Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

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.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

May 4

Trimmer vs shaver

What is the difference between electric trimmer and electric shaver? --Yoglti (talk) 01:43, 4 May 2013 (UTC)

• About $15. μηδείς (talk) 01:52, 4 May 2013 (UTC)

The shavers are intened to get down to bare skin. The trimmer is intended to leave a short length of hair protruding above the skin ("stubble"). The trimmer likely has an adjustable setting to vary the amount of hair left, whereas the shavers have one setting ("as close to the skin as comfortably possible"). -- 71.35.109.118 (talk) 02:50, 4 May 2013 (UTC)

Just my original research; trimmers operate by a pair of toothed blades that slide past each other as one oscillates back and forth, like a small hedge clipper, while shavers are either a rotary blade that runs underneath a circular grill so that it nips the hairs off that stick through the grill, or a thin rectangular blade with lots of sharp slots which oscillates beneath a grill in similar fashion. the shaver appratus being thinner and thus more precise than the trimmer setup. Gzuckier (talk) 05:10, 5 May 2013 (UTC)

How energetic x-rays (kV) is required to reach above background?

How energetic x-ray photons (kV) is required for them to be stronger than background radiation ..? Electron9 (talk) 02:40, 4 May 2013 (UTC)

Your question does not make sense in the English language. I assume you meant to ask How energetic do X-ray photons (described in terms of the equivalent electron acceleration voltage) need to be to be stronger than the background radiation on Earth's surface? This is not a valid question. Do you mean the natural background radiation, or the averaged exposure due to nuclear fallout from accidents and explosions, medical X-rays taken during your life, use of nuclear isotopes in medical diagnosis and treatment etc? I will assume that you meant the natural background.

The higher the X-ray energy, the more penetrating it is. And if X-ray photons have fully penetrated a substance, then no energy was transfered to the substance and it cannot have been affected. This is why X-ray images taken to show bone structure are a lot less harmfull than X-rays taken to show soft tissue structure, where similar exposure times are used. It means that the natural X-ray exposure we experience includes X-rays from very high energy sources remote in the universe. In terms of exposure effects, very low energy man-made Xray sources very much over ride natural exposure.

Also note that in terms of effects on life, X-rays are just another sort of ionising radiation. The exposure to just natural X-rays is not important, but the total exposure to all sorts of ionising radiation can be.

Ratbone 124.178.43.47 (talk) 09:47, 4 May 2013 (UTC)

Maybe, he's talking about the cosmic microwave background? Plasmic Physics (talk) 10:43, 4 May 2013 (UTC)

I meant if you have a x-ray tube. How high acceleration voltage is needed to measure a higher dose than from ground rock (1 mSv/year?). I heard that CRT-TV-sets with acceleration voltage below circa 10 kV didn't make it out of the TV-set. So that only sets with higher voltage had any measurable radiation. Electron9 (talk) 13:30, 4 May 2013 (UTC)

Only the smallest CRT TV sets had an acceleration voltage as low as 10 kV. 17 to 20 kV is more typical for black and white sets, early colour sets were up to 25 kV. However, at typical voltages the X-rays are so soft normal materials used in sets (glass, wood, etc) stopped them.

You are still asking the wrong question - you are confusing photon energy with beam power. You can get a high effective dose from the lowest acceleration voltage that will produce X-rays of sufficient energy to penetrate the tube window - about 18 to 20 kV or so. You need to understand that Xray tubes are designed to produce Xrays - so the tube windows are constructed appropriately. TV sets are designed NOT to emit Xrays. For instance, the glass at the front of the picture tube is a three-layer sandwitch up to 18 mm thick and often lead loaded. Internally, older colour sets with internal parts such as the regulator triodes were designed so that Xrays from the triode had to pass through (typically) 2 layers of 12 mm plywood and a steel sheet barrier.

What affects dossage is the electron beam current and the exposure time. It is similar to exposing black and white photographic film with light. You can use a low power white light (say a 0.5 W krypton torch glode running at 4000 K filament temperature) or a high power light red light (say a 60 W globe run on low voltage so that the filament is running at only 1600 K and light output is reddish-orange). The first is analogous to making Xrays with a high voltage but a low beam current; the second is analogous to making Xrays with a low voltage but a high beam current. In both cases the higher power will have the greatest effect.

Not to be neglected is the fact that Xrays are emitted from Xray tubes in a fan-shaped beam, somwhat like light fans out from a light globe. This means that the further you are away from the Xray tube, the lower the dose, as you intercept a smaller fraction of the fan-shaped beam.

As I recall, you previously asked a question about making a homemade Xray apparatus. DON'T DO IT. You have so little undersanding of Xrays, you would be certain to cause harm to yourself and your friends.

As I said before, it is the low energy (ie from low acceleration voltage) that cause tissue damage. Very high energy Xrays pass through without lossing energy. If energy is not lost to the material passed through, there cannot be any effect on the material.

Ratbone 120.145.203.168 (talk) 15:21, 4 May 2013 (UTC)

There is information missing from your question. No matter how high the Voltage is, if no electron's are beamed down, no X-rays are produced. To answer your question you need to tell us the total number of electrons used by the machine per year. In other words, you have to tell us the current used by the machine. Other things to consider: How far from the X-ray source are you? Is there any radiation shielding? Dauto (talk) 15:28, 4 May 2013 (UTC)

Let's assume an x-ray tube and measurement 1 cm from the designed tube exit. If one study just one electron, how energetic (keV) does it have to be when striking the anode for the byproducts to just to make it out of the glass? before any shielding. If one electron makes it out, further electrons can make it. But if none makes it out, it won't matter how many there are. Ignoring the probabilistic nature of particles. Electron9 (talk) 16:09, 4 May 2013 (UTC)

Quite apart from the fact that what comes out depends on the thickness and type of glass, both of which will depend on the size and type of tube, which you haven't specified, it doesn't work that way, you can't calculate on the basis of a single electron, which may only result in one or 2 photons. Photons get absorbed on a statistical basis - some get thru, some don't. The fraction getting thru rises as the energy increases. Wickwack 120.145.8.232 (talk) 02:32, 5 May 2013 (UTC)

Spin

If the moon did not exist our earth would spin faster. How short would our days be on the equator? Pass a Method talk 06:26, 4 May 2013 (UTC)

Not necessarily. The most popular theory Giant impact hypothesis is that the moon was formed in an impact that span the earth up to have something like a five hour day. Otherwise it would probably have something in between the very long days of Mercury and Venus and the roughly equal day of Mars is my guess, maybe somebody has worked out a typical value to be expected. Dmcq (talk) 10:46, 4 May 2013 (UTC)

What makes you think the Earth would spin faster? Dauto (talk) 12:14, 4 May 2013 (UTC)

Using debatable assumptions: momentum must be conserved, ergo, lunar recesion decreases Earth's angular velocity. Plasmic Physics (talk) 12:31, 4 May 2013 (UTC)

Also tidal locking between the Earth and the Moon is transferring rotational energy from the Earth into orbital energy in the Moon, and friction in the tides converts some Earth rotational energy into heating the Earth. Both of these cause the length of Earthdays to gradually increase. BTW, the day/night cycle are the same length no matter where you are, (as long as you are not within the polar circles. Did you mean the length of daylight? CS Miller (talk) 14:11, 4 May 2013 (UTC)

I'm not the OP, I'm just infering their logic. I'm certain, they are refering to the period of the angular motion of the Earth, not the length of daylight. Plasmic Physics (talk) 04:43, 5 May 2013 (UTC)

Hassium

Emsley's Nature's Building Blocks (both editions) say that IUPAC did not feel Hesse merited having an element named after it as a reason for their changing the name to hahnium in 1994. Does anyone know why they felt this way? It's quite odd in light of all those elements named after places! The only reason I've found that they mentioned themselves is that they wanted elements named after Hahn and Meitner to stand side by side on the periodic table to honour their joint discovery of nuclear fission. (Yes, this is for an article.) Double sharp (talk) 08:51, 4 May 2013 (UTC)

I guess no one seems to know the answer, which was not entirely unexpected as I've been searching for it for months. :-) Double sharp (talk) 12:44, 8 May 2013 (UTC)

How to get shine/glow in face like celebrities?

They have glow in face [1][2][3] How can I get this glow? Note it is not medical advice, just a health and beauty question. --Yoglti (talk) 09:03, 4 May 2013 (UTC)

That's just the choice of lighting on the part of the photographer, nothing more. Someguy1221 (talk) 09:08, 4 May 2013 (UTC)

These examples are paparazzi happy-snaps! What lighting choice have they got but their mono flash and ambient illumination?--Aspro (talk) 19:20, 4 May 2013 (UTC)

It's makeup too. Yes, even for Tom. Looie496 (talk) 14:50, 4 May 2013 (UTC)

See section: 'Add some glow:[4]--Aspro (talk) 19:15, 4 May 2013 (UTC)

And there's Photoshop and Airbrushing. HiLo48 (talk) 23:43, 4 May 2013 (UTC)

Oh yes Photoshop. That will only cost you about £400. Whereas GIMP is about £ 000,000,000 per free download Aspro (talk) 00:42, 5 May 2013 (UTC)

Yes, I'm well aware of that, but where I come from the word Photoshop has become a generic verb meaning to use any computer software to enhance/modify a digital image. Maybe I shouldn't have Wikilinked it. HiLo48 (talk) 00:47, 5 May 2013 (UTC)

A lower-case p would be indicated in that case (cf. thermos, hoover, xerox, google ...). -- Jack of Oz ^[Talk] 01:37, 5 May 2013 (UTC)

I haven't stopped putting a capital G on Google, even when using it as a verb. Has the lower case G become the recognised norm? Am I old and behind the times again? HiLo48 (talk) 01:42, 5 May 2013 (UTC)

Don't worry. I spend most of my life pretending to know what people are talking about. I even get it right sometimes. You have your good days and your bad days ...

But about Google: It has become far and away the most popular search engine; a lot of people would not even know there are others out there, or how to find their names. This means that those who do choose some other engine are consciously dissociating themselves from Google, and would not be using that word. So, maybe the verb has two existences and two meanings:

(a) google = to use any search engine in general (including Google); and

(b) Google = to use Google specifically (this would be used by people who use other search engines often enough that using Google, when and if they ever do, is a conscious choice).

Caveat: Most of the preceding is made up. -- Jack of Oz ^[Talk] 02:18, 5 May 2013 (UTC)

A high school student (obviously an excellent, reliable source) told me the other day that the most popular search term on Bing is "Google". (Actually, it's probably "google", but he didn't write it down, so I'll never know.) (Have we got far enough away from this topic yet? Sorry everyone.) HiLo48 (talk) 02:30, 5 May 2013 (UTC)

"Bing"? μηδείς (talk) 02:37, 5 May 2013 (UTC)

Yep, Bing. -- Jack of Oz ^[Talk] 02:53, 5 May 2013 (UTC)

Bing is used when you croon the internet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:28, 5 May 2013 (UTC)

Bing Crosby did certainly star and croon in a film were Danny Kay sang “There once was an ugly duckling” but I don't think Danny was referring to Bing growing up be to " A Very-Fine-Swan Indeed!" If you get my point. Dammit what was that film?Aspro (talk) 16:08, 7 May 2013 (UTC)

That would be Hans Christian Andersen (film). -- Jack of Oz ^[Talk] 21:04, 8 May 2013 (UTC)

efficiency

what is more efficient, a dolphin or shark moving its tale, OR, a machine as strong as the dolphin's or shark's muscles with a rotor? — Preceding unsigned comment added by 123lmon (talk • contribs) 13:16, 4 May 2013 (UTC)

Dolphins and sharks are much more efficient, they move their bodies in response to the actual flow of water so that it gets altered in the most optimal way. Count Iblis (talk) 13:34, 4 May 2013 (UTC)

Cooling of smartphones

Smartphones have nowadays as much as processing power as laptop did a while ago. However, when laptops had that much processing power, they had a cooling fan. Why don't smartphones don't need a cooling fan? Why do laptops need them? 123lmon (talk) 13:21, 4 May 2013 (UTC)

When a computer chip processes, that means electrons are whizzing around through it. That heats it up; if it heats up too much, it can actually melt the processor core. Newer chips can run much cooler than the ones of a few decades back — much cooler. The most common smartphone processor is known as ARM, and it was specifically engineered to have very low heat output and relatively low power requirements. So something on par with a smart phone, or even an iPad, doesn't really require a specialized cooling source, because they've been engineered to dissipate what little waste heat they have pretty effectively. (They don't alway succeed — the iPad will basically shut down if its internal temperature exceeds 95ºF.) Older processors, or modern processors of the speed that would be found in a laptop or desktop computer, still usually require fans to keep from overheating. --Mr.98 (talk) 13:43, 4 May 2013 (UTC)

Also the operating voltage of CPUs is gradually dropping - it used to be 5 Volts, and is now 0.8V (I think). The capacitance of each transistor is gradually decreasing, these both reduce the amount of power needed for each gate to change state, and thus for each operation the CPU performs. CS Miller (talk) 14:05, 4 May 2013 (UTC)

The low-power technology that permits all of that computation with such long battery life is the same thing that minimizes heat production. In the end, the energy from the battery turns (almost 100%) into heat inside the case...so things with long battery life and small batteries run cooler than things with short battery lives and large batteries. SteveBaker (talk) 14:06, 4 May 2013 (UTC)

I think smaller die geometries also plays into this. Electron9 (talk) 14:16, 4 May 2013 (UTC)

Also, the procesors used in cellphones where designed quite recently from scratch with an optimised instruction set. Intel compatible processors used in PC's and laptops have always been designed with backward compatibility stretching back to the original 8086 CPU designed in the early 1980's. Maintaining compatibility means they are a lot more complex internally. Also, the actual processor core is only part of what consumes power. A PC processor has to interface with external devices, external memory, and other bus devices. Cellphone procssors are one-chip devices that aviod the need for much power dissipating interface circuitry. Ratbone 120.145.203.168 (talk) 15:32, 4 May 2013 (UTC)

ARM goes back to 1983. I'd hardly call that "recently from scratch" ;-). It is a RISC architecture, although modern processors put a lot of additional functionality into silicon. --Stephan Schulz (talk) 22:26, 4 May 2013 (UTC)

To sum it up:

• Efficient heat paths (little has really changed over the years however)
• Less voltage
• Less capacitance (due to less wire surface?)
• Efficient use of existing gates (MIPS, ARM, etc)
• Integrated peripherals

Electron9 (talk) 16:14, 4 May 2013 (UTC)

About the point of ARM and other RISC like architectures, note that Intel is desperately trying to compete in the tablet and smart phone market. (To a lesser extent, so is AMD in the tablet market.) The Atom (system on chip) isn't really used in any significant smart phones and even in tablets has only really found success in Windows 8 ones but most reviews have found that it isn't terrible, for example performance and battery life seem somewhat comparable to similar speced ARM devices. Edit: Although I believe one additional problem is the newer A15 and similar architectures e.g. Krait as well as their lower powered contemporaries e.g. A7 are now starting to become common and the current gen Atom SOCs are less able to compete. Although this is likely helped a great deal by Intel's process advantage, in addition even before the smart phone let alone tablet market really took off they were already heading quite heavily to power efficiency (including various ways of reducing power when idle). As for why they haven't had much success getting major manufacturers to use them in significant product lines, I suspect cost is a factor, even with Intel's efforts including discounting. Another reason is because there's little advantage even if it's not necessarily worse. In fact ARM has the advantange in the Android smart phone and tablet world. Although Dalvik is a VM, a fair few apps on the Android market place use the NDK and while there has been an x86 NDK for a while, you still have to convince developers to actually compile for it. Edit: Actually I removed the process advantage claim. Although Intel does generally have a process advantage and this may play a factor in the SOC, it's far from clear cut at the moment because their current SOCs are still using older processes. See also [5] which suggests an additional problem is Intel's baseband is still behind major competitors, obviously significant for smart phones and any tablets with mobile network support. Nil Einne (talk) 18:57, 4 May 2013 (UTC)

It looks like Intel is now trying to exploit its process advantage for the Atom processor rather than just thinking of it as the runt of the litter. They'll not be able to achieve a knock out and a monopoly so I don't see the strategy behind that as anything it does there will eat into the price differential it charges. I think they would have been better off just offering their process to others for the low end or even making ARM's themselves making sure it kept the differential and beggared the other manufacturers. Anyway I'm sure Intel's strategists are far more expert than me so the next few years should be quite interesting. Dmcq (talk) 07:46, 5 May 2013 (UTC)

Science of mating in humans

In humans, mating and relationships have evolved into being sophisticated but could it be argued that the process of "picking up" women in nightclubs actually takes this back to being more animalistic. — Preceding unsigned comment added by Clover345 (talk • contribs) 13:44, 4 May 2013 (UTC)

Well, it could certainly be argued - but I'm not sure that the argument would be a valid one. What exactly is your question here? If you're asking: "Is the process of picking up women in nightclubs 'animalistic' behavior?" then we first have to ask what is meant by "animalistic". We are, after all, animals. Animals have a huge range of mating behaviors - from female spiders that eat their mates immediately after copulation to love-birds that mate for life and die soon after their mate is killed. I'm sure you could find at least one other species that exhibits comparable behavior to the one you're referring.

However, I think you're somewhat missing the point here. You're probably seeing this behavior from only one side - the male. Sure, men go out to nightclubs with the specific goal of finding a woman to mate with...but women go to nightclubs in the knowledge that this is a common thing to happen. This in itself is a sophisticated, nuanced, layered behavioral pattern...it's not so different from composing sonnets and singing outside of a woman's bedroom window...or whatever else you'd consider "sophisticated". SteveBaker (talk) 14:03, 4 May 2013 (UTC)

A Martian would be better at answering this one. As homo-sapiens ourselves, we can't step back and objectively separate ourself from what we 'think we are' from our basic animal instincts. Humans (with the exception of a few of my neighbors) have also developed a complex form of 'culture' in conflict to our basic instinct. Picking up women in nightclubs is no different in modus operandi from searching for mates in 16th century church congregations. Anthropologists consider (or so they tell me) that both early and modern primitive groups consist of about 140 to 160 individuals. Once their juvenile children's hormones start running wild, they need to mix with other individuals of their same age but from different geographical locations (to avoid the instinctive aversion to incest and all that). In the modern world, one of these opportunities presents itself in nightclubs. 200 hundred years ago the equivalents could have been down at the bubbling brook were teenagers get together to go skinny-dipping and splash water at each other (– at least, that is what they probably told their parents when they got home that night – who in-turn had probably frequented the same spot on the bubbling brook when they were young). So the world goes round and round. Singing sonnets outside of a woman's bedroom window may have worked for Shakespeare in his time but in this modern age, it would likely end up with one being committed to a mental hospital for observation.Aspro (talk) 20:26, 4 May 2013 (UTC)

Or arrested for stalking. HiLo48 (talk) 22:53, 4 May 2013 (UTC)

Or as Jerry Seinfeld put it, "Yelling out the car window and honking the horn are about the best ideas we've come up with so far." ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:46, 4 May 2013 (UTC)

Are you saying Jerry_Seinfeld#Personal_life is a good role model?Aspro (talk) 21:29, 4 May 2013 (UTC)

You could do a lot worse. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:34, 4 May 2013 (UTC)

May 5

can one derive a language's grammar from sample code

Hello, this is out of idle curiosity, but can one derive a language's grammar from sample code? In other words, is it possible to write a program that, if fed code in some language wrote the EBNF that parsed the code , like this:
program xxx; var x: integer; begin x:=17; write(x); end. ===>
program::="program" ident; var-section main-block "."
var-section::="var" ident ":" type ";" etc, etc. (the names of the rules themselves need not be meaningful, obviously)
I suspect the program needs to have a way of knowing what the tokens are so it can tell between keywords and user-supplied identifiers. If the code sample was really big (it need not be a real program, either), such that it had every non-terminal in it and/or there were several snippets for when you can't put everything into one (one with no, one with a single and one with several variable declarations, for example), could one derive a complete grammar (or one of if there can be many) of the language? Thank you everyone in advance Asmrulz (talk) 01:42, 5 May 2013 (UTC)

Grammar induction is the article, though unsurprisingly the research focuses on natural languages. I don't know anything about this but I doubt you could find exactly the correct grammar of a programming language this way. Many programming languages don't have context-free (EBNF) grammars. For example the expression (A)(b) in C-like languages could be a type cast or a function call depending on how A was previously declared. -- BenRG 04:40, 5 May 2013 (UTC)

Hmmm...yes and no.

Strictly - no, it's not possible because you'd never know whether there might be some kind of construct that's not present in the example programs that you fed it. For example, you could pick an enormous corpus of C and C++ programs and never find a single one that uses the "goto" statement. I have written millions of lines of C/C++ code - and and read tens of millions more written by co-workers - and never once encountered a "goto". Even if you did find a few rare examples, it wouldn't be clear what the rules about jumping into and out of loops and subroutines are because you simply wouldn't have enough examples to deduce those things. I bet that it would be impossible to deduce the arcane rules for "goto" even if you took every C and C++ program ever written and analysed the whole lot.

But imperfectly - yes: Children can learn to understand and speak any language on the planet simply by listening to examples - and (in principle) anything that the human brain can do, you can do with a sufficiently powerful computer. However, children (and the adults they grow into) learn the language imperfectly...nearly everyone has some kind of failure of linguistics built into their brain.

SteveBaker (talk) 15:37, 5 May 2013 (UTC)

If the system only has source code, no it cannot extract the grammar. Children are able to learn laguage because they are exposed to two things: the language and its results. For instance Mother may say the word "custard" a few times while serving custard, so the child can associate the word custard with the actual stuff. Children also learn to speak because when they try it, their parents correct them. (Child: "wan custard"; Parent: "No, I want custard, please")

A computer program that deduces the grammar could in theory be constructed if it has access to both the source code, can run the source code, and can alter the source code. It motly cannot work out the complete grammar, for the reasons others have posted. Neither do humans ever completely master the vocabulary and grammar of spoken and written languages.

In practice, constructing a program that can deduce grammar of a computer language is probably not possible, because of the difficulty in understanding the meaning and scope of the output. I once wrote a program for an embedded processor in a hand held device. Each time you press the single "go" switch on it, after entering the 6-digit challenge number issued by the secure server you are trying to log into, it displays a 6-digit keycode that, with your own personal password, will enable you to log in. The keycode is generated by mashing the challenge (which was generated from a random number) and to the user appears to be another random number. No two challeges will ever be the same within a certain very low probability, and no two keycodes will ever be the same. Keying in the same challenge twice will give you two different keycodes. What is the proposed grammar extraction program to make of that?

Wickwack 120.145.68.194 (talk) 23:47, 5 May 2013 (UTC)

If you're correct about children needing parental feedback when they attempt to produce language from what they've learned about the grammar - then all that's needed to provide this for a grammar-learning program is access to a compiler for that language and a means to detect whether the resulting program compiled correctly. That's pretty much all a child gets.

But in this case, the computer has several advantages. Firstly, it's only being asked to learn the rules of the grammar - not to interpret what programs written in that grammar actually do. Your example of a tricky program is irrelevent...it's only tricky use of the grammar (like x=y++++z; or something) that's going to throw it. For example, it just needs to deduce that if a statement begins with the keyword "while", it is always followed by an expression surrounded by round brackets - followed by a statement. The program would have no idea that "while" is a looping construct or that the expression will not be executed once the expression evaluates to 'false'.

That's quite different from a parent pointing at a bowl of custard and saying "custard" to a child...the child is learning vocabulary in that case. I don't think parents ever explicitly teach things like "words that are verbs that end in "ed" are in the past tense".

Secondly: I also don't believe that children learn syntax by producing statements and being corrected. Our grandchild was quite able to understand "Fetch grandpa the duplo" long before she could speak a single word...and I'm fairly sure that children who do not have the ability to speak are perfectly able to learn enough grammar to understand what people say to them.

Thirdly, the program is only (presumably) being fed legal programs - where children hear all kinds of broken sentences, incorrect grammar and so forth.

SteveBaker (talk) 19:51, 6 May 2013 (UTC)

I agree, if the grammar extraction program has access to the compiler code, it can work out the grammar. It is an alternative to accessing the output. In fact, if you (or a machine) has the compiler source code, then you (or a machine) HAS the grammar to hand - all that may need to be done is to write it more concisely. I don't think that was what the OP had in mind though. He has talking about feeding the grammar extractor only examples of source code. Re your next point, undertsanding the vocabulary is essential to determining grammar - as BenRG pointed out. You have a point regarding the ability of children to understand spoken language with limited ability to speak themselves (and thus opportunities to hear corrections from others) - this has been an interesting field of study by certain linguists and psychologists. It appears that it is because children are born with a built in understanding of a "prototype" grammar, though it isn't English grammar. This is likely an advantage that a computer program cannot have, as there is an infinite range of possible computer proagram grammars. Finally, a grammar extraction machine that can deduce things like "statements can begin with while", as they do in some lenguages, or that "programs begin with program and end with end" as they do in Pascal, is not going to be generally useful. Many computer languages simply don't work that way - almost all assembly languages included. Ever tried to work out what someone else's assembly language does, having obtained a listing from ROM, which does not include any comments or pretty printing? That's a task fundamentally easier than deducing a grammar, never the less it isn't easy, dependent in practice on good guesses, exploring dead ends, and often very very difficult. Wickwack 60.230.238.42 (talk) 00:21, 7 May 2013 (UTC)

You're completely missing the point (again!) - the idea isn't to understand what a program DOES - the goal is to understand the grammar of the language that the program is written in. Sure, machine code programs can be hard to understand - but the grammar of the assembler is trivial: <label>:<opcode><argument>,<argument><comment> ...with a few of those parts being optional. I didn't say that the grammar extractor would have access to the source code of the compiler - just a means to generate a program and test whether it's legal or not...a boolean "good/bad" flag. But I don't think this is necessary. This is a difficult problem - but with enough variety of source code to examine, I think it's possible. However "enough variety of source code" might be a very tough barrier to making this work...as I explained with the difficulty of deducing the peculiar rules for the "goto" statement in C and C++ - given that almost nobody uses that horrible construct anymore. Just as children have "protogrammar" hard-wired, we could give our program knowledge such as "Most programming languages allow variables that start with a letter and are followed by any number of letters, digits and underscores" or "Most programming languages allow numbers that start with a +, - or a digit..." or "Some languages allow whitespace anywhere, others don't - figure out which of those is true before you start". There are all sorts of things that are common to so many languages - that you'd be able to figure them out. Of course there are deliberately obtuse languages (like Whitespace (programming language) that would defeat these rules...so this has limited value. SteveBaker (talk) 14:07, 7 May 2013 (UTC)

Sounds like you haven't worked with assembly code, Steve. The construct <label>:<opcode><argument>,<argument><comment> only exists at the time of writing. What gets stored in ROM (or whatever other form of memory is used) does not contain the labels or the comments. In any but the most trivial assembly routine, figuring out what are constants and what are opcodes can be a major effort in itself - they look the same, have the same range of values. Opcodes and constants both vary in byte length. And some smart-arse programmers not only use recursive techniques, some use self-modifying code. I can remember finally nutting out one bit of code where the author called the routine with two different entry points - one entry point restored and ran the routine pretty much as is, another entry point used a trick to use an opcode byte as a constant to change another opcode and completely change what the routine did!

I realise that the OP's question does not require the grammar extractor to understand what the program does, however it does need more than just source code of the target language. Yes, you didn't say that it needed access to the source code of the compiler - I misread that bit. However it did make me realise that being able to run and alter the source code is not the only way. However, your idea of just being able to run it thru the compiler to see if there are no compiler errors, or being able to run the program and see that there are no run time errors is not sufficient. If it was, there would have been no need for all the thousands of hours I've spent debugging code that did compile ok, and debugging code that ran ok too, until I or a colleague hit it with the right test case. And in some cases, after a couple of years use, the customer reported a bug! Even very strongly typed languages like Pascal can compile ok when the grammar has been violated. For example, passing a constant and then mistakenly treating it as a var (or a pointer) will compile ok, but the runtime result will usually be very different, and only sometimes trigger a runtime error. And as for that horrible nasty thing used for embedded control, the FORTH language, which is not typed at all and with which you can do anything one's smart arse lateral thinking heart desires..... That's why I misread what you said - I automatically assumed you didn't intend a simple go/no go run test because it is insufficient.

Wickwack 121.215.9.73 (talk) 14:59, 7 May 2013 (UTC)

Sodium hydroxide for washing dishes?

If I add sodium hydroxide to the water when washing up, I can convert triglycerides to the dark side and have the cleanest dishes ever? — Preceding unsigned comment added by 78.144.202.9 (talk) 02:07, 5 May 2013 (UTC)

Sure, go ahead, wash your dishes with drain opener, what do we care? Just make sure you wear gloves and googles and rinse very thoroughly. Looie496 (talk) 03:13, 5 May 2013 (UTC)

Internet search engines have the most surprising uses.  :) -- Jack of Oz ^[Talk] 03:18, 5 May 2013 (UTC)

Which triglycerides? Plasmic Physics (talk) 04:36, 5 May 2013 (UTC)

It doesn't matter, the lye will take care of any of them. --Jayron32 04:53, 5 May 2013 (UTC)

That depends on whether the lye is added in excess. Plasmic Physics (talk) 07:04, 5 May 2013 (UTC)

I'm just trying to figure out if the OP actually knows what they are talking about, because, by not defining 'triglycerides', there is no way to unambiguously interpret the question. Plasmic Physics (talk) 07:08, 5 May 2013 (UTC)

Triglycerides that make my dishes greasy? What are my options? 78.144.202.9 (talk) 07:15, 5 May 2013 (UTC)

Ordinary dishwashing liquid. NaOH is total overkill, and dangerous. -- Jack of Oz ^[Talk] 07:19, 5 May 2013 (UTC)

Doesn't that depend on how much I use? I could make it up to a less threatening concentration, or just add it to the water in its solid form... would it pop if I did that? — Preceding unsigned comment added by 78.144.202.9 (talk) 07:22, 5 May 2013 (UTC)

And when I said, what are my options, I meant re: the different types on triglycerides. — Preceding unsigned comment added by 78.144.202.9 (talk) 07:49, 5 May 2013 (UTC)

Sodium hydroxide is equally corrosive at all concentrations, except at 0 and 100 %. Varying the concentration only changes the reaction rate. Changing the amount, shifts the reaction equilibrium. Regardless, of concentration or amount of hydroxide used, it will still corrode glazes on cermics such as crockery, repeated use will strip the glaze off completely. While it does accomplish the task of degreasing, it also attacks the very thing you're trying to clean.

Note: it does not 'pop' when dissolved, that would be sodium metal igniting elemental hydrogen, given off by sodium metal. Plasmic Physics (talk) 08:26, 5 May 2013 (UTC)

Not to mention, how difficult it is to rinse off. If not rinsed completely, all food consumed from its surface will tase bitter and brackish, or similiar to baking soda, and it will damage your shelves. Plasmic Physics (talk) 03:38, 6 May 2013 (UTC)

It will also damage aluminium, zinc and tin. Rivets will tend to be eaten away. Graeme Bartlett (talk) 12:15, 5 May 2013 (UTC)

(Assuming those elemental forms and that type of object, are participant to this system.) Plasmic Physics (talk) 12:58, 5 May 2013 (UTC)

Adding to the list of others things you probably shouldn't wash your dishes in, you might enjoy this series from a professional chemist. Shadowjams (talk) 20:09, 5 May 2013 (UTC)

An alternative alkali to use is ammonia solution. It turns fats into soap, and cuts through high grease build up very fast. Try not to breathe the vapour. Graeme Bartlett (talk) 11:36, 9 May 2013 (UTC)

Pope alexander of the borgia family used vitriol or sulfur as a mood anhancer..

I cannot find anything anywhere on the internet about the ancient use of vitriol or sulfur as a mood enhancer nor how it was prepared and the side effects..can anyone please help me??

5/4/2013 10:28pm... — Preceding unsigned comment added by Jaime71355 (talk • contribs) 02:28, 5 May 2013 (UTC)

I'm afraid you might be mixed up -- I've never heard of anything like that and can't imagine how it would work. Is it possible that you're thinking of arsenic, which was sometimes used as a stimulant? Looie496 (talk) 03:18, 5 May 2013 (UTC)

I thought the Borgias only used arsenic against their enemies? 24.23.196.85 (talk) 06:06, 7 May 2013 (UTC)

Beef vs. chicken

Why is it alright to eat rare/medium beef but not chicken? Is salmonella not a problem with beef? DRosenbach ^{(Talk | Contribs)} 03:48, 5 May 2013 (UTC)

Because rare chicken tastes terrible. --Jayron32 04:04, 5 May 2013 (UTC)

Rare chicken is eaten in Japan, mostly in Kagoshima prefecture, in sashimi style like [6] and [7]. The taste is OK. But there's always a possiblity of Campylobacteriosis. I've eaten rare chicken twice, but nothing happened. Oda Mari (talk) 07:43, 5 May 2013 (UTC)

You can also get sick from undercooked beef. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:24, 5 May 2013 (UTC)

Neither is "alright" - you can get sick from any type of food. It's really about statistics; and you've no doubt been exposed to more educational campaigns advising you about poultry - because that's where the majority of the reported infections come from. You are more likely to find hazardous bacteria in commercially-raised chicken than in commercially-raised beef. You can get sick from any harmful bacteria; and those bacteria can live almost anywhere - fruits, vegetables, meats, poultry, and non-food sources... but according to a report I found by browsing the USDA.gov website's food safety pages, An Economic Assessment of Food Safety Regulations: The New Approach to Meat and Poultry Inspection, salmonella accounts for more than half of all food-borne illness death, and accounts for about the same percentage of total health-care expense. E. coli infections, typically found in beef but also including all other sources, accounts for less than one tenth that amount. There is much speculation about why this is true: it is plausible that in the "natural environment," more chickens have illness, per capita, than cows. It is plausible that chickens are raised in conditions that are less sanitary or less healthy than cows. It is plausible that different regulations concerning beef and poultry contribute to a different epidemiology. It is plausible that testing for salmonella is less effective - or that hazardous quantities of poultry-borne salmonella are harder to detect than hazardous quantities of other food-borne pathogens. (In fact, the report I linked details each of these possibilities, with additional data). Nimur (talk) 18:27, 5 May 2013 (UTC)

And it's not just about eating rare vs. well-cooked meat. There's also the issue of defrosting frozen cooked meat. You can do that once, but if there's any left unused, you should get rid of it. If you refreeze it and defrost it a second time, it would no longer be safe to eat. This is particularly a risk for chicken, but it's true for all meat to some degree. -- Jack of Oz ^[Talk] 20:02, 5 May 2013 (UTC)

Different species harbor different organisms and the risk/transmission profile for them differs. There's not a lot of design beyond that. The one thing Nimur didn't mention is processing practices. Chickens are processed in bulk differently than cattle (the cleaning and defeathering for instance), and that can facilitate cross contamination. That said, even a single chicken from the backyard, dressed individually should probably be fully cooked. Shadowjams (talk) 20:07, 5 May 2013 (UTC)

• Great, but I think the OP is asking for illumination on “is it alright to eat rare/medium beef but not chicken.” This puts it so simply that even a child can understand: “Poultry roasts, however, have an added complication: Unlike solid beef roasts, chickens and turkeys have internal cavities that can be contaminated with bacteria. The central cavity will be the last part of a roast to cook, so to be safe, it's important to cook a whole chicken or turkey until a thermometer inserted into the thickest part of the thigh registers 165°F.” [8] So, in other words (and to answer the OP's question). It is not so much the bacteria but the nature of the meat that requires a cooking temperature to ensure that all pathogenics become 'toast.' Personally, I think raw meat is fine, providing that the chief buys it himself and knows what s/he is doing. But those artisans are far and few between. Having experienced food poisoning, I now trust only in people that have a solid local recommendation. Even if they comment : “ Uyee loook at mi daughter one more time like that … an' I'll smasher you face... OK? Bon appetite.”Aspro (talk) 17:12, 10 May 2013 (UTC)

Does frequent reading/writing affect neurology of spoken language?

The phenomena described in this article seem like they could be explained more or less like so: "Fans speak by reading their mental writing aloud; mundanes write by transcribing their mental speech." Have any studies examined how frequent reading and writing, and infrequent speaking, affect the brain structures or activation patterns associated with language? NeonMerlin 05:43, 5 May 2013 (UTC)

Athletes and alcohol

This is a hypothetical question, not medical advice, because I'm not a professional athlete. Before athletes compete, they follow a strict diet but say for example if they had a heavy night of drinking, a few days before, not a night before, how would that affect their performance on the day because I'm sure a few athletes must have tried this before whether, intentional or not. — Preceding unsigned comment added by Clover345 (talk • contribs) 12:06, 5 May 2013 (UTC)

None directly; the body has plenty of time to metabolize alcohol in a few days' time. The most likely avenue of affecting performance, in my opinion, is for the drinking and associated behavior to result in an arrest. Being in jail, or being suspended for having been in jail, is a sure means of preventing an athlete from performing normally. — Lomn 13:09, 5 May 2013 (UTC)

What about junk food? Do you think that would affect then more a few days before since they follow such a strict diet normally? Clover345 (talk) 14:33, 5 May 2013 (UTC)

It doesn't have a significant effect, the diet is relevant only for the long term. On the short run what counts is only if you are getting enough calories. Count Iblis (talk) 15:34, 5 May 2013 (UTC)

As this is a reference desk, here's one; The effects of Alcohol on Endurance Performance. It highlights these effects on the day after drinking:

• Dehydration
• Potassium and sodium depletion
• Impaired temperature regulation
• Impaired balance and co-ordination
• Reduced total work output

"... the ACSM recommends skipping anything beyond "low amount social drinking" for 48 hours prior to the event. It can take your body up to three days to purge itself of alcohol. One drink (sorry) over the course of an evening is your best bet." Alansplodge (talk) 16:46, 5 May 2013 (UTC)

You might find this article fascinating. Shadowjams (talk) 19:54, 5 May 2013 (UTC)

Optimizing learning habits

I've recently started playing games that are meant to improve the players' skill at solving simple arithmetic operations (such as 5×4 or 448÷32), which made me think about the way our brains study. For example, we will likely feel a bit uncomfortable whenever we make a mistake, which I suppose is the brain's way to make us more cautious. On the other hand, being too cautious would make us slower and therefore the learning process would take more time.

In order to accelerate my learning I wanted to know what consideration there are to the act of studying. What is the best time to study new information or to practice information that I've already learned? In the calculations games, should I prefer practicing each operation individually (first a list of additions, then subtraction and so forth) or all combined? Should I waste time to recalculate wrong results or should I move on? And how significant is it anyway?

In case the subject is too wide to detail, describing just the considerations of one habit (e.g. studying time) would also be great. I'm also interested in recommended books. Thanks! 79.181.175.168 (talk) 12:11, 5 May 2013 (UTC)

On whether to practice each operation individually or all combined, it really depends on what you want to achieve. If one particular operation is giving you problems, it would be a good idea to do that one individually. If you aren't having specific problems with any operation, it would be a good idea to do all combined, although I cannot quite remember the reason. Double sharp (talk) 15:11, 5 May 2013 (UTC)

Opinions differ widely on these sorts of things - from my own experience, there is no direct link from educational theory to educational practice to perfectly designed textbooks and educational systems. When you get to the act of "doing", there are just too many variables, and your own enjoyment of a system is one of them. But read up on Paul Pimsleur and spaced repetition. Basically, repeating immediately, then increasing the delay between each repetition, is the proven technique for memorising. This may or may not relate to solving mathematical puzzles, but I suggest it is a place to start. IBE (talk) 11:54, 6 May 2013 (UTC)

Is the blood test influenced by water?

I saw a nurse that say that if someone don't drink water before he come to a blood test, then his blood wouldn't come out as properly. My questions are: 1. Is it true? 2. Assuming this is true, How long it takes to the water to come into the blood circulation from the moment of the drinking. מוטיבציה (talk) 21:10, 5 May 2013 (UTC)

What 'blood test' would that be referring to. Richard Avery (talk) 21:40, 5 May 2013 (UTC)

Drinking a lot of water can dilute the blood - which I suppose would affect measurements of the amount of some substance per milliliter of blood...so yes, I assume it's true. Healthy kidneys are able to excrete 1 litre of water per hour...so the time it takes to return to normal will be at least one hour for every liter you drank. SteveBaker (talk) 22:23, 5 May 2013 (UTC)

It seems to me the question refers more to cases where people are (mildly) dehydrated and have low blood pressure as a result, causing problems with drawing blood... Count Iblis (talk) 23:08, 5 May 2013 (UTC)

As the OP supposes, it is not a question of affecting lab measurements, it is a question of how easy or difficult it is for the nurse to get blood out of the patient. Mild dehydration in basically healthy patients does not affect difficulty in drawing blood. In elderly patients, and in patients who have been given intravenous chemotherapy, the peripheral veins that are normally chosen to draw blood, which are the same ones they tend to choose for intravenous drips, tend to harden and partially close down. In such patients, drawing blood can be quite difficult, but if they drink plenty of water 20 to 60 minutes before, it can be easier. In my experience, (as an elderly patient who has had chemo) it seems to depend on the experience and skill of the nurse. Older nurses, and nurses that have specialised in taking blood (phlebotomists) don't seem to have a problem regardless, as they will choose a better vein, and they are better at getting the canula in. Time of day also matters. If a doctor orders a blood test that requires fasting (for which the normal way is to get the blood taken before breakfast), on a cold morning nurses cannot get blood out of my arm veins at all - blood has to be taken from a foot vein, which requires a doctor's direct supervision for some reason. Wickwack 120.145.68.194 (talk) 23:27, 5 May 2013 (UTC)

Just a slight correction, the term is phlebotomist, it has nothing to do with plebs or botany :) Vespine (talk) 02:28, 6 May 2013 (UTC)

Last summer my GP practice had a notice up to the effect that patients who have booked morning blood tests should drink a pint of water after they get up and before they come for their blood test, so the phlebotomist there obviously think it affects the process. --TammyMoet (talk) 10:33, 6 May 2013 (UTC)

Interesting. I have about 6 blood tests a year these days, and the issue has never been raised. When it's a fasting test, they always ask when was the last time I ate; but otherwise, no questions. -- Jack of Oz ^[Talk] 10:41, 6 May 2013 (UTC)

You have to book an appointment to get blood taken, Tammy?? Another reason why I'm glad I don't live in the UK and have to put up with the NHS. We in Australia (not noted for a good caring medical system either) just rock up when we get round to it. I've never had to wait more than 5 minutes. Wickwack 121.221.85.77 (talk) 14:19, 6 May 2013 (UTC)

We do have a choice: I can go and sit in the out-patients at my local hospital and queue to have my blood taken without an appointment, or I can make an appointment to see the phlebotomist at my GP's surgery, or at one of several pharmacies around town, or I can arrange for a private phlebotomist to come to my house for a fee of £15 and take my blood. The advantage of the GP option is they have free parking. The disadvantage is that, when I faint (which I do from time to time) while having the blood taken, they have to call an ambulance and get my husband out of work and I go to A&E. If I'm at the hospital, I get charged parking fees of £2 per hour. If I faint they wheel me round to the recovery area and make an internal call to my husband, who works in IT there. Guess which I prefer. --TammyMoet (talk) 19:00, 6 May 2013 (UTC)

We have these choices: 1) go to the phlebotomist at a GP's premises (all are private) - if you faint, they'll just get the doctor to sort you out - calling an ambulance to take you away from a doctor on hand and to to A & E where you'll have to get past the triage is just plain silly. No parking fee, due to competitive pressure; 2) Go to a laboratory's blood taking outlet - all private - there are heaps of them all over the place, typically in shopping centres - no parking fee. What would happen if you faint is unknown to me, I guess they would have to call an ambulance, but maybe not - all phlebotomists are fully trained State Registered Nurses. 3) Go to the phlebotomist at a private hospital - no parking fee usually; 4) Go to the phlebotomist at a public (ie Goverment owned) hospital - pay an outrageous parking fee and wait. Public hospital phlebotomists are the most skilled though. If you genuinely can't leave home, a nurse from the Silver Chain will come, take blood, admister treatments etc. Silver Chain are a Not-or-Profit organsiation and there is no fee regardless of what service is provided. However, if you can think rationally and talk, they will ask for a donation and can be quite aggressive about it. For those with terminal cancer and want to spend their last months or days in their own bed at home, away from hospital noise and hospital food, Silver Chain are absolutely marvelous. Overall, yep, I'm glad I don't live in the UK and have to put up with the NHS. Wickwack 60.230.238.42 (talk) 00:47, 7 May 2013 (UTC)

May 6

A few chemistry questions

A few chemistry questions… Please explain how to solve (no calculator allowed).

Assume that gaseous substance A undergoes a first order reaction to form gaseous substance B. At a certain temperature, the partial pressure of gas A drops to 1/8 of its original value in 242 seconds. What’s the half life for this reaction at this temperature?

I just plugged in numbers for the original value, calculated the new value, then looked at the answer choices and figured out the half-life. But how would this be done mathematically (without answer choices)? The answer is 80.7 seconds.

Equal masses of He and Ar are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 11 atm?

The answer is 10 atm. How?

A 160 mg sample of NaOH (MM=40) is dissolved to prepare an aqueous solution with a volume of 200 mL. What is the molarity of sodium hydroxide in 40 mL of this solution?

The answer is .0200 M. The only explanation I can come up for this is that the molarity in 200 mL is .02 M, but then why wouldn’t it change when looking at it for 40 ml? Does it not change? Molarity changes with volume though?

If .15 mol of K2CO3 and .10 mol of KBr are dissolved in sufficient water to make .20 L of solution, what is the molar concentration of K+ in the solution?

The answer is .40 M. How?

Vessel A containts 32 grams of O2 gas while Vessel B contains 32 grams of CH4 gas. Find the ratio of the pressures of the gas in Vessel A to Vessel B and the ratio of the average kinetic eneriges in vessel A to Vessel B.

For the pressures, I just found the mole ratio was 1:2 and said moles is proportional to atm, so it’s 1:2. That’s correct answer. Is that correct logic?

How do you find the ratio of the average kinetic energies? I thought it was r1/r2 = r_1/r_2 = √(M_2/M_1 ) but that answer would be 1:1.4 yet the answer key says the ratio is 1:1.

Thank you!!! --Jethro B 00:42, 6 May 2013 (UTC)

Generally, a functional knowledge of simple arithmetic and introductory algebra are considered prerequisites before students begin stoichiometry. Each of these questions are essentially solved by trivial application of simple algebra. (With a little rounding and liberal application of critical thinking, you can solve much more difficult problems than these with no calculator - even pencil/paper are unnecessary for these problems). Other questions are spot-checks to verify that you understand terminology (like the difference between concentration and volume). Can you help us understand your background so we can lead you in the right direction? Nimur (talk) 01:35, 6 May 2013 (UTC)

If you believe that the stoichiometry and algebra is simple, then please provide some answers for me... I don't have an issue with algebra or stoichiometry. However, you can't just do stoichiometry in each of these problems - they test information across various units and different things need to be applied for each one to understand how to do the stoichiometry. The picture here isn't stoichiometry, but rather the specific units each question deals with, whether it's solubility, gas laws, kinetics, etc...

So if someone could provide an explanation of how to solve them (or some of them), and I note that they are not all the same stoichiometry, I'd appreciate it.

P.S. If you're really interested in my background, you can send me an email - it's not something I will publicly reveal. I will say that I consider myself skilled in the subject area and have proven this in the necessary courses by scoring highest, but there are always specific little things that you either don't know or forget (to put this in context, these are selected from a document of 75 questions, and are the ones I have trouble with. It's just a few, but I'd like to know how to solve them). --Jethro B 02:06, 6 May 2013 (UTC)

I have no idea how much chemistry you, as an otherwise-anonymous poster, already know. If you're a new student of chemistry, you deserve some directed conceptual explanations. If you're an advanced grade-schooler, you need some detailed help with mathematics you wouldn't know yet. And if you're a physics undergraduate, you need a stern talk about life-choices, and we need to yell "apply the equipartition theorem" at you (for the last problem). Without knowing what type of help you need, it's difficult to help you.

For example, "Equal masses of He and Ar are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 11 atm?" Look up the atomic mass of Helium and Argon if you don't already know them. Helium's atomic mass is four, and argon's is forty (for the purposes of our discussion, without a calculator, and ignoring some irrelevant decimal places). The ratio 4:40 is simplified to 1:10; and the question gives you a total partial pressure of 11... one plus ten is eleven. The math is alarmingly simple - but only if you already know that partial pressure is proportional to the molar mass ratios. That is a simple fact, but it's one you need to learn somewhere (presumably in a chemistry class). Do you need help with these concepts or do you just need a reminder to apply them?

Every other problem had a similarly simple arithmetic answer, as long as you recognized the concept that was being asked. Nimur (talk) 02:52, 6 May 2013 (UTC)

These questions look like they're on the level of College level chem/AP Chem, which I know. Yes, if you can do what you did with the pressure question - state what concept is applied here and how - that's great. I don't need a detailed explanation, I should be able to understand it. The helium, with the lower mass, would exert more pressure than the Argon? --Jethro B 03:18, 6 May 2013 (UTC)

Here's my attempt to point you in the correct direction for these questions. An additional overall hint is don't be afraid to start slinging algebraic equations around. You might have an idea of how to solve things "if only I knew T (or V, or ...)". Don't get discouraged - just try representing it by a variable and calculate through algebraically. It's quite possible that the T's or V's will cancel and you'll find you don't actually need to know them to solve.

• Equal masses of He and Ar ... as Nimur discusses above - the key point is that partial pressures are distributed like the molar ratio of the gasses (each individual molecule contirbutes equally to the pressure for ideal gasses).
• Assume that gaseous substance A undergoes a first order reaction ... You'll need to undestand what a first order reaction is. Drawing from examples of first order reactions, it should be clear what the reaction and stochiometry is. From that, you should be able to calculate final amounts of A & B from the given partial pressures, and from the starting and ending amounts and the rate equation determine the half life.
• A 160 mg sample of NaOH ... Questions can have superflous information to catch out those people who are blindly combining numbers. If you're confident in your understanding of what molarity is, the 40 mL shouldn't throw you.
• If .15 mol of K2CO3 ... Start by calculating what the molarity of the K2CO3 and KBr would be seperately in the final solution. Then figure out what each would contribute with respect to K+ ions. The final K+ concentration is simply the total contribution for the K+ ions.
• Vessel A containts 32 grams... This is a straightforward application of the ideal gas law. You can do PV=nRT for both vessels to find the ratios of pressures. Likewise, you can also write the equation for the average kinetic energy, then take the ratio and cancel like terms. One catch is that they're likely talking about the per molecule or per mole average, rather than a per mass average or something like that, so keep that in mind as you write the expression for the average kinetic energy.

Hopefully that should be sufficient to get you on your way. -- 71.35.116.214 (talk) 04:22, 6 May 2013 (UTC)

• A half life reduces the amount of something by half. The statement that it is a first order reaction merely emphasizes that there is a half-life, i.e. no matter how much is present, half of it is gone in the same amount of time. Half of half of half is 1/8, so the half life is 1/3 the "eighth life".

• Helium weighs 4 amu, argon weighs 40. To make equal masses you need 10x as many particles of helium. So there are 10 times as many particles of helium as argon flying around in the gas. Ideally all the particles have the same range of energies, so the helium particles will sock a wall ten times as often as argon particles and therefore be exerting 10x the pressure.

• The next one is a dirty trick. An aliquot of a solution has the same molarity as the stock it is taken from. Molarity is moles / volume, so you could make up 0.02 with 160 mg in 200 ml or 32 mg in 40 ml or (easiest for calculation) 800 mg = 0.2 mol in one liter!

• 0.15 mol of K2something contains 0.30 mol of K. Add 0.10 mol of K from the other and you get 0.40.

• Your logic is right. But if you put the two gasses in the same vessel, they won't push a membrane (or the invisible boundary between them) one way or the other, nor will they transfer energy from one to the other because they are more importantly at the same temperature. This implies they're carrying the same kinetic energy. See kinetic theory, which says the energy per particle depends only on the temperature. Wnt (talk) 03:12, 7 May 2013 (UTC)

For the potassium ion question, it's true that there are 0.40 moles of K⁺ in the solution, but the question asks for molar concentration, not the amount of substance, and gives the volume as 0.20 L. Unless you specify units of moles/200ml (a rather strange choice), you need to divide by the volume. This gives a concentration of 2M, so it seems the answer given in the OP's answer book is incorrect.please correct me if I am missing something obvious here... Equisetum (talk | contributions) 09:39, 7 May 2013 (UTC)

Reading my answer I feel I need to engage in a little auto-pedantry and point out that you actually divide by the concentration even if you do chose units of moles/200ml, it's just that the concentration is then 1 (if you don't conceptually divide then the units don't come out right, which even five years after doing my last dimensional analysis still makes me nervous). Equisetum (talk | contributions) 09:44, 7 May 2013 (UTC)

Sorry! I was rushing near the end and didn't notice the incorrect "right answer" was in M not mol. Wnt (talk) 15:57, 7 May 2013 (UTC)

I want to change a reference on the Elephant Cognition page.

I posted the following comment on the Elephant Cognition talk page but nothing has been done to change it.

The source [Dubroff, M Dee (August 25, 2010). "Are Elephants Smarter than Humans When It Comes to Mental Arithmetic?". Digital Journal. Retrieved 2010-08-29.] Is just an flake article talking about the journal article [Irie-Sugimoto, Naoko ; Kobayashi, Tessei ; Sato, Takao ; Hasegawa, Toshikazu."Relative quantity judgment by Asian elephants ( Elephas maximus )"Animal Cognition, 2009, Vol.12(1), pp.193-199]. Shouldn't the actual journal article be cited with the link being something like <http://journals.ohiolink.edu/ejc/article.cgi?issn=14359448&issue=v12i0001&article=193_rqjbaem> ? — Preceding unsigned comment added by reku68 (talk) 19:57, 22 April 2013 (UTC) — Preceding unsigned comment added by 129.110.5.89 (talk)

You can edit the article yourself! I'll put the article on my watchlist, and if you mess something up, I'll help fix it. Regards, Looie496 (talk) 14:49, 6 May 2013 (UTC)

What kind of bug is this?

Hi there. For the last few weeks, I've been finding little bugs, about one every day or so. I get rid of it, but there's usually one there the next day anyway. It's very rare for me to see more than one at once, but it has happened. They almost always appear in the same area of the room, and whenever I see them they're always on a wall, and rather low to the ground. I don't recall ever seeing them outside of this room, either. I was wondering if anyone could help me identify what it might be? I took a Photo of the bug (apologies for image quality, it's the best I could get out of my old iPhone 3GS camera). I live in England, in case this helps narrow it down. Thanks for any help I might receive. 86.134.231.216 (talk) 12:29, 6 May 2013 (UTC)

It looks like a shield/stink bug. I don't know which species though. Plasmic Physics (talk) 12:46, 6 May 2013 (UTC)

To test it, does it stink when you try and catch it, or otherwise disurb it? Plasmic Physics (talk) 12:50, 6 May 2013 (UTC)

I don't think so. They move so slowly (hell, if I look straight at one it's hard to tell whether it's moving at all - it's only when I look away for a bit and then look back that I can tell it's moved, usually), and they're incredibly tiny (three millimetres top estimate). I can't rule it out for certain though, as I didn't try actively sniffing it or anything like that. If I see another one, I'll update. The last time I had a visitor I asked her, and she guessed at woodworm, though she stressed it was just a guess. I looked at all the insects linked in the woodworm article, though, and they all looked too elongated, whereas these are all rounder. I haven't noticed any wood damage on anything wooden nearby, either. 86.134.231.216 (talk) 13:07, 6 May 2013 (UTC)

I don't know much about bugs (I'm sure there's a word for the logical study of bug, probably not bugology), but I do know that species can vary considerably in size within the same superfamily. Take Tessaratomidae, they are a famly under stink bug, and they are giants compared to the other families. I would not be surprised if there was a family of dwarf stink bugs, of which this one is a member. I ny case, that's just my opinion. Plasmic Physics (talk) 13:20, 6 May 2013 (UTC)

The study of insects is entomology. Anyway, the picture has very little detail, but PP's guess of a sheild bug is pretty good. That's good enough for casual purposes, but only narrows it down to ~7000 species... Anyway, as for why this is a good guess: note that the elytra seem to be incomplete, and the pronotum has the general shape we expect in shield bugs. Note that many stink/shield bugs will not display any odor when disturbed. Even the (recently very common) brown marmorated stink bug only rarely produces odors, in my experience-- so that's not a very good criterion. Finally, when trying to ID an insect, remember that things like color, markings and size are not very informative. The pros usually focus on gross insect morphology to get to Category:Orders_of_insects, and then use fine features to get to family or genus. In generally, getting any insect ID down to species is very difficult, even for experts. The exceptions are things like honey bees and monarch butterflies, but even then, there are several close relatives look-alikes that can easily fool amateurs. SemanticMantis (talk) 15:43, 6 May 2013 (UTC)

Are we looking at the same picture? What I see looks like a carpet beetle, family Dermestidae. --Dr Dima (talk) 19:17, 6 May 2013 (UTC)

Agreed. Looks nothing like a stinkbug. --jpgordon^{::==( o )} 19:33, 6 May 2013 (UTC)

What something 'looks like', is down to opinion, and by definition, an opinion cannot be false or true. So, it may not look like a stink bug to you, but it does not inherently invalidate my opinion. Plasmic Physics (talk) 01:13, 7 May 2013 (UTC)

Well, I only said shield bug was a good guess :) Anyway, if you think the elytra are completely covering the hindwings, then I suppose it could be a beetle. I thought the elytra looked incomplete, which would rule out beetles. But the photo is pretty bad. I was mainly trying to point out some of the diagnostic features that we could look for. "Looks like" doesn't hold much water for insect ID. There are several thousand species of beetles and sheild bugs, and many of them will look rather similar when photographed in this manner. SemanticMantis (talk) 21:26, 6 May 2013 (UTC)

The posterior dorsal section of the insect appears more tappered than rounded, which is why I recognise it as a shield bug. Plasmic Physics (talk) 01:30, 7 May 2013 (UTC)

That's probably more down to the poor quality of my photograph than anything else. As SemanticMantis said, it's hard to really make any kind of judgement on such a photograph. Not really your fault. Going off the tips from Dr Dima and Jpgordon above, I did a bit of Googling and found quite a number of council websites mentioning carpet beetles, and in particular they tend to mention the Varied carpet beetle, which I think this is. Considering a lot of these pages (and the WP article) mention bird nests, I might have to get on the phone with the council (I live in a council flat) and see what they can find out. Thanks again everyone for your help, and apologies once more for the poor quality of my photograph. 86.134.231.216 (talk) 05:41, 7 May 2013 (UTC)

Ah, I concur, the dorsal perspective of the varied carpet beetle does indeed look similiar to the photo. Plasmic Physics (talk) 08:01, 7 May 2013 (UTC)

I also go with Dr Dima and JPG, this image helps to confirm it is likely to be a Varied Carpet Beetle. Richard Avery (talk) 06:47, 7 May 2013 (UTC)

Meteor trail color

Why the trail color of this meteor shifts from green on the left to blue? A kind of redshift since it approaches from the left? Brandmeister^talk 16:23, 6 May 2013 (UTC)

A meteor would need to travel something like a couple of thousand times faster than they do to give visible redshift. I don't see much blue, I see green which comes from the meteor's copper or magnesium, and red which happens when Earth's atmospheric gases are heated. At higher altitudes there is more oxygen and the metal emission dominates, lower altitudes have more nitrogen which gives a deeper red. This green-to-red is not uncommon, see here. The article on meteors mentions color, and there is more at Nasa and good ol' web searches on meteor color. 88.112.41.6 (talk) 17:07, 6 May 2013 (UTC)

The image was captured with a consumer digital camera, and according to the file's metadata, the image was further post-processed in Adobe Photoshop. Be very very careful drawing scientific conclusions from such images. Digital cameras are incredibly complicated, and if you aren't sure what digital processing has been applied (as well as a very good understanding of all the optical and electronic characteristics of the camera), you should not jump to conclusions about things like color. In other words, a digital camera with color is not the same as a spectrophotometer. Nimur (talk) 17:12, 6 May 2013 (UTC)

Didn't do google search this time, but thanks anyway, solved. Brandmeister^talk 17:48, 6 May 2013 (UTC)

Tetrahydrofuran

If a site is contaminated with tetrahydrofuran (specifically, I am talking about the Seymour Hasardous waste site), would removing all contaminated soil at the site remove all contamination from the site and/or prevent the future spread of contaminants from the site?--149.152.23.33 (talk) 22:34, 6 May 2013 (UTC)

Removing all of the contaminated soil, by definition, removes all of the contamination as well. 24.23.196.85 (talk) 22:57, 6 May 2013 (UTC)

Note also that THF is only mildly toxic, highly volatile and rapidly biodegradable -- so digging up all that soil might not even be necessary or worthwhile, it might be just as effective to simply allow the THF to evaporate/leach out/break down over time while taking strict measures to prevent any further contamination. 24.23.196.85 (talk) 23:13, 6 May 2013 (UTC)

May 7

Practically insoluble

Is there a defining characteristic according to any particular school of thought, that distinguishes between 'partically insoluble' and 'insoluble'. My question is inspired by the difining characteristic of an 'existant isotope', that it must have a half-life greater than the time it takes for the nucleus to internally differenciate (~10^-14 s). Plasmic Physics (talk) 01:23, 7 May 2013 (UTC)

Please clarify. By "partically insoluble", did you mean "partially insoluble", or "practically insoluble"? And what does the half-life of an isotope have to do with this? 24.23.196.85 (talk) 04:12, 7 May 2013 (UTC)

I mean 'practically insoluble'. The isotope statement demonstrates a pragmatic approach to semantics in an area of science. Plasmic Physics (talk) 04:22, 7 May 2013 (UTC)

Terms like "practically insoluble" and merely "insoluble" are imprecise terms. If you want precision, you would use defined numerical measures of solubility such as solubility product and molar solubility and mass percent solubility as shown at solubility table. There aren't "hard and fast" cut-offs between terms like "slightly soluble" "practically insoluble" and "totally insoluble". It's a bit fuzzy around the edges. Generally, something is "soluble" if the solubility product indicates that it will dissolve extensively, that is the solubility product is significantly higher than 1. Things which are considered insoluble have solubility products which are very tiny, while something "slightly soluble" would have a solubility product near 1. But yet again, there are no hard cut-off lines here. It's somewhat subjective. --Jayron32 05:09, 7 May 2013 (UTC)

Personally, I'd say a substance is "practically insoluble" if no decrease in weight of the solid phase can be detected after placing it in the solvent, and "completely insoluble" if the dissolved phase doesn't even show up in spectroscopic analysis. But that's just me. 24.23.196.85 (talk) 05:43, 7 May 2013 (UTC)

Explosive experiments

Why is there no speciality laboratory glassware for experiments that involve explosively unstable compounds, like nitroglycerine? Such experiments seem to involve ordinairy glassware, that readily turns to shrapnel in these explosions. Is it not possible to create thickly walled composite glassware that is heavy and shock resistant? Take a test tube as an example, to enable efficient heating and cooling, a thermally conductive metal bottom can be fused into the underside of the test tube. Of course, this will result in a make-shift cannon, but it should be possible to attach a force dissipator. I'd like to think that chemists would try and keep their lab in one peace. Plasmic Physics (talk) 01:50, 7 May 2013 (UTC)

Is this actually a wide spread problem? How many scientists do you know who have been injured or killed by explosions? Or how many labs have been blown up? I suspect anyone working with explosive compounds has strict operating and safety procedures in place already. If they are working with quantities large enough to blow up the lab, I hazard a guess they have bunkers or similar special areas where the compounds are restricted to. Vespine (talk) 02:12, 7 May 2013 (UTC)

It's not a problem very often encountered. For scenarios, see [9] as linked in a previous discussion on this reference desk. Plasmic Physics (talk) 02:38, 7 May 2013 (UTC)

There are bombs and hoods and vessels and even ranges to handle explosives. Why would someone with more than one year's chemistry think a test tube would be an ideal or idealizable place to conduct such experiments? μηδείς (talk) 02:48, 7 May 2013 (UTC)

Concerning chemical experimentation of such explosives. Plasmic Physics (talk) 02:52, 7 May 2013 (UTC)

I see that I probably should never have given you advice on how to make that nitric acid after all... 24.23.196.85 (talk) 04:00, 7 May 2013 (UTC)

No, that was fun, but I did not make nitroglycerine, if that's what you're infering. Plasmic Physics (talk) 04:17, 7 May 2013 (UTC)

Have you had two years of chemistry, Plasmic Physics? Knowing that (and the meaning of your last sentence fragment) will help us guide our suggestions. μηδείς (talk) 04:21, 7 May 2013 (UTC)

Yes, I've had two years. My last sentence fragment reasserts the cntext of my query, since you seem to have missed that from the link I gave. You speak of bombs and such, which is hardly applicable. Plasmic Physics (talk) 04:26, 7 May 2013 (UTC)

Actually, do you know what a bomb is? μηδείς (talk) 05:00, 7 May 2013 (UTC)

Hint: This word has a different meaning in chemistry than in everyday usage. 24.23.196.85 (talk) 06:00, 7 May 2013 (UTC)

I see: you're talking of a bomb calorimetre. It is still not applicable. I'm talking about experiments, where detonation (or deflagration) is an undesireable reaction. Plasmic Physics (talk) 06:53, 7 May 2013 (UTC)

No, a bomb calorimeter is a specific type of bomb, there are others about which we don't seem to have articles, although the sense is mentioned at wiktionary. μηδείς (talk) 16:24, 7 May 2013 (UTC)

Thomas Klapötke is a professor in Munich, the link above also mentions him. He has a large interest in high energetic materials and green bombs. One of his favorites is hydrazine azide (N₅H₅). I saw the material which is highly explosive and the people used normal glass ware to handle it. They were behind a several layer glass window reaching around with their arms. The used a set of leather and chainmail gloves for their hands. The use of more than a few hundred milligramms was not considered a problem but nobody I knew did it. Uranium hexaazide and the selenium and tellurium azides were handled in a very similar way. Klapötke also told the story of having a bromoazide in a flask and somebody opened a door and the induced pressure difference was enough to induce the explosion. The high speed of the explosion leaves only fine dust of the glass mostly incapable to penetrate the normal labcoat. He said only a few glass particles reached him making it very painful to close the safety belt when he went home that evening.--Stone (talk) 07:48, 7 May 2013 (UTC)

For a lack of better words: Bingo! Plasmic Physics (talk) 07:53, 7 May 2013 (UTC)

I think Plasmic might like [10] this series, not to seem like I'm spamming it, but I did find it good reading, and I don't know a thing about chemistry. Shadowjams (talk) 07:54, 7 May 2013 (UTC)

I do appreciate a good read, however, I've already linked to that site near the start of this discussion. Plasmic Physics (talk) 09:54, 7 May 2013 (UTC)

The high energy working group was never a place for me to join. The place was dangerous. One PhD student had a hole in his palm and nearly died. The small round flask simply explodes in his hand. Although the fun to do the fall hammer test or the other tests to get physical data of the explosives would have been a nice work. --Stone (talk) 13:38, 7 May 2013 (UTC)

My late father in law was an industrial glassblower, and worked for a polytechnic which be came a university. His job was to make such specialist glassware if it was possible. So you may not be able to buy such stuff off the shelf, but it would be bespoke. --TammyMoet (talk) 17:49, 7 May 2013 (UTC)

Can such extraordinairy requirements be met by a glassblower's skill? Considering that the walls of such a vessel would be on the order of several centimetres thick (2-3 ?) and would be laminated with two different types of glass? Plasmic Physics (talk) 23:56, 7 May 2013 (UTC)

Aeronautical Engineering

Why do the technicians, space scientists and engineers wear white coveralls, masks, boots and gloves while working on an spacecraft? — Preceding unsigned comment added by 117.200.240.10 (talk) 05:44, 7 May 2013 (UTC)

Same reason that nurses or lab techs wear white coats -- so that any dirt or contamination on their clothes would be immediately visible. Why do British soldiers wear red coats, and French ones wear brown pants?  ;-) 24.23.196.85 (talk) 05:56, 7 May 2013 (UTC)

The colour is not that important. In front of my office there is an image of the integration of the Dawn spacecraft and two of the engineers wear black suits. The colour could be used as a colour code like the white ones do the checking while the green ones do the documentation and the black ones do the actual work. The clean room levels like class 10000 force you to wear the protective garment. Most of the dirt in the clean room is introduced by the persons working there and the clean room garment is there to seal it and make it stay with the person. We had the choice for our clean room to get green, light and dark blue, pink, black and white.--Stone (talk) 07:29, 7 May 2013 (UTC)

There can be psychological reasons. Not all spacecraft work will require clean room conditions. The company I worked for in the 1990's had several large data centres at different locations. The supervisor of one centre set about using every opportunity to tell his team how good they were, and had them all issued with white coats. It worked - the fault rate in his data centre went down, significantly lower than the other centres, and equally lower than before he took over. The colour did not matter, and maybe he could just as well issued them with uniform shirts or something. What did matter, is that wearing a white coat reinsforced in their minds the concept that they were good at their job and took care in it - and people rise or fall to their own perceptions.

Some factories I've worked in go to a lot of trouble to keep the place neat and clean, with everything in excellent condition, and issue different sorts of coats to different sorts of workers. It's the same thing - a proud worker is a good worker. A sloppy workplace tends to get sloppy workers.

In many places, wearing a white coat or whatever is what you do - just as managers wear a tie, and senior managers wear a dark suit.

Not to be forgoten is that workers like wearing lab coats as they reduce wear and tear on your own clothes, and the cost of cleaning the coats is a tax deduction. — Preceding unsigned comment added by 60.230.238.42 (talk) 12:16, 7 May 2013 (UTC)

Wickwack 60.230.238.42 (talk) 09:57, 7 May 2013 (UTC)

I am skeptical. How do you know it wasn't some other practice by the same manager? The mere fact that he was apparently eager to come up with new ideas/directives might have convinced other people there that somebody was paying attention. I do believe the first response that it is meant to make dirt show up - no matter how clean an area is supposed to be, the way it gets dirty may well be something very obvious. Wnt (talk) 16:43, 7 May 2013 (UTC)

There's simply NO issue with dirt in a data centre. There's no issue with dirt in most places lab coats and the like are worn. In most cases its about convention and image. If you are a customer (whether you are a representative of a government buying a satellite, or an individual getting a vetinary to look at your sick dog. All other things being equal, who are you going to deal with - the outfit whose staff are dressed in jeans, t-shirts, and thongs (= flip-flops in USA-speak) or the outfit whose staff are dressed in neat coats, proper leather shoes, and maybe wearing ties? I knew the data centre guy very well, and I knew everyone in his team. How he got his team, comprised as it was of techs just the same as the techs in the other centres, to do a lot better did not go unnoticed by management. As I said, the white coats were not the only thing he did - praise was the key to the performance improvement, by making them feel they were the best. The white coats were a part of his strategy to get them to percieve themselves as top class, and through that, improve. It's Leadership 101 actually. Wickwack 120.145.46.40 (talk) 00:35, 8 May 2013 (UTC)

Biplane vs. fighter jet

Suppose there's a dogfight between a World War 1 fighter biplane (for example, the Fokker Dr. 1 -- which was actually a triplane, but you get the idea) and a modern fighter jet (like the Mig-29). What would be the outcome of such a battle? Would it be an easy kill for the Mig, as I believe it would be? Or would both planes be unable to harm each other, as I've been told by a fellow aviation fan? (For the sake of argument, let's suppose both planes are piloted by top aces -- for example, Red Baron in the Fokker, and Ivan Kozhedub in the Mig -- so pilot skill is not a factor.) 24.23.196.85 (talk) 05:53, 7 May 2013 (UTC)

I'm not sure the Fokker Dr. 1 has the maneuverability necessary for evasion of an R-73 fired from ten kilometers away. The Fokker also couldn't return fire at that range, as the MG 08 that was its sole armament has a range of 2-3.5 kilometers. --Jayron32 06:02, 7 May 2013 (UTC)

That's what I'm thinking too -- provided that the missile can track the Fokker (which is the argument the other guy used -- he claimed that neither heat-seeking nor radar-guided missiles would have enough of a signal to track, and that the Mig wouldn't be able to get a shot with its Gatling gun because its higher stall speed and wider turning radius will make it overshoot. Personally, I don't buy it, but I'm looking for confirmation from someone more knowledgeable.) 24.23.196.85 (talk) 06:15, 7 May 2013 (UTC)

Why wouldn't radar-guided missiles have something to track? The Fokker should be large enough to show up, shouldn't it? It is much smaller than a Jet (5m long x 7 m wingspan for Fokker vs. 17m long x 11m wingspan for the MiG) but the resolution of the radar should be good enough not to confuse the Fokker with a duck... --Jayron32 06:31, 7 May 2013 (UTC)

...the Mig wouldn't be able to get a shot with its Gatling gun because its higher stall speed and wider turning radius will make it overshoot... That sounds like wishful thinking. Aircraft routinely destroy slow-moving and stationary surface targets. While it's plausible that our hypothetical MiG can't sit on the Fokker's six and follow it oh-so-slowly around, I don't see any practical problem with the MiG strafing the Fokker at its leisure. And it really shouldn't take that many 30mm cannon rounds to finish off the Red Baron. TenOfAllTrades(talk) 06:46, 7 May 2013 (UTC)

The OP's friend exhibits (as Spock says of Khan) two-dimensional thinking. The MiG can strafe the Fokker while diving on it or climbing up at it; he does not need to patiently sit right behind it as it chugs along. The MiG's astonishing power means it can trivially climb to a point a mile above the Fokker and then can dive down at its leisure. -- Finlay McWalterჷTalk 09:50, 7 May 2013 (UTC)

The Fokker would be helpless, Red Baron or not. The differences in technology, capabilities, and armament are so vast that I don't think there is any scenario where the older plane would pose any sort of threat. This is, after all, a plane that first flew a mere 14 years after the Wright Flyer. To even things up slightly, you'd have to take away the MiG's radar and missiles (or add them to the Fokker, although that might make it too heavy to fly), but I still don't think there's much the Fokker could do. You may as well ask a Model T to outrun a Corvette. --Bongwarrior (talk) 07:05, 7 May 2013 (UTC)

I'm going to go out on a limb here, and suggest that none of us are fighter pilots (the 8 year old me would be disappointed)... however that said, I bet if a Mig29 flew over the top of a biplane it might make it crash just because of its wake. Who needs a 30 mm when you have 1000 knots. Shadowjams (talk) 07:52, 7 May 2013 (UTC)

Indeed: the MiG's engines generate a massive jetwash and the wings a sizeable vortex - safe operating distances to avoid another aircraft's wake turbulence is measured in nautical miles. The MiG can easily get his to envelop the Fokker, which would probably shatter its airframe. -- Finlay McWalterჷTalk 09:59, 7 May 2013 (UTC)

During the Falklands war I believe Harrier jump jets were able to avoid Exocet missiles by staying still , this fooled the Exocet missiles into considering them as decoys and looking for something else. I'd guess a Fokker would be considered as practically stationary by such a missile. Dmcq (talk) 09:34, 7 May 2013 (UTC)

Exocet is an anti-ship missile. Argentine air forces in the Falklands War#Armament lists the AAF's offensive missile capability in 1982. -- Finlay McWalterჷTalk 09:42, 7 May 2013 (UTC)

Sorry one of their anti-aircraft missiles anyway and it's about the only name of a missile I heard of in the war!, I'm no expert on military weaponry, I know the NRA goes on at length about assault rifles and automatic rifles but it all passes over my head. Dmcq (talk) 10:31, 7 May 2013 (UTC)

It's good that you mention the MiG 29 specifically, because that leaves open (at least theoretically) the possibility of the most Tom Clancy-ish, fighter-jockily silly strategy the MiG can employ. He can fly ahead and beneath the Fokker, perform a Pugachev's Cobra, and strafe the Fokker as it passes in front of him. There's some chance that might not be safe (particularly that the gun exhaust, expelled into such an unusual air envelope, would stall the port engine), and it'd be idiotic to do in an actual conflict. But I'd put good money that somewhere, when his boss was off golfing, that some VVS Colonel has tried this to see if it works. -- Finlay McWalterჷTalk 10:11, 7 May 2013 (UTC)

The Fokker can come down to tree top level and jink about between tall trees and hills. This would make it just about impossible for a jet fighter to strafe, and it may make it difficult to hit with rockets as well. Isreali Mirage fighters found it very hard to hit MiGs as the lower stalling speed of the MiGs allowed them to come down to low altitudes and jink about. The Americans had a similar experience in the Korean War - the slower older generation MiGs could avoid being hit by coming down lower, and if the American overflew, pull back and hit the American. Not that I expect a Fokker with WW1 guns could hit a departing and rotating MiG29. It wasn't all that easy to hit other WW1 fighters. And modern fighters can take a lot more punishment anyway. The "dirty' stalling speed of a MiG29 is thought to be about 230 km/hr whereas the Fokker DR1 triplane stalled at 72 km/hr. As far a strafing goes, imagine trying to hit a door size target while passing it at 160 km/hr - pretty damm difficult - for both. So I tend to think the OP's friend is more right than wrong. Wickwack 60.230.238.42 (talk) 11:57, 7 May 2013 (UTC)

Let's do the math. don't know the stall speed of the MiG 29, but its landing speed is higher than that. Looking at a roughly equivalent US fighter, the F/A18 Super Hornet, it lands at about 240 km/h (arresting gear says US equipment can stop an aircraft at 130kt). The maximum speed of the Fokker is 185 km/h; let's say he's sustaining 170 km/h. So if the MiG is chasing the Fokker, as slowly as he can, he's gaining at about 1 km/minute. The MiG's Gryazev-Shipunov GSh-301 cannon has an effective range of between 1.2 and 1.8 km. So the MiG comfortably has a full minute to strafe the Fokker. The MiG carries 150 rounds, which (at the 301's cyclic rate) he can fire off in as little as 5 secondsl; he only needs a handful to kill the Fokker. This isn't an unusual mission for an air-superiority fighter - it would be expected to be able to shoot down cruise missiles, light aircraft, helicopters, and reconnaisance drones. -- Finlay McWalterჷTalk 12:13, 7 May 2013 (UTC)

You've missed the point. The Fokker can evade by flying as SLOW as possible, and he can turn on a sixpence, due to flying slow and because it's a triplane designed for manoeverability. That's what the MiG pilots did in the Isreali/Arab war and the Korean War - they slowed down as much as they could and darted about at treetop level, thus turning their slow speed to advantage. The MiGs would sometimes even lower wheels, as the "dirty" stall speed is lower than the "clean" stalling speed (with more drag you can fly a bit nose up with more throttle - the aircraft is then stable at a lower speed). What matters then is not just the MiG gun range but the rate of fire and the spread. The MiG29 in this case won't have a steady target for 1 minute, he has a moving target passing through his sights, if he's lucky, for a second or so. Even if they are flying straight and level, which would only happen if the Fokker pilot is a complete fool, the closing speed is not 230-170=60 km/r, its 230-72 = 158 km/r so the MiG pilot still has only 23 seconds, not one minute. In practice he has even less, because he'll want to pull up to avoid a collision. He'll have maybe 8 seconds at best if the Fokker pilot is a complete fool. Wickwack 60.230.238.42 (talk) 12:31, 7 May 2013 (UTC)

To all intents and purposes, engaging an elderly triplane would present the same problems as engaging a small observation helicopter, a scenario which I imagine fast jet pilots practice regularly. To Dmcq, although it is possible for the Harrier to rotate its jet nozzles to cause rapid deceleration, a tactic known as Vectoring in Forward Flight or "Viffing", I have read that this tactic was not employed during the Falklands War, although there was much press speculation that it would be. Our Vectoring nozzles article disagrees, so more research needed. Alansplodge (talk) 13:30, 7 May 2013 (UTC)

Argh - stupid argument. The Mig wins very, very easily...and in at least three or four different ways. The Fokker will be destroyed before it even knows that the Mig is nearby.

Simplistically - the Mig has the capability of deploying nuclear bombs - so it flies at high altitude above the Fokker - drops a nuke and it's game-over for everything within several miles of the target point - but the shock wave would shred the cloth-covered wings from a distance of ten miles. Accuracy isn't needed.

OK - let's assume that the Mig doesn't have that weapon load - or that it simply isn't desperate enough to use such a drastic solution.

Flying low and slow isn't going to help the Fokker. It's speed range is 45 to 115mph - about the speed range of a car. It can turn pretty tight for a plane - but nowhere near as tightly as a modern car. It's radar and thermal signature is also comparable to a car. So can the Mig destroy a car? Sure - it has a bunch of air-to-surface missile options...taking out a moving car is child's play for those kinds of systems. Truck convoys are classic modern military targets - and a Fokker is not much different.

The point is that "dogfighting" simply doesn't enter into the equation...the Fokker will be destroyed from five miles away by any one of dozens of possible guided or unguided missile options.

Even if the Mig is somehow forced to use it's cannon - the range of that weapon is about one and a half kilometers...it's perfectly capable of strafing stationary targets - and it has laser guidance...taking out a car (or the Fokker) would be child's play. That gun can take out most "soft" targets with a three round burst.

If your friend is still skeptical - ask this: Is the Mig capable of shooting down helicopters? The speed, altitude and manouverability range of a military helicopter is a close match for the Fokker. Helicopters can fly at any speed from zero to over 100mph - they can literally turn on a dime...manouverability and slow flying won't help the Fokker one iota. I absolutely guarantee that there is a whole range of weapons that this aircraft can carry that are ideally suited to taking out helicopters.

Even without weapons of any kind - a combination of hot jet exhaust, supersonic shock wave and massive air vortices would disrupt the flight path and the health of the pilot enough to do it great harm...being in the open cockpit of a plane made of cloth in the wake of a Mach 2 flyby would not be a survivable thing! You can try to argue that the Fokker can turn fast enough to avoid being close to the Mig - but the math says otherwise. Let's suppose the Mig lines up on the Fokker from a mile away. At 1500mph, the Mig will cover that mile in a little over 2 seconds. The Fokker (at top speed) can cover about 300 feet in that time - and if it's going slowly enough to turn tighly, then it'll be under 100 feet away...so even with the best possible reaction time, and the most direct flightpath away from the oncoming jet the Fokker will be hit by supersonic shockwaves at something like 200 feet from the Mig. Recall the Mythbusters episode where a blue angel aircraft trashes stuff on the ground in a 200 foot altitude, Mach I flyby? Well, double the speed and you get four times the energy...yeah...that's what happens to the Fokker.

Silly argument - trivially dismissed on multiple grounds.

SteveBaker (talk) 13:49, 7 May 2013 (UTC)

A very convincing argument by Steve. I had forgotten about laser guided weapons - something not available in the Isreali-Arab and Korean wars I used as examples of succesful evading by slow craft. My first thought was that you shouldn't include nuclear weapons, on the basis that nobody is going to approve the deployment of such an expensive weapon just to destroy a triplane. But on second thoughts, you should include it, as the scenario of a Fokker triplane or any of its contempories being used in a war today is silly anyway. Wickwack 120.145.46.40 (talk) 00:51, 8 May 2013 (UTC)

Zero point energy and the volume of the universe.

Why doesn't the zero-point energy density of the vacuum change with changes in the volume of the universe? And related to that, why doesn't the large constant zero-point energy density of the vacuum cause a large cosmological constant?

Is it allowed to postulate / hypothesize on this topic on the reference desk, or is there a separate science forum / talk page for that? Robert van der Hoff (talk) 06:49, 7 May 2013 (UTC)

Robert, the idea is that a header is a **short** (up to about 7 words) pointer to what the question is about, the meat of which then appears below the header. -- Jack of Oz ^[Talk] 07:32, 7 May 2013 (UTC)

(I made a more concise title and transferred the L-O-N-G title into the message body). SteveBaker (talk) 12:59, 7 May 2013 (UTC)

We don't encourage using the reference desk simply to initiate discussion - especially when it's to discuss some idea that you had. However, there is a reasonable question here that we can possibly answer. SteveBaker (talk) 13:01, 7 May 2013 (UTC)

You hit the nail right on the head. That is indeed a very deep mystery that is yet to be satisfactorily answer by modern physics. Naive calculations show that the cosmologic is about 120 orders of magnitude off (If memory serves). Supersymmetry improves that to "only" 60 orders of magnitude. Dauto (talk) 22:28, 7 May 2013 (UTC)

Why do we need omega-3 fatty acids?

What would the evolutionairy basis be for the need for omega-3 fatty acids? As a land based species it doesn't make sense that we require a nutrient which is most prevelant in oceanic fish.11:17, 7 May 2013 (UTC) — Preceding unsigned comment added by 137.224.252.10 (talk)

Just a relavent thought; omega-3 supplements are a waste of money, since they have a poor bioavailability. To quote a certain Big Bang character, "All you're buying, is expensive urine". Plasmic Physics (talk) 12:20, 7 May 2013 (UTC)

There are many plant sources of omega-3 fatty acids, so since the premise of your question is false, your question is ultimately unanswerable. It is certainly very highly present in fish, but it's also bioavailable in many foods that would have been food sources for people for thousands of years. --Jayron32 12:41, 7 May 2013 (UTC)

Also, if you go back far enough, we were oceanic fish! If Omega-3 fatty acids became an essential part of our piscine metabolism back then, they may have persisted as such after we (i.e. the ancestors of all the tetrapods) crawled up on land. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:32, 7 May 2013 (UTC)

• Omega-3 is important for brain development. [11] et al. That is why the Aquatic ape hypothesis has developed traction over resent years. Later on, when farming was learnt, other sources of Ω 3 were found. Plasmic Physics appears to be confusing water soluble vitamins. The excess of those, get extricated in urine but dietary fatty acids are broken down and used by the body as fuel. The kidneys don't filter them out. They get metabolized instead into useful fuel in most cases. An excess of Vitamin A (fatty acid based) however can lead to Vitamin poisoning and you can't piss that out either; hence hypervitaminosis. Therefore, I can't see what befit Plasmic Physics comment was to this OP's question. Perhaps he knows something I don't?--Aspro (talk) 15:24, 7 May 2013 (UTC)

Not at all Aspro, the study I that read, specifically refers to omega-3 acids administered orally. It states that they generally have low bioavailability, or are not in a form which is readily absorbed through the digestion tract. Plasmic Physics (talk) 23:32, 7 May 2013 (UTC)

We produce chemicals we need internally with enzymes (coded for by genes) that create a metabolic pathway for the chemical to be produced. Some such pathways may be unique and metabolically costly. In any case, if a nutrient is highly available in your natural diet (like vitamin C in the vegetables our ancestors ate) then the gene for the enzyme necessary to make that nutrient may be mutated or lost without harm. Once the gene is lost, people whose diet becomes unnaturally restricted can become ill (scurvy, beri beri) due to the lack of the nutrient. μηδείς (talk) 16:21, 7 May 2013 (UTC)

I found another source - seal oil - while searching omega-3 and Namibia (I continue to suspect an ancient origin of human feet and hairlessness in the wildly variable conditions of the Okavango, even if very good evidence traces the known origin further north) - anyway, apparently Nambia exports, or recently used to export, substantial qualities of seal oil as an omega-3 supplement. Here's one manufacturer's claim from Canada. [12] Apparently high omega-3 levels are true of all fish-eating mammals [13]. (It wouldn't surprise me if fish-eating birds were another source for less finicky palates...) Wnt (talk) 16:31, 7 May 2013 (UTC)

bioremediation

Can Tetrahydrofuran be phytoremediated? According to http://apps.echa.europa.eu/registered/data/dossiers/DISS-9d87f855-86db-4392-e044-00144f67d249/AGGR-9e7de3e4-b992-48c1-b99b-cbbabe912a48_DISS-9d87f855-86db-4392-e044-00144f67d249.html Tetrahydrofuran is not very bioaccumilative, which leads me to think phytoremediation is not effective. — Preceding unsigned comment added by 149.152.23.34 (talk) 15:25, 7 May 2013 (UTC)

Also, can tetrahydrofuran be removed from the Seymour Hazardous Waste Site by Air sparging?--149.152.23.34 (talk) 18:26, 7 May 2013 (UTC)

Based on the properties of THF, I think some form of bacterial remediation would be the most promising method. BTW, what exactly is the nature of contamination at the Seymour waste site? 24.23.196.85 (talk) 00:00, 8 May 2013 (UTC)

Remote Sensing

I am trying to learn how remote sensing developed over the course of time beginning in the seventies. It would be helpful to find the Proceedings for the Annual Meetings of The American Society for Photogrammetry during that period of time. Where can I find them? Clues: not WorldCat and not the American Society for Photogrammetry and Remote Sensing. — Preceding unsigned comment added by Bobgustafson1 (talk • contribs) 19:21, 7 May 2013 (UTC)

Venus fly trap digestion

I understand that the digestion process of the prey of a Venus fly trap may take several days, but how long does it take for the prey to actually die? What is the process that kills it? Against the current (talk) 20:07, 7 May 2013 (UTC)

If no one is able to answer here, you could ask at Wikipedia talk:WikiProject Carnivorous plants.

—Wavelength (talk) 21:30, 7 May 2013 (UTC)

I don't know how long it takes for the bug to die, but the process that kills it is almost certainly chemical poisoning. 24.23.196.85 (talk) 00:18, 8 May 2013 (UTC)

Insects breathe through trachea that open via spiracles on the sides of their abdomen. Once digestive juices get in these they will smother, if not already. μηδείς (talk) 00:56, 8 May 2013 (UTC)

Why does stirred water reverse direction slightly just before reaching a stop?

Stirred me tea with a tea bag in it. Round and round the tea bag goes, in the direction stirred. Eventually the tea bag comes to rest... well, almost: before it does it goes back a small amount in the opposite direction. What causes this reverse? It's as if the water is slightly elastic. At first I thought it may be an illusion caused by watching the bag going round. But on careful observation I am sure it does go backwards. --bodnotbod (talk) 22:44, 7 May 2013 (UTC)

Maybe the teabag strayed across the centre of the vortex, and the remaining angular momentum created a torque in just the right way to turn the teabag in the other direction. Plasmic Physics (talk) 23:19, 7 May 2013 (UTC)

Water is most certainly not elastic, it does not retain a memory of a previous state. Plasmic Physics (talk) 23:23, 7 May 2013 (UTC)

It is worth considering that we are dealing with a three-dimensional flow here. It might be worth trying it in a glass rather than a cup, to see if that helps explain it. AndyTheGrump (talk) 23:28, 7 May 2013 (UTC)

I think this could be a backflow caused by the vortex collapsing on itself as the flow velocity drops toward zero. FWiW 24.23.196.85 (talk) 00:12, 8 May 2013 (UTC)

The teabag could be "elastic".... It would almost certainly have less mass then the water, could it be somehow rebounding off the water? Vespine (talk) 00:14, 8 May 2013 (UTC)

Isn't this how they power the TARDIS? μηδείς (talk) 00:52, 8 May 2013 (UTC)

You're thinking of the Heart Of Gold, but close. Tevildo (talk) 01:04, 8 May 2013 (UTC)

Actually, I was just making sure people were paying attention. :D μηδείς (talk) 01:44, 8 May 2013 (UTC)

Sodium carbonate electrolysis?

Carbon dioxide scrubber says that you could electrolyze a sodium carbonate solution to get CO2 out from the carbonate returning it back to sodium hydroxide. But there is very little about that in google (like searching for sodium carbonate electrolysis) so I have a question: What gasses will be generated at the cathode and the anode while electrolyzing sodium carbonate in water?118.136.5.235 (talk) 23:28, 7 May 2013 (UTC)

Anode -- CO2 only; cathode -- none (if the product is NaOH). However, it is possible to electrolyze molten sodium carbonate all the way to sodium metal, in which case both CO2 and oxygen will be generated at the anode, and hydrogen at the cathode. Also, converting sodium carbonate to sodium hydroxide does not require electrolysis -- simply distilling a hot solution of the carbonate with steam under vacuum can produce the hydroxide by stripping out the CO2 (this is actually done on an industrial scale in some coke plants). 24.23.196.85 (talk) 23:55, 7 May 2013 (UTC)

This isn't strictly electrolysis, as this is not a redox reaction. The oxidation states of all elements stay the same on both sides of the reaction. It is merely a non-redox Chemical decomposition of a metal carbonate. You get sodium hydroxide merely because sodium oxide pretty much instantly forms sodium oxide in water. You need to use electric current to generate enough energy in a water based solution, as you can't get enough energy from heating it, but you can use heat to decompose solid sodium carbonate into sodium oxide and carbon dioxide just fine. The water present in solution, however, prevents this from happening when heated: you can't get the solution much above the boiling point, which is not a high enough temperature to cause the decomposition. --Jayron32 00:01, 8 May 2013 (UTC)

May 8

Predicting the history can be wrong

Is there any other field in science besides astrophysics and predicting the far distance events in astronomy involves speculations and unreliable guesses. My mind is straight-forward-thinking that is why I thought academic research papers are just well-written, I was never aware they have guesses and unreliable speculations. Plate tectonics:, I have seen several different websites discussing how will the continents reshape itself in the 100s of million year future, all the scientist just come up with 10s or different results. I thought prediction the geology history are quite accurate, because of the fossils we have gives us. I thought prediction 500 million years ago to 600 million years ago, dating things that far back are still pretty accurate. Between Mesozoic and Jurassic period, and 70 million years ago up to today geological scale, I never hear any observation error based on where the continents were placed. I there is errors found in Mesozoic, Jurassic, where may they have messed up?--69.233.254.115 (talk) 00:29, 8 May 2013 (UTC)

It's much easier to go backward than forward. Going backward is like putting together a jigsaw puzzle. For example, the east coast of South America fits neatly into the west coast of Africa, and when you line them up, the surface rock formations also match nicely. But going forward requires understanding the mechanisms that make plates move, and the simple fact is that we don't. We can project forward about 100 million years by assuming that plates will continue to move at their current rates, but beyond that, everything is guesswork. We know that plates sometimes change their direction of motion, but we don't know why. (The most popular theory is that the motion is driven by mantle plumes, but that theory is controversial and in any case nobody knows for sure how mantle plumes change over time.)

Even I, who like to think I understand this stuff to some degree, have been tricked by all the speculations. I have a National Geographic atlas that confidently shows the state of the Earth 250 million years in the future, with all the continents coalescing into Pangaea Ultima. It took me a lot of reading to figure out that this is really no more than one person's wild-ass guess.

But to step back from this, making predictions of this sort is simply part of the process of science. Scientists know that every prediction is based on theory and data, and the weaker the quality of the theory or data, the less meaningful the prediction. Geologists know enough not to take these plate tectonic predictions very seriously. The problem comes when predictions are fed to the general public, who don't have enough background knowledge to judge them. Looie496 (talk) 01:24, 8 May 2013 (UTC)

Probably the best, and these days the most important, is the science of climate change. Climate change boffins use computer models to predict what tempertures, sea level, and storm activity will be like 50, 100, or more years to come. Almost all expect all three to increase, but the range of predictions does not inspire confidence that this is a well understood science. All modelling is done by making simplifying assumptions - that is, what are at best judement calls, and at worst, no more than wild guesses, as to what factors to include and what factors to ignore, in order to make computer modelling simple enough to actually do.

Wickwack 120.145.46.40 (talk) 02:02, 8 May 2013 (UTC)

Nasal congestion and sleep

Whenever I have a cold I notice that my congestion is completely gone when I wake up in the morning, and that it comes back within a few minutes of waking up. Does this phenomenon have a name / has it been studied in the literature? Could it potentially be exploited in medications? DTLHS (talk) 01:19, 8 May 2013 (UTC)

It nearly always works the other way round for me. But either way, you can buy decongestant medicines from chemists. Wickwack 120.145.46.40 (talk) 01:25, 8 May 2013 (UTC)

Sinuses will drain differently depending on your attitude, but you really need to take it up with a doctor. μηδείς (talk) 01:42, 8 May 2013 (UTC)

Can sun actually magnify electromagnetic waves as depicted in Three Body (science fiction)?

--朝鲜的轮子 (talk) 01:19, 8 May 2013 (UTC)

Bird question

What bird species consume (1) the most insects by weight, and/or (2) the most flying insects by weight (in absolute terms, not relative to their body size)? 24.23.196.85 (talk) 01:55, 8 May 2013 (UTC)