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November 5

7 or 10 listeria species?

I'm confused because in the beginning of the article is written that "Listeria is a genus of bacteria that contains seven species:", and later in this article itself:" The genus Listeria currently contains ten species: L. fleischmannii, L. grayi, L. innocua, L. ivanovii, L. marthii, L. monocytogenes, L. rocourtiae, L. seeligeri, L. weihenstephanensis and L. welshimeri.". so what's right? 213.57.99.33 (talk) 03:50, 5 November 2014 (UTC)

Another one: "the overt form of the disease has a mortality rate of about 20 percent" while in this article itself says: "The case fatality rate for those with a severe form of infection may approach 25%". it looks like as if many people the article without reading the previous things. 213.57.99.33 (talk) 03:55, 5 November 2014 (UTC)

Without getting into the specifics of this article; this may be the case of people (likely multiple different editors) adding information from multiple sources and different times. I would not be entirely surprised that different sources would disagree on exactly how many species of Listeria there were, or that different studies would come out with different data as to mortality/fatality rates (especially where the sources may not even be measuring comparable things). --Jayron32 04:00, 5 November 2014 (UTC)

If all the sources are reliable, the solution is to say there are 7-10 species with a 20-25% fatality rate. As for why they can't agree on the number of species, there could either be disagreement on whether 3 are listeria, or whether those 3 are separate species or just strains of other listeria species. StuRat (talk) 12:08, 5 November 2014 (UTC)

This all seems reasonable. I'll remind the OP that Misplaced Pages:Wikipedia_is_not_a_reliable_source, and this kind of thing is to be expected, especially in biology/taxonomy, where there are few universally "correct" answers. Even textbooks have this kind of issue, but they are written by experts who know when to leave out details, or know what study is most relevant for the current topic. SemanticMantis (talk) 15:52, 5 November 2014 (UTC)

Why does infusion bag need an expiration date?

I would like to understand why does "infusion bags" need an expiration date. What does it say when the date comes? it says this is a time it has a high potential to be contaminated? the same question about Oxygen tanks that have an expiration date. 213.57.99.33 (talk) 05:25, 5 November 2014 (UTC)

I suppose the assumption is that you expect those things to be "sterile", uncontaminated, fresh, etc with a HIGH degree of certainty. Under ideal conditions, I guess you'd expect the oxygen in a sealed tank to remain uncontaminated "oxygen" for a very, very long time, but there are seals, gaskets, perhaps lubricants, which do not last indefinitely. tanks can get knocked around, dropped, bags get handled, bent, folded... To be certain the item you have is "good" it should be below a certain age. Vespine (talk) 05:53, 5 November 2014 (UTC)

Also, plastic infusion bags may contain chemicals which slowly leak into the contents. The longer they sit, the more leaching occurs. And the manufacturers probably only test them to a certain age, so can't say one way or the other if they are good past that age. StuRat (talk) 12:05, 5 November 2014 (UTC)

It's commonly the case with medical supplies that the legal requirement to specify how long the product is good for is onerous for the manufacturers to test. If I come out with some new infusion bag, if I want to stick a 10 year expiration sticker on it - then I have to prove to the FDA that it'll still be OK in 10 years - and it could easily take me 10 years of testing to prove that...even if I know that the plastics it's made from should last for 1,000 years. Since I'll go bankrupt if I have to sit around for 10 years testing without being able to sell a single infusion bag, I'm much more likely to test for 1 year and put a 1 year sticker on it...even though the product might easily last 100 years.

The FDA created this rule in 1976 - and they weren't trying to be very subtle about it. So *all* drugs, *all* supplies and *all* medical devices are required to have an expiration date, even if they are some simple mechanical item or something that seems to be obviously safe - like a gas cylinder. This is why cotton balls used in hospitals cost twenty times what cotton balls sold to the general public for makeup removal cost...and have an expiration date of a few years - even though they are the exact same product you use at home with no expiration date.

There was a case some time ago (see ) when the US military had a small mountain of drugs that they'd stockpiled in case of some hypothetical emergency - which were due to expire quite soon, or which had already expired. The cost of dumping all of those drugs lead them to actually test their viability and they found that 15 years after the expiration date, 90% of the kinds of drugs they had were still just as good as the day they were purchased...so they extended the expiration dates. But it's rare for organizations to have such gigantic stock-piles of unused drugs (or infusion bags or whatever), so the cost of re-testing them by far exceeds the cost of tossing them out and replacing them. So in general, tons of completely usable, safe, materials are dumped just because nobody can afford to keep testing them.

SteveBaker (talk) 16:22, 5 November 2014 (UTC)

Wouldn’t disagree with anything Steve said yet to add only that infusion bags can become contaminated over time by the plasticisers used in plastic that the bag is made from. See the section PVC and DEHP in medical products: --Aspro (talk) 22:16, 6 November 2014 (UTC)

the Oxygen in the tanks is in liquid or gas condition?

213.57.99.33 (talk) 08:40, 5 November 2014 (UTC)

The critical point of oxygen is -118.56°C (ref Wolfram Alpha). Thus it needs to be kept below that temperature to be liquefied. LOX (liquid oxygen) is used for rockets, but not generally for other purposes. CS Miller (talk) 12:23, 5 November 2014 (UTC)

supercritical oxygen could be thought of as a liquid if it is condensed to the density to be expected of liquid oxygen; but it would still (even under those conditions) more closely resemble a gas, as the molecules will still have enough kinetic energy to overcome the bonding energy necessary to hold the molecules in a true "liquid" phase. That's the molecular definition of a supercritical fluid: the temperature at which the kinetic energy of the molecules is greater than the energy needed to hold the molecules together. --Jayron32 13:42, 5 November 2014 (UTC)

Liquid at 200-300 bar. --Kharon (talk) 12:24, 5 November 2014 (UTC)

Why would you say that, Kharon? With a critical point of 154.581 K, 5.043 MPa = 50.43 bar, room temperature (non-cryogenic) O2 at 200 bar is a supercritical fluid, but it is far above its critical temperature, and at a pressure where its molar volume is still four times that liquid oxygen, so as Jayron32 points out, its physical behavior will be very gas-like. Were you, perhaps, thinking of carbon dioxide? -- ToE 08:08, 9 November 2014 (UTC)

Both. You can get industrial/hospital oxygen in both compressed gas ranges and liquid ranges. The large Dewer tanks are liquid and have oxygen vapor that is extracted. Most hospitals will have liquid as the refill requirements does not require purging. Compressed oxygen in a tank (like portable ones) need to be evacuated and have a vacuum pulled on them to meet codes for medical oxygen refills. --DHeyward (talk) 21:28, 10 November 2014 (UTC)

Man turns mobile off whilst committing crime?

I've taken the liberty of moving this to Misplaced Pages:Reference desk/Humanities#Man turns mobile off whilst committing crime?, which discusses legal and social matters. Wnt (talk) 13:31, 5 November 2014 (UTC)

Note: if you are actually interested in how precisely companies can determine when a cell phone was off, I'd probably recommend the Computing refdesk, but be clearer when you ask that you're interested in technical capabilities rather than admissibility. Wnt (talk) 13:38, 5 November 2014 (UTC)

How common are capacitors that can hold a charge for several days?

Are there any household machines (or anything that private people use) that use these? The wash-machine maybe, the car? How much electricity can they be charged with?--Senteni (talk) 18:36, 5 November 2014 (UTC)

I can't answer with numbers, but proper safety practice calls for adding Bleeder resistors. Ariel. (talk) 19:54, 5 November 2014 (UTC)

Old televisions (CRT type) have large capacitors. Rmhermen (talk) 22:17, 5 November 2014 (UTC)

There are few (if any) modern household appliances that do this - mostly because it's potentially dangerous. I have a couple of laser cutters that have capacitors that retain enough charge after a couple of hours to produce a three inch spark at a few thousand volts...these are hardly "household" appliances but plenty of hobbyists have them. so they fit the "anything that private people use" category.

Our article mentions the flash unit on a disposable camera as containing a potentially lethal capacitor...those things are becoming rare - but you still probably still find them in people's homes.

I once got electrocuted by one of those. It went in one side of the finger and came out the same side, close by. It kind melted a bit of skin, turned that part white from pinkish yellow and made a burnt skin smell. Holy crap, those things can kill? (If the heart is in the path and it can't be restarted in time is the easiest I assume). Sagittarian Milky Way (talk) 21:53, 9 November 2014 (UTC)

Supercapacitors can store immense charges - but they start to blur the line with rechargeable batteries, which, in a sense are just capacitors too. SteveBaker (talk) 23:58, 5 November 2014 (UTC)

Just to help us get a feel for it, can you quantify the size of your capacitors? Are we talking a few Farads, or many? SemanticMantis (talk) 15:22, 6 November 2014 (UTC)

• If the two ends of a capacitor are very well insulated from each other, its ability to hold charge is determined by its leakage rate. I believe that most ordinary capacitors are capable of holding a charge for days without major loss. Low-leakage capacitors can hold a charge for months. The maximum charge that a capacitor can hold is determined by its dielectric breakdown point, which depends on the quality of construction. Looie496 (talk) 16:25, 6 November 2014 (UTC)

understanding the waveform representation

If an oscillogram depicts a wave around the x axis, and there are values that are positive and negative for the y-axis. The y-axis represents frequency, but how can the frequency be negative? And don't we need multiple values at the same time on the y-axis for all frequencies? Think https://en.wikipedia.org/Praat#mediaviewer/File:Spectrogram_-_mot%C3%A1ngo_mwa_basod%C3%A1.png --Senteni (talk) 19:57, 5 November 2014 (UTC)

An oscilligram depicts amplitude vs. time (not frequency vs. time). Typically, there is some sensitive element that responds to sound waves (such as a microphone transducer), and the y-axis is proportional to the back and forth fluctuations in that element caused by passing sound waves. Dragons flight (talk) 20:04, 5 November 2014 (UTC)

On the image in question, the upper trace is an oscillogram (with positive and negative y-axis values), and the lower trace is a spectrogram (with only positive y-values). Tevildo (talk) 20:12, 5 November 2014 (UTC)

That's a confusing plot to say the least. The upper window appears to be the time history of the sound waveform, in black. As such it will oscillate around 0 Pa. I suspect the vertical blue lines represent the occurence of peaks in the time history, the interval of which is plotted as its reciprocal in the blue curve in the lower plot. The lower plot is what I'd call a spectogram, a 2d representation with frequency on the y axis, time on the x axis, and intensity of that frequency and time represented by grey scale. I do not understand the left and right hand y axis notations, the red dots appear to be some sort of peak picking algorithm. Greglocock (talk) 22:38, 5 November 2014 (UTC)

It's not confusing if you are familiar with spectrograms. I would go so far as to call this a "standard" plot format for certain types of digital signal processing. Nimur (talk) 22:34, 5 November 2014 (UTC)

Oh yes, try explaining to an engineer why there are two y axis scales and no explanation as to which data uses which one! Greglocock (talk) 22:38, 5 November 2014 (UTC)

Regarding the plot arrangement: there are two plots. One who is familiar with waveform analysis will very quickly visually identify that the two plots correspond to a waveform and a spectrogram. One who is unfamiliar would do well to read the caption.

Regarding the colors: the image has a caption:

• light blue line = pitch (as documented)
• dark blue lines = pulses
• red dots = formants (as documented)

Here is a link to the Praat software tool official website.

Here's a tutorial, Praat Sound Window, from UNC's computational linguistics program.

Nimur (talk) 22:44, 5 November 2014 (UTC)

Black Holes, Dark Matter, General Relativity

Why aren't dark matter, black holes and general relativity labeled as pseudoscience? All three concepts fit the description of pseudoscience very well. We do not need to delete these articles, just label them correctly. Wavyinfinity (talk) 21:28, 5 November 2014 (UTC)

Who says they're pseudoscience? ←Baseball Bugs carrots→ 21:35, 5 November 2014 (UTC)

Because e.g. black holes are not pseudoscience. Our article defines: "Pseudoscience is a claim, belief or practice which is falsely presented as scientific, but does not adhere to a valid scientific method, lacks supporting scientific evidence or plausibility, cannot be reliably tested, or otherwise lacks scientific status."

Black holes are considered plausible by the astrophysics community. They have plenty of scientific evidence for their existence and most published results about them conform to the scientific method. We even have a whole section on Black_hole#Observational_evidence. The same goes for dark matter and general relativity (they are topics in science, not pseudoscience), which I think you'd know if you'd read the articles carefully. I'm assuming good faith here, but you should know that your question sounds a bit like trolling. SemanticMantis (talk) 21:37, 5 November 2014 (UTC)

(edit conflict)No, they don't fit the description you claim, because they are attempts to explain observations. Science starts with evidence and develops theory to explain it. (I agree that sometimes speculative science puts forward a theory that goes beyond the available evidence, but it then looks for evidence to confirm or refute the extended theory.) Have you read the articles that you link? (Do you believe in infinity? ) Dbfirs 21:38, 5 November 2014 (UTC)

Read the essay on the user's page and it will be clearer where he's coming from . ←Baseball Bugs carrots→ 21:41, 5 November 2014 (UTC)

The definition of pseudoscience (at least according to Wiktionary) is:

"Any body of knowledge purported to be scientific or supported by science but which fails to comply with the scientific method."

(Other dictionaries define it similarly)

So:

1. Do these fields of study "purport to be scientific"? Well, yes...duh!
2. Do they "comply with the scientific method"? Yes, they do. They propose hypotheses, they make predictions that are (at least in principle) testable, they don't make unfalsifiable claims, they perform experiments and/or observations in an effort to prove (or disprove) those predictions. They publish results in peer-reviewed mainstream journals. Experiments and/or observations are repeated independently where possible. This is "THE SCIENTIFIC METHOD" at it's finest.

Now, it's very possible that any or all of these things might turn out to be false. But that's not the acid test of pseudoscience.

Pseudoscience is something like Homeopathy where they make scientific claims (in this case that diluting some active ingredient to the point where there is none left leaves a stable 'imprint' in the water - and that the resulting water can cure illnesses) - but they do not create working hypotheses, they do not perform experiments (like a double-blind drug trial would do), they don't do peer reviews and publish results in mainstream journals. They are making clearly testable scientific claims yet NOT following the scientific method...so they are pseudosciences.

A religion, on the other hand does NOT make scientifically testable claims (their claims are generally non-falsifiable) - so the scientific method is inapplicable, even in principle - so they are not pseudoscience.

Pseudoscience is NOT the same thing as bad science or unproven science or disproven science. So even if you believe that black holes do not exist - that doesn't make the field of study "pseudoscience".

Cold fusion is a good case in point. It was claimed to occur, they tried to do experiments to prove it, the experiments were written up, peer reviewed and published, efforts to repeat the experiments failed - and now it's (generally) believed to be false. But it's definitely science and not pseudoscience because they followed the scientific method. Our article correctly labels it as "pathological science" - but not pseudoscience.

Misplaced Pages has very clear rules about pseudoscience and how it's determined and labelled - and the things you mention are not remotely it.

If you want a target to attack, you might try Freudian psychoanalysis (for example) - which makes scientific claims and has historically failed to do serious experimentation to back up those claims.

SteveBaker (talk) 23:37, 5 November 2014 (UTC)

It's nice that you all are trying here, but I feel the need to bring forth this rather reliably true aphorism: You cannot reason a person out of a position they did not arrive at via reason. The entire question above, and their entire main Misplaced Pages page screams "Science is hard and stuff, and it's easier to reject the things I don't understand than to either a) understand it or b) trust the people that do". It does no good to argue with people this far out of touch with reality. At best we can remind the rest of the world how silly they are. But people like this are a lost cause. --Jayron32 00:23, 6 November 2014 (UTC)

Given the following quote on the user's page, the full screen of discussion here is somewhat amusing:

"1. Hit and Run tactics. Post things on public forums like Einstein was an idiot, Stephen Hawking is a pawn for the mathematical priests of establishment. Do not respond to the replies, just post these things and then do something else with your time. You must insert ideas that can not be said otherwise because they are taboo. These taboo statements are incredibly dangerous to establishment."

MChesterMC (talk) 09:23, 6 November 2014 (UTC)

"The establishment", sure. It would be interesting to see a public opinion poll as to what percentage of the public either knows or cares about this subject. ←Baseball Bugs carrots→ 11:51, 6 November 2014 (UTC)

I suggest you take greater caution in the future. I'm not going to report you, but your topic ban seems very broad "everything related to astrophysics or cosmology" User talk:Wavyinfinity#Arbitration enforcement topic ban: Pseudoscience so it can likely be said to apply to the RD, particularly since, as many including the topic closer have suggested, you appear to be either trolling or soapboxing/POV pushing rather than asking a genuine question even if it's not clear you're trying to harm wikipedia by advocating for changing articles. I presume you know it's very broad, since you were blocked for fooling around with a wikiproject . Nil Einne (talk) 18:01, 6 November 2014 (UTC)

How would Freud Interpret This Dream?

Just out of curiosity i always wanted to know how sigmund freud would interpret this dream, with his theory of dream analysis.The dream itself is something like this a man walks down a flight of stairs following a trail of blood to find his father lying in a pool of blood. This has always been something i wanted to know. Help from my fellow wikipedians would be greatly appreciated, THANKS. — Preceding unsigned comment added by 173.52.22.58 (talk) 22:45, 5 November 2014 (UTC)

We can never know what a dead person would think, but you can read about what he did think!

The Interpretation of Dreams (1900) is available at no cost in German from Project Gutenberg, and in English from other websites. Several other translations are listed in our article. Another of his works, Dream Psychology (1920) is available in English from Project Gutenberg.

I read The Interpretation of Dreams a long time ago. Reading Freud's own writing proved to me to be the most damning cases against Freudian psychology as a scientific enterprise. Nimur (talk) 22:52, 5 November 2014 (UTC)

If someone else's interpretation can help you, walking down stairs "might suggest being in control of a changing situation." Bleeding (from the same source) "could mean hurtful remarks, for instance being told we are not loved." Seeing a dead parent is "either the beginning of independence from parent or repression of the emotions they engendered in us."

In my absolutely unprofessional opinion, you murdered your father and mostly forgot about it. Also, your house is haunted. InedibleHulk (talk) 23:03, November 5, 2014 (UTC)

The dream is about anxiety. Now, donate 5 dollars to your favorite charity, in my name. ←Baseball Bugs carrots→ 23:11, 5 November 2014 (UTC)

• Of course we can't know what Freud would have said, but it isn't hard to guess. The fundamental tenet of Freud's theory was that all dreams consist of wish fulfilment. What sort of wish is being fulfilled in that dream? Well, another basic tenet of Freudian theory is that every male child has an Oedipal desire for his mother and therefore is jealous of his father. So this one is pretty easy. (My personal view is that the idea of dreams as wish fulfilment has some validity, but doesn't apply to all dreams and in any case Freud's use of it was utter bullshit.) Looie496 (talk) 16:12, 6 November 2014 (UTC)
  • I always figured Freud was into that, and assumed everyone else was too. ←Baseball Bugs carrots→ 16:29, 6 November 2014 (UTC)

Can an healthy man use a medical oxygen for breathing?

I've heard that using of a medical oxygen when it's not needed, is harmful. That's right and based on a reliable source? 213.57.99.33 (talk) 23:18, 5 November 2014 (UTC)

I think this is bordering on medical advice - and we're not allowed to provide that here on the ref desk. SteveBaker (talk) 23:22, 5 November 2014 (UTC)

The OP should consult Google, which I expect would have many references (albeit many of them bad information). ←Baseball Bugs carrots→ 23:26, 5 November 2014 (UTC)

No, the OP should consult a doctor. SteveBaker (talk) 23:38, 5 November 2014 (UTC)

Oh, please. The OP is seeking information, not advice, and even if advice were sought, we are at liberty to provide information not related to a specific case. Aside from pointing out that medical oxygen is essentially pure oxygen, the oxygen toxicity article linked by InedibleHulk below is probably a good place to start. Essentially, unless unusual conditions exist or where ambient pressure is elevated above that at sea level, there is no reason to suggest that breathing pure oxygen, especially over a limited period, would be harmful to the majority of individuals. —Quondum 00:09, 6 November 2014 (UTC)

I'm pretty sure we're allowed to say oxygen toxicity exists. InedibleHulk (talk) 23:46, November 5, 2014 (UTC)

Thank you. I've found this article: Oxygen therapy, and it refers this issue. (By the way, it's so interesting to understand why this information is bordering on medical advice - when it's in the article.213.57.99.33 (talk) 23:51, 5 November 2014 (UTC)

The issue is that what's in the article has been massaged over the years by many editors to be good, well sourced content. What gets written here is not in the same class. Anyone can write anything they think of here. Not to be trusted. (Not even my comments.) HiLo48 (talk) 00:01, 6 November 2014 (UTC)

Though if we refer people to that good, well-sourced content, it's not us they're trusting. If they even need to be trusting in the first place. The question didn't suggest "I'm considering taking oxygen I don't need. What should I do?" to me. Just looking for a source to verify whether it's generally harmful. Almost every question here can be taken with suspicions about the asker's reasons, but if they're not provided, I assume generic curiosity. Telling people to consult a doctor is medical and often financial advice, even if the assumption that they need one is correct. InedibleHulk (talk) 00:24, November 6, 2014 (UTC)

Hyperventilating with pure oxygen is necessary if you need to hold your breath for a long time. Count Iblis (talk) 04:29, 6 November 2014 (UTC)

• If the OP is a medical volunteer he should also ask his supervisor whether he should be researching such questions here. I had a friend training as an EMT in college who lost his job because he listed a patient's body temperature as 95F when tradition required it be rounded to the nearest even number. Should you suddenly come out with "but I was told on wikipedia that..." you may find yourself summarily dismissed. μηδείς (talk) 17:12, 6 November 2014 (UTC)

Our article on oxygen toxicity covers the main points that I'm aware of as a former clinical data analyst and biomedical engineering technologist. Further than that, I agree we oughtn't to be giving advice on when and how oxygen ought to be used to questioners. We don't know what their health status or their reasons for asking are, and any information beyond sourced material in the oxygen toxicity article falls under the general medical advice prohibition here.

It occurs to me that the OP seemed to be asking how safe medical oxygen was compared to, say, oxygen intended for SCUBA mix or welding oxygen. The same hazards listed in our article on oxygen toxicity apply regardless of whether the oxygen is USP (prepared according to the specs in the United States Pharmacopeia for medical use), non-medical oxygen for SCUBA or other nonmedical life support applications, or industrial oxygen (except that additional hazards may exist when industrial (welding) oxygen is used owing to impurities. loupgarous (talk) 01:02, 7 November 2014 (UTC)

Both oughtn't and ought not have become rare in North America. Oughtn't in particular may not be understood  :) Count Iblis (talk) 19:47, 7 November 2014 (UTC)

November 6

filling an oxygen in the bottles from three others continuously

I've noticed when the First-Aid-responders fill their small tanks, they fill the oxygen by three big tanks. It says, they take one small tank (2 liter approximately) and connect it to one big tank and open the tap, after a minute they close the tap they pass the small tank to another tank big one for a minute, and eventually they do the same processes with another big one tank (third time...) I'm volunteer student, and I would like to understand what happen here... 213.57.99.33 (talk) 00:08, 6 November 2014 (UTC)

My supposition is that this arrangement results in a higher final pressure for all the small tanks than if the three big tanks were simply connected in parallel, or used individually. The first big tank loses the most pressure, but the pre-pressurisation of the small tank to whatever its pressure is results in the second big tank losing much less and retaining a higher pressure, and the repetition on the second tank preserves most of the pressure in the final topping-up tank. —Quondum 00:25, 6 November 2014 (UTC)

(edit conflict) Can you point to any images or documents that show this behavior? The process you describe is probably specific to the equipment being used, so I doubt we'll be able to give any kind of a definite answer without more context. Dragons flight (talk) 00:27, 6 November 2014 (UTC)

Here's a nice article from Praxair (one of the largest commercial suppliers of gas products in the United States): An Inside Look. I know from personal experience: it is really complicated to fill a tank with cryogenic liquid/gas like Liquid Oxygen! There are a lot of safety procedures and a lot of practical problems. For example, do you tap from the top or the bottom of the tank? The answer depends on what you are doing. As you fill, the temperatures and pressures in the supply- and the destination vessel are changing - gas always flows from high pressure to low pressure. If there's a gas pressure head, it will drive the liquid to flow in the same direction - even working against gravity! If you aren't carefully watching the pressure, you might be using the small tank to fill the big tank! Be sure to follow safe procedures when you are working with oxygen (... it is a strong oxidizer)! Nimur (talk) 00:39, 6 November 2014 (UTC)

(EC) It sounds like you're referring to a Cascade storage system used for transfilling. Note that images e.g. you can see may be a bit confusing (and I didn't find the explanation in our article very good and most search results are just vendors). It looks like all the tanks are connected together and there is only one output valve you connect to, which may suggest you're using them all at once. However as can be seen in this video , you only open one of the large tanks at a time, moving from low pressure to high pressure which seems to be similar to what you were describing (well you didn't know/mention pressure differentials).

The reasons appear similar to what Quondum said, and as described in the video and also to some extent here . You basically start with a low pressure tank, fill the bottle to equilbrium, and then close it and move on to the next higher pressure one until you reach the desired pressure. That way you can end up with a relatively high pressure in the last larger bottle (which you may not use at all, if your earlier ones are high enough).

Once the last/highest pressure larger bottle is below the minimum pressure needed for you final fill or alternatively if the first/lowest pressure is so low it's rarely useful (like if the tanks you're filling would generally be at a higher pressure), you can just remove the lowest pressure bottle (to be an empty to be filled. And replace it with a full bottle, now the new last tank. You renumber the bottles rather than moving them around, I presume because it's safer and easier.

So you don't end up with a lot of low pressure bottles that are below the minimum needed but still have a fair amount of oxygen (or whatever), in other words, you get more from each large bottle for a given pressure. I'm not sure but there may also be an advantage in possibly reduced temperatures changes, a lower pressure differential and easier monitoring for safety reasons.

The disadvantage may be , although I'm not sure that using a single bottle will help in any way. It may be the alternative the commentators in that link are thinking of is professionally/externally filling the small bottles rather than using a cascading storage system to fill the small bottles by someone for who it isn't their primary job.

BTW, it's somewhat unclear to me if in your example the larger bottles are all connected together (although I note you seem to have added the same video below). As mentioned, this appears to be the norm in such systems (based on the images and vendors) and there would seem to be advantages (namely you aren't moving and reattaching the smaller bottle so much which would seem to be an avenue for mistakes) but I guess it's possible for cost or other reasons, in your example they aren't. I presume they otherwise work similar.

P.S. In terms of numbers, if you only ever use 3 in this set-up before you need to replace the lowest pressure one, then I guess there's probably no advantage to adding 4 more to get 7. Unless for some reason you prefer to keep the "empty" ones in situ and simply unnumber or whatever and don't use them until they are replaced in bulk. Which is possible, since they are probably quite heavy and there are likely additional safety precautions. Nil Einne (talk) 01:28, 6 November 2014 (UTC)

It's kind of what we see in this video (but we have only three big tanks, here there is 7 I think). I must to say, that the three big tanks that I'm talking about they are the same thing: oxigen. (it's written on) 213.57.99.33 (talk) 01:02, 6 November 2014 (UTC)

That cascade storage system article makes a lot of sense. Basically, I assume that the site wouldn't want to return every oxygen container to be refilled the moment its pressure drops below whatever they're filling the little containers up to. Not when you can still use the depleted containers to fill little containers that are nearly empty... the rest follows logically. To me this seems very similar in concept to a countercurrent exchange. Wnt (talk) 02:52, 6 November 2014 (UTC)

This is a really neat analogy. With enough bottles in the cascade, one would expect that energy put into the compressed gas in the small cylinders is transferred from the cascade with efficiency approaching 100% (asymptotically); also, the cooling due to decompression will be asymptotically zero. —Quondum 14:08, 6 November 2014 (UTC)

The relation between Pulmonary embolism and birth

From time to time we hear about women who get PE (Pulmonary Embolism) as a result of birth. My question is what is the relation between the two. And why does the birth raise the risk of getting it? 213.57.99.33 (talk) 01:13, 6 November 2014 (UTC)

In this freely-available, high-quality article describing the risk factors for venous thromboembolism (e.g. PE), the authors note that the risk starts rising in the first trimester, and is primarily attributable to changes in the blood levels of clotting (and natural anticoagulant) factors. They argue teleologically that the shift to increased tendency for clotting might protect against hemorrhage, a major cause of death during pregnancy. -- Scray (talk) 02:02, 6 November 2014 (UTC)

Thank you deeply! now it makes sense. 213.57.99.33 (talk) 02:14, 6 November 2014 (UTC)

Air permeability of glass

Hi. the article on Spontaneous Generation has this picture of a glass flask sealed by Louis Pasteur in the 1860s. Let's assume for the sake of argument that there are no microfractures from the sealing process, and the glass is all uniformly unblemished. Is the air inside it the same air (in other words, all the same atoms) that were sealed in 150 years ago? My Dad and I had a disagreement; he felt that the majority of it would have cycled through, my impression was that, even if it's not "all" the same air it's surely mostly the same. Looking for data with Google gave me inconclusive info, but it seems like glass is (to some greater or lesser degree) permeable by air. Does anyone have any info on just "how" permeable it is? Anyone care to make an estimate of what percentage of the atoms currently in the flask (stored carefully but not exhaustively so in a lab and then a museum archive) would have been in there in the 1860s? Obviously, there would be some degree of temperature and thus pressure fluctuation driving air in and out (assuming glass is to some degree permeable). Clearly it's not very permeable by water because there's still broth in it (though whether the amount of broth has changed in the last 150 years is a separate question), but H2O would seem (to this non-chemist) to be a much larger molecule than H or N or O that make up the majority of air. 75.140.88.172 (talk) 08:07, 6 November 2014 (UTC)

I find it HIGHLY unlikely. The internuclear distance between the silicon and oxygen atoms in SiO₂ (glass, quartz, etc) is about 1.67 angstroms (0.167 nanometers).. Air is basically a mixture of O₂ and N₂. The internuclear distance between oxygen and nitrogen atoms in molecules of O₂ and N₂ is 0.120 nm and 0.110 nm respectively: . So, IF you had a sheet of glass that consisted of a SINGLE atomic layer of silicon dioxide the pore size would JUST be big enough to let a molecule of air slip through OCCASIONALLY, if it hit the EXACT hole at the EXACT right angle, maybe. In glass as thick as that flask, you've got a network many trillions and trillions of atoms thick; there just aren't any pores large enough to let any molecules of the air through, given the tolerances we're talking about here. Ain't no way. Assuming there isn't any other way for the air to leak out, it certainly isn't coming through the glass itself. --Jayron32 12:21, 6 November 2014 (UTC)

Diffusion does occur in solids. Water, in fact, is particularly fast as it actually reacts with silica up to about 1% of its normal density! At high temperatures, the effective diffusion coefficient is high enough that the glass is quite permeable indeed; I get a 6-meter scale length for the diffusion profile after 150 a. However, at room temperature the Arrhenius equation predicts so much slower a process that the scale length is just 3 μm. The diffusion coefficients for air are theoretically larger at high temperatures (above 1500 K, which (coincidentally?) is the glass transition temperature for fused quartz), but because it cannot diffuse chemically, the activation energy is almost twice as large and the room temperature rates are much smaller. It looks like room-temperature nitrogen can cross only about one atomic layer in the glass even over 150 a. --Tardis (talk) 14:53, 6 November 2014 (UTC)

Nice explanations, I think the OP has a good answer now. Related: does anyone think this would be worth adding to our article on Long-term_experiments? On the one hand, we could say the experiment is over, and helped disprove spontaneous generation. On the other hand, we could say that it has only disproven spontaneous generation on a ~150 yr time scale! I see this jar as similar to the Oxford_Electric_Bell (which is also included in the article). The Oxford Bell is similarly not really an active experiment, it's just a neat old science artifact that is still around. SemanticMantis (talk) 16:36, 6 November 2014 (UTC)

• Isn't the much larger electron cloud of Si going to be more important in stopping diffusion than the relative internuclear distances, nucleii being point particles for the purposes of this exercise? Also, N2 and O2 are much bigger molecules than H2O, aren't they? I imagine trying to sneak a pair of apples through a wall of bricks a mile thick. Of course, if the internal surface of the glass oxidizes, could not a charge differential eventually lead to the loss of a few O2 molecules or SiO2 molecules from the outside. Maybe over the length of time the flask will simply shrink as (X)O2 is lost from its outer skin? μηδείς (talk) 18:55, 6 November 2014 (UTC)

  Glass contains no O2 molecules, nor strictly, does it contain any SiO2 molecules. Silicon dioxide (quartz, glass, etc.) is a network solid and does not contain any discrete molecules, as such. The formula SiO2 is merely the ratio of Silicon to Oxygen in lowest terms and does not imply the existence of discrete molecules as such. The actual composition is basically this pattern of atoms repeated billions and billions of times in all dimensions. --Jayron32 02:46, 7 November 2014 (UTC)

I am entirely aware of that. My point is that on the inner and outer surfaces we should expect places where there are imperfections. Should oxygen react with the inside surface, the change of charge might induce the release of oxygen from the outside of the bottle, perhaps at a hugely slow rate. Obviously if the oxygen can't react with the inside surface of the bottle you can drop my suggestion. I don't think you've said that. The idea is the same as reducing rust in iron by attaching a sacrificial zinc plate to it. μηδείς (talk) 20:19, 8 November 2014 (UTC)

Right, and in case anyone doesn't know, the structure in the bottle walls is not precisely that pattern, because glass is an amorphous solid. SemanticMantis (talk) 14:17, 7 November 2014 (UTC)

Sideeffects of Madras Eye

Recently, people who suffered Madras Eye(Conjuctivitus)are found having some sideeffects in addition. The skin of their whole back is reddish with itches. Is this the sideeffect of Madras Eye.117.193.119.71 (talk) 16:31, 6 November 2014 (UTC)

See what Pinkeye has to say about it. Anecdote: I've had it in the past, and my back was unaffected. ←Baseball Bugs carrots→ 16:58, 6 November 2014 (UTC)

Conjunctivitis is a type of disease caused by many different pathogen. The OP should look at Madras Eye and if that doesn't help, google ("Madras Eye" and "Back Rash") if this is a question of curiosity or, if he has a rash, ask a doctor about it. μηδείς (talk) 17:02, 6 November 2014 (UTC)

Also see Hives for the back itches. Ariel. (talk) 12:03, 7 November 2014 (UTC)

Oils and the Trachea

Can some edible large-chain Oils, and especially Mineral-oils "find there way" into the Trachea and "Settle" there? while food is swallowed?, if yes, can it be problematic to Humans&Animals consuming them?, thanks. Ben-Natan (talk) — Preceding undated comment added 17:40, 6 November 2014 (UTC)

This sounds like some sort of bizarre plot to kill Batman in the 1960 TV series. Not a direct answer, but see cough, and aspiration pneumonia. μηδείς (talk) 18:58, 6 November 2014 (UTC)

If I understand correctly, Whenever oils get into the Trachea, the Cough-able Organism would Cough till they come out? (As clued, I don't know if I understand correctly). Ben-Natan (talk) 21:09, 7 November 2014 (UTC)

You might also want to look thru Lipid pneumonia. Mihaister (talk) 23:04, 7 November 2014 (UTC)

It still not clear to me if oils consumed by Eating can in some cases, accidentally go into the Trachea\Lungs? Ben-Natan (talk) 03:11, 8 November 2014 (UTC)

Absolutely, I am sure you can accidentally choke on some oily food. You will most likely cough. But if your lungs are unhealthy or you cannot cough (say, an elderly stroke patient with aspiration pneumonia,) lipids in the food could be a major problem.

Or are you perhaps talking about like sewer pipes getting clogged with a waxy build-up where restaurants dump their cooking oil down the drain? That's been illegal for years in much of the US for just the point you suggest. μηδείς (talk) 05:35, 8 November 2014 (UTC)

I didn't know about the US restaurants doing that and I'm not a US resident of any kind... Gladly, My lungs are just well and I can cough in such a choking case case - It is good to get this data from you and I'll keep it in mind and hope others do. It's good to know that indeed. Ben-Natan (talk) 13:07, 8 November 2014 (UTC)

Ugh. I just looked up mineral oil aspiration on PubMed and found this and a whole bunch of mostly shorter term studies with similar results noted - see the search for more. Wnt (talk) 09:44, 8 November 2014 (UTC)

T

Kindle region restriction

I've taken the liberty of moving this to WP:Reference desk/Computing#Kindle region restriction. Wnt (talk) 20:42, 6 November 2014 (UTC)

How much oxygen liquid will be in the same tank

If I have 2.4 liter oxigen tank in the room temprature,how much oxygen liquid will be in the same tank in condition of the boiling point? How can I calculate it?5.28.172.180 (talk) 20:52, 6 November 2014 (UTC)

Are you asking how much volume 2.4 liters of liquid oxygen would take up once it has boiled and been brought to room temperature at standard pressure? -- ToE 22:27, 6 November 2014 (UTC)

I think the OP is asking "If we cool the tank from room temperature to the boiling point of oxygen, what will be the volume of the liquid?" To answer this, we need to know the pressure of the oxygen tank at room temperature. From this, we can work out the mass of the oxygen using the ideal gas equation - we know p, V, T and R, and the molar mass of oxygen is 32 g/mol (it's actually 31.9988, but 32 will do for this calculation). The density of liquid oxygen is 1.141 g/cm (from our liquid oxygen article), which enables us to calculate the volume from the mass. Tevildo (talk) 22:45, 6 November 2014 (UTC)

Sorry for my abstruseness. I mean to ask: how much oxygen liquid could enter in the same tank of 2.4 liter oxygen (gas)? 149.78.27.187 (talk) 03:13, 7 November 2014 (UTC)

2.4 litres of liquid oxygen have a mass of 2.738 kg (this just uses the density). It wouldn't be possible to use the oxygen tank to store liquid oxygen, as the tank is not insulated, and the oxygen will boil off. If you want to know how much liquid oxygen is needed to fill the tank with oxygen gas at room temperature, we still need to know the (maximum) pressure. 2.74 kg of oxygen in a 2.4 litre tank at room temperature would require a pressure of about 900 bar, which is much higher than the maximum pressure of a normal oxygen tank. Tevildo (talk) 11:40, 7 November 2014 (UTC)

Thank you, bu it's my mistake. I've found that the 2.4 liter is the volume of the tank (not weight), but the oxygen needs to be more less of this. So the question is to know how much is it, if it was changed to liquid. In simple words, if you take the tank of 2.4 liter (volume) and you change the state of matter, how much liquid it will be. 149.78.27.187 (talk) 00:19, 8 November 2014 (UTC)

You may be interested in the concept of molar volume, which allows you to do quick calculations while avoiding explicit use of the ideal gas law. The molar volume for 1 atmosphere of pressure is 24.465 L/mol at 25 °C. One mole of O₂ masses 32 g, so if you divide by the density, 1.141 g/cm, you find that one mole of liquid oxygen takes up only 28.05 cm. If you divide that into the 24,465 cm molar volume you can show that when liquid oxygen boils off and reaches 25 °C at 1 atmosphere of pressure it increases in volume by a factor of 872. Thus you would need a 2094 L balloon to hold the result of boiling off 2.4 L of liquid oxygen. But I think that you are asking about storing that O₂ in a tank instead of a balloon, so as Tevildo says, you need to specify the pressure of that tank, as the higher the pressure the smaller the volume is needed to contain the same amount of gas. From our oxygen tank article: "Oxygen is rarely held at pressures higher than 200 bar / 3000 psi due to the risks of fire triggered by high temperatures caused by adiabatic heating when the gas changes pressure when moving from one vessel to another." 1 atm (standard atmosphere) of pressure is just over one percent more than 1 bar. If we compress our 2094 L of O₂ to 200 atm (2393 psi -- note that 3000 psi is the working pressure of the AL80 scuba tanks commonly used in the United States), then the volume will decrease by a factor of 200 to 10.47 L. (See Boyle's law, one element of the ideal gas law.) Thus you need a 10.47 L, 200 atm working pressure tank to hold the same oxygen as held by a 2.4 L Dewar flask filled with liquid oxygen.

So the take away here is that O₂ at 200 atm takes up 4.36 times as much volume as when liquefied.

( 1 atm / 200 atm ) * (24.465 L/mol) /

In practice, most medical O₂ tanks I have seen are pressurized to 2200 psi which is only 150 atm, but searching online I see that 230 bar (3336 psi or 227 atm) high pressure medical oxygen cylinders are available, so the actual multiple you want will depend on the working pressure of your tank.

Is this what you were looking for? -- ToE 13:53, 7 November 2014 (UTC)

Looking at his question, and using the numbers given above, I think the answer he wants is a 200atm, 2.4L tank of oxygen is equivalent to approximately 550ml of liquid oxygen. 75.140.88.172 (talk) 01:13, 8 November 2014 (UTC)

Thanks!!! ToE, this is just what I looked for! But I would like to see the formula again in a normal writing because I don't understand this form of presentation. May you put it into the LaTex? for example (I'm not sure it's accurate): ${\displaystyle {1atm \over 200atm}*{24.465 \over 32}etc}$ 5.28.179.11 (talk) 03:02, 8 November 2014 (UTC)

OK, so Tevildo's original interpretation of your question was correct, but that's no problem because our two interpretations are simply reciprocals of one another. Note that Tevildo's use of the ideal gas law is a good way to solve this. I suggested using molar volume because I though it an easier way to conceptualize the problem as opposed to just plugging some numbers into a mysterious equation.

Prettifying(?) my fractions (per your request) we have the expansion ratio for liquid oxygen boiling off at 1 atm and reaching 25 °C room temperature as ${\displaystyle {\frac {24.465{\text{L/mol}}}{\frac {32{\text{g/mol}}}{\left(1.141{\text{g/cm3}}\right)\cdot \left(1000{\text{cm3/L}}\right)}}}=872}$, and if you then compress that to 200 atm you get the ratio ${\displaystyle {\frac {1{\text{atm}}}{200{\text{atm}}}}\cdot {\frac {24.465{\text{L/mol}}}{\frac {32{\text{g/mol}}}{\left(1.141{\text{g/cm3}}\right)\cdot \left(1000{\text{cm3/L}}\right)}}}=4.36}$.

So if you take 2.4 liter of oxygen at 200 atm and 25 °C and then liquefy it, the final volume will be ${\displaystyle {\frac {2.4{\text{L}}}{4.36}}=0.550{\text{L}}=550{\text{mL}}}$, the answer given above by 75.140.88.172.

Now I'm concerned that this may just look like a big confusing fraction, but it is very understandable. The 872 is just a ratio, with the molar volume at 25 °C & 1 atm on top and the volume per mole of liquid oxygen on the bottom, that calculated by dividing the molar mass by the density (after converting the density from grams per cm to grams per L). Note that the concept of molar volume works because one mole of any gas (ideally) has the same volume (at any given temperature and pressure). Once liquefied, different compounds have different molar densities, so the bottom half of the ratio is specific to liquid oxygen. -- ToE 13:02, 8 November 2014 (UTC)

If you are up to the math, you should try to rework the problem using the ideal gas law (as suggested by Tevildo) and confirming that the results are the same. I'd suggest using R = 0.08206 L·atm·mol·K, as that matches most of the units we have been working with here, leaving you only to convert 25 °C from Celsius to Kelvin. -- ToE 13:10, 8 November 2014 (UTC)

Thank you for the explanation of the formula. But now I noticed it's not 200 atm but it's 200 Bar. Is it the same for you? Could I put the atm's value into the formula too?5.28.179.11 (talk) 01:27, 9 November 2014 (UTC)

You have several options. 1 bar is 100,000 Pa (Pascal, the SI unit of pressure equal to 1 Newton per square meter; note that 100,000 Pa would typically be written 100 kPa) while 1 atm is 101,325 Pa. Since the two units differ by only 1.325%, you could just keep the previous answer of 550 ml, figuring that it is close enough. After all, do you really know the volume of the nominally 2.4 L pressure cylinder to an accuracy of 1%? Alternately, you could plug the correct pressure of 200 bar = 197.4 atm into the equations above in place of the 200 atm. You will get an expansion ratio (after boiling off and compressing) of 4.42 (the previous value times 1.01325) and a final volume of liquid oxygen resulting from taking 2.4 L of O2 at 200 bar and 25 °C and liquefying it of 543 ml (the previous value divided by 1.01325). But if you know from the start that you are working with bar, you might as well use appropriate molar volume of 24.789 l/mol for ideal gases at 1 bar and 25 °C. (Note that this value is 1.01325 times the atm based molar volume we used earlier.) This would give us an expansion ratio of ${\displaystyle {\frac {1{\text{bar}}}{200{\text{bar}}}}\cdot {\frac {24.789{\text{L/mol}}}{\frac {32{\text{g/mol}}}{\left(1.141{\text{g/cm3}}\right)\cdot \left(1000{\text{cm3/L}}\right)}}}=4.42}$, and ${\displaystyle {\frac {2.4{\text{L}}}{4.42}}=0.543{\text{L}}=543{\text{mL}}}$ of LOX.

If you are up to the math (and it is as easy or easier than what we did here), I still suggest that you confirm this number using the ideal gas law, but now that you are using bar you should use R = 0.08314 L·bar·mol·K. -- ToE 07:10, 9 November 2014 (UTC) Dare I link to real gas?

November 7

Sun/Star

Hi everyone!

I would like some help with the following questions please:

1. Does a star’s solar mass increases/decreases as they evolve/age? Partly done: View Bulletin 6, 10, 11 below.
2. Is Blue staggers real or fake?  Done
3. After a protostar is formed, what comes next a blue star or an orange star? Y
4. Pre-main sequence or post-main sequence star, is it the protostar creation period or the protostar itself? Y
5. Main sequence star, can a blue star fall in the main sequence period… or main sequence is just called an yellow star from ZAMS?
6. Is the following, the true steps a star’s life follows? – protostar (baige colour), Blue star (after its fully formed), yellow star, orange star, red star, white star, neutron star (what colour?), black star (black hole).
7. What is a dead star?
8. What is a black hole? A ‘dead star’ or a ‘black hole’ just like a drain.
9. When was ‘Dark age’ and when was ‘reionaziation’ epoch? Did Reionaization occur during the dark ages?  Done

(Russell.mo (talk) 01:38, 7 November 2014 (UTC))

1. A star's mass decreases over time for several reasons 1) It is giving off a ton of energy in the form of light, and energy is mass. 2) It is also shedding mass directly in the form of solar wind. Early in their life they are gaining mass as they actually form as gravity pulls them together, but eventually they start to lose mass.
2. The only references I can find to blue staggers are the plant Dicentra cucullaria aka Dutchman's Breeches: . They're quite real.
3. You can read more about the life cycle of stars at Stellar evolution.
4. See above
5. See above
6. See above
7. See above
8. See black hole
9. The dark ages can mean many things, I assume you mean the one from astrophysics. You can also read about the reionization epoch at the article titled Reionization.

I hope that helps some. --Jayron32 02:41, 7 November 2014 (UTC)

You deserve the masochist's barnstar for that one, Jayron. μηδείς (talk) 02:43, 7 November 2014 (UTC)

In this context, "Blue staggers" is probably luminous blue variable, and, yes, they do exist. Tevildo (talk) 02:47, 7 November 2014 (UTC)

Or possibly a Blue straggler star. CS Miller (talk) 12:26, 7 November 2014 (UTC)

I've read through point 3, 8, the things I mentioned were unclear that's why I asked... Can some help me understanding by explaining in simple terms please? -- (Russell.mo (talk) 18:45, 7 November 2014 (UTC))

If you could point out passages from the stellar evolution article which are unclear, perhaps we can help make them more clear. The article is fairly well written and quite accessible, but if there are words or statements in that article that you are struggling with, let us know, and we'll try to explain them a bit differently if we can. --Jayron32 21:41, 7 November 2014 (UTC)

Thanks Jayron32. I appreciate it. I have to come back to this topic at a later time I think I have muddled a few things up myself in my course work. In the meantime if you and others can help me out with the followings to understand it better, I will be grateful.

6)

In the H-R diagram it illustrates a blue star evolves into a white star, then to an orange star. In the articles it defines a white star appears after the red star phase. This is the time it degenerates the outer layers… When do you see/does a white star appear?

7 & 8)

It says it is a dead star, meaning it doesn’t have no fuel to burn, though it can accrete matter from nearby star/ISM/GMC. Can it spark up again? Note, I know that this is a hypothesis, no black hole exist yet...

In Star Trek, it shows that spock’s friend, from his world, fires a red liquid into their planet and destroys the planet, by creating a “black hole”. Spark also creates a black hole using the same liquid from the enemy ship and goes back to the past or something, by entering the black hole… I don’t get the “black hole”? is there two types of black holes? One a dead star and one that takes you into the past...?

10. What is the limit for a star to follow the Henyey track, “< 0.5” mass or “>”, to follow through the main sequence. One article says “< 0.5”, another “> 0.5”…

11. Can a star possess 1 or 2 solar mass during the main sequence stage, post main sequence stage, while it’s in a white dwarf or neutron dwarf or black dwarf stage?

12. What gets created first? A star or a planet? Is there a chance of a vice versa?

13. What will occur if two stars collide?

14. A star burns hydrogen into helium during its main sequence stage (in the core). What occurs in the shell? What kind of fusion takes place in the shell? When the supply of hydrogen is finished at the core, helium fusion takes place into the shell. What happens in the core?

14.1. How many layers of shell does a star have/create? According to calculation “four” if it is a massive star but at what solar mass? and what about the small solar mass star?

14.3. When it goes to the red giant phase (post main sequence) it burns helium into ________. What occurs in the shell? What kind of fusion takes place in the shell?

14.4. What kind of molecules can a star create/what kind of things can a star burn/fuse in the core and in its shell?

(Russell.mo (talk) 13:14, 8 November 2014 (UTC))

6) Stars don't evolve diagonally along the "main sequence" of the HR diagram (though it looks that way). As they age, stars move horizontally left-to-right in the diagram, roughly speaking, though even that has some variability. If you check out the diagram at File:Zams and tracks.png, you'll see that stars generally evolve from blue colors (hottest, youngest) towards the redder colors (coolest, oldest). Heavier stars start out bluer on the scale, but they all generally trend that way. The color of a star is governed by the principles of blackbody radiation, which connects the peak color of a hot object and its temperature. The specific way in which a star ages depends on what happens when its supply of hydrogen runs low, but they all generally expand in volume and thus cool off some, gradually becoming redder.

7 & 8) The existence of everything outside your own mind is an unproveable hypothesis, black holes are at least as proven as anything else. We have identified many hundreds of black holes. Anyone that tells you that we haven't found any black holes, or that they are "just a hypothesis" can be ignored as entirely not understanding anything about science and understanding. They're plainly wrong. Also, any question regarding "why" some bit of physics happens in a work of fiction has one answer "because the people who wrote the work of fiction wrote it that way." Fiction means "something people invented to entertain people" and physics that happens in fictional worlds is still "physics made up to entertain people". How black holes work in the fictional world of Star Trek is up to the whims of the writers, and has no necessary connection to real-world science.

10) The Henyey Track applies to any star of greater than half of a solar mass (from the mass of 1/2 of our own sun to greater).

11) Stars can be any mass at all; 2 solar masses is actually pretty small for a star. The largest stars are well over 100 times the mass of our own sun; on the main sequence the largest stars are the bluest and hottest.

12) The stars and planets generally form together in the Protoplanetary disk. As the protostar begins to accrete mass towards itself and as it starts to spin at the same time, the matter around the forming star flattens out into a disk. Planets form as eddies in the spinning disk form their only little balls of matter which also accrete material towards themselves. A star is just a bigger ball of matter than a planet is in this giant, swirling disc-like cloud; stars are balls of matter whose gravity is high enough to fuse hydrogen, but the entire process that creates stars (swirling discs of diffuse matter which slowly concentrate into dense balls) creates the planets that form around them. Many decades ago, before Exoplanets were discovered, it was thought that our own system, with a bunch of planets circling a star, may be rare. Now, the general belief is that nearly every star system should have a collection of these planets around them. Our ability to find them is only limited by the fact that they're fiendishly hard to find. But if you consider the basic premise of the cosmological principle, that our own perspective on the universe is not privileged or unique, the same process that formed our sun and planets is forming suns and planets all over the universe in the same way, billions and billions of times.

13) Read Stellar collision.

14 & 14.1) The article Stellar structure contains the basics of different types of stars; the "layers" of a star will vary with the kind of star you're dealing with.

14.3) Carbon. See Triple-alpha process.

14.4) The articles nucleosynthesis, Stellar nucleosynthesis, and Supernova nucleosynthesis will help you understand how various elements are formed in stars. As far as I know, the hot plasma of a star is far to hot for molecules to form in any meaningful sense. For a molecule of anything, you'd need to be cool enough to form stable, neutral particles, and stars aren't cool enough. --Jayron32 15:23, 8 November 2014 (UTC)

I've gathered the articles, I'll read through them. Thanks for the little summary along. Regards. -- (Russell.mo (talk) 16:18, 8 November 2014 (UTC))

I have few more questions I would like help on, could you kindly help me please, or direct someone who would be able to help.

1)

Dark Ages

Before decoupling occurred, most of the photons in the universe were interacting with electrons and protons in the photon–baryon fluid. The universe was opaque or "foggy" as a result. There was light but not light we can now observe through telescopes. The baryonic matter in the universe consisted of ionized plasma, and it only became neutral when it gained free electrons during "recombination", thereby releasing the photons creating the CMB. When the photons were released (or decoupled) the universe became transparent. At this point the only radiation emitted was the 21 cm spin line of neutral hydrogen. There is currently an observational effort underway to detect this faint radiation, as it is in principle an even more powerful tool than the cosmic microwave background for studying the early universe. The ‘Dark Ages’ are currently thought to have lasted between 150 million to 800 million years after the Big Bang.

Reionization, 150 million to 1 billion after the Big Bang

In Big Bang cosmology, ‘reionization’ is the process that reionized the matter in the universe after the "dark ages", and is the second of two major phase transitions of gas in the universe. As the majority of baryonic matter is in the form of hydrogen, reionization usually refers to the reionization of hydrogen gas. The primordial helium in the universe experienced the same phase changes, but at different points in the history of the universe, and is usually referred to as ‘helium reionization’.

They found the galaxy UDFj-39546284 to be at a time some 480 million years after the Big Bang or about halfway through the Cosmic Dark Ages at a distance of about 13.2 billion light-years.

I’m confused, with the highlighted bits. When did the reionization occur and when was the dark ages?

2)

The dark matter clump together under gravitational attraction due to the initial density perturbation spectrum caused by quantum fluctuations. This derives from Heisenberg's uncertainty principle which shows that there can be tiny temporary changes in the amount of energy in empty space. Particle/antiparticle pairs can form from this energy through Mass-energy equivalence, therefore enacting a gravitational pull, which will cause other nearby particles to move towards it, disturbing the even distribution and creating a centre of gravity. The gravity of these denser clumps of dark matter then caused nearby matter to follow suit, and start falling towards the centre. This resulted in a clouds of gas, predominantly Hydrogen to form, and within these clouds began to form the first stars. These clouds of gas and early stars, many times smaller than our galaxy, were the first protogalaxies.

I don’t understand this highlighted bit, hydrogen was there from before, right? During the “Dark ages”.

3)

View the link (https://en.wikipedia.org/Star#Classification) and explain please why this is the second time it defines a white star occurs twice during its evolution phase . I actually don't get it. The diagram you told me to look at earlier in the other discussion does not have a white star line during its evolution phase.

4)

A blue dwarf is a hypothesized class of very-low-mass stars that increase in temperature as they near the end of their main-sequence lifetime. – Can you tell me when a white dwarf appears, after the blue or red star? Does it depend on its mass, when it fails/falls/breaks apart?

This article Dwarf star displays names of some main sequence stars which should be in the post main sequences phase. I don’t understand why?

Can someone please check if the following step are correct?

1. Protostar formation

2. Pre-main sequence phase:

Blue star to Yellow star, (assuming that it passes through the white star phase or straight to yellow just like the way Jayron32 mentioned. Pre-main-sequence star says what Jayron32 says too. ). Blue dwarf and Pre-main sequence star article mentions that it can go straight from blue to white depending on its mass.

3. Main sequence – (What kind of stars are they talking about in this article?):

3.1 Yellow Star/dwarf – Note: G-type main-sequence star article mentioned the word post main sequence to white dwarf, not to a red star/dwarf? the Star article mentions post main sequence to the red giant star.

3.2 Orange Star/dwarf

4. Post main sequence :

4.1 Red giant star (Star article say it’s a post main sequence star.

4.2 Red dwarf (Dwarf star and Red dwarf article say it’s a main sequence star when its intricacies are similar as red giant and red supergiant.

4.3 Blue dwarf (Dwarf star, blue dwarf article say it’s a main sequence star. This and the Blue stragglers article define the word hypothesis/hypothetical/theoretical. Should a blue dwarf (T tauri star) come after the protostar formation? which is real? Does it also come after the red giant phase? Note: Whether it is a theory or hypothesis, how can a red star/dwarf turn blue star/dwarf without accreting molecules? A cooking gas fire turn from blue to yellow to red, it doesn't go white colour. What is the reason it turns white in colour?

4.4 Red supergiants (Dwarf star and Red supergiant and article say it’s a main sequence star. Red dwarf article has some information similar as Red supergiant.

5. What sequence phase are the following :

5.1 White dwarf - apparently its a post main sequence phase/star defined in G-type main-sequence star article.

5.2 Neutron star

5.3 Black hole – I don’t understand how this occurs. I thought the clashes between the molecular clouds of galaxies will create a black hole. All I understand that it occurs when a massive star collapses. Can you go inside it? Is it like a worm hole? it seems like a black dwarf to me after re-reading both articles. According to analysis, black hole are called the massive stars and black dwarfs are called the less massive stars. The article also mentions that the Milky Way galaxy holds a black hole at the center of the galaxy. In the Milky Way article I didn't see any black hole star at the centre of the galaxy.

5.4 Black dwarf – this article states that no black dwarf exists yet… What’s the difference between Black hole and black dwarf.

5.5 Brown dwarf – Where do I put this?

(Russell.mo (talk) 16:00, 9 November 2014 (UTC))

• I'm not sure why you are so resistant to reading the article titled Stellar evolution. For one, it presents a more nuanced view of the life cycle of stars. Stars do not merely follow a neat, orderly pattern of colors. Depending on their size and specific composition they live different types of lives. It would be better for you to read the Stellar evolution article and come to understand a more complete, accurate, and nuanced view of the life of a star, rather than looking for some universal list of colors which doesn't really represent a good heuristic for understanding the processes involved. Just read the article and let go of the little timeline you're trying to develop. --Jayron32 02:46, 11 November 2014 (UTC)

Lol I'm just running out of time, that's all. I have read the article Stellar Evolution once before, its just re-reading when I don't have the time. Thank you for replying back Jayron32 -- (Russell.mo (talk) 11:45, 11 November 2014 (UTC))

Not done: On hold until

Prestressed concrete failure

Is it correct to say that the failure of a prestressed beam is explosive due to the stresses which have built up in the concrete? — Preceding unsigned comment added by 194.66.246.101 (talk) 19:06, 7 November 2014 (UTC)

This is just off the top of my head: As the 'tensional' stress is in the rebars, The failure is not down to the stress in building up in the concrete. High alumna cement (for example) when poorly mixed (too much water) may start to crumble and loose the 'compressive' strength required to hold the rebar stress in place- which is imposed during casting. The compressive stress within the concrete is already imposed in casting and curing, so should not (I think) build up over time. Off the top of my head again: I think that rebars lose about 5% of their strength per decade. Therefore, by my reckoning the stress on the concrete is ever diminishing not building up. Err.. does that make sense. It is not the build up of stress “in the concrete” but the reduction of the concrete’s ability to resist the tension stress imposed on it by the rubars.Also, cracks in the concrete can allow water and atmospheric oxygen to get down to the rubars. This makes them corrode. The corrosion not only weakens the rubars, it also causes them so expand volumetrically, which makes the concrete cocoon spall off. Which will further weaken the structure. Possible leading to an 'explosive' or rapid unscheduled disassembly of the building or structure (in other words - it collapses). This maybe the phenomena of which you maybe inquiring about. --Aspro (talk) 19:49, 7 November 2014 (UTC)

But let's say you apply a load to a prestressed beam, you increase the bending on it and hence I would have thought you have increased bending stress on the beam. And then that stress builds up eventually causing failure. — Preceding unsigned comment added by 194.66.246.16 (talk) 10:28, 11 November 2014 (UTC)

actually I suppose that bending stress is in the rebar and not the concrete. But could you argue that the opposing force of concrete which is trying to stay in compression is causing an increase in stress? — Preceding unsigned comment added by 194.66.246.16 (talk) 10:30, 11 November 2014 (UTC)

The deal is that concrete is very strong in compression - but incredibly weak in tension. When you apply weight to a beam, the top of the beam is compressed but the bottom is tensioned. So simple concrete beams snap rather easily - often under their own weight. So the idea is to apply artificial compression forces to the beam when there is no weight on it. Then when you do apply weight, the top part gets compressed both by the load, and by the artificial compression source...the bottom is compressed by the artificial compression MINUS the tension caused by the load. If you get the tension right, the bottom of the beam is still in compression - so it's still strong. Hence, the rebar (or cable system or whatever) that pre-stresses the concrete isn't being stressed by the load directly - but rather by the beam itself. When you load the beam, the top of it is increasing the tension in the rebar - but the bottom of it is reducing the tension - so the average doesn't change. If everything works out right, the rebar doesn't get any extra forces applied to it at all when a load is applied to the concrete. The concrete does all of the work.

When something fails (anything really), it's tough to say whether the result will be "explosive" or rather gentle. The failure modes are many - some will release the energy rapidly, and others more slowly. So it's hard to say what will happen without a lot more information about the application. SteveBaker (talk) 20:55, 11 November 2014 (UTC)

Organic chemistry question

Say, in an organic compound, we have a main chain of nine carbons (-nonane); on the sixth carbon there is a propyl side chain (normal position), while on the fifth carbon there is an isopropyl side chain; would the preferred IUPAC name be "5-isopropyl-6-propylnonane" or "5-s,6-dipropylnonane"? Thanks 74.15.5.210 (talk) 21:41, 7 November 2014 (UTC).

Neither. It would be 4-propyl-5-isopropylnonane. Always number from the end which gives you the lowest numbers for your side chain. --Jayron32 21:45, 7 November 2014 (UTC)

Actually, it might be 5-isopropyl-4-propylnonane. I think you put side chains in alphabetical order. But you would still always number from the short end. You'd never have a 5,6 nonane, because 4.5 nonane is a lower way to name the same molecule, whatever the side chains are. --Jayron32 21:47, 7 November 2014 (UTC)

5-isopropyl-4-propylnonane is correct according to the IUPAC rules for alkanes. Longest chain gets the root name, then side chains in alphabetical order, then lowest (total) numbering. Mihaister (talk) 23:00, 7 November 2014 (UTC)

Why don't new complex lifeforms keep on arising from microbes?

Complex life evolved just before the start of the Cambrian, presumably due to rising oxygen levels. What is not clear to me is why all complex life forms of today can be traced back to having evolved in that time period rather than microbes forming new complex life forms much later. Count Iblis (talk) 23:21, 7 November 2014 (UTC)

What do you mean by "complex life"? Sure, animalia complexity greatly increased at that point... but other kingdoms of multicellular life may have had different times for that. Certainly there were different times for complex life conquering different regions, i.e. in the sea vs. on land. That said, I think some of the issue may come down to competition. A "new" complex form or transitional form may not be well enough adapted to conditions/niches to outcompete against existing complex lifeforms. Think about it like this. Go to a forest, and imagine some plant that is currently nothing like a tall tree, but is currently alive (i.e. some part of the ecosystem). What evolutionary pressure does it have to go towards being a tree? Even if that pressure exists, how is it going to outcompete existing trees for the same resources along the way? It can't. Now, if a fire comes through and wipes out all of the trees, but somehow that one plant survives, it might evolve along a parallel path to a form similar to trees. But in the case of complex lifeforms, we're here, and not terribly absent from anywhere that we can thrive. --OuroborosCobra (talk) 23:40, 7 November 2014 (UTC)

The evolution of multicellular organisms was not a single event. There are multicelluluar plants, multicellular animals, multicellular fungi, etc., so the multicellularity has evolved independently multiple times. The Cambrian explosion gave rise to the majority of multicellular animal groups known today, apparently under the effect of predation pressure: growing larger is a good strategy to not be eaten. Still, pluricellular and multicellular organisms kept evolving after the Cambrian explosion. For example, Volvox - a colonial (pluricellular) organism - evolved from single-cell green algae ancestors in Triassic. --Dr Dima (talk) 00:06, 8 November 2014 (UTC) (It is interesting to note that Volvox seems to have evolved right around the Triassic–Jurassic extinction event, when the predation pressure was probably reduced). --Dr Dima (talk) 00:20, 8 November 2014 (UTC)

In Power, Sex, Suicide Nick Lane argues that the formation of the eukaryotic cell is an exceedingly unlikely event, and that without the eukaryotic structure, microbes will not evolve into effective multicellular organisms (other than colonies). Once this hurdle is passed, however, complex lifeforms can evolve readily. —Quondum 03:36, 8 November 2014 (UTC)

• Species largely evolve by adaptation and isolation. If there's a niche like an mammal-uninhabited island with plants with fruit, birds like the Dodo and the Kakapo can evolve from pigeons and parrots in strange new ways to fill the ecological niche elsewhere held by monkeys and rodents. But the macroscopic niches are mostly filled, and filled by better adapted animals. There's just no open higher position to be promoted to. Unles the earth is hit by a large asteroid Chicxulub or has a major tectonic or outgassing event Permian extinction, or some miraculous new chemical process that produces energy but poisons other life forms, like photosynthesis Oxygen crisis evolves, the grey goo are likely to be our next mighty new microbe rulers, whom I, for one, welcome. μηδείς (talk) 05:27, 8 November 2014 (UTC)

Thanks for all the answers. I guess that eliminating competition should also be possible in a laboratory. Although evolution takes a long time, in the lab you could engineer the right circumstances. So, could we create new animals de novo in the lab within a reasonable time frame using mainly natural selection and a minimal amount of engineering? Count Iblis (talk) 19:40, 8 November 2014 (UTC)

I've added a few more links to my above answer, in case they are useful. Count Iblis. Consider mammals. Marsupials and monotremes paralleled every form of land placental from the mole to the Rhino. But neither the egglaying platypus nor the pouched opossum could evolve into a truly flying or full aquatic form. It was only with the arrival of the placenta that bats and whales could swim and fly without losing their vulnerable young. You might also look at what Amazon.com did to Borders and what the internet is doing to print and broadcast media. The radically new business models have opened up new niches, but have driven a lot of other industries to or close to extinction. μηδείς (talk) 22:00, 8 November 2014 (UTC)

• I think a reason may be that slime molds are paraphyletic - so if a new multicellular life form arises, at least on land, you would probably call it a slime mold. I don't know if the taxonomy has been revised since last I looked; it certainly was too confused for me to say that none of them evolved after the Cambrian. There are many other "non-multicellular" life forms that certainly look otherwise - Volvox, Spirogyra, colonial choanoflagellates, etc. The definition of multicellular life can be fine-tuned to exclude many of these things, but the way our article uses it, it credits at least 46 separate origins. Wnt (talk) 15:17, 9 November 2014 (UTC)

I agree with the relevance of Wnt's comment, but pretty much and presumably all known phyla of animals date back to the Cambrian explosion. There's a difference between grade-lifestyle and clade-genetic relationship. For example, insects, pterosaurs, birds and bats have all accomplished the grade of flying animal, while whales, bats, elephants and shrews all belong to the placental clade. The slime molds are worse than paraphyletic, they are polyphyletic. They don't form a coherent group at all. This would be the same as for the groups we call worms and shellfish. There are many unrelated groups of animals well call worms, like flatworms, earthworms, and nematodes; or shellfish which are simply things like crabs and clams that are edible sea creatures that don't meet the Kosher definition of edible fish, which must have both fins and scales. μηδείς (talk) 22:19, 9 November 2014 (UTC)

The Cambrian explosion was indeed a big deal, but for all known animal phyla to date back to that point is essentially a tautology. Any "phylum" that arose more recently could be grouped with some sister group with similar characteristics from before they split, and joined into a single phylum from Cambrian times. And of course this only describes animals, whose multicellularity is rarely at issue. Wnt (talk) 17:57, 10 November 2014 (UTC)

I am not quite sure what you are trying to qualify, Wnt. It would help if you would point out some traditional phyla that don't date to about the Cambrian explosion, if you are implying there are many. Land plants and fungi seem to date to this period as well. I'll grant phylum is an artificial term, but even if we just look at the proliferation of the deepest clades they seem to date to that era. But I suspect we are probably in agreement, actually. μηδείς (talk) 18:27, 10 November 2014 (UTC)

November 8

Illacme plenipes

Is it the only animal (as of now) having the highest number of legs? — Preceding unsigned comment added by IEditEncyclopedia (talk • contribs) 05:18, 8 November 2014 (UTC)

As it says in the linked article, it has "more legs than any other creature on Earth".--Shantavira| 08:13, 8 November 2014 (UTC)

It's a little bit philosophical: what is a "leg"? Insect legs and human legs aren't really "the same thing", in that the insect leg is attached to a segment; we can see human somites and our legs are of course much bigger structures than that. Really, human legs are derived from fins and fins are special structures that arose in vertebrate evolution, much like tube feet are structures specific to echinoderms. All these structures are marked by Distal-less, but then again, so are jaws (which you might say are modified legs, though) and many other things. See But if we allow tube feet as a sort of "leg" - which certainly would be controversial - then some echinoderms, with tube feet numbers ranging from hundreds to thousands, ought to beat the millipedes handily, or should I say footily. Wnt (talk) 09:29, 8 November 2014 (UTC)

"USE NO OIL" - why?

On the Oxygen's tank is written: "USE NO OIL", and my questions are: 1. why? 2. what can happen? 3. what is the meaning of "use no oil" (it's wide). Is it forbidden to me to touch in the Oxygen's tank while my hand has oil? I would like to get specific examples for no uses or cases that happend. THANKS 5.28.179.11 (talk) 09:27, 8 November 2014 (UTC)

Apparently spontaneous combustion. See , a 1919 book referring to that guideline being already well established. Many modern guides have identical advice, but I didn't see the explanation on this example: It is well known to hapless astronauts and emphysema patients alike that increasing the amount of oxygen increases the risk of fire and general mayhem. I remember reading that the internet celebrity who lit his charcoal grill with liquid oxygen had to make sure not to let it soak into the briquettes, as they could become high explosive. That said... because this advice is so old, I wonder if there are known safe lubricants. (I looked up silicon grease and found one blurb saying 'safe to use' and one saying 'not safe to use', so I should defer to someone who actually knows the topic!) Wnt (talk) 09:37, 8 November 2014 (UTC)

(edit conflict) It's in reference to the fittings, piping, and other equipment that would connect to it. Those oils have a habit of being flammable, which is a pretty bad thing to have in a high-oxygen (pure and/or at high pressure) situation. Such equipment is often marked "cleaned for oxygen service", meaning they have made sure there is no residual oil from the machining/manufacturing and that pieces that are often lubricated or would contain oil for some other reason aren't. Or at least that a special grease is used that is safe for this special situation (I have no idea what their chemical composition is though). DMacks (talk) 09:44, 8 November 2014 (UTC)

As indicated above, common hydrocarbonus lubricants can under go such rapid oxidization in pure oxygen that they can spontaneous ignite - and from there, ignite metals and all that surrounds the apparatus. Fully fluorinated lubricants can be used on high pressure oxygen systems though (the fluoride atoms shield the oxidisable atoms from the oxygen atoms getting at them) the but for the average user (say using an oxyacetylene welder in a workshop) – what does he know about the chemical composition of lubricants available to him. So it is safer to declare Use No Oil. For lower pressure systems, silicone grease may be permitted in certain circumstances.--Aspro (talk) 13:01, 8 November 2014 (UTC)

Unfortunately our Oxygen clean is just a redirect to Oxygen tank. The subject is addressed briefly in the next to last paragraph, and two references are provided (one from NAVSEA, the other from NASA) that may be downloaded for more information. -- ToE 13:26, 8 November 2014 (UTC)

For an exploitation of this phenomenon in fictional form, see Isaac Asimov's murder mystery A Whiff of Death. Asimov was of course a Biochemistry researcher, familiar with such apparatus. {The poster formerly known as 87.81.230.195} 90.200.134.192 (talk) 01:10, 10 November 2014 (UTC)

LED stovetop heating elements

How does an LED stovetop heating element work? Arn't LED's suppose to be cold, and why does a stovetop LED stove work at all? How many watts does an LED stove use on high/medium/low?74.111.59.85 (talk) 15:32, 8 November 2014 (UTC)

The most likely answer is they don't work. I can't find any mention of them in any searches. Perhaps you're thinking of a cooktop which works via some other method, perhaps induction cooking, and uses LEDs for something else. Such as as indicators for the placement of pots on one of the new "freedom"/any position induction cooktops with multiple small elements (so you can place the pot or pan anywhere on the cooktop rather than in defined locations as with traditional style cooktops like although that doesn't have LEDs for such purposes). Or alternatively to give fake flames like (people have also been doing that with fireplaces for a while although those are obviously not using induction and I'm not sure they were always using LEDs). Unless you have some further sources which demonstrate these claimed LED cooktop heating elements, I'm not sure if we can help more. Nil Einne (talk) 16:05, 8 November 2014 (UTC)

BTW, I should mention that I don't think it's accurate to say LEDs are cold. LEDs generally have a far higher luminous efficacy than incandescents or halogen lamps, meaning they produce more light for a given amount of energy. Nowadays they are often even somewhat better than fluourescents. But dealing with heat from a high powered LED is one of the big problems as it will reduce efficiency and also reduce lifespan. In relative terms the amount of heat is not much and definitely not something you'd cook with although you could burn your finger touching a high powered LED and I wouldn't call something like that 'cold'.

Of course other than probably killing it, the reason not to use LEDs would be there is no reason. The LED doesn't provide any advantage over a simple resistive heating element for a cooktop. Even if far infrared LED existed and I don't think they do, infrared is useful for some things like cooking in an oven (although these use simple resistive heating and infrared is generally only part of the heating) or room heating in some cases, examples of where you want to transfer heat over a distance to a surface. It's not really that useful for heating pots and pans on a cooktop.

Nil Einne (talk) 16:33, 8 November 2014 (UTC)

Trees shedding leaves

Related: Misplaced Pages:Reference desk/Archives/Science/2014 September 28#Trees shedding leaves

When deciduous trees shed their leaves in the autumn, what is the sequence of species for the day on which the last leaf falls? In other words, which species is the first to become completely bare of leaves, which is the second, and so forth? At least, are there overall trends with regard to class or order or family or genus?
—Wavelength (talk) 16:59, 8 November 2014 (UTC)

Anecdotal experience is that smaller, younger trees tend to turn first. ←Baseball Bugs carrots→ 17:08, 8 November 2014 (UTC)

Leaf fall is a fairly random event which occurs due to wind and precipitation. Some trees will keep some or most of their leaves all winter, especially some oak species. Rmhermen (talk) 18:08, 8 November 2014 (UTC)

In the US coastal NE lots of dead leaves, mostly oak, don't fall until as late as the following spring, especially oak. As for changing color, the maples, ornamentals, shrubs and fruit trees like wild cherry seem to turn first, then the oaks (which are the largest) a few weeks later. This may not be helpful if you live further inland where hardwoods besides oaks are predominant. μηδείς (talk) 18:20, 8 November 2014 (UTC)

There is a lot of variation. Within species, it will depend on the local environment (understory/canopy, soil conditions, moisture, etc.), and the age of the tree. Within a given locale, timing might be loosely correlated with taxon, but around the world, plant functional type is a bigger issue, and this incorporates things such as successional status, nitrogen fixation abilities, morphology, and so on. Two trees of the same functional type but distantly related will behave more similarly than trees that are closely related by have very different functional type. Also note that in the tropics, trees are not seasonally deciduous but instead drought deciduous. In that light, the order of drop may change depending on variations between years, such that species A drops first in some years, but species B drops first in others. I concur with the anecdotes from Bugs and Medeis above. On the topic on young trees, they drop sooner in part because they also leaf out sooner, to be able to get light before the canopy_(biology) closes. The same tree will behave differently if it is in a treefall gap, compared to a closed canopy. Is this for a WP article? I can probably dig up more specific references if I know the target better. To even start on figuring out a general list of order-of-leaf-drop, we'd have to specify both a region and a forest type. SemanticMantis (talk) 19:12, 8 November 2014 (UTC)

(ec)It will depend on where you live. In the Northern hemisphere the Ash is generally one of the first to lose it's leaves . It also depends on the health of individual trees and how much rainfall there has been . Richerman (talk) 19:16, 8 November 2014 (UTC)

SemanticMantis, no, this is not for a Misplaced Pages article, but just to satisfy my curiosity, although editors are still welcome to use the information to contribute to one or more Misplaced Pages articles, perhaps in Category:Periodic phenomena.

—Wavelength (talk) 19:46, 8 November 2014 (UTC)

Good call. The phenology page already has the category of periodic phenomena listed, but it doesn't show up in the category page for me (yet?). I also added leaf-fall, though changes will take time to propagate. SemanticMantis (talk) 20:44, 8 November 2014 (UTC)

Infinite space

If space is infinite, then does that mean that my exact clone is writing this same question on an exactly same wikipedia as this one in a different planet somewhere? — Preceding unsigned comment added by 88.115.38.169 (talk) 19:07, 8 November 2014 (UTC)

Not necessarily. One can construct an infinite list of numbers, no two of which are the same. Space being infinite doesn't require repetition, though it certainly makes it more probable. In part it depends on what you assume "infinite space" means. If you assume it means the same local physical laws and similar densities of mass and energy extending infinitely in all directions, then there are variations of that argument that would all but require that nearly everything is repeated infinitely many times. However, you can also construct theories about the universe where space is infinite but the details of physical laws and other parameters vary sufficiently that no two large scale regions are ever exactly identical. Dragons flight (talk) 19:23, 8 November 2014 (UTC)

In the generic case predicted by inflation theory, your identical copy is about ${\displaystyle 10^{10^{29}}}$ meters away from you. Count Iblis (talk) 19:35, 8 November 2014 (UTC)

Of course, if there is an infinite multiverse there could be many copies of you playing out an infinite number of scenarios. However, am I right in thinking that if the big bang theory is correct, this universe must be finite as the big bang happened at a finite point in the past? Richerman (talk) 21:09, 8 November 2014 (UTC)

The Big Bang happened at specific time, but it didn't happen at a specific place. From the point of view of us living inside the universe, and from the limited region we can see, the Big Bang was an event that affected all of observable space simultaneously. It is unknown if the universe extends infinitely in space beyond the region that we can see. Common theories about the geometry of space include both infinite and finite options. Dragons flight (talk) 17:12, 9 November 2014 (UTC)

You can create an unending list of numbers that don't repeat, but once you say, and that is all there is you have made it finite. Space is unbounded, like the way the surface of the earth has no edge, while it does have a definite area. Applying the term infinite to actual physical existence may be a convenience, but it cannot be taken literally. You might want to search the archives, this topic has beaten to death an infinite number of times. μηδείς (talk) 21:51, 8 November 2014 (UTC)

Let's consider a real "unending list of numbers"...like the digits of Pi...which is infinite and never repeats and seemingly has no pattern to it. Those numbers are only globally unique. I can (in principle) find a sequence of 100 digits of pi...then look for another place within pi where those exact 100 digits occur again in the exact same order. We know for sure that such a place exists within pi because there are only 10 (a "googol") possible ways to have 100 consecutive digits - and so you're guaranteed to see duplicated strings of 100 digits, in an infinite number of places along the number, spaced roughly 100 googol digits apart. If you're a little "number animal" that lives inside pi - then even though pi itself never repeats on a macro scale, your local world of 50 digits is far from being unique...for 100% sure. So the portion of the universe that we can see must be replicated an infinite number of times through the entire infinite universe. As a being that lived far out on the edge of the identical-seeming section of one of those copies, you'd be able to see that things look a little different than they do in our copy...but no information that you'd discover about that would ever reach earth because of the speed of light limitations. So our earth and the earths in those other bubbles would never be anything other than utterly identical. SteveBaker (talk) 20:06, 10 November 2014 (UTC)

There are theories that do take infinite space literally, and theories that don't. Right now we don't know, though a globally flat universe (a very popular model) is literally infinite. See: Shape of the universe. Also, you are using the technical term "unbounded" in an inaccurate way. The surface of the Earth is bounded but has no edge. A surface is bounded if the shortest distance between any two pairs of locations within is always less than some finite number. So spheres are bounded (which in most cases is a synonym for finite), but you would have been correct if you said they have no boundary or edge. I assume that the similarity between "bounded" and "boundary" is probably the source of the confusion, but in technical uses they don't mean the same thing. Dragons flight (talk) 17:12, 9 November 2014 (UTC)

But that's just smuggling the idea of infinity in. Essentially you are saying you (they) have redefined boundedness, so that if something is unbounded, there are two points the shortest distance between which is infinity. So now I am supposed to talk of the universe, the surface of the earth, being unboundaried? You're just declaring yourself the winner by setting the terms of the debate. Any infinite model of the universe is incoherent because it means existing things exist in no relation to or definable proportion to the universe. In other words, however big the universe is, it actually isn't, because its bigger than it is. μηδείς (talk) 05:59, 11 November 2014 (UTC)

That's always been the definition of the term, nothing has been redefined. Also, it does not mean that there are two points the shortest distance between which is infinite, it means that there is no number so that for all pairs of points then distance between them is less than that. The natural numbers are unbounded, yet each is a finite distance from any other; "unbounded" does not mean "infinite distances", but "no maximal distance" - there is nothing that seems to prevent this from applying to the universe at this point.Phoenixia1177 (talk) 11:55, 11 November 2014 (UTC)

It's easy to create toy universes that are spatially infinite and mathematically well behaved, such as Conway's Life on an infinite board. It's plausible that the real world has a description of that form. -- BenRG (talk) 18:34, 9 November 2014 (UTC)

But again, if you're a glider - the 1000x1000 square grid around you will be replicated someplace else in that infinite board with another glider just like you within it. It doesn't matter whether the universe is infinite and never truly repeats - it only has to repeat on a scale that a human can detect it for there to be identical worlds with identical Steve's and BenRG's on them discussing the same exact questions. Conway's life has a "speed of light" limit, just like our universe does - so the concept of "visible universe" applies there just like it does here...and there will be lots of repeats of those places. You can argue the same way with Penrose tiles, they don't repeat over the entire universe - but there are arbitrarily large, finite areas that are precisely identical within the universe. SteveBaker (talk) 20:06, 10 November 2014 (UTC)

• We actually have pretty decent articles at infinite monkey theorem, multiverse, and block universe, with many links, references and "see also"s within. SemanticMantis (talk) 22:19, 8 November 2014 (UTC)

(...and if you like stories about the multiverse and kung-fu action, I recommend The_One_(2001_film)  :) SemanticMantis (talk) 22:22, 8 November 2014 (UTC)

The tough part here is figuring out things like cardinality of the continuum. How many universes are there - a countable infinity or an uncountable infinity? And even so, how do they map?

For example, consider an infinite set of universes containing two (2) hydrogen atoms. In the first universe, they are 1 meter apart, in the second two meters apart... up to infinity. Now there are no universes in this infinite set of universes that contain two hydrogen atoms that are one and a half meters apart, nor three hydrogen atoms. But this is a countable set of universes. I suppose you could have the hydrogen atoms arbitrary distance apart for an uncountable set of universes corresponding to the real number line... but still have none with three hydrogen atoms. So it's one thing to have infinite universes and something else to have so many freaking universes that you literally can't spare one single possibility, or half of them, or even nearly all of them. What is infinity divided by half, infinity minus one? I don't know ... infinity doesn't seem to worry about its security against thieves much. If there's a way to prove that every universe has to exist I'd be glad to hear it. hmmm, not really, come to think of it, because there are a lot of really bad universes... Wnt (talk) 22:41, 9 November 2014 (UTC)

Ignoring parallel universes...if our universe is infinite...AND fairly similar to what the see around here in terms of laws of physics and matter/energy distribution...AND if the positions, momentums and such of all particles are quantized, then if you took any random cubic parsec of it, there is only a finite number of ways that the matter and energy within that space can be distributed. That number is ungodly huge...but it's finite. So in an infinite universe, there must be infinite numbers of cubic parsecs that are utterly identical to each other at some point in time. That doesn't guarantee that there are identical copies of thecubic parsec centered on earth...but it would be AMAZINGLY unlikely that there wouldn't be an exact copy of earth...and you and me someplace out there. The question is whether the preconditions that I specify are vin fact true...and the answer to that is "we don't know". But it does seem plausible.

The glitch with the notion of an "infinite" universe, at least from the mathematical standpoint, is the implication of an infinite amount of mass and energy. It renders Conservation of energy irrelevant. ←Baseball Bugs carrots→ 06:44, 10 November 2014 (UTC)

That's not true. Conservation of energy only applies to closed systems. An infinite system can't be closed...but each individual cubic parsec (or cubic centimeter or whatever) can be measured - tracking the mass/energy passing into and out of it - and the conservation laws apply perfectly well. SteveBaker (talk) 19:41, 10 November 2014 (UTC)

Except that the evolution of such a cubic parsec is determined by random factors (e.g. nuclear decay), which means even identical regions will not stay identical over long time periods. MChesterMC (talk) 09:40, 10 November 2014 (UTC)

That's true - but if all we're concerned about is whether there is an identical earth out there right at this precise instant (which wasn't identical a picosecond ago, and won't be identical a picosecond from now)...then our OP's question is answered. Also, most of those tiny fluctuations take a while to produce noticable changes at the macroscopic level. So our parallel worlds would stay sufficiently parallel to be recognizable for a while. At first, weather changes would be noticeably different - one copy of earth gets a storm, another doesn't - some people get struck by lightning and others don't...and before you know it, the place is quite different. BUT if we have an infinite universe, then even those random factors must come out the exact same way on an infinity of identical earths...and in an infinity of others, those random factors make some very slightly different earths start to look more and more identical. Infinity is a VERY big place - where all of these things will happen. SteveBaker (talk) 19:41, 10 November 2014 (UTC)

The cubic parsec example is interesting, and sort of gets at the underlying philosophy a little better. To take a variant on it: suppose you have an infinitely large stormcloud and you want to see if you get exactly the same snowflake twice. You imagine that water has to stick to itself by certain laws, and therefore, from each snowflake there are only so many possible configurations. Yet... the assumptions about the infinite stormcloud matter. What if it is some sort of cosmic accretion disk spanning the gamut from cosmegg to Big Rip and every one of the infinite cubic parcels is at a different temperature, pressure, and/or chemical composition? Then it might be impossible to have any snowflakes in all but a countable few parcels in one infinitesimal sliver of space, and one might be unique. In the same way, our "infinite universe" might be made up of infinitely more void and cold space than warm places like Earth. We might have one 'tiny' visible universe of stars suspended above a bottomless pit of (to us) uninteresting possibilities. Wnt (talk) 16:20, 10 November 2014 (UTC)

Right - so in my description of the cubic parsec, I started out by saying that I was assuming that the hypothetically infinite universe was at least somewhat uniform. If we were indeed (for example) at the lowest entropy part of the entire infinite universe - then we could very well be unique. But other, lower entropy parsecs would still have to be identical. So while there could just maybe be no other copies of me...there could absolutely HAVE to be an infinity of other cubic parsecs that were absolutely identical...there just aren't enough possible configurations of particles and energies within a cubic parsec to allow them to all be different.

It's like trying to take 100 dice and setting them up with unique numbers showing on the top faces of all of them. Sure, you can have just one, utterly unique '6' - but of the remaining 99 dice, you need lots and lots of 1's, 2's, 3's and so on. You can only have at most 5 unique dice - and if you do that, the remaining 95 have to be all 1's or something. For us to be unique in an infinite universe, there has to be something VERY weird going on to have just one of those dice coming up '6' from natural processes alone...much more so if there are a million dice, or a trillion of them...or yet an infinite number of dice with just one '6'.

So if there are N possible configurations of a cubic parsec (N being an insanely large, but finite, number), it's plausible that M of them are unique in the infinity of space and N-M are each repeated an infinite number of times. But we'd have to be REALLY super-special for that to happen...and random quantum variations in the other M cubic parsecs would somehow have to be happening in the universe such that none of the infinite numbers of them can ever change to replicate one of those 'unique' cubic parsecs by chance alone. If the odds of it happening is non-zero, then in an infinite universe, there are an infinite number of places where it happened - so our unique parsec doesn't stay unique.

That seems possible but highly unlikely. If the universe is infinite, I'm pretty sure there is an infinite number of another Misplaced Pages reference desks answering this exact question right now...and an infinite number that had the discussion a thousand years ago...and another infinite number where the font is a bit nicer. SteveBaker (talk) 19:41, 10 November 2014 (UTC)

SteveBaker (talk) 19:41, 10 November 2014 (UTC)

@SteveBaker: you make a good argument, but there are still two things that nag at my mind...

• Can you rasterize an object? Per Tron, in theory, you take down the positions of all nuclei and electrons with enough accuracy that you could tell, simply from their positions, if they are bound together. Oh, yeah, and also their momenta, since otherwise it might just be a thermal collision, and to keep track of what is moving which way. But now we have tiresome Doctor Heisenberg haranguing us. Even from a "god-level perspective", can you actually get these measurements with enough accuracy that you could "scan" two people and say that they are actually similar, or is it physically impossible to have that much confidence in your measurements? Could one scan be a person and the other be an exploding soup of unconscious mishmash but they still come up as identical in your analysis?

• How many parameters are encompassed by "uniform"? If you assume a "reasonably homogenous" universe, maybe the average overall entropy is the same. But you assume also that, say, the alpha constant is the same, Planck's constant is the same, gravitational constant is the same... Question is, are you assuming uniformity only of a long list of constants, or do universes, on an infinite or multiverse scale, have an infinite number of constants and potential variations of physics that are simply not noticed by us because all of them are the same in our little region? A reasonably uniform universe might have most of them almost exactly the same but there's always something at ten, hundred, thousand standard deviations away from what it is here. Wnt (talk) 16:15, 11 November 2014 (UTC)

There are a lot of considerations here. I did say that we were assuming the laws of physics are the same everywhere - and I'm presuming that "constants" are indeed "constant" (seems reasonable!)...and I'm not talking about multiverses or extra dimensions or hyper-anything. Just our regular, boring universe - but assuming it to be infinitely large (it might be!) and more or less uniform in content...similar densities of stars and galaxies and that kind of stuff. These are not unreasonable assumptions - I'm just asking for the same approximate degree of uniformity that we see in the visible universe...so that if you teleported somewhere utterly random in the entire infinite universe - the general numbers of stars and galaxies and such would look pretty similar to what we have here. This is surely a reasonable default guess for what would be out there if the universe were infinite.

As for the "rasterize" question. Yes, certainly if we try for a PERFECT comparison between two planet-earths, we would run in to Heisenburg issues. HOWEVER: How much difference would it make if the third proton on the left of the fifth water molecule from the tip of your nose was moving 1% faster or positioned a few picometers to the right? Our macroscopic lives follow largely predictable paths despite quantum-level uncertainty - so two earths could still be sufficiently identical - even if, at the instant we compare them, there are tiny heisenburg uncertainties preventing a direct comparison.

What you're arguing about is the conditions for perfect identicality - which could easily be problematic. But what our OP is asking is whether (at the macroscopic scale) there are an infinity of Steve's typing identical answers into identical Wikipedias...and for that degree of identicality - there certainly could be an infinite number. I'd agree that 20 seconds after we do the comparison - the two Steve's we happen to be comparing are having slightly different thoughts about what they want for lunch due to quantum effects in their respective brains. But we have an infinite number of Steve's - and even if only 0.00000000000000000000000000000000000000000000000000001% of them agree that a Chicken Korma would go down really well right now - there are STILL an infinite number of them making that exact same decision. These variations cause gradual differences between worlds that seem identical right now. But infinity is...**BIG**...and there is room for an finite amount of variation and still have an infinite number of arbitrarily identical Steve's out there to whatever degree of precision you demand that identicality...even if there are also an infinite number who come back after having a Big Mac for lunch - *wishing* that they'd gone with the Chicken Korma.

SteveBaker (talk) 16:59, 11 November 2014 (UTC)

@SteveBaker: Well, it's a red flag that each "possibility", as determined by the rounded-off position of the atoms, could represent any number of different quantum states, and perhaps can't even be determined with sufficient precision except by violating laws of physics. (I'm very much not sure, but I don't think we really can determine the position of each atom to know whether it could be bound to another, without having enough looseness in the momentum that it might only be rebounding. I don't think it's just random fluctuation of water molecules we're dealing with. It's one thing to use an atomic force microscope to figure out the usual appearance of something, but something else again to do so with sufficient accuracy that you could remake a cell from the data) It underscores that the assumption that all possible configurations of atoms have some positive possibility may not be true. More to the point, our own configuration of atoms might have zero probability. (I don't know how, but somehow zero times infinity is not reliably zero) Some other configuration might come up infinitely more often, due to a potentially infinite number of underlying quantum states that all round off to the same thing. (One such possibility perhaps is "sector collapsed to a black hole"?) Infinity is such a tricky thing, every time you think you have it cornered it slips away. (Who would naively imagine that an infinite series of positive numbers could add up to less than an infinite result?) So I remain skeptical. Wnt (talk) 18:17, 11 November 2014 (UTC)

Let us re-read the original question here: "If space is infinite, then does that mean that my exact clone is writing this same question on an exactly same wikipedia as this one in a different planet somewhere?"...so we don't have to care about things that are too small to measure - or impossible to measure for Heisenburg-ish reasons. All we care about is the macro-scale similarities. Is there a clone of our OP writing this same question? There can be a VAST variation in the positions of atoms, energy quanta and all sort of other quantum-scale stuff - but unless those make our OP's clone noticeably different, we're still seeing the same person, writing the same question - and the only reasonable answer to our OP is "Yes". And actually, since there are an infinite number of such clones, you can choose amongst them to find the MOST accurate copies if you so desire - because there is still an infinity of them. Suppose you find a clone but because of the tiniest quantum-scale difference, he correctly capitalized the word "Misplaced Pages"...OK, not a sufficiently accurate clone to our OP...but never mind, there are still an infinity of clones who incorrectly typed a lowercase 'w' just like our OP did. No matter how close you look - right down to the precision that quantum theory allows, there can always be an infinite number of these clones. In the end, you can pick amongst the infinite number of nearly-clones to find in infinity of more exact clones. Once the differences between our Earth and the clones' Earth are literally too small/insignificant to measure - then there is no practical difference whatever - and there are STILL an infinity of those out there. SteveBaker (talk) 19:24, 11 November 2014 (UTC)

Well, my point was that the current OP may be infinitely improbable, probability zero. How is it we're considering a probability-zero event? Well, maybe those are the only ones that are selected by the anthropic principle. So far, the lack of cosmic neon signs in Hubble photos gives us some reason to suspect that worlds like this one are, at least, extremely unlikely; just how unlikely remains an open question. Wnt (talk) 21:35, 11 November 2014 (UTC)

November 9

Falling into a black hole

Suppose an astronaut in a modern spacesuit gets teleported to 10 Schwarzchild radii from an active galactic nucleus, inside the accretion disc. How long does she survive? Will the hot gas in the accretion disc cook her to death? Would the X-rays and gamma rays kill her within a few hours? Or will she survive long enough to be ripped apart by tidal forces?

I know that a quasar's accretion disc is extremely hot, but by earthly standards, I think it's still a near-vacuum. Hence my confusion about the survivability of the environment. --50.46.159.94 (talk) 05:42, 9 November 2014 (UTC)

The pressure caused by the heat alone is a breaking force a significant fraction of the inward desire. In Jupiter, where the forces are exactly balanced, it's hotter than the surface of the Sun and pressurized enough to turn hydrogen metallic and the ionizing radiation would kill a human in short order. A Cessna (a small airplane) will vaporize on the surface of the Sun within 1 second, according to xkcd what if, and the surface of the Sun is only 0.001 times the density of air and only partially surrounded by opaque plasma. The gravity, heat and X-rays is far above this at the event horizon of a black hole, so I would guess it's not survivable. Also, if the black hole is huge enough, tidal forces would not be able to kill. However, fuzzball theory mentioned in a previous thread on black holes a few weeks/months ago states that in that case the body substance would be disintegrated to quarks, gluons etc. and join a ball of string extremely instantly (within a few Planck lengths at 670 million miles an hour). In that case tidal disruption is impossible. Sagittarian Milky Way (talk) 09:09, 9 November 2014 (UTC)

I'd like a further explanation of the pressure at the center of accretion disks. I was just looking at this in the very different context of a Herbig-Haro object where a protoplanetary disk spits out a stellar jet in one or two directions along its axis. But the situation seems sort of the same: gravity pulls all this material in, it "piles up" somehow, and then it gets shot out in jets along the direction the material isn't accreting from. But how much does it "pile up"? And why doesn't it find a way to pile up in a more typical spherical shape rather than reaching escape velocity? And above all, how much actual pressure are we talking about? Is this (in your case) a black hole with an atmosphere??? Wnt (talk) 14:58, 9 November 2014 (UTC)

Bugs?

This split cashew has been roasted and salted for a while, but are these larva?

— Preceding unsigned comment added by DRosenbach (talk • contribs) 16:22, 9 November 2014

Stomped on this one. Have you thought of asking your local Food and Drug Administration office. If they don't have an insect expert at hand, ask them to forward you image to an entomologist. If and when you get an answer, your image could be useful on what ever WP article we have for cashews.--Aspro (talk) 20:04, 9 November 2014 (UTC)

They sure look like larva to me, yes. StuRat (talk) 20:44, 9 November 2014 (UTC)

Yes, maggots. Are they live? Was the nut like this when you opened it, or did you leave it sit out? If they were canned, take them back for a refund. If they were from a local producer let him know. μηδείς (talk) 22:03, 9 November 2014 (UTC)

Think you mean retailer rather than producer (the US imports cashew). Next: “This split cashew has been roasted and salted for a while” so why should they be alive (if they are in fact larva)? Finally: “If they were from a local producer let him know.” So what exactly do you think he is going to do about it!!!? If you have ever worked in the retail business, you will know that customers are forever coming into complain. If a retailer followed up each ever complaint... Do you think the business proprietor or manager would have any time left over to get around to serving any customers? That is why I suggested that the OP goes to his local FDA. That is what they are their for and they can call on expert that can provide learned analyses. Cashew are boiled or steamed so are safe in this respect, but they would realize that a US citizen deserves a proper answer as to what he is consuming when he has doubts. It also gives the FDA a rare opportunity to assure John Doe's that they (the FDA) is doing a good job (cough, cough).--P.g.champion (talk) 21:34, 10 November 2014 (UTC)

I don't think the FDA cares about every worm in an apple. The right person to complain to is obviously the manufacturer of the product (or at least who is listed on the container), who probably has the option to choose which farm, inspect the nuts at the time of sale, etc., and is powerfully motivated not to have this happen too often. Wnt (talk) 15:58, 11 November 2014 (UTC)

Verily. Cashew may be advertized as Raw but it is very unlikely that they have not been heat treated due to presence of urushiol in completely raw nuts -thus the heat treatment killing any meanies at the same time. So health-wise, one can consider store purchased cashews are safe to feed to pigeons and chipmunks. Otherwise why did Tom Lehrer (and girl fiend) offer peanuts and not cashew to their feathery friends?. .--Aspro (talk) 22:22, 10 November 2014 (UTC)

Or just eat the nuts, maggots and all. Once they are cooked they are harmless.

Jack, eating rotten cheese, did say,

Like Samson I my thousands slay;

I vow, quoth Roger, so you do,

And with the self-same weapon too.

Greglocock (talk) 23:43, 9 November 2014 (UTC)

symbol of Diploma Supplement what does it say?

I saw on this site (Medical university) that they show the symbol of "EU" (on the side of the side in the slide: accreditation) ,and I don't understand what it says. If I get a diploma of this university, can I work with it in Europe without to pass any exam? and what it says about the university? (every university in Ukrane can do the same procedure?) Thank you 5.28.158.164 (talk) 17:17, 9 November 2014 (UTC)

No. If you click on the logo it tells you that it is "A document describing the knowledge and skills acquired by holders of higher education degrees. It provides additional information to that included in the official degrees / diplomas and/or transcript, making it more easily understood, especially by employers or institutions outside the issuing country" and it is not "an automatic system that guarantees recognition" Richerman (talk) 21:37, 9 November 2014 (UTC)

The logo in question is that of TEMPUS, an EU organization that "supports the modernisation of higher education in the EU's surrounding area." This is the relevant page from their website. Tevildo (talk) 21:44, 9 November 2014 (UTC)

Er, no it doesn't seem to be. There is a Tempus logo there also, but the one in question is the Europass logo from the European Centre for the Development of Vocational Training. Richerman (talk) 22:00, 9 November 2014 (UTC)

What does it say? (I mean about Tampus) 5.28.158.164 (talk) 01:57, 10 November 2014 (UTC)

TEMPUS is an organisation dedicated to improving the standard of educational qualifications across Europe. Richerman (talk) 10:22, 10 November 2014 (UTC)

How complex is the brain of a common shrimp?

In other words, I know it's more of a fused ganglion thing going on, but is there some measure of average complexity for them, eg. the total number of neurons or an encephalization quotient figure or something? I'm unable to find much of anything on the subject and the only crustacean listed on the wiki page listing animals by number of neurons is the lobster. — Preceding unsigned comment added by 142.105.176.81 (talk) 20:24, 9 November 2014 (UTC)

Shrimp is not an official biological category, so you have to be more specific. See harlequin shrimp which live in mated pairs, and mantis shrimp for one mean critter. The latter are believed to have perhaps the most elaborate visual system of any animal, being able to se up to 16 primary colors, compared to our three. μηδείς (talk) 03:04, 10 November 2014 (UTC)

"Shrimp" can mean different things in common language and science, but mantis shrimp aren't even Decapoda, so they're not shrimp in any scientific categorization. As explained in our article, shrimp usually refers to the grouping of Caridea and Dendrobranchiata suborders of Decapoda when used in scientific contexts. Anyway, here's a recent article titled "Brain evolution in decapod crustacea" . It doesn't give an ecephalization quotient, but it has other measures of the size and complexity of the brains of shrimp-ish organisms. It would be a good starting place for anyone interested in shrimp brains. SemanticMantis (talk) 17:51, 10 November 2014 (UTC)

Nevertheless, my Mantis shrimp are better than your shrimp, Mantis. μηδείς (talk) 18:19, 10 November 2014 (UTC)

Bisulphate of baryta

What is Bisulphate of baryta? The substance is named in Conan Doyle's "A Case of Identity", and it appears in an 1858 chemistry book, but I can't understand what composes it. The latter source

gives a reaction that includes it:

RO , BaO + SO, 2HO = RO

By looking at the name, it is the same as barium bisulfate Ba(HSO
₄)
₂. Plasmic Physics (talk) 20:55, 9 November 2014 (UTC)

According to it is Ba(HSO
₄)
₂ – barium bisulphate. Ruslik_Zero 20:57, 9 November 2014 (UTC)

That reference claims it exists. Another reference is at 100 Chemical Myths saying it does not. Graeme Bartlett (talk) 00:26, 10 November 2014 (UTC)

Looks like it's CAS# 25105-31-1; SciFinder has a several reports for its synthesis, including X-ray crystallography and vibrational spectroscopy in 1970s–1990s. DMacks (talk) 09:44, 10 November 2014 (UTC)

Looks like DMacks has the CAS number, but here's a public web link to a structure: which is simply Ba 2(H2O4S). Simply, that is, until you go to place the positive charge on the barium... The story is at s:A Case of Identity; though I didn't read it I only see a brief mention of it as being a compound Holmes identified, so there are no 'claims' to confirm about it. The OP's chemistry book source has an unfamiliar way of dealing with chemical formulas, but it should be clear that no named atoms but barium, sulfur, oxygen, and hydrogen are present, consistent with "barium bisulfite". It further says that when the substance is heated on platinum, "fumes of sulphuric acid are evolved in great abundance", leaving neutral sulphate behind. Barium sulphate is BaSO4; subtracting that from the above formula yields H2SO4 in equal proportion. So we have one Ba+, one neutral H2SO4, one bisulfate HSO4- ... and a neutral hydrogen left over?? Hmmm. It would be tempting to suppose that you could have true barium bisulphate, i.e. 2Ba+ 2HSO4-, and you can heat that to liberate 1 H2SO4 and leave behind 2 BaSO4. However, it is hard to believe that someone would mistake the amount of sulfuric acid liberated per barium ... especially to think there is more produced than the compound possesses. Either there's a silly clerical error or ... something odd. Anyway, I think we see what kept Sherlock busy for a day. Wnt (talk) 16:50, 10 November 2014 (UTC)

Why does weather anomalies happen?

Hi,
Last year there was a great storm in NY, and the temperature dropped severely.
My question is why those anomalies happen? Exx8 (talk) 20:50, 9 November 2014 (UTC)

You ask an extremely broad question, so we can't provide specific answers. Have you read our Weather article? It may answer your general questions. If you want answers on a specific storm, we may be able to provide more details. Nyttend (talk) 20:56, 9 November 2014 (UTC)

The sort of extreme events you are referring to are called Global weirding by some scientists, see: and . Much of it seems to be caused by climate change affecting the Jet stream. Richerman (talk) 22:36, 9 November 2014 (UTC)

The most common reason for a rapid temperature drop is when a cold front arrives. Rain can also lower the temperature quickly, since it forms where the air is usually much colder. And temperature naturally drops as the Sun sets, so a cold front, with rain, arriving at sunset tends to magnify the effect. There are also more rare reasons for the temperature to drop suddenly, such as downbursts/microbursts. StuRat (talk) 01:30, 10 November 2014 (UTC)

An anomaly, in this context, is something that's rare and hard to predict. Rare weather events come about because of a coincidence of several not-so-unusal things happening at the same time. So slightly elevated temperatures in one place with high humidity someplace else and maybe particular wind patterns at some other place...none of them very unusual individually...come together to make something that is very unusual. These events are often unpredictable for much the same reasons. Also, weather patterns are inherently chaotic - in the mathematical sense of that word. SteveBaker (talk) 02:06, 10 November 2014 (UTC)

November 10

Efficiency of body at energy conversion

I want to find out how efficient a person's body is at converting the chemical potential energy of food into mechanical work (eg. lifting a weight). The article food energy says the food energy realised by respiration is converted to muscular output with roughly 20% efficiency. But this leaves out earlier stages in the chain: presumably not all of the potential heat of combustion of food is realised in respiration; and also I think about 10% of the energy from food has to be `ploughed back', so to speak, into the work of digesting food, so there's another 10% energy loss. I think there may be other inefficiencies.

Then there's that whole thing about, if you hold a 100 pound barbell over your head for an hour, that's not `work' according to the physics definition of the term because there's force but no distance; but it certainly is `work' according to the common English sense of the word – rather hard too, in fact.

Finally, how much mechanical work can a reasonably fit person do in a day? (Eg. in joules.) How about a top athlete? -- Communpedia Tribal (talk) 05:24, 10 November 2014 (UTC)

According to Horsepower#History_of_the_unit, a reasonably healthy human can burst at 1.2 horsepower (890 W), an athlete at 2.5 hp (1,900 W). A healthy human can sustain 0.1 hp (75 W) indefinitely, and an athlete 0.3 hp (220 W) for a few hours. Also note, that the body normally has to burn food just to keep you warm (Thermogenesis#Non-shivering_thermogenesis); if you are exercising heavily then the waste heat is more than enough for warmth, so that saves the body from using food for warmth. CS Miller (talk) 10:31, 10 November 2014 (UTC)

• The net thermal efficiency of a healthy human is about 20%. See also, basal metabolic rate. μηδείς (talk) 18:17, 10 November 2014 (UTC)

What makes this difficult to answer is that "efficiency" is defined in terms of useful work done (our article says: "Efficiency generally describes the extent to which time, effort or cost is well used for the intended task or purpose.") - but the definition of "intended" or "useful" is tough to nail down here. For example, when you run...the energy conversion into kinetic energy is one measure of efficiency - but the muscles generate heat, and as warm-blooded creatures, generating heat is "useful" - so do you count the incidental heat generated by the muscles when running as a part of the useful energy or as a part of the waste energy? Clearly it depends on the situation. In a hot climate, that extra heat is a major problem because it has to be removed from the body somehow - but in a cool climate, we might deliberately use our muscles to increase heat production. So when we're shivering, the kinetic energy generated is "waste" and the heat produced is "useful" - which is a complete reversal from the situation when we're running.

So until you can meaningfully partition wasted energy from useful energy, calculating efficiency is difficult.

That gets worse when you think of things like the energy consumption of the brain. Our brains use about 25% of our energy production...but (for example), a lizard gets by with only about 2% of it's energy devoted to brain functions. If we're simply trying to run fast in a straight line, then that 25% consumption is nearly all wasted because it should be possible to run in a straight line using only 2%...but if we're actively navigating to find the shortest route then thinking more equates to running less, so the brain's contribution to getting from A to B is just as "useful" as piling on more kinetic energys - and so it should be counted. But what about if we're using the time to compose poetry or design the next high-tech widget...then how do you account for that brain energy?

So, (as is often the case here) we need to tie down our terms rather more precisely in order to deliver a reasonable answer.

SteveBaker (talk) 19:01, 10 November 2014 (UTC)

The brain using 25% of our energy is a common trope for which you provide no source, {U|SteveBaker}}. Is our article wrong when it says the brain uses about 20%, while the liver uses about 30, and the heart only 7? μηδείς (talk) 21:25, 11 November 2014 (UTC)

The value of the electron in the world of science

Did it true, that since the discovery of the electron world science had not progressed, because the electromagnetic electronic balance of all elementary particles is always been the same (equal) and always been constant?--Alex Sazonov (talk) 09:32, 10 November 2014 (UTC)

No. Science has made plenty of progress. There is a fringe theory around that says that once a physical quantity is measured then it causes other similar measurements to come up with the same value. Some kind of precedent setting. I don't know what this is called and I don't trust it. Graeme Bartlett (talk) 12:17, 10 November 2014 (UTC)

(ec)No, not at all. There is plenty of science that is progressing all the time. E.g. all of computer science, or special relativity, or the decoding and application of DNA. Or, to stay subatomic, the discovery of quarks (with non-integer charges) and the whole standard model.--Stephan Schulz (talk) 12:23, 10 November 2014 (UTC)

Pretty much all of modern geology has progressed a lot, starting with plate tectonics, which is the Sine qua non for geology. Plate tectonics started as a concept some 20 years after the discovery of the electron (though under a different name) and made major leaps forward in the 1950s and 1960s. Nearly all of meaningful discoveries in meteorology, astrophysics, psychology, etc. etc. came about in the 20th century, while the discovery of the electron occurred in 1897. The discovery of the electron was certainly very very important, but it isn't like it was the only thing that happened in science in the past 120 years. --Jayron32 13:01, 10 November 2014 (UTC)

Atomic electric charge of all elementary particles is always been the same, so it turns out, that in the natural nature are always been only once electrons!--Alex Sazonov (talk) 13:36, 10 November 2014 (UTC)

Except quarks. --Jayron32 13:59, 10 November 2014 (UTC)

And, to be pedantic, protons and positrons. --Stephan Schulz (talk) 15:00, 10 November 2014 (UTC)

Atomic structure of all elementary particles is been the same (universe), so we can conclude that in the natural nature are always been only once electrons, as ideal atoms.--Alex Sazonov (talk) 17:28, 10 November 2014 (UTC)

That statement makes no sense whatsoever in English. AndyTheGrump (talk) 17:32, 10 November 2014 (UTC)

It makes even less sense in the 3000+ other languages of the world. --Jayron32 17:33, 10 November 2014 (UTC)

You might be interested in One-electron_universe. SemanticMantis (talk) 17:42, 10 November 2014 (UTC)

Electrical properties in the natural nature had only once electrons!--Alex Sazonov (talk) 17:47, 10 November 2014 (UTC)

No, they didn't. Saying it over and over again doesn't make it so. --Jayron32 17:52, 10 November 2014 (UTC)

Are you thinking of the plum pudding model, a now-discredited model of the atom? It suggested that the atom consisted of electrons floating in a goo, without any other specific components. Meanwhile, Graeme Bartlett, what do you mean? It sounds like you're describing a researcher with a form of confirmation bias, whereby he's prejudiced toward finding results similar to the one he already got. Nyttend (talk) 20:33, 10 November 2014 (UTC)

I heard it on a podcast recently, but I can't remember exactly which one, or who was the proponent. It was more of a theory of reality. It said that various measurement values were indeterminate until they were first measured and thereafter all future measurements would come back the same. Graeme Bartlett (talk) 22:39, 10 November 2014 (UTC)

The OP's rantings remind me more of Prout's hypothesis, which was actually considered a reasonable conjecture until disproven, which held that all elements were composed of aggregations of hydrogen. Prout proposed his hypothesis because all pure isotopes were multiples of the mass of hydrogen-1 (protium), which implied that hydrogen was in some way fundamental. He was wrong, but in interesting ways. Prout's hypothesis provided an important step in the discovery of the proton and neutron, which (to a rough approximation) DO weigh the same as hydrogen does, and explain why Prout's hypothesis works. Still, it has nothing to do with electrons, and the OPs repeated insistence that everything is somehow made of electrons (it isn't), or that electrons have the smallest fundamental charge (they don't) or that all science since the discovery of the electron is somehow directly derivative of it (it isn't). --Jayron32 23:15, 10 November 2014 (UTC)

Are Mark 60 CAPTOR naval mines being phased out?

This site says: "The CAPTORs are gone, and the SLMMs will be phased out in 2012." in reference to the Mark 60 CAPTOR naval mines. Is this true? I can't find any other collaborating sources. I don't usually trust random online sources, but the author, Scott C. Truver, is on the editorial board of Naval War College Review. WinterWall (talk) 11:39, 10 November 2014 (UTC)

I think this is better asked at Humanities, because notions of chivalry, budget, and perhaps international law are involved. How gone is "gone" is another question for them to chew on. The science aspect I see in the source is Suggestions that the Navy acquire modern foreign mines have been met with “not invented here” indifference. Here it might be worth pursuing what technological improvements the "modern" mines have that the U.S. ought to copy. Wnt (talk) 17:01, 10 November 2014 (UTC)

I did a little reading on the topic; and my conclusion was, roughly summarized: I don't know. But I found some good reading material!

Our Department of Defense keeps a pretty tight lip on its capabilities regarding undersea warfare. You can read about the Navy Undersea Warfare Center and the Naval Mine and Anti-Submarine Warfare Command, but ... there's not much information on technologies or capabilities. Compare this to the websites of the Air Force or the Army, where the public websites advertise all kinds of nifty specifications about airplanes and armored vehicles and guns, arguably for the purposes of recruitment. This is consistent with everything I know about submarines: they're pretty much Top Secret, so there's no good reason to make noise about even their mundane factual details.

I went to the website of the Department of Defense to see if there's any public information - budgets or press releases or speeches. There's a 1996 speech: Three Musts for Affordable Naval Mine Warfare, by Paul Kaminski - who would have had a pivotal role in executing the national defense policy for naval mine technology. And if you search the public Defense Department budgets, there are line-items scattered among the results for naval mine warfare technology development and system acquisition. So this is an ongoing effort; but it's not highly publicized. It is probable that the Navy can not justify losing a capability, even if that capability has no immediate application to any existing conflict.

Even still, it seems cheaper and easier to deploy undersea mines from surface ships and aircraft. There are no shortage of news reports on that: for example, the P-3 Orion Practices Aerial Mine Laying in Gulf of Thailand. To deter enemy mine-laying, there are a variety of effective techniques, from aerial surveillance to diplomatic efforts. When possible, the Navy would prefer to keep its submarines out of the spotlight, because their much more critical role - second strike - depends on keeping them out of combat.

Finally, I would direct you to read this statement from the Department of Defense. In 2014, the United States made a critical policy statement, reversing many years of prior policy: "The United States will not produce or otherwise acquire any anti-personnel landmines in the future." On the whole, the Defense Department has decided that antipersonnel land-mines are not a good thing, from a defense standpoint. They bring bad publicity; they are hazards to friendly forces; and mines persist for a long time after the conflict is over. When confronting conventional state-based opponents, it is easier to enforce treaty-compliance through diplomacy, and avoid mine-warfare by "gentleman's agreement;" and when fighting a non-state actor in asymmetric warfare, there is little advantage in deploying the mines ourselves; in fact, our biggest problem in the last few wars has been that the asymmetric opponent had far too easy access to land mines and improvised explosives. The reversal of American policy is huge - landmines are a very big problem throughout the world, even in places where conflicts "ended" many years ago.

Important to note, though, that anti-vehicle landmines and naval mines were not mentioned in the policy statement. Evidently, the Defense Department had no comment on those topics.

Nimur (talk) 16:46, 11 November 2014 (UTC)

High humidity in refrigerator

If the relative humidity inside a refrigerator is high (in the high 80s range), what could be the cause? --173.49.12.187 (talk) 13:02, 10 November 2014 (UTC)

Here are some possible answers to your question. --Jayron32 13:12, 10 November 2014 (UTC)

I have that problem in my fridge, too, in the summer, when the house air is humid. In fact, water drips from the divider between the top freezer and bottom fridge. I simply put a bowl under where it drips and dump it regularly. I think of it as a fridge plus dehumidifier. The fact that it's dependent on house humidity implies that keeping the humidity in the house low will solve the problem, too. StuRat (talk) 16:36, 10 November 2014 (UTC)

My parents' fridge has a little heating element which when turned on evaporates the condensation that otherwise drips from the freezer to the fridge. She gets upset if it is activated, and then accuse people of spilling water on the refrigerator door! My OR would be to leave a jar of baking soda in the fridge as a desiccant and stir it occasionally until it cakes up. This is actually a recommended use by the manufacturer (see the box) to keep the fridge "fresh". μηδείς (talk) 18:09, 10 November 2014 (UTC)

Baking soda is most probably the most cost effected method normally, as it is cheap. Yet, if one has very high humidity then maybe Blue Indicating Silica Gel might be better Blue Indicating Silica Gel. One rejuvenates it in the oven. If on the other-hand, (say for augments sake) one's daughter's boyfriend always raids your fridge every time you go out (in the hope that by by leaving them together – alone- without Mom and Dad's eyes following and analyzing their every interaction; in the faint, faint hope that they ignore everything the have seen on TV and might discover the same magic- Oh that's for another time). Then leave a diaper in the fridge. That has silica gel in it too and will bring down the humidity. Should the boy- fiend see this diaper, then come to terms with the fact that he is probably dating a member of the Adams family, then you're almost home and dry. Suggest however, one uses, unused diapers in the fridge.--Aspro (talk) 23:36, 10 November 2014 (UTC)

The ambient humidity is not the problem. The refrigerator was recently serviced for a different problem. There is another refrigerator in the same area. The relative humidity inside the latter is the 40s. --173.49.12.187 (talk) 02:18, 11 November 2014 (UTC)

You misunderstood me. I'm not saying that a properly operating refrigerator should drip water when it's humid in the room. I'm saying a malfunctioning fridge may only drip when the ambient humidity is high.

Some models of fridge have a drip pan under the fridge to catch drips, so they admit that this is a possibility. But my question is just what is supposed to happen to your ambient moisture ? It enters the fridge each time the door opens, and is likely to condense at the lower temperatures, and it has to go somewhere. A heater to evaporate condensed water and blow it outside the fridge is one way to handle it. Personally I think pouring the waste water down the drain is a better option, rather than using energy to evaporate it and put it right back into an already humid room, where it will again enter the fridge the next time the door is opened. StuRat (talk) 04:52, 11 November 2014 (UTC)

The drip pan is normally mounted on top of the motor/compressor unit, and uses waste heat from it to evaporate the condensate. CS Miller (talk) 12:36, 11 November 2014 (UTC)

Lets break this down into tiny steps: The two fringes may be working at different temperatures. The lower temperature fridge (one would think) has the lower humidity. Second. Humidity meters are notoriously hard to calibrated (unless one has a laboratory grade instrument). Are the same instruments (thermometer, hygrometer) being used to measure both interiors? The average hygrometer bought at the local store are mostly not worth the money. So it one has two they may well not agree with each other.--Aspro (talk) 22:14, 11 November 2014 (UTC)

Nearest-planet-to-Earth graph

Is there somewhere a graph plotting the Earth–Mercury distance, the Earth–Venus distance and the Earth–Mars distance all against time (for at least a few years around now)? Or is there free data somewhere from which I could build this graph myself? 85.226.205.208 (talk) 18:04, 10 November 2014 (UTC)

This website has utilities that will let you do exactly that, for every planet in the solar system. --Jayron32 18:21, 10 November 2014 (UTC)

FYI, Venus will always be the closest at least once a year, since its orbit is closest to ours, and with its quicker period it laps us at least once every calendar year. μηδείς (talk) 21:57, 10 November 2014 (UTC)

You might find http://www.fourmilab.ch/solar/solar.html to be helpful.

—Wavelength (talk) 22:05, 10 November 2014 (UTC)

Thanks for all the suggestions! I was a little confused as to how to gather data series from those pages, so I ended up writing a little Python script to send repeated requests to the Fourmilab page, and output the distances to a CSV file. I hope they'll forgive me for flooding the server. It made for a very interesting graph indeed! 85.226.205.208 (talk) 12:52, 11 November 2014 (UTC)

Cool, care to share your graph(s)? It would probably be well placed on our Commons, and could be used in a variety of related articles. SemanticMantis (talk) 14:59, 11 November 2014 (UTC)

November 11

Copper in homopolar motors

I've noticed that most simple homopolar motors use primarily copper wires in their structures. Is there something specific about copper or is it just because it does not attract magnets? Will a zynk or an aluminium wire work in a homopolar motor then? 128.68.216.15 (talk) 00:19, 11 November 2014 (UTC)

Copper is an excellent electrical conductor. Plasmic Physics (talk) 02:19, 11 November 2014 (UTC)

Yes. I believe silver is a better electrical conductor, but that would cost too much. StuRat (talk) 04:41, 11 November 2014 (UTC)

Copper is also quite flexible, so it survives vibrations better than other metals like silver and aluminium. Silver actually conducts electricity a little better than copper - and for something like an electric motor, the slightly worse conductivity of aluminium would hardly be noticeable. Price is not a small matter - and historically, copper was cheaper than aluminium...but since the world is rapidly running out of copper ore - we'll be seeing aluminium wiring used a lot more than it is right now. SteveBaker (talk) 04:57, 11 November 2014 (UTC)

Copper-clad aluminium wire is also used for some purposes, although often controversially when used for twisted pair data cabling purposes . (It's more established in the high frequency coaxial market.) Also Copper-clad steel although that's not exactly new. I think these examples demonstrate some other advantages of copper such as relating to corrosion or oxidation, although some of them are probably not relevant to the motor case, e.g. Galvanic corrosion, but see our articles also also or other discussions. (As an aside, copper clad wire has some disadvantages too such as the current difficulty separating the metals meaning recycling is difficult .) Nil Einne (talk) 11:55, 11 November 2014 (UTC)

How fast would a spacecraft be travelling?

In our article Taurus Molecular Cloud 1, there are a couple of videos that zoom in from a more distant perspective. If a spacecraft were able to travel as the speed depicted in the video, how fast would the craft actually be travelling in the depicted timeframe and distance? 99.250.118.116 (talk) 01:03, 11 November 2014 (UTC)

I don't think the viewpoint is changing at all. It's like the zoom lens on a camera - you're changing the field-of-view of the lens - not physically moving the camera through space. If you were moving from earth to a place where things looked that big without zooming, you'd have to cover most of the the 430 lightyear distance in about one minute. Let's call that 400 lightyears per minute...which in "classical" terms would be about 200 million times faster than the speed of light. Unfortunately, you can't travel faster than light...so that can't happen. But the problem is a bit worse than that. Because of relativity, the faster you travel, the more compressed distances seem to you. So you wouldn't have to travel faster than light to get there that quickly...going somewhere quite close to the speed of light would be enough to get you from here to there within a minute...from your perspective. However, if you were sending those photos back to earth via telemetry, it would take over 400 years, no matter what. SteveBaker (talk) 04:03, 11 November 2014 (UTC)

Note that in any "cloudy" environment, a ship would see changes as obscuring dust moved across the field of view that aren't replicated in the video. Also, in practice moving so close to the speed of light would impose really severe distortions on the field of view. Wnt (talk) 15:49, 11 November 2014 (UTC)

The end of Rosetta (spacecraft)

Rosetta (spacecraft) is in orbit around a comet and it is planned that it will land a probe on the comet tomorrow. The article says the mission will end Dec 2015. At first I assumed that the comet would go near the sun and the Rosetta would burn up, but a bit of research shows that it will only approach to 1.2 AU and will only go out as far as 5.7 AU. We have seen Mars surface explorers keep going in a hostile environment for many years past the original planned mission. At the closest approach there should be no problem with "too much sun." . So why couldn't the mission continue a lot longer than the projected Dec 2015 ending? Is it just a matter of having answered the set questions, and other projects needing attention? It should not need propellant to stay in orbit around the comet. Would there be too little solar power after Dec 2015 to run the reaction wheels from time to time for orientation correction and to keep the computers and heaters going? How about out at 5.7 AU? Edison (talk) 19:14, 11 November 2014 (UTC)

I note that Solar panels on spacecraft says "The Rosetta space probe, launched March 2, 2004, will use solar panels as far as the orbit of Jupiter (5.25 AU)..." How far out from the Sun will Rosetta be in Dec 2015? Edison (talk) 19:27, 11 November 2014 (UTC)

Probably the money that was allocated to keep the ground station operative runs out at the formal end of mission. This has spelled the death of many vehicles. NASA sometimes extends missions - but only when they are generating new science...and it may be that the instruments on Rosetta will have extracted about all they can by December. You only need just so many photographs of a comet. But also, as the craft gets further from the sun, the solar panels produce less and less energy. The specifications say they produce 850 watts at 3.4 AU. When you double the distance, you get one quarter the amount of power...so at 5.7 AU they are probably only generating about 300 watts. It doesn't take much extra distance to make a huge difference to the power availability. As the amount of sunlight reduces, the need to heat the spacecraft to keep the electronics alive increases - so you have increasing demand and decreasing supply. I also wonder whether the spacecraft's orbit is as stable as you imagine - given that the asteroid doesn't have a nice spherical shape - and its' mass is reducing all the time and at unpredictable rates. SteveBaker (talk) 19:59, 11 November 2014 (UTC)

There might be new information as the comet moves away and cools. Will its weak gravity draw back at least a portion of the outgassed vapor and emitted particles, so that they redeposit? If I recall correctly, Rosetta was 19 miles or so from the comet, so its orbit should be less effected by the duck or potato shape of the comet than if it were close by. The comet is putting out huge amounts of water vapor presently (a liter every 15 seconds if I recall correctly). I wonder if passing through the vapor will push Rosetta farther away, or degrade its orbit and bring it in until it hits the comet. Is there any reason Rosetta would not follow the comet indefinitely? Edison (talk) 22:39, 11 November 2014 (UTC)

Magnets and heat

I've heard that enough heat can ruin a magnet. How much heat are we talking about exactly? For example is it possible to ruin a neodymium magnet by boiling it in a cooking pot? 89.178.237.122 (talk) 20:27, 11 November 2014 (UTC)

This page on a magnet supplier's website says that some neodymium magnets can be be demagnetised permanently at a temperature of 80 °C, so yes, boiling one in a cooking pot might do it, though it is dependant on multiple factors - precise makeup, shape, and exposure to reversed magnetic fields. AndyTheGrump (talk) 20:41, 11 November 2014 (UTC)

In short, no, boiling the magnet won't ruin it. Curie temperature is what you need to reach, i can't see a reference in that article for neodymium but you might be able to google it.Vespine (talk) 22:06, 11 November 2014 (UTC)

Depends on the exact composition of the material. Some Rare-earth magnets are build specifically to withstand high operating temperatures, such as those used in electric motors (e.g. ). Mihaister (talk) 23:47, 11 November 2014 (UTC)

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