Wikipedia:Reference desk/Archives/Science/2015 June 30

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June 30

How is it that one mole of any gas occupies 22.4 l?

How is it that one mole of any gas occupies 22.4 l at STP? Yogesh Khandke (talk) 03:26, 30 June 2015 (UTC)

Ideal gas law DTLHS (talk) 03:32, 30 June 2015 (UTC)

You mean V = NRT/P will always be constant = 22.4 l? I will have to do the numerical. Thanks Yogesh Khandke (talk) 04:32, 30 June 2015 (UTC)

OK, V = (1 x 8.314 x 273)/101325 = 0.0224 cu m, or 22.4 l, and also the since equation has only one intrinsic property which is set to 1, N = 1, whatever value we get, it will be constant for all gases. Still, physically I still don't get the "how"? See we have one mole being made up of 6.022 x 10^23 atoms/ molecules of carbon di oxide, oxygen, or whatever gas, what is I see is one atom the size of a foot ball, the other a golf ball, another a table tennis ball, at STP, how do these equal number of different sized balls fit in one size 22.4 L? Yogesh Khandke (talk) 05:00, 30 June 2015 (UTC)

I don't know the answer but I imagine that the size of the molecules is a very small percentage of the size of the distance between them in the gas. ----Seans Potato Business 12:21, 1 July 2015 (UTC)

Ask yourself, how much of the 22.4 L is actually occupied by gas molecules, and how much is occupied by the empty space between gas molecules? The actual size of the molecules doesn't matter because most of the volume is actually empty space. Dragons flight (talk) 06:27, 30 June 2015 (UTC)

Well, it matters some. It's the b parameter of the van der Waals equation. --Trovatore (talk) 06:33, 30 June 2015 (UTC)

Indeed. The OP's surprise that all gases occupy the "exact same" volume might be tempered when we explain that all gases are not ideal. For most gases - and in particular, near standard temperature and pressure conditions - the behavior is nearly ideal. Small non-idealities are introduced when we use other equations to enhance the ideal gas equation; and the perfect volumetric equivalence for all species of gas goes away. Nimur (talk) 12:43, 30 June 2015 (UTC)

Even more generally: Equation_of_state#Cubic_equations_of_state. Thermodynamics! shoy (reactions) 12:48, 30 June 2015 (UTC)

The ideal gas law can be derived from the kinetic theory of gases. As Dragons flight says, one of the assumptions of simple kinetic theory is that the size of each molecule is very much smaller than the average distance between molecules. Another assumption is that the average kinetic energy per molecule is proportional to the temperature of the gas. So if we increase the mass of each molecule by a factor of 4, but keep the temperature and volume the same, the average kinetic energy decreases by a factor of 4. And hence the average speed of each molecule is halved. Now that molecules are travelling at half of the original speed but with four times the original mass, each collision with the walls of the container imparts an average impulse (change in momentum) that is twice the original average impulse. But collisions happen only half as often as they did before because the molecules are travelling half as fast. So the pressure on the container walls (average force per unit area, which is average impulse per unit time per unit area) is unchanged - the increased impulse in each collision is balanced out by the smaller number of collisions per second. This is a "hand waving" explanation - for a more rigorous derivation, see our kinetic theory article . Gandalf61 (talk) 11:17, 30 June 2015 (UTC)

• I need to digest the information provided, many thanks. Yogesh Khandke (talk) 02:39, 1 July 2015 (UTC)
  • Take your time -- it's not simple. The easiest thing is just to assume that the gas is "ideal", which essentially means that molecules are points and that there are no inter-molecular attractions. Once you've gotten your head wrapped around the properties of ideal gases, you can get into situations that depart from the ideal gas behavior (referred to as "real" gases). These mostly have to do with low temperatures and/or high pressures. Short Brigade Harvester Boris (talk) 02:51, 1 July 2015 (UTC)
    • The answers above are excellent, but I might add that the ideal gas law is a model, an approximation; it works well in many of the situations we deal with frequently (ie RTP) but it gets further and further from reality when its assumptions begin to break down. One such breakdown is at very high pressure, where molecule size becomes relevant. Another is at low temperature, when intermolecular interactions become significant. And so forth. Vanamonde93 (talk) 01:35, 2 July 2015 (UTC)

I think the root of the surprise is that people think that if you have some big gas molecules banging off each other, they'll collide more often and so they'll bounce away more. The thing is, the molecules that collide more often will collide more often on the way out toward the wall anyway... the issue isn't how often they collide in mid-air, but simply how many, with a certain mass, and a certain range of speeds, are striking the outer edge of the container - which doesn't depend on whether they are big or small or how far they go before they bounce off the next molecule and draw another random velocity -- from the same histogram of speeds. Wnt (talk) 03:47, 4 July 2015 (UTC)

Bose-Einstein condensates

Bose–Einstein condensation at 400, 200, and 50 nanokelvins. The peaks show that as the temperature goes down, more and more atoms "condense" to the same energy level.

This image appears at Bose–Einstein condensation (network theory) with the same caption. It confuses me: is left 400 and right 50 or vice versa? Saying "400, 200, and 50" sounds like they're going left to right, but it looks like more and more atoms "condense" to the same energy level as you go from right to left, i.e. it's 50, 200, and 400. Nyttend (talk) 12:30, 30 June 2015 (UTC)

It confuses me too! There are no axis labels, and the image description page and the articles do not directly explain what is being plotted. I could make assumptions that we're looking at a two-dimensional histogram, but I'm not sure if the horizontal axes represent position, phase-space, or something else. I'm not sure if the vertical axis represents particle count, particle energy, or something else. I'm even less certain what the three instances of the graphs represent, but this is the only item directly described in the caption (apparently the parameter that varies between each graph is temperature).

The graph was contributed by a Wikipedia editor nearly ten years ago, but it is not referenced from a publication. If we can find a suitable replacement, or a suitable reference to explain it, we should improve or replace the image. You could try contacting the image uploader via their talk page. Nimur (talk) 12:39, 30 June 2015 (UTC)

I remember reading a while back that the graph represents the number of atoms present in an energy level. From what I remember, the ‘higher’ the graph the more atoms are present at that energy level. The flat nature of the graph on the left indicates that the atoms are all relatively evenly distributed among energy levels (which is expected in normal conditions). The graph on the right (specifically the peak) indicates an extremely high number of atoms concentrated in a specific energy level.208.87.234.202 (talk) 13:15, 30 June 2015 (UTC)

...which corresponds to the lowest temperature, as the caption explains. Lowest temperature is on the right-hand side. 129.2.106.82 (talk) 13:54, 30 June 2015 (UTC)Nightvid

Yes, that description is consistent with that given here [1], it claims that that the images are of a velocity distribution, though it does not give explicit temperatures, nor the axis labels. A key point is that the right image is coolest. The right image has almost all peak, with very little variance around it. The center image has a peak, but also some variance. The left image has almost no peak, and reflects the "normal" variation of velocity. The page linked above is the lab web page of Prof.Dr. S.O. Demokritov, and I'm willing to call that reliable enough for these purposes. As a stop-gap until better images or sourcing can be found, I've slightly modified the caption. SemanticMantis (talk) 14:00, 30 June 2015 (UTC)

Yes. The key is the red. The more red, the more condensate. The peaks are an illusion since the temperature is lower on the right. They aren't larger on the right but the energy difference as a percentage is larger for the peak. Higher Q factor to borrow from a different field. --DHeyward (talk) 06:28, 1 July 2015 (UTC)

Fate of coronary artery plaques after rupture

When someone has a heart attack due to a ruptured plaque in a coronary artery, and then gets clot-busting drugs in the emergency room, why doesn't the clot re-form after the drug wears off? Isn't the rupture still there? 129.2.106.82 (talk) 14:03, 30 June 2015 (UTC)Nightvid

The "clot-busting drugs" you refer to are more commonly referred to as "blood-thinners." It is dangerous to stop taking a blood thinner at any time, not just after heart attack treatment. A study on Warfarin and Xarelto at Duke University in 2012 found that heart attack/stroke risk increased rapidly when ceasing blood thinner use. Further studies have both validated and partially contradicted that study. The contradictions have to do with further refinement of the population based on other treatments, history of heart attack/stroke, and end-results that are similar, such as pulmonary embolism or deep-vein thrombosis. For most patients, the blood thinner dissolves the plaque and allows for normal clearance in the urine. There are some, a vast minority, who become threatened. Therefore, new procedures are constantly being developed to break down and capture the plaque rather than release it into the heart or the rest of the blood stream. It would be best, of course, if cardiovascular disease was stopped before it began. As it is, most hypertension and cardiovascular specialists are simply trying to improve a very bad situation. 209.149.113.185 (talk) 15:48, 30 June 2015 (UTC)

I'm talking about the drugs used only for the acute MI, such as Tissue Plasminogen Activator, which are discontinued. If the different drugs such as thinners are enough to prevent a new clot, would they also have been enough to prevent the first one, if they had been taken early enough? 129.2.46.176 (talk) 01:46, 1 July 2015 (UTC)Nightvid

What do inspectors of nuclear facilities search for?

When foreigner inspectors of nuclear facilities visit a country, how can they know whether a bomb isn't hidden somewhere else? Or that more enriched plutonium is not hidden somewhere else? Atomic bombs don't have actually a huge volume that would be tricky to hide. --Bickeyboard (talk) 17:02, 30 June 2015 (UTC)

They look for blatant evidence of wrongdoing. The way it has worked in the past, primarily with Iraq and then Iran, they schedule a specific time to visit a specific installation. The date is set well enough into the future to ensure that there will be nothing questionable at the facility. Then, the inspectors do a walk-through. During the Iraq inspections, there was a lot more public information about the cleanup before inspections, including surveillance photos showing trucks moving "stuff" from the inspection facility to a non-inspection facility. With Iran, there is far less information, but the inspections are still scheduled well in advance and limited to specific installations. 209.149.113.185 (talk) 17:12, 30 June 2015 (UTC)

That's exactly the problem. How can they find anything this way? --Bickeyboard (talk) 17:31, 30 June 2015 (UTC)

Basically, they don't. It's a charade for political purposes mainly. The only concrete benefit to the inspector is that it prevents some wrongdoing. If the inspected facility knows they are going to be inspected, they will avoid doing what they are not supposed to do (at least temporarily). It is a way of getting minimal compliance when there would otherwise be zero compliance. Gnome de plume (talk) 17:35, 30 June 2015 (UTC)

While some of the responses above are quite cynical, they are also un-sourced commentary. Perhaps you would like to read about the IAEA's work, including work related to the Nuclear Nonproliferation Treaty, Monitoring in Iran, and Monitoring in the DPRK. Treaty compliance, inspection, and external auditing is not easy, but it's also not a "charade." Nimur (talk) 17:54, 30 June 2015 (UTC)

It's not that easy or bad. To separate out U235 you need large and complex machinery. Similarly for Plutonium. And these materials are relatively carefully accounted for, so it's not that easy to make some of it vanish. Checking the books is part of the inspection. Talking to the personell is part of the inspection. It is not very easy to keep a secret when a large number of people are necessarily involved in it. --Stephan Schulz (talk) 17:43, 30 June 2015 (UTC)

These inspections are of the nuclear power stations (while in Iraq, the inspections included buildings accused of housing chemical weapons). It is well-known where Iran built their enrichment facility and it is not included in inspections. 209.149.113.185 (talk) 17:54, 30 June 2015 (UTC)

Do you have a source for this information? If not, you should reconsider whether your comment merits inclusion in this encyclopedia's reference desk. First, to which inspectors do you refer? Secondly, to whom are these speculative facts well-known? Thirdly, which reliable source reported that the inspectors intentionally avoided such facilities? If you cannot directly attribute these allegations to anybody, you might need to read our guidelines on unsupported attributions and reliable sources. Nimur (talk) 17:58, 30 June 2015 (UTC)

The IAEA, already linked above, does not inspect the enrichment facility itself. They ask Iran to report on it, but never actually set foot in the facility. Further, it is well-known where the facilities are. You can get a list on Wikipedia: Nuclear facilities in Iran. How is this controversial? To be more correct... I must point out that an enrichment plant was built and shown to inspectors in 2009. It was not operational at the time and access has not been documented with the IAEA since. I am happy to be corrected with documentation tha the IAEA *has* been in an operational enrichment facility. Your complaint is that you just disagree. 209.149.113.185 (talk) 18:05, 30 June 2015 (UTC)

Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council resolutions in the Islamic Republic of Iran, (29 May, 2015). The IAEA asserts that it has independently verified many facts. It asserts that several technical visits were arranged, conforming to the "Framework for Cooperation," including technical visits to centrifuge facilities and the Lashkar Ab’ad Laser Centre. The Agency asserts (in this and other reports) that it has physical access to numerous facilities in Iran: "Iran has continued to provide the Agency with managed access to centrifuge assembly workshops, centrifuge rotor production workshops and storage facilities." (Page 1 of the report). Non-proliferation inspection, in particular when conducted under the auspices of the United Nations and the IAEA, does not mean "unrestricted access to anything and everything in the nation;" there are rules about what is covered. For starters, read IAEA Safeguards to learn what they inspect, why they inspect it, and under what international legal frameworks these inspections occur. Here is a list of locations relevant to the implementation of safeguards in Iran. If you think something is missing, perhaps you should make a convincing case to the Commission.

IAEA's Director General stakes his professional reputation, and his funding, on the veracity of such public documentation. I would not be surprised if there have been many more confidential internal findings, technical visits, and reports; but these are the reports that are available to the casual, uncredentialed, unprivileged internet reader at no cost. Nimur (talk) 19:32, 30 June 2015 (UTC)

We are apparently seeing different information in the same document. I see "managed visits" to facilities to produce and store centrifuge parts. Those facilities are not the enrichment plants - those are just part factories and warehouses. This is important because the number of parts produced is directly related to the number of centrifuges in operation. If there are no hidden parts being used, the IAEA can make an assumption about the number of centrifuges in use and detect more being used. As for enrichment operations, it is stated that environmental samples are taken to determine the operations. What does that mean? I take it to mean samples of the environment: air, water, and soil. There are also many instances where it is stated that the claims being made are based solely on statements from Iran. I want to make it clear that it is obvious that the IAEA is inspecting Iran to the best of its ability. I simply believe (based on the wishy-washy language of IAEA reports) that its ability is limited when it comes to physical access to an operational enrichment centrifuge. 209.149.113.185 (talk) 19:53, 30 June 2015 (UTC)

All of these are fair critiques. International inspections are not easy and it is plausible that there could be corruption, incompetence, or oversight. We are all entitled to interpret the facts and publications subject to our own biases. I personally do not think there is significant corruption, incompetence, or oversight; I think the media poorly portrays the complexity of the problem, and presents a dramatically over-simplistic "good-guys and bad-guys" narrative with respect to nuclear safety. I imagine that if the tables were turned, and foreign inspectors showed up at your home, workplace, hospital, school, laboratory, or power station, carrying paperwork written in legalese in a foreign language, insisting that they had a right to inspect your things, you would not let them have free run of the place. You probably would call for your local or national government to help you kick these invaders off of your property! So it is with international inspectors in Iran. These international agencies run a very fine line between enforcing international laws (agreements, rather) - even when approved by the local government - and also complying with local laws.

You can find many opinion pieces and policy reviews that applaud the IAEA, and you can find many more publications that harshly criticize their work. Here's a perspective piece from the RAND Corporation, an organization that I find to be very well-informed and less susceptible to flimsy political biases than most media outlets: The Days After A Deal With Iran: Implications for the Non-Proliferation Regime. What irks me is not your bias or your opinions: I respect your right to those viewpoints. Surely I have my own biases and opinions...! But at least, when we contribute on the Reference Desk, we need to back up any claims with informed citations, so that all readers of our encyclopedia can form their own opinions.

Nimur (talk) 20:25, 30 June 2015 (UTC)

There was a computer virus released through Siemens I thought that gave a pretty good idea of the number of centrifuges Iran was using. The virus varied the spin rate too quickly and caused the centrifuges to become unstable and destroy themselves. There was quite a bit of data regarding repair that didn't quite jive with published accounts. --DHeyward (talk) 06:37, 1 July 2015 (UTC)

You are thinking of stuxnet. I'm not sure about gave a pretty good idea of the number of centrifuges Iran was using, I believe it was 'reverse engineered' to a degree, but I don't believe it "reported back" any information like number of centrifuges in Iran. In fact if I remember correctly, Iran was deduced to be the target mainly because that's where most of the infections were reported. Vespine (talk) 06:44, 1 July 2015 (UTC)

Nice video and lecture re IEAE at http://www.fourmilab.ch/documents/nuclear/plutonium.html and http://www.fourmilab.ch/documents/nuclear/uranium.html GangofOne (talk) 06:54, 1 July 2015 (UTC)

Correct, Stuxnet couldn't report back because the centrifuge facilities do not have any form of connection to the Internet. That is what made Stuxnet so special - it was designed to get to a network that it had no means of reaching (until someone broke security protocol and brought in Stuxnet on a USB drive). Also, the "released through Siemens" statement is most likely incorrect. While it is easy to find countless blogs that claim Siemens was involved, the evidence based on the language in the code of Stuxnet and the purpose of Stuxnet points towards Israel. It is important to note that Israel has denied any involvement with Stuxnet. 199.15.144.250 (talk) 12:44, 1 July 2015 (UTC)

There is even one more step involved. StuxNet infects PC's that are on the net - then installs itself onto memory sticks and USB music players. They bet that people would take these infected devices, put music on them and plug them into PC's that were NOT on the Internet so they could listen to music at work. Those PC's were then infected - but that's not what killed the centrifuges. Stuxnet actively seeks out PC's that were running a very specific application that the Iranians used to design software for the microprocessors that drive the centrifuges. That infected design software would then add extra code into every microprocessor application that the Iranians wrote that would check to see if it was controlling a centrifuge - and do to the nasty deed. It hid itself very well, so not even using the debugging software would find it...because the debugger was also infected. So not only were the centrifuges off-net, but so were the PC's used to write the software for the centrifuges. It required software engineers (who really ought to know better!) to bring infected memory sticks and music players from home to plug into security-sensitive machines at work. Very, very, clever - exceedingly hard to pull-off.

SteveBaker (talk) 22:31, 1 July 2015 (UTC)

I should have been more clear. Siemens didn't create it, but I think they helped isolate it. The amount of tech support needed from Siemens was the indicator of the damage and scope of the program. Siemens wasn't called out to fix one centrifuge controller and they know how many times Siemens went and how many techs. JTAG is a wonderful thing. --DHeyward (talk) 22:37, 1 July 2015 (UTC)

I don't see it mentioned here, but I recall news coverage of the IAEA having left cameras at inspected sites, then complaining when seals were broken. I don't think we're giving this a proper answer - maybe try on the Humanities desk and you'll find someone more familiar with international protocols. Wnt (talk) 00:59, 6 July 2015 (UTC)

There was one case where the inspectors collected dust just lying around in the building, had it analyzed, and found an isotope that shouldn't have been present, had they been doing only what they claimed. StuRat (talk) 01:04, 6 July 2015 (UTC)

Star & Stellar Evolution

Hello, Can some check this two articles please, I believe its not done appropriately; information(s) might need to be migrated from one another... Regards -- Space Ghost (talk) 20:44, 30 June 2015 (UTC)

What exactly is the problem? I suggest that you post your suggestions to Talk: Star and Talk: Stellar evolution, or, if you know what the improvement would be, be bold and edit. Do you have a specific question? Robert McClenon (talk) 01:54, 1 July 2015 (UTC)

No, apology.

My English is not very good, therefore I'm not being bold enough to edit the articles...I don't wish to give out wrong information or make WP look like idiots English language usage type of thing, to others; if you know what I mean... Plus I have not come to English learning yet.

'Smoking' is my subject not 'science', so I always try to recheck with you guys as I'm learning... I've learnt most of it before, I'm learning it again in detail, and coming across some things, e.g., Star, Stellar Evolution, Star Formation, protostar and so on, all articles should be merged into one article named 'Star' and 'redirects' should be used for 'star formation', 'Stellar Evolution', 'protostar', 'pms' and so on. Because when someone wants to learn something it will be easier for them this way. I thought mentioning it here would give the upper hand...in what to do... -- Space Ghost (talk) 19:12, 1 July 2015 (UTC)

Does anyone know, to whom I can speak about this? This one (Star) article has 5 babies (extra articles), not required...Its just needs to be organised... -- Space Ghost (talk) 19:45, 1 July 2015 (UTC)

You can try at the talk pages, but a better place would be Wikipedia:Proposed_mergers. There you can propose the merges and your reasons. I think people will disagree with your proposal, but I'm not sure. I understand your perspective, but we have different articles for a reason. If one article covered all that, it would be huge and hard to navigate. Also, not everyone who looks up stars wants to know all the details about their formation and evolution. However, there is a lot of redundancy stellar evolution is discussed in star, so maybe you should take it to proposed mergers. It would be interesting if nothing else. Here's one thing you can easily do: make sure that each page has links to the other pages. For example I just went to star and searched for "stellar evolution" - the words do occur, but they are not wiki-linked! There is a later link, but I see no reason not to link it at first mention. That's a way you can improve articles without even writing any new English. Beware of WP:OVERLINK, but don't worry about it too much. Overlinking is better than underlinking. So you can go to these and help make WP better just by linking articles together. That way people who want to learn will find it easier to find other related articles. SemanticMantis (talk) 19:57, 1 July 2015 (UTC)

They are linked hierarchically but perhaps it can be more direct. For example, star has a section for formation. There is a main article for star formation that has a subsection for protostar that is also a main article. Wikipedia is generally built this way. Some degree of flattening the links (i.e. a protostar reference in the star article that short circuits the star formation article) is sometimes helpful but I don't think merging will be in WP's interest due to size. Sometimes, the "What links here?" function can help with navigation. WP can be a cyclic graph which is sometimes the bane and anathema to persons that prefer flatter or acyclic graphs. --DHeyward (talk) 00:55, 2 July 2015 (UTC)

You both have valuable points, I don't think everyone will agree with my idea either now; because some people like dividing their learning's, the article might be long/big/vast and so on. If WP articles are built the way it is seen, it won't change...

If I find anymore article(s) in different subject(s) with a similar issue, then, (I don't know,) I might notify, for the sake of it.

Anyway, thanks for clearing my head friends. Love you all (not in a gay way!). -- Space Ghost (talk) 07:35, 2 July 2015 (UTC)