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March 5

Does drinking water right after a meal makes us fatter?

humans who drink water (let's say a glass or two) right after eating a bowl of pasta \ or a sandwich, would they theoretically gain more fat then those who won't drink ?, does this phenomenon has a literal name? 79.183.98.234 (talk) 03:51, 5 March 2013 (UTC)

Seems very unlikely. What's the source of that bizarre idea? Looie496 (talk) 05:23, 5 March 2013 (UTC)

No Primary source, it's just something i heard and in first sight made some sense (when thinking about the water interrupts the enzymes in their work).

Probably because they will gain weight, that being the weight of the water, at least until they pee it back out. StuRat (talk) 05:43, 5 March 2013 (UTC)

There are a bunch of theories running around (Google [ water with meals ]) involving diluting digestive acid and thus hindering digestion, diluting digestive acid and causing more to be produced, thus helping digestion, causing the food to empty into the intestines faster and thus hindering digestion, causing the food to empty into the intestines faster and thus making you become hungry sooner, and the fascinating theory that if your body really needs food you will have no trouble eating enough to meet that need without extra water, but once you start overeating you need to "wash the food down".

As far as I know, there are no scientific studies supporting any of these theories, but we do know that simply keeping a log of what you eat helps with weight loss, so anything that makes you think about what you are eating rather than finishing off a large bag of chips while watching TV is probably a Good Thing.

The best unproved diet theory I have heard of is a fellow who kept all his food in a guest house a mile from the main house, and any time he wanted to eat anything, from a full meal to a snack, he had to walk two miles to fetch the food, and another two miles if he had leftovers he wanted to put in the refrigerator afterwards. If anyone wants to buy me some property with a lot big enough to try this, let me know. I suppose having the food at the top of ten or twenty flights of stairs would work as well. :) --Guy Macon (talk) 09:32, 5 March 2013 (UTC)

There's a more modest approach which can help, too. During a meal, you can put healthy things on the table, and make people get up to get the unhealthy things. For example, leave the salt in the cupboard, but put other spices on the table. Laziness can accomplish changes in our diets which willpower can't. StuRat (talk) 22:18, 5 March 2013 (UTC)

There is such a thing as water weight gain (as explained here), but as Guy Macon said, its only temporary. Some quack diet pills are simply diuretics, which cause temporary weight loss, but neither have anything to do with "fat", only the "weight" of water. — Preceding quack comment added by 74.60.29.141 (talk) 12:25, 5 March 2013 (UTC)

This may come from a junk-science email that's circulating in social media right now (my g/f sent me a copy yesterday) - it lists a bunch of very specific times (before/after meals, before/after sleeping, exercise, you name it) when you should or should not drink very specific amounts of water. That's a complete load of B.S.

The best dieting book I've seen is "The Hacker's Diet" (Wow! We have an article about it!) (it's a free download, or read online at http://www.fourmilab.ch/hackdiet) - and it really does work. The beauty of it is that it's science-based, with actual references - and he spends much time explaining the science behind how it works. The author doesn't make money from it - so you also know it's not some get-rich-quick idiot promoting yet another fad diet. SteveBaker (talk) 15:26, 5 March 2013 (UTC)

Manipulating water intake -- more, less, timing or intake, even diuretics-- will make no significant long term difference to anyone's weight. Total distraction. All effective weight loss plans involve eating less over an extended and indefinite period of time. All the popular diets work to the extent that following them results in eating less for a prolonged period of time. Even following the low carb recommendations of Gary Taubes, whom many people extol as opposing the "calories in" approach, actually results in reduced calorie intake to be effective. No matter how you dress it up and what you call it and what you eat, the only thing that produces long term significant weight loss is eating less over an extended period of time. alteripse (talk) 22:50, 5 March 2013 (UTC)

You can be tricked by salt. Eating more salt causes increased water retention and increased weight thereby. This is one or the reasons for the "My low calorie diet did not reduce my weight" phenomena - their low calorie diet wasn't very tasty, so they added salt. Salt can be at the heart of the "I exercised more, and gained weight" experince, incorrectly blamed on the "muscle weighs more than fat" nonsense (volume for volume it weighs about the same, and the body can't change muscle size as readily as it can change fat quantity anyway). This is more of a problem for older people - in middle age and younger the kidneys are pretty effective at getting rid of excess salt. Wickwack 120.145.159.132 (talk) 01:41, 6 March 2013 (UTC)

Wickwack, total nonsense. Salt and water fluctuations from day to day amount to less than a kg (2 lbs). In severe kidney failure (needing dialysis) or congestive heart failure a patient can retain more than that but temporarily, but it needs to be removed by dialysis or diuretics. The fantasy that overweight people have that it is just water is just a wishful fantasy. alteripse (talk) 11:03, 6 March 2013 (UTC)

There appears to be zero evidence supporting the above claim.

BTW, I have finally found the answer! --Guy Macon (talk) 10:10, 6 March 2013 (UTC)

It would appear that Wickwack is correct. Muscle density is about the same as fat density. It happens that I was diagnosed with Meniere's Disease. The standard advice you get for this, from medical practictioners, is to reduce your salt intake as much as possible. My doctor told me that when I do this, my weight will drop a few kg. Initially the drop is typically because patients then find food boring, and eat less. He told me that this is temporary as after a few weeks I will get used to how food tastes without salt and my appetite will return. But there is typically a permanent weight loss as without so much salt I'll have less fluid retention. I won't look much different, and won't need new clothes, as I won't have lost any fat on a long term basis, but I'll weigh less because I'll have less fluid in me. Experience has shown that doctor was right on the money. Floda 124.182.38.179 (talk) 12:41, 6 March 2013 (UTC)

Alteripse, do you have any references to support your nonsense? Perhaps you should check your facts before posting. One should be very wary of advice on this subject given by those who work in the diet/weight loss industry. However, take a look at this Government website: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Fluid_retention. It says in the first paragraph (titled "Summary") that fluid retention is caused by excessive salt intake, as well as a few other causes. Googling salt and water retention will give you quite a number of sites supporting this fact, quite well known to jockeys and other sports people whose weight determines what class or handicap they compete in. Incidentally, day to day variation in weight can be and often is, considerably greater than the single kg you indicated. I've worked outdoors for much of my career. In temperatures of 45 C and greater, quite typical in many parts of Australia, the average person in outdoor work can loose 5 to 8 kg or even more per half-day shift in a full shift day. We sure do get thirsty though. Younger men need to take considerable extra salt or quenching their thirst after their shift will cause problems. But just so we are clear, in regard to salt in my earlier postings, I was talking about reasonable long term changes in weight due to changes in salt intake. Wickwack 58.167.229.59 (talk) 13:42, 6 March 2013 (UTC)

Wickwack, this started out as a question about water drinking and its relation to fat weight. Such questions are rarely about fluctuations of 1 kg, but from people who are distressed at degrees of overweight from 5 to 50 kg. When someone well-intentioned but relatively ignorant of physiology posts about fluid retention and salt intake without explicitly referring to end-stage kidney or heart disease, the information is usually irrelevant to the questioner's fat weight concerns or simply erroneous. The salt and water answer to "how can I weigh 0.5 kg less tomorrow" of course can be "empty your bladder before you step on the scale", or "temporarily drop a kg with a diuretic pill or a few hours of work in the hot sun". If you want to gain half a kg you can eat very salty food and drink a lot of fluid and it might take your body a day to unload it. While this might be of intense interest to a wrestler who needs to drop 0.5 kg to wrestle in his usual class in 2 days, do you really think this is at all relevant to significant long term weight loss for significantly overweight people? Of course not; it was distracting nonsense. There simply are NO "reasonable long term changes in weight due to changes in salt intake", just short term fluctuations much smaller than your claims. Healthy people do not lose 10% of their body weight ("5-8 kg") by a day of working and sweating and stay healthy. alteripse (talk) 19:35, 6 March 2013 (UTC)

Go look up climate stats for northern Australia. Or Saudi Arabia. Then, ask yourself, do humans live and work there? The answer of course is: temperatures around 45 C qite normal in summer and yes, we do live there and like everyone else we need to work and earn a living. And no, we don't get sick or suffer health issues, we get used to it. But we can't change physics. Such temperatures are so far above body core temperature (37 C) that we are wet with sweat all day - and that means weight loss well above 1 kg. Few people would find a gain or loss of only 1 kg of note - you started this particular nonsense. The odd silly tourist from England sometimes dies, because they are not used to it. Wickwack 120.145.63.10 (talk) 00:12, 7 March 2013 (UTC)

Wickwack, Alteripse is right and you are wrong. In particular, your comment above that starts with the words "You can be tricked by salt" is completely unsupported by any actual evidence. Your "This is one or the reasons for the 'My low calorie diet did not reduce my weight' phenomena - their low calorie diet wasn't very tasty, so they added salt" statement is not science. It goes against everything we know about human physiology. It is just plain wrong to say that the small amount of water retention from increased salt can overcome the much larger reduction in body fat that comes from eating less and moving more. There is no evidence supporting your claims. --Guy Macon (talk) 21:21, 6 March 2013 (UTC)

I'll say this one more time: Take a look at this website: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Fluid_retention. It is a Government health website of a Western country, so is trustworthy, unlike many websites established by those in the diet/weight loss business. Here is a direct quote form the summary: Causes [of fluid retention] include the body's reaction to hot weather, a high salt intake, and the hormones associated with the menstrual cycle. Neither Guy Macon nor Alteripse have provided any refrences to support their refutation of this. Wickwack 120.145.63.10 (talk) 00:12, 7 March 2013 (UTC)

You can say it as many times as you like but it doesnt make it true. And your website doesnt even back up your claims of a large or long term weight effect. Dont demand we "prove" your misconceptions are misconceptions. You have no idea what you are talking about, and dont understand the websites you are citing. alteripse (talk) 00:21, 7 March 2013 (UTC)

Wickwack, perhaps this is a partly a language problem. No one is arguing that weight cannot fluctuate due to salt and water intake and loss. We are arguing that the magnitude is both small and not cumulative. By small, we mean usually less than a kg in people with normal hearts and kidneys. Loss of enough water and salt to reduce your weight by 10% gets you to prostration and the edge of hypovolemic shock, not just thirsty, so you need to re-adjust your understanding of sweat losses and salt gains to much smaller amounts. More importantly the weight gain or loss with salt is not cumulative. You can gain a kg or so by salt intake in a week but you dont gain another kg every week you continue the high intake-- the body readjusts. Look up atrial natriuretic hormone for one of the mechanisms. So for people interested in long term weight gain or loss of more than a kg, your information about salt and water intake is completely irrelevant. Worse, it promotes a common fantasy among overweight people that "I'm not fat, it's just fluid retention". A kg might be, the other 20 kg are not. That is why your comment was both inaccurate and unhelpful even though a nugget of it--- that small weight fluctuations can be attributable to fluid and salt gains and losses--- is true. You have not, and will not be able, to find a citation that proves that large or cumulative weight changes over time can be caused by either. Sorry to get you so riled up, but can we lay this to rest please? alteripse (talk) 02:58, 7 March 2013 (UTC)

This reminds me of an old Friends episode, where they were viewing a rather fat Monica on old home video:

Monica: "Remember, the camera adds ten pounds."

Chandler: "OK, so exactly how many cameras were on you ?" StuRat (talk) 03:18, 7 March 2013 (UTC)

Are there any research about compounds of francium?

I am just struggling with some information seemed to be original research in Chinese wikipedia.--Inspector (talk) 10:25, 5 March 2013 (UTC)

How about: Electronic properties of francium diatomic compounds and prospects for cold molecule formation

Have you tried Google Scholar → "francium compounds"

74.60.29.141 (talk) 13:05, 5 March 2013 (UTC)

That might be helpful about Francium, but I still wonder if there are any about francium hydroxide and francium sulfide, because some data in those two articles in Chinese looks like OR.--Inspector (talk) 00:50, 7 March 2013 (UTC)

Unknown elements in the universe?

Is it possible that some unknown elements exist in the universe, even in the Milky Way galaxy, which are not known to humans? And if unknown elements really exist, how reliable and accurate is astronomical spectroscopy? --PlanetEditor (talk) 12:45, 5 March 2013 (UTC)

Have you read Chemical element, Periodic table and Island of stability? What makes an element is the number of protons in its nucleus (its atomic number), and we know all the elements with ANs between 1 and 118. Elements with higher numbers than this would probably be very unstable, and would quickly decay into other elements. However, see the Island of stability article for a possible exception. Rojomoke (talk) 13:22, 5 March 2013 (UTC)

Thanks! --PlanetEditor (talk) 14:48, 5 March 2013 (UTC)

So the quick answer is "No"...as Rojomoke points out, the behavior of atoms (and therefore how we name them) depends on the number of protons they have and we've found absolutely all of them up to element number 118 or so. Above that, they get unstable and fall apart about as fast as you can make them! The only slight possibility is that "Island of stability" idea. It's thought that the general trend is that adding more and more neutrons and protons makes atoms increasingly unstable...which means that above element number 118, things get even more unstable - so there aren't any more elements worthy of discussion beyond that. However, the concept behind this "Island of Stability" thing is that there might maybe be some much larger number of neutrons and protons that would again produce stable atoms...so maybe something with an atomic number like 200 would be stable enough to exist for a long time. That's not a proven theory though - it's not clear whether it's true. HOWEVER - even if it's true, it might well be that there are no natural processes (inside stars, basically) that would create such gigantic atoms in the first place. So even if the island of stability is real - the odds are good that these elements would still not be found in nature. Indeed, if they were commonplace, you'd expect to see mysterious unaccounted spectral lines in the light from distant stars caused by these gigantic atoms. I don't think we see that - Astronomers aren't scratching their heads about a bunch of mystery spectral lines. Hence either the island of stability isn't real - or these elements are too hard to create for them to exist naturally in large enough quantities.

(One of the things that upsets me about watching Star Trek is their continual reliance on mysterious new elements with crazy behaviors. That kind of thing just isn't scientifically reasonable. Their "dilithium" crystals - that power their engines - are a weird exception. There really is a substance called that - it's a compound formed from two lithium atoms - but you can't have crystals of it because it's a gas...still, those guys are smart...maybe they can fix that!)

SteveBaker (talk) 15:09, 5 March 2013 (UTC)

If they can have transparent aluminum, they could have crystalline lithium. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:18, 5 March 2013 (UTC)

Ah - be careful: Scotty was talking about Aluminium oxynitride - aka "transparent aluminium". It's a completely clear, bullet-proof material - and it would be great for making large water tanks for transporting whales. SteveBaker (talk) 15:40, 5 March 2013 (UTC)

How about unknown molecules that exist in the universe? ScienceApe (talk) 17:35, 5 March 2013 (UTC)

Well, for sure, yes. We find new molecules in plants, animals - even within our own bodies all the time. There are (potentially) an infinite number of different molecules. SteveBaker (talk) 20:55, 5 March 2013 (UTC)

There still is not (imo) a satisfactory explanation for dark matter. — Preceding opinionated comment added by 74.60.29.141 (talk) 19:33, 5 March 2013 (UTC)

True - but it's not going to be anything like normal atoms - so we wouldn't call that material "an element". SteveBaker (talk) 20:55, 5 March 2013 (UTC)

• By the way: it looks like the OP had their question answered with the 1st response.
  • I agree - but a little clarification sometimes helps.

Neutron stars may contain unusual elements, as they can add neutrons as fast as they drip out of the atoms. Graeme Bartlett (talk) 09:41, 6 March 2013 (UTC)

Thank you everyone. --PlanetEditor (talk) 16:22, 6 March 2013 (UTC)

One great example (of recently discovered crystal, not a new element) is crystalline deuterium, a macguffin I used in fiction to build a new generation of hydrogen bombs. It's real, and the super-strength nukes would be quite compact, too, as the 15,000 tons per bomb would occupy no more than 105m³ in real life, a density that exceeded my expectations. (They were weapons of sterilization, not merely of mass destruction. However, some tons of mass do get lost in the process...) - ¡Ouch! (^{hurt me} / _{more pain}) 08:07, 8 March 2013 (UTC)

I think this all comes back to the question of "how reliable and accurate is astronomical spectroscopy?" - and I have no idea. What are the odds that the spectral lines of Element 200 have been written off as some combination of hydrocarbons? Wnt (talk) 00:09, 10 March 2013 (UTC)

Top and Tail trains - how can both locomotives be helping?

This [1] discusses push-pull trains, saying ".... a push–pull train, especially a long one, may have a locomotive on both ends so that there is always one locomotive pushing and one locomotive pulling. In this case, caution must be used to make sure that the two locomotives do not put too much stress on the cars from uneven locomotives.... It is usual to arrange things so that the trailing locomotive supplies less power and that the locomotive at the front does more pulling than the locomotive at the rear does pushing."

I think I can grasp how both locomotives could help to move a rigid train. (If I'm pushing a car and you're pulling it we both help it to move.) But exactly what would happen if every coupler had a centimetre of slack? If the rear locomotive is of any use it will be compressing at least some fraction of the car (wagon) couplings and pushing some fraction of the train. Assuming the front locomotive is doing anything useful at all it will be stretching the couplings of the front cars (wagons) and pulling that part of the train. But how can both locomotives be useful unless they have exactly the same power (with the middle coupling slack)? If all the couplings are compressed or stretched, won't one locomotive have to do all the work?

I am sure I've misunderstood something or that I have not explained my puzzlement very well. Obviously the actual answer, which I cannot visualize, arrives at an equilibrium. I'm sure one of you clever clogs will help me resolve this. So that I can sleep. Your Username 19:18, 5 March 2013 (UTC) — Preceding unsigned comment added by Hayttom (talk • contribs)

Gee thanks, now I won't get to sleep either!  — Preceding sarcastic comment added by 74.60.29.141 (talk) 19:41, 5 March 2013 (UTC)

It could be that the front engine is pulling the front half, and the rear engine is pushing the rear half. CS Miller (talk) 20:03, 5 March 2013 (UTC)

Ok, try this for a thought experiment (I make no claims for real trains). You've worked out the rigid case, but wonder about small amounts of slack. Consider instead very large amounts of slack. In this instance, the back pusher is really only pushing a few cars that have compressed linkages, and the puller is only pulling cars with taut linkages. If pusher and puller and all cars are equal, then only the central linkage is neither taut nor compressed. So far, I think you are right in that regard. However, if the back pusher is weaker, that will just push the loose linkage toward the back of the train, until at some point, as you say, the puller does all the work. Of course in the real world, linkages don't have that much play, because of backlash_(engineering) issues. But I thought thinking about very loose links would make the situation more clear. Also modern linkages appear to have some range of elastic deformation, meaning that they have states between totally taut and totally slack. See the many options at Railway_coupling SemanticMantis (talk) 20:07, 5 March 2013 (UTC)

Good question and I think we really need a loco driver to answer it definitively. I would imaging that the leading cab informs (continuously) the rear cab of both the speed and horse power (load) the rear cab is required produce to to achieve a bit bit less than 50% of traction required to push buffer-to-buffer all of the wagons based on its own speed (ie. Push less than half of all the wagons). The rear loco delivering some what less than 50% could then leave a safety margin of several wagons in the middle, that are either pushed or pulled but ovoids all wagons being pushed which would lead to wagons being buckled off the line. The lead cab would be able to tell from its own speed changes if this balance was being kept. Long heavy trains such as these would have a lot of inertia, so I would imagine that there is ample time for the crew to make fine adjustments. --Aspro (talk) 20:14, 5 March 2013 (UTC)

It seems that Railway coupling buffers act as hydraulic dampers, which dissipate kinetic energy, (and make the connection semi-rigid) so it is essentially the same as your rigid example. See photo→

~:74.60.29.141 (talk) 20:50, 5 March 2013 (UTC):~

I don't actually know the answer either - but I used to work with railroad locomotive simulators and a few non-obvious data points are worth mentioning:

1. On very long trains, of the sort that have rear locomotives, the length of the train typically exceeds the length of the longest hill on the trip. This can lead to some very counter-intuitive situations, such as the locomotive needing the most power as it heads down over the crest of a hill because all of the weight is still climbing up it - and in reverse, the brakes often need to be on during the uphill parts because most of the cars are still heading downhill.
2. When the train stops on level ground, rookie drivers tend to come to a very gentle stop rather than stopping more abruptly as they should. This leaves you with tight couplings and the train may find it impossible to start moving again because it has to overcome the static friction of all of the wheels at the same time rather than accelerating one car at a time.
3. The issue of acceleration, starting and stopping is by far the hardest part. Long trains have very little air resistance (their cross-section is tiny compared to their length) - and steel wheels on steel rails produces very little rolling resistance. The amount of power required to keep the train moving is much less than you might expect. I suspect then that the rear locomotive is there for those kinds of situation where acceleration or braking (or perhaps both - but at opposite ends of the train) is required.
4. There are other complications when going around long, tight turns where the train is like a string that wants to be pulled straight - the forces that pull the train cars sideways are enormous - so derailment is alarmingly easy. Having the train being pushed from behind as well as pulled from the front dramatically reduces those forces.

Train dynamics are a deeper subject than you might think! SteveBaker (talk) 20:51, 5 March 2013 (UTC)

(ec) One problem I see with pushing only, is that, when the train stops, all the couplings will be fully compressed, and starting a train like that would be difficult, as you must overcome the static coefficient of friction for every car, simultaneously. This could be handled by either having the rear locomotive brake when it stops, to stretch out the couplings, or it could back up a bit, for the same purpose, before starting.

Another possible problem with pushing is that it will tend to push cars off the tracks, while pulling will tend to pull them back onto the tracks. Under normal conditions, this wouldn't be a problem, but there may be situations where pushing will cause it to derail, but pulling won't. With this in mind, only using the rear locomotive to pull it's own weight, and not the train, might make sense. When the train heads the other way, that locomotive can do all the work, while the now rear locomotive just pulls it's own weight. StuRat (talk) 20:57, 5 March 2013 (UTC)

• I think people are overthinking this -- it's actually pretty simple. Just imagine the case of a single weight that is being supported from above by a stretched string. Suppose somebody pushes upward on the weight from below, but not strongly enough to lift the entire weight. Still, the force the string needs to exert will be reduced, even though it remains stretched. Looie496 (talk) 22:59, 5 March 2013 (UTC)

No. The mass is distributed along the whole length of the train. Your analogy is not applicable. Think of a heavy chain. Lift the bottom link and the total wait can only reduce by the mass of that link. Now your out of bed, have a strong cup of coffee.--Aspro (talk) 00:00, 6 March 2013 (UTC)

Funny – the above two posts are a bit like two locomotives themselves: Each carrying part of the weight; both of the two models are valid in a certain range of applicability. The chain model ceases to be valid when all buffers are pushed in, and the front locomotive will be directly pushed. That is of course rather rare (such as when it decelerates faster than the rear locomotive, or maybe in certain terrain situations). In that event, the solid model applies. — Sebastian 00:57, 6 March 2013 (UTC)

Oh Really? What about when all buffers are pushed in and the forward cab brakes or comes to a curve and buckles or pulls the wagons off the track. As I said above, a balance of force needs to be maintained to prevent this (ie. less than 50%) to prevent what you call the solid model. See SteveBaker's post above. He has got the handle on this too. Looie496's analogy was a was a piece of string. Have you ever tried to 'push' a piece of string? What's funny about that? P.S. Maybe you’ve drunken way too much coffee this morning. --Aspro (talk) 02:11, 6 March 2013 (UTC)

Lots of good food for thought. Thanks, everybody! [more inputs welcome...] Your Username 05:55, 6 March 2013 (UTC) — Preceding unsigned comment added by Hayttom (talk • contribs)

Not a proper answer, just deduction: Logically, the front locomotive should tug on all the cars with (up to 100% of) maximum power. The train should be designed not to rip apart under maximum power, regardless of whether it is stopped or moving. So the locomotive should pull the front car, second car, third car etc. all with the maximum length of the connector, until either the train is moving slowly or else it is totally stopped because the coefficient of static friction on the last car, plus the coefficient of rolling friction on the cars already moving, is enough to totally counter the front locomotive's pull. Either way, the back locomotive, once started, should start pushing cars ahead of it, all with the minimum slack between them in a pile - until the total friction totally stops it, or until the front in the series of stacked cars is moving at full desired speed, for example if it is being pulled by the front locomotive. So I predict that you'll have longest lengths at the front of the train, short connector lengths at the back, maybe something in between at a point between. If the locomotives vary in power relative to one another, the number of cars at each length should vary accordingly to take up the load. (i.e. moving a middle car from "all the way forward" to "all the way back" reflecting whether it is being pulled from in front of it or pushed from behind it) Wnt (talk) 00:19, 10 March 2013 (UTC)

Technical side of feeding electricity into the grid

Can you feed in electricity at any point of an electric grid? Even if these point of access was conceived for households to consume energy? OsmanRF34 (talk) 19:41, 5 March 2013 (UTC)

Not sure on the technical aspects of it, but this power company has a special two-way meter that calculates the difference between power generated at home versus power consumed from the grid, and has an option that pays you for excess power generates. See [2]. This website here also implies that a simple two-way meter is all that is needed; there does not appear to be any other special equipment needed for you if you are producing excess power that is getting added back to the grid (i.e. production exceeds consumption). --Jayron32 19:53, 5 March 2013 (UTC)

Regulations would require a safety systems which ensure that in the event of a local distribution circuit going down, that one doesn’t continue to pump power in to a dead circuit which could endangers the utility workers trying to fix it. Other than that, there is is not technical reason that stops one and many households in Europe already do so.--Aspro (talk) 20:26, 5 March 2013 (UTC)

That's true so long as most people don't do it. However, if everybody had a windmill and their property was covered with solar panels, you might find that too much power was fed into the grid on windy, sunny, cool days, when neither electric heaters nor A/C use that electricity up. StuRat (talk) 20:46, 5 March 2013 (UTC)

Too much power! Oh, that will be the day. We humans will find lots of ways to use it up as fast as its produced. On sunny days, why bother with charcoal? Just have and electric barbecue, or an under-floor cooled garden patio, etc.--Aspro (talk) 21:01, 5 March 2013 (UTC)

"Too much power" is a very real issue in load balancing of an electrical grid. If the power generated exceeds the power consumed, the grid voltage will rise, with all the problems involved in running things above their design voltage. --Carnildo (talk) 03:11, 6 March 2013 (UTC)

A commercial power-station's output is in the range of gigawatts. I don't know of an grid where total domestic input exceeds the main generating force. The large utilities already have to adjust between base load and peak demand, so micro-generation is not likely (in the foreseeable future) lead to such a scenario that you suggest. --Aspro (talk) 15:56, 6 March 2013 (UTC)

The total domestic production doesn't need to exceed the main generator production, to cause problems. Kiet has an example, right below, where this happens in Australia. As electricity prices go up, and prices for solar panels and windmills come down (especially with government subsidies), we might see more of this. StuRat (talk) 16:36, 6 March 2013 (UTC)

As others have said, electricity can be injected into the grid at any point. Essentially, this is what power companies do anyway - most grids have evolved over time with various large and small power stations at various locations. Technically, no special meter is required for customers who generate their own power (by sola panels) and feed it back into the grid. The standard electrodynamic meter inherently reads correctly in both directions - it will run backwards if power flows from house to grid. However, in most cases, what the power company pays you for power is different to what they charge you for power. For example, the power company in my area charges approx 12 cents/kW.hr for what you draw, and pays you 22 cents/kW.hr for what you give back. There's no sense in this - they do it because the Government passed a law to compell them to, to encourage take up of solar power and keep the greenies happy. Where there is no Govt law or Govt subsidy to the power company, the power company will typically pay less than what they charge for power drawn. They need to install special 2-way meters in order to tell which is which.

A minor reason (can be a strong reason for some power companies) is that their existing accounting systems cannot sensibly handle a meter reading lower than the previous reading - it will be treated as the meter having gone round the clock. The extra reading for power feed back by consumers with solar is entering into a special add-on computer system for accounting.

A technical issue does exist with two much power feed by consumers back into the grid. The isssue has arisen with Australian power companies due to the rediculous and stupidly high subsidies on photo-voltaic power. A power company must supply to consumers a voltage within specified limits, otherwise appliances will not work correctly and/or be damaged. A typical specification in 230 V countries is +,- 7%. (Note that in many British Commonwealth countries the spec is more complex due to political reasons). A power company will traditionally install and configure its infrastructure so that the voltage at any one consumer at 4 AM (when draw is mimimal) is under the upper limit. The voltage at houses during business hours can go to the upper limit during business hours, while everyone is at work and school. The voltage will drop in proportion to draw, so that at about 6:00 PM when people com home from work, turn on aircon and start cooking, the voltage will drop the most. The power company installs transformers and cables etc large enough so that the 6:00 PM voltage reamins greater than the low limit. If too many consumers install solar power, it can cause the street voltage to rise above the upper limit, as the peak solar output will always be during business hours. This may force the power company to alter transformers for a lower zero load voltage, which of course will cause the evening droop in voltage to go below the lower limit. To counter that, the power company will have to install heavier cables to reduce the variation.

Generally though, for solar power installations, the invertor used is required by law to shut down if the voltage on the line is outside (too low or too high) limits. This has led to the Australian experience that the first people in the street to install solar power get quite a large reduction in the power bill. They tell their neighbours, who then install their own systems. Sooner or later, there is too much capcity, the voltage rises, and the invertors automatically shut down. Then everyone (including the early adopters) finds their power bills drop a lot less than they expected.

Kiet 120.145.55.126 (talk) 01:24, 6 March 2013 (UTC)

That's relly interesting Kiet, do you have a reference where I can read up more about that? Searching "Solar Power Oversupply" only gets articles about too many panels being on the market. 124.191.176.111 (talk) 06:34, 6 March 2013 (UTC)

I don't know any online references. It has been reported in Australian trade journals. When I get a spare moment, I'll check back issues and post some references. Keit 124.182.29.31 (talk) 07:55, 6 March 2013 (UTC)

Something nobody has mentioned yet is that the waveform of the power being added to the line must be in phase with the waveform existing in the line - phase differences can cause all sorts of problems. Roger (talk) 16:03, 6 March 2013 (UTC)

This last issue is resolved by using an inverter approved for grid connection. Itsmejudith (talk) 17:34, 6 March 2013 (UTC)

March 6

Silent Supernovae

Is it right to say that when a star goes supernova, it is an acoustically silent event, even if one could (hypothetically) witness it from a close distance? And because sound cannot travel through space, this would also apply to events such as Gamma Ray bursts, and even the Big Bang itself, correct?Honeyman2010 (talk) 04:50, 6 March 2013 (UTC)

This seems to be a common question. Sound can and does travel through space, as it is not a complete vacuum. However, due to it being a pretty good vacuum, the sound propagated is not what human ears could detect, even if the human could function in that vaccuum. You would need absolutely immense ears. Go to the top of this page, and try "sound in space" and similar strings in the Search Reference Desk archives field, and you'll be entertained for quite a while. Wickwack 120.145.35.223 (talk) 05:17, 6 March 2013 (UTC)

And, when the particles blasted off during the supernova hit you, they would make quite a racket, indeed. StuRat (talk) 05:29, 6 March 2013 (UTC)

Not to mention, vapourise you in the process. I mean planets in orbit have a difficult time surviving such an event, what chance have a mere human? If our sun were to go supernova, Jupiter would be stripped entirely of its atmosphere and be left a metallic white-hot cinder only just larger than earth. The outer gas giants beyond should fare better. Plasmic Physics (talk) 08:06, 6 March 2013 (UTC)

If you were in that star system, sure. But if you were far enough away, you're spaceship would just get noisy when the particles hit. StuRat (talk) 16:30, 6 March 2013 (UTC)

Or do it the Native American way: touch your ear to the dark side of a planet. The chances of survival are still somewhat low... ;) - ¡Ouch! (^{hurt me} / _{more pain}) 08:04, 8 March 2013 (UTC)

As for the Big Bang, yes, you would hear it, but it would not sound like a bang. It would sound more like a very, very ,very loud, high pitched hum, which would decay both in volume and pitch in an exponential way. You'd hear it because space was not as vacuous as it is today. Plasmic Physics (talk) 07:24, 6 March 2013 (UTC)

After this much time, it has decayed to such an extent, that it is not discernable from background noise. The sound would initially have been audible for millions of years. Plasmic Physics (talk) 07:28, 6 March 2013 (UTC)

Considering a gamma ray burst, would it not create secondary sound as it irradiates the listening device, creating a large amount of static. Plasmic Physics (talk) 08:09, 6 March 2013 (UTC)

Big Bang and light

Is it true that all matter can be converted into light? If so, is the coverse true? If that is also true, could the primeval atom have been pure light in a metastable state, which spontaneously condensed into matter, such as particle-antiparticle production from gamma radiation. How many electron volts would a single photon have to represent to contain the total universal energy and all its mass. Plasmic Physics (talk) 07:51, 6 March 2013 (UTC) "Let there be light." Plasmic Physics (talk) 07:54, 6 March 2013 (UTC)

If matter fell into a black hole, or quantum tunneled into a black hole, the hole may then decay into Hawking Radiation, which may be mostly photons. So the future of matter may the formation of cool photons. You will have to say how big is the universe to get an answer to the total energy in the universe. As the universe ages the visible universe expands, so we do not actually know the size or mass of the universe. Graeme Bartlett (talk) 09:33, 6 March 2013 (UTC)

Well, the most obvious problem is that there's no such thing as light before electroweak symmetry breaking. If you believe inflation, the energy of all the particles in the universe came from the energy of the field that caused inflation, which is similar to the present-day Higgs field or dark energy. So they did come from pure energy, in a way.

According to Google the density of the universe is around 5·10⁻³⁰ g/cm³, and the radius of the visible universe is about 46 billion light years, and it's spatially flat, so the total mass in the visible universe is around (5·10⁻³⁰ g/cm³) (4/3) π (46 Gly)³ ≈ 10⁹⁰ eV/c². But that's just the part we can see. -- BenRG (talk) 22:13, 6 March 2013 (UTC)

What would happen to such an energetic photon if released into our universe today? Plasmic Physics (talk) 08:14, 7 March 2013 (UTC)

Some questions about the Universe

I have some questions about the Universe.

1. Is the Universe finite or infinite? Universe is the sum total of all matter and energy. The unknown part of the Universe, i.e. the part that extends beyond the observable universe, may be finite or may be infinite. What are the current opinion regarding this?

2. If the Universe is finite, then it must have edges or boundaries. I want to know what is beyond that boundary? Is that pure vacuum?

3. If the Universe is infinite, then why is it said that the Universe is flat. An infinite object is not supposed to have any shape.

4. According to the Big Bang theory, the Universe, at its beginning (the very early Universe), was rapidly expanding and cooling, and then expanded gradually. I want to know is there any explanation how did this very early Universe originate? --PlanetEditor (talk) 13:31, 6 March 2013 (UTC)

(Q4) If I'm not wrong, Stephen Hawking said something like at the very very early stages of the Universe, it (the Universe) was just like a very small balck hole. As time does not exist in a black hole, there was no time before the Big Bang. There is no cause or origination for the Universe because there was not time for a cause to exist in. It just "popped up" like a proton, which IS possible according to some elaborate Science laws. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:44, 6 March 2013 (UTC)

If you're talking about the stuff in A Brief History of Time, that was never mainstream; it was just a description of his own (highly speculative) research. -- BenRG (talk) 21:53, 6 March 2013 (UTC)

re Q2: finite does not imply edges or boundaries. The surface area of the earth is finite, for instance, but has no edges, (according to modern theories). Imagine a 4th dimensional sphere analog that we're on the 3d surface of. Now imagine that sphere expanding, and now you have the expanding universe we experience, where there is no particular center to the expansion which is uniform all over. Gzuckier (talk) 18:15, 6 March 2013 (UTC)

(Q1) According to the Shape of the universe article, the infinite flat model is currently the most popular of the models of the universe that fit the currently available data. Red Act (talk) 21:54, 6 March 2013 (UTC)

1. Nobody knows. If you asked cosmologists to guess, I suspect a majority of them would say infinite, but that doesn't mean much. 2. As Gzuckier said, it doesn't imply there's a boundary, but there could be a boundary. There would be nothing outside of it, which is not the same as vacuum. Light can't propagate through nothing. 3. An infinitely large object can have a shape. For example an infinite plane and an infinite paraboloid have different shapes. 4. Nobody knows, but if you asked cosmologists to guess, most of them would guess some kind of inflation. -- BenRG (talk) 21:53, 6 March 2013 (UTC)

Thank you everyone. --PlanetEditor (talk) 10:12, 7 March 2013 (UTC)

However I would have liked a bit more explanation of Q4. The religionists use this issue as an excuse to prove the existence of God. --PlanetEditor (talk) 10:20, 7 March 2013 (UTC)

If you haven't seen it already, Big_Bang#Speculative_physics_beyond_Big_Bang_theory. You really are stuck in a bind, there. Either you have something exist before the Big Bang, and then have to explain where that came from; or you have a theory such as Hawking's where a beginning is (allegedly) not required. Neither class of theories is likely to satisfy. Someguy1221 (talk) 10:45, 7 March 2013 (UTC)

Hawkins' explanation that time is compressed inside a black hole - and that's (effectively) what the early universe was like - may or may not be correct, but at least it offers one possible explanation for the "Origin of Everything" question that doesn't result in an infinite regress. The idea that this is an argument for the existence of God is a silly one because one only has to ask the question "So...what created God then?" to demonstrate that adding a supernatural being as the creator of the universe doesn't help to answer the ultimate question If the early universe was "caused" by something, then you're in the infinite regress of asking what that cause was and what was the cause of the cause and so forth. Hawkins' approach is elegant in that by pointing out that time inside a black hole is crunched into nothingness and therefore there is no "Before" in the case of the big bang - it was there for a literally infinity amount of time. He might not be right - but at least there are possible "ultimate origin" explanations that do not require gods and other mystical junk to make them work. SteveBaker (talk) 22:04, 7 March 2013 (UTC)

Thank you Someguy and Steve. --PlanetEditor (talk) 09:07, 8 March 2013 (UTC)

Statistics of hysterectomies

Why are hysterectomies so common in women above tha age of 50 if its such a major operation? Clover345 (talk) 14:48, 6 March 2013 (UTC)

I think the article on Hysterectomy actually does a good job of going into some of the issues. The major downside of the surgery (aside from risk) is loss of the ability to bear children, which is usually a moot point by the age of 50. The upshot to the surgery, such as benefiting cancer risk or severe pain, will often outweigh that downside, although for sure there are a lot of these being performed. ~ Amory (u • t • c) 15:24, 6 March 2013 (UTC)

From personal experience in the UK, if there is no good reason to remove a uterus then they won't. Fibroids or adenomyosis stop responding to oestrogen as less and less is being produced, and shrink of their own accord. I'd like to see up to date statistics on this. --TammyMoet (talk) 16:23, 6 March 2013 (UTC)

Prove relation

Given $P(x,t)=|\Psi (x,t)|^{2}$,

and $J(x,t)=-{\frac {ih}{2m}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

I want to prove the following relation

${\frac {\partial }{\partial t}}P(x,t)+{\frac {\partial }{\partial x}}J(x,t)=0$

I denote complex conjugate with asterisk. I believe I can think of examples of functions Psi for which it's not true. Here is my working so far anyway.

$={\frac {\partial }{\partial t}}|\Psi (x,t)|^{2}-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

$={\frac {\partial }{\partial t}}\left(\Psi (x,t)\Psi ^{*}(x,t)\right)-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

$=\Psi ^{*}(x,t){\frac {\partial }{\partial t}}\Psi (x,t)+\Psi (x,t){\frac {\partial }{\partial t}}\Psi ^{*}(x,t)-{\frac {ih}{2m}}{\frac {\partial }{\partial x}}\left(\Psi ^{*}(x,t){\frac {\partial }{\partial x}}\Psi (x,t)-\Psi (x,t){\frac {\partial }{\partial x}}\Psi ^{*}(x,t)\right)$

It's not clear at all that this is zero to me.

150.203.115.98 (talk) 15:19, 6 March 2013 (UTC)

maybe this is a homework question, so we should be wary. I don't know much about this area, but I'd try integrating J first. Let me know if I'm out on a limb. IBE (talk) 17:19, 6 March 2013 (UTC)

You should differentiate the expression in parentheses (by x) then you should substitute derivatives by time from the 1D Schrodinger equation in free space. After that everything will be obvious. Ruslik_Zero 18:15, 6 March 2013 (UTC)

Reverse osmosis semipermeable membranes

Semi-permeable_membrane says that membranes used in reverse osmosis are made of polyimide while Thin-film composite membrane says that they are made of polyamide.

What's correct?--Gauravjuvekar (talk) 16:42, 6 March 2013 (UTC)

Looking through a number of suppliers of such membranes, most just describe them as "Thin Film", but Dow's datasheet states that their membranes are polyamide. On the other hand, this patent is for a polyimide membrane. I think it's safe to say that both _can_ be used. Tevildo (talk) 22:36, 6 March 2013 (UTC)

This site lists lots of polyamide membranes, a few "Thin Film" membranes, and a few cellulose acetate membranes. Polyamide seems to be the most common material. Tevildo (talk) 22:45, 6 March 2013 (UTC)

Meteor fragments and aircraft

There is LOTS of discussion about meteors/comets/etc impacting the Earth, the History of the big ones, etc. HOWEVER, I heard somewhere that 40 TONS of material impact on the Earth's atmosphere daily. ALL discussions I've read say something like "most" of this material burns up in the Earth's atmosphere, leaving particles "smaller than grains of sand" etc. When most folks read this phrase, they say "no problem". HOWEVER, I would imagine that a particle not much bigger than a grain of sand could have a disastrous effect should it strike the wing of a flying aircraft. How come there aren't more recorded (or hypothesized) cases of aircraft being affected by meteor fragments? Thanks, Jack Murray p.s.- This is a WORLDWIDE question p.p.s. - How do I know what to search on in Wikipedia to find out if anyone addressed this? — Preceding unsigned comment added by Jaqmur (talk • contribs) 17:14, 6 March 2013 (UTC)

Regarding your last question, "How do I know what to search on in Wikipedia to find out if anyone addressed this?", knowing what search terms to use to finds the answer to a question is known as Google-fu, and it's a skill you learn through practice. If you meant where do you search, there's a search bar at the top of every reference desk page where you can search the desk archives. 90.193.232.228 (talk) 17:43, 6 March 2013 (UTC)

Particles the size of a grain of sand will rapidly decelerate to free-fall speed, due to air resistance. A grain of sand at that speed is not a problem for an aircraft. However, many such grains of sand are, and we get those by flying through a volcanic plume. StuRat (talk) 18:00, 6 March 2013 (UTC)

Just in case you're still struggling with Google, I had a go myself. I typed aircraft "meteor strike" into the search bar (the words within the "quote marks" means that Google will only show an exact match for that phrase). I found a data analysis blog called Revolutions - How much of a threat are meteors to aviation? Using some complicated calculations, the author states that the chance of a meteor strike on a single aircraft are "about 1 in a billion, give or take". However, given the number of aircraft using the sky, "there's about a 4.3% chance of a meteor strike on at least one airliner in the next 20 years". Alansplodge (talk) 18:16, 6 March 2013 (UTC)

It's called terminal velocity, not "free fall speed". μηδείς (talk) 23:28, 6 March 2013 (UTC)

"Free fall speed" is a synonym for "terminal velocity". StuRat (talk) 05:08, 7 March 2013 (UTC)

Aircraft regularly encounter hail stones. Hail is capable of stripping paint and abrading windshields so pilots use their weather radars to avoid heavy rain and hail. Despite that, damage more serious than stripped paint and abraded windshields occurs occasionally. A meteor fragment the size of a grain of sand, falling at its terminal velocity, is nowhere near as hazardous to an aircraft as a hail stone falling at its terminal velocity. Dolphin (t) 00:14, 7 March 2013 (UTC)

How do we know the fragments would be at terminal velocity? Objects only reach terminal velocity in free fall; a meteor may strike the earth at many orders of magnitude faster than its terminal free-fall velocity, and it may take some distance to slow down to terminal velocity. A meteor could be moving quite fast when it strikes the plane; there's no requirement that it be moving as slow as terminal velocity. --Jayron32 06:05, 7 March 2013 (UTC)

The OP has prefaced the question with most of this material burns up in the Earth's atmosphere, leaving particles smaller than grains of sand. The question excludes particles much larger than grains of sand. Meteors disintegrate in the Earth's upper atmosphere. By the time a fragment the size of a grain of sand falls to the altitude at which aircraft operate, a long time will have elapsed and it will be at its terminal velocity. True, the geological record shows evidence of very large meteors having reached the Earth's surface, leaving large craters, but the question doesn't extend to consideration of such large meteors. Dolphin (t) 06:17, 7 March 2013 (UTC)

Gotcha. Yeah, in that case a grain of sand at its terminal velocity is still a grain of sand at terminal velocity, and carries very little energy, certainly not enough to damage anything on an aircraft. The origin if the sand itself is irrelevant. If the sand were really hauling ass, then maybe, but sand in free fall is still sand in free fall, even if it came from space. --Jayron32 06:23, 7 March 2013 (UTC)

I interpreted the OP to be asking about a high-speed aircraft striking a particle that has no horizontal velocity and almost zero vertical velocity. Dolphin (t) 06:37, 7 March 2013 (UTC)

Re your last question. I read that as "How do I find out if anyone has answered this very question I'm asking here?". You just search for this page by its name, Wikipedia:Reference desk/Science, using the search function. Then scroll down to find the right thread. -- Jack of Oz ^[Talk] 00:41, 7 March 2013 (UTC)

From playing around with numbers at this impact simulator, it looks like any meteor smaller than about 50 cm in diameter is going to be moving at its terminal velocity by the time it reaches the typical airplane. For a piece of sand, that terminal velocity is a few miles per hour, so most of the impact speed will come from the airplane's movement, not the rock's movement. --Carnildo (talk) 01:56, 7 March 2013 (UTC)

Thanks for all the info. Jaqmur (talk) 14:35, 7 March 2013 (UTC)

The thing to bear in mind when thinking about meteors and such is that if you halve the diameter of a roughly symmetrical object, you reduce it's cross-sectional area by a factor of four and it's mass by a factor of eight. So the aerodynamic drag forces on small particles (which depends on their cross-sectional area and not on their mass) are much larger compared to their initial kinetic energy (which depends on their mass) than for big rocks. So these sand-grain sized meteors slow down to their terminal velocity very quickly - where a mountain-sized meteor hardly slows down at all.

Do a mental experiment - take a rock the size of your fist and imagine how far you can throw it - 20 feet maybe? How far do you think you could throw a grain of sand? A couple of feet maybe? Both objects leave your hand at about the same speed just as large and small meteors are entering the atmosphere at about the same speed.

So for meteor dust, it's going to be moving at terminal velocity - which is when the gravitational force (which is proportional to its mass) balances the drag force (which is proportional to it's cross-sectional area) - with very tiny mass and less tiny cross-section, it's moving very slowly. But the hailstone is obviously moving a lot faster because the ratio of mass to cross-sectional area is much higher than for the dust. More importantly, since kinetic energy (which is what goes into damaging the plane) is proportional to the SQUARE of the speed multiplied by the mass - these low-mass, low-speed sand-grains don't have enough energy to do much damage...and as Carnildo pointed out - the speed of the airplane is by far the biggest contributor in terms of relative velocity.

Hitting meteor dust is much less damaging than hitting even a raindrop or a snowflake...it's about as bad as hitting the smoke particles from the airplane a mile or two ahead of you.

SteveBaker (talk) 13:21, 8 March 2013 (UTC)

Film problems

Not sure if this should go here or on the entertainment desk, but...

While watching The Aztecs (Doctor Who), I noticed two problems:

1. In episode 1, the image jerks upwards for a fraction of a second and then returns to normal.

2. There is considerable background noise, sounding a lot like rain.

Why do these effects occur? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:19, 6 March 2013 (UTC)

1) This sounds like a problem I've sometimes seen when projecting a film. Presumably it was copied into a digital format, but, if that process involves using a film projector, and the operator is rather careless, this could be the result. Or, perhaps that happened when filming. Were they doing any hand cranking: [3] ? (This techniques was sometimes used to change the recording speed of the film, manually.)

2) This might be an original issue with the sound recording. Wind noise can sound like that, if they don't cram the microphone inside a dead cat to prevent it. British TV of that era had notoriously low production values, so it wouldn't surprise me if this happened. StuRat (talk) 20:34, 6 March 2013 (UTC)

1) Then why is the image stable for the entire episode with the exception of that momentary jerk? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:39, 6 March 2013 (UTC)

1) Probably a torn sprocket hole or two messed up the timing, then it was able to recover. This type of thing happens more often than you might think. It's just that in a Hollywood production, as bad as the plots are, they do an extraordinary job of fixing any production quality problems like this which crop up. Watching foreign films and TV, I've been surprised to see microphones repeatedly in the frame, characters calling each other by the wrong names (possibly by the actor's name), and worse mistakes, all making it onto the final film. In a Hollywood production, this type of thing ends up on the blooper reel. StuRat (talk) 20:43, 6 March 2013 (UTC)

A 1964 Dr. Who? I wouldn't be surprised to see one of the crew wandering around the back of the frame eating a sandwich. Gzuckier (talk) 21:03, 6 March 2013 (UTC)

In Terrence Malick's The Thin Red Line, if you watch the DVD copy on a computer, you can see a crew member standing about staring at the camera holding a clipboard on the far edge of the frame in one of the love scenes. Can't be seen on a TV. – Kerαunoςcopia^◁_galaxies 03:15, 7 March 2013 (UTC)

<coughs> No period after "Dr". See Dr. Who (the Peter Cushing Dalek movies). Tevildo (talk) 22:53, 6 March 2013 (UTC)

Our article on negative cutting doesn't say anything, but sometimes a negative cutter will foobar a splice. Projectionists have been known to cut out single frames of their favorite shots, using cheap splicing tape or cement to piece the film back together. Also damage happens to film, sometimes a single frame or sprocket can become damaged and either cut or, if unnoticed, left in the film. If the Dr Who episode was made from a print, rather than a negative, this could be what happened, though a solid jump up and down probably means there was a splice. (The thickness of the cement/tape jerks the film about in the telecine or projector.) By the way, regarding projectionists cutting out frames, there shouldn't be a problem with sound sync anymore (it's been a while) since I think sound CDs are now synchronized to code printed on the actual film edge. In the old days, though, if someone cut out a splice, you would hear a pop/jump in the sound about a second later. – Kerαunoςcopia^◁_galaxies 03:15, 7 March 2013 (UTC)

Did the BBC actually spend the money in 1964 to shoot Dr who on film? It would have been cheaper to shoot on video tape. The first programs were lost, and The Aztecs is from several months later. I just watched it on Netflix, and it had the look of videotape. Perhaps it got converted to film at some point for distribution and rebroadcast. Doctor Who (series 1) says that the series only transitioned from videotape to film in the 2005 relaunch, which they perversely call "Series 1." Edison (talk) 04:23, 7 March 2013 (UTC)

Our article on that episode makes it clear that it was first recorded using videotape, then converted to film so that the tape could be reused (because video tape was extremely expensive at that time), then later converted back to a video format using the VidFIRE process. Looie496 (talk) 06:22, 7 March 2013 (UTC)

Genetic disorders that come out due to inbreeding.

The article on the Amish states

Since almost all Amish descend from about 200 18th-century founders, genetic disorders that come out due to inbreeding exist in more isolated districts (an example of the founder effect).

I have always thought that inbreeding, while it does increase the incidence of certain disorders, does not create new ones by itself. Am I correct? If not, can anyone of you provide examples of genetic disorders that come out due to inbreeding? --190.19.83.213 (talk) 02:19, 7 March 2013 (UTC)

You are correct, but I think you are misreading that quotation. It is basically saying the same thing you did. StuRat (talk) 02:29, 7 March 2013 (UTC)

"Come out" is a misleading term. By far the most common type of genetic disease associated with inbreeding is autosomal recessive enzyme or other protein deficiencies. If the carrier (heterozygote) rate in the US population for an autosomal recessive mutation that causes blue hair disease in homozygotes is 1%, but the carrier rate in an intermarrying subpopulation, like Amish, or Ashkenazi Jews, or Yupik Eskimos, is 6%, then the likelihood of a carrier marrying another carrier is 6x higher, and the rate of homozygous blue hair births in that population will be 36x higher than in the general US population. alteripse (talk) 02:41, 7 March 2013 (UTC)

Jumping from a airplane with wingtip sails

Cardinals on their way to the conclave. PrimeHunter (talk) 15:35, 6 March 2013 (UTC)

This picture is taken from the humanities.

My question is:

Is it safer to jump out from an airplane with wingtip sails because of reduced wingtip vortices? -- Toytoy (talk) 03:18, 7 March 2013 (UTC)

Maybe if the chutes are going to open immediately, as they seem to in the pic. On the other hand, if the chutes wait a bit to open, then they will be clear of the vortices before opening. StuRat (talk) 03:23, 7 March 2013 (UTC)

Our article, Wake turbulence, doesn't mention hazards to parachutes, but does say that vortices are generated when the wings are creating lift. I suspect that the pilot would take this into account when people are jumping out of his or her aircraft, but perhaps another editor has some experience in this field. Note that the RAF has been dropping paratroopers since 1941, but has never possessed one with wingtip devices until it acquired some C-17s in 2002. Alansplodge (talk) 18:01, 7 March 2013 (UTC)

On large aircraft such as the one pictured here, the wingtip vortices are too far outboard in any case to affect parachutists jumping out of that aircraft. FWIW 24.23.196.85 (talk) 04:57, 9 March 2013 (UTC)

March 7

could you compare a hot air balloon with a plane and helicopter?

Let's say we want something to get to 10,000 feet from ground while expending as little energy as possible. Three ways of doing it are: the something is a plane. The something is a helicopter. The something is a hot-air balloon. All of these require energy to get up to their heights. Can you give me an idea of how these energies compare? (for the same weight). I would think that the hot-air version is least efficient as you are basically heating a huge volume of air. But then again you only do it ONCE and then just "float" up. Whereas the other two require continual energy even to just maintain level flight. Still, how do these three compare in terms of total energy required to lift to 5000 feet from ground? 91.120.48.242 (talk) 07:46, 7 March 2013 (UTC)

I think the answer will depend on whether "for the same weight" means "for the same total weight" or "for the same payload". Lifting the total weight of a small plane or helicopter using a hot air balloon sounds quite inefficient (hand waving theoretical justification: considered as a heat engine, the operating temperature of the balloon is lower than the plane or helipcopter engine so its theoretical maximum efficiency is lower). But for the same payload (say five people), the balloon could be more efficent because it has no heavy engines/wings/rotors. Gandalf61 (talk) 09:19, 7 March 2013 (UTC)

Could you be a bit more precise or explain your reasoning further? In particular I don't understand your argument about "the operating temperature of the balloon is lower than the plane or helipcopter engine so its theoretical maximum efficiency is lower". What does the plane or helicopter have in its favor?

Also, is there some theoretical argument to be made about kinetic energy here? I can imagine some kind of theoretical proof that heating the air around an object and encapsulating it is guaranteed to be the most efficient use of those joules of power. On the other hand, I can imagine that there is a theoretical argument to be made based on air resistance (how lift is generated). Any ideas? 91.120.48.242 (talk) 10:20, 7 March 2013 (UTC)

See heat engine, fuel economy in aircraft, aerodynamic drag and drag coefficient. I don't think there is going to be a clear cut answer. If this is a homework question then the point of it is probably to see how many different arguments and variable factors you can come up with, to show that you understand the complexities that may lie behind an apparently simple question. Gandalf61 (talk)

The wiki article suggests a hot air balloon will mass 3.5 tonnes for 5 passengers. That surprised me. So perhaps you could do your calculations based on 5 people as a payload. FWIW the helicopter will almost certainly be the worst possible choice, and I have a suspicion that rather expensive aircraft might be the best. Greglocock (talk) 22:41, 7 March 2013 (UTC)

The answer (not one of the choices given) is almost certainly the glider. It needs a tow to get off the ground, but after that there is no energy expenditure at all. It only relies on the pilot's ability to find suitable thermals to get to height. SpinningSpark 23:11, 7 March 2013 (UTC)

I strongly disagree. You're conveniently ignoring the energy cost of towing the glider to an altitude high enough to be able to reach the first thermal before it hits the ground again. That's most definitely not a zero energy cost! The (powered) airplane, the helicopter and the hot-air balloon can (and will) benefit from those very same thermals. As a practical issue, navigating the hot air balloon to get to where they are might not be possible...and a high speed fixed wing aircraft might have trouble staying inside the thermal - but a powered airplane could be designed to be just as good at catching thermals as the glider, yet get into the air more efficiently than your gliders' towing system can.

Location matters though. If you were starting the experiment near to the base of a 10,000 foot tall mountain - on the side where the wind is blowing gently up-slope - then a hang-glider could probably make it to the top without a tow, using slope-lift and truly zero energy. But if you're on a flat, featureless, windless, uniform surface (hence no thermals and no slope-lift) then your best bet is probably the fixed wing aircraft. If you're on a flat surface and there is plenty of wind - then maybe a kite is what you need?

I suspect that a rocket would be the best option. According to rocket engine, chemical rockets can be 60% efficient...that's better than either jet or piston engines. Also, a fixed-wing aircraft has massive drag due to those big wings - the rocket can be designed to be almost any shape you like - so it can be aerodynamically optimal. Fixed-wing aircraft have to travel quickly in the horizontal direction in order to get enough lift to gain altitude - so they need to spend more time getting to altitude than the rocket does - and therefore they expend more energy overcoming drag and gravity.

Calculating "energy costs" is tricky though. An airplane is re-usable, but the rocket probably isn't...so do we include the construction costs into the calculation? If we don't then we can use a hydrogen balloon...the hydrogen "cost" is a part of the construction cost - but if that's not included then this technology can do the job at zero energy cost. Sadly, you either have to throw away some of the hydrogen at altitude in order to get back down again - or you have to expend energy in some other way to get back down...so unless this is a one-shot mission, then that's another consideration.

Without tighter rules, this debate can get silly. Suppose we put the payload onto a large spring so it's flung into the air with enough speed to get to 10,000 feet. The energy cost is now that of compressing the spring. We can do that using a very slow, highly geared solar powered motor that takes an entire year to slowly compress the spring. If the glider is allowed to get "free energy" from thermals, then my spring launcher can certainly get "free energy" from sunlight. What's more, since my payload is the only thing I have to get to 10,000 feet - I don't have to waste energy launching some kind of vehicle along with it. For some payloads, this makes a lot of sense.

SteveBaker (talk) 13:59, 8 March 2013 (UTC)

A good glider pilot can make use of the thermal rising from a plowed field. That won't get you much height, but it can you enough to get somewhere else. I'm not saying you can get to 10,000 feet from a low height in every circumstance, but an experienced pilot has at least a possibility of doing it, even starting from a flat landscape. SpinningSpark 18:54, 8 March 2013 (UTC)

OP here. Thanks for the response guys :) You guys went off in your own direction, which is fine and interesting, but actually only prompted by my "topic-setting" sentence which seemed general. The rest of my comment mentioned in specific the three things I was interested in comparing the theoretical energy requirements of: a hot-air balloon, an airplane, and a helicopter. Perhaps we can add that the hot-air balloon is assumed to be inflated by ambient-temperature air at ground. So while of course a helium balloon can get there for "free", and so can a glider riding thermals, what I'm really interested in is helicopter and airplane craft "powered" by an engine versus using those joules simply to heat a balloon. I agree that perhaps there are no clear-cut or theoretical arguments to be made here. I was hoping some argument about air density at different temperatures, versus a coefficient of friction argument about air, could be combined to come to a theoretical proof that of the three proposed things we are comparing, one has a better theoretical limit. 86.101.32.82 (talk) 11:55, 9 March 2013 (UTC)

Mean from a wavefunction

Thanks for your help with the previous question. Now I would like to prove this identity:

$\int _{-\infty }^{\infty }p|{\tilde {\Psi }}(p)|^{2}dp=\int _{-\infty }^{\infty }\Psi ^{*}(x)(-ih{\frac {\partial }{\partial x}})\Psi (x)dx$

Working

$\int _{-\infty }^{\infty }p|{\tilde {\Psi }}(p)|^{2}dp$

$=\int _{-\infty }^{\infty }p\left|{\frac {1}{\sqrt {2\pi h}}}\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right|^{2}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left|\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right|^{2}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)^{*}dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\Psi (x)e^{-ipx/h}dx\right)\left(\int _{-\infty }^{\infty }\Psi ^{*}(x)e^{ipx/h}dx\right)dp$

$=\int _{-\infty }^{\infty }p{\frac {1}{2\pi h}}\left(\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }\Psi (x)\Psi ^{*}(y)e^{-ip(x-y)/h}dxdy\right)dp$

$={\frac {1}{2\pi h}}\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }\int _{-\infty }^{\infty }p\Psi (x)\Psi ^{*}(y)e^{-ip(x-y)/h}dpdxdy$

But, the inner integral does not converge ! ! !

150.203.115.98 (talk) 10:46, 7 March 2013 (UTC)

Shouldn't this be at Wikipedia:Reference desk/Mathematics? --Guy Macon (talk) 12:10, 7 March 2013 (UTC)

That inner integral is the Dirac delta function; if you want a more rigorous derivation that avoids invoking the delta function, you have to use (and prove) the fact that transforming to momentum space and back is a unitary tranform. In general:

<psi|A|psi> = <psi|U-dagger U|A|U-dagger U|psi>

for U some arbitrary unitary transform. U-dagger denotes the Hermitian conjugate (which is equal to the inverse of U because U is unitary). Then the state |psi> transformed under U is |psi'>= U|psi>, and thus <psi'| = <psi|U-dagger, and the transformed operator A is

A' = U|A|U-dagger, so we indeed have:

<psi|A|psi> = <psi'|A'|psi'>

In your problem the momentum operator p = -ihbar d/dx is diagonal in the momentum representation, so you can take it out of the Dirac brakets. Count Iblis (talk) 12:58, 7 March 2013 (UTC)

How is the inner integral a dirac delta function? 150.203.115.98 (talk) 13:49, 7 March 2013 (UTC)

It's the derivative of the Dirac delta; to see this, differentiate the integral identity for the Dirac delta w.r.t. its argument. Count Iblis (talk) 15:44, 7 March 2013 (UTC)

Are you sure? I thought $\delta (y-x)={\frac {1}{2\pi }}\int _{-\infty }^{\infty }e^{ip(y-x)}dp$. This one is ${\frac {1}{2\pi }}\int _{-\infty }^{\infty }pe^{ip(y-x)}dp$. 150.203.115.98 (talk) 16:10, 7 March 2013 (UTC)

Yes, the derivative of the delta. So, if you put z = x-y and differentiate both sides w.r.t. z, and move the derivative under the integration sign, you'll get a factor p in the integrand as a result fo taking that derivative. Count Iblis (talk) 16:30, 7 March 2013 (UTC)

And then you would have to make a integration by parts to move the derivative over to one of the PSI functions and finally use the delta function to get rid of one of the outside integrations completing the desired proof. The only thing to keep in mind is that some of the steps of this proof need to be further explained (if you care for mathematical rigor), specially the reversal of the order os derivative and integration mentioned by the Count in his last post. A rigorous proof requires special treatment for the delta function because it is not a normal kind of function. Dauto (talk) 17:17, 7 March 2013 (UTC)

Hydrogen solubility in copper

What is the hydrogen solubility in alpha-copper at 100 kPa and 25 °C? Values should be stable up to 50 MPa. Plasmic Physics (talk) 12:32, 7 March 2013 (UTC)

Growth between 18 and 24

Do any significant changes or growth occur between 18 and 24 years of age? Most people can't tell the age differences in this age group. — Preceding unsigned comment added by Clover345 (talk • contribs) 13:05, 7 March 2013 (UTC)

We've had a previous instance of a similar question here. Have a look at the links there and get back to us if you need further. --TammyMoet (talk) 13:12, 7 March 2013 (UTC)

−

thanks. Do you think these statistics change though. Most people think that young people looked older 20 years ago. Why is this? Clover345 (talk) 13:36, 7 March 2013 (UTC)

Well, we know that the onset of puberty has shifted (at least in developed countries) over the last 200 years, and we know that average human height changes with respect to environmental conditions and the like, so yes, these statistics can certainly change. As for "people looking older": that's highly subjective and speculative, and I doubt we can verify it, much less meaningfully extrapolate to "why". — Lomn 14:14, 7 March 2013 (UTC)

“Most people think that young people looked older 20 years ago.” I think every generation has this perception. Looking through my family photograph albums, people clearly tend to stay with the clothes, hairstyles and social etiquette they became accustomed to in their younger years – thus that style become thought of as looking mature by the later generation. Actors and actresses often dress in the latest styles for the reason that it makes them (they think) look younger and use modern jargon. I've noticed on some recent American films (if you can call 1990 recent), such as the Memphis_Belle_(film), that the director and makeup artists went to lengths, to have the actors playing the air crew, appear to conform to image of modern youths of that age – to emphasis just how young the original crew of the Memphis Bell really were. It is more striking when you look at World War II RAF officers with their short-back-and-side haircuts, neatly trimmed moustaches and panache for voicing understatements. So it is not really a perception of 'older in age' but recognition of older cultural values. --Aspro (talk) 15:06, 7 March 2013 (UTC)

There are real differences though which may make new generations look relatively younger. Decreased tobacco, alcohol, and other drug use, decreased time working as youths/increased time spent in school, decreased time in the sun, higher sunscreen use, decreased manual labour, better hygiene, and better diets, can all increase youthfulness. I think many of these things are working to make newer generations appear younger, minus those who use tanning beds to an extreme and those who are overweight. 70.48.212.115 (talk) 16:01, 8 March 2013 (UTC)

Unfortunately the answer offered to that September question is astonishingly bad. The answerer clearly did not know what he was talking about and did not read the relevant article: puberty clearly says there is a relationship between timing of puberty and completion of growth because both are dependent on several years of estrogen and androgen. Aspro is closer than Lomn to answering this current question, in the sense that perception of age of young adults is more influenced by clothing and hairstyles than by actual earlier pubertal onset. The degree of earlier puberty in this century is much smaller than popularly supposed. The late changes of puberty have not changed as much as the early changes. Surveys of boys and girls suggest menarche is occurring perhaps 3 mos earlier now than in the late 1960s, but thelarche may be occurring as much as 1-2 years earlier. The nature of the widening gap in uncertain; one possible explanation is that the early changes come from environmental estrogens and are not true puberty, which has been only slightly hastened. The phenomenon in boys is even smaller. Progression and timing of late stages of puberty do not seem to have changed much in the last 50 years. On average maximum adult height is reached at average ages of about 15 and 18 y for girls and boys (wide individual variation of course). The outward changes of facial appearance in late teens and early twenties that serve as age cues to us involve thickening of the skin, recession of the frontal hairline, slight thinning of the hair in both sexes, but increasing facial hair, especially in men. Men's beards continue to get heavier throughout this period-- but again with large inter-ethnic and inter-individual variation. Men also continue to have some increase in shoulder musculature and width in late teens as height growth is finishing. Acne often improves. But all of these changes have been far smaller over the last century than the changes of hairstyle and dress and I vote with aspro that our questioner's impression was entirely based on those features. alteripse (talk) 16:21, 7 March 2013 (UTC)

Plane lens?

Can a "lens" be plane, meaning not being curved at all? 117.227.203.61 (talk) 13:28, 7 March 2013 (UTC)

You might be interested in fresnel lens. They are flat at the gross scale, but have tiny ridges at the fine scale. SemanticMantis (talk) 13:34, 7 March 2013 (UTC)

not being curved at all? 117.227.203.61 (talk) 13:38, 7 March 2013 (UTC)

Well, a Fresnel lens can either have the individual segments be curved ([4]) or flat ([5]). The curved segment version focuses more clearly, but the flat segmented kind has application where you don't need a clear image, such as focusing sunlight for solar energy. StuRat (talk) 15:25, 7 March 2013 (UTC)

If the material has a uniform refractive index throughout the plane, no, that can't be a lens. 131.251.133.27 (talk) 14:10, 7 March 2013 (UTC)

then what it is called? — Preceding unsigned comment added by 59.161.101.17 (talk) 14:26, 7 March 2013 (UTC)

Ah, a window? TenOfAllTrades(talk) 14:32, 7 March 2013 (UTC)

If the faces are plane but non-parallel, it will be a prism. If they are it may be called a plate (as in plate glass and photographic plate). Note that TOAT's suggestion of 'window' is not (I presume) whimsical - apertures sealed by flat glass (or other materials) in scientific instruments may also be called windows: one that springs to mind is the mica window used in the designs of Geiger Counters I was taught about in school (which are probably now obsolescent, like myself). {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:41, 7 March 2013 (UTC)

Mica windowed Geiger Counters are not obsolescent, in fact I have one sitting behind me in my lab as I write this (used for contamination monitoring during and after biological radiolabeling experiments). Equisetum (talk | contributions) 16:42, 7 March 2013 (UTC)

Though if you're allowed to vary the material composition (specifically, its refractive index) across the plane, then you can build GRIN devices (see gradient-index optics). TenOfAllTrades(talk) 14:34, 7 March 2013 (UTC)

There's also a pinhole lens, which can be a planar material with a small hole. Note that they reduce the brightness of the object considerably, so are most useful for focusing bright objects, like the Sun, or with time exposures. StuRat (talk) 16:16, 7 March 2013 (UTC)

There are also plain lenses made of a material with negative refraction index. Ruslik_Zero 18:52, 7 March 2013 (UTC)

Isn't space itself curved? Aren't all so-called straight or plane objects intrinsically curved? -- Jack of Oz ^[Talk] 23:05, 7 March 2013 (UTC)

See Geodesic and Geodesics in general relativity for the concept of straight lines in curved spacetime. --Carnildo (talk) 00:37, 8 March 2013 (UTC)

See gravitational lens. SpinningSpark 06:51, 8 March 2013 (UTC)

Russian MBT Designs

It is known that Russian tanks are smaller and have a less area exposed to fire , but does that make a big difficulty for opponents to hit it ? in other words does it worth to exhaust the tank crew for this reason ? — Preceding unsigned comment added by Tank Designer (talk • contribs) 15:18, 7 March 2013 (UTC)

Yes and no. The T-90 is about a foot lower than the M1 Abrams, but their guns are roughly the same distance below turret top. So in the open, the T-90 presents a slightly smaller target. In a hull-down position, this distinction in height doesn't matter, though the T-90 turret is also somewhat smaller. Our article there further notes that US tanks can typically depress their main gun farther than Russian designs, which results in the Russian design potentially exposing more of the tank body (particularly if using a natural slope). For aerial threats, the two tanks have roughly the same size.

As for the last, the Gulf War demonstrated a clear advantage for US-manned M1s with air superiority against Iraqi-manned T-72s. For the rest, I refer once again to the evidence of design philosophy: each military fields the tanks they believe best match their doctrine and probable opponents, but unless and until it comes to open warfare, anything further would be conjecture. — Lomn 16:04, 7 March 2013 (UTC)

Having talked with a Gulf War tank crew veteran, he claimed that the US advantage in tank-to-tank combat was due to their automatic targeting system, allowing US tanks to hit the target with the first shot, while Iraqi tanks averaged about 3 (for those which managed to survive that long). StuRat (talk) 18:01, 7 March 2013 (UTC)

I've read quite a bit about the Persian Gulf War (of 1991), and talked to a few veterans, and it is my opinion that the chief American advantage in tank-to-tank combat was avoiding it. From the Combined Arms Research Library, here are the memoirs of one Captain Enloe, an officer in a mechanized infantry brigade, Persian Gulf War: 2d Battalion, 18th Infantry Regiment (Mechanized), 197th Infantry Brigade. "At 280515 Feb 91, all elements were ordered to stop all movement, a temporary cease fire was immediately in effect throughout the entire theater of operations. In absolute disbelief, we came to a halt and formed into a Task Force Tactical Assembly Area." Ground operations in Desert Storm famously lasted less than one hundred hours, most of which were spent driving from formation assembly areas to to other formation assembly areas.

Our original poster may find the digital library collection full of interesting information about modern armored doctrine. Nimur (talk) 18:21, 7 March 2013 (UTC)

Thank you very much Mr. Lomn

Filter paper to concentrate interesting things for microscope viewing?

Hi Folks, I have a pretty good microscope (1000x oil immersion) but am a total amateur as a scientist. I live on the ocean and would like to see interesting things like tardigrades, nematodes, plankton, etc. I'm not that interested in things at the bacterial level. Looking at plain seawater it takes a long time to find neat stuff so I was wondering if I could run a bunch of seawater through filter paper to concentrate creatures. What kind of filter paper should I use? Maybe a coffee filter would work but I don't mind buying the real thing. Any other suggestions for easy interesting things to see? Thanks! — Preceding unsigned comment added by 72.165.55.147 (talk) 17:46, 7 March 2013 (UTC)

The problem with filters is that the critters will all be stuck in the filter, and you'd need to use more water to flush them back out. Swamp water seems to be crawling with critters, so you might try that instead of ocean water. I also suggest starting a slide on a low magnification, then finding something of interest, before zooming in to max res.StuRat (talk) 17:53, 7 March 2013 (UTC)

First, usually freshwater is used for this type of thing: there are plenty of freshwater tardigrades (and nematodes and plankton too). I've found water bears in wet moss, on the edge of ponds, etc. It's easiest to find the bigger things, of course, and tardigrades can get up to 1 mm. However, I am not sure if the reason fresh water is more common is because there are more critters to see, or if it's just more widely available...

I think your idea is worth trying. As Stu says, some critters will get caught on the filter, but if you filter e.g. 1 L and then use 0.1 L to flush them back, you'll presumably have a 10X concentration, which could make your hunting up to 10X easier. I'd start with a filter of about 0.4 mm and see how it goes from there. You could also filter out coarse debris first with a 2mm sieve. As for other interesting thing to see (in freshwater/pond scum), bdelloid rotifers, hydras and volvox are all pretty cool. In ocean water you'll probably find more (and more interesting) diatoms, though they are also in fresh water. SemanticMantis (talk) 19:19, 7 March 2013 (UTC)

I think the best way to concentrate these critter is to use patients. I may take a long time to go through a bucket full of sea water with an eye dropper drip-by-drip but that the best way IMHO. You can take advantage of sea water stratifying. Not easy close to shore, because the wave action mixes it up. However, go a little off shore and you have the photosynthesising hungry stuff in the upper surface areas and the bottom dwelling stuff ... err... on or within the bottom sediments – like nematodes . Text books should tell you their natural habitat and all you need to do is take sample from those areas. For instance, a suitably weighted metal tube, hack-sawed off like a giant hypodermic syringe, with a cord attached for retrieval, can by used to get bottom sediment samples. This hunt (a male trait) makes microscopy more satisfying then just going mindlessly through the mechanics of preparing a slide and peering down the lens. A good cook book, can also help to solve the disposal problem of most sea life that is too big to go on the microscope stage. This alone, can only add pleasure to your hobby. I’m salivating at the thought. Don't forget also, many seaweeds are edible too and they have microscopic life crawling all over them. Go down to you local Japanese delicatessen and you'll have to pay good dollars for seaweed. Collect your own and its a double win situation. Forget filter paper - unless it for coffee. --Aspro (talk) 20:06, 7 March 2013 (UTC)

I would suggest using patience, as using patients might be considered unethical, although you could use patients to grow some parasitic organisms into an easier to see size. :-) StuRat (talk) 03:29, 8 March 2013 (UTC)

P.S. For other interesting thing to see, go down to the landings an buy some of the stuff that comes up in the nets that are not of commercial value. Some critters that the fishermen bring in make Alien look like a loveable puppy. With a few sharp dissecting tools, there are things that would take more than a life time to explore. A good book on the microscopic dissection of marine zoology would help to give you an idea of how to slice them up for best viewing under the 'scope. These critter also often have tiny little parasites on them so inspect them carefully, as they make for good viewing too... Also, whilst you may have never seen some off these critters on the supermarket fish counter, what’s left over from your dissections are very probably edible as well. It's a crying shame that it usually only goes into cat food. --Aspro (talk) 20:39, 7 March 2013 (UTC)

Regulatory genes that account for monocot physiology

Is there some sort of regulatory gene regime like the homeobox genes in animals that accounts for differences between monocots and (eu)dicots as a suite? Or are things like parallel venation and monocotyledony separate, unrelated innovations? Thanks. μηδείς (talk) 20:40, 7 March 2013 (UTC)

I don't know. But I found this reference in the homeobox article: A Comprehensive Classification and Evolutionary Analysis of Plant Homeobox Genes. Mol Biol Evol. 2009 December; 26(12) (open access here [6]) - A quick glance leads me to believe it would answer your question, but I can't really read that stuff. SemanticMantis (talk) 20:51, 7 March 2013 (UTC)

That source basically says that analogs of the homeobox genes exist broadly in plants from algae to flowering, but it doesn't focus on flowering plants or answer the question as to whether monocot innovations are a suite of characteristics due to one regulatory system or not. μηδείς (talk) 21:03, 7 March 2013 (UTC)

Flirting

If flirting a subconscious human behaviour? Do animals do it or only humans? Clover345 (talk) 22:57, 7 March 2013 (UTC)

Flirting behavior is by definition a human behavior; it can be conscious or subconscious. For (slightly) analogous behavior in animals, see courtship display and courtship_in_animals. SemanticMantis (talk) 23:46, 7 March 2013 (UTC)

if its subconscious, is it an emotional response? — Preceding unsigned comment added by Clover345 (talk • contribs) 23:51, 7 March 2013 (UTC)

Flirting in primates does not brake down into simple conscious or sub-conscious behaviour. The opposite sex can often detect conscious willful manipulation. However, if the basic animal instinct of sexual attraction is satisfied (emotional) then the higher intellectual demands requiring compatibility come into play. In the past, when people often did not travel far from their village and and expectations were less, like-married-like. Now, in the modern age, with cheap travel... like still marry like (so they hope) – but from further afield, because they have been brought up to be more fussy. The down side is that in the US and some other countries, singletons are chasing the impossible dream. Many animals flirt as part of their courtship.--Aspro (talk) 00:41, 8 March 2013 (UTC)

For specifically subconscious flirting behavior, see Proteans. Evanh2008 ^{(talk|contribs)} 22:57, 8 March 2013 (UTC)

Psycho-acoustics

are the explanations of psycho-acoustic simulation per the Hank Risan article consistent with science in this area? --_nonsense ferret 23:33, 7 March 2013 (UTC)

Wikipedia has an article on Psychoacoustics with references. You could use that to help your research. --Jayron32 02:13, 8 March 2013 (UTC)

March 8

Radiative transport?

Does the "Radiative transport" linked in the Sievert integral article mean the same thing as "Radiative transfer"? Or is this "Radiative transport" referring to some physiological aspect of radioactivity? I can't tell from the references. Thank you. Praemonitus (talk) 00:21, 8 March 2013 (UTC)

The former. The integral pertains to a layered medium, with $\varphi =0$ normal to the layers, such that $x\sec \varphi$ is the distance along a line at angle $\varphi$ to the normal to a point x away in the normal direction. Then the exponential decay of radiation over distance (in the simple case) is invoked. I'm not sure what should be taken from the weighting by angle; there may be compensating terms involving solid angle subtended at each end of the line segment. I think "radiation transport" (as it says: note the first word) is a common synonym for "radiative transfer"; it might deserve a redirect. --Tardis (talk) 03:08, 8 March 2013 (UTC)

Thank you for the clarification, Tardis. Praemonitus (talk) 05:23, 9 March 2013 (UTC)

Mixing chemicals

Hello. Can you tell me what would complete the following reaction, which I added together into a beaker. I have noted the solution is both black, and very acidic.:

C3H6O + H20 + NaCl + HCL + C3H8O + KCL + BaCl2 + HNO3 + CoCl2 + K2Cr2O7 + K2CrO4 + H2SO4 + K4Fe(C2O4)4·2H2O → ?

Thanks, Albacore (talk) 03:07, 8 March 2013 (UTC)

It depends on the initial concentration of the hydrochloric and nitric acids, many of the reagents in that reaction aren't reagents at all, and may only at best act as catalysts. The final solution is black because of colloidal carbon. Plasmic Physics (talk) 03:41, 8 March 2013 (UTC)

Also, barium sulfate may crash out of the solution, and if the chromate/dichromate is concentrated enough, they may oxidize the isopropyl alcohol to acetone. Of course, if the sulfuric acid is concentrated enough, it will dehydrate all organic compounds in the mixture to carbon like Plasmic said -- but if the nitric acid is highly concentrated, then it might in turn oxidize the carbon to CO2 (which will bubble out of the solution because of its low solubility in acid)! So if I had to guess, I'd say your solution contains the following: H2O (solvent), C(s), C3H6O(aq), Na+(aq), Cl-(aq), H3O+(aq) (lots of), K+(aq), BaSO4(s), NO3-(aq), Co+2(aq), Cr2O7(aq), HSO4-(aq), CO2(g), and Fe+2(aq). 24.23.196.85 (talk) 06:43, 8 March 2013 (UTC)

Oh, I forgot the oxalic acid H2C2O4(aq) (which will be fully protonated because of the acidity). 24.23.196.85 (talk) 06:48, 8 March 2013 (UTC)

A biological question about myself

we cannot offer diagnosis or medical advice
The following discussion has been closed. Please do not modify it.
I once took an otc pill was for Common coldness (it was in 2011) and contained: Dexchlorpheniramine maleate Pseudoephedrine for an unkown reason, it maid my hand-skin very dry !!!, so much so, that after 5 days some of the skin on the middle of the upper hand (next 2 where the fingers start-out), and also, in some cushions of the hand, skin could be easily ripped off from this areas (and it wasn't painful). other Antihistamine drugs didn't do that 2 me (except 2 one which i think contains the same AH molecule mentioned above, but don't take my word for it). could you at least try 2 tell me about this very interesting mechanism? thanks 4 your time. Ben-Natan (talk) 05:50, 8 March 2013 (UTC) The drug is a common antihistamine decongestant combination. Your skin changes were either (1) an effect of the respiratory infection for which you took the drug-- several of them can cause late skin desquamation and peeling; (2) an allergic reaction to either component of the drug; or (3) due to something completely unrelated. Note that an allergic reaction to a drug is different than a "side effect"-- what you describe is not a recognized side effect of either drug. I suspect the first possibility is most likely. The only way I can think of for you to determine whether it was a drug effect would be to take it again for a few days: if it didnt happen again, it probably wasnt the drug. Note that this is speculation because you asked for it and not medical advice. alteripse (talk) 12:41, 8 March 2013 (UTC) This is a one-off trial with a sample size of one person and no double-blind control. Literally nothing can be deduced from it. Without other information, there is zero reason to assume that the effect on your skin had anything whatever to do with the medication - rather than some chance encounter with some chemical or biological agent over some several days before you skin condition popped up - or as a side effect of the disease that caused you to take the drug in the first place. To even credit the question as something worth answering, you'd first have to take a thousand people, give half of them the medication and the other half a placebo, count the number that have skin problems and see if the result is higher for those taking the medication than those that didn't. If that's a big enough difference, then it's a side effect and you can start to ask why it happens. But if not...then this is not a meaningful question. Since the manufacturers most certainly did some kind of a trial like this for all of the active ingredients, then if this were a reasonably common side-effect, it would be printed on the label someplace. So check the label - and if it describes this symptom, then we can probably find the cause somehow. If not - then it was almost certainly something else that caused your skin issues. SteveBaker (talk) 14:20, 8 March 2013 (UTC) Hi. For the first answerer, anytime i take the drug, the exact thing happen, i took it again before and after the aforementioned time. thanks. Ben-Natan (talk) 17:16, 8 March 2013 (UTC)

the human singing voice - effects of age

Until age 50, I had a soprano voice and could sing a high A without difficulty. In the 15 years since, it has dropped an octave. I now sing (croak) lower than my husband does. I am aware that voices change over time and that women's voice generally get lower. What physical changes account for this please? And does it matter? There have been no illnesses which might explain it and my speaking voice has not much changed. Thank you. — Preceding unsigned comment added by 109.12.62.161 (talk) 07:59, 8 March 2013 (UTC)

One of the illnesses that affect voice, and that affects many females over the age of 50, is hypothyroidism. I presume you've ruled that out. --TammyMoet (talk) 10:25, 8 March 2013 (UTC)

Firstly, we're not allowed to diagnose medical issues here on the Wikipedia reference desk - that's a huge "No-no" for use! So our advice has to be limited to "Go see a doctor"...and something like this does have the potential to be indicative of medical issues that you might not otherwise have noticed (see Vocal cord dysfunction for a range of alarming possibilities), so that's especially good advice in this case.

Our vocal cord article suggests that menopause can specifically change a woman's singing voice, and since this evidently happened in your early 50's (which is plausibly the age when menopause happened for you) the timing is right for that to be the cause here.

If all else fails...there is always helium! :-)

SteveBaker (talk) 14:37, 8 March 2013 (UTC)

And menopause causes a lowering in the voice frequency due to changing hormone levels (a higher testosterone to estrogen ratio, which also can cause facial hair). I wonder if anyone has studied if hormone replacement therapy reduces or reverses this effect ? StuRat (talk) 16:14, 8 March 2013 (UTC)

Does the concept of a "quantum speed" make any sense?

I am currently taking a Quantum Chemistry class at university and to test our knowledge on quantum mechanics, the professor just posted a rather interesting question. The question is:

"Does the concept of a 'quantum speed' make any sense?"

I thought this question in two ways:

1) Speed as a continuous variable is not quantizable. This means a "quantum of speed" doesn't exist, and therefore the concept of a "quantum speed" does not make any sense.

2) Since speed is the magnitude of velocity and velocity is the time derivative of position, the speed of a particle trapped in a box (say, a 1-D infinite square well potential) is represented by || d/dt [xΨ(x,t)] ||. Taking the position operator on the wave function yields a position with an imaginary part, and taking the magnitude of the time derivative of a complex position should be able to yield a real solution. Would the real solution represent the "quantum speed"

Am I at all on the right track with these two approaches? Hope to hear you guys' insights! — Preceding unsigned comment added by 169.232.187.44 (talk) 08:28, 8 March 2013 (UTC)

What evidence do you have to support your theory that "speed as a continuous variable is not quantizable"? It might be true, but is it established as a fact? See Planck length and Chronon. Also see [ http://arxiv.org/pdf/quant-ph/0004086.pdf ]. --Guy Macon (talk) 10:19, 8 March 2013 (UTC)

The Planck length is just a distance at which quantum gravitational effects should become large. There's no particular reason to think that distances are quantized in units of the Planck length. Anyway, there's no Planck speed—or rather the Planck speed is c, which isn't particularly helpful in this context. -- BenRG (talk) 23:09, 8 March 2013 (UTC)

Perhaps an overly simple approach: aren't speed and temperature essentially the same thing, on a quantum scale? Isn't temperature quantized? --Mr.98 (talk) 12:50, 8 March 2013 (UTC)

Sorry for the digression, but no, absolutely not. Speed and temperature are not remotely the same thing. In fact temperature has nothing directly to do with kinetic energy. Temperature is a measurement of the relationship between entropy and internal energy. This is the statistical mechanics approach to temperature, and it is far more fundamental than the kinetic approach. Temperature can even be negative, that is, below absolute zero, which is obviously not possible for speed or kinetic energy. --Trovatore (talk) 17:13, 8 March 2013 (UTC)

Define a linear speed operator S by defining it on the functions exp(i k x) (which form a complete set), as

S exp(i k x) = hbar |k|/m exp(i k x)

Then S is defined for all states. You then need to check to see if S is a Hermitian operator. Count Iblis (talk) 15:51, 8 March 2013 (UTC)

In physics, I believe there are some massless particles which can only go the speed of light, while particles with rest mass can go speeds below, or, theoretically, above the speed of light, but not precisely that speed, as getting there would require infinite energy. A complicating factor is that the speed of light itself varies, depending on the medium. StuRat (talk) 16:04, 8 March 2013 (UTC)

If you're implying that particles can't travel faster than the speed of light in a medium, that's absolutely wrong. They can and do break the "light barrier" in water all the time, and the result is Cerenkov radiation. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)

(Mostly responding to StuRat) The speed of light in a medium is just the speed of light in a medium and has nothing intrinsically to do with the speed of anything else. The universal constant c has nothing intrinsically to do with light, even though it's often called "the speed of light in vacuum" or even just "the speed of light". So your second sentence isn't a complicating factor in any physical sense. It's just a pun on the phrase "the speed of light". -- BenRG (talk) 23:09, 8 March 2013 (UTC)

To the OP: maybe I'm missing something here, but why can't you apply the momentum operator to the wavefunction, calculate the inner product of the result and the wavefunction, and integrate over all space? That would give you the expectation value of momentum. Divide that by mass and you'll get the classical analogue of velocity for a wavefunction. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)

I wonder if this question had some specific context—i.e. there was something in the lectures or readings recently that looked like it was about "quantum speed", and the question is whether that's accurate or misleading. Without context it's hard to know what to say. Speed is an observable in quantum mechanics, as other people have already said. It's not quantized in general (though it can be in particular cases like the particle in a box), but not being quantized doesn't mean it's not quantum—"quantum X" and "quantized X" generally mean different things. -- BenRG (talk) 23:09, 8 March 2013 (UTC)

There isn't a really specific context that I can provide I'm afraid. We just wrapped up 3D particle-in-a-box and moved onto the harmonic oscillator approximation. The professor is pretty big on the interpretation of Quantum Mechanics though. I suppose the context for a "quantum speed" comes frmo the latest Verizon adverts where they allow the users to upgrade to a faster internet speed called "quantum." I think that's where he based the problem off of. In regards to 140.180.243.114, taking the momentum operator and then dividing it by the mass does seem to be a much quicker way to determining the velocity! — Preceding unsigned comment added by 169.232.187.164 (talk) 00:22, 9 March 2013 (UTC)

Something about coelomates

In here (page 95), the classification chart of animals into different phyla is given. I'm having trouble understanding how coelomates are further divided. Can anybody help? Thank you. --Yashowardhani (talk) 09:30, 8 March 2013 (UTC)

The chart on that page clearly shows that coelomates are divided into Annelida, Mollusca and Arthropoda on one branch and Echinodermata and Chordata on the other. Wikipedia uses a 'superphylum' notation to name those two branches - so the Echiondermata and Chordata are both "Deuterostomes" (with a couple of other phyla tossed in that your chart doesn't mention) and the Annelida and Mollusca are all in the super-phylum "Lophotrochozoa". Wikipedia's chosen classification places the arthropoda in the "Ecdysozoa" super-phylum.

The trouble with these classifications is that they are changing rapidly as we discover more about the animals involved - and the entire structure of the tree is a matter of heavy debate with some biologists preferring a DNA-based approach, others an evolutionary approach - and with both laboring under some horrific mis-classifications made by observation of body structure alone dating back to Victorian times. Your book looks like it was probably published about 8 years ago...and things are changing faster than that!

SteveBaker (talk) 15:04, 8 March 2013 (UTC)

Some of the clades you mention, are fairly certain and stable such as the crown deuterostomes and the ecdysozoans. The big problem is the protostome/deuterostome dichotomy has turned out to be as flawed as the dicot/monocot dichotomy, with protostomy and dicotyledony turning out to be non-diagnostic symplesiomorphies. The linked information Yashowardhani provided would have been considered simplistic and out of date decades ago--it's basically suitable merely as an introduction to the fact that such concepts exist, as might be okay for non-science majors. There are plenty of popular books like Assembling the Tree of Life that are slightly more updated and at least bring up the issues that are at question. (Even that will be outdated, however--the field is in a huge flux, see Afrotheria for an unexpected recent yet now undoubted grouping.) μηδείς (talk) 01:25, 9 March 2013 (UTC)

The solubility of francium hydroxide: is it OR?

In Chinese article of francium hydroxide it is claimed that francium hydroxide is soluble in water along with this source:Maddock, A. G. (1951). "Radioactivity of the heavy elements". Q. Rev., Chem. Soc. 3 (3): 270–314. doi:10.1039/QR9510500270.. In English article of francium there is a similar claim using the same source says"Nearly all francium salts are water-soluble." But in the DOI page all I can say is an abstract of the research focusing mainly on the actinium series. So does this article actually describe the solubility of francium salts?

The article says "nearly all francium salts are soluble". That's it; no further details are given. It doesn't say water-soluble, though this is implied by the context. Chris (talk) 15:29, 8 March 2013 (UTC)

After all, the article might mean "soluble in molten tungsten"... :) --Guy Macon (talk) 17:05, 8 March 2013 (UTC)

What??? The wikipedia article did say water-soluble. You mean the doi article?--Inspector (talk) 23:57, 8 March 2013 (UTC)

Cinnamon Wattle

Hi!

How has the plant Cinnamon Wattle got its scientific name Acacia leprosa? Does it have something to do with leprosy? --213.214.155.24 (talk) 12:13, 8 March 2013 (UTC)

The word indeed derives from the original Latin word for leprosy (as of course does the English word itself), and in biological nomenclature is sometimes used to indicate a spotted or blotched appearance (as a sufferer of leprosy might have). Although it's not obvious in the pictures in our article on the Cinnamon Wattle, it looks as if the 'leaves' do have a slightly mottled appearance due to their texture. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:42, 8 March 2013 (UTC)

This says: "Acacia; from Greek acis, a thorn. leprosa; having a whitish, mealy or scaly surface, presumably referring to the phylodes.". And according to leprosy: "The word leprosy comes from ancient Greek Λέπρα [léprā], "a disease that makes the skin scaly"". So the name basically refers to the scaly nature of the plant - and both "leprosa" and "leprosy" come from a common base term for scaliness. The plant itself has nothing whatever to do with leprosy. SteveBaker (talk) 14:45, 8 March 2013 (UTC)

Drat, I misread the title, and now I'm hungry for cinnamon waffles. StuRat (talk) 16:10, 8 March 2013 (UTC)

This here's the wattle, the emblem of our land,
you can stick it in a bottle, or hold it in your hand

— Monty Python

Amen. -- Jack of Oz ^[Talk] 04:27, 9 March 2013 (UTC)

specilization of the cell wall of epethilia

please i want it very soon

specilization of the cell wall of epethilia — Preceding unsigned comment added by 41.37.24.186 (talk) 16:07, 8 March 2013 (UTC)

See Epithelium, but "the epithelia" includes every type of tissue in the body, apart from muscles, nerves, and tendons. Without knowing the specific type of epithelium you need information about, it's not really possible to answer the question. Tevildo (talk) 18:07, 8 March 2013 (UTC)

Why azane, not nitrane?

All the examples listed at Substitutive nomenclature are constructed as main part of element name + "ane": borane, oxidane, phosphane. So why is azane not called "nitrane"? — Sebastian 16:44, 8 March 2013 (UTC)

It's named after azote which is an alternate name for nitrogen which has now fallen out of use. Dauto (talk) 18:58, 8 March 2013 (UTC)

Cool, thanks! BTW, German "Stickstoff" expresses the same idea, meaning "suffocating substance". — Sebastian 19:33, 8 March 2013 (UTC)

There's also Guns 'n' Roses copyright. μηδείς (talk) 01:13, 9 March 2013 (UTC)

Which they stole from Roy Acuff. 24.23.196.85 (talk) 03:37, 9 March 2013 (UTC)

Weird chemistry dream: The scent of a proton

I had an odd dream last night in which I was back in chemistry class. The teacher had a device which could strip the electron from atoms of hydrogen, leaving positively charged protons, which we sniffed via a tube stuck up the nose. They had an unpleasant acrid smell. Now in reality, would such a gas of low energy low density hydrogen atom stripped of electrons have a smell? I know that normal hydrogen is odorless. This is quite distinct from proton beam therapy. The Proton article in the section "Interaction of free protons with ordinary matter" says that such protons might combine with another atom or molecule to make "Bronsted acids," which makes the "acrid" scent in the dream plausible. Is such an experiment possible (however inadvisable)? Edison (talk) 17:56, 8 March 2013 (UTC)

It must have been an awesome dream! 140.254.121.60 (talk) 19:30, 8 March 2013 (UTC)

Maybe you were smelling ozone. The protons can also be called ionized hydrogen, and ions are generated during lighting storms which also makes ozone, which you can smell. Ariel. (talk) 20:18, 8 March 2013 (UTC)

Acrid: "Smells like Akron". :-) StuRat (talk) 22:51, 8 March 2013 (UTC)

Didn't you mean this Akron? 24.23.196.85 (talk) 03:40, 9 March 2013 (UTC)

Nope, Akron, Ohio, with that lovely rubber volcanization scent. StuRat (talk) 04:20, 9 March 2013 (UTC)

To be smellable, a substance must be volatile and soluble. (Volatile to get to your nose, soluble to penetrate the aqueous and lipid layers that surround the olfactory nerve cells.) I'm guessing that by the time a proton reaches your olfactory receptors, it's hydrogen, though as you point out other substances might be possible. - Nunh-huh 03:48, 9 March 2013 (UTC)

caffeine ==> adenosine receptors

Is caffeine a competitive agonist for ATP on the adenosine receptors? ATP stands for adenosine triphosphate, and it is used by cells as an energy source. Similarly, caffeine somehow gives you energy. Is it possible that they work the same way? 140.254.121.60 (talk) 19:27, 8 March 2013 (UTC)

The chemical that activates adenosine receptors is adenosine, not adenosine triphosphate. I am unaware of any evidence that ATP acts as an agonist at adenosine receptors. So I believe the answer to all these questions is no. You can look at our article on caffeine for more information. Looie496 (talk) 23:23, 8 March 2013 (UTC)

Adding water causes liquid soap to gel

We decant liquid dish soap from a large commercial bottle into a pump-action dispenser beside the kitchen sink. Recently in rinsing out the liquid remaining in the bottle by adding water, I found the resulting diluted soap lathered up well on the sponge and was then easier to rinse off the dish being washed. However, when I added water to the dish soap in the dispenser (about 1:3 ratio), I was dismayed to discover the lower part in the dispenser turned into a gel that resists dilution with water. What's going on here? -- Deborahjay (talk) 19:49, 8 March 2013 (UTC)

If you put the dispenser in warm water for a while, does the gel dissolve? --Guy Macon (talk) 20:00, 8 March 2013 (UTC)

I can't try that without recreating the original problem - I poured the entire contents of the dispenser into a large bowl and combined it with my fingers, then added much more water so it's highly diluted now. -- Deborahjay (talk) 20:23, 8 March 2013 (UTC)

I think what Guy is getting at is that the water temperature might make a big difference, with the water mixing much better if hot. Was the water a uniform temperature in both cases ? The other big difference might be the surface area. Presumable, on the plate, there was much more surface area available for mixing than in the dispenser. Next time, you might want to just add a little hot water to the dispenser, mix that in, then add a bit more, until it's all mixed. StuRat (talk) 22:48, 8 March 2013 (UTC)

March 9

Why do ceiling and walls get darker except for the corners

My room used to be white but darkened because of smoke, etc. Except for the very corners that seem to be unaffected. A professional painter tells me this is very common. How would smoke even know it's in a corner? Joepnl (talk) 00:00, 9 March 2013 (UTC)

Just a WAG, but my guess is that it has something to do with the way that air currents distribute the smoke around the house; the corners may present perturbations to air flow that prevent as much smoke from getting into the corners as along the surface. --Jayron32 00:05, 9 March 2013 (UTC)

In that case I'd expect a big white spot in the "very 3D-corners", where there are three angles at the same time giving reason to the smoke to not stick to the wall. The white stripe seeminglingy has the same width everywhere. I was thinking that it might have to do with the way the paint was applied (using a paint roller for the large areas and a brush for the corners), but the white stripe also appears next to lights that were installed after the painting was done. Joepnl (talk) 01:19, 9 March 2013 (UTC)

Doesn't laminar flow decrease exponentially with proximity to a surface? Wouldn't that imply airflow in room corners is minimal, and that wsmoke would more likely escape a room before getting into its extreme corners? I am reminded of H. P. Lovecraft. μηδείς (talk) 02:03, 9 March 2013 (UTC)

It's an effect called ambient occlusion. SteveBaker (talk) 05:00, 9 March 2013 (UTC)

science writing

Why is science writing usually done in the third person, passive, past tense? — Preceding unsigned comment added by 99.146.124.35 (talk) 02:52, 9 March 2013 (UTC)

Because it's always done that way. I'm serious. That's what my high school science teachers told me almost 50 years ago. Oh, there's also the fact that we lost marks if we did it any other way. HiLo48 (talk) 02:59, 9 March 2013 (UTC)

Well, there is actually a reason: to maximize objectivity. First-person writing brings ego into the picture, and when ego comes in, objectivity goes out. Looie496 (talk) 03:10, 9 March 2013 (UTC)

My impression is that most papers are written in the present tense, first person plural (even if there's only one author). Popular books about science are written in the past tense insofar as they're histories, in the third person insofar as the author wasn't involved, and in the first person insofar as he/she was involved. I think the passive voice is used mainly where the subject would otherwise be "scientists in our (sub)discipline" and it would be silly to keep repeating it. You do often see "our results are summarized below" instead of "we summarize our results below", but there's nothing wrong with that. -- BenRG (talk) 04:58, 9 March 2013 (UTC)

Glomerular Pore Radius

Hello. Given the filtration coefficient, how can one find the pore radius in order to calculate the "pore surface area to pore length" ratio? I am referring to the formula: $K_{f}={\frac {r_{0}^{2}S}{8\mu l}}$ where $r_{0}$ is the pore radius and ${\frac {S}{l}}$ is the ratio. A link to a journal article would be appreciated. Thanks in advance. --Mayfare (talk) 03:28, 9 March 2013 (UTC)

Eggs and potatoes

Eggs and meat cook from the outside in, but potatoes and root vegetables cook evenly (if that's the right way to put it). I suppose that it has something to do with the fact that eggs and meat contain more protein, but what is the reason for that difference? Sjö (talk) 08:27, 9 March 2013 (UTC)

There might be a small difference in thermal conductivity as you suggest, but the main difference is that potatoes and root vegetables are normally cooked for much longer at only 100C, so the difference between inside and outside is not really significant because the whole object has been at a constant temperature for a long time. Eggs are normally cooked for a short time so delays in heat flow are noticeable, with the yolk never reaching 100C in some cases. Meat is normally cooked for longer, but at a higher temperature, and not covered in water, so low thermal conductivity and restricted heat flow becomes very important. Those who like their meat "rare" never allow the inside to reach 100C, even if the outside has reached several hundred degrees. If you try grilling potatoes and root vegetables, you will see that they also cook from the outside in. Dbfirs 09:44, 9 March 2013 (UTC)

I can assure you that potatoes and root vegetables do indeed cook from the outside in, and I really have no idea where you got the notion that the inside of a potato cooks at the same rate as the outside. Do you have any references to that effect? --TammyMoet (talk) 10:53, 9 March 2013 (UTC)

Does vitamin D insufficiency known as a potential Obesity cause?

My Nutritionist told me that there may be a connection. my endocrinologist told me: "take at least 10 drops !!! (off 400 IEA)"). is there a connection between being with bmi like 29 (near obese) to this vitamin? thanks Ben-Natan (talk) 08:49, 9 March 2013 (UTC)

That seems unlikely. New Zealand is pretty close to the ozone hole, and apparently we're the sixth fatest country in the world. Plasmic Physics (talk) 10:38, 9 March 2013 (UTC)

what is Nec?

in many scientific words like Necrosis, Adiponectin, and also in such as Necromancer there is the morpheme Nec. what is the meaning? Ben-Natan (talk) 10:15, 9 March 2013 (UTC)

It comes from the Greek prefix necro, meaning death. Don't know whether Adiponectin uses that particular meaning though. --TammyMoet (talk) 10:46, 9 March 2013 (UTC)

The etymology of the nect element in adiponectin is from Latin nectere meaning to connect or to bind. SpinningSpark 11:47, 9 March 2013 (UTC)

How can we predict properties of an element and its compounds when that element is not available or too unstable to experiment?

One early example of those might be Mendeleev's prediction for germanium and its compounds, which includes some densities and melting points. How are those kinds of predictions made? Just simple linear regression, and in some cases by theoratically calculating the Van der Waals Force? Do we know how accurate it can be? Can we apply such methods to other elements and their compounds? Is it original research to make such predictions?--Inspector (talk) 10:10, 9 March 2013 (UTC)

Planck derived units

What is the difference between one Planck length per Planck time; and one Planck length per second? Isn't the latter one meaningful when describing quantum speed? Plasmic Physics (talk) 10:49, 9 March 2013 (UTC)

The Answer to "Relaxing Voices"

This is from January 2011; my original question was deleted because it was too "medical" sounding, and my follow-up question was therefore poorly explained on my part because I didn't want it removed. Anyway, from this thread: "Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep." I didn't know how else to explain this. well just now, some random video on YouTube was being pushed on me ("featured"?), so finally I watched it and I noticed all these "ASMR" videos that seem to be a thing now. I Googled ASMR and it took me to Autonomous sensory meridian response—that's precisely what I've been looking for for decades (long before people discovered this on the Internet). It's a "dizzy" feeling one experiences when certain individuals talk quietly.Reflectionsinglass (talk) 11:59, 9 March 2013 (UTC)