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July 4

Trivalve moluscs

Do these actually exist? It's just that I seem to remember reading something about them years and years ago somewhere... --Kurt Shaped Box (talk) 00:30, 4 July 2008 (UTC)

I see trivalves mentioned fairly often in fantasy fiction and science fiction. There's also this story about Constantine Samuel Rafinesque concerning a discovery of a trivalve mollusk, which was a joke played on him by John James Audubon. There's also a page from Google books about the incident. ~Amatulić (talk) 00:52, 4 July 2008 (UTC)

Is tungsten ferromagnetic?

I checked the article, and all it said was no data... ScienceApe (talk) 06:12, 4 July 2008 (UTC)

I am pretty sure the answer is no. Graeme Bartlett (talk) 06:48, 4 July 2008 (UTC)

No, it isn't. Though some tungsten-containing compounds are. 131.111.228.15 (talk) 07:44, 4 July 2008 (UTC)

Well I know they use tungsten projectiles in railguns, so if it isn't ferrous, then how do they propel it? ScienceApe (talk) 16:32, 4 July 2008 (UTC)

The projectile (and rails) of a railgun only need to be good conductors; no ferromagnetism required. Algebraist 16:40, 4 July 2008 (UTC)

Seems like it. Thanks. ScienceApe (talk) 17:52, 5 July 2008 (UTC)

where do herring gulls and black back gulls sleep at night?

Does anyone know what sort of places they usually sleep in? They seem to all leave the town and the local landfill area at night and all go off in the same direction. I'd like to be able to drive out and see them sleeping one night. —Preceding unsigned comment added by 84.67.233.220 (talk) 07:29, 4 July 2008 (UTC)

I believe Gulls are naturally cliff dwellers, I imagine they would roost on cliff faces if they're near the sea. For urban gulls, buildings would present a similiar landscape. —Preceding unsigned comment added by 62.25.96.244 (talk) 09:42, 4 July 2008 (UTC)

Just to note that I am not a Gull and am not called Cliff. --Dweller (talk) 15:05, 4 July 2008 (UTC)

Battery-powered microphone amplifier

Can someone suggest a battery-powered circuit for amplifying the output of an electret mike to drive a headphone (the type commonly used for portable media players)? The circuit should draw very little power, require no more than 2 AA batteries, and be buildable using easy-to-find parts. —Preceding unsigned comment added by 71.175.20.73 (talk) 11:45, 4 July 2008 (UTC)

You might look at [1], they are a huge producer of ICs and sell all kinds of audio amps. You would probably be best to purchase from [2]. Depending on your requirements, this could be a good starting point for selecting them [3]. You should know the impedance of your headphones. The data sheets of all these audio amplifiers should have sample schematics of simple circuits that you can start from. Depending on your input, you might need a preamp. It is also important to note that if it is a condenser mic, you will need to bias the microphone as well. Gjmulhol (talk) 12:13, 4 July 2008 (UTC)

On a side note, be careful about grounding. Audio signals are very sensitive to bouncing ground planes. Gjmulhol (talk) 12:17, 4 July 2008 (UTC)

"Grounding" is important, as is shielding of microphone leads, to prevent hum from influence of the powerline frequency electricity, but certainly no earth-ground connection would be needed. Edison (talk) 14:04, 4 July 2008 (UTC)

Termite control in Scarborough, Ontario, Canada

Dear Wikipedians:

Does anyone know some termite control shops that are located in Scarborough, Ontario, Canada?

Thanks.

74.12.39.232 (talk) 15:31, 4 July 2008 (UTC)

• PCO Pest Control used to sponser my T-Ball team, but a phonebook or a google are better bets. WilyD 15:34, 4 July 2008 (UTC)

Hi. Have you tried yellowpages.ca? Thanks. ~AH1^(TCU) 15:41, 4 July 2008 (UTC)

Overlapping tidal radii

Hi. On an issue of SkyNews magazine, I read that stars can have large zones where an object will orbit it, 1.5 - 15 light-years in radius. It said that the Sun's zone, called the tidal radius, is 3.5 light-years. It also said that they can overlap. This made me wonder.

The nearest star system, Alpha Centauri/Rigil Kentarus/Toliman, is 4.3 light-years away from us. If the sun's tidal radius is 3.5 light-years, I'd expect Alpha Centauri's radius to be a bit larger as it has higher total mass, say 4.0 light-years. This leaves 3.2 light-years of overlapping tidal space at the horizontal plane diametre. Well, is it plausable that AlphaCen has an oort cloud of comets, just like the sun?

I would like to know (and this is not homework, and I don't know if I'm able to calculate this):

• The volume of overlapping space, in cubic light-years;
• The number of Oort cloud comets estimated to be orbiting the Sun in that space;
• The approximate percent of the Sun's tidal sphere surface that is within the overlapping zone;

Or, is the tidal zone not a sphere, but an elliptoid, just like the Heliophere? Oh no!!! Is the spherical model a good approximation? Or is it possible to calculate the same parameters for an elliptoidical model? Would we know in which direction the tidal elliptoid extends farthest and its shape, if it is indeed an elliptoid? Why is the Heliosphere elliptoidical, does its direction change over time, what direction does it point in, does it have any effects on comets just entering the Heliosphere, and could its shape be caused by Nemisis?

Consider the known non-returning comets, with eccentricities of ≥1. Do we know any which have the open end of the parabola(/hyperbola?) pointing towards the AlphaCen direction? Might they be from/going towards the AlphaCen system? Might some be coming back? Are there any other star systems which have tidal radii overlapping ours? Three or more overlapping together? Could this explain some Oort cloud collisions that send the comets plunging towards the sun?

How will AlphaCen's negative radial velocity change this zone over time? What about Gliese...(something, forgot its number, in Ophiuchus) and Barnard's Star as they approach our Sun? Is there an article concerning the subject of orbital tidal radii (and I'm not referring to the Roche limit, which "orbital radius" redirects to)? Might this explain some extinctions?

Using current extimates, about how many comets are sent towards our sun due to the overlapping tidal zone from AlphaCen per each specified specific period of time (eg. per year, per century, per millenium, and how many actually arrive)? Or is it not possible to answer some of these questions due to limited knowledge data? Thanks. ~AH1^(TCU) 16:17, 4 July 2008 (UTC)

I've never heard of "tidal radius" before, and our article on it redirects to Roche limit, which has nothing to do with what you're talking about. The closest term to what you describe that I've heard is Hill sphere, but that's for one object orbiting another, rather than two separate stars. So, I'm not really sure what a tidal radius is meant to be (I can't see what your description has to do with tidal forces, for a start!). The maximum distance at which you can have a stable orbit around a star is going to depend on the other stars around it, and there won't be any overlap (they might go right up to eachother, though, I'm not sure if there would be a region of instability inbetween or not). It's certainly not going to be a sphere. An orbit around the sun in a plane perpendicular to the direction of Alpha Centauri could be larger than the distance to Alpha Centauri, I suppose, but one in the same plane as Alpha Centauri would be unstable if it got too close to the star. --Tango (talk) 16:47, 4 July 2008 (UTC)

A (crude) diagram used to vaguely illustrate the concept of stellar "tidal radii". ~AH1^(TCU) 01:54, 5 July 2008 (UTC)

Hi. What I (and the magazine) mean by tidal radius might have nothing to do with tidal forces. It states that close orbits around a star can be stable, but the tidal radius, according to the magazine, is, beyond which, an object will no longer be within the gravitational reaches of the star.

Within the "tidal radius", objects like planets, comets, and other bodies are close enough to the star to be able to orbit it. Beyond that distance, the gravitaional forces of the rest of the galaxy cause any object to be lost to the star's grip. It also says that wandering comets might enter the Sun's tidal radius, perhaps from another star's orbital field, and be captured by the sun's gravity and form an orbit.

I see how a star's gravitational field can be affected by other stars, but perhaps it is referring to the zone in which a minor body (and perhaps another star) can be affected by/orbit the star. It also refers it to as the "tidal limit". It also says that some stars' tidal limits can overlap. The tidal limits may, indeed, go right up to another star, but I don't think it does in the case of Sol/AlphaCen.

The magazine goes on to approximate the tidal zone as a sphere, saying Altair's stretches 30 deg across the sky. It says that some comets may have entered the tidal limits of other stars or were flung out to empty space to become "vagabonds", and that those might enter our Sun's tidal radius and possibly may have been seen from Earth, but that is speculation.

Also, some orbits of comets are not a complete ellipse, but have two parallel or angled ends, forming a parabola. My question is, might some of those parabolic comets' orbits have come from or are heading towards the orbital boundaries of other stars? What about AlphaCen in particular?

The estimate of 3.5 light-years for our Sun's tidal boundaries would suggest that an orbit leaving this zone, probably already parabolic as opposed to elliptical, would be lost from the Sun's gravitational force and become an interstellar "vagabond". If it enters AlphaCen's zone of gravitational attraction but have already exited ours, might it form a new orbit, perhaps still parabolic due to its great distance of entry, around AlphaCen?

The distances in space are great, but if say AlphaCen had an Oort cloud similar to ours, and our Oort clouds overlapped, could a select few comets be influenced by other comets' orbits and gravitational attraction, so that their own orbits end up destabilised and plunge towards one of the stars?

If a comet was heading towards or around the AlphaCen system, could Proxima, itself more massive than Jupiter and (currently) closer to us than AlphaCen itself, act like Jupiter does in our solar system, flinging comets' orbits towards AlphaCen or our own Sun? If a comet approaches AlphaCen, could interactions between stars A and B cause a star-grazing comet to act differently than one near the Sun, and have its orbit drasticly changed (if it survives)?

Also, and this is speculation: if comets were theorised to have been one of the harbingers of life on Earth, might some of those same comets, containing similar organic compounds, have survived an interstellar journey and struck a planet in another star system, producing life there? Could the same have happened to Earth, from other star systems? Thanks. ~AH1^(TCU) 01:16, 5 July 2008 (UTC)

I can't see anything to stop comets from our Oort cloud being perturbed and ending up orbiting another star, but I expect it would be very unlikely due to the distances involves (the perturbation would have to be very precise, or it would miss the other star). If this kind of thing did happen, it could possibly transfer life between stars, this is called exogenesis. However, I really don't see how the regions in which you can have stable (closed) orbits around two stars could possibly overlap - how would an object in that overlap "know" which star to orbit? If you had an object orbiting one star and an object orbiting the other such that their orbits intersect at one point, their apoapsis (further distance from the star they are orbiting), directly between the two stars. Then, at that intersection point, both objects would be travelling in the same direction (perpendicular to both stars), although possibly at different speeds. One object would then need to fall towards one star and the other towards the other star, but why would they go in different directions if they started out going in the same direction? The objects could "choose" to fall towards either star, so the orbits would be unstable. --Tango (talk) 01:32, 5 July 2008 (UTC)

convert -

A hole guage of 10-32 -> diameter(inches) —Preceding unsigned comment added by 75.60.90.55 (talk) 19:50, 4 July 2008 (UTC)

I'm assuming that 10-32 is refering to a screw size. Take a look at [4] for dimensional information. -- Tcncv (talk) 20:02, 4 July 2008 (UTC)

Or here: Unified Thread Standard. --Heron (talk) 21:02, 4 July 2008 (UTC)

Simple mechanics.

Let's say there's a stick lying on the ground and I kick it. Well depending on where I hit it and at what angle, the stick will gain some linear momentum and some angular momentum. If I always kick it staight on (i.e. perpendicular to the stick), then only the position matters. So my question is, how can I determine how much angular and linear momentum the stick will possess as a function of the kick's position? Now I gave this question a shot, and my guess is that because the stick has a bit of thickness, the angle between the force and the radius of rotation changes depending on rotation, and that product of the sin of the angle and the force would give the angular acceleration and so on. Is this right? A second and somewhat related question, why does the stick always spin around the center? —Preceding unsigned comment added by 65.92.4.238 (talk) 22:43, 4 July 2008

This is actually a bit difficult to work out (and easily confuses me still)

Basically it depends on amongst other things, the way the weight in distributed in the stick, I'll assume that the stick is straight and has equal thickness - so that the weight is evenly distributed along the length of the stick.

You can work this out using newtonian mechanics, you need to know about conservation of momentum, conservation of angular momentum (see also torque)

Let's say the stick is L long and you kick it at distance d from the middle (ie d<L/2)

(You also need to be able to calculate the Moment of inertia of the stick by integration, this is in fact mL²/12 (from List_of_moments_of_inertia) IF you want to calculate the exact numbers)

Suppose your kick at distance d gives an impulse 'S' to the stick, this impulse can be split into rotational and translational (straight line) momentums..

Assuming that the stick rotates about the centre for simplicity.

The rotational momentum can be viewed as one end of the stick moving forwards at speed V2 and one end moving backwards at speed V2, the translational motion can be viewed as the stick moving at speed V1 from the middle (combining all these gives the overall motion)

The linear motion is therefor mV1 (m is the mass of the stick) (ie the momentum)

The speed of rotation about the centre is given by V2=L/2 x A (A is the angular speed of rotation in radians per second.

The rotational torque is given by speed of angular rotation x angular moment of inertia = A x m x L² /12

since A = 2 x V2/L the torque = V2 x m x L /6

If you supplied an impulse of 'S' to the stick at distance d the torque about the centre was S x d

So S x d = V2 x m x L /6

and S = mV1

So m x V1 = V2 x m x L /6d

ie rearanging gives V1/V2 = L/6d

This means the ratio of the angular speed and linear speed can be calculated and it depends on how far from the centre it was kicked.

Additional work gives a general formula for collisions of two objects using similar methods.

(Apologies for any mistakes I've made whihc I'm sure other will point out..) The method is similar to what I've tried to describe above.87.102.86.73 (talk) 01:46, 5 July 2008 (UTC)

Your second and related question is one I find difficult to explain.. BUT if you consider the stick mentioned above, and consider it rotating about somewhere other than the centre of mass - you'll find that the stick would be violating the 'laws of conservation of momentum' since it's centre of mass would be moving about.. there for its momentum would be changing over time without an external force (ie newtons law that a body moves in a straight line unless acted upon by another force - in this case the body would be effectively 'spiraling about a point') - in general if you try to make a stick do this it will tend to rotate about it's centre and any extra speed will simply turn into linear momentum. Sorry if I haven't explained that very well.87.102.86.73 (talk) 01:52, 5 July 2008 (UTC)

Bounce

Why does a ball bounce when it hits the floor? —Preceding unsigned comment added by 65.92.4.238 (talk) 22:44, 4 July 2008 (UTC)

When it impacts the floor, it deforms by flattening at the bottom, this absorbs the kinetic energy of its motion and converts it into elastic potential energy. That elasticity then causes the deformation to undo, the ball returns the being spherical and is propelled upwards. Does that help? --Tango (talk) 23:27, 4 July 2008 (UTC)

Why does a steel ball bounce higher than a tennis ball when the tennis ball deforms more then? --antilived^{T | C | G} 01:15, 5 July 2008 (UTC)

Because more energy is lost to heat and sound when the tennis ball deforms and reforms than when the steel ball does. I'm not really sure why... --Tango (talk) 01:34, 5 July 2008 (UTC)

I have never seen a steel ball bounce higher than a tennis ball... Plasticup ^T/C 03:47, 5 July 2008 (UTC)

You haven't bounced it on the right surface. Try bouncing it off of another piece of steel. Someguy1221 (talk) 09:38, 5 July 2008 (UTC)

There's an excellent demonstration of this at the Exploratorium. There, the steel ball bounces off a very large piece of steel and each bounce of the ball is nearly as high as the previous bounce (so very little energy is being lost on each bounce).

Atlant (talk) 20:55, 5 July 2008 (UTC)

Or off another steel ball, as in the Newton's cradle. There's a good reason why they make those things out of steel balls and not tennis balls - steel is more elastic than a rubber bladder. --Heron (talk) 13:41, 5 July 2008 (UTC)

Okay cool. So theoretically, an object which is perfectly rigid would not bounce, right? —Preceding unsigned comment added by 65.92.4.238 (talk) 04:09, 5 July 2008 (UTC)

That's an excellent question. I think it depends on how you take limits. A "perfectly rigid" body should have an infinite elastic modulus, because it never has any strain, regardless of its stress. So one logical way to end up with a "perfectly rigid" body is to take an elastic body and let its elastic modulus go to infinity. When this body is at rest on the ground, the gravitational potential energy it started out with is completely in the form of elastic energy, which I believe is ${\frac {1}{2}}\,{\text{stress}}\times {\text{strain}}$. If the elastic modulus continues to increase, the stress must also increase to keep the elastic energy the same, so our "perfectly rigid" body would end up having infinite stress (in order to have a finite elastic energy with zero strain). If you accept this, then the body should bounce perfectly elastically (i.e. it should return to the same height it was dropped from and never lose any energy), because inelasticities are caused by strain. —Keenan Pepper 05:23, 5 July 2008 (UTC)

An alternative way of looking at this would be to say that a perfectly rigid body has no way of absorbing/losing the energy on impact (since it cannot deform)- therefor it would bounce perfectly.87.102.86.73 (talk) 12:07, 5 July 2008 (UTC)

For illustration, see the ball bouncer demonstration in the references of the Liquidmetal article, showing how steel balls bounce against three different materials: steel, titanium, and a metallic-glass compound called LiquidMetal. =Axlq 18:11, 5 July 2008 (UTC)

From Collision: "Collisions can be elastic, meaning they conserve energy and momentum, inelastic, meaning they conserve momentum but not energy, or totally inelastic (or plastic), meaning they conserve momentum and the two objects stick together." I'm not sure what perfectly rigid would mean, but the type of ball that doesn't bounce at all is called totally inelastic (the energy is absorbed by making the floor move down). --Tango (talk) 12:27, 5 July 2008 (UTC)

Well not really. The ball could have collided with the earth in a perfectly elastic manner, but the mass of the earth made its movement imperceptible. —Preceding unsigned comment added by 65.92.4.238 (talk) 17:02, 5 July 2008 (UTC)

It's not actually possible for something perfectly rigid to exist. Because of that, it's impossible to say what would happen if it did. If you were to magically fix the atoms in position with relation to each other, the electron orbitals in the atoms would distort as they get closer, so the atoms themselves wouldn't be perfectly rigid. If you were to throw two such bodies against each other, my best guess is that the enormous pressure would cause the two bodies to pass through each other somewhat, and the parts inside each other would be forced in every direction, canceling it out. The circle where the two surfaces overlap would still exert a huge pressure and force the two apart. More simply, they'd bounce off of each other perfectly elastically and extremely quickly, but still slowly enough that for a short time, they'd be partially inside each other. If only one body was "perfectly rigid" as I defined it, I have no idea what would happen. If you want to make the object more rigid by not having the electron orbits distort, their waveforms would take up the whole universe, and the Pauli exclusion principle would mean that no electron could have the same state as any in the rigid body, and they couldn't be the same as each other. Besides the ridiculously high energy states of the electrons this would require, it would also mean that said principle wouldn't be keeping the atoms from occupying the same space, so the rigid body probably wouldn't have any resistance from falling through the ground. Disclaimer: I'm not only not a physicist, but I only just finished high school, and the physics I learned there really doesn't apply here, so don't be surprised if I'm wrong. — DanielLC 16:29, 5 July 2008 (UTC)

Just because it can't exist, that doesn't mean we can't address the question. Usually when we deal with things like objects bouncing, we focus on the arangement of atoms indirectly by assigning certain constants, which were determined experentally, and don't take quantum mechanichs into account, just like we may, in classical mechanics, we cometimes treat an object as a single point, even though that would violate Heisenberg's uncertainty principle. So what my question is really asking is, using the laws of physics that we normally use to adress such phenomena as bouncing, how would a perfectly rigid body act? —Preceding unsigned comment added by 65.92.4.238 (talk) 17:13, 5 July 2008 (UTC)

A perfectly rigid body also cannot exist from the standpoint of Special Relativity. When one part of the ball is accelerated/stopped by the collision, the information of the collision cannot travel faster than the speed of light to other parts of the ball, so they cannot stop immediately. Icek (talk) 16:12, 7 July 2008 (UTC)

Relativity and communication speed

If a spaceship traveling at near light speed were equipped with a radio-wave Internet connection, how would special relativity affect measurements of its bandwidth and latency? NeonMerlin 23:05, 4 July 2008 (UTC)

The latency depends on the distance. As the latency changes quickly, the time-out would need to be rather large or change with the predicted distance of the spaceship.

If the spaceship travels towards Earth, then the bandwidth is larger, if it travels away from Earth, the bandwidth is smaller (see Relativistic Doppler effect). This just means that the spaceship traveling towards Earth will receive the bits at a higher rate, and the one traveling away from Earth will receive the bits at a lower rate. Icek (talk) 07:48, 5 July 2008 (UTC)

July 5

Houdini exhumation

I followed the story of the proposal to exhume Houdini's remains. Some of his relatives wish to examine his remains to confirm whether or not he was the victim of arsenic poisoning, while others object to the exhumation. The latest information I can find dates from March, 2007. Joseph Tacopina represented the pro-exhumation faction then, but I would like to know who prevailed. Does anyone have current status on this case?Avid Djinn (talk) 00:08, 5 July 2008 (UTC)

Not exhumed as of 2008-03-04 according to:

Costella, Annmarie (2008-03-04). "Houdini exhumation to test for poison". NYDailyNews.com. Retrieved 2008-07-05. they have yet to file court papers to have Houdini's body exhumed.

-- Jeandré, 2008-07-05t18:26z

Future Indian Ocean Earthquake

Hi. Will there be another possible Indian Ocean Earthquake like the 2004 Indian Ocean Earthquake in the future? When will it happen again? What will be the possible magnitude of another future Indian Ocean earthquake? Sonic99 (talk) 00:52, 5 July 2008 (UTC)

It's not known. Earthquake prediction is poor. PrimeHunter (talk) 01:10, 5 July 2008 (UTC)

Hello again there Sonic, take a look here for some insight. ;-) -hydnjo talk 01:12, 5 July 2008 (UTC)

The answer to the first question is yes. There will be another very large earthquake on that fault eventually. Whether it will be tomorrow, next year, next decade, or 5000 years from now is largely impossible to predict. Dragons flight (talk) 01:45, 5 July 2008 (UTC)

According to Nature (journal), the recent earthquakes did not sufficiently release the accumulated fault strain and there is still the possibility of a magnitude 9.0 quake. The fault ruptures every 200-230 years and there is a 200-km zone that has not ruptured since 1797, so do the math.

Furthermore, it now appears that the active fault extends northward along the coast of Burma up to the coast of Bangladesh, and large quakes there would produce devastating tsunamis in the Bay of Bengal.

That said, the comments above about trying to predict exactly when an earthquake will strike are quite valid. (Although I did just read something interesting about using increased neutron flux for short-term prediction [5]). Franamax (talk) 22:59, 5 July 2008 (UTC)

Antarcticine

can anyone tell me more about this glycoprotein in terms of anti-aging? I have googled it but cannot find a suitable answerSwinstarr (talk) 02:46, 5 July 2008 (UTC)

There's a good bit of information in this article. Someguy1221 (talk) 09:34, 5 July 2008 (UTC)

Metrication in Greece

According to an 1866 report in the US House of Representatives, "Greece has introduced [the metric system] with some modifications." - I'm wondering what exactly these modifications are. It'd also be interesting in general to have more information about the history of metrication in places other than France and English-speaking countries. --Random832 (contribs) 07:33, 5 July 2008 (UTC)

For Greece, see Konstantinos Nikolantonakis' "Weights and measures: the Greek efforts to integrate the metric system" from section 5.1. For Italy, Spain, Portugal, and the Netherlands see the abstracts and PDFs at the 2nd International Conference of the European Society for the History of Science, Symposium R-8 pages. -- Jeandré, 2008-07-05t18:11z

Spin

Do electrons actually spin?? where does the intrinsic angular momentum value come from? —Preceding unsigned comment added by 116.68.73.39 (talk) 07:58, 5 July 2008 (UTC)

No one knows. Their electromagnetic properties (charge, magnetic dipole moment, conservation of angular momentum during particle interactions, etc.) exhibit behaviors similar to what a spinning macroscopic object with a non-zero charge distribution would produce, which is I believe why that characteristic is called "spin". --Prestidigitator (talk) 08:46, 5 July 2008 (UTC)

Overview of spin might be of interest. Jdrewitt (talk) 11:13, 5 July 2008 (UTC)

Some hold the view that the 'spin' is not in any way equivalent to a rotation, but is in fact comparable to a chirality of the electron - the two spins being equivalent to 'left' and 'right handed versions' of the particle.87.102.86.73 (talk) 12:35, 5 July 2008 (UTC)

Electrons have zero size but non-zero angular momentum. This is weird. Make your own mind up about what to call it. "Spin" seemed like a good word at the time. -- Tim Starling (talk) 13:35, 5 July 2008 (UTC)

Then how/why is the Classical_electron_radius defined? Jdrewitt (talk) 15:43, 5 July 2008 (UTC)

It answers how and why in that article you just linked to. — DanielLC 15:53, 5 July 2008 (UTC)

Well I wouldn't say it answers exactly how and why (at least why r_e isn't defined) but then that's quantum mechanics for you! Jdrewitt (talk) 15:58, 5 July 2008 (UTC)

Classical electron radius is a useful characteristic length for the extent of the electric field around an electron. However, the mass and charge of the electron is concentrated at a point at the centre. Models for the electron involving a distribution of charge have been rigorously disproven. Under classical electrostatic theory, this leads to the rather embarrassing result that an electron has infinite electric potential energy. Solving this problem was one of the early challenges for quantum electrodynamics. -- Tim Starling (talk) 00:17, 6 July 2008 (UTC)

Quantum numbers

I've learnt about quantum numbers describing electrons, but are there quantum numbers for other particles(fermions, in particular)? If they have spin, there must be other quantum numbers too. If so, how are they different from those of the electrons? —Preceding unsigned comment added by 116.68.73.39 (talk) 08:02, 5 July 2008 (UTC)

The quantum numbers you refer to come about from the wave equation for an electron "orbiting" the nucleus of an atom. There will be quantum numbers describing any particle in any kind of potential, but there may not be the same number of them and they may not take on the same values. Some quantum numbers (such as spin) do seem to be intrinsic to the particle though. The quantum number and spin (physics) articles may be a good place to start learning. --Prestidigitator (talk) 08:59, 5 July 2008 (UTC)

Can crouching, breathing deeply, rising quickly lead to fainting?

Is this an old wives' (or young high schoolers' :-) tale or not? Someone at school said if you bend your knees in a crouch, take bout 15-20 deep breaths, then try to stand up quickly, you pass out. Do you?

Either way, exactly what problems can this cause? I was tempted to try taking 20 deep breaths like that, then lay down from that position one night but even that I was too scared to do, just in case. Would that have caused a problem.

And, in case, there is anyone else reading this - please be like me, don't try it at home.209.244.187.155 (talk) 15:11, 5 July 2008 (UTC)

Finally fixed my edit - sorry for the apparent incompetence :-)

Anyway, I would think it might, by inhaling and exhaling deeply 10-20 times, you relax the muscles enough that they become too weak to supprt you right away, but aside from fainting I'm not sure there would be any other problem, unless you hit your head on something.

Still, I agree - NEVER do that.Somebody or his brother (talk) 15:14, 5 July 2008 (UTC)

Hi. Have you read our article on brownouts? Thanks. ~AH1^(TCU) 16:10, 5 July 2008 (UTC)

I think this is similar to the choking game. --Mark PEA (talk) 17:26, 5 July 2008 (UTC)

This sounds like nothing to be worried about, but you might find Orthostatic hypotension and Hyperventilation interesting reads. Even if this did cause you to black out, I'd be more concerned about hitting your head when you collapsed than from hypoxic brain damage. --Shaggorama (talk) 00:40, 6 July 2008 (UTC)

I tried it inbetween the corner of two walls and a cushion. I crouched on the balls of my feet and bent to where I could keep my balance with my fingertips on the cushion and took 20 deep breaths, each of 2-1/2 to 3 seconds inhaling and 2-1/2 to 3 seconds exhaling. I felt a little faint at times breathing and when I was done I stood up quickly and felt very faint, particularly for the first couple of seconds after standing, but I didn't fall or feel in danger of falling. I came directly here to type this and I still don't feel entirely un-faint. I'm 25, male, and in average-good shape. -LambaJan (talk) 17:13, 6 July 2008 (UTC)

wow...uh, thanks for taking one for the team, I guess. Be safe. --Shaggorama (talk) 04:19, 7 July 2008 (UTC)

I doubt the breathing has all that much to do with it in terms of oxygen intake -- as Shaggorama said, it's probably just a form of head rush. Speaking as a non-doctor, I'd assume that the deep breathing serves to lower your heart rate and generally calms you down, which also lowers your blood pressure. When you get up quickly, hey, it's orthostatic hypotension time, baby! A comparable thing has happened to me once or twice. In one memorable instance, I was expecting a really important phone call and took a nap, and when the phone rang, I woke up and immediately dashed out of bed. I remember taking a couple of steps and heading for the phone, and then the next thing I knew, I came to on the floor feeling kind of nauseous and with the phone on my hand, evidently immediately after passing out, as the caller didn't even realize that anything out of the ordinary had happened. (I don't think I'm particularly susceptible to it, really, but I've certainly learned to not just spring on my feet as quickly as I can when I wake up.) -- Captain Disdain (talk) 12:02, 7 July 2008 (UTC)

electromagnetic force uses photons as a mediator

is this saying that when I play with magnets there are photons being exchanged?

How about when I play with built-up charges in a Van de Graaff generator? —Preceding unsigned comment added by 71.147.33.238 (talk) 16:15, 5 July 2008 (UTC)

From my shaky understanding:

• When you play with magnets, you are moving a magnetic field, no photons are being exchanged per se. If your magnet causes electrons to move in a conductor, the moving electric charges will cause an electromagnetic field to emanate, this is propagated by photons.
• Similarly, with a VdG generator, you are creating an electrostatic field, again no photons involved. When you ground the generator though, lets say through a spark gap, you can hear it on a radio - again, moving electric charges generate an electromagnetic field which propagates through space by means of photons which eventually strike the radio antenna and cause electric charges to move there.

Don't know if that makes it clearer and I welcome any other views on this. Franamax (talk) 20:12, 6 July 2008 (UTC)

The current standard-advanced-physics view is that the electromagnetic force (that is both electricity and magnetism) is mediated by virtual photons. That is, when two particles interact via the electromagnetic force (e.g attract/repel each other) a virtual photon is traded between them, and it is this virtual photon which carries the energy and momentum between the two particles. Feynman diagrams are one way to visualize the process. Virtual photons are different from regular photons in that they are (literally) living on borrowed time, and can't be detected directly. In some sense they're a convenient fiction, but one which works remarkably well (that is, the world acts like it should if virtual photons existed). I'd encourage anyone interested in the topic to read QED: The Strange Theory of Light and Matter by Richard Feynman. It is a remarkable well written and understandable book. -- 128.104.112.147 (talk) 20:09, 10 July 2008 (UTC)

Why do s-orbitals always take part in hybridistion?

In hybridisation of atomic orbitals, why do s-orbitals always take part?Ashudeep2singh (talk) 16:54, 5 July 2008 (UTC)

Hybridization leads to stabilization: if s overlaps p, the s electrons go down in energy (see LCAO). But more philosophically, why not? No seriously...the s orbital is spherically symmetric, so no matter what direction you look (i.e., the directional orbitals (p, d, etc) with which you might hybridize), there is electron-density there in the s. An s orbital can constructively overlap with p, d, etc because it is in the same place, and electron delocalization is a good thing. DMacks (talk) 18:52, 5 July 2008 (UTC)

To expand on that - when constructing a bonding orbital, it is impossible to ignore the s orbitals because they are spherically symmetrical.. you could imagine a p³ orbital instead of a sp³ orbital - but anything that bonds to that p³ orbital would probably have significnt orbital overlap with the relevent s orbital as well..

However in construction of say sp² orbital you will note that the other orbital that remains is a single p orbital.. in this sense this gives an example of a hybridised set of orbitals in which one orbital does not contain s 87.102.86.73 (talk) 10:09, 6 July 2008 (UTC)

Platypus evolution

Regarding the platypus, according to this, http://en.wikipedia.org/wiki/Platypus#Evolution it seems the platypus contains some genes that are more similar to birds. This I found unusual because mammals evolved from Synapsids, and not birds, which evolved from true reptiles. So basically I'm asking how do you explain this similarity with birds, when mammals did not evolve from birds?

I would also like to know what kind of sex chromosomes reptiles have. The article said, "the sex chromosomes of the Platypus are more similar to the ZZ/ZW sex chromosomes found in birds.", well if amphibians and reptiles don't have those chromosomes, then that would raise a lot of questions about what platypus evolved from. The article in Nature said that the platypus shares two genes found previously only in birds, amphibians and fish. I'm not sure if they are referring to the sex chromosome though. But even if they are, they are insinuating that reptiles don't have those sex chromosomes. Well that's strange because birds evolved from true reptiles and not synapsids which probably did have those sex chromosomes. If reptiles don't have those chromosomes, well it raises a lot of questions. ScienceApe (talk) 17:51, 5 July 2008 (UTC)

Well, I think the point is that the platypus diverged from the rest of mammals very early on. My guess is that the genes in question that are no longer found in any other mammals probably have to do with the egg laying aspects, etc. To my mind the issue is not "what the platypus evolved from" but "what did the very early mammal genome look like?" It seems not unreasonable to me that it could contain all sorts of elements in it that were quickly filtered out (through a number of possible issues, like founder's effect) but the monotremes seem to have skipped out on the big filter. But this is just speculation. --98.217.8.46 (talk) 19:15, 5 July 2008 (UTC)

That doesn't really address the concerns I mentioned. In particular the sex chromosomes reptiles have. ScienceApe (talk) 23:41, 5 July 2008 (UTC)

I don't know much about sex chromosomes and evolutionary lineages but according to ZW sex-determination system, it's found in birds, fish and insects. It also mentions "Chromosomes in the ZW region in birds are autosomal in mammals, and vice-versa; therefore, it is theorized that the ZW and XY couples come from different chromosomes of the common ancestor. A paper published in 2004 (Frank Grützner et al, Nature; doi:10.1038/nature03021) suggests that the two systems may be related. According to the paper, platypuses have a ten-chromosome–based system, where the chromosomes form a multivalent chain in male meiosis, segregating into XXXXX-sperm and YYYYY-sperm, with XY-equivalent chromosomes at one end of this chain and the ZW-equivalent chromosomes at the other end." Sex-determination system is also helpful It sounds to me like platypuses have both ZW like and XY like sec chromosomes. My guess is that this is similar to their ancestors including their last common ancestor with birds. Birds eventually moved to ZW exclusively as did some fish and insects. Mammals moved to XY exclusively. Reptiles largely lost this completely and depend on temperature. I presume the journal article will provide a lot more answers. Don't forget to consider convergent evolution in any thoughts you have. Also do remember that modern true reptiles, even those considered living fossils like the tuatara are not the last common ancestor of birds, not even close (recent taxonomic and molecular work has shown that they have changed significantly since the Mesozoic era) Nil Einne (talk) 17:36, 6 July 2008 (UTC)

Evolution of sex may be helpful too Nil Einne (talk) 17:42, 6 July 2008 (UTC)

The LHC and the end of the world

Recently, someone asked here whether or not the Large Hadron Collider would cause the end of the world. Our answer was, of course, inconclusive but if you're keeping track, you can at least find the minimum value of how much longer we have here. Just FYI...

Atlant (talk) 21:00, 5 July 2008 (UTC)

Personally, I'm convinced the continued failure of the LHC to go online is a global example of quantum immortality ;-) Someguy1221 (talk) 21:18, 5 July 2008 (UTC)

Hi. Um, I thought the website said it was going up tomorrow, but now it has apparently been moved to next month, what's going on? Thanks. ~AH1^(TCU) 23:40, 6 July 2008 (UTC)

What the hell is going on here!?

Quantum gravity, quantum black holes, quantum chemistry (?!!). gravity bends time (and is really just acceleration), multiverses, etc., etc., etc. The world of the big and the small is just so mentally.....megawhelming! Please, -someone help me get a grip!--THE WORLD'S MOST CURIOUS MAN (talk) 21:32, 5 July 2008 (UTC)

Quantum gravity, quantum black hole, quantum chemistry, general relativity, multiverse...You'll really have to ask a more specific question if you want us to help you find an answer. Someguy1221 (talk) 22:04, 5 July 2008 (UTC)

Quantum theory in general? Fribbler (talk) 22:59, 5 July 2008 (UTC)

Instrumentalism might make you feel a little more comfortable as a way of reading scientific theories. Or less. I think it was Steve Martin who said that, "College philosophy teaches you just enough to really fuck you up." --Shaggorama (talk) 00:33, 6 July 2008 (UTC)

From a purely corporate point of view I can tell you that these scientists can "suck my ./..", when a scientific realm has products you can buy then I'd worry if I didn't understand, and maybe take notice of what they were saying.

Hope that helps with your 'megawhelmedness', capitalism loves you, and protects...87.102.86.73 (talk) 16:12, 6 July 2008 (UTC)

Seriously though there probably is name for the point of view of 'show me something that works', probably not a popular point of view in some circles... Good luck!87.102.86.73 (talk) 16:13, 6 July 2008 (UTC)

Better not go for an MRI then, you might come face to face with the quantum device that makes it work, then you'll have to come back here and strike-through your post. Franamax (talk) 20:04, 6 July 2008 (UTC)

Or use GPS, which requires those pesky "gravity bends space and time" corrections. --Stephan Schulz (talk) 22:01, 6 July 2008 (UTC)

Or use a working device using quantum entanglement for secure distribution of encryption keys. [6] Heck, you might even be able to buy shares someday! Franamax (talk) 23:16, 6 July 2008 (UTC)

The above would be of use if I were sick, lost and paranoid.. What if it want butter on the other side of the bread?87.102.86.73 (talk) 14:01, 7 July 2008 (UTC)

Well, you could spread it on the wrong side and hope for quantum effects to redistribute it as desired. Or you could just put the butter next to the bread and hope for the best. Better get an XXL Finite Improbability Generator, or you might be in for a long wait. --Stephan Schulz (talk) 14:08, 7 July 2008 (UTC)

July 6

Colorado 14ers

I am curious about Colorado peaks. How many are there over fourteen thousand feet high? I have seen many different numbers, most of them in the fifties. —Preceding unsigned comment added by 75.169.1.13 (talk) 00:28, 6 July 2008 (UTC)

Here's the list of them. See also a WP list. Oded (talk) 01:05, 6 July 2008 (UTC)

Trans Ischemic Attack - same symptoms as stroke in sever cases?

Reading elsewhere, it seems like a transient ischemic attack is only a warning and brain cells don't actually die. Yet, your article speaks of TIAs that can last more than 10 minutes, and seems to say that brain cells do die. So, would the same things as mentioned in stroke apply when it comes to symptoms and treatment, then? In other words, can one experience weakness afterward, maybe periods of aphaxia where one can't talk for a few minutes at a time, etc.? Would rehabilitation be needed even with a TIA or series of them, even if there was no actual stroke that occurred?

Side question - can one be paralyzed on both dies of the body with a TIA/stroke? My hunch is "yes," if in the right place.

I guess it's one of those thigs that will really only be helped once the TIA article grows.209.244.30.221 (talk) 00:35, 6 July 2008 (UTC)

Yes and yes. TIA is code for "Minor stroke." The key is "transient." A stroke is ischemia caused by a thrombus (blood clot) in the brain that often requires thrombolytic therapy to be corrected and may cause permanent brain damage if not treated in time. The difference between a stroke and a TIA is that in a TIA, the thrombus often dislodges itself before serious damage occurs. Sometimes not. A TIA that causes damage is basically a stroke that treated itself, but a little late. Usually if there's any serious damage, they call it a stroke instead of a TIA. --Shaggorama (talk) 02:22, 6 July 2008 (UTC)

The difference between a transient ischemic attack and a stroke is the duration. If the symptoms last less than a day, what happened was a TIA; if longer, it was a stroke. They can't be told apart until the 24 hours passes. By definition, though, if the symptoms have disappeared within 24 hours, then there is no residual deficit after that time. A TIA by definition doesn't need rehabilitation, because the neurologic symptoms have disappeared. - Nunh-huh 02:27, 6 July 2008 (UTC)

This reputable link may help. [7] Richard Avery (talk) 07:39, 6 July 2008 (UTC)

I liked your link so much I edited the article to reflect the info. Thanks Richard, and don't be afraid to be bold. --Shaggorama (talk) 08:32, 6 July 2008 (UTC)

Thanks, all, great article; that really helped. —Preceding unsigned comment added by 209.244.187.155 (talk) 10:50, 6 July 2008 (UTC)

brilliant blue fcf

What is the meaning of fcf in "brilliant blue fcf"? What is fcf stand for in the colouring agents, e.g. in Brilliant Blue FCF, Sunset Yellow FCF. Gcllau (talk) 04:04, 6 July 2008 (UTC)

food coloring something (anon cmt)

FCF doesn't google all that well. I'm going to guess that it's "Food Colouring Formula". Franamax (talk) 05:11, 6 July 2008 (UTC)

Wow there isn't much out there, although I vaguely remember having the same question during a chem lab. All I can find is "Food Contact Formulation" (found at the bottom of here). If you search google for that, one of the summaries lists "fast green food contact formulation", and there is indeed a Fast Green FCF. Hope it helps --Bennybp (talk) 05:52, 6 July 2008 (UTC)

Unexplained Magnetic Phenomenon - Childhood question

Why only, Burnt Matchstick Heads get attracted to a magnet and not unburnt ones. What chemicals are produced after burning that are magnetic in nature and why.
I used to try these scenarios -

1) Matchsticks with heads attached (Wax Paper sticks and Wooden ones).
2) Only Matchstick heads without sticks.
3) Matchstick Heads crushed to fine powder.(To see if weight effects it)

-In all cases only burnt up material got attracted to the magnet.

Regards praneel (talk) 04:19, 6 July 2008 (UTC)

Unable to confirm. My strike-on-box matches seem to be unmagnetic both before and after they are burned. Perhaps you can be more specific as to brand/type and testing procedure? Dragons flight (talk) 04:34, 6 July 2008 (UTC)

I forgot the mention this important thing. You have to let the matchstick burn for a while (up to the middle)and gently remove the burnt head from the Burnt Stick with tweezers. Make sure you do it so gently that no burnt wood is left inside the head. This reduces the weight of the head Otherwise it won't work if you put off the flame just after you lite the match.

I went to the market and bought all available brands and did the experiment. Regardless of brand all burnt heads (removed from the burnt stick)are attracted by the magnet. I think I can shoot this video and give that link here. If you want quick results you can remove the head before burning (easy with wax paper matchsticks) or scrape off the powder in chunks as large as possible without any specs of wood. Then burn them.praneel (talk) 05:33, 6 July 2008 (UTC)

None of the active ingredients in a match head, as listed in our Match article, would become ferromagnetic when burnt, but perhaps your matches contain an impurity such as iron (III) oxide (plain old rust). Iron oxide is not ferromagnetic, so an unlit match containing it would not be attracted to a magnet. However, when a match burns, it releases carbon and carbon monoxide [8], both of which are reducing agents. These would reduce the iron oxide to pure iron, which is ferromagnetic and would be attracted to your magnet. Just a guess. --Heron (talk) 10:51, 6 July 2008 (UTC)

Note that Gamma ferric oxide is indeed ferromagnetic. It what youve got coating your old cassette tapes! —Preceding unsigned comment added by 79.76.248.187 (talk) 19:09, 6 July 2008 (UTC)

Evolution of Evolution

• Can evolution evolve ?
• Can it evolve faster or slower ?
• Can it choose to briefly suspend itself ?
• Can it build on notions of constructivism ?
• Can it sustain bio-diversity and climate change ?
• Can evolution explain the golden number ?

- 69.157.240.224 (talk) 04:24, 6 July 2008 (UTC)

No - no - no - no... All of your questions are based on the terrible (but popular) misconception that evolution has some form of intelligence. Evolution is nothing more than a process. Considering evolution of species, it is a description of how species become different over time primarily based on genetic drift and survival of the fittest. Discussing "evolution of evolution" would require redefining evolution to have some attributes which can evolve. Since evolution doesn't have attributes which evolve, it cannot speed up, pause, or build up any notions. When it comes down to it, your understanding of this will dramatically increase if you look at it from the complete opposite way. Species evolve - even if they are incapable of comprehending what evolution is. The rate at which species evolve is not easy to measure because it happens by chance, not design. Species cannot stop evolving because that would require both a lack of genetic mutation and a perfect fit into the environment that cannot be improved. Species do not evolve on purpose. Giraffes did not get together and vote on how long their necks should be. So, any notion of purpose for evolution is ridiculous. Because species evolve, the total of species changes to better fit the environment. The environment changes, so the species evolve to fit it better. This is ongoing and does not change. The total sum of bio-diversity increases and decreases with environmental changes, but (to my knowledge) has never decreased to one and only one species. Evolution has nothing to do with the golden number. In fact, you can pick any number you like (such as 42) and find that it pops up all over nature. Trying to draw causation from coincidence will lead to nothing but folly. -- kainaw™ 05:04, 6 July 2008 (UTC)

Well, on the "faster or slower" question, it depends what you mean by it. Mutations can spread much more rapidly through a population under some circumstances. For example, if the population is very large and has a lot of diversity, mutations don't spread very quickly—you get regression to the mean. If, however, you end up with a population bottleneck, then suddenly your entire population can end up with a given mutation quite rapidly. The idea that evolutionary change happens in "spurts" rather than just gradually at a constant pace is known as punctuated equilibrium. It's not "faster" in the sense you probably mean though—the popular idea that if you "speed up" evolution you'll get some sort of result. What it means is that traits spread to populations quicker. --98.217.8.46 (talk) 14:49, 6 July 2008 (UTC)

A species can evolve traits that increase or decrease the rate of mutation. It can evolve its preferences for sexual selection. Do those count as evolution evolving? Evolution is required to sustain biodiversity. As for climate change, see Daisyworld. Nothing physical can effect anything mathematical, like the golden ratio. Evolution might be able to explain why people care about the golden ratio, or why it occurs so often in nature, but not the number itself. — DanielLC 15:30, 6 July 2008 (UTC)

• Can evolution evolve ? - Sort of, see the folowing responses.

• Can it evolve faster or slower ? - Yes, both due to changes in the environment and possibly due to changes in the species itself. Sexual reproduction, for example, seems to increase variation in offspring to bring about more rapid adaptation. Some species also appear to have a much high rate of mutation than others. More mutation is better in that it makes for quicker evolution but bad in that more offspring are "defective". Thus, species with many offspring are able to benefit from higher mutation rates without losing a critical number of offspring.

• Can it choose to briefly suspend itself ? - No.

• Can it build on notions of constructivism ? - No, although you may have to explain what you mean better here.

• Can it sustain bio-diversity and climate change ? - If you mean does evolution lead to bio-diversity and species which can survive climate change, then the answer is yes.

• Can evolution explain the golden number ? - I doubt it. StuRat (talk) 19:03, 6 July 2008 (UTC)

If the rate at which evolution occurs can change, "Evolution" doesn't consciously change that rate. That's a bit like saying that "Rain" consciously decides whether to rain more heavily or not.

I blame the creators of Heroes and X men (and the like) for giving children a false impression of what evolution is. I wouldn't mind if creators of fiction were banned from using the word "evolution" unless they used it to describe Biological Evolution as explained in that article. Zain Ebrahim (talk) 12:42, 7 July 2008 (UTC)

That is why I said "no, no, no..." Evolution is nothing more than a word used to describe a process. It is not a living, thinking, planning thing. It has no speed. It has no purpose. This question is no different than asking "Does the Dewey decimal system speed up or slow down?" The only way to provide an answer is to redefine evolution as having some sort of speed or attribute of evolution itself. Once you redefine evolution, you are no longer talking about evolution. -- kainaw™ 12:59, 7 July 2008 (UTC)

I don't quite follow when you say that evolution has no speed. The rate at which mutations occur and genes diverge from the starting point is certainly both measurable and variable. I take it you aren't calling those items by the name "evolution", then ? StuRat (talk) 03:20, 8 July 2008 (UTC)

A mutation is a mutation. It is not evolution. Three mutations is just three mutations. It is not evolution. Evolution is a process by which some mutations (not all of them and not in any specific frequency) help a species better fit into an environment. It isn't based on a lot of mutations or very few mutations. Claiming that it is going faster or slower indicates that evolution is in control of the mutations - perhaps with a purpose in mind. Evolution is not in control of anything. It is an abstract term used to define the relationship between beneficial mutations and how well a species fits into the environment - including divergence of species. The biggest hurdle in explaining evolution is trying to break people of the habit of saying things like "evolution made that bird have a pointy beak so it could get ants out of holes in the rocks." Evolution did not make the bird have a pointy beak. Mutations did that. Evolution did not have a goal of getting ants out of holes in the rocks. As the beaks got pointier, some birds just found it easier to stick their beaks into the holes. Had their beaks got wider, they would have used them for some other purpose. As I stated, trying to give it speed requires redefining evolution to be "the rate at which mutations change a species" - which is not a proper definition. -- kainaw™ 13:50, 8 July 2008 (UTC)

It's just a manner of speaking, like saying "the Sun rose" instead of "the Earth rotated into a position such that from my location on the Earth's surface, the Sun became visible above for horizon". It's also easier, although less precise, to say "evolution changed reptiles into birds", than to say "a number of mutations occured in reptiles, some of which were beneficial and thus were retained into subsequent generations, eventually leading to the development of birds". StuRat (talk) 04:43, 10 July 2008 (UTC)

Unleaded fuel

How can the effects of using leaded fuel or LRP in a car that is supposed to use unleaded fuel be overcome —Preceding unsigned comment added by Razzmetazz (talk • contribs) 05:34, 6 July 2008 (UTC)

Feel free to ignore this if you want but may I ask why? According to Tetra-ethyl lead "and the only countries in which leaded gasoline is extensively used are Yemen, Afghanistan and North Korea[citation needed]." I presume if you are living in Yemen, Afghanistan or North Korea, you probably have a car which is not designed to use leaded fuel. In any case Catalytic converter doesn't mention any methods to prevent fouling with lead. My gut feeling is it's difficult if possible. More likely you'd have to use a significantly different catalytic converter which is pointless since you might as well just switch to unleaded fuel and if you can't, e.g. because your Afghanistan your vehicles are probably already so polluting that equiping them with catalytic converters is somewhat pointless, there's more effective things to do first (e.g. switch to unleaded fuel). Presuming you've made the mistake of using leaded fuel in a car with a catalytic converter, our article mentions "Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or sublime the catalytic contaminant, removing it from the catalytic surface. However, removal of lead deposits in this manner is usually not possible due to lead's high boiling point. In particularly bad cases of catalytic lead poisoning, the catalytic converter may actually become completely plugged with lead residue". My suggestion would be to just replace the catalytic converter... Nil Einne (talk) 17:21, 6 July 2008 (UTC)

If you're going to burn fuel with lead in it, you might as well replace the catalytic converter with a piece of regular exhaust pipe too. But would there be additional concerns with fouling of the various mass-flow sensors in the engine-management system? Franamax (talk) 18:03, 6 July 2008 (UTC)

I'm going to make an educated guess here that you may have based your question on incorrect info. Many years ago gasoline grades in the US were called "Regular", "Unleaded", and "Premium". At that time the "Regular" and "Premium" both meant leaded gasoline. However, at some point it became illegal to sell leaded gasoline in the US, at which point the grades were called "Regular", "Plus", and "Premium" (the names vary slightly from brand to brand). The "Regular" and "Premium" now have a different meaning, as they, along with "Plus", refer to unleaded gasoline only. However, I could certainly see how someone might think that, since the grade called "Unleaded" had disappeared, that this meant that unleaded gasoline was no longer sold. StuRat (talk) 18:51, 6 July 2008 (UTC)

It is possible that the questioner is making a false assumption based on good knowledge. If you have a car that is designed to run on leaded gasoline, using unleaded gasoline will reduce the effective octane level a tiny bit (about 85 instead of 87 octane). It isn't enough to really notice. Now, if you assume this applies in reverse, you will think that you can take a car designed for unleaded gasoline, put leaded gasoline in it, and get an effective boost in the octane level. Sorry, but that isn't true. All you will do is throw off the engine's timing (effectively lowering the octane level) and increase lead pollution in the air. The key is understanding that the engine is timed for the specific type of gasoline it is intended to use. If you use a different type of gasoline, the timing will be off. You won't use the combustion of the gasoline to its full potential and, in the end, run at what could be effectively be referred to as a lower octane level. The gas doesn't actually lose octane. The engine just doesn't use it properly. -- kainaw™ 00:05, 7 July 2008 (UTC)

The reason for asking the question is that we will be touring Africa and most reports we get from fellow travellers is that unleaded fuel is not available most of the time. Iam not sure if the term unleaded is still used and if not that may be the cause for the confusion. I was trying to establish if any precautions could be taken should the situation arise and we are forced to use leaded petrol —Preceding unsigned comment added by Razzmetazz (talk • contribs) 06:52, 8 July 2008 (UTC)

Well, leaded fuel will ruin the catalytic converter. Other than that, there won't be much noticeable damage. Extended use can cause buildup in the catalytic converter, leading to exhaust problems and (worse case very rare scenario) blowing out the exhaust system. If you just plan to replace your catalytic converter when you return, you should be fine. Personally, I'd flush the gas tank upon return also. Not only is unleaded gas difficult to find in some places, regulated gas is even harder to find. You will have no way to know what was in the "gas" that you purchased (especially in areas where you aren't allowed to watch them pump it): water, apple juice, ping pong balls... -- kainaw™ 18:05, 8 July 2008 (UTC)

Courage

What is the most coragious felin? And the most coragious animal? Francesco —Preceding unsigned comment added by 87.20.213.78 (talk) 08:25, 6 July 2008 (UTC)

That's difficult to answer - how do you distinguish bravery and stupidity? There are plenty of animals that wouldn't be scared of something dangerous simply because it's not something they would ever encounter in their natural environment, and have never encountered before. That's not bravery, it's just ignorance. --Tango (talk) 13:19, 6 July 2008 (UTC)

Most courageous animal? Must be deers. When faced with several tons of steel running toward them at 70 mph, most deers would choose to stand their ground instead of running. Never have I seen another species display such gallantry so consistently :) --71.175.20.73 (talk) 13:48, 6 July 2008 (UTC)

Same with several hundred tonnes at 100 mph. An antler charge on an intercity train... that was brave (and messy). --BozMo talk 14:43, 6 July 2008 (UTC)

In general, many female animals with young display incredible bravery when threatened. Courage is probably related to fighting skill, I'd nominate polar bears and especially wolverines, which even bears don't mess with. Franamax (talk) 17:59, 6 July 2008 (UTC)

I'd disagree , surely courage is measured in part by the odds against you, meaning that flys/ants etc are extremely brave (and with a life expectency to match...)87.102.86.73 (talk) 19:40, 6 July 2008 (UTC)

Yes, there was a case of a house cat which rescued it's kittens from a burning building, one at a time, and burned both of it's ears off in the process. That's quite the act of bravery. StuRat (talk) 18:43, 6 July 2008 (UTC)

Personally, I'm not sure I'd ascribe "courage" to most animals at all. I tend to think of courage as a willingness to face danger/pain/struggle, but that presupposes an awareness and anticipation of the danger/pain/etc. If an animal acts on instinct, without awareness of the potential consequences of its actions, then for me those actions don't seem courageous. I'm sure there are exceptions for some actions by some more intellectually capable animals, but to the degree that much of animal behavior is instinct devoid of foresight or planning, then I'd see those actions shouldn't be interpreted as courageous at all. Dragons flight (talk) 18:54, 6 July 2008 (UTC)

Yes, we are antropomorphizing here. Blame it on that documentary about the penguins. However sometimes what we call courage could also be interpreted as stupidity, a lot of courageous acts are performed by humans acting on what you could call instinct, i.e. insufficient assessment of the risks. It seems to me that at least some of the people who rescue someone from a smashed-up car in a pool of gasoline must reflect later and think "what the hell was I doing?". Franamax (talk) 19:56, 6 July 2008 (UTC)

And, instinct or not, a mother facing down a predator to protect her young satisfies your criterion of "willingness to face danger" with "awareness...of the danger". Franamax (talk) 19:59, 6 July 2008 (UTC)

I don't feel that an animal standing it's ground, like a deer as described above, is *necessarily* brave. Some animals become paralysed with fear. This fear may be misconstrued as bravery or courage.

As for the most courageous animal, the well-bred German Shepherd dog. But then, I'm a bit biased.

I think most people tend to give animals human emotions. A silly practice if you ask me.

Ruairí Óg the Rogue (talk) 05:13, 7 July 2008 (UTC)

Animals don't defend their young because of bravery; they do so because it increases the possibility of their genes being passed down. The behaviour is due to instinct, not conscious choice, and the mother may not even feel fear while defending their children. --Bowlhover (talk) 04:43, 10 July 2008 (UTC)

Depends on the species. Humans are considered animals, are they not? You wouldn't say the same thing about us. 70.212.230.44 (talk) 07:45, 10 July 2008 (UTC)

Oh, but I would. Even humans usually think irrationally during emergencies and act on instinct, so I doubt other primates would reason out the advantages of disadvantages of different courses of action during an emergency. -Bowlhover (talk) 04:36, 11 July 2008 (UTC)

Life in free-fall

Hi, how would menstruation work in free-fall? At first I thought tampons might work, but then you can't reach the uterine wall with a tampon.

Also, does gravity play a roll in how a fetus is attached to the uterine walls? Any help would be much appreciated. Thanks. --Kjoonlee 14:23, 6 July 2008 (UTC)

According to various google hits ([9]), gravity is not required for menstruation, so it happens with no difficulty in space. I have no idea how it works, though. [10] says that pregnancy in space appears to be possible. --Tango (talk) 15:46, 6 July 2008 (UTC)

First, tampons aren't inserted into the uterus, just the vagina. They would have no problem reaching the vaginal wall since they expand when wet, and this works fine without gravity. The only concern is that gravity may be important in removing the menstrual fluid quickly, before it starts to decompose. I imagine bedridden women have faced this issue before, however. Menstruation obviously still "works" in zero-g, but it may be a bit less efficient, meaning women need to be extra careful not to do other things which might make the situation worse, like leaving the same tampon in too long. They may be more susceptible to toxic shock syndrome in zero-g than normal gravity, if they aren't careful. StuRat (talk) 18:36, 6 July 2008 (UTC)

Menstruation is probably less problematic in space than when bed-ridden because women in space can move around. This is important if period pains are to be avoided. Itsmejudith (talk) 20:59, 6 July 2008 (UTC)

Iron lattice

The lattice spacing of iron given at [11] is 286.66 pm. Can this be calculated? How? Thanks, *Max* (talk) 18:26, 6 July 2008 (UTC).

Typically experimentally by X-ray crystallography

Alternatively: knowing the density of the solid, the atomic mass, and the number of atoms per mole, and assuming a crystal structure you can make a good estimate with out using x-rays..

Please ask if you require further information on either method.87.102.86.73 (talk) 19:38, 6 July 2008 (UTC)

I wanted to know how it could be calculated from the electromagnetic forces between the atoms. Is this possible? *Max* (talk) 03:26, 7 July 2008 (UTC).

You can certainly do molecular modeling calculations to minimize the energy for a collection of iron atoms. For your purposes, you would want some sort of ab initio quantum chemistry methods, as any of the simple molecular mechanics or Semi-empirical quantum chemistry method approaches would likely be based on observed interatomic distances, so you wouldn't really be calculating them. DMacks (talk) 04:09, 7 July 2008 (UTC)

You could try to get an estimate this way.. even using classical inverse square electric field. - but a computer would help a lot - simply place the charged iron nuclei in the desired lattice and add the electrons randomly to the lattice.. then let the electrons and nuclei move under the resultant forces (do this stepwise) until some sort of equilibrium is found... NOTE you need to introduce a arbitrary barrier around the nucleus to prevent the electrons falling into the nucleus (ie a bounding spherical shell within which the electrons are not allowed to go)..

You can repeat this experiment with smaller and smaller bounding spherical shell and maybe even calculate the limit as the shell radius tend to zero. (you can also replace electrons with N pseudo-electrons of charge e/N to get a better approximation to electron density) This I suspect would work quite well...

I can't think of a method that you could easily do on paper though.. not without resorting to heavy maths or a heavyily simplified model.87.102.86.73 (talk) 13:17, 7 July 2008 (UTC)

What potentials would there be between the atoms if I used molecular mechanics? *Max* (talk) 19:32, 7 July 2008 (UTC).

Van der waals and electrostatic. VdW is probably the major one if you're doing simple molecular mechanics and considering atoms as point-masses that include their valence electrons...would have parameters (Lennard-Jones potential constants, for example) for the idealized interatomic spacing. Which is based on experimental determination of those parameters:) DMacks (talk) 02:29, 8 July 2008 (UTC)

Wouldn't molecular mechanics be not much use in terms of calculating Fe interatomic distance since the models used need force/distance formula and an estimate of interatomic distance to work: which was what was supposed to be being calculated.87.102.86.73 (talk) 06:22, 8 July 2008 (UTC)

Flashes from Zen Vision W

The flashes from my Zen Vision W, which I told you about earlier, are real, not my imagination. I've just seen one while looking directly at the device. The screen flashed a solid light gray for about a tenth of a second, while the device was turned off. What is the cause of this? JIP | Talk 17:33, 5 July 2008 (UTC)

So the backlight turned on by itself? --antilived^{T | C | G} 23:43, 5 July 2008 (UTC)

Seems like that, yes. And it turned off by itself immediately afterwards. JIP | Talk 18:18, 6 July 2008 (UTC)

Redirected from Wikipedia:Reference desk/Miscellaneous#Flashes from Zen Vision W87.102.86.73 (talk) 19:33, 6 July 2008 (UTC)

For the record the previous question was here Wikipedia:Reference_desk/Miscellaneous#Weird_flashes_from_Zen_Vision_W, it seems the light is real, and not imagined.. what causes this.?87.102.86.73 (talk) 19:33, 6 July 2008 (UTC)

I'm not sure about Zen Vision W, but most media players feature only a soft-off power switch. This means that even when the device is in a power-off state, the internal circuitry is still on, but consumes only a very small amount of electricity. So, these flashes could be caused by a faulty component, broken connection, or even a firmware bug. You should first check whether these flashes still happen with the battery removed. —Preceding unsigned comment added by 85.222.93.28 (talk) 00:27, 7 July 2008 (UTC)

I doubt the battery is removable (without voiding the warranty, that is). Secondly, what would that prove? I think I can pretty much guarantee that if you remove the battery, it's not going to do any flashing -- no power, no light, surely? -- Captain Disdain (talk) 11:51, 7 July 2008 (UTC)

What about somesort of residual charge in the light driver (note I don't actually know if its fluorescent source or Electro-luminesencent..)

I also think I've seen a similar effect say ~15mins? after a electronic fluorescent light has been switched off (see linked original question), additionally I vaguely remember a similar effect from old black and white TV's after they had been switched off.. I suggested some sort of cascade process... but where would the residual voltage come from?? and what would cause the electron cascade to start: cosmic rays? 87.102.86.73 (talk) 13:09, 7 July 2008 (UTC)

Never exclude the possibility of a firmware bug activating the backlight when you wouldn't expect it.

Atlant (talk) 17:40, 8 July 2008 (UTC)

The battery isn't removable, but it is detachable. The Zen Vision W has a user-usable (for want of a better word) switch at the bottom that severs the connection between the battery and the device. It can be reattached immediately afterwards. I find this a very useful way of doing a hard reset, and it avoids the possibility of losing the battery. I have not tried whether the flashes happen with the battery detached. JIP | Talk 18:01, 8 July 2008 (UTC)

Citing

Hello. I am making a registry of the most commonly cited sources that I use. When citing in APA style, must I include the author's title (i.e., Dr.) as part of the first name initial? For example, would the following be correct?

Jenkins, Dr F., Van Kessel, H., Davies, L., Lantz, Dr O., Thomas, P., & Tompkins, D. (2002). Chemistry 11. Canada: Nelson Thomson Canada Limited.

Thanks in advance. --Mayfare (talk) 20:07, 6 July 2008 (UTC)

Almost certainly not, I can't recall ever seeing a 'Dr.' title in a citation..87.102.86.73 (talk) 20:13, 6 July 2008 (UTC)

No, you don't use titles at all, much less professional ones. --98.217.8.46 (talk) 20:15, 6 July 2008 (UTC)

Note that the page APA style is actually a very good resource. --Several Times (talk) 20:14, 7 July 2008 (UTC)

Breeding spiders

My jumping spider, (I think Dendryphantinae) has spun a nest, and laid her eggs. The spiderlings have hatched but are still in the nest (they can't/don't come out). When raising spiderlings should they be taken out of the nest or left on their own until they come out themselves? (Maybe someone who has raised Tarantulas can tell me what is done in that case). Pro bug catcher (talk • contribs). 21:41, 6 July 2008 (UTC)

I'm not a spider expert but it seems unlikely to me that human intervention would be helpful in this situation. The spiders aren't waiting for you. They are probably only marginally aware of your existence. --98.217.8.46 (talk) 21:46, 6 July 2008 (UTC)

There are many (too many) spiders that make my yard their home. I often see nests teeming with tiny legged specks moving all around. After a while, they come out, sling out a little sting of web, and float off. Then, I have dozens of them trying to make a new home on my car. -- kainaw™ 23:57, 6 July 2008 (UTC)

July 7

what kind of snake?

Does anyone know what kind of snake this is? I spotted it in the forest near Multnomah Falls in Oregon, United States. Shown with a US nickel. Thanks! Dar-Ape 01:12, 7 July 2008 (UTC)

Almost certainly a worm snake. See more here. --Sean 14:22, 7 July 2008 (UTC)

Well, according to our article Carphophis, the American species of worm snakes range no farther west than the eastern Great Plains. I don't think one could pop up in Oregon. I'm no herpetologist, but of all the Oregon snakes in this list yours most resembles, to me, a rubber boa. Deor (talk) 22:47, 8 July 2008 (UTC)

A Rubber Boa seems most likely. Thanks a lot! Dar-Ape 02:11, 9 July 2008 (UTC)

What percent of heart attacks go undetected each year?

I'm not talking about ones where the person dies, and they just guess; I mean, is there some estimate of how many people might have really mild ones and not know it. I read that Bo Schembechler likely had one. I suspect it's someone common in high stress jobs to just think you're having angina when in fact you're having an actual heart attack.

If untreated, would the person who had one just recover naturally, or would there still be problems? I guess if they 'slow it down" for a few weeks then are back at it, they could for a while, right? Or, would an untreated, yet mild, heart attack still cause problems later? A friend I know thinks they might have had one, though they thought at the time it was angina; they eventually went into another field that was less stressful, and any bouts with shrotness of breath left.209.244.30.221 (talk) 01:15, 7 July 2008 (UTC)

I don't know enough about the topic to comment on the rest of your questions, but I'm pretty sure that if someone dies of a heart attack, they don't have to guess: a post mortem medical examination is going to show that as the cause of death pretty conclusively. (Also, if your friend thinks they might've had a heart attack, they should go and see a doctor. Frankly, I'm a little shocked if they haven't figured this much out by themselves. I mean, exactly what does it take for them to start to consider seeing a doctor if that doesn't do it?!) -- Captain Disdain (talk) 01:48, 7 July 2008 (UTC)

I know people say this all the time, but Wikipedia will not give you medical advice. If your friend thinks he has a medical problem he ought to consult a licensed physician not a bunch of anonymous folks on the internet, brilliant though we are. That said, I doubt the statistic you are looking for exists. By definition, data is not collected on heart attacks that go undetected, so it is very hard to compile information on them. Plasticup ^T/C 02:56, 7 July 2008 (UTC)

Captain Disdain, I am not shocked at all that his or her friend hasn't "figured this out," considering my best friend's dad actually *knew* he was having one and *still* drove himself to the hospital, a very dangerous thing to do! (Don't try this at ome.) And, he'd been in denial for a couple days before, when he was having chest pains, despite his family insisting he go. We don't know how much in the past this friend had one, so perhaps he cut back on a lot of stuff, got more exercise, when when he stopped having angina after a while, forgot about it. But, that is definitely not a safe way to handle your health.Somebody or his brother (talk) 14:10, 7 July 2008 (UTC)

Up to ~40% of heart attacks are not recognized [12]. Any heart attack has the potential to cause lasting damage. Looking for that damage is in fact the easiest way to detect the signs of a heart attack in patients who had an episode and didn't recognize it. If your friend did have a heart attack, there is a good chance that an EKG would be able to confirm, and as always we'd encourage you to speak to a doctor. Dragons flight (talk) 03:37, 7 July 2008 (UTC)

Neat study. Thanks DF. --Shaggorama (talk) 04:32, 7 July 2008 (UTC)

Similiar heartbeats

Is it possible for tow unrelated people to share very similar cardiac patterns for a prolonged period of time. 69.157.226.161 (talk) 01:49, 7 July 2008 (UTC)

I would imagine any healthy people are likely to have similar cardiac patterns. Any difference from the norm usually indicates a problem. --Tango (talk) 01:55, 7 July 2008 (UTC)

The resting heart rate is similar amongst humans, though it depends on body size and shape. You're heart rate is also constantly changing depending on your current level of activity. It is possible for your heart rate to appear to match someone else's exactly, but only briefly. --Russoc4 (talk) 02:44, 7 July 2008 (UTC)

Heart rhythms are so similar that EKG machines are tuned to pick up very minor fluctuations. I have a slightly long Q wave by 2 milliseconds (usually) and it is always picked up on an EKG. So, if you aren't looking into the millisecond range for differences in heart rhythms, you'll likely see nearly identical rhythms running at different rates (ie: 70 beats a minute compared to 80 beats a minute). -- kainaw™ 04:27, 7 July 2008 (UTC)

Can vets tell what Animal species

Media:Example.ogg —Preceding unsigned comment added by 98.203.9.163 (talk) 05:31, 7 July 2008 (UTC)

Depends on the animal, probably. Dogs and cats—of course. All of the ones you see are of the same species (Canis lupus familiaris, Felis catus, respectively). Cows? Horses? Probably not, unless they are a large animal vet. Exotic animals? Maybe if they work at a zoo, but even then, I doubt they know them all off hand.--98.217.8.46 (talk) 16:04, 7 July 2008 (UTC)

Hertz.

What is the difference between 50Hz and 60Hz?

Could a 60Hz supply damage a 50Hz appliance? —Preceding unsigned comment added by 41.241.32.81 (talk) 06:09, 7 July 2008 (UTC)

Hertz is a measure of frequency. In this case, it describes the number of times that an AC current changes polarity per second. It's effect depends on the appliance, but in principle yes, it could. More important is the difference in voltage that often goes with the difference in frequency. Some appliances will not work at all, some at a different speed, and some may be damaged. Modern electronic devices usually have power supplies that accept a range of voltages and frequencies (50-60Hz, 100-240V nominal). Check your appliance for a type sign. --Stephan Schulz (talk) 10:58, 7 July 2008 (UTC)

If you say the type of appliance then someone here will probably know whether it is likely to be damaged or not. Itsmejudith (talk) 11:01, 7 July 2008 (UTC)

Hertz is the number of cycles per second. The polarity changes twice in each cycle, so 60Hz changes polarity 120 times in a second. — DanielLC 17:48, 7 July 2008 (UTC)

Thanks. I was grasping for the correct word "cycle" (and failing), so I carefully changed "denotes" in my original draft to "describes" in order to be unwrong. ;-) --Stephan Schulz (talk) 21:47, 7 July 2008 (UTC)

chemitry

why are most types of glassware use in a chemical laboratory made of pyrex? —Preceding unsigned comment added by 125.60.237.218 (talk) 13:14, 7 July 2008 (UTC)

It's not always 'pyrex' though most borosilicate glasses are often refered to as pyrex.. the reason is its thermal shock resistance..

I recommend reading both the links pyrex and borosilicate glass.87.102.86.73 (talk) 13:25, 7 July 2008 (UTC)

note a lot of specialised lab glass ware will be made out of quartz, but only very specialised stuff.87.102.86.73 (talk) 13:20, 7 July 2008 (UTC)

The thermal shock resistance is true, its also the fact that borosilicate glass is even more chemically inert than regular glass, especially to things like hydroxide. Quartz is often used for things that need to be optically pure (like spectrometry cuvettes). EagleFalconn (talk) 14:05, 7 July 2008 (UTC)

Need Help Identifying Scary and Fast Bug.

Every once in a while, before I turn on the water to take a shower, a bug that looks really hairy or has a thousand legs darts out of nowhere and scares the poop out of me. It is realy, really fast and I am not around a camera to take a picture. Do you know what kind of bug this is? BTW - I live in New England, USA. --Anthonygiroux (talk) 13:17, 7 July 2008 (UTC)

Please get rid of the P word. 208.76.245.162 (talk) 13:33, 7 July 2008 (UTC)

which one 'poop' or 'picture'? Richard Avery (talk) 14:12, 7 July 2008 (UTC)

A house centipede? Deor (talk) 13:46, 7 July 2008 (UTC)

Sounds about right to me. I also live in New England and occasionally got those guys in bathrooms where there were cracks in the walls and things like that. They eat bugs so they're supposedly helpful but damned if they aren't the ugliest, creepiest creatures. And if you swat them, they fall apart into about a million tiny pieces... --98.217.8.46 (talk) 16:10, 7 July 2008 (UTC)

Hi. Ah yes, that's probably what I thought they were. I live in Southern Ontario, I've seem them around before, and they're an invasive species. Just as I suspected, the article says they are venomous and can bite, but are usually not dangerous. Thanks. ~AH1^(TCU) 17:00, 7 July 2008 (UTC)

I find centipedes are difficult to kill because they are fast, smart enough to hide behind things, and seem to know when they are being hunted. I use Hot Shot Wasp & Hornet spray, which can spray a narrow stream several feet. This allows me to hit them before they escape, and it kills them quickly. Open a window after spraying. StuRat (talk) 03:14, 8 July 2008 (UTC)

"Universe in My Thumb"

Someone told me that there is (or could be) a whole universe in my thumb. Do you know what they mean by that? --Anthonygiroux (talk) 13:19, 7 July 2008 (UTC)

I personally have no idea. Maybe it was an idiom? — CycloneNimrod  ^Talk? 13:24, 7 July 2008 (UTC)

They might have meant something like the concepts described in Parallel universe (fiction)87.102.86.73 (talk) 14:06, 7 July 2008 (UTC)

Sounds like somebody's been watching National Lampoon's Animal House. I can't find a transcript, but there's a scene where some of the characters get high, and then Pinto realizes that "our universe could be a cell in the thumbnail of some larger being?" --LarryMac | Talk 14:24, 7 July 2008 (UTC)

Both MIB and MIIB show this philosophical idea in their closing scenes. Layman's models for atoms and solar systems look quite similar but I'm sure if you said they are similar a scientist would throw a fit. So, really this seems more like a humanities question than a scientific one. -LambaJan (talk) 17:38, 7 July 2008 (UTC)

The humanities guys might talk about it a little more, but ultimately I think we could all come to the same conclusion. Plasticup ^T/C 18:21, 7 July 2008 (UTC)

There are theories about universes within universes - I believe a universe within our universe would look like a black hole. It's all highly theoretical and bordering on unscientific, though. I can't find any mention of the theory in Wikipedia, oddly... --Tango (talk) 21:08, 7 July 2008 (UTC)

We don't need Wikipedia here. What about the episode of The Simpsons that opens with the universe morphing into Homer's brain? That's where I get my science knowledge anyway, same as I get my religious knowledge from Life of Brian! :) Franamax (talk) 02:07, 8 July 2008 (UTC)

It's a pretty classic, and admittedly mind-blowing concept, especially if you're, oh, about 12 when you first come across it. (Or pretty thoroughly baked.) Anyway, there's no scientific basis for it, but the idea is that since there's a vast microscopic, atomic and even sub-atomic level of existence all around us that we cannot really perceive, there could be tiny, tiny universes anywhere. (Comic book readers may be familiar with Marvel's Microverse, which may be based on the concept, or perhaps introduced it to awed kids everywhere.) And, yes, as Delta House helpfully points out, that means that our universe could just be a speck under some unimaginably vast being's fingernail -- we could merely be a part of some much, much larger system that we will never be able to perceive or understand. Repeat until you go "Whoa. Dude." -- Captain Disdain (talk) 06:35, 8 July 2008 (UTC)

Perhaps:

To see a World in a Grain of Sand

And a Heaven in a Wild Flower,

Hold Infinity in the palm of your hand

And Eternity in an hour.

-William Blake (1709-1784)

Sandman30s (talk) 12:21, 8 July 2008 (UTC)

Ever read Horton Hears a Who! by Dr. Seuss? --Shaggorama (talk) 12:24, 8 July 2008 (UTC)

How could this be?

Tomoji Tanabe is 112 and seems to be extremely healthy. My grandmother is 86 and is in hospital sick. Higher ages seem to be more common in females, so how was this jumble caused? 208.76.245.162 (talk) 13:31, 7 July 2008 (UTC)

Tomoji is an Outlier, and furthermore, comparing two individuals' lifespan will often deviate from what might be expected. Not to be heartless, but compared to average lifespan, 86 is pretty good. Dar-Ape 14:04, 7 July 2008 (UTC)

Genetics plays a big role - we can't really say much more without knowing the history of your family's health and Tomoji's, as well as their personal habits. So many things go into this that it's very hard to pin down one thing and say, "This should make this person live longer."

However, I completely understand your need to, emotionally, with your grandmother sick like that. Sometimes, we really can't understand why anyone has to grow old and die. We can only answer like in the classic Sesame Street episode about the death of the lovable Mr. Hooper - "just because." You're in my prayers.Somebody or his brother (talk) 14:16, 7 July 2008 (UTC)

"...new life makes losing life easier to understand." - If I could", from the album In Between Dreams by Jack Johnson --antilived^{T | C | G} 23:59, 7 July 2008 (UTC)

In answer to the second question [13] is of interest Nil Einne (talk) 18:40, 8 July 2008 (UTC)

sunrise and sunset

my teacher said that we see the sunrise and sunset approx. two minutes earlier and two minutes later respectively. so daytime is extended by a total of four minutes. this happens due to atmospheric refraction of light. but, at noon, we see it as it really is (there is no early or late viewing). why is this so? —Preceding unsigned comment added by 122.50.250.178 (talk) 13:41, 7 July 2008 (UTC)

Atmospheric refraction, I think. Dar-Ape 14:07, 7 July 2008 (UTC)

Also, the apparent position of the sun in the sky is about 500 seconds behind where it actually is due to the amount of time it takes light to travel from the sun to the earth. Snell's law would probably be a good read as well, and the basis for atmospheric refraction. Note that when the index of refraction changes, the speed of light changes as well. I'm somewhat skeptical of there being no time difference at noon as the sun rarely strikes the atmosphere at 90º even at noon in most places (and even if it did, wouldn't there still be a time delay because of the change in n?). EagleFalconn (talk) 14:13, 7 July 2008 (UTC)

The time it takes light to travel to the Earth makes it look like the sun is where it was 500 seconds ago, which is pretty much where it is now. The Sun isn't moving; the Earth is spinning. — DanielLC 17:42, 7 July 2008 (UTC)

That 500 seconds is a red herring. The movement of the sun is not what causes sunrise and sunset. The relevant movement is entirely on our end. APL (talk) 18:07, 7 July 2008 (UTC)

Doesn't change the fact that what I said is true. Yes, the effect is about 0.4 arcminutes, but its still worth noting as the atmospheric refraction article also deals with travel time and how the index of refraction causes the light to bend above the horizon. EagleFalconn (talk) 21:11, 7 July 2008 (UTC)

But the 500 second delay won't increase the length of the day by any amount of time, because you have the same delay to shorten it in the morning. It only really has to do with refraction. --Wirbelwindヴィルヴェルヴィント (talk) 17:08, 8 July 2008 (UTC)

"Also, the apparent position of the sun in the sky is about 500 seconds behind where it actually is due to the amount of time it takes light to travel from the sun to the earth." The light time is accurate, but the apparent position of the Sun is its actual position. Suppose that at 00:00, two rays of light leave the Sun. One is headed for the current position of the Earth, while the other is directed towards the location Earth will be at 500 seconds later. At 00:08:20, the first ray completely misses any human eyes, while the second is detected. Notice that the path taken by the second ray is exactly the same as a line drawn between its source and Earth, so it is the the Sun's true position that is noted by observers. --Bowlhover (talk) 05:23, 9 July 2008 (UTC)

Hertz.

Could i change a 60Hz generating set to 50Hz?41.241.32.81 (talk) 15:11, 7 July 2008 (UTC)

Depends quite what you have operating at 60Hz. Read the user manual, whatever it is. -mattbuck (Talk) 15:32, 7 July 2008 (UTC)

Stores like radio shack have outlet converters for travelers to use. I'm sure you can find one on ebay or something as well. -LambaJan (talk) 17:42, 7 July 2008 (UTC)

A large 60 Hz alternator (such as is found in peakers or baseload generators) would likely be damaged if operated for any prolonged period at any substantial loading at 50 Hz. They have underfrequency relays which automatically trip them off line at a higher frequency than 50 Hz. Not familiar with the limitations on operating small alternators at reduced frequency, but I have my doubts. In some cases it might be possible to rewind a generating set for 50 Hz operation. Utilities also used rotary convertors to change the frequency, such as 60 Hz to 25 Hz and vice versa. Edison (talk) 19:11, 7 July 2008 (UTC)

menigocele

why is cough impulse present in a meningocele —Preceding unsigned comment added by Dr.Rameshs (talk • contribs) 15:49, 7 July 2008 (UTC)

I presume you are referring to meningocele as in spina bifida? I'm not entirely sure, presumably due to stimulation of one or more thoracic nerve roots. The effect can be simulated too, I believe. See this. — CycloneNimrod  ^Talk? 16:21, 7 July 2008 (UTC)

Finding a positive cough reflex is diagnostic in certain types of meningoceles. I am unable to detect any websites which cover this issue. I assume it is related the raised intrathoracic pressure caused by coughing. This pressure is then transmitted to the cranium via the blood vessels and thus to the meniningocele via the cerebrospinal fluid channel. The positive cough reflex would indicate that the meningocele is filled with cerebrospinal fluid which is continuous with the normal cerebrospinal fluid circulation. Richard Avery (talk) 12:32, 8 July 2008 (UTC)

About Hedgehogs

Someone recently asked me if Hedgehogs can climb walls, since I don't know the answer I thought I'd ask here. Apparently one of our neighbours had a hedgehog in their garden recently and they wonder how it got in there, so do you think it's possible for a hedgehog to climb a 6ft (~1.8m) tall wall? Can they climb vertical surfaces at all? --Hibernian (talk) 16:01, 7 July 2008 (UTC)

I doubt they could climb something like that. However, they dig pretty well and wouldn't have any trouble making their way under a wall that isn't actually sunk into the ground, or isn't sunk very deep at all. -- Captain Disdain (talk) 16:14, 7 July 2008 (UTC)

They certainly can. I've found many sources, but the most reliable is Nature Magazine - Letter to the Editor - The Climbing Powers of the Hedgehog. It may only be an anecdote, but Nature would never have published it were there not some element of truth; Nature does NOT like to be proven wrong! -- Skittleys (talk) 17:07, 7 July 2008 (UTC)

No. Echindas climb walls; hedgehogs run really fast. — DanielLC 17:34, 7 July 2008 (UTC)

Hedgehogs are very adept climbers. Climbing up is not a problem. Getting down is. Similar to cats, their claws curl inward. So, when going up, they can dig in and pull themselves up. When going down, their toes curl under and they tumble. Strangely, many species of hedgehogs only have curled claws on the front paws. On the back paws, they have what appears to be more like toenails, not claws. As such, they grow straight outward. I used to think this was limited to the four-toed species, but I've been assured that it is in some species of five-toed hedgehogs as well. For an anecdote, I watched a hedgehog climb a four-foot tall fence made of chicken-wire and hop from the top of it onto the ground. He could have dug under the fence rather easily, but he must have decided that climbing was easier. If you read about pet hedgehogs, you'll see that it is very important that your hedgehog cage has a latched roof or you'll have a hedgehog on the loose by morning (unless you have one of those weird "I'm too cool to climb" hedgehogs). -- kainaw™ 17:41, 7 July 2008 (UTC)

Cats curl inward? --Trovatore (talk) 03:53, 8 July 2008 (UTC)

Oh yes! Got scratched by mine yesterday and boy, they don't half dig in well. — CycloneNimrod  ^Talk? 08:36, 8 July 2008 (UTC)

That would be cats' claws, I think, not cats. --Trovatore (talk) 08:39, 8 July 2008 (UTC)

Thanks for the info guys. I'll pass that along to them, interesting to know. --Hibernian (talk) 10:01, 8 July 2008 (UTC)

orgasms

what techniques could a hypothetical male use to increase the strength and duration of his orgasms? —Preceding unsigned comment added by Singing Cone (talk • contribs) 16:57, 7 July 2008 (UTC)

hypothetical good diet and exercise. -LambaJan (talk) 17:45, 7 July 2008 (UTC)

And as always, practice makes perfect. Plasticup ^T/C 18:16, 7 July 2008 (UTC)

Maybe it's my dirty mind, but I can't help laughing at Plasticup's username in relation to this question. 79.75.144.130 (talk) 18:33, 7 July 2008 (UTC)

Yeah, it is your dirty mind you bad boy/girl you! -hydnjo talk 02:12, 8 July 2008 (UTC)

I feel a little violated... Plasticup ^T/C 14:22, 8 July 2008 (UTC)

Odd. You should be feeling fulfilled. Matt Deres (talk) 13:41, 10 July 2008 (UTC)

At orgasm I think some discussion is listed. Also, you could find a fetish. Mac Davis (talk) 22:30, 7 July 2008 (UTC)

See Expanded Orgasm. It's about as scientific as you'll get while avoiding answering spam emails. Fribbler (talk) 23:23, 7 July 2008 (UTC)

Be watchful about becoming priapismated! -hydnjo talk 03:47, 8 July 2008 (UTC)

If poisoning occurs (with depilatory wax)

I have some depilatory wax that has instructions saying what to do if poisoning occurs. Now I thought depilatory wax was just a mixture of glucose-like compounds, which sounds harmless. What might be in the wax, and why is it poisonous? 203.221.127.206 (talk) 17:18, 7 July 2008 (UTC)

There should be a list of the ingredients on the packaging. You can then check each one for potential toxicity. It may be that there are no really toxic compounds in it but it could cause a mechanical blockage in the digestive system which would be very dangerous. Exxolon (talk) 18:39, 7 July 2008 (UTC)

A collection of glucose-like compounds would burn when you tried to heat it and wouldn't work as a wax very well. It's more likely a mixture of, well, waxes, which are lipids. Glucose is in a different class of compounds called carbohydrates. --M1ss1ontomars2k4 (talk) 23:01, 7 July 2008 (UTC)

Yeah, that's what I thought too - but check out this [xxtp://www.ehow.com/how_2109787_homemade-depilatory-wax.html homemade stuff] (chg xx to ht - spam filter), definitely glucose-like! In fact, it looks pretty yummy, you could eat it when you were done (guess you'd be spitting out some extras though) :) Franamax (talk) 23:10, 7 July 2008 (UTC)

I think that's because the sugars have polymerized into a long sticky chain. Still not technically a wax, but sticky and semi-solid enough to help with depilation. --M1ss1ontomars2k4 (talk) 00:49, 8 July 2008 (UTC)

Color and Smell changes, Why?

I have moved my question here on the advice on Dismas so it will hopefully received better responses.

-A year or so ago I wanted to know how much cum I could produce in a week, so I used a plasitc bottle every day (sometimes several times a day although the amount would be less each time) to collect it. By the end of the week there was a fair amount, but thats not why I am asking this question. The cum really began to smell rank, like some sort of industrial strength wood glue. It also turned from white to a yellowish color. What caused this, because it was scealed in a bottle and no bacterias could get in? Are there bacterias in the cum when I comes out of me? Does drinking Yakult make this problem worse? ~ ~ ~ ~ —Preceding unsigned comment added by Mud Flood (talk • contribs) 16:39, 7 July 2008 (UTC)

Changes in diet have an effect on sweat, urine, and feces, so it's not out of the question to think that diet would affect semen samples as well. Also, there was a question on one of the ref. desks a week or two ago about the smell of semen. One of the responses said that it contained compounds that are similar to ammonia, so that may be where you're getting the "rank" smell from... Dismas|^(talk) 18:36, 7 July 2008 (UTC)

Ah, thank you. However, this smell changed over time (in a sealed environment). When I cumed to begin with it smelled fine, but over a week smelled like strong wood glue. I don't think this can be attributed to diet unless there are certain compounds in the food which change over time as well. I was more wondering if bacteria or other microorganisms were at work, and if they somehow got to the cum after I ejaculated or if they were present from within me. Mud Flood (talk) 18:42, 7 July 2008 (UTC)

Personally, I don't know and think this would have received better responses on the Science desk instead of Miscellaneous. My own ideas would be that either A) chemicals in the semen are breaking down due to time, exposure to light, exposure to air, etc. B) something is reacting with the plastic container, or C) the container wasn't clean enough to begin with and something is, again, reacting. One more thing I just thought of... pre-ejaculate contains chemicals to help the sperm survive through the urethra. It basically keeps the chemicals in urine from killing the sperm. There could be something going on with that as well. Dismas|^(talk) 18:59, 7 July 2008 (UTC)

Surely something as simple as decomposition would account for the change? Organic material that isn't refrigerated tends to go bad, particularly if it isn't refrigerated. Mere contact with air and light cause things like this to degrade. Also, it's hardly a sealed jar if you keep opening it up several times a day, especially in a non-sterile environment. I mean, did you thoroughly wash your hands and your penis every time before embarking on this grand scientific experiment, for example? Did you wear rubber gloves? Are you sure the jar was sterile to begin with? Did you somehow ensure that nothing contaminated the sample before it ended up in the jar? (And bear in mind that just touching it a little with a fingertip is inevitably going to slap a bunch of bacteria in it, which, after a week of growing, multiplying and going to work, are going to wreak merry hell with the sample -- and, in fact, the same pretty much applies to the tip of your penis, so getting a completely uncontaminated sample is going to be pretty much impossible.) There's a reason why they don't store the sperm samples in labs or sperm banks in jars on countertops.

Also: Ew. Not to dis the curiosity or the act in itself (hey, if this kind of thing works for you, it's fine by me), but a jar full of week-old sperm doesn't strike me great mood-setter. If you want to know how much of it you produce, you could just measure it by emission and keep a log or something, just so you don't have to live with that, uh, wood glue smell. Let me tell you, the chances of that jar's contents ever getting any better the longer you keep it around aren't too great... -- Captain Disdain (talk) 21:53, 7 July 2008 (UTC)

I'd say its just decomposition of the compounds. Here's a question: Did you get the idea from 4chan, or did you create the idea on 4chan? :) Mac Davis (talk) 17:20, 8 July 2008 (UTC)

Personally, I'd start worrying about fluoride in your drinking water affecting Our Precious (bodily) Essence.

Atlant (talk) 17:28, 8 July 2008 (UTC)

Just in case no one else mentions it, I feel it my duty to recount one of my favorite jokes:

A young male student was caught pleasuring himself in his bedroom by his housemaster.

Housemaster; Perkins, you should not be doing that! You should save it for when you are married.

Perkins (pointing to a shelf lined with full liter jars above his bed) I am Sir, look! —Preceding unsigned comment added by 79.76.144.199 (talk) 00:17, 9 July 2008 (UTC)

Measuring Power

What is the easiest/cheapest way to measure a current of ~1 pW? Orders of magnitude (power) mentions an FM receiver as being able to have a precision as low as 10 fW. Could I build/buy a similar receiver, but not necessarily as precise? Or is there an easier way? Thanks, *Max* (talk) 19:48, 7 July 2008 (UTC).

At the risk of being pedantic, current is measured in Amps, while power is measured in Watts. It would probably help to be more detailed in what you want to do. Dragons flight (talk) 21:33, 7 July 2008 (UTC)

I meant that the power is in the form of an electric current. I want to put something in the circuit that measures the power, which is about 50 pW with a precision of <1 pW. *Max* (talk) 21:46, 7 July 2008 (UTC).

In general, people don't usually measure power, instead they measure current and voltage and derive the power involved. Which is why it would be helpful to know more about the circuit. Also, is there a time resolution involved? It's a lot easier to say that the average power over many minutes is 50 pW than to measure 50 pW with, for example, millisecond precision. Dragons flight (talk) 21:59, 7 July 2008 (UTC)

That's not exactly true. A bolometer directly measures the electric or optical power delivered through a transmission line by dissipating that power in an appropriate load impedance and measuring the heating effect the incoming power has upon the load. 50 pW is a pretty small amount of heating power, though, so you need a pretty fancy (e.g. cryogenic) bolometer to measure that sort of power level.

Atlant (talk) 17:21, 8 July 2008 (UTC)

I think you have the wrong term. Bolometers are primarily used to measure the power contained in electromagnetic radiation. I can't imagine any circumstance where you would hook one up to a power line directly and the article doesn't mention such uses. Dragons flight (talk) 17:28, 8 July 2008 (UTC)

The article is incomplete. See this PDF from Agilent Technologies [14]

Atlant (talk) 17:45, 8 July 2008 (UTC)

I don't know the current/voltage, just the power. Both are small, but I don't know how small. I do not need precise measurements over short periods of time, I just need to know whether it is operating at full power or not. *Max* (talk) 22:54, 7 July 2008 (UTC).

If you really want to measure power... measure the temperature inside a thermos, put the component in and seal the thermos as well as you can, leave it in there for a while and measure the new temperature.

Seriously though, what are you actually measuring? Power dissipated across something? More information is needed. --antilived^{T | C | G} 23:36, 7 July 2008 (UTC)

Max, I think you might need to define the question a little better. Are you talking about DC current, long-wave AC, RF AC? Antilived's first part won't help - putting a 50pW radiator inside a thermos will take an awful long time to heat your coffee. But they are right that we need to know more about the problem. If that steps across some patent you are trying to get, it will make it much more difficult to help out. Franamax (talk) 01:36, 8 July 2008 (UTC)

Radio antennas pick up radio frequency electromagnetic radiation. The voltage picked up by the antenna might be microvolts. The impedance could allow you to calculate the current and the power. Or you could work backwards, using the gain of the radio frequency amplification stages and the output voltage to calculate the input voltage, which, combined with the impedance, would give you the input wattage to an AM or FM or TV receiver. Is this what you were talking about? Edison (talk) 03:11, 8 July 2008 (UTC)

Yeah, I couldn't believe that 10fW spec for a receiver, so I found some specs and worked backward. Whadda'ya know - it's on the order of femtowatts, who would have thought en:wiki was a reliable source! And yes, frequency will be very important if the intent is to measure and calculate power (VxA) flowing through something, OTOH if the aim is to measure power dissipation, then wouldn't a sensitive calorimter be more appropriate? (Especially at these low power levels where the measuring device could appreciably distort the measurement? Just asking! )Franamax (talk) 03:28, 8 July 2008 (UTC)

Pet Budgerigars and mirrors

Does anyone know what the latest thinking is WRT to allowing a singly-kept, caged Budgerigar access to a mirror? Is it generally considered to be (by experts) a good or a bad thing now, in terms of the effects upon the bird's psychology? --Kurt Shaped Box (talk) 21:36, 7 July 2008 (UTC)

I'm no expert, but personal experience with different birds over the years indicate strongly that a mirror keeps the bird company, and combats boredom. Budgies are sociable birds. If you don't want to put in a mirror, I'd say get your bird a partner to share the cage. ~Amatulić (talk) 23:47, 7 July 2008 (UTC)

The problem seems to be (there is always debate about this on bird forums) that a single budgie can become too attached to his/her reflection and go all obsessive-compulsive - or can become frustrated and very aggressive due to the reflection refusing to 'answer back'. My inside budgie doesn't have a mirror - but he gets lots of playtime with me/general outside the cage playtime and seems relatively sane. --Kurt Shaped Box (talk) 00:09, 8 July 2008 (UTC)

I take it budgies aren't smart enough to figure out it's their own reflection ? StuRat (talk) 03:02, 8 July 2008 (UTC)

Our article on self-awareness claims that the existing evidence so far suggests that only bottlenose dolphins, apes, and elephants are self-aware (and mirrors often factor into those experiments). Meanwhile, our sun conure had a mirror for a while and never interacted with it one way or another. And "the parrot in the mirror" is a running gag in the Monty comic strip.

Atlant (talk) 17:14, 8 July 2008 (UTC)

From the mirror test article and other Internet sources, it seems that very few animals can pass the test. Even humans younger than 18 months cannot recognize themselves in a mirror. --Bowlhover (talk) 17:34, 8 July 2008 (UTC)

My friend owns an African Grey, which I have babysat for him on occasion. He has a mirror in his cage, which he doesn't seem to be interested in at all. I don't know whether he actually recognizes his own reflection as him or not - but he obviously understands that it's not really another bird. It's not scary, it's not something that he can pick up and throw, it's too smooth to scratch himself on and it's doesn't have a chewable texture, so it appears to be largely irrelevant to him. --Kurt Shaped Box (talk) 19:03, 8 July 2008 (UTC)

I've never seen a budgie that understands the concept of 'mirror'. Put one in the cage and the bird will spend all it's free time pressed up against it, beak-tapping and cooing. Sometimes the budgie will even try to feed or mate with its own reflection. It's a similar deal with cockatiels, as far as I know. I can understand why some may consider this to be unhealthy. --Kurt Shaped Box (talk) 19:08, 8 July 2008 (UTC)

If a budgie isn't psycologically capable of recognizing a mirror for what it is, why would he be capable of any psychological harm from having a mirror? Seems to me that providing a source of entertainment and company is beneficial, not harmful. When I had a budgie, he kissed and fought his mirror, but played with me when I was around, flying to my shoulder and nibbling my ear. The mirror kept him occupied at other times.

Personally, I think the folks arguing about potential harm are anthropomorphizing their pets too much. ~Amatulić (talk) 14:59, 9 July 2008 (UTC)

I think the problem is that the mirrors will reflect the bird's own personalities back at them. An affectionate bird may appreciate the mirror, as he thinks that another affectionate bird has been placed in the cage, while an aggressive bird might be stressed out, thinking another aggressive bird is next to him and he must always keep one eye open. StuRat (talk) 04:33, 10 July 2008 (UTC)

Airplane engines "opening" up

I've noticed on several flights over the last year that upon landing, a metal sheath on the engine seems to slide backwards, revealing what appears to be a grill. The planes were some Boeing model with Rolls Royce engines. Anyone know what the engines were doing? 151.152.101.44 (talk) 22:36, 7 July 2008 (UTC)

Those reverse thrust to slow the plane down. --M1ss1ontomars2k4 (talk) 22:47, 7 July 2008 (UTC)

See thrust reversal. They are used when the plane is still going at a high speed and brakes aren't very effective yet. --antilived^{T | C | G} 23:50, 7 July 2008 (UTC)

This is correct, and by the way, reverse thrust is also available on some propeller planes by reversing the pitch of the propeller (i.e. rotating each blade around its long axis so that it angles the other way). But it should be added that reverse thrust doesn't contribute all that much to a plane's ability to stop; it's the brakes that absorb most of the kinetic energy. It has to be that way, really; a plane has to be able to land safely if the engines stop running, and in that case reverse thrust would not be available. --Anonymous, 06:57 UTC, July 8, 2008.

Strips of metal hanging in unfinished buildings

In two seperate buildings under construction, hanging from the (temporary?) metal floors are dozens or hundreds of shiny strips of metal. Does anyone know what are these for? 151.152.101.44 (talk) 22:36, 7 July 2008 (UTC)

Hmm, I've worked in the construction industry in Ireland, and those strips were the remnants of metal bands used to contain pallets of blocks or bricks. They get everywhere! Fribbler (talk) 23:45, 7 July 2008 (UTC)

Could be straps that will be used to hang stuff below those floors (hung-ceilings in the level below, etc)? DMacks (talk) 02:23, 8 July 2008 (UTC)

Organic chemistry reaction

Hello; what's the expected product of this reaction? My guess was this, but something tells me I should have considered turning the hemiacetal back into a dialdehyde first. --M1ss1ontomars2k4 (talk) 22:57, 7 July 2008 (UTC)

My guess would be conversion to the 4hydroxy butaldehyde first, followed by condensation to give a hydrazone, maybe something else happens after that?87.102.86.73 (talk) 02:05, 8 July 2008 (UTC)

Note: protonation at the hydroxyl allows the condensation to occur without making the aldehyde first.

I've no idea if the resultant compound undergoes further reactions eg protonation at hydroxyl, followed by electrophilic aromatic substitution..87.102.86.73 (talk) 06:19, 8 July 2008 (UTC)

Under normal conditions the hydrazone of 4hydroxy butyraldehyde is the final product. --Stone (talk) 06:26, 8 July 2008 (UTC)

Yeah, that turns out to be correct. Thanks! --M1ss1ontomars2k4 (talk) 05:11, 9 July 2008 (UTC)

July 8

Saving electricity by unplugging apliances?

How much electricity would be saved by unplugging the following except when on (which is a total of 2-3 hours a month): 22-inch TV, about 10 years old; DVD player, 3-4 years old; 13 inch TV, 20 years old. There really aren't any displays that keep going on any of them. Just wondering if I'd save my electric bill any with that. (I don't quite want to give up cable yet, though it's tempting. I only have the basic, though, so it's not much, less than $15 a month.) I wouldn't really have to cut costs like that, but I'm just wondering, is it worth it? Do appliances that aren't on but still plugged in waste a lot?209.244.30.221 (talk) 02:03, 8 July 2008 (UTC)

The old TV's will definately lose a lot of electricity if left in standby.. If there's a proper power off switch on them (not standby) using that will also work. The DVD will probably use hardly any energy in standby.87.102.86.73 (talk) 02:08, 8 July 2008 (UTC)

This all depends on your appliances. Any information given would be purely anecdotal. For example, I have everything on power strips. When I leave a room, I turn off the power strip and completely cut electricity to all devices in the room. I noticed a savings immediately. My monthly electricity bill dropped around $30/month. Since you can get power strips VERY cheap, it wouldn't be much trouble to get a few, use them to turn off anything not in use, and see what the change in your electricity bill turns out to be. I've heard some people say that their bill didn't change at all. I've heard others claim to cut their bill down to practically nothing. As I said, it is all anecdotal. -- kainaw™ 02:17, 8 July 2008 (UTC)

As long as they are actually switched off, unplugging shouldn't make any difference. If they are just on standby, though, they could well be using a lot of electricity and switching them off completely, either with an off switch or by unplugging, could save you a noticeable amount on your bill. --Tango (talk) 02:20, 8 July 2008 (UTC)

There's a definition: Parasitic_load - but it's just a stub. I've seen parasitic load described as up to 5% of total power, add in there the cost to air-condition the extra heat. Appliances more than 15 years old or so probably don't have a standby mode, very new appliances are increasingly subject to stringent standby power standards. In Canada, I think the latest is 5 watts maximum per appliance.

One way to check is to put your hand on the device to see if it's warm at all. I remember a cable converter box I had that would be -hot- to the touch, a good indication that I was spending money for nothing at all (except in winter, when we would huddle around it). Franamax (talk) 02:33, 8 July 2008 (UTC)

Addendum: unplug your cellphone charger and any other power adapter that has a transformer in it, so any voltage converter or AC/DC converter. They will always have a parasitic load, whether or not they have the actual appliance plugged in. Also, almost every modern PC has a standby mode - the "On" switch at the front sends a boot command to the motherboard, which is sitting there using a small amount of power even when it's off. The switch at the back is the one that makes zero power load. Kainaw is right - put a physical switch in to be sure everything is really turned off, off, off. Franamax (talk) 02:41, 8 July 2008 (UTC)

I endorse the idea that using a power strip to turn off the power will save on the electric bill. The problem is that some TVs and VCRs want to re-scan all the available frequecies when power has been off, to determine which channels are active. A VCR may also require resetting the clock and calendar when poser is restored. All the little AC adapters/wall warts are power vampires which waste energy. Edison (talk) 03:06, 8 July 2008 (UTC)

Actually the electronic power supplies switched mode power supply aren't that bad.. If your power supply contains a transformer then it will have a parasitic load. You can usually tell the difference by the weight (transformers are heavy).. (Switch them off anyway)87.102.86.73 (talk) 06:16, 8 July 2008 (UTC)

As it depends very heavily on the design of the specific appliance, go to the hardware store and get yourself one of those plug-in electricity meters - go between an appliance and the wall socket, and measure how much electricity is passing through. Use this to find out how much your appliances use when on standby, and multiply that by the cost of electricity in your area. — QuantumEleven 14:06, 8 July 2008 (UTC)

Have you seen a wattmeter in hardware stores? All I have seen are multimeters, which let you see volts or amps but not watts. The power factor is unknown, so measuring the volts and then the amps really does not show the power consumed. The cheapest one I see online is the "Kill A Watt" meter [15] which shows volts, amps, Hz, watts, or kilowatt hours, for about US$33. It might take a while for the savings from shutting off parasitic loads to pay for the meter. It would be a good rental item or a loaner from a community green organization. An online site [16] gives some watt measurements via the Kill A Watt for various electronic products, but I do not see thorough coverage of the idling power use by TVs and power adapters. "Energy Star" rated appliances are still allowed to consume 15% of maximum power usage when in power saving mode[17]. The article Standby power covers this subject pretty well, as does the Howstuffworks article "Fight vampire power" [18]. Edison (talk) 17:08, 8 July 2008 (UTC)

Survival versus reproduction

To what extent can a high reproduction rate in a species compensate for a low survival rate? NeonMerlin 03:26, 8 July 2008 (UTC)

If the goal is "how many offspring survive" (i.e., maximize number that reach reproductive age in order to pass on genes), it doesn't matter whether how many offspring you have. You don't need to have many if you can be sure they will survive, but if they're likely not to survive, you'd better have a lot of them to make sure some survive. 2 at 50% mortality is the same result as 100 at 99% mortality. DMacks (talk) 04:20, 8 July 2008 (UTC)

Check out r/K selection theory. I think that page needs some work, tho' . . . Robinh (talk) 12:48, 8 July 2008 (UTC)

Space Time

This may be a dumb question but, Why do large masses like our sun bend space time?67.127.172.33 (talk) 06:09, 8 July 2008 (UTC)

It's not a dumb question at all. Have you checked out our article on gravitational time dilation? -- Captain Disdain (talk) 06:23, 8 July 2008 (UTC)

science

myopia —Preceding unsigned comment added by Sandeep123456 (talk • contribs) 12:25, 8 July 2008 (UTC)

Do you have a question? If it's not answered in our article myopia, feel free to come back and ask it. Algebraist 12:32, 8 July 2008 (UTC)

Perhaps the question is just too small to read. --Several Times (talk) 20:50, 9 July 2008 (UTC)

Or perhaps the question will follow, but we're just too short-sighted to wait for it ? StuRat (talk) 04:23, 10 July 2008 (UTC)

ibs

IBS-Irritable bowel syndrome-how is it reffered to in other languages?I have tried,unsuccessfully to find info on it in Slovenija and dont really know how to go about it. —Preceding unsigned comment added by 78.151.86.182 (talk) 13:08, 8 July 2008 (UTC)

http://sl.wikipedia.org/wiki/Driska

87.102.86.73 (talk) 13:18, 8 July 2008 (UTC)

If you're actually in slovenia and you need help then just approach someone in the street (preferably a doctor) and say "jaz drek sebi". They should understand and be able to help you.87.102.86.73 (talk) 13:29, 8 July 2008 (UTC)

Let's stop poking fun at a chronic and potentially debilitating medical condition, shall we? Plasticup ^T/C 14:28, 8 July 2008 (UTC)

Srečno drek vaš hlače po Slovensko! 87.102.86.73 (talk) 14:35, 8 July 2008 (UTC)

Except that IBS is a medical term for a collection of different symptoms,only one of which is diarhoea... —Preceding unsigned comment added by 78.151.86.182 (talk) 13:38, 8 July 2008 (UTC) And your obviously literal translation of I'm s......g myself is completely meaningless,78.151.86.182 (talk) 13:51, 8 July 2008 (UTC) Dear 87.102.86.73,how do you end up with this clumsy translations? —Preceding unsigned comment added by 78.145.20.205 (talk) 16:33, 8 July 2008 (UTC)

I can't read the language but I would say http://www.ivz.si/ would be a good start for your search. Jdrewitt (talk) 17:02, 8 July 2008 (UTC)

One of the neat little features of wikipdia that alot of folks don't notice is great in making just this kind of translation. If you look on the bottom left of most articles, you'll see what other languages the article is offered in. Scroll over the language links (and look at the status bar) or click them to see the name of the article translated. Off the bat I can tell you (from the links in the IBS article):

• German: Reizdarmsyndrom
• Spanish: Síndrome irritable de intestinos
• French: Côlon irritable
• Hebrew: תסמונת_המעי_הרגיז
• Netherlands: Prikkelbare-darmsyndroom
• Japanese: 過敏性腸症候群
• Polish: Zespół jelita drażliwego
• Portuguese: Síndrome_do_cólon_irritável
• Russian: Синдром раздражённого кишечника
• Suomi: Ärtynyt suoli
• Swedish: Irritabel_tarm
• Thai: โรคลำไส้แปรปรวน

Neat trick, right? Also, for the record, there is a language reference desk where you can pose questions like this. --Shaggorama (talk) 03:34, 9 July 2008 (UTC)

Um, in general that's not necessarily a translation. It's the corresponding article in those wikis, or the article that some user or bot has decided is the corresponding one. This can be problematic as content is not always divided up the same way in the different language WPs, so which link is best to make is not always obvious. The interwiki bots can be very bullheaded in changing back to the wrong link, or at least they used to be; I haven't seen that so much in a while -- maybe someone improved the code. --Trovatore (talk) 07:47, 9 July 2008 (UTC)

Thank you v much,Jdrewitt,that was exatcly what I needed.78.146.221.170 (talk) 14:26, 9 July 2008 (UTC)

Brain communication and handedness

If you were born left handed, but brought up right handed, would that improve your brains intra communication and make you smarter or not? —Preceding unsigned comment added by 79.76.157.193 (talk) 15:57, 8 July 2008 (UTC)

I don't think it'd make you smarter as such, perhaps more ambidextrous and it might improve your co-ordinational ability.. It's still not entirely known why you are born right or left handed, and some still think it's a matter of how you are raised. Others think, as the article states, it could be due to which hand was used more in the womb. — CycloneNimrod  ^Talk? 16:58, 8 July 2008 (UTC)

You haven't given a reason for your assumption that improving the brain's intracommunication makes a person smarter. Simply increasing signals doesn't equate to intelligence. During a seizure, there is a lot of communication going on - and it just messes everything up. So, why would intracommunication lead to being smarter? -- kainaw™ 17:57, 8 July 2008 (UTC)

I don't think the OP was suggesting more signals = more intelligence. More likely the assumption was, perhaps correctly, that more neurons and connections (at least more knowledge) — CycloneNimrod  ^Talk? 22:07, 8 July 2008 (UTC)

bond energy

a C=C bond energy is less than twice a C-C bond energy but a C=O bond energy is more than twice a C-O bond energy, just can't figure out why, please help--scoobydoo (talk) 17:37, 8 July 2008 (UTC)

See bond energy (especially the distance correlation). -- kainaw™ 17:53, 8 July 2008 (UTC)

holes in chest

A couple of my (male) friend have like holes in their chests, (I suppose some girls probably may too but I don't go into changing rooms with them, (as much as I might like to)). Anyway, as I was trying to say before I was interrupted, like where their ribs should be I suppose the ribs are there but they're not normally shaped. I suppose (not studied too closely). What is this? Anyone got any good weird pictures? (as abnomalities go I suppose it is fairly harmless, unless you want to become such salubrious occupations as male stripper/porn stud/actor).

PS not this [19], or this [20]

ooh, actually like this http://www.youtube.com/watch?v=HR31UetCWno

I can't click your links, but I think I understand from your description. Medically, it is known as Pectus excavatum. I have heard it referred to as a Concave Chest. Plasticup ^T/C 20:04, 8 July 2008 (UTC)

If their sternum goes inwards (concave), then it is indeed pectus excavatum. I did some pretty extensive work to that article a few months ago. Pectus carinatum is where the sternum protrudes outwards. There are loads of images available on the net if you just search around a bit :) I'd disagree about it being fairly harmless though, there are several medical conditions which are more likely if you have PE (such as mitral valve prolapse and it can also put pressure on the respiratory system). Let's not even start with the psychological damage it could have on a teenager, for example. — CycloneNimrod  ^Talk? 22:11, 8 July 2008 (UTC)

How to determine the right direction of an insert in a plasmid?

Hey guys. I need an immediate help. I have this biology lab about plasmids that we are required to inset a cDNA into a plasmid. one of the fundemental question of the lab is how can we determine that we put the insert in the right orientation? they talk about the use of restriction enzymes and to see the results of agaron gel electrophorisis. can somebody explain this to me? or at least guide me to a website that i can find in it useful information. Thank you, —Preceding unsigned comment added by 84.109.50.42 (talk) 20:47, 8 July 2008 (UTC

See restriction enzyme and sticky ends. --Mark PEA (talk) 21:37, 8 July 2008 (UTC)

Briefly, there are specific palindromic sequences in DNA (called restriction sites) that marks the site that restriction enzymes will cut. You find a site in your cDNA and another in your plasmid. You then calculate what theoretical fragment sizes you would expect depending on which orientation the cDNA is in your plasmid. You then cut the DNA at these sites and separate the fragments by agarose gel electrophoresis. You then compare the size of the bands on your gel with the theoretical sizes, and that will tell your the direction of the cDNA in the plasmind. As Mark notes above, if you use non-complementary sticky ends to clone your cDNA in the first place, then you don't have to worry about this. Directionally is only really a concern with blunt end cloning or by using complementary sticky ends. Rockpocket 05:34, 9 July 2008 (UTC)

Purity of CO₂

Are there other gaseous byproducts besides carbon dioxide resulting from the Hall-Héroult process and if so or if not is the carbon dioxide pure enough to use to make soft drinks? Mimus polyglottos (talk) 21:34, 8 July 2008 (UTC)

You can expect some sulfur dioxide Perfluorocarbon and hydrogen fluoride and other fluorides to be produced. It is very unlikely to be suitable for human consumption in a concentrated form. The reason is that the carbon is not pure and there will be other contaminates in the electrolyte. Graeme Bartlett (talk) 00:25, 9 July 2008 (UTC)

Talk:Composition of the human body

Out of curiosity, the exact elemental composition of a male human who was perfectly healthy with a mass of 90,000 grams would be what exacty? As well, what would the mass of the chemicals, and what chemicals, be for the chemical composition? This question also is asked for the material and tissue composition. Earthan Philosopher (talk) 22:22, 8 July 2008 (UTC)

This question was asked on the talk page of the very article that has the answer... I guess the only thing lacking is how to convert the percentages given into masses: If 65% of a 90,000 gram body is oxygen, then there is 0.65x90000=58500 grams of oxygen, the others are calculated the same way, just replace the 0.65 with the appropriate number. --Tango (talk) 22:36, 8 July 2008 (UTC)

But if 3.8 grams is of iron is definite, then how can you have an exact percentage of elements by mass. Also it says that there are other elements as well. Plus there are two ammounts of percentages that state that the percentage is less than .05 or .01 percent, so how would you know the exact ammount of those elements. and these don't answer my questions of chemicals and material and tisuue compositions. Earthan Philosopher (talk) 23:00, 8 July 2008 (UTC)

The composition is always going to vary from person to person. All the figures are approximate. 3.8g in a typical person is a fraction of one percent, so it's not going to cause the other figures to be inaccurate. The components not given in the table are also in very small amounts, so don't cause any inaccuracies in the other figures. I don't know about the chemical distributions, other than that Water#Effects on life says humans are 60-70% water. --Tango (talk) 23:20, 8 July 2008 (UTC)

Personal question though, ( if you are religious, do not let this bias your answer please) if you were to get all the components and put them in the right structure, do you think it would be possible to create artificial human life? —Preceding unsigned comment added by Earthan Philosopher (talk • contribs) 01:05, 9 July 2008 (UTC)

If it were possible to put them all together in just the right way, then yes. It would be impossible to distinguish a "real" human from an artificial one, so if one is alive, they most both be. The real question is whether that is possible, and the answer there may well be "no". The uncertainty principle prevents a perfect reconstruction, so there is always going to be some level or error. Whether it's possible to get it close enough or not, I don't know. Certainly not with current technology or anything in the foreseeable future. There have been attempts at creating much simpler artificial life, though, see Synthetic life. --Tango (talk) 01:24, 9 July 2008 (UTC)

Just thinking

Not sure if this is science or philosophy etc but posting here initially until told otherwise. Anyway I was just sitting here thinking, then I thought: Why is the human mind so damn inquisitive? —Preceding unsigned comment added by 79.76.144.199 (talk) 00:04, 9 July 2008 (UTC)

I suppose inquisitiveness has some evolutionary benefit, perhaps because it leads to the invention of tools and other ways of shaping the environment to suit our needs (agriculture, domestication of animals, etc.). It also leads to exploration, which allows populations to expand and new resources to be discovered. --Tango (talk) 00:58, 9 July 2008 (UTC)

I don't know, but if you find the answer, you'd be in a good position to improve this section: Curiosity#Causes. --Allen (talk) 05:10, 9 July 2008 (UTC)

Not only the human mind: most mammals (and possibly other animals) also exhibit curiosity. (Try lying down in a field full of cows - if you remain still, their curiosity overcomes their fear, and you will soon be surrounded by them!) Dbfirs 08:31, 9 July 2008 (UTC)

my BG sound

How 2 make my BG sound like upright DB? —Preceding unsigned comment added by 79.76.144.199 (talk) 01:30, 9 July 2008 (UTC)

You don't. Unfortunately (in this case) they're completely different. An acoustic BG would do better because you'd have a mic picking it up instead of a pickup. Other than getting a little mic from, like some kind of a headset or something and clipping it close to the strings where you're plucking them and getting the signal from there (which might actually almost work). I'd suggest lowering your pickups so they don't work quite as efficiently and you have to pluck a bit stronger like you'd do on a DB (no, lowering the volume won't have quite the same effect) and EQing the mid a bit stronger than high and low. No effects, obviously. If that doesn't work I can't imagine what else will. -LambaJan (talk) 02:54, 9 July 2008 (UTC)

Just for my benefit: what is BG and DB? Fribbler (talk) 11:06, 9 July 2008 (UTC)

bass guitar, double bass. 163.1.148.158 (talk) 11:09, 9 July 2008 (UTC)

Oh, another thought about EQing. Try turning the tone knob to cut the bass levels and let the high through. after that, if it's too tinny, back the high off a bit. I don't know what kinds of controls you have available but between the bass and the amp you can probably get a decent mix. The last thought I have is keeping your bass volume lower than normal and turning your amp volume a bit higher to compensate. It might be a total crap idea in practice but it makes sense in my head. -LambaJan (talk) 13:33, 9 July 2008 (UTC)

And buy a fretless bass. 80.229.160.127 (talk) 17:52, 9 July 2008 (UTC)

Megabats as “flying primates”?

Is there, at present, a dispute in the mainstream scientific community as to whether bats are monophyletic?

I ask because I am skeptical of this edit to the article Flying primates theory. It seems to me that as of 2008, the DNA evidence is pretty clear that all extant bats have a common ancestor not shared by any other extant mammal. Is that correct, and if so does the DNA evidence confirm the monophyly of bats, or is the DNA evidence just one part of the puzzle to be considered along with morphological evidence in the question of whether bats are monophyletic? --Mathew5000 (talk) 03:37, 9 July 2008 (UTC)

I don't know, but at a glance it looks like the edit you're pointing to was not good. The abstract of that Nature article doesn't just assert that bats are monophyletic; it asserts that there is consensus for that position, so it seems important for the article. Generally, I think DNA evidence is always just one part of the puzzle, in principle... genes and morphology, in a broad sense, are both just traits on which to base our phyletic inferences. But since genes are generally the cause of evolutionary changes in morphology, it makes sense to me that DNA-based phylogenies are often seen to trump those based on morphology. I like how the authors of this paper put it: "When molecular data produce a robust phylogeny that conflicts with morphology, we suggest a third approach: reevaluate the morphological evidence." --Allen (talk) 05:03, 9 July 2008 (UTC)

There was indeed quite a bit of controversy regarding bat monophyly prior to the existence of more advanced genetic sequence alignment software and such, up to about the mid 1990s. The more recent genetic comparisons found that some of the research supporting bat diphyly back in the 1980s wasn't exactly as solid as it had originally appeared (and it wasn't the most solid evidence in the first place). More recent phylogenies were recently confirmed by fossilized bat ancestors, which appear to have been previously undiscovered intermediate steps in bat evolution. These ancient bats shared some major similarities in ear structure with both older fossils and modern bats, for example. I have sources regarding this topic, but they unfortunately aren't accessible right now, so I'll post them later. --Several Times (talk) 17:27, 9 July 2008 (UTC)

Ah, here they are. This report, which unfortunately only offers the abstract for free, explains the confirmed bat phylogeny well. This paper by Eick et al may be a better one, as it is not only free, but examines some characteristics which make bats especially unique. --Several Times (talk) 23:32, 9 July 2008 (UTC)

Lice

If lice "spend their whole lives on their victim", why do they sometimes wait inside head clothing? 208.76.245.162 (talk) 03:53, 9 July 2008 (UTC)

I'm guessing that lice don't choose to be removed from their hosts, but that contact by headgear inevitably dislodges some individuals. Lice can only survive 24 hours when unattached to a host, according to http://www.healthcaresouth.com/pages/askthedoctor/headlice.htm. --Bowlhover (talk) 07:05, 9 July 2008 (UTC)

Lice 2

Can you catch lice from other animals? 208.76.245.162 (talk) 03:54, 9 July 2008 (UTC)

Not usually, no. Lice that feed on humans only feed on humans. But it must have happened at least once. --Allen (talk) 05:06, 9 July 2008 (UTC)

Mortice Locks

If you have a mortice lock in your door, but no key, can a locksmith make a key for it? I'm in the UK, if that makes a difference. 195.60.20.81 (talk) 09:43, 9 July 2008 (UTC)

Possibly a very skilled one.. but it would probably be easier to unscrew the lock, and replace it with a new one. Is the door open?87.102.86.73 (talk) 12:58, 9 July 2008 (UTC)

If you have a camera, our article on Mortise lock could really do with a picture. Plasticup ^T/C 14:14, 9 July 2008 (UTC)

As long as the locksmith can take apart the lock, no special skill is required in cutting a key for it. Each of the levers is so many millimetres wide, and the key cutting jig is set up to those measurements. However, it might indeed be cheaper to buy a new lock and keys. Note also that most locks can have the levers or tumblers changed so that they accept a specific key (of the same brand). Very useful if you want to cut down the number of keys you have to carry around.--Shantavira|^{feed me} 15:10, 9 July 2008 (UTC)

Many locksmiths and even hardware stores have an assortment of blank skeleton keys which can be cut to fit a given mortise lock. In a given brand of mortise lock, there were not that many different keys, and some manufacturers made a set for a given house numbered one through 6 or whatever, and supplied two keys per lock. If your front door was a number five, then your front door key would fit the house down the street which had a number five lock on the front door. Some locksmiths no longer will make a skeleton key to fit a customer's mortise lock, beause it takes a bit of expertise and customers do not want to pay the price required. The skeleton key blanks must have the correct central shaft size to fit the lock. New locks with new keys can be installed if you wish to maintain the appearance. Edison (talk) 03:29, 10 July 2008 (UTC)

I've actually done this myself with needle-files (years ago when I had the time and patience). It is not too difficult for a 3-lever lock (typically 150 different combinations), and remakably simple for the 1950s-style back-door mortice locks which were often identical, but it is a skilled task for a modern 5-lever lock (thousands of different keys), and would, in general, cost more than buying a new lock (£12 to £50 in UK depending on quality). Some locksmiths who stock that particular brand will be able to look at the levers and immediately set up their key-cutting jig to make a key to fit. Others will offer to replace just the levers complete with matching keys, but you will need to find specialist locksmiths for these options. Most key-cutters can only copy existing keys. Dbfirs 07:48, 10 July 2008 (UTC)

Minnesota Skid

What is a 'Minnesota Skid' and why should the tires not be locked up when performing one? 128.252.139.248 (talk) 13:19, 9 July 2008 (UTC)

--Anthonygiroux (talk) 14:13, 9 July 2008 (UTC)

Black people, poison ivy, lice

My black neighbor and her white husband both assert that black people are not susceptible to poison ivy; indeed, she walks right through the patch of it that separates our houses while he avoids it. My daughter's pediatrician asserted to me (on an occasion when my daughter had head lice) that she has never seen a case of them on a black child. These are credible sources, but I find the claims themselves questionable. I know about the malaria/sickle-cell connection, but is there any evidence that people of (fairly recent) African descent are immune to these ailments? --Sean 13:35, 9 July 2008 (UTC)

This would suggest that it is not true. Fribbler (talk) 13:43, 9 July 2008 (UTC)

Heh. That's the most informal text I have ever seen in PubMed.

From my observation, immunity to poison oak / poison ivy can be acquired. My father was allergic to it in his youth, until one day he had to cut through a field of the stuff. He came down with a terrible full-body rash, but after that, contact with the plant no longer affected him. ~Amatulić (talk) 14:03, 9 July 2008 (UTC)

My guess would be that the immunity to poison ivy is an individual thing, rather than all black people, and the lack of head lice cases is due to them being harder to spot on black person. That wouldn't result in no cases at all, but perhaps your paediatrician hadn't treated many black children, either due to being in a predominantly white area or simply being new to the job. --Tango (talk) 14:07, 9 July 2008 (UTC)

I am Koyukon Athabaskan and I am immune to poison/ivy/oak and so is my immediate family. I will ask my other relatives about this --Anthonygiroux (talk) 14:11, 9 July 2008 (UTC)

Also, my friend is half Athabaskan and half African-American and she is also immune to poison ivy/oak. Also, she said there was an outbreak of lice in her elementary school in California and she was the only one that wasn't affected. Go figure... --Anthonygiroux (talk) 14:13, 9 July 2008 (UTC)

In a quick scan of one of my patient databases, I found 272 patients labelled as "black" with an ICD9 code of 626.6 (Poison Ivy/Sumac). Also, I am white and I am completely immune to poison ivy (and all related "poison" plants). It may be that blacks are more likely to me immune, but all it takes is one case to prove that they are not all immune. -- kainaw™ 14:42, 9 July 2008 (UTC)

There was an episode of Mythbusters where they tested a bunch of vodka myths, one of which was that application of vodka helps with poison oak rash. (It didn't.) I recall that they actually had a bit of a problem with that one, because it turned out that they had a lot of trouble finding someone from their staff who was allergic to the stuff -- they had to go through four or five people before they found one who actually reacted to it. I think all of them, with the exception of Grant Imahara, where white. I also seem to recall they said that 90% of the people weren't immune to it; they just happened to have a small statistical bump there... Anyway, your neighbor's wife apparently is one of the lucky 10%, but that certainly doesn't mean that all black people are. -- Captain Disdain (talk) 14:56, 9 July 2008 (UTC)

Thanks to all that answered. I suspect that she had heard this myth, and then suffered confirmation bias when she found herself to indeed be immune. --Sean 15:30, 9 July 2008 (UTC)

According to this page, because of their specific hair type (curly), African-Americans are less likely to have head lice infestations, but they are not "immune". (I would also suspect the prevalence of very short hair amongst African-American men to play a factor in that as well). According to this page, people of African descendent not in the US do get head lice infestations more frequently, because the local lice in said areas have adapted to their specific hair types. --98.217.8.46 (talk) 18:22, 9 July 2008 (UTC)

Sensitivity to poison ivy can also show up later in life. As a youth I walked through the stuff on several occasions and had no reaction of any kind. Later, in high-school, I was helping to plant some trees and unknowingly came into contact with some ivy "spikes" and got a beautiful rash. Matt Deres (talk) 14:48, 10 July 2008 (UTC)

primates

Why no primates in parts of North/South America? Surely they could make it along the coast and settle in new hampshire?87.102.86.73 (talk)

Isn't that an image of where primates are native to, rather than where they are present? — CycloneNimrod  ^Talk? 14:36, 9 July 2008 (UTC)

I'm not aware of chimp colonies in conneticut...87.102.86.73 (talk) 14:40, 9 July 2008 (UTC)

(try again) Why are no primates native in parts of North/South America? Surely they could have made it along the coast and settled in new hampshire?87.102.86.73 (talk) 14:57, 9 July 2008 (UTC)

There are plenty of primates in New Hampshire.-Wafulz (talk) 15:06, 9 July 2008 (UTC)

(try again) Why are no non-human primates native in parts of North/South America? Surely they could have made it along the coast and settled in new hampshire?87.102.86.73 (talk) 14:57, 9 July 2008 (UTC)

From the looks of the distribution map, the primate range ends at the south side of a large expanse of desert in Mexico and this would be a formidable barrier to transit northward. I believe author Jared Diamond gave this as a reason for a lot of differences between North and Central America. Franamax (talk) 15:43, 9 July 2008 (UTC)

This image seems to show a subtropical dry forest link along the east coast, maybe it's not accurate enough. would this be a barrier (lemurs live in subtropical dry forest in madagascar..)?87.102.86.73 (talk) 16:02, 9 July 2008 (UTC)

Actually if you blow up the primate map, it shows a little tongue in just that part, apparently ending at the Rio Grande. So I guess they made it as far as the river and then either couldn't or didn't cross. Funny, it looks so easy when Clint Eastwood does it. :) I'm not sure how wide the river is in the last stretches before the mouth. Franamax (talk) 16:54, 9 July 2008 (UTC)

Nowadays we take so much water out of the Rio Grande that some years it never reaches the ocean - so that would be zero width. Rmhermen (talk) 17:38, 9 July 2008 (UTC)

A more intriguing question is, why are there any non-human primates native to the Americas, considering that monkeys evolved well after Africa and South America were separated by ocean. The article New World monkey is brief and unsourced on this point; it suggests that some monkeys came to South America on a raft of vegetation. But could enough monkeys have made it that way to form a viable population? --Mathew5000 (talk) 17:36, 9 July 2008 (UTC)

((The previous question title Wikipedia:Reference_desk/Science#Megabats_as_"flying_primates"?? seems to suggest one possible theory... (joke) ))87.102.86.73 (talk) 17:50, 9 July 2008 (UTC) (or maybe not a joke - I've no idea actually)87.102.86.73 (talk) 18:04, 9 July 2008 (UTC)

This question is as old as theories of evolution itself. But yes, the current theory is that they floated on across one way or another, though it is still considered a pretty open question. This chapter from an anthro textbook sums up the major theories about it, and their respective deficits. There are some who theorize that they might have made it around Asia and North America, but that is controversial as well. --98.217.8.46 (talk) 21:32, 9 July 2008 (UTC)

• The probable reason why there are no primates in North America is there is no good habitat linking New Hampshire with Mexico. New World Monkeys are exclusively arboreal, unlike the Old World monkeys which have some terrestrial species such as macaques and baboons. The temperate species of Old world monkeys are the species most able to adapt to a wide range of diets and foraging strategies, including the ground. American monkeys are excluded from North America by three factors - there is no continuous dense forest between South Mexico and the US, the forest that is there is unable to sustain primates without them traveling to the ground (which American monkeys don't - yet), and the two million years since the Ithmus of Panama formed hasn't apparently been long enough for primates to move northwards that far. Sabine's Sunbird talk 02:41, 10 July 2008 (UTC)

Thanks, that's a good answer. Though it seems from the links above that there once were (tiny) primates in north america (the article mentions the mississipi) - those must have just died out then? (ps I had no idea the Isthmus of Panama was 'new'; thanks for telling me.)87.102.86.73 (talk) 10:04, 10 July 2008 (UTC)

Engine slows you down?

People sometimes talk of using the engine/gears of their car to slow them down instead of the brakes. My question is; where does the kinetic energy of the car go when you use this method of slowing down? —Preceding unsigned comment added by 79.76.156.19 (talk) 14:45, 9 July 2008 (UTC)

friction in part, as well as rotational energy, additional energy can be lost in having to compress the gases in the cylinders of an engine that lacks sufficient fuel input to operate at the current speed.87.102.86.73 (talk) 14:48, 9 July 2008 (UTC)

Yep. The article isn't great, but engine braking explains this a little bit. Friday (talk) 14:58, 9 July 2008 (UTC)

Ok. You are traveling at 60 mph in top gear. You then slam it into second gear with your foot off the accelerator. Youll slow down alright, but the engine rpm cannot suddenly increase to the required rate demanded by the road speed and gearbox. So I ask again: where does all that KE go? —Preceding unsigned comment added by 79.76.156.19 (talk) 15:21, 9 July 2008 (UTC)

HINT people don't usually 'engine brake' by changing gear, but by gradually taking their foot of the throttle Doing what you describe may damage the clutch, the gearbox and your head as it slams into the steering wheel/windscreen (see also whiplash) - always wear a seatbelt.87.102.86.73 (talk) 16:57, 9 July 2008 (UTC)

Hmm? I downshift for engine braking quite frequently- I don't imagine this is uncommon at all. Friday (talk) 17:50, 9 July 2008 (UTC)

Do you slam it into second gear with your foot off the accelerator at 60mphr?87.102.86.73 (talk) 18:01, 9 July 2008 (UTC)

You just answered it.. the engine rpm would have to increase - this would mean an increase in rotational energy... -direct analogy: flywheel 87.102.86.73 (talk) 15:24, 9 July 2008 (UTC)

Engines have a certain amount of moment of inertia (and a flywheel). You cannot instantaneously increase the rotational energy of anything with non zero moment of inertia. So when you suddenly let your clutch in, what happens to the excess energy whilst the engine is getting up to the required rpm? —Preceding unsigned comment added by 79.76.156.19 (talk) 16:00, 9 July 2008 (UTC)

The clutch slips. Franamax (talk) 16:04, 9 July 2008 (UTC)

OR.(edit conflict) It would be the same as suddenly connecting to a flywheel - in one case the wheels would skid. Also note that because the gas in the engine is compressable it acts as a torque converter - (ie like an 'elastic band')87.102.86.73 (talk) 16:05, 9 July 2008 (UTC)

Aha! so its not your engine that dissipates the energy: its your clutch or your skidding tyres, right? —Preceding unsigned comment added by 79.76.156.19 (talk) 16:12, 9 July 2008 (UTC)

Until the engine is fully revved up to speed, yes (partly). As the engine revs up, it is increasing its kinetic energy and dissipating energy through the vacuum effect, and the clutch is slipping at the same time. Possibly the tires too, I've never dumped a clutch that hard. Once the engine is revved up, the clutch locks and it is only the engine slowing things down after that. Franamax (talk) 16:26, 9 July 2008 (UTC)

I'm not sure the clutch slipping dissipates much energy, it just allows the energy to be transferred from the kinetic energy of the car to the rotational energy of the engine gradually. It's the engine that finally dissipates the energy. The clutch probably does get warm in the process, so some energy will be lost that way, but probably not much. A better option would be to lift the clutch gradually, I would expect. --Tango (talk) 16:36, 9 July 2008 (UTC)

I always feather out the clutch when downshifting in engine braking. Dumping it and letting the engine rev up that fast is awfully hard on things (IMO). Franamax (talk) 16:43, 9 July 2008 (UTC)

I suspect that some energy is eventually transferred to the engine because its been speeded up. Also some energy must be lost in the clutch. Question is, what proportion of energy is stored in the engine (as angular momentum) and what proportion lost in the clutch as heat? I propose its half and half, but is there a proof?

I have no proof, but in practical terms, you either blip the throttle a bit to get the revs up and/or feather out the clutch when you downshift in engine braking. The aim is to dissipate as little energy as possible in the clutch - once you can smell it, you know you did it wrong. Also note to the above, if you release the clutch fast enough to lock the wheels and skid, you've 1) put maximum stress on the entire driveline; and 2) lost control of your vehicle. Nice theoretical exercise, but do it with someone else's car, and do it on a test track. Franamax (talk) 08:53, 10 July 2008 (UTC)

When a throttled engine, like most gasoline engines, is operated at closed throttle, the engine acts as a positive displacement vacuum pump, moving (rarefied) air from the low-pressure intake manifold to the atmospheric-pressure (or so) exhaust manifold, against a pressure gradient. This requires energy. See manifold vacuum, which I think covers engine braking better than engine braking. -- Coneslayer (talk) 15:44, 9 July 2008 (UTC)

Muscles

My biology teacher said muscles can only contract, never relax on their own, and need an opposing muscle to contract otherwise your arm would be stuck in the same position. I don't believe this. If I lift my arm it'll drop if I stop contracting the top arm muscle without the bottom muscle doing anything. Is my teacher right or they full of crap? RHODOPSIN DRINKER (talk • contribs) 15:23, 9 July 2008 (UTC)

Gravity may be causing this.87.102.86.73 (talk) 15:29, 9 July 2008 (UTC)

Muscles can relax, but that won't move the body part back to where it was, you need something to move it back. That could be another muscle, or gravity, or someone pushing your arm, or whatever. Muscles come in pairs to move limbs, or whatever, in different directions - bicep and tricep, for example. --Tango (talk) 15:47, 9 July 2008 (UTC)

What your teacher was probably trying to hint at is they can contract and relax but only in one direction. This is why you require an adjacent muscle to move it back. — CycloneNimrod  ^Talk? 15:59, 9 July 2008 (UTC)

Yes, if you are standing and try to let your arm follow its own course, it will fall down because of gravity. But if you are lying on a bed and then try to do same thing, or in other words if you try to stretch your arm in the horizontal direction, you will need the tricep muscles to do that. Biceps are to move your wrist towards your face, triceps are to do the opposite. DSachan (talk) 03:39, 10 July 2008 (UTC)

some naive hypothesis at odds with basis of physic- what wrong with them ?

I- In nature exist an unique particle where all kind of energies have the same value,where each physic law fit precisely.in this particle the matter is concentrated "in extreme" inside of " tiniest" portion of space.The concentration is so dense that is no room to accept the tiniest increment of matter and the gravity is so strong that do not permit any decrease of matter. This mean that the unique particle do not interact with common particles known by science and evidently is undetectable by whatsoever phenomenon known till now. Is it a black hole? It is not a hole . It is matter with it constituents: electric charge and charge of gravity.It is the brick in the structure of each common particle. The only variable in structure is radius of space occupied by par of unique particles. —Preceding unsigned comment added by 70.133.175.56 (talk) 15:49, 9 July 2008 (UTC)

I think you need to give a reason why such particles of opposite charge would not just clump together.. Otherwise your description sounds very similar to something like protons and electrons.87.102.86.73 (talk) 16:08, 9 July 2008 (UTC)

• "...where all kind of energies have the same value..."

I have no idea what that's supposed to mean.

• "in this particle the matter is concentrated 'in extreme' inside of 'tiniest' portion of space. The concentration is so dense that is no room to accept the tiniest increment of matter."

If it's a particle, it has no volume.

• "...and the gravity is so strong that do not permit any decrease of matter."

A black hole is anything with so much gravity that nothing can leave it, though Hawking radiation will appear right next to the event horizon, leave, and take some of the black hole's mass with it. I think quantum physics prevents anything smaller than a Planck mass (about the size of a small flea) form a black hole, so if it is a particle, it's very heavy.

• "This mean that the unique particle do not interact with common particles known by science and evidently is undetectable by whatsoever phenomenon known till now."

Force carriers are among the Hawking radiation, so it does interact with common particles.

• "Is it a black hole? It is not a hole ."

Thanks to Hawking radiation, it's not black, either. "Back hole" is a misnomer.

• "It is matter with it constituents: electric charge and charge of gravity.It is the brick in the structure of each common particle."

I have no Idea what any of that is supposed to mean.

• "The only variable in structure is radius of space occupied by par of unique particles."

Assuming it is a black hole, the no hair theorem, which may or may not be true, states that the only variables are mass (which can be calculated by volume), charge, and angular momentum. I'm not sure that's what you meant, though. — DanielLC 17:48, 9 July 2008 (UTC)

Did you actually see the title "...naive hypothesis..."??87.102.86.73 (talk) 17:53, 9 July 2008 (UTC)

July 9

Self-replication in open thermodynamics??

Conway's Game of Life was named as such only because the patterns are "life-like" in their complexity, and not because GOL represents a simulation of actual organisms. John von Neuman's self-replicating cellular automata was actually designed by hand, not discovered. We know that open (dissipative) thermodynamical systems give rise to spontaneous order, and the reason is because effective dissipaters of gradients are "fed more" by the source for logical reasons. This is why funnel clouds are self-sustaining in a tornado storm. It is also the reason that Benard Cells form in boiling water. Does there exist any such thermodynamic simulation in which self-replication is the "order" that arises spontaneously? I hope I am not the first person on earth to have asked this question! paros (talk) 00:48, 10 July 2008 (UTC)

You're certainly not the first to suggest it, but the first I've heard of it without reference to the thermodynamic objection to evolution. That said, many would say that the origin of life is the ultimate example of what you're asking. If you're specifically asking about something that has actually been observed, the only thing I can think of are protein-coacervates, which are capable of spontaneously forming from solvated proteins of a suitable nature, accreting more of them, and splitting upon reaching a critical size. Someguy1221 (talk) 03:49, 10 July 2008 (UTC)

Why does the temperature decrease with increasing altitude?

Gidip (talk) 16:46, 9 July 2008 (UTC) :This should answer your question pretty well. Per the below comment, disregard my link :) — CycloneNimrod  ^Talk? 17:09, 9 July 2008 (UTC)

I very much dislike the explanations given in the above link, and would point to the Lapse rate article and the explanation given in this section. Also, it's not always true that temperature decreases with increasing altitude.—eric 16:59, 9 July 2008 (UTC)

Agree, the explanation in the external link looks terrible to me. Volcanos? Franamax (talk) 17:12, 9 July 2008 (UTC)

Check out Earth's atmosphere for a description of the temperature changes due to increasing altitude (it doesn't just go down) and a discussion of some of the reasons. PhySusie (talk) 18:55, 9 July 2008 (UTC)

Thanks everyone. Gidip (talk) 19:05, 9 July 2008 (UTC)

"cynical but open minded" etc

On a programme "revealing" an illustionist I heard mention of a list of statements which most people thought applied to themselves more than to the general population. These are used by spoof mind readers etc. I have tried on WP psychology articles and google etc. Can anyone point me to such a list? --BozMo talk 17:29, 9 July 2008 (UTC)

The Forer effect and cold reading articles list some, but it sounds like you may have read those already. --Bennybp (talk) 17:41, 9 July 2008 (UTC)

No, I hadn't. Thanks for the steer. --BozMo talk 19:14, 9 July 2008 (UTC)

Formula to determine water flow rates and temperatures to maintain tank temperature.

I am looking for a formula or to be pointed in the right direction.

I have a tank of water.
I withdraw water from the tank at a constant rate, use it to cool a manufacturing process, and then return the water to the tank.
At the same time, I withdraw water from the tank at a constant rate, push it through a heat exchanger to extract heat from the water, and then return the water to the tank.
What temperature can I expect to maintain in the tank or what will be the rate of temperature change in the tank?

Assume:
Clean soft water.
Tank size: 500 gallons
Tank starting temperature: 75°F
Heat absorbed from the manufacturing process: 50 kW
Process flow: 16 gpm
Water temperature from the heat exchanger: 45°F
Flow rate from the heat exchanger: 30 gpm

The values above are likely to change, so I am looking for help on the formula.

Thank you for your assistance.
--Mikewbum (talk) 17:36, 9 July 2008 (UTC)

Mmmh 'gpm' as flow rate, does that mean 'grammes per minute'? (if it does it looks like your water will boil..) Sorry gpm is gallons per minute right?

Also you need more information (I think) to calculate how much energy is transfered per second in the heat exchanger.. that would depend on its design - ie how long the 'pipe' is that goes throught the water at 45F, and how good a conductor the exchanger is made of..

If you can supply a figure in watts for the heat exchanger, either as maximum or as a function of 'water in temperature', that would make it very easy.87.102.86.73 (talk) 17:58, 9 July 2008 (UTC)

In SI units it is incredibly easy but I don't use imperial. Roughly cooling 1 litre 1 degree Kelvin takes 4.2kJ so cooling 30 gallons=135 litres (imperial galloons?) by X F=Xx5/9 K takes Xx135x4.2x5/9 If X was 30 it gives roughly 10,000kJ a minute or 166kW say. But you only need to sink a third of this so the temp diff will fall to about 10F. Someone can correct the conversion and maths but that's the idea. --BozMo talk 19:25, 9 July 2008 (UTC)

To answer your q for clarification: taking 30F gives a heat transfer of 166kW but you only needed a heat transfer of 50kW to balance flow out with the 50kW in (that's the sink a third of that bit). So since the heat transfer is linear on the temp difference the stable temp diff would be about 10F. The important thing in the calc is to think in terms of "litre-degrees" of water as an energy unit. Then you work out how many litres how many degrees per minute and convert it to kW. --BozMo talk 20:41, 9 July 2008 (UTC)

If 50 kW out of the original 166 kW is used to cancel the 50 kW input of energy, shouldn't the remaining 166-50=116 kW cool the water by 20 degrees, which is two-thirds of 30 degrees? --Bowlhover (talk) 07:38, 10 July 2008 (UTC)

Except I think you want 30 U.S. gallons = 113.5 L so only 8F. Rmhermen (talk) 22:09, 9 July 2008 (UTC)

Thanks but its the other way round. Less water higher temp diff so 12F... --BozMo talk 22:27, 9 July 2008 (UTC)

Name of hard cardboard-like stuff

Hi all,

What's the name of that really stiff cardboard with tiny dimples/holes in it (dimples look like they were made with a needle)? This stuff is thinner than chipboard, yet stiffer and less papery than paperboard or corrugated cardboard. Any thoughts? Thanks! — Sam 19:18, 9 July 2008 (UTC)

Pegboard? APL (talk) 20:57, 9 July 2008 (UTC)

Ryvita? —Preceding unsigned comment added by 79.76.156.19 (talk) 21:20, 9 July 2008 (UTC)

Coroplast? --Sean 22:56, 9 July 2008 (UTC)

Hardboard, or one of its fiberboard kin. -- Finlay McWalter | Talk 23:00, 9 July 2008 (UTC)

Oriented strand board? Try looking through Category:Engineered wood. Dar-Ape 01:17, 10 July 2008 (UTC)

Hmmm... none of those, I'm afraid, and I had looked through all the categories. I guess I'll just go find it at my hardware store and ask there. Thanks! — Sam 13:52, 10 July 2008 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

Perfluorocarbon

Do the Perfluorocarbons make suitable refrigerants? Mimus polyglottos (talk) 19:57, 9 July 2008 (UTC)

The article says they are used as such (see the Other Applications section). Fribbler (talk) 20:05, 9 July 2008 (UTC)

Pakistani President Pervez Musharraf and his glasses.

Pervez Musharraf has glasses and I heard on T.V he cannot see without them. What's this illness? 190.49.95.195 (talk) 20:39, 9 July 2008 (UTC)

Eyeglasses are commonly worn by people who have one or more of the the following : Myopia, Astigmatism (eye) , Hyperopia, Presbyopia; however none of these are commonly referred to as an "illness." --LarryMac | Talk 20:46, 9 July 2008 (UTC)

I think this is really an English usage question, not a science question. When we say that someone "cannot see without his glasses", we just mean that he sees very badly without them. For example, maybe he has a severe case of myopia, astigmatism, or some such condition. --Anonymous, 04:55 UTC, July 10, 2008.

Penises

Today I read that 82% of men in the world have not been circumcised, and that outside the US erectile dysfunction is less common or to a lesser degree. Can this be verified? Mac Davis (talk) 20:50, 9 July 2008 (UTC)

I'm relatively sure, but with no citation, that 82% is an incorrect percentage. I'll have a look tomorrow when i've slightly more time. — CycloneNimrod  ^Talk? 22:31, 9 July 2008 (UTC)

We have an article, Prevalence of circumcision, with a lot of references in it. As for ED, I guess that could be related to obesity rates. Fribbler (talk) 22:35, 9 July 2008 (UTC)

Remember that correlation does not imply causation. Drownings increase in the summer, and so do ice cream sales, but ice cream doesn't cause drownings. --98.217.8.46 (talk) 01:15, 10 July 2008 (UTC)

Perhaps drownings increase ice cream sales ?

Pallbearer: "This sure is hot work, hold up for a sec while I get a nice triple scoop with sprinkles for my free hand." StuRat (talk) 03:46, 10 July 2008 (UTC)

I'd say the higher incidence of "ED" (or "LD", as I like to call it) in the US is because pharmaceutical companies in the US just love to call a normal part of aging a disease (so they can get people and/or insurance companies to fork out billions to buy their drugs). StuRat (talk) 03:43, 10 July 2008 (UTC)

(What's LD ? laser disk? lingam??)87.102.86.73 (talk) 10:38, 10 July 2008 (UTC)

LD = "limp ....". :-) StuRat (talk) 13:53, 10 July 2008 (UTC)

I'm really looking for an answer other than "carefully" here...

How do hedgehogs, porcupines, enchiladas, pangolins and any other type of spiny/razor-coated mammal that I haven't thought of actually mate without injuring each other? --Kurt Shaped Box (talk) 21:11, 9 July 2008 (UTC)

They flatten their spines (a bit like we do really :)) —Preceding unsigned comment added by 79.76.156.19 (talk) 21:15, 9 July 2008 (UTC)

See [21] for a description of porcupine mating. Dragons flight (talk) 21:17, 9 July 2008 (UTC)

In short, "very carefully" :-) --Carnildo (talk) 22:11, 9 July 2008 (UTC)

Hedgehogs do not have to be very careful. First of all, the spines are not that sharp. I regularly handle them with my bare hands. Only the babies have sharp quills (because they are so small). Second, the female has the ability to protrude her vagina well behind her spines. Her tail is very short and when curled upwards, the anus and vagina move behind it. Third, the male's penis is almost halfway up his abdomen. For reference, consider if yours was a few inches above your belly button. So, the male doesn't have to fully mount the female. he just slide up behind her a bit. His only real risk is having the female turn and bite if she's not in the mood. -- kainaw™ 22:28, 9 July 2008 (UTC)

Mindtrap

One of the question in the game "Mindtrap" is similar to this:

A guy who weighs 99kg wants to cross a bridge, but the maximum capacity is 100kg and he's carrying three 1kg gold balls.

He crosses it by constantly juggling all three in the air.

Is this legit? —Preceding unsigned comment added by 65.110.174.74 (talk) 23:48, 9 July 2008 (UTC)

No, he can't even cross the bridge juggling one ball, let alone three. The force required to slow the ball down while he's catching it will take the bridge load over 100kg. Of course, footsteps would have the same effect, so he probably wouldn't make it with zero balls. -- Tim Starling (talk) 00:14, 10 July 2008 (UTC)

But of course the Engineers who designed the bridge would have included a large factor of safety, so he should be fine ;-) Fribbler (talk) 00:19, 10 July 2008 (UTC)

And, of course, in the traditional manner of juggling three objects, two are frequently in the juggler's two hands at the same time. Deor (talk) 02:46, 10 July 2008 (UTC)

According to Newton's third law, every force has a corresponding force that is equal in magnitude and opposite in direction. For the man to send a ball upwards, his hands must apply a force greater than the gravitational force pulling the ball down. The ball in turn applies a pressure downwards, so the bridge experiences three forces:

(1) the force of gravity on the man (99 kg)

(2) the force needed to stop the downwards acceleration of the ball, which is equal to the weight of the ball (1 kg)

(3) the force needed to accelerate the ball upwards, thereby reversing its downward motion (a positive value)

Even juggling one ball would inevitably collapse the bridge. (Technically, kg is a measure of weight and not force, but I'm using the unit for convenience.) --Bowlhover (talk) 03:23, 10 July 2008 (UTC)

Just to be pedantic - kg is a measure of mass, not force. Weight is a type of force (force due to gravity). --Tango (talk) 14:07, 10 July 2008 (UTC)

I suggest he toss the three balls across first then walk very gingerly across the bridge. StuRat (talk) 03:39, 10 July 2008 (UTC)

He could also just take the balls across one at a time, or roll them across :p --Shaggorama (talk) 06:09, 10 July 2008 (UTC)

If the man's planning to carry his balls across, he'd better not lift his feet. Since the bridge can only withstand the force equivalent to the gravity on a 100 kg object, if his feet ever hit the deck, the additional force delivered would collapse the bridge. --Bowlhover (talk) 06:40, 10 July 2008 (UTC)

Gold is running >US$900/oz...surely with 3kg, he could shave off a little and just pay some lighter dude to carry the stuff across or a personal trainer to help him lose slightly more than 2kg of flab and carry them all himself. DMacks (talk) 12:25, 10 July 2008 (UTC)

Some interesting and good ideas but I personally wouldn't trust some lighter dude to take my 3kg of gold balls across a bridge which I potentially couldn't cross. Heck even if I could cross the bridge I'm not sure I'm going to trust some lighter dude. 3 kg won't weigh the dude down that much and he/she's going to have a head start of the length of the bridge at the very least. Nil Einne (talk) 18:05, 10 July 2008 (UTC)

What kind of bridge is that? Is it made out of bottlecaps and cardboard? He's either really fat or really muscular. Either way, that bridge shouldn't exist, and if he values his gold that much he can go take a different bridge. Unless he's crossing the moat from his castle (well he is carrying his money as gold balls) there's always a bank around that you don't need to risk your life on a ridiculous bridge to get to. Maybe he can use the money to find a competent engineer. -LambaJan (talk) 20:25, 10 July 2008 (UTC)

July 10

PMS citation needed

Dear Mr. editor,

I assume only male editors of a certain sort (who don't know women well, or aren't even interested) would feel that, under the description of PMS symptoms, "increased arousal and sex drive" needs citation as it might be "challenged"--by other males, no doubt. There is such a strong desire in the patriarchy to see generally normal conditions women go through (conditions that are counterproductive and not useful to Wall Street, or the male and extremely virile Spirit of Business) as 'diseases' in need of cures, that it has blinded many young men from discovering women for themselves. It makes many of us women who are self-aware and highly educated feel uneasy.

As a 27 year old woman who "suffers" from increased arousal and sexual desire before the onset of the period, and who knows many others who do, I find the feeling of the editor offensive.

pissed off in Brooklyn! —Preceding unsigned comment added by 69.112.205.26 (talk) 00:40, 10 July 2008 (UTC)

...did you have a question somewhere in there?

Oh, never mind, I'll answer one I am going to pretend you asked: just about every piece of information in Wikipedia should be cited in one way or another. (A lot of the time this doesn't happen, but that's still the ideal we strive for.) Why? Because it means that the information we put in here is verifiable, which means that if you read it, you can go back and see that it's not just something somebody on the internet made up.

Let me put it this way: a male editor of a certain sort, who doesn't know women well or isn't even interested, and is definitely kind of a dim bulb -- you may have met people like this -- may believe any kind of insane and stupid crap about women he happens to read on Wikipedia, even if it happens to be written by some malicious and misogynistic jerk. He has no way of knowing whether that information is any more real than the information about increased arousal and sexual desire before the period, and if there are no references cited, he has no easy way of checking whether this it's true. Whose purposes does that serve? (You may argue that people aren't that stupid, and I can only point out that a lot of people are, in fact, exactly that stupid.) If the facts we put in are verifiable, that means he can check the source for the information and see whether it's true. -- Captain Disdain (talk) 01:04, 10 July 2008 (UTC)

_______________________________ Thanks, Captain, for replying.

The question was implicit, which you responded: why the need for citation. While I completely agree with you, what ticked me off was that that was the ONLY 'symptom' the editor FELT needed citation, which I didn't emphasize above. So why not all of them?

For any of us who have even cursory knowledge of how women's sexuality and completeness as human beings has been denied throughout the ages ('penis-envy,' 'frigidity,' dispute of the existence of so-called 'G-spot'--basically calling into question anything that suggests women's affirmation of their 'virility'), a need for citation on particularly THAT point can appear as a symptom of something in need of overcoming. And I don't mean 'overcoming' as in practicing political correctness and affirmative action, that doesn't work. What works, and what every intelligent man knows, is paying attention to women's experience of their own bodies, beginning with one's girlfriend.

It's acceptable to tag any uncited statement with "citation needed" based on only a feeling. The policy on Wikipedia is to assume good faith; if an editor's actions can reasonably be explained as an attempt to improve the encyclopedia, we should treat it as such. A quick glance at the external links in premenstrual syndrome revealed that none reported increased sexual desire as a symptom. In fact, http://familydoctor.org/online/famdocen/home/women/reproductive/menstrual/141.html even listed "not feeling as interested in sex" as a characteristic of PMS. [22] and [23] list only changes in libido, implying libido sometimes increases and sometimes decreases. It's very probable that the editor who inserted the "citation needed" tag actually did believe that the statement regarding sexual drive is false, for there are plenty of reasons for that belief.

69.112.205.26, please sign your posts using ~~~~, like so: --Bowlhover (talk) 04:24, 10 July 2008 (UTC)

Another reason it may have been tagged is because the symptoms section is globally cited with 3 sources. I quickly browsed those sources and the 'symptoms' you mentioned aren't on any of them (I didn't check the others individually, just your fun ones). Maybe the people who originally posted those symptoms recognized a new one that wasn't from their citations and wanted it cited separately. Also, as a guy I'll admit reading that part of the article had a "really?" effect on me. Browsing around I saw various sources comment that there are more than 150 listed symptoms for PMS, so it must be listed in the literature somewhere if you want to go to the trouble of improving the article. --Shaggorama (talk) 06:04, 10 July 2008 (UTC)

The {{fact}} tag appears to have been added by a female editor.[24] Assumptions are always dangerous, in real life and here on Wikipedia. Franamax (talk) 08:32, 10 July 2008 (UTC)

The user is asking an excellent question. There is a good deal of information about the subject, though it may not be easily obtainable without a trip to a good academic (university) library. Here are two scholarly references that summarize a great deal of prior information.

Hedricks, Cynthia A. 1994 "Sexual behavior across the menstrual cycle: A biopsychosocial approach." Annual Review of Sex Research, 5: 122-172.

Wood, James W. 1994 Dynamics of Human Reproduction: Biology, Biometry, Demographics. NY: Aldine de Gruyter. Chapter 7: "Fecundability and Coital Frequency". See especially pp. 305-314, "Empirical patterns of intercourse."

Summarizing, the pattern of arousal and intercourse across the menstrual cycle is not simple. One pattern is a sharp decrease in intercourse during menses, followed by a sharp increase, a decrease, another increase around mid-cycle, another decrease, and another increase toward the end of the canonical 28 day cycle. Other women enact a different pattern, with a large mid-cycle increase, and still others have an increase toward the end of the 28 day period, as the questioner points out. All of these patterns are normal, meaning that they occur in women in good physical health and are not the result of physical or mental illness. Note that no single pattern characterizes all or most women.

Both Hedricks and Wood go into a great deal more detail, and give figures and citations to this body of work. The questioner might find the Hedricks and Woods' references very interesting.

Concerning the issue of verifiability and anger about what the questioner took to be knee-jerk masculine disdain and ignorance, I would like to apologize to her on behalf of Wikipedia. I also feel that Captain Disdain owes the questioner an apology for an uncivil, indeed, impolite answer.

Once again, it is an excellent question with very complex answers. I hope that I've at least supplied a starting point for more investigation and reading.

Timothy Perper (talk) 16:31, 10 July 2008 (UTC)

I would have to disagree with your apology suggestion. I don't find Captain Disdain's reply at all rude. In fact, the original questioner was rather rude and appears to be going on a long off topic rant that has nothing to do with the reference desk and didn't even ask a clear cut question in the first instance. Not only were the somewhat offensive assumptions of the questioners pointless, they have also been shown to be likely incorrect which just goes to show why you should never make pointless assumptions (the questioners could have simply 'asked' why it was the only sentence fact tagged without the long rant.) Captain Disdain did an admirable job under the circumstances. If the question asker had bother to do a bit of reading on policy and a bit of research, she could have improved the article herself and maybe even helped "blinded young men" and "self-aware and highly educated (women)" by producing a better quality and properly referenced article. Nil Einne (talk) 18:01, 10 July 2008 (UTC)

I quite concur. It's not the easiest thing in the world to be simultaneously angry, misandrist, and homophobic, but our original questioner manages it as though it were second nature to her. Perhaps because it is. - Outerlimits (talk) 18:06, 10 July 2008 (UTC)

Dang, I just lost out on being first to say that Captain Disdain has nothing to apologize for, they did their best to answer a (non-)question neutrally, the user went on to thank them for their answer. And the question was about referencing, not asking for the references themselves. Nil Einne, I'm not too happy though with you discussing a "pointless off-topic rant", the OP did have a point on a particular topic, they just didn't make it very clear. Franamax (talk) 18:05, 10 July 2008 (UTC)

Nonetheless, this is a reference desk, not a ranting desk. Or maybe that's just me lording my patriarchal power over Wikipedia. --LarryMac | Talk 18:10, 10 July 2008 (UTC)

Wow, are all the 14-year-old boys logging on today? If you can't help answer the question, don't post to the thread. This is a reference desk, not a place to retaliate in kind to people asking questions. If the question doesn't make sense, ask for a better question. We're supposed to welcome people here. Franamax (talk) 18:55, 10 July 2008 (UTC)

This is a place to answer questions with courtesy and the assumption of good faith. I won't respond to the other comments. They have nothing to do with the question asked. We are here on Wikipedia as a public service, and not to insult people. If the references I supplied helped, well, good, that's what an encyclopedia does. I am not here to call people names, like angry, misandrist, homophobic, pointless, and so on. Leave that home when you sign on to Wikipedia. Timothy Perper (talk) 19:39, 10 July 2008 (UTC)

Trying to provide a good-faith answer: PMS/PMDD has a very loose, variable set of symptoms, some of which are contradictory from woman to woman(or even within the same woman's experience). For instance, one might lose her appetite and even become nauseous, while another might have cravings for food she normally dislikes. So if you're dealing with a list of symptoms that anyone-- including any woman-- can edit, there will be "O RLY" reactions from some woman as well. (I'm a woman, by the way, and I was a little surprised at your entry "increased need for emotional closeness", because in my experience I usually want to be left alone at that time.)207.233.86.98 (talk) 20:49, 10 July 2008 (UTC)

High Frequency Electric Signal Over a Buffered Solution

When measuring the capacitance of electrodes in a buffered solution, why is it advisable to operate the circuit at a high frequency (above 1 MHz)? Is this to avoid electrolysis? —Preceding unsigned comment added by 140.247.153.158 (talk) 02:12, 10 July 2008 (UTC)

Do trees ever grow up ?

Say one of those lovely Druids nailed somebody to a tree so they would wiggle less while being disemboweled, would that nail still be the same height from the ground (assuming the soil level hasn't changed) ? I'm guesing that for a normal tree the height wouldn't change, but for bamboo and other similar fast-growing trees that it would be higher. StuRat (talk) 03:31, 10 July 2008 (UTC)

For any tree that is still increasing in height, you would expect that nearly all portions of its trunk would continue to get higher over time. Upward growth in trees includes not just growth at the tips, but pushing and stretching along nearly the entire length of the tree. Dragons flight (talk) 04:59, 10 July 2008 (UTC)

Hmm. I just erased my post saying that trees definitely do grow upward over time, based on my experience seeing fences lifted way above where they were originally strung. I know for sure that young trees grow upwards and I recall seeing fence-lifting on more mature (8-10" dia.) trees too. I'm stuck at this question though: most of a mature tree trunk consists of dead cells, other than the heartwood and cambium if I'm not mistaken (and I probably am) - so how would those dead cells grow upward with the tree? Do they separate and become less dense? Franamax (talk) 08:14, 10 July 2008 (UTC)

Mmmmh - 'fresh' cells can 'grow' by stretching ie elongation. At 8-10" maybe the cells still have some stretch left. By the time the tree is say 1foot diameter or more I'd imagine that the only way it can grow is out ie around.87.102.86.73 (talk) 10:50, 10 July 2008 (UTC)

Apologies if this would be a second question, but wouldn't they also grow out, stretching the remains over time? I guess it depends on the type of tree, I'm thinking of giant oaks here...209.244.30.221 (talk) 14

14, 10 July 2008 (UTC)

Bamboo is a grass, not a tree. — DanielLC 16:34, 10 July 2008 (UTC)

Bamboo is definitely a grass, but I think it meets our definition of tree as well. "Tree" is a growth form, not a clade. But then our definition of tree, requiring apical dominance, seems odd to me. A typical open-grown oak (surely a tree) doesn't have apical dominance, does it? (And I hope somebody knows the answer to Franamax's question.) --Allen (talk) 17:49, 10 July 2008 (UTC)

A tree doesn't "grow" in the way that you or I grew (where our head slowly moves higher and higher from the ground). Any given point within the envelope of a tree will remain in exactly that same place (+/- some bending and bugs) forever more. What happens is that every year, an entirely new layer of tree is deposited on the entire outside of the old tree.

The upshot is that branch you walked into mowing the lawn ten years ago is probably still there in exactly the same place to whack you on the head this year, but it's now a thicker, stronger branch. Well, unless it got shaded by things above it in which case the tree, forever optimizing its exposure to sunlight, may have discarded the branch entirely.

So if you're nailed to a tree and the nails were inserted dead level (horizontally), you'll be located at about the same height up the tree for as long as it takes you to fall to pieces.

Atlant (talk) 20:15, 10 July 2008 (UTC)

You may be right about trees after a certain stage of development, but your statement certainly doesn't apply to seedlings, so maybe a better way to ask the question is, "When, and how quickly and completely, do trees lose the capacity for stem elongation?" --Allen (talk) 21:45, 10 July 2008 (UTC)

Ammonium methanide

Is ammonium methanide an existing chemical compound? - Xxxx00 (talk) 07:28, 10 July 2008 (UTC)

By methanide do you mean CH₃^- or maybe carbide - either way the compound doesn't exist because both anions are too basic and will deprotonate the ammonium giving ammonia and a hydrocarbon.87.102.86.73 (talk) 09:47, 10 July 2008 (UTC)

There's also 'methanide' which is a generic tradename for a compound see http://www.chemindustry.com/chemicals/573762.html and http://www.flexyx.com/M/Methanide.html

This compound is already a ammonium type compound see quaternary amine87.102.86.73 (talk) 10:30, 10 July 2008 (UTC)

Thanks. --Xxxx00 (talk) 16:44, 10 July 2008 (UTC)

Decibel question

I apologise in advance if this is a stupid question: is it possible to convert between two different types of decibels? Specifically, from dBu to dBm. Thanks! Xenon54 11:03, 10 July 2008 (UTC)

Not without further information, since the dBm is a unit of power, while the dBu measures voltage. Algebraist 11:24, 10 July 2008 (UTC)

What do you mean by further information? If it helps any, I need to convert 56 dBu to dBm. Xenon54 12:07, 10 July 2008 (UTC)

You need to know the impedance. Is it 50 ohms, 75 ohms, 300 ohms or 600 ohms? —Preceding unsigned comment added by 79.76.204.247 (talk) 14:14, 10 July 2008 (UTC)

Seventy-five ohms. Xenon54 15:11, 10 July 2008 (UTC)

+56 dBV is one hell of a voltage especially in 75 ohms. Dont you mean -56 dBV? —Preceding unsigned comment added by 79.76.204.247 (talk) 15:36, 10 July 2008 (UTC)

I meant dBμV (aka dBμ and dBu). Sorry I didn't make that clear. Disregard this question, I found the answer anyway. Xenon54 15:45, 10 July 2008 (UTC)

And electric power is voltage times current/ --Bowlhover (talk) 11:32, 10 July 2008 (UTC)

GAS TO ELECTRIC POWER

QUESTIONS: 1. PLEASE,HOW IS GASES BEEN CONVERTED TO GENERATE ELECTRIC POWER?

2. WHAT IS THE BASIC PRINCIPLES BEEN APPLIED? —Preceding unsigned comment added by 41.205.163.220 (talk) 12:07, 10 July 2008 (UTC)

This really sounds like a homework question, so I doubt anyone's going to just give you the answer. You may want to check out our articles on natural gas and gas turbine. Also, I know that caps lock is cruise control for cool, but it'd still be nice if you didn't SHOUT. -- Captain Disdain (talk) 12:35, 10 July 2008 (UTC)

pharmacy education in europe

i was studying b.pharmacy 3year i listen in europe some countries offer free or lessfee education where i can get total information —Preceding unsigned comment added by Anil kakkerla (talk • contribs) 12:29, 10 July 2008 (UTC)

Some European countries offer free or subsidised tertiary education to their citizens and (often) long term residents; students from abroad generally pay hefty fees (indeed many British universities are heavily dependent on the large fees they extract from foreign students). -- Finlay McWalter | Talk 12:39, 10 July 2008 (UTC)

Exercise

With which of the following exercises would I use more energy?

• A: Cycling for 30 minutes at a heart rate of 130 bpm
• B: Increasing the resistance/speed so that my heart rate reaches about 150 bpm but I'll only be able to last about 13 minutes.

I cycle at the gym so air resistance isn't a factor at higher speeds. Thanks, Zain Ebrahim (talk) 13:03, 10 July 2008 (UTC)

According to the manual for the bikes in our PT room, the formula for calories burned (energy used) is: calories/hr = (VWR÷100+.0083V³)×7.2. V is the average velocity of the bike (if it wasn't stationary). W is the weight of the rider. R is the resistance setting. I assume that resistance settings change from bike to bike, but you can see that heart rate is not part of this equation. -- kainaw™ 13:17, 10 July 2008 (UTC)

I think that's based on some kind of average of human muscular energy expenditure. If you go with increased resistance you'll probably build a bit more muscle and stronger muscles use more energy (So, I'd personally go with B) -LambaJan (talk) 13:48, 10 July 2008 (UTC)

I don't know the exact relationship, but I do know anecdotally that heartrate is typically considered very closely tied into the level of exertion and the number of calories burned in an exercise. Can anyone confirm/deny? The article on aerobic exercise is mute on the issue. EagleFalconn (talk) 13:51, 10 July 2008 (UTC)

An increase on 20 bpm isn't very much at all. You aren't burning many more calories per minute at 150 bpm than at 130 bpm. If burning calories is your goal you are better off working out on setting A for 30 minutes than at setting B for less than half that time. Plasticup ^T/C 16:28, 10 July 2008 (UTC)

I think the pertinence of heart rate is that you want to work hard, but aerobically. If your heart rate during exercise is outside of a particular range, your muscles don't receive enough oxygen and becomes more reliant on an anaerobic metabolism resulting in acidosis. In other words, watching your heart rate allows you to do more work longer. --Shaggorama (talk) 18:56, 10 July 2008 (UTC)

African Americans and Sickle Cell Anemia

What will happen if a African American from USA who has Sickle Cell Anemia contracts a bout of malaria? --Anthonygiroux (talk) 13:04, 10 July 2008 (UTC)

Those with sickle-cell anemia should have double sickle-cell genes (one from each parent), which would make them quite resistant to malaria. So, if they did manage to contract it at all, the symptoms should be quite mild. StuRat (talk) 13:44, 10 July 2008 (UTC)

Non-steam coal engine technology?

Is there a type of technology that would use plenty of coal to burn, but does not generate steam? I am thinking of a hypothetical renaissance or industrial society that has access to mining and lots of coal (or a similar fossil fuel??) but very little water. (I'm assuming that steam engines require a quantity of water to boil.) Could the smoke alone from the coal or other primitive fossil fuel be used instead of steam to power heat engines, gears and primitive machines, possibly with the help of bellows, etc.? --Sonjaaa (talk) 13:51, 10 July 2008 (UTC)

A majority of energy and electricity generating technologies work on precisely the principle you describe. By burning the coal, water (or in the case of solar thermal energy a high boiling liquid) is boiled and the steam used to power a turbine. I guess you could use alternatives such as some other liquid that boils lower, such as ethyl acetate or acetonitrile, I personally don't know if there are any particular aspects of water that make it more desirable than other liquids besides its ubiquity on Earth and non-toxicity (which are pretty good reasons). FYI, even nuclear reactors operate on this principle...one of the major challenges and one of the really cool things happening in alternative energy is moving away from the turbine model because it is somewhat wasteful (heat transfer to the turbine, moment of inertia requirements for rotation, losses due to friction). Among the technologies that do this are solar panel, though even wind power is just a

turbine turned by wind instead of boiled water. EagleFalconn (talk) 14:16, 10 July 2008 (UTC)

If you were to use the gases resulting from the burning of the coal alone, I guess in theory, you could generate power that way, but it'd be so inefficient as to be completely pointless. Heating water gives you a lot of steam to work with, and high-pressure steam is pretty powerful. (Steam engine explosions can be pretty devastating.) The reason for this is that when a liquid turns into a gas, it expands a great deal and thus generates pressure. You can harness that power.

Just burning coal, on the other hand, generates heat and smoke, but not all that much pressure; you get some gas out of it, sure, but nowhere near enough to generate a meaningful amount of pressure -- it's essentially just carbon and whatnot carried on the hot air that rises up from the fire. Using bellows wouldn't really make the smoke pressure any higher, it'd just help the fire get hotter by delivering more oxygen into it. (I guess you would get some additional pressure from the act of pumping in the air, but then you could just pump air in the first place and skip the part with the coal altogether.) Of course, an additional problem would be that in order for the coal to burn in the first place, it would need two airways -- one to remove the carbon that would choke the fire (a chimney, in other words) and another to let in fresh oxygen. This means that there wouldn't be a great deal of pressure building up, since there would be nothing to contain it. I guess you could rig up some sort of a wind mill type of thing operated by the hot gases surging up the chimney, but it wouldn't be efficient. The pressure would just be too weak. -- Captain Disdain (talk) 14:25, 10 July 2008 (UTC)

Two paths - one for oxygen, one for exhaust, need to increase pressure. I think we already have this solved - internal combustion engine. Now only need a way to get the coal into the chamber - coal gas is one way and was available in the time of steam engines. Rmhermen (talk) 15:24, 10 July 2008 (UTC)

That's an interesting idea. I'm not an engineer, so I have no idea how viable that would be, or how well it would fit in with the fairly primitive technology parameters given by the original poster (it strikes me as more advanced than I inferred the question to allow, but maybe I'm wrong)... but I dig it. -- Captain Disdain (talk) 15:57, 10 July 2008 (UTC)

A Stirling engine may be what you're looking for. It's a type of engine that works off of two gas chambers one heated and the other cooled. Except for leakage, no fluid is lost, and the fluid involved is typically just air anyway. APL (talk) 14:31, 10 July 2008 (UTC)

I've heard of steam engine trains having some device to condense some of the water and reuse it that was used when the train went through large areas with no water. This probably was't the most efficient way, but they just needed it to be efficient enough, and didn't want to have to build a new engine. — DanielLC 16:29, 10 July 2008 (UTC)

This was a major issue for oceangoing steamships. Seawater was aggressively corrosive to most equipment of the day, and was a nuisance to use in boilers because it would leave solid salt deposits on evaporation. Obtaining frequent freshwater refills is even more difficult at sea than on long stretches of wilderness railroad. Consequently, closed-cycle systems were developed that condensed the steam (after expansion and extraction of most of its energy) back into liquid water.

I will also note that one of the products of combustion of hydrocarbons is water vapour; if you had a cold surface you could fairly readily condense some of that water out for use from the exhaust of your system. (If you look at the tailpipe of a car right after starting the engine on a cold day, you'll often see drops of liquid water.) TenOfAllTrades(talk) 17:51, 10 July 2008 (UTC)

The oldest part of what is now the London Underground system was originally operated using condensing steam locomotives, but it was done to keep steam out of the tunnels, not to economize on water. In fact when the route now called the Circle Line was completed, the condensing became a major issue because the condensing tanks had to be drained and refilled with cold water in order to keep working, and once the route was a continuous circle there was no place where a long enough stop was possible. So after that the drivers sometimes had to release steam into the tunnels after all. (And clearly this is irrelevant to the original question, for which some other sort of engine is wanted.) --Anonymous, 22:52 UTC, July 10, 2008.

Both World War II Germany and apartheid-sanctions era South Africa made extensive use of coal to produce a direct substitute for gasoline. Franamax (talk) 18:50, 10 July 2008 (UTC)

You can run a diesel engine or a gas turbine engine on powdered coal. There are problems with doing so that have never been fully solved however, specifically the abrasive nature of the ash, although powdered coal was one of the target fuels for the original diesel engine invention. The USSR also had a powdered-coal MHD plant near Moscow but this was reported to not have been a success. --BenBurch (talk) 19:00, 10 July 2008 (UTC)

You may be interested in the Thermoelectric effect (Peltier effect). Series of wires of different metals heated on one side and cooled on the other can cause a current to flow - no fluid needed. The efficiency and scalability is not all that great, but as an added benefit, they can function equally well as Peltier coolers: add current, and get a temperature gradient. -- 128.104.112.147 (talk) 19:33, 10 July 2008 (UTC)

Note: you could still operate a steam engine in the conditions you describe by having a closed system with condensors - so that no steam is lost - you'd need some water - but only at the beginning - such a set up would be better suited to a stationary engine since those condensors would probably take up a bit of room..87.102.86.73 (talk) 19:42, 10 July 2008 (UTC)

Static build up on my cable modem?

I frequently need to power-cycle my cable modem to get it to work -- once every two or three days. The technician says that this is most likely because of static buildup. (1) Is this really the most likely explanation? (2) Could I solve this by grounding the box in some way? Like, say, attaching a wire between the metal end of the coax cable and the ground pin of a wall outlet?

Thanks! — Sam 13:59, 10 July 2008 (UTC)

It would depend on the symptoms you're experiencing. My best guess says probably not, most networking hardware that I'm familiar with is grounded, particularly stuff that your internet service provider is going to want back. The way to know if its already grounded is to see if it has one of those 3 pin plugs (if you're in the United States). From my experience with tech support, power cycling on a cable modem is usually necessary due to voodoo (which is to say, theres no discernable logic as to why you really need to...you just do). If static charge really is the answer, grounding the box should solve the problem. I would recommend against using the ground pin on the wall outlet though, you'd be better off (its easier and safer) to attach the modem via a wire to something else that is already grounded (the power supply on your computer, for example). EagleFalconn (talk) 14:23, 10 July 2008 (UTC)

Oh, and an afterthought. I don't know that unplugging your cable modem and then plugging it back in would actually get rid of a static charge on the thing. If its already grounded, that shouldn't be the problem. If its not, unplugging the thing should result in it maintaining the charge because it'll have no where to go (air is a very good insulator). EagleFalconn (talk) 14:29, 10 July 2008 (UTC)

I've come across a lot of networking stuff (albeit I've never used a cable modem) with simply a power supply brick. Unplugging it in itself may not help with static buildup but if the case is made of metal when you touch it and you're grounded you're likely to discharge the thing. If this is the case then simply going through the same motions as when you unplug it without unplugging it should do the trick though Nil Einne (talk) 17:40, 10 July 2008 (UTC)

inequalities for one-dimensional Schroedinger equation (moved from Math desk)

For concreteness, I assume that I have the one-dimensional, time-independent Schroedinger equation on a finite interval (from -1 to 1, say) with two potentials U and U' which go to plus infinity at both boundaries -1 and +1, so that both Schroedinger equations have a purely discrete spectrum. Further I assume that U' > U in the whole interval -1 < x < 1. What then can be said about the energy eigenvalues? Specifically, is it true that E'_n > E_n for all n? In which book the answer to this question can be found? —Preceding unsigned comment added by 193.144.64.159 (talk) 14:39, 10 July 2008 (UTC)

This isn't very helpful (yet) as I'm still working out the problem. But I can tell you that using proof by contradiction that E_n != E'_n, though I can't tell you whether its greater or less than (yet). I'll post something more complete when I've got a full answer. You may want to study the particle in a box, as its essentially the problem you're proposing here. EagleFalconn (talk) 15:05, 10 July 2008 (UTC)

I've hit something of a roadblock. The problem is that we don't know a specific form for U or U', and so its somewhat challenging to really try to evaluate the energy. I've got a good guess, but I'd seek verification. E'_n must be greater than E_n if U' > U because if the potential were to increase then for the particle's wavefunction to exist in the space of the increased potential its energy must increase. My basis for this is quantum tunneling, but I don't know how accurate that really is. I'm going to do the obvious thing (that I should've done before) and move this question to the Science desk. EagleFalconn (talk) 15:56, 10 July 2008 (UTC)

Well, my intention is to find lower bounds for the energy eigenvalues E'_n of an ugly potential U' by the energy eigenvalues E_n of a nice potential U (concretely the box potential). So the fact that the specific form of U' is not known is unavoidable. I think that it is easy to prove that the inequality holds for the lowest eigenvalue, E'_1 > E_1. The question is what can be said about the higher eigenvalues. —Preceding unsigned comment added by 193.144.64.159 (talk) 16:13, 10 July 2008 (UTC)

almost certainly the same behaviour as for the lowest enegry solution, is the box potential flat? 87.102.86.73 (talk) 17:34, 10 July 2008 (UTC)

The box potential is an arbitrary function U'(x). I feel like the OP is perhaps trying to come up with a method to describe an arbitrary potential in the form of a known potential? OP, is that correct? If so, I feel like you might be better off making it the subject of your PhD thesis...EagleFalconn (talk) 17:46, 10 July 2008 (UTC)

The "box" potential is the infinite square well potential. And yes, I want to use the known energy eigenvalues of the Schroedinger equation of the square well potential to find bounds for the eigenvalues of the ugly potential U', which is known only numerically, but which can be bound by the infinite square well. —Preceding unsigned comment added by 193.144.64.159 (talk) 18:14, 10 July 2008 (UTC)

The potential inside the box. What is that? can it be anything, or a flat finite value? or something else?87.102.86.73 (talk) 18:26, 10 July 2008 (UTC)

note if the potential inside the box is constant at G then the energy eigenvalues have a simple relationship E_n'=E_n-G , if the potential inside the box is not flat then you will almost certainly be looking at a completely different wavefunction solution. Did any of that help?87.102.86.73 (talk) 18:35, 10 July 2008 (UTC) (that was for U'=G, U=0)

My intuition is that what you are trying to prove is actually not guaranteed to be true for any eigenstate other than the first one, however I don't have any rigorous counter examples.

That said, if you know the U' potential numerically, you can apply to eigenstates of the U potential (i.e. sine waves) plus perturbation theory to estimate the energy change. Through second order:

$E_{n}'\approx E_{n}+{1 \over 2}{\int _{-1}^{1}\psi _{n}(U'-U)\psi _{n}^{*}dx}+{1 \over 4}\sum _{k\neq n}{|{\int _{-1}^{1}\psi _{n}(U'-U)\psi _{k}^{*}dx}|^{2} \over {E_{n}-E_{k}}}$

Where E_n' is the energy of the n-th eigenstate of U' and ψ_n and E_n are the n-th eigenstate and eigenenergy of U.

In an expansion like this, one can easily see that the leading order correction is negative (more binding energy) if U' < U everywhere. However the second order terms are only negative everywhere that E_k > E_n, i.e. if k > n for the box potential. It strikes me as possible that one could construct potentials U' where higher order terms gave rise to a net perturbation for the high order eigenstates that was opposite in sign from what you expect even with U' < U everywhere. Regardless, if you know the numerical form of U' then application of perturbation theory is probably a good bet. Dragons flight (talk) 19:01, 10 July 2008 (UTC)

Hi, finally I believe that I solved the problem by myself. Here it goes, tell me if you find an error. We introduce the Hamiltonian

$H(s)=-{d^{2} \over dx^{2}}+U+s(U'-U)$

and study its eigenvalue problem

$H(s)\psi _{n}(s)=E_{n}(s)\psi _{n}(s)$

Acting with

$\int dx\psi _{n}^{*}(s)$

on that expression and performing the derivative w.r.t. the parameter s leads to

${d \over ds}E_{n}(s)=\int dx\psi _{n}^{*}(s)(U'-U)\psi _{n}(s)\geq 0$

from which the statement follows. What do you think? —Preceding unsigned comment added by 193.144.64.159 (talk) 19:20, 10 July 2008 (UTC)

No, that doesn't work.

$\int dx\psi _{n}^{*}(s)$ gives $E_{n}(s)=\int dx\psi _{n}^{*}(s)({-d^{2} \over dx^{2}}+U+s(U'-U))\psi _{n}(s)$

$=-{\int dx\psi _{n}^{*}(s){d^{2} \over dx^{2}}\psi _{n}(s)}+{\int dx\psi _{n}^{*}(s)s(U'-U)\psi _{n}(s)}+constant$

The derivative is:

${d \over ds}E_{n}(s)={-{d \over ds}\int dx\psi _{n}^{*}(s){d^{2} \over dx^{2}}\psi _{n}(s)}+{\int dx\psi _{n}^{*}(s)(U'-U)\psi _{n}(s)}$

However the first term is not guaranteed to be zero, unless ψ commutes with the x derivative, which in general it will not. Dragons flight (talk) 19:41, 10 July 2008 (UTC)

Process Engineering

1. WHAT IS PROCESS ENGINEERING? —Preceding unsigned comment added by 41.204.224.41 (talk) 16:06, 10 July 2008 (UTC)

• See Process engineering. --jpgordon^∇∆∇∆ 16:10, 10 July 2008 (UTC)

some naive hypothesis at odds with basis of physic----- what wrong with them  ?

is true for low and high velocities but is not true for super high velocities when (C^2-V^2)^0.5 is comparable with another kind of velocities :Э=((f*m0)/r0)^0.5 which belong to the object in movement and has to do with gravity. If we ad in denominator this velocity , regardless it may be negligible small,we will have another meaning : the formula became determined and fall the absurdity of infinity. The revised formula will be :S0= C/((C^2-V^2)^0.5 + Э0). When V=C we'll have S0= C/Э0 that is not infinity. Further: the common particle in movement gain mass and shrink in radius via the formula: m=m0*s and r= r0/s all the way that velocity go up. So one component in denominator go dawn the other go up , when they equal we'll have Smax. After this V go 0, Э go C, S go 1 and m go M , r go R that is the common particle became an unique particle. The formula in dynamic supposed to be:

S=C/((C^2-V^2)^0.5+Э0*S0) = 1/((1-β^2)^0.5 +γ0(1/((1-β^2)0.5+ γ0))) here γ0=Э0/C For electron Э0=1.4687204*10^-11 cm/sec, S0=M/m0=2.0411812*10^21. For proton Э0=2.969794925*10^-8 ,S0=1.111662*10^18

III-- The formula for unique particle is M= e/f^0.5 gr. [The formula for common particle is m= f*M^2 / (r*C^2)] Here :"e"is the electric charge = 4.8032041*10^-10 cm^3/2*gr.^1/2*sec^-1

f^o.5 supposed to be gravity charge = 2.5832150*10^-4 cm.^3/2 *gr^-1/2 *sec^-1. let name f^0.5=i we'll have +i,-i

It is known that electric charge are two kind :plus and minus the different sign attract each other the same repel.

The gravity charge too has two sign plus and minus . Here the same sign -- attract the different-- repel.

It came that the unique particle has fore combination of charges : M-I(-e,-i), M-II(+e,+i), M-III(-e,+i),M-IV(+e,-i)

As a charged particle the single unique particle never stand free, it is always in liaison with the same mate.

We'll have ten possible " par combination " depending by each particles charges.Let see them.

The electric force of two unique particles will be:F= (F^o.5)^2= (e/r)(e/r). where "e" can be plus or minus.

the gravity force will be: F= (F^0.5)^2= f*M^2 / r^2 = ((f*M/r)/f^0.5)^2=(Э^2/f^0.5)*(Э^2/f^0.5)= (Э^2/i)(Э^2/i).

Here Э^2=C*Э0. The forces inside the particle will be: e^2/r^2= (CЭ)^2/i^2,or:(e/r)(e/r)=(CЭ/i)(CЭ/i). —Preceding unsigned comment added by 70.133.175.56 (talk) 16:09, 10 July 2008 (UTC)

I'm afraid I'm having a lot of trouble following your work. If you could point me to a previous post or some kind of reference where you start at the beginning, I might be able to help, but as it is a lot of your symbols are for things I don't think you're defining and I feel that perhaps we're stepping in in the middle of your derivation. Is anyone else having more luck following this math? EagleFalconn (talk) 17:54, 10 July 2008 (UTC)

I think it's a continuation of this thread. I can't make head nor tail of it myself. Franamax (talk) 18:46, 10 July 2008 (UTC)

Clawed Lobster Population

How many clawed lobsters (as opposed to Spiny, Reef, etc) are there in the world.

68.166.120.162 (talk) 19:22, 10 July 2008 (UTC)Andrew

I suspect many lobsters are called Claud. Some have other names :)

quantum mechanics, laplacian

For three dimensions the laplacian operator is used in the schrodinger equation. Why is a linear sum of the partial derivatives used and not the square root of a sum of the squares?87.102.86.73 (talk) 19:29, 10 July 2008 (UTC)

See Laplacian. Essentially, its that the Laplacian is the del operator dot the del operator. EagleFalconn (talk) 19:54, 10 July 2008 (UTC)

If I take it to be related to 'momentum squared' I can see the reason for a linear sum..

But if I take "d²/dx² of wavefunction" to be proportional to E_x then I expect a 'pythagorean sum'.. hence the confusion - one way of looking at it gives different results to the other.?87.102.86.73 (talk) 21:15, 10 July 2008 (UTC)

Energy is a scalar, not a vector. Hence the idea of treating at as the magnitude of an energy vector would make no sense. Dragons flight (talk) 21:19, 10 July 2008 (UTC)

Oil from plant cuttings and wood chips

LS9, Inc. is a company that claims to have microbes capable of eating biomass and producing crude oil. Naturally with the price of crude oil headed toward $$$ per barrel you would expect many such claims. The question is whether such claim are bogus. If not what microbes can do this? -- adaptron (talk) 20:31, 10 July 2008 (UTC)

It is possible that they are a scam, but its not certain. Note that they do not claim to produce crude oil (although they misuse the term petroleum), but rather "a portfolio of drop in compatible hydrocarbon-based fuels and chemicals". Something like this was recently on the Nature Podcast, so it is at least not outright impossible. Whether it is cost- and energy efficient and work on an industrial scale is a different question... --Stephan Schulz (talk) 20:48, 10 July 2008 (UTC)

Two questions about calorie use

1. According to an online calorie calculator, one can burn about 75 calories by walking at a moderate pace for 30 minutes. About how many more calories are burned if one is carrying a ten-pound load(say, a backpack) for the entire duration of that walk? Is there a formula that determines additional calorie use when carrying burdens of various weights?

2. Does "intellectual activity" use up any significant amount of calories? Say that two people of the same weight, health and metabolism are both lying still and watching TV. However, one is paying close attention to the show, making lots of mental notes on the activity, while the other is just kind of taking it in, without much conscious thought. With that in mind, could one lose weight by doing difficult mental math problems if conventional exercise is not an option? 207.233.86.98 (talk) 20:42, 10 July 2008 (UTC)

from: http://malaysia.answers.yahoo.com/question/index?qid=20070311174445AAWxTft&show=7

"Energy consumption in the brain is related to learning. In other words, once you've learned something (like mastering that chess game), the energy consumption goes down."

"Energy consumption by the brain is 230-247 calories, based on 17 calories/gram and human brain sizes of 1,350-1,450 grams. During periods of peak performance, adults increase that energy consumption by up to 50%, according to psychology lecturer Mark Moss, of the University of Northumbria.

While this may not seem an extraordinary amount of energy, the brain may use 30% of a body's total energy, while being only 2–3% of total body mass." —Preceding unsigned comment added by 68.166.120.162 (talk) 20:50, 10 July 2008 (UTC)

Closed Timelike Curve question

My question is basically this: Suppose you receive a bottle from the future containing Carbon-14 and Nitrogen-14, and a piece of paper listing their proportions. You then measure the proportion for yourself, and come up with an answer. You write it down and send it and the bottle to the past. However, for this to be the same (as is required to be a stable time loop), the Carbon-14 must not have undergone any radioactive decay in the period between when you received it and when you sent it back. How does this work? --Zemyla^t 23:15, 10 July 2008 (UTC)

I think people who believe that this sort of time travel makes sense would answer that you just can't do this one. Just like you can't have a closed timelike curve that involves you killing your grandfather. --Allen (talk) 23:52, 10 July 2008 (UTC)

Here we go: Novikov self-consistency principle. --Allen (talk) 23:54, 10 July 2008 (UTC)

Since the process starts with you receiving something from the future, an event you have no control over (at least, not yet), you can't force such a cycle to happen since you can't sent the bottle back if you didn't receive it in the first place. Therefore, it's simple enough to just assume no such bottle would ever arrive from the future so the problem will never come up. The alternative is to assume one of the theories of time travel involving alternate realities so the bottle doesn't go back in time to your universe, it goes to an alternate one and the paradox disappears - I've never found those theories convincing, though. --Tango (talk) 23:57, 10 July 2008 (UTC)

Can I feed Rich tea and other hard biscuits to the larids?

I've been tidying a relative's house up today. She's been in hospital for months and is going to be well enough to come home soon, so I'm getting things ready for her. I went though the cupboards and found lots and lots of out of date biscuits. So, I've got like 20lbs of old biscuits in my house now. They're not mouldy or anything but I'm not gonna be eating them. I was going to feed them to the always hungry seagulls instead of just binning them but I wanted to check here before I do. I know not to feed them anything with chocolate on it but can gulls safely eat hard, dry biscuits like rich teas? I've seen the way they gulp their food and I don't want them to hurt their throats because of me. Thanks a lot. --84.67.208.62 (talk) 00:22, 11 July 2008 (UTC)