it seems like it would save them a lot of time and energy, if they could ride it. StuRat (talk) 18:33, 16 April 2010 (UTC)

I believe that I've read about birds (unsure of the species) flying above the summit of Mt. Everest - which, IIRC pokes up into the jet stream. --Kurt Shaped Box (talk) 20:47, 15 April 2010 (UTC)

Tropical birds have been known to ride in the eye of a tropical cyclone, as that was the only spot with calm winds where they could survive, only to end up thousands of kilometres from their starting point when the storm makes landfall over a non-tropical region. ~AH1^(TCU) 16:25, 17 April 2010 (UTC)