Wikipedia:Reference desk/Archives/Science/2008 October 20

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 20

Stuffy noses -- one side is blocked, then the other, then both.

During a cold or the flu, how does one nostril become completely blocked? Sometimes they both are, sometimes none. And it seems to change sides for no apparent reason. What's going on inside my head? --64.123.119.182 (talk) 01:56, 20 October 2008 (UTC)

We cannot offer medical advice. Please see the medical disclaimer. Contact your General Practitioner. Paragon¹²³²¹ 03:07, 20 October 2008 (UTC)

Good thing no one asked for advice then, isn't it? - Nunh-huh 03:08, 20 October 2008 (UTC)

Definitely not a medical advice question; anatomical curiosities are different. Unfortunately, I have no idea what the answer is. Something to do with sinus pressure. --Masamage ♫ 03:57, 20 October 2008 (UTC)

Since it's your face and not mine, I can't speak directly to your experience. Here's mine: I've had ear nose and throat problems all my life, especially terrbile sinus headaches (took me a decade of living with a cat to figure out I was allergic to it). I almost always get them on the same side of my head, which puzzled me until I realized: it was the side I slept on. Mucus is a fluid, albeit an especially goopy one, and if you preferentially sleep on one side more often than on the other, I wouldn't be surprised if that's also the nostril that's getting stuffed first. --Shaggorama (talk) 04:49, 20 October 2008 (UTC)

It's also not simply that "nostril that feels clogged" = "nostril that's obstructed by mucus". Congestion consists of swelling of the nasal mucosa; it's as likely to be this swelling as it is actual mucus obstructing air passage. In a paper discussing a system to measure differential air flow in the left and right nares, , there's a statement of some things that can change the sensation of which nostril is obstructed:"left naris becomes less congested ", " patient changes head position that affects air flow or swelling").[1]. The side you sleep on is also the side that's more "dependent" and could be more congested as well as more blocked by mucus. - Nunh-huh 06:31, 20 October 2008 (UTC)

One would also have to take into account the state of the nose before it became infected. It is possible that your nose has been injured at some time and the airway somewhat reduced during the healing process or you may have a small nasal polyp that is affecting one side of the nose, but only causing a blocked sensation when the mucosa is inflamed and swollen. Richard Avery (talk) 13:44, 20 October 2008 (UTC)

I did read/hear that it's normal to breathe predominantly through one nostril, with the nostril used alternating every couple of hours. Unfortunately I can't remember where or cite a reliable source, as it's just one of those factoids you pick up. AlmostReadytoFly (talk) 15:13, 20 October 2008 (UTC)

Yes I heard that. But here is a source [2]--GreenSpigot (talk) 01:06, 21 October 2008 (UTC)

Hmm, not what one could call a reliable source. A blogger citing other dodgy sites. Mentalphysics?? Richard Avery (talk) 07:52, 21 October 2008 (UTC)

OK heres another nostril--GreenSpigot (talk) 17:04, 21 October 2008 (UTC)

And another: Nasal cycle--GreenSpigot (talk) 17:08, 21 October 2008 (UTC)

Gravity waves

See Gravity wave. Anyone know what shape the wave is? It obviously isn't a sine wave. -- SGBailey (talk) 16:46, 20 October 2008 (UTC)

Do you mean the waves that that article are talking about (waves on the ocean, for example) or the waves in general relativity? The former are probably sine waves (if they're periodic at all, a tsunami is a gravity wave, but is just a single wave). The latter will depend on the source, two objects in a circular orbit around their centre of mass will probably give off sine waves (a GR expert may come along and say I'm wrong in a minute, I'm just guessing based on the animations in our article, gravitional waves, they look to me like they are oscillating as a sine wave). A more complicated system will give off something more complicated. --Tango (talk) 18:33, 20 October 2008 (UTC)

The shape of a gravity wave is too complex to have a simple name, it seems. See Airy wave theory for the simple, sinusoidal approximation. That article links to the more complex, nonlinear models. One of them is the trochoid, a shape that resembles simple nonlinear waves reasonably well. --Heron (talk) 21:14, 20 October 2008 (UTC)

I suppose I meant what shape is the animation of a surface gravity wave shown. What reason did the author have for making it the shape he has? -- SGBailey (talk) 21:39, 20 October 2008 (UTC)

Ah, I get you. Sorry. It's pretty close to a sine wave, but I agree it doesn't look exactly like one. I no idea why the creator chose that particularly wave, but they are still active so you could always ask! --Tango (talk) 22:07, 20 October 2008 (UTC)

The proper word is cnoidal wave, (google it!) but this does not have a wiki entry. And I learned about these 20 years ago, so I'm not an expert! Robinh 07:23, 21 October 2008 (UTC)

Vaccine versus Control group testing

In the information sheet for an oral vaccine against travellers' diarrhea and cholera, there is a table comparing "adverse events reported".

The two most commonly reported "events" are:

• abdominal pain, reported by 16% of those who received the vaccine and 14% of the control group, and

• diarrhea, reported by 12% of those who received the vaccine and 11% of the control group.

My question is about the methodology of such a comparision. I assume that people in the two groups are given the same information. What information are they likely given about what they are receiving?

Speaking personally, I think I would be likely to react differently if I were told:

"Please drink this. It contains one hundred billion inactivated cholera bacteria."

than if I were told:

"Please drink this. It will stop you from getting diarrhea."

- - -

Aside from the specific question of what the people in this test were told, in general what is the proper approach as to what people in such tests SHOULD be told? Wanderer57 (talk) 17:14, 20 October 2008 (UTC)

See double-blind study for more information on the generally accepted means of doing medical research of this nature.--Jayron32.talk.contribs 17:29, 20 October 2008 (UTC)

That article says: "Single blind describes experiments wherein information that could introduce bias or otherwise skew the result is withheld from the participants." I suppose either of my suggested wordings would introduce bias and thus could not be used. But it seems to me the participants have to be told "something". What can they be told? The article doesn't cover this. Wanderer57 (talk) 18:00, 20 October 2008 (UTC)

They'll be told something along the lines of: "Please drink this, it is either a vaccine against diarrhoea or a placebo." Everyone will be told the same thing and the person saying it doesn't know which one each person is getting (that's the "double" bit of "double blind"). --Tango (talk) 18:36, 20 October 2008 (UTC)

Bouncing off the atmosphere

You often hear people using the expression "bouncing off the atmosphere" to describe what happens if a spacecraft re-enters the atmosphere at too shallow an angle. This makes it sound as if the atmosphere is an elastic substance that can absorb the kinetic energy and return it - that can't be right, can it?

I think that the spacecraft would experience a force directly opposite to its direction of travel, and that this would slow it down. If the deceleration was inadequate, the spacecraft would return to space, but with reduced kinetic energy.

I remember when young reading about this affecting the height of the apogee, and I think I now know why. If the craft was in an elliptical orbit, the loss of kinetic energy at the perigee would reduce the potential energy of the apogee, due to the exchange between the two energy types as the craft orbits. This would progressively reduce the apogee until the orbit was near circular, when it would re-enter properly and land, crash or burn up.

If the craft was in a hyperbolic orbit it would still lose energy, possibly enough to be captured by the earth.

Is this what actually happens, or have I got this wrong? If correct, why "bouncing off"?

--J987 (talk) 19:56, 20 October 2008 (UTC)

I don't think the force is directly opposite the direction of travel - there will be lift as well as drag. I'm not quite sure how all that works, though, so I'll leave that to someone else. You are right about air resistance circularising an orbit, although it would probably re-enter some time before the orbit became circular. As the apogee drops, the object spends more and more time in the thicker part of the atmosphere and the apogee drops faster and faster, the final drop from being above significantly atmosphere to being on the ground would probably happen in less than one orbit. A hyperbolic orbit will certainly lose energy if it goes through an atmosphere, whether that could lead to capture or not, I don't know, it's certainly plausible. When probes to Mars, and similar, enter Martian orbit they sometimes (maybe always, I don't know) use their rockets to enter a higher elliptical orbit and then use atmospheric breaking near periapsis to circularise the orbit - they have rockets to prevent it going beyond circular and crashing, of course (I believe they keep the periapsis above the significant atmosphere and use rockets to periodically dip down into it, lose some energy, and then use the rockets to lift them back to safety). --Tango (talk) 20:16, 20 October 2008 (UTC)

Think "rock skipping off a pond". SteveBaker (talk) 02:50, 21 October 2008 (UTC)

The command module is almost exactly cylindrically symmetric. So one would think that the drag would indeed be opposite in direction to its motion through the upper atmosphere. But the mass distribution is non-symmetric; the spacecraft thus travels non-axially. This is (apparently) enough to generate a lateral force that can indeed cause the skipping phenomenon that stevebaker mentions [I find to my horror that rock skipping does not exist! There was a brilliant paper in Nature a few years back. I'll write a stub when I get a minute]. HTH, Robinh 07:17, 21 October 2008 (UTC)

Er, that's my bad. See stone skipping. Robinh 07:51, 21 October 2008 (UTC)

Fixed with a redirect. (It's a weird dialectic thing: British-English reserves the word 'rock' for things bigger than your head (or so) - smaller 'rocks' are called 'stones'...hence: stone skipping. This usage doesn't appear in US English where 'rocks' can be as small as maybe a centimeter or so before they might be called 'stones' - so the article needs to be called rock skipping...which would be an altogether more impressive feat in Britain!) SteveBaker (talk) 13:46, 21 October 2008 (UTC)

Thanks Steve. I'm British but never really thought about this difference between rocks and stones. I think 'rock' is the substance and so stones are made out of rock. Anyway, the Nature article I referred to uses 'stone skipping'. I ought to reference it in the article. Happy Wednesday, Robinh 06:58, 22 October 2008 (UTC)

4D

I've read part of Flatland and a sequel to it, and I've read The Planiverse, and I've run across a few other stories that ponder life in two or fewer dimensions. What about more dimensions? It seems like there would be even more technical problems to overcome in building a sensible lifeform and an environment for it to live in, but it shouldn't be impossible. Obviously the musculature would have to be as different from ours as ours is from that of an Ardean, since it has four dimensions to grow in and probably more complicated shapes to move around, and naturally ratios like height-to-weight would have to be rethought, but there's no reason it shouldn't work. Anyone run into anything like that? Black Carrot (talk) 20:24, 20 October 2008 (UTC)

I'm pretty sure people have considered life in 4D, although I can't find anything explicitly about it. I remember hearing somewhere that the extra dimension means particles are less likely to meet eachother (more ways to miss, I guess) which slows down reactions so life might not be possible (or would at least be less likely) - that was as part of an attempt to explain why our universe has 3 dimensions using the anthropic principle (in 2 dimensions you have problems with things like a body falling apart if you try and have a tube going all the way through to make a digestive system which causes lots of restrictions on how life could work, and in 1 dimension you can't change the order of particles from their initial conditions which restricts pretty much everything, so 3 dimensions turns out to be the optimal number for life to evolve). --Tango (talk) 22:14, 20 October 2008 (UTC)

Hi. Wouldn't the fourth dimension be time (and 5-11 branes)? Thanks. ~AH1^(TCU) 22:49, 20 October 2008 (UTC)

(sigh) Yes, this universe has three space dimensions (plus an unknown number at the very tiny scale, yada yada) and one time dimension, but when such questions are raised I, at least, assume that they're about a universe with N macroscopic space dimensions. —Tamfang (talk) 00:20, 21 October 2008 (UTC)

Another reason for exactly three dimensions is that in higher spaces there are no stable orbits (which I don't entirely understand so don't ask me). Also, in even-numbered spaces every signal rings forever, they say (which I understand even less). —Tamfang (talk) 00:23, 21 October 2008 (UTC)

I'm sure it has appeared several times in science fiction. The best example I can think of off the top of my head is Greg Egan's novel Diaspora, which has parts of it set in a five-dimensional universe (and other parts in weirder settings yet). Digging further, some novels in Iain M. Banks's Culture series (I think Excession in particular, but it's been a while since I read them) depict normal space as a "brane" in a higher-dimensional hyperspace, but I don't recall much being really made of it. Robert Reed's short story "Coelacanths" includes the memorable phrase "The universe is fat with dimensions." And of course there's Robert A. Heinlein's classic short story "—And He Built a Crooked House—". —Ilmari Karonen (talk) 23:32, 20 October 2008 (UTC)

Yes, I mean life in more-or-less R^4. Yes, I realize that the fancies of theoretical physics would have to be drastically re-fantasized. I'm thinking macroscopic, and assuming that the tiny things will sort themselves out. Macro things include gravity (Should it drop as the cube of the distance?), ratios of forces (No tree can be more than 350 feet tall, no land animal much bigger than an elephant), friction (Can you tie a rope?), and geometry (WTF with the skeleton?). I've read And He Built a Crooked House, which is a good story but more like life in a three-dimensional CW complex than life in R^4. I'll take a look at the five-dimensional one, but I'm guessing it goes more for "dimensions are really nifty" in its exposition than laying out a blueprint. To give some idea what direction I'm going in with this, I was inspired by the comic-off between Munroe and Katz, specifically Munroe's string theory comic. The joke is fun, but flawed. If you put people into four dimensions directly, they'll fall apart. If you expand them into lifeforms with four-dimensional volume, then you could just as easily weave four-dimensional ropes to hold them in. So... what would that look like? I'm surprised nobody's written about this. Black Carrot (talk) 18:19, 21 October 2008 (UTC)

The knots didn't fall apart because the ropes they were tied in were woven in three dimensions. They fell apart because they were essentially one-dimensional. If you used a two-dimensional sheet, it would work. See Knot theory#Higher dimensions. — DanielLC 23:35, 21 October 2008 (UTC)

Egan's Diaspora actually goes into some detail about physics and the geometry of life in 5-space. —Tamfang (talk) 01:12, 22 October 2008 (UTC)

Well, to see how odd would be life in a many dimensional world (as the ones conjectured by modern phisic theories), consider the following situation. You live in a 50 dimensional spheric planet, say of the same diameter of our old 3D Earth. Imagine you are having your whisky, or whatever, a gin tonic if you prefer, at home, so you have taken some small cubes of ice from the fridge, and now you go to the terrace with your glass. Now suppose you forgot one ice cube on the table in the kitchen... Question: how much will be increased the level of seas on the planet, due to your lazy behaviour? :) --PMajer (talk) 20:43, 22 October 2008 (UTC)

I picked up Diaspora at the library yesterday, and finished reading it tonight. Good book. It was more detailed than I expected, but it still didn't answer many questions. Most of the descriptions of multidimensional space focused more on people's reactions to it than the space itself or anything in it. I also ran into the work of a guy called Hinton, which although it doesn't deal with four-dimensional lifeforms does at least go in some detail into ways of solving problems in 4D. The question remains open if anyone gets any more ideas. The knot thing brings up a more specific question that probably hasn't been answered: What knots are actually practical in four dimensions? Is there the equivalent of a granny or hitch knot for all-round usefulness? (And, obviously, the "ropes" wouldn't be thickenings of one-dimensional objects, they'd be thickened surfaces, like cloth.) Black Carrot (talk) 07:44, 24 October 2008 (UTC)

Possible non-conventional ways to counter global warming?

Hi. First of all, this is neither homework nor legal/medical advice, and I'm not exactly probing for oponions, I just want to know about the plausibility of these scenarios.

• Jumping simutaneously

This occured to me after remembering a joke on an April Fools' day, but I thought it might have a bit of plausibility. Consider people around the world simutaneously jumping at diffent times of each 24-hour period, say during the local early afternoon. People would jump at timed intervals around the world at a set local time, so that about 3 billion jumps would occur in one 24-hour period, daily, more so in the summertime than in the winter. I don't know if this would violate conservation of momentum or something, but if people simutaneously jump when their heads are facing closer to the sun, their downward forces would be pushed into the ground, and their upward forces into their bodies and thus not into the Earth. Would that be able to, over a long period of time, propel Earth into a very slightly farther (and more eccentric) orbit? Or, would it cause more problems than it would solve (they're saying that river dams and strong cyclones could cause earthquakes on stressed fault line zones)?

• Due to conservation of mementum this does not work. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

  I don't know if this is so much "conservation of momentum" as "...then you land". CoM is what makes the Earth move in response to your jump. Then, however, gravity kicks in and undoes everything you just did. — Lomn 03:22, 21 October 2008 (UTC)

• Painting albedo:

This idea is to paint urban items such as buildings, roofs, roads, etc, white, as long as it doesn't use much more oil, such as painting a roof white instead of a different colour. After all, there is the "urban heat island" effect, so this would cool down the city and also reflect more heat into space.

• could assist Graeme Bartlett (talk) 23:01, 20 October 2008 (UTC)

• Firing gravitons

Yeah, I know, gravitons aren't even proven to exist. However, if they do exist, and we can find out the mechanism for their creation, then maybe we could place graviton-generating stations around the world, and when it's dark at night, the machines could either point toward the Earth and switch on, and pull the Earth toward the machine, or they could point toward space, and the stream of gravitons could pull the Earth away from the sun, and they wouldn't propel the Earth toward the sun because they have no mass. Or, is this technicly not plausible, or would have too little effect even if we did somehow succesfully make one?

• You would be better off typing a rope to Mars. The theoretical graviton still has to obey conservation of momentum, so unless they move something else it will not work. Also it will require colossal energy, perhaps by burning fossil fuels? I don't think so. Graeme Bartlett (talk) 23:01, 20 October 2008 (UTC)

• Complete sequestration

I know, you've all heard of carbon sequestration, but this time without storing the carbon dioxide somewhere. Some sort of catacystic converter would separate the CO2 into oxygen and pure carbon, which would then be made into diamonds.

• would require too much energy to do, and burning coal to carbon dioxide and then forming pure carbon produces no energy, Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

I'm not talking about producing energy, I'm talking about removing greenhouse gases from the atmosphere. ~AH1^(TCU) 23:47, 20 October 2008 (UTC)

But the greenhouse gases are in the atmosphere because of the need to produce energy! You might end up producing more gases than you would convert. Also, it would far more useful to produce carbon nanotubes instead of diamonds. =) « Aaron Rotenberg « Talk « 12:15, 21 October 2008 (UTC)

• Methane removal

Instead of burning methane in oxygen, store them with tubes, whether it be animal gas or garbage gas or clathrate gas or permafrost gas, and burn them in an oxygen-free environment, under high pressure. The hydrogen would float off into space, and the carbon would again be made into diamonds.

• Produces no energy. You will have to look at the Standard enthalpy change of formation of methane which is negative. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

I'm not talking about producing energy, I'm talking about removing greenhouse gases, and if it requires energy then what's wrong with using renewable energy. ~AH1^(TCU) 23:47, 20 October 2008 (UTC)

Where is this reneweable energy going to come from? One of our biggest problems is that we are still outputting a lot of CO2 and other greenhouse gases from fossil fuel power stations and this is forecas to rise in a number of countries. If we could magically switch to using 100% renewable energy everywhere, we would probably have done enough that global warming is no longer a significant concern Nil Einne (talk) 04:19, 22 October 2008 (UTC)

• Filling in of sea water

It's impossible to tell by looking at the title, but there are small spaces left in the Earth's layers when oil and gas are drilled, correct? Why not direct some of the sea water into a tunnel system that works like a piston, so that the water can go down, and heat cannot go up. Next, the water would be channeled into those gaps in the Earth's layers. This, if plausible, would allow for less sea level rise.

• the space here is very small compared to the rise in ocean levels. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

• Ocean water supply

If the freshwater resources in the future are too small, and sea level rise has risen a lot, then could it be possible to get water from a bit below the surface of the sea especially near polar countries, to avoid the oil slicks and also avoid the lower salty layer, so you'd have almost fresh but slightly brackish water that would take less energy to convert?

• Under the sea surface the water is usually salty. More salty water sinks below fresh water, so any fresh water would be floating on top (temporarily). It would be easier to melt the ice to get fresh water. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

Is any of this plausible? Again, I'm not asking for opinions, just for if this might be plausible, which is a factual query. Thanks. ~AH1^(TCU) 22:46, 20 October 2008 (UTC)

Seawater is already pumped into the spaces from which oil is extracted, to force the oil out. It's really a very small amount of water. -- Finlay McWalter | Talk 22:58, 20 October 2008 (UTC)

The only one that does not require Science Fiction technology, does not violate major natural laws, and is not based based on misconceptions, is number 2 (painting). It is a minor effect, but will be somewhat amplified since you can also reduce aircon in those building.--Stephan Schulz (talk) 23:00, 20 October 2008 (UTC)

And white roofs are already widely advocated to reduce urban heating and keep buildings cool: [3]. Dragons flight (talk) 23:04, 20 October 2008 (UTC)

Number 2 is not only possible, but it has even already been implemented, although unintended. In Almeria, the widest greenhouse area in the world, they could measure a surface air temperature reduction of 0.3°C in one decade. More about it here Mr.K. (talk) 09:41, 21 October 2008 (UTC)

Physics (Electric fields)

2 charges are separated by a distance of $4.3\times 10^{-9}$ m. The force between them is $2.8\times 10^{-8}$ N

(a) What will be the force between them at separations of $8.6\times 10^{-9}$ m and $1.29\times 10^{-8}$ m? (b) The potential energy stored in the field between the charges is $1.2\times 10^{-16}$ J when they are at a separation of $4.3\times 10^{-9}$. What will be the energies stored in the field when they are at separations of $8.6\times 10^{-9}$ m and $1.29\times 10^{-8}$ m?

Ive done (a) (answer = $7.0\times 10^{-9}$ N and $3.1\times 10^{-9}$ N) but I have no idea how to do (b). Can someone help me out a bit --RMFan1 (talk) 23:19, 20 October 2008 (UTC)

The potential energy is larger if the charges are larger, and is larger if they are closer together. In fact, it is equal to a constant times the charge of one object, times the charge of the other object, divided by the distance between them. If the charges are in Coulombs and the distance is in meters, then the constant is 8.99x10⁹ Newton meter²/Coulomb², per [4]. The Wikipedia article Electric potential energy explains this in detail. The Simple English Wikipedia also explains it at [5] , but they round the constant to 9 x 10⁹. Does that help? Edison (talk) 23:50, 20 October 2008 (UTC)

Part (b) is very similar to part (a) and you should be able to do the same thing you did for part (a) (whatever that was) but using the potential energy formula instead of the force formula. -- BenRG (talk) 23:54, 20 October 2008 (UTC)

energy obeys an inverse square law. The energy will vary inversely with the square of the distance. Thus E1 * D1² = E2 * D2². The point of the first energy/distance pairing is to give you the values of E1 and D1. D2 values are given in in the second part of part (b); that makes this a one unknown equation (E2). --Jayron32.talk.contribs 00:34, 21 October 2008 (UTC)

There's a mistake in that solution, but I think the corrected version would be too close to a giveaway given this was a homework question, so I'm going to stick to this warning... -- BenRG (talk) 13:00, 21 October 2008 (UTC)

Scientific Formula

Hello, I am looking for a scientific formula relating to an experiment on this webpage: [6]. Is there an equation that allows one to use the length of the tube and the width of the tube to determine the wavelength? I hope my question is clear, thank you ahead of time. Marcus Lupus (talk) 23:44, 20 October 2008 (UTC)

read the page itself. Its there, about 1/5th to 1/4th of the way through the page. --Jayron32.talk.contribs 00:30, 21 October 2008 (UTC)