Wikipedia:Reference desk/Archives/Science/2014 August 27

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August 27

Are fusors dangerous?

Say you have a fusor on your desk, and you switch it on, are the neutron emissions dangerous? If you are just sitting there without any shielding? 69.121.131.137 (talk) 00:00, 27 August 2014 (UTC)

Despite a very nice-looking Wikipedia article, and extensive interest in the popular-science and amateur "home-brew nuclear physics experimenter" community, these devices do not actually exist. The ones that "do exist" do not actually undergo nuclear fusion. If they did exist, and they emitted neutrons, the relevant article would be neutron radiation, § health hazards.

If you review the more reputable sources that our article cites, you will find, for example, some experimental apparatuses at the Fusion Research Laboratory of the University of Illinois at Urbana-Champaign. Reviewing the photos and descriptions on their website, if I were in the vicinity of their laboratory, I'd be much more worried about electrocution and electrical fires than neutron emissions. (The PI may be a tenured faculty member at a respectable engineering university, but something about his website makes me worry that basic fire-safety is an issue in his lab). Long before you get neutron emissions, you'd probably get hazardous x-ray emission via bremsstrahlung. ... And he knows it!

But you don't have to take my word for it (even though I've spent a lot of time in physics laboratories)! You can check out the Division of Research Safety website from the university (here is their radiation safety manual, including information on personal protective equipment, dosimetry, and procedures); or, in fact, just track down the equivalent health and safety office at any similar research facility. For example, Los Alamos National Laboratory has a very useful set of webpages that are available to the general public: Health & Safety at LANL. Physics laboratories that work with "uniquely hazardous materials" will usually have stringent guidelines and procedures to make sure that researchers and bystanders are not exposed to dangerous conditions.

(Apologies to the enthusiast amateur "home-brew nuclear physics experimenters" ... but what-ever you think you're building, it's just not that exciting to actual scientists. We, too, know how to create corona discharge by applying high voltage to ionize a low-pressure gas, creating a glowing plasma: it's called a fluorescent light bulb, and I have several hanging from the ceiling).

Nimur (talk) 01:02, 27 August 2014 (UTC)

The US Navy seems to think they exist, Nimur. http://www.nbcnews.com/science/science-news/low-cost-fusion-project-steps-out-shadows-looks-money-n130661 - So far, the Navy's spent US$12 million on the Polywell fusor.

Since there's some justifiable scepticism regarding NBC News's hot news flashes (they ARE the House of Exploding Pickups), here's the Park group ("EMC2, Inc.") paper on their latest results with the "Wiffle Ball" fusor design: http://arxiv.org/pdf/1406.0133v1.pdf

Getting back to the original poster's question, bremsstrahlung X-radiation is one danger, assuming the fusor operates at anywhere near peak efficiency and that deuterium or tritium are introduced into the fusor as "fuel". It's probably worth having a Geiger counter operating in the vicinity (ionization chamber meters aren't apt to be sensitive enough) if you're running a fusor with heavy hydrogen isotopes as "fuel".

A greater danger to the operator is electrostatic discharge or actual high-voltage/high-current leakage from the grids of the fusor, ESPECIALLY a home-brewed fusor (effective containment of high-voltage charges in grids with corners and curves in them being a black art ever since solid-state electronics replaced vacuum tubes for high-voltage applications). As to whether or not fusors exist, I can assure the reader they do, indeed, exist. Whether the energy released from an operating Farnsworth-Hirsch fusor ever approaches the power put INTO the device is a moot point, electrostatic inertial fusion does exist, the machines to produce it exist, and have existed for decades.

If mere presence in a physics lab conferred the sort of absolute knowledge required to deny the existence of fusors, janitors at those facilities would have the best jobs on Earth. Just think - hang out in a physics lab long enough and you can dispense with all those advanced math courses, blow off thesis committees... gangsta paradise! loupgarous (talk) 03:44, 27 August 2014 (UTC)

You are of course entitled to your own interpretation of a news article?

The Department of the Navy spends $12 million every hour just driving buses that move janitors to swab the decks of their ships and research labs. In the world of high-energy physics and Navy research programs, this is not a large amount of money. The cost to the average American taxpayer is a fraction of a penny per year. It would not be the first, nor the last, time that risky research was funded; nor the last time that a junk scientist managed to get funding for a pet project; nor the last time that the popular press misrepresented a science story to sell copy (or drive web traffic). Nimur (talk) 04:14, 27 August 2014 (UTC)

You're saying, then, that the WB grid fusors don't exist because the Navy didn't spend US $1.2 billion on it, which is a low-ball estimate of DoE expenditures on the National Ignition Facility, or the approximately US $18 billion which the thermonuclear fusion power research community has spent so far not getting fusion to work?

So far, by the most rational measure of "pathological science" (as defined by the Knolls Atomic Power Labs' Irving Langmuir), it's the thermonuclear fusion power effort that qualifies as "junk science" - barely detectable results, poorly reproducible results, and a highly-politicized environment which is the only environment in which it can survive. Unless you're hiding some evidence that thermonuclear fusion is, US$ 18 BILLION dollars later, even close to break-even, and I wish you'd produce it, if it does exist.

However, I did take the NBC News article with a grain of salt; published scientific journals such as the ARXIV article I linked have confirmed the comparative viability of the Polywell fusor for years. The return on investment of inertial electrostatic confinement fusion research like the Polywell fusor research is literally three orders of magnitude higher than that of thermonuclear fusion power research - read the .pdf I linked to and show me comparable progress toward break-even in thermonuclear fusion power. loupgarous (talk) 04:47, 27 August 2014 (UTC)

This isn't my area of expertise, but it does look very suspicious. The only people who use the word "fusor", as far as I can tell, are amateurs who build vacuum-tube devices that make pretty lights and think that they're somehow advancing the cause of fusion research by doing so. The word "fusor" does not appear in arXiv:1406.0133, which is about a polywell fusion device, which has its own article. I suspect the thing is never going to work, and the Navy probably shouldn't be funding it, but calling it a "polywell fusor" seems like an attempt by the fusor aficionados to pretend that they're real fusion researchers. I suspect ITER is not going to work either, but this is also irrelevant to whether we should have an article about "fusors". -- BenRG (talk) 05:44, 27 August 2014 (UTC)

If you had actually read the article on Polywell fusion devices, you'd know they're an evolutionary development of the Farnsworth-Hirsch fusor, one which was developed from considerable research by Dr. Robert Bussard undertaken over many years. So, the Polywell device is indeed a "fusor" - specifically, a development of the Farnsworth-Hirsch fusor.

I'd say, based solely on publishable results, what you refer to as "fusor aficionados" have as much right to describe themselves as "real fusion researchers" as the prime investigators connected with the National Ignition Facility. loupgarous (talk) 06:41, 27 August 2014 (UTC)

Since the disapointing Fleischmann–Pons experiment in 1989, most scientists consider claims of achieving Cold fusion dead and they now have a reputation as pathological science. 84.209.89.214 (talk) 13:08, 27 August 2014 (UTC)

"most scientists" sounds like WP:WEASEL to me. I've cited research papers in respected parts of the scientific literature in this discussion, and all the attacks on anything that isn't thermonuclear fusion power research have nothing but hand-waving supporting them. When you have something that's not a weasel-worded attack with no support, come back. loupgarous (talk) 14:44, 27 August 2014 (UTC)

Well our article says

Attempts to resolve these problems include Bussard's Polywell system, D. C. Barnes' modified Penning trap approach, and the University of Illinois's fusor which retains grids but attempts to more tightly focus the ions into microchannels to attempt to avoid losses. While all three are IEC devices, only the last is actually a "fusor".

So it does actually say the Polywell device is not a fusor. I'm not saying it's right. Frankly our article is terrible. I removed one sentence in the LEDE. Then took a look at the picture which is sourced to blogspot and the amateur section which includes few RS and gave up trying to improve it further. However it does demonstrate there appears to be disagreement.

The fact that the Polywell was developed from fusor research doesn't of course prove it's a fusor unless your definition of fusor which says anything which developed out of fusor research, regardless of design, functionality etc is a fusor which for most people makes little sense. (Under such a definition, even a device which isn't intended for nuclear fusion may be a fusor.)

Nil Einne (talk) 15:18, 27 August 2014 (UTC)

Here are specific references: a 2009 statement by the American Physics Society: the APS does not endorse cold fusion findings that were presented on television. Here's a 1999 article from Science, bringing attention to the UIUC program: DOE reviews cold fusion grant. It does not take much effort to learn the history of these specific research angles: the proponents have been discredited and the experiments have been panned in many reputable sources. Nimur (talk) 15:20, 27 August 2014 (UTC)

I should clarify that after looking more carefully, perhaps the sourcing in the amateur section wasn't quite as bad as I thought. In particular, it seems main of the Youtube videos are actually of interviews and the like and not primary sources. However many of these seem to have copyvio issues since they don't look to have been uploaded by the copyright holder. More importantly, even if the sources are nominally RS, it's likely more attention needs to be paid to whether the source appears to be saying they've independently verified the claim of neutron's being detected, or just reporting the person's claims. Many media are want to simply report these sort of feel good stories about wonder-kids. Even the one where a letter from the Duke of Edinburgh was received I wonder how much research was done. I'm not sure that "random person says they did whatever and got some media attention for it" is something we need in the article. Some of the examples include somewhat reputable science shows, who I would expect probably did some verification, so there are probably some examples that should stay, but I definitely think the article needs attention. Nil Einne (talk) 12:47, 28 August 2014 (UTC)

Vfrickey/loupgarous, I realize the Polywell article currently links to the fusor article, but this doesn't tell us anything about the world outside the Wikipedia bubble. Is there any evidence that the word fusor is used in the peer-reviewed literature? As I said, it's not used in the preprint you linked (which in any case is unpublished). Also, please read xkcd.com/978 ("Citogenesis") if you're not familiar with that problem. -- BenRG (talk) 17:45, 27 August 2014 (UTC)

To answer your question, I actually ran a search for the term "fusor" and found not really a "peer-reviewed article" reference to "fusors" but one in the Web page of the University of Technology at Eindhoven, the Netherlands in which the term "fusor" is explicitly defined as the sort of fusion reactor this university is developing. http://www.tue.nl/en/university/departments/applied-physics/research/plasma-physics-and-radiation-technology/science-and-technology-of-nuclear-fusion/fusion-research/fusor/

"The principle of the Fusor

The fusor is an Inertial Electrostatic Confinement fusion device. It can create fusion reactions by accelerating ions by means of an electrostatic field. The electric field is generated by two concentric spherical electrodes, of which the inner one is mostly transparent and strongly negatively charged. The ions are accelerated inwards and most will pass the transparent electrode. After the electrode, they continue converging inwards, creating a high density of high energy ions in the center of the fusor. Collision with each other or with neutral background gas particles then results in fusion reactions."

TU Eindhoven's a reputable research organization. If the point you're making is that the term "fusor" isn't a rigorous term used by "real fusion researchers" (to quote a previous poster), I'd say that a university's using the term "fusor" to describe a major part of their graduate fusion energy research and education program contradicts that viewpoint. You're welcome to your own opinion, of course.

Of course, anyone can find ways to prove me (and the University of Technology at Eindhoven) wrong. I've wasted more time arguing about the meaning and validity of the term "fusor" than the challenge to it warrants. If you want to declare "victory" on this point, you can do so to my serene indifference. loupgarous (talk) 14:44, 29 August 2014 (UTC)

Hehe, that reminds me of the time I spotted a crazy sentence about "glucojasinogen" :) omfg those papers are still online as they were ... Wnt (talk) 18:28, 28 August 2014 (UTC)

Our Polywell article was edited after I wrote (at the time correctly) that it said the Polywell reactor concept was a development of the fusor. And, as you all point out, it's not a "fusor" in that it uses a "virtual cathode" rather than an outer grid to inertially and electrostatically confine a plasma in which fusion may occur. Thanks for cleaning up the Polywell article, whoever did it, it's much more accurate now.

As far as the introduction of "cold fusion" into the discussion, my reaction is "huh"? Equating Pons-Fleischmann "cold fusion" with Dr. Bussard's very well-reasoned and documented work and that of the Park team (which in the ARXIV paper I quoted documented the achievement of just such the working plasma trap required to make the Polywell concept work for power generation) is disingenuous at best - a smelly red herring wrapped up in weasel words. A very dishonest way to attempt to "win" points in a pointless argument. loupgarous (talk) 13:30, 29 August 2014 (UTC)

Huh? The only edits to the polywell article since this discussion began are possibly [1] (I didn't check the time frame carefully enough to ensure these edits were after this discussion, but the last edit before was 18th August so there was definitely nothing else). Our article still says "The polywell was developed by Robert Bussard, as an improvement over the fusor" if that's what you're referring to (which doesn't actually tell use whether a polywell is a fusor).

Actually our article on polywell in a number of instances does strongly imply a polywell is not a fusor since it frequently talks about them in comparison etc. (The closests it comes to calling the polywell a fusor is where it says " referenced older research with traditional fusors".) It does basically says the polywell was developed out of fusor research in the main article as well (although that could mean a lot of things and not necessarily that fusors remain a useful field of research).

Again, I'm not saying our article is right per se, simply that it says this and has said this since at least a week (probably much more) before this discussion began so I think there has always been dispute in both our articles where polywell devices are correctly called fusors.

Nil Einne (talk) 15:29, 29 August 2014 (UTC)

This topic has gone a bit off the rails. Let's be clear, you can generate nuclear fusion by accelerating particles to sufficiently high energy and smashing them together. At least some of the devices called "fusors" are doing that and create excess neutrons, which is pretty clear evidence of nuclear reactions. This principle has even been exploited to create commercially viable neutron generators. What you can't do is get more energy out of the process than you put into it. Ion beam mediated fusion, like most forms of thermal non-equilibrium fusion, requires ridiculously more energy to operate than it produces. Using numbers for a fusor built as a physics lab thesis project, they required about 1000 W of energy input to generate 3×10⁶ neutrons / second, indicating a fusion energy output of about 1×10⁻⁶ W. In others words, about a factor of 10⁹ from being a useful energy source. More generally, anyone who looks at these things critically will realize that ion beam mediated fusion can never be a net energy source, the reaction cross-sections are just way too small. Everyone in the physics community know this, but that's not really the point. The point of building a fusor is to have a source of neutrons you can turn on and off easily, and with fewer restrictions on handling and disposal when compared to radioactive isotope neutron sources. That said, the "fusors" built by hobbyists are generally toys. If they work at all, their neutron flux is generally so low as to be of little utility. Dragons flight (talk) 16:43, 27 August 2014 (UTC)

To respond to the original question, without a measure of radiation from the device in question it would be impossible to say with certainty. The toy "fusors" created by hobbyists are unlikely to be very dangerous. The physics lab example above, 3×10⁶ neutrons / second, would be a biologically significant dose of radiation assuming one remained a few feet from an unshielded device and it operated continuously for many months or years. Professional neutron sources (which probably aren't what you mean by "fusor") can deliver neutron doses that would be likely fatal after less than an hour of exposure. Dragons flight (talk) 17:56, 27 August 2014 (UTC)

Thanks for pushing the discussion back to the original question. I remember Farnsworth-Hirsch fusors being used in the "Oil patch" to generate enough neutrons to allow neutron activation analysis of core samples (giving an idea of the elemental composition of the sample by gamma-ray spectrometry of the neutron-activated core samples). I'd say that level of neutron flux would be biologically hazardous.

There are now flashlight-sized radiation detectors that do neutron dosimetry as well as gamma-ray dosimetry and spectrometry (so that the radiation source can at least partly identified simply by comparing the gamma-ray spectra identified by the device to the Chart of the Nuclides, and there are hand-held devices that'll do that for you, too).

The only things you left out in the "danger profile" of the "toy," hobby-grade fusors are (a) bremsstrahlung X-radiation from the air and anything else being accelerated by and into the high-voltage grids - the resulting collisions create the X-rays, and (b) the high voltage itself being present at points on the device's casing as insulation breaks down inside the device. loupgarous (talk) 00:11, 28 August 2014 (UTC)

Isn't bremsstrahlung only caused by charged particles though? 108.170.113.22 (talk) 14:46, 28 August 2014 (UTC)

Internally, fusors generally involve accelerating charged ions to high energies, which can then produce X-rays. Not sure how big a problem that actually is. Dragons flight (talk) 18:23, 28 August 2014 (UTC)

As Nimur pointed out upthread, bremsstrahlung is a higher probability hazard than neutron flux from "desktop fusors." Even if something marketed or built as a "fusor" doesn't actually succeed in producing nuclear fusion (which, using heavy hydrogen isotopes as "fuel," would involve neutron flux as a product of the fusion reaction), bremsstrahlung was more possible and a greater hazard.

And as Nimur also pointed out correctly, high voltage "leakage" from the grids and other HV circuitry inside the fusor would be a greater hazard still, and the one deserving the most attention. But some CRT displays (notably older color televisions) create enough x-rays as a consequence of bremsstrahlung-like collisions of electrons with metallic grids or masks to have been a health concern (if you spent lots of time far too close to a older color CRT), so it's not an issue with "fusors" that can be disregarded totally. loupgarous (talk) 13:30, 29 August 2014 (UTC)

In simple words please - Mitochondrial DNA

Does the Mitochondrial DNA has any significant impact on one's phenotype (Later edit clarification: I mean to everything except basic Metabolism)?... In my Biology or Biopsychology Textbook I haven't seen any mention for such impacts... thank you for this clarification!, Regards. Ben-Natan (talk) 03:52, 27 August 2014 (UTC)

Mitochondria do two main things - burn glucose and oxygen to make energy, and make proteins. Since every part of your observable appearance, traits and activity - your "phenotype" - depends on the action of proteins in your body (peptides, neurotransmitters and structural proteins) the simple answer is "yes".

It's an overly simplistic "yes," to be sure - the 37 genes in mitochondrial DNA are the tools used by nuclear DNA - the true "blueprint" of the body containing all the other genes - to make those proteins. Nuclear DNA has the information needed to say how the proteins are made by the mitochondria.

But if the mitochondrial DNA don't work correctly (a) cells stop using glucose and oxygen to make energy, or (b) transcription of information to make proteins doesn't work right and illness of one sort or another occurs. Nuclear DNA can be described as the WHY of cellular DNA, the information needed to make proteins correctly. Mitochondrial DNA is the HOW of cellular DNA, the 37 genes that are used to do the cell's business, and is just as essential to the phenotype of a healthy organism. loupgarous (talk) 04:05, 27 August 2014 (UTC)

I've added a clarification above: I know it plays a basic and vital role in Metabolism and making proteins, but is there anything extra to it in relation to the phenotype? I once heard of a researcher which tried to link Homosexuality in males to differences in mitochondrial DNA (Sounds to me like a desperate attempt to "prove" Homosexuality is genetic - a claim that seems to me to be disproved by Monozygotic twin research as can be hypothesized from this vid - 1:50). What is your opinion of this? Ben-Natan (talk) 05:33, 27 August 2014 (UTC)

The reference desk will not answer requests for opinion. Nimur (talk) 06:11, 27 August 2014 (UTC)

I believe I was clear in my explanation of how mitochondrial function impacts an organism's phenotype. The 37 genes of the mitochondrial DNA (in h. sapiens) control oxidative phosphorylation and protein synthesis, but the actual information which codes for synthesis for individual proteins is in the nuclear DNA, not the mitochondrial DNA. The phenotype's affected in very broad strokes when the mitochondrial DNA doesn't work right (or works more efficiently than is usual). Individual traits are, however, coded for in the nuclear DNA. loupgarous (talk) 06:18, 27 August 2014 (UTC)

The OP may be interested in Mitochondrial disease Nil Einne (talk) 14:49, 28 August 2014 (UTC)

You might find this paper interesting, in which the authors search for mitochondrial miRNA. Because quite small pieces of RNA can affect the overall activity of other genes - any other gene - it is possible to use mitochondria to fine-tune other genes in a way that is maternally transmitted. For example, small RNAs produced from longer noncoding mitochondrial RNA may affect the cancer phenotype [2]. (I really ought to look into this further, meant to a while ago...) Wnt (talk) 14:05, 27 August 2014 (UTC)

mass &weight

spring balance measures weight of a body whereas common balance measure mass. if so does the readings shown by the two differ? — Preceding unsigned comment added by 117.218.119.166 (talk) 05:56, 27 August 2014 (UTC)

Sure! Think about how each scale would register if you were in an (accelerating) elevator.

For more fun, think about how each scale would register during your freefall stage if you took them skydiving. Nimur (talk) 06:10, 27 August 2014 (UTC)

Strictly speaking, a pan-balance measures mass (in kg or lb), and a spring-balance measures weight (in newtons, or pound-force, but displayed in kg or lb). Spring-balances are affected by the local gravitational force (it changes by a few percent), etc. CS Miller (talk) 08:45, 27 August 2014 (UTC)

Does the pan balance really measure mass, or does it compare the weight of the arm weights against the weight of the object being weighed, which has the indirect effect of measuring mass because the local gravitational force cancels out? The actual measurement of mass is much more difficult under ordinary conditions than the measurement of weight.

True, but if you consider diffs in the gravitational field between the two pans, you also need to consider electromagnetic fields, air currents, etc. StuRat (talk) 18:26, 27 August 2014 (UTC)

I didn't say or imply that differences between gravitational fields should be considered. I meant that, for all practical purposes, the two pans, or the pan and the arm, are in the same local gravitational field. However, what is actually being compared is the weight of the object being weighed and the weight of the arm. Mass is being measured indirectly. It isn't important what the exact local force of gravity is, because it cancels out. (Likewise, below, it isn't important what the mass of a satellite is, because M2 is cancelled out in solving Newton's equation for M1.) Direct measurement of mass requires something like a Cavendish torsion balance. Robert McClenon (talk) 23:06, 27 August 2014 (UTC)

Mass is always a physical-mathematical expression of weight values!--Alex Sazonov (talk) 18:37, 29 August 2014 (UTC)

Measuring Mass

In order to determine the mass of a small object, the gravitational field of a large object is used. In order to determine the gravitational field of a large object, its gravitational effect on a small object is used. A small object is something like a grain of salt, a breadbox, a human, a car, or a fully loaded 747, that does not have a gravitational field that is large enough to support stable orbits. The mass of a small object is measured by weighing it in the local gravitational field of an object having a large enough local gravitational field to be useful for the purpose, such as the Earth. (An additional restriction is that the object has to be solid and the experiment must be done on its surface. The Moon would be satisfactory, but you have to get there first. The Sun will not work for the purpose; its gravitational field is sufficient, but it isn't solid.) The mass of a large object is measured by observing the orbital motion of a small object around it. (For this purpose, the Moon can be used to measure the mass of the Earth.) The mass of the small object is not important. The most distant and most massive object that has had its mass measured in this fashion is Sagittarius A*, the black hole at the center of the Milky Way. Robert McClenon (talk) 13:39, 27 August 2014 (UTC)

As to the original question, mass of small objects is difficult to measure directly. A Cavendish torsion balance is an early high-tech experiment. Mass is measured by measuring weight and adjusting for local gravity. Robert McClenon (talk) 13:39, 27 August 2014 (UTC)

There's an article Mass versus weight. They seem to be exactly proportional in the same gravitational field and this is an assumption in Einstein's General Theory of Relativity. People still try to do more accurate tests of this in various circumstances. This has been checked for instance by balancing different types of substances e.g. iron and nickel against each other using a torsion balance and then seeing if they still balance with a beam balance. Dmcq (talk) 16:59, 27 August 2014 (UTC)

Why would you say that measuring mass directly is so hard? Why can't you use (for example) conservation of momentum. Take a known mass (the international standard kilogram, I'm sure they wouldn't mind lending it to you for a few hours!) - get it moving at a known speed (easy to measure with high precision) and whack it into your test object. Assuming a relatively inelastic collision, you only have to measure the resulting speeds to know their relative masses to reasonable precision. There are any number of ways to figure mass - take almost any physics equation with mass in it...heat the object up using a known amount of energy and measure the temperature rise - it'll be inversely proportional to the mass. None of these approaches requires any information about gravity or weight. SteveBaker (talk) 18:22, 27 August 2014 (UTC)

What is a "relatively inelastic collision", and how accurate is the assumption that a collision is inelastic? How did you determine the heat capacity of the material that you are heating? To determine the heat capacity of the material that is being heated, didn't you need to know its mass in the previous experiment (the measurement of heat capacity) in the first place? It is true that the second experiment, measuring mass by knowledge of heat capacity, is measuring mass, but most methods of measuring mass either involve its direct equivalence to weight or its indirect equivalence to weight (in a previous experiment). Robert McClenon (talk) 23:06, 27 August 2014 (UTC)

The measurement of mass doesn't necessarily require a gravitational field. An inertial balance measures mass based on inertial effects of the object being measured. --108.36.90.238 (talk) 13:40, 29 August 2014 (UTC)

Small linguistic digression: This weight–mass distinction is not as uniform as some people (e.g. high-school physics teachers) would have you believe. There is a perfectly respectable usage of the word weight that is simply synonymous with mass. For example, when you buy bulk items by weight, you are paying for the quantity of matter, not for how much force it exerts. Granted, you might use a spring scale you measure that quantity, and that would vary depending on the local gravitational field — but that's merely a source of systematic error of measurement, not a reflection of the thing that in principle you're trying to measure. --Trovatore (talk) 18:46, 29 August 2014 (UTC)

What is meant precisely by "structure" in materials science?

The science of materials science is all about determining properties of a material from its structure. What is meant precisely by "structure"? 131.217.255.4 (talk) 06:46, 27 August 2014 (UTC)

The spatial arrangement of atoms/molecules in the solid material. Plasmic Physics (talk) 07:37, 27 August 2014 (UTC)

"Structure" (as defined in http://www.merriam-webster.com/dictionary/structure): "the way that something is built, arranged, or organized".

In materials science, "structure" means how materials are made at the molecular level, generally to find out how useful they are for a given job.

Metals and alloys, for example, are almost always crystalline in structure, with the outer electron shells determining how individual atoms in the crystal are organized. The shape memory phenomenon can, for example, cause there to be two or more different crystalline structures for a metal or alloy sample, depending on its temperature at any given time.

Metals also expand and contract at different rates and temperatures, so that when strips of two different metals are bonded together (in what's known as a "bimetallic strip") the difference in how each metal expands causes the strip to move in predictable ways from side to side - which is useful in analog thermostats.

Also, the hardness of an object can be determined by its crystalline structure. Carbon can be very slippery and soft in its "graphite" form, or very hard in its "diamond" form. That's a classic materials science issue.

Chemical compounds which are not crystals also are studied in materials science. Polymers (chains of various atoms or compounds) are studied in materials science to determine how suitable they are for a given application. Some polymers are very durable (they don't come apart easily when rubbed or struck), some (like graphite) slide apart very easily.

The motion of electrons through various materials is another branch of material science with numerous modern applications. Addition of tiny impurities in a silicon crystal, for example, cause electrons to flow under some conditions and not others - this class of materials is called "semiconductors," and is crucial in the manufacture of computers and many other electronic devices. Materials science research has turned up similar properties in titanium dioxide, which potentially is cheaper and less hazardous to work with than silicon and the toxic, flammable compounds of carbon and various metals used as dopants to make silicon a semiconductor.

Superconductors are combinations of metals and other elements which have little or no resistance to the flow of electrons at low temperatures, causing less power to be wasted in Joule heating of electrically-conductive wire over long distances, or in devices such as electrical motors which use very large lengths of wire to turn electrical current into motion. Inertia and gravitational force may change around some superconducting substances as the shape of local space changes.

Properties can be engineered into a given substance by changing its structure at very small levels of physical scale, in what is known as nanotechnology. Certain carbon nanostructures such as nanotubes can be used as structural materials to make very light, durable objects; some carbon nanostructures are being investigated for their usefulness as materials to replace lead and lithium in batteries.

These are only a few ways in which the structure of various substances make them more or less useful for given applications in engineering. Materials science is expanding as our knowledge of how different substances are made and behave under different circumstances grows. loupgarous (talk) 07:55, 27 August 2014 (UTC)

How can you control the structure of a material? 131.217.255.4 (talk) 09:15, 27 August 2014 (UTC)

Generally speaking, in Chemical engineering a desired material is obtained by Chemical synthesis or chemical separation, e.g. by Distillation. Then chemical analysis or structural analysis of the product may be done by Crystallography or Microscopy. 84.209.89.214 (talk) 12:27, 27 August 2014 (UTC)

A standard way of influencing the crystalline structure of e.g. steel is via heat treating and quenching. --Stephan Schulz (talk) 17:58, 27 August 2014 (UTC)

Intellect of human

Is intellect of human being a product of natural selection in which human population is represented by different types of human?--Alex Sazonov (talk) 08:44, 27 August 2014 (UTC)

I think that, during the segregations of human population which is represented by different types of human the intellect of human is been revealed. And also, the mobility of the human type is always explained by the presence in its habitat of many types of human. The competition between the types is represented in the natural environment as the competition is not equal to each other types--Alex Sazonov (talk) 11:23, 27 August 2014 (UTC)

Evolutionary psychologists (see article) argue that much of human behavior is the output of psychological adaptations that evolved to solve recurrent problems in human ancestral environments. 84.209.89.214 (talk) 12:01, 27 August 2014 (UTC)

Is this yet another white-supremacy argument? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:52, 27 August 2014 (UTC)

What type of human is more biologically stable a type of black human or type of white human, so that in what type of human always contains a preservative of the human genome?--Alex Sazonov (talk) 13:31, 27 August 2014 (UTC)

Heritability of IQ, Evolution of human intelligence, Nations and intelligence, Race and intelligence, scientific racism, and History of the race and intelligence controversy cover about everything related to this question I believe. Please use either use the Wikipedia search facility via the little box on the top right of the page or Google to try and find answers before posing questions. Dmcq (talk) 14:20, 27 August 2014 (UTC)

Lasers that curve

Is it possible to make a laser that curves? 108.170.113.22 (talk) 18:06, 27 August 2014 (UTC)

Light is only truly curved by gravity...lots of gravity - so firing a laser close to something the size of a star would be enough to bend the light slightly. To bend it a lot, you'd need a black hole or a neutron star or something equally compact and massive. You can bend it (abruptly) by passing it through a lens - anything with a change in refractive index will to it. Lasers are also "curved" by passing them through fibre optic cables that can be bent...although in that case, they are really reflecting off of the sides of the glass and the laser beam is really heading in a straight line. SteveBaker (talk) 18:12, 27 August 2014 (UTC)

(Edit conflict) All you need is a sufficiently large mass near the laser... WegianWarrior (talk) 18:13, 27 August 2014 (UTC)

There is a rather strange effect you can get by varying the phase across a laser beam to make light bend a little, see Airy beam. Dmcq (talk) 18:47, 27 August 2014 (UTC)

However you can bend ordinary light, you can use that method to bend laser light. Everything mentioned above works for ordinary light as well: gravity, materials of different refractive index (see also gradient-index optics), reflective materials... --Bowlhover (talk) 18:59, 27 August 2014 (UTC)

Right. Another classic demonstration is to bend light with a stream of falling water, like this image shows [3]. More info here [4]. SemanticMantis (talk) 21:25, 27 August 2014 (UTC)

Wrong. A large mass will act as a prism and refract the laser, not bend it. μηδείς (talk) 21:27, 27 August 2014 (UTC)

What is the difference between refracting and bending? In any case, a gravitational lens is usually said to bend light, not refract it. --Bowlhover (talk) 03:19, 28 August 2014 (UTC)

The laser beam is a shaft of light of some finite width moving in parallel. If It were "bent" by a gravity source, the photons closer to the gravity source would bend more and those further away less. This would cause the coherent beam to fan out like a ray of light going through a prism. It would differ in that the laser is not white light, so you would not get a rainbow. μηδείς (talk) 16:38, 28 August 2014 (UTC)

The beam does fan out the way you describe, that's why gravitationally lensed galaxies appear distorted. However, the deflection is independent of wavelength (achromatic) that's why you don't get a rainbow, no matter whether the light is white or not. --Wrongfilter (talk) 19:35, 28 August 2014 (UTC)

It took me a while, but I think I finally figured out that this is exactly what Medeis is saying. The light fans out, whereas the word "bend" suggests that it does not fan out. Is that what you meant, Medeis? --Trovatore (talk) 03:08, 29 August 2014 (UTC)

Yes, you interpret me correctly. When I hear "bend" I imagine the width of the ray remaining constant like a road that makes a 45 degree curve or a garden hose that bends around the base of a trunk of a tree. That's not what you'd get, a continued constant width after the bend. You'd get a fanning similar to white light going through a prism (except no breaking up of the light into a spectrum) or like gravitational lensing.

OK, clear now. I think part of the reason your original statement was confusing is that the usual sort of prism that people think of (triangular cross-section, made of more-or-less uniform glass) does not cause a monochromatic beam to fan out, whereas the gravitational field does cause a monochromatic beam to fan out. Given that lasers are ordinarily (nearly) monochromatic, your "act like a prism and refract the laser, not bend it" tended to convey exactly the opposite impression from what I now see you meant. --Trovatore (talk) 18:15, 29 August 2014 (UTC)

If you mean that the light will instantaneously change direction in the same way that light refracting across an interface changes direction, then no, that's not correct. The light's path will change continuously as it passes near a big mass, hence "bend". If perhaps you mean that the light path can be described using similar mathematics to refraction, then this is true. In the linear approximation, light traveling near a large mass behaves as if it were passing through a medium with a continuously varying index of refraction $n\approx 1+{Gm \over rc^{2}}$. Of course, a continuously varying index of refraction causes a continuous change in direction. However, since the effective index of refraction (and the angle of incidence) change most rapidly close to the mass, near all of the bending happens near the closest approach. We sometimes approximate that change in the light's direction as instantaneous, but it isn't really. Dragons flight (talk) 03:20, 28 August 2014 (UTC)

Forces of magnetism always distort anything, even light, because all magnetic spaces are always distorted by force of magnetism.--Alex Sazonov (talk) 07:07, 28 August 2014 (UTC)

That only holds true while Eternia exists as is. Under certain conditions, dark matter can become greater than regular matter. Around that time, light can not only bend independently, but whip, and even the fundamental power of Grayskull eventually kneels. Of course, in that fictional movie, the good guy won as usual. InedibleHulk (talk) 07:40, 28 August 2014 (UTC)

Please put 'humorous' replies in small font so people don't somehow imagine they're real (I added <small> tags to your reply for you). SteveBaker (talk) 14:36, 28 August 2014 (UTC)

I think it's Mr. Sazonov's post that needs some indication that it's not real. Asmrulz (talk) 16:01, 28 August 2014 (UTC)

Yeah, I'd normally go small on things like this. Since his wasn't, I figured my reply should be equal. At least I bolded the "fictional movie" part. InedibleHulk (talk) 22:29, 28 August 2014 (UTC)

• Dmcq, the link to Airy beam is interesting, especially that it has very real and varied applications. I wish the article were a lot longer! Wnt (talk) 10:47, 28 August 2014 (UTC)

• Lasers only appear to go in a straight line when they're passing through a medium of constant refractive index. All you need to make the beam gradually curve is a continuous gradient of refractive indices. A nonuniform mixture of gases with different refractive index values, or colloidal suspensions (ie. fog or smog both scatter strongly, for light scattering: contrast = refractive index difference) would work just fine. The atmosphere already does this. But most lasers don't have long enough coherence lengths (we're talking very shallow gradients, in the case of the atmosphere) for this to be a relevant effect. Edit Just noticed Bowlhover already mentioned Gradient-index optics, so my answer is a little redundant, I suppose. (+)H₃N-Protein\Chemist-CO₂(-) 12:24, 28 August 2014 (UTC)

What originated as the acronym LASER for the phenomenon "Light Amplification by Stimulated Emission of Radiation" became the term laser for the device that emits light. One hears the usage extended in colloquial expressions "to print on a laser" (meaning the equipment that employs a laser device) and "to laser the material cutouts" (as a verb meaning to cut with a laser beam). A similar descent from technical innovation to colloquiality is heard in "I listen to music on my transistor" (meaning a radio receiver that employs transistors). However the OP and some responders here clearly understand "laser" to mean the beam of light that the device projects. That usage is undocumented and there is no precedent for it in the phonetically related terms MASER, GASER or TASER. 84.209.89.214 (talk) 14:00, 28 August 2014 (UTC)

• So, you think they're actually asking if you can make a curved laser diode. What would be the significance of that? I thought it was fairly obvious that they were asking if you could make the beam curve, regardless of their exact wording.(+)H₃N-Protein\Chemist-CO₂(-) 14:14, 28 August 2014 (UTC)

It's risky trying to base an argument on presuming someone else's ignorance. One might suspect that the diode laser is the only kind you have heard of. If I assume you are aware of the other kinds of lasers then please reciprocate the kindness by not telling me what I wrongly think in a mocking way. 84.209.89.214 (talk) 15:16, 28 August 2014 (UTC)

"One might suspect that the diode laser is the only kind you have heard of" Not unless they were being bizarrely pedantic. The OP was clearly asking if the beam could be curved, not if the acronym itself could be curved, and certainly not if the emitter could be curved. Neither of those interpretations of the original question make sense in any logical way.(+)H₃N-Protein\Chemist-CO₂(-) 15:22, 28 August 2014 (UTC)

When you find yourself repeating what is in your own words "fairly obvious" then it's time to consider what you are missing here. If we don't hear more prattle from you about imaginary misinterpretations, no one will miss you. 84.209.89.214 (talk) 16:13, 28 August 2014 (UTC)

Language changes - sometimes rapidly. LASER does indeed stand for all that good stuff...but the word "laser" has gained many meanings that stray far from the acronym's more limited meaning. Most dictionaries now treat it as a word with noun, verb and adjective forms that has long ago left behind the derivation from the acronym. Merriam-Webster now has the first usage example: "doctors using a laser to perform delicate eye surgery"...but you can't really have "A Light Amplification by Stimulated Emission of Radiation" - it would have to be "doctors using laser...", not "doctors using a laser...". So if you say "a laser", you simply have to be using the word in some new meaning as "a device employing the principle of LASER". I see hardly any uses of the word 'laser' where it could be replaced by the expansion of the acronym 'LASER'. SteveBaker (talk) 15:06, 28 August 2014 (UTC)

84.209.89.214, that's one gigantic genetic fallacy. 108.170.113.22 (talk) 16:07, 28 August 2014 (UTC)

How so? Do you criticize etymology - the study of the origins and development of words? 84.209.89.214 (talk) 16:20, 28 August 2014 (UTC)

Whether I do or not is irrelevant to the fact that you invoked a fallacy. In fact your question is a fallacy itself, an ad hominem. 108.170.113.22 (talk) 16:34, 28 August 2014 (UTC)

The question "How so?" invites you to explain the fallacious conclusion that you have twice claimed exists in something I have said. Since you fail to do so, and since merely asking you whether you are criticizing something is a question you can't handle with anything like a "yes" or "no", I think the effort of getting a coherent explanation of your objection exceeds the likely reward. If I were in your place as OP, I should be grateful to the many responders who have volunteered time to give your question consideration. 84.209.89.214 (talk) 17:28, 28 August 2014 (UTC)

See etymological fallacy. Since the OP himself responded, we now know your interpretation of the question is flawed, and there's no need to debate this further. --Bowlhover (talk) 18:26, 28 August 2014 (UTC)

I think you should clarify exactly WHO you mean is misinterpreting WHICH question. 84.209.89.214 (talk) 20:05, 28 August 2014 (UTC)

Ok. I got it, finally. You're not questioning the meaning of the original question at all. You're simply discussing the origin of the colloquial term 'Laser'? I originally assumed your statement was correlated with the OP's question. It doesn't appear that I'm the only one who assumed that, but apologies if I contributed to this derailment. (+)H₃N-Protein\Chemist-CO₂(-) 20:56, 28 August 2014 (UTC)

The OP, instead of arguing with users here, needs to explain precisely what he means by "a laser that curves". ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:57, 28 August 2014 (UTC)

Bending light traveling through vacuum is difficult, requiring gravity lenses as described above. If you don't mind the light traveling in a medium, a fiber laser is another way; just bend the fiber that the coherent light is traveling through.--Wikimedes (talk) 05:15, 29 August 2014 (UTC)

And while the OP probably didn't mean this, the ring laser comes to mind, even though at no point do the actual beams of light curve, the phase information between two beams of light split from one original laser beam changes just enough when the entire apparatus moves to be detectable. That's how "ring laser gyroscopes" work in navigation. It's sufficiently sensitive that ring lasers were used at one time (may still be, for all I know) as guidance mechanisms in ICBMs. loupgarous (talk) 13:44, 31 August 2014 (UTC)