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June 18

Rhenium

Why is rhenium so rare? Double sharp (talk) 04:11, 18 June 2012 (UTC)

My guess would be: because it has an odd atomic number, and is not frequently produced by nucleosynthesis during supernovae. Plasmic Physics (talk) 04:19, 18 June 2012 (UTC)

It's very dense (21.02g/cm3) so it probably sank to the core of the Earth when it was still molten as did iridium. Also like iridium, it is very siderophilic, so it "likes" to dissolve in molten iron e.g. the Earth's core. According to it's only rare on the Earth's surface, not in the universe as a whole, so that rules out Plasmic Physics's hypothesis. 203.27.72.5 (talk) 04:36, 18 June 2012 (UTC)

Rarity is relative. Plasmic Physics (talk) 04:48, 18 June 2012 (UTC)

Touché. It could indeed be rare compared to other elements in the universe, but especially rare on the Earth's crust due to the processes I described. I can think of lots of elements with odd atomic numbers though, and many of them are not rare at all. 203.27.72.5 (talk) 05:10, 18 June 2012 (UTC)

According to Synthesis_of_precious_metals#Rhenium, W and W are formed from the irradiation of naturally occuring tungsten with neutrons (readily available in stellar conditions) and these decay into Re (stable)and Re (half-life 10 years). So it may be generated in high metallicity stars. 203.27.72.5 (talk) 06:10, 18 June 2012 (UTC)

It is not that rarer than the other similar metals, but its chemistry is not leading to a strong enrichment in any minerals and therefore tit is hard to extract. Only Molybdenum ores contain significant amounts of rhenium. --Stone (talk) 10:01, 18 June 2012 (UTC)

"It is not that rarer than the other similar metals"

Don't forget that this graph is a logarithmic scale, so it really is a lot rarer than most elements; just estimating from the graph I'd say it's the 4th least abundant non-radioactive element. It's almost 10 times less abundant in the universe than gold.

Uranium and the late REE are less abundant but they are produced in considerable larger quantities. The amount the solar system and the amount we can extract are two very different things.--Stone (talk) 06:22, 19 June 2012 (UTC)

Also, to the IP above, note the trend in the graph with the odd-numbered elements: due to the Pauli exclusion principle, they are less abundant on average (save Hydrogen of course), and Rhenium is one of the heaviest stable elements, well beyond Iron-56, which is the last element which can be sustainably produced in stellar nucleosynthesis. I had never heard of the Goldschmidt classification though, clearly this plays a role in its rarity in Earth's crust. Thanks for the interesting read! -RunningOnBrains 12:37, 18 June 2012 (UTC)

If the subject of the origins and abundance of the elements interests you, I highly recommend P. A. Cox's The Elements: Their Origin, Abundance, and Distribution http://www.amazon.com/The-Elements-Origin-Abundance-Distribution/dp/019855298X which is perhaps the most fascinating and well-written science books I have ever read. I cannot recommend it strongly enough. μηδείς (talk) 17:04, 18 June 2012 (UTC)

Bird song identification

Just wondering if anyone out there can either identify a bird from a transliteration of its song, or point me at a site that can? Quite high pitched "didit, didit, didit" - UK Midlands. --TammyMoet (talk) 09:55, 18 June 2012 (UTC)

It's possibly a member of the Titmouse family - the name "tit" imitates the sound they make, as well as providing humerous material for many Carry On films. You can hear a Great Tit in this YouTube recording. Alansplodge (talk) 12:55, 18 June 2012 (UTC)

In the end I played my Bird Songs CD and they identified it as a wren. Personally I thought it may be a song thrush given the repetitive nature of the call, but I'll go with a wren. I hadn't heard it before, but I felt sure I'd seen it in a bird identification book. --TammyMoet (talk) 14:33, 18 June 2012 (UTC)

Xenon diiodide and krypton dibromide

Shouldn't xenon diiodide and krypton dibromide both exist, as they are isoelectronic with, respectively, the triiodide and tribromide ions? Whoop whoop pull up 13:03, 18 June 2012 (UTC)

As you were told the last time you asked "why does/doesn't X given Y that is isoelectronic with it", you need to consider things like charge, electronegativity, etc. and also do a literature search before claiming something doesn't exist. That literature search would often reveal why not, as part of studies of analogous compounds. People really do study and publish "let's extend a known series into not-yet-known territory" articles on a regular basis--both of your proposed compounds have been studied (one even experimentally). DMacks (talk) 16:20, 18 June 2012 (UTC)

• I really doubt these exist, given the low electronegativities of iodine and bromine. Xenon has an electronegativity of 2.6, so iodine and bromine (2.4 and 2.8 respectively, I believe) don't have the muscle to get xenon in a bond setup.--Jasper Deng (talk) 16:29, 18 June 2012 (UTC)

One is a known excimer complex; it indeed does have a very short lifetime and readily decomposes to the elemental forms. DMacks (talk) 16:36, 18 June 2012 (UTC)

Which one? Whoop whoop pull up 18:53, 18 June 2012 (UTC)

Prospective ligands around xenon has to be sufficiently electronegative to tease out an atomic obital to leach onto. Xenon has a pretty stable ground state arrangement of atomic orbitals, it's not going to sit iddle, while an unwelcome guest is trying to take advantage of it - it's going to fight it, and look for the first opportunity to get rid of it. Bromine and iodine are too weak to contend with a heavy weight like xenon. Plasmic Physics (talk) 23:40, 18 June 2012 (UTC)

If my explaination seems a bit abstract, it's because I anthropomorphise my molecules and atoms, I give them personalities and character. Their behaviour is easier to visualise that way. Plasmic Physics (talk) 00:18, 19 June 2012 (UTC)

Plasmic, I'm concerned about your explanation. A quick glance at a descriptive chemistry textbook (in my case, Greenwood and Earnshaw's Chemistry of the Elements, 1st ed.) shows that xenon displays extensive chemistry, with oxidation numbers of +2, +4, +6 and +8 and a full range of coordination numbers from 0 to 8, and that xenon dibromide and xenon dichloride had also been detected by 1986. The chemistry of krypton, however, was much less developed at the time of writing, with only KrF₂ and a handful of complexes being known. From what I can recall of lectures from a couple of years ago, krypton chemistry still lags behind, argon is restricted to a couple of highly unstable compounds and neon is still effectively inert: using xenon as your example of non-reactivity might not be the best choice. Brammers (talk/c) 09:22, 19 June 2012 (UTC)

I didn't say that it was non-reactive, I said that it is one tough customer, that doesn't like sharing, not that it can't. Plasmic Physics (talk) 10:13, 19 June 2012 (UTC)

Interesting that Kr and Xe are less electronegative than several of the halogens (and even O and N!)--things with which halides form moderately stable compounds. DMacks (talk) 10:32, 19 June 2012 (UTC)

Electronegativity is only realy applicable when discribing the relationship between atoms in a bond, first you have to form the bond. Plasmic Physics (talk) 10:57, 19 June 2012 (UTC)

Clues to calculate sun's future

Average people would thik when sun dies nobody knows, but scientific forecast, figuring out what will happen to our solar system in billions of years future is quite easy, not like what non-educated peoples might think. I wonder how do scientist come up with these variables, maximum size of the giants, net of sun's mass loss, how much longer they have on main sequence. Do they send a spacecraft to another stars, or astronomers basically use special powered telescopes? I thought when they send a spacecraft to another stars, then they are able to get these informations quite easily. What makes the informations fuzzy? Spacecraft? The technologies on spacecrafts are usually pretty strong on collecting informations? or to look at foreign stars/solar system they use a special powered telescope, which the variables like maximum giants radius, net star's mass loss might be sketchy causing scientist to come up with countless of different stabs. Does the data memory depend on how far away they are from our solar system? Further away they are from our solar system, do the virtual data memory get weaker? --69.226.45.94 (talk) 21:17, 18 June 2012 (UTC)

We are a long way from being able to send spaceships to other stars. They are so far away that any crew would be dead, and the ship would be out of energy, long before it arrived at even the closest star (beyond the Sun). StuRat (talk) 21:20, 18 June 2012 (UTC)

Almost all of our knowledge of other stars comes from stellar spectography. Even helium was discovered by this method. μηδείς (talk) 21:51, 18 June 2012 (UTC)

You mean, helium outside our solar system was discovered by this method, right? 203.27.72.5 (talk) 22:09, 18 June 2012 (UTC)

Nope, you meant what you said. That's pretty amazing. 203.27.72.5 (talk) 22:11, 18 June 2012 (UTC)

The furtherest man made object from Earth is Voyager I which is not heading towards any particular star, but will pass within 1.6 lightyears of AC+79 3888 in about the year 42000. Voyager II will pass by Sirius in about the year 300000. Pioneer 10 would take until the year 2000000 to reach Aldeberan but it probably won't get there anyway. Pioneer 11 is headed vaguely in the direction of Scutum. Is hasn't arrived there yet, but when it does, I'll let you know. 203.27.72.5 (talk) 22:07, 18 June 2012 (UTC)

As the others point out, our predictions about the solar system are largely based on observations made from earth. The space probes and things like the Hubble telescope also contribute information. This tells us about the way things (probably) are in the solar system. To predict the future, scientists take this information and feed it into mathematical models which are based on physical laws. But all models are "wrong", in the sense that they make simplifying assumptions, and all of our observations of the universe have errors and "noise" in them. Me, I'm still amazed this stuff is accurate and precise enough to put a man on the moon :) SemanticMantis (talk) 22:27, 18 June 2012 (UTC)

I've read before that all of the Apollo missions were possible without any relativistic corrections to the Newtonian mechanics. In that regard I don't think putting a man on the moon needs such great accuracy in the underlying physical models. 203.27.72.5 (talk) 22:34, 18 June 2012 (UTC)

We had yellow stars, maybe tons of it which have came off the main sequence, and collapse into white dwarf. I thought scientist use the same model what happened to similar sun-like stars, and use that to see what will happen to our sun. i wonder if you ever thought about that.--69.226.45.94 (talk) 23:18, 18 June 2012 (UTC)

Stellar evolution is far too slow to observe, save for the dramatic nova and supernova events. We can draw similarities between the states of all different stars in the sky, then sort them into categories, and then apply theory from the known physical properties of matter and energy to generate hypotheses on which categories of star result from what conditions. The main variabilites in stellar condions are mass, metallicity, temperature and age. Theories that prove useful in explaining the different observed states of stars allow us to model stellar evolution and then, by constructing a model using the current age, metallicity and mass of our star, we can make some assumptions about how it's evolution may progress.

We don't watch main sequence stars become white dwarfs. We see white dwarfs and we see main sequence stars and we hypothesise that white dwarfs develop from main sequence stars through mechanisms that we propose. We then collect evidence to support these hypotheses in the form of spectral data (chemical composition), brighness measurements (temperature), etc. 203.27.72.5 (talk) 23:34, 18 June 2012 (UTC)

HV Electrical transformers - do they really need a hand to help them go bang?

Hi. I'm watching a video on Youtube in which a High Voltage transformer block on a power pole overheats, and promptly explodes in a complete mass of hell. My question to the desk is this: Why do the companies who make these things see fit to fill them with something explosive to keep them cool and happy?

If they overheat or flat out short, they (can, and often do,) explode - and mineral oil & the coolants used are highly explosive, which only seems to add "fuel to the fire", so to speak. Is this a design flaw, or are there really no alternatives to the inclusion of such highly combustible materials in the making of these products?

 BarkingFish  23:03, 18 June 2012 (UTC)

We have some information in Transformer#Cooling and Transformer oil. There's just not much that is economically viable and has the right thermal properties to be useful (shame PCBs are outlawed). It's also hard to appreciate how much energy there is in an arc flash. There's just not much at all that can withstand it. I should also point out that the materials are not explosive by nature and are not really highly flammable either. But they can be made to burn given a large enough added energy, or to boil just a small enough amount to get a BLEVE. DMacks (talk) 23:40, 18 June 2012 (UTC)

Don't forget the amount of energy flowing from the power line that is capable to power hundreds of households. Which when the electrical characteristics of the transformer fails can end up in a small enclosed container. And easily create something like combined steam explosion and fuel vapor bomb. Electron9 (talk) 04:01, 19 June 2012 (UTC)

See Transformer oil. It insulates and cools transformer windings. There are also air cooled transformers ("dry types"), but they must be securely protected from moisture, may need cooling fans, and do not seem to offer as high a power rating for a given volume and weight. They would fail if rain, snow etc got into the windings, and are not good candidates for poletop use. Transformer says that some dry types are now made in sealed tanks, insulated and cooled by sulfer hexafloride, which sounds like a good idea if the cost is not too high for typical distribution sizes and size and weight are comparable. It would probably be harder to keep a distribution transformer gas-tight for decades than to keep it liquid-tight. The transformer oil is sometimes mineral oil, similar to motor oil. It does not seem to be all that explosive at normal temperatures, but if it is heated above its flash point and sprayed out in little droplets, then you can get an impressive fireball. I have seen a relatively small oil-filled padmount transformer blow open and burn the face off the bricks of a brick wall. PCB was less flammable than mineral oil, but it could produce dioxin in an arcing fire and has generally been replaced. Silicone oil is a replacement which is not very flammable, but I've heard (no ref handy) it can be explosive if it gets contaminated with water. A transformer which steps down 12000 volts to 240/120 volts might well have 10000 amps of fault current flowing into a short or arc inside the transformer, should one occur. This could happen if there is an insulation failure in the windings, if the oil level drops low, if water leaks in when a gasket fails, if overheating due to overloads causes paper insulation to break down and release moisture , if the oil becomes carbonized from tap changer operation or overheating or arcing at loose connections, or even because lightning struck near the transformer. (I have seen 60 year old transformers with oil as dark as coffee), still in use, but utilities do regular tests of the fluid in larger transformers. It could also be caused by a switching error or resonant conditions in a cable-fed system ("ferroresonance"). It is then up to the primary high voltage fuse to interrupt the current before the metal container fails and flaming oil shoots out. High voltage power fuses are cleverly designed, but complicated gadgets. Some have an overcurrent element which melts, causing a strain element to release a spring which causes an arc inside a tube containing boric acid, the ionized particles of which interrupt the arc. This might ideally happen in less than the first half cycle of fault current. Other fuse types can't interrupt until the current hits a zero at the zero point of the sine wave. The vast majority of the time, the primary fuse quickly does its job, and only customers served by the one faulted transformer lose their power, with others only seeing a momentary dimming of lights until the fuse operates. Then a utility lineman shows up in an hour or whatever and tries replacing the fuse and relivening (if there is no obvious damage) in case it was just a weak fuse or a lightning glitch. If the transformer won't reliven, then the lineman calls for a replacement transformer, and in a city, might be able to temporarily feed the outaged customers from the next transfomers, if the secondaries extend down the alley. When the transformer fuse fails to interrupt, the thousands of amps of fault current continues to transfer many megawatts of power into the faulted transformer can until the transformer catches fire or an upstream backup fuse operates on a delayed basis, likely killing the power to other transformers as well. Edison (talk) 19:46, 19 June 2012 (UTC)

Mitsubishi makes sulfer-hexaflorude insulated transformers in distribution size and up: . No info on price, mean time between failures, and size/weight for a given KVA capability. Other manufacturers emphasize substation and high voltage gas insulated transformers. Edison (talk) 20:04, 19 June 2012 (UTC)

A common measure of the estimated energy released by an arc-fault is in equivalent amount of TNT, and common values appear to be are on the order of a few pounds per second of arc in the 15 kV primary transformer/switchgear level, down to "only" a few ounces-worth (about a hand grenade or so) for end-user secondaries. DMacks (talk) 20:19, 19 June 2012 (UTC)

If Edisons figures on volt and currents are correct the transformer is attached to a line that transfers the energy equalient of 12 000 V * 10 000 A / (4.2*10^3) = 28 571 gram = 28 kg of TNT per second! or the power that a Boeing 747 uses. Electron9 (talk) 01:24, 20 June 2012 (UTC)

Regarding fuses etc.. how come a CME is able to bypass fuse and over voltage protections of the electrical grid? Electron9 (talk) 01:24, 20 June 2012 (UTC)

Power system engineers calculate the fault current at some location, such as a transformer, by starting with the voltage at the source, then factoring in the source impedance as well as the impedance in the transformers and lines between the source and the fault, and any arc impedance at the fault. As a result, there will be some voltage drop. If a conductor is solidly grounded at the fault, then the voltage to ground would be very low. The phase to ground voltage from a 12 kv 3 phase circuit would be 7200 max, so it might be much smaller in a fault due the the voltage drop of the system conductors. Thousands of ampere at thousands of volts is quite possible on the distribution system. In some situations, you want pretty high fault current so that the fuses or breakers will "coordinate" in such a way that only the closest upstream protective device operates, to minimize the outaged area and decrease the extent of equipment burned up. You are still talking an arc at a temperature of thousands of degrees, unless it is a metal to metal fault. Lots of heat is produced, and lots of sprayed flaming oil and expanding gases. One hopes the fault is extinguished in a fraction of a second. Edison (talk) 19:58, 21 June 2012 (UTC)

June 19

Is there a medical term for the physical feature of a very "triangular" head?

For instance (not to label a living person with something, just to give an example of what I'm talking about), there's this video footage of Arsenio Hall. When he's face-on, you can see the very pronounced pointedness of his head. We humans like to name things, so what about that? 69.243.220.115 (talk) 00:52, 19 June 2012 (UTC)

Hi. While there almost certainly isn't a specific term for the triangular head shape, it is possible that Hall could have been born with a condition known as Craniosynostosis, which causes the bones in the skull to fuse earlier than they should, it's caused by either a failure of the bones to grow correctly, or in some cases, by a failure of the brain to grow.  BarkingFish  01:04, 19 June 2012 (UTC)

Let's invent one: mantis head. :-) StuRat (talk) 01:07, 19 June 2012 (UTC)

Maybe people like that are just from France. --Jayron32 03:18, 20 June 2012 (UTC)

I don't think I understand Modulation (music) , but I did have a question about it.

Or may be I don't understand Key (music) either. These are articles that are probably just fine for people with at least some musical background but are incomprehensible for people like me. Lines like "The methods by which the key is established for a particular piece are not easy to explain" or "The key signature is not a reliable guide to the key of a written piece", don't help much either. Could someone add Key (music) (for nerds) that says: "To recognize the key , the software would have find the first note probably played by calculating the average of all notes played and look up the frequency in a table" or something like that? There is nothing in either article that is a recipe to find out if Frère Jacques even has a key or what it could be. The question I wanted to ask is, is http://www.youtube.com/watch?v=OSRCemf2JHc Popcorn modulated at 1:07 but I've come to realise that that would be like a 6 year old asking why the exact value of Pi cannot be written on a piece of paper without understanding multiplication. Joepnl (talk) 01:31, 19 June 2012 (UTC)

I agree that the article is too technical. Here are the basic things it helps to understand. (1) An octave is divided into 12 intervals that are equally spaced in pitch -- the interval between consecutive notes is called a semitone. In other words, there are twelve semitones in each octave. (2) A key consists of a subset of semitones. The two most common types of key are called major and minor. (3) In a major key, the notes are at intervals of 2-2-1-2-2-2-1 semitones. The starting note of the sequence is called the keynote. (4) In a minor key, the notes are at intervals of 2-1-2-2-1-2-2 semitones, starting from the keynote. There are also other kinds of keys with different numbers of notes and different spacing. (5) The easiest way to tell the keynote of a tune is to know that the tune usually ends with that note, or with a chord based on that note. Looie496 (talk) 02:19, 19 June 2012 (UTC)

You can change one major key into another one by changing only one note in it by a semitone. C major is the white notes on a piano keyboard:

     ... C D EF G A BC D EF G A BC D EF G A B ...
     ... * * ** * * ** * ** * * ** * ** * * * ...
     ... \__________/\__________/\__________/ ...

If you shift the star under each F up by a semitone, making it F#, then you get

     ... C D EF G A BC D EF G A BC D EF G A B ...
     ... * * * ** * ** * * ** * ** * * ** * * ...
     ... ______/\__________/\__________/\____ ...

which, as I've marked, is the same repeating pattern of stars, but starting from G instead of C. That's G major. Instead of sharping F, you can flat B, which gets you F major. Those are the only two "directions" you can go from C—other single-semitone changes don't get you the same repeating pattern. If you go in the flat direction from G it takes you back to C. If you keep sharping things from G you go to D, A, and so on. Eventually, after sharping everything, you get to C# major (seven sharps). You can keep going, double sharping the notes until you get to C-double-sharp major (fourteen sharps), then triple-sharping them, etc., but composers don't stray that far from their original key. You'll see the occasional double sharp and that's it. The principle of modulation between keys is that keys like F, C, and G major are close to each other in the sense of having a lot of notes in common, so in principle you can shift imperceptibly between them by altering notes that you happen to not be playing at the moment. Thus the exact moment at which the key changes is not well defined.

Equal temperament is a thing that exists, but it's not especially relevant here. If you want to play a lot of different keys on an instrument that can only play a fixed set of pitches, like a piano, you may want equal temperament. If you're playing an instrument that can produce a continuous range of pitches, like a violin or the human voice, then temperament is meaningless, but you still have this system of related major keys. In equal temperament C and B-sharp and A-triple-sharp and so on are the same sound frequency, but in general they're not the same, because the half steps and whole steps above are not generally all the same size—they are adjusted slightly so that certain intervals between them sound pleasing to the ear. By the time you get from C major (zero sharps) to B-sharp major (twelve sharps) the frequency has shifted a bit—specifically, by a factor of (3/2) / 2 ≈ 1.014. -- BenRG (talk) 07:25, 19 June 2012 (UTC)

Find and listen to Howard Goodall's five-part documentary Big Bangs on the history of music. A large part of his focus is on tone, key and temperament. See http://www.youtube.com/watch?v=AJX76zHAaFA but look for better links. It is quite excellent and will educate you on all you need to know. μηδείς (talk) 05:41, 19 June 2012 (UTC)

(Also, listen to http://www.youtube.com/watch?v=IZ4LCejQg8o μηδείς (talk) 05:41, 19 June 2012 (UTC))

I watched about three minutes of the first one and gave up. I don't see what this question has to do with equal temperament, except in a very indirect way. The second one seems even less relevant, though it is pretty, I guess. -- BenRG (talk) 07:25, 19 June 2012 (UTC)

My point was the documentary would give you concrete perceptual examples, rather than just abstract theory on paper. (Although if you just want abstract theory reading will be quicker than a five hour documentary.) Kind of like the difference between a guided tour through a painting gallery or being blind and listing to a lecture on wavelengths in respect to colour. The second video was just a pleasant digression, sorry. μηδείς (talk) 16:51, 20 June 2012 (UTC)

On propositional logic

In Propositional logic, under the heading of "Basic Concepts", they list the possible cases that may occur when one considers two propositions and an operation "connecting" (in lack of a better term) them, namely:

1 - P is true and Q is true

2 - P is true and Q is false

3 - P is false and Q is true

4 - P is false and Q is false

then, when the operation "material conditional" (P -> Q, read as "if P, then Q") is discussed, the following is written: "(...)It expresses that Q is true whenever P is true. Thus it is true in every case above except case 2, because this is the only case when P is true but Q is not. Using the example, if P then Q expresses that if it is raining outside then there is a cold-front over Kansas.(...)"

My question is: Should case 3 not represent a failure for the operation as well?200.119.78.115 (talk) 01:43, 19 June 2012 (UTC)

No, because there is no statement making the state of P conditional on Q, only vica-versa. 203.27.72.5 (talk) 02:01, 19 June 2012 (UTC)

If you said "Q if and only if P" then 3 would fail.165.212.189.187 (talk) 14:03, 19 June 2012 (UTC)

(EC) No. "If P, then Q" says nothing about whether Q will be true or not in the case of P being false, so case 3 doesn't contradict "if P, then Q". Looking at it another way, if Q is true, then "if P, then Q" doesn't imply anything about whether or not P is true. You can look at the mistake you are making as being the logical fallacy called affirming the consequent. Red Act (talk) 02:10, 19 June 2012 (UTC)

I don't really like the way they wrote that, though, as we don't have enough info to know if 3 or 4 are correct. It should be stated, that "If P is true, then we know that Q is true. However, if P is false, then we know nothing about whether Q is true or false." For a specific example "If it has been raining for an hour, then the ground is wet". However, if it hasn't been raining, that doesn't guarantee that the ground is dry. Snow could have melted, a water main could have broken, etc. StuRat (talk) 02:13, 19 June 2012 (UTC)

And that, StuRat, is why we have the Simple English Misplaced Pages article on propositional logic. 203.27.72.5 (talk) 02:21, 19 June 2012 (UTC)

It seems that our article is both unnecessarily complex and misleading, I can't see how that's an improvement in any case. And the Simple English version is just a stub and doesn't address this issue. StuRat (talk) 02:25, 19 June 2012 (UTC)

How is it misleading? And I don't think it's unnecessarily complex. It's just rigourous, as demanded by the subject matter. 203.27.72.5 (talk) 02:28, 19 June 2012 (UTC)

I just added to the Simple English version, to cover this case. The portion of logic discussed in this question is quite simple, and yet many probably couldn't understand it reading through our overly complex article. This is true of many of our math and science articles. (There are topics that can't be accurately described in simple terms, like quantum mechanics, but this isn't one of them.) StuRat (talk) 02:42, 19 June 2012 (UTC)

My thoughts on the quality and usability of Wikipedea articles: As time goes on, more and more articles seem to be written longer and longer, and more and more difficult for lay people to asimilate. A large fraction of Ref Desk questions ask things that the OP's could have answered for themselves by consulting relevant WP articles. So why do they ask? Because a) lazyness, b) they didn't think to search, c) they didn't know the terminology to search with, or d) they did consult a relavent article, but it di not answer their question because (1) it didn't cover it or (2) they didn't understand it. Item (d) is significant and we should adress that. I think that if a WP article is longer than about 100 - 150 lines, and/or uses lots of specialised terms (whether linked to term articles or not), there should be a sort of executive summary - a short few paragraphs that 1) give an overview of the deeper coverage to follow, 2) avoid as much as possible the use of specialised terms, 3) allow the reader to decide quickly whether the following content is likley to be of interest/help or not.

In some articles, I also think there should be a standard section "Common misconceptions" - this can significantly improve understanding, and reduce cyclic editing. Common misconceptions in science can range from silly urban myths thru to non-obvious errors in early textbooks that just keep on being copied from one reference to another.

Wickwack121.215.61.16 (talk) 03:32, 19 June 2012 (UTC)

I agree, except that long and complex aren't the same thing. A short article can be utterly incomprehensible, while a long one can make perfect sense. (At some point a long article should be broken into smaller articles, though, just because it's easier to load pages and navigate that way.) For an example of an article where I provided the easy to understand intro, see Weighted mean#Examples. StuRat (talk) 20:49, 19 June 2012 (UTC)

Thanks to RedAct and StuRat for addressing the question, but wouldn't that just imply nothing about the material conditional itself? What I mean to say is that, even though it may be the case that statement 3 doesn't contradict "if P, then Q," statement 3 does not imply anything at all about its truth. The OP.200.119.78.115 (talk) 04:45, 19 June 2012 (UTC)

The fact that it doesn't tell you anything is why it needs to be true. Saying "all ravens are black" is equivalent to saying "for every thing in the world, if that thing is a raven, then that thing is black". The only way to ensure that these statements are equivalent is to make the "if P then Q" part true whenever P is false (in this case, make it true for all non-ravens). If it was false for any non-raven then the whole sentence would be false independently of whether we had found a non-black raven, which wouldn't make sense. Only a non-black raven can falsify the sentence, not any of the other three cases. -- BenRG (talk) 05:51, 19 June 2012 (UTC)

There's something implicit here that needs to be said: "if", the English word, has lots of layers of meaning, and interacts with concepts like relevance and causality. "if", in propositional logic, is a lot simpler (and less informative). Various exotic logics bring some of these features back, but they can be a big pain to work with; it turns out that what is going on in people's heads when they speak and understand sentences is very complicated. (also, for most purposes, simple logics are powerful enough to reconstruct those features on an as-needed basis) Paul (Stansifer) 23:45, 19 June 2012 (UTC)

The semantics of the material implication is as it is. If this captures the "intuitive meaning" of a conditional statement, and if not, if there is anything better, has been discussed a lot among philosophers and logicians. At least for propositional logic, the answer sems to be "not quite, but no" ;-). --Stephan Schulz (talk) 10:01, 19 June 2012 (UTC)

Right — it's the closest you can get by looking only at the truth values of the component parts. The natural-language conditional looks at more than that; it also looks at the meaning of the component parts. This is much harder to get at formalistically, but attempts have been made. The OP may want to look at relevance logic for more information. --Trovatore (talk) 21:01, 19 June 2012 (UTC)

Inventory of asteroid contents?

Where can one find an inventory of the contents of asteroids within the asteroid belt, or closer? (iron, titanium, uranium. gold, H3 etc) Electron9 (talk) 03:54, 19 June 2012 (UTC)

Do you want to know what the average elemental composition of the entire population of asteroids is, or do you want a list of asteriods with their individual elemental compositions? And also, what is H3? 203.27.72.5 (talk) 04:16, 19 June 2012 (UTC)

"list of asteriods with their individual elemental compositions?" is the favorite. Ie which asteroid does one select to mine X ..? Electron9 (talk) 13:15, 19 June 2012 (UTC)

H3 is the most common substance in the universe. Evanh2008 04:18, 19 June 2012 (UTC)

Correction: Most common molecular ion in the universe. Someguy1221 (talk) 04:29, 19 June 2012 (UTC)

Correction: Ions have charges. "H3" (no charge indicated and the 3 is not subscript) doesn't mean anything as far as I can see other than a 2001 film. 203.27.72.5 (talk) 04:39, 19 June 2012 (UTC)

Truer than what I said originally. How about: "H3 is the most common molecular ion of the most common element in the universe"? Evanh2008 04:31, 19 June 2012 (UTC)

(EC)So H₃ then? I doubt much hydrogen is going to be present on asteroids except as water or ammonia. According to hydrogen it is most commonly found in the plasma and atomic state, not as H₃ or any ion thereof. 203.27.72.5 (talk) 04:36, 19 June 2012 (UTC)

Look up trihydrogen cation. Whoop whoop pull up 11:38, 19 June 2012 (UTC)

The original poster may have meant Helium 3 rather than the very unlikely triatomic hydrogen or H3+ ion. Graeme Bartlett (talk) 13:03, 19 June 2012 (UTC)

Correct :-) Electron9 (talk) 13:15, 19 June 2012 (UTC)

So He then? Not very likely on asteriods other than as a product in a decay chain, so very trace amounts. Anyway, I still don't know what the OP is asking for, a catalogue of asteriods with their individual compositions, or the abundance of chemical elements in the solar system's asteriods in general. 203.27.72.5 (talk) 20:45, 19 June 2012 (UTC)

There's presumably He-3 on asteroids for the same reason it's on the moon - they've been bombarded by solar wind for billions of years and it builds up. --Tango (talk) 21:55, 19 June 2012 (UTC)

Which, from the article on He-3, is present only at ppb levels, and it's the product from tritium beta decay. 203.27.72.5 (talk) 22:47, 19 June 2012 (UTC)

He-3 is useful in fairly small quantities, so ppb is enough for people to be considering going to the moon to extract it. If you're mining asteroids anyway, you might as well keep hold of the He-3 while you're at it (most plans for asteroid mining involve extracting pretty much everything of value from an asteroid, rather than mining them for a specific thing). --Tango (talk) 13:51, 20 June 2012 (UTC)

milk and aging?

have there been any studies on whether consumption of milk affects aging? 99.43.78.36 (talk) 04:14, 19 June 2012 (UTC)

I can't speak to studies, but it's high in lactose so bad for diabetes and annoying to the lactose intolerant, but high in calcium and vitamin D so good for osteoporosis. Jeanne Calment swore by chocolate, cigarettes and, especially, olive oil. μηδείς (talk) 05:19, 19 June 2012 (UTC)

illegal immigrants in the us

Paramagnetism

Why are ${\displaystyle BN^{-}}$ and ${\displaystyle BN^{3-}}$ paramagnetic but not ${\displaystyle BN^{2-}}$? --150.203.114.37 (talk) 09:59, 19 June 2012 (UTC)

Paired and unpaired electrons. Plasmic Physics (talk) 10:08, 19 June 2012 (UTC)

We have a paramagnetism article that talks about its causes and the relevance of electron-spin. DMacks (talk) 10:09, 19 June 2012 (UTC)

Are you sure that you have the correct formulae? Plasmic Physics (talk) 10:10, 19 June 2012 (UTC)

Yes. --150.203.114.37 (talk) 11:25, 19 June 2012 (UTC)

SO for clarity, is it true that ${\displaystyle NO}$ is paramagnetic? Yes? --150.203.114.37 (talk) 22:23, 19 June 2012 (UTC)

Yes. Plasmic Physics (talk) 22:50, 19 June 2012 (UTC)

NO and BN2-

How do you derive molecular orbital diagrams for molecules, and in particular, nitric oxide (NO) and ${\displaystyle BN^{2-}}$? --150.203.114.37 (talk) 11:28, 19 June 2012 (UTC)

You have to run modelling software, or run spectroscopy experiments to find the energy levels. Plasmic Physics (talk) 11:34, 19 June 2012 (UTC)

You can make an educated guess, but there is a good chance to be wrong. Plasmic Physics (talk) 11:36, 19 June 2012 (UTC)

Radium

Is there a commercial source for a gramm of radium bromide? I know that this is highly regulated and neither possessing nor transporting it would be possible if it is not a university or research institute. Extracting was done during the uranium production, but I doubt all companies producing uranium would also isolate radium our days. The alternative method to produce it directly by irradiating a lighter atom with neutrons seems less favorable in the radium case.--Stone (talk) 12:24, 19 June 2012 (UTC)

If you can get your hands on an old borehole logging neutron generator, then you could extract the radium-beryllium neutron source and make some radium bromide (provided the radium hasn't substantially decayed into radon. It will need to be an old source, as the new ones use americium-beryllium. You'd also be breaking the law unless you're properly licensed to do all of this work with radioactive materials and have access to a hot cell. It's not available commercially as far as I can see. There are better radioactive sources available so the uses would be very specialised and most likely research only. 203.27.72.5 (talk) 21:08, 19 June 2012 (UTC)

Whatever you do, don't say something like "I am an Al Qaeda terrorist agent interested in making a dirty bomb" or you may come to the unwanted attention of various intelligence agencies. μηδείς (talk) 22:56, 19 June 2012 (UTC)

T.h.e.i.r/s.y.s.t.e.m.s/h.a.s/a.l.r.e.a.d.y/s.p.o.t.t.e.d/t.h.i.s/d.i.s.c.u.s.s.i.o.n\ Plasmic Physics (talk) 23:50, 19 June 2012 (UTC)

They have software that scans the internet for keywords. Something's going to be flagged, if it mentions this and air bus on the page. Plasmic Physics (talk) 23:54, 19 June 2012 (UTC)

Actually, it turns out they do still use radium sources for density measurments over long distances (up to 300m) in the construction industry. They also still use it as a neutron generator because some states in the US apparently regulate Ra less strictly than Am. Get your hands on one of those, crack it open, and Bob's your uncle. The material inside may already be radium bromide since it appears to be one of the more stable chemical species. It's probably bound up in some kind of ceramic matrix though. 203.27.72.5 (talk) 03:00, 20 June 2012 (UTC)

No no I want to know who is producing that stuff. Buying is less of a problem for small quantities, but where do the people producing the small radium radiation sources get their material for manufacturing? There are only a few possibilities, one is that they have a few gramm stockpile somewhere from the good old times in the first quarter of the 20th century when the stuff was produced mainly in US from Utah and Canadian uranium ore or in Belgium from Kongo uranium ore or in Austria from Joachimsthal uranium ore. The other possibility is that some body somewhere is still operating an extraction plant.--Stone (talk) 09:00, 20 June 2012 (UTC)

AIR BUS A380

DOES AIRBUS A380 NEED FOUR WHEEL NOSE LANDING GEAR. — Preceding unsigned comment added by 78.93.35.44 (talk) 13:17, 19 June 2012 (UTC)

No. 2 wheels. More at Airbus_A380#Integration_with_infrastructure_and_regulations. --Tagishsimon (talk) 13:49, 19 June 2012 (UTC)

Don't you mean "No. 2 wheel"? There is only one No. 2 wheel. Whoop whoop pull up 03:02, 20 June 2012 (UTC)

No, he means exactly what he said. (You have read the first word as an abbreviation for "number"; it is actually a full sentence: "No.") -RunningOnBrains 17:50, 20 June 2012 (UTC)

Well, actually, it's not a full sentence, as it lacks a verb. But I guess that's really one for the language desk... 203.27.72.5 (talk) 21:40, 20 June 2012 (UTC)

Ah, thanks. Whoop whoop pull up 20:53, 20 June 2012 (UTC)

Shower Cream

what exactly is Shower Cream and how does it work? Its a alternative to soap. How does cream rinse off? does it leave a oily film behind?--Wrk678 (talk) 13:42, 19 June 2012 (UTC)

We have an article Shower gel. What it doesn’t appear to say is that the thickening agent is often Sodium polyacrylate. Being water soluble, it all washes off. --Aspro (talk) 16:40, 19 June 2012 (UTC)

Logically, it should be easier to rinse off, being closer to a liquid in it's natural state than bar soap. You probably have already used liquid detergents, such as hand dish washing liquid, so you know it can rinse off. StuRat (talk) 17:06, 19 June 2012 (UTC)

That makes no sense. Diesel is closer to liquid than NaCl at STP but that doesn't make it easier to rinse off. 203.27.72.5 (talk) 21:25, 19 June 2012 (UTC)

The underlying assumption is that both are water soluble, as Aspro already stated. Given that assumption, my statement is correct. StuRat (talk) 03:20, 20 June 2012 (UTC)

The bar soap is already dissolved when it's in the lather on your skin. The difference in solubility and viscosity between a lather of bar soap on the body and a lather of shower gel is going to determine the ease with which it can be rinsed off not whether the bar soap was a solid before you formed the lather or not. 203.27.72.5 (talk) 03:35, 20 June 2012 (UTC)

When using an old shriveled bar of soap, it can break up, leaving me with solid chunks in my armpit hair. This is not particularly water soluble (apparently the more soluble parts already dissolved in water, leaving behind the less soluble bits) and much harder to get out than liquid soap/detergent. StuRat (talk) 03:41, 20 June 2012 (UTC)

I believe that is just because the pieces are large. If they really dissolved in your armpit as quickly as you wanted too then you'd have to spend alot more money soap. Unless you use some special soap that has pieces of oatmeal or pumice or rocks in it or something like that. Sagittarian Milky Way (talk) 16:58, 20 June 2012 (UTC)

Yes, I've used bar soaps containing oatmeal and pumice. However, just being completely dried out seems to make regular soap less water soluble, too. I'm sure it would dissolve eventually, once the water soaks back in, but that's longer than I have in the shower, so I'm left trying to pick the chunks out of my pit hair as the water turns icy cold. Thus, I've switched to liquid soap/detergent. StuRat (talk) 18:18, 20 June 2012 (UTC)

It would seem that some of you folks do not have to clean your own shower cubicle. Those of us that do know that having to clean soap scum off the walls is a problem that does not exist with shower gel. This is the reason why hotels these days leave shower gel in the rooms/suites, and not soap cakes - it saves them cleaning labour. They get less incidence of blocked drains too. Wickwack121.221.33.192 (talk) 06:50, 20 June 2012 (UTC)

You're right, I don't clean my own shower cubicle, but I also use shower gel, so apparently I'm saving someone some effort. 203.27.72.5 (talk) 07:57, 20 June 2012 (UTC)

I still say Sorbolene is best. -- ♬ Jack of Oz ♬ 00:04, 23 June 2012 (UTC)

I think you guys missed the boat here what I was referring to the shower cream it's not the same thing as shower gel I've seen videos of doctors recommending something called shower cream for people with eczema because it does not contain detergents that's why I was asking how washes off, If it is cream--Wrk678 (talk) 17:44, 21 June 2012 (UTC)

The difference between cream and gel is the proportions of the ingredients use. So from the point of view of your question - the terms interchangeable. If they weren’t we would have said so.--Aspro (talk) 22:53, 22 June 2012 (UTC)

Oh yeah, I used something like that once. It was made from dairy milk and was called moo-goo or something like that. It was awful and definitely made me feel dirtier after I showered than before. 203.27.72.5 (talk) 21:21, 21 June 2012 (UTC)

If it really does contain milk cream and no soaps or detergents, then it won't wash off, but neither does leave-in conditioner. And, yes, I'd expect it to feel slimy, much like moisturizer does when first applied. StuRat (talk) 21:20, 23 June 2012 (UTC)

Thermodynamics

If I have a freshly-boiled cup of tea and pour milk in, will it be cooler in 10 minutes than if I wait until 10 minutes are up before pouring the milk in?--Gilderien Chat|List of good deeds 19:20, 19 June 2012 (UTC)

Why dont you try it and tell us your findings?165.212.189.187 (talk) 19:25, 19 June 2012 (UTC)

I can't start drinking caffeinated drinks at this time in the evening....I'm playing keys for the olympic torch tomorrow.--Gilderien Chat|List of good deeds 20:13, 19 June 2012 (UTC)

I don't think that all the 270 results you get if you put "coffee cooling" into the "Search the Reference desk archives" at the top of the page are people who have previously asked just this question, but certainly many of them are. --ColinFine (talk) 20:14, 19 June 2012 (UTC)

Argh.....this is turning out to be much more complicated than I imagined....I initially thought that as heat lost through radiation is something like ${\displaystyle t^{4}}$ the milk added first would be cooler, but now I see it could depend on the shape of the cup, the specific heat of the cup, the thickness of the cup...--Gilderien Chat|List of good deeds 20:22, 19 June 2012 (UTC)

And, as we have pointed out in the past, the only really relevant thermal loss processes are conduction and convection; these are empirically well-modeled using Newton's law of cooling, for an appropriately-chosen time-constant. If you want to correctly model the effects of radiative cooling, you'll need incredibly precise thermometers - the sort of equipment that few people have at hand for kitchen chemistry. Nimur (talk) 20:24, 19 June 2012 (UTC)

Adding the milk right before you drink it will cool it the most, if we assume the milk is in the fridge during that 10 minutes. However, if both the milk and the tea were out, then it would depend on the relative initial temps of each versus room temp, the types of containers, etc. StuRat (talk) 20:27, 19 June 2012 (UTC)

I was assuming the milk remained at a constant temperature until pouring....though am I to believe that the same overall answer, if not precisely the same temperature change, is obtained whether radiative cooling is included or not?--Gilderien Chat|List of good deeds 20:32, 19 June 2012 (UTC)

If you pour your tea out into a cup that is in a Environmental chamber maintained at the same temperature as the tea it will obviously be at the same temperature when you come to put the cow juice in. However, if the ambient temperature is lower, the tea will loss heat at a rate depending on that ambient temperature. The lower the ambient temperature the less local heat energy will be available to radiate back into the cup of Rosie Lee -hence it will cool faster due to its higher energetic state. Pour the in milk first (the proper way) and the infusion of tea after. Then it will be warmer ten minutes later than if you had done it vicky-verky. In a power station it is the done thing to add more heat to steam after the first turbine because it is easier to add heat to something already hot, than when its cold -so it goes the other way too.--Aspro (talk) 20:46, 19 June 2012 (UTC)

An easy way to visualize it is to consider a cup half full of water at 100°C. It will cool at a rate that decreases over time e.g. takes 1 minute to reach 90°C, 3 minutes to 80°C, 6 minutes to 70°C, 10 minutes to 60°C and so on and so forth. The reason its rate of cooling decreases is because the temperature difference decreases i.e. very hot things transfer heat to very cold things faster than moderate temperature things do.
If when it reaches 60°C (or after 10 minutes) we add to it exactly the same amount of water again but this time at 0°C, the final temperature of the now full cup will be 30°C.
If instead of that, we add the 0°C water right at the start, the full cup will be at 50°C and over the next 10 minutes will cool at a much slower rate (following the above trend it would take 21 minutes to reach 40°C).
If you think of the first half-cup as your tea, and the second one as your milk, it's easy to see that in the first case the tea ends up much colder than in the second one. The exact rate of cooling will depend on your cups dimensions, material, etc. but the cooling will always be fastest at the start and slow down as the temperature difference between the ambient and the tea decreases. 203.27.72.5 (talk) 22:41, 19 June 2012 (UTC)

If you leave the milk out to warm as well, both liquids will cool (come to room temperature) more quickly, since smaller masses having greater surface areas. If the milk is kept refrigerated and added later it will depend on the relative volumes, temperatures, and surface areas. You'd have to do the calculus, which is what I believe StuRat said above. μηδείς (talk) 22:53, 19 June 2012 (UTC)

Not quite. I said that the refrigerated milk should always be added last, if the object is to cool the tea the most. It's only when the milk is warming as the tea is cooling that it gets rather iffy. StuRat (talk) 03:12, 20 June 2012 (UTC)

If you leave the milk out it will warm, not cool. One mass will cool and the other will get warm. The net effect will be that the temperature of the tea with milk in it will be slightly higher (by an amount proportional to the fraction of the drink made up by the milk, the temperature change in the milk between when it was taken out of the fridge and when it was poured, and the heat capacity of milk). 203.27.72.5 (talk) 23:02, 19 June 2012 (UTC)

Actually, it has been observed that, under certain conditions, water at or near the boiling point will actually drop in temperature due to radiative heat loss faster than colder water. Sometimes extremely hot water will freeze before water that was actually closer to the freezing point to begin with. See Mpemba effect. If that effect always holds true (and it doesn't), I would say that the tea would actually be cooler if the milk were added immediately. Evanh2008 23:09, 19 June 2012 (UTC)

No controlled experiment has confirmed that supposed effect. I hope the relevant artilce doesn't say otherwise. μηδείς (talk) 02:34, 20 June 2012 (UTC)

Inventory of asteroid contents per body?

Is there an inventory per asteroid body on what contents they have, within the asteroid belt or closer? (iron, titanium, uranium. gold etc) Electron9 (talk) 22:27, 19 June 2012 (UTC)

No one has been there yet to check. Assumptions of contents would be made on surface features which would indicate whether they were carbonaceous asteroids or stony asteroids or so forth. See asteroid spectral types. μηδείς (talk) 22:48, 19 June 2012 (UTC)

For small bodies we generally assume there is no differentiation i.e. if the surface is iron then we assume it's a lump of iron, if the surface is ice we assume it's a lump of ice. For the larger ones there is most likely different materials in the different strata. The spectral data is also only any good for materials that are present in some decent concentration. If there's a few ppm of gold (or ppb of He-3), you won't see that from spectral data. 203.27.72.5 (talk) 23:08, 19 June 2012 (UTC)

I had some thought of some space organization like NASA etc would have either used the reflected wavelengths from the sun or a high energy laser to figure out the contents through absorption/emission spectrum ? maybe there are other methods that works better. Electron9 (talk) 00:31, 20 June 2012 (UTC)

That's exactly what they do. But you can't see trace elements that way because the signal from them is so weak, and you can only see surface materials, not the interal structure. The other ways are to send probes to sample them directly, which would take a long time per asteriod, or sample directly from meteorites. Watching gravitational interactions with other objects may also help to deduce their mass, and if their volume is known the density and likely composition can be established. 203.27.72.5 (talk) 01:11, 20 June 2012 (UTC)

Has any such laser/sun or mass to gravity interaction measurements been done, or is planned? Electron9 (talk) 01:27, 20 June 2012 (UTC)

I'm not aware of any volume of data available from gravity interaction analyses, but if you have a look at asteroid spectral types as μηδείς suggested, it explains how asteriods are classified according to surface composition. 203.27.72.5 (talk) 02:18, 20 June 2012 (UTC)

Why would Body surface area be the perfect measure for medication dosages?

From the article: "For many clinical purposes BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass." The article also has a few lines of criticism.

I've heard, from a pharmacist, the rumour that while finding correct formulas to calculate the body surface area from length, weight, etc has been studied at length, the very ratio behind using BSA instead of, for instance, weight, has not been studied for ages. Is that true? My (layman) guess would be that you'd have a range of formulas for the right dosage depending on the kind of medicin. One might include age and weight, another might be sugarlevels combined with gender, etc. Instead, the amount of skin seems to be holy. Is the rumour true and is this some kind of "soft" Lysenkoism? Joepnl (talk) 22:37, 19 June 2012 (UTC)

The BNF uses the formula: ((surface area of kid in m) / 1.8) x Adult Dose. The figure of 1.8 refers to the average surface area of an adult.--Aspro (talk) 22:54, 19 June 2012 (UTC)

1.8 is an adult? My surface area was a full 2.7 m when I was so young I was 5'6" or several inches shorter. On the pediatrician's medical record. Now I had some potbelly but everything else is slim like a snake. If your limbs are thinner and shorter than adults and your torso not wider, significantly rounder (fatter), or taller and your head/neck is small and thin then where is the extra 50% surface area going to come from? Sagittarian Milky Way (talk) 16:46, 20 June 2012 (UTC)

Isn't giving a figure for body surface area akin to giving a figure for the length of the coastline of Britain. It depends on the fineness of the measurement. SkyMachine 00:56, 20 June 2012 (UTC)

Not really, the skin is rather smooth, unless you go down to the level of including the surface area of pores, and nobody would do that. StuRat (talk) 03:06, 20 June 2012 (UTC)

The clinical purpose of calculating body surface area is for determining the dosage of certain types of drugs and expecially for determining chemotherapy dosage. Many of these drugs or their metabolites are mainly excreted via the kidneys. It appears that the rate at which the kidneys can do this is roughly proportional to an eqivalent or notional internal surface area, and this is in turn proportional to body surface area. A similar situation arises for drugs that are exceted via the intestines - there is a rough alignment of intestine internal surface area and body surface area. There may be no rigorous science in this, but basing dosage on BSA has been found to work fairly well. The weight of intestines and other organs tends to the cube of height whereas the processing area tends to the square of height, but weight is of little importance when the rate at which a given quantity of drug excreted is proportional to the internal surface area. So many factors affect the half life of drugs in the body that any sort of precision in dosage is pointless. Wickwack121.221.33.192 (talk) 04:58, 20 June 2012 (UTC)

Would women get extra drugs compared to a man the same height & build just because their beautiful curves and breasts add surface area? Sagittarian Milky Way (talk) 16:46, 20 June 2012 (UTC)

BSA is a notional value calculated by a simple formula (engineers and scientists will note that it make no dimensional sense) based on only height and weight. Within the precision required (which is no real precision at all), there is no difference between males and females. In real life, men have slightly greater surface area due to wider shoulders while lacking visually apparent curves at breasts and thighs but, as explained, this is of no importance in regard to required dosing precision. Wickwack121.215.54.198 (talk) 02:34, 21 June 2012 (UTC)

Fine then, a man of the same mass and height would be denser due to less body fat and have less surface area. Sagittarian Milky Way (talk) 23:57, 21 June 2012 (UTC)

Your Body surface area is 2.7 m at 5 foot something and skinny as a bean pole? Please post a photo on Misplaced Pages Commons and I'm sure we can find an article to add it to.--Aspro (talk) 22:10, 20 June 2012 (UTC)

Maybe it was a typo then. At the time I pictured a square meter with my cross section and it didn't seem like there's enough but it's from the doctor so.. I supposed maybe it would work out if you really did the math. Sagittarian Milky Way (talk) 23:57, 21 June 2012 (UTC)

Hum...Typo. That's a shame! Don't get me wrong; I wasn’t thinking about you as a freak or anything like that but we need images on our articles such as 'Homunculus'. For example this . To think I might have discovered a hitherto unknown and new example, out in the wild, got me rather exited there -for a moment. It was purely out of academic interest that I was curious as to what you might look like.--Aspro (talk) 16:33, 22 June 2012 (UTC)

Diamagnetism

What causes diamagnetism in a molecule of two atoms? --150.203.114.37 (talk) 22:38, 19 June 2012 (UTC)

The largest contributor is the spin multiplicity. Only singlet state molecules tend to be diamagnatic. Plasmic Physics (talk) 22:44, 19 June 2012 (UTC)

Is it true that anything which is not paramagnetic is diamagnetic? --150.203.114.37 (talk) 22:41, 19 June 2012 (UTC)

Yes. Plasmic Physics (talk) 22:44, 19 June 2012 (UTC)

(edit conflict)

1. Molecular orbital theory will show whether there are any unpaired electrons in the molecule. If there are none the molecule is diamagnetic for reasons I can't understand yet.
2. Not quite. Some substances are ferromagnetic (a stronger form of paramagnetism), but yes if it isn't that either the substance is diamagnetic.--Jasper Deng (talk) 22:45, 19 June 2012 (UTC)

(edit conflict) In your question earlier today about paramagnetism, you were advised to read the article paramagnetism. I bet if you use the search box at the top of this helpdesk you can find an article that might have information about diamagnetism among our 6,942,044 articles. You might even be able to guess what its name might be. It has information about what causes this effect at an atomic/molecular/electronic level and what types of materials exhibit it vs other types of magnetism (in particular, giving a clear "no, but may be overwhelmed and un-noticeable" to question #2). DMacks (talk) 22:45, 19 June 2012 (UTC)

June 20

Weird brown egg

Does anyone know what the bumps are at the bottom of the egg? Smallman12q (talk) 15:26, 20 June 2012 (UTC)

It's an egg defect. More specifically, an irregular calcification. Quite common in home-grown eggs, and also far from rare in industrial eggs. For more info, see this resource , which would describe the defect as "pimples", or perhaps a "misshapen egg." SemanticMantis (talk) 18:02, 20 June 2012 (UTC)

I suspect that those who produce eggs for supermarkets sort out the ugly ones like this, and use them for other purposes, like in precooked baked goods. StuRat (talk) 18:10, 20 June 2012 (UTC)

Yep. All you have is a little extra eggshell. Absolutely nothing wrong with the egg. There IS something wrong with an egg marketing system that wants ignorant customers to think that all eggs are identical. HiLo48 (talk) 18:36, 20 June 2012 (UTC)

Just wait until they engineer cube-shaped eggs, to better fit in the shelf space. :-) StuRat (talk) 18:39, 20 June 2012 (UTC)

It's just a matter of time, and not at all biologically impossible. Gallstones are often cubical, for example. In any case, there appears to be some readiness among the egg-consuming public for cubical eggs, and you can make your own in the comfort and privacy of your own humble abode with this: ]. Dominus Vobisdu (talk) 18:48, 20 June 2012 (UTC)

Gallstones are crystalline. Lots of crystals have a cubic structure. Eggs are not crystalline, so the existence of cubic gallstones is not evidence that you could get cubic eggs. --Tango (talk) 21:59, 20 June 2012 (UTC)

Do fish have tongues ?

StuRat (talk) 18:27, 20 June 2012 (UTC)

Yes. Here's an article describing how fish tongues work a little differently from mammal tongues . Unless, of course, the tongue has been replaced by this tongue-eating parasitic louse. SemanticMantis (talk) 18:31, 20 June 2012 (UTC)

Thanks. They must be shorter than the tongues of other animals, because I've never seen one stick it's tongue out (except maybe that one that uses it's tongue as a lure). StuRat (talk) 18:37, 20 June 2012 (UTC)

Are plastic houses doable?

Plastic is known to be very durable, even if it would possibly be more expensive than mortar and bricks. OsmanRF34 (talk) 19:35, 20 June 2012 (UTC)

Doesn't seem like a good idea, for several reasons:

1) Plastics outgas toxic fumes, so the house might be too toxic to live in for the first year or so.

2) Plastics are flammable, again giving off toxic fumes when they burn. This is true of wood, too, but to a lesser extent. Burning plastics can also stick to human flesh, like napalm.

3) Plastics tend to degrade under UV light. A protective coating might help here, though.

4) Plastics have a high coefficient of thermal expansion, and some become noticeably softer when hotter and harder when cold. Thus, they could crack in winter and sag in summer.

5) Plastics don't have as much compression strength as other common building materials, like bricks. StuRat (talk) 19:40, 20 June 2012 (UTC)

Seems all was said then, about my revolutionary idea. :( OsmanRF34 (talk) 19:46, 20 June 2012 (UTC)

It might have been revolutionary in the 1960s, but plastic houses have been around for a long time. A Google search will turn up lots of hits. Dominus Vobisdu (talk) 19:48, 20 June 2012 (UTC)

6) Plastics are highly susceptible to creep. --Carnildo (talk) 00:31, 21 June 2012 (UTC)

Note that plastics are used extensively in building houses, though. Here are a few ways:

a) Carpets made from synthetic fibers (outgassing from these can be a problem, too).

b) Thermal insulation made of Styrofoam, etc.

c) Plastic vapor barrier sheets in walls.

d) PEX plumbing.

e) Wire (electrical) insulation. StuRat (talk) 20:01, 20 June 2012 (UTC)

You're conception of "house" seems to be a bit culturocentric and narrow, Stu. Dominus Vobisdu (talk) 20:07, 20 June 2012 (UTC)

If you're talking about igloos, grass huts, etc., I don't tend to call those "houses", no, those are other types of dwellings. StuRat (talk) 20:11, 20 June 2012 (UTC)

No, I'm not. Think about the houses that most of the planet lives in, not most of the people in your neighborhood. Dominus Vobisdu (talk) 20:16, 20 June 2012 (UTC)

Face it StuRat, you are a culturocenting culturocentor. μηδείς (talk) 20:20, 20 June 2012 (UTC)

At least some of those features, like electrical wiring, are widespread in houses around the world (excluding other types of dwellings). StuRat (talk) 20:27, 20 June 2012 (UTC)

Top Gear presenter James May built a two-story house out of lego. Wasn't the most liveable of places though. . LukeSurl 21:22, 20 June 2012 (UTC)

I think electric wiring with plastic insulation is pretty universal. In additon to the features StuRat listed, there's also vinyl floor covering, which in some cases goes right through the house, and the adhesives that hold the whole mess together. The extensive use of plastics in the constrution of houses, combined with the large amount of plastic in furniture, white goods, sterosystems, etc. seems to belie StuRat's claims about outgassing of plastics making homes unlivable after construction though. 203.27.72.5 (talk) 21:37, 20 June 2012 (UTC)

Small quantities of plastic aren't a problem, but large quantities, like certain floor coverings, can cause sick building syndrome. StuRat (talk) 21:44, 20 June 2012 (UTC)

There are already houses built that use a great deal of plastic. White/brown/etc ultraviolet resistant PVC foam insulated weatherboarding clad the outside. Double glazed UV PVC windows and doors stop the wind blowing through. Inside surfaces are clad in plastics. Plumbing often is now mostly plastic. Much of the wood furniture is made from chip wast, formed into sheets by bonding with plastic. The jacuzzi is often plastic. The carpets are made from synthetic fibre (plastic). And in hot climates they are surrounded by drought resistant astro-turf; surrounded in turn by plastic white picket fences.--Aspro (talk) 21:48, 20 June 2012 (UTC)

Does the house come with free health insurance for cancer, asthma, birth defects, eczema and breathing mask with suit ..? :-) Electron9 (talk) 14:33, 21 June 2012 (UTC)

Smokeless powder compared to bullets

Lets say you shoot a blank cartridge. Would the escaping gasses accelerated out the muzzle have a total kinetic energy greater than a bullet accelerated by those same escaping gasses? The reason I ask is if the gasses are doing work on the bullet, shouldn't there be inefficiencies involved that make the total energy imparted to the bullet less than the total energy that the escaping gasses would normally have if there were no bullet? ScienceApe (talk) 19:52, 20 June 2012 (UTC)

Yes, given the same amount of powder in either scenario, the bullet will get some of the kinetic energy, and the gases will get some (or all, if there is no bullet). However, that kinetic energy from the gases will quickly dissipate by moving air, while the bullet will keep most of it's kinetic energy far longer and farther. However, shooting somebody point-blank with a blank can still kill them, as the gases still have sufficient potential energy to do so at that distance. StuRat (talk) 19:56, 20 June 2012 (UTC)

What StuRat said isn't wrong, but the line between kinetic energy, sound energy (in the pressure wave) and heat is a bit less obvious in this situation. Whether there is more energy as kinetic, heat or in the pressure wave at any given point depends on how you want to delineate each. 203.27.72.5 (talk) 20:48, 20 June 2012 (UTC)

June 21

Boiling hotter, boiling faster?

It's a commonly noted fact that salted water boils hotter than unsalted water. But my question is, does it boil faster? If I have a pot of salted water, will it boil away faster than an otherwise identical pot of unsalted water? If I synchronize the pots by when I turn the flame on? If I synchronize the pots by when they begin to boil? Thanks. Someguy1221 (talk) 00:38, 21 June 2012 (UTC)

Possibly of interest. Short Brigade Harvester Boris (talk) 00:45, 21 June 2012 (UTC)

Assuming both start at ambient temperature, the salted water will boil slightly slower, since it has to heat up further to reach it's boiling point. 203.27.72.5 (talk) 00:47, 21 June 2012 (UTC)

I suppose another consideration is that salt water has more entropy than non-salted, so it will resist evaporation. That will lead to it losing less heat and possibly boiling faster. That will of course depend on the concentration of salt and ambient humidity, etc. 203.27.72.5 (talk) 00:50, 21 June 2012 (UTC)

Scratch that. The higher entropy of the salt water is what makes the boiling point higher to start with. The amount evaporating will still increase as the temperature approaches the boiling point. The salt water will boil ever so slightly slower, and hotter. As an aside, any food in the pot will cook faster in boiling water at 100°C than it will in not-yet-boiling-salt-water at 100°C. This is because steam at 100°C has much more internal energy than water and can transfer it to the food faster through the agitation of a rolling boil. 203.27.72.5 (talk) 01:08, 21 June 2012 (UTC)

Keep in mind that a given volume of pure water actually contains more HO than the same volume of salt water. Because salt water is an imperfect mixture, NaCl (or rather, its dissolved ions) represents a statistically significant portion of the "water", and salt does not boil at 100C. The specific thermic properties of NaCl notwithstanding, you're actually starting off with less water to begin with in the case of salt water. I'll let people smarter than me tell you what that means in practical terms. Evanh2008 01:16, 21 June 2012 (UTC)

In practical terms, nothing. Dissolving NaCl in water doesn't appreciably change its volume, which, incidentally, is why brine is much denser than water and tends to sink. This drives various climatic processes as I understand it. 203.27.72.5 (talk) 01:49, 21 June 2012 (UTC)

Using genetics to determine the potential for undiscovered species

I often read stories about a new species of plant/animal being discovered. My question is: Can the genetic code of a plant/animal specimen provide clues to the existence of a yet-to-be discovered species. Take tree frogs, for example. They cover a pretty wide range of variations and species, and it is likely a new species is yet to be discovered. Could a scientist interested in tree frogs look at the genes of a known species, and extrapolate the potential for other, undiscovered species of tree frogs to exist...or at least the potential to exist? Quinn 03:23, 21 June 2012 (UTC)

Well, sure -- the potential, not the actuality. But I suspect if you knew more about genetics you would realize that that fact is not very interesting. People who do genetic engineering invent new species every day -- many of them have the potential to exist before they are created, in a theoretical sense. The number of viable gene combinations is unimaginably huge. Looie496 (talk) 03:45, 21 June 2012 (UTC)

Do genetic engineers really make new species? As in, they modify the genetic material to such an extent that a population of organisms with the modified genetic material cannot mate with the general population of organisms with natural genetic material to produce viable offspring (but can produce viable offspring within their own population). I was not aware of that being possible. 203.27.72.5 (talk) 04:06, 21 June 2012 (UTC)

It's possible. Take, for example, a very extreme case of engineered underdominance, described in theoretical capacity in this paper, section 5 if you can access it. You can also cheat and just make an organism incapable of mating for some stupid reason, like engineering a self-fertilizing nematode to have no opening through which to mate. It's self-fertilizing, so it's still viable, but now reproductively isolated. And finally, what is actually done, but may not count as "engineering", us using colchicine treatment to change the copy number of chromosomes in a plant. The resulting plant cannot yield anything but sterile offspring with the plant of origin (as the progeny will have a sterility-inducing odd number of chromosomes). So in that sense, it is at least reproductively isolated, if not a new species. You decide if that's genetic engineering. Someguy1221 (talk) 04:22, 21 June 2012 (UTC)

Answering the original question, yes, it can provide clues. You can take any two species, there were almost certainly intermediate genetic steps between those two organisms and their most recent common ancestor. Any one of those intermediate organisms may have itself given rise to more than one descendant species. So when you are looking at a phylogeny and there appears to be a large gap between two closest relatives, a biologist will often suspect that some extra species might fit in there. For example, Caenorhabditis elegans has essentially no close relatives (at least by comparison to other members of Caenorhabditis), and there is currently a $5000 prize offered to whichever lucky field biologist finds a species that is more closely related to elegans than anything else. But there are a couple problems with this. It's possible that all of those intermediate forms separating two closest relatives may have not given rise to any other species, or alternatively, those other species might all be extinct. Someguy1221 (talk) 04:31, 21 June 2012 (UTC)

Solar Energy and Its Production

How many units are present in 1 KW of electricity? What is the present cost of the project for producing 1 MW of electricity with the help of solar panels, etc. without the inclusion of the cost of land? — Preceding unsigned comment added by 122.172.176.45 (talk) 04:07, 21 June 2012 (UTC)

1 kW is 1000 Watts of power. A Watt is 1 Joule per second. A Joule is the energy required to accelerate an object with a mass of 1 kilogram at 1 meter per second per second for 1 second. The kilowatt is therefor a derived unit, and is a combination of the base units kilograms, meters, and seconds. You can also express it in terms of these base units as Mg·m/s. 203.27.72.5 (talk) 04:13, 21 June 2012 (UTC)

As for your second question, it depends on where the solar panels will be located. Different areas have very different incident sunlight. Solar panels will also cost different amounts in different places due to logistics, supply of raw materials, labour, government subsidies, etc. 203.27.72.5 (talk) 04:25, 21 June 2012 (UTC)

Solar panels vary considerably but a solar panel that can produce 250W measures about 1m x 1.6m, you'd need 4000 of those to get 1MW under ideal conditions. Expect to pay $500 for such a panel and you get about 2 million bucks for the solar panels alone. It would also take up about 6400 square meters of space if they were installed edge to edge, which I'm sure is probably not practical. Then you have to install them and also all the infrastructure needed to collect and condition and invert and whatever else you need to do, I wouldn't be surprised if it was another 2 million. Having said that, I'm sure you could get a good deal if you were buying $4 Million dollars of solar power equipment, but this is only intended as a very rough ballpark figure. Vespine (talk) 05:08, 21 June 2012 (UTC)

To put that in perspective, a rugby field minus the try zone is 6800m.

By "units" the OP may be refering to the terminology used by power companies/authorities when charging for the use of electricity. For example, in Australia, 1 Unit is 1kw for 1 hour - about the energy consumed in one hour by 17 60 watt incadescent light globes, or the energy consumed in one hour by a small bar radiator. As to the OP's second question, the answer given above is entirely right, however, without govt subsidies, solar power is so costly compared to fossil fuel generation, no same person would ever consider it, unless fossil fuel generation cannot be used at the location. The unsubsidised cost of panels, electronics, batteries, installation, etc, for 1 kw for 24 hours a day is of the order of $200,000, with a service life of about 10 to 15 years. By using solar power to back feed power into the grid, rather than owner-conmsumption, batteries are eliminated, however without govt subsidies and a value per unit (kw-hr) of the order of 6 to 10 times the normal electricity charge, it is not cost effective. Ratbone121.215.67.177 (talk) 05:23, 21 June 2012 (UTC)

So using that definition of unit, 1kW is 1/3600 units. 203.27.72.5 (talk) 05:27, 21 June 2012 (UTC)

No. Kilowatts (kw) are the units of power. Units, as used by power companies, are the units of energy. Energy is power multiplied by time. 1 kw for 1 hour (or 2 kw for 1/2 hour, etc) is 1 Unit, as I previously stated. By your use of 1/3600, you possibly were thinking of 1 kw.second. Ratbone121.215.67.177 (talk) 06:44, 21 June 2012 (UTC)

Yeah, so ${\displaystyle 1Unit=1kWhr=1kW\times 3600s=3600kJ}$

${\displaystyle \therefore 1kWhr\times 1/3600=1kW}$

1kW is the energy per 1 second, and over the hour that sums to 3600kJ. I didn't express myself very clearly though. What I should have said was, "you can't ask for a conversion factor between power and energy. That's like asking for a converstion factor between distance and speed." 203.27.72.5 (talk) 08:20, 21 June 2012 (UTC)

Yes, and now that we have the diffrence between power and energy sorted out, you can see that Vespine's answer is really nonsense. I could use solar panels of arbitarily small area to charge a storage device (battery or capacitor), and then discharge it thru a very low resitance. The power upon discharge could be a megawatt, if only for a microsecond. Ratbone58.167.254.173 (talk) 16:53, 21 June 2012 (UTC)

I wouldn't say it's complete nonsense. It calculates the minimum size required to generate 1MW continuously, assuming continuous sunlight. Of course in reality, we don't have continuous sunlight, so to replace a 1MW gas turbine it would need to be far larger than his estimate and it would need to store most of its energy for later consumption (peak energy requirements for most areas are in the early evening). Since the OP is asking for a cost of all of the components excluding land, perhaps his idea is to stick solar panels on a large number of houses? If this is the case you'd also have to account for the slope of the roof and how it affects the amount of sunlight incident on the panel. 203.27.72.5 (talk) 20:44, 21 June 2012 (UTC)

Evidently, wikipedia has an article on this topic. 203.27.72.5 (talk) 08:23, 21 June 2012 (UTC)

There is also an article on the Kilowatt hour. Jørgen (talk) 08:44, 21 June 2012 (UTC)

What is RNA ‘Ribonucleic acid’ and what is DNA 'Deoxyribonucleic Acid'

What is RNA ‘Ribonucleic acid’ and what is DNA 'Deoxyribonucleic Acid' — Preceding unsigned comment added by 175.140.179.46 (talk) 06:41, 21 June 2012 (UTC)

Have you checked the articles DNA or RNA? I imagine they would have something to say on the subject. Evanh2008 06:43, 21 June 2012 (UTC)

Cells~~(*for cells questions)

What are the three main categories of organelles within the cytoplasm? — Preceding unsigned comment added by 175.140.179.46 (talk) 06:48, 21 June 2012 (UTC)

3) Those which try to get people on Misplaced Pages to do their homework for them. StuRat (talk) 06:57, 21 June 2012 (UTC)

Looking at organelle, I was disappointed to discover that they aren't female organs, but perhaps that article will have the answers you seek. However, at first glance, I only see two categories listed, but definitions may vary, so I suggest you consult your textbook. StuRat (talk) 07:01, 21 June 2012 (UTC)

Now you made me look up "female organs"... 92.80.52.54 (talk) 08:26, 21 June 2012 (UTC)

after classifying plants

In the novel La tournée de Dios by Enrique Jardiel Poncela God comes down to Earth and, well, stuff happens. Anyway, in one of the chapters God is invited to a botanical garden and ask to the staff "and when you have classified all plants and animals, then what?"

Anybody has a good answer to God?--85.55.200.82 (talk) 10:58, 21 June 2012 (UTC)

• Then we start to make our own animals and plants by genetic engineering! But I expect that God would point out that humans have not looked every where yet for life forms, especially at other planets. Graeme Bartlett (talk) 12:06, 21 June 2012 (UTC)

There's a lot to untangle here. First: taxonomy is a distinctly human concept, and our taxonomies are constantly being rearranged, due to new information and new techniques (e.g. systematics, phylogenetics and cladistics are used much more currently, compared to the morphological comparisons used in the past. Second: life form themselves are constantly speciating, and I'm not sure that the rate of classification of new species is greater than the worldwide rate of speciation. So, it is entirely possible (and IMO likely) that we will never "finish" classifying life. Finally: suppose we did. It is a very narrow view of botany and zoology to think that classification is a primary concern (surely God would know better ;). In the modern era, much more research is done in other areas. Even if we had classified all life (and it stopped speciating), we'd have plenty left to discover. How do birds migrate? How does bark form on trees? Why don't naked mole rats get cancer? How do symbioses form? How does a bee hive function collectively? These are all very simple questions that have not yet been completely answered. Actually I would be more concerned that rigorous classification is getting too little attention these days; I've heard many biologists lament that the last of the great taxonomists are dying, and the younger generation is not filling in the ranks. SemanticMantis (talk) 13:34, 21 June 2012 (UTC)

Nice try, Semantic. God is obviously a young earth creationist, so he doesn't believe in speciation. 203.27.72.5 (talk) 20:56, 21 June 2012 (UTC)

Ha! Well, I'm not here to discuss religious beliefs, but suffice it to say that not all who believe in a god believe in YEC. Unfortunately, it seems to be the case that the craziest religious people make the most noise :-/ SemanticMantis (talk) 21:28, 21 June 2012 (UTC)

Once you've classified them, you can catalog the infinite number of ways to combine and cook them? Not sure I understand the question. μηδείς (talk) 21:55, 21 June 2012 (UTC)

TV with a particular type of EPG

I am in the UK. I need to buy a small television, and I have only one requirement and that is that the current live TV channel is displayed within a small window in the EPG, i.e. I can continue to watch and listen while browsing the channels. Unfortunately this information is missing from almost all the online descriptions of the many different models available, and the manufacturers' websites turn out to be useless. The only comparison chart I've been able to find is this one for video recorders, and it only lists a few obscure brands and none of the big names. However, I strongly suspect that is the manufacturer that is significant rather than the TV model, as they tend to use basically the same software for much of their range. My trusty Philips set-top box does what I want perfectly. But I have looked at friends' Sanyo, Toshiba, and JVC TVs, and they are no good, so it seems that what I want is a minority feature. Before you say ask the salesman, in my experience they are mostly clueless in the UK when it comes to buying electrical equipment, so I thought I would risk a little original research and ask whether any UK refdeskers have this feature on their TV and if so what is the make and model?--Shantavira| 11:16, 21 June 2012 (UTC)

Most retail salespeople are technically clueless. The best bet for now and long term is likely an PC with one or more DVB-T/C/S receiver cards and MythTV etc. The TV industry is quite dumbed down, computers is the game. Electron9 (talk) 14:37, 21 June 2012 (UTC)

I have a fairly recent-ish Sony flatscreen - it doesn't have your desired feature. It overlays the EPG on top of the current picture, pretty much obscuring it. So scratch them off the list. You might be advised to wander into Currys, Dixons, John Lewis, etc., and see if you can get their salespeople to show you this function working on one of their TVs. --Tagishsimon (talk) 14:42, 21 June 2012 (UTC)

Agreed, you can't trust salesmen, get them to show you the feature before you buy a model. I've had the same problem with cars, they either don't know how the "fancy buttons" work, just make it up as they go along, or outright lie to you. I test everything out myself before I agree to buy, and you should take your TV for a "test drive", too. StuRat (talk) 03:53, 22 June 2012 (UTC)

how much friction does water flowing through a (decent-sized) pipe undergo? if the pipe is long enough, would it not flow out, even vertically?

The question is how much friction water flowing through a (decent-sized) pipe undergoes, and whether, if the pipe is long enough, the water wouldn't even fall out the other side vertically, despite gravity and the other side being lower?

My thought process is as follows. It's very hot where I am right now. I noticed that the water that flowed out of the shower (set to cold water only) was still, after a moment, very very cold. Even standing a few feet away a draft of cool air hit me. If I had run it a very long time, it would have cooled my whole apartment off, which doesn't have an air conditioner in it. Of course, running water just for cooling is wasteful.

My next thought was: well, I'm not actually using it. Could someone hypothetically just run it, in a (clean) configuration that makes a big narrow wall of water with very large surface area, and simply (the water is still clean) feed it back into the system. Probably that would be possible. But it wouldn't be fair to the neighbors across the street (you could run it into their water intake) even if it's clean and sterile, because it's now warm. Why should they get warm water in the heat? (assuming they also want cold water.)

My next thought was: ah, but do you know who DOES want warm water: extreme latitudes where it's winter now. And vice versa. (If they cooled water, I would want it).

So here is my next thougth. Hypothetically, if we had a very long pipe between winter places that want warm water and summer places that want cold water, and we set the pipe to exactly the same altitude between the two places, then wouldn't the tiniest push (or vertical drop, like an aqeuaduct, which drops only a tiny amount over distance) of the end at either place cause the water to in the correspondeing direction? Since it doesn't actually take work (the physics concept) to keep something moving at the same momentum and altitude, less friction, the only thing that would stop such a scheme working for the next 100 years is if it were built is...water resistance in the pipe.

so, the question is: what IS that resistance? What stops my scheme from working, if anything? THe scheme is free cooling for summer climate and free heating for winter climate by running a water-based heat exchange between them with almost no work performed after building the aparatus. 84.3.160.86 (talk) 11:19, 21 June 2012 (UTC)

by the time the water's reached the other side of the world it would have reached ambient temperature. Besides friction is considerable-try an experiment using drinking straws joined together, and blow down them. It would be easier to heat water through geothermal power or something. As for cooling, its generally reasonably cold a few meters under ground-which is why your water is cold in the first place. — Preceding unsigned comment added by 109.155.4.192 (talk) 12:17, 21 June 2012 (UTC)

I'll answer the 2nd question first: The flow of water in a pipe is indeed determined by a form of friction - the viscosity of the water resists the movement of water against a surface. The flow of fluid (eg water) through a smooth pipe can be calculated by means of the Fanning-Darcy equation. There are two forms of Fanning-Darcy, one for simple laminar (stright line) flow, and one for turbulent flow. For laminar flow, the Fanning-Darcy equation is:-

F = ( ΔP π D ) / ( 128 μ L )

where F is the flow rate in m/s; ΔP is the pressure difference along the length of the pipe in Pascals, π is 3.14.., D is the diameter of the pipe in meters, μ is the absolute viscosity of the fluid in mPa.s, L is the length of the pipe in meters. For turbulent flow, the formula is somewhat more complicated. To find whether you have laminar or turbulent flow, calculte the Reynolds Number:-

Re = ( 4 ρ F ) / ( π μ D )

If the Reynolds number is less than 2000, the flow will be laminar; if above 3000 it will be turbulent; between these 2 limits, some engineering judgement is required.

All this means that (a) you will always get some flow no matter how long the pipe, and (b) the flow is inversley proportiona to pipe length, and proportional to the 4th power of the diameter (laminar flow; for turbulent, it is proportional to diameter raised to the power 19/7).

As to the first question: Water walls are sometimes seen as a decorative feature in restaurants and hotel lobbies. It has some psychological effect in cooling perception, but the actual cooling effect is minimal, essentially being due to the conduction of heat from the air to the water over the water wall surfcae area. As far far more effective method of cooling is to evaporate the water, as the latent heat of vaporisation of water is very high. This is the principle being evaporative type airconditioners, often nicknamed "swampies" in the trade due to the use of wood shavings and the like to provide a very large surface area in a small volume.

Don't forget that humans sweat - this is our built-in personal swampy, and makes you feel cool when in moving air, even if the air is not cool. You don't have to actually feel wet with sweat for this to work.

Ratbone58.167.254.173 (talk) 12:31, 21 June 2012 (UTC)

Also note that someone (or something, or some process ;-) has already put this system into production, and it seems to work well with only minor hickups so far! However, the tenants are playing with the thermostat and may possibly break it. --Stephan Schulz (talk) 13:57, 21 June 2012 (UTC)

Good point, and well put too! Ratbone58.167.254.173 (talk) 15:40, 21 June 2012 (UTC)

Water evaporation (usually spraying) is efficient for cooling and spreading legionella.. Electron9 (talk) 14:40, 21 June 2012 (UTC)

Water evaporation does NOT spread legionella (bacteria can't hide in individual water molecules), however water spray or mist does spread it. However this must be seen in the proper context. When a large number "legionaires" who were at the Belevue-Stratford Hotel in 1976 got sick, the reason was investigated, and was shown to be an infection with a type of bacteria not previously known to science, sourced from the building aircon cooling towers. They named this "new" bug legionella. Soem years later, patients at an English hopital got sick and died. An investigation showed legionella was the cause, again sourced from airconditioning cooling towers. These and other incidents led to the rapid implementation of laws in various countries requiring owners of large buildings with aircon cooling towers to sample the water regularly and dose the water to keep the legionella count below arbitarily determined levels. It has since become very apparent that (a) almost invariably only people with compromised immune systems (such as hopital patients already sick and/or on prescribed drugs) are susceptable to legionella, and (b) legionella is ubiquitous in the enviroment - one of the most common forms of bacteria around. It can be argued that these laws are unnecessary - certainly they were enacted in haste without a true understanding of the issue. I worked for 6 years as a building manager responsible for several multi-storey sites with aircon cooling towers. Our aircon legionella count, due to dosing with bacteriacide per legal requirements, was lower than the count in water straight from the city water supply. Nobody legislates about legionella in domestic swampy airconditioners - it isn't necessary. Ratbone58.167.254.173 (talk) 16:09, 21 June 2012 (UTC)

Science of weight loss and fitness

Can anyone direct me to some good source of science on the subject? Also I would like to ask a couple of questions, Are raw eggs any better than cooked eggs? Should you take protein just before working out or you just need to have them in your diet? Bastard Soap (talk) 14:09, 21 June 2012 (UTC)

The science on this is still very much uncertain, you could search in some scientific journals, like here:

http://www.ajcn.org/search?fulltext=protein+exercise&submit=yes&x=0&y=0

Count Iblis (talk) 16:03, 21 June 2012 (UTC)

Unless they are burnt, proteins are broken down into the same amino acids whether they are cooked or not. Cooking has the huge benefit of killing potentially dangerous bacteria. So long as you do not burn the eggs you will not lose any nutritional values. Boil or scramble them. If convenience matters, one or two eggs scrambled in a bowl and then microwaved for about a minute (until dry, you may need to stir once) will come out quite nice. Since just one egg already exceeds a normal person's daily recommended cholesterol you might look into other sources like whey protein. Consult a professional. μηδείς (talk) 16:35, 21 June 2012 (UTC)

My understanding is that those cholesterol recommendations are out of date, because of considerable data showing that dietary cholesterol has only a weak influence on the buildup of cholesterol in arteries. But in any case none of this protein stuff really matters except to extreme bodybuilders, and you certainly don't need major protein supplementation to achieve weight loss. Looie496 (talk) 18:04, 21 June 2012 (UTC)

It's so strange to not have definite answers about this stuff, it's what most people are most interested in and the science is very lacking.Bastard Soap (talk) 22:04, 21 June 2012 (UTC)

My own experience suggests that some of the fundamentals of nutritional science are totally flawed like the link between calorie intake and weight. On theoretical grounds, you would not expect there to be a strong link, because if you increase your calorie intake, you'll eventually reach a dynamical equilibrium where you burn the same amount of calories as you are consuming. That your weight should be linked to that dynamical equilibrium is not clear at all. The argument that if you eat more than you burn, you'll store more fat, is a red herring, as it doesn't address the issue of dynamical equilibrium.

People who are naturaly thin have been tested in an experiment where they were given 5000 Kcal/day to eat. Their weights didn't increase by a lot at all.

Then my own experience also contradicts the idea of there being a strong link between calorie intake and weight. I consume about 3500 Kcal/day, yet I only weigh about 60 kg. Some of my obese friends and family members eat a lot less than I do, but they don't eat healthy foods. This suggests that what matters is the vitamins and the minerals you consume. The body needs these to burn carbohydrates and fat efficiently. Count Iblis (talk) 02:04, 22 June 2012 (UTC)

Perhaps excess calories go undigested in some, but I can't believe your metabolic rate goes up tenfold it you eat ten times as many calories. You'd burst into flames. StuRat (talk) 03:34, 22 June 2012 (UTC)

gauss and gauss meters

Could someone please explain to me in very simple terms (I am not a physicist or a scientist, but an archaeologist) what a gauss meter measures and how to interpret the results I get from it? I am not really clear on what gauss represents, either. Thank you. — Preceding unsigned comment added by 184.9.192.187 (talk) 14:15, 21 June 2012 (UTC)

A gauss meter measures the strength of a magnetic field. See Gauss (unit). Red Act (talk) 14:39, 21 June 2012 (UTC)

Please see Magnetic survey (archaeology). In very simple terms, buried objects distort the Earth's magnetic field at the surface. By measuring the field at a large number of points, you can create a map showing where the field varies and by how much. --Heron (talk) 18:05, 21 June 2012 (UTC)

See also gaussmeter. Red Act (talk) 19:01, 21 June 2012 (UTC)

Have you ever looked at iron filings lining up like the Earth's magnetic field due to a magnet? Where the lines are more spread out the magnetic field is weaker. Where the lines are more densely packed the field is stronger. The Gauss meter is measuring the (invisible to you) density of those lines. μηδείς (talk) 03:06, 22 June 2012 (UTC)

What feels like a throat but isnt'?

I've been practising martial arts for a while now and I would like to get a good test of my kill strikes. Are there any common fruits or foods or other common objects which have a similar consistency and strength to the human throat or solar plexus?Bastard Soap (talk) 14:29, 21 June 2012 (UTC)

If you don't get queasy easily, get a dead pig, they are somewhat close to us biologically - skin, bones, meat. The carcass is gonna get ripe on you though. Compare that feel with melons and such to find something that feels similar - or at least looks cool when you make a mess of a melon in front of your friends. A more practical way is to look in your local yellow pages for companies that sell martial arts equipment; they can sell you a practice dummy that won't break or turn rancid. 88.114.124.228 (talk) 17:50, 21 June 2012 (UTC)

'Tis should be a strange world if we should feel comfortable with answering "I would like to get a good test of my kill strikes."

I've removed the question, and OP you should obviously give this some some thought thought before you get you get into any trouble. --80.99.254.208 (talk) 19:37, 21 June 2012 (UTC)

They give some advice in Human Wrecking Balls. Count Iblis (talk) 19:47, 21 June 2012 (UTC)

Wow, I did not expect this from wikipedia. All of martial arts is about making yourself a weapon and to be used only if absolutely necessary, I have no intention of using it except if I'm attacked by some rabid dog, I just want to know if I'm able to. If I wanted to kill someone I'd get a knife jesus.Bastard Soap (talk) 21:22, 21 June 2012 (UTC)

Veiled legal threats, ad hominem and crystall ballery aside, I don't see how this question violates policy, or how removing it is appropriate. I've replaced it. 203.27.72.5 (talk) 22:11, 21 June 2012 (UTC)

I second the meat hypothesis. Vespine (talk) 23:10, 21 June 2012 (UTC)

Grapefruit. μηδείς (talk) 23:28, 21 June 2012 (UTC)

Robots

Could you make a robot with real human skin? 176.250.196.132 (talk) 15:26, 21 June 2012 (UTC)

Well you can get human skin book covers, so I don't see why that shouldn't be extended to robots. Access for maintenance would be a bit tricky, and of course the skin would be dead and not very convincing if you're trying to make an android.--Shantavira| 15:59, 21 June 2012 (UTC)

But can you make an android with living human skin. 176.250.196.132 (talk) 17:46, 21 June 2012 (UTC)

In principle, yes. But you would have to work out a way to supply it with all the necessary nutrients and complex molecules, which means adding an artificial bloodstream and a lot of very complex biochemical fabricating machinery. I can't imagine any possible benefit that would be worth the enormous effort. Looie496 (talk) 17:53, 21 June 2012 (UTC)

Oh, it's essential. Non-living matter can't travel backwards in time. Apparently, unless it's covered by living matter — that part never seemed to be explained in detail, but anyway it was a nice excuse to show a (fairly chaste) nude of Summer Glau on broadcast TV in prime time. --Trovatore (talk) 19:11, 21 June 2012 (UTC)

Uh-oh. Not only has Skynet acheived self-awareness, it's asking questions on the Misplaced Pages Ref Desk.FlowerpotmaN·(t) 19:16, 21 June 2012 (UTC)

Would it be possible that in the distant future, it wouldnt be so complex, with advancing biological research? 176.250.196.132 (talk) 21:54, 21 June 2012 (UTC)

Well, you can already remove human bone and replace it with metal. It's not such a big leap to remove all human bones and replace them with synthetic materials, though it would be much more technically difficult (you might exceed the $6million budget). Then you could look at doing a brain transplant, but instead of a brain, install some sort of computer control device. I'd say the technology will be that advanced relatively soon, but unfortunately, the we've long since past the times where that might be ethically possible. 203.27.72.5 (talk) 22:03, 21 June 2012 (UTC)

Even such a limited thing as bones illustrates the difficulty. Replacing one bone is relatively minor, but bone marrow is what generates blood cells, so replacing all the bones would leave you with mere plasma for blood. Looie496 (talk) 22:26, 21 June 2012 (UTC)

You could use perflourocarbon blood substitutes. HominidMachinae (talk) 23:59, 21 June 2012 (UTC)

A much lower level of technology could provide fake skin indistinguishable from the real thing. StuRat (talk) 03:06, 22 June 2012 (UTC)

Sorry StuRat, but the laws of time travel cannot be fooled. 203.27.72.5 (talk) 03:58, 22 June 2012 (UTC)

Refractive index

What kind of material has the highest refractive index?--Jsjsjs1111 (talk) 15:52, 21 June 2012 (UTC)

Ten seconds on Google found the following: Zzubnik (talk) 16:02, 21 June 2012 (UTC)

When asking what material has the highest refractive index, it's necessary to specify what wavelength you're interested in, because the refractive index varies widely with the wavelength, in a non-uniform way. The link Zzubnik gives refers to a material that has a maximum refractive index of 38.6 at frequencies near 0.3 THz, which corresponds to a wavelength (in vacuum) of about 1 mm. However, standard refractive index measurements are taken with light with a wavelength in vacuum of 589 nm (the sodium D line), which is more than a thousand times smaller. The highest refractive index at that wavelength listed in our list of refractive indices, at least, is 4.01, for germanium. Red Act (talk) 16:59, 21 June 2012 (UTC)

As for at least germanium the info should be combined with for what wavelengths that the material is transparent for. Electron9 (talk) 17:40, 21 June 2012 (UTC)

For minerals in light you can check out rutile (2.9) and hematite (3.22). Around absorption lines you can get some rapidly changing high numbers. Also for artificial substances look at Barium titanate and Lead zirconate titanate which will have very high values at longer wavelengths. Graeme Bartlett (talk) 21:35, 21 June 2012 (UTC)

Creep (deformation)

At my job, I'm often moving around big stacks of boxes (just a few at a time; I don't have any power machinery to help me) that are full of newspapers. As you can imagine, the stacks tend to lean if the boxes aren't placed properly, and improper placement of boxes toward the bottom of stacks can result in damage. In some stacks, there are different sizes of boxes, with the wider ones sitting on top of the narrower ones, and the wider ones are damaged — look at this:

__________________________
|________________________|
|________________________|
|________________________|
|________________________|
|________________________|
|________________________|
|________________________|
|________________________|
|________________________|
|  ____________________  |
\/ |                  | \/
   |__________________|

The edges of the bottom of the lowest wide box have nothing under them, so the lowest wide box is gradually squished and its edges splay out around the top of the not-so-wide box. I've never seen this happen instantly — I can put a big stack of heavy wide boxes on top of a single not-so-wide box, and they all just sit there without problems, but if I come back a few weeks later, there is substantial damage even if nobody else touch the stack. Is all of this an example of Creep (deformation)? I don't understand the article well enough to say either yes or no. Nyttend (talk) 21:30, 21 June 2012 (UTC)

It's analygous to creep, but not exactly the same thing. Creep is essentially caused by stresses in metals having an effect on the solid state diffusion through the crystal lattice, so as to increase relaxation. That's why being close to the melting point dramatically increases creep. In this case I think the friction between the sheets of newspaper prevents instant relaxation but as it sits and goes through a few day/night cycles of heating and cooling the sheets will move a tiny amount accross each other as the aggregate structure deforms around the smaller box placed underneath. 203.27.72.5 (talk) 21:56, 21 June 2012 (UTC)

(EC)It's an example of slow permanent deformation, so it probably can be considered an example of creep. Our article won't help you though with mechanism by which it occurs as the cardboard (I'm assuming that's the material that the boxes are made from) won't deform like a metal or ice. No doubt there are many papers written on this topic and here's the sort of apparatus that can be used to test the creep behaviour of corrugated cardboard boxes. Mikenorton (talk) 22:03, 21 June 2012 (UTC)

And here's a paper on just this sort of behaviour . Mikenorton (talk) 22:09, 21 June 2012 (UTC)

What a great question and reference/answer! SemanticMantis (talk) 00:00, 22 June 2012 (UTC)

Why exactly does water stop bullets?

Hello. Mythbusters recently showed a clip from the time they tested shooting bullets into water, and watched how they disintegrated a few feet in. Apparently they blamed this stopping power on the "incompressibility of water". Nevermind water is not exactly "incompressible" (just very hard to compress); does saying "water is (nearly) incompressible" (or something similar) really explain the bullet-stopping power? Or what exactly would you have to say about water to explain why it's so effective against bullets? Thanks in advance. --Kreachure (talk) 23:28, 21 June 2012 (UTC)

well, nothing is exactly incompressible. --Trovatore (talk) 23:42, 21 June 2012 (UTC)

Well, I'm sure when they say "incompressible", they mean "by human means" and the like. :) --Kreachure (talk) 01:46, 22 June 2012 (UTC)

There are a few factors at play. First of all, many modern bullets for civilian use are what they call frangible, or meant to break up or mushroom on impact. This is so that they transfer their energy more quickly and more completely into the target. Virtually every hunting round falls into this category and even non-frangible civilian ammo is jacketed soft-point at best. Only the military uses fully jacketed rounds that do not deform normally in use. The water causes the round to start to mushroom or break apart (depending on the type of round) and this destroys its aerodynamics (hydrodynamics?) and causes it to lose speed more rapidly due to resistance. In addition the density of the water rapidly saps kinetic energy from the bullet. Remember most bullets are VERY fast but actually don't have all that much in terms of actual momentum because they typically weigh comparatively very little. if you take into account the fact the round is being pushed out of shape it can lose speed in as little as a foot or two of water. the rounds that perform best in water are smaller, very fast and smooth-nosed rounds like the 9x19mm Parabellum (as proven on mythbusters) but if the round is too tiny it will fracture (as mythbusters saw with the 5.56mm NATO round). There are special rounds designed for underwater use, in use by Russia notably in a modified AK-47 frame. The rounds are designed like flechettes or darts with a very low cross-section and long length and designed for hydrodynamics. I have NO basis for this but logic would indicate there may also be a hydrodynamic influence, if the bullet created a low-pressure cavitation behind it, that would further slow it. HominidMachinae (talk) 23:45, 21 June 2012 (UTC)

To further what Hominid said, civilian ammunition is designed to break up because that causes the most damage to flesh. It might seem counter intuitive that military ammunition has a key design element that inhibits it from damaging flesh, but that's an historical artifact from the hague convention. Anyways, since flesh is mostly water, the round behaves in water much the same way as it does in flesh; its cross-section expands and it breaks up. 203.27.72.5 (talk) 01:12, 22 June 2012 (UTC)

As to what physical processes cause it to break up, when the bullet is travelling though air, it has very little to resist its motion. When the tip of the bullet makes contact with water/flesh, the resistance is much greater and it slows very quickly (it may still be travelling quite fast, but it's rate of deceleration is very high). This sends a shockwave through the length of the bullet which causes it to break apart. The shock wave travels at the speed of sound (in the metal that the bullet is made out of) with respect to the bullet. Since the bullet itself may be going faster than the speed of sound, the shockwave may not reach the back of the bullet until it's already travelled more that it's own length into the flesh. If the bullet has a soft nose, the lead at the front will also be deformed and material will be forced down into the nose and cleave it apart leading to the mushroom effect. If it has a hollow nose, this effect can be even stronger.

The flechette style rounds that Hominid mentioned are made of hard metals that don't break up easily (such as steel alloys) and as he said, their small cross section aids them in getting through flesh without being clogged up with flesh in the nose (like a hypodermic syringe). You could say that the fact that air is compressible is what leads to it not resisting the bullet's motion. You could also just say that its density is so much lower that there is less mass to heave out of the way. The fact that water/flesh is compressible is important in the damage caused by bullets also; a compression wave originiates at the point of impact and propagates through the body potentially causing damage to organs far away from the bullet's path. 203.27.72.5 (talk) 01:22, 22 June 2012 (UTC)

Excellently put, I'd also like to point out that military ammo has other constraints on it other than maximum flesh damage. A full metal jacket round is kinder on barrels especially when firing fully automatic (important if you want your rounds to be compatible with your squad support weapons), it also has greater armor penetration. To top it all off the noses of hollow points (unless capped) have problems feeding in some automatic mechanisms, that was the reason the smooth-nosed 9mm Parabellum was invented to begin with. Some self-defense experts advise using revolvers for defense and concealed carry for that very reason, you can carry a mushrooming round without risking a feed jam, and if a round misfires you can just pull the trigger again and rotate the cylinder. HominidMachinae (talk) 01:37, 22 June 2012 (UTC)

Not to trivialize an interesting discussion but, could you then say in simple terms that water can stop bullets "because water is much denser than air, and a bullet encounters so much resistance when in water that it can't clear a path and breaks apart"? I hope I'm not oversimplifying too much. Apart from this, the shockwave aspect that was mentioned I find very hard to believe. Do you mean that things that are slowed very fast are destroyed by the resulting shockwave, rather than by the "being slowed" itself? If this is the case, could you provide other examples where this happens? --Kreachure (talk) 02:04, 22 June 2012 (UTC)

I'm not sure that you're grasping the concept of a shockwave. The nose of the bullet slows first. The particles (of Pb) that comprise the nose slow down and the bonds to the particles immediately behind them are compressed. This compression continues in a wave through to the back of the bullet. At points such as lattice defects the bond compression may be enough to break the bonds and consequently break the bullet apart. You can't distinguish the shockwave caused by the deceleration from the "being slowed" itself. 203.27.72.5 (talk) 02:28, 22 June 2012 (UTC)

I don't think you're oversimplifying much, except that the mechanism of the bullet mushrooming is vital to understanding the issue here, and why some bullets might NOT be affected that much by water. HominidMachinae (talk) 02:30, 22 June 2012 (UTC)

A full Coke can certainly can stop relatively low speed projectiles such as air rifle pellets, or projectiles with poor aerodynamic characteristics like shotgun pellets. It might stop a .22 or .177. It would have a better chance if you shot it length ways down from the spout. It won't stop a .50cal though. Not even length ways. 203.27.72.5 (talk) 02:34, 22 June 2012 (UTC)

Speed of sound in lead is 1 km/s, while pistol rounds travel half that fast. Ergo no shockwave inside the bullet. Hcobb (talk) 02:42, 22 June 2012 (UTC)

Your conclusion does not follow from your premise. The abrupt change in velocity is what constitues the shockwave, not the velocity itself. 203.27.72.5 (talk) 02:50, 22 June 2012 (UTC)

Um, water stops bullets for the same exact reason human the human body stops bullets. It's mostly made of water. μηδείς (talk) 02:55, 22 June 2012 (UTC)

June 22

Photosynthesis, CO2, etc.

So, I have a few questions concerning photosynthesis, carbon dioxide and this whole global warming issue:

1. How long does it takes green plants/trees to start photosynthesis?
2. On average, how much oxygen is produced by trees through photosynthesis?
3. Can plants get carbon dioxide "poisoning" (i.e., having too much?)
4. I came up with a thought a little while ago. Companies that burn fossil fuels for energy just dump that carbon dioxide gas into the atmosphere. Why can't companies transfer the gas into say, a greenhouse beside the factory, with plants that could simply convert that CO2 into oxygen, as a way to reduce emissions into the atmosphere?

Thanks, 64.229.5.242 (talk) 00:16, 22 June 2012 (UTC)

1: Plants start photosynthesis as soon as the cotyledons break the soil surface, not long after germination. (At least most of them. Some vascular plants never photosynthesize, such as Indian pipe or broom rape).

2: You'll have to specify what you mean. mass per year per plant? Which plant? Mass per year per hectare? What community? This is a broad area of research. For starters, put /plant "carbon fixation" estimate/ into google scholar, or see e.g. here for some methods that focus on certain forest types (O2 production will be related to CO2 fixation, which is a more common key term).

4: Plants do tend to grow better/more with more CO2, but sometimes their insect pests and plant pathogens also do better too. So whether your proposal would help much is unclear. SemanticMantis (talk) 00:31, 22 June 2012 (UTC)

5: (which you didn't ask) I don't think that most air pollution comes in nicely sorted flows. It is probably very challenging and expensive to selectively isolate CO2 from industrial sources. But, still an interesting question: I think pairing greenhouses with factories in some way could probably work out well... :) SemanticMantis (talk) 00:31, 22 June 2012 (UTC)

I'm only going to touch on the last question. Plants are not infinite CO2-->Oxygen conversion machines, and that's because the CO2 is not actually being converted into molecular oxygen. Water is broken up into hydrogen ions and oxygen, while the carbon dioxide is converted into carbohydrates (don't get on me about all the ions and electrons, I don't feel like keeping track). Some of those carbohydrates are burned for energy, and actually just get spat back out as carbon dioxide (and water vapor). The carbon dioxide that disappears is from the carbohydrate mass that is used to build the physical stuff of the tree itself. In this sense, the tree is acting as a carbon sequestration system. While a tree is growing, it is certainly removing CO2 from the atmosphere, but once it stops growing it has zero net impact. You'd have to keep planting new trees in perpetuity to continually cancel out the emissions of a factory. In fact, the article I linked to gives a lot of ideas on this. Someguy1221 (talk) 00:36, 22 June 2012 (UTC)

3:It is possible, although plants use CO2 for a carbon source and produce O2, plants alos need to breath in O2 just like animals do. If you placed a plant into a jar of CO2 and gave it no light, it would suffocate to death. In the atmosphere, if CO2 levels rise, so will the global temperature which hurts plants in a vast number of ways, higher respiration (anti-photosynthesis) rates, increased pest levels and spread of pests to previously cold areas, more severe weather events, aka hurricanes, floods, droughts, decreased stability in percipitation, increased rate of evaporation from soils, etc.

4:Greenhouses often increase CO2 levels to increase growth rates, up to 1500ppm (4x normal), over that it begins causing headaches in workers and has diminishing economic returns. I know of greenhouses that burn coal for heating and buy CO2 to pump into because, to paraphrase the owner "the emissions would severly damage the crop"...so he put up a smokestack so the neighbouring farmers can deal with his problem. Unique Ubiquitous (talk) 01:29, 22 June 2012 (UTC)

Exhausts contain more than just CO₂. They may also contain CO and NO_x which are bad news for animals (including people). I don't know what they do to plants though. Is there an eqivalent of heme in plants? 203.27.72.5 (talk) 01:33, 22 June 2012 (UTC)

Several pollutants are known to mess with a plant's stoma. Either they force the stoma shut when it should be open - reducing CO2 uptake thus stopping photosynthesis, or forcing them open when they should be closed - increasing water loss to critical levels. By heme, I expect you mean something for gas transportation? If so, then no, live plant cells are never too far from the air, I say live because cells say in the middle of the trunk of a tree are dead and don't need air. Cells, apart from the epidermis, are kinda loose allowing air to diffuse through the air spaces between them. And yes, roots also breath on their own and for plants like rice, which grow on flooded land, they have special air spaces which go from the above water plant to down below. Unique Ubiquitous (talk) 02:42, 22 June 2012 (UTC)

To answer the OP's question 4: It is not practical for factories and processing sites to set up a greenhouse next door, as the land area required is huge. And its not necessary - oxygen and carbon dioxide difuse through the atmosphere with great facility. The percentage oxygen and percentage carbon dioxide in the air is negligibly different whether in rainforrest areas, deserts, or major industrial areas. Rainforrests in Indonesia can deal with carbon dioxide emitted in Australian industry for example. What we need politicians world wide to do is act more strongly to protect, nurture, and grow green plant areas. Wickwack120.145.68.66 (talk) 03:46, 22 June 2012 (UTC)

Actually, we'd be better of in terms of CO₂ sequestration if we grew green plant areas and then cut down all of the trees and stuck them somewhere where the cellulose won't break down and then grow more trees on that land and repeat. Also, massive sources of CO₂ are often located far away from built up areas (i.e. coal/gas fired powerstations, smelters, etc.) so the land requirements aren't the big issue you make them out to be. Also, the comments about CO₂ from Australia being dealt with by Indonesian rainforrests misses the OP's point; you can use the very high concentrations in exhaust gas to speed up the process. 203.27.72.5 (talk) 03:55, 22 June 2012 (UTC)

Deflecting a lead bullet with a magnetic field

Hi, I found this discussion on repelling bullets with a magnetic field. Since most bullets are made of lead, is it indeed possible to deflect bullets with a strong enough magnetic field, either using lead's diamagnetic properties, or eddy currents, or something else? How would this work? --Kreachure (talk) 02:29, 22 June 2012 (UTC)

If you shot a lead bullet at a magnetar, yes it would probably be deflected by the magnetic field. It would also be attracted by the extreme gravity, so catch-22. If you tried to make a massive magnet that would appreciably deflect lead bullets away from you, it would also cause damage to your tissues due to the diamagnetism of water (the effect a magnetic field has on water is about half of what it has on lead). 203.27.72.5 (talk) 02:44, 22 June 2012 (UTC)

Ah, interesting. I suppose the user of such a magnet would require a magnetic shielding suit of some sort to be effectively protected. Or is it too optimistic to think that the material's permeability wouldn't fail under such a powerful magnetic field? --Kreachure (talk) 03:16, 22 June 2012 (UTC)

The issue isn't magnetizing the user, but exerting magnetic force upon him. While the former is bounded as you suggest, the latter is not. Someguy1221 (talk) 03:19, 22 June 2012 (UTC)

Hmm, I don't follow. Isn't being inside a magnetic field required for magnetic forces to be felt? Magnetic shielding not only prevents magnetization, but "isolation from external magnetic fields" as the article says. What do you mean by "bounded"? --Kreachure (talk) 03:32, 22 June 2012 (UTC)

While my understanding is that you could shield the user from the magnetic field using concentric spheres of magnetically permeable metals, that metal in and of itself would probably be sufficient to stop the bullets. Then you'd only need to turn on the magnetic field to kill your enemies once they get close enough... 203.27.72.5 (talk) 04:13, 22 June 2012 (UTC)

Why are mammals smarter than other animals?

Not sure if this question has any meaningful answer, but I thought I would throw it out there. I was just reading Great white shark and I just thought to myself, why are they so dumb? Especially compared to Orcas. Assuming that mammals are indeed (typically) smarter than other animals, which I believe is true. But why is this? Is there a correlation with warm bloodedness and intelligence? Is it just that some mammals happened to (coincidentally) evolve intelligence, and then from there animals that evolved from them were intelligent as well? Dolphins are intelligent... Orcas are intelligent. Pigs are intelligent. Dogs are intelligent. Great apes are intelligent. Humans are intelligent. Seems that animals that eat meat are typically more intelligent that herbivores. But if I'm not mistaken we have a closer common ancestor with deer than we do with dolphins right? Not sure. In terms of lifespan, do mammals typically live longer than other animals? ScienceApe (talk) 04:21, 22 June 2012 (UTC)

Some birds are also very intelligent, such as crows. They are also warm blooded and many eat meat. A large brain does have a high energy demand, and energy density is higher in meat than in vegetation. Octopuses are apparently quite intelligent too. Hunting also requires a high degree of intelligence, so carnivores have an advantage in the evolutionary selection there. 203.27.72.5 (talk) 04:32, 22 June 2012 (UTC)

(ec)No, some of the longest living animals are reptiles, in the turtle family specifically. Also, there are some intelligent birds, like parrots, and even intelligent cephalopods, like cuttlefish. StuRat (talk) 04:29, 22 June 2012 (UTC)

Whales also have a very long lifespan. Trying to work out an average for two entire classes so you can compare them is both difficult and largely meaningless though. 203.27.72.5 (talk) 04:36, 22 June 2012 (UTC)

A higher body temperature and both a greater relative and absolute brain size. Anecdotally, my vegetarian friends are also much dumber than their meat-eating counterparts.Just kidding...friends don't let friends become vegetarians.203.27.72.5 (talk) 04:41, 22 June 2012 (UTC)

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