Wikipedia:Reference desk/Archives/Science/2009 July 1

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July 1

Cyan stays behind

Why does the cyan pigment in various colored posters get retained rather than the other ones? I've seen posters and other materials exposed to the sun and/or rain having only a faded cyan colored image.--Lenticel ^(talk) 01:30, 1 July 2009 (UTC)

Perhaps because the cyan dyes are less susceptible to photodegradation (breaking down due to light exposure)? --Jayron32.talk.contribs 03:49, 1 July 2009 (UTC)

Different pigments have different lightfastness, and the difference in the lightfastness isn’t due just to the color of the pigment per se. For example, the Monastral Blue cyan pigment has better lightfastness than the Tartrazine Yellow Lake yellow pigment, but the Hansa Yellow G yellow pigment has better lightfastness than the Peacock Blue (erioglaucine) cyan pigment. The reason the cyan pigment in multiple posters appears to have the best lightfastness of the pigments used is because in any part of the world, certain pigments tend to be the most commonly used there, due to economic and other factors. For example, in Europe, the Univit Blue Primaire and Major Blue Primaire cyan pigments are popular, which both have a lightfastness of 8, and the Major Yellow Solid and Major Yellow Primaire yellow pigments are popular, which have a lightfastness of 5 and 3, respectively.[1] Red Act (talk) 04:00, 1 July 2009 (UTC)

Is this genetically possible?

Is it genetically possible for a black man and a white woman to produce children that appear to be completely white?[2] —Preceding unsigned comment added by 67.184.14.87 (talk) 02:57, 1 July 2009 (UTC)

You would have to give a precise definition of "black man", "white woman", and "completely white" for that question to be answerable. None of these are scientifically defined concepts. If the real question is whether Michael Jackson could have fathered Michael Jackson's children, the answer is that I don't know. Looie496 (talk) 03:12, 1 July 2009 (UTC)

based on Mendelian inheritance probably not. But human skin color is not simply due to the interactions of a dominant black gene and a recessive white gene like the classic black mouse x white mouse experiment. In fact, we still don't know much behind the genetics of skin color. So it is possible but we just don't completely understand the genetics. --Lenticel ^(talk) 03:30, 1 July 2009 (UTC)

I'd say "yes". If the black man was actually mixed race (one black parent, one white parent) then they could, theoretically, give all the skin colour determining genes from the white parent to their child, resulting in a white child. Plenty of people of mixed heritage look plenty black enough to be called a "black man". I don't know what the odds of it happening are, though - the genes determining skin colour are rather complicated and I don't begin to understand them (I'm not sure anyone does). --Tango (talk) 03:50, 1 July 2009 (UTC)

The genetics of skin color is complicated and not completely understood, but a fair amount is known. Red Act (talk) 05:52, 1 July 2009 (UTC)

Statistically, it depends on whether the white-determining part of the gene is recessive or dominant. In all the attention that has been paid to race, has this ever been investigated? - GlowWorm. —Preceding unsigned comment added by 98.17.43.38 (talk) 04:36, 1 July 2009 (UTC)

It isn't determined by a single gene, so the concept of dominance doesn't really apply. --Tango (talk) 04:48, 1 July 2009 (UTC)

As Looie496 points out, this isn’t really a science question, since “black man”, “white woman”, and “completely white” are all subjective, unscientific terms. However, in my subjective opinion, Vin Diesel looks “completely white” in most photos I’ve seen of him, even though one of his two parents is African-American. Also, Wentworth Miller definitely looks “completely white” to me, even though his father would count as a “black man” at least according to the one-drop rule. Red Act (talk) 04:47, 1 July 2009 (UTC)

It's debatable as to whether the term “race” is biologically meaningful. For example, according to the race article, in a survey taken in 1999, 69% of the physical anthropologists and 80% of the cultural anthropologists surveyed disagreed with the statement "There are biological races in the species Homo sapiens." Increasingly, in scientific circles, concepts such as “population” and “clinal gradation” are used, instead of trying to divide people into “races”. Red Act (talk) 05:12, 1 July 2009 (UTC)

Lamarckism (once popular, but more recently said to be discredited) says that acquired characteristics, such as a black man managing to turn his skin white, could be passed on to his children. Edison (talk) 05:33, 1 July 2009 (UTC)

It's not just said to be discredited, it is discredited. We not only have enormous amounts of evidence for Mendelian inheritance but we have a considerable understanding of the mechanism behind it. --Tango (talk) 05:49, 1 July 2009 (UTC)

To answer the OP's question: If, by "black" and "white", he/she means "pure black" (i.e. with only black ancestors and no white ancestors) and "pure white" (i.e. with only white ancestors and no black ancestors), then, IMHO, the children would probably look like light-skinned black children (I think "mulatto" is what they used to be called, but I'm not sure); if, however, either parent had even a slightly mixed ancestry, then a wide range of appearances would be possible, from white with a somewhat tan complexion to a fairly dark black. So my own answer to the OP's question would be "probably yes", but that's just my own unscientific opinion. FWiW 76.21.37.87 (talk) 07:09, 1 July 2009 (UTC)

It is genetically possible, see albinism and Leucism. Single genes that can result in hypopigmentation, include tyrosinase, CD117 and microphthalmia-associated transcription factor Rockpocket 07:28, 1 July 2009 (UTC)

But then who do you count as a “black” ancestor or a “white” ancestor? Median skin color, for example, varies in a fairly gradual cline as you consider a series of populations along a path from sub-Saharan Africa, through northern Africa and the Mediterranean area, and up to northern Europe. See this map of skin colors. At what point along that path do you consider the gradually changing median skin color to no longer be “black” and start to be “white”?

You’d also need to define how far back you’re looking when you’re considering who an “ancestor” is. According to the Environmental factors section of the human skin color article, it only takes about 500 to 1000 years for the average skin color of even a fairly isolated migrating population to adapt to be what’s ideal for the amount of UV light that the sun shines on a given latitude.

And what all phenotypes do you consider when you’re categorizing an ancestor as “black” or “white”? Presumably more than just skin color? But if you look at all the world’s populations, the other phenotypes that you might use to distinguish “black” and “white” don’t necessarily vary in sync with skin color, since the sun exposure that creates an evolutive pressure on skin color is different from the other environmental factors that create evolutive pressures on other phenotypes. Red Act (talk) 08:08, 1 July 2009 (UTC)

People seem to think this is a purely theoretical question and we don't really know. Well, look, here. Yes it is possible, yes it happens, and yes very few people (if any) have no ancestors of a different 'race' if you go back 20 or 30 generations. 89.168.19.118 (talk) 10:10, 1 July 2009 (UTC)

What is this thing? Strange life form?

Please see this video of some form of life(?) in a drain: http://www.liveleak.com/view?i=890_1246374233 The sites comments are all stupid, but I was wondering what it actually is? The only sensible suggestion seems to be that they are some form of Bryozoan but that doesnt seem to fit either.--58.111.133.169 (talk) 09:28, 1 July 2009 (UTC)

I'm a bit suspicious because: The water's very clean, the lighting is ok, the camera work is kind of ok (not too jerky when walking, focus changes a bit strange), the pulses the thing does look quite destructive - if they do that too much, they look like they'll fall off the wall. I'm no expert in sewer lifeforms or film-making, so I'm very ready to be corrected in everything I said. Aaadddaaammm (talk) 10:18, 1 July 2009 (UTC)

Apparently they are fairly well known in the industry

http://www.kdvr.com/kdvr-prehistoricsewermonstercaug-5439314,0,673974.story —Preceding unsigned comment added by 58.111.133.169 (talk) 12:08, 1 July 2009 (UTC)

That story says "in 20 years of sewer work, they had never seen anything like it before." - that doesn't sound like "fairly well known in the industry" to me! The first video makes it look like these things are pretty big - but that's a robotic camera in a fairly narrow tube - so they could be as small as a centimeter or so. I agree that this appears to be something like a bryozoan - and our article says that there are 8,000 species of them to choose from, so it would take an extensive and difficult search to rule out that possibility. SteveBaker (talk) 12:22, 1 July 2009 (UTC)

---

http://www.youtube.com/watch?v=TcKpx2DxGwY

The video claims it's from a sewer, but I don't buy it. It looks like the camera is zoomed in on something else, indicating that everything in this video is tiny. The water seems to be behaving like it's just a small quantity of water as opposed to how water would behave in a normal sewer... So what the heck is it? ScienceApe (talk) 19:00, 1 July 2009 (UTC)

I think its a viral video for an upcoming movie. The Host 2, perhaps? --69.148.26.115 (talk) 05:16, 7 July 2009 (UTC)

I don't know what the "creature" is, but it looks like a pretty normal sewer pipe to me (a small one, but they come in all sorts of sizes). --Tango (talk) 19:02, 1 July 2009 (UTC)

Oh ok. I kinda figured by "sewer" they meant the ones you can walk through. ScienceApe (talk) 19:07, 1 July 2009 (UTC)

My guess would be internal medical imagery, probably during some surgery, perhaps with some type of artificial irrigation. Bus stop (talk) 19:05, 1 July 2009 (UTC)

But the water wouldn't be on the ground like that if it was something inside of a body right? ScienceApe (talk) 19:07, 1 July 2009 (UTC)

It looks just like a ceramic pipe to me... --Tango (talk) 19:47, 1 July 2009 (UTC)

---

The above content has been moved here from a section below. Abecedare (talk) 19:10, 1 July 2009 (UTC)

The video is legitimate. According to Raleigh city officials:

... staff biologists have confirmed that the "creature" is actually a colony of tubifex worms. The colonies attach themselves to roots that gradually work themselves into weak points in the pipes. "They seem to respond to the light from the camera," Buchan said. "That light is pretty hot." The worms naturally occur in sewage and pond sediment and are actually sold both live and dried as fish food in pet stores.

See more details in this news report. Abecedare (talk) 19:58, 1 July 2009 (UTC)

(EC), I think the same result as Abecadare: [3]. Aaadddaaammm (talk) 20:05, 1 July 2009 (UTC)

about gills the shark has

Generally, the shark has 5 gills, but i heard there is a kind of shark which has 6 gills. Is it true? How does it look like? —Preceding unsigned comment added by Patrickyu (talk • contribs) 09:49, 1 July 2009 (UTC)

Hexanchiformes have six or seven pairs of gill slits. Within this order members of the genus hexanchus, which includes the bluntnose sixgill shark, have six pairs of gill slits. Gandalf61 (talk) 10:14, 1 July 2009 (UTC)

There's also the sixgill sawshark, in the Pristiophoriformes order. Red Act (talk) 10:20, 1 July 2009 (UTC)

Counting of visible gill slits has to be repeated on the other side of the shark. Cuddlyable3 (talk) 22:32, 4 July 2009 (UTC)

Gravitation and Electromagnetism

Suppose the sun explodes at this moment and separates into two halves traveling in opposite directions at high velocities. The sun's gravitational field will change immediately and affect the Earth's orbit instantly (slightly at first). But it will take about 8 minutes for the electromagnetic radiation from the exploded sun to reach Earth. Why does gravitation have an immediate effect on distant objects, but the effects of electromagnetism are delayed? If gravitons exist, they must travel faster than the speed on light. How is this possible? David 70.55.183.195 (talk) 13:06, 1 July 2009 (UTC)

Actually, the gravitational effect would also take ~8 minutes to get to us, since it too travels at the speed of light in a vacuum. See Speed of gravity for more info. - Akamad (talk) 13:09, 1 July 2009 (UTC)

Gravity chat

If the speed of gravity was in fact infinite, would it be possible/practical to build a gravity-based telecommunications medium with enough bandwidth to, say, have a chat session with someone on Mars? Let's say 10 bytes per second. For the transmitter I'm thinking something like an array of heavy objects on maglev tracks that you scoot back and forth to indicate on and off bits, and a LIGO-type rig for the receiver. --Sean 13:29, 1 July 2009 (UTC)

As was stated above, the speed of gravity equals the speed of light, so it is not infinite. Discussing what would be possible if it was infinite is not scientific and cannot be answered by scientific means, which means it is out of scope of this reference desk. --TheMaster17 (talk) 13:52, 1 July 2009 (UTC)

Given fallibility, is there really such a thing as an unscientific discussion about imaginary physics? The discussion could be outside of any existing body of knowledge, and futile, but that's not the same as unscientific. 213.122.68.63 (talk) 15:37, 1 July 2009 (UTC)

Science has to be falsifiable. If I theorise that "If the speed of gravity were infinite real time communication with Mars would be possible" then that isn't falsifiable since there is no experiment that can show it to be true or false since the premise is false. Obviously it is possible that our understanding of gravity is flawed and it does travel at infinite speed, but that makes the question unanswerable since the premise would mean we have no real understanding of gravity on which to base an answer. --Tango (talk) 17:28, 1 July 2009 (UTC)

Right. We could similarly note that if the speed of light were infinite, LEDs could allow real-time conversations with Mars, or that if the speed of pigeons were infinite, RFC 1149 would finally be worth implementing. — Lomn 14:00, 1 July 2009 (UTC)

I do agree that just asking how the relevant equations would change if one of the constants was different is not "unscientific" at all. There have been many instances where measured or theoretically derived constants were incorrect, and the last time I checked questions about the propagation of gravitational waves were still considered active research. There is nothing wrong in a little careful speculation, and it does not make it "unscientific" (it is not asserting a non-falsifiable theory or anything like that). --98.217.14.211 (talk) 20:23, 1 July 2009 (UTC)

I don't think making the speed of gravity infinite can be considered as just changing the value of a constant. "Infinity" is not a real number so all the equations that are based on the speed being a real number (ie. any equation in which the constant appears) will cease to work. --Tango (talk) 20:36, 1 July 2009 (UTC)

The OP never said the transmitter must be located on Earth. Cuddlyable3 (talk) 22:21, 4 July 2009 (UTC)

Amended question

Since the responses to my first run at this question focused on the science rather than the engineering, I'll try again: would it be possible to build a reasonably fast machine for moving mass around on Earth that could be detected on Mars (after a suitable delay!). --Sean 19:19, 1 July 2009 (UTC)

I think your question was perfectly reasonable. We have a theory of infinite-speed gravity, namely Newton's, and wireless gravitational communication is possible in Newton's theory. To communicate wirelessly you only need a change in the charge distribution in one place to affect the field in another. It doesn't matter how long it takes for it to happen.

Take a generic 1/r² force law (instantaneous or retarded, doesn't matter). I'll write it as $F=\pm {\tfrac {GMm}{r^{2}}}{\hat {r}}$, though M and m might be electric charge and G might be the Coulomb force constant. Let the emitting and receiving stations be separated by a distance D. Suppose the emitting station consists of a charge M moving in a circle of radius d at a frequency ω in the plane perpendicular to the line between emitter and receiver. It's easy to see that the force at the receiving station will "precess" around a central value at the frequency ω. Because the force is aligned with the source, the slope of the force vector relative to the emitter-receiver line is d/D, so the amplitude of the circular component is about d/D times the absolute value of the force, or ${\tfrac {GMmd}{D^{3}}}$. Of course, this force has to be added to the influence of every other object in the universe, but the time-varying component will still be there and you will probably still be able to detect it, as long as relatively few nearby objects are rotating at that exact frequency. That's how radio communication works, roughly. However, this doesn't work for gravity, because there's no way to detect the force! The only way to detect force is by the associated acceleration, and the only way to detect acceleration is by comparing to a nearby inertial object, but there are no such objects in this case because gravity acts on everything equally. All you can detect is the local variation in the force, i.e. the first derivative. The first derivative will look like a spring force law, ΔF = k Δx, but with three different constants k along three perpendicular axes of symmetry. In this case the symmetry axes are obvious: the line between emitter and receiver, the (time-varying) direction between the object and the center of rotation, and the direction perpendicular to those. The force constants along those three axes are, respectively, $\left(2-\left({\tfrac {d}{D}}\right)^{2}\right){\tfrac {GMm}{D^{3}}}$, $\left(2\left({\tfrac {d}{D}}\right)^{2}-1\right){\tfrac {GMm}{D^{3}}}$, and $-{\tfrac {GMm}{D^{3}}}$. The first of these doesn't help much because it's constant. But the other two axes rotate into each other over time, so we will see a sinusoidal variation in the force constant in that plane with an amplitude of $\left({\tfrac {d}{D}}\right)^{2}{\tfrac {GMm}{D^{3}}}$ and a frequency of 2ω. This will lead to a sinusoidal oscillation in the distance between two test particles. The amplitude of that oscillation is proportional to the distance, and the (unitless) proportionality constant is ${\tfrac {GMd^{2}}{(2\omega )^{2}D^{5}}}$. And that, at long last, is what LIGO measures. According to online sources it's most sensitive at around 200 Hz, where its design detection threshold is about 10⁻²³. So let's plug in some values. Take M = 10 kg, d = 10 m, 2ω = 2π × 200Hz, and D = 56 million km (the closest approach between Earth and Mars). And the result is... about 10⁻⁶⁷. So the answer is: not a chance in hell. Note that that's just to unambiguously detect the existence of the carrier signal—never mind modulating it, and never mind doing so fast enough to communicate at 80 bps. -- BenRG (talk) 19:37, 1 July 2009 (UTC)

Hmm, I think there's something wrong with my brilliant argument because it makes orbiting pulsars very undetectable too. Better ignore it for the time being. -- BenRG (talk) 20:02, 1 July 2009 (UTC)

Why do you have the tidal forces following a sping-like law? I thought they followed an inverse cube law. --Tango (talk) 20:37, 1 July 2009 (UTC)

Possible? Eh, maybe, sorta, kinda, in a hideously expensive utterly impractical sort of way, if we worked out all the necessary science and engineering first. Our gravitational wave article covers the underlying principles of such a system. Or we could use perfectly good electromagnetic methods of communication. — Lomn 19:42, 1 July 2009 (UTC)

Note: part of the reason we're unlikely to ever care about this, as a practical matter, is that gravity is 10³⁶ times weaker than EM radiation. It's very difficult to construct a scenario in which perceived advantages of gravitational communication outweigh this massive roadblock. — Lomn 19:45, 1 July 2009 (UTC)

I think that's why he originally asked the question about a universe where gravity moves faster than EM radiation. -- BenRG (talk) 20:02, 1 July 2009 (UTC)

Question regarding dBm

In a book I've been reading, I found the following statement (among other similar statements):

200 mW –3dBm = 100 mW

Is this correct? Why is the result 100 mW and not 198 mW? If it is, what's the explanation for it?

Thanks. 93.108.139.109 (talk) 16:22, 1 July 2009 (UTC)

It is correct, but in perhaps a dfficult form for beginners to understand. See dBm. dBm is logarithmic unit of power, so it is non-linear. Power in dBm is defined as 10 * log (P / 1 mW), where P is a power in mW. Using the properties of logarithms, adding and subtraction in logs is equivalent to multiplying and dividing. So since the inverse log of 3 dBm is 2, -3dBm is the same as saying divide by 2. Usually people wouldn't mix units of mW and dBm in the same equation, but the author probably thought it would be okay since -3dBm is very easily recognized as being one half. —Akrabbim^talk 16:32, 1 July 2009 (UTC)

It's still wrong though. dBm is an absolute unit, so 3 dBm is close to (note, not exactly) 2 mW under all circumstances, just as -3 dBm is about 0.5 mW. In no case can "-3 dBm" mean divide by 2. Only "-3 dB" can mean that. So the OP's expression, if it means anything at all, must mean ~198 mW. If the writer intended it to mean 200 mW / 2, then he should have written 200 mW x (- 3 dB), although that's still an incorrect use of the terminology. --Heron (talk) 17:08, 1 July 2009 (UTC)

The equation seems poorly stated, since -3dBm could mean subtraction of 3dBm, or it could mean divide by 2. Edison (talk) 18:18, 1 July 2009 (UTC)

You're right, it really is the question's fault. What I explained in my first answer, is if 200 mW is converted into dBm (23 dBm), and then 3 dBm is subtracted, then the answer is 20 dBm, or 100 mW. Or, if we wanted to convert the second term into mW, we wouldn't know if we were adding .5 mW or subtracting 2 mW from 200 mW. Now that I think about it, adding or subtracting dBm from mW is very ambiguous, and meaningless in equation form. —Akrabbim^talk 19:37, 1 July 2009 (UTC)

You should never add (or subtract) things that are measured in different units, so the equation is clearly nonsense. It could work as an abuse of notation, but, as you say, it is rather ambiguous as to what the abuse is meant to mean. --Tango (talk) 01:48, 2 July 2009 (UTC)

With respect the first response contains errors. -3dB is the same as saying divide power by 2 (more exactly by 10^.3 = 1.99526...). That is a dimensionless ratio. The little "m" in -3dBm means 1mW divided by 2 which is 0.5mW. That is a power. What the OP read in an unspecified book is flat wrong and the author should have written

200 mW -3 dB = 100 mW

or

200 mW - (-3 dBm) = 199.5 mW

Cuddlyable3 (talk) 22:00, 4 July 2009 (UTC)

humane meat harvesting

Florida stone crabs are said to be one of two animals whose meat can be harvested without killing it. What is the other animal?

Some species of lizards drop their tails when they are grabbed. That is a potential for some meat without harming the lizard. Best that I can come up with. 65.121.141.34 (talk) 18:12, 1 July 2009 (UTC)

Autotomy appears to be the relevant concept here, and there are more than two species that could conceivably have meat harvested in this fashion. Additionally, I would submit that severing an animal's appendages is not inherently "humane" if you're examining the moral issues of eating meat. — Lomn 19:04, 1 July 2009 (UTC)

A traditional food of the Maasai people is a blood porridge of some kind, the blood having been harvested from cattle that they keep around for that purpose. Blood isn't meat, I suppose, but I don't think too many vegetarians drink it. --Sean 20:06, 1 July 2009 (UTC)

This question would be much more interesting minus one "e" ;-) --Stephan Schulz (talk) 20:08, 1 July 2009 (UTC)

What? We don't need to be humane for mat harvesting ;)--Lenticel ^(talk) 00:23, 2 July 2009 (UTC)

Leaving them alive but less able to survive? what's humane about that? - KoolerStill (talk) 08:41, 2 July 2009 (UTC)

Pregnancy in Space

Is there any evidence people could not conceive, gestate, and give birth to children in space? I'm curious if there has been any multi-generational studies of animals in space and how that data would correlate with people. Would the fetus develop properly in the absence of gravity? TheFutureAwaits (talk) 17:44, 1 July 2009 (UTC)

[4] from 1995 describes some experiments with pregnant rats in space for part of the gestation, and says that multigenerational animal experiments were planned for the International Space Station. A 2002 NASA report [5] says on page 32 that they still would like to do multigeneration studies on primates in space, but offers no hint that any multigeneration studies had been done by then. If you email NASA they might be able to search their database and provide a more definitive answer. Edison (talk) 17:50, 1 July 2009 (UTC)

Animals in space lists the longest animal flight as 90 days - unfortunately the tortoises involved didn't quite have enough time to make multiple generations. Other shorter lived animals have flown though. Rmhermen (talk) 22:18, 1 July 2009 (UTC)

I assume you mean "in zero gravity". It's possible to closely simulate terrestial conditions in space, in which case I can't imagine any reason why pregnancy would not proceed as usual. Dcoetzee 01:37, 2 July 2009 (UTC)

As we have even less experience with living beings in "artificial gravity" than we do with "zero g", I would be hesitant to say that there would be no effect. Rmhermen (talk) 02:54, 2 July 2009 (UTC)

My Astronomy professor said that there seems to be some problem with pregnancy in space, in that it seems to cause miscarraiges in animals. If it is the same for humans—and it very well may be—then on long voyages, women may have to spend nine months in a rotating chamber that simulates gravity. —Pie4all88 ^{T C} 03:11, 2 July 2009 (UTC)

As has been pointed out, it is not yet verifiable whether a rotating chamber inducing a gravity-like force is "identical" to terrestrial conditions. There are a lot of confounding factors beyond the first-order net "downward" force that is felt inside a rotating chamber. Nimur (talk) 03:17, 2 July 2009 (UTC)

I see there's another thread about artificial gravity, so I'll read through it when I get a chance. Thanks for the info! —Pie4all88 ^{T C} 07:19, 2 July 2009 (UTC)

See reproduction and pregnancy in speculative fiction. Robinh (talk) 07:41, 2 July 2009 (UTC)

Ungrounded alternator

I'm curious to know the potential difference between one of a single-phase alternator's lines and the ground when this alternator has its neutral not connected to the earth? --Email4mobile (talk) 17:47, 1 July 2009 (UTC)

Good question. It is undefined, since you have specified no neutral to ground connection. The voltage in practice might be anywhere from zero to the output voltage from either conductor to ground, since there will be leakage current and capacitive coupling to ground. In practice, if there were a voltmeter from each output line to ground, the measurement circuitry would constitute a high impedance ground connection and would determine the voltage measured. If only one voltmeter were connected to one line at a time, it would pull the measured line down and force the unmeasured line higher. Three phase equipment in factories is sometimes designed to be operated ungrounded, because the first unintentional ground does not cause fault current. Ground indicator lights or equivalent relays are used to detect such a ground, and it can be found and fixed without necessarily having an emergency shutdown, There, similarly, the ungrounded phases rise to a high potential to ground while the grounded phase goes to a low or zero potential to ground. Edison (talk) 18:13, 1 July 2009 (UTC)

Thank you very much indeed. I've tried to find an explanation for that problem once, and assumed the capacitive effects. However when I started simulating that measured voltage via mathematical equations I was stuck by the equivalent circuit to be analyzed due to my insufficient knowledge in this subject and poor imagination of capacitance and impedance patterns. It would be more helpful if you know a reference which details this problem (and have a good day/night. I'm going to bed).--Email4mobile (talk) 18:52, 1 July 2009 (UTC)

An alternator with its neutral not connected to ground? Wouldn't that be extremely dangerous?! 76.21.37.87 (talk) 04:27, 2 July 2009 (UTC)

Is the alternator in your car connected to earth ground? Do you feel yourself to be indanger in the car because there is no wire from the neutral terminal to earth ground? How about in an airplane? How about in the International Space Station or the Space Shuttle? There is a neutral but it is not connected to earth ground. How about on a ship? In the early days of marine elecrical systems, some countries used the phase and neutral isolated from the ship hull, and others used the hull as a ground to which the neutral was connected. It is possible that a load element or the alternator winding itself might have graded insulation, with a lower insulation level near the terminal that is supposed to be at earth potential, like the frame of the alternator, particularly if it has a very high voltage output. In such a case, the case of the alternator might be at a dangerously high voltage, or the insulation might fail. A low voltage alternator is likely to have the same insulation level at all points on the winding, and the neutral and phase wires are likely to be of the same insulation rating. In that case the alternator, switch, fuse, wires, and load would probably work with or without the grounding of the neutral. It is basically a safety measure, so that there is less risk of a dangerous voltage on the neutral or frame, or on unswitched and unfused conductors. It also allows fuses or circuit breakers to operate if the phase or intended hot wire becomes accidentally grounded through a break in the insulation. Edison (talk) 00:05, 3 July 2009 (UTC)

Regarding the car/plane/ship alternators: although they are not connected to earth ground, they are connected to the bodywork/airframe/hull instead, so technically they are still grounded, even though there's no connection to earth ground. Note also that in all these cases, the bodywork/airframe/hull would act as a Faraday cage and thus protect the occupants from getting zapped even if the insulation fails on the alternator. What I meant was that an alternator with its neutral not connected to anything at all would likely be dangerous, especially if it operates at a high voltage. 76.21.37.87 (talk) 03:48, 4 July 2009 (UTC)

Position basis of a wave function

In literature I'm reading about intro quantum mechanics talking about single particle wave functions, they often discuss them in terms of the position basis (including here: wave function) and other continuous bases like the momentum basis. I was under the impression that wave functions as functions over the points in space lived in L²(C), since they use that inner product and norm. But the position basis (or any other uncountable set) isn't a basis of L² and similarly Dirac delta functions aren't in L² since functions that are equal a.e. are put in the same equivalence class. If not L²(C), then what Hilbert space are wave functions supposed to live in? What's going on here? —Preceding unsigned comment added by Rckrone (talk • contribs) 18:40, 1 July 2009 (UTC)

If it is a good book, this should be declared in some kind of intro section. Ah, and if you really have a good book on quantum mechanics, please tell me, for I don't know any. Sorry if this isn't helpfull. Hoping there will be better responses. I would like to know the answer myself, too. 93.132.130.9 (talk) 20:04, 1 July 2009 (UTC)

The Dirac delta "function" is not a function at all, not even in ${\mathbb {R} _{\infty }}^{\mathbb {R} }$. There's no way you could arrange for its integral to be 1. Expressions involving the delta function are really implicit limits of expressions involving normalized Gaussians or suchlike as the width goes to zero. The delta function by itself wouldn't make sense but an expression incorporating it is legitimate as long as the limit of the whole expression exists. Likewise the position "basis" is really a limit of fuzzy Gaussian-like distributions of position, and one requires (or at least hopes) that expressions that define quantities of physical interest converge sensibly in the limit. That's how I think of it, anyway. -- BenRG (talk) 22:00, 1 July 2009 (UTC)

One does not have to pretend that statements involving deltas are just shorthands for statements about limits. The dirac delta function is a perfectly good mathematical object, it's just not a bona fide function on the reals. It's a measure or a distribution or something (depending on your point of view). Algebraist 22:04, 1 July 2009 (UTC)

It's a functional rather than a function. Looie496 (talk) 01:11, 2 July 2009 (UTC)

But Dirac delta functions aren't in the dual of L² either. δ_x would the functional that maps f to f(x), but an element of L² is an equivalence class of functions that are equal a.e., so they're free to differ at x. On the other hand thinking of it as an idealized limiting case definitely clears some things up, but I'm still not satisfied with the idea of the position "basis." It's certainly not the limit of some sequence of bases. It has the wrong cardinality among other problems. Rckrone (talk) 04:00, 2 July 2009 (UTC)

The delta function, as a functional, is not quite the mapping from f to f(x); that's a simplified definition. See Dirac delta function#The delta function as a distribution for more info. Looie496 (talk) 15:52, 2 July 2009 (UTC)

What the heck is this?

Moved question and responses to an earlier section where the same question is posed. Abecedare (talk) 19:08, 1 July 2009 (UTC)

Plain water

For some reason drinking plain water makes me feel sick, but I can consume any other drink just fine, even flavoured water, which doesn't seem like it would be different enough to... be different. What's the deal? Vitriol (talk) 22:39, 1 July 2009 (UTC)

Is it any plain water or just the plain water from a certain area? What about bottled water? There are places which have tap water I find very unpleasant, possibly even to the point of making me feel unwell. It's just the taste, as far as I know. --Tango (talk) 22:37, 1 July 2009 (UTC)

I dunno if water from the ice dispenser and the tap would be different, but if it is then both make me wanna barf. And it's definitely not the taste. Vitriol (talk) 22:39, 1 July 2009 (UTC)

Presumably the ice dispenser gets its water from the tap? When you say "flavoured water", do you mean water that is bought with flavouring or tap water with orange squash or similar added? If its the latter, then it must be the taste, that's the only thing that is different. --Tango (talk) 23:27, 1 July 2009 (UTC)

My understanding is that fluids with low osmolarity (concentration of dissolved substances) are hard for the stomach to absorb, and that almost any dissolved substance will help. Looie496 (talk) 01:07, 2 July 2009 (UTC)

You'll have to be clearer what you mean by plain water. If you're drinking distilled water, the sort used for scientific experiments, that's going to taste bad and cause the problems described by Looie496. But tap water usually contains a variety of dissolved impurities. If your tap water makes you feel sick, it's probably something in the water, perhaps some kind of allergy (since it's evidently not making everyone sick). Dcoetzee 01:41, 2 July 2009 (UTC)

It can't be something in the water if other drinks made from that water are fine, though... --Tango (talk) 01:44, 2 July 2009 (UTC)

If the same water which makes you sick when plain does not make you sick when something is added to it, the cause of the illness is probably psychosomatic; there is no allergan or pathogen in the water, but for some reason the thought of drinking plain water sickens you... --Jayron32.talk.contribs 03:52, 2 July 2009 (UTC)

I concur. Richard Avery (talk) 07:43, 2 July 2009 (UTC)

Yeah, I have a similar problem and I strongly suspect it's psychosomatic. If I drink any plain water within an hour or two of waking up, I generally feel rather sick - but I can drink tea, or orange juice or whatever and feel fine. I can also drink plain water later in the day and feel fine. I can't think of a good scientific reason for this, so I assume it's just my brain playing with me - or just the fact that the tap water here tastes a little horrible and I'm more delicate in the morning! ~ mazca ^talk 08:35, 2 July 2009 (UTC)

Water memory? ;-) Axl ¤ [Talk] 06:23, 2 July 2009 (UTC)

It may not be psychosomatic. It's possible that the water that's been sitting in your household plumbing all night has picked up some dissolved chemicals - and that the oxygen dissolved in it has dispersed - making it taste 'flat'. Later in the day - when everyone in your neighborhood is using lots of water - and the stuff that's been in your pipes all night has been flushed or showered - you should be getting more aerated water that hasn't been soaking up who-knows-what from your pipes all night. Ergo: Either run water to waste for a few minutes before drinking any - or perhaps shake the stuff up vigorously with air to aerate it. SteveBaker (talk) 11:26, 2 July 2009 (UTC)

Try half-filling a bottle with the water, closing it, and shaking it pretty hard for a little while, to dissolve some air into the water. That may make it more palatable to you. Or, add a few drops of lemon juice. 208.70.31.206 (talk) 07:42, 2 July 2009 (UTC)

I get this too, i always thought it was to do with stomach chemistry, drinking plain cold water would be a shock to your system and dilute your pre breakfast stomach juices. I think even adding a spoon of sugar in tea or orange drink or whatever you put in the water would give the empty stomach something to do, so to speak, rather then just diluting it. Mind you, the first thing I usually drink is a hot black coffee with no sugar, so maybe the temperature has something to do with it? There are some chinese people at my work that drink plain hot water from the urn, they believe it's better for you then cold water. Vespine (talk) 00:06, 3 July 2009 (UTC)

The article Water purification describes the wide range of methods and chemicals used in municipal water purications, which may leave traces that the OP finds unpalatable. Cuddlyable3 (talk) 15:39, 4 July 2009 (UTC)

'Karl Malden nose'

What is the proper name for the nose condition sometimes colloquially called 'Karl Malden nose' (where the person's nose is all bulbous and has a strange texture to the skin)? Note, I don't know if KM actually had this - but his death today reminded me of the subject. --90.240.60.140 (talk) 23:01, 1 July 2009 (UTC)

Not being familiar with Malden, I can only suggest Rosacea. Nanonic (talk) 23:12, 1 July 2009 (UTC)

Possibly rhinophyma? Ginogrz (talk) 23:17, 1 July 2009 (UTC)

Rosacea of the nose, as seen in people like Karl Malden and W.C. Fields was commonly called "gin blossom", as alcohol-thinned blood tended to make the thin blood vessels in that part of the nose rupture it used to be assumed (incorrectly) that alcohol caused the problem ed note: changed due to valid point made by Richard Avery below ; the swollen nose is similar to cauliflower ear. See also the description of the origin of the band name of the Gin Blossoms, who took their name from the phenomenon. --Jayron32.talk.contribs 03:48, 2 July 2009 (UTC)

"alcohol thinned blood tended to make the thin blood vessels in that part of the nose rupture". Do you have a citation for that Jayron? The scientific cause of rhinophyma [[6]], [[7]], [[8]]appears to be unknown at present although there are a number of associated signs that can predict its occurrence. Richard Avery (talk) 07:41, 2 July 2009 (UTC)

So fixed... --Jayron32.talk.contribs 12:33, 2 July 2009 (UTC)