Wikipedia:Reference desk/Archives/Science/2012 November 1

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November 1

Comet Shoemaker–Levy 9

Comet Shoemaker–Levy 9 hit Jupiter in 1994 at a speed of .0002c. What would have happened to the comet and to the planet if it had hit at:

• .02c
• .2c
• .9c
• .99c
• .9999c

?Magog the Ogre (t • c) 02:28, 1 November 2012 (UTC)

Jupiter is not a solid body like Earth. It is a giant gas planet, comprising mainly hydrogen and helium. It is the largest planet in our solar system but its density is very low. When the comet struck Jupiter the result was fireballs and plumes of gas. Dolphin (t) 02:45, 1 November 2012 (UTC)

I know what Jupiter is, and I know what happened in the actual collision. I'm not asking about that though. Magog the Ogre (t • c) 02:49, 1 November 2012 (UTC)

The first question is easy: the comet would easily be obliterated, because that's what happened to Shoemaker-Levy 9. What happens to Jupiter is harder to answer. Even at 0.0002c, according to our article, "Astronomers had expected to see the fireballs from the impacts, but did not have any idea in advance how visible the atmospheric effects of the impacts would be from Earth." Since even 0.02c is 100 times faster, and the kinetic energy of the comet would be 10000 times greater, I doubt there are reasonable models about what would happen to Jupiter, aside from "absolutely nothing in the long run, because the comet's mass is utterly negligible compared to Jupiter's". --140.180.252.244 (talk) 05:43, 1 November 2012 (UTC)

When you get up to near light speed, though, I wouldn't be surprised if it shot right through and out the other side (actually an equivalent mass of Jupiter material might shoot out the far side, similar to Newton's cradle). StuRat (talk) 09:43, 1 November 2012 (UTC)

I suspect that imacting a mass of gas with something moving near the speed of light would probably result in the destruction of most atomic nuclei involved and lots of high-energy radiation blasting out. That radiation would also have some pretty impressive effects on whatever it strikes nearby. Looking up relativistic impact on Google Scholar doesn't bring up anything that sounds like it would apply to your question. 209.131.76.183 (talk) 12:05, 1 November 2012 (UTC)

I had hoped the relativistic kill vehicle article would have some information, since it's the same concept, just aimed. But alas, it seems not. 146.87.49.21 (talk) 14:20, 1 November 2012 (UTC)

I'm not sure how reliable it is, but I found an estimate of about 7*10^11 kg for the mass of SL 9. According to that article, the realitivistic kinetic energy at .99c would be somewhere on the order of 10^13 megatons of TNT, which Orders of magnitude (energy) puts somewhere around the kinetic energy of the moon at orbital velocity. I have no idea what whould happen if you released that energy into Jupiter, but at least that gives a general idea of the energy involved at that speed. 209.131.76.183 (talk) 14:41, 1 November 2012 (UTC)

To me this sounds like an ideal question for XKCD what if? OpenToppedBus - Talk to the driver 14:58, 2 November 2012 (UTC)

A question about the lead section for the article quantum state

Consider a system with just 1 hydrogen atom. The wave function for the electron only requires 3 quantum numbers $\{n,\ell ,m_{\ell }\}$. This wave function can give hydrogen's probability density in position space and momentum space. So, what other information about the position or momentum of the electron are not specified? I think we should delete the last phrase about the position or momentum of the electron.--LaoChen (talk)04:57, 1 November 2012 (UTC)

"Probability density" is not the "position", but only the chance of finding it in a position or that it is usually or mostly in the vicinity of a position. That is, there is no "the electron is at the following coordinates:" type of answer. Likewise, there is not an exact solution for the momentum (maybe only an approximate range of likelihood). It is mentioned in these types of terms later in the lead itself, and then discussed further in the article using a bunch of math. One of the key statements there is "In quantum theory, even pure states show statistical behaviour." DMacks (talk) 09:00, 1 November 2012 (UTC)

Is it possible to heat granite by using dielectric- or induction heating ..?

Is it possible to heat rock like granite by using dielectric heating or induction heating ..? Electron9 (talk) 05:46, 1 November 2012 (UTC)

Of course. Any material has dielectric loss and some degree of electrical conductivity, and so does granite. However, I would expect the conductivity of granite to be sufficiently low that induction heating would be quite impractical. Dielectric heating certainly would be practical. If you google dielectric properties granite, you'll get all the info you need to determine the power level and optimum frequency needed. See http://mars.mines.edu/pub/76EPropertiesRocks.pdf. You could also of couse obtain a thin (a few mm) sample of granite polished for 2 sides parallel and test it with a Q-meter fitted with a dielectric loss adapter. Most university physics labs and electronics labs have Q-meters. Ratbone 121.221.211.20 (talk) —Preceding undated comment added 06:06, 1 November 2012 (UTC)

Perhaps "practical" was the missing keyword ;-), I just hope the microwave oven won't go up in smoke like it would if a spoon is forgotten inside it. If I tried with a rock instead. Electron9 (talk) 00:43, 2 November 2012 (UTC)

A microwave oven is only one kind of dielectric heater. A microwave oven canc ertainly heat granite, but its frequency and other parameters will not be optimum. If you are just going to try a piece of granite or whatever in a domestic oven, I suggest you incude a glass of water to aborb some of the enegery, until you have verified the the piece of granite is getting hot in a reasonable time. If the granite gets warm at about the same rate as an equal volume of water, it will be safe for the oven without the water.

There is another important consideration: DO NOT heat unknown pieces of granite to reach anywhere near 100 deg C. If you do, any included moisture will cause an explosion.

Ratbone 60.230.218.171 (talk) 01:42, 2 November 2012 (UTC)

Magnetic field vs various computer parts

What would the effect of a strong magnetic field on an old (2004) desktop computer be? I understand the effects of magnetic fields on CRT monitors and hard drives, but what would happen to the motherboard, videocard or audiocard, dvd/cd writer/reader and the other parts? Would they be able to continue to operate? They (talk) 09:40, 1 November 2012 (UTC)

If it is not powered on at the time, there will almost certainly be no effect. If it is powered on, I still doubt you'll have problems unless you're talking about an incredibly strong (and probably changing) field. The only components that are in theory affected by magnets are the speakers, fan and DVD drive motors, and possibly the inductors in the voltage regulator circuits. None of those should be affected by any magnets you'll encounter in a normal household. If you're interested in higher-strength fields I suppose you could research what sort of requirements there are for a computer that runs in an MRI lab. 209.131.76.183 (talk) 11:58, 1 November 2012 (UTC)

Magnetic fields can have a huge effect on PCs. About 5 years ago, I was installing Linux on a PC a work, and it would crash at different points in the install process. This machine was about 2004 vintage. I tried reseating and replacing components to no avail. After the 8th or 9th combination of parts, some old, some new, the install was successful. The difference was, that my radio/cassette wasn't sitting on top of the case for this install! Bench space was limited and it was the only place to put it. I put the radio on top of my CRT monitor, switched it on, and the picture went a bit "funny". Moral: don't use a PC with a radio/casette on top of it. What is puzzling is that the PC had a steel case, which I think should have acted as a Faraday cage, but perhaps there were holes in it, which let the magnetic field in. I guess if I hadn't been listening to the radio, the install would have gone a lot smoother... --TrogWoolley (talk) 14:45, 1 November 2012 (UTC)

Only Mu-metal stop magnetic fields in practice but is expensive. And Faraday cages only protect from electric fields. Electron9 (talk) 00:48, 2 November 2012 (UTC)

From our articles there appear to be many options - currently topping the charts at permeability (electromagnetism) is something called metglas. Wnt (talk) 15:38, 2 November 2012 (UTC)

Why do you think this was due to a magnetic effect? I would suspect RF interference triggered noise problems in the power supply. An unshielded AC power cord draped down from the radio through the cables on the back of the PC could also introduce noise, but crashes wouldn't be too likely from that. The systems we build here put standard PC components (including hard disks) very close to multi-HP electric motors without any problems. Random crashing type issues tend to come from poor routing of cables that carry significant current along side data cables. I've never seen anything we could attribute to the magnetic field of the motors. 209.131.76.183 (talk) 12:56, 2 November 2012 (UTC)

Speaker interference due the shape of the magnetic field and the frequency. The conductive path is also conceivable. Electron9 (talk) 21:37, 2 November 2012 (UTC)

Does flashing 12:00 damage the display

Does a flashing 12:00 damage an LCD display over time or it has no effect?Smallman12q (talk) 12:54, 1 November 2012 (UTC)

No effect. LED displays are not susceptible to burnout the way incandescent bulbs are. — Lomn 13:21, 1 November 2012 (UTC)

Ah, LCD (liquid crystal) and LED (light emitting diode) are different techonlogies.... (Note also that there are also VFD (vacuum fluorescent display) clocks used in some applications, which are yet another technology used in a variety of consumer goods.) I suspect that the unsourced answer above is incomplete at best, but I'm pressed for time to do the research right now. Does anyone want to offer some references? TenOfAllTrades(talk) 15:14, 1 November 2012 (UTC)

Ten is correct, and I botched my acronyms. Regardless, from a practical end-user standpoint, the blinking display has no functionally damaging effect on the device. I will note that the searching I have done indicate that datasheets list the MTBF for the backlight on an LCD assembly, but take as a given that the LCD itself will last indefinitely. At the same time, I'm confident that, at sufficiently fine scales, there is an effect caused by a blinking display that is distinct from the effects caused by either an always-off display or an always-on display. Therein lies the peril of ever answering simply "yes" or "no" on the Science desk, even if one or the other is likely the most useful response. — Lomn 15:33, 1 November 2012 (UTC)

What causes the flashing? My assumption is there is nothing mechanical doing it, hence nothing that will wear out quicker than a steady light would. Please correct me. μηδείς (talk) 21:34, 1 November 2012 (UTC)

Incandescent bulbs wear out faster when switched on and off despite the lack of a direct mechanical effect. Thus, "nothing will wear out quicker" should not be assumed as a general rule. — Lomn 23:14, 1 November 2012 (UTC)

LCD display segments (in the simple backlit and pasive types used in clocks & clock radios) have a square wave voltage applied to the backplane (not to be confused with the backlight), an electrode common to all segments. A segment required to be "on" has a second square wave voltage applied out of phase to the backplane - it thus has an AC voltage across it. A segment required to be "off" has an in-phase squarewave applied to it - it thus has zero voltage difference across it. In both cases there is no DC voltage ever across the display segments - this means there cannot be any electrolytic degradation. The flashing is caused by swapping over the phase every half second or similar time. The segments themselves emit no light and draw no current, so there cannot be any electrochemical action. There is no wearout mechanism. In theory, LCD displays of this type last indefinitely regardless of whether they are on or off. Flashing 12:00 indefinitely cannot do any harm. In practice, LCD's do have a quite limited life due to impurities in manufacture, and sealing may fail, but being on or off will not affect that. Ratbone 60.230.218.171 (talk) 01:33, 2 November 2012 (UTC)

Some OR, the timer clock on our oven has been flashing for over 10 years. It started out flashing 00:00 but now it only does something like -- __| (all the other "strokes" having worn out) 121.45.180.226 (talk) 11:06, 2 November 2012 (UTC)

In the battle of wills (you refusing to set the time, with flashing 12 indicating you should set it), it looks like you won. 82.131.132.190 (talk) 23:05, 3 November 2012 (UTC)

Batch image merge (microscopy software question?)

I have a number of micrographs of cells takrn under brightfield and UV illumination (with a green filter). I'd like to obtain merged images from each of these pairs. What might be the easiest way to batch process all these files? I have The GIMP and ImageJ but I am not familiar with scripting. — Preceding unsigned comment added by 129.215.47.59 (talk) 14:20, 1 November 2012 (UTC)

How many do you have? With GIMP you can merge a pair in a few seconds of work, using drag & drop (presuming they are aligned perfectly). Unless you have hundreds of pictures, it might not be worth the effort of looking for a more sophisticated solution. Looie496 (talk) 14:58, 1 November 2012 (UTC)

A good tool for batch processing of images is ImageMagick[1]. It has a command-line tool that can be used to perform all sorts of operations, so it is easily scriptable. 209.131.76.183 (talk) 15:08, 1 November 2012 (UTC)

ImageMagick is great. It's available as a command-line tool, or as a set of libraries that you can link into software that you write. It's also free software. On the other end of the spectrum is the commercial Image Processing Toolbox for MATLAB. While this software cam be very expensive, it is superior to ImageMagick in many respects: performance, ease-of-use, and depth of coverage of common tasks. If you're going to specialize in image processing, it's a good idea to learn both tools, as they're common throughout the industry and academic worlds. For almost any image-processing job, either MATLAB or ImageMagick is the right answer when you're in the "prototyping" phase. Nimur (talk) 16:26, 1 November 2012 (UTC)

For microscopy images ImageJ is something of a standard free tool. (I use it too). If you know a little (really little) programming you can hack together a ffew lines of java code to make a macro that will do this in imageJ. In fact for a batch merge job, I would expect googling to turn up plenty of ready to eat macros. good luck.Staticd (talk) 04:50, 2 November 2012 (UTC)

Is there any known plant that is pollinated by the predators of its parasites?

Greetings,

Is there any known plant whose main pollinators, or seed dispersers, actually visit it to feed on its parasites? I can vaguely imagine how such a route of dispersal could evolve with time, but I'm not aware of it actually being found anywhere. Thanks, ליאור • Lior (talk) 16:08, 1 November 2012 (UTC)

It would seem unlikely except by chance unless the parasite were eating the anthers, in which case they themselves might also be pollinators. μηδείς (talk) 23:34, 1 November 2012 (UTC)

There's a 3-way relationship between fig trees, pollinator wasps, and parasitic wasps: [2]. StuRat (talk) 03:27, 2 November 2012 (UTC)

Well, you have to be careful about how you assign causation here. For instance, the Braconid wasps are generally parasitoids of common plant parasites. They commonly lay eggs in caterpillars that eat plants. Specificity varies, but some species of wasp will seek out specific species of caterpillar, which in turn are highly selective, and only appear on certain plants. The catch is, adult braconids drink nectar, and in turn can pollinate by transferring pollen (mentioned here [3]). So yes, some individual plants are pollinated by insects that were attracted to the plant's parasites. This not necessarily a tight, or common relationship, but it does happen. SemanticMantis (talk) 17:21, 2 November 2012 (UTC)

Fascinating! I can't find any relevant theoretical paper which models the plant-parasite-braconid population dynamics. Many thanks, ליאור • Lior (talk) 17:06, 3 November 2012 (UTC)

"Hurricane" vs "Post-Tropical 'Super Storm'"

Many insurance policies reference "hurricane" damage separate from regular "storm damage, with different deductibles and claim criteria, etc.. Since Sandy was "side-graded" to a Post-Tropical storm doesn't that mean that the hurricane language in insurance policies is a moot issue in this case? I know that insurance companies would argue to the hill if the shoe was on the other foot. Technically the storm was NOT a hurricane when it made landfall as it did not meet the necessary criteria to be one.165.212.189.187 (talk) 16:24, 1 November 2012 (UTC)

Nevermind. googled: sandy not a hurricane.165.212.189.187 (talk) 16:32, 1 November 2012 (UTC)

I disagree with the nevermind. Interesting question. Do regular home insurance policies really distinguish specifically hurricane damage from other wind damage? Would it really make a difference for coverage if a storm was 73 mph or 74 mph? What if it was hurricane force winds but not a cyclone (not rotating) and thus not a hurricane, just a hard wind? Duoduoduo (talk) 20:21, 1 November 2012 (UTC)

Yes, there is wind insurance and hurricane insurance clauses/riders. Did you google sandy not hurricane? The govt is going to closely monitor the ins cos to ensure that they do not enforce the hurricane aspects of policies where applicable.68.83.98.40 (talk) 01:16, 2 November 2012 (UTC)

Specifically [4] Duoduoduo (talk) 14:57, 2 November 2012 (UTC)

Slowing neutrinos

Could an exceeding intense beam of very very low frequency radio waves slow down an occasional neutrino? I'm thinking intensity could help a little with the low cross section, and the low frequency would mean any interactions that did happen would absorb energy from the neutrino. I'd like to be able someday to have a pound or so of ultraslow neautrinos in a small box.Thanks, Ricfh Petrson198.189.194.129 (talk) 18:52, 1 November 2012 (UTC)

Others may be able to comment more authoritatively, but no, I don't see how that could work. Radio waves are purely based on the electromagnetic force, whereas neutrinos interact only via the weak force (and of course the gravitational force).

Supposing you did get your pound of neutrinos, what do you imagine would hold them in the box? --Trovatore (talk) 18:57, 1 November 2012 (UTC)

Somewhere in outer space in free fall, if the neutrinos were traveling sufficiently slowly, say .1mm/century, then they would stay in there for a while, although the box would only serve as a marker to tell you what they were inside, it couldn't prevent them seeping out at all.--Are we absolutely sure they don't interact with EM?? I guess if that's true, there is no way to slow them down.198.189.194.129 (talk) 21:35, 1 November 2012 (UTC)

There's something called electroweak unification, but per our article, it happens only at very high energies. I suppose there must be some remnant of it at lower energies. --Trovatore (talk) 22:37, 1 November 2012 (UTC)

The remnant at low energy is the EM force and weak nuclear force. Neutrinos only feel the weak nuclear force part of it. However, if you had something extremely dense that would slow neutrinos down (via exchange of W (electron neutrinos only) and Z bosons) but I think matter would become a black hole first before getting near 1mm/century.Dja1979 (talk) 03:37, 2 November 2012 (UTC)

Mercury can slow neutrinos down, but not by that much. 24.23.196.85 (talk) 05:08, 2 November 2012 (UTC)

Hmmm. Our article on deuterium says it's been used as a target for neutrinos - I wonder if enough of that ultra-dense deuterium we were just talking about could really do something fun with them? Wnt (talk) 05:30, 2 November 2012 (UTC)

The detectors for neutrinos are chosen not by how much they interact with neutrinos, but how easily you can detect interaction with neutrinos without getting distracted by other events. In particular, large underground chambers filled with water or chlorine is used, because those materials are not too expensive to get very pure in large quantities, and are transparent so the Cherenkov radiation of the fast electrons kicked off by neutrinos can be detected. Heavy water (with deuterium) is used for a similar reason. – b_jonas 18:53, 3 November 2012 (UTC)

Sun's magnetic field

Roughly, what's the stength of the Sun's magnetic field on Earth? 65.92.7.202 (talk) 19:02, 1 November 2012 (UTC)

According to Sun#Magnetic field,

The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400 μT (at the photosphere) reduces with the cube of the distance to about 0.1 nT at the distance of the Earth. However, according to spacecraft observations the interplanetary field at the Earth's location is around 5 nT, about a hundred times greater.[80] The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the sun.

Duoduoduo (talk) 20:26, 1 November 2012 (UTC)

Can someone paraphrase that in lay-English for us idiots? μηδείς (talk) 20:47, 1 November 2012 (UTC)

Not me. I was hoping the OP would understand it. But the article Earth's magnetic field#Intensity says

The intensity of the field is greatest near the poles and weaker near the Equator. It is often measured in gausses (G) but is generally reported in nanoteslas (nT), with 1 G = 100,000 nT. A nanotesla is also referred to as a gamma (γ).[10][11][12] The field ranges between approximately 25,000 and 65,000 nT (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field of about 100 G.

So, although I know absolutely nothing about this, it looks to me that the sun's 5 nT at Earth location is dwarfed by the Earth's 25,000 to 65,000 nT. Duoduoduo (talk) 22:36, 1 November 2012 (UTC)

The strength is 5 nT. Almost all of that is due to electrical currents surrounding the Sun. --140.180.252.244 (talk) 22:37, 1 November 2012 (UTC)

Well, I am not sure why anyone wuld be talking about tens of thousands of nano teslas, but if the sun's field is 5 at the earth, compared to the earth's 25-65,000, that gives an idea of scale. What is the 100 G, 100 giga teslas? I suppose a tesla must be a local measure then, not a sum across the entire flux. Am I wrong? μηδείς (talk) 23:33, 1 November 2012 (UTC)

G is Gauss, the other metric unit of magnetic field density. (The Tesla is the SI unit, while the Gauss is the cgs unit.) --Carnildo (talk) 02:18, 2 November 2012 (UTC)

Capacitor charging question

I am working on a project which uses a solar panel, and some other electronics, to charge a 10 farad capacitor. I would like the microcontroller to display the time remaining for the capacitor to be fully charged, but cannot find or work out the necessary equation.

Is it possible to work out the time remaining, with the microcontroller having access to the following values:

• The supply voltage
• The current going into the capacitor
• The voltage across the capacitor
• The resistance between the supply and the capacitor
• The required voltage across the capacitor
• And, if necessary, previous values of the above.

85.210.44.120 (talk) 19:41, 1 November 2012 (UTC)

With a supply voltage $V_{s}$, resistance R and capacitance C the voltage over the capacitor will increase over time t according to (see Capacitor#DC_circuits)

$V=V_{s}\left(1-\exp \left(-{\frac {t}{RC}}\right)\right)$.

If the voltage over the capacitor now is $V_{1}$ the time is now

$t_{1}=-RC\ln \left(1-{\frac {V_{1}}{V_{s}}}\right)$.

The time at which it will reach the required voltage $V_{r}$ is

$t_{2}=-RC\ln \left(1-{\frac {V_{r}}{V_{s}}}\right)$,

so the time left is

$\Delta t=t_{2}-t_{1}=-RC\ln \left({\frac {1-V_{r}/V_{s}}{1-V_{1}/V_{s}}}\right)=-RC\ln \left({\frac {V_{s}-V_{r}}{V_{s}-V_{1}}}\right)$.

This formula should work if you have these values, but I wouldn't trust the voltage you meassure over the capacitor while it is charging to be correct since there is always an inner resistance in the capacitor. Either you stop charging temporarily to measure $V_{1}$ or you measure the inner resistance in advance and use this and the charging current to calculate the real capacitor voltage from your measured value. Ulflund (talk) 23:29, 1 November 2012 (UTC)

.

Unfortunately, Ulfund is incorrect. A solar panel operated below its open circuit voltage, which it necesarily will be until the capacitor is charged, act as as a constant current source, and the current is directly proportional to the intensity of light falling upon it. A capacitor has a voltage directly proportional to the product of current (in amps) and elapsed time (in seconds) divided by the capacitance (in farads). Therfore, approximately (approximate because the change over from constant current to constant voltage of a solar panel is not abrupt), the time remaining is given by:-

T_remain = C ( V_oc - V_cap ) / I

where V_oc is the open circuit voltage of the panel, and V_cap is the capacitor voltage at the measurment time.

A capacitor of 10 Fards is likely to be of the supercapacitor type (http://en.wikipedia.org/wiki/Supercapacitor) and these have significant internal series resistance compared to other types, as only supercaps are available in the size cited, and are the most suitable type wrt self discharge. However in this application it is small enough to be neglected in the calculation of time remaining.

Keit 58.169.250.75 (talk) 00:46, 2 November 2012 (UTC)

My calculations were based on the assumption of constant charging voltage. For constant current the formula given by Keit should be used instead, and I agree that this is more likely to be the best approximation if the capacitor is charged with a solar panel. Ulflund (talk) 07:43, 2 November 2012 (UTC)

spiders

I have a lot on spiders in my basement are there any traps for them, or what is a good way to get rid of them?--Wrk678 (talk) 19:51, 1 November 2012 (UTC)

I was going to say 'insecticide' - but does insecticide even work on spiders? I've never thought about that before... --Kurt Shaped Box (talk) 20:05, 1 November 2012 (UTC)

Why do you want to get rid of them? Do you enjoy having extra insects around? Marnanel (talk) 20:11, 1 November 2012 (UTC)

I think it would depend on what spiders the OP has. Some of them are horrible critters to have about the home. --Kurt Shaped Box (talk) 20:20, 1 November 2012 (UTC)

My first instinct would be to head to my favorite internet search engine and type in exterminate spiders. If faced with a serious infestation, beyond what internet remedies suggest, I'd look at the local yellow pages for pest/insect control (yeah, spiders are not insects, but those guys will know what to do, whether the enemy has six or eight legs.) 88.112.36.91 (talk) 20:15, 1 November 2012 (UTC)

I put the question to Google (sorry, no special knowledge) and got [5] which sounds plausible - they say pyrethrins, resmethrin, and allethrin work on them but only if you more or less spray them directly, which is near pointless, so use housekeeping measures. Bottom line is that if you beat the insects, you beat the spiders. But I also got a hit for the vastly less "reliable" source eHow (Wikipedia blacklists www.ehow.com/facts_5906696_safe-insecticide-spiders.html as a link), which makes the curious claim that natural oils of lemon and citronella, detergents, horse chestnuts, and osage hedge apples would repel spiders. Not sure if these are indeed horse chestnuts! But the claims are all over the Web, and not facially implausible. The Telegraph says, well, they don't know, but "conkers sound like bonkers". [6] There sure are a lot of biology projects people could get good studies published about if funding were greatly expanded instead of cut for a change, but that doesn't sound likely. Our article on osage/horse apples cites a study saying that it actually is an insect repellent [7] based on the presence of elemol, said to be comparable to DEET in the publication. Looking it up, I see it repels ticks [8] so I count this one as "probably confirmed", pending replication of results. Oh, and someone's investigating the conkers. [9] And that's why I like to consider non reliable sources seriously. Wnt (talk) 20:36, 1 November 2012 (UTC)

Horse chestnuts work quite well against spiders, if you've got good aim. --Carnildo (talk) 02:22, 2 November 2012 (UTC)

Cleaning the basement will also work. If you remove all the spider webs regularly, the spiders will leave. Count Iblis (talk) 20:33, 1 November 2012 (UTC)

• Spiders are a self-controlling problem--they'll either eat your pests or themselves. The underlying question is, what is their food source? You are surely infested with something else, unless this is just a recent hatching from one colonist. I, myself, never kill spiders (nor most insects unless they are dedicated pests like ants, roaches, and flies). Of course we don't have many dangerous spiders in the US NE--some areas do. If you must, use bug spray or other bug control measures. Spiders have the same underlying physiology as insects and are subject to the same poisons. If you are really desperate, I know an old lady who will help, but at a price. μηδείς (talk) 20:42, 1 November 2012 (UTC)

I dont have any insects down, there just spiders, and I would like to not use chemicals.--Wrk678 (talk) 23:54, 1 November 2012 (UTC)

Well, there's no such thing as a spider trap. And they aren't magic, they do have to eat, so there must be some non-spider infestation unless this is just a crop of very recent babies from an egg sac. Try cleaning thoroughly and making sure their is no water source, because you are obviously supporting some sort of little ecology with water and food of some sort. μηδείς (talk) 02:17, 2 November 2012 (UTC)

I've seen glue boards trap spiders, but you'd need a massive number of them to get all your spiders. If there's nothing flammable around I tend to use fire to kill them. Specifically, I use a fireplace lighter to burn them and their webs. This avoids me getting spider webs and spider guts on myself. I also use a broom to get at spiders and webs out of reach (I push the bristles into the spiders to kill them). And to answer the Q someone posed above about why not leave them alive, that person apparently never had spiders lower themselves onto their face while they were sleeping and driving. Either one can ruin your day or night, trust me. StuRat (talk) 03:18, 2 November 2012 (UTC)

Well, I don't sleep in my basement, either! LOL. But I have had the occasional spider walk on me while I was in bed. Is no biggy. "Spiders in the basement" is about as vague as "bugs upstairs." Are they web builders? Are they wolf spiders? Are they all adults, or is this a hatching? Basically all we have here is an expression of an ick factor with no factual facts to go on. Might as well suggest moving unless we get more concrete information. And the fact remains that you don't get spiders unless they have a food source, which itself needs food and water. μηδείς (talk) 03:24, 2 November 2012 (UTC)

Or they can come in from outside. Houses are amazingly transparent to insects. Gnats can come right through window screens, and much larger insects have ways of getting in, too, although I don't quite know how (or I would stop them). StuRat (talk) 04:28, 2 November 2012 (UTC)

Yes, that's entirely possible, in which case the OP will be really upset when all their egg cases hatch in the Spring. He'll need to find how they are getting in. I have had half-a-dozen of those cute stink bugs in the last two months. They seem to be able to teleport through walls. μηδείς (talk) 16:48, 2 November 2012 (UTC)

As with most questions posted on the reference desk, the correct answer is also the most obvious: tetramethrin, methoprene and cyanide will do the job equally well. 203.27.72.5 (talk) 05:37, 4 November 2012 (UTC)

Cyanide would be too dangerous. 24.23.196.85 (talk) 02:42, 6 November 2012 (UTC)

Has 24.23.196.85 seen the New York Times today? Israel and Iran 2010. Almighty God always proves his little mystic right ! Cinquefoil (talk) 03:26, 6 November 2012 (UTC)

Question regarding the conversion of one Tesla to one Earth atmosphere

Hi All, and thank you in advance for your consideration. Is it possible to convert one Tesla to one Earth atmosphere, and what would that value be?Gavinth (talk) 21:15, 1 November 2012 (UTC)

Well, if you set Planck's constant, the gravitational constant, and the speed of light all to a dimensionless value of 1, then all units become dimensionless numbers, so presumably you could make this conversion in that sense. See natural units. Whether the result would have any articulable meaning is another question. --Trovatore (talk) 21:18, 1 November 2012 (UTC)

This sounds like a pretty good argument against dimensionless units! But to be clear, one tesla (unit) = one kg s^-2 A^-1, and one atmosphere (unit) = 101325 Pascal (unit) = 101325 kg s^-2 m^-1. So the number of Teslas in 1 atm is equal to 101325 A/m. Now you just have to figure out what that means. :) Actually, it might be easier to think of it as: an atmosphere is defined as 101325 newtons per square meter, and a tesla as one weber per square meter; the ratio is the number of newtons of force per weber of magnetic flux emerging from the bounded region in question. Wnt (talk) 21:55, 1 November 2012 (UTC)

No, it is not possible to convert 1 Tesla to 1 Earth atmosphere, because the two measure different quantities. In the same way, a length cannot be converted to an area, a temperature cannot be converted to kilograms, and a position cannot be converted into m/s. --140.180.252.244 (talk) 22:33, 1 November 2012 (UTC)

You can convert anything to anything, given the right assumptions. For example, kilograms of weight can be converted to newtons - if you know the gravity of the planet you have in mind. Wnt (talk) 22:55, 1 November 2012 (UTC)

I'm just guessing, but maybe the OP meant the magnetic field in the Earth's atmosphere, rather than the air pressure commonly known as 1 atmosphere (that doesn't make much sense to me). If so, Earth's magnetic field at the surface ranges from 0.25-0.65 mT, so one Tesla would be 1538-4000 times this field. - Lindert (talk) 00:35, 2 November 2012 (UTC)

What's more likely is that the OP is a troll. He's using an unregistered name, he's not showing an IP address, and he's asked a question designed to see what you do with it. The best way to deal with trolls is to ignore them. — Preceding unsigned comment added by 60.230.196.221 (talk) 03:42, 2 November 2012 (UTC)

See here. Count Iblis (talk) 16:27, 4 November 2012 (UTC)

Is there a name for "hating forks aiming for someone"?

If a fork or any long object is "pointing" at you or someone else and you deliberately change its position so it's pointing at nobody, is there still hope? Moreover, does this behaviour have a name or reason? (The subject doesn't mistake the fork for a gun and this is not a request for medical advise) Joepnl (talk) 23:12, 1 November 2012 (UTC)

It is called Superstition and has no reason at all. Pointing a folk at someone won't cause anything to happen so neither will turning it. CambridgeBayWeather (talk) 23:43, 1 November 2012 (UTC)

Unless it's loaded. Clarityfiend (talk) 00:17, 2 November 2012 (UTC)

If you mean forks that are just sitting there with nobody holding them, that would be a type of obsessive/compulsive behavior, akin to refusing to step on cracks in the sidewalk. Looie496 (talk) 02:36, 2 November 2012 (UTC)

Yes, an obsessive-compulsive disorder. StuRat (talk) 04:22, 2 November 2012 (UTC)

Well, it doesn't really rise to the level of OCD unless it is so severe that it interferes with the ability to lead a normal life. Lots of people have a quirk or two of this sort. Looie496 (talk) 15:00, 2 November 2012 (UTC)

I believe many people with an OCD can lead a normal life. StuRat (talk) 17:32, 2 November 2012 (UTC)

According to DSM4, a diagnosis of OCD requires that: The obsessions or compulsions cause marked distress, are time consuming (take more than 1 hour a day), or significantly interfere with the person's normal routine, occupational (or academic) functioning, or usual social activities or relationships.. Looie496 (talk) 17:56, 2 November 2012 (UTC)

To lay off the medical advice, what do you call such obsessions/compulsions when they're not meeting those criteria? Obsessions and compulsions? Is there any distinction between those a person comes up with idiosyncratically, as opposed to, say, a Middle Eastern tradition that pointing your foot at someone is offensive? Wnt (talk) 18:15, 2 November 2012 (UTC)

They are still obsessions or compulsions, the word that is in play here is disorder. The Middle Eastern thing seems like more a matter of culture. Lots of cultures treat pointing at somebody, in various ways, as an assault. That may go back to our primate ancestry: in monkeys, merely looking at another monkey is often treated as a threat and leads to an angry response. Looie496 (talk) 22:57, 2 November 2012 (UTC)