Wikipedia:Reference desk/Archives/Science/2007 March 26

= March 26 =

Battery operated power strip?
Is there a way to power a device that needs to plugged into an outlet, such as a lamp, with a battery?


 * Yes. The usual way is with an inverter, which converts DC to AC (and usually steps up the voltage in the process).  Depending on the device to be powered, there may be other solutions as well. --Steve Summit (talk) 00:38, 26 March 2007 (UTC)


 * Note that permanently running things like incandescent lights off batteries is quite expensive, as the batteries need to be constantly replaced. Using rechargeable batteries is better, but they still have a limited life and will need to be constantly recharged.  Lowering the power requirements for the device, such as by going with fluorescent lights instead of incandescent, is a good idea.  An uninterruptible power supply will provide battery backup for short periods of time. StuRat 01:39, 26 March 2007 (UTC)


 * You can buy cheap 12 volt inverters in most car parts stores for around $20 to $30 (I scored a couple of really good ones from WalMart for around $27 recently). They are intended to be plugged into the 12v auxiliary socket of your car - but you can easily wire them up to a stand-alone car battery.  A car battery plus inverter will run low wattage things like table lamps for many hours.  I keep a couple of old car batteries around (fully charged) and have used them to power a small TV, a 40 watt table lamp and a DVD player for over 6 hours per battery - so these make a cheap alternative to an emergency generator.  When you purchase an inverter, you need to check the maximum current they can provide and make sure that you get one with a fuse so you won't damage it if you accidentlly overload it.  SteveBaker 03:34, 26 March 2007 (UTC)
 * The most efficient solution is to use DC appliances powered directly from the batteries. These are made for recreational vehicle and camping applications and for boats. 12 volt compact fluorescent lights are a great choice. For example, one is listed (at the very bottom) at for $12.75, which uses 13 watts to give the brightness of a 60 watt incandescent light. You could also buy an Uninterruptible Power Supply intended for use with computers as a standby power device, charge it up, and use it to power 120 volt ac devices within its power range for a limited time. If the devices uses far less power than the maximum rating of the UPS, it would be able to power it for far longer than the rated backup time. Edison 14:31, 26 March 2007 (UTC)

Or you could attach the battery to an electrical generator so that it creates electricity as it falls, and then lift it back up again and let it fall again, thereby transfering both your energy and the batteries energy into electricity which can then be used for other things :] HS7 17:56, 26 March 2007 (UTC)


 * HS7 - please cease putting these intentionally misleading replies into honestly asked questions - it is a form of vandalism. If you do not cease forthwith I'm going to complain to the admins. SteveBaker 03:08, 27 March 2007 (UTC)


 * I think it was just a joke. StuRat 03:12, 27 March 2007 (UTC)


 * And a pretty good one, I thought, evoking the classic method (er, classic alternative method, if you insist) of determining the height of a building using a barometer. (And it certainly wasn't misleading, once you figured out what he meant.) —Steve Summit (talk) 23:01, 27 March 2007 (UTC)

It's not misleading, it would actually work, I just happen to be more practically minded than most people :) HS7 14:34, 27 March 2007 (UTC)


 * It's exceedingly misleading. Go calculate what it would take to power a mains-powered 120v lamp by your means.  It's ridiculous. SteveBaker 04:14, 28 March 2007 (UTC)

c:)

6N Chromosome Number
One of my reproduction problems has me stuck. Banana plants have a 6N chromosome number and thus cannot reproduce sexually. Why is this. I am thinking that after the first meiotic division each of the two cells would have 3N chromosomes and wouldn't be able to undergo a second meiotic division because there is no way to split up these chromosomes evenly, but I am not sure if my thinking is right. Can anyone give any other suggesions? Thanks! 71.253.34.212 02:03, 26 March 2007 (UTC)purecontrol


 * Your thinking is right. See this page on polyploid plants. Briefly, "In the formation of gametes during normal meiosis, homologous chromosomes must pair up with each other during synapsis of prophase I. Like other odd polyploids (with 3 sets of chromosomes), bananas are sterile and seedless because one set of chromosomes (A or B) has no homologous set to pair up with during synapsis of meiosis. Therefore meiosis does not proceed normally, and viable gametes (sex cells) are not produced. Since banana fruits (technically berrylike ripened ovaries) develop without fertilization they are termed parthenocarpic. Without viable seeds, banana plants must be propagated vegetatively (asexually) by planting corms, pieces of corms or sucker sprouts." - Nunh-huh 04:37, 26 March 2007 (UTC)

GPS
Isn't it possible for GPS equipped units of all kinds, types and sizes to be programmed with "no trespass" zones that inclused a good safety margin to keep users out of trouble with foreign governments or even local law? 71.100.160.159 02:14, 26 March 2007 (UTC)
 * Not sure what you mean by "unit", but I don't see why not.   --Bmk 02:34, 26 March 2007 (UTC)


 * Cell phones to patrol boats... 71.100.160.159 05:15, 26 March 2007 (UTC)


 * GPS just gives coordinates (and maybe the time) but nothing more. Yes, devices can be programmed to associate ranges of coordinates with trespass zones or any other zones, but retrofitting all existing GPS software to include it would be a very costly and difficult undertaking, and unless required by law would be unlikely to occur. —Pengo 13:27, 26 March 2007 (UTC)


 * Also note that such zones are dynamic, as areas may be shut down or have their zones extended due to terrorist threats, etc., with little warning. Thus, keeping the device updated would be a problem.  You could download new info to it each day via a wireless Internet connection, but there's no guarantee that governments would supply this info electronically in a timely manner. StuRat 15:19, 26 March 2007 (UTC)


 * The united states can turn off or degrade the un-encrypted signal (what civilians use) form the sattelites at will. This can be used to stop non-US-military recievers from working worldwide, or in a large geographical area. Degradation within a precisely defined area like you describe is not possible. See the article on GPS edit: re-reading your question there is no reason this couldn't be done but it would require cooperation from every single gps unit in use which seems infeasible. No doubt some digital maps included in the units will have relevant info such as restricted areas but there is no way to mandate this or make sure this info is up to date. I could always build my own GPS reciever that has no knowlege of these zones. -- Diletante 17:17, 26 March 2007 (UTC)

Airplane GPS's routinely include airspaces and warnings as you approach them. Also, they can create spaces around other airplanes using ADS-B or Mode S traffic alerting. But it has nothing to do with the GPS system, rather it's the mapping and tracking software that's provided by the manufacturer. GPS only provides coordinates (acutally, I think it only provides time and satellite ID number IIRC). Anything that relates to a map or is a derived quantity such as velocity or track is provided by software. --Tbeatty 08:50, 27 March 2007 (UTC)

What are the Effects of Orgasm/Ejaculation Cessation in Males
I am curious about this subject on three points:

1) Changes physiologically to the male body over a period of days, weeks, months, and years when orgasms and ejaculation is stopped. (i.e. increase in size of testes, higher risk of heart attack due to hardening of blood vessels, or etc.)

2) Chemical changes in the brain and/or chemical makeup of bodily fluids. (i.e levels of seratonin, dopamine, and etc.)

3) Psylogical effects of cessation. (i.e. irriation, nervousness, elation, hyperactivity, or etc.)

Thanks. --67.177.170.96 02:43, 26 March 2007 (UTC)


 * More frequent messy sheets ...assuming you mean Orgasm/Ejaculation casued by masturbation or Sexual intercourse. 71.100.160.159 05:17, 26 March 2007 (UTC)


 * For the first answer, I am personally skeptical and would like to see a reference. For the first question, it is normally taken to be unhealthy for a male to go without ejaculating for more than about two weeks. Although the prostate fluid can be reabsorbed, the prostate should be drained fairly frequently studies show, and the male has a higher chance of prostate cancer and more disorders of the prostate if it is not. I would not recommend it. To keep this from happening in a male that cannot or has trouble ejaculating normally, the solution is prostate milking. Psychological effects probably would not be all that bad unless he was teased or tempted or really wanted to. I don't believe there would be any problems or much change necessarily on chemical balances in the brain or in the blood, would there? [' Mαc Δαvιs '] ( How's my driving? ) ❖ 07:02, 26 March 2007 (UTC)
 * Jeez, Mac. Your answers should come with a warning label: This health advice is being provided by a teenager who often has no clue what he is talking about but is never in doubt. —The preceding unsigned comment was added by 69.136.100.93 (talk) 11:33, 26 March 2007 (UTC).
 * Sorry, read it on Wikipedia. If you don't think it's right I'd be glad to see some references. As for my rechecking, I didn't find where I read it on Wikipedia, but I did find "Sterilization by vasectomy may increase the risk of prostate cancer, though there are conflicting data. More frequent ejaculation also may decrease a man's risk of prostate cancer. One study showed that men who ejaculated five times a week in their 20s had a decreased rate of prostate cancer, though others have shown no benefit.  " Oh, and thanks for signing out dedicated user, so no body knows who you are. [' Mαc Δαvιs '] ( How's my driving? ) ❖ 17:58, 26 March 2007 (UTC)
 * See the "Medical aspects of abstinence" subsection of Sexual abstinence, and the "Benefits" subsection of Masturbation. MrRedact 10:11, 26 March 2007 (UTC)

I believe the seminiferous ducts in the testicles can rupture, causing sharp pain, but no permanent damage. Frequent erections may also be expected. StuRat 15:13, 26 March 2007 (UTC)

Personally I recently lost any desire to do anything like this for a few weeks (I still haven't worked out why) and during that time I didn't notice any physical effects, or any changes to my mood, other than what I would normally expect :) However as for the first reply, I did find that I appeared to recovered this desire whilst asleep :) HS7 17:48, 26 March 2007 (UTC)

This was almost certainly an effect though as it was the only time this has ever happened to me, and it was a few months ago :) HS7 17:52, 26 March 2007 (UTC)


 * Without suggesting this is necessarily the case with you, such an experience is sometimes a symptom of depression, or a side-effect of the use of certain pharmaceuticals (some legal, some not). JackofOz 04:16, 28 March 2007 (UTC)

Ionic Equations
I would appreciate any help on how to balance ionic equations.

I've checked the articles here and searched the internet extensively, but to no avail.

I also know nothing of redox/oxidation/reduction etc.; since I haven't yet covered that in school, so I need to know hot to balance the aforementioned equations without any knowledge of redox reactions or electrolytes.

I can balance normal chemical equations, but not ionic ones.

An example of what I cant solve, would be:

Pb2+(aq) + OH- ---> Pb(OH)2(s)

--Xanton111 17:08, 26 March 2007 (UTC)

the 2+ counts as 2, therefore needing to be neutralised by 2 1-s (shown just as -s):) HS7 17:23, 26 March 2007 (UTC)

I just need to know:

a) The "goal" of solving the equations. b) The method of solving them, while making sure the mass is equal on both sides as well as the charge.

a) is to make the charge multiplied by the number of molecules/atoms for each different molecule/atom the same ie. b) 2 molecules of charge +3 and 3 or charge -2, giving 6 each :) As for making the mass equal, I have no idea, but you will need the Relative Atomic/Molecular Masses for each molecule/atom :( HS7 17:35, 26 March 2007 (UTC)


 * If you already have the equation, as you do, but without coefficients, then you only need to worry about balancing the number of atoms. I find a chart useful for this:

Reactants | Products --+-  1 Pb    |   1 Pb   1 O     |   2 O   1 H     |   2 H


 * So, it is apparent that we need to add an extra O and H to the reactants to get them to balance:


 * Pb2+(aq) + 2OH- ---> Pb(OH)2(s)


 * This gives us:

Reactants | Products --+-  1 Pb    |   1 Pb   2 O     |   2 O   2 H     |   2 H


 * If the atoms balance then the masses will balance automatically. In this case, the atomic masses for Pb, O, and H are approximately 207, 16, and 1 grams/mole, so we would have 207 + 32 + 2 or 241 grams per mole on both sides.  Note that balancing the number of atoms on each side can be far more complex, requiring an iterative process, in some cases. StuRat 18:06, 26 March 2007 (UTC)

Sorry about my answer, I wasn't thinking properly :( HS7 14:08, 27 March 2007 (UTC)


 * Warning: Thinking improperly is punishable as thoughtcrime. :-) StuRat 17:15, 28 March 2007 (UTC)

Mie Scattering and Cylinders
Can Mie Scattering have a >1% effect on UV-Vis measurements of nanoporous membranes? (Pores are 200nm in diameter and .5mm long, centers ~500nm apart, alumina membrane refractive index=1.6) There are papers that analytically take Generalized Mie Theory from spheres to infinitely long ellipsoids (taken to be cylinders), but I not only cannot interpret the purely theoretical papers but I also am unsure of whether the lack of a cylinder scatters in a similar fashion as an actual cylinder (I assume so -- just switch the indices of refraction of the solid and air). Why am I asking? I am seeing some funky business in transmittance and reflectance measurements.Chillliman 17:13, 26 March 2007 (UTC)Chillliman


 * A quick rough answer would be yes, as the 200nm would be on the same order of magnitude as your UV wavelength. However if the light is propogating parallel to a straight cylynder there may not be much effect.  But are your pores straight cylinders, or randomly aligned as in a sponge?  If you look at how much of the surface is pore it would be approx 200/500 squared or 0.16 - so there may be a 16% effect compared to pure alumina on the gross material point of view.

GB 02:51, 27 March 2007 (UTC)

Some math
Transferred to WP:RD/MATH -- atropos235 ✄ (blah blah, my past) 23:21, 26 March 2007 (UTC)

Value of fp in the Drake equation
The Drake equation, used to estimate the number of advanced civilizations in our galaxy, is dependent of several values, one of which is fp-the fraction of stars that have planets. What is the currently accepted (or least controversial) value for this variable? The Drake equation article says that Drake used .5, but considering how much our understanding of extrasolar planets has developed in the past few years, are different figures accepted now? Thanks for any information on this topic. GhostPirate 20:20, 26 March 2007 (UTC)


 * .5 probably isn't crazy. I think any astronomer would agree it's between .1 and 1, and the Drake equation is so imprecise anyhow this number probably isn't a big deal.  There are other factors to - fp probably increases with time,  for instance (metallicity, actually, but these are related, right?) and who knows what else?  My guess is its more like .9 or something, but any good astrophysicist will tell you .5 = .9 WilyD 20:36, 26 March 2007 (UTC)

I don't think we currently have enough data to come up with a good estimate. Current techniques mainly detect only huge planets in nearby systems. It's quite possible that every star has small terrestrial planets, but we just can't detect them yet. StuRat 21:02, 26 March 2007 (UTC)


 * StuRat summed it up nicely. Current observations focus on stars of about the same mass as the Sun, on the main sequence, but nobody's spent any significant time looking at close or medium binaries, which are fairly common. The (naive) assumption in the past was that these can't form planets, but HD 188753 A put an end to that, and theory is starting to catch up. Of the stars we do look at, about 10% have planets (as it says in the exoplanet article), but - for now - we're limited to gas giants within about 5 astronomical units, or closer bodies down to about 15 Earth masses. Models that "explain" (used loosely) the solar system predict terrestrial planets to be quite common; but then the solar system is something of the odd one out at the moment. Still, expect the number to go up. 0.5 is as good a guess as any, frankly. Spiral Wave 00:47, 27 March 2007 (UTC)
 * Compared to the uncertainties in the other numbers in the equation, 0.1 to 1.0 is a pretty tight range. I agree that 0.5 is a pretty good number to plug in, but if you really want to look where the uncertainties are, look at almost any of the other 'guesstimated' values! SteveBaker 02:59, 27 March 2007 (UTC)

Neutral methyl orange
If someone has already answered here than ignore and delete this.

What couler us Methyl orange when mixed into neutral solutions.--I.W 21:08, 26 March 2007 (UTC)
 * Neutral solutions have a pH of 7. The Methyl orange article says that it is yellow when in solutions with a pH above 4.4 -- atropos235 ✄ (blah blah, my past) 22:55, 26 March 2007 (UTC)

GPS Signal degradation
What is the effect of heavy cloud cover on the signal strength of a conventional automotive GPS receiver? Thanks for any help!

dondd:Dondd 23:23, 26 March 2007 (UTC)


 * Quite a bit, though I am not expert enough to quantify. Splintercellguy 23:57, 26 March 2007 (UTC)


 * I've found it to be significant for hand-held GPS's - but the TomTom unit I have in my car doesn't seem to be affected badly enough to cause a loss of navigational ability. The worst conditions for the hand-held units seems to be when you are standing under trees that have been soaked with rain. SteveBaker 02:52, 27 March 2007 (UTC)

Theoretically it should have little effect as the rain drops are small compared with the wavelength of the signal. GPS wavelength is bigger than C band which is little affected by cloud or rain. GB 02:54, 27 March 2007 (UTC)
 * Hmm, Seeber (2003) Satellite Geodesy, in explaining why higher frequencies are not used (as here would be much less refraction in the ionosphere at higher frequencies) states:"With higher frequencies the atmospheric absorption in the troposphere increases. Without rainfall, the absorption can be neglected for frequencies between 30 MHz and 30 GHz. With precipitation, however, signals in the frequency domain > 1 GHz experience considerable attenuation."The L1 and L2 GPS frequencies are 1.6 and 1.2 GHz.&mdash;eric 21:25, 27 March 2007 (UTC)
 * Also,our GPS article explains that moisture in the air affects the propagation velocity of the GPS signals. So even if the signal is not attenuated, its accuracy could be significantly compromised, since of course GPS measurements depend intimately on phase and propagation velocity. —Steve Summit (talk) 12:09, 28 March 2007 (UTC)