Wikipedia:Reference desk/Archives/Science/2013 March 3

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March 3

Bell's inequality

Is the following statement about the experiment used in Bell's inequality correct?

We have a pair of entangled particles. One particle encounters a detector with a polarizer at some angle and one of two things happens (1)The particle is measured collapsing the wave function and leaving the other particle in the correlated state, or (2) the particle is not measured but is absorbed, breaking the entanglement and leaving the other particle in an unknown state.

(In addition to whether it is correct, should it end with the words 'unknown state' or 'random state'?)

Thank you. RJFJR (talk) 00:11, 3 March 2013 (UTC)

It's a measurement whether the particle is absorbed by the polarizer or not. If it's not absorbed it's an interaction-free measurement, but it doesn't matter—the particle states are correlated either way. Also, you don't get a nonclassical result from a single pair of entangled particles or with a single kind of polarization measurement. You need to repeat the experiment many times, randomly reorienting the polarizer each time (just two orientations are enough). -- BenRG (talk) 01:41, 3 March 2013 (UTC)

There's been more than one experiment measuring Bell's inequality. See Bell test experiments. In the "typical" two-channel experiment, a coincidence counter only activates if both entangled particles got through their respective polarizers. If one photon got absorbed, it simply isn't counted. --140.180.251.41 (talk) 22:52, 3 March 2013 (UTC)

How accurately can we predict the properties of an element and its compound by trends from other elements of a series? How to prove it?

I am just curious if Mendeleev's method (if any) of predicting chemical and physical properties of elements such as Germanium do apply to other elements. I am currently confused on some original research issues on francium and francium hydroxide.--Inspector (talk) 03:02, 3 March 2013 (UTC)

I don't really understand the question, but for anything it could possibly mean, the answer is yes. I suspect you're looking for more information than that, but you'll have to clarify what you really want to know. Looie496 (talk) 03:08, 3 March 2013 (UTC)

I'm not sure how to quantify how accurately the periodic table predicts properties. How does 9 out of 10 prediction units sound ? StuRat (talk) 03:39, 3 March 2013 (UTC)

Let's say: by which method did Mendeleev come out with the prediction for germanium and its compounds? Just simple linear regression? Can we apply such methods to other elements undiscovered or too unstable to experiment? Is it original research to make such predictions?--Inspector (talk) 05:50, 3 March 2013 (UTC)

magnets strength

you have two magnets,same size each and same strength.are they stronger when they are replying from each other rather than attracted to each other.?? my test show they are atronger replying from each other. ```` — Preceding unsigned comment added by Westfall272 (talk • contribs) 04:50, 3 March 2013 (UTC)

I assume you mean "repelling" each other. Well, the force varies dramatically with the distance, and you would probably place them in contact to test the repelling force, so that would then seem higher. StuRat (talk) 04:52, 3 March 2013 (UTC)

if they was .015 apart would repelling still be stronger ```` — Preceding unsigned comment added by Westfall272 (talk • contribs) 05:03, 3 March 2013 (UTC)

.015 what? Evanh2008 ^{(talk|contribs)} 05:05, 3 March 2013 (UTC)

15 thousands apart — Preceding unsigned comment added by Westfall272 (talk • contribs) 05:10, 3 March 2013 (UTC)

I know how to read fractions, yes. I have no idea what it is a fraction of in this context. Millimetres? Inches? Centimetres? Parsecs? Evanh2008 ^{(talk|contribs)} 05:14, 3 March 2013 (UTC)

I think this "clarification" was hilarious :). 86.101.32.82 (talk) 06:08, 3 March 2013 (UTC)

Yes, like when Sheldon Cooper requested alcohol from the bartender, and was asked which type, to which he responded "ethyl alcohol". StuRat (talk) 16:40, 3 March 2013 (UTC)

And somewhat akin to Sheldon Cooper, in their several years on the RD (and multiple different identities), the OP has shown very limited ability to learn how to ask questions on the RD, like what sort of details should be specified,; and to be able to answer queries from those seeking to help in one go. Nil Einne (talk) 14:45, 5 March 2013 (UTC)

.015 of a inch````` — Preceding unsigned comment added by 4.131.77.179 (talk) 06:01, 3 March 2013 (UTC)

What's with all the digressions? If they're the same distance apart, then the forces should be the same strength, just in opposite directions. Clarityfiend (talk) 07:20, 3 March 2013 (UTC)

This is the hardest I've laughed looking at this board. Had to comment. – Kerαunoςcopia^◁_galaxies 08:56, 5 March 2013 (UTC)

"This machine destroys EVERYTHING"

[[1]] What is this machine called, and what is its normal diet? — Preceding unsigned comment added by 75.35.96.60 (talk) 09:13, 3 March 2013 (UTC)

It's an industrial shredder. SpinningSpark 09:53, 3 March 2013 (UTC)

Specifically, one intended for processing industrial solid waste. Horselover Frost (talk · edits) 09:58, 3 March 2013 (UTC)

Lots more videos here. The one doing refrigerators is pretty cool. SpinningSpark 10:00, 3 March 2013 (UTC)

So, what would happen if you fed one of those machines into another? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:03, 3 March 2013 (UTC)

Feeding you into one would be much more entertaining. SpinningSpark 23:41, 4 March 2013 (UTC)

Actually, this is a good question. It is the basis of the Chinese term "矛盾" - see our article Irresistible force paradox. — Sebastian 00:27, 5 March 2013 (UTC)

@Baseball Bugs: check out March 2008 Robinh (talk) 02:32, 5 March 2013 (UTC)

How long will a brass key retain functionality if used as a doorknob?

The door requires high force to open, enough to deform a well-built ~1.5mm gauge 2-turn key coil, but elastically. So what is that, a couple dozen pounds? It's efficient and allows one-handed entry, but something tells me this was outside it's intended use. Sagittarian Milky Way (talk) 13:26, 3 March 2013 (UTC)

If it's truly within the elastic deformation range (no plastic deformation), then you're talking about eventual failure from metal fatigue. The closer it is to the plastic deformation range, the fewer cycles it can withstand before fracture (could be thousands, millions, billions, or trillions of cycles). Unfortunately, the micro-cracks which lead to fracture can't always be spotted before failure. And, when it does fail, it might break off in the lock, requiring a locksmith to fish it out. And, it's more likely to break off on the coldest day of the year, due to metal being more brittle at low temps (not to mention Murphy's Law). So, I recommend getting a stronger key, and put the brass key in your wallet as a backup. StuRat (talk) 16:32, 3 March 2013 (UTC)

Most keys seem to be made of brass, though some have a silvery plating. The lock might need lubrication (WD-40 or a graphite product), adjustment so binding is corrected, or replacement if worn out or damaged. A new lock can generally be keyed like the old one if that is desirable. Edison (talk) 02:21, 4 March 2013 (UTC)

followup aerodynamics question

(On a purely theoretical level, just to help me understand aerodynamics).

If we take a normal glider wing that is somehow in sections, and manually (for the sake of argument) rotate and fix the sections to have different angles of attack, and perhaps push the start of the wing to be a bit away from the center (as in the designs here - http://www.youtube.com/watch?v=MkZ2bTWvRns - where the wings are held away from the center of turn), then is the new wing something like optimal for a helicopter rotor? Or are there STILL going to be issues that make it completely wrong on a theoretical aerodynamic basis? (Not a practical basis - I'm not even suggesting a specific mechanism for turning the Angle of Attack of the different sections, nor do I have one in mid). Just trying to understand aerodynamics. If there are still issues, what are they? I am just trying to increase my theoretical understanding, thank you. 86.101.32.82 (talk) 16:57, 3 March 2013 (UTC)

Most aircraft already have a varying angle of attack to improve stall behavior. This causes the stall to form at the wing root first, improving controllability and recovery at the stall onset. By now, you know where to look for more information on aerodynamics fundamentals, right? The Pilot's Handbook of Aeronautical Knowledge is available for free from the FAA -http://www.faa.gov/regulations_policies/handbooks_manuals/ - or you can buy a hard-copy for about thirty dollars. If you need a more advanced aerodynamics textbook, I'm sure we can recommend some more. Nimur (talk) 22:00, 3 March 2013 (UTC)

Perhaps you have misunderstood. I am asking about varying it from one moment to another moment possibly a few minutes later, when it should be in a different configuration. (Kind of like how the wing is in sections here: http://en.wikipedia.org/wiki/Boeing_X-53_Active_Aeroelastic_Wing if I have interpreted that photo correctly). I couldn't find more information about that photo. So, this is a very esoteric question I'm asking about, and not at all the typical change in AoA from tip to stem of a fixed wing. Rather, about the possibility of changing between two radically different "fixed" states (perhaps over the course of a few minutes) where one is like a glider, and the other state is like a pair of helicopter rotors, meaning that AoA angle is radically different between stem and tip in the latter configuration, not to mention that one of the wings is now facing the due opposite direction! 86.101.32.82 (talk) 22:10, 3 March 2013 (UTC)

Note: I think I misinterpreted that photo. If you click on it and zoom in (direct link: http://upload.wikimedia.org/wikipedia/commons/5/57/EC03-0039-1.jpg ) , it looks like it's just stripes painted on, not movable sections. Well, imagine it's movable sections instead... 86.101.32.82 (talk) 22:12, 3 March 2013 (UTC)

What is your question, exactly? You asked whether there are "issues." Of course there are issues - as with any engineered system, there are tradeoffs, including weight, reliability, aerodynamic efficiency... a full enumeration of all issues is covered in our article on airfoils. Using today's technology, we can build sophisticated machines that deform in a variety of interesting ways, and we could build an airfoil that does almost anything. But, we typically build the airfoil that falls in our design envelope - trading against the lightest, safest, cheapest, and most reliable design. Usually, lightest- and cheapest- and safest- are all far more important criteria than "most aerodynamically efficient." Your proposal vaguely suggests that if we made a very sophisticated design and analyzed its performance, we might improve efficiency; I'm sure we could derive from first principles and solve airfoil equations for your proposed idea; but that won't solve the problems that aeronautical engineers need solved in this decade. (You don't see a lot of deformable-wing aircraft flying around that just that need optimizations for better deformable-wing performance!) So, what exactly is your question? Are you just seeking mathematical modeling techniques for analyzing airfoil performance in the general-case? Or do you want a specific run-down of the top problems for an unspecified design that does not currently exist, and is only vaguely specified by your question? Nimur (talk) 22:29, 3 March 2013 (UTC)

lightest, cheapest, safest and so forth might bemore important criteria than "most aerodynamically efficient" but not the issues of interest to me at the moment. As I hoped to mention, my only real aim is to improve my personal understanding of aerodynamics. As such the trade-offs that go into actual systems are of less interest to me, though of course I am happy to read those as well. I am not really interested in improving the efficiency of existing systems or anything like that: there is no practical interest inherent in my question, and no interest in actual design constraints faced by aeronautical engineers this decade or any other.

In all, I would say the characteristics / run-down of the top problems for a partially specified hypothetical model that does not exist (nor have reason to exist, nor is practical, nor is posited to be practical in the sense that I am not requiring the wing to be able to support the weight even of its power plant nor asking about how that might be possible). It relly is exactly as you say: trying to improve my understanding of general principals through this mental exercise.

So, the question is, given an attempt to turn external torque into lift, where does a glider that is posited to be able to deform in segments to approximate the shape of a helicopter rotor (possibly pushed away from the center of rotation as in the videos here http://www.youtube.com/watch?v=MkZ2bTWvRns ) meet its primary problems? What are the primary characteristics of such a deformation?

would we need to imagine like a T1000 shapeshifting material if we wanted to talk about an efficient wing shape - or would turning sections of the wing approximate the correct new shape?

"shape memory alloys" exist. If we somehow posit that by applying or removing an electric field, a wing would deform or return to one of two configurations, but obviously the weight and volume of metal had to remain the same, then could the same material be a good glider wing and good helicopter rotor?

Basically I'm trying to understand the relationship between these two things, but positing a way to turn between the two by turning sections of a wing thru some unspecified mechanism (that I don't intend to discover): in this case (with this conceit) could both shapes be close to optimal to generate lift, as a glider (very large glide ratio) and helicopter (great lift from rotation) respectively? Or what "issues" are there and so forth. just help me understand some basics. 86.101.32.82 (talk) 22:48, 3 March 2013 (UTC)

The problem Gamera's airfoil faces is that no material is known to exist that is both very light, and can sustain very high dynamic loads, particularly shear stress and bending moment. Because no such material exists that meets the requires parameters, the team had to design a complicated structure - summarized in their Rotor Blade Fact Sheet - using a complicated truss structure. If the power source were something other than a human, the inputs to the equations would be different, and the required parameters would be different: a different rotation speed and torque would be available; and so a different aerodynamic loading would be present; and a different gross takeoff weight would be possible. If so, the team could use aluminum or metallic blades - as does a conventional helicopter - with corresponding reasonable sizes and weights - and these stress and strain issues would not be problematic. Hopefully this helps explain why their aircraft looks so unconventional. Nimur (talk) 23:09, 3 March 2013 (UTC)

More on the tradeoff between weight - and stiffness - Gamera Structures, part of the full project publication listing. Nimur (talk) 23:12, 3 March 2013 (UTC)

can you talk about this inflatable glider:

can you talk about this inflatable glider, http://www.eaa.org/apps/galleries/gallery.aspx?ID=305&p=2 - as we do not have an article on it. It is a glider called "woody jump". How does an inflatable glider work in theory?

Aren't the stresses that a glider meets something that inflatable is totally inappropriate for? If not, then could you talk about the theoretical possibility of my previous question in terms of a rubber outside shell that snaps shut for one configuration (either helicopter rotor or glider, whichever is the profile that fits inside the other) or can be inflated to change into the larger cross-section (helicopter rotor or glider) optimal shape?

This is not intended to be practical or anything like that. I ask these questions simply to gain understanding of fundamental principals of aerodynamics. thank you. 86.101.32.82 (talk) 17:07, 3 March 2013 (UTC)

That's quite a light design, so the stresses are much less than, in, say, a metal plane. However, inflatable wings can handle more stress than you might think, provided they have the proper cross-members. Those aren't just big hollow balloons, I bet, but rather separate chambers. And remember that the very first planes were made of canvas, string, and a bit of wood, so not all that strong, either. But, during heavy winds, you should avoid flying either those early planes or the inflatable ones. I take it it's designed for hobbyists, not serious flyers. StuRat (talk) 17:35, 3 March 2013 (UTC)

So, what's the worst that happens in strong wind? And without the strong wind - can the form of the inflated wing be optimal? (for completely still wind)? Or is it still going to be worse for some reason than a real fixed wing? 86.101.32.82 (talk) 17:59, 3 March 2013 (UTC)

In a strong wind the glider would be difficult to control, and the wings might rip apart. It is difficult to get thin wings with such an inflatable design. However, the reduced lift from having short, fat wings is compensated for by the lower weight. Most lighter-than-air (or nearly so) craft have similar trade-offs.

The flexibility of inflatable wings also provides the possibility for wing warping, but I'm not sure if this design takes advantage of that. StuRat (talk) 18:24, 3 March 2013 (UTC)

But who says "short, fat wings"? I mean, in the specific design I asked you about, we have a long wing that is a normal wing (either a normal pair of helicopter rotors or a normal glider wing) with a rubber shell. you can blow up the rubber shell (and possibly slightly turn the whole wing) to take on a new shape. Who says that has to be short and fat? especially given that it can be several separate components blown up along the length of the wing like this (-)(-)(-) (cross-section). i realize this is not practical in the slightest, but theoretically, what's wrong with the new long, inflated wings? 86.101.32.82 (talk) 20:01, 3 March 2013 (UTC)

They wouldn't be strong enough to support the lift if they were long and thin. If you add heavier materials to support them, then you lose the whole advantage of light, inflatable wings. One thing I might change is making the inflatable wings clear, with a black surface in the center, so that solar heating would make them warmer, and thus lighter. Of course, they would need to be flexible enough to allow this expansion. StuRat (talk) 20:18, 3 March 2013 (UTC)

I don't understand what you're referring to when you say "One thing I might change".. you mean on the Woody Jump? Surely the volume to surface area is so small, even if it were totally empty inside, the lift would be negligible. I don't think heating up (which reduces the density of the air inside) makes much of a difference, neither would filling it with helium etc. it's just not big enough. (I think).

But secondly, where you say that "they wouldn't be strong enough to support the left if they were long and thin" - how do you know, I mean if there is a rigid structure inside? (as in my example) For example, the rigid structure could specifically be joined to the surface by as many cross-members as you need that are also inflated. We're not talking about one long rigid inflated wing that has to keep rigid through its inflation, but rather, an inflatable portion over a fixed wing. That means it can be joined by supports/cross-members wherever you want. In this case, do you think there could be a viable design that is firstly a fixed wing with a rubbery uninflated portion over it, but if inflated, the rubbery portion would expand AND be supproted by cross-members? Or this would not exist for some theoretical reasons you can tell me now? Thanks. This is all just theory, no intention to build anything like htis. 86.101.32.82 (talk) 20:56, 3 March 2013 (UTC)

I wouldn't expect the lift from hot air inside to be much, but enough to justify the design change (a few ounces make a difference on a glider). Filling it with helium would also help a bit, but that gets expensive quickly, since you can expect it to leak out over time, so you'd need to top it off periodically. Alternatively, you could try to use a compressor to suck it back out after each flight, but you'd only get so much back.

As for a design with rigid wings that have balloon surfaces attached, what's the advantage there over just a fixed wing glider ? The whole point of making it out of inflatable parts is to avoid the weight from rigid wings (with another benefit being that's more portable, when uninflated). StuRat (talk) 21:13, 3 March 2013 (UTC)

StuRat, in practical terms my whole line of questioning is simply meant to increase my theoretical understanding of aerodynamics, so don't read anything more into it - no intention to build this or anything like that. So my question about "As for a design with rigid wings that have balloon surfaces attached," is whether it could be used as a theoretical framework for my exercise that I raised earlier: http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#second_theoretical_question_about_aerodynamics . Basically, as a theoretical question, I want to understand if starting with a long glider wing, and then selectively changing the angle of attack in sections along the length of the wing, and possibly pushing the whole thing off of center, we could build an aerodynamically 'efficient' helicopter rotor. It's not intended to really be practical or anything like that. Just "aerodynamically efficient.". Any thoughts? 86.101.32.82 (talk) 21:33, 3 March 2013 (UTC)

I'm afraid I don't know much about helicopter design, which is why I didn't answer that Q. Hopefully somebody who does know about it will answer soon. StuRat (talk) 21:53, 3 March 2013 (UTC)

There is something else I can add about gliders, though. You can also place solar panels on top, and use those to power small props. While this isn't strictly a glider, it doesn't require any fuel. Here's several NASA built: NASA_Pathfinder (they also had batteries, so they could fly at night). I see no reason why you couldn't combine an inflatable design with flexible solar panels and a small prop, to extend flight time more. StuRat (talk) 22:03, 3 March 2013 (UTC)

Well let's not complicate the question by adding solar panels, which are quite heavy. I think it's a quite appropriate question to ask: if the power source, motor, etc didn't even have to be on the plane, but you received a direct line of mechanical power (compressed air, whatever), then it terms of simple aerodynamic efficiency, could a glider wing turn in sections and inflate to become an efficient helicopter rotor? (possibly being pushed off a bit away from center). Or if not, why not? I realize we will have to let someone else answer. 86.101.32.82 (talk) 22:15, 3 March 2013 (UTC)

I recently had the privilege of getting up close to some Super Cobras. My first impression was, "wow, the rotor blades are the size of my Citabria wings!" (You can check the actual dimensions to be precise; this was just a first-impression reaction). My point is, some helicopter blades already look a lot like a glider wing - some even look like they've got the aspect ratio of Citabria wings. But, the thing to remember is that helicopter blades, fan blades, propeller blades, and fixed wings are all just airfoils. And when we talk about efficiency of these airfoils, we have to be careful to define "efficiency": the method we use to evaluate an airfoil's efficiency depends on what we want to use the airfoil for. A glider is intended to have a very very very high lift-to-drag ratio, so that the aircraft maximizes its glide slope. A Citabria wing is designed to provide high lift at low speed; this means that it has a poor lift-to-drag ratio (inefficient!) in comparison, but it also means I can get my aircraft off the ground before I hit the numbers (the POH lists a takeoff roll of 340 feet at gross takeoff weight, and you can find videos of Citabrias taking off or landing with ten-foot rolls in strong headwinds!) A helicopter rotor is different from both of these airfoils; it is designed to provide lift and remain stable while the helicopter is operating in its normal flight envelope. Moral of the story: "efficient" isn't good enough to summarize airfoil performance. Efficiency is a good summary for Carnot engines, but not for aircraft performance. You need a lot more numbers: including, but not limited to, stall speed, wing loading, lift to drag ratio, drag coefficient, ... and of course, it will help to sweep each of these parameters across a variety of conditions: atmospheric conditions like density altitude; attitude (angle of attack, including non-ideal attitudes like rolls, especially if you care about stall/spin performance); and of course, reliability, safety, weight, and so on. If aerodynamics were reducible to a single parameter, aerodynamical engineers wouldn't have earned a reputation for solving some of the hardest mathematical and engineering design problems ever surmounted! Nimur (talk) 22:54, 3 March 2013 (UTC)

Note: the name "woody jump" is incorrect. Laurent de Kalbermatten of Switzerland has developed two inflatab;e wing fliers; the "Woopy-Jump" hang glider and the "Woopy-Fly" ultralight. See [ http://woopyjump.com/ ] A Google search on those two terms will give you lots of information. --Guy Macon (talk) 12:06, 4 March 2013 (UTC)

Also note that Woopy has an internal aluminum and carbon fiber spar. See [ http://www.generalaviationnews.com/2010/05/woopy-and-the-one-hour-concept/ ] --Guy Macon (talk) 12:11, 4 March 2013 (UTC)

How to tell type 1 diabetes from type 2 ?

I ask because Diabetes#Diagnosis seems to neglect this, and I'd like to fix the article. StuRat (talk) 20:21, 3 March 2013 (UTC)

According to Diabetes mellitus type 2#Diagnosis, "If the diagnosis is in doubt antibody testing may be useful to confirm type 1 diabetes and C-peptide levels may be useful to confirm type 2 diabetes, with C-peptide levels normal or high in type 2 diabetes, but low in type 1 diabetes." Tevildo (talk) 20:32, 3 March 2013 (UTC)

Thanks. Perhaps that info should be copied into the main article. (I wonder why separate articles are even necessary.) StuRat (talk) 20:58, 3 March 2013 (UTC)

Not quite. There is no single gold standard test, but rather a combination of parameters. Type 1 diabetes is easier to define and is characterized by insulin deficiency with normal insulin sensitivity at all prodromal and early treatment stages, and by far the most common variety of type 1 is caused by autoimmune destruction of the beta cells. There is less relationship with obesity and a higher incidence in childhood. The insulin deficiency reaches more complete lack in fewer years. The genes so far discovered associated with type 1 diabetes are involved in regulation of the immune system. In contrast type 2 diabetes is characterized by both insulin resistance and by insulin deficiency. In the early years before and after the diagnosis, the insulin deficiency is partial but reversible insulin depletion after prolonged hyperglycemia can be as complete as in type 1, which is why low c-peptide levels are poor discriminants between the two. Type 2 has a strong association with obesity, especially in young patients. The genes thus far identified as associated with type 2 are nearly all involved with metabolic pathways of energy metabolism or islet development. Heritability of type 2 is stronger than type 1. The incidence increases throughout life, with relatively few cases in childhood. However children and adults with type 2 can have positive antibodies (IAA, GAD, ICA), but typically only one or two and at lower titers. Children and adults with type 2 can develop ketoacidosis because of the insulin deficiency. So you can make a set of parallel columns describing heritability, age, weight, ketosis, acidosis, and antibodies, and perhaps a third of newly diagnosed diabetic patients will have characteristics from both columns. Furthermore, as the number of mechanistically distinct types of diabetes continues to proliferate (dozens now), the old designation of type 1 or 2 is becoming obsolete. alteripse (talk) 21:09, 3 March 2013 (UTC)

Thanks. Also, is it possible to have both types ? Would the tests show this ? StuRat (talk) 21:16, 3 March 2013 (UTC)

This page claims that you can have both. --Guy Macon (talk) 22:06, 3 March 2013 (UTC)

Yes. Neither are rare diseases. I call it "type 1+2", and use to apply to adolescents who got ordinary type 1 but became heavy with time, have strong family history of type 2, and have other features of metabolic syndrome. It's not a formal designation. alteripse (talk) 03:08, 4 March 2013 (UTC)