Suppose we have a 1 litre container of water (or any other drinkable liquid). Is it theoretically possible to pressurize the container to, say, 300 ml capacity so that this smaller container would still be able to contain 1 litre of water (something like black hole)? Specifically, is there any material capable to withstand the associated water pressure while being flexible enough to allow the needed external pressure?--[[Special:Contributions/89.76.224.253|89.76.224.253]] ([[User talk:89.76.224.253|talk]]) 10:05, 28 March 2011 (UTC)
Suppose we have a 1 litre container of water (or any other drinkable liquid). Is it theoretically possible to pressurize the container to, say, 300 ml capacity so that this smaller container would still be able to contain 1 litre of water (something like black hole)? Specifically, is there any material capable to withstand the associated water pressure while being flexible enough to allow the needed external pressure?--[[Special:Contributions/89.76.224.253|89.76.224.253]] ([[User talk:89.76.224.253|talk]]) 10:05, 28 March 2011 (UTC)
:It's doubtful. You would need a pressure of ''at least'' [http://www.wolframalpha.com/input/?i=2.2%C3%9710^9+Pa+%2F+%28300+ml+%2F+1000+ml%29 7.333×10^9 Pa] <small>(Hope I did the math right.)</small> Which is a pretty immense pressure. But since the [[bulk modulus]] of water is non-linear with pressure, the real pressure is probably much much higher. I can't find info on how non-linear. [[User:Ariel.|Ariel.]] ([[User talk:Ariel.|talk]]) 10:57, 28 March 2011 (UTC)
:It's doubtful. You would need a pressure of ''at least'' [http://www.wolframalpha.com/input/?i=2.2%C3%9710^9+Pa+%2F+%28300+ml+%2F+1000+ml%29 7.333×10^9 Pa] <small>(Hope I did the math right.)</small> Which is a pretty immense pressure. But since the [[bulk modulus]] of water is non-linear with pressure, the real pressure is probably much much higher. I can't find info on how non-linear. [[User:Ariel.|Ariel.]] ([[User talk:Ariel.|talk]]) 10:57, 28 March 2011 (UTC)
:I remember seeing an old film clip about what must have been the [[Bathysphere]] returning from the deeps after a test run. When its door bolts were ginergly loosened, a huge quanity of water gushed out under pressure, several times the volume of the sphere. So, yes. [[Special:Contributions/92.15.14.99|92.15.14.99]] ([[User talk:92.15.14.99|talk]]) 11:56, 28 March 2011 (UTC)
:I remember seeing an old film clip about what must have been the [[Bathysphere]] or [[Benthoscope]] returning from the deeps after a test run. When its hatch bolts were gingerly loosened, a huge quanity of water gushed out under pressure, seemingly several times the volume of the sphere. So, yes. [[Special:Contributions/92.15.14.99|92.15.14.99]] ([[User talk:92.15.14.99|talk]]) 11:56, 28 March 2011 (UTC)
== Methanopropylenes ==
== Methanopropylenes ==
Revision as of 12:04, 28 March 2011
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Irradiation has to take place in a specialized irradiating facility. Sushi and sashimi is prepared using extremely fresh fish. I think it would make it rather prohibitive, unless you're imagining that every Japanese restaurant would have a gamma irradiator or a radiation source on premises. The cost would be huge. --Mr.98 (talk) 01:08, 23 March 2011 (UTC)[reply]
I think that food irradiation equipment is dangerous in untrained hands, they contain Cobalt-60, which is not something you'd want your waiter fiddling with. APL (talk) 01:32, 23 March 2011 (UTC)[reply]
Irradiation could kill the microbes in raw fish, but it wouldn't do anything to stop a variety of chemical reactions that would rapidly reduce it to slime. Any sort of raw meat is full of enzymes that will rapidly break it down if they aren't either denatured by cooking or suppressed by refrigeratiion. Looie496 (talk) 02:56, 23 March 2011 (UTC)[reply]
I was just expanding on the "parasites" statement. That said, while irradiation "wouldn't do anything to stop" spoilage, I also don't know that it would necessarily cause spoilage. Couldn't one irradiate while refrigerating? I agree with APL's comment about cost as the most obvious problem. -- Scray (talk) 03:41, 23 March 2011 (UTC)[reply]
Radiation can change the taste, particularly if the food contains fat, eg fish, so it is reserved for things like herbs with strong flavour and low fat. Graeme Bartlett (talk) 09:29, 23 March 2011 (UTC)[reply]
The purpose of irradiation is to extend the shelf life of foodstuffs. Sashimi is not suposed to have a significant shelf life. Simply chilling the fish works well - don't fix what ain't broke. Roger (talk) 12:41, 23 March 2011 (UTC)[reply]
Although I would agree that one purpose (and the most prevalent current purpose) of irradiation of foodstuffs is to extend shelf life, that was not the OP's question. They asked why irradiation isn't used on sushi and sashimi. They did not say what purpose they had in mind. I would agree with your comment, except that chilling doesn't kill many important parasites, and User:APL previously proposed (in this thread) that it might be used to kill parasites. I don't know whether that's been tried, but the articles I linked (and their reliable sources) do indicate that raw fish (as may be found in sushi & sashimi) are an important contributor to human parasitosis. -- Scray (talk) 16:35, 23 March 2011 (UTC)[reply]
Indeed I seem to recall during one of the US spinach E. coli someone suggesting routine irradiation of spinach (and possibly other foods) would reduce those sort of outbreaks and other occasional food poisonings from such food stuffs, the primary thing stopping it was unwarranted consumer concern. (I'm not saying I agree with their view nor do I see the need to get in to discussions about whether better hygiene and farming practices may have more merit simply pointing out there are plenty of cases when irradiation is used for reasons other then improving shelf life.) Also as our article notes irradiation is used with various fruits for import into places like New Zealand, Hawaii and Australia to try and stop the introduction of pests not currently present in the local environment. Our article also notes various other examples which don't seem to be simply about improving shelf life. Nil Einne (talk) 12:03, 24 March 2011 (UTC)[reply]
Why do you believe that they are not irradiating sushi? Since a couple of weeks, indeed, they are using irradiation on sushi, sashimi and many other foodstuff. 212.169.184.141 (talk) 12:58, 23 March 2011 (UTC)[reply]
In case it's not perfectly clear, 212.169.184.141 is making a joke about the accident at the Fukushima power station. APL (talk) 14:01, 23 March 2011 (UTC)[reply]
I am writing this question in reference to President Obamas Tax Proposal on enviormental improvment projects that gives the American Peaple a Tax break when purchasing an recycling item? Please send me any in formation regaurding this issue? I am also in the means of working in a working on a enviormental project of a large scale which objectives is to confine or section off unwanted flying debris.I aim on marketing my product and can use any information that will help the future coustomer. Thank you God Bless Joseph I.Montoya Alavedga (talk) 01:00, 23 March 2011 (UTC) Jim[reply]
I searched, but I can find no information about such a program or a proposal to make such a program. Can you give more information about it? Where did you hear about it? When? Is it a proposal, or an actual program? Ariel. (talk) 02:06, 23 March 2011 (UTC)[reply]
From what I understand it, inflationary cosmology posits a rapidly-expanding primordial false vacuum which at a certain point is punctuated by the formation and growth of low-potential true vacuum bubble universes, of which our universe is one such bubble. In this view, which genesis corresponds to what people refer to when they refer to "the big bang"-- the original initial-state of the false vacuum multiverse, or the initial formation of each bubble universe? Cevlakohn (talk) 05:40, 23 March 2011 (UTC)[reply]
What you're describing sounds like "old inflation", which is dead as a theory as far as I know, having been replaced by slow-roll inflation—see Inflation (cosmology)#Early inflationary models and the following section. That doesn't really affect your question, though. The answer is that the "big bang" happens at the end of inflation. Technically, though, it refers to a time just before the end of inflation, when there would have been a singularity if the post-inflationary model were correct back to the beginning of time, which it isn't since the inflationary model takes over at some point. So the "big bang" that subsequent times are measured from never actually happened. (See Age of the universe#Explanation.) -- BenRG (talk) 07:56, 23 March 2011 (UTC)[reply]
Probably teaching you to suck eggs, but you might find further information and useful links from the Physiology section of the Thyroid article and from the Thyrotropin-releasing hormone article. At first glance it looks as if the primary known modifier is temperature, but I suppose that in turn may be affected by circadian rhythms. {The poster formerly known as 87.81.230.195} 90.201.110.155 (talk) 11:33, 23 March 2011 (UTC)[reply]
There has not been a great deal of research on this. Recent papers still cite PMID578614, a study from 1977, which says that there is a rhythmicity: "Thyroxine: Pooled data showed peak values from 8 a.m. to 12 a.m. and lowest levels from 11 p.m. to 3 a.m.". Looie496 (talk) 17:04, 23 March 2011 (UTC)[reply]
I was reading the previous posts about this and none address the possibility of setting off a bomb a a point in the fault that has been identified as having the most potential energy built up (where the most tension exists) to trigger a natural earthquake that might not have happened for another couple of years. Could this be plausible?165.212.189.187 (talk) 14:44, 23 March 2011 (UTC)[reply]
We've discussed this very topic before. Basically:
1) The force required would exceed that of even the most powerful nuclear bombs, unless the fault was ready to go anyway, in which case it would go soon on it's own.
I don't think #1 is quite right. It's true that the comparisons are not the same (though talking about energies released is usually more misleading than clarifying), but it's not clear that large (e.g. megaton range) nuclear weapons could not induce quakes. I think a more accurate answer would say: "we don't know how to do this, we don't have great indications that it would work, but we haven't done much research on this point." Nuclear weapons have effects like small, localized earthquakes; whether one of those could, in the right set of conditions, set off a large earthquake that is "ready to pop," we don't know for sure one way or another.
The relevant article is induced seismicity. As you can see, most academic research focuses on long-term trends, mostly related to changing the structural integrity and the pore pressure in the subterranean strata because of long-term pumping/extraction of ground-water, natural gas, or petroleum. Nimur (talk) 15:24, 23 March 2011 (UTC)[reply]
I think that any further research into controlling earthquakes should be made in the future on other planets where any adverse reactions would be of little consequence since no one is living there. ScienceApe (talk) 19:47, 23 March 2011 (UTC)[reply]
Sounds good to me. Using bombs to set off earthquakes is a topic that's been raised here surprisingly often - I seem to recall some that were before the recent quake in Japan - and I admit I'm mystified by the very idea. No disrespect. You get an earthquake either way, but by using a bomb to trigger it you now also have a nuclear explosion beside Los Angeles (or San Francisco or wherever) to top it off. That doesn't seem like a good trade off to me. And who is going to assume the liability for intentionally causing an earthquake? Every person who so much as chipped a nail during the intentional quake would take part in a class action suit against whoever pulled the trigger. Forget the science; operationally, this is just a terrible idea that nobody in their right mind would assume responsibility for. Matt Deres (talk) 20:47, 23 March 2011 (UTC)[reply]
Taking into account large scale effects (such as non-negligible evolution of the scale factor a(t)) is it right to say that the events which make up my light cone (i.e. those that I can see at a given point in spacetime) are all the points displaced by null 4-vectors (those for which the spacetime interval is zero).
Sorry, I don't know if I am being foolish, but I am having trouble taking into account the evolution of a(t) over the photons time of flight. —Preceding unsigned comment added by 92.21.86.36 (talk) 15:19, 23 March 2011 (UTC)[reply]
Your light-cone is formed by all the null geodesics that pass to your current world point. The tangent vectors to these geodesics are null vectors everywhere. The term "geodesic" takes into account the evolution of a(t) and also space-time curvature due to the matter distribution in the Universe (gravitational lensing). --Wrongfilter (talk) 17:16, 23 March 2011 (UTC)[reply]
Your confusion arises because you're viewing null four-vectors as being displacement vectors. The whole idea of a displacement vector has very little use within general relativity (none that I'm aware of), because unlike in Newtonian mechanics or special relativity, the coordinates used to label events in general relativity don't in general have any physical significance independent of the metric tensor. For example, in general relativity you can't in general get the spatial or temporal distance between two events simply by subtracting the coordinates of the two events. The concept of a vector that does continue to be valuable in general relativity is the tangent vector, such as is used in Wrongfilter's explanation above of a light "cone" in general relativity as consisting of a set of null geodesics. Red Act (talk) 02:55, 24 March 2011 (UTC)[reply]
Only if very close to each other. Cell phones don't have the power or antennae necessary to send messages long distances. StuRat (talk) 16:17, 23 March 2011 (UTC)[reply]
Does very close means some hundred meters? And, is it indeed a minor technical modification, or would it be a huge source of interference among cell-phones?Quest09 (talk) 16:19, 23 March 2011 (UTC)[reply]
Yes, on that order (although what lies in-between has a major impact on range). They would want to use a different frequency for this to avoid interference (specifically, in the US, they would use the FRS and GMRS frequencies). And, of course, walkie-talkies are already designed for this function, and better at it, by using more power (resulting in them going dead much sooner) and having bigger antennae. Ironically, old cell phones were more suitable for this purpose than new ones, since they had the long antennae and big batteries required. StuRat (talk) 16:17, 23 March 2011 (UTC)[reply]
Smart-phones could handle this over very short distances with their Wifi or Bluetooth functionality. Probably only a software change is needed. APL (talk) 18:18, 23 March 2011 (UTC)[reply]
True. The OP is asking about having a cell phone (which uses base stations normally) ALSO being used to directly call other cells phones. StuRat (talk) 23:15, 24 March 2011 (UTC)[reply]
See Carbon filteringIt depends what form the iodine takes. Carbon filters are not good at removing inorganic salts, so radioactive iodine in the form of, say, sodium iodide would not be removed well. On the other hand, most organic iodine compounds (iodomethane, for example) should be removed reasonably well. I'm not sure what chemical form radioactive iodine fallout is likely to take, and I'm having trouble finding any references. Buddy431 (talk) 19:19, 23 March 2011 (UTC)[reply]
You could precipitate the iodine by adding an excess of silver nitrate. Filtering this solution and then treating with something like sodium carbonate or sodium sulfate would then precipitate the silver, excessive ingestion of which can lead to argyria.--Atemperman (talk) 20:12, 23 March 2011 (UTC)[reply]
Before playing around with poisonous chemicals you should consider the short half live of I-131. The simplest and safest way to deal with it is to wait until it has decayed naturally. Provided that you have access to "older" water. 95.112.197.146 (talk) 21:22, 23 March 2011 (UTC)[reply]
Amino acids and fatty acids in durian
The main site, a few minutes of Googling, and nutritiondata.com are unhelpful in providing details on the fatty-acid and amino-acid profiles of durian. Anyone have a clue? --Atemperman (talk) 20:15, 23 March 2011 (UTC)[reply]
Shape of the Universe
Hi, I'm sure my question is answered somewhere in Wikipedia, but my brain has glazed over somewhat, and I'm hoping someone can spell out the answer in simple terms. As far as I understand it, the standard model of the Universe says that at the time of the Big Bang all of space was concentrated into a tiny region, which then began to expand. I visualise this as being like surface of an expanding balloon, except in 3D space rather than 2D space (probably I got this from some science show on TV). Yet at Shape of the Universe it says "Within the Friedmann-Lemaître-Robertson-Walker (FLRW) model, the presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model". Is this consistent with the earlier picture I drew? How can something closed and finite, like the 3D analogue of the surface of a sphere, ever become infinite and flat throuh expansion, without some sort of "rupture" event? If the Big Bang is accepted, then how can the Universe now be any shape other than "closed", like it was originally? 86.181.202.145 (talk) 23:20, 23 March 2011 (UTC)[reply]
Sorry, I'm not sure if this a rhetorical way of saying that according to the usual model it wasn't initially closed, or that you don't know but want to raise it as a suggestion? 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)[reply]
A possible problem is that the "balloon" model is misleading. The balloon expands in 3 dimensions. All of space is represented as 2 dimensions on the surface of the balloon. Everything inside and outside the balloon is not part of space. Only the surface of the balloon is space. Then, you think that space is 3 dimensions, so it is an expanding balloon. Well, the space on the balloon is only 2 dimensions. If you want 3 dimensional space, you need a four dimensional balloon - which is very hard to imagine. So, you have to drop the idea that space is three dimensions if you want to imagine the balloon, which is a spherical model. What if, instead of a sphere, the big bang blew out a ring shape that expanded to a tube? Then, the 2D space would be on the surface of an expanding tube. What if the big bang blew a ring that wasn't hollow in the middle? It is a disk that gets wider and wider, but remains flat? Then, the 2D space would be on an every-increasing flat space. You can imagine cones, cubes, or any other kind of strange shape you like. I like the idea of two conical shapes expanding out of a singularity in opposite directions. I know the data doesn't support it, but I like imagining that shape for space. -- kainaw™02:23, 24 March 2011 (UTC)[reply]
I understand the dimensionality issues. I think the only purpose of introducing the balloon is because it's otherwise difficult for ordinary mortals to imagine any type or curved or closed space. 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)[reply]
I think I'll trot out this image that I made a few months ago (that I've so far used only on the reference desk). This is not an accurate depiction of our universe, but it is an accurate depiction of a FLRW universe with different values for the adjustable parameters of the FLRW model. What's nice about these particular parameter values is that the spacetime you get is the spacetime of special relativity. This diagram is plotted in special relativistic x and t coordinates, with the future at the top and the past at the bottom, and light travels along 45° diagonal lines. (To get the full four-dimensional version of the diagram, rotate it in the third dimension around a vertical axis through the center to get a cone shape, then rotate that through the fourth dimension to get a hypercone.)
It may look like this toy universe is finite and expanding at the speed of light, but to a cosmologist, it's infinite. Cosmological time is measured by clocks that are moving with the Hubble flow. Because of time dilation, the Hubble-flow clocks near the sides of this diagram tick slower. All clocks show the same elapsed time at the surface of last scattering (the upper boundary of the bright region marked "opaque plasma"). This surface, which is shaped like a hyperbola (or a hyperboloid when you rotate the image into four dimensions), represents the universe at a particular time (the last scattering time), and as you can probably see, it's infinite in size and contains an infinite number of galaxies (spaced more or less evenly). It's also negatively curved, even though the spacetime is flat. And it's expanding, but not at the speed of light or any other particular speed; rather, the distance between galaxies is increasing at a rate that's proportional to the distance between them.
So this is what it means for the universe to be "smaller in the past" and yet infinite at all times, and this is how you can get an infinite universe without any faster-than-light expansion. The details are slightly different in the real world, but the idea is the same. -- BenRG (talk) 06:56, 24 March 2011 (UTC)[reply]
This is very interesting and cool. But, having seen it the last time you posted it, what I'm still unable to quite figure out is, does it (or at least, can it) have infinitely many distinct baryons in a spacelike 3-d slice? And if not, are there models that do, that are consistent with observations? I had thought there were, but in your picture it looks like an infinite spacelike slice does not have uniform density; it falls off as you move away from the center line of the drawing, and the total number of baryon world lines could be finite (though perhaps it wouldn't have to be). --Trovatore (talk) 19:09, 24 March 2011 (UTC)[reply]
Along lines of constant cosmological time, the density is uniform with respect to the spacetime interval (but not with respect to Euclidean distance on the diagram, which is why it looks like it's falling off). So, yes, there are infinitely many baryons. If you take a horizontal slice through the diagram (constant special-relativistic t coordinate), you still get a picture of the whole universe, since all of the worldlines have to cross every slice, but it's not uniformly dense; it's actually the Klein model of the hyperbolic space. -- BenRG (talk) 00:03, 25 March 2011 (UTC)[reply]
Here's a silly animation I just made to illustrate the uniform density (linked because inline animations are annoying). This shows the entire diagram above being successively Lorentz boosted with the bottom vertex (the "big bang") held fixed. If you look at the lines representing the Hubble flow, they don't appear to move. Actually, they are moving "one galaxy to the left" on every animation frame (as you can see by looking at the here-and-now dot). You can keep boosting like this forever in either direction, bringing new galaxies to the center, without the density ever changing. -- BenRG (talk) 03:43, 25 March 2011 (UTC)[reply]
March 24
Falling of the Newton's Apple
As we all know the reason of the falling of the Newton's apple on earth is that it's acceleration towards earth is greater than the acceleration of earth towards apple.
Therefore would Newton's apple fall OR accelerate towards earth if it's size (both mass and volume wise) increased exactly to size of the earth?
An increase an extra mass might shift them to new orbit But would they have weight pressure on each other as both equal and opposite accelerations cancel each other?74.198.150.220 (talk) 00:13, 24 March 2011 (UTC)Eccentric Khattak#1-420[reply]
The acceleration of the apple is due entirely to the mass of the Earth. It is unrelated to the mass of the apple insofar as all objects at the Earth's surface accelerate at 9.8 m.s-2, regardless of their mass. Similarly, the acceleration of the Earth towards the apple is due entirely to the mass of the apple and is unrelated to the mass of the Earth.
If two planets of equal mass are close enough to influence each other to a measurable degree, both would have the same acceleration, but in opposite directions. There is no science behind the idea of equal and opposite accelerations cancelling each other. If two objects are gravitationally attractive and have equal accelerations in opposite directions, they collide! Dolphin(t)00:47, 24 March 2011 (UTC)[reply]
I think the problem here is the common misconception of action and reaction forces "cancelling" each other out. That isn't the case. When an object gravitationally pulls on another object, the reaction force is that second object pulling back on the first object. The end result is the exact same - the two objects accelerate toward each other and collide. 99.236.18.156 (talk) 01:25, 24 March 2011 (UTC)[reply]
Also, it's only your perception that the apple is the one object "falling", because you're sitting on the ground and the apple looks so small compared to the earth. As far as you perceive, "you and the earth" could be very light and falling towards a massive apple composed of white-dwarf matter. It's all about your frame of reference regarding relative motion of the apple. DMacks (talk) 09:09, 24 March 2011 (UTC)[reply]
I thought that acceleration was absolute? In other words, it really is the case that the apple is accelerating much more than the Earth, not just one's perception... 109.153.232.142 (talk) 18:43, 24 March 2011 (UTC)[reply]
It's true that proper acceleration is absolute. For example, if there are two rockets in deep space that are approaching each other at an accelerating rate due to one of the rockets having its thrusters on, it's possible to perform a local experiment (an experiment involving only short distances and times) to determine whether you're on the rocket with its thrusters on, or on the rocket that's coasting. Indeed, the experiment is trivial; you don't really even need an accelerometer: If you're pressed up against a surface of the room you're in, then you're in the accelerating rocket, but if you're floating around in your room, then you're in the coasting rocket.
However, gravity does not involve a proper acceleration, because gravity in reality is a fictitious force. Regardless of whether you're in a room attached to the apple, or in a room at the center of the Earth, you're just going to float around in the room, because you aren't undergoing any proper acceleration either way. (If you're in a room attached to the surface of the Earth, then you will be pressed against the floor, but that's because you're undergoing a proper acceleration upward due to the non-fictitious intermolecular forces the floor is imparting to the bottoms of your feet, that prevent your comoving frame from being an inertial frame of reference.) Red Act (talk) 22:11, 24 March 2011 (UTC)[reply]
How about this. You and I are in two rockets at a great distance from the Earth-apple system, such that the gravitational effects are negligible. Using a powerful telescope, you operate your rocket so as to keep level with Earth (specifically, so that a line from you to Earth is at right-angles to the Earth-apple axis), and I do the same to keep level with the apple. Would we not be able to tell that I have to accelerate more than you? 86.176.210.13 (talk) 12:38, 25 March 2011 (UTC)[reply]
DMacks' post doesn't seem to me to be a very good one, because it seems to be implying that there is no difference gravitationally between a system consisting of a small-mass apple and a large-mass Earth, and a system consisting of a large-mass "apple" and a small-mass "Earth". That isn't correct. Although no local experiment performed in the apple's frame of reference will detect any acceleration of the apple, if distances involved are large enough, a nonlocal experiment in the vicinity of the apple can detect a tidal force due to the Earth, that's vastly greater than the tidal force that the Earth experiences due to the apple.
I probably should never have even brought up gravity being a pseudo force that doesn't really cause an absolute acceleration, since the topic being discussed here is Newtonian gravity. In the Newtonian view, gravity is a force that's every bit as real as any other force, and it produces an acceleration that's absolute, in that the magnitude of the acceleration is invariant with respect to any Galilean transformation, and the direction of the acceleration is invariant with respect to any Galilean transformation that doesn't involve a rotation. General relativity views matters differently, but getting into that here would be an off-topic digression that would be unhelpful to the people using this thread to better understand Newtonian gravity. Red Act (talk) 17:29, 27 March 2011 (UTC)[reply]
You'll note that I specifically framed my response as exactly the local experiment. I did so because that's how the classic apple-falls-from-tree experiment is usually described. With substantially larger distances, or impartial (external) observers, obviously things are different than for observer as part of one of the close bodies. DMacks (talk) 20:33, 28 March 2011 (UTC)[reply]
The force on each will be identical and opposite, the magnitude given by Newton's law of universal gravitation (I'm assuming the Newtonian model; don't ask me about relativity!). Whether they have any "weight" as they are falling depends on the definition of "weight", I think (whether it is defined as the gravitational force or the reaction force against some supporting surface such as the ground). By analogy with astronauts in orbit, who are usually termed "weightless", any falling object would also be "weightless". 86.176.210.13 (talk) 12:46, 25 March 2011 (UTC)[reply]
Several responses but still not sure which one of the following is the true representation of Newton gravitation?
1- According to Newton's law of gravitation the force of attraction between aforementioned masses; F = G (m)*2/(Diameter)^2= some figure
2-According to their separate analysis the weight of aforementioned masses over one another are just the meeting of heads of two arrows (equal in magnitude but opposite in direction). Say these two arrows represent two point loads which may cancel each other.
So according to separate analysis of the theory can I assume that weight of a 1 kg of a sphere on earth decrease by increasing it's mass till it becomes weightless when it's size reached exactly to the size of earth (both mass and volume wise) - Although common sense is opposite 74.198.150.216 (talk) 23:26, 25 March 2011 (UTC)Eccentric Khattak#1-420 ¶
GO[reply]
As the mass of the sphere increases, the gravitational force attracting it to Earth increases too, in proportion, according to Newton's law. If the sphere is resting on the ground, then this gravitational force is exactly balanced by the reaction force of the surface that the sphere is resting on. The sphere is not subject to any net force, but it still has a weight, which is equal in magnitude to both the gravitational force and the reaction force. If the sphere is falling towards Earth then, depending on one's definition of "weight", it may be considered weightless. 02:16, 26 March 2011 (UTC) —Preceding unsigned comment added by 86.160.211.9 (talk)
What's striking about that page, and the "Physiological issues" section in particular, is how monumentally bad it is. I don't see one claim regarding the physiology of sex in that section that is supported by a reliable source. There are a few statements about rodent development in microgravity that have some support, but that's not the subject represented by the title. -- Scray (talk) 04:22, 24 March 2011 (UTC)[reply]
I saw a science program on TV that considered this. One thing they suggested was a sort of hammock, but with a top on it too, so the parties involved wouldn't float away from each other. Then there's the hygiene issue, with bodily fluids floating around. StuRat (talk) 05:04, 24 March 2011 (UTC)[reply]
I cheated flagrantly on this one and clicked-through the original image to find out it was taken in Malaysia. Searching Google Images I decided it looked like a Malaysian Bay Owl. Searching that term, I got back to the original image which says that it is "Taken in Bird Park Penang, Malaysia. Oriental Bay Owl (Phodilus badius). Thanks bubo_strix for ID." ... which is a wrap --- provided bubo_strix is the right person to copy off of at exam time ;) Wnt (talk) 03:37, 24 March 2011 (UTC)[reply]
: Cheated?? No you didn't, you thought it through and used a successful strategy to achieve the goal and attributed the image. No one was hurt, humiliated or robbed. Contrary to some people's opinion this is not a competition arena. Well done! Richard Avery (talk) 08:11, 24 March 2011 (UTC)[reply]
Well, I cheated in the sense that I didn't learn anything about the taxonomy of owls, and if I see another photo like this that doesn't offer more information on click-through, I'll be clueless.
Hi. In this page, there is a simple "derivation" of time dilation with 2 identical clocks - one in a rocket and one in lab (with both being observed from the lab). My question is: wouldn't length contraction cause the lab to observe the length of the clock (L) to be different in the moving rocket than the clock in the lab? That derivation assumes that the length (according to the lab) doesn't change. Is that true? 163.202.48.108 (talk) 10:19, 24 March 2011 (UTC)[reply]
If I'm interpreting the diagrams correctly, the 'clocks' in each frame (lab and rocket) are both oriented perpendicular to the direction of the rocket's travel. The Lorentz contraction only occurs in the direction of travel, so the clock doesn't get narrower. TenOfAllTrades(talk) 13:17, 24 March 2011 (UTC)[reply]
Few months ago, I received an ore from my uncle, who is geologist. He claims that the ore he gave me is sperrylite (platinum arsenide). The ore looks somewhat golden-gray in colour, while many samples on the internet is silvery white. This make me curious.
Thus I conduct some experiment, the other possible ore that look like this is pyrite, but it is much more golden. When I put in in hydrochloric acid, it produce few tiny bubbles and change the hydrochloric acid to slightly yellowish in colour. If it was pyrite, I expect it to bubbles more.
So I decided to show the ore's photo here and hopes wikipedians will help me identify it better.
And ends my curiousity. The picture of the ore and its streak can be viewed here,in my blog:
Wikimedia Commons has media related to Sperrylite.
I do not have equipment to find its specific gravity,but with porcelain streak plate (which I use bottom of my porcelain crucible) it did produce black streak,the picture of it can be viewed at my blog.So,does this confirm the material I have is sperrylite? —Preceding unsigned comment added by 175.140.146.69 (talk) 13:24, 24 March 2011 (UTC)[reply]
As Chris.urs-0 says it would be good to check the hardness, if it is Sperrylite you would expect it to be able to leave a scratch on a penknife blade. Mikenorton (talk) 13:48, 24 March 2011 (UTC)[reply]
Also did your uncle say where it came from? If someone gives me a lump of something to identify (half the time it's a lump of slag), that's the first question that I ask. Mikenorton (talk) 14:06, 24 March 2011 (UTC)[reply]
Sperrylite has a specific gravity of 10.6 - roughly the same as lead - so dense that even without proper equipment it should be possible to make a rough estimate that rules it in or out. Just measure the ore like a block, in three dimensions, and compare the volume that gives you to its weight. If this crude estimate comes in around 7 or higher, then it's not galena, and you know it must be something good.
Materials with the same hardness don't leave a streak on each other, but sperrylite can be hardness 6 to 7. Sperrylite has a poor cleavage, and its polished surface has a metallic lustre. Arsenic is poisonous, don't forget to clean the porcelain, pls. --Chris.urs-o (talk) 06:04, 25 March 2011 (UTC)[reply]
Triggering an earthquake
Suppose an earthquake is about to happen that would release X joules of energy. We trigger the earthquake prematurely by detonating nuclear devices with total energy Y, with Y much less than X. Is there any way, even in theory, for the resulting earthquake to release much less than X joules of energy? Or will the released energy be closer to X-Y? --140.180.18.11 (talk) 17:21, 24 March 2011 (UTC)[reply]
Some seismologists have suggested that the common occurrence of foreshocks before many large earthquakes (about 70 % for M>7 events) suggests that they are part of a preparation process in which a series of smaller earthquakes (which would be similar to the nuke in your question) form a sort of cascade continuing until the mainshock is triggered. However many foreshocks seem instead to be just indicators of the enhanced stress levels that eventually trigger the mainshock, this is supported by an observed relationship between the rate of foreshocks and the rate of aftershocks. In this case the foreshocks (or any other source of energy) do nothing to trigger the mainshock. Mikenorton (talk) 17:44, 24 March 2011 (UTC)[reply]
In my lifetime, seismologists seem to have become less certain about the possibility of precise earthquake prediction. How would you know where to do your nuclear detonations? HiLo48 (talk) 17:50, 24 March 2011 (UTC)[reply]
The nearest peak is Evans Peak, almost completely obscuring Alouette Mountain - check it out on google earth (which is what I did), the shape is distinctive. Mikenorton (talk) 20:28, 24 March 2011 (UTC)[reply]
Body heat sun's heat
Is it true that the human body produces more heat than an equivalent volume of the sun's matter. As Dr. Al Khalili states. Sounds improbable. Phalcor. — Preceding unsigned comment added by Phalcor (talk • contribs) 20:23, 24 March 2011 (UTC)[reply]
I think that would depend on what part of the sun. At the core, I don't think so: 150 g/cm3 at 13.6 million kelvin. At the corona, however, it may reach similar temperatures, but it so thin that the same volume will actually contain less overall heat than the human body. --T H F S W (T·C·E)20:29, 24 March 2011 (UTC)[reply]
Yes it's true. The sun is very dilute - but enormous. Take a look: power per mass for sun = 1.934×10^(-4) W/kg power per mass for human = 1.6 W/kg. (A human outputs an average of 100 Watts per day[4]). A human can put out 8,000 times more power than the sun - and that's a resting average. At peak power a human can do about 9 times as much, so 75,000 times as much as the sun. But the sun is absolutely stupendous in total mass, so even as dilute as it is it puts out a huge amount of power. Also, be aware that all the power in the sun is generated in the core, so calculating just in the coregets 0.0088 W/kg (at most), which is still tiny compared to a human. Ariel. (talk) 20:36, 24 March 2011 (UTC)[reply]
As above, depending on what you mean, it's plausible. The sun's output is about 4*1026 J/s, whereas a human's output is around 100 J/s (assuming about 2500 kcal fully converted to heat -- it's probably wrong, but I don't think it's orders of magnitude wrong). The sun is about 1027 m3 in volume, a human about 0.1 m3 (all numbers from Google searches). Dividing those pairs of numbers, the sun radiates 0.4 J/sm3 while a human radiates 1000 J/sm3. So humans are stupendously more heat-producing per unit volume! Well, if you compare a human (where all of the volume is producing heat) with the sun (where only a small portion -- the core -- of the sun is actually producing heat). I've little doubt that the numbers would swing if restricted to the portions of the sun where fusion actually occurs. — Lomn20:39, 24 March 2011 (UTC)[reply]
I just added numbers from only the core to my reply above. And they are so small I wonder if we can ever make fusion power work! The sun's core has a density 100 times that of water, and yet produces power so slowly, how can we hope to beat it? Ariel. (talk) 20:52, 24 March 2011 (UTC)[reply]
The reaction that happens in the sun is different from the reaction that happens inside a fusion power plant. The sun fuses Hydrogen. A power plant fuses deuterium and tritium. Dauto (talk) 22:53, 24 March 2011 (UTC)[reply]
One minor thing: you're listing power per mass rather than power per volume -- adjusting that, the human body only has a 2:1 edge. Not quite the swing I was expecting, but back into the realm of cautionary notes about back-of-the-envelope calculations. — Lomn21:17, 24 March 2011 (UTC)[reply]
Just one last crazy thought on this subject. If we could find a way to artificially duplicate the heat production efficiency of the human body in a machine, perhaps we would have an efficient power plant. Comment not seriously expected. Phalcor (talk) 21:29, 24 March 2011 (UTC)[reply]
As far as I know nuclear reactors do not have iodine or even iodide in them. So how has the Japanese nuclear disaster resulted in radioactive iodine in tap water? How did it get there, where did it come from? Thanks 92.24.188.210 (talk) 20:50, 24 March 2011 (UTC)[reply]
BTW, Iodine-131 has a half life of only 8 days, so the damage will be limited. The other main product is Cesium-137, which lasts a lot longer, but unlike iodine has no biological role, so is not stored by the body. Ariel. (talk) 20:57, 24 March 2011 (UTC)[reply]
If it has a short half-life, that means it gives off all it's radiation in a short period, making it even more dangerous if it's in your thyroid during that period. Also, if it causes DNA changes, those could then take years to progress into cancer. StuRat (talk) 23:09, 24 March 2011 (UTC)[reply]
Our article on 137Cs says that it does mimic potassium...it's not stored (highly incorporated into biochemical/biophysical structures) but it sure does pass through lots of pathways before clearing (which takes several months). DMacks (talk) 21:26, 24 March 2011 (UTC)[reply]
The main difference is that the radiation from cesium is spread out in the body, rather than concentrated in the thyroid, so it's far far less harmful. (The body can handle low levels of radiation, but the concentrated radiation from iodine in the thyroid causes more harm than would be expected by the low dose.) Ariel. (talk) 22:27, 24 March 2011 (UTC)[reply]
Yah, although probably not for the water in Tokyo. It's yield in reactors is low (about 1/3 of I-131), it's half life is so long that it's not very radioactive - it's almost 1 billion times less radioactive than I-131, and when it does decay the decay energy is low and is less harmful (about 1/10 of I-131). Overall while I-129 is carcinogenic, I-131 has not been found to be[5]. (With a biological half life of 11 days to a few month, the I-131 is cleared out of the body before it can do much harm.) Ariel. (talk) 01:17, 25 March 2011 (UTC)[reply]
That sounds a little like you've mixed up the two isotopes in the last two sentences? I-131 has a shorter radioactive half-life than the 11 days, so I don't know why you'd focus on that. It's true that the PDF claims that I-131 has not specifically been found to cause cancer, but I'm not sure what they mean by that (the increase in child thyroid cancers from nuclear testing and Chernobyl is pretty well-documented, I think, and for the reasons you yourself give, it's more likely to have been I-131 than I-129). --Trovatore (talk) 18:31, 25 March 2011 (UTC)[reply]
Thanks. What happens to the fission products when the reactor it working normally? Where do they go? Do they eventually end up in landfill, for example? 92.24.188.210 (talk) 21:16, 24 March 2011 (UTC)[reply]
Comet Tuttle is correct; the US doesn't do any civilian reprocessing of spent fuel. It was considered at one point but killed in the 1970s because of the security implications. (Inventory control is a very serious problem with reprocessing. In a large plant like the Rokkasho Reprocessing Plant in Japan, the amount of "material unaccounted for" is, no matter what you do, going to be on the order of several Nagasaki-sized bombs per year. That means you essentially cannot detect theft or diversion through inventory control alone, which is rather unsettling. This isn't a matter of building better instruments — there is some inevitable loss in the process that you cannot account for, even at best times, and that adds uncertainty in your ability to track it. It may only be 1-2% of lost material, but when that material is plutonium, "a dab'll do ya".) We don't even do waste disposal at the moment. Things are stuck in a really horrible political/legal/technical situation and there has been little progress so far. There is currently a Blue Ribbon Commission that is supposed to be figuring this out. Good luck to them. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)[reply]
In the US, they stay in a swimming pool there at the reactor, for at least 5 to 20 years (see spent fuel pool), then they may stay in the pool forever, or may be pulled out and put into dry cask storage. The Yucca Mountain plan was formed because there was no US national policy to deal with spent nuclear fuel. As the Yucca Mountain article states, the US still has no functioning policy; it's sort of cut off or suspended at the moment, and court challenges are ongoing. Comet Tuttle (talk) 22:14, 24 March 2011 (UTC)[reply]
Highly radioactive fission products have short half lives, and decay relatively quickly into more stable things. So your immediate waste is very hot, but after a year or five in the spent fuel pool, they cool off pretty considerably. The problem is that the "more stable" things are still radioactive — and because they are more stable, they stay that way for thousands of years. But the stuff that ends up in the waste site (in countries that actually have waste sites) is not as "hot" as the stuff that comes right out of the reactor, or is stored in the spent fuel pool. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)[reply]
Is there a country operating a long term waste storage site for comercial nuclear waste? I know that Germany, Finland, Sweden try to find one or already built tunnels for storage, but operational is non of the facilities.--Stone (talk) 09:33, 25 March 2011 (UTC)[reply]
Is it just me or is nuclear power just ridiculously irresponsible? I mean, is it so important to have power that making more and more super-toxic waste is somehow an acceptable outcome? Yes this is a moral question, not a technical one. But I'm still interested in others' opinions. Vranak (talk) 18:15, 25 March 2011 (UTC)[reply]
Other forms of power source either contribute to global warming and pollution or are not economically robust enough. Actually nuclear power is considered widely as relatively "greener" than other conventional sources.--Netheril96 (talk) 18:26, 25 March 2011 (UTC)[reply]
Is there anyone who understands the science and still thinks that solar, wind, etc. can replace fossil fuels without nuclear? As far as I can tell, Greenpeace's belief in renewables is a matter of faith. Their whole existence as an organization depends on the viability of renewables; therefore, renewables must be viable, from their perspective. Kind of like the right doesn't believe in global warming because it's inconsistent with the optimality of the free market. It is difficult to get a man to understand something when his salary depends upon his not understanding it, as someone once said. -- BenRG (talk) 21:59, 25 March 2011 (UTC)[reply]
I think the Greenpeace people would suggest that the answer is renewables plus a radical restructuring of society to use less energy. Which could work from a technical point of view. But shows little evidence of political traction. If you look at the kind of world that Greenpeace people imagine, it's smaller — more local, shorter distances, less reliance on technological advance. It's not an ugly world in many ways (though we need to recall that the "good old days" of smaller living were not so great for the vast majority), but I don't see any evidence to think that the trends of the world are going in that direction. --Mr.98 (talk) 22:28, 25 March 2011 (UTC)[reply]
Nuclear power itself isn't irresponsible, but some of the issues surrounding it are. Building a plant in a populous area without adequate safeguards is irresponsible. Building a plant without a long-term storage solution (already prepared) for the nuclear waste is irresponsible. StuRat (talk) 22:39, 25 March 2011 (UTC)[reply]
coriolis effect in deep space?
the coriolis effect on water down the plug hole due to the rotation of the earth seems easy to grasp, but when I look at Hubble deep space photos of spiraling/spinning galaxies, all of those I've seen seem,(from the telescopes view point) to be spinning in the same direction. Given the apparent random nature of the universe it seems that coincidence is unlikely. Could the universe, as a whole, be spinning, having the same effect on the galaxies? And if so, could that cause the red shift effect attributed to universal expansion. Phalcor (talk) 22:56, 24 March 2011 (UTC)[reply]
Water down the hole does not spin because of Coriolis.
It would be interesting to see numbers on how many galaxies observed are aligned with the Milky Way (or some other axis) vs. opposite to it. Wnt (talk) 00:02, 25 March 2011 (UTC)[reply]
Hmmm, proving that their Galaxy Zoo annotators are biased isn't quite the same as proving that the galaxies are truly unbiased. We have the precedent of matter vs. antimatter to suggest that tiny asymmetries can exist and become very important, so I'll hold out for a truly reliable count of all the visible galaxies. ;) Wnt (talk) 08:06, 25 March 2011 (UTC)[reply]
It would be very remarkable if spiral galaxies showed a preference for one orientation as viewed from the Earth, because this would mean we occupied a privileged position in a non-isotropic Universe. Our spiral galaxy article says that there is some evidence that the axes of spiral galaxies tend to be aligned with their local galaxy filaments, but there is no mention of any correlation of spin direction. Gandalf61 (talk) 10:14, 25 March 2011 (UTC)[reply]
I don't see why it would imply we were in a privileged position. As an extreme example, suppose all galaxies had their spin axis pointing in the same direction. You'd be able to see that from anywhere in the universe, not just here. Or am I missing something? --Trovatore (talk) 22:20, 25 March 2011 (UTC)[reply]
If all galaxies had their axes pointed in the same direction, we would see some of them winding clockwise and others winding counterclockwise, depending on whether they are "above" or "below" us with respect to the universal axis. If we were really seeing more clockwise than counterclockwise galaxies, there would need to be something very spooky going on. It wouldn't necessarily place us exactly at a globally privileged position unless the tendency towards clockwise were equally strong in all areas of the sky, but it would kill isotropy. –Henning Makholm (talk) 23:27, 25 March 2011 (UTC)[reply]
Well, but we don't have to assume we're stupid. If we see all the galaxies in one direction spinning dweezil and all those in the other direction going widdershins, then we get fifty-fifty in terms of total numbers, but we're allowed to say that's strange, and it already means there's a preferred axis to the universe (or at least the part of it we can see). --Trovatore (talk) 01:20, 26 March 2011 (UTC)[reply]
I'm unsure what it is you're arguing for here. Gandalf said that if we were to get total numbers different from 50-50, that would be very remarkable, and it looked like you disagreed with that statement. Now you seem to be saying that some conceivable observations could total to 50-50 and still be remarkable -- which is true, but does not oppose Gandalf's original statement. Am I misunderstanding you somehow? –Henning Makholm (talk) 16:03, 26 March 2011 (UTC)[reply]
To be clear, I was only interested in the spin relative to a specific axis, but a significant error rate in spin determination relative even to the original photograph pretty much kiboshes any further working of the data. Wnt (talk) 21:48, 26 March 2011 (UTC)[reply]
By the way, can we reliably observe which way distant galaxies spin? It's often easy to see visually which way the spiral arms are curled, but how well is that known to correlate with the kinematics of the disk? I suppose we can measure the Doppler shift of spectra at different ends of the major axis of the galaxy's elliptical image in the sky, but that does not seem to resolve the question unless we know somehow which end of the minor axis is closer to us. –Henning Makholm (talk) 16:03, 26 March 2011 (UTC)[reply]
True, and that can be easily seen from the fact that interstellar gas obscures the further side. see for instance the picture of the sombrero galaxy that I included. Dauto (talk) 17:45, 26 March 2011 (UTC)[reply]
Sure -- but on the other hand, I cannot see the spiral arms in that image. Are there angles under which a typical spiral galaxy shows both clear spiral arms and clear occultation of the far side? Have enough of those been surveyed that we can say with certainty that spiral galaxies predominantly spin with the arms leading or arms trailing? If so, which one is true? And how common (or not) are exceptions? –Henning Makholm (talk) 14:34, 27 March 2011 (UTC)[reply]
I never did find a clear statement of which way the arms of a spiral galaxy point, but I found Spiral_galaxy#Alignment_of_spin_axis_with_cosmic_voids which is interesting. But this suggests that galactic spin axes are influenced by the proximity to the void, rather than some universal spin. While it hints that galaxy spin axes might be nonrandom (for example, if the voids were aligned with one another) it would further conceal any universal spin. Wnt (talk) 23:22, 27 March 2011 (UTC)[reply]
I don't know anywhere to point you for this. But isn't it intuitively obvious? Stars closer to the center move faster; that's just ordinary orbital dynamics. So the arms trail the spin. --Trovatore (talk) 05:33, 28 March 2011 (UTC)[reply]
It's not obvious to me: the spiral arms are supposed to be density waves whose macroscopic movement differs from that of the actual stars in the galaxy. And if the spiral arms participate in the galaxy's differential rotation, then they ought to be wound so tightly they would be smeared out completely by now -- unless there's something that periodically creates fresh spiral/radial structure. –Henning Makholm (talk) 03:31, 29 March 2011 (UTC)[reply]
March 25
An interesting light wave problem
Dear Wikipedians:
I have encountered the following interesting light wave problem:
Two waves of light in air, of wavelength 612.6 nm, are initially in phase. They then travel through plastic layers as shown in figure below, with L1 = 4.07µm, L2 = 3.60µm, n1 = 1.41, and n2 = 1.56. In wavelengths, what is their phase difference after they have both emerged from the layers? Do not enter units with your answer.
The solution is almost correct but you are missing the fact that the two waves do not emerge from the plastic layers at the same position because the layers have different thickness. BTW, you are not deceiving anybody. We know that's homework. Dauto (talk) 03:46, 25 March 2011 (UTC)[reply]
I think the easiest way to deal with this is to subtract 1 from the refractive indexes for each; that way you're not counting the total number of wavelengths but just the number of extra wavelengths (or the number of cycles while the light is held up by the refractive material). Wnt (talk) 08:02, 25 March 2011 (UTC)[reply]
The instruction "Do not enter units with your answer." goes against good teaching practice. Phase might be expressed in degrees, radians, wavelengths, gradians, myriogrades, distance at a given frequency and speed of propagation or something else. ALWAYS state your units! Cuddlyable3 (talk) 13:17, 25 March 2011 (UTC)[reply]
The problem states that the units should be wavelengths. I think that the problem requires units to be excluded because this is a problem to be solved online and graded by a computer and the program was not designed to deal with units and verify whether they are correct. Dauto (talk) 15:06, 25 March 2011 (UTC)[reply]
In the phrase "..surveys of commercial jerky have shown total viable counts up to 7 log cfu/g" what exactly does '7 log' mean?
tl;dr How many cfu's per g are there in "7 log cfu"? 220.244.35.181 (talk) 13:56, 25 March 2011 (UTC)[reply]
If I saw "Here is a table of the log cfu count" I would expect to see the common (base ten) Logarithm of the specified variable, with the"characteristic" power of ten as well as the "mantissa" representing the number multiplied by a power of ten, (if I remember the terminology correctly). I have not seen 10,000,000 represented as just "7 log." How would, say 15,000,000 be presented in this notation as "7.18 log?" I see no reference to this in the article Logarithm. Edison (talk) 17:02, 25 March 2011 (UTC)[reply]
Biologists seem to use this "log" notation in a very imprecise and unpredictable way (by my standards as a numerical scientist). I have heard an M.D. colleague use weird terms like "one and a half - seven log" (for "15,000,000"). It seems more common to consider biologist's usage of the "log" as a shorthand for "order of magnitude" - in other words, "15,000,000" would be "seven log" ; you would write the exact value as 15 x 106 if you needed precision. If you scan through microbiology literature, you can see similar usage. Here's Basic Mathematics for Microbiology from the University of Leeds: "The number of cells can be expressed in another way. Four is two squared (power 2), eight is two cubed (power 3), sixteen is two to the power 4, thirty-two is two to the power 5 an so on. The power or exponent in each case is increasing by one unit, although the numbers they represent start to jump in very big steps. The term logarithm (log) and exponent are interchangeable to some extent." Nimur (talk) 20:22, 25 March 2011 (UTC)[reply]
OP Here. Thanks for your assistance. At first I was considering that log 7 would mean 77 -- as Edison points out, a mantisa is not given. What's remarkable is that in the several research papers I'm reading, the same type of unit is given over and over again -- always "X log cfu/g" 220.244.35.181 (talk) 18:59, 25 March 2011 (UTC)[reply]
There is such a thing as a logarithmic unit—decibels are an example. Never having seen the unit "cfu" before, I would have guessed (correctly, as it turns out) that "log cfu" is a logarithmic unit with (for example) 7 log cfu = 107 cfu. It's probably safe to assume that the base of the logarithm is 10 in this sort of situation. -- BenRG (talk) 21:30, 25 March 2011 (UTC)[reply]
My question basicly is since squinting improves vision why people haven't come up with artifical means to emulate it, so one wouldn't have to? As the eye is optic system in theory it shoud be possible. To do so first one would need to know what it does tto eye. I found two theories why squinting works. There is idea that it squeezes the eye (which may be valid because some refraction errors are caused by eye beeing elongated, but when you squint you move eyelids, so I'm not sure if muscles used for squinting acctualy squeeze the eye). Secondly I did a search on reference desk archives and found some suggestions that it changes aperture (but the pupil can naturaly get smaller - so why dosen't that happen and one has to squint instead?). Secondly there is the question on how to acctualy emulate it. For example, aperture might be hard to reduce with glasses (I know about pinhole glasses, dosen't look ike a practical solution to me), but I suppose contacts might work (i.e. you coud paint an opaque ring on them) ~~Xil (talk) 17:26, 25 March 2011 (UTC)
Contacts DO work! —Preceding unsigned comment added by 165.212.189.187 (talk) 17:39, 25 March 2011 (UTC)[reply]
I assume you're thinking this would be advantageous because it would be one-size-fits all - that is, no need for tailoring pinhole lenses to the defective eyes? (By the way, why don't pinhole glasses produce upside-down images?) 213.122.56.174 (talk) 18:32, 25 March 2011 (UTC)[reply]
That's acctualy good question - the eyes themselves work like camera obscura and it is brain that flips the image. So either the image gets fliped twice (or it might be the opposite - the brain dosen't boder seeing how it is correct) or maybe it dosen't because it is very close to the eye and perhaps the fliping effect occurs only in darkness. At any rate I've never seen inage fliped when looking trough any small holes (you can try yourself with a dark sheet of paper). And to answer your question - No, it is not that one size fits all, but that I believe it actualy offers better correction, according to pinhole occluder (assuming it works the same) it compitely removes effects of refractive errors ~~Xil (talk) 22:41, 25 March 2011 (UTC)[reply]
The light going through the pinholes takes the same path it normally would (unless you make them so small the wave-properties of light start messing with it). It's just that you don't have all the other light. Normally, the light is random when it hits the lens of your eye, and then focuses as an inverted image on your retina. With pinhole glasses, it would make an inverted image on your eye, which pretty much ends up traveling straight and making an inverted image on your retina. Your brain is capable of flipping an inverted image, but it takes a while for it to do it. It's not something that will happen so fast you don't even notice it. — DanielLC05:59, 28 March 2011 (UTC)[reply]
The problem with pinholes is that they don't allow enough light through, so they make everything darker. Also, they eliminate peripheral vision. StuRat (talk) 21:07, 25 March 2011 (UTC)[reply]
The "reducing the aperture" advantage basic gets you to pinhole glasses, so that's not much of an option, as noted above. As for deforming the shape of the lens and changing the distance between the lens and the cones and rods on the back of the eye, that could work, but sounds rather complicated and uncomfortable. I don't see how that's better than glasses, contacts, or corrective eye surgery. StuRat (talk) 21:12, 25 March 2011 (UTC)[reply]
If it is the squeezing, the only way I see it reproduced is by surgicaly inserting implants that squeeze the eye to correct shape or something along those lines. Also I myself think pinhole glasses is BS, but why not pinhole contacts? I'm thinking that they are so close to eye that effects on vision (and looks) would be minimal ~~Xil (talk) 22:41, 25 March 2011 (UTC)[reply]
Contacts could fix the appearance, sure, if the "mask" was black to match the pupil. However, the fundamental limitations of pinholes, which are a lack of light and peripheral vision, still remain. So, regular contacts are a far better choice. StuRat (talk) 22:55, 25 March 2011 (UTC)[reply]
Incidentally, I'm not sure if you're making this mistake, but many do, so I will mention it: The advantages of a pinhole lens only works for a single pinhole (or one for each eye). You can't just poke lots of holes in something and have it work, collectively, as a giant pinhole lens. The reason is, that while the light coming through each pinhole is focused, the light from each pinhole is not in focus with the light from the others. Thus, you would need a normal lens to adjust all these different focused images into a single one.
Perhaps, in the future, a digital image from each pinhole could be combined with the others to provide a nice, focused "collective" image, with an infinite focal depth. I believe that the compound eyes of some insects work something like that. StuRat (talk) 23:05, 25 March 2011 (UTC)[reply]
I figured so, I was acctualy surprised to see what pinhole glasses look like (this would be yet another proof of it being BS :) wonder why some people think they work?) How about reducing transparency of the lens, instead of making it complitely opaque ? Need be, you would turn to look, even if you hadn't reduced peripheral vision, so all you need is vague notion that you should do that ~~Xil (talk) 23:20, 25 March 2011 (UTC)[reply]
Well, that would lose some of the benefit of the pinhole, since some unfocused light would get in, making it slightly blurry. Meanwhile, the image the eye sees would still be somewhat darker and have somewhat reduced peripheral vision. So, not a very good compromise. Perhaps a pinhole contact in one eye and a regular contact in the other might be a somewhat better compromise. This would give you normal vision in the normal contact eye, while providing an infinite depth, focused image of bright objects in the pinhole contact eye, but without any peripheral vision there. This might work similar to how jewelers and some others wear special glasses with one microscope lens and one normal lens. I expect that this would work best in bright light, like when working in Antarctica in the summer. It would be good advice to swap which eye gets the pinhole contact each day, as permanently using such a lens might have some bad effects on the eye (you'd likely need different pinhole lenses for each eye, as the shapes of the corneas vary). StuRat (talk) 23:32, 25 March 2011 (UTC)[reply]
I did an image search for "pinhole occluder", and found they have many holes (at one end) and look very much like the pinhole glasses. I hesitate to draw any conclusion from that, though, since I don't know exactly how they're used. (They also look a lot like large plastic serving spoons; appearances can be deceptive.) 213.122.59.22 (talk) 07:30, 26 March 2011 (UTC)[reply]
I have 20/10 vision when I squint things get blurry. so I attributed it to the distortion of my eyelashes and the additional liquid that the eyelids channelled to the center of the eye directly over the pupil, the I never thought about the squeasing also affects it. —Preceding unsigned comment added by 98.221.254.154 (talk) 00:51, 26 March 2011 (UTC)[reply]
Maybe you could conduct a survey to find correlations between "how" the person squints (cheek forehead muscles tight, loose, eyes almost totally closed or almost totally open), and what type of vision they have nearsighted; farsighted and severity of each, even eyelash color.98.221.254.154 (talk) 01:34, 26 March 2011 (UTC)[reply]
That would work as long as the person has only one eye condition which often is not the case. Therefore I think that artifical model is more acceptable, which is why I am asking it here - probably people with knowledge in optics or human anatomy can answer about causes and effects ~~Xil (talk) 04:23, 26 March 2011 (UTC)[reply]
I think that making a pinhole with one's fingers is more effective and less uncomfortable than squinting for any prolonged use. Wnt (talk) 15:46, 26 March 2011 (UTC)[reply]
Reverse osmosis versus evaporation for concentrating an aqueous solution
How do RO and evaporation compare in terms of energy use for concentrating an aqueous solution? How about in terms of capital investment? (If it matters, I am not thinking about huge scale, maybe 100's of liters a day). ike9898 (talk) 17:34, 25 March 2011 (UTC)[reply]
Partly answering my own question - this paper addresses the comparison in the context of concentrating milk. The bottom line answer seems to be "it depends". I'm still interested in your insights ReFDeskers. ike9898 (talk) 18:14, 25 March 2011 (UTC)[reply]
vacuum space
I don't understand how vacuum space has the ability to "expand." Was all the vacuum space that we observe in the current universe "inside" the big bang or "among" it? The word expand makes me think of two objects being "forced" apart by something between them growing, instead of them simply moving apart based on their inertias which results in more space between them. —Preceding unsigned comment added by 165.212.189.187 (talk) 17:45, 25 March 2011 (UTC)[reply]
Space is a convenient fiction; spacetime is closer to reality. Spacetime doesn't expand, or change in any way, since it covers all of history at once. "Space" is a slice of spacetime. Any given slice is different from any other slice, so there's an element of arbitrariness in any attempt to match certain points of one slice with certain points of another. If you have a triangular piece of spacetime like the one in this diagram, you can slice it horizontally and say that space is globally expanding (in the sense that each successive slice has a larger total area) and the galaxies have relative velocities that carry them apart. Or you can slice it into hyperbolas, which are all infinite, and say that space is always infinite; but the hyperbolas are nested in such a way that it's useful to say that each one is locally larger than the one before it, and you can even attribute the separate of the galaxies to this local expansion. But general relativity doesn't care about any of this. From the perspective of general relativity, the motion of the galaxies is the same as any other motion. It's fine to say that it's due to inertia. (And gravitation.) -- BenRG (talk) 21:21, 25 March 2011 (UTC)[reply]
Yes, that was a good answer for the question except that it might go over the head of the person that asked the question but such is physics. Dauto (talk) 03:26, 26 March 2011 (UTC)[reply]
Yes, it was a good answer, but most of us struggle to understand the complexities. I thought the expansion was the result of inertia (reduced by gravity) and also dark energy, but BenRG is the expert on this. Dbfirs10:43, 26 March 2011 (UTC)[reply]
I'm really not an expert on anything but the simplest aspects of cosmology. And if my last reply sounds profound then I've failed. I want to write answers that are so easy to understand that everyone can see how trivial they are. General relativity is just lines on a curved surface—nothing to it. I hope the original poster will return to say whether my reply was helpful at all. "Expansion is the result of inertia (reduced by gravity) and also dark energy" sounds perfectly correct to me, by the way. -- BenRG (talk) 08:07, 27 March 2011 (UTC)[reply]
OP here, So some parts of the universe are expanding but others are not? Just because 2 objects are moving away from each other means that the universe is expanding? Am I expanding? —Preceding unsigned comment added by 98.221.254.154 (talk) 13:35, 27 March 2011 (UTC)[reply]
We all tend to expand a bit with age, but the expansion of the universe seems to be an expansion of the space between galaxies. The space within galaxies and especially within solar systems seems to be prevented from expanding by gravity and the presence of matter. Metric expansion of space gives some detail. Dbfirs16:27, 27 March 2011 (UTC)[reply]
Yes helpful. Could dark matter be a result of matter "trapping" empty space within its atoms, which can then be moved separately from the rest of empty space? —Preceding unsigned comment added by 98.221.254.154 (talk) 01:47, 28 March 2011 (UTC)[reply]
Electromagnetic waves
Electromagnetic waves are often produced by accelerated charged particles. but accelration is a relative quantity.does it mean that wether there is a wave or not depends on the observer? —Preceding unsigned comment added by 178.18.17.91 (talk) 19:08, 25 March 2011 (UTC)[reply]
Motion is relative, but acceleration isn't. If you and I are each in rockets and we look out of our windows and see that we are accelerating towards each other, we can tell which of us is actually accelerating by which of us is being pressed into our chair. --Tango (talk) 19:29, 25 March 2011 (UTC)[reply]
Bird Identification - Junco?
Can you help identify this bird? I photographed it in late October in the San Francisco Bay area of California. I believe it is a Dark-eyed Junco, per my field guide, but before I add this photo to any article, I would like one or more experienced second-opinions.
While we're at it, here's another one from the same day, unidentified bird that a friend tells me might be a flycatcher. Ideas? Nimur (talk) 20:31, 25 March 2011 (UTC)[reply]
Hi. I am looking for the name of a flammable plastic. Specifically it is commonly used in blinds in front of windows and has a flash point temperature lower than that of ordinary paper. Any ideas? Thanks. ~AH1(TCU)22:23, 25 March 2011 (UTC)[reply]
Given that white light and all electromagnetic particles/waves travel at the same known speed in vacuum/space. (relative measurement uncertainty 4 parts per billion), and that light is slowed as it passes through another medium such as air,and I'm assuming that a massive gravitational field is another medium, and also that since white light can be easily seperated therefore is not truly homogenous. Is it possible that the red light and the blue light might be slowed and or deflected at slightly different rates, such as when it passes close to a galaxy. If that is possible and if the red light is then traveling slightly faster than the blue light then any end target(earth)would receive red at a greater rate than blue. any light receiver (camera) operating on a long time exposure would then receive more red than blue within the given time frame. If this were so (lots of if's here)then the resulting photo. would show predominance of red which might be misinterpreted as red shift indicating rapidly receding light source. We know that red and blue are refracted at different rates. perhaps the speed is effected similarly. Has anybody done any work on that?Phalcor (talk) 22:35, 25 March 2011 (UTC)[reply]
A gravitational field is not a medium in that sense. The reason media slow down light is because the light is continuously being absorbed and re-emitted. That doesn't happen in a gravitational field. What does happen, is the light is curved and gains or loses energy (gaining energy makes it bluer, losing energy makes it redder). It doesn't change speed. --Tango (talk) 22:56, 25 March 2011 (UTC)[reply]
Tango, the picture where light is absorbed and reemitted in medium is inaccurate. That's a more apt description for what happens inside the sun where indeed a photon gets absorbed and reemitted as it finds its way out and follows a random walk and exchanges energy with the medium changing its frequency. When light goes through a medium like glass, air, or water, none of those things happen. It follows a straight path and keeps a constant frequency. A better description would be that light in vacuum and light in a medium are different kinds of animals because light in a medium will also include oscillation of the medium particles along with the oscillation of the electromagnetic filed. Dauto (talk) 00:38, 26 March 2011 (UTC)[reply]
Adding to what I said above. While red light and blue light move at different speeds on a medium, all light moves at the same speed through empty space whether there is some gravitational field or not as Tango correctly explained above and even if red light were to move faster that would not lead to red-shift because red-shift is not measured by comparing the amount of red and blue light. Red shift is measured by the shift of the spectral line of Hydrogen. Dauto (talk) 13:51, 26 March 2011 (UTC)[reply]
If there is no dispersion then the phase velocity is constant and identical to the group velocity, but if dispersion is present, they are different from each other and vary as a function of the frequency. Dauto (talk) 01:33, 26 March 2011 (UTC)[reply]
March 26
time
if I was using a telescope and looking at a clock 10 light minutes away, which I saw was 10 minutes behind mine, 8:50 and 9:00, respectively, and then started travelling to the clock, observing it the whole time, I know it depends on my speed, but what would I observe the clock doing in relation to mine; what time would the clock display? —Preceding unsigned comment added by 98.221.254.154 (talk) 01:21, 26 March 2011 (UTC)[reply]
Given that ly is mesurment of distance light travels in certain time you can easily calculate it, but the result depends solely on speed. At 10 minutes you'd see 10 minute delay, at nine minutes you'd see nine minute delay and so on upto no delay when you are at the clock. Assuming you travel at speed of light, it would be 9:10 when you reach the clock. While you're on your way you'd observe clock hands moving clockwise (i.e. not backwards in time) and the clock being behind in accordance to how far you are from the clock, so at 9:01 there would be 9 minute delay and you'd see that it is 9:52, 9:02-8:54, 9:03-8:56, 9:04-8:58, 9:05-9:00, 9:06-9:02, 9:07-9:04, 9:08-9:06, 9:09-9:08, 9:10-9:10 ~~Xil (talk) 04:39, 26 March 2011 (UTC)[reply]
The twin paradox is about acceleration. There is no need to assume any acceleration is going on in this problem. --Tango (talk) 15:35, 26 March 2011 (UTC)[reply]
The wording is somewhat ambiguous, but on first reading I assumed that "started travelling to the clock" meant that the observer was initially at rest with respect to the distant clock, and then accelerated as they "started travelling". I imagine Dauto made the same assumption. Gandalf61 (talk) 16:32, 26 March 2011 (UTC)[reply]
If you travel much slower than the speed of light (so it would take you several days to reach the clock), then we can ignore relativity and the solution is fairly simple. If the clock is 10 minutes behind yours now and we know it will exactly match yours when you arrive, then you must see it ticking faster than yours by such an amount that, in the time it takes you to reach the clock, it's ticked 10 minutes more than yours. If it took you 20 minutes to reach the clock (which is much too fast for us to neglect relativity, but it makes the maths easy!), your clock would have progressed 20 minutes and the other clock 30 minutes, so the other clock is ticking 1.5 times a second, from your point of view. If you take into account relativity, then your clocks wouldn't show the same time when they come together and the whole thing gets rather complicated. --Tango (talk) 15:35, 26 March 2011 (UTC)[reply]
If you don't take relativity into account, it probably could be be reduced to simple formula, similar to calculating when will two trains traveling towards each other at diffrent speeds meet, I find it hard to produce it without pen and paper, sorry. You would probably assume that all things except for your speed, which would be, x remain constant. Say if you would be traveling at half the light speed at 9:01 you would be 9.5 light minutes away from clock, so you would observe 9.5 minute delay and observe that time on the other clock is 8:51:30. I might be terribly wrong, but I don't see how relativity could make the answer any diffrent, if you are traveling at light speed. We assume that both the observer and the clock are in same state (not influenced by gravity or anything), we assume that the observer has never been at the clock (so twin paradox dosen't really apply, because it concerns traveling away and then back to a point of reference influenced by gravity etc.), his clock is synchronised with clock he observes and he does observe some effects of relativity as for him it appears that clock he monitors is delayed. If you have a diffrent idea on what would happen go ahead and tell us what he would observe ~~Xil (talk) 16:33, 26 March 2011 (UTC)[reply]
Twin paradox has nothing to do with gravity and it does apply here (half a trip still requires relative motion leading to time dilation). Dauto (talk) 17:07, 26 March 2011 (UTC)[reply]
So, here is the math. Let's say you move with a speed for a distance . A time elapses from the point of view of the clock you are looking at through the telescope which was initially synchronized with yours. Because of time dilation the time elapsed on your clock will be given by , where . Therefore when you finish the trip the two clocks won't be synchronized anymore and the difference between them will be . Dauto (talk) 17:32, 26 March 2011 (UTC)[reply]
... isn't that the wrong way round? (Perhaps it depends on who is doing the observing.) Each observer sees the other clock moving more slowly, but their own clock moves at "standard rate". The effect is symmetric. Dbfirs16:55, 27 March 2011 (UTC)[reply]
The effect is not symmetric because one of the clocks must accelerate to start approaching the other clock just like in the famous twin paradox situation. Dauto (talk)
Sorry, yes, I meant that the effect is symmetric whilst travelling at a constant relative speed. It is the effects of the acceleration that creates the paradox. Dbfirs07:23, 28 March 2011 (UTC)[reply]
prediction
Is saying what I am going to do, and then doing it exactly as I described "predicting/manipulating the future"? Is answering someone's question before they ask it, because you know what they are thinking, "information travelling faster than light"? —Preceding unsigned comment added by 98.221.254.154 (talk) 03:22, 26 March 2011 (UTC)[reply]
It is being able to control your own acctions to accomplish your goals and drawing on your expierience form numerous similar situations you've been in. You can do so with a large degree of certanty about what is going to happen, but that is not what people usualy describe as beeing able to predict and manipuate the future - if you could predict that your friend is going to get in car crash if he turns left and it happens it would be predicting future as you have no means to predict random accidents, if you convince your friend not to take that turn you are manipulating the future (but still we can never be certain that the crash would occur) ~~Xil (talk) 04:55, 26 March 2011 (UTC)[reply]
I would say that that is predicting the future, as there could be events which prevent you from doing what you planned. Of course, if you do keep the prediction, it's not very impressive. Similarly some psychics predict that there will be "unrest in the Middle East", and they don't deserve much of a prize for that prediction, either. StuRat (talk) 06:47, 26 March 2011 (UTC)[reply]
The second question could be generalized to "is simulation a potential means of time travel", and when phrased like that it sounds fairly reasonable (if confusing). 213.122.59.22 (talk) 08:12, 26 March 2011 (UTC)[reply]
Physics entire goal is the ability to make qualitative and quantitative prediction about the future, but it still flatly denies the possibility for superluminal information transfer. This should highlight how they are different. —Preceding unsigned comment added by 92.20.201.71 (talk) 11:01, 26 March 2011 (UTC)[reply]
Anything you do is manipulating the future. I'm not sure if it counts as predicting if it's something you have control over, but looking it up it seems to work you're still telling in advance, even if you have a hand in it. Answering someone's question before they ask it does not involve information traveling fast. They gave the information before-hand, if unintentionally. — DanielLC05:47, 28 March 2011 (UTC)[reply]
Question about the sub-division of "g"?
Since "g" of an earth may be the combination of inter-gravitational forces between its masses of water, soil, rocks ......[on large scale]. Thus would there be any difference in "g" for the falling of an object due to the following different underlying masses
1- Just above the deepest and largest sea water (mass wise)
Yes, mass differences in the ground or water directly under an object will affect the local g by a measurable amount, but not an amount people would notice. StuRat (talk) 06:42, 26 March 2011 (UTC)[reply]
Also read our article on gravity anomaly. The gravity anomaly is the measured difference between the expected and actual value of the gravitational force. It is useful when exploring for underground minerals and hydrocarbons. Mapping the gravity anomaly is also useful for calibrating extremely precise aircraft avionics on autopilots and trackers. Usually, though, it is very expensive to perform large gravity mapping surveys, so most of the data isn't available for free on the internet. I did find this example through a web-search: this United States Geological Survey webpage, Airborne Gravity Survey and Ground Gravity in Afghanistan. Their website has scientific information, as well as photos of the aircraft and the equipment used to measure gravity very precisely. Note that you can see the gravity anomalies trend along the terrain and geology, correlating well with the mountainous regions and the river valleys. Other methods of gravity survey include satellite- and ground-based observation and mapping. Nimur (talk) 15:04, 26 March 2011 (UTC)[reply]
Just a guess, but could it be a safety feature, so that if the train jumps the rail, those will catch one set of wheels, so the cars won't be able to hit the sides of the bridge ? StuRat (talk) 06:39, 26 March 2011 (UTC)[reply]
Nice find. Note that the inward bend at the ends is so that a derailed train won't run into the end of the guard rail, making things even worse. StuRat (talk) 21:14, 26 March 2011 (UTC)[reply]
mosquito bites and race
Can anyone find information about why mosquitos prefer to feed on Europeans than Africans? My own research has found that when sleeping in the same bed, I get bitten all over, whereas my friend does not at all. The scientist in me can't work out why it is the case, what is it about mzungus that they find so tasty? Thanks 41.138.85.43 (talk) 11:33, 26 March 2011 (UTC)[reply]
Isn't it possible that certain people attract or dis-tract mosquitos more than others. Some people simply do not get bitten. Your presumption that they avoid Africans is mis-placed if it's based solely on the fact that mosquitos are more attracted to you than your one African friend. 220.244.35.181 (talk) 11:47, 26 March 2011 (UTC)[reply]
No, his/her argument is that Africans are less likely to be bitten by mosquitoes than Europeans are. Malaria rampant areas are virtually free of Europeans, so your counterargument doesn't stand. That said, his/her argument is still fallacious, as it is a plain dicto simpliciter.--Netheril96 (talk) 12:55, 26 March 2011 (UTC)[reply]
I have heard the same "mosquitoes like the white skin" story. There are also various stories running around the Internet[6] saying that mosquitoes prefer blondes to brunettes, and blondes are rare in Africa. But I also wonder if there are any differences in the probability that an individual mosquito bite will turn out to be itchy - whether due to enzymatic reaction, immune tolerance, or some kind of mental desensitization. For that last, after all, you see so many scenes of people in Africa with flies crawling on them that will make an American squirm just watching the video. I wonder if it's so different from being accustomed to tolerate cold weather. Wnt (talk) 15:44, 26 March 2011 (UTC)[reply]
I don't think this is a safe generalization: there are also white people who seem to get bitten a lot less than other white people. The fact is that mosquitoes are sensitive to a pretty wide range of chemicals, and the specifics are not at all well understood. Even the mechanism of the most widely used repellent, DEET, is not all that clearly understood. Until recently the prevailing theory was that it blocks the ability of the mosquitoes to sense the chemical that attracts them, but anybody who uses it in the field can easily see that it has a strong repulsive effect. Looie496 (talk) 17:00, 26 March 2011 (UTC)[reply]
Certainly a sample size of n=2 is not adequate for drawing such a conclusion. You and your friend different in things other than just race, presumably, including clothing, deodorant, shampoo, diet, etc., even blood type. How much of that matters to mosquitos, I know not, but isolating race as the only variable is surely fallacious in this case. --Mr.98 (talk) 18:05, 26 March 2011 (UTC)[reply]
Fission products in environment => nuclear reactor breach?
If radioacctive iodine has been found in the environment, is that conclusive evidence that at least one of the Japanese nuclear reactor pressure vessels has split or cracked open, or could it come from the stored fuel rods? Thanks 92.29.127.59 (talk) 15:13, 26 March 2011 (UTC)[reply]
A rough guess: if it is Iodine-131, that probably means it is from the reactor (it is a short-lived fission product and its existence would only be significant in a reactor that had recently been running). If it is Iodine-129, it could be either. But the older the fuel, the more Iodine-129 you'd find, so significant amounts of it would probably be more indicative of a spent fuel pool breach. But I am not a physicist. --Mr.98 (talk) 18:01, 26 March 2011 (UTC)[reply]
(ec) No one can know from afar what really happens but iodine decays very quickly and is only produced by fission or neutron capture so it looks improbable that it comes from spent fuel rods. As far as I understand the pressure vessels are not absolutely tight but have valves that regulate pressure. So my idea is that some fuel rods are damaged and the fission reaction is partly going on, producing new iodine that is released from the containment via safety valves. 77.3.187.97 (talk) 18:16, 26 March 2011 (UTC)[reply]
The fission has stopped definitely. If they open the security valve to reduce pressure you vent iodine, there is enough iodine in the reactor even after four or five half lives.--Stone (talk) 18:20, 26 March 2011 (UTC)[reply]
I admit that I don't know how much total iodine is inside the core and how much has been released but how would you know that the fission has stopped "definitely"? 77.3.187.97 (talk) 18:29, 26 March 2011 (UTC)[reply]
The fission is only working with the moderator (water) and without the control rods. Two possible cases: It is very hot and the water is gone -- no chance for fission. Everything is molten -- No reaction, because you have a molten block with no water inside. Two last point the neutronradiation would have been detected and without cooling the reactor would simply melt away if not only decay heat but also the much higher heat production of fission would be present.--Stone (talk) 19:23, 26 March 2011 (UTC)[reply]
OK, I see your point(s). If there is no other type of moderator (as graphite like it was used in Chernobyl), fission would stop. But if there was some problems with the control rods (? jammed from the earth quake and not completely inserted ?), wouldn't fission resume when new cooling water was inserted? Of course, only partially, not full scale as in normal operation. Another question: how would one detect neutron radiation from within a water filled containment? Wouldn't even the concrete of the containment shield that completely? 77.3.187.97 (talk) 20:11, 26 March 2011 (UTC)[reply]
The control rods were inserted after the earth quake before the tsunami. The reactor always stays within a very thin margin of criticality where the secondary neutrons are used to keep control. If something goes really critical you leave this safe way and get a bomb like explosion.--Stone (talk) 20:57, 26 March 2011 (UTC)[reply]
A slow fission reactor cannot undergo a "bomb like explosion". You get lots of radiation and heat, and maybe a small explosion, but nothing on the order of a fission bomb. --Mr.98 (talk) 22:14, 26 March 2011 (UTC)[reply]
Not a nuclear bomb explosion scale, but a explosion more like a small grenade. The conversion rate in a nuclear bomb is high while it is low in a criticality accident. But it is enough to produce enough heat to divide the critical mass into separate parts.--Stone (talk) 08:38, 27 March 2011 (UTC)[reply]
Surely you can see the need to clarify what one means by a "bomb like explosion" when one is talking about critical masses. Most people still think nuclear plants can go off like nuclear weapons, which is not true. They have their own problems, but that's not one of them. --Mr.98 (talk) 10:06, 27 March 2011 (UTC)[reply]
Does symbolic actions make people change their behaviour?
Today's Earth Hour and the discussion of the pros and cons of it made me wonder what research there is about whether people who participate in some symbolic action (like signing a petition or wearing a button) are more or less likely to do something more substantial for the same cause (like donating money and time or sacrificing some of their comfort). I recall reading at least ten years ago about some study that seemed to show a positive correlation, but I don't remember it well. Sjö (talk) 18:25, 26 March 2011 (UTC)[reply]
Note that correlation doesn't mean causation. That is, observing Earth hour doesn't necessarily make them more environmentally responsible. It's probably the other way around, that people who already were environmentally responsible are those who choose to observe Earth hour. Then there's also the possibility that non-environmentalists might do Earth day just so they can say "I've done my part, now I am done". StuRat (talk) 19:29, 26 March 2011 (UTC)[reply]
The article gives some data developed by the experiment. Presumably, policy makers could use this in decisions - e.g., how much greenhouse gas can be avoided if monopoly utilities are allowed to run amuck and raise prices 200%, which allows them to feel better about taking the campaign contribution. Wnt (talk) 21:26, 26 March 2011 (UTC)[reply]
Is that assuming that any power which can be cut for an hour can also be cut permanently ? That's completely untrue. I can cut my heat for an hour, but if I cut it permanently my pipes would freeze in winter (as would I). StuRat (talk) 21:51, 26 March 2011 (UTC)[reply]
A resounding "yes". Symbolic actions are extremely powerful in terms of effecting human behaviour.It is the human mind's suseptability to symbolism that produces the Ra-Ra to the flag,the puchase of a new car when when the old one is still good,The badge and button wearing, choice of dress style,The Symbolic identification of ones self for others to see. The very identification of homo-sapiens as distinct from earlier hominids is based largely on appreciation of symbolism. The earliest known symbolism,"art"about seventy thousand years ago marks the generally accepted transition to modern humans. Symbolism effects not only the person taking the action but also those who witness it. I suggest you look up the acheivements of public manipulation through symbolism acheived by "Edward Bernayse" throughout most of the twentieth century. I beleive that will give you a much fuller appreciation of the power of symbolism.Phalcor (talk) 17:01, 27 March 2011 (UTC)[reply]
Does this idea violate any laws of thermodynamics? Suppose that air is not saturated -- i.e. evaporation for a naked body of water should be faster than condensation. Suppose I place a large bowl with a large surface area, full of oil.
Suppose water occasionally does condense on the oil. Some of the water will re-evaporate, but some will sink to the bottom -- and a pool of water starts to collect at the bottom of the oil, unlikely to evaporate. Over time, I will accumulate more and more water. Is any law of thermodynamics being violated here? (Or does the oil conceivably become warmer and warmer, lowering likelihood of condensation with each new water being condensed?) AFAIK, oil is acting only like a heterogeneous nucleation-promoting catalyst -- it shouldn't change the equilibrium constant.
It occurs to me that agitation might allow faster introduction of water vapor into the oil, upon which it condenses. This would expend work, which would conceivably then allow the equilibrium constant to change. I however did not study heat engines and chemistry in my general chemistry classes. Are there any relations between mechanical agitation and work -- and say the amount of water I can extract from the air? John Riemann Soong (talk) 18:32, 26 March 2011 (UTC)[reply]
I don't see any inherent reason why the first approach would violate thermodynamics laws. However, as a practical matter, the few molecules of water which would condense on the oil would evaporate again before they formed drops large enough to overcome the surface tension and sink to the bottom. Therefore, I think a significant temperature difference would be required to get it to work. Perhaps in the morning, if the bowl of oil was in the shade, and stayed cool for some time, water from the warmer air would condense in sufficient quantities to form drops that would sink to the bottom. However, note that oil isn't required for this. You can have a large funnel to which dew will adhere in the morning, then drip down into a bottle at the bottom. The small hole at the top of the bottle slows to evaporation rate back out of the bottle. You could, I suppose, put some oil in the bottle too, to further slow the evaporation rate, but then you'd have oil mixed in with your water, and the oil might go rancid. As for agitation, that would likely just produce a mixture, like you get when you shake up salad dressing. It would eventually settle out, but it could take many hours or days. Also, the energy used might better be spent on a dehumidifier to collect your water. StuRat (talk) 19:22, 26 March 2011 (UTC)[reply]
In concept you're introducing some energy when the water droplet falls under the oil (if you come up with a way to make this work). So it's not a true Maxwell's Demon, but one using energy to do sorting. Wnt (talk) 21:29, 26 March 2011 (UTC)[reply]
The experiment you've described, unfortunately, isn't realistic. As StuRat notes, if the oil is in thermal equilibrium with the humid air, and the air (and oil) are both at a temperature higher than the dew point, then macroscopic amounts of water will never condense out on the oil's surface. You certainly won't ever get droplets large and heavy enough to overcome the surface tension of the oil in order to sink to the bottom.
Even if you start out with water below the layer of oil, the system will still return to the 'proper' equilibrium eventually; you've neglected to consider that water's solubility in oil is low but not zero. There will be a (very slow) transfer of water out of the liquid phase, into the oil-dissolved phase, and back into vapour. (Depending on the temperature and thickness of the oil layer, this is a process which could require months, years, or centuries, but it will happen.) This evaporation through the oil will continue until the air reaches 100% humidity for the temperatures, or until the supply of liquid water is exhausted. Agitation will speed this process, in that it will speed the equilibration of water across the water-oil and oil-air interfaces. TenOfAllTrades(talk) 04:37, 27 March 2011 (UTC)[reply]
And apart from all the other technicalities, from a purely practical standpoint. Having experienced on more than one occasion a sudden camping trip, I can tell you that to collect a useful amount of water by natural condensation (no matter how you do it) will require a surface area much, much,much,much,much greater than a large large bowl.Phalcor (talk) 19:36, 27 March 2011 (UTC)[reply]
Solution to the colatitude part of Schrödinger in a Hydrogen atom
For some research I'm doing, I'm trying to work through the derivation of the solution to the Hydrogen wavefunction to garner a better understanding of the mathematics behind it. In my searches, I've found that not many people include a detailed explanation of the math behind the differential equation involved in the colatitude () part; most textbooks or informational sources that I've found have simply said something along the lines of, "This is a very hard differential equation. Here's the answer:" I know the final answer comes out to be the associated Legendre function, but I would like to know how this is derived.
I did find, this, however. This page outlines how to set up the differential equation, and this page shows how to solve it. I understand the first page entirely, but I'm caught up on the second page. Specifically, the part when the author expands the nth derivative to obtain Equation 3.3. My questions
Why does the author switch from trying derivatives of to trying those of ? My first thought was to get the sign of the middle term to match the original DE, but when he derives the (n+1)th derivative, the sign changes due to the fact that n-(n+1)=-1, so I don't really see why he chooses that as his function. Can anyone explain that?
Where the sum comes from in the (n+1)th derivative?
I think there's a typo in Equations 3.3 and 3.4.. Should the derivative operators not be instead of ?
Also, I don't understand Equation 3.4.. Why can we just randomly throw in the term?
You might have better luck searching for discussions of the spherical harmonic differential equation. It's reasonable enough for discussions of the hydrogen atom to skip the spherical harmonic part, since the spherical harmonics are an area of study in their own right.
I'll attempt to answer your questions: 1. I think he tries first, and then, since that doesn't quite work, tries instead. Trial and error (informed by long experience) is one of the most useful techniques for solving differential equations. 2. I think this comes from a sum of the coefficients of . If you do a few derivatives by hand you should see what's going on. Note that is a typo; it should be . 3. Yes, that's another typo. 4. You're defining a separate function for each , and these functions are only meaningful up to a constant factor, so it's fine to throw in a factor that depends only on . -- BenRG (talk) 21:03, 26 March 2011 (UTC)[reply]
The standard practice of solving (associate) Legendre polynomial equation is power series method.The current Wiki article on that method is incomplete as it only pertains to nonsingular equations, which is almost useless when you encounter special functions. You may find several textbooks on mathematical physics most useful.--Netheril96 (talk) 16:33, 27 March 2011 (UTC)[reply]
another current
could we ever ever find another type of current something like oscillating current or rotating current instead of alternating or direct current. Is there only ac and dc? Is there such a thing as magnetic current with magnetic monopoles flowing and that creating a electric field — Preceding unsigned comment added by Lufc88 (talk • contribs) 19:29, 26 March 2011 (UTC)[reply]
Well, there's only the possibilities of current being constant (DC) or variable (AC). However, a variable current could vary in different ways. You could have other frequencies, a square wave or sawtooth wave, versus sinusoidal, etc. You could also have the amplitude of the wave stay positive or negative over the entire cycle, versus alternating between them, but I don't see much advantage in that. In any case you can change the voltage or amperage or wattage, independent on the carrier wave used. StuRat (talk) 20:16, 26 March 2011 (UTC)[reply]
Sort of but not really. Real magnetic monopoles have never been found but the theoretical motivation for their possible existence is fairly strong. Dauto (talk) 21:36, 26 March 2011 (UTC)[reply]
Depends on what you mean by "each". If "each" means counting separately each group identified by modern science as a distinct species, the answer is definitely "no". Staecker (talk) 20:09, 26 March 2011 (UTC)[reply]
What is possible, however, is them taking some livestock and such on board so they would have a starting point to rebuild after a regional flood (not a worldwide flood, of course). So, there could be a grain of truth there. StuRat (talk) 20:12, 26 March 2011 (UTC)[reply]
If you take "each" to mean some arbitrary level between genus and kingdom, then you could fit them and perhaps even the feed necessary for them. John Woodmorappe wrote a book in which he calculated that it was possible if you brought one pair of each "kind", as he put it, and in some cases only brought young animals. His work has been harshly criticized [7][8], also by other creationists [9].Sjö (talk) 21:23, 26 March 2011 (UTC)[reply]
And, of course, there would be no way to get all the species we have now, from that, unless you assume that God made it happen. In this case, why did God need Noah's Ark ? StuRat (talk) 22:34, 26 March 2011 (UTC)[reply]
Judaism holds that it was a miracle. Even by the time of the Talmud it was known that it could not have been done by ordinary effort. The text supports this as well (Genesis 7-8 and 7-9) - the animals went in, not Noah took them in. The reason God needed Noah was that the ark was an attempt to get the rest of the people to repent by building an ark so publicly (which is also why it took so long to build). Additionally it's the same reason man needs to plant seeds, rather than just have food appear. Ariel. (talk) 02:08, 27 March 2011 (UTC)[reply]
It seems impossible to collect and store away a million species of beetle, for example. But the biological species concept is a construct of modern science, not faith. (For comparison, it's written that God cursed the serpent to crawl on its belly. Which serpent?) And if you allow for arbitrary divine intervention, you can suppose that the beetles all arrived on their own, or were transported on a divine wind, or needed no food, or could occupy the same physical space, or could produce offspring with different genetic codes - obviously, once God gets involved, the laws of physics are kind of out the window. Wnt (talk) 21:39, 26 March 2011 (UTC)[reply]
That would seem a bit pointless at least for Noah. According to Noah he died 350 years after the flood. Even if he was screwing a wife every hour (on average) for the whole 350 years that would only be 3068100 wives with none of them more then once over the 350 years even if the wife didn't get pregnant. One woman every hour for 350 years seems a little extreme even if he was like horny teenager all those years. Nil Einne (talk) 11:06, 27 March 2011 (UTC)[reply]
Check this. I asked a similar question last year and got some really interesting, in depth answers. It was suggested, from a rough calculation that we could build a ship large enough to carry two of every land animal (in fact we have built much larger ships) - and that the dimensions given in the Bible are not wholly unreasonable for the task on a purely volumetric level. It's the 'keeping everything alive for 40 days and 40 nights' bit and the technology level of the time that's the major problem. --Kurt Shaped Box (talk) 22:54, 26 March 2011 (UTC)[reply]
Not only 40 days, but a little over a year. 40 days and 40 nights is how long it rained and then it took some time for the water to retreat. Which makes it even harder to store the necessary feed.Sjö (talk) 08:27, 27 March 2011 (UTC)[reply]
It depends on whether you mean a planetary flood, or a "known world" flood as defined for the writers of the story. It seems quite possible that a major flood could have struck the fertile crescent and Noah could have built a ship that could have held an arbitrarily large number of the local megafauna from that area. Or, even more likely, that the story could date from oral tradition about the flooding of the Black Sea (see Black Sea deluge theory) which may have been the source of many middle-eastern flood stories. --Jayron3223:38, 26 March 2011 (UTC)[reply]
It was the Noah's Ark story that first began to turn me away from religion. My Sunday School teachers wanted to have me believe it literally, then when I questioned the logic of that, started to tell me all sorts of variations. I realised that there was an unlimited number of these variations, and that if every piece of the Bible needed that level of interpretation, one could be certain of nothing it contained. HiLo48 (talk) 00:20, 27 March 2011 (UTC)[reply]
I've never understood why people try to explain miracles and still stay within the religion! If it's not a miracle then what's the basis for your religion? Someone can't just come and say "I'm God's messenger, listen to me" - you have to prove it, by indisputable miracles, not just interesting coincidences and fancy words. Ariel. (talk) 02:11, 27 March 2011 (UTC)[reply]
Um, it doesn't say that. The 7 is only the clean (i.e. kosher) animals (and birds). However it is ambiguous if it means 7 pairs (i.e. 14) or 7 animals (14 seems more correct). Says nothing about one to watch. Ariel. (talk) 09:05, 27 March 2011 (UTC)[reply]
how did engineers calculate loads and stresses before the arrival of Newtonian physics and calculus?
I'm thinking Greeks, Romans -- Gothic architects who built those flying buttresses, etc. What mathematical tools did they use for their calculations? Did they build little models and then assumed the forces would scale? When building really large monuments for example, and some engineer came up with some experimental idea, how did the ancients test their ideas? Presumably there was a great deal of trial and error involved, but I usually don't hear about ancient engineering disasters. John Riemann Soong (talk) 20:56, 26 March 2011 (UTC)[reply]
There would be little sign left of most ancient engineering disasters, since the materials are likely to have been reused or eroded since then, and the rulers wouldn't be likely to record their failures in writing. One exception I know of is some ancient Egyptian pyramids which are now just piles of rubble. Another is some Easter Island statues that seem to have been abandoned before finished, due to cracks, etc. StuRat (talk) 20:59, 26 March 2011 (UTC)[reply]
Also note that, just as Newtonian physics is technically "wrong", but is still useful in many cases as an approximation of quantum mechanics and relativity, earlier models may have been "wrong", but still useful tools. And note that they don't have to understand why a particular model works, just that it works, to use it for good results. Finally, they likely just allowed more of a margin for error, if there was more uncertainty in their calculation methods, by using thicker beams, bigger stones, etc., than were actually needed. This might actually explain why some of their projects lasted so long. Roman aqueducts may not have been meant to last for thousands of years, but the calcs they made might have made them seem less stable than they really were, which they then compensated for by over-engineering them, especially once the larger margin-of-error is considered. StuRat (talk) 21:04, 26 March 2011 (UTC)[reply]
Well, I don't know of a source that deals with the topic comprehensively, but there were quite a number of Gothic cathedral projects that either fell down as they were being constructed or didn't last very long. Looie496 (talk) 21:14, 26 March 2011 (UTC)[reply]
What mathematical techniques did the ancients use? In building monumental projects did they ever make use of advanced Euclidean geometry and infinite regressions? I note the ancients talk of Diophantine equations and explored relatively intricate problems. I suppose the idea of the Riemann sum actually went way back? Did the ancients use to do something like approximate an integral by simply splitting up the problem into tiny easy to calculate approximations? Did mathematics drive engineering, or did engineering problems drive mathematics? John Riemann Soong (talk) 21:18, 26 March 2011 (UTC)[reply]
One approach which requires very little math is to construct different scaled models. If the 1/10th scale model supports 10 times the weight of the 1/100th scale model, it's reasonable to assume that the full-scale model will support 10 times that weight. If the 1/10th scale only supports twice as much weight, then the full-sized project is likely to only support twice that. Certainly not perfect, but might give them a good ball-park estimate. StuRat (talk) 21:28, 26 March 2011 (UTC)[reply]
My understanding is that the tools of Gothic architecture and Romanesque architecture were developed with a mix of very non-general theories and practical experience. They had functional theories of arches, for example, long before they had the calculus. They worked with new ideas on smaller structures before using them on big ones. They no doubt had their failures, as well. --Mr.98 (talk) 22:12, 26 March 2011 (UTC)[reply]
And of course, they did have their documented failures, such as famously, Beauvais Cathedral, which pretty much marked the end of Gothic architecture's relationship with "bigger is better" mentalities. —Preceding unsigned comment added by 92.20.201.71 (talk) 22:20, 26 March 2011 (UTC)[reply]
Flying buttress says "Early flying buttresses tended to be far heavier than is required for the static loads involved ... Later architects progressively refined these designs and slimmed down the flyers", and it also has a "remedial" section which mentions how they were sometimes retrofitted. I think there is a much more famous example of this than the parish church in the article - there's at least one cathedral which had buttresses added after construction - but I can't remember where it is. Fonthill Abbey's tower collapsed several times, but that was because William Thomas Beckford was incredibly rich and in a hurry, and willfully negligent in designing it. 213.122.22.239 (talk) 22:19, 26 March 2011 (UTC)[reply]
(ec) Not everything in the Principia was new. I think that ancient people had a good quantitative understanding of weight, normal forces, and static friction, which are all you need to build stone structures that stay up. You don't need a concept of acceleration or even velocity. The stones are your atoms, and there are only finitely many stones, so you don't need calculus. You do need vectors, which the ancient Greeks already had. -- BenRG (talk) 22:23, 26 March 2011 (UTC)[reply]
There's also just plain old experimentation; i.e. instead of calculating what might work, you just go ahead and build it, and if it doesn't, you try something different. The Bent pyramid shows such experimentation "on the fly". When the pyramid's slope angle proved unstable, the builders simply adjusted it mid construction to make it work. There are likely dozens of long lost and forgotten pyramids which failed before the ideal angle and construction methods were tripped upon when building the Pyramids at Giza. The same is likely true of other great construction projects (castles, cathedrals, fortresses, city walls, etc.) Mostly trial and error, and then if it works repeat it... --Jayron3223:31, 26 March 2011 (UTC)[reply]
Agreed. The spire of Lincoln Cathedral fell down in 1237 when it was less than 10 years old. It was replaced with a bigger one - said to have been 160 metres high, making it the tallest structure in the world, but that was blown down in a storm in 1548. They got the hint - it was never replaced. Another factor is that medieval masons verbally passed the tricks of the trade on to their successors in secret. Each mason therefore had generations of practical knowledge of what worked and what didn't, filed away in his head. The passing-on of secret information in this way survives symbolically in modern Freemasonry. Alansplodge (talk) 15:36, 27 March 2011 (UTC)[reply]
Many cathedrals fell down, probably churches also. Georgian houses were badly built and often fell down. Only the good ones have survived. Many buildings in the third-world fall down. 2.97.210.137 (talk) 21:44, 27 March 2011 (UTC)[reply]
Double Recombination
Hello. A wild-type female fruit fly mates with a yellow, chocolate, cut male (all traits recessive). The percentage of progeny of various types is as follows:
40.53% cho, y+, ct+
7.85% cho, y, ct+
1.84% cho, y, ct
0.05% cho, y+, ct
0.03% cho+, y, ct+
2.08% cho+, y+, ct+
8.07% cho+, y+, ct
39.55% cho+, y, ct
I determined that the ct gene is in the middle. Is the distance between y and ct 84 cM or 16 cM? How can I calculate the expected percentage of double recombinants? Thanks in advance. --Mayfare (talk) 21:44, 26 March 2011 (UTC)[reply]
I ran across [10] but for some reason I'm having trouble finding a good simple Web-based site for this sort of calculation (see LOD score).
Now to go over the genes one-by-one. First, let's work out the raw recombination fractions.
40.53 + 0.05 + 0.03 + 39.55 = 80.16% (cho+, y OR cho, y+), 7.85% + 1.84 + 2.08 + 8.07 = 19.84% (cho, y OR cho+, y+)
40.53 + 7.85 + 8.07 + 39.55 = 96.00% (cho, ct+ OR cho+, ct), 1.84 + 0.05 + 0.03 + 2.08 = 4.00% (cho, ct OR cho+, ct+)
40.53 + 1.84 + 2.08 + 39.55 = 84.00% (y, ct OR y+, ct+), 7.85 + 0.05 + 0.03 + 8.07 = 16.00% (y+, ct OR y, ct+)
Now with just the raw fractions it's pretty obvious that cho and ct are close together, with y probably closer to ct than to cho. How probably is where the finer analysis comes in. Note that there's no "84 cM" result possible - you can't get more than a 50/50 ratio. The alleles are labeled + or mutant to distinguish them, but what they are labelled doesn't actually matter. It's apparent that they started as cho, y+, ct+ and cho+, y, ct chromosomes at the beginning (the two main unrecombined types coming out of the cross.
The next thing we'd like to know is the working out of the mapping function. Kosambi's mapping function seems to be pretty popular in Drosophila; Haldane's mapping function is a simpler version that ignores that one crossover might affect the probability of another. See [11]. Now according to [12], m = 1/4 ln [(1+2r)/(1-2r) for 0 <= r < 0.5 (m = map distance, r = recombination). So 16% adjusts to 16.58 map units, 4% adjusts to 4.00 map units, and 19.84% adjusts to 21.00 map units. That gives us a basic suggestion that we have y <- 16.58 -> ct <- 4.00 -> cho. Because this is (I assume) a homework problem, this adds up nicely to y <- 20.58 -> cho as opposed to 21.00 calculated, and the double recombinants y+ ct cho and y ct+ cho+ are in fact very uncommon (the latter source gives a way to use double recombinants to work out the order more precisely). Still, a good program could maximize the LOD scores for a more precise result, and give a better idea of the confidence of the mapping. Wnt (talk) 23:21, 26 March 2011 (UTC)[reply]
He's saying Fukushima emitted "1.3 × 10e17 becquerels per day", and saying that "In the 10 days it burned, Chernobyl put out 1.76 × 10e18 becquerels". So he's comparing the daily rate of Fukushima vs the 10-day rate of Chernobyl. If you assume Fukushima's rate was constant over 10 days, it would have emitted 1.3 x 10e18 over the same 10 day period. So the two 10e18 cancel out, and you're left with the ratio 1.3:1.76, which is (roughly) "50 per cent more". -- Finlay McWalter ☻ Talk23:26, 26 March 2011 (UTC)[reply]
During baking, the fuse of my apartment went off. I have no doubt that the oven is to blame. Is it secure to turn the oven on again or will the fuse go off again and again? 212.169.191.85 (talk) 23:43, 26 March 2011 (UTC)[reply]
Fuse going off may have resulted in some other electrical devices turning off, however if it is not the case it will indeed go off again ~~Xil (talk) 00:13, 27 March 2011 (UTC)[reply]
Length of time should only matter if you are running the circuit over its rated load. Circuit breakers don't actually trip at the stated number. The greater the overage the faster they trip. If you run just slightly over, it can take a very long time (hours even) to trip. I would attempt to find out what other devices are on the circuit, because an oven should be the only device on the circuit! Then add up all the labeled power draws, and compare to the circuit breaker. Ariel. (talk) 02:26, 27 March 2011 (UTC)[reply]
Your options are to get an oven which draws less power (including spikes), switch it to a circuit which can handle more, or upgrade the present circuit. You could also replace the circuit breaker, it might just be overly sensitive (popping below the rated limit). A more risky approach is to change the circuit breaker to one which allows more power to be drawn. This can cause a fire, though, so only an electrician who knows how much that circuit can handle (and the entire fuse box) should do that. StuRat (talk) 00:29, 27 March 2011 (UTC)[reply]
It should be possible to acctualy calculate if it will happen - I believe you sum power in watts of all devices turned on and divide it by 220 (also watts) and you get how many amperes this set up produces, if it is greater than safe limit of the circuit breaker it will go off ~~Xil (talk) 01:35, 27 March 2011 (UTC)[reply]
It's not quite as simple as that, because the power demands of each device aren't constant. If all the spikes hit at once, you can have a problem with a circuit that seemed fine before. StuRat (talk) 02:02, 27 March 2011 (UTC)[reply]
I don't see why leaving a stove on for a long time would draw more current than turning it on for a short period. In fact, an already-hot oven might draw less current on average than one that's heating up from a cold start.
See my reply a bit higher up, but basically circuit breakers don't trip immediately at their rated setpoint, there is a time * overage lag. Ariel. (talk) 02:52, 27 March 2011 (UTC)[reply]
I can understand the delay mechanism for a slight overload of an old-fashioned fuse, but how would a delay be implemented mechanically in a modern circuit-breaker? Dbfirs07:02, 27 March 2011 (UTC)[reply]
Is all life on earth decended from a common ancestor
According to the article Last universal ancestor, "A universal common ancestor is at least 102860 times more probable than having multiple ancestors…"
Does this infer that the probability that all life on earth is decended from a common ancestor is 102860 times more likely than the tree of life containing more than one starting point (i.e. more than one transition from none life to life)? It seems a startlingly large number if it implies that say plants and animals could not have evolved separately.
That's exactly what it is stating. You would have to read the original source to understand where it comes from and what were their assumptions. Does it surprise you that plants, animals, fungi, bacteria, etc ... all have a common ancestor? Dauto (talk) 00:45, 27 March 2011 (UTC)[reply]
You mean "imply", not "infer" (very common error). I understand it to mean 102860 times more probable than the scenario in which there was more than one starting point for life. Grammatically, it's not a great sentence. "having" is awkward... it's a dangling participle, or something like that... 86.179.115.46 (talk) 00:48, 27 March 2011 (UTC)[reply]
That figure of 102860 suggests a degree of mathematical precision that is not realistic. The source is a print one, so difficult to check. I would prefer that the statement was softened somewhat to something like "A universal common ancestor is far more probable than having multiple ancestors…" HiLo48 (talk) 00:54, 27 March 2011 (UTC)[reply]
Looie's Law: Any probability less than 1 in 106 is meaningless, because there is always at least one chance in a million that you make a mistake in working out the answer. Looie496 (talk) 01:36, 27 March 2011 (UTC)[reply]
Yea, when I hear of DNA matches to within one chance in a trillion, I always wonder what the real chance is of a false positive, when you include the chance the technician accidentally tested the same sample twice. StuRat (talk) 02:00, 27 March 2011 (UTC)[reply]
It is conceivable that there could be multiple origins of life, yet still all life shares a common ancestor. For example, there could have been a simple self-perpetuating lipid vesicle with some basic amino acid polymers, and a self-perpetuating RNAzyme, and the two became symbionts of one another. Or there might have been two original simple RNAs that merged into a single genome. But what's pretty clear is that a ribosome is found in any known kind of modern life capable of reproducing itself, and those ribosome sequences are similar by more than just chance. Wnt (talk) 02:34, 27 March 2011 (UTC)[reply]
It's likely that mitochondria are a separate life form that at some point became part of our cells, since they have their own genetic code. However, them and our cells probably both had a common origin further back. StuRat (talk) 04:52, 27 March 2011 (UTC)[reply]
Note that mitochondria have their own ribosomes - you can even tell from sequence and structure that they're the bacterial type rather than the eukaryotic type. Wnt (talk) 22:58, 27 March 2011 (UTC)[reply]
The number looks meaningless to me. They seem (based on the quote in our article - the paper is behind a paywall, so I can't read it) to have constructed several models and examined how likely our current observations are under each model. You can't convert that to the probability of each model being true without some prior probabilities and I can't see where they would get them. --Tango (talk) 14:30, 27 March 2011 (UTC)[reply]
I think that Paul Davies has suggested that there may exist life forms separate from our branch right now on Earth that we haven't managed to detect. Count Iblis (talk) 14:38, 27 March 2011 (UTC)[reply]
I suppose eventually it will come down to at exactly WHAT point do we call it life? I think the common misconception might be that there would have had to be a truly one off unique, even miraculous event which lead to all life. But I don't believe that's necessarily the case, there was probably LOTS of instances of "whatever it was" that led to life, and some of those elements might have "come together" to form the "proto-life" many times, only to "die out" later, possibly much later. All that we can be fairly certain of is that there would have been one "lineage" which all living things today can be traced back through, that's the universal common ancestor, but there could have been countless other "false starts" and "dead ends". Having said that, I wouldn't personally 100% rule out that some strange extremophile might still be found from a different original lineage, I think it's quite unlikely at this stage, but not 0%..Vespine (talk) 00:55, 28 March 2011 (UTC)[reply]
Relativity Question
Is it possible for a pulse in the following case to deviate from it's original path.
For simplicity let a spaceship is moving with 0.9c from east to west relative to the following observer on asteroid.
Dimension of the spaceship are
Width = 2 light second,
Length = 10 meter (adjusted with length contraction)
An observer on asteroid (not co-moving) in the middle of east and west fire a pulse perpendicular to direction of spaceship such that after sometime the same pulse strike the longitudinal side of ship during it's passage by asteroid.
For ONBOARDB observer:
A pulse enter at one longitudinal side, travel inside for two second and then out through the other longitudinal side.
For observer on ASTERIOD:
1- A pulse will change it's direction from its original path after entering the ship
2- A pulse will travel for sometime inside ship but not perpendicular to the direction of ship
3- A pulse will start traveling again in straight line after leaving the ship but this time not on it's original straight line (which was before striking the ship).
68.147.41.231 (talk) 07:00, 27 March 2011 (UTC)Eccentric Khattak#1-420 ---- [GO][reply]
The angle of the light beam is different with respect to the two different rest frames. The difference is given by the relativistic aberration formula. If, with respect to the asteroid rest frame, the light beam is perpendicular to the ship's motion, it will enter the ship and collide almost immediately with the back of the ship. With respect to the ship rest frame, it will be sharply angled toward the back of the ship and, again, hit the back almost immediately. -- BenRG (talk) 07:28, 27 March 2011 (UTC)[reply]
Getting rid of hazardous nuclear plant parts
If there is a decay heat even after the reactor's shutdown, the best way seems to dismantle the most dangerous parts of Fukushima plant, such as fuel rods and take them hell away or just destroy. Why this is not being done?--89.76.224.253 (talk) 09:56, 27 March 2011 (UTC)[reply]
They're too hot to take away right now — that's the whole problem. And "destroy" them how — bombing them, essentially spreading them into the air? Dump cement on them and hope for the best? These aren't prudent strategies. The latter is what you do when you've truly given up on reducing the radiation levels. Once things are "cool" enough to move, yes, they'll be dismantled, put into safe places, disposed of, cleaned up, and so forth. But you can't do that until you've gotten them to reasonable temperatures, and let some of the worst of that radiation dissipate (which is why the spent fuel was being kept in those pools in the first place).--Mr.98 (talk) 10:03, 27 March 2011 (UTC)[reply]
It takes about 5 - 10 years before you can place them in Dry cask storage. BTW, the reactors that were already shut down were just supposed to be temporary shutdowns while they did maintenance. They don't want to "destroy" or get rid of anything. They just want to shut it down, let the radiation fade, do their maintenance, then start them back up. Ariel. (talk) 11:49, 27 March 2011 (UTC)[reply]
Agreed. Restarting plants, of the same design and in the same location, as those that just failed so miserably, wouldn't be popular. StuRat (talk) 18:57, 27 March 2011 (UTC)[reply]
That didn't stop them at Chernobyl. While the reactor that melted down obviously wasn't restarted (there wasn't much of a reactor left by the end), the other reactors on the same site continued to operate for more than 14 years. Of course, the political situation was a little different. --Tango (talk) 20:53, 27 March 2011 (UTC)[reply]
Quite different. Still, the obviously reckless attitude of the Soviet Union towards their people's safety may have been a contributing factor in it's disintegration, by robbing it of the public support it needed when challenges from Gorbachev and then Yeltzin appeared. StuRat (talk) 22:55, 27 March 2011 (UTC)[reply]
Not wanting to be too pedantic, but Chernobyl took place on Gorbachev's watch. The handling of it was a colossal blunder on his part. It certainly did lead to vast distrust of the Soviet officials, especially amongst Ukrainians. Today its memory and experience are a major part of the post-Soviet identity of Ukrainians, Belarussians, and others in the affected area. It's also generally odd to talk about the Soviets losing public support when challenged by Gorbachev — Gorby was the Soviet Union. His efforts at reform opened up attacks from others — like Yeltsin, among others — that eventually led to the USSR falling apart. But that was not in any way Gorbachev's goal: he was trying to be a reformer, not a revolutionary. He really did believe in the USSR and Communism, at the time. --Mr.98 (talk) 00:37, 28 March 2011 (UTC)[reply]
Gorby wasn't in power when the unsafe plant was built. And, in his case, the hard-liners might have retained control if they had more of the public behind them. (And hard-liners dropping dead every few minutes helped Gorby out, too.) StuRat (talk) 04:15, 28 March 2011 (UTC)[reply]
Q:If there is a decay heat even after the reactor's shutdown, the best way seems to dismantle the most dangerous parts of Fukushima plant, such as fuel rods and take them hell away or just destroy. Why this is not being done?
This is what they will do... eventually. To do this however, they need to have electrical power restored to the equipment that extracts the rods from the core so as to place them in the spent fuel ponds. Obviously, it helps to have the working area decontaminated as well and this too will take time. Also, with the restoration of power, radioactive water (in the ponds and else where) can be passed through ion exchange material to remove the radioactive isotopes and thus bring down the exposure suffered by the recovery workers still further. If any fuel rod have partly melted in the core, they can be left in situ. Any residual heat from these will only be a small fraction of the current heat output (this is said without knowing if or how much meltdown has occurred). After the fuel rods have cooled sufficiently, they could then be shipped off (to say England) for processing. The Fukushima plant can be mothballed until such time that the radiation has decade to a level that permits the buildings on the site to be demolished and reclaimed for reuse. So in answer to your question, they can't remove the rods from the pile until they get these other things get done. --Aspro (talk) 21:40, 27 March 2011 (UTC)[reply]
It may be years before the rods are removed from the reactors. At Three Mile Island, it was six years before the reactor was defueled, although a different political climate and lessons already learned might shorten that. Japan does it own reprocessing with its own risks. (See Tokaimura nuclear accident) But it is unclear if melted-down rods covered in boron and sea salt can be successfully or economically reprocessed. Rmhermen (talk) 22:34, 27 March 2011 (UTC)[reply]
That rotation curve looks wrong to me too. It's based on a 40 year old paper that fits observation to a polynomial. That paper indicates the possibility that a shallower inner minimum (of about 125 km/s) might also be a good fit to the observations and I think that the shallower minimum makes more sense from the dynamical point of view. A more recent source might be valuable to help solve this inconsistency. Dauto (talk) 15:41, 27 March 2011 (UTC)[reply]
The statement in the article refers to Fig. 9 in this paper. There are several data points that indicate a (narrow) dip down to below 100 km/s. This is regardless of the polynomial that is fitted to the observations (sic!). I haven't looked for newer data yet, but I point out that the dip should be located within the bulge of Andromeda, i.e. in a region that might well be supported by random motion rather than ordered rotation. --Wrongfilter (talk) 17:35, 27 March 2011 (UTC)[reply]
snow on tree flowers
So my school's trees are blooming.....and then it snowed last night, putting about half an inch on the ground. Are these flowers (that grow on trees) likely to die? =( John Riemann Soong (talk) 12:46, 27 March 2011 (UTC)[reply]
I was just discussing this with my husband. We have a camellia about to bloom. At the same stage last year there was a sharp frost which resulted in the flowers being blighted and either rotting completely, or developing brown edges to them. I think it all depends on (a) the amount of frost and (b) the makeup of the flower. Some flowers are more waxy than others, and these flowers seem not to be too troubled with frosts.--TammyMoet (talk) 13:36, 27 March 2011 (UTC)[reply]
Note that flowers being covered in snow may actually insulate them from colder air. That may or may not be enough to save them, though. StuRat (talk) 19:00, 27 March 2011 (UTC)[reply]
I've removed your email address to prevent you getting spammed - we'll respond here. A car couldn't travel as fast as the speed of light, since nothing with mass can, so that is a meaningless question. A car travelling at 99.9% of the speed of light would still see the road being lit by its headlights normally. Light always appears to move at the same speed relative to you, regardless of how fast you are moving. That seems very strange, but it is true. --Tango (talk) 18:52, 27 March 2011 (UTC)[reply]
Calling it "a meaningless question" is imprecise enough to be well-nigh a meaningless statement. The core of the issue with the question is that in order to realize the premise of the question, one would have to posit that the laws of physics were different from the way we understand them now. So the answer to the question would depend heavily on how one adjusted the laws of physics to allow for it to happen. (So the question is not so much "meaningless", as it is "underspecified" - as Dauto hints, one can extract great meaning from the question if one looks at what you need to do to the laws of physics to make everything work out.) - That said, while we can't answer the question exactly as written for *at* the speed of light, we can make a slight but mathematically rigorous alteration, and look at what happens as one approaches the speed of light in the limit (mathematics). For the answer to that physically allowed and practically identical question, we find that the passengers in the car, as well as observers on the side of the road, will always see light coming from the headlights traveling at the speed of light. However, in the limit, length contraction means that the length of the road will appear to shrink towards nothingness for the passengers in the car (as the length of the car shrinks towards nothingness for observers on the side of the road). The effect of this is that in the limit, there is no "road ahead" for the passenger, as all points on the path of the car shrink to virtually the same point (that is, all points are an infinitesimally small distance away from each other). For the observer on the side of the road, the light from the headlights travels at the speed of light, but so (less an infinitesimal delta) does the car, so the light reaches a given point on the road ahead only an infinitesimal fraction of a second before the car does. Again, this really isn't "the road ahead" so much as "the road immediately in front of". Whether you call this "lit by its headlights normally" is highly dependent on what you consider to be normal. -- 174.24.203.209 (talk) 20:57, 27 March 2011 (UTC)[reply]
In short, the laws of physics are the same in every inertial frame. To the passengers in the car, light still goes at the speed of light, but the road is length contracted. However one should probably note that the passengers velocity in their frame is still zero, and they are no closer to the speed of light than when they started. So the extent to which the anyone has "approached the speed of light in the limit" is questionable. —Preceding unsigned comment added by 92.20.201.71 (talk) 22:37, 27 March 2011 (UTC)[reply]
What Tango said is correct. I just want to add that Einstein sited that question and other similar questions as inspiration for his theoretical investigations that eventually lead to the development of relativity. Dauto (talk)
I notice a lot of heated hair styling equipment (blow dryers, flat irons, curling irons) tout the fact they are coated with or contain tourmaline. Yet the entry on the mineral doesn't give any clue to why this would be a benefit to products like that. Any ideas? --70.167.58.6 (talk) 19:27, 27 March 2011 (UTC)[reply]
The main term used seems to be 'tourmaline ceramic', which is probably a ceramic made by sintering tourmaline powder (that's a guess of course). Lots of wild claims about being a great source of negative ions - whatever that's supposed to mean, see here. Mikenorton (talk) 20:19, 27 March 2011 (UTC)[reply]
Tourmaline is a sort of gemstone because it has hardness 7. If you had sand in your hair it shouldn't scratch a tourmaline coated surface. But I have no idea if that's the real reason. Wnt (talk) 23:03, 27 March 2011 (UTC)[reply]
Blossoming wild shrubs in SE England
Today in the countryside of south east england I saw many example of white flowering bushes in the hedgerows. They did not have any thorns or spikes so I think that means they could not be hawthorns or sloes. They had five-petalled flowers. What could they have been? One of them at least that I looked at closely looked slightly pinkish, due to things (sorry my botanical vocabluary is not very good) adjacent to the white blossoms which were begining to burst out from the buds.
I also saw some pink blossom on what I think was a cultivated shrub, what could that have been please, at this time of year? Thanks —Preceding unsigned comment added by 2.97.210.137 (talk) 21:03, 27 March 2011 (UTC)[reply]
They looked like hawthorns except they did not have any spikes or thorns. The leaves must have been different. The ones I recall seeing were a simple leaf shape with a serrated edge. 2.97.210.137 (talk) 21:48, 27 March 2011 (UTC)[reply]
Almost certainly Blackthorn. A cold snap in March is called a Blackthorn Winter because it coincides with the hedges being white with their blossom. Hawthorn blossoms in late April - also known as "Mayflowers" (it hasn't realised that we changed to the Gregorian calendar a while ago). There very often aren't thorns on new blackthorn growth. I think you're unlikely to find many damson hedges in England although damson is a very close relative of blackthorn - they're both from the Prunus family. Alansplodge (talk) 00:30, 28 March 2011 (UTC)[reply]
angular momentum in beta decay
Fermi beta decay is usually done without accounting for spin. The relevant term is the DOS of the final state, so:
If a spin-S particle decays into two particles spin s1 and s2, how does one account for this in the DOS of the final state. Is it just increased by a factor (2S+1) as this is the number of ways of aligning s1 and s2 to make s1 + s2 = S. (Is that right?) —Preceding unsigned comment added by 92.20.201.71 (talk) 22:28, 27 March 2011 (UTC)[reply]
When I "suck it in" -- what is "it" and where does it go? I find even with a full breath in my lungs I can still "suck in" my gut a fair bit (though less), so it can't all be lung expansion/contraction. The Masked Booby (talk) 22:41, 27 March 2011 (UTC)[reply]
External intercostal muscles can flare (lift, like a bucket handle) the ribs to increase the volume of the thorax. If the epiglottis is closed then air cannot enter the lungs (to balance the pressure difference between the newly-reduced-pressure thorax versus the outside atmosphere). If the diaphragm is relaxed, the relatively-mobile abdominal contents have greater pressure from outside than the thorax, thereby tending to move them into the thoracic cavity. Abdominal muscles, including the rectus abdominis and obliques (abdominal internal oblique muscle, abdominal external oblique muscle) can also play a role in pushing abdominal contents up against the diaphragm. -- Scray (talk) 01:06, 28 March 2011 (UTC)[reply]
I do not like wearing sunglasses as they make colours look grey or other tints. Do pinhole glasses reduce the amount of light while still letting you see colours? Are they suitable to use as sunglasses? Thanks 2.97.210.137 (talk) 23:02, 27 March 2011 (UTC)[reply]
Only colored lenses change the color. You need to get photo-grey sunglasses. They shouldn't change or reduce the color. (Except that colors in shadows might not be bright enough to distinguish anymore, but that's also true of pin-hole glasses, which will also reduce peripheral vision.) StuRat (talk) 23:11, 27 March 2011 (UTC)[reply]
Depends on what you're doing. If you're just looking around, then sturat is right. I've used (photo.grey) for many years in tropical sun (Guatemala) and they have only minimal effect on colors. but if you're doing something that requires only a narrow field of vision, such as painting pictures in sunlight, then color perception is important and pinholes might be better.Note also that photo grey get darker in sunlight and lighter in shade. very convenient but they are usually more expensive.Phalcor (talk) 05:13, 28 March 2011 (UTC)[reply]
March 28
Melting point of graphite: Lower in Japan?
This article says that graphite plugs in the Kukushima Daichi reactors "start to melt" at 350 C. That seems implausible, since graphite is used in various applications in a solid state at much higher temperatures, as in arc lights. Could graphite really melt at 350 Celsius? The Graphite article does not appear to state a melting temperature. Edison (talk) 00:05, 28 March 2011 (UTC)[reply]
That article actually says 350°F, which is even lower (177°C). That does seem to be a mistake. According to this article: [15], graphite melts (technically it sublimes, or turns to vapor) at around 3652-3697°C. This assumes normal atmospheric pressure though, could that be the difference ? StuRat (talk) 00:29, 28 March 2011 (UTC)[reply]
My guess is the "graphite plugs" are not made of pure graphite, but have something else in them which is what does the melting. Our carbon article says that carbon in normal atmospheric pressures doesn't even HAVE a melting point as it sublimates at about 3900 K. Even given that, 177 deg C still sounds wrong. Vespine (talk) 00:36, 28 March 2011 (UTC)[reply]
Another thought, could the plugs come loose, due to contraction and/or expansion ? They wouldn't need gravity to pull them out, if water can then get underneath them and turn to steam. This certainly isn't "melting", but some reporter could possible get confused and call it that. StuRat (talk) 01:24, 28 March 2011 (UTC)[reply]
Yep. my book (columbia enc.) gives carbon (12 that is)melt.pt 3550 C. gas off 4827 C. definitely sounds like journalistic error or typo.Phalcor (talk) 04:01, 28 March 2011 (UTC)[reply]
Carbon-graphite impregnated epoxy resin sealing rings are widely used in industry and the epoxy breaks down around 350 deg... and a few degrees less if it is wet heat. They don't melt, they become soft and crumbly and start to smell very unpleasant. Fairwinds (oh the irony) have posted a diagram of the projected radioactive leak path.--Aspro (talk) 10:11, 28 March 2011 (UTC)[reply]
What country are you in? Anyway, do celebrities do this, or register the car under their agent's name? I've made the title more descriptive. CS Miller (talk) 06:11, 28 March 2011 (UTC)[reply]
As of a decade ago (last time I had to care), it was possible in California for someone other than the legal owner of a car to submit the registration paperwork provided that the legal owner signed the forms and all other necessary documentation was provided. You have to show up in person to get a driver's license, but someone else could submit registration paperwork. Not sure if that is still the case, or whether different rules apply in different states. Dragons flight (talk) 08:51, 28 March 2011 (UTC)[reply]
Pressurized storage of liquids
Suppose we have a 1 litre container of water (or any other drinkable liquid). Is it theoretically possible to pressurize the container to, say, 300 ml capacity so that this smaller container would still be able to contain 1 litre of water (something like black hole)? Specifically, is there any material capable to withstand the associated water pressure while being flexible enough to allow the needed external pressure?--89.76.224.253 (talk) 10:05, 28 March 2011 (UTC)[reply]
It's doubtful. You would need a pressure of at least7.333×10^9 Pa (Hope I did the math right.) Which is a pretty immense pressure. But since the bulk modulus of water is non-linear with pressure, the real pressure is probably much much higher. I can't find info on how non-linear. Ariel. (talk) 10:57, 28 March 2011 (UTC)[reply]
I remember seeing an old film clip about what must have been the Bathysphere or Benthoscope returning from the deeps after a test run. When its hatch bolts were gingerly loosened, a huge quanity of water gushed out under pressure, seemingly several times the volume of the sphere. So, yes. 92.15.14.99 (talk) 11:56, 28 March 2011 (UTC)[reply]
Methanopropylenes
Hi. I recently had a dream about "methanopropylene" (I know, I'm so weird). The name could refer to either a propylene plastic impermeable to polar methano-molecules such as methanol in gaseous or liquid form and to chemicals produced by methanogens, or polymers derived from methanols. The only Google item I could find relavent to my topic, in fact the only website in existance remotely related was this, but any idea what type of chemical methanopropylenes would constitute and what potential they have? Thanks. ~AH1(TCU)11:46, 28 March 2011 (UTC)[reply]
Resolved
Resolved
