Wikipedia:Reference desk/Archives/Science/2007 April 12

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April 12[edit]

Wastewater treatment with galvanic agglutination[edit]

In the world is there any known operating application of galvanic agglutination for treatment of wastewater or sewage? Zohaizolo 00:46, 12 April 2007 (UTC)

No one is having a go at this, so I will have a stab. Electrostatic precipitation would not work in water as it conducts too readily. However passing current through waste water is used to recover heavy metals such as chromium, nickel or silver. This would be used at the point where the water is contaminated in the first place to enure that there is a good yield. GB 06:48, 12 April 2007 (UTC)

differentially-sized particle self-sorting[edit]

(I tacked this question onto a thread from a few days ago, but it got archived before anybody answered it.)

While rummaging through a bin of assorted and different-sized Lego bits the other day, I was reminded of the principle that in a mixture of dry particles of different sizes, the small ones will tend to filter to the bottom while the large ones, contrariwise, rise to the top. I think this phenomenon has somebody's name attached to it -- does anybody know what it is? —Steve Summit (talk) 02:12, 12 April 2007 (UTC)

Brazil nut effect? Sometimes called the muesli effect (or so says the article). I don't know if it has a completely scientific name. --Bennybp 03:40, 12 April 2007 (UTC)
Yup, that's the effect, all right! Thanks. (I thought it had a "scientific" name, but maybe not.) —Steve Summit (talk) 01:46, 13 April 2007 (UTC)


Why do we automatically grimace when we feel pain? How is it to our benefit to signal when we're hurt and potentially vulnerable? --Wyckyd Sceptre 02:41, 12 April 2007 (UTC)

Perhaps to warn others related to us (and carrying our genes) that there is danger here (like a poisonous snake), which they should avoid ? StuRat 03:00, 12 April 2007 (UTC)
I've often been intrigued at how stoic my dogs are when in pain (pain which does not surprise them, that is). For example, my guy Lucky had a bad ear infection which I basically had to debride, and he would whine a little, but make no facial expression. --TotoBaggins 12:59, 12 April 2007 (UTC)
Do dogs have the muscles needed for facial expressions? --Carnildo 19:34, 12 April 2007 (UTC)
I was surprised how cooperative my cat was while I had to remove a tick from her skin. I guess squirming and grimacing as a response to pain is an illogical and culturally learned behavior. Nimur 02:18, 13 April 2007 (UTC)
I would guess that momcat would bite ticks off the kittens, so your cat now thinks of you as momcat. StuRat 18:18, 13 April 2007 (UTC)

Embryos, yolk sacs, placentas, and conservation of mass[edit]

I was trying to explain to my husband today that early in a pregnancy there is no placenta, and that the embryo survives and grows off nutrients in a yolk sac. Unfortunately, I know very little about biology, and wasn't able to answer his remaining questions. Where does that yolk sac come from? I mean, I know it's an integral part of the embryo to start with, but where do the nutrients come from? Does the ovum start with all the required nutrients in the beginning? Does the endometrium have any role to play early in the pregnancy?

The article prenatal development didn't help all that much. It didn't even tell me when the placenta forms and starts doing its work.

Thanks, moink 02:55, 12 April 2007 (UTC)

The ovum has a lot of nutrients, but like all other cells, it must absorb nutrients from its surroundings while growing. That's how the embryo manages to assemble a york sac. --Bowlhover 04:05, 12 April 2007 (UTC)
You have the right idea- early embryonic development in humans is very similar to that of non-mammalian vertebrates like reptiles and birds. The actual yolk sac however does not directly supply nutrients to the developing embryo. In fact, in the first seven days following fertilization the embryo is little more than a collection of dividing cells known zygote which migrates from the oviduct to the uterus. At around day seven, the embryo (which is known as a blastocyte) becomes slightly more organized and secretes enzymes that allow it to implant itself in the uterine lining or endometrium. The endometrium is highly vascularized (it contains an extensive network of capillaries). During the process of implantation, these vessels are eroded so that the blastocyte has access to maternal blood supply for nutrient exchange. At this point a great deal of differentiaon occurs at once leading to the development of tissue that eventually becomes the placenta. Among these is a fluid yolk sac that forms directly below the embryo proper. While this sac does not function as it would in birds and reptiles, its membrane is the site of early formation of blood cells that later migrate to the embryo. The articles associated with Developmental Biology. Other articles that you may want to check out are Mammalian embryogenesis and Yolk sac. If you can, try to get a hold of N.A. Campbell's and J.M. Reese's Biology (Benjamin-Cummings: San Francisco, CA)- its the reference source I used and is quite delightful to read (for a text book at least). CONGRADULATIONS TOO :)AggieAnnieM 09:14, 12 April 2007 (UTC)

Spider identification[edit]

Hey my cuz saw a black spider with red dots

this is really all that she gave me on describing it but it was in her room a while ago. anyone know perchance what it is or what kind it is?? Maverick423 03:06, 12 April 2007 (UTC)

Widow spiders, a genus of 31 species, tend to have red dots. See the image (right) for an example. Rockpocket 04:04, 12 April 2007 (UTC)

Rooted growth on face[edit]

What is a growth that can be located on a childs face that has roots. Starts with "S" for the first word and the 2nd word starts with "N"? added by User:

Moved this to its own sectionTwas Now ( talkcontribse-mail ) 05:20, 12 April 2007 (UTC)
I think you may have to provide more specific information. The only thing I can think of is a sebaceous nevus [1]. Rockpocket 06:10, 12 April 2007 (UTC)

Coefficient of relatedness calculation[edit]

Isn't the calculation of the coefficient of relatedness in evolutionary genetics not actually equal to the fraction of the genome two individuals share in common? For example, a child will have a coefficient of 0.5 with its parent. However, the fraction of the genome shared is actually much higher, > 99%. It seems that the coefficient more accurately describes the percentage of genes shared above the baseline of the species. For two people to have a coefficient of relatedness approaching zero, they would have to be "unrelated" (ie, as unrelated as humanly possible). But if the coefficient of relatedness between two humans can theoretically be zero, then the coefficient of relatedness between a human and (say) a bonobo would be negative, since there is even less genetic similarity. But there must be an inclusive benefit associated with helping primates, since we do in fact share some genes, so shouldn't the coefficient calculation come out to be a positive number? --JianLi 03:57, 12 April 2007 (UTC)

In terms of the relatedness co-efficient, instead of thinking about it about overall DNA identity think about it in terms of functional genetic units: loci. Two different alleles might be 99% identical at the DNA level, differing only at one basepair, but since they function as distinct genetic units they can be considered as completely different in terms a relatedness co-efficient. Therefore for any given locus, it doesn't matter if it is 99% identical (another human) or 20% identical (a fish), its not the same and therefore does not add positively to the co-efficient. If you consider this method of calculation, a human that differs from you with a polymorphism in every locus (co-efficient = 0) but still 99% identical in DNA, is no different than another animal that differs at every locus but is only 20% identical at the DNA level.
There is a theory (though I don't have access to a specific reference at the moment) that suggests we care more about, or empathise more with, animals that share a greater proportion of our genome than those that don't. For example, animal rights activists tend to focus their attention (in descending order) on primates, dogs and cats, rabbits, mice and rats, chickens, fish. They rarely mention flies and worms, which are experimented on and killed in much high frequencies, and no-one cares about yeast or bacteria. One might say we care more because the primates are more like us, but it essentially amounts to the same thing. If that is true, then there may well be an argument for considering inter-specific relatedness as a factor. Rockpocket 04:22, 12 April 2007 (UTC)
That makes a lot of sense, considering it at the loci level rather than the nucleotide level. But even so, humans probably have a large proportion of loci in common with each other. Do two humans with a coefficient of relatedness approaching 0 actually share no loci in common? I cannot imagine that I only share 50% of my loci with either of my parents. It seems thus that the coefficient actually designates the degree of relatedness above a baseline? But if so, the definition seems to run into the problems I describe below, namely where to demarcate the baseline. --JianLi 07:15, 12 April 2007 (UTC)
The coefficient of relatedness between two individuals represents the probability that a particular allele is shared by the two individuals over and above the baseline that is shared among all members of that species. In fact, for a coefficient of 1/128 or smaller (for example, a third cousin), that allele is about as likely to be found in a random individual as your third cousin (or whatever). − Twas Now ( talkcontribse-mail ) 05:27, 12 April 2007 (UTC)
Right, so why is the baseline set at the species level? Why not the genus? Doing so would yield different results, yet I can't see a principled reason to choose one taxon over another.
1) If the baseline is set at the species level, then interspecific comparisons would yield zero to negative coefficients of relatedness. However, this defies the logic that we share common loci with non-humans, and it would therefore behoove our inclusive fitness to help non-humans. Admittedly, as Rockpocket points out, the amount shared would be low if we considered loci rather than nucleotides. But we must share at least some loci with, say, non-human primates.
2) Try this thought experiment: Consider that the coefficient of relatedness between you and your mother is 0.5. Presumably you share 50% of all the loci above the baseline for humans. A large percentage of the human species dies out, reducing the amount of genetic diversity and therefore setting higher the baseline of human-ness. If the baseline becomes higher, the probability that a particular allele is shared between you and your mother over and above the baseline goes down, since elements which you used to share above the baseline are now considered below the baseline. Yet the 0.5 calculation is unchanged. And I would guess that the benefit to inclusive fitness of helping your mother is still the same. How do you explain this?
--JianLi 07:03, 12 April 2007 (UTC)
Those are all valid points, but they are theoretical considerations. Co-efficients are merely ways of representing relatedness for our calculations, it doesn't really matter what the baseline is or what the numbers are in practice because we don't have a magical way of determining such detailed genetic relatedness phenotypically. Humans presumably use visual and societal indicators to estimate relationships. They may also use odor cues. Other animals definitely use odor cues, and pheromone cues also (perhaps involving MHC-class proteins), to estimate relatedness. What is certainly clear, though, is that our ways of determining relatedness in a practical way is not at a resolution where we can distinguish between subtle percentage differences in the genome.
So consider if there was a set of 40 genetically encoded pheromone cues in mice the encode their entire repertoire. Each mouse expresses a different set of 8 cues as an identity "barcode". This gives mice quite a large scope for generating different identities. Now consider that each baby mouse will share 4 cues with each parent and siblings, two with each grandparent and 1 with each great-grandparent. If mice can detect each of the 8 different pheromones they will have the ability to sniff each other and determine relatedness with a resolution good enough for their own immediate family, but not much further. They can also detect the other mice pheromones, and know these represent other mice, but they will not have context within their own family to give meaning to those cues in terms of relatedness (unless, of course, they share expression of one or more of the 8 i.e. with a distant cousin). However, these other cues do distinguish other un-related mice from other species which don't have the same code. In this scenario, this code reflects relatedness co-efficients, but in a much simpler manner than we could calculate theoretically. It also explains a mechanism for detecting differences in inter- and intra- specific relatedness. I should say that the system I describe is currently hypothetical, however, I happen to know that there is a paper in the peer review process at a rather significant journal that describes a novel pheromone family and evidence it may follow this rough schema. Rockpocket 08:35, 12 April 2007 (UTC)

permanent magnet depletion[edit]

i would like to know if permanent magnets can be demagnetized by having them attract objects a long period of time (e.g placing a metalic object within it magnetic field but keeping it at a distance by any means)

i know that generating magnetic repulsion long enough can demagnetize a magnet but i am curious about the oposite —The preceding unsigned comment was added by (talk) 05:10, 12 April 2007 (UTC).

Having a magnet attract a piece of steel actually makes it last longer. There are rare earth magnets that will lose there magnetisation if separated from their magnet keeper. If you use such a magnet in a motor, it is not wise to remove it from the motor. GB 06:35, 12 April 2007 (UTC)

well i wasnt expecting this,

i know that perpetual motion is impossible but woudnt this mean that its possible to make a system where you could get energy out of the pull generated ??

Work requires distance. So, you eventually pull whatever you are trying to move all the way to the magnet. Then, the work is done. You need to move the magnet, which requires work, so you have to power that somehow - for a net loss in energy. You can try to pull something that spins around, making it spin and stay a specific distance from the magnet. However, you will need to keep moving the attracted items around or the closest one to the magnet will have the most force on it and it won't spin. Again, your work of moving things around cancels out any benefit from the system. It all comes down to the common mistake that energy is all we need. There is plenty of energy in every atom of everything around you. Making that energy do work is the key. --Kainaw (talk) 13:13, 12 April 2007 (UTC)
Exactly. There is a common misunderstanding about the difference between force and energy. An object such as a magnet can exert a force without either creating or consuming energy. Your fridge magnet exerts a force on the door of your refrigerator - but it requires no energy to do so - so it won't "run down" in the sense that a battery does. There are various processes that can destroy the magnetic effect - but they are chemical or crystallographic in nature - nothing to do with "running down" in the sense that a flashlight battery does if you leave it turned on. It's the same with gravity. The earth exerts a force to keep this laptop on my desk - but it doesn't require energy to do that. When something is pulled by a magnet (or gravity or some other force) - it moves towards the source - and THEN energy is expended - but the energy doesn't come from the magnet (or planet or whatever). The idea is that when something metallic is some small distance away from the magnet, it has "potential energy" (magnetic potential energy) by virtue of being that distance from the magnet. As it is influenced by the force that the magnet exerts, it moves towards it, giving up that potential energy in the process in order to overcome friction, and to give it kinetic energy. As the object gets closer and closer to the magnet, it goes faster (and gets warmer if it's overcoming friction) as it's potential energy decreases (because it's getting closer to the source of the magnetic force). When it hits the magnet, there is no more potential energy left - the kinetic energy gets converted to heat and sound as a result of the collision and it's all over. The force between the magnet and the object is still there - but no more energy is needed to keep them stuck together. If you now pull the object away from the magnet again, you need to expend energy to do that because you are giving it back that potential energy - and that energy has to come from somewhere. But in no part of this did the magnet expend anything. In fact, the reason the magnet stays stuck to your refrigerator is precisely because it doesn't have any energy. Since it would require energy to move the magnet away from the fridge door, and the magnet has no source of energy to do that - it stays stuck there. A non-magnetic object has no force to overcome - so it doesn't need to expend energy to move away from the door - it's free to fall off. You can replace the word "magnet" with "planet" and "magnetic potential energy" with "gravitational potential energy" and you get a similar scenario when something falls towards the ground and then you pick it up again. Planets don't "run out" of gravity! This misunderstanding is at the heart of a large number of claims for perpetual motion machines - people don't understand magnets - they appear to be a magical source of infinite energy - when in fact they merely exert a force. SteveBaker 14:07, 12 April 2007 (UTC)

you would need to find some way of making the metal drop once it has reached the top. I tried to do this, but didn't have any magnets, so I couldn't test my idea. Basically there was a layer of some sort of nickel/copper/iron alloy along the bottom of the magnet, and a slope that forces the rising object sideways so it passes under this layer and is no longer attracted to the magnet, and in falling, or possibly rising, could turn a turbine. It sounds like it could work, but probably wouldn't as it also sounds perpetual.

Egg Mass loss.[edit]

Apparently a freshly laid egg is 40% heavier than an egg about to hatch... Where does all the extra mass go? Gaseous transfer of waste through the shell? Is it always near 40% for any type of egg? Capuchin 06:53, 12 April 2007 (UTC)

  • Where did you read/hear that? -= Mgm|(talk) 10:17, 12 April 2007 (UTC)
It was one of the factoids on Steve Wright's Afternoon show on BBC Radio 2. I'm pretty sure his factoids are meant to be verified facts and not factoids. If it is bullcannon, please let me know :) - I can't find sources either proving or disproving it. (I now see that Steve Wright is mentioned on the factoid article as using the alternate meaning of the term, so I hope it is true! Although in a recent quiz he did ask which planet shares a name with a Disney dog, that one made me pretty angry.) Capuchin 10:21, 12 April 2007 (UTC)
A guess: The mass is lost dissipated as the energy (in the form of heat) that is required for the chick to form? − Twas Now ( talkcontribse-mail ) 10:40, 12 April 2007 (UTC)
Thanks for the guess, but I dont think a chick embryo would be so efficient as to convert such a percentage of the mass into energy so that most of it is used for growing, and 40% is wasted as heat. (the hen has to sit on the egg anyways to incubate it, doesnt it, so i doubt there is that much heat given off)? I'm guessing too however, it seems a bit much for me. Capuchin 10:48, 12 April 2007 (UTC)
Could it be a trick question? Because the egg in utero (or whatever it is, I'm not a chicken gynocologist) is floating and therefore less subject to gravity? Anchoress 10:51, 12 April 2007 (UTC)
I'm fairly certain he said a freshly laid egg compared to an egg about to hatch. And wouldnt that make the egg at the beginning lighter? Or am i misunderstanding your point? Capuchin 10:52, 12 April 2007 (UTC)
Yeah, the egg at the beginning would be lighter, which is what your original post says. The freshly-laid egg is 40% heavier than an egg about to hatch. Did you mis-type? Anchoress 11:03, 12 April 2007 (UTC)
My original post states that the egg gets lighter as it matures.. I think you are reading it wrongly. Some misunderstanding is going on. IT starts heavier, and loses 40% mass. Or are we misunderstanding "beginning". By that i mean the freshly laid egg. Capuchin 11:07, 12 April 2007 (UTC)
Uh... It's pretty difficult to mis-read "Apparently a freshly laid egg is 40% heavier than an egg about to hatch..." - a freshly-laid egg is 40% heavier than an egg about to hatch. You're saying that an egg in utero is lighter. I think I'm not misreading anything. But... if what you're actually saying is that eggs get lighter the 'older' they are, I think it's simple. Evaporation. The shell is porous, the egg is hot, even refrigerated eggs lose mass (and volume) over time. Anchoress 11:28, 12 April 2007 (UTC) I am sooooooooooooooo dumb, super sorry Capuchin. It was totally I who misread, you're 100% correct. Super sorry to inadvertently offload my dumbness onto you. Please forgive me, I don't know what is misfiring in my brain tonight. So... ignore my stupidity and yeah, I think it is evaporation. I'm going to bed now, or just to crawl under a rock cuz I'm soooo embarrassed. Like my grandfather said, bless his soul, "The definition of positive is "being wrong in a loud voice"." lolz. How he knew that I don't know, because he was almost never wrong. Nite! Anchoress 11:40, 12 April 2007 (UTC)
Do you mean in utero as in the hen's womb? I mean about to hatch as in about to be born from the egg, not in the hen's womb at all. Maybe evaporation will explain it well, Thanks. Capuchin 11:34, 12 April 2007 (UTC)
It's okay I still love you, have a good sleep, Thanks again. I was beginning to get a little confused myself, It's like the egg gets born and then the chick gets born! I think that's where the confusion was comign from :) Capuchin 11:43, 12 April 2007 (UTC)
I can't make any sense of this. Did he suggest it on 1st April by any chance? A quick Google threw up this, all of which I suggest should be taken with a pinch of salt.--Shantavira 11:33, 12 April 2007 (UTC)
Definately was around easter, not on the 1st. THe best answer there confirms it. Suprised that I cant find any more rigorous evidence though. Capuchin 11:36, 12 April 2007 (UTC)
  • Normally the humidity of incubated eggs is kept high to limit water loss. According to "Effects of increased water loss on growth and water content of the chick embryo", it is typical for chicken eggs to have an approximately 12.5% loss of mass during incubation, but you can have a loss of as much as 25% under "water-stress" conditions that reduce viability from 85% (control) to 20% (dryer conditions during incubation). I saw a similar value for water loss from ostrich eggs --JWSchmidt 14:06, 12 April 2007 (UTC)

I'd go with water loss and other gases. After all, an egg starts out quite runny, but the bird that results isn't "runny", so likely has a substantially lower water content. Note that if that much mass was converted to heat it would be like a nuclear weapon, according to E=mc^2. StuRat 16:06, 12 April 2007 (UTC)

It would be far more efficient than a nuclear weapon. I think that a small part of the egg mass loss is also due to the embryo's metabolism, organic material is converted to water and carbon dioxide for energy production. The carbon dioxide also escapes. Icek 21:32, 12 April 2007 (UTC)
The info is in Egg (food) under "Air Cell". From experience, eggs that are near hatching, are lighter than fresh eggs. The hen sitting provides humidity, to reduce water loss. Polypipe Wrangler 22:31, 12 April 2007 (UTC)

Quantum physics[edit]

reposted following erroneous deletion --Dweller 10:30, 12 April 2007 (UTC) I was interested in this topic, which redirects to the broader article Quantum mechanics. I looked at the "Applications" section of this article. As a total layman, it seemed to me that most of the (Physics) examples cited are of the science explaining how things work that already worked before we had the explanation, or theoretical applications of things that might work that don't yet work.

I'd be grateful if someone could post here (and to the article) some relatively well-known (POV, I know) devices or applications that have been devised because of our developing understanding of Quantum Physics. Perhaps it's just that I misread the article, or am too hung up on the difference between Physics and Chemistry in this field, which I guess may be irrelevant. Thanks. --Dweller 08:24, 12 April 2007 (UTC)

The Laser is certainly the prime example.—Preceding unsigned comment added by (talkcontribs)
Thanks. Perhaps I read it wrong, but I thought that the article was saying that Quantum Physics explained the behaviour of lasers, rather than the laser being invented because of understanding of Quantum Physics. Which is it? --Dweller 10:33, 12 April 2007 (UTC)
It is listed under applications on the quantum mechanics page and the history section on the laser page explains how the device was derived from quantum mechanics over about half a century before it was finally built. (I think my browser caused the deletion - sorry). —The preceding unsigned comment was added by (talk) 10:35, 12 April 2007 (UTC).
Thanks. --Dweller 10:42, 12 April 2007 (UTC)
Another example is Superconducting Quantum Interference Devices - highly sensitive magnetometers used in medical imaging applications and mineral prospecting. I don't think these devices could have been developed without a detailed understanding of quantum effects. Gandalf61 11:07, 12 April 2007 (UTC)
It keeps suprising me how well-spread the believe is that quantum mechanics has no relevance to technology, although it is really the opposite. To start with the laser example: The principle of the laser was already implied in Einstein's explanation of the photoelectric effect via the quantization of light (1905, the thing he later got the Nobel prize for). This explanation of Einstein, was after Planck's formula for blackbody radiation the second step on the way to understanding quantum mechnics. The photoelectric effect not only explains the laser, but also light emitting diodes, all kinds of fundamental research tools to study materials and muc more. Niels Bohr's model of the atom was quantum mechanics and helped to understand the periodic table. of course, only after quantum mechanics was developped to a fully fledged mathematical formalism (see von Neumann and others), we got the atomic orbital model, whithout which we still had no clue why the whole of chemistry works as it does. All modern chemistry is based on this quantum mechanical theory. The same holds for all the basic models of solid state physics, such as the electronic band structure of solids, that is the basis of our understanding of, e.g., semiconductor physics and hence all modern electronics. Bragg scattering (see also X-ray crystallography), a prime example of wave-particle duality, is the basis of most techniques to understand the atomic or molecular structure of crystals, including those of biological proteins, and nuclear magnetic resonance, widely used in medical imaging, molecular biology research etc., would be unconcievable without an understanding of the quantum nature of nuclear spins. And this list probably still left out more than it included. Simon A. 13:01, 12 April 2007 (UTC) +
Another example would be scanning tunneling microscopy, which works via quantum tunnelling, and was probably used in the design of the CPU you used to post your question. --TotoBaggins 13:12, 12 April 2007 (UTC)
Nice list, you covered everything I could think of plus some. I just wanted to drive home the point that you cannot even nearly describe the behavior of microelectronic and optoelectronic devices without QM. It gives you the theory necessary to describe interactions on the scale you are interested in. Even something as seemingly simple as current flow through a bulk semiconductor requires an understanding of QM to have insight into why, for example, carrier drift velocity saturates and in some materials gives rise to a negative differential mobility at high fields. If all you had to work with was Ohm's law, there is no possible explanation for this phenomenon. With the band structure (derived with the Kronig-Penny tight binding approximation) model, you can attribute this negative differential mobility to a higher-energy, lower curvature band beginning to populate and thereby reduce the net differential velocity with higher field rather than increase it. Understanding of this effect allows one to optimize the electrical field operating point as well as construct devices like the Gunn diode.
Various forms of tunneling are another set of purely quantum mechanical effects that are necessary to understand for both the consideration of parasitics (things that somehow diminish device performance) as well as for principle device operation. Structures as simple as an ohmic contact (the electrical interface between a semiconductor device and a conducting wire) and as complicated as HFETs/HEMTs, RTDs, several types of laser diode, etc; all are designed to use quantum tunneling in their primary operation. A more familiar example of quantum tunneling might be the gate leakage current parasitic associated with modern VLSI CMOS (your microprocessor, for example).
So here's one testimonial from a semiconductor guy to tell you that QM is just as important as Maxwell's equations and Kirchoff's circuit laws in the field of microelectronic engineering. -- mattb @ 2007-04-12T13:27Z
Incidentally, nobody has explicitly stated this yet so I'll mention it. Lasers use a quantum mechanical process called stimulated emission which was first predicted by Einstein in the early twentieth century. Without understanding stimulated emission and how to construct a device that reaches the necessary population inversion, you cannot make a laser (even if you DO understand the physics, they are tricky devices to build). -- mattb @ 2007-04-12T13:31Z
Quantum tunnelling is my personal favorite - without it, the computer you are sitting in front of right now wouldn't be working! Memory chips rely on this highly non-Newtonian phenomenon which takes advantage of the fact that energy is quantised and the Heisenburg uncertainty principle works the way we expect it to. I'm a little concerned that the questioner belittles the value of understanding how something works that 'already works'. Without explanation, we could never be entirely sure that something that we think works is actually functioning as we expect it to. For example - before Einstein, we believed that we could make clocks that "worked" - but only after his special relativity did we come to understand that our clocks only "work" if they aren't moving very fast relative to us. This turns out to be quite significant in some applications. Understanding how something works either confirms or denies our belief that it actually does work - and there is great value in that - even if nothing obviously new comes out of it. SteveBaker 13:48, 12 April 2007 (UTC)
Well, ETOX/Flash memory uses tunneling (and hot electron injection). DRAM and (perhaps more obviously) SRAM do not. Of course the effect is present in modern DRAM, but it's part of the parasitics that necessitate periodic refreshing. However, your first sentence is still true; most practical ohmic contacts are realized by making the Schottky barrier so thin that a large tunneling (field electron emission) current dominates the I-V characteristics of the metallurgical junction. While it's not nearly as glamorous as DRAM, you can't make a practical semiconductor device without good ohmic contacts. :) Edit: Not that Flash is the only type of semiconductor memory that actively uses tunneling; EEPROM and SONOS (both similar to Flash), MRAM, and a novel construction called DT-RAM ("DT" for "direct tunneling"). -- mattb @ 2007-04-12T15:21Z
Don't forget - radioactive decay as we observe it is inexplicable without QM tunnelling; radioactive decay products are ejected at lower kinetic energies than the height of the coulomb barrier they penetrated! --bmk

Distance per dollar map[edit]

Where can I find a railrod or highway map that shows construction cost in distance per unit of money using a system of color gradients similar to the color gradients used to indicate rain and wind intensity in online weather radar? For instance: an area in downtown Boston that costs a million dollars per 10 feet would be red versus a million per mile in rural areas which would show as light blue. Nebraska Bob 12:53, 12 April 2007 (UTC)

I'm not sure there is such a map. For one thing, the government agencies and private companies that build roads often don't like to release high cost info, as it makes them rather unpopular. So, you would need to file Freedom of Information Act requests, then take them to court if they refused, and repeat this many times throughout the US to get the info to build such a map. Also note that sections with suspension bridges and such would be off the scale as far as costs go. StuRat 15:40, 12 April 2007 (UTC)
Your first task is to create a rigorous, robust definition of the cost-per-mile. Without a universal definition, you will have an extremely hard time making fair comparisons between two stretches of road (for example, what if land rights or hourly labor cost more in one area? Is that part of the road cost? What about large stretches of route built as part of larger contracts, do you use the simple average cost, or try to quantize down to individual sections? What about bridges and tunnels, which cost many times more per mile, but are usually just averaged into the "route" cost? Nimur 16:58, 12 April 2007 (UTC)
To clarify here... the very point of using a distance per unit of money map is to overcome this problem since the location and distance covered in a day, week, month or year can be equated with costs for the same time periods. The question then becomes not how much have we spent to build this mile but rather how much did we spend and how far did we go today. Nebraska Bob 06:27, 14 April 2007 (UTC)
Try the US Bureau of Transportation Statistics. I don't know what they have for railroad data, or construction data in general, but they might at least have pointers to where you can get it. Construction costs vary based on the values of real estate, as you mentioned. As far as road building goes, you can probably get more data from the state departments of transportation. (In fact, I think government agencies are more willing to provide cost data, since it's a matter of public record.) For an example, check out the Crosstown Commons reconstruction project at the Minnesota Department of Transportation. --Elkman (Elkspeak) 17:02, 12 April 2007 (UTC)

Motion sickness[edit]

Is it possible that if you were to be driving or piloting a vehicle, then you would not be suffering from motion sickness, but you would (if susceptible) if you would be the passenger? —The preceding unsigned comment was added by (talk) 14:19, 12 April 2007 (UTC).

Absolutely. — Lomn 14:41, 12 April 2007 (UTC)
I guess that this could be possible, I think of it somewhat similar to tickling yourself. If you tickle yourself, it doesnt tickle! Because you know exactly where you're going to touch, if someone tickles you, even if you see them going to tickle you and you know where theyre going to touch, then it will tickle. Perhaps in the same way, if you are driving and know exactly the forces that are coming, you will avoid becoming motion sick, whereas a passenger, even though they can see the road and interpret where the forces will come, they cannot control it exactly, and so feel sick. This is purely me reasoning though, and may be complete babble! :) Capuchin 14:44, 12 April 2007 (UTC)
I agree (with the answer, not with the answer being complete babble). StuRat 15:34, 12 April 2007 (UTC)
It's certainly worse for passengers than for drivers, but drivers can suffer. Imagine you were piloting a small boat in a huge swell. I bet it would affect you to some degree. Also, trainee pilots get airsick: it says so here. Presumably trainee drivers/pilots who don't get over it give up. --Heron 21:15, 12 April 2007 (UTC)
With most types of vehicle the front is the more stable than the rear, so the driver has the most comfortable seat to start with.--Shantavira 07:52, 13 April 2007 (UTC)
Also, the driver has the steering wheel to hang onto, so she doesn't have to move around as much. Myself, I find I get less motion sickness the more I'm concentrating on something other than how sick I feel. So if I'm driving, then I have something else to worry about.Snorgle 10:11, 13 April 2007 (UTC)
Also, you get motion sickness more often if you are facing backwards, but the driver is always facing forwards. – b_jonas 16:28, 13 April 2007 (UTC)


please include history, like inventor, naming person, first isolated person all with images of them —The preceding unsigned comment was added by Narasinga (talkcontribs) 14:36, 12 April 2007 (UTC).

Sounds like homework to me. Have you read our article on staphylococcus? Splintercellguy 15:01, 12 April 2007 (UTC)
Nobody invented Staphylococcus. − Twas Now ( talkcontribse-mail ) 22:12, 12 April 2007 (UTC)
Louis Pasteur is usually credited as the discoverer of Staphylococcus as a cause of human disease. See page which has his photo and this site regarding his various discoveries. - Nunh-huh 22:28, 12 April 2007 (UTC)

Headphone magnets[edit]

Why do my iPod headphones repel each other magnetically they are brought near each other (only when they are plugged in)? Sould I be worried about the possible magnetic current running between my ears when I wear them? Not paranoid or anything, just curious. Lenoxus " * " 15:24, 12 April 2007 (UTC)

Why worry? I'm sure there are plenty of websites that will sell you head magnets to do anything from increase memory to cure cancer. I still see those silly wrist magnets in the store. The fact is that magnets are not harmful (or beneficial). An MRI puts your head through much stronger magnetic fields and, to date, they have not produced either beneficial or harmful effects. --Kainaw (talk) 15:28, 12 April 2007 (UTC)

You might have heard somewhere that magnetic fields can be dangerous, but those are far more powerful than the electromagnets in headphones. StuRat 15:31, 12 April 2007 (UTC)

Speakers generally work by vibrating a magnet attached to a membrane. The membrane is vibrated by an electro magnet that pulses to the frequency of the sound. Czmtzc 15:39, 12 April 2007 (UTC)
Yeah, you have magnets in just about every loudspeaker. You've been holding magnets up to your head your entire life! Panic! -- 15:52, 12 April 2007 (UTC)
You may be interested in bioelectromagnetics; the study of the effects of magnets on the body. As far as I know, the only known effects of magnetic fields are subtle changes in behaviour, and even this is in doubt (the observer-expectancy effect and subject-expectancy effect mean that testing this sort of thing on humans is notoriously fraught with error). Very strong fluctuating "transcranial magnetic stimulation" (ie; a magnetic field through the head) can cause brain cells to start firing without any stimulus, but I doubt iPod headphones could generate the kind of frequency or magnetic flux density required to produce a pulse. Laïka 12:47, 13 April 2007 (UTC)

Space Station Expeditions[edit]

As you may know, a new expedition recently went to the space station. Does that mean the previous one comes back? Nick 15:58, 12 April 2007 (UTC)nicholassayshi

Usually there is a partial or total crew transfer. See International Space Station and this handy List of International Space Station Expeditions, which details crew / transfers. Nimur 17:02, 12 April 2007 (UTC)

Can SETI Detect Our Own Transmissions?[edit]

With all the signals we send, purposedly or incidently, into space, does some reflects back to earth by bouncing off closed-by celestial bodies (the moon, Mars, asteroids)? And if so, can these reflected signals be picked up by SETI?--JLdesAlpins 16:59, 12 April 2007 (UTC)

If SETI listens for such things, then SETI will hear these things. You can read up on directional antenna and frequency allocation: SETI usually operates in radioastronomy or amateur radio bands, and a real concerted effort should use a highly directional antenna to avoid interference from unwanted signals. Nimur 17:04, 12 April 2007 (UTC)
SETI uses directional antennas and has a list of potentially interesting targets in deep space that it points those antennas to for a while. This is at least true for a part of the SETI project, I don't know what it does besides that. —The preceding unsigned comment was added by (talkcontribs).
Incidentally, "real" astronomers use reflected signals all the time. Some even initiate the signal from earth, while others use space-probes. I met with a radio-astronomer who is mapping mineral content on Mars[2] with synthetic aperture radar, interfering with a signal sent by the Mars Polar Observer. Here is a very technical scientific paper from NASA about similar work. Nimur 17:13, 12 April 2007 (UTC)
One thing I have been very curious about is this: Has a proof of concept ever been demonstrated for SETI? That is, have we ever beamed some random TV broadcast at a SETI receiver, then demonstrated that SETI detects an intelligent signal? It seems like this is the only reasonable way to proceed; if we can't detect terrestrial intelligence from the radio band, then we have no hope of doing it for ET intelligence. In my opinion, anyways. --bmk
Surely bmk is not suggesting that television signals contain intelligent information! Nimur 02:13, 13 April 2007 (UTC)
Inferred from , there probably has been millions of Radio Frequency Interference spike detections (i.e. detecting random junk from Earth). I'm not sure whether these include "reflected" Earth signals. I'd assume that these score pretty low. —AySz88\^-^ 19:12, 12 April 2007 (UTC)
As an aside, this concept was used to do "satellite reconnaissance" before Sputnik was even launched - the US briefly watched Soviet air-defence radar systems by detecting their reflections from the Moon. Shimgray | talk | 11:57, 13 April 2007 (UTC)
SETI not only can detect these signals - but they have to go to some considerable trouble to screen them out. Fortunately there are all sorts of cues that tell them when the signal is from nearby - for example, they don't use just one single radio telescope - they use a bunch of them. If the source of the signal is significantly closer to one telescope than the other - then it's pretty clear that it's a nearby signal which will be ignored. SteveBaker 22:06, 13 April 2007 (UTC)
I thought they only used the Arecibo telescope (and they only get limited time slots on that). Can you remind us all of the 'whole bunch' that they use? Or even one other? —The preceding unsigned comment was added by (talk) 22:17, 13 April 2007 (UTC).
See Allen Telescope Array. SteveBaker 02:14, 14 April 2007 (UTC)

Quantum physics in only one or two dimensions[edit]

What does it mean when people say "quantum physics in one dimension" (or two dimensions)? Are they talking about cases where all quantities are constant over the other dimension(s) or thin sheets or strings that are almost two- and one-dimensional, respectively? —Bromskloss 17:10, 12 April 2007 (UTC)

It usually means to take all vectors and replace them by a scalar value, replace some operators (nabla by d/dx) and compute from there on as if nothing was wrong. The results sometimes have some meaning in the real world. Sometimes they are pure fiction.—The preceding unsigned comment was added by (talkcontribs).
For example, there may be a symmetry of the problem. Some atomic physics is radially symmetric, for example. In this case, a properly conditioned one-dimensional equation may fully describe the system. (It is more likely that spherical coordinates are used, rather than "sheets" or "lines", which would be reduced-dimension Cartesian coordinates). If properly set up, radial symmetry is a powerful simplifying tool. Some ("non-intuitive") changes might be necessary, such as a modified volume element for integration. Nimur 17:30, 12 April 2007 (UTC)

Thanks for your answers. They further go on and say that "the charge and spin of an electron move independently in one dimension", "electrons form, in two dimensions, new particles with a charge that is one third of an electron charge" and that "low dimensional systems have become accessible to laboratory experiments". What do you make of that? They seem to be not just pulling it out of the air. —Bromskloss 17:44, 12 April 2007 (UTC)

Who said that? The last one sounds really strange. Maybe they are talking about the dimension of the phase space of the studied system? That would mean they are working with few particles that have a small number of degrees of freedom. —The preceding unsigned comment was added by (talk) 17:58, 12 April 2007 (UTC).
To give you some better idea how it works. Suppose you want to understand the movements of planets around stars. You start with a one dimensional model and find two possible classes of movements. First one: The planet crashes into the star. Second one: The planet has escape velocity and drifts away. If you add another dimension and reinvestigate the problem, the two original solutions remain valid, but a third solutions arises: The planet circles the star. If you go to three dimensions you will find out, that nothing new happes here. The planets trajectory is always in a plane. So the easiest way to analyze orbital mechanics with two bodies is to use two dimensional physics. —The preceding unsigned comment was added by (talk) 18:07, 12 April 2007 (UTC).
That makes some sense. So, would a two dimensional electron gas be such a system? —Bromskloss 18:24, 12 April 2007 (UTC)
That is a good example. It this case you have restricted the movement of particles in one dimension by a very large force and you can therefore ignore the third dimension to predict the movement of the particles. However if you look more closely you will see that the energy levels that the electrons occupy can only be explained by a three dimensional analysis of their quantum states with respect to the crystal. The two dimensional part of the analysis works as a good approximation to derive some properties of a transistor but not for all. Two or one dimensional physics is a mathematical trick to make matters more simple. The three dimensional case is always correct (if the theory itself is), but sometimes more difficult to compute.
There is a lot of interesting discussion of this in the appendices of the sci-fi book "The Planiverse" (an interesting read by the way). The conclusion from several physicists was that matter can't really exist in a 2D universe - forces behave really strangely - all sorts of the physical phenomena simply can't work. SteveBaker 20:25, 13 April 2007 (UTC)
Followup: I think the problem is that in the 3D world, forces decrease as the square of the range. This happens because the field spreads out on the surface of a sphere whose area quadruples every time it's diameter doubles. In a 2D world, forces are constrained to the surface of a circle - who'se circumpherence increases as a linear factor of range. Thie means that all forces are effective at much greater ranges but don't intensify anywhere near so much when you get close to the source. This in turn makes atoms and chemistry in general completely impossible. It's been remarked that our universe only works because the fundamental constants are pretty much exactly what they are...changing the number of dimensions would be a vastly more profound change. SteveBaker 02:11, 14 April 2007 (UTC)


hey guys well as you all may have already figured out; im in love with nuclear energy and radation and stuff(guess you can say im sorta the radiation guy). anyways ive been wanting to place all the questions i asked about radiation in my talk page for furture refrence for me (or anyone intrested); however, i do not even know how to access the arhives for this desk. can someone provide alink or something? thanks Maverick423 17:11, 12 April 2007 (UTC)

At the top of this page, there is a box with subjects (Comptuers, Science, Math, Humanities.... and Archives). Click on Archives. You'll then be able to open the archives for this page. --Kainaw (talk) 17:17, 12 April 2007 (UTC)

O man it was that easy eh when i spotted it i nearly kicked myself! thanks much!!!! Maverick423 17:19, 12 April 2007 (UTC)

Hi, radiation guy! Care to post a link to where you will put your reference? I'd like to check it out. —Bromskloss 17:53, 12 April 2007 (UTC)

Instead of making copies, I suggest just providing links to each individual question, like this:Wikipedia:Reference_desk/Archives/Science/2007_April_5#Nuclear_Shelter. (Don't worry, material in the archives doesn't decay.) However, I'm sure it will get glowing reviews, either way, just don't spend half your life working on it. If you have enough nuclear related topics linked from your talk page, other people might even go there to discuss such things, once a critical mass is reached. StuRat 19:04, 12 April 2007 (UTC)

o thanks StuRat that sounds like a much easier idea =) and for —Bromskloss i will place them here Radioactive questions. beware of radiation poisoning =) Maverick423 19:26, 12 April 2007 (UTC)

Just for the heck of it im also ganna put all the questions about radiation and nukes and stuff that i have read and stuff since i started here Maverick423 19:57, 12 April 2007 (UTC)

phosphorus coated quartz[edit]

A local rock shop just obtained some quartz crystals which phosporesce (and floresce. They are pitted, rough but clearly quartz. They are described as being a novelty of the 1940s, "phosphorus coated quartz". Some have the unusual property of florescing one color and phosphorescing at a higher color after exposure to UV. What is this stuff and how is it made? 18:59, 12 April 2007 (UTC)

Prostacyclin and Thromboxane[edit]

The picture found in the prostanoid article suggests that thromboxane is synthesised from prostacyclin. The eicosanoid article shows a different pathway. Which is correct? Ta for your help. Mmoneypenny 20:55, 12 April 2007 (UTC)

It looks to me like thromboxane synthase uses PGH2 as a substrate, and that our diagram has a misplaced arrow. [3]. But probably we should let someone who knows better say so before making changes. - Nunh-huh 21:23, 12 April 2007 (UTC)
I agree there is a bogus arrow in Image:Prostanoid synthesis.svg. The correct pathway is shown at Synthesis and biological properties of pinane-thromboxane A2. --JWSchmidt 22:40, 14 April 2007 (UTC)

First forensic crime-solver[edit]

believe Who was the first forensic scientist to solve a crime using DNA?

Genetic fingerprinting says the technique was invented in 1985. It probably had a gradual transition period before it was widely accepted as legal evidence. You should note that no crimes are ever solved via DNA evidence (or any evidence, for that matter). Many factors, such as uncertainty and error preclude "proof" - but even beyond that, legal proceedings are about more than just factual evidence. Mitigating circumstances, motivations, and other subjective ideas are relevant. Given all of this, it will be hard to pinpoint a single scientist who single-handedly ever solved "the first case." Nimur 02:04, 13 April 2007 (UTC)
I'm not sure that very many law enforcement officials would agree with you about the 'no crimes are ever solved via DNA evidence' assertion, Nimur. If a crime is committed, DNA evidence is collected, and a suspect is identified and convicted using the DNA evidence, most law enforcement would agree that the crime was solved using DNA evidence. The dichotomy I believe is between the various degrees of burden of proof depending on the severity of the crime and the jurisdiction, vs the statistical probability of error. Anchoress 02:09, 13 April 2007 (UTC)
Maybe I over-emphasized. I was just trying to illustrate that there's more to the legal system than factual evidence. Especially if a technology is new, it probably has less weight in the eyes of the legal experts, regardless of its scientific accuracy. Thus, it would be hard to say which case was the "first" when forensic DNA evidence was the decisive factor. Nimur 02:22, 13 April 2007 (UTC)
That is 100% true. Thanks for clarifying! Definitely, the popularity and perceived reliability of different types of evidence wax (and sometimes wane) over time. Lie detector tests, hypnosis, fingerprinting, etc. Anchoress 02:32, 13 April 2007 (UTC)

Are there cokroaches in Ireland?[edit]

Hi all,

I heard somewhere that there was no cokroaches in Ireland? I wonder if it is true because I've just visited an aparment in Dublin and I think I've just seen a cokroaches... (And by the way, is it true there is no snake?) and if everything is true , Why? Thanx a lot -- Sebb-fr 21:09, 12 April 2007 (UTC)

According to entomologist, James P. O 'Connor, "Over 70 species of insects are regularly to be found in the average Irish home... ranging from from tiny booklice to large cockroaches" [4]. There are also snakes kept in Ireland as pets and thus probably some that have escaped into the wild. However, neither snakes nor cockroaches are indigenous species of Ireland, the animals there presently have been introduced. Rockpocket 21:28, 12 April 2007 (UTC)
Though further research reveals the locals of Clear Island claim otherwise. Rockpocket 21:31, 12 April 2007 (UTC)
The original myth (or whatever you want to call it) was that the snakes could not swim across the channel to Ireland from England. This is flawed, and they could have probably got aboard boats. Either way, they were kept as pets and some may have escaped as said above. JoshHolloway 11:16, 13 April 2007 (UTC)
The legend is that Saint Patrick charmed all the snakes out of Ireland. The reason there are no indigenous species of snake in Ireland is the same reason there are no penguins in Uganda or no koala bears in Hawai'i: there was barriers preventing their migration to and/or survival in these regions. [5] Rockpocket 17:33, 13 April 2007 (UTC)
There are no koala bears in Australia either. :) JackofOz 21:52, 14 April 2007 (UTC)

Some of everything else in australia though, even though it has never been connected to the rest of the world.

See Pangaea. JackofOz 00:00, 16 April 2007 (UTC)

Masses into amount of moles[edit]

Hi, I need your help. The question is to convert the mass into amount of mole with the following: 4.2 kg of H20. This is not homework. —The preceding unsigned comment was added by (talk) 21:32, 12 April 2007 (UTC).

A mole is simply a number. This number of carbon-12 atoms weighs 12 g. If you have the same number of water molecules, how heavy is the water? --Bowlhover 21:43, 12 April 2007 (UTC)
Raw data for you
Oxygen consists of
Oxygen 16 with probability 0.9976
Oxygen 17 with probability 0.0004
Oxygen 18 with probability 0.0020
Hydrogen consists of
Hydrogen 1 with probability 0.999850
Hydrogen 2 with probability 0.000115
Hydrogen 3 with probability 0.000035 22:37, 12 April 2007 (UTC)
Since water is H2O there are
(3 types of first H) * (3 types of second H) * (3 types of O)
which gives 27 types of H2O molecules, each with its own atomic weights.
You need to calc the probability of each type of water molecule and
then multiple it with the atomic weight.
Then you need to calc the probability distribution function of
the average atomic weight of water molecule.
Figure out the upper bound and lower bound with 3 sigma probability from
the PDF and then work out the number of moles with upper bound and
lower bound. 22:44, 12 April 2007 (UTC)
That's not really necessary. At the level of precision indicated (one decimal point!), you can simply say that the molecular weight of H2O is 18 and go from there. - Nunh-huh 22:46, 12 April 2007 (UTC)

4.2 kg of water is about 233.33 moles. We have an article on stoichiometry which can give the background to help you figure out how these sorts of unit conversions work. Nimur 01:55, 13 April 2007 (UTC)

Significant figures might also be worth a look.... TenOfAllTrades(talk) 14:38, 13 April 2007 (UTC)


I need your help and that is Make the following onversions: a)64.3 g of PbBr2 to moles b)3.33 x 10^25 molecules of I<sub2 c)0.846 mole of HF to molecules d)39.8 moles of CO2 to molecules. e)8.50 grams Hg(NO2)<sub3 to moles. f)0.35 mole C6H6 to grams. g)4.85 x 10^25 formula units Cu2S. h)308 formula units of MnC204 to moles. This is not homework.

Sure looks a lot like it. We're not going to do it for you, either. Just add up the constituent weights of the atoms and find the molar mass, then do some division. This may help. -Wooty Woot? contribs 22:00, 12 April 2007 (UTC)
And, again, our stoichiometry article. Nimur 02:15, 13 April 2007 (UTC)

Long term shaving[edit]

Can shaving soft-skinned parts of your body for a long time get the skin to get "used to it" or "harden"? PitchBlack 21:48, 12 April 2007 (UTC)

A callus may form, but I don't think it as likely to form than if you were to, say, play the guitar. − Twas Now ( talkcontribse-mail ) 22:10, 12 April 2007 (UTC)
I've been shaving daily for a little over 20 years. It is still just as painful as it was the first day. --Kainaw (talk) 01:34, 13 April 2007 (UTC)
Kainaw, I hope you are a woman, because if shaving a male beard hurts, you are doing something very wrong... ;-) [And forgive my ignorance, but I always thought that women's shaving as opposed to waxing of legs doesn't hurt either.] And given that that the questioner seems to be, according to his user page, a male teenager, who might be new to this shaving business, he will be relieved to hear that, yes, facial skin gets used to shaving, and ceases to get so irritated. A shaving lotion without alcohol is nice, too. And for the occasional cuts: practice removes this problem as well. Simon A. 09:05, 13 April 2007 (UTC)
Or he could use an electric shaver - no cuts, no hassle, no mess. I've been using an electric ever since I needed to start shaving (though it's mainly just to keep my beard and moustache tidy these days). --Kurt Shaped Box 09:58, 13 April 2007 (UTC)
Your skin will not actually harden, but you will get used to it. Some tips: 1. Use a good quality razor. In my life I have gone from Trac_II to Mach3 to using a Gillette_Fusion (5 blades) and I have seen noticable improvement in quality with each razor. In particular the newer razors don't nick as often, and last longer between having to replace the blades. I would replace trac 2 blades once a week, mach 3 blades once a month, and I could go longer with the new fusion blades. 2. replace the blades when they start to get dull. Dull blades hurt a lot more than new blades. 3. I usually shave in the shower, or immediatle after. The hot water softens the hair and makes it easier to shave. If I don't have hot water to shave with it hurts. I don't get cuts, but more ripping rather than cutting seems to happen. As for "other soft parts" yes they will also get used to shaving after a few times.-Czmtzc 12:36, 13 April 2007 (UTC)
Some say you should just use one blade with some high-quality shaving lotion not out of the can and without any "soothing" additives and non-glycerin (or was it glycol?). ;) I heard that razors will not dull if they never get wet, and it's actually the water that does the dulling, and hair can't bend steel. Is there any truth to this? At that thickness it probably can. [Mαc Δαvιs] (How's my driving?) ❖ 20:01, 13 April 2007 (UTC)

steel is as strong as spider webs, and they break really easily.