Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

September 18

radar system in electric trains

can RADAR system be installed in ELECTRIC TRAINS to detect the presence of another train in that track and any faults in the track? The key idea is to detect the presence of another train in the same track and find any faults in the track such that the automatic brakes are applied and the train is stopped automatically preventing accidents and any collision! is it feasible?if so how the system should be designed? plz provide a detailed explanation with circuit diagram. — Preceding unsigned comment added by Ajayfame.47 (talk • contribs) 01:40, 18 September 2011 (UTC)[reply]

In the US at least, I think there is already some system that detects where trains are on tracks and relays the info to a central headquarters for each line. There is also system for checking safety on tracks I think; at least on Amtrak's Northeast Corridor I believe there is. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 02:20, 18 September 2011 (UTC)[reply]

Here in Spain they let a little bit current flow through the track to know that it's still there. Otherwise, trains run in a dedicated track, so there's no big chance of collision. Trains are also tracked through GPS, so a central tracking office always know where they are. Other, less predictable problems, however, like a truck on the track or some repairing service train, could trigger an accident. 88.8.79.204 (talk) 02:40, 18 September 2011 (UTC)[reply]

Here in the USA, all of the most important railroads are protected by track circuits. This is a brief description of how they work: A small low-voltage current is passed through the rails, which activates a sensor that keeps the lights green as long as the track is intact and unoccupied; when a train enters the track, it temporarily sets up a crowbar circuit for as long as it remains on that track, causing the current to bypass the sensor, which detects the loss of current and changes the light to red; if the track is broken, this results in an open circuit, which also interrupts the current and changes the light to red. I believe that in most other civilized countries (Canada, Europe, Russia, etc.) a similar system is in use. And yes, it's perfectly feasible to integrate this system with an automatic brake for the train and/or with a lighted diagram for the dispatcher's use, and/or with a light display in the engineer's cab (as is done on many American mainlines). 67.169.177.176 (talk) 03:01, 18 September 2011 (UTC)[reply]

So, would RADAR be suitable ? No. Both oncoming trains and broken tracks could be behind a hill or bend, and thus hidden from RADAR (in the case of broken tracks, even a slight rise or bend would hide them). And, even if the broken tracks weren't hidden, seeing the break in a RADAR image at that shallow of an angle in time to stop might be impossible.

As for stopping trains based on automated systems, you could expect many false alarms with such a setup. And, if the braking is severe, that may also injure or kill people on board the train. StuRat (talk) 02:58, 18 September 2011 (UTC)[reply]

See Automatic train stop and Automatic train control for more info. Yes, it is perfectly feasible to stop trains based on automated systems, as you will see in these 2 articles. As for concerns about braking being too severe, this danger can be avoided with proper system design and calibration. 67.169.177.176 (talk) 03:04, 18 September 2011 (UTC)[reply]

Railways generally use(d) physical infrastructure (ie track circuits mentioned above, signals etc) for train safety. The idea that radar could be used to detect a train ahead on the line is not realistic and not used. eg just think of curves, tunnels, hills and other obstacles that would prevent it working properly.

RADAR is used in trains - eg one use is to detect speed of a locomotive ('super creep speed control') The article about the safety system European Train Control System also mentions the use of radar as one of a set of methods of calculating position. It isn't clear but I would guess this is to detect speed (as in a Radar gun)83.100.239.6 (talk) 12:44, 18 September 2011 (UTC)[reply]

An radar based experimental obstacle (ie fallen tree not train) detection system is described in New Scientist no.3783 , 24 Feb 1964, p 489 A similar system was trialled on the Tokaido Shikansen line in the 1960s [1] [2] [3] (none of these links are very informative about whether or not it every became a permanent fixture)

If it was tried back in 1964 and isn't in widespread use yet, you can pretty much assume it was a failure. They rarely follow-up such stories with news of a failure. StuRat (talk) 19:29, 18 September 2011 (UTC)[reply]

One source said the system couldn't distinguish a bird sitting on the radar transmittor from a fallen tree further away - probably fail - though these things can go unnoticed too if they work and are not glamorous.Imgaril (talk) 23:42, 18 September 2011 (UTC)[reply]

Trains often are moving or standing still on adjacent tracks, and when a train came around a curve it would be very hard for radar to tell a train on the same track up ahead from a train on the adjacent track, since both would be directly ahead of the train with radar. GPS sent to a central office with a computer monitoring for conflicts is a better bet, as is the old block system long ago installed on railroads in many countries. Edison (talk) 19:39, 18 September 2011 (UTC)[reply]

Rocking back and forth: symptom of...?

{{rd-deleted}} should've been used here. →Σ τ c. 05:24, 19 September 2011 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

I associate it with autism, but is that true? Quest09 (talk) 02:20, 18 September 2011 (UTC)[reply]

What kind of autism? I associate it more with either insanity or the beginnings of PTSD. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 02:23, 18 September 2011 (UTC)[reply]

Insanity is really not a very precise concept - it could include autism, PTSD and many other disorders. Autism confirms my association. However, I don't see how it relates to PTSD ... Quest09 (talk) 02:34, 18 September 2011 (UTC)[reply]

Nor is Autism. It is a very very broad collection of... different behaviours I guess you would say, hence Autism Spectrum Disorder. I don't think autism really counts as a form of insanity in most of the cases of its many different forms (or any really). The repetitive behaviour you're thinking of is when some forms of autism include OCD that causes people to do repetitve behaviours. By PTSD I am saying think of someone like a rape victim who is holding their knees while on a chair or something else and is rocking back and forth while crying (think of something out of a movie). The result of a traumatic event. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 02:40, 18 September 2011 (UTC)[reply]

Yes, I could imagine that, but I still wouldn't know if traumatic experiences produce the body rocking symptom, or how this is associated with other disorders. Quest09 (talk) 02:48, 18 September 2011 (UTC)[reply]

There are entire books written on this subject. See this for example. I don't know much about PTSD related rocking, although I see mentions of that in some literature too.

That said, rocking (along with arm flapping and some other similar behaviors) are often associated with autism but not OCD. OCD associated compulsions are often cleaning, counting, and checking related, whereas autism compulsions are much more about ordering and touching.^{http://affect.media.mit.edu/Rgrads/Articles/pdfs/Lewis+Bodfish-1998-Repetitive.pdf} There are also a host of other behaviors strongly associated with autism that do not show up anywhere near as much with OCD behavior... like echolalia, rocking at early ages, and tourettes like ticks. Some of the drug treatments that are common in OCD only work marginally if at all in autism on the same behaviors.^{http://www.nature.com/npp/journal/v30/n3/abs/1300627a.html}

This question exploded its scope quite quickly in the above... what is a more precise question that you want to know? I interpret your original question and responses as wondering what the biological / neurological basis of rocking is. It's possible that multiple things cause rocking behavior, or perhaps there's a single unifying cause of rocking behavior shared by many patients with varying disorders, or perhaps some patients experience multiple disorders at higher frequency. Any of these explanations are possible; I'm certainly in no position to know for sure which is right. The two studies I cite above are a little old, but they may be a place to start. Shadowjams (talk) 06:29, 18 September 2011 (UTC)[reply]

Context is important here. Methamphetamine and opioid withdrawal will produce a rocking back and forth motion in addicts. Viriditas (talk) 13:30, 18 September 2011 (UTC)[reply]

See "A New York researcher has pinpointed for the first time brain regions in children with autism linked to "ritualistic repetitive behavior," the insatiable desire to rock back and forth for hours or tirelessly march in place.". Alansplodge (talk) 16:55, 18 September 2011 (UTC)[reply]

Hmmm, odd, I've never seen that sort of behaviour associated with a form of autism, then again I'm really only familiar with a very mild form. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 17:06, 18 September 2011 (UTC)[reply]

You probably mean Asperger, but anyway, body rocking seems a pretty common behavior among autistic persons, among other things. Quest09 (talk) 01:04, 19 September 2011 (UTC)[reply]

Social science statistics - weighting outliers?

Hello

I have an introductory course to statistics this semester, and as such my knowledge of the mathematical aspects are limited. Therefore, I must stress that the following is a question about method, sooner than how to do this mathematically. I want to know if someone has thought this thought before, and devised a scientifically sound method.

Let us say we have 500 respondents in eg. the European Social Survey. A range of questions have been asked, but we're concerned with the dependent variable Happiness ratings, and have found a strong correlation to Income. In this example, we've checked for other variables and have found the correlation remains. However, there are statistical outliers: Perhaps 30-50 of our respondents are extremely un/happy, despite their income. Did they just make a joke of their survey? They are ruining what would otherwise be a perfectly linear relationship.

The question is: Is there a method for removing or weighing these respondents differently? In the ESS, if we look at these 50 respondents and the many many other questions they answered, does there exist a method whereby we assert their 'outlierness'? Meaning their propensity to answer on the far ends of the scales. I'd imagine one can look at a range of scales and judge how far they lie from the average on each - and assign a value accordingly. By doing so, in our example we may find that 10-20 individuals answered in jest; the rest, however, are 'genuine' outliers.

Thank you in advance for any help!

88.91.84.136 (talk) 12:29, 18 September 2011 (UTC)[reply]

I believe the usual standard is to discount outliers that lie outside of two standard deviations from the mean. I believe this is the 95% confidence interval. But it has been decades since I did this stuff... --Jayron32 13:00, 18 September 2011 (UTC)[reply]

If you want to automate outlier detection, you first need a model of your expected distribution. In my previous employment, I wrote complicated modeling programs to estimate state vectors for certain systems, and then optimized a distribution fit that minimzed the error of the curve-fit, ignoring error due to outliers. The theory of measuring error for multidimensional problems is very complicated, but most people in the social sciences will recognize at least the least squares method, which minimizes the sum of the squared error for each element. What this means in practice - for outlier detection - is that your distribution implicitly results in "soft edges" - a smooth transition from "normal" to "outlier." If you want to define other types of distributions with more sophisticated outlier rejection, you need to redefine your error function or your error measure. Nimur (talk) 15:00, 18 September 2011 (UTC)[reply]

The problem with just ignoring anyone more than two SDs from the mean is that you are ignoring the possibility that your distribution isn't actually normal at all (that's where the 95% comes from - it's the proportion of a normal distribution that is within 2 SDs of the mean - you need to go higher than 2 SDs, really, since you expect 1 in 20 people to be outside 2 SDs, so out of 500 people there should be 25 outside 2 SDs and they aren't outliers, they are just regular extreme values). If you have a very strong reason to believe that your distribution is normal (or approximately normal, perhaps by the central limit theorem), then sure, remove people that are a long way from the mean. If you don't have a very strong reason to believe it's normal, though, then you need to consider the possibility that they aren't outliers and that your distribution genuinely has a long tail. --Tango (talk) 15:28, 18 September 2011 (UTC)[reply]

But central limit theorem only applies for uniformly-random distributions! I can name dozens of scenarios in the physical sciences, and probably thousands of scenarios in the social sciences, where the data is not uniformly random. The answer to a political poll question, for example, shouldn't be uniformly random. As Tango points out, this means your distributions are complicated - possibly with multiple peaks - and so you need a more sophisticated classifier. If you treat these situations as bell-curves, you will (1) poorly fit your bell curve, (2) discard "outliers" that contained valuable data, and (3) include data points that fit the bell-curve, but do not fit to your desired model distribution. Nimur (talk) 16:38, 18 September 2011 (UTC)[reply]

The CLT applies to any distribution, not just uniform ones. If you are taking the average (or sum) of enough identically distributed, independant random variables, then it will be approximately normal, regardless of what the distribution is. That's why normal distributions come up so often. There are plenty of situations where normal distributions don't apply, of course, which is why you can't just blindly assume that anyone more than 3 SDs from the mean is a mistake. --Tango (talk) 13:11, 19 September 2011 (UTC)[reply]

This is a delicate issue: as soon as you start removing data, you raise the possibility of forcing the data to fit your hypothesis by removing the points you don't like. The two main precepts for avoiding that are (1) decide on your criteria before you collect the data, and (2) make sure that the criteria you use do not specifically select against data that don't fit your hypothesis. Even then it's always nicer if you can find a method of analysis that allows you to use all of the data, even if it weakens your findings a bit. Looie496 (talk) 16:40, 18 September 2011 (UTC)[reply]

Specifically to answer the OP's original question about social-science surveys: the standard practice is to discreetly hide questions amongst the surveys that should have "known answers" - or, questions that are intended to duplicate earlier questions. If someone is answering the survey questions in a joking way, or by selecting "choice A" for each question, these "easy questions" end up with improbable answers, and that entire survey can be discarded. This is similar to a captcha. I'm sure there are variants of this technique, and they probably have been widely researched. Nimur (talk) 16:47, 18 September 2011 (UTC)[reply]

Thanks, Nimur, for bringing it back to the OP's question. As far as I know, there are three ways to deal with outliers, one tactical (the one given by Nimur, to design the survey questions to expose them) and two mathematical. The first of these is the one given, to remove figures that fall more than 3 standard deviations away from the mean. This is hard if you are dealing with multivariate data, but not impossible. Also, if you know the data are normally distributed, there is no justification for removing outliers - contrary to Tango's comment, it is exactly when you don't know the distribution that you must consider removing outliers, which happens frequently. The other mathematical method is to use Robust statistics which are ways of removing outliers or downweighting them according to some predetermined algorithm. Perhaps one could call the "3 standard deviations" rule a kind of robust statistic, but it is usually done along with other tests, and requires a lot of inspection by the naked eye of graphical representations of data. The discipline of Robust statistics is really an attempt to automate this process, and achieve similar results. Hope this was useful. It's been emotional (talk) 06:49, 20 September 2011 (UTC)[reply]

Could you elaborate on your comment about normal distributions? If I know something is normally distributed, but I see points more than 3 SD from the mean (on a sample size that means there shouldn't be such extremes - obviously if you have a million data points, you expect a few to be more than 3 SDs from the mean and would need to either look at 4 or 5 or whatever SDs or count how many extreme values you have an compare that to the number you expect, although if you did the latter I'm not sure how you would deal with the surplus) then I know something has gone wrong with those points. If I don't know the distribution, then I don't know if something has gone wrong with those points or if they genuinely are that extreme. There are some distributions where you fully expect some points to be very extreme. It's those distributions where you shouldn't be removing points that look like outliers, since they aren't really outliers - they are consistent with the distribution. Consider the discrete distribution with 5% chance of being 0, 90% chance of being 50 and 5% chance of being 100. The mean is obviously 50. The standard deviation is just over 15. That means 10% of the distribution is more than 3 SD from the mean. It would obviously be wrong to remove 10% of your data points as errors in that situation. --Tango (talk) 18:00, 20 September 2011 (UTC)[reply]

Yes, you are correct from the point of view you describe - I wasn't clear about your terminology. To clarify what I said, the data come from some distribution or other, and if you repeatedly get extreme scores, more than you would with a normal distribution, then your distribution is by definition not normal, since the distribution is the thing that the actual data (not the "ideal" data) are taken from. At least that was the terminology in robust statistics, as I understood it, and I was under the impression it was orthodox across all of statistics. I may have been wrong. You are clearly assuming there is an underlying distribution which is the thing you want, with some measurement error superimposed upon it, creating the extreme scores. Then you are correct to reason as you do (as far as I understand it) but you must be quite certain you know the shape of the true distribution if you just label something measurement error. Admittedly, that happens often, or at least we often know a distribution is close enough to normal to call something an error. The situation I was discussing was effectively the same, but hypothetically if your actual data are normal, you will not have anything called an outlier, so removal of outliers assumes the actual data are not normal, but nearly so. If you have a totally different distribution, things change, but often the trick is to transform the data so you get a normal or nearly normal distribution, say by taking a logarithmic plot. As far as the OP is concerned, the techniques I gave above are the three in use that I am aware of, and the rest is a more technical discussion. Hope I've been clear, and thanks for your comment, It's been emotional (talk) 14:23, 21 September 2011 (UTC)[reply]

It's not clear to me why you need to remove the outliers. If you have scatter plot then for each value of the income you a probability distribution for the happiness, and unlike the mean, the maximum of this function is not strongly influenced by the outliers. By sampling the data and using extrapolation techniques, you should be able to quite accurately construct the curve that traces the maximum of the probability distribution. Count Iblis (talk) 19:07, 20 September 2011 (UTC)[reply]

If the outliers are extreme enough, they could influence the best-fit curve quite a bit. If you are trying to find the best straight line to fit your data points and there are few data points that clearly don't fit on the line, including them in your least-squares (or whatever method you are using) doesn't make much sense. You can draw one of two conclusions - either a straight line isn't appropriate or the data points are erroneous. You shouldn't try and draw a straight line through points that clearly aren't linearly correlated, since that doesn't work for either conclusion (if a straight line isn't appropriate, why are you drawing one? if the points are erroneous, why are you using them?). --Tango (talk) 19:33, 20 September 2011 (UTC)[reply]

physics of shrinking and growing physical objects and people

I don't know why my question was removed, I specifically marked it as non-troll. I would like to know the physics of shrinking and growing physical objects and people, i.e. whether it will ever be possible or already is, etc. 82.234.207.120 (talk) 13:05, 18 September 2011 (UTC)[reply]

A big fat NO, it is certainly not possible! At least not in the sense that you are talking about - the only way things can shrink is by becoming denser. The space between particles can decrease, but the particles themselves cannot. Plasmic Physics (talk) 13:34, 18 September 2011 (UTC)[reply]

I've warned this user about posting wasteful and nonsense messages here. --RA (talk) 13:45, 18 September 2011 (UTC)[reply]

Such blue-sky questions need not be wasteful. Why can't we shrink or expand an object? Because it's made up of atoms. Conservation of mass dictates we can't just make some of the atoms go away, even if there were some way to choose a "representative sample" of atoms in a person to make go away without harming them (which we also can't do). The actual size of the atoms is dictated by the atomic radius and such considerations, based ultimately on the effective size of the electron orbitals that form the basis of chemistry. The atoms need to contact one another by Van der Waals forces in order to stay in the same overall state (liquid, solid...) as they were, and overlap is strongly prohibited by the Pauli exclusion principle. Now getting down to brass tacks, what would we need to shrink or expand something? Well, barring those other possibilities, we'd have to change the size of the atoms themselves, i.e. change the Compton wavelength of the electron - the electron mass, or the base speed of light in vacuum, I think. Nobody has the slightest clue how to do this in a person-sized area, or how you'd keep such a fundamental change confined there. Wnt (talk) 14:31, 18 September 2011 (UTC)[reply]

It's not immeadiately obvious that you couldn't shrink a person by removing some of the atoms and leaving a representative sample behind. You would probably need to do it by removing entire cells, rather than trying to shrink cells. Within a cell, you can be at the point where individual molecules play vital roles. It's not usually the case that an individual cell plays a vital role within the body (the one exception I can think of is the brain - we don't really know how memory is stored, but there is a good chance individual cells are involved). So, apart from the brain, there is nothing at the fundamental physical level to stop you shrinking a perosn (although we obvious don't have anything close to the technology to do it). The big problem you would have if you tried to shrink someone by removing cells is that different things scale in different ways. If you halve someone's height, you quarter their surface area and you eighth their volume. Take bones, for instance. Their strength is roughly proportional to their cross sectional area. The weight they need to support is proportional to the volume of the body. That means that if you halve someone's height, their bones will end up twice as strong as they need to be to support the body. That may not sound like a problem (although it's clearly a problem for growing people - if you double someone's height, their bones will be half the strength they need to be and the person will collapse under their own weight), but it means the body is now massively inefficient. The body is a very delicate balance with everything doing just the amount it needs to and no more. If you mess with that, everything will go horribly wrong. Obviously, you can have small animals, but they aren't just scaled down versions of larger animals. --Tango (talk) 15:12, 18 September 2011 (UTC)[reply]

Hi, OP here. I'm not so much interested in the theoretics (obviously it is in some sense "possible", as there are animals that live on that scale...) I am interested technologically in what the state of the art is in this matter. I do not even know what word to search Wikipedia for, I can just describe the technology as I have right now... 82.234.207.120 (talk) 16:42, 18 September 2011 (UTC)[reply]

Animals live at many size scales because of their different evolutionary pasts, and ecological niches. We can't shrink individuals, but we can shrink species, given the desire and time. See e.g. the chihuahua or shetland pony. 108.15.146.137 (talk) 17:27, 18 September 2011 (UTC)[reply]

I'm sorry if I'm not making myself clear. I've trolled elsewhere, but this question is serious: whether it's fantasy or reality, what is the NAME of the technology in question? Should I just resort to guessing Greek and Latin roots? Surely, since this possibility has appeared at least in fiction, there is a name for what we're talking about. What is the technology in question, whether it exists, is theoretical, or is fantasy? I would like to look up more about it... Thank you! 82.234.207.120 (talk) 17:34, 18 September 2011 (UTC)[reply]

Shrink ray pretty much covers it. Franamax (talk) 18:24, 18 September 2011 (UTC)[reply]

Thanks. I never thought to check such a pedestrian name, which is as far from Greek or Latin as the article is from having any scientific content. I was hoping for something more... 82.234.207.120 (talk) 18:49, 18 September 2011 (UTC)[reply]

There is no actual or theoretical process for shrinking objects. It is purely an invention of fiction writers, and hence there is no science to speak of. Dragons flight (talk) 18:56, 18 September 2011 (UTC)[reply]

It is possible in classical physics, allowing you build computers that can solve non-computable problems see e.g. here. Count Iblis (talk) 18:59, 18 September 2011 (UTC)[reply]

Ah yes, the old-time ball-bearing computers, that takes me back. ;) Franamax (talk) 19:29, 18 September 2011 (UTC)[reply]

Objects grow and shrink all the fnording time: Thermal expansion. Hcobb (talk) 19:04, 18 September 2011 (UTC)[reply]

And, if objects are allowed to be mostly gas, then they can expand and contract quite a bit more. (Also, if they are allowed to take in or expel a fluid, like the puffer fish with water or air.) StuRat (talk) 19:25, 18 September 2011 (UTC)[reply]

That is not the same though, the OP is talking about shrinking the dimensions of an object on all scales. Essentially creating a situation where the object shares properties with a fractal structure, the dimensional proportionallity is constant at every magnification. This would require changing universal constants, which is unonceivable in this universe. Plasmic Physics (talk) 23:42, 18 September 2011 (UTC)[reply]

A Pantograph can be used to make smaller or larger copies of drawings and objects. Cuddlyable3 (talk) 17:06, 20 September 2011 (UTC)[reply]

Peanuts used as ingredient of Dynamite?

I've read somewhere that peanuts are used as an ingredient in dynamite, and i was wondering if this was true. Thanks. — Preceding unsigned comment added by RocketMaster (talk • contribs) 15:48, 18 September 2011 (UTC)[reply]

Peanut oil (as with other vegetable oils) contains triglyceride from which one could extract glycerol which could be used to make nitroglycerin which is the exciting constituent of dynamite. But there are lots of other sources of industrial glycerol, and I don't think there's anything special about peanuts per se. -- Finlay McWalterჷTalk 16:00, 18 September 2011 (UTC)[reply]

Yes. At first glance, this would seem unlikely, but as our dynamite article states, the explosive is made from "sawdust (or any other type of absorbent material) soaked in nitroglycerin". The article lists "powdered shells" as one of the alternatives to sawdust, so it would seem possible that peanut shells have been used. On the other hand, our peanut article states that "Peanuts have a variety of industrial end uses. Paint, varnish, lubricating oil, leather dressings, furniture polish, insecticides, and nitroglycerin are made from peanut oil". There doesn't seem to be a direct source for this, but our glycerol article states that glycerol is a used to manufacture nitroglycerine, and it would seem that, via saponification, it will be possible to produce glycerol from peanut oil. So, to sum up, I think the answer may well be that you could make dynamite using peanuts as a raw material, though whether they are normally used is another question. AndyTheGrump (talk) 16:12, 18 September 2011 (UTC)[reply]

Indeed, any vegetable oil could be used, sunflower, corn etc... A possible source appears to be Peanuts: the illustrious history of the goober pea, Andrew F. Smith, p102 - reading it out loud to you it appears that the USA used vegetable oils sourced in the 'far east' ie the philipines prior to WW2. (also happend during WW1 too same book p.69) During WW2 alternative sources had to be found due to japanese control of these areas - this turned out to be peanut oil. See also How peanuts helped to save the free world.Imgaril (talk) 16:30, 18 September 2011 (UTC)[reply]

One possible lead could be the work of George Washington Carver, who was a botanist known for working with, among other things, peanuts. He had supposedly catalogued several hundred uses for peanuts. --Jayron32 04:58, 19 September 2011 (UTC)[reply]

Corvid intelligence

Why are corvids (e.g. crows and magpies) so smart? --75.33.217.234 (talk) 17:23, 18 September 2011 (UTC)[reply]

Because they have smart brains. Dauto (talk) 17:26, 18 September 2011 (UTC)[reply]

What survival advantage do they gain that outweighs the extra energy that's required to maintain an improved brain? Why didn't other birds develop this? --75.33.217.234 (talk) 17:28, 18 September 2011 (UTC)[reply]

A better answer is because of their social structures, ecological niches and life history. Most corvids make their living extracting food from a wide variety of sources, and being able to survive in fairly wide range of environmental conditions. Having complex, adaptive cognitive abilities (learning, communication, tool making) is very beneficial for this life style. Post (EC): other birds have different lifestyles. Also, some other birds are quite 'smart', see e.g. african grey parrot.108.15.146.137 (talk) 17:36, 18 September 2011 (UTC)[reply]

Yes, that of course is the key issue. I suspect that it is probably related to their omnivorous feeding habits - they will exploit a wide range of food sources, and being able to locate and exploit resources that more specialist feeders can't may well require a higher level of intelligence (and probably, a better memory too - they may well exploit resources that are only available on a seasonal basis, and at limited locations, and would need to remember them over long periods). Many corvid species are strongly social too, which can often imply higher levels of intelligence. And yes, Parrots are likewise highly intelligent, social, and able to exploit a wide range of food sources. AndyTheGrump (talk) 17:40, 18 September 2011 (UTC)[reply]

By extension, would the push for vegetarianism perhaps be a conspiracy to "dumb down" the naturally omniverous human species? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:09, 18 September 2011 (UTC)[reply]

The pursuit of food is a pretty negligible portion of what most modern humans use their intellect on. I can go to the supermarket and get a billion choices with very little effort. In fact, arguably vegetarians are spending more time thinking about their food choices than most people, though I would still argue that it is a relatively small part of what they use intelligence for. Dragons flight (talk) 18:54, 18 September 2011 (UTC)[reply]

Funny, there's research on exactly this topic. Here's a small, on point sampling: [4] [5]. The primary indicators seem to be 1) highly social groups and 2) long developmental period before adulthood. They also seem to have vast spatial memories because they're hiding food when they're not dropping children off for their neighbors to raise. They're kind of the grifters of the bird world. Google scholar for "corvid intelligence" and you'll find a ton of research. Shadowjams (talk) 22:17, 18 September 2011 (UTC)[reply]

It's all about the High vocal center. (It seems Corvids are songbirds, by the way, or at least vocalistbirds.) Card Zero (talk) 08:53, 19 September 2011 (UTC)[reply]

Jurassic Park

Were any dinosaurs venomous (like the Dilophosaurus in Jurassic Park)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:35, 18 September 2011 (UTC)[reply]

Nobody really knows: venom glands do not fossilize. The living animals most closely related to dinosaurs are birds and crocodilians, and none of them are venomous. A group of scientists claimed to have fossil evidence that the dinosaur species Sinornithosaurus was venomous, but their arguments have been disputed (see the article). Looie496 (talk) 18:47, 18 September 2011 (UTC)[reply]

Yeah no one knows, but we can infer some things based on animals today. Smaller, more frail predatory animals tend to be venomous to help them assist in taking down prey. Larger animals have no need of such things as their sheer size, strength, fangs, claws are more than enough to take down prey. So it's pretty safe to assuming that a t.rex probably had no venom while smaller dinosaurs.... I don't know, it's possible but there's no reason to believe that they did. Birds are directly descended from theropod dinosaurs, and they can be quite small, however I don't believe any of them are venomous so it's prolly safe to assume that none of their ancestors did either. ScienceApe (talk) 23:17, 18 September 2011 (UTC)[reply]

Dilophosaurus, unlike the runty specimen in Jurassic Park, were also actually fairly large theropods. In contrast, the Velociraptor depicted there were waaay oversized.-- Obsidi♠n Soul 08:32, 19 September 2011 (UTC)[reply]

The raptors in Jurassic Park were more like Deinonychus, weren't they? --Kurt Shaped Box (talk) 18:48, 19 September 2011 (UTC)[reply]

Naked ones with genius-level brains. LOL. Artistic license, I guess.-- Obsidi♠n Soul 19:14, 19 September 2011 (UTC)[reply]

To be fair to Michael Crichton, it wasn't (widely?) known that raptoroid dinosaurs had feathers when the books were written. --Kurt Shaped Box (talk) 19:32, 19 September 2011 (UTC)[reply]

Our understanding of dinosaurs has changed a LOT since those days. The idea that birds are actually dinosaurs and that theropod dinosaurs were very similar to birds was virtually unknown in the public eye, and Jurassic Park helped changed that image in the eyes of the general populace. For that, you have to give Michael Crichton a lot of credit. ScienceApe (talk) 21:22, 19 September 2011 (UTC)[reply]

Oh don't get me wrong, I <3ed the book (s, if you include The Lost World). :P Though I covered my eyes through almost the entire film when I first saw it (long before I read the book) as a kid. LOL. Dad just found it hilarious. :( -- Obsidi♠n Soul 22:47, 19 September 2011 (UTC)[reply]

There are a small number of bird species (e.g. the Hooded Pitohui) that can secrete poison in their skin and feathers for defence purposes - but they're not strictly 'venomous'. --Kurt Shaped Box (talk) 18:48, 19 September 2011 (UTC)[reply]

There is some evidence that Komodo dragons use venom (our article discusses it), so I don't think arguments of that sort are very compelling. Looie496 (talk) 23:41, 18 September 2011 (UTC)[reply]

No, I don't think one (debatable) example to the contrary really invalidates my arguments. Generally speaking we observe larger animals relying on physical attributes other than venom to bring down prey. ScienceApe (talk) 03:02, 19 September 2011 (UTC)[reply]

A BBC Radio 4 trailer I heard less than 2 hours ago, for a forthcoming episode of a current BBC TV series about dinosaurs, made reference to a flying or gliding dinosaur - non-avian but closely related to "true" birds - that was described as venomous: it may have been Sinornithosaurus as referenced above.

Whether or not this turns out to be accurate, I don't think that ScienceApe's argument above (in the topic's third post) is valid, because although extant birds are indeed descended from theropod dinosaurs (I would say they "are" therepod dinosaurs), they are only descended from one or at best a small number of species out of the very many other dinosaur species, theropod and otherwise, that existed. Their (alleged) lack of venom within the extant clade can therefore at the most only suggest that their particular ancestral species (or to be generous, genus) was probably non-venomous, without saying very much about their "non-ancestors." In practice I suspect that such a characteristic could both evolve and be lost multiple times in different lines over the couple of 100 million or so years that the scope of the OP's question. {The poster formerly known as 87.81.230.195} 90.193.78.49 (talk) 19:10, 19 September 2011 (UTC)[reply]

Sinornithosaurus was proposed to have been venomous, but this has been soundly debunked. It was based on blatant misinterpretation of the specimens (teeth out of socket, etc.). MMartyniuk (talk) 22:38, 19 September 2011 (UTC)[reply]

No, you misconstrued my post. I was using process of elimination. Basically what I was saying was that we can safely assume that none of the dinosaurs that birds evolved from had any venom. I wasn't talking about any of the other dinosaurs in regards to that argument, but again we have absolutely no evidence that any of them possessed any venom so there's no reason to believe any did. ScienceApe (talk) 23:40, 19 September 2011 (UTC)[reply]

Today there are poisonous reptiles, poisonous snakes, poisonous mammals, and at least one poisonous bird species. It seems rather absurd to suppose, a priori, that there would never had been a poisonous dinosaur, given that they were around for 160 million years, seemed to occupy a huge variety of ecological niches, had huge diversity in form (from the gigantic to the tiny). --Mr.98 (talk) 19:51, 19 September 2011 (UTC)[reply]

I never said there wasn't. I said there's no reason to believe there was because there's no evidence, nor any logical reason to believe that any did based on the rationale I gave before. ScienceApe (talk) 21:27, 19 September 2011 (UTC)[reply]

It's your logic that I'm disagreeing with rather explicitly. There is no reason to suspect that there wouldn't be at least one venomous dinosaur species. The rationale you gave is poor; dinosaurs came in all sizes and occupied all niches. The evidence is hard to parse on account of the fossil record; it doesn't prove the negative case whatsoever. --Mr.98 (talk) 22:30, 19 September 2011 (UTC)[reply]

It's possible, but there's no reason to think it's a certainty. It's a fun fantasy, but it's just that. You may as well make the same argument for, say, fully marine ornithischians. There needs to be some kind of evidence to make it science. To quote Futurama, "nothing is impossible if you can imagine it! That's what being a scientist is all about!" (he said, sarcastically). The bottom line is you need to realize there is a big difference between saying "there were never any poisonous dinosaurs" and "there is no evidence there were ever any poisonous dinosaurs." You can't prove a negative, but science is about disproving positives. MMartyniuk (talk) 22:35, 19 September 2011 (UTC)[reply]

Mr.98 you basically just pulled out the argument from ignorance, which is commonly used by theists in regards to claims that god exists. They say that "Yes I can't prove god exists, but you can't disprove it either", which is an absurd argument. You essentially did the same exact thing. Yes dinosaurs lived in all kinds of environments and came in all kinds of sizes, but there's absolutely no proof that any of them had venom. Does that mean that none of them were venomous? No, but there's no reason to believe any of them did either. I don't have to disprove something when there has not been a positive made in the first place. You need solid evidence in order to make that claim. ScienceApe (talk) 23:40, 19 September 2011 (UTC)[reply]

The short answer is: we don't know, but perhaps our research will yield evidence to support the hypothesis. Lots of diverse critters have evolved toxic bites, stingers or spurs such as insects, octopuses, stingrays, platypuses and snakes. In addition, even though birds are now rather benign towards us, they are not a good representative sample of what we should expect to find before the mass extinction occurred (most dinos were nothing like today's birds). Therefore, hypothetically, if I were to find some lively pint-size odd-looking but-cute dinosaur being playing about in the bushes or near me, I'd be cautious enough to treat it as if it were a lethal viper, for I would believe it to be possible. --Modocc (talk) 16:47, 20 September 2011 (UTC)[reply]

Was the format of the Voyager Golden Record's decipherability tested with humans?

After coming up with what to draw on the surface of it as well as the format to be used for encoding images in the analog grooves of the record, did they ever see if humans who were not "told the answers" could figure out what the drawings meant and could read the images off the record? Peter Michner (talk) 20:24, 18 September 2011 (UTC)[reply]

Humans would, of course, recognize the figures as humans, and would have a head-start in many other ways. However, a technologically advanced alien civilization might be better equipped to rig up a record-player than some isolated tribe of humans. StuRat (talk) 20:37, 18 September 2011 (UTC)[reply]

Actually, that particular record at the link provided doesn't seem to be the one with two naked Homo sapiens. I mainly want to know the factual yes-or-no whether they presented that record in the image to some other Homo sapiens prior to the launch and said, in so many words, "Can you decode this?" Peter Michner (talk) 20:42, 18 September 2011 (UTC)[reply]

The main problem with testing the golden record is that essentially any modern human is going to recognize that it is a phonograph, and immediately be able to make huge leaps and bounds based on that alone. I'm not sure how you could "test it on a human" for that reason: if you gave it to a human who you presume could work it out (a scientist, to be sure, not your average day laborer), they'd know quite a lot just by the appearance of it. More tricky would be the Arecibo message that StuRat refers to — even recognizing the human figure as human (which you wouldn't be able to do unless you figured out what the width/height of the signal was supposed to be) wouldn't really make the rest of it obvious to you without a lot of patient study. I think the idea behind both is that the alien equivalent of scientists would spend some time hemming and hawing over it, just as we did the Egyptian hieroglyphs. It's not expected that they'd be able to decode it in a day. --Mr.98 (talk) 23:00, 18 September 2011 (UTC)[reply]

I agree any success of a human doesn't say anything about aliens' success, but, simply, did they give a human a crack at it before they sent it up? That's all I want to know. I'm asking about the existence or non-existence of an event before a certain time in history. Peter Michner (talk) 23:50, 18 September 2011 (UTC)[reply]

I didn't recognize it was a record the first time I saw it; in fact, I didn't know what a record was until much later. I seem to remember that the answer is yes, and that the bright scientists it was presented to couldn't decipher it. However, the closest thing to a confirmation I found on Google was this highly sketchy website:http://www.thesupernaturalworld.com/forum/index.php?showtopic=3996

"'I've shown the plaque to lots of people, including some really bright students,' said Park. "They couldn't make heads or tails of it.'"

However, this refers to the Pioneers plaques, not the Golden Record. Sorry for not having a better answer; hopefully somebody will, because I'm also curious. --140.180.16.144 (talk) 03:33, 19 September 2011 (UTC)[reply]

That made me curious, can anyone understand this:

AB●C●●D●●●E●●●●F●●●●●G●●●●●●H●●●●●●●I●●●●●●●●J●●●●●●●●●

AKA BKB CKC EKE FKF GKG HKH IKI JKJ

ALBKB BLCKD CLDKF DLEKH ELFKJ

AMAKA BMBKB AMBKA BMCKB CMDKG

I'm using arbitrary symbols and the principles outlined in Carl Sagan's Contact, heh. -- Obsidi♠n Soul 06:19, 19 September 2011 (UTC)[reply]

For the record I interpret A to M as... (see comment in Wiki source) but this relies heavily on our cultural conventions for writing such things. Even tiny changes would make it harder. Wnt (talk) 21:43, 20 September 2011 (UTC)[reply]

I actually thought of using something other than base-10 (for aliens which have 12 fingers, or aliens which use the number of their eyes to count, etc. LOL), but well... that was a quick test and I can't exactly transmit it with pulses of light etc., heh. And saw the error now.. eesh. In Sagan's novel the primer was also all in binary. -- Obsidi♠n Soul 02:27, 21 September 2011 (UTC)[reply]

As for the message. I found an interview of Frank Drake that mentions him testing out the Arecibo message on Sagan. Quote:

I took [Carl Sagan] to lunch one day and presented him with the message already decoded. I asked, “Can you understand this?” This was a test to see if the message was understandable to a very knowledgeable Earth scientist. We eventually learned that nobody could interpret all of the message; each scientist only could interpret the part relevant to their discipline. So Carl got the numbers right and the planetary system right, but he didn’t get the DNA chemistry.

It's not the Golden Record though :/ -- Obsidi♠n Soul 06:19, 19 September 2011 (UTC)[reply]

A-J are 0-9, K is =, L is + and M is *. That's just basic arithmatic, though, and I was expecting you to be doing basis arithmatic because I'm familiar with Sagan's work. It's not completely unreasonable to assume that a technologically advanced alien culture would also have the same expectation. Try explaining anything more complicated and it gets a lot harder. --Tango (talk) 18:13, 20 September 2011 (UTC)[reply]

Yay! Yep agree of course. But I'm happy I made contact. ;) Obsidian Soul phone home. ROFL. -- Obsidi♠n Soul 02:27, 21 September 2011 (UTC)[reply]

The Golden Record was shown to humans before being put aboard Voyager. Many different humans were involved in designing it and deciding if it will provide any benefit to anyone who might find it. I believe there is confusion about what is on the Golden Record. On one side is primarily information about getting audio and video from the record. If you don't work with audio or video electronics, you won't get it. If you do, you will recognize the waveform representations and, possibly, figure out how to get audio and/or video from it. Once you do that, the record contains sounds and pictures of things around Earth. There is nothing much to decipher. You may not recognize which specific species of bird is making one of the bird calls on the record, but you'd recognize it as a bird. You may not know who one of the photos is of, but you'd recognize it as a photo of a human. -- kainaw ™ 18:46, 20 September 2011 (UTC)[reply]

Genital cutting reduces/increases the risk of contracting HIV?

According to this, http://en.wikipedia.org/wiki/HIV#Sexual it says that male circumcision reduces the risk of contracting HIV, while female circumcision may increases the risk of a female contracting HIV. That doesn't make sense to me. Why would there be any correlation at all? ScienceApe (talk) 23:12, 18 September 2011 (UTC)[reply]

Male and female circumcision are two quite different procedures. Hence, no wonder that they produce different results. In the case of male circumcision, it reduces the possibility of infections and therefore it reduces the possibility of having more open ways for the HIV virus to enter the body. Quest09 (talk) 00:00, 19 September 2011 (UTC)[reply]

How does it reduce the possibility of infections? How does removing the clitoris increase the possibility of infection? ScienceApe (talk) 02:57, 19 September 2011 (UTC)[reply]

Unsurprisingling, the former is discussed extensively at Male circumcision#Sexually transmitted diseases and Circumcision and HIV. It doesn't exactly seem surprising there is some effect. Nil Einne (talk) 04:59, 19 September 2011 (UTC)[reply]

Doesn't say why though. Just that there's a correlation. ScienceApe (talk) 09:47, 19 September 2011 (UTC)[reply]

You're mistaken. Our article says:

Langerhans cells are part of the human immune system. Three studies identified high concentrations of Langerhans and other "HIV target" cells in the foreskin[97][98][99] and Szabo and Short suggested that the Langerhans cells in the foreskin may provide an entry point for viral infection.[28] McCoombe, Cameron, and Short also found that the keratin is thinnest on the foreskin and frenulum.[100] Van Howe, Cold and Storms criticised Szabo and Short's suggestion as "pure speculation".[101] Fleiss, Hodges and Van Howe had previously stated a belief that the prepuce has an immunological function.[101] Waskett criticised their specific hypothesis on technical grounds.[102] A study published in 2007 by de Witte and others said that langerin, produced by Langerhans cells, is a natural barrier to HIV-1 transmission by Langerhans cells.[103]

Dowsett (2007) questioned why it was just males that were being encouraged to circumcise: "Langerhans cells occur in the clitoris, the labia and in other parts of both male and female genitals, and no one is talking of removing these in the name of HIV prevention."[23]

and

A newer study, published in PLoS in January, 2010, points out that gross changes in the penis's microbiome occurs following circumcision, and this may play a role in protection from HIV and other sexually transmitted diseases

It's true it doesn't say precisely why there's a correlation, this shouldn't really be surprising since there isn't even unanimous consensus there is a correlation or more particularly to who and in what circumstances, how great it is and in particular, what the effect would be of greater circumscion and taking these, whether it should be recommended as a means to reduce the spread of HIV. So most studies concentrate on testing these hypothesis. However it seems clear no one is that surprised a correlation either way may exist since circumscion is a fairly significant change and you can come up with plenty of hypothesis on why the correlation is there either way.

Nil Einne (talk) 03:38, 20 September 2011 (UTC)[reply]

Yea, those two procedures have little to do with each other. Female "circumcision" is about preventing girls from having premarital sex. So, if it works, that should prevent disease transmission. Male circumcision is more about improving hygiene, by preventing the accumulation of smegma under the foreskin. Since that smegma could contain contagions after sex, eliminating it should reduce the infection rate. StuRat (talk) 05:23, 19 September 2011 (UTC)[reply]

What's stopping them from washing their penis? ScienceApe (talk) 09:45, 19 September 2011 (UTC)[reply]

Many people don't wash their hands after going to the toilet. What's the chance of them washing their penises? --Colapeninsula (talk) 10:38, 19 September 2011 (UTC)[reply]

Well then it seems like this study is rather deceptive because this would be an issue of proper hygiene reducing the risk of contracting HIV rather than circumcision reducing the risk of contracting HIV. ScienceApe (talk) 15:23, 19 September 2011 (UTC)[reply]

That's a bit like saying that obesity is really about poor food choices and has nothing to do with the availability of cheap junk food. Obviously, both play a role. StuRat (talk) 19:14, 19 September 2011 (UTC)[reply]

I don't think so. If the issue is about preventing the accumulation of smegma and improving hygiene then just cleaning your penis would accomplish the same thing. Not having foreskin just allows a lazy person to have approximately the same amount of protection as a man who cleans his penis. ScienceApe (talk) 21:05, 19 September 2011 (UTC)[reply]

Even if it were just about hygiene (and that seems unlikely), it is not necessarily "laziness" that prevents people in sub-Saharan Africa from meeting Western standards of good hygiene. Less than half of Africans have access to safe drinking water. If you are hauling a 50 pound water barrel on your back for miles from the river / well, and you have to boil it to drink it, then it isn't surprising that you wouldn't often want to spend much of it on washing yourself. A simple intervention that cuts HIV transmission by 50% in African populations is still a big deal regardless of the circumstances. Dragons flight (talk) 21:26, 19 September 2011 (UTC)[reply]

I'm not actually talking about Africa though. I'm talking about circumcision in general, that just so happens where they decided to do the study. The point is, the WHO is saying that circumcision is a good way to prevent the contraction of HIV when it's not because of that, it's because of good hygiene. If it's not just about hygiene, then I want to know what causes it. That's what the original question was asking. ScienceApe (talk) 22:32, 20 September 2011 (UTC)[reply]

The WHO makes policy wide considerations and aren't really there to provide individual advice. If you want that, I suggest you see your doctor. From a policy wide view point, circumcision may very well be a good way to prevent the contraction of HIV, regardless of the reasons (altho it's clear from the sources there is some question about how effective it is likely to be as a public health measure and whether the benefits always outweighs the costs and ethical issues). Finding out the reasons may provide other avenues for some reduction in some instances, it doesn't necessarily make the recommendation wrong particularly since we live in the real world not your magic world where people will always do what you say. I think it's clear from the sources many suggest other behaviour changes like greater condom usage and reduction of the number of concurrent sex partners will likely provide a more effective benefit but again because we don't live in this magic world, it isn't a magicly achievable goal. P.S. Note that is with others, I'm not suggestion hygiene improvement is the sole or even main reason for the reduction, I'm just pointing out even if it is your argument doesn't make sense. P.P.S. Note that because we live in the real world, you'll notice the sources often do discuss the risk of behavioural changes like a reduction in condom usage and other riskier behaviours that may arise from circumcision and a false sense of security even though there's clearly shouldn't be considered in your magic world. Nil Einne (talk) 23:43, 20 September 2011 (UTC)[reply]

Nil, you're clearly agitated. I recommend laying off of the personal attacks especially regarding "my magical world", be mature please. You are arguing a strawman when you accused me of wanting individual advice. Please don't do that, I never asked for that. You are now making the argument that if the issue were solely about hygiene improvement then my argument doesn't make sense. Actually yes it does, because if WHO recommends circumcision as a good method to reduce the incidence of contraction of HIV, then it's deceptive because circumcision doesn't reduce it. Proper hygiene does. The main problem with advocating this, is that circumcision advocates will use this as a reason to justify circumcision in males, when in fact it has to do with hygiene, not circumcision. Like I said, it's deceptive. ScienceApe (talk) 03:16, 21 September 2011 (UTC)[reply]

And a predictable percentage won't engage in proper hygiene, even where convenient, and can then infect others, even if those others do engage in proper hygiene. For another example, we could deliver contaminated drinking water in pipes and just say "well, they should know to boil it before they use it", but you could still predict a higher rate of disease than if it's properly sterilized by the water department.

Health authorities have known for a long time that just telling people what to do is insufficient to stop disease. If it were that simple, many contagious diseases would have been eliminated long ago. StuRat (talk) 22:04, 19 September 2011 (UTC)[reply]

That's not really a good example because they are providing a service to people. Sex is not a service the government is providing to people, it's something that they do on their own. If we were to use your analogy, then it would be more akin to the government providing prostitutes for people. If they were crazy enough to do this, they would at least test their prostitutes regularly, have a brothel or whatever that has health codes and enforce proper hygiene, require their customers to use condoms, etc. ScienceApe (talk) 22:32, 20 September 2011 (UTC)[reply]

Study Finds Circumcision Helps Prevent HIV and Other Infections says: "Families of anaerobic bacteria, which are unable to grow in the presence of oxygen, are abundant before circumcision but nearly disappear after the procedure. The researchers suspect that in uncircumcised men, these bacteria may provoke inflammation in the genitalia, thereby improving the chances that immune cells will be in the vicinity for HIV viruses to infect." Alansplodge (talk) 18:57, 19 September 2011 (UTC)[reply]

The article doesn't affirm that the bacteria causes inflammation. There's also aerobic bacteria on the penis. Where's the evidence that the anaerobic bacteria causes inflammation while the aerobic bacteria does not? It seems like another hygiene issue. A normal circumcised penis does not get inflamed unless there's an infection. That doesn't really make sense in any case. The penis becomes enlarged during sex anyway. ScienceApe (talk) 03:16, 21 September 2011 (UTC)[reply]

Morison, Scherf, Ekpo, Pain, West "The long-term reproductive health consequences of female genital cutting in rural Gambia: a community-based survey" Tropical Medicine and International Health 6:8 643-53 mentions a number of possible risk factors resulting from female circumcision. The labia normally has a protective function covering the vagina, and female circumcision often involves removing the labia, thereby exposing the vagina to infection, etc. There's a risk of scar tissue, keloid formation, cysts etc on vulva, which could tear or become inflamed during intercourse or childbirth. There's also a risk of damage to the urethra, perineum, or anal sphincter, which could result in fistulas or other complications. Anything that results in an open wound around the vagina will increase the likelihood of HIV infection. --Colapeninsula (talk) 10:48, 19 September 2011 (UTC)[reply]

I don't know. The labia has a protective function, but the foreskin does not? Wouldn't the labia also trap in vaginal fluids and such that may contain contagions? There's also scar tissue from circumcision as well. Seems suspect that most of the arguments given for why foreskin increases the risk of contraction of HIV, is reversed for the labia. Scar tissue, open wounds, complications are also ignored with male circumcision is regarded. Don't you think there might be some bias involved here? ScienceApe (talk) 21:16, 19 September 2011 (UTC)[reply]

The female reproductive tract is, of course, designed to retain "foreign fluids" (semen), so it's not going to make much difference one way or the other. The male reproductive system doesn't need to retain any foreign fluids at all, though, especially in an anaerobic environment. StuRat (talk) 23:25, 19 September 2011 (UTC)[reply]

It wouldn't? I don't really believe that. Opening up the vulva causes semen to drip out. I know, because I've seen it. ScienceApe (talk) 22:21, 20 September 2011 (UTC)[reply]

I think your missing the point. Firstly our article notes there may be an increased risk if men engage in sexual intercoure before full healing. More importantly, if there is indeed a correlation, there is a correlation whatever the reasons. There are plenty of reasons either way it could make a difference. Nil Einne (talk) 03:30, 20 September 2011 (UTC)[reply]

Actually I think you missed the point. I was asking what those reasons were, because I'm aware they are saying there is a correlation. Ok so then by insinuation, that risk associated with scar tissue with female circumcision should be alleviated after full healing has occurred as well. ScienceApe (talk) 22:21, 20 September 2011 (UTC)[reply]

I don't care what you're asking here as I've already provided other answers as have others. You're suggesting there is some 'bias' and that 'complications are also ignored'. You're missing the point that researchers are working back from the evidence and trying to determine the cause (but not that hard since it isn't that important to most of them at this stage) so the issue of 'bias' or 'complications are also ignored' doesn't come in to it. The researchers aren't there to prove something to the satisfaction of ScienceApe, particularly if SA isn't even going to completely read our articles (and the real sources would anyway be the peer reviewer articles not our likely inaccurate summary of them). Also no one said there is no risk after full healing, my point was simply that your statement the risk was ignored was ignored was clearly wrong. And you still don't seem to understand that the different nature of the procedures (and FGC isn't one procedure anyway, there is a large variety of procedures which go under that name) means the healing etc could be rather different. Nil Einne (talk) 23:41, 20 September 2011 (UTC)[reply]

You're getting angry now. You need to calm down. If you don't care, please don't participate in the discussion. You have not provided any answers that do not relate to hygiene, which is what I asked in the previous post I made. No, it seemed like there was bias in the reasons I've been given. A claim was made that female circumcision increases the risk of contraction of HIV because of scar tissue. However that would also be present in male circumcision so it doesn't make sense. A claim was made that foreskin traps fluid that may contain contagions, but so would the labia so it also doesn't make sense. Based on the answers I was given, things didn't make sense so I was questioning whether there may be bias in the rationale given. There might not be, but it's possible given that there is a history of people advocating circumcision for cultural reasons and then using bad science to give the illusion that their advocacy has practical benefit. Your personal attacks are really uncalled for. Please stop that or don't participate in this discussion. ScienceApe (talk) 03:08, 21 September 2011 (UTC)[reply]

The answers given thus far make sense. There appear to be many ways in which circumcision can affect the risk of HIV (both proven and hypothesised), including hygiene, scar tissue, Langerhans cell density etc. That different effects dominate in vastly different environments is completely reasonable, and is apparently backed up by the statistics. If you're looking for evidence of cultural bias influencing the science, you would be best off examining the papers that focus on the statistical links between HIV and circumcision. Your current approach of asking questions to which no one knows the answer (read carefully: this has been mentioned a few times) has not and will not get you far. Teshmanesh (talk) 10:36, 22 September 2011 (UTC)[reply]

No they don't because they contradict each other as I already stated. I'm not looking for evidence for cultural bias (that's a strawman logical fallacy), I just suspect it given the poor rationale given for why there is a correlation. Yes, no one knows the answer to my question, so what? There's nothing wrong with me asking questions, in fact more people should have been asking questions about this because the study is rather poor. The study wasn't carried out very well with proper controls, namely controlling for hygiene to ensure that it wasn't a factor. ScienceApe (talk) 11:55, 22 September 2011 (UTC)[reply]

I am not a scientist or doctor, but I can't help feeling that you are all missing one vital fact. HIV is contracted through blood or bodily fluid intermingling. With uncircumcised males the foreskin has a high potential for this form of transmission due to its delicate nature and high risk of damage during sexual acts. Ergo remove the foreskin and you remove a high proportion of the risk it posed. Simples yess!!Petebutt (talk) 23:40, 22 September 2011 (UTC)[reply]

September 19

Surface charge on a conductor

So if there is a net charge in a solid spherical conductor let's say, we know that the charge will flow to the surface and arrange themselves to minimize its electrostatic energy (as far apart from each other as possible). But what happens to its one and two dimensional analogs? For a very super thin circular conducting disk, would the charge all go to the perimeter (the circumference)? And for a very thin needle, does the charge go to the ends? If not then what happens? 67.40.134.8 (talk) 02:23, 19 September 2011 (UTC)[reply]

I'd say no, because those things cannot be true 2- or 1-D analogs. In the real world the disk, for example, actually still has two large faces, and even if it were one atom thick it would still effectively have one large face, over which the electrons or holes would distribute. (If it were so thin that its thickness could not accommodate even one layer of electrons, the same would be true of its edge). However, due to the geometry of the edge or ends there would, I suggest, be higher concentrations of charge there, which is what we observe in, for example, St Elmo's fire or on lightning conductors. 90.193.78.7 (talk) 11:35, 19 September 2011 (UTC)[reply]

{edit conflict) In the case of the 3d charge at the surface the field inside the sphere is zero (see shell theorem) - because the field is zero everywhere inside the sphere this means that there is no net force on charges inside a spherical surface of charge.. This actually means that you could have a charge distribtion in the solid spherical case of charge on the surface and a percentage of the charge in a spherical shell inside the sphere. A third band of charge is not possible since one of the bands would lie outside the inner band and experience a net force - causing the charge to move to merge with the surface charge..

~~(This means that your initial assumption of edge charge on a spherical body may not be absolutely true)~~ Sorry about that - just spotted my error - ignore

Did that make sense so far (you probably need to be familiar with "shell theorem" or maybe Gauss' law for gravity as applied to electric charge..?)

As I remember it's a specific property of the spherical case that the field inside is zero. This is definately not true within the 1D (needle) case, and as I recall not true inside the 2D (disc) case either.

Therefor it seems quite possible that you can get equilibriums where the charge is not all at the edge (I ignore the cases where some charge is at the absolute centre).

To be certain in the 2D you would need the field potential inside a symmetrical "flat ring" of charge .. only with this information can you be certain - if it is zero everywhere inside then the case is the same as the 3D case, if not then other equilibrium arrangements will apply.

Can you/ have you got that potential due to a ring of charge?

For the 1D case I can propose at least one case - charge at the edge, charge in the centre, and a pair of charges neither at the edge or in the middle held in equilibrium by the centre and edge charges.. - this is a possibility different from the 3d sphere case. I can't say if there are other cases too.Imgaril (talk) 11:50, 19 September 2011 (UTC)[reply]

Just for the record it looks like calculating the field potential inside the 2D ring is fairly tricky (for a non-maths degree holder) and I couldn't find the answer easily searching - if you need to pursue this for the 2D case you might be better off asking at the maths desk..Imgaril (talk) 12:19, 19 September 2011 (UTC)[reply]

apologies if all that just muddied the water by the way - the answer in at least the 1d case is that its not the same as for the 3d case - I'll leave a note on the maths desk about this too

You may find this of interest: Lightning rod#Should a lightning rod have a point?. --Tango (talk) 12:02, 19 September 2011 (UTC)[reply]

That charges end up at the surface of a conductor doesn't follow from "minimization of electrostatic energy". It follows from that and Coulomb's law, but that means that the intuitive idea that "the chages are repelling each other so they will move as far apart as possible and therefore they end up on the surface" is incorrect. Replace the 1/r^2 law by an 1/r^3 law and you'll find that the charges will reside in the bulk, not on the surface.

What does always happen in electrostatics (Coulomb's law or no Coulomb's law), is that in equilibrium, the electric field has to be zero inside the conductor. If not, then forces would act on charges and they would therefore move around. Applying Gauss' law (which is equivalent to Coulomb's law) then yields the result that charges reside on the surface of a conductor.

In case of a needle, the charges don't go to the point of the needle. What does happen is that a electric field near the needle point is large. You can see this intuitively as follows. The electric field inside the needle is zero, this means that the electric potential in the needle is constant. Now, the electric field jumps if you move from inside the needle to outside the needle because of the surface charges, but the potential changes in a continuous way.

What then matters is how much charge must flow to the point of the needle to make its ptential the same as on the rest of the needle. Of course, the smaller an object, the less charge you need to raise its potential. That the electric field does get large near the point, can be seen as follows. Instrad of the needle, consider a big charged sphere connected to a thin wire. The total charge on that wire will then be very small. Now, you can write the potential V(r) at position r as the summation of Qi/(r-ri) over all charges Qi located at positions ri (this summation can be replaced by an integral over the surfaces involving surface charge densities). Then because there are hardly any charges on the wire, the potential V(r) is practically the same as what it would be if there were no wir cnnected o the sphere, except very close to the wire (small q means that q/(r-ri) will become large only if r becomes close to r1).

A bit away from the wire, the potential is practically the same as what it would be if the wire weren't there. Suppose the wire extends very far for the sphere. If you approach the wire, the potential will at first hardly increase and only at the last moment will the potential increase to the value it has inside the wire (which is the same as the potential of the sphere). So, compared to approaching the sphere, you get the same increase in potential if you approach it from infinity, but in case of the wire it now all happens at the last moment. The rate of potential increase is the maginitude of the electric field, and that is thus much larger near the wire. Count Iblis (talk) 16:11, 19 September 2011 (UTC)[reply]

I don't see what's wrong with saying that the charges move to minimize electrostatic energy, and that ends with them all on the surface. It may be false in a fictitious world with a 1/r³ force law, but it's true in the real world. And with a 1/r force law you will end up with a nonzero field in the bulk at equilibrium, unless I'm missing something.

It's qualitatively true that the charges move to be "as far apart as possible"; it's just not clear what that entails. When the charges are all on the surface they'll be much closer to their nearest neighbors than if they were distributed through the bulk, so it's not obviously better. It comes down to the nature of the force. If it falls off quickly then nearer neighbors are more important and the charges might prefer to be in the bulk. If it falls off slowly then the distance to faraway charges matters and it might be better to be on the edge.

As far as I know, the explicit answer to the original question is that in d dimensions with a 1/r^k force law, the particles will end up on the surface if and only if k ≤ d−1. So they don't go to the edge of the disc or the ends of the needle (in 3 dimensions) -- BenRG (talk) 23:29, 21 September 2011 (UTC)[reply]

Arctic Survival, Part Deux

Not sure if this is really a science question per se, it's mostly a follow-up from above. I know that Alaska requires pilots to carry survival gear, and I'm guessing that they're far from alone on that, but what is included in that survival gear, and what of that would be present on a commercial airliner? I'm guessing that you could have a pretty good weekend in ~~Dallas~~ Vegas with all of it, but what's typically in it? SDY (talk) 07:07, 19 September 2011 (UTC)[reply]

See survival kit, which will give you some idea.--Shantavira|^{feed me} 07:19, 19 September 2011 (UTC)[reply]

I don't know if jetliners have a survival kit, but if yes, what for? People rarely survive a jetliner accident. Quest09 (talk) 09:21, 19 September 2011 (UTC)[reply]

I believe they usually do. It doesn't cost much to do so, so the gain doesn't need to be much to make it worthwhile - that gain may be mostly PR. Of course, people used to say similar things about life jackets. People said they were just their for show because nobody ever survived a water landing in a commercial passenger jet. People don't say that anymore, since there was an extremely successful water landing on the Hudson recently (extremely successful as in everyone escaped with only a few minor injuries - the plane was obviously a write-off). It is extremely unlikely that a survival kit on a plane will ever get used, since accidents usually happen at take-off or landing (when rescuers are very nearby) and those than happen in mid-flight are usually due to some kind of catastrophic failure that results in everyone being killed on impact. It is possible that circumstances could occur in which it would be useful, though. --Tango (talk) 11:56, 19 September 2011 (UTC)[reply]

I don't remember if any one has to use a life jacket to be rescued. I think they were rescued by boats. Quest09 (talk) 13:10, 19 September 2011 (UTC)[reply]

In that case yes, but one can't always have their water landing be in the center of a large city with dozens of boats around. Googlemeister (talk) 13:35, 19 September 2011 (UTC)[reply]

No, you can't have your water landing the way you like it most. On the Hudson River, without victims, and with TV cameras filming you is fine. However, the most common outcome is that if something happens at take-off or landing, rescue would be easy, as above; and on mid-flight, rescue would b difficult, but you have even less reason to expect survivors. Are life jackets just a question or PR? Quest09 (talk) 18:27, 19 September 2011 (UTC)[reply]

Probably not. Ditching an aircraft (a water "landing", really more of a controlled crash) is often easier than trying to set it down on land, especially if there are control failures or the landing gear doesn't work. If you ran into a Gimli Glider or similar situation at sea where you're forced to land well short of your destination, you don't automatically lose all the passengers. Single engine naval aircraft (e.g. the F-35C) are pretty rare for exactly that reason - if you lose your one engine, you're screwed. The Canadian air force specifically went to the two engine CF-18 instead of the single engine F-16 the US uses, precisely because losing an engine in the Great White North is a big deal. SDY (talk) 22:20, 19 September 2011 (UTC)[reply]

FYI, according to the article "Ditching", the average survival rate for an emergency water landing is about 75%. This is of course highly dependent on the location and manner of the crash. 67.169.177.176 (talk) 00:44, 20 September 2011 (UTC)[reply]

Just because they were rescued by boats doesn't mean they didn't need life jackets. Our own article says "Evacuees, some wearing life-vests, waited for rescue on the partly submerged slides, knee-deep in icy river water. Others stood on the wings or, fearing an explosion, swam away from the plane." but it's not clear if there would have been enough space on the wings and slides for all passengers who wouldn't have wanted to enter the water without lifejackets. Remember plenty of people can't swim or even keep themselves afloat in water for long (and it was very cold and I guess it was fresh water too) so even if it only took 2 minutes for the boats to come there's no guarantee they would have survived, particularly in the panicked situation of that sort. Definitely from a rescuer POV even if they could have saved everyone without life jackets I'm sure they were happier they didn't have to worry (much) about trying to rescue people drowning because they couldn't stay afloat. In any case, this isn't the only water landing. There is incidentally a risk of people opening their life jackets prematurely, if you listen to the instructions they give before takeoff they always say to inflate one side just before or as you jump out and the other side after. I watched a MayDay episode once which mentioned some people died because they trapped when they opened their lifejackets before they reached the doors and then as the plane was already partly full of water they were taken to the surface and couldn't get out. (I believe it is Ethiopian Airlines Flight 961 which is mentioned in the water ditching subsection.) Nil Einne (talk) 01:17, 20 September 2011 (UTC)[reply]

Life jackets also make extra floating wreckage to find if everything goes terribly wrong, even if they were not of much help to the passengers on that plane. Googlemeister (talk) 13:09, 20 September 2011 (UTC)[reply]

You might like to look at Alaskan Survival Equipment Requirements, and Lets Fly Alaska Aviation Survival Kit, also Alaskan & Canadian Survival Kit Regulations. Alansplodge (talk) 12:38, 19 September 2011 (UTC)[reply]

That doesn't apply to jet-pilots. Quest09 (talk) 13:10, 19 September 2011 (UTC)[reply]

I was answering the question: "I know that Alaska requires pilots to carry survival gear... but what is included in that survival gear?" Airliners is a seperate issue - I couldn't find much on that I'm afraid. Alansplodge (talk) 18:41, 19 September 2011 (UTC)[reply]

Fuel/Air ratio

I have split this question into its own section. Nimur (talk) 21:20, 19 September 2011 (UTC) [reply]

Why multi cylinder engines need high fuel air ratios than single cylinder for same throttle opening — Preceding unsigned comment added by 173.254.204.203 (talk) 20:37, 19 September 2011 (UTC)[reply]

I know of a couple of considerations regarding multi-cylinder engines and fuel/air ratio. First, balancing the fuel/air ratio between cylinders in a multi-cylinder engine is an issue, there are various tricks to acomplish this, but I imagine in some applications they just up the the mixture to avoid problems. Second, multi-cylinder engines have slightly poorer combustion chamber cooling and at high loads require a richer mixture to avoid knocking. Neither of these issues leads add up to a huge difference and only make a difference under high load, under low load the mixture will be very near 14.7:1 for all gasoline engines. There may be other issues that I don't know about though. --Daniel 00:50, 20 September 2011 (UTC)[reply]

Thanks for above answer but as per some books.since fuel is having higher inertia.so the fuel air ratio while distribution into many cylinders gets disturbed.thats why we give a richer mixture for same throttle opening in comparision of single cylinder engines.i am talking according to H.B. gupta .automobile engineering book present in google book.please comment on this argument presented by book author. 203.197.246.3 (talk) —Preceding undated comment added 09:57, 20 September 2011 (UTC).[reply]

That applies only to engines with an intake manifold and not to engines with one carburetor venturi or fuel injector per cylinder. Cuddlyable3 (talk) 16:38, 20 September 2011 (UTC)[reply]

Airplanes

Hi. Who was responsible for the invention of airplanes?70.82.113.90 (talk) 21:54, 19 September 2011 (UTC)[reply]

Well, many people contributed, but the Wright Brothers are usually given the credit for developing the first one actually capable of flying. StuRat (talk) 21:57, 19 September 2011 (UTC)[reply]

The Wright Flyer III was the first practical airplane, but it's far from the first flying machine. Flyer I is recognized as the first powered, controlled, heavier than air human flight, but there are quite a few qualifiers in that "first," and there's a question of whether "invent" implies the idea, which the Wright Brothers didn't come up with, they just made it work. Santos-Dumont would contest their claim anyway, but the original question isn't specific enough to give a rock-solid answer. First flying machine gives a whole bunch of claims to consider. I'm guessing that John Stringfellow (first powered) or George Cayley (first controlled) are good candidates to the original question, though the Wrights get credit for getting "controlled" and "powered" on the same device, which makes the thing actually worth considering instead of just a curiosity. SDY (talk) 22:10, 19 September 2011 (UTC)[reply]

Flyer I was not, technically speaking, an airplane (unable to leave ground effect...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:22, 20 September 2011 (UTC)[reply]

But the Flyers 2 and 3 certainly were. (Which means that the Wrights still beat Santos-Dumont by at least two years.)67.169.177.176 (talk) 03:54, 21 September 2011 (UTC)[reply]

George Cayleyj's gliders were not fully controlled -- it was Otto Lilienthal who first figured out how to control a flying machine during turns, and it was not until the Wright Brothers came up with wing warping that an adequate control system came into existence. Likewise, Stringfellow's machine might have been powered but could not actually fly (insufficient power-to-weight ratio), which makes either the Wright Brothers, Karl Jatho or Gustave Whitehead the first to make a powered flight. (Note that Whitehead's machine, although adequately powered, was not fully controlled, and Jatho's had no controls at all). 67.169.177.176 (talk) 00:39, 20 September 2011 (UTC)[reply]

This is similar to the question recently about whether Edison invented the light bulb. He didn't literally invent the light bulb. But he did invent the first practical light bulb. And the Wrights developed the first practical airplane. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:21, 19 September 2011 (UTC)[reply]

Only if you learn about it from American sources. British schoolchildren learn that Joseph Swan invented the first practical lightbulb before Edison, although Edison got the American patents first and loadly claimed in marketing that he invented it first, and they agreed to share the credit and sell Ediswan lightbulbs. No doubt French children learn something else again. 86.164.76.231 (talk) 10:43, 20 September 2011 (UTC)[reply]

I know Russian children learn that the lightbulb was invented by Lodygin (whoever he was...) But then again, in Russia they even used to claim until quite recently that Mozhaisky was the one who invented the airplane, even though his steam-powered contraption could do no better than to hop off the ground after running down a ramp and immediately stall out upon leaving the ground. 67.169.177.176 (talk) 03:52, 21 September 2011 (UTC)[reply]

See, this is all why I prefer the James Burke perspective on technological and scientific change. We tend to think of history in terms of the Great Man theory, and scientific progress is no different: We assume that scientific and technological progress happens when a lone genius invents some novel idea out of whole cloth and changes the world. We are stuck on looking at "the man" as a scientific hero, and so we have those heroes: Newton, Einstein, Edison, Jobs & Wozniak, etc. ignoring the fact that scientific progress happens not in giant leaps, but in tiny incremental changes. People like Einstein and Edison and the Wright Brothers get the "credit" because they have good marketing more than anything else. What the so-called Great Inventors and Great Minds have in common is more publicity than anything. There are inventions and ideas which do cause major paradigm shifts; but these things are always the product of many years of incremental change, and the final "credit" goes to the guy who was there when it happened; it is quite likely that if the Wright Brothers didn't get there first, someone else would have within a few months or so, given the sheer number of people working in the field. --Jayron32 02:52, 21 September 2011 (UTC)[reply]

Make that three years or so. 67.169.177.176 (talk) 03:58, 21 September 2011 (UTC)[reply]

Meh. There were many people in the months both before after the very first Wright Flyer in 1903 who had similar success in "flying" a plane (Richard Pearse, Karl Jatho, Horatio Frederick Phillips, etc.) and none of them is any less impressive than the December, 1903 flights by the Wright Brothers. The Wrights simply had better publicity. What Alberto Santos-Dumont did had some good publicity as well, but his was yet another incremental design change over other designs. Had he not done what he did, any of a number of other engineers, through similar trial-and-error, would have arrived at a similar design as well. If the Wrights had never made their flight, we'd still have the same state of modern aviation we have today; the credit would have changed but the ultimate historical events would have occured anyways. Heck, pick anyone of the random other people I cited above; the Wright's credit would have gone to them instead, and we'd be exactly where we are today. --Jayron32 04:13, 21 September 2011 (UTC)[reply]

Pearse did not actually fly, but only made a couple of short, practically uncontrolled hops a few yards long, each of those hops ending with a crash into shrubbery. (Is that what you call "impressive"?) Jatho actually made a short flight before the Wrights did, but it was much shorter (200 ft. distance) than the Wrights' flight (852 ft. distance) and was likewise uncontrolled; he then gave up all attempts to further develop his contraption. And Phillips did not make his first flight until 1907, a half year after Santos-Dumont and almost three and a half years after the Wrights! 67.169.177.176 (talk) 04:26, 21 September 2011 (UTC)[reply]

Sometimes there are setbacks. Check out this early version of a Batman-like cape/parachute:[6] ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:26, 21 September 2011 (UTC)[reply]

Wow, this gives a whole new meaning to the term "crash dummy"... (Not to disrespect his tragic death, but I mean, couldn't he stick to dropping dummies from the tower until he had at least a reasonable chance of survival?) 67.169.177.176 (talk) 06:35, 21 September 2011 (UTC)[reply]

Sir George Cayley invented the concept. --Swedmann (talk) 01:23, 23 September 2011 (UTC)[reply]

Right, the concept of fixed-wing (as opposed to flapping-wing or lighter-than-air) aircraft using airfoils to create lift. I never said otherwise. However, he did not realize the need for roll control (Lilienthal was the first to do so, and the Wrights were the first to actually achieve it), and of course he didn't put any powerplant on his gliders (for the simple reason that none was available). Which means that his machines were neither powered nor fully controlled, and therefore do not count as airplanes. 67.169.177.176 (talk) 05:59, 23 September 2011 (UTC)[reply]

Feces

What is the average buoyancy and density of a regular feces? 75.6.243.251 (talk) 23:51, 19 September 2011 (UTC)[reply]

What type of shit are we talking about here? Sir William Matthew Flinders Petrie | ^{Say Shalom!} 23:57, 19 September 2011 (UTC)[reply]

Type 3 on the link you gave me. 75.6.243.251 (talk) 00:18, 20 September 2011 (UTC)[reply]

The density is about that of water (which makes sense, as it is about 75% water). The average is somewhat greater than water (sorry, I don't have a number): most poop sinks. There has been great debate among the, uh, well, among certain segments of the population, about whether sinking or floating poop is indicative of good or bad health. Hardcore vegetarians and especially vegans have been known to claim that poop in a healthy person should float. Despite these claims, it is generally difficult to get floating poop through diet alone (and, needless to say, I don't think there are any real convincing studies that show that floating poop is indicative of health). The factors that can cause poop to be less dense are

Higher Fat Content, and
More integrated gas

While some variation in feces is normal, it is true that certain diseases can cause Malabsorption, which can lead to greasy, floating stool. Other chronic, abnormal bowel movements can be indicative of other problems - see the last link I have provided. If you are concerned about your poop, you should seek advice from a medical professional. [7], [8], [9] [10] Buddy431 (talk) 06:31, 20 September 2011 (UTC)[reply]

I thought you might be interested in this: Bristol_Stool_Scale --TammyMoet (talk) 08:13, 20 September 2011 (UTC)[reply]

That link was the first supplied. Dismas|^(talk) 08:27, 20 September 2011 (UTC)[reply]

Yeah, I already saw that, and don't need two links. 75.6.243.251 (talk) 23:52, 21 September 2011 (UTC)[reply]

Could you possibly find me the exact number for density and buoyancy? I'm not seeking medical advice; I read the series of notices at the top already. 75.6.243.251 (talk) 23:52, 21 September 2011 (UTC)[reply]

Dynamics of hypercanes

There is a theory (hypothesis) that exists which states that water temperatures around or above 120°F would result in hypercanes, which would taller, faster, and more compact than normal hurricanes. Obviously at this point the dynamics of the hypercane would be different than that of a hurricane, but how would they be different (the plume of water vapor penetrates the stratosphere, different patterns of air currents form, etc.)? --Melab±1 ☎ 02:22, 20 September 2011 (UTC)[reply]

The dynamics of ordinary hurricanes aren't understood well enough to simulate their interiors and eyewalls yet, so probably nobody can say. 208.54.38.175 (talk) 04:53, 20 September 2011 (UTC)[reply]

I don't think they would penetrate the stratosphere -- the tropopause is essentially a very strong inversion layer, and any weatherman knows how tough it is for air currents to penetrate those. FWiW 67.169.177.176 (talk) 04:59, 20 September 2011 (UTC)[reply]

Our article says "A hypercane's clouds would reach 30 km (19 mi) into the stratosphere". StuRat (talk) 05:09, 20 September 2011 (UTC)[reply]

Gallium arsenide

If taking the MO diagram into consideration, is it correct to say that for the monomer of gallium arsenide has a bond order of four, and that the resulting molecule is a zwitterion?

There is one sigma bonding orbital, and three degenerate pi bonding bonds, gallium only contributes by one third to the pi orbitals, not by half. As is my understanding, electrons are indistinguishable and there is no way to tell which electrons in the pi orbital associates with which atom. However, since a bond order of four means that gallium has an excess of electron density around it, and arsenic has a defficiancy around it. Meaning that, there is a unit charge of 1- on gallium and 1+ on arsenic. Note that the bond order is an integer, meaning that the charge difference must also be an integer. Plasmic Physics (talk) 02:36, 20 September 2011 (UTC)[reply]

Not sure where you get GaAs has a bond order of 4 via the MO diagram. It isn't an "expanded octet" molecule, so you should be able to work out an MO using just the valence level s and p orbitals, I get the resulting monomer to have the following MO configuration:

σ(4s) = 2
σ*(4s) = 2
σ(4p) = 2
π(4p) = 2
π*(4p) = 0
σ*(4p) = 0

That's 6 bonding electron, 2 antibonding electrons, and that give me a net of 4 electrons, or a bond order of 2. So Gallium Arsenide is predicted by M.O. theory to have a double bond, not a quadruple bond. When I work out the formal charge on said molecule, I do get formal charge of -1 on the gallium and +1 on the arsenic, however. The whole "quadruple bond" thing does exist, but not in compounds like this. In this case, the only way a quadruple bond gets predicted is by "lewis theory" or valence bond theory; since you only have 8 valence electrons to play with, the only way to "complete the octet" is to have 4 shared pairs of electrons; but what you see here is an example of where lewis theory falls short compared to MO theory. Actual quadruple bonds require participation of d-orbitals, and I don't see anywhere that this molecule would have d electrons which participate in the bonding. Even if you involve the d-electrons from the nearest d-orbitals in an expanded MO diagram, all of the bonding and antibonding electrons from that contribution should cancel. --Jayron32 17:06, 20 September 2011 (UTC)[reply]

Well, I'm looking at the valence MO diagram as given in a lecture slide. It gives the following configuration:

s² (sigma)
p_x² (sigma)
p_y² (pi)
p_z² (pi)
s*⁰ (sigma*)

In this diagram, there are no antibonding orbitals. Plasmic Physics (talk) 00:16, 21 September 2011 (UTC)[reply]

It shows that the sigma* is higher in energy than the p orbitals. Plasmic Physics (talk) 00:24, 21 September 2011 (UTC)[reply]

I'm not sure that make sense, unless there is significant overlap between the bonding energies of the s and p orbitals. In nearly all MO diagrams I know of, the order for the valence level MO has the sσ followed by the sσ* before any of the p-orbital contributions. Some molecules have some difference between how the p-orbital MOs order (some go σ - π - π* - σ* and others go π - σ - π* - σ* (see Molecular orbital diagram). I am not ruling out the unusual MO diagram you show above, I suppose it is possible, just not an organization I have ever seen. I would check with your professor after class, and ask them personally to explain the slide. --Jayron32 00:29, 21 September 2011 (UTC)[reply]

The gallium arsenide MO diagram is used to describe the formation of exitons in semiconductors. It calls the two degenerate pi-type HOMOs, the valence band; and the antisigma-type LUMO, the conduction band. Plasmic Physics (talk) 00:57, 21 September 2011 (UTC)[reply]

Ah. If you are dealing with conduction/valence bands, you have steped outside of molecular bonding into the world of metallic bonding and Network covalent bonding. See Electronic band structure for an overview. Band theory has its own quirks and rules which may not directly corrolate to expectations of discrete molecules as described by standard MO theory, since they have different applications: MO theory is designed for discrete molecules, while band theory is designed for network and metallic solids. There's probably ways to make the theories work together somewhat, but basically it's "Different game, different rules". So go with what your professor says. My band theory is a little rusty. --Jayron32 02:41, 21 September 2011 (UTC)[reply]

So, the MO diagram is not correct in this demostration? I'm confused. Plasmic Physics (talk) 03:57, 21 September 2011 (UTC)[reply]

No, let me reiterate what I said a few posts ago: it may very well be, but what you need to do is ask him personally to explain it to you to your satisfaction. The MO diagram you described is not one of the "standard" MO diagram orders I am used to (not that it is wrong, just not a standard order) and that may (or may not) be because we're dealing with a different type of bonding, since gallium arsenide is a network solid (and does not exist as discrete molecules, normally) then the band model may be more useful in understanding its electronic structure than the MO model (since MO deals with molecules). I assume that your professor was attempting to demonstrate some connection between the MO model (homo-lumo) and the band model (valence band-conductance band) as there is a connection between them; so you'll have to ask him about the particulars of why he uses that specific MO diagram (or an MO diagram at all, since gallium arsenide is not normally a molecular substance). --Jayron32 04:02, 21 September 2011 (UTC)[reply]

Oh. However, the diagram has the title of MO diagram of GaAs monomer. Plasmic Physics (talk) 04:59, 21 September 2011 (UTC)[reply]

That's why I said talk to the guy who made the diagram. He would know. --Jayron32 15:18, 21 September 2011 (UTC)[reply]

OK, I'll do that. Thanks. Plasmic Physics (talk) 23:18, 21 September 2011 (UTC)[reply]

sweet potato flavor

The flavor of sweet potatoes seems to be effected by boiling too long but not by removing sprouts or rotten spots and then boiling for no more than 5 hours. The inside of a sweet potato that has grown sprouts, however, seems to have cavities surrounded by root like projections from the stem inside the potato. Are these cavities just the result of the spouts taking energy and nutrients from the sweet potato itself? --DeeperQA (talk) 03:33, 20 September 2011 (UTC)[reply]

I would think so, but mostly the result of taking water out, which is most of the mass. StuRat (talk) 05:04, 20 September 2011 (UTC)[reply]

No more than 5 hours? Don't you mean minutes? --TammyMoet (talk) 08:10, 20 September 2011 (UTC)[reply]

Boiling for five hours? You have to be British. I've cooked thousands upon thousands of sweet potatoes in my life, and I've never boiled one. Baking is best. As for the cavities, enzymes break down the starch in the sweet potatoes into sugar, which is then absorbed and transported by the root-like projections to the growing sprouts. The loss of mass represents the mass of the sugar transported along with the water it is disolved in. Dominus Vobisdu (talk) 10:21, 20 September 2011 (UTC)[reply]

Not neccesarily british. I boil sweet potatoes. I peel and cut them into thin slices, add salt and boil for 20 min (or until soft,) mash the sweet potatoe, add milk or cream, cinnamon, and sugar. Then heat the mixture until it is no longer flows as a liquid, avoid burning by stirring.

I admit, sweet potatoes are take longer to boil, but it can be sped up by using smaller chunks. Plasmic Physics (talk) 12:14, 20 September 2011 (UTC)[reply]

We both boil and bake sweet potatoes. And fry em, caramelize them, and mash em, and eat young leaves in salads besides. And @Tammy, they take ages to cook, not like actual potatoes, sweet potatoes are generally massive tubers with thick skin.-- Obsidi♠n Soul 15:31, 20 September 2011 (UTC)[reply]

Are you sure you don't mean yams ? They are massive, while a sweet potato is close in size to an russet potato. StuRat (talk) 17:56, 20 September 2011 (UTC)[reply]

Sweet potatoes do tend to be slightly larger than regular potatoes and certainly have tougher skin. --Tango (talk) 19:10, 20 September 2011 (UTC)[reply]

You can get both very large and fairly small sweet potatoes. E.g. I currently have one that is over 850g and it's far from the largest one I've ever had. It also depends somewhat on the variety. They do tend to be a different shape from potatoes. Nil Einne (talk) 23:31, 20 September 2011 (UTC)[reply]

It's also probably a difference in harvesting time. Sweet potatoes are not cultivated extensively here as they can survive pretty easily without human intervention when planted along otherwise unarable land. They are harvested from feral plants, so they've usually been growing for quite a while. More like New Zealand kumara sweet potatoes (which is confusingly called 'yam' in the US), but not quite as large (by far) as true yams of course. I also suspect that smaller sizes are a result of market homogenization, as they are easier to handle and cook at those sizes. Potatoes here on the other hand, are tiny, averaging at only 3 in in diameter. ;) - Obsidi♠n Soul 02:19, 21 September 2011 (UTC)[reply]

I'm British. I usually bake or roast sweet potato, although I do sometimes boil and mash them (usually mixed with something else). Baking and roasting are a much better use of them, though. They certainly don't need to be boiled for 5 hours, though (and 5 minutes wouldn't be long enough, so I'm sure what the OP means...). --Tango (talk) 19:10, 20 September 2011 (UTC)[reply]

I boil them, along with many other items, as part of a perpetual stew, in winter. Thus, they may be boiled many times over many hours before finally eaten, but they seem to hold up fairly well (although the skin falls off). StuRat (talk) 19:15, 20 September 2011 (UTC)[reply]

I prefer nuking the small-to-medium sized ones whole in the microwave for about five to seven minutes, flipping them over about midway though the cycle to redistribute the heat. --Modocc (talk) 21:43, 20 September 2011 (UTC)[reply]

You use a nuclear weapon to cook potatoes?! 67.169.177.176 (talk) 05:03, 21 September 2011 (UTC)[reply]

In the USA, at least, to "nuke" is slang for using the microwave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 21 September 2011 (UTC)[reply]

Now added at List of words having different meanings in British and American English: M–Z :-) Ghmyrtle (talk) 08:25, 21 September 2011 (UTC)[reply]

"Nuke" is also used in American English the way it's used in British English. The microwave stuff is an additional slang usage in American English. It's also worth pointing out that "nuke" has also been used (at least in America) as a slang term for a nuclear power plant. (See No Nukes) ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:08, 21 September 2011 (UTC)[reply]

Nah, it's current slang in the UK too. We all have slang terms we don't recognise: doesn't make it an international difference. And you should have a reliable source to reference the difference before you add it to an article. 86.164.60.149 (talk) 17:54, 21 September 2011 (UTC)[reply]

If you look, there doesn't seem to be a reliable reference in the entire list. Googlemeister (talk) 21:02, 21 September 2011 (UTC)[reply]

Yes, it does look like junk. Anyone up for finding references, and cleaning out the nonsense? It shouldn't be too hard, given how popular the topic is. I guess I could go through it at the weekend, but that shouldn't stop someone else who's looking for something to do (I do hate formatting proper inline references). 86.164.60.149 (talk) 22:10, 21 September 2011 (UTC)[reply]

To me, to "nuke" a foodstuff, is too charr it beyond recognition, unintentionally of course. Plasmic Physics (talk) 10:36, 21 September 2011 (UTC)[reply]

Yes, that would be another meaning "to get rid of or destroy". StuRat (talk) 23:09, 21 September 2011 (UTC)[reply]

Eyelids twitch when scratching toes

When I scratch my toes (and sometimes other body parts) the scratching sensation somehow transmits and reaches my eyelids, and they begin to twitch. I think this is common to all people. What is this phenomenon? Gil_mo (talk) 06:26, 20 September 2011 (UTC)[reply]

It's not universal. I would guess the nerves have some "cross-talk" in your brain, a form of synesthesia, similar to grapheme-color synesthesia, where numbers and colors are linked. StuRat (talk) 06:32, 20 September 2011 (UTC)[reply]

It's not common to me either. I can sometimes smell my own nose, strange... Plasmic Physics (talk) 07:00, 20 September 2011 (UTC)[reply]

hmmm, puzzling Sean.hoyland - talk 07:35, 20 September 2011 (UTC)[reply]

I was referring to scratching a very itchy toe (or between toes), not just anytime. Gil_mo (talk) 07:51, 20 September 2011 (UTC)[reply]

What happens when you have very itchy eyelid and scratch it ? Also, since you say it's sometimes other body parts too that trigger the eyelid, perhaps it's the finger that you use for scratching that's wired to your eyelids... Sean.hoyland - talk 08:35, 20 September 2011 (UTC)[reply]

hall effect

can a simple hall effect circuit test magnetic fields of the order of picotesla .even a true/false judgement i.e. if the field is present or not judgement would help??can any one help. if the input is provided to a pc could we get some better analysis ..if yes please guide.? 203.197.246.3 (talk) —Preceding undated comment added 09:52, 20 September 2011 (UTC).[reply]

I really don't think so.. The potential generated by even the best designed hall probe is going to be very small in a picotesla field - this will have to be amplified - but there is a limited to how much amplification is possible -eg limited by thermal noise etc. Here http://cat.inist.fr/?aModele=afficheN&cpsidt=15394074 they get the sensitivity down to microtesla.. ie ~0.2V per T - that would have you measuring ~~ 0.2 picovolts very small)

I would guess that there might be a way to get it to work - but - it would require a specially designed sensor - or some elaborate microscopic construct using the hall effect in a more complex system (integrated circuit integrated with hall effect sensor?? + low temperatures?) Imgaril (talk) 10:12, 20 September 2011 (UTC)[reply]

I note that http://www.tristantech.com/prod_lab_meas.html (which uses a SQUID to detect magnetic fields) mentions a Picovolt Measuring System which is cryogenic - this suggests that a the measurement of the ~pV level signals from a hall effect sensor are within the bounds of possibility - but it would need to be very cold.Imgaril (talk) 11:58, 20 September 2011 (UTC)[reply]

What is a chest node?

A kind editor has added the information that the famous operatic tenor Jonas Kaufmann has, as the source puts it, "recovered from surgery to remove a chest node". I would like to wikify this, but when I looked at Node I got rather lost. Any guidance please? almost-instinct 12:14, 20 September 2011 (UTC)[reply]

Presumably nodule (medicine) is meant. A vocal fold nodule is a common singing injury. It might be something else, though. This news item [11] with the words "vical nodules" in the URL and the comment "A node in the chest has nothing to do with vocal nodules" doesn't make things much clearer. Sounds like it's one of those probably-not-cancerous lumps people sometimes randomly get. (To be less vague, I was thinking of a benign tumor.) Card Zero (talk) 12:21, 20 September 2011 (UTC)[reply]

Thank you very much. I've found this from an open letter JK wrote to apologise for pulling out of a tour: "The fact is that I need to have an operation to remove a node in my thoracic area". Does that help? almost-instinct 12:42, 20 September 2011 (UTC)[reply]

That letter is also on the page I linked to: it looks like it originates from a Japanese tour promoter's site, and is the official piece of information on the matter. Even Jonas Kaufmann himself might not know what he means by "node". Googling "chest node" brings up some breast cancer forums, though. Perhaps it was even malignant: whatever it was, it's gone now. Tumor seems the best article to link "node" to (unless somebody else knows better). Oh wait! I think it means Lymphoma, possibly, where the node in question is a lymph node? Card Zero (talk) 12:49, 20 September 2011 (UTC)[reply]

Since all JK has said on the subject is "node in the chest" -("I’m pleased to say that the operation to remove a node from my chest that I had to undertake earlier this month went very well and that the recovery is making good progress") - and there's ambiguity I had best not link either to benign tumour or lymphoma. If people want to be vague about their medical state, that's their perogative I suppose. Thank you for your help: hopefully it'll be useful if more detailed information comes out almost-instinct 13:03, 20 September 2011 (UTC)[reply]

Yes, just link to "tumor", it covers all the bases. I searched for Jonas Kaufmann "lymph node", and found a half-visible Google cache of a Twitter comment by one naomip86, which says that JK confirms in a comment left somewhere, written in Japanese, that the node is indeed a lymph node; but I have a feeling this might not qualify as a reliable source. Card Zero (talk) 13:15, 20 September 2011 (UTC)[reply]

Congratulations on getting so close to Absolute Zero on the Reliability Index ;-) Yes, I'll do that, thanks. almost-instinct 13:21, 20 September 2011 (UTC)[reply]

Maybe, though, that refers to the original letter, which is written first in Japanese, here [12] and I think it has the Japanese for "lymph node" in it. Somebody here (Kagetora?) can do a reliable translation of that. Card Zero (talk) 13:24, 20 September 2011 (UTC)[reply]

Oh yes! Google translate gives it "must undergo surgery for resection of lymph nodes in the chest". I shall await (semi)patiently almost-instinct 13:28, 20 September 2011 (UTC)[reply]

I'm a native ja speaker. Yes, it's "lymph nodes" in the letter in ja. The ja word is リンパ節. [13] Oda Mari (talk) 15:07, 20 September 2011 (UTC)[reply]

For reference, here is what Eijiro says. KägeTorä - (影虎) (TALK) 16:02, 20 September 2011 (UTC)[reply]

Thanks, you two. Sorry for suggesting "tumor", which Almost-instinct added to the article and then had immediately reverted by somebody else. I've changed it to "lymph node" now, let's see how that goes down. Card Zero (talk) 16:52, 20 September 2011 (UTC)[reply]

Thank you everyone, its all settled and accepted now :-) almost-instinct 21:34, 20 September 2011 (UTC)[reply]

dry versus disolved borax powder in air

I am careful not to breath the dust when adding the powder to laundry but can find no caution about spraying a dissolved solution of borax in water. Is spraying this solution dangerous and if so what kind of respirator mask should be used? --DeeperQA (talk) 17:31, 20 September 2011 (UTC)[reply]

A respirator seems like overkill, but do leave the laundry area after spraying and ventilate the area (with an open window). StuRat (talk) 17:58, 20 September 2011 (UTC)[reply]

Here's a MSDS http://www.anvilfire.com/21centbs/material/33850-usborax-borax.pdf - generally little threat to you. Don't drink it. It's also alkaline so if you get a lot on your skin it may eventually burn/sting/itch. Washing with water will remove contamination.

Here's a MSDS for a 1% solution - http://www.sciencelab.com/msds.php?msdsId=9925661 - I really couldn't decribe it as dangerous - but don't breath in the spray (this applies to just about every spray you can name - starch, furniture polish, etc - most of which are of greater hazard)

If you are concerned about this sort of thing wearing a cheap dust mask will stop you breathing in any mist. If you are using a lot or use it everyday in a job (like these guys who use to treat timber [14]) then I'd recommend wearing a dust mask, and the gloves. Imgaril (talk) 20:33, 20 September 2011 (UTC)[reply]

Yes, thanks. This is just the information I need since the sprayer being used was a paint sprayer and one person had already noticed a reaction like a cold with mucus production but an ironically with an increased ability to breath like he had used an antihistamine. The key was that when he tried to treat a slight sour throat with vinegar it stung well beyond anything he had ever experienced. --DeeperQA (talk) 21:44, 20 September 2011 (UTC)[reply]

Just FYI: Breath is a noun, breathe is a verb. --Trovatore (talk) 21:48, 20 September 2011 (UTC)[reply]

Anyone who doesn't know that must be a blond (or blonde). StuRat (talk) 02:51, 21 September 2011 (UTC) [reply]

I will reprogram my grammar/spell checker. --DeeperQA (talk) 22:12, 20 September 2011 (UTC)[reply]

BTW, what's a "sour throat"? Methinks treating it with vinegar would only make the problem worse... 67.169.177.176 (talk) 04:02, 21 September 2011 (UTC)[reply]

We can't give you medical advice concerning whether your application of borax is safe for you. In general, borax is something that exists in the environment, in evaporite deposits, and has been dug up and traded for 4000 years.^[15] It is true that in high doses it has health effects, including harmful reproductive effects, but I would think that the wind blowing in a place like Boron, California can't be that tremendously terrible. I'd think a person can get over passing, casual exposure to the compound without the need to take extraordinary precautions. Wnt (talk) 01:57, 21 September 2011 (UTC)[reply]

WTC escape solution

Several people scaled the WTC towers using a camming device and the window washer apparatus channels or rails. Is there any type of descent system using the channels or rails (versus a parachute stored in your cubicle) to get you from high up in a building to the ground without killing you? --DeeperQA (talk) 22:10, 20 September 2011 (UTC)[reply]

I wouldn't try to slide down the face of a high-rise building if I was you -- the risk of slipping and falling to your death is just too great. (You have to remember that the people scaling the towers were trained professionals, as are the window washers.) That said, it's often possible to climb to the roof of a burning building, from where you could be rescued by a helicopter. I wonder why they didn't try this on 9/11... 67.169.177.176 (talk) 04:10, 21 September 2011 (UTC)[reply]

There probably wasn't time to get such a rescue operation going. While only the first one was burning, they could have tried the Phillipe Petit approach. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:16, 21 September 2011 (UTC)[reply]

Also, a fire of that type would be extremely problematic for a helicopter. The large amount of smoke would have visibility be almost 0, there were those tall spires on top were a hazard, and a fire like that also creates nasty wind conditions above it. I would expect that only military chopper pilots have been trained for that kind of a rescue, unless the NYFD has helicopters of their own for that sort of thing. Googlemeister (talk) 13:49, 21 September 2011 (UTC)[reply]

In the 1993 WTC bombing,elevators were stopped and stairways were filled with smoke. Police helicopter did rescue a number of people from the roofs of the two buildings,despite heavy smoke, although that was never part of the official emergency plan. Several groups of people were lifted from the roof of the South Tower. Emergency Services personnel were lowered and sawed off any projections which were in the way of the chopper. One person was similarly rescued by rope from the roof of the North tower. This annoyed the Fire Department, who insists on the right to "rescue" people, so very strong doors with a remote operated lock were installed to prevent a repeat rescue by the police chopper. Unfortunately, the office which could have remotely unlocked the door was destroyed by the plane impacts on 9/11, so there was no roof access for the people trapped in the restaurant. Edison (talk) 18:39, 21 September 2011 (UTC)[reply]

And that was the NYFD's doing, you say? If that's true, then whoever ordered this is a mass murderer and deserves to be burned at the stake! 67.169.177.176 (talk) 22:46, 21 September 2011 (UTC)[reply]

A long enough rappelling rope could be tied inside the building, but nobody expected to need such a rope, and breaking the window from the inside might have been difficult. Dualus (talk) 06:41, 21 September 2011 (UTC)[reply]

And I don't think rappelling past a part of the building that is burning is going to work either from smoke inhalation or the heat. Googlemeister (talk)

There were some sides of the building that weren't spewing flames, and unless the heat melts the rope, it's probably easy enough to slide past 10 floors fast enough to survive. As for breaking the windows, plenty of victims contacted by cellphone before the collapse said that they had been able to break open windows. 70.91.171.54 (talk) 18:59, 21 September 2011 (UTC)[reply]

It is very rare for a highrise fire to start out with flames coming out all sides of the building., There is typically a long time during which there is intense fire on one side, with some sides cool enough for a person to be lowered. This is why fire escapes outside buildings were traditionally there: builders and fire safety officials did not dismiss the ability to walk down the north side when there was a fire on the south side. I worked in a high rise building which had an employee who could not walk working in an office several floors up. The boss bought a rescue harness and a l-o-o-ng rope to lower the employee to the ground from a window in the event of elevators being unusable in a fire. The employee and coworkers agreed that the employee would instead be carried down the stairs, either seated in an office chair or over a shoulder in a fireman's carry, rather than having a team of people lower the employee via a rope. But it was feasible, and was tested by lowering an equivalent weight. I've always thought a personal lowering device for a highrise would be easy to build. A long wire cable on a reel, a centrifugal brake to control the unreeling speed to a safe one, and a bosun's chair. Trapped people could be lowered one at a time, and the seat could be cranked back up after each use. Nothing innovative or high tech required. A metal eyebolt could be installed above a window on each side of the building to allow using the noninvolved side. It might even be possible to insert rescuers into a burning highrise at a floor above the fire, to install such several such devices and supervise the lowering of trapped people. One could go fancy and wear fireresistant garb, helmet, gas mask, etc, or just rely on the rapid descent speed to get past any hot or smoky area and get people out faster. Edison (talk) 19:08, 21 September 2011 (UTC)[reply]

Are you seriously thinking that hundreds of people rappelling 1000 feet to the ground from a burning building is remotely feasible? Googlemeister (talk) 20:55, 21 September 2011 (UTC)[reply]

Yeah, much more sensible to ensure the doom of each and every one of them by a lack of planning, and by ignoring simple means of leaving a high place without going thud. Rarely are the trapped people 1000 feet above the ground, and it rarely is the case that hundreds of people are trapped. The people who survived because of a communal or personal descent rig would be quite happy not to have been incinerated or asphyxiated. Edison (talk) 23:44, 21 September 2011 (UTC)[reply]

True, but a system that relies on rappelling 1000 feet down the face of a building would not have been practical, since it can only be used by highly skilled mountaineers. On the other hand, some kind of "communal descent rig" (I'm thinking of something along the lines of an external, rope-suspended elevator) might well have been a practical idea for an emergency escape system. 67.169.177.176 (talk) 01:13, 22 September 2011 (UTC)[reply]

Plane crash on Mount Everest

What would happen if a plane crashed near the top of Mount Everest? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:26, 20 September 2011 (UTC)[reply]

The plane remains would be there for ever as a monument to human endeavor/stupidity. Dauto (talk) 23:03, 20 September 2011 (UTC)[reply]

Depends on the type of plane, the speed it was traveling at, the weather,etc. At that altitude it is likely everyone on board would die, as they would not be prepared for the extreme cold and thin air, presuming they survived the impact in the first place. Specialized high-altitude helicopters can indeed reach such an altitude to perform rescues, as documented at Mt. Everest#2005: Helicopter landing but as I said the survivability of such a crash would be near zero. Also, I'm fairly certain air traffic is re-routed specifically to avoid such a thing. Alaskans know to stay away from Denali in the air because it is so massive it creates its own weather. Beeblebrox (talk) 23:22, 20 September 2011 (UTC)[reply]

Something I read in a book about Everest once. "There is no 'trapped on Everest' - only 'dead on Everest'", or something along those lines. If you're up there somewhere and any potential rescue isn't immediately at hand, then you might as well be on the moon for your chances of survival. --Kurt Shaped Box (talk) 00:58, 21 September 2011 (UTC)[reply]

In general, mountain peaks above the 8000-meter line are referred to as "the death zone" -- a person who finds himself unexpectedly trapped in that zone would certainly perish. 67.169.177.176 (talk) 04:47, 21 September 2011 (UTC)[reply]

Time for a very ignorant question: Suppose a large jet with a large amount of fuel crashed right at the summit. Might the resultant explosion be strong enough to blow away part of the summit, thus shortening the mountain's height? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:02, 21 September 2011 (UTC)[reply]

ABSOLUTELY NOT! To do this would require a multi-megaton atom bomb at the VERY LEAST! 67.169.177.176 (talk) 06:25, 21 September 2011 (UTC)[reply]

Apparently Everest's height is measured to an accuracy of ±0.21 m. It may not be unreasonable that a major crash could make a measurable difference. A plane crashing with a near-full fuel tank has been known to make quite an impact. Mitch Ames (talk) 12:16, 21 September 2011 (UTC)[reply]

You could knock off the snow on top which is a few feet if I recall. Not enough to help anyone. Googlemeister (talk) 12:59, 21 September 2011 (UTC)[reply]

If you dropped a bomb on it, you could probably take a few metres off the top (basically, the same amount as the depth of the crater you would create if you dropped it on flat ground, give or take). Near-full fuel tanks don't really explode, though, they just burn. Empty fuel-tanks explode because they are full of fuel vapour, which is explosive. Liquid fuel isn't. If the tanks were empty, though, the amount of fuel vapour wouldn't be enough to cause any but a small explosion, not enough to significantly damage the mountain. --Tango (talk) 17:23, 21 September 2011 (UTC)[reply]

I didn't necessary expect significant damage, but I expected that something would happen. Obviously, it depends on the amount of force involved, and the precise angle and landing point. Looks like it would take a lot more than a conventional airplane to knock it down below the height of K2, which I think is about 800 feet shorter than Everest. The various answers provide a lot of insights. Thank you! Aside: Everest was photographed from the air long before it was climbed, but they kept a safe distance. It also occurs to me that if a plane is in that much trouble, it probably wouldn't even make it to Everest - it would probably crash on one of the somewhat-lower peaks in the vicinity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:38, 21 September 2011 (UTC)[reply]

Highest an aircraft can fly

What is the highest up an aircraft can fly (and I mean something like a jet plane, propliner, or helicopter, not something like Apollo 11 or the Space Shuttle)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:35, 20 September 2011 (UTC)[reply]

About 100 km altitude. This is where the speed needed for the aerodynamic forces to overcome gravity becomes similar to the speed needed to stay in orbit. Count Iblis (talk) 22:51, 20 September 2011 (UTC)[reply]

The current record is less than half that, about 37.5k, set in 1977. See Fédération_Aéronautique_Internationale#Records. SDY (talk) 22:52, 20 September 2011 (UTC)[reply]

An airplane can fly a LOT higher than 37,500 feet. And wouldn't the jet engines be starved of air long before the altitude reaches 100 kilometers? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:00, 20 September 2011 (UTC)[reply]

That's probably intended to mean 37.5 km, not kilo-feet. Yes, getting air-breathing engines up to 100 km would be quite a challenge. Even the MIG-25 record of 35+ km was done using a zoom climb, not sustained engine performance. But several experimental aircraft have been fitted with rocket boosters in addition to their normal jet engines. --Stephan Schulz (talk) 23:12, 20 September 2011 (UTC)[reply]

Yes, although the original statement may not have be entirely clear (although can be inferred in the context of the discussion), the article they linked to as their source unsurprisingly is clear. Nil Einne (talk) 23:25, 20 September 2011 (UTC)[reply]

As for the highest sustained flight: Lockheed_SR-71_Blackbird#Records says "On 28 July 1976, SR-71 serial number 61-7962 broke the world record for its class: an 'absolute altitude record' of 85,069 feet (25,929 m)." That's 25.9 km. StuRat (talk) 03:05, 21 September 2011 (UTC)[reply]

Does the X-15 count? 67.169.177.176 (talk) 04:03, 21 September 2011 (UTC)[reply]

The X-15 was a rocket with wings. The Blackbird was a ramjet. So probably not. I do recall reading in The Right Stuff about Yeager taking I think his conventional plane so high that the sky turned black, which means you're pretty much in space. At that point the engine conked out and the plane went into a dive that destroyed it (it "augered in"), but Yeager bailed out successfully. (It's been a long time, I hope I haven't conflated 2 or more stories into 1.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:10, 21 September 2011 (UTC)[reply]

If the plane in question was the Bell X-1 or any derivative thereof, then the engine was a liquid rocket -- which means that it conked out because of fuel exhaustion, not because of thin air. As for the dive, in this case it might have been caused not by the engine failure, but by inertial coupling. FWIW 67.169.177.176 (talk) 06:29, 21 September 2011 (UTC)[reply]

I didn't dream it after all. It was an F-104. The article discusses the Yeager mishap. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:47, 21 September 2011 (UTC)[reply]

For a standard fixed wing aircraft, a very high altitude requires a very high lift body with an extremely high stall angle, and/or a ridiculous amount of excess thrust (which would basically make it more of a rocket than a traditional airplane). Lynch 7 17:37, 21 September 2011 (UTC)[reply]

As I recall from the last time I read about this in any detail, the ability of a plane to achieve a high altitude is dependent on its type of engine, as you're indicating. A standard prop plane can only go so high because it can only go so fast. A conventional jet can go higher because it can go faster. And a ramjet can go very high because it can go very fast. In fact, I think the way a ramjet works is that, "The faster and higher it goes, the faster and higher it can go. Up to a point, of course, as it still needs air. Rockets don't need air, as their fuel is self-contained. Obviously. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:43, 21 September 2011 (UTC)[reply]

The F-15 Eagle can reach 100,000 feet in a zoom climb. The SR-71 can reach even higher altitudes in sustained flight (or at least so they say). 67.169.177.176 (talk) 22:52, 21 September 2011 (UTC)[reply]

And I would still call the SR-71 an airplane, so I think it qualifies, ramjet or not. StuRat (talk) 23:05, 21 September 2011 (UTC)[reply]

Yes, absolutely, the Blackbird was/is an airplane. The X-15 was a "rocket plane". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:46, 21 September 2011 (UTC)[reply]

Battery acid?

Ok, I've just returned from my yearly camping trip to Interior Alaska. We use a small battery powered fan most nights to supply a little breeze and some "white noise". One night the batteries began to fail while we slept, waking my wife, who replaced the batteries in the dark while half awake. When we woke in the morning the batteries seemed to be dying again already, and upon further inspection a thin, foamy liquid was seeping out of the battery door. It turned out three of the four D cells were in correctly, but one was backward. After discovering this I knocked the batteries into the trash and we cleaned the fan up. I got some of this liquid on my fingers. They seemed to tingle a bit but did not turn green, burn, or begin dissolving. Maybe I've seen too many cheap movies. So my question is: Was this substance battery acid? How corrosive is it? Why did the batteries still work at all when one was improperly installed? Can I guilt trip my wife for endangering my life or should I feel bad for not waking up and doing it myself? (that last one obviously not a scientific question but more of a domestic matter) Beeblebrox (talk) 23:36, 20 September 2011 (UTC)[reply]

See Alkaline battery#Leaks and Carbon zinc battery#Leakage and environmental concerns Nil Einne (talk) 00:15, 21 September 2011 (UTC)[reply]

I'm surprised that the fan worked on half its normal voltage (the reversed cell would cancel out one third of the three correct cells), but it would be the reverse current that overcharged the reversed cell and caused the leakage because the hydrogen produced in attempting to charge the cell would force zinc chloride out of the cell (your description doesn't sound like potassium hydroxide from an alkaline cell). Zinc chloride is a skin and respiratory irritant, so I hope you washed your hands well, but I've had it on my hands many times without ill effect, so don't accuse your wife of attempted murder. The three cells that were not reversed probably needed only a good wash to be used again. Dbfirs 00:45, 21 September 2011 (UTC)[reply]

Small DC motors can operate at various voltages, such that increasing or decreasing a voltage will increase/decrease a motor's torque and speed. The limiting factor is usually the excess heat that is produced in the motor's winding if one is operated too long above its rated voltage. --Modocc (talk) 01:36, 21 September 2011 (UTC)[reply]

Indeed it isn't uncommon (well more common in the past before the widespread availability of fan speed controllers) for someone to operate a 12V DC fan on 7V and occasionally even 5V in a computer. They don't always work, particularly at 5V but a fair few do. Nil Einne (talk) 05:31, 21 September 2011 (UTC)[reply]

The tingling you felt from the foamy liquid was potassium hydroxide which is not an acid but a base. It's very corrosive to metal, and if you rinsed your hands well, then no harm done. Just be glad you didn't wipe your eyes after touching it, or you would have been in substantial pain and possibly at risk. Dualus (talk) 06:59, 21 September 2011 (UTC)[reply]

High-power alkaline batteries contain aqueous potassium hydroxide, but it doesn't normally leak as a liquid in my experience, which is why I thought that acidic zinc chloride from cheaper batteries was more likely, especially because of its deliqiescence. We agree that washing hands is important whichever it was. Dbfirs 08:51, 21 September 2011 (UTC)[reply]

I've had one alkaline battery leak in decade.. However if the battery was reversed with a voltage of 4.5V across it the chemistry would change - possibly oxygen would be evolved (and maybe hydrogen at the other electrode - though this is supposed to be absorbed by the manganese dioxide) - if so this would cause an increase in pressure and break the safety seal - evolution of gas might also explain the foamy nature of the leak.

generally if it's an alkaline battery the electrolyte (liquid) feels very soapy - and also tends to sting on even the slightest skin cut (or skin damage - including tiny cuts you wouldn't have otherwise noticed) - if you didn't notice this (you have skin like a rhino or) it was a 'dry cell' - these also can produce gas if connected the wrong way round.Imgaril (talk) 11:11, 21 September 2011 (UTC)[reply]

Re: guilt tripping your wife - all modern batteries have a safety release valve - that breaks when pressure builds inside the battery - this makes the batteries safe - if they didn't have these than exploding batteries are a real possibility. However the evolved gas may be a mixture of hydrogen and oxygen - a real explosive mixture - it's unlikely to be enough to kill you (though the explosion might have deafened you and set fire to your tent in an extreme example) .. the rest is up to you.Imgaril (talk) 11:19, 21 September 2011 (UTC)[reply]

Regarding that battery type, they were non-rechargeable Duracell alkaline batteries. Anyhoo, my fingers didn't fall off, the fan still works, and my wife had to go back to work after our vacation 2 days before I did so I guess the guilt trip is cancelled as well. Thanks for the replies! Beeblebrox (talk) 23:45, 21 September 2011 (UTC)[reply]

September 21

Highest internal temperature of cold blooded animals

What is the highest internal temperature cold blooded animals (Ectotherms) can tolerate from their external environment and can warm blooded animals tolerate a higher internal and external temperature? --DeeperQA (talk) 00:49, 21 September 2011 (UTC)[reply]

I would expect that cold-blooded animals can withstand a higher internal temperature. After all, they are designed to handle a wider range of internal temperatures. However, that doesn't necessarily mean they can withstand higher external temps, since warm-blooded animals may have more effective cooling methods, like sweating. StuRat (talk) 02:54, 21 September 2011 (UTC)[reply]

Okay, so what would be the dividing line? At what temperature would warm blooded survive and cold blooded would not? --DeeperQA (talk) 04:08, 21 September 2011 (UTC)[reply]

There isn't really a strong dividing line; animals like the sloth tend to blur it. --T H F S W (T · C · E) 05:14, 21 September 2011 (UTC)[reply]

It sounds like the question is more relevant to Poikilotherm and Homeotherms rather then cold or warm blood. In particular this image. Vespine (talk) 05:45, 21 September 2011 (UTC)[reply]

If I'm reading that chart correctly, mammals do better than reptiles with internal temperatures over 35°C, reptiles go dormant at 37°C, and mammals go dormant at 42°C (but, in the case of mammals, the exterior temp could be quite a bit higher before their internal temp would reach that). So, that seems to say that mammals can tolerate both higher internal temps (which surprises me) and external temps (which doesn't). StuRat (talk) 03:31, 22 September 2011 (UTC)[reply]

You might like to read Boiling frog, though the article doesn't really answer any questions. Dbfirs 08:40, 21 September 2011 (UTC)[reply]

Moment magnitude conversion

How can I convert a Molment Magnitude measure into a richter scale measure?

See the article Moment magnitude scale. For any medium sized earthquake (from say 3.0-6.0 or so) the scales are almost identical. The Moment Magnitude scale is more accurate for measuring small and large earthquakes than the Ricter scale, so the two scales diverge at either end. --Jayron32 02:32, 21 September 2011 (UTC)[reply]

When the moment magnitude scale was set up it was intended to match the Richter scale exactly at lower magnitudes, but provide more accurate magnitudes above about magnitude 7 as the Richter scale tends to saturate at around this value. This is because of the measuring technique, with the Richter scale and the related surface wave magnitude and body wave magnitude scales, using relatively short period (i.e. high frequency) waves, while modern seismometers use a wide range of frequencies, capturing the full energy output of the earthquake. Mikenorton (talk) 15:35, 21 September 2011 (UTC)[reply]

Earthquake question

It is known that Earthquakes occur when several tectonic plates move relative to each other.The boundry between them are large areas.Then why we say about the points like hypocenter or epicenter and not large areas? — Preceding unsigned comment added by 49.244.180.209 (talk) 02:10, 21 September 2011 (UTC)[reply]

Because the "slips" happen in relatively isolated locations. Rocks seem very rigid, at least on a human scale, but when measured in continent sized chunks they have some elasticity to them (scientists call this Elastic modulus). You can think of it this way: When you tear a paper, you don't tear it all at once, you tear it one little point at a time. An earthquake is generally one little tear happening in one location. The rocks don't break all along the fault, they tear along it. --Jayron32 02:30, 21 September 2011 (UTC)[reply]

If the plates moved smoothly past, there would be no quakes. But they "snag" at certain points. When these break free, you have a quake, centered around the snag. StuRat (talk) 03:08, 21 September 2011 (UTC)[reply]

Scientists who deal with earthquakes precisely do not really talk about epicenters. They talk about fault mechanics. For example, this research group, Crustal Deformation and Fault Mechanics, uses geophysical data to model the actual rock behavior more accurately than just a point-source earthquake. You can see some illustrative diagrams of their research; including some nice 3D diagrams of earthquake data. Here is some more work from another researcher, shear dynamics. Today's journalists find a dot on a map easier than a thorough scientific analysis, but if they did a little research, they'd see that earthquakes are actually very complicated, dynamic, volumetric events. Nimur (talk) 23:48, 21 September 2011 (UTC)[reply]

why are the pictures of actual size molecules are countable?

how is it that we know so much about the structure of molecules (numbers of atoms (from various kinds in it) or their aesthetic arrangement) but we haven't really see them (i know of only 2 photos of molecules in "reality".

i would like to know about a text-book who contains photos of molecules, i must look in it. i believe that there aren't such photos here in Wikipedia in molecule only because of copyright problems. thanks. 109.66.42.35 (talk) 10:17, 21 September 2011 (UTC)[reply]

There aren't any photographs possible. Visible light has too long a wavelength to resolve detail on that scale. All that is possible is either a CGI constructed using data obtained by non-optical nanoscopes, or a translated image using an xray crystallography. Plasmic Physics (talk) 10:33, 21 September 2011 (UTC)[reply]

(edit conflict) We can't take photographs of molecules because they are too small compared to the wavelength of visible light, so we have to use indirect methods to infer the details of their composition and structure. Some of these methods are described under Molecular geometry determination in the molecular geometry article. Gandalf61 (talk) 10:37, 21 September 2011 (UTC)[reply]

One can create images of atoms using a scanning tunneling microscope. That doesn't use light either, but you can definately image individual atoms using the technique. --Jayron32 15:16, 21 September 2011 (UTC)[reply]

indeed!, we can see individual atoms.. as we all can see in the article atom. so why are the photographs of molecules are so countable (1-2), you could use google to see this 2...thanks. 81.218.145.251 (talk) 15:34, 21 September 2011 (UTC)[reply]

There are no photographs of individual atoms or molecules. What you see are images created by taking the output from some very fancy electronics and doing a lot of complicated signal processing on it. Gandalf61 (talk) 22:39, 21 September 2011 (UTC)[reply]

Which is to say, we get into unusual and counterintuitive definitions of "seeing" when we start talking about things the size of atoms or molecules. It's a fair point to say we can visualize them; it's also a fair point to note that this is an especially mediated/manipulated form of visualization. --Mr.98 (talk) 02:03, 22 September 2011 (UTC)[reply]

Infact I used an AFM just the other day. Plasmic Physics (talk) 23:14, 21 September 2011 (UTC)[reply]

Thinking: if you're not actually perceiving visually the nanometric objects, then is still right too call it microscopy or nanoscopy? Why not call it micrography or something similiar? Plasmic Physics (talk) 03:10, 22 September 2011 (UTC)[reply]

There is this, the picture part way down is the letters "IBM" arranged out of individual atoms, I can't find if there is a wiki article about it. Vespine (talk) 03:26, 22 September 2011 (UTC)[reply]

redundant rails

When travelling on mainline railways I often find that there are long sections of rusty rails between the rails in use. What are the purposes of these? Difficultly north (talk) 11:49, 21 September 2011 (UTC)[reply]

In the UK it's common to leave old rails (or cut off rails) in the track bed, or next to the track when they have been replaced - this is a management/cost issue where the effort/equipment does not exist to recycle the rails.. (or it is more cost effective to allow this wastage)

In some cases what appears to be two rusty rails will be seen between the running rails - these may be fixed to the sleepers (railroad ties) across a rail expansion joint - they are added to add stability keeping the track in allignment at points were there is a gap in the connectivity of the running rails. (I'm assuming you wouldn't have confused what you saw with Gauntlet track).Imgaril (talk) 12:15, 21 September 2011 (UTC)[reply]

No not Gauntlet track. I am often seeing it anywhere on the National Rail network. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)[reply]

Rails left in the track bed tends to be a temporary thing, either delivered and not yet installed or the old rails awaiting uplift. More often than not, somewhat counter-intuitively, the rusty rails are the new ones. --Tagishsimon (talk) 16:54, 21 September 2011 (UTC)[reply]

Okay. I'll take a photo of what I mean tomorrow but I think yours sounds more sort of what I'm referring to. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)[reply]

Yup, I'm fairly confident we're talking about the same thing. Installing long welded rail takes time, and track possession times are short, so the job gets broken down into delivery, assembly, installation, dismantling, uplift, etc. --Tagishsimon (talk) 22:45, 21 September 2011 (UTC)[reply]

I think you're talking about guard rails. They are there to make sure the train doesn't go to the side if it derails. You see them mostly on bridges and other sturctures where a train leaving the track during derailment could cause a lot of damage to nearby structures. Here's a good picture: [[16]]. BTW, I remember going through this tunnel as a kid when my folks would take me to New York. The tunnel is in Nay Aug Park in Scranton, PA. Dominus Vobisdu (talk) 16:14, 21 September 2011 (UTC)[reply]

Sorry, I'm not referring to guard rails. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)[reply]

Did you mean like these [17] ? or these [18] ?? or even these [19] ??? . Imgaril (talk) 18:49, 21 September 2011 (UTC)[reply]

I see loose rails here too, but never on the tracks, that would just be dangerous. They usually lie next to the tracks. Plasmic Physics (talk) 23:11, 21 September 2011 (UTC)[reply]

I'm not sure anyone has alleged they're on the tracks (meaning on the rails), so much as on the track bed. The first two photos in Imgaril's post are them. --Tagishsimon (talk) 23:15, 21 September 2011 (UTC)[reply]

I meant track bed. Those rails in the photo clearly serve a purpose. I may not know what it is, but I do know that steel is expensive, and it wouldn't be used if there was no reason. Plasmic Physics (talk) 01:02, 22 September 2011 (UTC)[reply]

The 'purpose' is explained in the text in the links - the rails are awaiting installation, or waiting to be taken away - as Tagishsimon described. (Unless you meant the photo above right)94.72.237.125 (talk) 01:10, 22 September 2011 (UTC)[reply]

How sealed plastic soda bottle tops are attached

I guess this is an engineering-related question. When you first get a bottle such as a 2-liter bottle of soda, the screw-off top is one with the ring that stays at the base of the neck after purchaser rips the cap/ring connection by twisting the cap. How is that cap/ring piece initially attached? Is it rammed on with high force, with the threads of the bottle and the threads on the inner side of the cap just temporarily distorting as they rub past each other? I've also seen metal cap/ring pieces on glass bottles, but metal would seem to be less elastic than most plastics. 20.137.18.50 (talk) 17:39, 21 September 2011 (UTC)[reply]

The rings have little plastic "wings" on the inside which allow them to be threaded on, but which "catch" when threaded off, thus allowing the ring-and-cap assembly to be put on the bottle, but preventing the ring from coming off when twisted the other way. --Jayron32 17:55, 21 September 2011 (UTC)[reply]

A ratchet effect then?

Yes. 70.91.171.54 (talk) 19:02, 21 September 2011 (UTC)[reply]

I'm fairly certain that the metal ones are placed on as oversize caps, and then cold formed to a tight fit (I'm sure there will be a video of this on youtube, but can't find one as yet). There's an article on these metal ones Screw_cap_(wine) - the links have more info about how they are attached.Imgaril (talk) 18:14, 21 September 2011 (UTC)[reply]

Those kinds with anti-tamper or lock rings are called PP (pilfer-proof) screw caps. Like Jayron said, notice the teeth inside the bottom-most portion of the cap (the bank) which is only loosely attached to the top. They are all pointing in one direction. When you screw them on, they are flattened against the skirt of the cap, thus offer no resistance. But once they reach the end of the threads, they encounter an open space underneath a flange, and they pop out, pointing against the thread. Screwing it off will now make the teeth catch on the lower rim and it will instead break along the pre-cut stress points and be retained. And yes they are screwed on by machines. From labor-intensive ones for small-scale production to fully automatic ones.-- Obsidi♠n Soul 19:11, 21 September 2011 (UTC)[reply]

Actually I used to have a job putting the tops on 2litre bottles of milk - a machine filled them, but humans screwed the tops on... The trick is to hold the top steady and rotate the bottle by pulling.. Working inside a fridge in the middle of summer and all the milk you can drink - paradise. (they probably have a machine now - that was 20 years ago when milk in plastic bottles, in metric quanities was still a novelty) These were the "ratchet type", a bit like File:Milk jugs in a row.jpg. The clicking of the rachetting action is quite a pleasurable sound. Imgaril (talk) 00:49, 22 September 2011 (UTC)[reply]

Heh, I imagine it would have been very dreary. :P And yeah. There's a dairy (for water buffalo milk) nearby, and they use small machines that still require a person to hold the bottle up to it, but the actual spinning of the cap into it are all done by the machine very quickly.-- Obsidi♠n Soul 06:33, 22 September 2011 (UTC)[reply]

Where do I go wrong in this statics problem?

Problem: If the load has a mass of 3.0Mg with its center of mass located at G, determine the horizontal and vertical components of reaction at the pin C when x = 3.9m

See a diagram here: http://postimage.org/image/358oy4cxw/. Image text: The jib crane is supported by a pin at C and rod AB.

I understand that there are essentially three unknowns (the magnitude of the force along the rod and the vertical and horizontal components of the force at the pin) and three equations (the sum of vertical and horizontal forces and the sum of moments must be zero):

$\sum F_{x}=\mathrm {pin} _{x}+\mathrm {rod} _{x}=0$

$\sum F_{y}=\mathrm {pin} _{y}+\mathrm {rod} _{y}-3000\mathrm {kg} *9.8\mathrm {m/s^{2}} =0$

$\sum M=4\mathrm {m} *\mathrm {rod} _{y}-0.2\mathrm {m} *\mathrm {rod} _{x}-3.9\mathrm {m} *3000\mathrm {kg} *9.8\mathrm {m/s^{2}} =0$

${\frac {-3.2\mathrm {m} *\mathrm {rod_{x}} }{4\mathrm {m} }}=\mathrm {rod} _{y}$

I solve this with matlab like this:

solve('pinx + rodx = 0',
      'piny + rody - 3000 * 9.8 = 0',
      '4 * rody - .2 * rodx - 3.9 * 3000 * 9.8 = 0',
      '-3.2 / 4 * rodx = rody')

The results are pinx = 33.72kN, piny = 2.421kN (and rodx = -33.72kN, rody = 26.98kN).

However when I enter the answer to the online system I got the problem from it says "Term 2: Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures." Term 2 refers to pin_y. The system is very lax with rounding and accepts any answer as long as the relative error is below a few percent. The value of g the system uses is exactly 9.8m/s^2.

Since I can enter the answer an unlimited number of times I varied pin_y in steps of .01kN a few steps to both directions until the message went away. That suggests that while pin_y might be close to correct pin_x is not. I've been thinking about this for a few hours and just cannot see my error. It's getting very frustrating. I'd appreciate if you could check that I have solved at least something correctly. If you can think out of the box and tell what is the real problem my online system wants answered it would be great. --19:49, 21 September 2011 (UTC) — Preceding unsigned comment added by 145.94.77.43 (talk)

In your last equation, I think the 3.2m should be 3m. Also, the second argument to solve is missing an "= 0", but not using Matlab I don't know if that's a bug or not. -- BenRG (talk) 22:16, 21 September 2011 (UTC)[reply]

Matlab solve() equates to zero by default, I failed to add a ' = 0' when copypasting. That 3.2 - .2 part was it. Thank you! This was a shamefully huge help. --145.94.77.43 (talk) 23:31, 21 September 2011 (UTC)[reply]

condensation in lungs

the inside of lungs is a fairly damp environment I presume, so does condensation form on the inside of the lungs when breathing cold air? If it does, where does all the liquid go? Does the person need to cough it out later? Googlemeister (talk) 21:11, 21 September 2011 (UTC)[reply]

Cold air contains very little moisture. Drying out would be a bigger problem. The inside of the lungs is warm enough to hold a lot of moisture, which is respirated. Remaining excess moisture would either be expectorated or be absorbed by the lung tissue. Dominus Vobisdu (talk) 21:17, 21 September 2011 (UTC)[reply]

Well cold air does not have to be dry. I was thinking where it was near freezing but foggy. Googlemeister (talk) 21:20, 21 September 2011 (UTC)[reply]

Even extremely humid cold air contains little moisture. Cold air can hold far less moisure than warm air can. When near freezing cold air with 100% relative humidity is warmed up to body temperature, it becomes very dry warm air. Dominus Vobisdu (talk) 21:31, 21 September 2011 (UTC)[reply]

Without directly answering: inhaled air is humidified and warmed by the upper airway, so that the partial pressure of water in alveoli is a fairly uniform 47 mmHg.). See Alveolar gas equation, Pulmonary gas pressures, Nasal concha. - Nunh-huh 21:22, 21 September 2011 (UTC)[reply]

Condensation forms when you have warm air and a cold surface. The situation you are describing is the reverse of that, so there shouldn't be any significant condensation. Looie496 (talk) 21:27, 21 September 2011 (UTC)[reply]

Well, it is possible, if you have air significantly hotter than body temperature at 100% relative humidity (or even supersaturated). I think I've had that happen in a hot shower, with the door closed, where it seems to become difficult to get enough oxygen. Opening the door solves the problem. A sauna might be another place where this might be an issue. Note that these same conditions would tend to cause hyperthermia, as well, although that seems to take a bit longer. StuRat (talk) 00:29, 22 September 2011 (UTC)[reply]

Pulmonary alveoli absorb moisture into the body along with oxygen; they have to do the former to be able to do the latter. When they fail to do so adequately, bronchitis results. 70.91.171.54 (talk) 22:37, 21 September 2011 (UTC)[reply]

Can you tell me something about vultures?

Do we know how intelligent vultures are, compared to humans and other birds? --95.150.167.139 (talk) 23:10, 21 September 2011 (UTC)[reply]

"humans and other birds"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:39, 21 September 2011 (UTC)[reply]

It would depend on deciding on a definition of intelligence that could be validly applied to both birds and humans. Even if you restricted it to just birds, there are many different "intelligences" that could be looked at. HiLo48 (talk) 00:20, 22 September 2011 (UTC)[reply]

Well, way above chickens, below parrots, and well below humans, for a start. StuRat (talk) 00:34, 22 September 2011 (UTC)[reply]

Vultures seem to be good at finding food, which is more than I can say for some humans and other birds. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:43, 22 September 2011 (UTC)[reply]

Here in the US, humans appear to be way too good at finding food. :-) StuRat (talk) 06:44, 22 September 2011 (UTC) [reply]

We have bad definitions of "intelligence" even for just human beings. But a rough estimate in comparing species can be found using the brain-to-body mass ratio and/or the encephalization quotient. I haven't been able to easily locate the numbers for a vulture. But that's what I would look for, anyway, to figure out where vultures in particular stand. Humans rank about twice of any animals for EQ. Some birds — especially corvids — have relatively high EQs. Most birds do not. I know very little about vultures in particular. --Mr.98 (talk) 02:00, 22 September 2011 (UTC)[reply]

September 22

What are/ may be floating conditions to float any thing over water surface

Sir/ Madam I wish to know what are the floating conditions to make any thing float over water surface(Normal potable water not salty).

Wish for an early reply

Thanx a lot — Preceding unsigned comment added by 182.156.153.151 (talk) 04:20, 22 September 2011 (UTC)[reply]

Is this a homework question? 67.169.177.176 (talk) 04:45, 22 September 2011 (UTC)[reply]

For specifically FLOATING, you're probably after buoyancy. Vespine (talk) 04:47, 22 September 2011 (UTC)[reply]

(EC) For a large object in a stable configuration, the object will float if the mass of the object is no more than the mass of a volume of water equivalent to the portion of the volume of the object that’s below the surface of the water, i.e., the mass of the object is no more than the mass of the displaced water. See Displacement (ship) and Displacement (fluid). For very small objects, surface tension can cause an object to float even if it has a greater mass than the displaced water. Red Act (talk) 04:49, 22 September 2011 (UTC)[reply]

In other words, for all but the smallest objects, if the object's density is less than that of water, it will float. Very small objects (sewing needles, etc.) can sometimes float despite being more dense than water, because they are supported by surface tension. 67.169.177.176 (talk) 05:11, 22 September 2011 (UTC)[reply]

And, of course, an object can still float despite being made of materials far denser than water, like steel, so long as they contain a far lighter material, like air, beneath the waterline, so that the average density of everything is less than water. StuRat (talk) 06:25, 22 September 2011 (UTC)[reply]

And, with a more liberal interpretation of the word "float", we could include a hydroplane, hydrofoil, hovercraft, or ground effects airplane (only the first two actually require water). StuRat (talk) 06:36, 22 September 2011 (UTC)[reply]

low boiling dopamine receptor agonists

Can someone help me brainstorm of new agonists I could use for fruit fly experiments? We've been working with cocaine for ... years and months, but I also want to try something else. For one, the success rate of aerosolising cocaine with a consistency amenable to experiment is rather unpredictable.

Feeding it into a test chamber by say, distillation often means the cocaine crashes out and crystallises on random surfaces, unable to be taken up by flies. For the love of the flying spaghetti monster, are there any agents better than cocaine that might be easier to administer through the air? (We cannot administer through their food, for various complex reasons.) elle _{vécut heureuse} ^{à jamais} (be free) 04:53, 22 September 2011 (UTC)[reply]

THC ? Nicotine ? Ethanol (might be a bit of an irritant, though) ? Or how about the chemical in some dry erase markers that just about makes me pass out ? StuRat (talk) 06:27, 22 September 2011 (UTC)[reply]

Those aren't dopamine agonists. I'd look at Pramipexole and Apomorphine because of their low molecular weight, but that's a lousy huristic for organic compounds, so what you really need is to go through Category:Dopamine agonists in CAS for an hour or two until you find something sufficiently soluble and volatile. 69.171.160.5 (talk) 06:52, 22 September 2011 (UTC)[reply]