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June 17

NIR and static

Hello

I had a question about Near Infra Red Spectroscopy. If we were conducting the measurements on a powder sample, is there any potential for the electrosatic forces within the powder to affect the readings in anyway?

Many thanks

114.77.39.141 (talk) 12:44, 17 June 2013 (UTC)[reply]

Yes - in science, almost everything has some effect on almost everything else. I would not consider the presence of an electrostatic field to be a primary contributor to the infrared spectrum for most materials. But, it is detectable - at least in some materials, with some very specialized equipment. For example, a near-field optical microscope can detect Raman scattering, and the spectrum of the Raman-scattered light may be affected by an applied electric field. In fact, I know of a specific professor who specializes in this sort of thing, and you can read his publications-list; and here is Electric field gradient effects in Raman spectroscopy (Physical Review Letters, 2000). I don't think powdered substrates are very good candidates for an NSOM microscope experiment; but in principle, the application of an electric field does have a small and measurable effect on the scattering spectrum. For most cases, in ordinary spectroscopy using ordinary equipment, the DC electric field has no significant effect on the infrared spectrum of a sample. Nimur (talk) 17:41, 17 June 2013 (UTC)[reply]

Dinosaur's genders

There was a line in the "Jurassic Park" film that said that dinosaurs could change their gender, or even have offspring by themselves when in a time of need. Just to confirm it: that was a huge artistic license, and in the real world dinosaur's reproduction did not work that way, right? Cambalachero (talk) 14:28, 17 June 2013 (UTC)[reply]

Did they claim that the dinosaurs of old did that? I don't recall them saying it. What I do recall is them saying that the dinosaurs in Jurassic Park had that trait because the bits of DNA that were missing from the archeological samples were replaced from frogs who do, in the present day, show this ability in times of need. Dismas|^(talk) 14:35, 17 June 2013 (UTC)[reply]

Of course there's much artistic license there, but it does not seem impossible. Our knowledge about dinosaurs is limited, but the process you describe, which is called Parthenogenesis has been observed in some modern-day reptiles (I'm talking about having offspring by themselves, not changing their gender). - Lindert (talk) 14:37, 17 June 2013 (UTC)[reply]

(EC) Well, we can't really be sure if dinosaurs could change sex or not. As I recall, the book had some "rationale" for this plot device. The idea was the partial genomes recovered were supplemented with frog DNA. And it is true that some frogs (and fishes, and a few other things) can change their sex, even after sexual maturity. The common example of this is the Common Reed Frog, you can find other examples by googling things like /frog fish sex change/. I don't think the book or movie had the dinos selfing, but I could be mistaken. Lastly, not to nitpick too much, but recall that gender is a social identity in humans (and perhaps a few other social animals), while sex is the biological concept. SemanticMantis (talk) 14:38, 17 June 2013 (UTC)[reply]

Temperature-dependent sex determination occurs in reptiles but not birds. It would probably be hard to figure out if it happens dinosaurs, which are generally agreed to occupy the "space" between reptiles and birds. Roger (Dodger67) (talk) 17:23, 17 June 2013 (UTC)[reply]

More specifically, dinosaurs lie between birds and crocodilians, not the much more distant lizards and turtle. Crocodilian eggs are known to beinfluenced in sex by external temperature, but I am unaware of sex change in adults. That usually occurs in species where the female is the larger sex (if the one large female is removed from a group of smaller males, the largest male will turn female), but this is not the case in crocodilians. μηδείς (talk) 18:16, 17 June 2013 (UTC)[reply]

Put another way, birds are dinosaurs, a subgroup of the theropods :) SemanticMantis (talk) 18:32, 17 June 2013 (UTC)[reply]

Yes, but all that proves is that some branches of the dinosaurs can't/couldn't do it. We still don't know whether some could. Actually, birds can kinda/sorta change sex. This article and others indicate that about one in 10,000 female birds will spontaneously change into males towards the end of their lives. Female chickens will grow rooster tails, start crowing and become quite defensive about males trying to muscle in on their hareem. However, they don't completely finish the job - they may change plumage and behavior and in most outward ways appear to be male - but they don't grow primary sexual organs to match - so they can't reproduce as males. There is no particular reason to assume that dinosaurs were unable to do that - so perhaps they did. However, that doesn't fit with the plot point in Jurassic park which was that somehow the dino's were breeding even though they'd all been created as females...so we're left with some very dubious handwaving about frog DNA, yadda, yadda, yadda. SteveBaker (talk) 18:47, 17 June 2013 (UTC)[reply]

That's like saying that my great aunt is changing into a great uncle because she's sporting a mustache :)). Dauto (talk) 14:18, 19 June 2013 (UTC)[reply]

As I recall, the book made it pretty clear that the sex change was an accident based on the frog DNA, and unexpected by the experimenters. As for real life, I would speculate pretty confidently (uh-oh...) that we can't know, because we're still short on dino sequence, and a fossil is a snapshot, not a video. (One of the beautiful things about biology is that certain speculations like this that are logically foolproof are often wrong) Wnt (talk) 23:27, 17 June 2013 (UTC)[reply]

Why do some algae make PUFA (poly unsaturated fatty acids)?

Some species of algae make a large amount of PUFA. This leads me to ask the question of, why? What are the functions of PUFA for single celled organisms? As I get it, one of the reasons is to maintain membrane fluidity under a variety of temperature and salinity conditions. But, why do different algal species make chains of varying lengths? For instance, some make C20:5 others C22:6. What's the added advantage of an extra double bond? Especially considering that these organisms tend to inhabit the same ecological space (thus enviromental effects are the same). If anyone has any ideas, or can refer me to papers published on the subject, I'd be eternaly grateful. 137.224.252.10 (talk) 14:53, 17 June 2013 (UTC)[reply]

As I've commented recently, it is hard to say "why" evolution does something. But I should point out that every organism has a cell membrane, made up of phosopholipids, typically 16-20 carbons long according to the article (which sounds right). Even in humans, which you would think would do more to regulate such things internally, polyunsaturated fatty acids incorporate into membranes and change their mechanical properties concerning "rafts" of lipid-modified proteins, cholesterol etc. [1] If you can name the species you have in mind it would be easier to try to research further about the specific system, but tracking exactly why two extra carbons are used by one rather than the other can't be easy, and might even be chance. Wnt (talk) 17:01, 17 June 2013 (UTC)[reply]

Race (biology)

The article Race (biology) is kind of incomplete. I still want to know how do biologists put into words the difference between humans who belong to what's socially considered different races. I understand that the socially relevant definition might be biologically inaccurate, but how do you express that? OsmanRF34 (talk) 17:04, 17 June 2013 (UTC)[reply]

Existing human races aren't different enough for scientists to consider them subspecies, which would lead to terms like Homo sapiens causcasicus. Individual traits which are considered racially salient include the cephalic index, objective descriptions of human skin color, eye color, and human hair. There are other traits like Steatopygia and the epicanthic fold, blood types, limb length, tooth shape, lactose tolerance, and many other things that can vary along with what is perceived as race. μηδείς (talk) 17:38, 17 June 2013 (UTC)[reply]

The problem is that many of these indicators vary more within a "race" than between races. That is the source of the statement that "race has no biological basis in humans". --Stephan Schulz (talk)

Right, your quote is a good answer to Osman's final question. It's not that the social notion of race is biologically inaccurate, it's that it is biologically unfounded, or perhaps ill-defined. SemanticMantis (talk) 18:36, 17 June 2013 (UTC)[reply]

That's a rather facile and unhelpful, but typical denial. Something like "naive social notions of race are rarely rigorously defined or helpful biologically" would be much more accurate. The desire to remove the term race from all scientific discussion is a political one, not a scientific one. μηδείς (talk) 19:01, 17 June 2013 (UTC)[reply]

I agree with μηδείς. Unless you believe that skin color varies more within a race (defining by a society) than between races, you have to admit that there is something biological there, and that some societies consider these differences to group people. It's not all chaos when it comes to the social identity. OsmanRF34 (talk) 22:44, 17 June 2013 (UTC)[reply]

The problem even with this trait is you are referring to, skin colour, is that if you go solely by it you will often be highly mislead. Someome with dark skin could easily be more closely related to someone with light skin. This shouldn't exactly be a surprise. A chimpanzee (either species) is far more closely related to a a human than a New World monkey even though both the monkey and chimpanzee have a lot more fur. And Opossums are quite distantly related to primates despite some having shared features like opposable thumbs and a prehensile tail. Nil Einne (talk) 00:17, 18 June 2013 (UTC)[reply]

To be fair to Stephan, if you define the traditional three old-world races, then compare the nominally Caucasian Saami people and Tamil people, you are going to find a far greater difference in skin color than you will betweeen any various populations of Sub-Saharan blacks. But that is taking a very specific and limited definition of race as if it were the only way that four-letter word beginning with arr could be used. Obviously it is quite reasonable to talk about the racial differences between Madagascans and Tanganyikans, or between Ainu and Japanese, as opposed to the linguistic or religious differences between such peoples. Arguing that the word has no use, or that there are no scientific correlates for some of the word's various senses, is simple sophistry. μηδείς (talk) 01:16, 18 June 2013 (UTC)[reply]

Biologists usually talk about differences in terms of ancestor groups and geographical regions. For example a paper might refer to people of sub-Saharan African descent, or people of Polynesian descent, etc. Looie496 (talk) 18:39, 17 June 2013 (UTC)[reply]

There are biological terms for groups of a species which vary by less than those of two subspecies. There's a population, a breed (as in cats or dogs), and a color phase, to start. Those seem closer to what we call "race", in humans. Of course, it's complicated because there's so much interbreeding between historically distinct populations in humans. So, we're all "mixed breeds", if you want to put it in those terms. StuRat (talk) 19:46, 17 June 2013 (UTC)[reply]
- Presumably the races arose due to lengthy isolations of groups from each other in prehistoric times. With that isolation having been significantly compromised in relatively recent times, and with more and more cross-race children being produced, the notion of race is getting increasingly murkier. We've got a ways to go, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:42, 17 June 2013 (UTC)[reply]

See Haplogroup. The way people have been classifying race is sort of like a dog pound that gets lots of French poodles and chihuahuas. Something is either a French poodle, a chihuahua, or "sort of like one or the other". Or, of course, it could be Spanish-speaking, in which case it is opted out of the classification scheme entirely. ;) Though what's sort of clear is that by and large, genetic variation beyond a certain point is called "black". Wnt (talk) 20:03, 17 June 2013 (UTC)[reply]

Spanish-speaking chihuahuas? I didn't know they really existed! 24.23.196.85 (talk) 20:15, 17 June 2013 (UTC)[reply]

Were you expecting it to speak Norwegian, perhaps, hmmm? Bielle (talk) 01:22, 18 June 2013 (UTC)[reply]

Conservation of momentum in time dimension

Is momentum something that applies and is conserved in all dimensions? So if I push something back in time, I can be accelerated through time? Or is that nonsense? --92.19.68.88 (talk) 23:20, 17 June 2013 (UTC)[reply]

First of all, there's no way to "push something back in time" -- this would in itself violate the laws of physics. 24.23.196.85 (talk) 23:37, 17 June 2013 (UTC)[reply]

I don't understand. Could a mass A travelling through time at a greater rate than another mass B, collide elastically with mass B and transfer some of its energy, increasing the rate of passage through time of B? Or do those laws apply specifically to three dimensions of which time is not one? --92.19.68.88 (talk) 23:48, 17 June 2013 (UTC)[reply]

You can interpet a particle moving back in time as its anti-particle moving forward in time. So, pushing an electron to move back in time is equivalent to that electron getting annihilated by a positron that it collides with. Two photons will be created, you do obviously have conservation of energy and momentum in the conventional sense. Count Iblis (talk) 23:54, 17 June 2013 (UTC)[reply]

If the OP would be so kind as to define acceleration "through time..." we might possibly answer the question. Acceleration is the rate of change of the change of position per unit of time. (In other words, the second derivative of position with respect to time). Is the question supposing to ask about the rate of change in the change in time per unit time? That quantity makes very little physical sense, whether it is expressed in plain English or expressed mathematically. Things don't travel through time; they change with respect to time. In other words, the latter part of the OP's question is nonsense. Nimur (talk) 00:18, 18 June 2013 (UTC)[reply]

Are we moving along a time dimension like a cart moves along a track in, say, x dimension? Or is that nonsense again? 92.19.68.88 (talk) 00:48, 18 June 2013 (UTC)[reply]

Obviously we are not moving along time in a cart! So the direct answer to your question is "NO!" But your question can be answered with a little bit more substance, albeit with a lot of abstraction - if you're willing to think a little bit abstractly.

In physics, we use very precise terminology. This helps us avoid logical errors or semantic ambiguity.

Matter has position. We say something has moved when its position changes: displacement. Let's say we have an object with a measurable position. In classical physics, we define this type of object to be a particle - just a thing with a position. If we measure a starting position (on the x-axis, for example), and a final position, we have a displacement - let's call it Δx for a displacement along the x-axis. If we know when we took the starting measurement, and when we took the final measurement, we also have a change in time: let's call it Δt. The average velocity is therefore, by definition, Δx/Δt. We can talk about the particle moving on the x axis during the experiment time. We can say that the object was at a position x₁ at time t₁. Equivalently, we can use time as a generalized coordinate and describe a position ( x₁, t₁) - but this is just a different way of describing the same event.

When we describe motion in this way, we are conducting the science of kinematics - the pure mathematical relationships of motion. When we attribute these motions to observable physical law, we are progressing to the science of dynamics - the study of physical motion.

In kinematics, we can easily consider time as just another coordinate, but when we study dynamics - in any of its forms, including the modern style relativistic mechanics, we find equations of motion where the dependence on time is not symmetric with respect to the dependence on position. One very trivial example of this is a simple case of energy conservation. We find that in many cases, potential energy and kinetic energy are interchangeable, but the dynamics of the real world show us that the dependence on position is a first-order effect; and the dependence on time is a second-order effect. We call this coupled first- and second- order time-space relationship Hooke's law and we use it to describe simple harmonic oscillation, one of the simplest and most fundamental physical descriptions of motion. (Some people use this to model the behavior of a "spring").

So: we can use mathematical abstraction to describe displacement in space, and displacement in time, using the same language; but when we study even the most simple cases, we quickly find that time- and space- do not behave in the same way. Dynamical systems almost always exhibit different properties - rates of change, stability, and so on - with respect to time and with respect to position. Nimur (talk) 01:12, 18 June 2013 (UTC)[reply]

Nimur's very excellent and easy to understand explanation is the inherent reasoning behind Minkowski space, which is the four-dimensional space created to do the geometric calculations behind special relativity. The four dimensions in Minkowski space are not identical. Three are "space-like" dimensions, which behave like space, and one is a "time-like" dimension, which behaves as time does. Space and time are all different dimensions, but they do not behave the same way, and cannot be treated equivalently, so one's "motion in time" is not equivalent to one's "motion in space" and one cannot discuss the two concepts as though they were interchangeable. --Jayron32 12:12, 18 June 2013 (UTC)[reply]

Yipes. The OP has asked a reasonable question, but the answers confuse and miss the point. An object does not have a position in space or time without specifying a slice through spacetime (e.g. "now"): it has a world-line through spacetime, and acceleration is a change in angle of this worldline: a curve in spacetime. Objects do not travel through spacetime. Energy–momentum is conserved in all four dimensions. — Quondum 01:50, 18 June 2013 (UTC)[reply]

Last week, the term "now" referred to last week; today it refers to today. Presumably if that change were to happen more quickly, it would be an example of the kind of thing the OP is talking about. Card Zero (talk) 01:53, 18 June 2013 (UTC)[reply]

Isn't that a bit like saying if a metre were longer, things'd be further apart? If by "that change" and "quickly" you are referring to some concept of movement through time in terms of elapsed time, you're confusing things. By "now" I simply meant a given instant in time as perceived by some observer. — Quondum 02:20, 18 June 2013 (UTC)[reply]

This is a sort of have-your-cake-and-eat-it-too question. There is no meaning in the idea of changing your rate of travel through time. You always go through time at a rate of exactly one second per second. Looie496 (talk) 05:08, 18 June 2013 (UTC)[reply]
- unless you speed up. --Jayron32 12:12, 18 June 2013 (UTC)[reply]
  - ... but it's your observation of someone else's time that appears to be "speeded up". Your own time remains always one second per second. Dbfirs 15:34, 18 June 2013 (UTC)[reply]

According to Noether's theorem the consevration of (linear) momentum arises from (or is, at least, intimately connected to) the invariance of physical laws under arbitrary translations in space. The equivalent conservation law that arises from invariance under translations in time is conservation of energy. Gandalf61 (talk) 13:09, 18 June 2013 (UTC)[reply]

June 18

Homozygote-to-heterozygote assortative mating

Are there any known examples of heterozygous genetic traits subject to assortative mating, but for which homozygotes prefer heterozygous mates and vice-versa? (This would be equivalent to the same allele coding a disassortative recessive trait and an assortative dominant trait. The reason I ask is that if autism-spectrum disorders were partly the result of a partially dominant trait, then people "square enough for the peg and round enough for the hole" would more often become partners and parents of those that needed them, as I have anecdotal evidence to suggest.) Neon Merlin 03:25, 18 June 2013 (UTC)[reply]

I have no answer here, only the observation that the same thought had occurred to me. I think the 'square enough/round enough' phenomenon you're describing is what's known as the 'broader autism phenotype'. If anyone can supply some genetics insight here, I'd be fascinated. Thanks! AlexTiefling (talk) 11:37, 18 June 2013 (UTC)[reply]

That article mentions disassortative mating, which I think is what you want (heterozygous mating with homozygous preferentially and v/v) - it's a keyword that will pull up things like [2]. You might also be curious about [3] (MHC disassortative mating?). Note that our article gives the opposite speculation - assortative mating - about autism. Wnt (talk) 21:57, 18 June 2013 (UTC)[reply]

Audio Source Signatures and Transforming

Given samples of two sources/instruments/voices performing/speaking the same piece in identical fashion is it possible to workout a transform between the two so that given new samples of one, we could transform it into a decent approx. of the other? For example, given a violin and an acoustic guitar playing various scales at various rates, could we generate an algorithm to map violin pieces to guitar pieces? What about for voices and speaking (This is my primary interest, but the situation is interesting in general)? Finally, what about less specific cases, for example: changing a male voice into a "female" voice (not a specific one, just removing male characteristics and adding feminine ones); or, with music, changing a string instrument to a brass version of it? I'd be interested in any information pertaining to this, including info on what characterizes one source from another (and the science/mathematics of it). Thank you for any help:-)Phoenixia1177 (talk) 04:52, 18 June 2013 (UTC)[reply]

To give you an entry into the literature, what you are asking for in technical terminology is a digital filter that transforms a recording of a violin into something that sounds like a guitar, or a recording of a male voice into something that sounds like a female voice. All of these things can be done, but some are simple and others required a very sophisticated filter. The main thing that gives a sound source its character is its power spectrum, but there are other important things too -- for example a guitar is plucked while a violin is usually played with a bow, and it is very difficult to transform a plucked sound into a bowed sound. Looie496 (talk) 15:06, 18 June 2013 (UTC)[reply]

This is definitely not easy stuff. There is software out there (eg this one) that can extract the pitch and duration of notes from simple music. (This is generally called "music-to-MIDI" because MIDI is the lingua franca of music synthesis) - and once you have that, you can relatively easily produce synthesized music played on any other instrument for which good synthesis exists. But if you have complicated polyphony or lots of different instruments playing different parts, then extracting the note information is much harder - perhaps impossible. Some software can do this in realtime - so that you can play music on a guitar and have it sound like a pipe organ or a xylophone...but, again, it's quite limited. Most good software takes longer to do the transcription than the music takes to play - so you can only use it on recordings.

There are "voice changers" out there (just google "voice changer" and you'll see a bazillion of them) - but they mostly just shift the pitch of the voice up and down or add distortion of one kind or another. They don't change other "characteristics" that might identify the gender of the speaker.

There is software out there that can make synthetic voices from sound samples of real people. I heard a very convincing demo of Winston Churchill reading some modern text that was created by dumping all of his recorded speeches into some analysis software - deducing the characteristics of his voice and then using that to synthesize his new speech. But software like this is quite new and specialized - it would probably require you paying a company who specializes in this kind of thing to do that work for you. I don't think the process is entirely automatic either.

SteveBaker (talk) 15:05, 18 June 2013 (UTC)[reply]

Thank you both for the answers:-) In general, I have an interest in this subject, but I do have an oddly specific need for a part of it. Supposing that I, a man, recorded my voice speaking with a female rhythm, vocabulary choices, inflection, etc. what would I need to do to it, mathematically, to make it passably feminine? I'm not wanting to do anything nefarious, but am making an fps for my own interest and use and don't feel like hunting down voice actors. Obviously, what I'm proposing isn't going to end up with a great sound for female characters, but it sounds fun and a neat side project to learn something from. (I've acted both male and female roles extensively, and written them, so I can imitate how a female speaks outside of actual physical properties.) On this elaboration, additionally, would it be feasible to modify a given masculine voice to sound like a different male speaker more easily? Phoenixia1177 (talk) 05:57, 19 June 2013 (UTC)[reply]

With regard to voice transformation, some work was done by NASA in the 1960's with a view to using analogue methods of bandwidth compression, which were never used. I remember they published an interesting paper, the essentials of which are: 1) the human voice comprises 3 frequency bands, low, originating in the chest & contributing to the quality of the voice; midband originating in the throat, contributing mainly to the the speech evelope and to the identity of the speeker, and high, originating in the mouth, contributing the intellence (ie conveyed meaning) of the speech. To convert male speech into female sounding speech, you need to suppress the mids and substitue new mids at higher pitch and with less harmonic structure. For best illusion, you need to shift the lows up in pitch a bit. You need to leave the highs alone, or you'll get a Donald Duck voice with poor diction. None of this is easy. I cannot find the NASA paper now, but this may give you some clues for your own search.

If you have (or a friend has) good electronics construction skills, you may find it easier to try the 1940's VODER approach - using a key or finger controlled electronic voice. See http://www.davidszondy.com/future/robot/voder.htm. Scroll down until you find the video clip. Do not be discouraged by the sound quality - the machine was built by a chap interested in encription and novelty, not high quality sound. Operators needed to build up considerable skill to operate this machine. However, about 30 years ago, myself and some other workers revisited the VODER idea for helping children who had lost their voice due to cancer and for who a throat box artifical larynch is not a option. The usual approach was to give them a pocket computer with a text-to-speech program, but the sound is so unnatural that people tended to ignore it. Or a device with some pre-recorded emergency messages ("please, where is the toilet?", "please phone my mum on 456-98765") which also tended to get ignored. And conversations were impossible due to the delay in typing. The idea was that they could take everywhere a pocket size VODER machine, which might be possible with 1980's electronics instead of 1940's electronics. We found that producing a tolerable child voice to match the child was not difficult, but we coudn't do an adult (male or female) voice, as to do that you need a full size hi-fi loudspeaker. We found that using the key arrangement of an English stenography/court reporter machine (which is a bit like a multi-key computer mouse, with 5 keys positioned to naturally fall under each thumb and finger tip. Different combinations of key pressed simultanously code for each steno "sound") and the right choice in key coding with pressure coded volume, made it easy to learn. A bright 8-year old could learn to make useful speech in a few hours, sounding much better than computer text-to-speech software, and could easily do it fast enough for a natural conversation. With the steno keyblock in the right hand, and a pitch control in the left, they could do a pretty good job at singing! Our project was not very successful however. Batteries then were not good enough, and we couldn't make it cheap enough. — Preceding unsigned comment added by 124.182.180.102 (talk) 07:01, 19 June 2013 (UTC)[reply]

Thank you for the response, very interesting. Unfortunately, I'm not good with electronics, nor do I know anyone who is. However, I will track down the NASA paper; it sounds quite useful. The VODER looks intriguing, I'll have to read up on it more; looking around on this topic has led me to a lot of articles on speech synthesis, which while different is related and fascinating. Thank you very much:-)Phoenixia1177 (talk) 07:16, 19 June 2013 (UTC)[reply]

my 2001 bmw 740i is rattling

what do i do? i can't figure it out and ain't got no money. it rattles upon slow acceleration and is a light vibrator noise coming from my right rear wheel. — Preceding unsigned comment added by 108.212.70.237 (talk) 05:38, 18 June 2013 (UTC)[reply]

I'm not a mechanic, but my personal opinion is that your wheels need to be balanced. Lucky for you, this can be done pretty easily and inexpensively at most tire shops. (BTW, if you "ain't got no money", perhaps you might consider selling your luxury BMW and buying a more affordable car to make ends meet?) 24.23.196.85 (talk) 06:13, 18 June 2013 (UTC)[reply]

Hmmm.. A 2001 740i could have been purchased for as low as $5000 if in poor condition and with no maintenance logs, even though it is a top line luxury vehicle. Sometimes young guys buy these before realising that a car costs a lot more to own than the purchase price, so the question could be genuine. Check the driveline: Check each universal joint. These rwd cars have a split prop shaft like trucks and some GM cars. Check the prop shaft carrier/bearing underneath the center of the car. When the resient mounting fails you get just the symptoms you describe. If the carrier and bearing are ok and the universal joints are ok, check things like engine mounts and suspension components. Note that if engine is misfiring one cylinder this can combine with other problems to cause rattles during mild acceleration. Also note that if te car has been correctly serviced by properly certified mechanics since new, all these faults are just about impossible. — Preceding unsigned comment added by 124.182.43.219 (talk) 10:20, 18 June 2013 (UTC)[reply]

I agree with the above suggestion. If you don't think you can do the checks yourself, look for an underbody shop that will provide a free inspection. They'll lift it up, look over things, and show you exactly what has gone wrong and what needs to be replaced. They'll provide you with an estimate, which I would expect to be $75-$250 in labor (assuming you're in the US) on top of the normal cost of the parts, depending on the exact problem. From there you can decide whether it is worth it to handle the repair on your own or not. 209.131.76.183 (talk) 14:30, 18 June 2013 (UTC)[reply]

It is unfortunate that you don't have the money to get it looked at by a professional. Wheel vibration has to be taken very seriously because the causes can be anything from something as simple as a balance weight fallen off of the rim - all the way up to a problem with wheel bearings or a broken axle that can literally cause the wheel to fall off at freeway speeds! With a car as old as this one, wheel bearing issues are quite likely - and if the car was for sale at a suspiciously cheap price, that could easily be the reason why!

It often takes an expert to figure out which of those things it is. At the very least, I'd want to get it put up on a lift so that the wheel and it's associated suspension parts can be examined properly. When you know how serious the problem is, you can judge whether you can fix it yourself, or whether you can afford to get someone to fix it for you - or maybe it's a problem you can just decide to live with (very unlikely in the case of wheel vibration!).

If you absolutely must do something yourself:

I suppose it could be something as simple as a loose lug nut or a bad tire (look for suspicious bulges or other signs that it's not perfectly round and smooth)...those are things you can easily check - but it's relatively unlikely.
You could jack up that corner of the car (make sure it's in gear or in park and with the parking brake on!) until the wheel is just off of the ground by a half inch or so - then try to wobble the wheel with your hands - both side-to-side and up-and-down. If you don't know what to expect (and I guess you don't), try the same thing with the wheel that's not causing vibration. Does they feel the same? If you can feel a definite difference between them then you probably have a wheel bearing problem - which is quite serious and potentially dangerous. If that's the problem then you're in a position where "If you have to ask the question - you're not qualified to fix it" - and this is going to cost you serious money to get it fixed. BMW's are amongst the more expensive cars to get work done on.
Going to a cheap tire place and asking them to balance the wheel might help - and shouldn't cost an arm and a leg.
Failing that, try to find a garage who will assess the problem for no charge - some places will do that. That would at least tell you whether this is something potentially life-threatening - or just an annoyance that should be fixed to avoid premature tire wear or something.

General "rattles" are only to be expected in a car of this age - and they may well be exacerbated by your wheel wobble - so get that seen to first. A rattle can be anything from a loose dashboard panel to a bent exhaust heat baffle to a broken motor mount! There is no way we can diagnose it for you without a lot more information.

I have to say: If you want a cheap car - then don't buy a cheap luxury car - those things are hard to maintain, the parts are expensive - and if you need professional help, remember that mechanics who specialize in luxury cars charge prices that only luxury car owners can afford!

If you have visions of becoming a "shade tree mechanic" and doing the work yourself then you need to start with something older, smaller and simpler!

SteveBaker (talk) 14:49, 18 June 2013 (UTC)[reply]

This is a rear wheel drive car with 4-wheel independent suspension, so a broken axle is most unlikely - the symptoms would be quite a bit more dramatic (think: extreme grinding noises; unable to move). However, a fauly wheel bearing is a possible cause of the rear wheel vibration only, especially if the car has high mileage and a history of poor maintenance (faults like this always come back to poor maintenance, which in turn is indicated if the purchase price was low). I agree with the rest of Steve's comments. The corrollary to them is that taking luxury cars to average mechanics can cost you even more than the expensive specialist mechanics. Simply because the average mechanic sees GM cars, Fords, Toyotas, etc all the time. Experience with them gives them the ability to diagnose faults straight away without having to puzzle them out with logical thinking. And they can get on the phone to their parts supplier (if they don't already have the parts) right away and call out a list off the top of their head. For car they hardly ever see they'll have to a) obtain/download the relavent parts manual (a story in itself these days) b) study it, c) work out what parts they need, d) find out where to get them and order and d) when they parts arrive, realise they need something else. And YOU pay for the time. The practical advantage of luxury cars is minimal these days anyway. All the major brands all have good design and good safety. The benefit of buying high end luxury cars is being able to say "look at me - I am a big success - I can afford it" - which does not apply if you bought an old cheapie. Back in the 1960's makes like BMW, Mercedes had clear advantages over GM and Ford, with their all-independent suspension, proper auto aircon, durability, and safety, but the gap has closed a lot now. Now you pay for the name. — Preceding unsigned comment added by 124.182.180.153 (talk) 23:18, 18 June 2013 (UTC)[reply]

Possible improvements in Wikipedia entry on Milankovitch Cycles

Introduction:

James Hansen's book, "Storms of My Grandchildren" make it clear that our understanding of Ice Ages, which has come about from a combination of Milankovitch Theory with much hard work by geologists on coring and complex analyses of those cores, is at the centre of our understanding of what is likely to happen to us as Global Warming picks up pace.

Unfortunately, even though I am a climate physicist of 40 years experience, engaged on writing a popular book on this subject, I cannot yet say I understand Milankovitch theory as described in this article (or any other popular books on the subject) well enough to write a simple but authoritative account of it for my readers.

I am not blaming the authors of the article at all for this -- it is genuinely a brute of a subject for anyone to get one's head around, and I have learned a lot from what they say.

My question:

Could the Reference Desk kindly get me into email contact with the authors of the article? In particular, with whoever provided the box, found on the right side of the first page of this article? Whoever the person is who came up with this box, it's clearly got nearly all of what I need to understand. I would like to email back and forth with him/her to explain what I am trying to do, and to work out some wording that satisfies both me and that person as a description of the physical things that govern the summer warming of icecaps. What's already there is very good. However, my purpose is to explain the observational history of the past few centuries that led to these astrophysical results, and this is the area where I most need the advice of the authors of the article. (Ivars Peterson's "Newton's Clock: Chaos in the Solar System", Freeman and Co 1993, unfortunately just misses giving what I need). 06:45, 18 June 2013 (UTC)~ — Preceding unsigned comment added by Neergtrish (talk • contribs)

Hi. Firstly, it's probably worth pointing out that almost all Wikipedia articles are collaborative efforts, so it's unlikely that there is a single 'author' of the article, which seems to be what you're looking for. Nevertheless, if you want to find out who has contributed to the article, simply click 'View History' at the top of the article and you will be able to see all the changes made throughout its history.

As for the image in the top right, this was added on 3rd June 2009 by Incredio. If you wish to contact them, the best way would be through their talk page. Some editors allow others to email them through Wikipedia's EmailUser, but Incredio has not enabled this, so on-Wiki communication is the only way.

Alternatively, since this is the reference desk, we may be able to help. If you post the questions you have about the article, maybe we can find some sources to aid your understanding. - Cucumber Mike (talk) 07:55, 18 June 2013 (UTC)[reply]

The basic problem here is that this just isn't how Wikipedia works. It's a collaborative environment - the idea is that any discussions you may wish to have about the content of the article should be publicly available to anyone who wishes to be involved in editing the article - either now, or in years to come. That discussion forms a valuable record of why particular editing choices were made. Hence private email communication between editors about article content is generally considered inappropriate - even in cases where the user allows you to communicate with them in private. By far the best thing for you to do here is to raise your concerns on the "Talk" page of the article itself - generally your input will be seen as interesting and valuable - so long as it is constructive and on-topic. Beware though that most of the time people here have little respect for your personal qualifications (after all On the Internet, nobody knows you're a dog) and you'll need to make your points by linking to reference information such as books and scientific papers that back up whatever point you're trying to make.

Another part of Wikipedia culture that's important here is encapsulated in the Be Bold philosophy. It's perfectly OK (indeed, encouraged) for you to dive in and fix the article yourself. If there is some problem with what you write, it may get reverted - or improved in some way by another editor - and that should be the starting point for a discussion thread on the corresponding talk page. It's more efficient to make a change to the article and only to discuss it if people disagree than it is to debate each change before it goes into the article.

If you absolutely must have private email communication, you could try enabling that for your own account and posting a request to the editors' talk page requesting that (s)he contact you via email. However, don't be surprised if the don't. Most editors (myself included) would prefer to keep communications about article content on the relevant talk page.

Wikipedia is a very different way of working than you may be used to - but it's surprisingly productive - and the outcomes are usually good. SteveBaker (talk) 14:07, 18 June 2013 (UTC)[reply]

The article (for convenience) is Milankovitch cycles, and I've added a thumbnail of the image in question here. Note that the creator, Incredio, has not edited Wikipedia since November 2012, and therefore is probably not paying attention to his or her talk page (but you never know). Looie496 (talk) 14:51, 18 June 2013 (UTC)[reply]

Yeah - but there are plenty of other people working on the article - and a vibrant, active talk page. If our OP raises his issues there, I'm quite sure that they'll be properly discussed and any problems swiftly dealt with or explained. SteveBaker (talk) 23:58, 18 June 2013 (UTC)[reply]

What's this turtle doing?

These two photos were taken just a few days ago in Vermont. I'm guessing that it's a common snapping turtle. It was a bit aggravated by me being as close as I was and I didn't want to bother it too much. What was it likely doing? Would the other two, for lack of a better word, divots in the soil next to the road in the foreground of the second image have been dug out by the turtle? Was she(?) laying eggs? There wasn't a large body of water near by. She was scratching at the dirt when I found her. Thanks, Dismas|^(talk) 07:11, 18 June 2013 (UTC)[reply]

Yes, laying eggs I think. They live is small streams, don't they ? So you might not know there's one nearby. Since turtles don't exactly travel long distances on land, I'd expect the stream it came from to be quite close (maybe even a drainage culvert). They don't seem to understand the danger of roads, either, unfortunately. StuRat (talk) 07:31, 18 June 2013 (UTC)[reply]

Snapping turtles prefer standing water, not flowing streams. They like warmer elevated areas for nesting, that roadside would have met both those requirements. μηδείς (talk) 16:54, 18 June 2013 (UTC)[reply]

Can neutrinos undergo gravitational lensing?

Thanks!76.218.104.120 (talk) 11:28, 18 June 2013 (UTC)[reply]

Yes. Like all elementary particles, neutrinos have mass/energy - therefore their paths are affected by gravity, and therefore they undergo gravitational lensing. Gandalf61 (talk) 11:36, 18 June 2013 (UTC)[reply]

More specifically, high-energy neutrinos (the only ones that we can detect directly) will follow paths that are essentially indistinguishable from the paths of photons in terms of gravitational lensing. — Quondum 13:58, 18 June 2013 (UTC)[reply]

Complex space & Quantum mechanics

I don't have a background in particle physics, but I have been doing some reading. I recently picked up on some ideas brought up with Imaginary time and the complex plane. So is it possible to project an imaginary axis on a 3D, maybe as (x,y,z,i), n-dimensional Euclidean space? I could only assume this logic could be used to explain occurrences such as particle-wave duality. In a similar way this little diagram (http://commons.wikimedia.org/wiki/File:Dualite.jpg) shows how what we may see as 2 separate figures may in fact be the same because we fail to see a superfluous axis of space. Bugboy52.4 ¦ =-= 13:51, 18 June 2013 (UTC)[reply]

I assume you mean the coordinates (x,y,z,it), since i is not a variable. If that's the case than yes, there's value in that approach as a way to better understand Minkowski space, but that is not related to the concept of particle-wave duality. Dauto (talk) 15:40, 18 June 2013 (UTC)[reply]

If you're thinking about complex numbers, three spatial dimensions, and time, the classic object building off of those is the quaternions. I'm not aware of applications to quantum mechanics, but they have been used for many types of theoretical physics, and you might enjoy reading up on them anyway.

“

Time is said to have only one dimension, and space to have three dimensions. […] The mathematical quaternion partakes of both these elements; in technical language it may be said to be "time plus space", or "space plus time": and in this sense it has, or at least involves a reference to, four dimensions. And how the One of Time, of Space the Three, Might in the Chain of Symbols girdled be.

”

— William Rowan Hamilton. Enjoy, SemanticMantis (talk) 19:12, 18 June 2013 (UTC)[reply]

What are the extra j and k axis in quaternions and its application in physics? this is fascinating, Id like to learn more. Oh and I was just considering the possibility since particles can appear and reappear or have a superposition then maybe we are only visualizing these particles from the perspective of our space because they are moving through an extra dimention. Bugboy52.4 ¦ =-= 23:05, 18 June 2013 (UTC)[reply]

The j and k are extra imaginary components - that is j^2 = k^2 = -1. Note that quaternions do not obey commutativity of product: ij = k, ji = -k for instance. Your ideas about particle-wave duality are off the mark. It has nothing to do with extra dimensions. Particle-wave duality really is simply a symptom of the inadequacy of the concepts of particles and waves to begin with. Dauto (talk) 03:47, 19 June 2013 (UTC)[reply]

I noticed that as well, how a product was able to have 2 seperate qoutients. Is there anywhere I can read more indept about this cerriculurly? 99.38.224.22 (talk) 04:36, 19 June 2013 (UTC)[reply]

If you like the quaternions than you might enjoy the octonions as well. The octonions have 7 different imaginary units. They do not obey commutativity like the quaternions plus they also do not obey associativity. That is (AB)C may be different from A(BC). Dauto (talk) 13:45, 19 June 2013 (UTC)[reply]

Quaternions are just mathematical conveniences - it's not that they have any particular physical significance. I use them a lot in 3D computer graphics to represent three-dimensional rotations because they have some particularly nice properties that are a huge improvement over using three angles or a 3x3 matrix. SteveBaker (talk) 00:35, 20 June 2013 (UTC)[reply]

Siphoning gasoline - which cars to choose?

I'm just watching something postapocalyptic and they need to siphon gasoline from abandoned cars. How would they know which contain the right type? Are there just two (diesel and unleaded)? Would it still be good after 20 years sat in the tank? — Preceding unsigned comment added by 89.241.228.217 (talk) 15:35, 18 June 2013 (UTC)[reply]

This is harder than it looks, because the nature of fuel can vary between countries and even between regions. (Of all of these the most comical, and I would think lucrative for the right people, is Opal (fuel); but I think it still is subject to stability issues despite the lower volatility) See Gasoline#Stability to get started. Wnt (talk) 16:15, 18 June 2013 (UTC)[reply]

Not hard at all - every car parts store sells siphons - and locking gas caps to prevent theft from your own car. And how many times have you had to alter your car when you went on vacation? Rmhermen (talk) 17:29, 18 June 2013 (UTC)[reply]

The neck of the gas tank is a different diameter for gasoline and diesel - in an effort to prevent people from accidentally grabbing the wrong hose at the gas station and filling their car with the wrong stuff...so it's easy to tell which is which if you know what you're looking for. Also, many cars now have stickers inside the gas cap telling you what octane range you need - which would also be a clue.

However, after 20 years, gasoline (and probably diesel too) is going to be almost useless for running a car on. The lighter fractions of the complex chemical brew will evaporate off and leave only the heavier fractions. As gasoline gets more than a year old - it gets harder and harder to start you car using it, and eventually, it flat out doesn't work. SteveBaker (talk) 19:25, 18 June 2013 (UTC)[reply]

Well, the "Opal" I mentioned has fewer volatiles - however, I think that the main problem isn't loss of volatiles, but reaction with oxygen to cause gummy deposits. I would allow for the possibility that ingenious postapocalyptic people can modify engines to be more robust (or find ancient relics or modern eco-prototypes that can choke down anything) but not be able to reach in and turn the key on a car they find beside the road, even with that battery they were carrying around in their backpack for such occasions. But I don't know these things well - it would be nice to hear an actual mechanic chime in. Wnt (talk) 20:56, 18 June 2013 (UTC)[reply]

There are details about what happens to "old" gasoline here Gasoline#Stability - suffice to say that 20 year old gasoline is going to be fairly useless as a fuel for cars. Incidentally - I checked up on diesel - and the problem is pretty much the same. This BP document says that diesel fuel is not "useable" after 6 to 12 months depending on temperature.

Truly, after just a few years, the gasoline in car tanks would be very poor for running cars...after 20 years, there's no chance. SteveBaker (talk) 23:53, 18 June 2013 (UTC)[reply]

All the above makes some assumptions. Internal combustion engines all around the world have used all sorts of horrible fuels, so long as you have air fuel and spark a mechanic will eventually get an SI engine to run, and a diesel engine is in theory not much less flexible. Greglocock (talk) 01:52, 19 June 2013 (UTC)[reply]

Usually diesel engine is more fuel flexible than gasoline engine, it can burn any heavy flammable liquid provided it have enough heat, but unfortunately they cannot accept gas like natural gas or woodgas, they need a ignition source for that 118.136.5.235 (talk) 11:44, 19 June 2013 (UTC)[reply]

Our Multifuel article discusses this - some military engines are designed to run on a crazily wide variety of fuels. Years ago, I had a friend who was a tank commander - he always claimed that his tank could run on anything from scotch whiskey to margarine - although that seems a little unlikely to me.

There are consumer vehicles out there marketted as Flexible-fuel vehicles - with that little green leaf logo on the back (which appears to be there to mislead people into thinking that these are somehow better for the environment)! Flex-fuel really means that the engine can cope with widely varying levels of ethanol mixed into the gasoline - but that wouldn't help them to run on 20 year old gasoline.

So, I suppose, our intrepid post-apocalypse folk had better find a suitable tank to be driving around in - and then they can run it on just about anything they can find out there. Of course that's not without problems. Most modern tanks are only able to drive an average of around 200 miles between breakdowns.

SteveBaker (talk) 13:05, 19 June 2013 (UTC)[reply]

The most multifuel engine so far is a gas turbine, and it could be improvised by attaching a combustion chamber to a turbocharger (see http://www.pfranc.com/projects/turbine/top.htm for example) and attaching another turbocharger turbine to the exhaust of it, it could be used for shaft power but it is much much much better to connect it to a electric generator

Source:Chrysler Turbine Car The article even said that it could run out of tequila, but the only problem and that is so huge is its directly connected to the wheel, and gas turbine is known as inefficient at idle — Preceding unsigned comment added by 118.136.5.235 (talk) 01:51, 20 June 2013 (UTC)[reply]

In a post-apocalyptic scenario, if you wanted to get from A to B and didn't care about the health of your engine at the end of it, then a normal diesel engine will run on a mixture of diesel fuel and gasoline/petrol. I accidentally put the wrong fuel in my old Peugot and pressed on regardless - it ran ok if a bit hesitantly. However, two weeks later, the head gasket failed resulting in a repair bill greater than the value of the car. Lesson learnt, but if it's the end of the world you might not be too fussy. Alansplodge (talk) 12:18, 20 June 2013 (UTC)[reply]

In the first year or two after "the big one", you might be right - but sooner or later, cars that still run are going to get rarer and rarer. If you take a perfectly well maintained modern car and leave it parked in the street for 20 years, it's not going to run again without a hell of a lot of restoration work! Such cars are occasionally found these days - the classic car nuts call them "Barn finds" (and yes, we have an article about that!) - because they are often found in disused barns. Here, for example is what a nice Jaguar XK120 looks like after it's been parked for 30 years.

So, 20 years after the apocalypse, once you do get a car running, it's likely that you most definitely WILL care about keeping it running. Just jumping into another one in the local baseball field parking lot, tossing out the skeletal remains of the driver, then turning the key and driving away from the encroaching zombie herd simply isn't going to work!

SteveBaker (talk) 16:50, 20 June 2013 (UTC)[reply]

Generic medications

I am a physician and today at work a dispute arose between our pharmacist and myself. Some of my patients complain that the medications they take often change their appearance in color and shape. They claim that some of the generic variants are in fact ineffective and they refuse to take them. I believe that there might be a scientific explanation why this happens. Different generic manufacturers probably use different fillers (clays) and in some cases the active chemical (medication) gets bound to them and passes the GI tract thus decreasing bio availability. Our pharmacist contends that all generics are tightly regulated by the FDA and such an event is not possible.

The question is: are the fillers regulated by the FDA?

Thanks, - Alex — Preceding unsigned comment added by 168.178.74.53 (talk) 16:27, 18 June 2013 (UTC)[reply]

They are in Canada. I doubt the US would be different. I have found, personally, with one specific drug, that the original and one of the generics work for me, but not another of the generics. My pharmacist says that this is not uncommon on an individual basis. Bielle (talk) 16:37, 18 June 2013 (UTC)[reply]

You should take a look at Generic drug#Quality standards. Ironically, it includes a statement that, "A physician survey in the US found only 17% of prescribing physicians correctly identified the USFDA's standards for bioequivalency of generic drugs". Looie496 (talk) 16:48, 18 June 2013 (UTC)[reply]

(Let me note that we are flirting dangerously close here to Wikipedia's prohibition against giving medical advice -- the fact that the questioner identifies as a physician isn't really relevant.) Looie496 (talk) 16:52, 18 June 2013 (UTC)[reply]

No, we are not. And yes, it isn't. --Stephan Schulz (talk) 17:54, 18 June 2013 (UTC) [reply]

Kainaw's criterion is not being breached. We can certainly answer this question. SteveBaker (talk) 19:14, 18 June 2013 (UTC)[reply]

I believe that it's well known that the packaging of generics can make a difference. Our article generic drug says "A generic drug must contain the same active ingredients as the original formulation. According to the U.S. Food and Drug Administration (FDA), generic drugs are identical or within an acceptable bioequivalent range to the brand-name counterpart with respect to pharmacokinetic and pharmacodynamic properties. By extension, therefore, generics are considered (by the FDA) identical in dose, strength, route of administration, safety, efficacy, and intended use." - which suggests that (in the USA at least) your patient's fears are unfounded. However, the article goes on to say "The FDA's use of the word "identical" is very much a legal interpretation, and is not literal." - so these generics are "legally identical" but maybe not actually identical.

Later in that article, under Generic_drug#Efficacy - it describes a study done in 2009 on oxybutynin that showed that the generic version was less effective - and the image there shows a clear difference in the rate at which bupropion is released between the generic and the original version of the drug. Our Bioequivalence article has more to say on the matter.

So, yes, there are probably some small differences. The question is whether these differences are sufficient to be truly noticeable by your patients. Clearly the FDA don't think they should be.

We should also suspect that a nocebo effect is taking place here - because the patients disbelieve that the generic is as good ("How can it possibly be as good? It's cheaper!") they are getting a reverse-placebo effect that is making them genuinely sicker for reasons unrelated to the content of the drug itself. They simply lost confidence in it and the nocebo effect did the rest.

An alternative hypothesis for what you're seeing is that (randomly) some patients get better after a while on the treatment and some get worse - regardless of whether they are taking the generic or the original drug. The ones who get better don't say anything - and the ones who didn't switch to the generic don't attribute their change to the treatment because it didn't change. But the patients who (by chance) get worse right around the time they switched to the generic version will always attribute the change to the first thing that comes to mind - which is that the generic drug doesn't work as well. Since you're only hearing from the ones who have something to complain about - you're going to see a rather severe "confirmation bias" effect going on here.

In terms of what you can do about it - that's a tougher matter. Having an authority figure (such as a doctor) boldly assert that the generic is utterly identical and just as good as the original might well have an effect - but we're into the realms of psychology and "bedside manner" rather than hard science. Worse still, if you yourself now have doubts over the generic drug - then that might well be subconsciously passed onto the patients, which would be a clear case where the nocebo effect could happen.

SteveBaker (talk) 19:14, 18 June 2013 (UTC)[reply]

I am the original poster. Thanks to everyone who responded. I am not sure I am doing this post correctly, I've never before posted answers. One of the later contributors extrapolated on the difference between generic and brand names. This is not my situation at all. We are talking about a perceptible difference between two generics. Today's case in one of many in my practice. In the environment I work in everything might be suspect (I am a prison psychiatrist. I see up to 30 patients a day). This case however stands out. The man said that he had taken citalopram for 7 years and it always worked for him. Two weeks ago he was given citalopram from a different maker and now he is complaining that it is not working, he is getting depressed.

About 15 or 20 years ago I read an article about an attempt to compare the bio availability of brand name Tegretol with various generic carbamazepines. Surprisingly some of the generics appeared to have substantially better bio availability than the brand name medication. That article led me to believe that the fillers are responsible for the difference and that they are not regulated.

Thanks. - Alex — Preceding unsigned comment added by 168.178.74.53 (talk) 20:17, 18 June 2013 (UTC)[reply]

One important consideration is that even though generics need to meet the same standards as all other drugs, they are in fact much less closely monitored. Also, because the profit margins are significant smaller for generic drugs than for branded drugs that not yet off patent, there is a very real and very significant pressure to cut manufacturing and distribution costs. That's a situation that is simply ripe for abuse. See for example the massive criminal fraud that pervaded generic manufacturer Ranbaxy: http://features.blogs.fortune.cnn.com/2013/05/15/ranbaxy-fraud-lipitor/ DrMatthias (talk) 20:28, 18 June 2013 (UTC)[reply]

There's also the possibility that the generics are outright counterfeits. You might want to have the patient return to the original med while you have the new generic tested, and also monitor any other patients who were switched to the new med. I personally am highly suspicious of any change to prescribed meds ("If it ain't broke, don't fix it").

As for differences in the binder, my dad had an interesting case where he was using a pill cutter on the name brand to split it into two, but then the generic equivalent just shattered into sharp shards when he tried to use it there. StuRat (talk) 20:38, 18 June 2013 (UTC)[reply]

The differences between generic and branded is likely to be similar to that between one generic and another. They certainly do differ in the binders and other non-active ingredients that they use - but (in theory) that's not supposed to make any difference because the FDA requires them not to. My previous comments about nocebo and observer bias still apply. It would probably be unethical - but I'd be strongly tempted to get a batch of the generic that your patient did fine on and dunk them into some food coloring to make them look like something else. If he continues to claim that it's not working then you may suspect the nocebo/observer-bias effect. Sadly, that doesn't help you to do anything about it. SteveBaker (talk) 23:42, 18 June 2013 (UTC)[reply]

There's also the possibility that your supplier may have supplied you with counterfeit drugs. I remembered last year in the UK we had a scare about this and I found this article (if you can get past the spam ads) confirming that the US also suffered. --TammyMoet (talk) 11:36, 19 June 2013 (UTC)[reply]

Generating electricity by evaporating water

Theoretically, if the relative humidity is r and the ambient temperature is T, then given N molecules of water, you can extract approximately an amount of W = -N k T Log(r) of work by letting the water evaporate (this is assuming the ideal gas law for water vapor, I leave this as an exercise for the Ref Deskers). This means that at a relative humidity of 60% at 20 C, one liter of water could theoretically generate about 69 kJ of energy.

The question is if we can generate electricity using a process that involves evaporating water. One can think of the following process. If we have two cups of water and we add salt to one cup, then one can generate electricity using electrodes one of which can absorb sodium ions, the other electrode can absorb chlorine ions. When the electrodes are saturated one puts them in the cup of water without salt, electricity will then run in the other direction as the ions from the electrodes dissolve into the water. This process exploits the difference in salt concentration of the two cups of water and it has been tested in practice. So, we can just use this process until the salt concentrations are equal. Then we wait until all the water has evaporated away, we then get the salt back and we can start the same process again. But this seems to me a cumbersome process that doesn't generate a lot of power. Count Iblis (talk) 17:01, 18 June 2013 (UTC)[reply]

I don't see how evaporation contributes to the energy generation there. Looie496 (talk) 17:42, 18 June 2013 (UTC)[reply]

Yup - and given that the world is neither short of salty water nor fresh(ish) water, why bother with the evaporation at all? Just swap the water over at the appropriate stage... AndyTheGrump (talk) 17:46, 18 June 2013 (UTC)[reply]

See osmotic power. You could certainly increase the concentration of some salt via evaporation and then use the resulting gradient to provide power. It's probably not very effective, though. --Stephan Schulz (talk) 17:58, 18 June 2013 (UTC)[reply]

There are of course other ways that evaporation of water can provide power - hydroelectricity is in most cases ultimately driven by the process... AndyTheGrump (talk) 18:09, 18 June 2013 (UTC)[reply]

One form of Ocean Thermal Energy Conversion involves warm surface water evaporating under reduced pressure, the vapor then driving a huge low-pressure turbine (essentially an enclosed windmill) and finally condensing on contact with cold deep-sea water. (Personally, I'm not so sure this would work at all -- and even if it does, it would be EXTREMELY inefficient because of the low temperature difference.) 24.23.196.85 (talk) 01:23, 19 June 2013 (UTC)[reply]

Merkel

How much does Angela Merkel weight in atomic mass units? --Wissbegieriges (talk) 18:16, 18 June 2013 (UTC)[reply]

Well, Ms Merkel's weight does not seem to be published anywhere I could find. This says that an average 58 year old caucasian woman weighs 70kg - and that the 25/75 percentile span is +/- 10kg. She doesn't appear to be excessively large or skinny - so that's a reasonable range. An atomic mass unit is 1.6x10^-27 so just divide one by the other and you'll have your answer - somewhere between 36,000,000,000,000,000,000,000,000,000 and 48,000,000,000,000,000,000,000,000,000. SteveBaker (talk) 18:44, 18 June 2013 (UTC)[reply]

Problems with the definition of the newton in relativity

If the newton is the force required to accelerate a 1 kg object at 1 m/(s^2), then that seems to be only accurate classically, because F=ma is not valid relativistically. In my opinion the Newton should be defined as the force that will cause a 1 kg m/s change in an object's momentum if exerted over the course of a single second. But do we actually gain by using a relativistic definition of the newton?--Jasper Deng (talk) 19:27, 18 June 2013 (UTC)[reply]

Forces need to be treated with a Lorentz transform when considering relativistic reference frames. If you do this correctly, "all the math works out." See Lorentz invariance with respect to momentum and force. Nimur (talk) 21:17, 18 June 2013 (UTC)[reply]

But the problem is, we have:

\mathbf {F} ={\frac {d\mathbf {p} }{dt}}={\frac {d}{dt}}({\frac {m\mathbf {v} }{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}})={\frac {m\mathbf {a} }{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}+{\frac {mva\mathbf {v} }{c^{2}({\sqrt {1-{\frac {v^{2}}{c^{2}}}}})^{3}}}

(if my differentiation is correct)

which means, a constant force does not lead to a uniform acceleration, so 1 N does not exactly produce an acceleration of 1 m/s^2 for a 1 kg object.--Jasper Deng (talk) 21:39, 18 June 2013 (UTC)[reply]

Note relativistic mass. In fact, this equation can be derived from the assumption that momentum remains conserved while mass increases, if I understand correctly. Wnt (talk) 22:02, 18 June 2013 (UTC)[reply]

Usually, when we refer to the mass of an object, we refer to its rest mass, I'm pretty sure.--Jasper Deng (talk) 23:40, 18 June 2013 (UTC)[reply]

When we refer to mass and we know we are worried about relativistic reference frames, we don't leave the interpretation up to chance! Specify what you mean. For example, the article I linked expressly defines inertial mass and invariant mass. The article defines and uses a different mathematical symbol for each value. Things get way too confusing if everyone is interpreting "mass" to mean different things! Nimur (talk) 00:19, 19 June 2013 (UTC)[reply]

I never really grokked what Lorentz transforms were for-- so thanks OP for the question and Nimur for the answer! SemanticMantis (talk) 02:23, 19 June 2013 (UTC)[reply]

The definition of the Newton doesn't specify which kind of mass is referred to.--Jasper Deng (talk) 05:39, 19 June 2013 (UTC)[reply]

Oh, is that so? Perhaps you aren't looking hard enough: there's a whole club full of unit nerds who get together and standardize this sort of definition - accounting for all sorts of theoretical and practical specifics. The more pedantically one nitpicks at such things, the more pedantic the responses have to become. Nimur (talk) 06:04, 19 June 2013 (UTC)[reply]

None of that is necessary. The Newton is defined as equivalent to 1 kg m / s^2. That definition works in relativety just as well as in classic physics. Dauto (talk) 03:32, 19 June 2013 (UTC)[reply]

Not really. For example, torque is measured in N m, which is equivalent to the joule, but is clearly a different kind of quantity.--Jasper Deng (talk) 05:37, 19 June 2013 (UTC)[reply]

Your statement is correct but misses the point. The Newton is not defined as a specific force acting on a specific mass creating an specific acceleration. It is defined as specific combination of base units. Now, if you really must see a unit definition as a description of a specific experimental set up (and believe me, you don't - but if you must) than just add the requirement that the accelerating object is at rest. Dauto (talk) 13:34, 19 June 2013 (UTC)[reply]

The meter, second, the kilogram, that's way too many quantities! The meter and the second are not independent physical quantities, mass and energy are the also the same quantites up to a conversion factor. So, you can just as well dump the Newton and work with e.g. the unit of power. Count Iblis (talk) 12:01, 19 June 2013 (UTC)[reply]

% fat-free

I'm wondering about how (under US regulations) a product can claim to be 97% fat-free when it's 80% fat. Any ideas? — kwami (talk) 23:04, 18 June 2013 (UTC)[reply]

On the face of it, that seems impossible - so I'm guessing there is something missing in your description. What exactly is the product and what are the other claimed ingredients? SteveBaker (talk) 23:20, 18 June 2013 (UTC)[reply]

Is that like those "low fat oils?" Either they have replaced it for soemthing else, or I don't know. OsmanRF34 (talk) 23:50, 18 June 2013 (UTC)[reply]

Varying definitions of "fat". HiLo48 (talk) 00:http://images.google.com/11, 19 June 2013 (UTC)

OK, it could have low saturated fat, or low monounsaturated fat, or low cis fat or whatever. But I doubt the marketing people are not aware that they are playing with the ignorance of the people who associate fat = bad, so low fat = good. OsmanRF34 (talk) 01:20, 19 June 2013 (UTC)[reply]

This page says "When a label claims to be 95 percent free, it is not saying—contrary to popular belief—that only 5 percent of the calories come from fat. The legal definition of 95 percent fat free is 95 percent of the weight of the product doesn’t contain fat". ( spam filtered 3fatchicks.com/does-95-percent-fat-free-mean-that-only-5-percent-of-the-calories-come-from-fat/ ). Perhaps not the most reliable source, but I think they're on to something, regarding the labels being regulated by weight, not calorie content. When I googled for this, I also found this link from the US FDA[www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/LabelingNutrition/ucm064911.htm], but it doesn't load for me. SemanticMantis (talk) 02:34, 19 June 2013 (UTC)[reply]

I typically see this with luncheon meats. I doubt weight alone would account for it, as I don't think sliced meat contains that much water. Even 98%-fat-free chicken soup is only 35% fat.[4] Weight would account for this meat,[5] which is 97% fat-free and 19% fat, but I've come across meats with similar claims that are 70 or 80% fat by calories. I can't figure that out. — kwami (talk) 05:12, 19 June 2013 (UTC)[reply]

If you had a drop of oil in a gallon of water, it would be 99.9999....% fat free by weight, and 100% fat by calories. This probably explains the other products, since they just bulk out the product with something with negligable calorie value (not just water, fibre is another example of a food type with nearly no calorie value). Of course, if the small amount of fat is contributing that much to the percentage of calories, the overall calorie content is probably less than the normal version. MChesterMC (talk) 08:25, 19 June 2013 (UTC)[reply]

From the the soup link, there are 2.5g of fat in 120mL (~120g) of soup. 2.5/120*100 = 2.08% fat, or just about 98% stuff that isn't fat. Since about 98% of the stuff in the soup isn't fat, it's reasonable for the manufacturers to call it 98% fat free. In terms of energy content (i.e. calories), at a rough approximation, (2.5g fat)*9cal/g = 22.5 calories from fat (the linked label has 25 calories from fat, which is close enough) and (10g carbohydrates)*4cal/g = 40 calories from carbohydrates, which account for 62.5 (or 65) of the 70 calories listed on the label. So fat, although only being 2% of the mass, accounts for about 35% of the calories. A similar calculation could be done using the linked information on chicken breasts.--Wikimedes (talk) 10:13, 19 June 2013 (UTC)[reply]

OK, so to summarize: We believe that the 97% and 80% numbers that our OP is seeing are percentages of different things. The 97% is the percentage of fat by weight and the 80% is percentage of calories that come from fat.

So imagine something like a bowl of lettuce with some small amount of cheese crumbled onto it. Suppose that 97% of the food is lettuce, which has almost no calories at all and 3% is cheese, which is almost all fat and therefore contributes 80% of the calories in that product. You'd be correct in saying that the meal is 97% fat-free, and that 80% of the calories come from fat.

Which number you care about is tricky. If you're trying to lose weight then neither number matters - all you should care about is serving size and calories per serving. If you're trying to eliminate fat from your diet, then the 97% fat-free number is the one you care about.

SteveBaker (talk) 12:43, 19 June 2013 (UTC)[reply]

Yes, I understand that. But chicken soup should be an extreme, as it's mostly water. I don't understand how luncheon meat, which has relatively little water (or fiber) can have a more extreme discrepancy than soup. — kwami (talk) 04:56, 20 June 2013 (UTC)[reply]

Can you give us some specifics? What brand of lunchmeat? Care to post a photo of the nutrition label, or at least transcribe it? --Trovatore (talk) 07:37, 20 June 2013 (UTC)[reply]

As for the soup, did you compare with this one? The difference of the calories is big. Oda Mari (talk) 09:42, 20 June 2013 (UTC)[reply]

In the US products which are basically 100% fat can be labelled "fat free", due to rounding down and absurdly small portion sizes. Pam cooking spray comes to mind: [6]. This requires some serious double-think to comprehend. StuRat (talk) 09:09, 20 June 2013 (UTC)[reply]

Ha, good find! SemanticMantis (talk) 15:00, 20 June 2013 (UTC)[reply]

I've never encountered the suggestion that 'X% fat free' should refer to energy (ie calories) rather than mass. Is this something that is done in the US? It seems obvious that the amount of fat in a thing is measured by the actual amount of fat in it. AlexTiefling (talk) 09:20, 20 June 2013 (UTC)[reply]

I've not encountered it before either. It's not done in the US.--Wikimedes (talk) 12:38, 20 June 2013 (UTC)[reply]

OK - so let's look at an actual can of spam with US labelling: PICTURE HERE.

Six servings per can - the can is about 3" tall - so you get a couple of 1/4" thick slices in a serving - which seems reasonable if you do not intend to die in the immediate future! It has 180 calories, of which 140 are from fat. So 78% of the calories are from fat. Total fat content is 25% of your daily value.

None of the percentages on the can are percentages by weight, or by calorie value. The "25%" number isn't 25% of the product - it's saying that if you eat four portions of spam (two thirds of a can) then you're getting the US government's recommended daily value of fat in your diet. We're also told that in a 56 gram "serving", there is 16 grams of "total fat" - so 28% of the weight of the spam is fat.

Conclusion: 78% of the calories are from fat. 28% of the weight is fat. The amount of fat is 25% of your recommended daily amount.

None of those numbers are remotely close to what the OP is seeing...so we need to know where those 97% and 80% numbers are coming from - they clearly aren't anywhere on the label of a "luncheon meat" product. SteveBaker (talk) 14:26, 20 June 2013 (UTC)[reply]

Yes, but the "X% fat free" labeling is usually not on the nutrition label, it's an advertising feature, usually on the front. For the spam above, the front of the can MIGHT say "72% fat free." -- because, by weight 28% is fat, and 72% is not. Here is a working link to the US FDA CODE OF FEDERAL REGULATIONS [7]. According to that,

“

(6) The term "_ percent fat free" may be used on the label or in the labeling of foods, provided that:

(i) The food meets the criteria for "low fat" in paragraph (b)(2) or (b)(3) of this section

”

-- spam probably doesn't meet the "low fat" requirements, but a similar product (e.g. spam lite) may well do so. SemanticMantis (talk) 15:13, 20 June 2013 (UTC)[reply]

Er, the 'X% fat free' figures clearly relate to the proportion of fat (however measured) in the product itself. All the percentages printed on the Spam can are percentages of the DV (or RDA, as we call it over here) of each of those things that one serving supplies. So you're comparing apples with oranges. Certainly the Spam can doesn't provide an answer to my question - the number of calories from fat is shown as an absolute figure, not a percentage. AlexTiefling (talk) 15:19, 20 June 2013 (UTC)[reply]

WARNING TO RESPONDANTS: A major problem with this discussion:

In UK English, "Luncheon meat" means spam and stuff like spam: minced up meat of dubious origins, ("mechanically recovered head meat" is a nicely evocative turn of phrase isn't it?!), often with large and visible chunks of fat in it, typically packed in aspic and sold in a can.
In US English, "Luncheon meat" (aka "Lunch meat") means thin slices of lean, pre-cooked, and mostly recognisable meat of the kind you might find on a delicatessen counter or pre-packaged in a plastic tub.

VERY different products! So when answering, it's going to be necessary to define which of those things you mean! SteveBaker (talk) 14:26, 20 June 2013 (UTC)[reply]

Thanks, Steve! I try to keep track of pondial differences, but that's one that had so far escaped my notice. --Trovatore (talk) 19:26, 20 June 2013 (UTC) [reply]

To be honest, even after close to 20 years of living in the US, it was a new one on me too. I only really understood the difference while looking for a luncheon meat nutritional label on Google images earlier today! SteveBaker (talk) 20:41, 20 June 2013 (UTC) [reply]

I was referring to US regulations, and so to deli-type meats, not Spam. I understand that "fat-free" is by weight, so I'm not surprised that something may be 97% fat-free at the same time it's 35% fat by calories, and I know that serving sizes may be made small enough to contain 0.5g fat, which is then rounded off to zero and claimed to be 0% fat. I've even seen butter substitutes that are both 100% fat-free and 100% fat, but those are exceptional cases. What I couldn't figure out was how deli-type meats could be 97% fat-free and 80% fat, as weight, water content, and rounding would not seem to be enough to explain them. I was hoping someone here would be familiar with this, but if not, I'll try to jot down the details the next time I'm at the market. — kwami (talk) 22:51, 20 June 2013 (UTC)[reply]

If you could snap a cellphone photo of the packaging - that would be best of all! SteveBaker (talk) 14:23, 21 June 2013 (UTC)[reply]

Cleaning the shower stall.

Recently moved into a house with a glassed-in shower stall - which has a whitish film coating the surface that looks like hard water deposits or soap residue or something. So far, we've tried to clean it with:

Calcium Lime Rust aka "CLR" - (now Phosphate-free)
CLR-brand shower cleaner
Scrubbing Bubbles
Vinegar with Baking soda
Bar Keepers Friend
Hard work with various scrubbers and cloths.

Result so far...nothing, zip, nada. Shower still has deposits on glass. I was quite surprised that CLR didn't get it clean - but maybe the new phosphate-free formulation isn't effective.

Any suggestions? OK...any PRACTICAL suggestions?! :-)

SteveBaker (talk) 23:35, 18 June 2013 (UTC)[reply]

I would try Acetic acid or Citric acid in reasonable concentrations (say 25% of Acetic acid). Adding baking soda is counterproductive, as it will neutralize the acid. --Stephan Schulz (talk) 23:48, 18 June 2013 (UTC)[reply]

OK - I double checked with my g/f and she has tried vinegar by itself...same problem. But according to Vinegar, the white vinegar we used is only 8% acetic acid - so maybe need to get some of the real thing. We're planning to try some neat lemon juice. SteveBaker (talk) 00:16, 19 June 2013 (UTC)[reply]

Be careful with the "real thing", if by that you mean glacial acetic acid. I understand that it's fairly nasty stuff. My dad said just the odor would knock you off your feet. --Trovatore (talk) 00:19, 19 June 2013 (UTC)[reply]

Over here, 25% Acedic acid is sold in 1/2l and 1l bottles, as "Essigessenzce" (essence of vinegar). It's primarily marketed as a food product (dilute 5-1 with wine, juice, or, boringly, water, to make various vinegars), but also for cleaning. --Stephan Schulz (talk) 06:47, 19 June 2013 (UTC)[reply]

Is it possible to reduce white vinegar (reduce in the cooking sense, not chemical)? Does it form an azeotrope, or can you obtain glacial without burning it? Plasmic Physics (talk) 00:22, 19 June 2013 (UTC)[reply]

If it corrodes metal should you reduce it in a Teflon coated kitchen vessel, under good ventilation or outside? Plasmic Physics (talk) 00:28, 19 June 2013 (UTC)[reply]

I don't remember off the top of my head, but the WP data page on acetic acid doesn't show any azeotropes on the distillation curve -- so yes, if you heat the stuff hot enough (116 C or more) you can get glacial acid. WARNING -- DO NOT try this at home without BOTH a fume hood AND a gas mask, because the smell would knock you out cold! (I know from experience -- I've accidentally inhaled just a tiny whiff of glacial acetic acid vapor, and it almost burned my nose right off!) Also, whatever you do, DO NOT concentrate acetic acid in a metal container -- it will undergo a single displacement reaction, forming the corresponding metal acetate (i.e. burning a hole in the metal) and releasing hydrogen gas (which could cause an explosion if you're using an open flame as your heat source). And no, a Teflon-coated saucepan WILL NOT do -- the Teflon degrades over time with high temperatures, and can also easily become scratched during normal use, exposing the metal underneath. Use a glass or plastic container instead. 24.23.196.85 (talk) 01:55, 19 June 2013 (UTC)[reply]

Except for being highly toxic and a disposal issue (i.e. you don't want it in the water supply), chromic acid will clean the white off of rice. It's great at getting sparkling glass, though it is nasty stuff. IIRC, you make it with a 50/50 mixture of concentrated sulfuric acid with a saturated solution of sodium dichromate. But again, it's so nasty, unless you have a means of using it in a well-ventilated space, avoid all skin contact, have proper breathing protection, and are scrupulously careful to properly dispose of every drop you use, it's probably not practical. But if chromic acid doesn't get it clean, it isn't meant to be clean. --Jayron32 01:16, 19 June 2013 (UTC)[reply]

Yes, maybe Steve Baker is scrubbing like mad a frosted glass. OsmanRF34 (talk) 01:22, 19 June 2013 (UTC)[reply]

Maybe not even deliberately frosted. Glass can become etched, and if it is etched, it can be as scrupulously clean and look milky or cloudy. --Jayron32 01:59, 19 June 2013 (UTC)[reply]

"Home is where you can scratch where it etches." ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:25, 19 June 2013 (UTC)[reply]

Hmmm, I thought I mentioned: "OK...any PRACTICAL suggestions" ?? :-) I don't think I'll be using chromic or glacial acetic acids!

@Stephan: I'll see if I can find some of this "Essigessence" stuff. Thanks!

I corrected the spelling above (too many languages for one head). Amazon seems to have 20% vinegar, which I guess would be close enough. --Stephan Schulz (talk) 14:07, 19 June 2013 (UTC)[reply]

@OsmanRF34: Yes, I considered the possibility that it's deliberately frosted - but it's clearly too subtle for that...also it exhibits a pattern that looks exactly like water droplets.

@Jayron: That's a definite possibility at this point...but it's hard to imagine how that would have happened. Perhaps calcium deposits from the water were scrubbed into the glass by some previous aggressive effort to clean it without chemical assistance. Are those deposits hard enough to scratch glass?

SteveBaker (talk) 12:05, 19 June 2013 (UTC)[reply]

(Oh - and incidentally, you don't need to distil your own glacial acetic acid - you can buy a bottle for $17 on Amazon.com!) SteveBaker (talk) 12:29, 19 June 2013 (UTC)[reply]

Perhaps nail polish remover and peroxide will clean it? Plasmic Physics (talk) 13:12, 19 June 2013 (UTC)[reply]

Nah, better not try that, not unless you have an affinity for explosive showers. Plasmic Physics (talk) 13:15, 19 June 2013 (UTC)[reply]

Now that is an effective test of the Wikipedia disclaimer. Please note acetone peroxide is one of those potent explosives used only by nutjobs because of a tendency to spontaneously explode when least expected, though most consumer formulations of hydrogen peroxide shouldn't be nearly concentrated enough (I think). Wnt (talk) 15:22, 19 June 2013 (UTC)[reply]

Have you tried undiluted bleach? this can remove soap scum and fungus pretty well. Graeme Bartlett (talk) 21:49, 19 June 2013 (UTC)[reply]

Use dilute hydrochloric acid from a pool supply store. We use it for removing calc build-up in pipes on an industrial scale, and also it cleans the glass windows on the work utes up real good. 39.214.158.84 (talk) 22:36, 19 June 2013 (UTC)[reply]

CONCLUSION : Figuring that the glass is probably etched rather than having some very resistant material on the surface, we tried using some of that Rain-X stuff that you put on car windshields to make them repel water better. It worked wonderfully! The haze is now invisible - and as a bonus, the water sheets off of it more easily. The only likely downside is that we'll have to re-do it periodically. Thanks for all of the advice! SteveBaker (talk) 00:28, 20 June 2013 (UTC)[reply]

Steve, I know you like do it yourself challenges. I've heard it is possible to take lightly etched glass and restore it using polishing compound and buffing machines. The goal is of course to polish out the surface and make it smooth again. I've never tried it myself, and I suspect there is a substantial risk of making things worse, but if you are feeling adventurous then I suppose you could look into trying that. Dragons flight (talk) 06:15, 20 June 2013 (UTC)[reply]

Yes, but at that point, simply replacing the three panes of glass would be a lot easier! Anyway - RainX seems to work well. SteveBaker (talk) 13:56, 20 June 2013 (UTC)[reply]

June 19

The psychology of flirting between men and women

Can anyone help me learn the basic instinct behind the actions men and women reflexively take when trying to attract each other? Out of all the junk Google spews at me whenever I try to research the subject I got one good link from one site that took me to another website that said, for example, that women try to make themselves appear smaller when flirting with a man and men try to make themselves appear bigger when flirting with a woman. This sounds interesting, like animal behavior. I'd like to learn the "Why" behind these primal? instincts within us ("Women try to make themselves appear smaller BECAUSE thousands of years ago...") as well as see a list of actions that men and women take when flirting with each other. I don't care about trivial modern stuff like "Women should wear red!" and "Men, don't wear too much cologne!" I'm trying to explore the basic or primal instincts in our brains that's left over from ancient times. — Preceding unsigned comment added by 174.65.51.113 (talk) 00:39, 19 June 2013 (UTC)[reply]

Have you tried Google Scholar instead of regular Google? It does a good job of seperating the wheat from the chaff. Select the "More" option at the top, then select "Even more" from that menu, and page down, there's a "Scholar" option on the next page. That's usually a good way to seek actual research and scholarly papers on topics. --Jayron32 01:11, 19 June 2013 (UTC)[reply]

The "Women should wear red!" thing is not trivial modern stuff. Dauto (talk) 03:25, 19 June 2013 (UTC)[reply]

Flirting is like foreplay. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:39, 19 June 2013 (UTC)[reply]

if a neutrino goes on a bullseye towards a nucleus will it usually pass right thru?

Or will the weak force interaction that I've read about probably occur? 2. Same questions for a neutrino on bullseye toward and into a lone proton. Will it usually just go past those 3 little quarks inside the proton like Road Runner or will it more likely interact? Thanks76.218.104.120 (talk) 05:16, 19 June 2013 (UTC)[reply]

Straight through most of the time. Some relevant detail in neutrino and neutrino detector. Dragons flight (talk) 05:33, 19 June 2013 (UTC)[reply]

One issue is the uncertainty principle meas that you don't know where that neutrino is or what path it follows. Graeme Bartlett (talk) 21:54, 19 June 2013 (UTC)[reply]

Searching for Jimmy Hoffa...

(For those of you not familiar with the case, Jimmy Hoffa was the head of the Teamsters Union who apparently was murdered by the Mafia in Detroit and buried in an unknown location, and they try to find him by digging up some new place every few years.)

My question is, in the latest excavation, they brought in a cadaver dog to sniff him out. Now, the remains of somebody dead for decades can't stink of decomp any more, right (at least in normal circumstances) ? So would the dogs do any good ? StuRat (talk) 06:29, 19 June 2013 (UTC)[reply]

According to [8] some dogs can still detect dry bones 30 years after death. Dragons flight (talk) 06:54, 19 June 2013 (UTC)[reply]

Just as importantly, they're a "possible benefit, no downside" option. Dogs have extremely sensitive noses, so even an insignificantly small amount of "fresh" material might still register with them. And if it doesn't, you're no worse off than otherwise. Matt Deres (talk) 16:37, 19 June 2013 (UTC)[reply]

% [Where is Jimmy Hoffa?

Missing ]. Tevildo (talk) 21:33, 19 June 2013 (UTC) [reply]

Perhaps Amelia Earhart flew him to a secret rendezvous in Shangri La with Judge Crater and D. B. Cooper. Edison (talk) 22:55, 19 June 2013 (UTC)[reply]

Someone once postulated a town called Craterville, named for the judge, to which every missing person since then would turn up. And probably all those missing socks from your dryer. Shangri-La works even better. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 20 June 2013 (UTC)[reply]

Trace element changing the properties of a whole substance

How can it be that, if you mix less than 100 parts per million of some trace element into a substance, it changes the properties (melting point, for example) of a whole substance? Why isn't this trace element insignificant? OsmanRF34 (talk) 13:34, 19 June 2013 (UTC)[reply]

That's because the property of a substance is not a democracy where every atom votes and whoever wins, caries the day. Look for instance at Doping (semiconductor). The trace elements provides electrons (and holes) that work as charge carriers. That drastically change the properties of the substance. Dauto (talk) 14:26, 19 June 2013 (UTC)[reply]

100 ppm is one part in 10000. Note the potential effect of a 10 g bullet or 10 g of Botulinum toxin (talk of overkill!) on a 100 kg human. --Stephan Schulz (talk) 15:55, 19 June 2013 (UTC)[reply]

That's a bad analogy - a human is a complex machine, not an homogenous substance. AlexTiefling (talk) 16:55, 19 June 2013 (UTC)[reply]

Indeed, and it's not the bullet that kills, but the energy of it, applied to the wrong place. You could also say that a little bit of sand changes completely the properties of a gear. OsmanRF34 (talk) 17:55, 19 June 2013 (UTC)[reply]

Ok, maybe Stephan's analogies are not the best, but your sand/gear one is pretty good! As Dauto says, bulk properties of a substance are not a democracy. In this case, a little bit of sand can make a gearbox freeze, even though there isn't much sand by weight. It's how the trace constituent interacts with the bulk that's important. That being said, you might get better, more physical/chemical answers if you tell us what specific systems or materials you're thinking of. We can't give a one-size-fits-all explanation for the effects of trace elements in bulk substances -- some trace elements have negligible effects, while others can have large effects. Here's another analogy that you might like better: reinforced concrete. The rebar is a small part of the total mass, but radically changes the tensile strength and ductility. In that case, humans need to organize the geometry of the rebar, but in materials, chemistry can conspire to set the patterning on its own. SemanticMantis (talk) 18:22, 19 June 2013 (UTC)[reply]

OK, imagine you have some wood and you mixture a trace of iron. It's hardness won't change much. But in other contexts, it's the trace that determines a higher hardness. Provided that no atom can bind to thousand of atoms, and that the relation of trace/substance is 1/several thousands, then, how can it happen? OsmanRF34 (talk) 19:09, 19 June 2013 (UTC)[reply]

You may be thinking about alloys. In this case, the mechanical properties of the material depend very much on the crystal structure of the material. Even a small amount of different material may either disrupt crystal formation or serve as a nucleus for the same, and hence lead to a different structure of the material. Imagine a square densely packed full of marbles in a regular structure. If only one of them is bigger, very many other marbles will have to move somewhat out of alignment to accomodate it. --Stephan Schulz (talk) 19:30, 19 June 2013 (UTC)[reply]

(EC, saying similar to Stephan above) I'm no materials scientist, but have a look at steel. Small amounts of carbon prevent flaws in the iron crystal lattice from forming, and thereby make steel harder than iron. I can't explain why from a chemistry perspective, but maybe somebody here can. What I understand more generally is that the crystal lattice is a higher-order structure, and a few atoms here and there can cause the lattice to have a very different structure. You might like the pictures at dislocation. From a more geometrical perspective, you may enjoy reading Tiling_by_regular_polygons#Archimedean.2C_uniform_or_semiregular_tilings. Consider that there is only one way to tile with squares, and only one way to tile with hexagons. BUT-- if you mix in a few small triangles, there are many tilings available, and each will have different structural properties. Atoms in materials aren't exactly like geometrical tilings, but the the lattice structures of compounds do strongly affect bulk material properties. Hope that helps, SemanticMantis (talk) 19:36, 19 June 2013 (UTC)[reply]

One of the weirder instances is Technetium - according to our article 55 ppm of one of its compounds will protect steel from corrosion. Pity that no non-radioactive nuclear isomer has yet been discovered ... Wnt (talk) 22:34, 19 June 2013 (UTC)[reply]

And never will... Dauto (talk) 15:41, 20 June 2013 (UTC)[reply]

Do you actually know that all the nuclear isomers are known, or that the undiscovered ones are less stable? Wnt (talk) 17:53, 20 June 2013 (UTC)[reply]

No to the first question and yes to the second. Note that the halflife of the most stable isotope is over a million years. Dauto (talk) 22:00, 20 June 2013 (UTC)[reply]

The thing is, sometimes the "m" isotopes are more stable than the lighter ones. So how do you know there isn't a super-m isotope? (True, it would have to something not made in supernovas, but surely there must be some things they don't make...) Wnt (talk) 15:47, 21 June 2013 (UTC)[reply]

Actin Protein

Hello, I have read in the article http://en.wikipedia.org/wiki/Actin that Actin is not found in nematode's sperm,can u please give refference to thi. I shall be very thankful, — Preceding unsigned comment added by 182.185.192.49 (talk) 14:03, 19 June 2013 (UTC)[reply]

Unfortunately the editor who added that fact did not provide a reference, but a search of Google Scholar for "actin nematode sperm" finds plenty of them. The paper that apparently first established this fact is PMID 7199049. Looie496 (talk) 15:17, 19 June 2013 (UTC)[reply]

Two related questions about lightning

It's a commonly believed factoid that either one lightning bolt, or one lightning storm delivers enough energy to power a major city for some impressive length of time.

Is this factoid anywhere near true? The article on lightning estimates a single bolt at half a gigajoule, which is a good amount of energy, but a major city would burn through that in moments.

The second half of the commonly believed factoid is that (Even though lightning will supposedly power a major city) there's no way to capture this energy, because it's delivered too fast.

To me, this doesn't ring true either. Project Gnome would have captured massive amounts of instantaneous energy for later use, and recreating it on the smaller scale of a lightning bolt doesn't seem impossible at all. In fact, it seems like it would be quite easy if the energy involved made it worth doing. (The Lightning rod of a tall building could be directed through a tall cylinder of material that could melt and store the heat energy long enough for it to be exploited.)

So my questions is, are either of these common factoids true? 75.69.10.209 (talk) 18:54, 19 June 2013 (UTC)[reply]

A quick googling suggests a five megajoule lightning strike could power a household for a month.

If we have a city of 2.5 million households, we would need 2.5 million lightning strikes a month. Which happens to be one strike per second, 24 hours a day, seven days a week, every day of the month, all year around. BOOM ...one second... BOOM ...one second... BOOM - all the time, from the moment you are born, to the day you die (probably due to being hit by lightning.)

This seems a rather implausible climate. If you have this kind of weather every day forever and ever, rather than worrying about your electric bill, move the hell out!

(Also see harvesting lightning energy.) 88.112.41.6 (talk) 19:35, 19 June 2013 (UTC)[reply]

Generally speaking, energy is more useful when it is released quickly, because we can always slow it down to the level we want. Speeding up its release on the other hand is more difficult. A good example is a pile driver. You put energy into it by raising it, but that slow release of energy into raising it wouldn't be enough to drive anything into the ground. The quick release of dropping the thing does the job though. 39.214.158.84 (talk) 22:28, 19 June 2013 (UTC)[reply]

5 MJ converts to about 1400 W hours; that would run my house for about an hour, not a month. Atlant (talk) 23:30, 20 June 2013 (UTC)[reply]

If you built a machine with a lightning rod to carry energy from a lightning strike down to an insulated chamber where the current melted metal or heated some phase-change substance, and then a heat exchanger used the stored heat energy to boil some working fluid and run a turbine or other engine coupled to a generator, you could produce energy until the heat reservoir cooled off. It sounds like an expensive machine, since the conductor would have to be strong enough to withstand huge mechanical forces, and insulated to a high level, not to mention the heat storage, turbine, generator, and utility interface. How would you arrange for the lightning to strike it frequently enough to operate it efficiently? I cannot imagine it would be cost effective to install such a machine on every hill, mountain top and tall building in a region, and then wait for the monthly lightning bolt. It would be like a wind generator waiting for the monthly gust of wind, or a solar panel waiting for the monthly hour of full sun. Ben Franklin built a machine which had a lightning rod (his invention) which charged a metal ball, which was then attracted to a grounded bell, with the cycle repeating. It probably generated milliwatts of energy several times a year for a few minutes, but it sounds more cost effective than the proposal, though at the risk of burning down the house. Edison (talk) 22:48, 19 June 2013 (UTC)[reply]

Though, if you were in one of the gas giant's atmospheres, it would work perfectly. The lightning strike density is so high in the lower levels, that you can read by the perpetual glow. Plasmic Physics (talk) 07:03, 20 June 2013 (UTC)[reply]

Evolutionary advantage of food allergies

Are there any evolutionary advantages of being allergic to specific foodstuffs? Horatio Snickers (talk) 21:26, 19 June 2013 (UTC)[reply]

Allergies are an over-reaction of the immune system, so I guess you could say one advantage is having an immune system. 39.214.158.84 (talk) 22:22, 19 June 2013 (UTC)[reply]

That a trait exists is not evidence of evolutionary advantage. It is merely evidence that it is not enough of a disadvantage to prevent the trait from being passed on. For example, if we go back hundreds of thousands of years in human history; and come upon a population of humans that develops a genetic predisposition to a peanut allergy, but also that population is never exposed to peanuts, it will never affect them, and the gene will get distributed until modern times, when modern food distribution systems allow peanuts to reach people with that genetic predisposition to the allergy. There's nothing advantageous about the gene, it's just that there was nothing disadvantageous to stop the spread of the gene, at least until modern times, and today there is still not much of a disadvantage, given modern medicine's ability to treat it, and people's ability to consciously choose to avoid the allergan. But the ultimate point is that not every single trait in the world represents an evolutionary advantage, and that a trait exists is not evidence that it is good for anything. See Mutation#By effect on fitness which briefly notes several types of mutations, such as "neutral mutations", which do not have deleterious effects on a population. --Jayron32 00:55, 20 June 2013 (UTC)[reply]

There are two other possibilities worth mentioned. 1) It's possible that everyone has the genes for a certain trait, but that the phenotype has incomplete penetrance. That is, everyone can get peanut allergies, but not everyone does. There is probably a genetic component to peanut allergies (see this twin study), though, so maybe that's not the case. 2) It's possible that a certain trait did not exist until recently, even though the genes that give rise to the trait are ancient. Following the hygiene hypothesis, we would say that throughout human evolutionary history, almost no one had peanut allergy, or any allergies for that matter. Rather, such a trait only arose in recently due to the change in our environment, which is why it was not selected out of the species. Someguy1221 (talk) 01:05, 20 June 2013 (UTC)[reply]

I don't think they have any advantage, it's just a defect. In the US at least, the cashews would say on the package something like "Packaged at a facility which also processes peanuts and other tree nuts" or simple "May contain peanuts". This is the clue that there may be cross-contamination. In some cases, it's just certain components of the food to which the person is allergic, like lactose in milk. Such people can have lactose-free milk or some other substitute, like almond milk. In extreme cases, such people would be advised to avoid all pre-packaged foods, restaurant meals, and meals prepared by others. Instead, they should buy all the raw ingredients and prepare meals from scratch. While this is a lot of effort, it's also what we should probably all be doing, to avoid all the unhealthy additives in everything we eat. StuRat (talk) 20:07, 18 June 2013 (UTC)[reply]

Milk allergy has nothing to do with lactose. The IgE antibodies are directed against milk proteins. See Lactose intolerance and the IUIS web page on milk allergens [9]. --NorwegianBlue^talk 20:00, 20 June 2013 (UTC)[reply]

Our article on Food allergy doesn't seem to have anything about it that I can see. There may be advantages even for just eating food never mind the immune system for all I know, after all putting petrol into a diesel car can destroy the engine, Is a diesel car that can happily use petrol really a better diesel car? Peanuts grow underground rather than in the trees so there would not be a reason even for our distant ape ancestors to gain immunity from anything in them. Dmcq (talk) 11:16, 20 June 2013 (UTC)[reply]

Here's the closest I can find, in the discussion section of this Science article, titled "Immunity, Inflammation, and Allergy in the Gut" [10], DOI: 10.1126/science.1106442

“

In the evolutionary battle against infectious disease, the immune system cannot afford to err on the side of caution, because failure to mount effective and vigorous immune responses will be exploited by pathogens. This is best exemplified by celiac disease, in which the high prevalence of HLA-DQ2 in the general population suggests an evolutionary advantage of this allele against infection, even in the face of the negative effects of the coincidental affinity of gluten peptides for HLA-DQ2 to cause celiac disease.

”

(emphasis mine )It is unclear to me whether scientists consider celiac disease to be a food allergy, but our article wheat allergy says there are similar proteins involved. The article is honestly a bit over my head, but it also discusses the role of that allele in food allergies. Anyway, I know it's a stretch, there it is. SemanticMantis (talk) 16:29, 20 June 2013 (UTC)[reply]

Whether celiac disease is an allergy or not, depends on which definition of "allergy" you use. It is an allergy in the sense of "a reaction of your immune system to something that does not bother most other people" [11]. It is not an allergy in the more restricted sense of our allergy article, which only discusses type I hypersensitivity reactions according to the Coombs and Gell classification. --NorwegianBlue^talk 20:00, 20 June 2013 (UTC)[reply]

It is difficult to imagine an evolutionary advantage of being intolerant to otherwise nutritional food. There is, however, an evolutionary advantage in having the Immunoglobulin E mediated responses that cause allergies. Our article mentions defense against intestinal parasites, possibly also protozoa. Food allergy is increasing rapidly (PMID 23578298), and is probably a recent disease. The hygiene hypothesis that others have mentioned, is a plausible explanation of the increase. We know that hay fever, also IgE-mediated, is a recent disease. It was first described by John Bostock in 1819, and at the time it appeared to affect only the middle and upper classes of society, consistent with the hygiene hypothesis. --NorwegianBlue^talk 20:51, 20 June 2013 (UTC)[reply]

There is one classic example of the situation that you find difficult to imagine.

Lactose intolerance is the norm for adult mammals - because you want babies to wean themselves off of mother's milk before the next litter is born. For most mammals, lactose intolerance is "being intolerant to otherwise nutritional food" - and it's a clear evolutionary advantage for them.

Humans evolved to have tolerance for lactose into adulthood soon after starting to farm dairy animals because the benefits of being able to consume milk products gave better survival rates than the benefits of lactose intolerance could provide. But that was thousands of years ago. In the meantime, we've kinda progressed past the point where either tolerance or intolerance of lactose makes any difference to reproductive success - so we've gotten "stuck" with some part of the population having the lactose-tolerance mutation - and others not. SteveBaker (talk) 02:11, 21 June 2013 (UTC)[reply]

Strictly speaking, lactose intolerance is nothing like an allergy. It does not lead to a histamine response or any other immune response at all. It's a digestive issue with no immune issues at all. It's the same sort of digestive intolerance that leads to the "bean reaction" whereby undigested sugars pass into the colon and feed the gut flora there. Many foods lead to such reactions, but milk products (in the absence of lactase) are particularly severe. --Jayron32 02:20, 21 June 2013 (UTC)[reply]

Although food allergies have doubled in the last twenty years, it is not a recent disease according to this source http://www.allergyclinic.co.nz/guides/39.html. --Modocc (talk) 03:59, 21 June 2013 (UTC)[reply]

There is an article published in Nature http://www.nature.com/nature/journal/v484/n7395/full/nature11047.html that hypothesizes that "allergic hypersensitivity evolved to elicit anticipatory responses and to promote avoidance of suboptimal environments." --Modocc (talk) 03:18, 21 June 2013 (UTC)[reply]

Neutron stars and black holes inside

Could a neutron star have many tiny black holes being constantly created and rapidly evaporating especially deeper inside? Or from impacts of incoming stuff at the surface? For neutron stars that are near the upper mass limit especially. Thanks.Rich (talk) 22:54, 19 June 2013 (UTC)[reply]

The weird thing about black holes is that the bigger they are the less dense they need to be. A very large supermassive black hole can actually be less dense than ordinary air. [12] So just because a neutron star is on the verge of becoming a hole doesn't mean that little pieces of it are at the verge also. Wnt (talk) 02:17, 20 June 2013 (UTC)[reply]

Your final sentence might be right, but this use of the word "density" is kind of bogus. Theoretically, once a mass becomes into a black hole, there is no force that can prevent all its mass from collapsing into an infinitely dense spacetime singularity at the center. This "density" calculation is apparently based on dividing the mass of the black hole by the volume within the event horizon (note that "volume" is also a bit problematic here, because there's no canonical coordinate system to measure it in). But nothing special happens at the event horizon; it's just empty space, but a marker from which you can't return. --Trovatore (talk) 02:45, 20 June 2013 (UTC)[reply]

"the bigger they are the less dense [the structures that gave rise to them] need to have been." Someguy1221 (talk) 03:14, 20 June 2013 (UTC)[reply]

That I'll buy. But I think it's confusing to say that the black holes themselves are less dense. --Trovatore (talk) 04:01, 20 June 2013 (UTC)[reply]

I feel ignoredRich (talk) 04:53, 20 June 2013 (UTC)[reply]

Why? Wnt answered your question. --Trovatore (talk) 05:16, 20 June 2013 (UTC)[reply]

I don't know enough for my opinion to matter, but subjectively I find Fuzzball (string theory) appealing. The notion of "singularity" doesn't smell real to me. I am content to measure the black hole's density in terms of the mass I can measure and the volume I can measure, and ignore what I can't which varies between models. Wnt (talk) 05:34, 20 June 2013 (UTC)[reply]

Hmm — my equally subjective view is that the black hole information paradox is no paradox at all, because the supposed reversibility principle that it violates should be false. That principle is based, albeit in a somewhat indirect way, on determinism, and determinism is wrong, because we have free will (in the strong sense incompatible with determinism). But I also don't know enough for my opinion to matter; I just find the queasiness that leads to these elaborate workarounds to be misplaced. --Trovatore (talk) 05:51, 20 June 2013 (UTC)[reply]

But how do you know that we have free will? I see no proof of that - and I believe that the hypothesis of the existence of free will is unfalsifiable. Using that to overturn what seems like an otherwise perfectly reasonable hypothesis makes no sense. But we're getting *way* off-topic here! SteveBaker (talk) 13:52, 20 June 2013 (UTC)[reply]

The problem, Trovatore, is that the reversibility principle we're talking about here (Which really is just the fact the the evolution operator must be unitary) cannot be false without messing up the conservation of probability. In other words, you will find yourself with a theory that predicts that some events will happen with a probability larger than 100%. That makes no sense which makes this kind of non-unitary theories complete rubbish. Dauto (talk) 14:11, 20 June 2013 (UTC)[reply]

Whether that can happen or not, depends on the local density within the star, and lifetime, and size of the microblackholes. They need to evaporate faster than what they can grow to ensure a stable existence of the neutron star. Plasmic Physics (talk) 05:02, 20 June 2013 (UTC)[reply]

These black holes would then convert the neutrons and other particles into photons which leads to heat production in the core. You'll reach dynamical equilibrium where this heat is radiated away and the core is at constant temperature. This means that the conversion of neutrons to photons leads to mass loss of the neutron star, eventually the lower mass limit where neutron stars are just stable will be reached, the neutron star will then explode. Count Iblis (talk) 12:47, 20 June 2013 (UTC)[reply]

Wouldn't microblackholes only form above a critical mass/volume density, or is the interior of neutron star sufficiently dynamic, that density fluctuations will lead to momentary sufficient densities for microblackhole formation? According to the first scenario, the neutron star will scintillate with microblackholes losing mass at a linear rate, until it reaches the critical density limit, whereupon the scintillation ceases completely. According to the second scenario, the star will scintillate indefinitely, but at an exponentially decaying rate, and lose mass correspondingly at, until it reaches bellow the minimum neutron star mass. Plasmic Physics (talk) 13:12, 20 June 2013 (UTC)[reply]

The point of what I said above is that the interior of the neutron star is not at the verge of forming black holes, when the entire neutron star is. That's the screwed up thing about it - it is a macroscopic property, not microscopic! According to Schwarzschild radius a region the size of the Earth would have to be 10¹¹ denser than a region the size of the sun to become a black hole, for example. It is very weird to picture there could be so much change (in the case of "fuzzball"s, even a change in the essence of the contents; in the case of the black hole, their loss of all ability to orbit one another) based on just adding some more matter. Wnt (talk) 21:32, 20 June 2013 (UTC)[reply]

June 20

Use of multiple transformers as a power bank

I'm wondering if and how it is possible to align multiple small transformers in series and parallel configuration (just as with batteries) to gain a higher output in amps and voltage without burning them out, starting with the weakest point. Would I need "flowback preventers" (don't remember the proper name but you sure know what I mean) [add: I guess I'm talking about a "foldback" or similar protection] on each transformer? Battery banks can not be compared to my intentioned "transformer bank", I know. That's why I'm asking for some professional input on how to achieve a working "transformer bank". Note: Transformers would have each an output of between 6 to 20 volts, with different output in amps of course. Note: a simple and cheap solution is preferred; Not that I'm cheap and simple myself but... :). Thanks.TMCk (talk) 03:01, 20 June 2013 (UTC)[reply]

You can do that but there's no point in doing it compared to having a bigger transformer with thicker wires. Batteries are put in series because the chemical process only generates a certain voltage and they are put in parallel because the manufacturers only produce certain sizes and the customers need to replace them. Neither of those is true for transformers. Dmcq (talk) 10:56, 20 June 2013 (UTC)[reply]

Actually, there *IS* a point to doing it and you'll occasionally see it done in practical circuits. Multiple physically-small transformers may fit into a space where a single large transformer won't because of "form factor" constraints. I have an inverter that uses four small high-frequency transformers operating together. Atlant (talk) 23:36, 20 June 2013 (UTC)[reply]

Are you talking about "naked" Transformers (i.e. AC) or a bunch of power bricks/PC power supplies (i.e. DC)? At any rate, yes, for transformers you would need some Rectifiers and Voltage_regulators. Most DC PSUs have some sort of Voltage_regulator built in. This can be very simple or quite complex as in an ATX power supply. In practice, these voltage correction circuits "fight" each other when a load is placed on the circuit. For example, if you needed a 600W PSU for your PC you could theoretically use 2x 350W PSUs. This is not a good idea for many reasons and is quite complicated to get right. See here: http://www.tomshardware.com/forum/298250-28-identical-power-supplies Just sell all the small ones on eBay and buy a big-ass one.196.214.78.114 (talk) 12:02, 20 June 2013 (UTC)[reply]

Sorry yes I'd read it as just straightforward transformers not switched mode power supplies which are another category of beast altogether and are more common nowadays. I wouldn't want to start sticking those together without a great deal of study, I think blue smoke if not a fire is altogether likely otherwise. Dmcq (talk) 16:20, 20 June 2013 (UTC)[reply]

Certainly transformers can be combined in series or in parallel, but if it is done haphazardly, some may be exposed to excess voltage or may have excess current drawn from them resulting in insulation failure or overloading, and the resulting in smoke, fire, and sparks. The transformer impedances must be considered, if they are not identical transformers, since a lower impedance transformer in parallel with a higher impedance one will "hog the load." The designer should make sure that there is adequate protection by means of fuses or circuit breakers for any condition where transformers or leads fail shorted or open. Many more things could go wrong with interconnected small transformers than with adequately large single transformers. Edison (talk) 19:17, 20 June 2013 (UTC)[reply]

Thanks to all of you for your answers. A few comments in response:
- Yes, Dmcq, I was thinking/talking about standard transformers that convert (120) AC current to DC. fluctuations in voltage are of no concern as they would be used to power non-sensitive equipment such as a low DC voltage but high amp power drill I.E., so the power source would be supervised at all times when in use besides being enclosed in a fireproof housing and protected by fuses for each single unit and a main fuse for the whole package. I might want to include a PC power supply I have laying around but most likely separated and to provide only power to a cooling fan for the unit.
- The main question for me is (and Edison touched that issue in his comment), Is it certain that the smaller transformers will "hog the load" and shorten out and if so, is there some protection other than a fuse that would disconnect the weak point as it would render the whole unit useless? Is there some simple component that would limit the amps drawn from a single transformer?
- Regarding rectifiers that I only know as converting AC to DC current: If I understood it correctly, it would also prevent backflow from higher rated units to lower ones. Is that a correct assumption?
- BTW, Edison, I don't intend to do it the "haphazardly" way; That's why I'm educating myself by asking the experts here, experts like you ;)
- Atlant, could you tell me in more detail about this "inverter that uses four small high-frequency transformers operating together?" I'd be truly appreciated :)
To sum it up, the point of the whole thing is to use all those abandoned power supplies I have laying around and put them to some good use.
Again, much appreciated for your input so far... and greedy as I am when it comes to knowledge, I'm still hoping for more :)) TMCk (talk) 01:28, 21 June 2013 (UTC)[reply]

Radioactive decay energy distribution

When a radioactive substance decays. Most decays ought to be within a quite narrow set of decay energies. But given the stochastic nature some decays ought to deviate from what the Poisson distribution implies. So that if 99.9999% of the energy is of circa 40 keV, then perhaps some very rare decays are 800 keV ..? Electron9 (talk) 06:42, 20 June 2013 (UTC)[reply]

Do you have a question? 139.193.214.10 (talk) 10:29, 20 June 2013 (UTC)[reply]

Where do you suppose the extra energy is coming from? Energy is conserved, you know that right? Dauto (talk) 12:12, 20 June 2013 (UTC)[reply]

Not so fast. Radioactive decays, like other quantummechanical transitions have a finite natural linewidth. In fact, the decay energies should follow a Breit-Wigner distribution which extends to arbitrarily large energies. This implies that the 800 keV that Electron9 mentions are indeed possible, although very rare. This does not violate conservation of energy because of the uncertainty principle. --Wrongfilter (talk) 13:04, 20 June 2013 (UTC)[reply]

"Stochastic nature" refers to the time of the decay, not the energy. The actual decay energy most generally (even for high-energy phenomena like the decay of a Z boson) follows a relativistic Breit–Wigner distribution and e.g. the alpha particle kinetic energy and nucleus kinetic energy can be computed from conservation of momentum. The decay width is equal to

{\frac {\hbar }{\tau }}

, where

\hbar

is the reduced Planck constant and

\tau

is the mean lifetime of the radioactive parent nucleus; this mean lifetime has a simple relation to the the half-life,

\tau ={\frac {\tau _{1/2}}{log(2)}}

. Notice that the widths are often very narrow, e.g. for ²²⁶Ra with a half-life of 1601 years it's about

9\cdot 10^{-27}

eV.

Apart from that, there are often several different decay energies, leading to a daughter nucleus in different energy states. Usually the daughter nucleus subsequently decays to its ground state by emission of gamma radiation.

Icek (talk) 13:11, 20 June 2013 (UTC)[reply]

The relativistic Breit–Wigner distribution is only relevant for resonances which happen when the particle's mass times its lifetime is of the order of Planck's constant or smaller. I don't mean to say that it would be wrong to use the Breit–Wigner distribution for long lived nuclei, but it's unnecessary. Due to the very sharp distributions obtained in those cases, you can simply replace the Breit–Wigner distribution with a Dirac's delta distribution. Dauto (talk) 13:56, 20 June 2013 (UTC)[reply]

So how does one calculate the probability that an energy above a certain level will occur?, ie how long time before an > 800 keV for substance x happens? or at least do an estimate if it's really complicated maths. Electron9 (talk) 14:29, 20 June 2013 (UTC)[reply]

The correct way to find this probabilities IS to use the Breit–Wigner distribution. My point is that for a long lived nuclei - say with life time longer than plank's constant divided by the decay energy, that probability can be safely set to zero. For example, if the decay energy is 40 keV, Than hbar/E = 6.6*10^(-16)/4*10^4=1.6*10^(-20) seconds. If the lifetime of the nuclei is much longer than 10^(-20) seconds, than the probability of a decay with an energy much different from the 40 keV becomes negligible. Dauto (talk) 14:54, 20 June 2013 (UTC)[reply]

How improbable is negligible? there's usually a lot of atoms around such that even low probability events occur. Let's say, how long time does it take for a substance of n mol of U-235 atoms to generate say 10 gamma photons with an energy of more than 800 keV ..? Electron9 (talk) 15:52, 20 June 2013 (UTC)[reply]

To answer that question, you must first re-derive the energy distribution to take into account the fact the system undergoes decoherence during it's lifetime. So, in the derivation of the Breit-Wigner distribution, it is assumed that you can describe the system as a superposition of the unstable particle and its decay products. That it will eventually interact with the environment is something that happens on a much longer timescale than the time scale for decay. In the case of an unstable long lived nucleus, the opposite is true, so you need to take that into account. What is clear is that the probability of having a decay with a significant different energy is exactly zero, and not just very small, because the mass of the unstable nucleus becomes well defined enough to eliminate that possibility entirely. Count Iblis (talk) 16:08, 20 June 2013 (UTC)[reply]

Below energies and above mean lifetimes for which the Breit-Wigner distribution is absolutely needed, one can use a Cauchy distribution (also known as Lorentz distribution).

Anyway, Count Iblis is correct in saying that for any practical measurements of long-lived isotopes, the measurement process introduces far more noise than the decay width. Analogous to Heisenberg's uncertainty principle there is a time-energy uncertainty; so one would definitely need longer than 1600 years in order to actually measure the decay width of ²²⁶Ra.

But if one would measure with a long enough time of observation, and sufficiently sensitive instruments, then I can give you a simple formula for the probability of the decay energy being higher than some energy E₁:

${\frac {\Gamma }{2\pi (E_{1}-E_{0})}}$

$\Gamma$ is the decay width ( $9\cdot 10^{-27}$ eV in the example I posted above) and $E_{0}$ is the decay energy (40 keV in your example). The formula is only valid as long as the energy difference is much larger than the decay width.

Icek (talk) 18:16, 20 June 2013 (UTC)[reply]

Neglecting for a moment that, as Count Iblis correctly pointed out, that probability really is zero, and assuming you are talking about perfectly isolated atoms so that coherence could be preserved, plugging in the data for U-235 in Icek's formula, the answer to the OP's question is that 1 in 3.7*10^37. That's about 6*10^13 moles of U-235 or 1.45 * 10^13 kg of U-235 or 1.45* 10^7 kilotonnes of U-235. That's about 3000 times the size of the world supply of U-235. (Or may be I'm confusing the supply of U-235 with the supply of Uranium in general in which case multiply by another factor of 140). In any case, it's clearly that the only sensible answer to the OP's question is "Not a snow ball's chance in hell". Dauto (talk) 21:51, 20 June 2013 (UTC)[reply]

I'm talking of a solid block of some decaying material, say 1 cm³ and if it's possible to use the emission of low probability, high energy photons, neutrons etc to detect such substance. The high energy would make detection through other materials and distance possible. Electron9 (talk) 23:22, 20 June 2013 (UTC)[reply]

Count Iblis and Dauto are not correct in claiming that the probability is really zero: Not with respect to the situation when one really has a sufficiently long observation time; and even less when talking about measuring within shorter times and possibly with some other interactions (because these things broaden the decay width). Even less so when one thinks about physics more generally: We don't know everything, and there could be some rare decay (e.g. proton decay) that results in the emission of the right particle at the right energy.

Electron9, it is in principle possible to do it with e.g. gamma rays (high energy photons) emitted from a solid block, and you can just plug the data for your particular isotope into the formula. But for anything but very short-lived isotopes it's pretty hopeless to really measure it, and it's difficult to produce solid blocks of 1 cm³ of very short-lived isotopes. And needless to say you have to care about a lot of other things like contaminants (other radioactive isotopes) in your block and broadening of the decay width by e.g. Compton scattering.

Icek (talk) 10:59, 21 June 2013 (UTC)[reply]

I agree that saying that something is "exactly" zero is shady. But the probability for what the OP is asking for is so incredibly small that for any practical purpose imaginable it can be effectively considered to be exactly zero. Dauto (talk) 14:08, 21 June 2013 (UTC)[reply]

It seems to me an artifact of pretending that one cannot identify the initial state of the system accurately enough for the decay with large energies of the decay propducts to be possible (in principle) at all. If you take this serious, then the effect is due to not having the initial nucleus in the state you thought you had. But nothing would stop one from preparing the correct initial state (within the available time limits) which then cannot decay with the decay products having such high energies. Count Iblis (talk) 14:31, 21 June 2013 (UTC)[reply]

Mailing list regarding Rodentia

Hello, could you please point me out a mailing list regarding Rodentia? --194.95.30.128 (talk) 10:59, 20 June 2013 (UTC)[reply]

Have you tried using Google? A quick search turned up some results... — Preceding unsigned comment added by 217.158.236.14 (talk) 11:24, 20 June 2013 (UTC)[reply]

What aspects of rodents in particular are you interested in - e.g. their physiology, their ecology, keeping them as pets or eradicating them as pests? This may help us narrow our replies. Equisetum (talk | contributions) 11:27, 20 June 2013 (UTC)[reply]

Here is a listserv for pet rats, hosted by Yahoo [13]. Using the key word "listserv" gives decent google results for many similar topics. SemanticMantis (talk) 12:39, 20 June 2013 (UTC)[reply]

Thanks everybody for the help. I already made some Google search, but I did not find anything useful. I am searching for a list focused on Rodentia on a mere biological basis (not for pest control or for pet keeping, sorry for giving this for granted). The main aspects I am interested in are taxonomy and ecology. Using Using "listserv" as a keyword improves the quality of Google results (still I need to find a suitable one, but I will keep searching). --194.95.30.128 (talk) 17:37, 20 June 2013 (UTC)[reply]

Here's a nice list of bio/eco lists [14]. There is one for shrews, and one for animal behavior, but not one for all things rodent. You could also join the very popular list ECOLOG, and ask there for good rodent science lists. Another key phrase for searches would be "small mammal ecology." SemanticMantis (talk) 18:43, 20 June 2013 (UTC)[reply]

Thanks for the hints. I am considering subscribing to ECOLOG, but first I will try to refine my Google searches, also on the basis of your indications. Strange anyway, I would have expected to find such a list much more easily! --194.95.30.128 (talk) 11:56, 21 June 2013 (UTC)[reply]

June 21

How does a paper airplane fly in the space station?

For a aircraft such as a paper airplane to fly in the air above the ground, the lift force upward should balance the weight force downward. The gravity is almost zero in the space station. How does a paper airplane fly in the air of zero-gravity environment? My guess is that without gravity, there will be frictional force downward due to the air, but I'm not sure how the paper plane behave. I have found an article titled "Zero-gravity flight of paper airplanes" by John Bain, NRC/NASA in 2000, but I can't access it. Could someone tell me what this article talked about? Thanks! Armeria wiki (talk) 03:52, 21 June 2013 (UTC)[reply]

If it's in free fall, why would the frictional force be downward rather than just backward? It seems to me that the airplane would go straight ahead, the direction affected only by the shape of the plane and the odd air current. Clarityfiend (talk) 04:36, 21 June 2013 (UTC)[reply]

My guess is that since there is no downward gravity force on the paper plane, the paper plane with certain initial velocity in the air will get an upward lift force, and it will fly forward and upward. There will be a backward air frictional force to gradually reduce the forward velocity of the paper plane, and a downward air frictional force since the paper plane will move upward. Armeria wiki (talk) 05:03, 21 June 2013 (UTC)[reply]

How about video demonstration: [15] -- Scray (talk) 05:06, 21 June 2013 (UTC)[reply]

Thanks! Could you please tell me what the video demonstrated? My internet connection is not good. Thanks! Armeria wiki (talk) 05:48, 21 June 2013 (UTC)[reply]

The paper, Zero Gravity Flight of Paper Airplanes (AIAA, 2000). Briefly, the paper describes a series of educational outreach programs for Houston-area students of various academic levels between 1998 and 2000; they design an experiment to launch and measure trajectories of a small toy airplane inside the NASA "Vomit Comet" KC-135A aircraft, in a ground laboratory, and in a computer simulation.

From the data collected, I'd say the paper airplane (actually, a foam space-shuttle toy and a student-made mechanical launcher apparatus) produces very little lift; its behavior is almost perfectly ballistic, with slight air resistance. So, in 1-G, the airplane travels in a just-barely asymmetric parabola; and in the 0-G of the KC-135A, the airplane flies in almost a perfect straight line. The paper delves into some more advanced math, and calculates the lift and drag more accurately; and studies the nonzero pitching moment of the paper airplane. And, there is some extra math to deal with the complexity of the rotating coordinate frame (because the KC-135A is not a perfect "0-gravity" environment - it is neither stationary, nor perfectly fixed acceleration, nor in a constant orientation); so I should say, the trajectories of the model aircraft inside the airborne lab need to be interpreted carefully.

It is worth stating that lift is a very nontrivial quantity to calculate: just because something has wings does not guarantee that it generates lift at any particular attitude. Nimur (talk) 05:34, 21 June 2013 (UTC)[reply]

After reading a little farther: During a final flight in year 2000, an improved launcher was used, capable of launching paper airplanes faster than before - at 25 ft/sec (17 mph) in ground and airborne experiments. In this experiment, airborne (0-gravity) trajectories actually show significant upward drift indicating that the model aircraft is pitching up and generating lift. Nimur (talk) 05:52, 21 June 2013 (UTC)[reply]

Thanks! I found this paper by John Bain by can't access it. Could their foam space-shuttle toy fly as well as a normal paper airplane with normal gravity? Armeria wiki (talk) 05:54, 21 June 2013 (UTC)[reply]

The specific model was a WhiteWings Space Shuttle foam airplane. I have never played with that specific space-shuttle toy, but I've spent enough time with a variety of foam and other model airplanes to know how they fly - they're quite a bit heavier and more rugged than an ordinary paper-airplane. One of the biggest problems facing a paper-airplane is its lack of inertia and its very light wing loading due to its very low mass - so a paper airplane is incredibly susceptible to gusts, turbulence, drag due to cross-sectional area, and because it is so easy to turn over, a paper airplane is easily upset to unusual attitudes that are unsuitable for stable flight. The foam airplane toys are much heavier, and while that weight does work against them, it also has advantages over paper in terms of stability and speed.

Because the WhiteWings Space Shuttle is roughly shaped like ... the Space Shuttle... it's not a great aerodynamic platform. Its wings are short and stubby, and its total wing area is small. This is probably a contributing factor to my earlier comment - its flight trajectory looks pretty close to ballistic in ground-tests - in other words, not much different from the flight-path of a brick. This is actually how NASA pilots described the Space Shuttle Orbiter: "un-flyable" and brick-like. Nimur (talk) 06:21, 21 June 2013 (UTC)[reply]

It seems that the paper airplane in air with zero gravity will get a upward lift force and fly up and forward. Since in the zero gravity space, there is no real "up" or "down" direction. What "up" means for the paper airplane is the direction perpendicular to the surface of its wings. So will the paper plane fly in a big circle trajectory if its initial velocity is large enough and the room of the space station is large enough once the lift force perpendicular to the instantaneous velocity of the paper airplane serves as a centripetal force? Armeria wiki (talk) 06:15, 21 June 2013 (UTC)[reply]

That is one very plausible trajectory - if a few conditions are met. The aircraft must have positive lift, and a positive pitching moment. The air - atmosphere - in the space-station's laboratory can't get too turbulent - which is a big if. The rate of pitching and the lift must be stable. Other effects - like rolling, yawing, and lateral movement - and drag - need to be negligible. If these conditions are met, the aircraft can maintain steady-state flight with a circular trajectory. Nimur (talk) 06:25, 21 June 2013 (UTC)[reply]

The other answers here are probably better, but just intuitively from my very low-grade efforts: my impression is that a crude paper airplane has lift because it inclines a bit upward. And the reason why it inclines upward is that it is heavy in the rear end. So with no weight, there's no lift... Wnt (talk) 08:00, 21 June 2013 (UTC)[reply]

Eh...well, not really. Lift (for a more or less planar surface like a paper airplane wing) is a function of angle of attack. Certainly, any paper plane that's trying to gain altitude from level flight needs a positive angle of attack. But in a zero g environment, it's not entirely clear which way is "UP"...so how does the airplane "know" what its' angle of attack is? When you think about it - it's when the velocity vector isn't parallel to the plane of the wing...then the wing deflects the air so that it is parallel - and that results in lift. So if you throw your paper plane such that it has a not-parallel-to-velocity attitude at launch - then even in zero g, it'll develop a flight path that deflects away from the original launch vector...which is the nearest thing to "lift" that you can reasonably talk about. Pretty soon, the pressure of deflecting that air downwards will cause a rotation towards making the wing parallel to the new velocity vector - at which point, the plane flies in a straight line. I suspect that this is the primary effect with paper planes in one-g environments too. You don't see paper planes flying along in a nose-up attitude to any great degree.

Remember, a "zero g" environment is just "free-fall" - and the paper airplane is in free fall even if you launch it on the surface of the earth. SteveBaker (talk) 14:19, 21 June 2013 (UTC)[reply]

(ec with Steve)

Wnt is describing flow deflection, which does produce lift (and drag). But, that type of lift depends on angle of attack and the shape of the object - not the object's weight. The angle of attack for a piece of paper is detemined by pitch, and pitch is determined by the pitching moment, which can be affected by weight - it is usually calculated by summing the weights and their moment arms. But it's not true that the absence of weight automatically yields zero pitching moment; nor that it yields zero lift... these are distinct parameters. For example, a trim tab on a paper airplane would still work in microgravity.

While Wnt's observation probably is valid for (paper) airplanes in normal conditions, it would start to break down in weird cases like microgravity. Nimur (talk) 14:30, 21 June 2013 (UTC)[reply]

I'm reminded of a competition that was run on my companies' summer picnic for the pre-teen kids of employees. They were given a single sheet of paper and told that they had 5 minutes to make a paper airplane that would fly further than the competition. My son (then 10 years old) scrunched his paper into a tightly wadded ball (he called it "Death Star") and easily won the first round of the contest ahead of about 50 other kids. There was considerable unrest amongst parents - and the contest organizers were thrown for a loop. They hastily changed the rules for the second round to prohibit scrunched up balls - so Oliver folded his paper into the thinnest possible wingless needle-like shape and easily won the second round too. The conclusion being that drag is overwhelming more important than lift for paper planes! SteveBaker (talk) 14:10, 21 June 2013 (UTC)[reply]

clostridium

If a wound is contaminated by clostridium species, it may favour developing of complications,,,one example I think is Gas Gangrene,, anyone knows other examples ??????? — Preceding unsigned comment added by 201.220.215.11 (talk) 04:09, 21 June 2013 (UTC)[reply]

Is this a request for medical advice, or a general question about bacterial infections and their outcomes? If the former, it is not permitted under Wikipedia Reference Desk guidelines and must be closed without response. If the latter, then referenced responses are welcome. Have you read Clostridium and Gas gangrene? Edison (talk) 04:15, 21 June 2013 (UTC)[reply]

Tetanus is another possible consequence -- have you looked at our Clostridium article? Looie496 (talk) 06:32, 21 June 2013 (UTC)[reply]

Melancholia

Is it plausible for an asteroid to follow a trajectory like that in the movie (enter the Solar System at high speed on the opposite side from the Earth; closely approach the Sun while remaining eclipsed thereby from the Earth at all times; fly by the sun at high speed, presumably with a close perihelion, while still remaining invisible to the naked eye; cross the orbits of Mercury and Venus and eclipse Antares while still remaining invisible to the naked eye; make a close fly-by of the Earth on the night side (close enough to illuminate it to civil twilight level); and finally, slingshot completely around the Earth and hit it from behind)? My intuition tells me this is probably an impossible trajectory, but could someone verify? Also, I remember a few years back there was a scare about a real asteroid (albeit one that entered the Solar System from the same side that Earth was on) which was predicted to slingshot around the Moon and hit the Earth (just like in the movie), but missed -- could someone please refresh my memory regarding the asteroid's catalog number, and whether it inspired the movie? 24.23.196.85 (talk) 05:48, 21 June 2013 (UTC)[reply]

Not a good answer this time, but: My first impression is that if a rogue planet comes heading for the Earth, odds are it will hit somehow, because odds are there's a rocket engine poking out the back of it. :) But for this exercise I suppose we should put aside active holographic camouflage and rapid acceleration.

For this exercise we should assume infinite bad luck. God (the god of bad sci-fi, to be precise) is clearly out to get these people. To begin with, that means that the rogue planet may execute a successful aerobraking maneuver through the outer layer of the Sun that leaves it with just enough energy to reach Earth's vicinity, despite having fallen into the solar system from great distance.

The premise is apparently that it is a stealth planet, practically invisible even on the same side of the sun, so provided we can swallow that (basically, a zero albedo) it is hard to picture seeing it on the far side, provided it doesn't occlude somebody's favorite star (odds?). (Presumably the dark layer is stripped away by passing through the Sun's outer layer and/or by passing within Earth's Roche limit, if it does)

Planet or no, it should obey some of the basic rules of orbital mechanics - ignoring the initial velocity being wrong, if it's at the orbit of the Moon it should take a month to orbit (or else move away, not nearer); if it's 24,000 miles away it should be in geosynchronous orbit, and if it is grazing the tops of the clouds it might indeed be in hours. I'm not sure if the figure in the article is in hours or days, but you could make some arguments based on that. Wnt (talk) 08:16, 21 June 2013 (UTC)[reply]

Speakers and headphone burn in

Is there truth in the fact that speakers and headphones sound better after a 100 hours or so of use? Why is this? Clover345 (talk) 08:15, 21 June 2013 (UTC)[reply]

According to this [16], yes - some headphones sound very slightly different after they've been used for some number of hours. "Better" is subjective...so is the number of hours and so is which brands of headphones sound better. I presume speakers are the same. There are mechanical components (the moving cone and the magnets it's connected to) that may well have less friction after they've had a few hours of wear - or the flexible cone gets more flexible after it's been bent back and forth a few million times. It's plausible that there could be some change like that.

HOWEVER: Audiophiles are notorious for spouting bullshit about what they can and can't hear. We've all seen those complete and utter nonsense discussions of $500 gold plated USB cables and how people claim that there is more "warmth" or "presence" through a $500 cable than a $5 one. To anyone who understands the first thing about digital signal processing, this is an incredibly stupid claim. Either the numbers in the audio data make it through the cable or they don't...there is no possibility of them losing high frequencies or something! You can transfer a picture from your camera to your laptop through a USB cable - and then do the same thing by removing the Micro-SD card from camera and plugging it into the computer - then compare the two binary files for that picture and they are byte-for-byte identical every single time. Same deal with the audio. It's complete nonsense that switching out a perfectly functional cable for a gold-plated one could have any effect at all unless the old cable was so bad that it didn't work at all.

Check out (for example) the "Monster Digital" USB cable - no longer priced at $500 as it once was - but still a somewhat exhorbitant $25. Here is a typical customer review: "Gives me a little more head room to work with recording vocals I notice.". The guys at Guitar Center say "Advanced design and construction maintain proper impedance to reduce jitter, resulting in better focus, clarity, and extended dynamic range." - complete and utter bullcrap!!

The whole field of audio is a very sad affair. Back 30 or 40 years ago, equipment didn't reproduce sounds very well and there was immense scope for tireless geeks to fiddle around with different components to try to get it better, to write long magazine articles about it - to argue at the pub about whether the such-and-such speakers are "warmer" than the so-and-so kind with or without the blarfatron-2000 pre-amp. They all had an immense amount of fun and became world-class experts. But with the arrival of digital audio, signal-processing and sophisticated computer design for things like speakers - you get essentially perfect quality from even the very cheapest devices - there is really nothing left to geek-out about. So we have all of these aging audiophiles, just desperate to find something to make them sound more expert than some kid who just listens to MP3's on the stock headphones of his $20 MP3 player. So you hear huge amounts of utter hogwash like "getting better headroom on vocals" with an expensive gold plated digital cable. If we ever get cars that can all do 0-60 in three seconds, drive 200mph and get 400mpg in utter comfort and which only cost $1000, the exact same thing will happen with car nuts...and that's about the scale of what digital did to most aspects of audio.

So while there is some evidence that there is some tiny change in the frequency spectrum of older headphones, I'm 100% skeptical about whether the human ear can tell - or whether it matters or not - or whether they get better or worse with age.

SteveBaker (talk) 13:45, 21 June 2013 (UTC)[reply]

Your points on digital audio cables are apt, and audiophiles do like to go on... that being said, mp3 is highly lossy, even compared to a CD. CD's also have compression that analog signals do not. Whether you can hear it or not, there is a clear scientific/engineering basis for why some people might say a good audio tape sounds better than an iTunes mp3, played through the same system. I personally only notice on songs with lots of range in pitch, loudness, etc. but my ears aren't that great ;) SemanticMantis (talk) 14:52, 21 June 2013 (UTC)[reply]

Just to devils-advocate a little, the cable linked speaks of charging faster. Is it possible that faster charging of a speaker will change its performance? Also, I may TOTALLY misunderstand what the role of the USB cable is here, but if you're transmitting digital data to the speaker plus power and the speaker deciphers it at the far end, then won't the speaker be drawing power in a pattern that directly matches the waveform of the music, i.e. be sending a pulsed analog signal back up to the computer power supply, where all manner of impedance effects on it etc. can then have some faint influence on the originating speaker? Wnt (talk) 15:54, 21 June 2013 (UTC)[reply]

crystals and molecular bonds?

From our article Crystal.

[...] new atoms can very easily attach to the parts of the surface with rough atomic-scale structure and many dangling bonds.

I am not sure I understand what are these "bonds" which attach the atoms. Are they similar to molecular bonds? If so, can we consider a crystal to be a single, very large, molecule? --Lgriot (talk) 11:12, 21 June 2013 (UTC)[reply]

A variety of bonds are possible which explains why crystals can have so many properties. In a salt crystal the bonds are ionic bonds which explains why salts can so easily be dissolved in water. In a diamond the bonds are covalent bonds which explains why diamonds are so strong. In water ice the bonds are hydrogen bonds which are weaker than either ionic or covalent bonds explaining the low melting point of water. In hydrocarbons the bonds are Van der walls bonds explaining the even lower melting points. Dauto (talk) 13:50, 21 June 2013 (UTC)[reply]

Thanks.--Lgriot (talk) 14:28, 21 June 2013 (UTC)[reply]

Resolved

Excercise

So I'm a little overweight, and I want to exercise but I find running not just physically, but also mentally frustrating, and it doesn't make me feel fresh or anything, unless I run for an hour or more. I mean I get bored when I run and listening to music doesn't help much either. So I want to do something that both takes a lot of energy and is fun, and I want to be able to do it on my own. Do you have any ideas? I like going hiking but I guess it doesn't take much energy, and some people say it's bad for your knees, is that true?--Irrational number (talk) 22:16, 21 June 2013 (UTC)[reply]