Wikipedia:Reference desk/Archives/Science/2013 February 19

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February 19

contracting rabies

I have looked extensively for information that would tell me if deer or elk can contract rabies. I have never heard of these animals becoming infected and would like to know if it is possible and/or how common.98.22.220.148 (talk) 01:40, 19 February 2013 (UTC)

Yes deer can get rabies, e.g. [1][2], though rabies is rather rare for deer. Based on the first link, of the 7000 rabid animals found in the United States each year, about 5 will be deer in the typical year. Dragons flight (talk) 02:04, 19 February 2013 (UTC)

Thank you!98.22.220.148 (talk) 02:47, 19 February 2013 (UTC)

All mammals can get rabies, apparently birds also but I don't know if that's ever been found in the wild. A factor which limits finding rabid animals is their survival of the infective event; for instance, small mammals like mice and rabbits aren't found infected, apparently because they rarely or never survive the attack by an infected animal. In a similar vein, deer or elk are unlikely to survive an attack by an infected large carnivore like a cougar, wolf, or even a large dog; but also are unlikely to be successfully attacked by something small like a rabid fox or raccoon so wouldn't get infected in an attack they could survive. Just my opinion. Gzuckier (talk) 19:53, 19 February 2013 (UTC)

Double-slit experiment and scale

When performed on subatomic "particles", like electrons and photons, I understand that the resulting interference pattern associated with waves is produced. When performed with much larger objects, like bullets, no interference pattern is observed. So, my question is, at what scale does the transition from wave behavior to particle behavior occur, and how does it occur ? Is there a gradual change from one to the other, or an instant change ? We could try larger subatomic "particles", like protons and neutrons, small atoms, large atoms, small molecules, large molecules, etc., until we get to the size of a bullet. StuRat (talk) 04:00, 19 February 2013 (UTC)

By theory, ALL well-defined objects should be subject to wave-like properties, per the de Broglie relations; it's really an engineering problem and not a science problem; that is, even for bullets, there should be an associated wavelength which could be calculated given the mass and velocity of the bullet; knowing that wavelength would give you the way to construct a set of slits through which the double-slit experiment should be valid, the issue is in the actual construction of them, which may be a physical impossibility due to the restraints imposed by using real materials in the experiment, but again this is an engineering issue, not one in the theory. In actual experimentation (according to information at the Matter wave article), the largest particles shown to diffract experimentally (and thus display real wave-like characteristics) have a mass just shy of 7,000 atomic mass units, which would be about the size of a smallish protein molecule (for comparison, hemoglobin has a mass of about 64,000 amu.) --Jayron32 04:56, 19 February 2013 (UTC)

And, at that scale, do we get a pure interference pattern, like a wave ? StuRat (talk) 05:01, 19 February 2013 (UTC)

Again, there are no theoretical limits here, just engineering limits. You can calculate all the parameters; the size and distance between the slits, the parameters of the interference pattern you get, for any arbitrary object, from an electron up to, say, a star. The parameters work to infinity in all directions; there is no hard limit where any well defined object stops following quantum behavior. Instead, there's a limit where the difference between quantum behavior and classical behavior becomes smaller than tolerances of our measuring devices, or where the actual means to construct, say, two slits to diffract bullets becomes a physical impossibility. But the math should work, and we have no reason to suspect that it would be wrong per se, just that the actual construction of an apparatus to test it would be impossible. --Jayron32 05:25, 19 February 2013 (UTC)

(edit conflict) Someone should check my math, but I just did the calculation of a 20 gram bullet (0.020 kg) fired at a speed of 1000 m/s, and came up with a de Broglie wavelength of 1.91 x 10^-40 m. For comparison, the charge radius of a proton is 8.75 x 10^-16m, which means that you could fit about 200,000,000,000,000,000,000,000 or so de Broglie wavelengths of the bullet within the radius of a proton. If you can create slits small enough and close enough to run a double-slit experiment on something like that, you're a better man that I. --Jayron32 05:43, 19 February 2013 (UTC)

Clearly a bullet wouldn't fit through those slits. Does that mean there's a hard limit where the particle is larger than the required slit ? StuRat (talk) 05:49, 19 February 2013 (UTC)

It also depends on velocity; I believe (and I may be wrong on this assumption) that objects moving closer to the speed of light could fit through smaller slits, due to relativistic effects on their dimensions. So, depending on how fast you can get your bullet moving, you could get it to squeeze through any arbitrarily sized slit. Practically, of course, you are correct, eventually, your object size and your slit size are moving in opposite directions, and you reach a limit where the slits become too small to fit the object in question through, at which point the experiment becomes impossible. See below, where I found the results of an experiment where the slits were only about 500 times larger than the diameter of the object, which is still pretty close in size. --Jayron32 06:12, 19 February 2013 (UTC)

I don't think so. Relativistic length contraction will only apply to the axis along which the object is moving. Your relativistic bullet would be just as wide as before, but shorter. You'd also run into the issue of higher speeds producing ever shorter wavelengths. Someguy1221 (talk) 06:21, 19 February 2013 (UTC)

Like I said, I wasn't too confident on that part. So, there would be a real physical limit, which is where the shrinking slit size and the growing object size pass. --Jayron32 06:31, 19 February 2013 (UTC)

There are ways to "cheat". The simplest demonstration is to have slits that are much narrower than the object's wavelength, but weaker effects can allow one to demonstrate interference and other quantum effects even if that isn't the case. However, in that scenario one needs to do the analysis of the situation more carefully and the measurements are generally harder. In the C₆₀ molecule interference demonstration, the C₆₀ have a diameter of about 1 nm and passed through slits ~50 nm wide with a 100 nm separation. However, in this case, the de Broglie wavelength is only about 2.5 pm (i.e. 0.0025 nm). In other words the slits were already orders of magnitude larger than the de Broglie wavelength, so the waves would only be very weakly diffracted, but the quantum effect was still large enough to measure. (In this case "large enough to measure" meant diffraction peaks separated by about 20 microns.) Dragons flight (talk) 06:33, 19 February 2013 (UTC)

There are theoretical limits. First, the wavelength you calculated is smaller than the Planck length, so it probably doesn't make sense to talk about it without a theory of quantum gravity. Second, unless they're cooled to near absolute zero, bullets emit blackbody radiation which leads to environmental decoherence within a much shorter time than you'd need for the experiment. Third, even if you do this at very low temperature, bullets have a lot of internal state (they're malleable, for example), which would likely record which-path (welcher-Weg) information, which destroys the interference pattern. Any one of these alone makes the experiment impossible. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

And I'm also interested in the reverse Q: What's the smallest object which can be fired thru the double slits, without a detector to show which slit, that still doesn't exhibit an interference pattern ? StuRat (talk) 05:37, 19 February 2013 (UTC)

I'm not really good with the optics calculations, but roughly speaking the more massive the object, the smaller its de Broglie wavelength is, so the smaller and closer you'd have to make the slits in a viable double-slit experiment. So, what you would need to do is calculate the relationship between slit size and wavelength, and then figure out what the smallest slits you can make are, and then use the de Broglie wavelength equation to calculate what mass corresponds to whatever wavelength you can diffract with the smallest slits possible to make. That would be the practical upper limit for an object you could successfully run a double slit experiment on. --Jayron32 05:47, 19 February 2013 (UTC)

Just for an example of a good double-slit experiment using massive particles, here is the results of such an experiment run on Buckminsterfullerene molecules (C₆₀, mass = 720.64 amu) which showed interference patterns consistent with theoretical predictions based on calculated de Broglie wavelengths. The slit sizes here are really freaking small: it required 50 nanometer slits spaced 100 nm apart. The diameter of one of these molecules is about 10.18 Å (according to https://sesres.com/PhysicalProperties.asp), which means that the slits are about 500 times larger than the molecules themselves. At some point, you'd reach the point where the slits become smaller than the diameter of the particles; this may (or may not) represent some sort of physical limit. I think you can count on relativistic effects to allow for an object larger than the slit to pass through it (that is, by firing the object at some speed very close to the speed of light, you can still get it to pass through a slit which is smaller than it is, when the slit and the object are at rest relative to each other), but we're getting out of the realm where I'm capable of doing such calculations, or even discussing it confidently in broad terms. --Jayron32 06:06, 19 February 2013 (UTC)

I don't see how you could use length contraction to get an object through a narrow slit, given that only lengths in the direction of motion are contracted. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

Yeah, like I had already said above, I was wrong about that. I'm still wrong about that. --Jayron32 13:32, 19 February 2013 (UTC)

Oops, sorry I missed that. -- BenRG (talk) 06:48, 21 February 2013 (UTC)

Small correction: 10 Angstrom = 1 nm, so it's 50 times larger, rather than 500 times larger. -- 205.175.124.30 (talk) 22:19, 19 February 2013 (UTC)

Imaging C60 in double-slit experiment

This post has reminded me of something I meant to ask.

Given that buckminsterfullerene has a diameter of 1 nm, each molecule can be imaged with e/m radiation of over 300PHz, which is soft x-rays and up. Is it possible to use a hard X-ray camera pointed in the same direction as the slits, (normal to the direction of the C60), and then fire individual C60 molecules in the experiment, to track each molecule? Or does this violate wave/particle duality? CS Miller (talk) 20:49, 19 February 2013 (UTC)

Presumably, just like other attempts to tell which slit they use, if successful, this would destroy the interference pattern, and you'd see the simple sum of particles passing through both slits, at the detectors, instead. As for how it can do this, we have to imagine that the x-rays in some way disturb the particles. StuRat (talk) 22:00, 19 February 2013 (UTC)

For the second part of your answer, you are probably right StuRat, a 3,000PHz photon has 2 fJ of energy, enough to accelerate a 60*12 amu object to 57.7 km/s; unless the molecule can complete the experiment in a few microseconds, it will probably be forced onto the far end of the container.

For the first part, if the camera was far enough away for the photos to reach it, after the molecules hit their detector, then the observation can't affect the interference pattern. (I think, I'm not strong on quantum mechanics). CS Miller (talk) 23:18, 19 February 2013 (UTC)

It will affect the interference pattern, because the photons carry information about the particle path just as much as the photographic film later will. Regardless, I don't think you can make a shadowgraph of nanometer-scale particles using x-rays. -- BenRG (talk) 06:48, 21 February 2013 (UTC)

wireless electricity transmission

please give me the details that how it possible to transmit electricity without wires(wireless)? what are the recent researches in this field? as well as what is the future of this?? — Preceding unsigned comment added by 49.50.96.200 (talk) 08:11, 19 February 2013 (UTC)

The wireless power article would be a good place to start. -- BenRG (talk) 08:15, 19 February 2013 (UTC)

Transmitting small amount of electricity wirelessly over small distances is easy, you can use things like electromagnetic fields to convey power a few inches. Transmitting large amounts of electricity wirelessly a long distance is more problematic. Tesla wanted to do it with radio waves, but this is quite dangerous, inefficient, and it's difficult to do billing (current radio and broadcast/satellite TV does transmit a tiny amount of electricity wirelessly, but needs electricity from wires to amplify the signal (with the exception of a crystal radio). You could also point a laser at a distant solar cell, and transmit electricity that way, but this would be inefficient and require a clear line-of-sight. StuRat (talk) 09:39, 19 February 2013 (UTC)

Talking of fields, this video shows transmission in a field.[3] Unfortunately, the camera used is not sensitive enough to actually convey how amazing this is when demonstrating it to the doubting Thomas's and grandchildren. When your eyes become light adapted to the darkness the tubes are bright enough to read by. If a factory or office near you is replacing its tubes, the old ones can be picked up for a few cents each. I'm surprised that this demo didn’t use balancing coils to enhance the power -(as the tube are only four to six feet long).--Aspro (talk) 15:55, 19 February 2013 (UTC)

Back in the dawn of time when I used to subscribe to Popular Electronics, they had a project that was a crystal radio with a one transistor amplifier stage, which was powered by another crystal radio which was tuned to a powerful local station. Never built one, but how cool is that? Gzuckier (talk) 19:58, 19 February 2013 (UTC)

Not very cool at all actually. Other electronics magazines reckoned it would not work. So I decided to investigate. Well, it would work in theory. Trouble is, you need to produce a voltage exceeding the saturation voltage of the transistor (V_CEsat) and a few 10's of microamps for it to work. With the most suitable germanium transistors of the day, that's about 100 mV into 2000 ohm or so. With a realistically sized long wire antenna, you need to be within visual range of the power source transmitter to get that. And you need an earth connection, << 2000 ohm, as well I set up a long wire antenna in a park next door to a long wave navigation transmitter (2 kW), using a water pipe as earth and could not get enough for the transitor to amplify. Ratbone 121.221.37.9 (talk) 03:05, 20 February 2013 (UTC)

Nice way to force the big guys to support the little guys. Now if we can just get Microsoft to support Linux. :-) StuRat (talk) 20:05, 19 February 2013 (UTC)

In the 1980's Microsoft sold Xenix - their version of UNIX that would run on a PC. My employer at the time had databases running on it. It was ok to use & maintain, if lacking in features. It was a utter market failure and Microsoft sold it off to SCO who marketed it as SCO Unix. I have it, at employer's expense, on one of my home computers for training/experience purposes, but seeing as the vastly better and more common Sun Microsystems UNIX o/s with your choice of GUI is free for home use, I don't know why anyone else would bother. Ratbone 121.221.37.9 (talk) 03:14, 20 February 2013 (UTC)

See Space-based solar power as one possibility. Note that this isn't directly "electricity" being transmitted, rather solar power being transmitted as a microwave signal to the ground, which then converts to usable electricity. — The Hand That Feeds You:^Bite 23:24, 19 February 2013 (UTC)

Classification of animals

In here (page 95) the classification of animals is shown. I'm having trouble understanding how animals with tissue level of organisation are further divided. Can anybody please explain? Thanks. --Yashowardhani (talk) 10:30, 19 February 2013 (UTC)

Our body cavity article explains this pretty clearly -- see the section called Grouping. If you need more information, please follow up. Looie496 (talk) 16:21, 19 February 2013 (UTC)

Thank you so much, the article helped a lot. Could you please also explain how coelomates are further divided? --Yashowardhani (talk) 11:22, 20 February 2013 (UTC)

Is it possible to discharge electricity by alternating current (AC)?

In discharge tube, electric discharge takes place when we supply direct current (DC). If we supply AC instead of DC, will the electric discharge take place in the same way as in case of DC? 27.62.227.241 (talk) 11:17, 19 February 2013 (UTC)

Yes, however there is an important difference. With DC, there must be sufficient voltage to start the discharge, ytermed the striing voltage. Once the arc has started, a gnenerally very much lower voltage is required to kepp it going. With AC, unless the arc is quite large, as in arc welding, the will stop each time the voltage goes to zero, 100 times a second (120 times in USA and certain other countries). Hence with AC the peak voltage must be kept continuously above the strike voltage in order to keep the arc going. Keit 60.230.216.137 (talk) 12:28, 19 February 2013 (UTC)

Electric discharge in gases and arc lamp are two relevant articles. DMacks (talk) 16:30, 19 February 2013 (UTC)

One thing you should notice that, in discharge tube (DC) cathode and anode never exchange their position, on the other hand, AC is fluctuating. 27.62.227.241 (talk) 16:54, 19 February 2013 (UTC)

Biochemistry

is that right that Glucose and Phosphat (or phosphorous) are the main ATP sources (and thus, sources for short-time energy), while, Creatine and Fat are the main "long term energy" sources ?.

thanks.

All (or almost all) of the biological energy sources go through ATP. The question is how the body regulates the conversion. The process of glycolysis is the main energy generating pathway in heterotrophs, so typically glucose is thought of as a primary energy source. It's certainly the case that blood glucose, when available, is typically used as the preferred external energy source. In contrast, energy generation from fat (acetyl-CoA production by fatty acid degradation, which ultimately leads to ATP production through the citric acid cycle and oxidative phosphorylation) is more complex, so it typically reserved for long-term energy storage. Even then, a portion of the fat isn't used directly, but instead is used for gluconeogenesis to produce blood glucose. Fat, being more energy dense than carbohydrates, tends also to be better for long-term storage of energy, although things like glycogen are used for medium-term energy reserves. As to the other compounds, phosphate/phosphorus by itself is not an energy source. It's role in energy metabolism is to serve as a building block of things like ATP. Creatine per se isn't an energy source, at least anymore so than standard amino acids are. The reason it's mentioned is because of creatine phosphate, which, like ATP, is a high-energy phosphoester that can serve as a store of energy. It's not used as an energy donor itself, though, instead functioning as a "buffer" for ATP in places like muscles, regenerating ATP when ADP levels are high, and being created itself from ATP when ATP levels are high. But that's more of a short/medium-term storage rather than long-term storage. -- 205.175.124.30 (talk) 22:13, 19 February 2013 (UTC)

Maybe the OP means polyphosphate (a universal acidocalcisome component, not just in polyphosphate-accumulating organisms) which holds energy-rich bonds comparable to those in ATP. For review see [4] [5]. I'm actually not quite sure what overall percent of the cell energy budget it represents in typical organisms. Wnt (talk) 23:25, 19 February 2013 (UTC)

Pantoon?

what is pantoon — Preceding unsigned comment added by 210.212.95.98 (talk) 12:57, 19 February 2013 (UTC)

Do you mean pontoon? StuRat (talk) 15:58, 19 February 2013 (UTC)

Or pantaloon or Pantone or platoon?--Shantavira|^{feed me} 16:12, 19 February 2013 (UTC)

Or Panton, pantun, Penton or Panettone? Red Act (talk) 16:16, 19 February 2013 (UTC)

Or Phantoon... --Tardis (talk) 01:56, 21 February 2013 (UTC)

Can you please give this word as used in a sentence. Pantoon could refer to a boat which as StuRat points out is an alternative spelling. We need the context to take this further.--Aspro (talk) 16:10, 19 February 2013 (UTC)

• Could also be Pantone (a system for color management)? Looie496 (talk) 16:13, 19 February 2013 (UTC)

The OP has 4 entries in the last 3 1/2 years. So figure it will be at least autumn before he gets back to this question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:43, 20 February 2013 (UTC)

How do you polish a copied key to make it work better?

I've noticed that duplicate keys made by automated machines have groove marks on the cut surfaces, transverse to the length of the key. I think the groove marks make a duplicate key difficult to insert into and pull out of the lock. Is there an easy way to polish way the groove marks without affecting the function of the key? --108.2.210.178 (talk) 13:29, 19 February 2013 (UTC)

I've always used 400-600 grit "flatting paper" (carborundum type sandpaper that is normally used wet esp. in the automotive bodywork industry.) It's hard enough to remove any superficial burrs but fine enough that it will take some hard work to actually alter the shape of the key. An emery board (used for manicures) also works well for the same reasons. 196.214.78.114 (talk) 14:03, 19 February 2013 (UTC)

Common "Pin tumbler locks" only depend on the height of the high spots and the depth of the low spots on the key. What makes the key harder to insert and remove is the grooves on the sloping parts. As you insert the key, the pins inside the lock have to slide up and down those slopes - so if they are rough, you'll find the key hard to insert and remove...AND you'll wear out the lock prematurely too.

Hence, so long as you don't reduce the height of the 'hills' or the depth of the 'valleys' of the key - you should be able to gently smooth off the slopes between them using a very fine emery paper or a polishing stone on a Dremel (or something similar) without affecting the ability of the key to open the lock. I would only do this on a duplicate key for which you still have the original!

SteveBaker (talk) 14:12, 19 February 2013 (UTC)

Rope walking

I have seen people walking on ropes taking a long stick in their hands. I know they use the stick to balance their body. How can we explain this in scientific terms? 27.62.227.241 (talk) 15:03, 19 February 2013 (UTC)

Our article on tightrope walking explains the basic mechanics -- the increased weight, coupled with the increased distance from center of mass, increases the moment of inertia which reduces the angular acceleration of the person. This slows the tipping process and gives the person time to correct. — Lomn 15:12, 19 February 2013 (UTC)

There's a similar counter-intuitive experiment you can do. Try balancing a ruler and then a yardstick (or meter stick) on your fingertips, vertically. You'd think the smaller one would be easier to balance, right ? Nope, you need to make much faster adjustments to keep it steady than the longer stick. StuRat (talk) 16:02, 19 February 2013 (UTC)

similarly, weight one ennd of a yard/meter stick and you'll find it's easier to balance vertically on a finget with the heavy end up in the air, than with the heavy end down at the finger end. Hey, that would be one heck of a field blood-alcohol test for cops to use, no? "Your honor, we could only slide the weight 6 inches down the meter stick before the defendant could no longer balance it, he was clearly inebriated?" Gzuckier (talk) 20:03, 19 February 2013 (UTC)

Phone signal disconnecting a mouse

Hi, this may seem like a question for the computing desk, but I am not interested in how to fix the problem, just the scientific reason behind what is happening - I don't even intend to fix it, it fascinates me so much I kind of like it...

My PC at home has a standard wired mouse connected via USB to the back off the PC. Every time I have my mobile phone on my desk, and recieve a call/text on it, the mouse "disconnects", the cursors won't move and the Windows "hardware disconnected" sound plays. I have observed this happening too many times for it to be a coincidence, and I actually have to sit far back from my PC if I want to use the mouse whilst on the phone. My question is why is this happening? Is it the phone signal inducing a current in the wire? The signal interfering with the infared sensor on the bottom?

To reiterate: nothing is particuarly special aboout the set up; it is a plastic cheap-ish mouse with a plastic coated wire connecting it via USB to the motherboard at the back. Again, nothing is special about my phone, and I have observed it happening with multiple phones (I am not sure about mice). Thanks! 80.254.147.164 (talk) 15:24, 19 February 2013 (UTC)

I have observed a "galloping sound" on my PC speakers when the cell phone is near the wires. So, I do believe it's picking up interference on the wires, in your case, too. I would hope that it would "reconnect" once the text is finished. Does it ? StuRat (talk) 16:08, 19 February 2013 (UTC)

Yes it does, I thought the "galooping" sound was due to the signal interfering with the magenets in the speakers? 80.254.147.164 (talk) 16:27, 19 February 2013 (UTC)

I did an experiment where I wrapped the speaker wires around the cell phone, then sent a text, and the galloping sound was much louder, despite the distance to the actual speakers being the same. StuRat (talk) 16:37, 19 February 2013 (UTC)

Clever, I might do the same with the wire on my mouse - see if I can get to happen away from the actual mouse but wrapped in its wire. I will report on my findings tommorow. YEAHH SCIENCE!!!! 80.254.147.164 (talk) 16:41, 19 February 2013 (UTC)

Cool, please let us know how it goes. StuRat (talk) 16:43, 19 February 2013 (UTC)

Sounds like Electromagnetic interference to me. The interesting question is whether it is the microcontroller inside the mouse or the USB host on the motherboard that is getting confused. Cand you try another mouse on that computer and/or another computer with that mouse? --Guy Macon (talk) 19:48, 19 February 2013 (UTC)

Yeah - it definitely sounds like electrical interference. I would suggest adding a ferrite bead to the mouse cord - but to be honest, it would be probably be both cheaper and easier to replace the mouse instead. You might also try changing the length of the cord - if it's acting as an antenna, that might fix it...but again, it's not an easy thing to do.

What's happening (probably) is that the mouse cord is acting like a radio antenna. The abrupt emission of radio waves from the phone to the cell tower acknowledging that it's there is evidently just the right frequency to be picked up by the USB cord and that's evidently enough to cause either the mouse or the PC to decide that something went horribly wrong. When you halve the distance between the antenna and the transmitter, you quadruple the amount of energy produced in the antenna. So when you consider that the phone signal has to be picked up by a cell tower several miles away - and when the mouse cable is just inches away, the power is going to be millions of times more than the cell tower sees. Moving the phone further from the USB cord would obviously be a good idea.

SteveBaker (talk) 20:26, 19 February 2013 (UTC)

determination of pesticides by QuEChERS method using LC-MS/MS

HI I WOULD LIKE TO KNOW WHETHER IT IS POSSIBLE TO USE CLOPYRALID AS THE INTERNAL STANDARD IN THE DETERMINATION OF TRYCLOPYR IN WHEAT GRAIN COMMODITY.WILL IT NOT ELUTE AT THE SAME TIME AS THE COMPOUND OF INTEREST OR COURSE ANY INTERFERENCES OF SOME SORT? — Preceding unsigned comment added by Tsbu (talk • contribs) 15:29, 19 February 2013 (UTC)

For reference, we have clopyralid, Triclopyr, Quechers and Elution. Rojomoke (talk) 18:56, 19 February 2013 (UTC)

I have too little experience to give you a good answer, but my impression is that it depends on the precise method used for the gas-liquid chromatography - what column, what gas, I think even the temperature program? The obvious thing to do is to make up three samples with either compound or both, and see what you get. Wnt (talk) 17:36, 20 February 2013 (UTC)

Polarized lens sunglasses

1) Is it true that, if you have two polarized lenses, arranged in series, so each photon passes thru both, and each lens blocks 50% of the light, that by varying the angle of rotation of one lens, so it's either in the same orientation as the stationary lens (both horizontally polarized or both vertically, for example), or at a 90° angle (so one is horizontal, and one is vertical, for example), you can vary the total blocking of light from 50% to 100% ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Yes, or nearly a 100%. If the light is bright enough some light leaks through.--Aspro (talk) 16:18, 19 February 2013 (UTC)

Why is that ? Is it some flaw in the polarized lenses, or does light have the ability to change it's polarization from one lens to the other, or is it just that you can never quite get exactly 90° ? StuRat (talk) 16:23, 19 February 2013 (UTC)

Because attenuation is not a "binary," "completely on" or "completely off" effect. Polarized light incident on a differently-polarized medium is attenuated. If we analyze one single photon, we can say "one single photon has a probabilty P% of passing through the medium." And if we analyze a large ensemble of photons as a continuous incident light source, then we say "the polarizer attenuates the light to P% of its incident value." Nimur (talk) 16:28, 19 February 2013 (UTC)

OK, so if it's not 100% blockage, what percent can be achieved ? StuRat (talk) 16:35, 19 February 2013 (UTC)

That depends on the thickness of the glass and the sensitivity of your experiment. At some point, increasing the attenuation of "wrongly-polarized" light will also increase the attenuation of "correctly-polarized" light, and soon we have an opaque material. Are you asking for the optical properties of many common glass? My go-to reference, Applied Photographic Optics, has a full chapter on polarization, and another on attenuation, and has lots of details about commonly-used glass. We can easily build polarizers that attenuate 50% of all light and 95% of oppositely-polarized light. Sunglasses are probably in that ballpark. Nimur (talk) 16:43, 19 February 2013 (UTC)

So, then, my set-up would vary from 50% to 95% blockage, as well, depending on the angle of rotation ? StuRat (talk) 17:08, 19 February 2013 (UTC)

2) Does anyone make such a pair of sunglasses ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Doubt it. We are talking rays not photons (which are packets of light energy). The medium used to filter light of one orientation only (were talking around 500 nano meters) have an angle of error and internal refraction. Hold two of the best polarization filters up to the sun and I reckon you will still see it. No 100%.--Aspro (talk) 16:36, 19 February 2013 (UTC)

P.S. Why are you asking? If you want to block out light competently why not use a thick bit of cardboard? Cornflake packets are cheap and readily available. A really low tech and practical solution. --Aspro (talk) 16:47, 19 February 2013 (UTC)

I'd like a pair which I can adjust. I'm aware of the ones which darken automatically in bright sunlight, but that fails in four respects:

A) They lag the light change, so, when driving under a bridge, everything can go black. I'd rather adjust my sunglasses going into a dark space, than have to take them off and put them back on. (Less chance of me poking myself in the eye this way.)

B) They don't adequately account for a single bright point of light ahead, like the old Airstream trailers (which should have been banned as a road hazard).

C) They don't account for my preference for light levels. Sometimes my eyes are bothering me and particularly photo-sensitive, so I'd like darker lenses. (Alcohol may be involved here.) :-)

D) At times I want to block more light to one eye than the other, right up to 100%. If I just had an eye drop in one eye, for example, which causes photosensitivity. (Yes, I could use an eye patch for this, but then I'd feel the need for a hook arm, peg leg, and parrot on my shoulder.) :-) StuRat (talk) 16:54, 19 February 2013 (UTC)

You don't strictly need any property of polarization, then; except to fine-tune the darkness. You can stack extra neutral density filters until the glass is as dark as you like, and use one rotatable crossed polarizer for fine adjustment. Nimur (talk) 17:08, 19 February 2013 (UTC)

Yes, but keep in mind that I don't want the minimum to go too high, either. For example, I wouldn't want sunglasses that can be adjusted to block between 90-99% of the light, as 90% might well be too much, in some cases. Of course, I could take them off, but then it might be too bright. Ideally they would be fully adjustable from 0% to 100%, but I don't think that's possible in something light enough for sunglasses, at present. Perhaps sunglasses with very tiny LCDs could do that, but this would increase the complexity and weight. StuRat (talk) 17:17, 19 February 2013 (UTC)

If it's any help, one can (or could) buy a similar arrangement for SLR cameras with one polarized filter rotating on another which is screwed to the front of the camera lens. A competent handyman could build a pair of these double adjustable filters into a spectacles frame. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 18:07, 19 February 2013 (UTC)

Cool, have any links ? StuRat (talk) 18:48, 19 February 2013 (UTC)

Here's a page of them from an online catalogue (click the less-than-obvious 'Learn more' links in the descriptions for further details). {The poster formerly known as 87.81.230.195 212.95.237.92 (talk) 14:04, 20 February 2013 (UTC)

Yikes, looks like the required 4 would cost me about 100 pounds. Any for 100 yen ? StuRat (talk) 05:29, 21 February 2013 (UTC)

could probably cobble something together from a couple pairs of the polarized variety of 3D glasses filched from the local showing of whatever is being foisted upon the public. Gzuckier (talk) 20:10, 19 February 2013 (UTC)

Note that the currently-popular RealD Cinema uses circular polarizers; it is possible to "cross" those, but it's more complicated than with the linear variety. (For instance, the two sides of a circular polarizer are not interchangeable.) --Tardis (talk) 04:42, 21 February 2013 (UTC)

A couple of "products" (I don't see any actual ordering information) that claim to do this with two different technologies:

http://www.allproducts.com/optical/hurricane/as01_print.html

http://www.photonics.com/Article.aspx?AID=29481

--Guy Macon (talk) 21:05, 19 February 2013 (UTC)

The first one claims to use my concept, but I'm confused, since they aren't circular. How could you rotate non-circular lenses relative to each other without having bits sticking out ? StuRat (talk) 21:55, 19 February 2013 (UTC)

Displacement vs. Distance

Suppose a person marks two points along the circumference of a piece of pizza. The person may measure the border of the pizza and calculate the distance from Point A to Point B along the perimeter of the pizza. That will be the distance. The displacement from Point A to Point B, if they are across from each other, would be the diameter of the pizza, while the distance, if measuring the border, is only the half-circumference of the pizza. In this example, the displacement is the shortest distance. I wonder how you apply it to the universe, which astronomers describe as being linear, parabolic or hyperbolic-shaped. The distance will probably mean how far one travels from Point A to Point B in the universe, but the displacement is presumably the shortest distance, even though this distance may be difficult to actually to calculate, because one may need to know how curvy is the curve of the universe. Is displacement really practical in the latter case? 140.254.226.230 (talk) 17:29, 19 February 2013 (UTC)

This concept of displacement requires that it be possible to embed the space in question in a higher-dimensional Euclidean space, and that there be essentially only one way to do this. In your example, the one-dimensional pizza border is embedded in our three-dimensional Euclidean space. However, there are many non-Euclidean geometries that cannot be embedded in a finite-dimensional Euclidean space, and even for those that can, the embedding is often not unique. So basically the answer is that unless an embedding space exists and we have some way of observing it, this concept of displacement is not practical. Looie496 (talk) 18:08, 19 February 2013 (UTC)

I suppose there are similar concepts in space flight. For example, the distance a space ship must travel between Earth and Pluto is not simply the minimum distance between the two, since you can't go that way. For one, the target is always moving, and, also, the spaceship will be rotating about the Sun with the velocity of Earth, more or less, once launched, not travelling straight out radially. If you add in detours around other planets on the way, the distance traveled becomes even longer.

Similarly, travel on Earth usually means along the surface, not through the crust. A great circle route is the shortest route on the surface, but detours are frequently needed, so total distance traveled from point A to B can be far more than the straight distance from A to B. StuRat (talk) 18:40, 19 February 2013 (UTC)

A great circle route is actually a good example of a geodesic. A great circle route is a geodesic within the 2-dimensional manifold of Earth's surface. Red Act (talk) 19:43, 19 February 2013 (UTC)

Although the concept of a displacement vector only really works in a Euclidean space, there's a related concept of a geodesic, which works in both Euclidean space and in a curved spacetime. Geodesics do not require any assumption that spacetime is embedded in a higher-dimensional space. Of all the spacelike curves between two events that are spacelike separated, the shortest such curve is a geodesic between the two events. In a Euclidean space, the length of the displacement vector between two points is the same as the length of the geodesic between the two points. Red Act (talk) 19:07, 19 February 2013 (UTC)

Really simple question about boiling water

I'm learning to use a wood stove that works simply by heating up and letting the warmth spread through the house, rather than through a central heating system; as such, its surface is quite hot. Upon advice from friends who have experience with these things, I've placed a small pan (one of these with the rolls removed) on top and filled it with water, so that the house will be humidified; I typically fill it by filling a cup at the sink and pouring it into the pan. The surface of the furnace is hot enough that it boils water that drips off the cup (even though it's cold water), but to my confusion, the water in the pan doesn't boil: tiny bubbles form at the bottom and the water gradually becomes steam, but despite sitting on top for hours it never boils. Why not? The Leidenfrost effect doesn't seem to apply here, since I filled the pan before starting the fire; the water has warmed gradually as the fire's gotten hotter. However, I witness the effect when little bits of water drip off the cup. Nyttend (talk) 17:48, 19 February 2013 (UTC)

Is it a cast iron stove? [[6]] spells out the basics of how this works, but cast iron heats up slowly and dissipates heat slowly - it is not a very fast conductor of heat. — Preceding unsigned comment added by 207.189.106.4 (talk) 17:57, 19 February 2013 (UTC)

It's cast iron, but I'm not sure how that's relevant. The iron under the pan (which is aluminium) is the same temperature as the iron on which little bits of water drip, so it's conducting just as much heat into the water. Nyttend (talk) 18:05, 19 February 2013 (UTC)

Aluminum foil (which this pan basically is) is a sucky heat conductor, especially given that its direct contact area with the stove is probably pretty small. I bet that you could place that pan on the stove without any water and press your finger against the bottom for a second or two without burning yourself (but if you want to try it, try a brief touch first to make sure). If you used a proper saucepan and the stove was hot enough, the water would certainly boil -- people cooked on stoves like that for ages. Looie496 (talk) 18:16, 19 February 2013 (UTC)

Aluminum isn't the best conductor, I agree. A copper pot would conduct heat better. Also, make sure that the pan is touching the stove continuously. (You sometimes get a warped pan that only touches at a few points, greatly reducing the conduction.) Ensuring that both the stove and pan are free of cruft like carbonized food is also important, as that's a good insulator, too. StuRat (talk) 18:25, 19 February 2013 (UTC)

I don't recommend this method of humidification, unless you have a freakin' big pot. The problem is that the water evaporates too rapidly, and burns the pan up when it runs dry. Also, scale accumulates on the pan as the water evaporates, leaving only it's minerals (unless you used distilled water, but that's expensive). I do actually use this method, with a huge junk stock pot at a low flame, so it takes about 2 days to evaporate. I'm unlikely to neglect it for that long. Also, note that this method of humidifying a home only makes a slight difference, as water vapor escapes through the wall cracks, chimney, etc., almost as fast as this method can add it, and, if you do manage to get the humidity up much, in winter, it may condense on nearby windows, possibly causing mold on the sills. StuRat (talk) 18:25, 19 February 2013 (UTC)

• You simply don't have enough heat capacity, meaning the temperature is high enough but the quantity of heat is not. Imagine trying to boil that water with a candle which also burns at above boiling temperature but provides only "heat quantity" for a real tiny tiny cup.TMCk (talk) 18:38, 19 February 2013 (UTC)

• I'd expect that the total heat capacity of the wood stove is more than enough to boil the water, it's just not being effectively conducted into the pan. StuRat (talk) 18:46, 19 February 2013 (UTC)

• Yes, but you don't get the whole heat capacity of the stove to the pot. (And heat is disapearing quickly once it reached the pot.)TMCk (talk) 18:57, 19 February 2013 (UTC)

Aluminium (regardless of spelling) is a very good heat conductor indeed - worse than copper, but much much better than stainless steel. See List of thermal conductivities. And that may indeed be the problem here. Heat is conducted into the pot via a relatively ineffective interface (the uneven surface of the foil on the uneven surface of the stove), and distributed very evenly through the pan. So all of the surface of the pan serves as a cooling surface, which probably keeps it slightly below 100 °C. --Stephan Schulz (talk) 20:23, 19 February 2013 (UTC)

If you have a cooking thermometer, preferably one with a probe, you could measure the temperature of the uncovered pan of water then put a cover on it and see if the temperature rises. Evaporation from the surface into the room might be keeping the temperature down. A pan or teakettle of water on a stove to humidify the air is a time-honored practice. But one small pan of water a day will not humidify a whole house very much. Edison (talk) 23:57, 20 February 2013 (UTC)

Buy a good humidity meter. Even then, they are not accurate but will serve as a rough guide ( a wet and dry bulb thermometer -even better). You may fine 35 to 40% relative humidity comfortable. A pan does not need to boil. If it does, you may end up with mildew in the colder parts of the house were it condenses. Below 40% this should not happen unless the walls/windows are very cold. The dryer the air, the more the warm water will evaporate due to partial pressure. However, by boiling, you will 'force' more water vapour into the air than partial pressure of water vapour would naturally course the water in the pan to evaporate. Which can lead to the mildew and stuff. PS. Just a little liquid water when evaporated creates an big increase in relative humidity - hence the need for a meter to see that your not over doing it. --Aspro (talk) 19:24, 23 February 2013 (UTC)

Gun safety

A lot of firearms accidents seem to involve people not realizing a gun was loaded. Why is it not possible / why hasn't it become normal for guns to be designed in such as way as to make it really obvious whether there is a round in the chamber? — Preceding unsigned comment added by 207.189.106.4 (talk) 17:55, 19 February 2013 (UTC)

It's nowhere near safe to make the round visible from the outside, since breech-loading weapons can only work if their chambers are sealed — otherwise the gases escape in wrong directions. Cartridges don't normally (in my experience) do anything to the rest of the gun when they're just sitting in the chamber, so I can't imagine a way that the presence of the cartridge could be used to change the way something else looks or feels. Nyttend (talk) 18:09, 19 February 2013 (UTC)

A few people have been in the news lately because of accidentally firing a loaded weapon that was in their breeches Gzuckier (talk) 20:19, 19 February 2013 (UTC)

Hmmm, bullets should change the ability of a magnetic field to be transmitted from one side of the chamber to the other, slightly, so you could possibly devise such a device using this principle. The added complexity of the gun might not be welcomed, though. StuRat (talk) 18:45, 19 February 2013 (UTC)

Clearly it's possible to do this. Mechanical, magnetic, electrical, optical - you can come up with a dozen ways to measure whether there is a bullet in the chamber or not. Why it hasn't become a standard feature is because there isn't a market for such weapons - people who buy weapons are clearly more concerned about cost than safety - and the legal/fiscal framework to compel such things hasn't been put in place in the target markets for gun manufacturers. A more subtle (but just as lethal) problem is that guns with magazines will typically leave one round in the chamber when you remove the magazine - and will fire it if the trigger is pulled. This fools a lot of people who think that removing the magazine unloads the weapon and many, many people have died as a direct result of this. There is a very simple, cheap fix for it that locks out the trigger when the magazine is removed - yet many weapons don't implement it. Why? It saves lives - but it's not always done. If we can't get something as simple as that fixed - then there is no chance for more difficult improvements such as you suggest. SteveBaker (talk) 20:07, 19 February 2013 (UTC)

Because in self-defense situations, it's not unusual to pop out the magazine before firing off that last round (for faster reloading) -- so if the trigger was locked when the clip is removed, it could actually cost the person his/her life. 24.23.196.85 (talk) 06:21, 20 February 2013 (UTC)

That's an idiotic argument. Tell me, how many deaths per year are caused by civilians being unable to reload in time in self-defense situations? On the other hand, this paper suggests that around 16 lives per year would be saved by these devices. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

Steve, please don't use words like "idiotic" here. Always be civil. StuRat (talk) 18:53, 20 February 2013 (UTC)

Indeed. Even something as simple as allowing the hammer to rest a fraction of an inch further in when there is no bullet in the chamber to impede it, which would then actuate some sort of indicator. Gzuckier (talk) 20:14, 19 February 2013 (UTC)

Which brings up something else I've wondered about; why do some manufacturers of semiautomatic handguns (maybe other varieties, I don't know) not have a safety? Because they're designed for use somewhere where instant use is a requirement and a safety would get you shot? All I can think of.Gzuckier (talk) 20:16, 19 February 2013 (UTC)

Actually a number of handguns do include what's called a loaded chamber indicator (LCI). On my Walther PK380, it's a simple notch cut in the back in the chamber which allows you to see if a round is in the chamber. Taurus and Glock handguns designed the extractor to "pop" out just behind the ejection port. Many others do as well. However, if you search google for handguns with loaded chamber indicator, you'll see a lot of people calling them stupid. Their argument is basically that if know enough to check the LCI, then you should know enough not to be stupid with guns and if you don't know enough to be safe with guns, you won't know enough to check. You can take what you want from that argument.

To Steve Baker's question about the gun firing with the magazine out of the weapon, that's known as a magazine disconnect. Our article says they are standard on the Browning Hi-Power and some Ruger rifles and pistols. It also notes that California has required magazine disconnects since 2007. Arguments against magazine disconnects are similar to arguments against LCI's but also include the convenience of not loading a clip for a single shot. Again, make of that what you will.

Finally to Gzuckier's question. There are wide variety of safeties in use. My Walther has a external safety switch which rotates a bar that should prevent the hammer from hitting the firing pin. I actually hate that safety and don't feel very safe with it because it allows the hammer to fall and relies on the bar not bending and being in tolerance. My SIG Sauer P250 has no external safety, but it has an internal automatic safety. The firing pin is locked in place and can't move until you pull the trigger back about half way and the internal safety releases. Glock advertises that it has 3 safeties, all internal, including a trigger safety, a firing pin safety and a drop safety. So basically whether you see a safety lever or not, any gun should have at least one safety that will prevent the gun from accidentally going off.Tobyc75 (talk) 01:08, 20 February 2013 (UTC)

Of course any mechanical safety system can fail or be bypassed. The only way to truly make a gun safe is to practice safe gun handling. That includes keeping guns and ammunition secure and away from children. It includes teaching children that guns are not toys and how to safely hand one. Finally it includes keeping them away from those who would harm themselves or others and addressing the problems or illnesses that make them a hazard.Tobyc75 (talk) 01:17, 20 February 2013 (UTC)

Thanks - interesting - Toby - to your point, I'm just astonished that police and military, who are presumably among the best trained in gun handling, still manage to end up confused about whether there is a round in the chamber. — Preceding unsigned comment added by Tilapidated (talk • contribs) 05:31, 20 February 2013 (UTC)

Loaded chamber indicators are actually VERY common on all but the cheapest firearms (for example, my Beretta has an extractor that sticks out and shows a small red panel when there's a round chambered); however, they are NOT foolproof, and even if it shows the chamber to be unloaded, you should still pull back the slide and take a look with your own eyes, just to make doubly sure. 24.23.196.85 (talk) 06:26, 20 February 2013 (UTC)

You'd think they could design one which sometimes incorrectly says it's loaded, but never incorrectly says it's unloaded. Shining a laser thru a pair of tiny holes in the barrel, such that it would have to pass thru the bullet to indicate an empty chamber, would be one such design. StuRat (talk) 06:35, 20 February 2013 (UTC)

Lasers require a power source, though. Lasers run out of juice, what happens? Does it just not register a bullet? (Bad) Does it refuse to disengage the safety? (Really bad if you're in a life-threatening situation) Unfortunately, it's just not practical. — The Hand That Feeds You:^Bite 12:26, 20 February 2013 (UTC)

I wouldn't make it disable the gun. If the battery was dead it just wouldn't indicate that the chamber is empty (which a light would indicate if the battery had juice when the chamber was empty). So, it would be back to the original gun, where you can't tell if it has one in the chamber or not. StuRat (talk) 18:57, 20 February 2013 (UTC)

Again this says that 20% of the roughly 450 deaths due to handgun accidents in the USA every year would be prevented by this device - 85 people a year would not be dead if such devices were universal. How many people would die each year due to forgetting to change the battery and then entering into a life-threatening situation when actually discharging their gun would save their lives. Numbers please? SteveBaker (talk) 15:28, 20 February 2013 (UTC)

Read more: http://www.time.com/time/magazine/article/0,9171,152446,00.html#ixzz2LS9ntPcI

Re: cops & military, they're still human. Even with all the training in the world, someone can be absent-minded or careless. Especially if something becomes routine (cleaning a gun), it's way too easy to fall into a habit of not checking because you "know" you unloaded it, just like last time. Except you didn't this time... — The Hand That Feeds You:^Bite 12:33, 20 February 2013 (UTC)

There was a case in the military recently[7] where a trained infantryman decided to scare his buddy in an effort to cure his hiccups...shot him in the head by mistake. Not just because he pulled the trigger by mistake, not just that he had a live round chambered when he thought it was a blank - but also because he thought that a blank fired at short range would be safe...three mistakes in a fully trained man who was around guns all the time. Whatever happened to "Never point a gun at something you don't want killed"? No amount of training stops this kind of ridiculous stuff from happening. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

A good story sure saves a person a lot of years in prison, even when nobody believes it. Wnt (talk) 17:30, 20 February 2013 (UTC)

From Gun safety:

"Treat firearms as if they are loaded

This rule is a matter of keeping a certain mindset. The purpose is to create safe handling habits, and to discourage reasoning along the lines of, "I know my gun is unloaded so certain unsafe practices are OK." The proposition "the gun is always loaded" is used as a shorthand, even though it may be assumed—or even positively known—that this is not true of a particular firearm.

Many firearm accidents result from the handler mistakenly believing a firearm is emptied, safetied, or otherwise disabled when in fact it is ready to be discharged. ... If a handler always treats firearms as capable of being discharged at any time, the handler is more likely to take precautions to prevent an unintentional discharge and to avoid damage or injury if one does occur." --Guy Macon (talk) 08:55, 20 February 2013 (UTC)

That rule would also have saved the life of Jon-Erik Hexum, who made a different error — he believed, correctly, that the cartridge was a blank, but was (apparently) not aware that discharging a blank cartridge at close range is potentially lethal. --Trovatore (talk) 08:59, 20 February 2013 (UTC)

On a related note, a local man died last year because he was showing off the safety features on his new gun. Pointed the gun at his head & pulled the trigger... but he hadn't fully engaged the safety, so it slipped.

Safeties are good, but they are not guaranteed to protect you, especially from user error. Just like a seat belt can help save your life in a car accident, but not if you failed to lock it fully in place. — The Hand That Feeds You:^Bite 12:35, 20 February 2013 (UTC)

If that gun incident didn't make the Darwin awards, it should have. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:41, 20 February 2013 (UTC)

Hey, we agree on something! :) Wnt (talk) 17:26, 20 February 2013 (UTC)

I feel confident in saying that "Try not to shoot yourself in the head" does not constitute medical advice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:41, 21 February 2013 (UTC)

Re: the laser — that's still a hole in the chamber through which gases would inappropriately be escaping, so it would be a bad idea regardless of the laser's merits. Nyttend (talk) 12:36, 20 February 2013 (UTC)

http://injuryprevention.bmj.com/content/9/4/307.abstract bears reading. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

• My Ruger mark III has a Loaded chamber indicator and cannot fire without a magazine.165.123.233.100 (talk) 17:48, 20 February 2013 (UTC)

• "Treat firearms as if they are loaded:" I still concur whole hardheartedly with Guy Macon . A ten year old properly drilled in gun safety until it become automatic will follow through on auto-pilot even when he grows older and gets his conscious mind distracted by the odd pretty looking girl passing by. A few colour photographs of the result that can come from accidental discharge adds encouragement to follows the rules until it becomes automatic. Little fancy indicators as an aid memoir are no substitute for repetition of action. I'd feel safer with a kid taught this way than with an adult that has just bought his first real gun. The big problem is, that these ruddy kids are usually better shots than I am; dam-it.--Aspro (talk) 18:21, 20 February 2013 (UTC)

• I agree completely. Even when I take a firearm out of a case, and I know I was the last one to touch it, I always check to see if it is loaded. It only takes one mistake to ruin a life.130.91.93.207 (talk) 18:50, 20 February 2013 (UTC)

• Exactly. You know that it was unloaded but you still check -every-time. It is not being over-cautious it's just automatic good gun sense. And it takes no effort when it has become automatic - in fact, it it goes against the grain to to try and behave differently. There is no excuse for accidentally discharges.--Aspro (talk) 19:02, 20 February 2013 (UTC).

I used to look at the reinsurance claims for the National Rifle Association's death and dismemberment policies, from a safe distance (London). Goodness, what a lot of foolish people. My favourite was an idiot who caught the trigger on a coat hook on his bedroom wall and shot his own leg - it was dismemberment insurance, so it must have been amputated later. The rather sadder ones were people who killed or maimed their own children, or allowed them to play with their loaded guns with predictable results. Get a safer hobby. Using the figures in the BMJ article linked by SteveBaker above, it seems that there were 1,005 firearms-related accidental deaths in the US in 2000. Alansplodge (talk) 21:59, 22 February 2013 (UTC)

Vacuum metastability event implosion?

All the sources I've seen state that freeing ourselves from the current horrid false vacuum where we slog along hindered by the heavy shackles of the Higgs mechanism will cause a zero mass vacuum state. Is there any chance it will do the reverse and unmask the "true weight" of all the virtual particles causing a sudden Big Rip? Hcobb (talk) 18:52, 19 February 2013 (UTC)

If you have a good internet source for what your talking about could you do me the favor of linking to it? I'd like to read it. μηδείς (talk) 19:15, 19 February 2013 (UTC)

It depends a bit on what you mean. If you define the "true vacuum" as a state where the vacuum expectation of all fields is zero, then that is pretty much equivalent to eliminating the Higgs mechanism and assuming all particles are massless. However, it isn't entirely obvious whether such a state would have lower total energy than our current state, or whether there are stable states intermediate between the current state and true vacuum. One can imagine that there might exist other stable vacuum configurations where the universe effectively has different physical coupling constants and the masses of fundamental particles are very different than their present values. However, we don't really have a concrete theory for why any of the coupling constants have the specific values that they do. Without an understanding for why the universe has the physics that it does, it is deeply speculative to imagine fundamental changes to that physics. So while it is in some sense "possible" under some theories that the universe could move to a configuration with very different masses (even heavier masses), such theories are essentially untestable within the limits of our present understanding, and hence we can't really draw many meaningful conclusions about such a possibility. Dragons flight (talk) 00:27, 20 February 2013 (UTC)

Vacuum metastability and the Higgs mechanism are two different things. The Higgs mechanism works because the "true" vacuum state of the Standard Model has a higher energy than nearby non-vacuum states, so it's inherently unstable (not merely metastable), and as the universe cools it inevitably ends up in a minimum-energy non-vacuum state, and we are small perturbations of that state, which we normally think of as the vacuum. It would make sense to call this a "false vacuum", but I can't remember ever hearing the term used in this context. There is no way the universe could ever "end up in" the true vacuum of the Standard Model since that is still as unstable as it ever was. Vacuum decay, on the other hand, happens when there's another vacuum that is stable and has a lower energy than our pseudo-vacuum, but is separated from it by a huge potential barrier, so our vacuum is almost stable but eventually will tunnel to that lower-energy vacuum. Our vacuum is called a false vacuum in that context. There may be no such lower-energy vacuum; if there isn't then our pseudo-vacuum is completely stable. Tunneling to a lower-energy vacuum leaves the energy difference in the form of real particles, so it does effectively "unmask the true energy density" of the false vacuum. I'm not sure that could be considered the energy of virtual particles. Different vacua effectively have different particles (virtual or real) and different laws of physics. Familiar particles like electrons make no sense in the true Standard Model vacuum, though technically all the pieces are there. -- BenRG (talk) 08:02, 20 February 2013 (UTC)

applications

what are the applications of the ultra thin capacitors? — Preceding unsigned comment added by 115.240.6.7 (talk) 19:20, 19 February 2013 (UTC)

Film_capacitor#Applications. SteveBaker (talk) 19:57, 19 February 2013 (UTC)

Speakers & moisture/humidity

Can you tell whether audio speakers have been damaged from humidity? Are there any specific kind of noises or loss of sound quality it might have? Thanks. Clover345 (talk) 21:06, 19 February 2013 (UTC)

Paper cone woofer? Polymer dome tweeter? Horn?

The basic tests you want to do are a complete visual inspection, then run some very low frequency tones (not too loud!) and listen for anything rubbing or rattling. Something like this: http://www.youtube.com/watch?v=BdQbQa-rIbw or this: http://www.youtube.com/watch?v=lfXXQfG1T3g --Guy Macon (talk) 23:06, 19 February 2013 (UTC)

How long was it humid for? This might allow mould to grow on the cone (is there antifungal agents doped onto the it?). CS Miller (talk) 23:22, 19 February 2013 (UTC)

Unless you plan to buy them, sell them, or make an insurance claim, wouldn't it just be easier to continue using them, and, if unsatisfactory, replace them ? That is, if they are damaged, but you can't tell by normal listening, does it matter ? StuRat (talk) 23:26, 19 February 2013 (UTC)

I have a feeling the sound might have got a bit cloudy Clover345 (talk) 23:46, 19 February 2013 (UTC)

Leave them in a warm, dry, well ventilated area for a day or two. Might be that the cones are damp and therefore heavier then what they should be. It's possible that could affect the sound. Vespine (talk) 02:39, 20 February 2013 (UTC)

I imagine it might differ by type of suspension; acoustic suspension (i.e. sealed box) shouldn't be affected too much, but the kind where the cone is suspended by a zigzag support of resin impregnated fabric or some such might well be affected by moisture/humidity. (In addition to how the stiffness of a cardboard type cone would affect breakup, traveling waves, etc.) Gzuckier (talk) 20:53, 20 February 2013 (UTC)