Wikipedia:Reference desk/Science

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The Wikipedia Reference Desk covering the topic of science.

Welcome to the science reference desk.
Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

  • Provide a short header that gives the general topic of the question.
  • Type ~~~~ (four tildes) at the end – this signs and dates your contribution so we know who wrote what and when.
  • Post your question to only one desk.
  • Don't post personal contact information – it will be removed. We'll answer here within a few days.
  • 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.

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.
See also:
Help desk
Village pump
Help manual

August 16[edit]

Spider Gender[edit]

Is it possible to know whether a spider is male or female? I know that with many species, the female is larger, but with most species being solitary dwellers, there are usually no other spiders to compare them with. KägeTorä - () (Chin Wag) 03:34, 16 August 2014 (UTC)

It's going to vary by species. For some, perhaps many, only the females build webs. For some tarantulas, the males have some sort of little hooks on their forelegs which are used to hold the female in check during mating. (Talk about a "two-bag date", eh?) ←Baseball Bugs What's up, Doc? carrots→ 03:51, 16 August 2014 (UTC)
I thought everybody knew that female spiders always have longer eyelashes; (I too, am educated from cartoons). (talk) 18:14, 16 August 2014 (UTC)
Called "tertiary sexual characteristics" on TVTropes. -- BenRG (talk) 21:10, 16 August 2014 (UTC)
This page suggests looking at the pedipalps (along with coloration and size). -- BenRG (talk) 21:10, 16 August 2014 (UTC)
The males of some species have six legs, a mosquito-like proboscis and manage hotels. InedibleHulk (talk) 21:25, August 16, 2014 (UTC)
Spiders are feminine in the gendered languages with which I'm acquainted. —Tamfang (talk) 05:48, 17 August 2014 (UTC)

Molecular term symbols[edit]

How do you I translate a MO diagram into a molecular term symbol? How about using

Molecular orbital scheme for the three forms of oxygen.png

as a teaching model? I understand the multiplicity number, I am most interested in the quantum number, but the remainder of the general formula is also important. Plasmic Physics (talk) 06:32, 16 August 2014 (UTC)

How does a Cross Vacuum Scale work?[edit]

A Cross Vacuum scale is a collection of 5 or 6 tubes with vacuum varying from a couple of torr to about .03torr. When a high voltage charge is placed across these tubes they glow, with different colours at different levels of vacuum. I would like to know why they glow and what voltage is required to excite these tubes.

Thanks for your help Rod — Preceding unsigned comment added by (talk) 10:32, 16 August 2014 (UTC)

A Cross vacuum scale consists of 6 Geissler tubes (see article) with different vacuums to show their effects on electrical discharge.

From a seller's description:

tube no. 1 at 10 Torr pressure : ribbon line discharge

tube no. 2 at 5 Torr pressure : crimson band discharge

tube no. 3 at 1,25 Torr pressure : crimson coloured discharge

tube no. 4 at 0,75 Torr pressure : stratifications

tube no. 5 at 0,05 Torr pressure : grayish-white light

tube no. 6 at 0,025 Torr pressure : glows with brilliant green flourescence of glass (talk) 11:05, 16 August 2014 (UTC)

Testing for alcohol in food[edit]

If you cook some dish using alcohol, how can you measure how much alcohol is left at the end? (I suppose there is a lot still, but I want to know how to test it empirically). OsmanRF34 (talk) 17:04, 16 August 2014 (UTC)

A hydrometer will allow testing of the liquid component, but presumably you're interested in the whole dish. Cooking with alcohol cites this paper, which anyone with a PubMed account can access - this doesn't include me, unfortunately. Tevildo (talk) 17:13, 16 August 2014 (UTC)
A hydrometer just measures density of the liquid component. That would be fine if one were to work with a solution of just water and ethanol, but breaks down if the mixture contains an appreciable amount of any other dissolved, suspended, or emulsified material which could quite significantly affect the density of the liquid.
The paper Tevildo linked noted rentention of anywhere between 4 and 85% of the original alcohol content, depending on cooking time, cooking temperature, and surface area of the cooking vessel. (Unsurprisingly, there was less alcohol retained during longer, hotter cooking in pans with larger surface area.) The method used was homogenization of the food sample and addition of water (to fully dissolve the alcohol), followed by centrifugation of the resulting slurry to remove solids. Gas-liquid chromatography was used to determine ethanol content, using the method described in Martin GE, Burggraff JM, Dyer RH, Buscemi PC. "Gas-liquid chromatographic determination of congeners in alcoholic products with confirmation by gas chromatography/ mass spectrometry." J Assoc Off Anal Chem. 1981; 64:186. I'm afraid I can't lay my hands on that paper, but Gas chromatography–mass spectrometry gives you an idea of the technique. TenOfAllTrades(talk) 19:14, 16 August 2014 (UTC)
Assuming you don't want to submit your dinner to a lab for testing, perhaps a home breathalyzer unit might give a rough indication of the amount of alcohol remaining. Take a bite of the food, then exhale into the device, and see what kind of a reading you get. Now it won't give you the percentage of alcohol in the food, but a higher number will mean there's more in the food. You could "calibrate" it by making a chart, with various test concentrations of alcohol in the food. Again, it wouldn't be highly accurate, but might be good enough to tell you if the kids should skip that meal or not. StuRat (talk) 01:24, 17 August 2014 (UTC)


After playing the last of us Im just curious is it possible for the fungus to somehow evolve or adapt into infecting humans and if so would the results be like in the game or will people just start climbing buildings and wait to die like ants do — Preceding unsigned comment added by (talk) 20:37, 16 August 2014 (UTC)

First, let's link The Last of Us. As for your question, well, I would say that nothing is impossible in biology. A science like physics, it is all about what can't be done. But biology is just a collection of things that happened. If you dream it, you can do it. But something like this is really, really unlikely without a whole lot of help, or a certain sort of luck. Wnt (talk) 22:03, 16 August 2014 (UTC)
A big diff is that ants do everything based on instinct, while humans have far more complex decision making processes. The advantage of instincts is that they require far less brain, but this also means they can be easily hijacked by activating just a few neurons. Changing human behavior in such a specific way would require a lot more than that. On the other hand, torqued up aggression or risk taking behavior can occur in humans as a result of diseases. StuRat (talk) 01:10, 17 August 2014 (UTC)
"A big diff is that ants do everything based on instinct, while humans have far more complex decision making processes." How do you know that? Can you prove it? ScienceApe (talk) 04:00, 17 August 2014 (UTC)
One fun way to show this is to lay down a circular scent trail for the ants to follow. They will happily follow the circle around and around, not noticing they are going in circles. Very reminiscent of the infinite loops a computer can get into. When you only have a very basic set of instructions to follow, this type of error can happen. StuRat (talk) 04:50, 18 August 2014 (UTC)
Mammals are highly resistant to systemic fungal infections. Mammalian body temperature is uncomfortably hot for fungi (it is even possible that a high body-temperature is partly an antifungal adaptation).
Also linking Cordyceps. There are a ton of parasites that control host behavior. Most of them don't use mammalian hosts. Here is a nice overview [1], and here is a very nice set of links to many more articles about parasite manipulation [2]. The plot for the game, while not necessarily biologically sound, is indeed informed by the many examples of parasites turning animals into "zombies". SemanticMantis (talk) 15:55, 18 August 2014 (UTC)
In general most fungi can not survive the elevated temperature of warm blooded species. Some theorize that this is the reason for warm blood in the first place. There are few that can, but they don't grow well. So it's unlikely that Cordyceps could infect a human, even an Immunocompromised one. Ariel. (talk) 18:27, 18 August 2014 (UTC)

August 17[edit]

A properties of acids and caustic alkalis[edit]

Does a microlife (germs, bacteria, viruses) been in the acids and caustic alkalis?--Alex Sazonov (talk) 11:56, 17 August 2014 (UTC) As I been knowing, the acid and excess acidic environment is been eating by them's.--Alex Sazonov (talk) 13:17, 17 August 2014 (UTC)

Snottite. Wnt (talk) 14:37, 17 August 2014 (UTC)
Acidophiles and alkaliphiles exist. Red Act (talk) 15:51, 17 August 2014 (UTC)
I been suppose that, anyone chemical environment is been a biological!--Alex Sazonov (talk) 17:15, 17 August 2014 (UTC)
Pretty much. See Extremophile#Classifications. Red Act (talk) 17:24, 17 August 2014 (UTC)
The most simplest form of biological is been chemical-physical materia or not it been biological?--Alex Sazonov (talk) 18:04, 17 August 2014 (UTC)
For a discussion of the simplest possible forms of life, see Abiogenesis. Red Act (talk) 19:08, 17 August 2014 (UTC)

I thinking that, a chemical oxides (химические окиси) and oxideis of chemical (химические окислы) are beening the absolute chemical environment.--Alex Sazonov (talk) 18:27, 17 August 2014 (UTC)

But so, the absolute chemical environment always had been a biologically properties and biologically specifications.--Alex Sazonov (talk) 19:28, 17 August 2014 (UTC)
These two sentences are hard to understand, mainly because the phrase "absolute chemical environment" doesn't make sense. But I presume the word "absolute" is a translation of "aбсолютный", which can also mean "perfect", and "perfect chemical environment" does make sense. I.e., I think the intended meaning of these two sentences is something like: "I think that oxides are the ideal chemical environment. However, the ideal chemical environment is a property specific to the organism." Red Act (talk) 19:57, 17 August 2014 (UTC)
I mean that, the absolute (ideal) chemical environment is been the zero biological, but of course it always had been a biologically properties and biologically specifications.--Alex Sazonov (talk) 10:15, 18 August 2014 (UTC) I think that, an oxides group is been the chemical environment of terminates biological, but not all chemical elements of oxides group made it.--Alex Sazonov (talk) 10:31, 18 August 2014 (UTC)

I been suggest that, an oxides group consisted from this: окиси, окислы, закиси, закислы, углеродные перекиси, углеродные перекислы, but I don’t know how it’s translate in English, because I had not got a special English translate.--Alex Sazonov (talk) 15:40, 18 August 2014 (UTC) The list partly translates as "Nitrous oxide, oxides, nitrous oxide, закислы, carbon peroxide, carbon перекислы". (talk) 11:04, 19 August 2014 (UTC)

I suppose that, a sulfates and sulfides are not been included in oxides group, because they had been an alkaline ash in most cases, that’s why they always been an alkalis.--Alex Sazonov (talk) 18:05, 18 August 2014 (UTC)

can we ban him already? as did ruwiki (talk) 21:03, 18 August 2014 (UTC)

I've proposed this on the talk page. Tevildo (talk) 23:30, 18 August 2014 (UTC)

I’m sorry for my English! Did the chemical hydrolyzing of complex (implex) chemical substances been? I been think that, in Nature been only the chemical hydrolyzing of simple chemical substances.--Alex Sazonov (talk) 18:05, 19 August 2014 (UTC)

Medical test result human error statistics[edit]

How common are test result errors in developed countries as a result of human error? — Preceding unsigned comment added by (talk) 15:33, 17 August 2014 (UTC)

I'm thinking This book may be just what you are looking for. --Jayron32 01:36, 18 August 2014 (UTC)

August 18[edit]

Conclusions of an autopsy[edit]

A recent case got me to thinking about what information can or cannot be concluded from an autopsy. So, two questions. (1) Can an autopsy determine if the decedent were moving (e.g., running) versus standing still when the decedent was shot? And (2) Can an autopsy determine the position of the decedent's body when he was shot (e.g., whether or not he was holding his hands up in a "surrender" position?)? If indeed the medical examiner can make conclusions about these two matters, how would he do so? Thanks. Joseph A. Spadaro (talk) 04:25, 18 August 2014 (UTC)

The position of the body should show if he was running (unless he survived for some time after being shot and changed his position). Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement. On grass his clothes should have grass stains. And the path of the bullet through the body would reveal the position of the part of the body it hit. If the body was vertical at the time, that would tend to indicate standing, while if it was angled, that would indicate running (accounting for the height and distance at which the bullet was fired).
Detecting the hands up position would be a lot trickier. If the shooter was close enough that the victim was sprayed with gunpowder residue, then the location and density of the spray would indicate that the hands were up, but with a distance shot this method wouldn't work. Blood spatter from the victim could be used in a similar way, but there might not be much spatter, especially if the bullet is small, doesn't exit the body, and the victim was wearing thick clothes, like a winter coat. On the other hand, with a case like the fatal JFK head shot, there was all kinds of spatter to work with. StuRat (talk) 04:57, 18 August 2014 (UTC)
Thanks. But, I still have some confusion. You said: The position of the body should show if he was running. Why is that? Once you are shot, don't you just sort of "plop" down, regardless of whether you were running or standing still? You also said: Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement. When your body hits the ground, wouldn't you get abrasions either way, whether running or standing still? Thanks. Joseph A. Spadaro (talk) 05:31, 18 August 2014 (UTC)
At the very least, if he was hit in the back instead of the front, that would indicate he was leaving the scene. ←Baseball Bugs What's up, Doc? carrots→ 06:52, 18 August 2014 (UTC)
In the specific case of Shooting of Michael Brown, that doesn't seem to be a significant factor. Okay there are suggestions from witness statements that he was shot in the back, which may be problematic if there's no evidence of sufficient risk to anyone at the time to justify such a shooting. But although it's difficult to say since we only have third party reports of the officers account, the main dispute, as I think the OP knows appears to be whether he was kneeling on the ground surrendering to the officer at the time, or rushing towards the officer at the time of the fatal shots, after an earlier alleged attempt to grab the officers gun, before he started to run away. Nil Einne (talk) 08:02, 20 August 2014 (UTC)
Momentum is a factor here. If the victim is moving quickly, they will keep moving quickly after being shot (unless shot with something large and fast enough to cancel out their forward momentum). I'd expect there to be a difference between abrasions resulting from a straight fall down or backwards, and abrasions resulting from a fall when running, which results in sliding across the ground for a small distance. MChesterMC (talk) 08:41, 18 August 2014 (UTC)
Moment of inertia seems appropriate, as well. Though I'm what "laymen" call an idiot, sometimes. InedibleHulk (talk) 22:02, August 18, 2014 (UTC)
A-ha. That all makes sense. Thanks! Joseph A. Spadaro (talk) 08:49, 18 August 2014 (UTC)
As for the abrasions, you'd expect them to be longer and deeper if the victim was running when they dropped on cement or stones, or for the grass stains to be darker and longer if they dropped on grass. Of course, if the wounds weren't immediately fatal, they might have stopped running before they dropped. Regarding the angle of the bullets, the first should best show the initial position of the victim, but with rapid firing the victim's position might not change much between shots. StuRat (talk) 17:07, 19 August 2014 (UTC)
  • The problematic word here is "concluded" the medical examiner will describe a bunch of facts, that a bullet entered in one location and exited at another, that certain wounds were found, perhaps any signs of intoxication, cause of death (blood loss, brain trauma). It will be the forensic specialists who argue the case in court who will try to convince the jury of their theories of what happened. They will argue the patterns show he must have been standing, running away, shot while falling, etc. μηδείς (talk) 16:48, 18 August 2014 (UTC)
A medical examiner can conclude lots of things, as Steven Hayne illustrated. —Tamfang (talk) 20:03, 18 August 2014 (UTC)
Of course, he can conclude all sorts of things, such as cause and approximate time of death, type of weapon used, trajectory of a bullet though the body. He can have his own theory, if asked to testify as a witness. But he can't conclude guilt or criminal fact in the legal sense, which is what the OP seems to be getting at, given the recent shooting in MO. μηδείς (talk) 22:13, 18 August 2014 (UTC)
Though, of course, he may be getting at The Huston Plan. Inconclusive, I declare. InedibleHulk (talk) 22:20, August 18, 2014 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 21:03, 19 August 2014 (UTC)

Mayer bullets[edit]

Mayer bullets compared to an AA battery

There is an article on Russian Wikipedia about something called Mayer bullets or Mayer slugs. According to Google translate the article seems to say these are used in shotguns. How does that work exactly? Is a cartridge full of propellant loaded behind the slug? Are the Russians still using muzzle loaders? Our article on shotgun slugs seems to show the slug always crimped to a shell, but in the images in the Russian article just shows the slugs by themselves. SpinningSpark 10:48, 18 August 2014 (UTC)

My guess is that they are a normal type of slug, normally fired from a complete shell. I think they are just pictured solo for illustrative convenience. If you do an image search for shotgun slug, you'll see lots of photos where the slugs are removed from the shell for comparison purposes. Here's an article all about modern slugs, and it mentions a guy named Mayer, but it's probably not the same Mayer [3] SemanticMantis (talk) 14:58, 18 August 2014 (UTC)
Yup, not the same Mayer. That's Steve Mayer of Winchester, we're looking for A. K. Mayer (А. К. Майера) who invented a slug in 1963. SpinningSpark 16:22, 18 August 2014 (UTC)
They certainly seem to be on sale as bullets only without a shell [4][5]. SpinningSpark 16:54, 18 August 2014 (UTC)
@Spinningspark: I found a video where a guy is shooting them. I have no idea how they are commonly sold, but he shows the single slugs, then packs one into a shell, then fires it from a seemingly normal Break_action shotgun [6]. This video seems to be the same guy, and shows a little more about how the shell is assembled [7]. I found the videos by searching /Майера ружье/, with the second word meaning "shotgun" in Russian, according to google translate. SemanticMantis (talk) 21:58, 18 August 2014 (UTC)
Thanks, that about answers it then. SpinningSpark 23:57, 18 August 2014 (UTC)

Nuclear contrail thingies[edit]

Upshot-Knothole GRABLE.jpg

Yeah, I'm sure that's not the correct term, but since I have no idea what they are, I also have no idea what their name is. You can see them in the image at right; I've seen better images of them before but wasn't able to find any with a quick check of Commons. They are quite distinct white-ish lines of what look like water vapor, and they seem to have a strange habit of appearing in the area of nuclear weapon tests. I have a guess as to what they are, but it's probably wrong, and I'm sure someone here knows. Thanks in advance! Evan (talk|contribs) 16:05, 18 August 2014 (UTC)

They are smoke trails from small rockets launched just prior to the nuclear detonation. The visual distortion of the trails provides information about the detonation. Trying to find the relevant articles... DMacks (talk) 16:11, 18 August 2014 (UTC)
Mentioned with cite at Effects of nuclear explosions#Other phenomena. I know I've seen more detail of the history of this use (originally discovered accidentally!). DMacks (talk) 16:21, 18 August 2014 (UTC)
Fantastic! Thanks for the speedy response. Evan (talk|contribs) 16:24, 18 August 2014 (UTC)
How about an entire book on the history and role of such rockets? NASA Sounding Rockets, 1958-1968: A Historical Summary. This book focuses on civilian sounding rockets, including many that were fired at White Sands, but if I recall, it also has a section on the early Army rockets launched during the Trinity test in 1945. The photograph posted in the original question is a 1953 test at a different Department of Energy facility, the Nevada Test Site. Those sounding rockets were almost certainly small Army rockets and their smoke-trails would have been used as an indicator of the winds aloft (after the blast) at various distances. For some tests, the rockets would also be equipped with radiological, physical, and chemical detection and sample-collection equipment. You can find historical records of such tests from the Nevada Test Site's OpenLibrary web-page, hosted by the Department of Energy's Office of Scientific and Technical Information. In just a few moments of browsing, I found a technical report on the specific purpose of sounding rockets during Operation Hardtack, Aircraft and Rocket Fallout (1959). If you're interested in the exact test pictured above (Upshot-Knothole Grable, (1953)), I'm sure you can spend a few more hours browsing those resources. Nimur (talk) 17:16, 18 August 2014 (UTC)
Sounding rocket.    —E: (talk) 17:41, 18 August 2014 (UTC)
Here is the accidental first use of visual effect I was remembering: File:Trinity explosion film strip.jpg. And according to ISBN 9783540304210 page 992, the smoke trails are actually not even from really rockets, just simple mortars (in this context they are only used for the smoke trails, not the object being lofted). DMacks (talk) 16:57, 19 August 2014 (UTC)

Water jet cutter as a weapon[edit]

About how effective would a water jet cutter be as a weapon?(ignoring the bulk of the surrounding hardware) Would the stream just dissipate into steam after a few feet? (talk) 16:37, 18 August 2014 (UTC)

Our article does say "The penetrating power of these tools has led to the exploration of their use as anti-tank weapons but, due to their short range and the advent of composite armour, research was discontinued.[citation needed]". Rojomoke (talk) 16:45, 18 August 2014 (UTC)
Yeah I saw that, but ya know. Citation needed, plus I want to know what causes the range to be limited. (talk) 16:57, 18 August 2014 (UTC)
Air resistance and turbulent flow limit the effective range at which you can shoot a stream of high-velocity liquid. You read a two-sentence overview at the terminal velocity section of our article on water drops. Momentum and energy - which you would want to direct into the target - are instead lost to the air around the stream of water as it "sloshes." The faster you move the water, the more it sloshes, because air flowing past the "edges" of the water stream induces a viscous flow shear force. Nimur (talk) 17:02, 18 August 2014 (UTC)
I remember reading that in the article when I first started at my current job (we have a waterjet cutting machine) and pointing it out to a colleague who laughed. When it comes to steel, particularly thicker/harder steel, it is very slow. To give some numbers, the M1A2 Abrahms tank apparently has armour 120mm thick (according to google, yeesh), the feed rate for that thickness is somewhere in the region of 2-3mm a minute. That means to cut through 1m of steel would take some 6-8 hours. In that time your tank could have driven 250-340 miles--Jac16888 Talk 17:34, 18 August 2014 (UTC)
The rate at which the machine could cut a slot might not matter if you could aim it sufficiently well - a single penetrating hole one millimeter in diameter would be plenty if you can hit exactly the right spot in the engine bay and have the water jet drill a 1mm hole through some vital engine part or electronics. But I agree that keeping the water flow focussed over significant distances would be the downfall of such a weapon. I doubt that it's practical beyond a foot or two. SteveBaker (talk) 20:27, 18 August 2014 (UTC)
1mm could take 30 seconds, which a long time considering at the same time a tank-turret is probably turning around to face you--Jac16888 Talk 21:48, 18 August 2014 (UTC)
That sentence, which evolved out of something posted by someone at Central Michigan University in 2007, was apparently inspired by the use of a water jet cutter in the video game Metal Gear Solid 2. See the original addition. I can't find anything using Google that would support that sentence, so I removed it. Red Act (talk) 20:32, 18 August 2014 (UTC)

Would shooting another liquid that has a higher density and/or boiling point at high velocity make a difference? Liquid metal perhaps? (talk) 22:31, 18 August 2014 (UTC)

You're on the right way, since most portable anti-tank weapons use metal, which behaves like a liquid at the kind of pressure involved. Generating that kind of pressure (I've read it's in the TPa range[citation needed], which is more than 107 times atmospheric pressure) using non-destructive equipment (in the sense that it doesn't blow itself apart in the process) is difficult even with today's technology. Sidney Alford#Early Inventions lists some shaped charges using water, so the idea isn't flawed as much as it hits its limits if applied to modern armor.
Also note that a [citation needed] tag does not necessarily indicate that the tagged statement is dubious; it indicates that a key fact is not backed by a source in the list of references. For dubious statements, we have the [dubious] tag. - ¡Ouch! (hurt me / more pain) 05:49, 19 August 2014 (UTC)
It is a common application in manufacturing engineering. See Water jet cutter. It only works on very short distance but is a very cost efficient, precise, fast and reliable technology to cut flat materials like steel plates. But it wouldnt make much sense as a weapon. --Kharon (talk) 16:51, 19 August 2014 (UTC)
Note that shaped charges don't work either if the range is too high or too low. If the distance between charge and target surface is off, the effect can be severely diminished or even completely fall flat.
From Shaped charge: The location of the charge relative to its target is critical for optimum penetration for two reasons. If the charge is detonated too close there is not enough time for the jet to fully develop. But the jet disintegrates and disperses after a relatively short distance, usually well under 2 meters. At such standoffs, it breaks into particles which tend to tumble and drift off the axis of penetration ; OTOH, a water jet cutter wouldn't work well even at 1m, where the shaped charge only begins to exhibit severe degradation. - ¡Ouch! (hurt me / more pain) 08:33, 20 August 2014 (UTC)

Kidney function questions[edit]

The other day I started wondering about kidney function. Firstly, does the filtering ability of the kidneys dynamically respond to waste concentrations in the blood? If a person happens to have high levels of urea, or salt, or something else in their blood does the body have the ability to increase the activity of the kidneys, or are they pretty much going to filter the blood at a fixed rate regardless? Secondly, for a fixed level of hydration, if one has more waste in the blood (e.g. urea / excess salt) does that lead the kidneys to excrete more water as well or is the water output about the same but the waste in the urine more concentrated? Dragons flight (talk) 23:10, 18 August 2014 (UTC)

First of all, it's important to clarify that the kidney only removes excess organic molecules and/or wastes. The answer to your first question, as far as I can tell, is yes. Refer to Clearance (medicine). Not sure about the answer to your second question, sorry. ceranthor 00:25, 19 August 2014 (UTC)
The removal of waste and water are largely independent (although obviously some water is needed to carry the waste out). If you drink a very large quantity of water, but don't eat much or do much, your urine will be clear, since it's mostly water. If you are dehydrated, but have eaten a lot and done a lot of exercise, your urine will be brightly colored, since it's much more concentrated with waste. Obviously that wouldn't be a safe test, but you can take some vitamin C, instead. That will turn your urine brighter yellow, which indicates it has a higher concentration of waste (vitamin C, in this case).
I suspect that salt is a special case, though, where the concentration of salt in the urine can't be changed much relative to the concentration in the blood. This would explain why eating salty things makes you thirsty, because the salt must be diluted, as it can't easily be removed at high concentrations. StuRat (talk) 00:38, 19 August 2014 (UTC)
I would suggest conceptualizing the kidney as an organ of absorption rather than merely excretion. For the example of Vitamin C, one should realize that all the vitamin C in the serum passes into the renal tubules, and then only a certain amount is reabsorbed. So the kidney isn't responding to a high level of vitamin C and excreting more, it's just excreting all the vitamin C regardless of its blood level, and then reabsorbing the same amount it always does. Salt, as StuRat says, must be considered separately, as it's not a simple matter of passive diffusion; there are a variety of means of regulating salt (active transport, hormones, countercurrent multiplication, etc.). You may be interested in the concept of obligatory water loss, which is the amount of water that must be excreted in order to remove waste products and thereby maintain health. - Nunh-huh 01:01, 19 August 2014 (UTC)
I see we don't have an article on obligatory water loss, but you will find a brief mention in dehydration. - Nunh-huh 01:01, 19 August 2014 (UTC)

August 19[edit]

Lowest Possible Temperature[edit]

We know there is a lowest possible temperature, but is there a theoretical highest? KägeTorä - () (Chin Wag) 01:18, 19 August 2014 (UTC)

WHAAOE. Absolute hot. --Jayron32 01:20, 19 August 2014 (UTC)
There's also negative temperature. Dmcq (talk) 16:09, 19 August 2014 (UTC)
So, if a system at negative temperature is brought into the presence of a system at absolute hot, which way will heat flow? The article says " If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system." - but I have no idea if that applies to absolute hot... SemanticMantis (talk) 16:52, 19 August 2014 (UTC)

Atoms as fact[edit]

When did the scientific consensus become that atoms are real? I read atomic theory, but it doesn't mention any point in time or event. Bubba73 You talkin' to me? 04:20, 19 August 2014 (UTC)

See there about Dalton in the section 'First evidence-based theory' and his presentations of the atomic theory at the start of the nineteenth century. His first oral presentation in 1803 is one good date and his textbook in 1808 is another. Dmcq (talk) 08:03, 19 August 2014 (UTC)
The term "atom" or "indivisible particle" was revived 1805 from ancient Greek philosophical speculation by John Dalton. In 1828 "atom" was evidently part of Christian truth with which Noah Webster was concerned in his dictionary. Understanding of the atom has progressed from the cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) to the Rutherford–Bohr model or just Bohr model for short (1913) whose image is most recognized today. The Bohr model is widely taught as real and gives an explanation of some spectral emissions. It may be said to have reached popular consensus though scientific consensus favours the quantum mechanical atomic model introduced by Wolfgang Pauli in 1925. (talk) 10:41, 19 August 2014 (UTC)
First of all, scientists don't think in terms of "facts" and "proof". The think in terms of "evidence". Dalton's atomic theory was well a well accepted conjecture by the middle 19th century, but the definitive empirical justification ("proof" if you want) is usually cited as Einstein's paper on Brownian motion in 1905 (his Annus Mirabilis. See Annus Mirabilis papers). The other parts of atomic theory, those dealing with the internal structure of atoms, built up over time, with the experiments and conjectures cited above by, who did a great job laying out the history of Atomic theory. There were also some false starts in Atomic theory, see Prout's hypothesis for a more famous one. --Jayron32 14:09, 19 August 2014 (UTC)
That is kind of what I was getting at. The 19th century chemists had a model that worked beautifully, but I don't think any of them "detected" an atom. Bubba73 You talkin' to me? 02:56, 20 August 2014 (UTC)
I'm sure I have read somewhere that atoms were widely accepted among scientists as a model by 1905 but there were still some who didn't. Einstein's Brownian motion paper which provided another way to calculate the size of atoms was an extra bit of useful evidence that atoms existed and weren't just an apparent building block of solids that was actually made up of other things of different sizes. (oops should have read Jayron's answer first) JMiall 18:53, 19 August 2014 (UTC)
There is a subtle confusion here. Once the experimental results were in and the math had been crunched, it would have been valid to say "The world operates as if matter was made of atoms" - but you still wouldn't know that there actually ARE atoms. These days, we've actually imaged them so we have direct evidence - but that's a rather recent thing. SteveBaker (talk) 05:24, 20 August 2014 (UTC)

Can you accelerate the decay of radioactive material?[edit]

Or do you always have to bury it and wait 10,000 years? OsmanRF34 (talk) 15:10, 19 August 2014 (UTC)

For practical purposes, decay rates for spontaneous radioactive decay are constant. Radioactive decay#Changing decay rates says "The radioactive decay modes of electron capture and internal conversion are known to be slightly sensitive to chemical and environmental effects that change the electronic structure of the atom, which in turn affects the presence of 1s and 2s electrons that participate in the decay process. A small number of mostly light nuclides are affected ... A number of experiments have found that decay rates of other modes of artificial and naturally occurring radioisotopes are, to a high degree of precision, unaffected by external conditions such as temperature, pressure, the chemical environment, and electric, magnetic, or gravitational fields". Gandalf61 (talk) 15:22, 19 August 2014 (UTC)
The key words here are *spontaneous* radioactive decay. While temperature, pressure, electromagnetic fields, etc. don't substantially increase decay rate, neutron flux will. See Nuclear transmutation#Artificial transmutation of nuclear waste for details. -- (talk) 16:21, 19 August 2014 (UTC)
Well surprisingly you can just about do the opposite see Quantum Zeno effect. And of course sending particles at something will start splitting it up, a nuclear bomb is a good example. Dmcq (talk) 16:02, 19 August 2014 (UTC)
You can sort of do that partly, by refining the material aka split it up into active and decayed matter with physical and/or chemical methodes of process engineering. This is actually done to an limited extend for some Time with radioactive waste because in most countries space in radioactive waste repositories is very expensive. --Kharon (talk) 16:35, 19 August 2014 (UTC)
You should be able to change a radioactive isotope into something else by bombarding it with enough of the right type of radiation. However, it may turn into something even nastier. Also, you are likely to get many different products, so now you need to separate the stable from the radioactive. There's also the risk that you might get more heat than anticipated, due to unknown interactions between all the products and radiation, and have an explosion or meltdown. StuRat (talk) 16:56, 19 August 2014 (UTC)
If you want to accelerate the decay, that means you want something "even nastier". Things that decay slowly are not very radioactive. But as Stu says, the problem is that you are likely to get many different products. I don't believe it's practical at present to convert all of a chunk of some substance into another by irradiating it. -- (talk) 00:24, 20 August 2014 (UTC)
It is possible using fast breeder reactors, but the anti-nuclear movement has stopped the development of large scale nuclear power making fast breeder reactors uneconomical at present. The Integral fast reactor was never completed, the article says: "Fast reactors can "burn" long lasting nuclear transuranic waste (TRU) waste components (actinides: reactor-grade plutonium and minor actinides), turning liabilities into assets. Another major waste component, fission products (FP), would stabilize at a lower level of radioactivity than the original natural uranium ore it was attained from in two to four centuries, rather than tens of thousands of years." Count Iblis (talk) 17:34, 19 August 2014 (UTC)
Giant resonance does not need fast breeding reactors or other sources of neutrons. But probably prohibitive amounts of energy. (talk) 19:12, 19 August 2014 (UTC)
Another option is to separate out the radioactive isotopes from the non radioactive material. This my make a valuable resource, or at the least make a smaller waste output. Graeme Bartlett (talk) 23:10, 19 August 2014 (UTC)

Decline of large aerial predators[edit]

The amount of large aerial predators seem to be nonexistent, which is counter-intuitive to me. Considering there used to be creatures with wingspans the width of a basketball court, what led to their extinction? Considering there are still whales and elephants, it seems weird to me that bustards are the largest bird left around, with no large bird-of-preys. Was it tied to lowered oxygen levels? Climate change affecting updraft? Trees growing taller to hide prey? Just curious. --Wirbelwind(ヴィルヴェルヴィント) 19:26, 19 August 2014 (UTC)

No large birds of prey? Tell that to the harpy eagle or the golden eagle. Here's a nice video about the harpy eating monkeys [8], and here's one about the golden hunting wolves [9]. As for the biggest flyers ever, what do you know of with a ~50 ft wingspan? (the width of a basketball court). Pterosaur_size tops out at ~35 feet, according to our article. The largest bird we have evidence of is currently Pelagornis_sandersi, which, with a wingspan of ~20 feet is admittedly ~2x the wingspan of our current leader, the wandering albatross. But enough with questioning your premise:
You're right that were some larger flyers in the past, but there were also lizard type things the size of school buses, and they went away too, most likely due to the Chicxulub impact. So the pterosaurs et al. went extinct due to massive disruption of the food chain, as all photosynthesis on earth was severely compromised for a long time (more info at dinosaur extinction). After that, everything was much smaller, and there was a lot of value on the R side of R-K selection. Now, we might ask the question, "why have no very large flying predators evolved again?" I think the key here is that size is relative. We lost most of our megafauna in the Holocene extinction, and even though that was pretty recent, things have pretty much stayed smaller since then. I don't personally think O2 levels or updraft patterns are the culprit, but that's hard to find references to support. Even though the Square-cube_law has never changed, I think its importance might be strengthened in a world with much more pathogens, complex food webs, greater diversity of terrestrial vertebrates, etc. The main thing to think of is the ecological niche, and, for whatever reasons, the niche space is just not there anymore, even if it used to be. SemanticMantis (talk) 20:13, 19 August 2014 (UTC)
A giant asteroid slammed into the Gulf of Mexico some 65 million years ago, setting off a chain of catastrophic events that ultimately led to the extinction of all big living creatures. Then mammals got bigger. And eventually they paid the price. Several mammoths and other big mammals died off during the Pleistocene/Holocene extinction event, which started around 50,000 years ago. whales were more mobile and could emmigrate to whenever they wanted. Animals bigger than elephants didn't have so much luck. If there is little food, you are better off being small and having lots of descendants as fast as possible. OsmanRF34 (talk) 20:19, 19 August 2014 (UTC)
Per Semantic Mantis, there are several birds of prey which can be strikingly large; it's just that humans rarely get up close to them to see them. All animals (aside from whales) are generally smaller than they were in the Mesozoic era and flying critters are no exception. However, that doesn't mean that all birds are pigeon-sized. Female bald eagles have a length of 3.5 feet or so (standing on the ground they'd come up past your belly button) and have a wingspan of 7.5 feet or more. The golden eagle noted by Semantic Mantis above can get even larger. Those are land-based raptors. Seabirds can also get pretty large; various kinds of pelicans can get as large as a person; 5+ feet in length with an over 8 foot wingspan. Obviously, they weigh less than people, but they are still quite big in size (bird physiology maximizes their ability to fly, and so tends to favor lower mass-to-size ratios than land animals). The grand-daddy of carnivorous birds is the California condor, which is a bit shorter than the largest pelican, but can have up to a 10-foot wingspan. Again, since most people never see one of these birds up close, it can be hard to judge them from context. If you ever do get to see one up close, it takes you aback at how big they can be. --Jayron32 22:00, 19 August 2014 (UTC)
When it comes to pterosaurs, this is an open question. There is even a question about the question itself. Based on the fossil record, it appears that the pterosaurs reached peak diversity in the early Cretaceous period and then sharply declines before being finished off by the K-Pg extinction. However, it's possible that at least some of this apparent decline may be due to gaps in the fossil record ([10]). It should be noted that as far as we know, there were never any large, predatory pterosaurs (the thing with pterodactyls carrying prey off to their nest is a Hollywood invention;they didn't even have grasping feet, or bird-like nests). Why a highly diverse group like pterosaurs never produced any predatory forms is an interesting question and I'm not sure if it's been addressed. There may have been small hawk-sized predatory pterosaurs (this has been suggested for Darwinopterus), but even the biggest ones like azhdarchids seem to have been stork analogues, picking off small prey like lizards and baby dinosaurs. I guess that's still predatory, but maybe not the way most people think.
It's true that birds have not yet ever attained sizes comparable to pterosaurs and are on average very small (pterosaurs were on average very big as adults with no known tiny species, probably because they took years to grow up unlike birds, and niches for small sized animals were occupied by babies of larger species). It has been suggested that birds are limited in size by their takeoff style. They need two well-developed sets of limbs - forelimbs for flight, and hind limbs for launching themselves into the air. That's two well-developed sets of muscles in creatures that need to stay as light as possible. Pterosaurs were quadrupeds and most had piddly little hind limbs. By all accounts, they both launched AND flew with the forelimbs, allowing the biggest pterosaurs to get a few times bigger than comparable birds.
I don't think there have ever been any really large aerial predators. The largest I can think of is Haasts eagle, which isn't as large as the largest flying birds today, though larger than the extant predatory ones. All birds that ever lived larger than this have either been vulture-type birds (scavengers) or seabirds, which eat fish and can get larger than normal by taking advantage of oceanic winds to aid flight. Dinoguy2 (talk) 23:23, 19 August 2014 (UTC)
'Large, flighted, actively-hunting bird' is probably one of the most energy intensive animal 'designs' possible. Imagine how much food a 150lb+ bird that chased down and subdued live prey would need to eat in order to remain alive, let alone thrive, given that flying birds have a much faster metabolism than mammals (from what I've seen, birds tend to eat a huge amount for their size) - and how much territory it would need to fulfil its hunting needs. Such a critter would certainly find it difficult to survive and almost certainly be amongst the first to die out, should the world ever take a turn for the worse. The condors are huge and carnivorous, to be sure - but they are also mostly scavengers and gliders. --Kurt Shaped Box (talk) 23:36, 19 August 2014 (UTC)

This is not a scientific answer because there is lack of scientific evidence for it. But I believe that not only is the percentage of oxygen higher in the past but the air pressure is higher in the past as well. In fact I believe the air pressure is 10 times to 50 times higher in the past than the air pressure is today. Therefore with higher air pressure in the past, flying creatures can be bigger because it can generate bigger lifts. Of course, air pressures leaves no "fossil records" and thus I am not able to offer any proof that air pressure is higher in the past. (talk) 00:56, 20 August 2014 (UTC)

We do not currently have a Thick atmosphere theory article, and Atmosphere of Earth#Evolution of Earth's atmosphere does not address pressure. (Faint young Sun paradox does discuss the posibilities of CO2 partial pressures as high as 10 bar, but long, long before the cambrian radiation, presumably only up until the GOE.) Here are a couple of interesting papers by Octave Levenspiel published in 2000 in ACS's Chemical Innovation: Earth’s atmosphere before the age of dinosaurs (with Thomas J. Fitzgerald & Donald Pettit, on the ACS site) and Atmospheric Pressure at the Time of Dinosaurs (on Levenspiel own site). -- ToE 05:01, 20 August 2014 (UTC)
According to Quaternary extinction event and given the many near extinct species, caused by overhunting and -fishing done by humans up till today, its almost certain there where some but Homo sapiens sapiens killed them all.
Even worse. Your contradiction regarding whales and elephants is wrong. We (as species) would likely have killed all whales and elephants by now if some international Commissions had not put a world wide ban on commercial whaling and ivory trading. --Kharon (talk) 02:37, 20 August 2014 (UTC)

August 20[edit]

Wheel base anf friction[edit]

Can we say that wheel base is proportional to friction acting on a vehicle,when brakes are applied.I think i solved a problem in h c verma(12 class physics) using this assumption.please correct me if i am wrong.

Sameerdubey.sbp (talk) — Preceding undated comment added 03:38, 20 August 2014 (UTC)

Wheelbase is normally understood to mean the distance between the front and rear axles of a vehicle. Your statement accordingly makes no sense at all. AndyTheGrump (talk) 03:41, 20 August 2014 (UTC)

I appreciate your effort in commenting Grump.See google bookpg 371,there's a derivation that has wheel base in numerator and denominator as well.Then what do you say?whether frictional force would increase or decrease with wheel base. please read derivation and then comment.Bit engineeering involved. SD — Preceding unsigned comment added by Sameerdubey.sbp (talkcontribs) 07:12, 20 August 2014 (UTC)

Link is broken. yes there is a bit of physics involved, that's a high school physics problem judging by the search terms, but your question is at best very misleading, but answering the most likely rendition , you are wrong. Greglocock (talk) 07:55, 20 August 2014 (UTC)

Mr cock ,justify whatever you want to say.let it be high school physics. SD — Preceding unsigned comment added by Sameerdubey.sbp (talkcontribs) 09:58, 20 August 2014 (UTC)

Velocity of Saturn's moons[edit]

Any of the many, doesn't matter - I'm writing a fantasy where there's a vehicle tethered to one of Saturn's satellites, towing it around one of the rings. My preference is for one of the Inuit, Gallic, or Norse moons, because their names are so cool, but I gather they're further out than the orbit of the rings.

Thanks for your indulgence

Adambrowne666 (talk) 04:42, 20 August 2014 (UTC)

Velocity relative to what? Saturn? If one end is tethered to the satellite, what's the other end tethered to? (It can't be Saturn, because it doesn't have a solid surface.) --Bowlhover (talk) 05:06, 20 August 2014 (UTC)
Note that if you have a tether running from the spacecraft to the moon, remember that you only need the tow to get the vehicle up to the speed of the moon - then you can cut the tether and the spacecraft will continue to follow the moon around. Of course the moon will have some tiny amount of gravity - so after that initial acceleration, you'd pretty much have a slack tether. So calling this a "tow" is a little confusing. SteveBaker (talk) 05:20, 20 August 2014 (UTC)

Can a shooting cause gradual brain death?[edit]

Hello. In a script I'm writing, a character is mortally wounded by gunfire. After a protracted period, the character suffers brain death. Is this plausible? I've read some articles on the subject and I'm not entirely sure how a bullet wound would lead to slow brain death. (talk) 05:36, 20 August 2014 (UTC)

Your question is misleading. If a human is suffering from a gunshot wound. The human will suffer from a slow brain death while they are also suffering from a slow liver death and a slow death for every part of their body. The blood system in a human body is for all parts of the human organ. So technically yes, the character will suffer a slow brain death. (talk) 05:59, 20 August 2014 (UTC)

Thank you for the response. I've been doing mental gymnastics trying to figure out how a person's brain would die slowly from indirect bullet wounds a la drowning, while idiotically overlooking the fact that the whole body would slowly succumb from such an injury. (talk) 06:28, 20 August 2014 (UTC)

In general terms, this would be the basis for the notion of charging Hinkley with murder 34 years after the fact. ←Baseball Bugs What's up, Doc? carrots→ 08:59, 20 August 2014 (UTC)
Presumably you mean not Olaf "Braindead" Hinkley the lead guitarist of Norwegian CyberPunk-Polka fusion band "Real Asset" that disbanded in 1979 but this Hinkley. If you propose a test case to try the contention that every "attempted" murder must in the natural order of things eventually succeed, the defence will likely point to the extenuating circumstance that so-called murder victims are all biochemically pre-programmed to die anyway. Observation of Brain death can lead to a false positive test on a patient that may recover with more time. Zack Dunlap in 2008 had a false positive of this type, likely due to temporary Cerebral edema. Such events feed the fear of being buried alive that has troubled humankind for centuries. Plato wrote in "The Republic" in 380 B.C., about an Armenian soldier who was revived two days after being pronounced dead. Fear turned to frenzy in the 19th century, when wrongful burial inventions were marketed with some success. The Safety coffin was a casket with a bell attached by a piece of string which might be pulled to alert people that the buried person was in fact alive (but it is not true that this is the origin of the phrase "saved by the bell"). However if the internee really is dead, his rest in peace or maybe pieces could be assured by a US patent in 1881 on deterring grave robbers by exploding shells that fit onto a coffin. (talk) 12:00, 20 August 2014 (UTC)
And I remember when the exploding whale video was the coolest thing. One slip-up with the arming mechanism and that would be a funeral to remember! Wnt (talk) 12:04, 20 August 2014 (UTC)
  • Although of course it's true, as others have pointed out, that a wound to any part of the body can eventually lead to general system failure which causes brain death, it's also quite possible for an injury directly to the brain to cause brain death after a protracted period -- days, weeks, months, or even years. The main causes of delayed brain death are (1) the initial injury causes swelling of the brain, which gradually crushes other parts, or (2) the initial injury causes an infection inside the brain. It can also happen that the initial injury causes a blood clot that eventually breaks loose, causing a stroke. Or you can get a subdural hematoma. Looie496 (talk) 13:59, 20 August 2014 (UTC)
According to our article Mortal wound, "A mortal wound is a very severe and serious injury ...... which leads directly to the death of the victim. Death need not be instantaneous, but follows soon after." Based on this, a wound that results in a slow lingering death would not usually be called a "mortal wound". CBHA (talk) 14:13, 20 August 2014 (UTC)

Question my nephew asked me to pass on[edit]

Eight ingots of pure sodium walk into a bar. The juke-box immediately starts playing this music. Why? --Shirt58 (talk) 12:27, 20 August 2014 (UTC)

The Batman Theme's lyrics are "nananananananana BATMAN". Na is the atomic symbol for sodium. --Jayron32 12:41, 20 August 2014 (UTC)
And as they begin to leave the establishment, someone could play Na Na Hey Hey Goodbye. ←Baseball Bugs What's up, Doc? carrots→ 13:07, 20 August 2014 (UTC)
Naa na na nana na naa, nana na naa, Hey Jude ... Gandalf61 (talk) 13:22, 20 August 2014 (UTC)
Presumably these songs fall within the genre of Light Metal. {The poster formerly known as} (talk) 13:24, 20 August 2014 (UTC)
Wrong answer! That light pop act from the 1980's "BaNaNaRaMA" are by definition an admixture of light and heavy metals. Or something like along those lines.--Shirt58 (talk) 13:56, 20 August 2014 (UTC)
Vic Bondi's band opened for them. DMacks (talk) 14:23, 20 August 2014 (UTC)

Plastics oxidation[edit]

Did the plastics had been oxidation by water?--Alex Sazonov (talk) 14:01, 20 August 2014 (UTC)