Wikipedia:Reference desk/Archives/Science/2008 July 31

= July 31 =

Touch pads
How can one interface with a capacitance based touch screen without the use of a finger or other body part? Nadando (talk) 00:15, 31 July 2008 (UTC)
 * Stylus? unless it has a thermal basis. See Touch screen. Julia Rossi (talk) 00:53, 31 July 2008 (UTC)

Odor spectrum
As a spectrum analysist, I'm wondering what different foods I should eat to give the broadest range of odors from my gaseous emissions. Any help appreciated! —Preceding unsigned comment added by ProperFraction (talk • contribs) 00:34, 31 July 2008 (UTC)


 * As an omnivore you could say it's already happening. Julia Rossi (talk) 00:55, 31 July 2008 (UTC)


 * Well from your link, I don't see much about increasing the range of smells emitted from the internals. Could you please be more precise? —Preceding unsigned comment added by ProperFraction (talk • contribs) 01:38, 31 July 2008


 * I don't think that more precision would be appropriate from we armchair Gastroenterologists. Please consult a medical professional for a more detailed response.  -hydnjo talk 04:48, 31 July 2008 (UTC)


 * More elements means more compounds! Increasing sulphur compounds in breath can be done by eating plants from the Alliaceae family, i.e., garlic and onions. When digestion comes into play, sulphur containing food like the above or food with a high percentage of sulphur-containing amino acids would be best, e.g. eggs. --Ayacop (talk) 09:18, 31 July 2008 (UTC)

Name of measure of time
Is there a measure of time that is some unit from the last planetary alignment? Graham (talk, contrib, SIGN HERE!!!) 03:08, 31 July 2008 (UTC)


 * Alignment of which planets? I'm not quite what you're looking for, do you mean a more concise way of saying "X years since the last alignment"? If so, there's nothing that I know of, you'll just have to write it out in full - you can pick your own abbreviation and use it after the first time, though. How about YSA ("Years Since Alignment")? --Tango (talk) 03:12, 31 July 2008 (UTC)


 * My understanding is that the planets in our Solar System have never actually aligned. They've gotten relatively close to being in a sort of line-ish sort of position, but never lined up in any real way.  So, without a real event, there cannot be any time since the event. --  k a i n a w &trade; 03:30, 31 July 2008 (UTC)


 * Do you know when this "sort of" alignment occured? And how exact was it? If it wasn't exact, and no event like this has happened before, I could use the creation of the solar system as my reference point and call it "cycle 0" or something like that. Graham (talk, contrib, SIGN HERE!!!) 04:31, 31 July 2008 (UTC)

Graham: See Syzygy for some enlightenment, especially the Syzygy section. =Axlq 04:56, 31 July 2008 (UTC)

is a good explanation of how unlikely it is. --Tango (talk) 21:05, 31 July 2008 (UTC)

Capillary waves on a lake
Today, while I was out boating, I noticed an interesting phenomenon. There was a large patch of "choppy" water--just small capillary waves with wavelengths being approximately 1-2 inches, caused by wind (i.e. not from boats). Then, just a short distance away, there was a large patch of very smooth water. I was wondering why there would be such defined differences in water turbulence in relatively the same area. I assume that it would be affected by varying air currents over the water and/or the water depth in the different areas, but I would like to know a little more on the subject. Any input would be appreciated. Thanks in advance!!

Dimblethum (talk) 06:54, 31 July 2008 (UTC)


 * You may have seen Langmuir circulation, whose wikipedia page is unfortunately a bit short on explaining the mechanics. EverGreg (talk) 11:21, 31 July 2008 (UTC)

Optical illusion, disappearing image
Can anyone tell me why image 18 in this gallery only appears at a distance? If the monitor matters, I'm looking at it on an LCD. Disappears completely when I get close to it. Someguy1221 (talk) 07:14, 31 July 2008 (UTC)


 * Try Figure-ground (perception) - this site has lots more. -hydnjo talk 11:02, 31 July 2008 (UTC)


 * I think this one is closer to the same illusion. -- BenRG (talk) 11:29, 31 July 2008 (UTC)


 * 'tis indeed! I was shy about linking to that site with its Dalí image beneath. ;-(  hydnjo talk 23:36, 31 July 2008 (UTC)


 * This also seems relevant: http://www.michaelbach.de/ot/fcs_SpatFreqComposites/index.html —Keenan Pepper 03:47, 1 August 2008 (UTC)


 * Note that shrinking the image in a photo editor, shaking your head violently, scrolling the page quickly, and dimming the light will all cause the image to become more prominent. This implies that the contrast between the white and dark bars hides the subtle colour differences in the dark bars.  When the bars are blurred by distance, most of the image becomes shades of grey or brown and the colour differences can easily be noticed.  The fact that dimming the light helps implies the white bars are overwhelmingly bright at close distances and causes all darker bars to seem completely black.  --Bowlhover (talk) 07:57, 1 August 2008 (UTC)


 * Although interesting enough, that figure doesn't work at all for me. Even if my nose is touching the monitor I can kind of still see the bear (obviously it's difficult to recognise as a bear but there's clearly a shape). Well unless I turn the contrast to an insanely low level Nil Einne (talk) 08:26, 1 August 2008 (UTC)


 * The image is quite clear to me at any distance... --M1ss1ontomars2k4 (talk) 03:31, 2 August 2008 (UTC)

semiconductors
What will happen to the characterstics of any semiconductor if we add an impurity with two or six electrons in valence shell???? 13:19, 31 July 2008 (UTC)swadesh


 * Looks a bit like homework, so see Doping (semiconductor) to find the answer yourself —Preceding unsigned comment added by 79.76.183.222 (talk) 16:08, 31 July 2008 (UTC)
 * Answer is not there..

Typically silicon ( and other group 4 semi conductors are doped with group 3 and 5 elements), doping with group 2 and 6 might be expected to have the same effect, but is not as likely, in the case of oxygen (6), formation of non conduting silica is likely, in the case of magnesium or calcium (2) - salt like compounds may form and 'salt out' to form separate phases. If they do not salt out -then expect properties similar to B doped Si, but more so.

In the case of other group 6 elements S, Se, Te I would expect an increase in conductivity (similar to P doping) but with the larger elements it may not be likely that the element will successfully incorporate itself into the Si matrix.

Was it Silicon you were specifically thinking about, or another semiconductor? - because in some cases metal atoms eg can increase conductivity in semiconductors by electron donation, or even convert non conductors to semiconductors.

You may need to be more specific.87.102.86.73 (talk) 17:00, 31 July 2008 (UTC)

Bug I.D. of the day
Can anyone make a guess about the species of an insect I found in my house last night (and foolishly released before photographing)? I'm in eastern Massachusetts. Features I remember are:


 * - generally appeared like something between a stonefly and a moth


 * - overall ~2 inches long


 * - Two pairs of transparent wings, which fold parallel to the perching surface when it's not flying (resulting in overall elongated heart-shaped profile.) Back wings shorter than front wings.


 * - feathery mothlike antenna


 * - long, narrow dark brown body. Very flexible, such that it almost looked limp hanging below the wings when in flight.

Any guesses, or leads? My wife and I have exhausted all the dichotomous keys and such that we could find.

Thanks, jeffjon (talk) 15:43, 31 July 2008 (UTC)


 * First thing to hit me is something like a lacewing. The green ones are the ones I usually see. --Wirbelwind ヴィルヴェルヴィント (talk) 18:23, 31 July 2008 (UTC)


 * That Chrysopa perla is definitely the closest yet. The trick will be finding one with that particular coloring and antenna type. jeffjon (talk) 18:52, 31 July 2008 (UTC)

Tree I.D. of the day
Can anyone make a guess about the species of a tree growing near my home (which I'll be photographing later)? I live in Belle Center, Ohio, but the property's owner told me some time ago that it's from her native Colorado. It's somewhat furry, and is (according to her) called an "elkhorn", but Elkhorn doesn't have anything like it, and nothing that I can find on Google (either searching for elkhorn tree or "elkhorn tree") is at all related to it. Nyttend (talk) 17:20, 31 July 2008 (UTC)
 * Here are the pictures. Nyttend (talk) 17:38, 31 July 2008 (UTC)


 * It's not quite "elkhorn," but could it be a Staghorn Sumac? Laenir (talk) 20:07, 31 July 2008 (UTC)


 * The leaves are the wrong shape for your basic wild staghorn sumac. This may be the cultivar Rhus typhina "Laciniata", the cutleaf staghorn sumac. Deor (talk) 22:33, 31 July 2008 (UTC)

Logical calculation
TWO + TWO _________ FOUR _________ In the equation above if W=2,Find T,F,O,U,R.such that no one of them will be same. —Preceding unsigned comment added by 195.225.63.218 (talk) 19:40, 31 July 2008 (UTC)
 * Assuming you mean 'no two are the same', there's a unique solution. The easiest way to find it is probably to consider the possible values of O. Algebraist 19:47, 31 July 2008 (UTC)
 * That assumes, of course, that T,F,O,U,R are whole numbers less than ten. Maybe that's why the OP is confused?  --Bowlhover (talk) 21:05, 31 July 2008 (UTC)
 * And please find the solution yourself.--El aprendelenguas (talk) 19:51, 31 July 2008 (UTC)


 * Got it! Assuming that each alpha was assigned to only one digit, the solution is unique. Proof in the margin. -hydnjo talk 21:23, 31 July 2008 (UTC)
 * Well done. Algebraist 21:26, 31 July 2008 (UTC)
 * Easy peasy! And, why isn't this at /math?  -hydnjo talk 23:18, 31 July 2008 (UTC)
 * And why are we whispering? --Shaggorama (talk) 06:15, 1 August 2008 (UTC)

unidentified bird
Hi. A few weeks ago, I saw a bird perched on a coniferous tree branch. I live in S. Ontario, and the reason I'm asking is because I tried to find it in whatbird.com (blacklisted), without success. It had a reddish head, yellow belly, and probably a green underside in a shade similar to the tree spines (between light and dark green, more light than dark). It was small, and it looked almost tropical. I think it might be outside of its normal range or something, because I don't recall having seen it before and I can't identify it using that website even if I allow for as many possibilities as possible. Any idea what it might be? Thanks. ~ A H  1 (TCU) 20:05, 31 July 2008 (UTC)
 * I have no answer but I will note, I read ON Nature regularly and rather than the bird being outside its range, there's an equal possibility that your province is moving underneath the bird. As in, ranges are shifting northward, you might need a different bird guide in future. If I recall, several species are now making appearances. Franamax (talk) 22:37, 31 July 2008 (UTC)
 * Is it a Ruby-crowned Kinglet, better images here? Julia Rossi (talk) 01:27, 1 August 2008 (UTC)
 * Franamx it looks like you just shifted westwards. ; ) Julia Rossi (talk) 05:34, 1 August 2008 (UTC)
 * Hi. Parts of it look similar to the Ruby-crowned Kinglet, but there are differences. My memory of this isn't very clear, but I was viewing the bird from underneath, and I could still clearly see the reddish head area, which was probably solid and extended town maybe to its eyes. My vision of faraway objects isn't perfect, but someone beside me also noted a greenish tail area. The belly area was sufficiently more yellow than the tail area. I don't remember seeing any markings or stripes. Could it be a tropical bird by any chance, maybe an escaped pet or a vagrant? Thanks. ~ A H  1 (TCU) 16:15, 1 August 2008 (UTC)
 * Sounds kind of like a Western Tanager, but Ontario is a bit out of their range. Take a look at the other tanagers, they are among the few birds in N. America that have really vibrant coloring. 161.222.160.8 (talk) 19:04, 1 August 2008 (UTC)

mega-tsunami dynamics
Hi. Can a megatsunami possibly be high enough (say caused by an asteroid or catastropic land/ice-slide or super-eruption) to reach into the stratosphere? This is not homework. If so, what would happen? Would it sweep away the clouds/air ahead of it, form some kind of fog, or would its tops freeze? If it freezes, what happens to the ice, or would it not be possible for a moving wave to freeze? What happens if an air blast hits the wave? From the same direction, and what about from the opposite direction or side? Can any tsunami possibly be powerful enough to push the ocean ahead of it and grow taller, or does that violate a law? If such a tall tsunami were "tripped" by some mountains, would its bottom slow down but its top keeps going? Is there any geological (or historic) evidence for such a tsunami? Thanks. ~ A H  1 (TCU) 20:16, 31 July 2008 (UTC)


 * Megatsunami should answer some of your questions. It says that they could possible by thousands of metres high, and the stratosphere starts at about 10,000m above sea level, so I guess it's just about possible that a really large one could reach the stratosphere. While it is very cold as those altitudes, I wouldn't expect the water to freeze - the wave is going so quickly that no individual bit of water is at that height for more than a fraction of a second. Clouds start all the way at the ground - that's what fog is - so it's certainly possible for a tsunami to reach cloud heights. I guess it would sweep the clouds away... it might sweep them forwards or upwards or destroy them completely, I don't know... I'm not sure what you mean by pushing the ocean ahead, the tsunami is a wave in the ocean, so in a sense that's what it's always doing. It only gets really tall, however, once it hits land, in the deep ocean it's just a couple of metres tall, although it's moving much faster. I'm not sure what happens when a tsunami hits a sudden bit of high ground but not higher than the wave itself, but presumably a megatsunami going over a mountain would work the same as a regular tsunami going over a hill, so someone probably has the answer. --Tango (talk) 20:56, 31 July 2008 (UTC)


 * Hi. Thank you for your reply. What I meant by pushing the ocean ahead was, is it possible for the wave to sweep away the ocean ahead of it and leave a lower sea behind it, so that it pushes the ocean into the wave itself, making it higher while being in the open sea, similar to what happens if you cup your hand slightly and sweep it along the surface of a pool? Or, does that violate some kind of physical law, or is a tsunami just not powerful enough because of low friction or something? Thanks. ~ A H  1 (TCU) 21:44, 31 July 2008 (UTC)
 * After reading through Megatsunami, I have some serious questions. The stated heights are at the shoreline, not the open sea, so I'd question whether a solid ocean wave could reach the stratosphere. Droplets, definitely maybe, given sufficient impact, but a solid wave? If a piece of the ocean is accelerated to the extent it can reach the stratosphere, wouldn't it exceed the speed of sound and break up in the shock wave? Additionally, the article cites shoreline damage to specific heights, fair enough - but I can move back and forth in the bathtub, the waves don't get higher than the edge, but the water definitely sloshes over at the end of the tub. My understanding of the tsunami generated by the 2004 Sumatra seismic event is that rather than the height of the wave at shore, it was the momentum of the water that carried it far inland and to higher elevations than the impacting wave itself. I'll be glad to get corrected on any of this. I don't think much of megatsunami right now though. Franamax (talk) 22:59, 31 July 2008 (UTC)


 * Hi. I don't know how to calculate a megatsunami's height, maybe something involving the amount of water displaced verses the ocean depth, etc, but the amount of water displaced by the Chicxulub impact was likely somewhere arount 2500 km3 (600 mi3). Assuming an ocean depth of about 100 metres, and the diametre of water displaced about 170 km, how high would the resulting initial tsunami be? Also, by the time it reaches the shore, it would already be squeezed by the mesozoic Niobrara sea, meaning it would have reached around the South Dakota area before hitting shoreline. The trajectory of the asteroid/comet impact was also likely more towards the north than the south. If the end of the sea was about 3000 km from the impact, and the sea was about 1000 km wide and 50 m deep, would the wave increase or decrease in height at that time? Would it sweep all the way into the Mezosoic Arctic ocean? Thanks. ~ A H  1 (TCU) 16:26, 1 August 2008 (UTC)


 * In order to travel effectively over great distances, a wave's amplitude must be much lower than the depth of water it is traveling in. Otherwise, the drag of the bottom causes the wave to break and dissipate energy interally.  I don't know what the physical maximum is for a tsunami that will comfortably travel across an ocean basin, but I'm fairly confident that it is more likely to be tens of meters rather than thousands.  Dragons flight (talk) 19:35, 1 August 2008 (UTC)


 * Some interesting information: when an asteroid hits the ocean floor and vaporizes, the cavity created is quickly filled by water, creating a water jet in the centre whose collapse causes the main tsunami. Even a 1 km asteroid can generate a jet 20 km high and a 1000-m tsunami (http://library.lanl.gov/tsunami/212/gisler.pdf, pg. 4). According to the graph on p. 5 of this paper, tsunamis produced by large asteroids can reach a deep water height of 10 km 1000 km from the epicenter, although the authors may be extrapolating too much for the data to be accurate.
 * The asteroid that hit Earth 3.47 billion years ago flooded all land except the mountains; the tsunami must have been at least several kilometers high for this to happen (http://news.nationalgeographic.com/news/2002/08/0823_020823_asteroid.html). --Bowlhover (talk) 20:45, 1 August 2008 (UTC)


 * Your first citation predicts a height of 10s of meters at 1000 km. Your second says they ignore wave dispersion, which means their predictions only really make sense for wave heights significantly shallower than the depth of the ocean it is travelling in (or at sites very close to the point of impact).  As I said above, you can't propogate a wave substantial distances unless its height is substantially smaller than the thickness of the ocean basin, otherwise it will break up on itself.  The transient "splash" from an impact might be enormous locally, but physics limits the effect it can have at great distances.  Dragons flight (talk) 22:25, 1 August 2008 (UTC)


 * True, but high tsunamis generated by asteroids can propagate as a solid wave for some distance, albeit not across oceans.
 * AH1: see the end of http://library.lanl.gov/tsunami/212/gisler.pdf for an equation relating wave height with the impacting asteroid's size, density, and velocity.  As http://library.lanl.gov/tsunami/00394718.pdf shows, tsunamis increase in height upon reaching the shallow continental shelf, and the factor by which the height increases depends on the topography but is around 3.  --Bowlhover (talk) 06:15, 3 August 2008 (UTC)

Quad-core processors
how do quad core processors work? —Preceding unsigned comment added by 24.140.68.142 (talk) 20:38, 31 July 2008 (UTC)

I've moved this question to the computing reference desk where you may get more responses. You can check progress here. Franamax (talk) 23:06, 31 July 2008 (UTC)