Wikipedia:Reference desk/Archives/Science/2010 August 27

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August 27

Lard as sunscreen...?

Sometimes you see characters in older cartoons and sitcoms smearing themselves with lard when sunbathing, instead of sunscreen. Obviously it's done on there because it looks funny - but did (do?) people ever actually do that in real life? Does lard, in fact protect the skin from the effects of UV radiation? --Kurt Shaped Box (talk) 00:07, 27 August 2010 (UTC)

Did people actually care about sunscreen back then? Or was it just a moisturizer/conditioner/etc, like one might use baby-oil or SPF-0 now when trying to get a dark tan? DMacks (talk) 00:23, 27 August 2010 (UTC)

Dunno, to be honest. I've met people who think that baby oil *is* a sunscreen. --Kurt Shaped Box (talk) 00:34, 27 August 2010 (UTC)

It's not a sunscreen its a suntan lotion. That is, there are products which intensify the tanning effect of the sun, or can be used as moisturizers to combat the peeling and drying from excessive sun exposure. The use of baby oil and lard is likely more for these effects (as in, "fuck cancer, I want a good tan"...) --Jayron32 02:23, 27 August 2010 (UTC)

Agreed, lipids won't block UV radiation, if they did, there would be no need for sunscreen. Here's a funny article where someone asked if salad dressing worked as sunscreen! My mum's told me before that in the 60s plenty of travellers in Greece used olive oil and sunbathed and, unsurprisingly, went redder than tomatoes. _{Are mothers a reliable source?} Smartse (talk) 11:48, 27 August 2010 (UTC)

What is the wind-water-solar climate change mitigation scenario atmospheric carbon projection?

In Jacobson, M.Z. (2009) "Review of solutions to global warming, air pollution, and energy security" Energy and Environmental Science 2:148-73 doi 10.1039/b809990c and Jacobson, M.Z. and Delucchi, M.A. (November 2009) "A Plan to Power 100 Percent of the Planet with Renewables" (originally published as "A Path to Sustainable Energy by 2030") Scientific American 301(5):58-65 what is the projected atmospheric carbon over time for their preferred wind-water-solar program?

What year do they start subtracting carbon and when do they reach 350 ppm?

I have asked also here, but I have been having better luck here at WP:RDS. Why Other (talk) 02:04, 27 August 2010 (UTC)

Per Dr. Jacobson, this is related to Eqn. 3 in http://www.stanford.edu/group/efmh/fossil/ClimRespUpdJGR%201.pdf

"[calculate] the time-dependent change in CO2 mixing ratio from a given anthropogenic emission rate, [and with that] the time-dependent difference in mixing ratio resulting from two different emission levels by subtracting results from the equation solved twice. Note that chi in the equation is the anthropogenic portion of the mixing ratio (this is explained in the text) and units of E need to be converted to mixing ratio. The conversion is given in the paper."

This almost might be ready for the math reference desk. Why Other (talk) 22:18, 27 August 2010 (UTC)

Maybe something like the scenario proposed by James Hansen's Alternative Scenario paper? ~AH1^(TCU) 18:38, 28 August 2010 (UTC)

Interesting, but the assumptions in that paper don't involve adjusting the CO2 emissions rate, which is what I am trying to do.

This is from a response to a pointer to this question I put on the Math Reference Desk:

"... This is a fairly standard problem in ODE's and the solution is a straightforward use of separation of variables....--68.40.56.142 (talk) 15:04, 28 August 2010 (UTC)"

I wish I had more experience with ODEs. Why Other (talk) 03:27, 30 August 2010 (UTC)

The separation of variables article describes it some, and a little more explanation is here. Basically the ODE is something like

${dy \over dx}=ay+b$

Separating variables gives you

${dy \over ay+b}=dx$

Integrating both sides,

${1 \over a}{\log(ay+b)}+C_{1}=x+C_{2}$

Exponentiating both sides, rearranging terms, and renaming some constants,

$y={ke^{ax}-b \over a}$

where $k=e^{a(C_{2}-C_{1})}$ or something like that. It's possible that I messed up that calculation somewhere (it's late and I haven't done this in a while) but it's a basic ODE technique.

That said, that linear model sounds oversimplistic for something as complicated as the earth/atmosphere system. See for example clathrate gun hypothesis. 67.119.3.248 (talk) 08:50, 30 August 2010 (UTC)

Sam and Ella over easy

In news reports about the recent salmonella outbreak in US eggs, they mention that people should avoid having lightly cooked scrambled eggs or eggs over easy. I haven't heard one yet advise not to have sunny side up and I would think that that would be more dangerous than over easy. Am I right in thinking that sunny side up would be more dangerous than over easy? Dismas|^(talk) 02:25, 27 August 2010 (UTC)

Sunny side up is less cooked (heated) than over easy, so it would be less likely to kill bacteria, yes. -- Scray (talk) 03:06, 27 August 2010 (UTC)

I know it would be bad for the egg industry which is no doubt already going to suffer a big hit because of this, but wouldn't you just stop eating eggs for a few weeks? Having said that however, that does remind me of how Oprah got sued for saying she wasn't going to eat beef during the mad cow incident. Vespine (talk) 04:05, 27 August 2010 (UTC)

It won't keep me from eating eggs. We get ours from our own chickens. 25 birds with more room than was in my first house! Dismas|^(talk) 13:35, 27 August 2010 (UTC)

Eggs are quite safe to consume (even contaminated ones), provided they're cooked properly. In this regard, they're no different than meat, and there's no reason to not consume them just because they might have salmonella. Personally, I always treat my eggs (and meat, especially ground meat) like it's contaminated. I think that it really speaks to how good our public health system (generally) is, that people now expect their eggs to be free of pathogens. Buddy431 (talk) 20:51, 27 August 2010 (UTC)

"Over easy?" I beg your pardon? As a non-American, I think I've just discovered another entry for List of American words not widely used in the United Kingdom. (Even though it's actually two words.) Can some one explain what it means please? HiLo48 (talk) 22:03, 27 August 2010 (UTC)

See Over_easy#United_States_and_Canada: It's a fried egg which cooked on both sides. Hence "over"...you have to flip it "over" during cooking. The yolk is left very runny and even the white is somewhat liquid inside the solid white 'pouch' formed by cooking it on both sides. And "easy" is the opposite of "hard". You could theoretically ask for your eggs "over hard" or "over medium" too - but I've never heard anyone actually do that. If you just asked for "fried" you get it fried on just one side. The myriad of only marginally different ways that Americans like their eggs cooked is guaranteed to perplex us poor Brit's the first time we undertake breakfast at "Dennys". SteveBaker (talk) 22:31, 27 August 2010 (UTC)

My mother always used to ask for "two eggs over medium". I haven't heard her do that in a while. But maybe I just haven't had breakfast with her in that sort of place for a while.

The one whose definition I've never been quite sure of is "sunny side up". I think that means the cook is supposed to spoon some of the hot fat on top of the egg, so that even the top gets a little bit cooked. But I don't know whether they all bother. --Trovatore (talk) 23:05, 27 August 2010 (UTC)

Once again, Fried Egg#United_States_and_Canada comes up with a definition: "'Sunny side up' — cooked only on one side; yolk is liquid; the egg white is often still a bit runny as well. This is often known simply as 'eggs up'. Gently splashing the hot cooking oil or fat on the sunny side uncooked white, i.e., basting, may be done to thoroughly cook the white. Covering the frying pan with a lid during cooking (optionally adding a cover and half-teaspoon of water just before finishing) allows for a less "runny" egg, and is an alternate method to flipping for cooking an egg over easy (this is occasionally called 'sunny side down')." SteveBaker (talk) 23:41, 27 August 2010 (UTC)

I prefer my eggs "Over Medium" and when I have breakfast at a restaurant, always order them as such. Almost without fail, I get them "Over Easy," notify the waitress, and get two more eggs for free. :-) Kingsfold (Quack quack!) 16:34, 31 August 2010 (UTC)

Sourdough starter

A recipe in a book on baking says to make starter for sourdough rye bread by mixing beer with rye flour in a mixing bowl, then covering the bowl with plastic wrap for 2 days at room temperature, beating it 3 times per day. It is supposed to bubble and smell sour, but is has not changed from hour one in 2 days. I thought sourdough relied on yeast from the air somehow entering the mix and multiplying. If the starter is covered by plastic, oxygen would be restricted and nasty anerobic bacteria would seem to be favored. Also how would environmental yeast get into the mixture? Would rye flour contain yeasts? Would beer (soon stale due to loss of carbon dioxide) furnish a culture to leaven the sourdough? The recipe does specify using yeast in addition to the sourdough starter when the dough is finally made. I have a sourdough starter of considerable longevity and vigorous activity which I use for regular bread baking, although with ordinary all-purpose wheat flour or bread flour. Would it make sense to add some of this to the rye flour/beer mixture? Edison (talk) 04:44, 27 August 2010 (UTC)

Some beers have got the same stuff, anyway: Saccharomyces cerevisiae What kind of beer are you using? Wikiscient (talk) 06:02, 27 August 2010 (UTC)

Are you using an unpasteurized beer? Something like Creemore Springs lager should do the trick, or any beer that is bottled with live yeast. The yeast will be dormant by the time you get it but will reactivate with a new food source. Industrial beer probably won't (and shouldn't) get the job done. Franamax (talk) 07:25, 27 August 2010 (UTC)

The recipe says as an alternative to beer to mix rye flour and water and cover with plastic for 2 days, beating 3 times per day, so they do not seem to be relying on yeast from the beer. Some recipe sites say that rye flour contains some natural yeast. The plastic wrap cover concerns me as stated above, and a cloth over the bowl seems to make more sense, to allow in some air. After 2 days and no foam, I fed the stuff with more flour and some water, then divided it in half and added some of my usual starter to one batch. The usual starter has been fed for years with milk, all purpose flour and sugar. Starters are supposed to be a combination of yeast and anerobic bacteria, with some complex conversions taking place to the raw materials. I just thought someone might have experience with or knowledge of establishing a rye flour starter. Edison (talk) 16:41, 27 August 2010 (UTC)

Sourdough starters are basically dough based cultures containing yeast and bacteria such as Saccharomyces cerevisiae and Lactobacillus acidophilus. Both types of microorganisms and their spores are found floating in the air and environment so there is likely some already in the rye flour. Since starters are just bacterial and yeast cultures, I think you can innoculate your rye flour/beer mixture with it to assure yourself higher success in making your rye starter. In fact, I would forgo making the rye starter and just use your bread flour starter for rye bread. -- Sjschen (talk) 17:02, 27 August 2010 (UTC)

There are many kinds of yeast and each gives a different flavor, so this wouldn't automatically give the same result. Looie496 (talk) 17:30, 27 August 2010 (UTC)

True, but that assumes the rye flour and bread flour supports very different yeast and bacterial cultures. -- Sjschen (talk) 20:32, 30 August 2010 (UTC)

mechanics

. Two forces are applied at two different points on a thin rigid rod ; the two points could be the end-points of the rod. Using equilibrium conditions prove that for the rod to be in equilibrium , the direction of forces must be collinear with the rod. —Preceding unsigned comment added by Khushal13 (talk • contribs) 05:10, 27 August 2010 (UTC)

Sorry, we don't do homework for you, but that said, do you understand the question? Especially do you understand what equilibrium, and collinear mean? Because once you do the answer should be easy. Ariel. (talk) 06:43, 27 August 2010 (UTC)

... but if you still haven't answered your question, perhaps our article on Moment (physics) might help. Dbfirs 12:03, 27 August 2010 (UTC)

If they were not collinear and opposite, wouldn't the rod tend to rotate or move? Edison (talk) 01:09, 28 August 2010 (UTC)

know

how to spell knownen like a knownen carcinogen? —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 05:30, 27 August 2010 (UTC)

1) This isn't a science question. 2) Try a dictionary like wiktionary e.g. wiktionary:Special:Search (yes I've tried and it works). In any case, it seems you've already answered your question. Nil Einne (talk) 06:03, 27 August 2010 (UTC)

It's just "known" like "known carcinogen". Wikiscient (talk) 06:24, 27 August 2010 (UTC)

White onion

What is the latin name of white onion? --Ksanyi (talk) 07:43, 27 August 2010 (UTC)

I believe that it's Allium cepa, but I'm not sure it's the only species of white onion. Someguy1221 (talk) 09:14, 27 August 2010 (UTC)

Mars drill

It would seem to me, that if Mars ever supported life, any traces of it would be deeply buried under its surface; so why not drill into it, or even easier, use explosives, to probe into deeper layers ? Or has this been done already ? —Preceding unsigned comment added by Rowen121 (talk • contribs) 08:36, 27 August 2010 (UTC)

This was the point of the Deep Space 2 mini-probes carried aboard the Mars Polar Lander (though whether you'd consider 0.6m "deep" I don't know); sadly, while (unlike MPL) they did successfully get to the surface they never "phoned home". --81.158.2.129 (talk) 10:07, 27 August 2010 (UTC)

"Our mission: to seek out new life ... and vapourise it". Gandalf61 (talk) 14:59, 27 August 2010 (UTC)

Mars has an atmosphere that contains water vapour and various chemicals so do not rule out the possibility of above-ground flying organisms. Cuddlyable3 (talk) 15:16, 27 August 2010 (UTC)

This is the same reason that the Mars rovers sought out craters on the Martian surface (preferably "recent" craters). Those cratering events are much more powerful than any explosion we could afford to send and thus hopefully probe deeply and dislodge a lot of buried material. I have also seen NASA technology development grants offered to people wanting to build a drill for space operations, but the size, complexity, and power requirements of such systems tend to be prohibitive. Dragons flight (talk) 15:24, 27 August 2010 (UTC)

There has been a lot of work on developing deep-drilling technologies for Mars exploration -- if you do a Google Scholar search for "Mars drill" you'll get a few dozen papers. I believe that a European probe that is already under construction is intended to be able to drill 2 meters deep; it can be expected that future probes will go quite a bit deeper. Looie496 (talk) 16:02, 27 August 2010 (UTC)

Subsurface exploration is difficult on Earth - and it's even harder in space. For historical perspective, you can read about profiling the lunar subsurface on Apollo 17. Getting underneath the soil is really hard. Drilling is difficult - it takes a lot of energy. Blasting is difficult - it requires dangerous chemical explosives, and these are consumables (so you only have a certain number of shots). If you can think of a different way to remove large amounts of dirt, NASA would love to hear about it: every year they hold a Lunar Robotics Mining Competition. Mars' soil is quite different than lunar regolith (and both are quite different from Earth soil) but the basic task is about optimizing parameters: how many kilograms of dirt; how many cubic meters of dirt; and how fast, how many joules of energy, what forms of energy (battery, chemical, solar, and so on). Nimur (talk) 16:33, 27 August 2010 (UTC)

The Beagle II probe carried a 'robotic mole' that was designed to tunnel around. (More like an earthworm than a mole, really.) Unfortunately, Beagle II did not successfully make a controlled landing. APL (talk) 19:54, 27 August 2010 (UTC)

Right with the European probe! It is ExoMars. The system will carry a 4 X 50cm drill which was already tested in a Mars chamber here on earth. Two meters into hard rock will be a big step in the understanding what the atmosphere does to the surface of Mars. The drill is a upgrade from the drill already under way to 67P/Churyumov-Gerasimenko. The first sample will not be delivered before 2019. I heared from MSL scientists that they envy us for the nice drill we get.

Who invented Galvani cell (aka galvani element)?

Who would be rightfully credited inventor of Galvani cell, is it Galvani or Volta or both of them or sbody else entirely?

Difference between Voltaic cell and Galvanic cell is also a bit vague to me... —Preceding unsigned comment added by Pudist (talk • contribs) 11:58, 27 August 2010 (UTC)

See the article Voltaic pile. A voltaic pile is a set of individual Galvanic cells placed in series. Luigi Galvani 1737 - 1798 and Alessandro Volta 1745 - 1827 were rivals as noted at Luigi Galvani#Galvani vs. Volta: animal electricity or heat electricity? and Alessandro Volta#Volta and Galvani. A "Voltaic cell" is a split Galvanic cell used for demonstrations. Cuddlyable3 (talk) 14:17, 27 August 2010 (UTC)

Velocity and acceleration

Overheard this on bus from what I assume to be two freshman college students... "This class sucks. We are given three mile markers and times and we are supposed to tell the car's velocity and acceleration. He doesn't tell us which method to use to calculate it, so I'm sure I'll get it wrong." Given three positions on a line with the time for each position, are there really many different methods to calculate velocity and acceleration? I can only think of dividing distance by time for velocity and, because there are three positions, subtracting the first section of velocity from the second section. -- kainaw™ 12:13, 27 August 2010 (UTC)

That's the only way that comes to mind for me too. Now granted, there are thousands of wrong ways...using constants that don't apply, mixing incompatible/unconverted units of measurement, plugging loose numbers into unrelated formulas, etc. So I'd say the odds are actually strongly favor getting it wrong. Assuming they didn't actually just pay attention in class or read the text. Which again the odds seem to strongly favor. DMacks (talk) 12:20, 27 August 2010 (UTC)

I imagine that's the intended solution, but strictly it would only work out the average velocities at the half mile points and I wonder if it's meant to be a little more sophisticated than that (hopefully, if it's college-level, it is?). I think there's enough information in the problem to use the suvat equations under the assumption of constant $a$.

We have three pairs of distances/times $(x_{1},t_{1})$, $(x_{2},t_{2})$ and $(x_{3},t_{3})$. We can apply $s=ut+{1 \over 2}at^{2}$ to the differences between any two pairs of these to get a pair of simultaneous equations in two unknowns $u$, the initial velocity and $a$, and then just use $v=u+at$ if we're desperate to know the final velocity explicity too, e.g.:

$(x_{3}-x_{1})=u(t_{3}-t_{1})+{1 \over 2}a(t_{3}-t_{1})^{2}$

$(x_{2}-x_{1})=u(t_{2}-t_{1})+{1 \over 2}a(t_{2}-t_{1})^{2}$

All the $x$s and $t$s are given so it's a lot less hairy once they substitute the numbers they've got. There's bound to be a flaw in my logic somewhere, though.

--12:49, 27 August 2010 (UTC) —Preceding unsigned comment added by 81.158.2.129 (talk)

Eliminate t₁ and x₁ which can both be zero. We are given x₂ = 1 mile and x₃ = 2 miles. So far, so good. Go ahead and solve v = f(t₁,t₂,x₁,x₂) and a = f(t₁,t₂,x₁,x₂). Cuddlyable3 (talk) 14:29, 27 August 2010 (UTC)

Yeah, I was hugely overthinking that with all that simultaneous equations guff. For the constant acceleration case it just boils down to solving the equation of a parabola, given three points ... --217.41.233.67 (talk) 15:10, 27 August 2010 (UTC)

Somebody (the student or the professor) has forgotten to state the implicit assumption of constant acceleration. If this is not specified, the problem is unsolvable (any high-order function that fits three points is acceptable). If constant acceleration is specified, this is a trivial parabola-fitting problem that can be solved on paper (or with a calculator if the numbers are ugly). Nimur (talk) 16:36, 27 August 2010 (UTC)

Yes, the 3 observations (t₁,x₁),(t₂,x₂), and (t₃,x₃) substituted into the function x=a+bt+ct²/2 gives 3 equations with 3 unknowns a,b,c. Bo Jacoby (talk) 14:40, 29 August 2010 (UTC).

No, velocity and acceleration are the two unknowns. We are not interested in calculating the car's position relative to the beginning of time. Normalise the observations to (t₁,x₁) = (0, 0) and we have 2 equations with 2 unknowns. Cuddlyable3 (talk) 21:22, 30 August 2010 (UTC)

A likely name for a science fictional superhard material

I've come up with the slapdash 1,8-Bis(hydridol)carbyne - but I have a strong feeling it's a neologism that would make a materials scientist laugh then vomit - can someone suggest something just as impressive-sounding but that would make a lick of sense to a scientist?

Thanks Adambrowne666 (talk) 12:18, 27 August 2010 (UTC)

It sure sounds technical though, maybe that's the only important part? From what I've seen, scientists are probably going to spot the fiction pretty easily anyway even if the name is correctly formed or scientifically valid--if they care to think about it at all--and nonscientists are going to be impressed with something technical-sounding even if it doesn't have any sensible meaning. DMacks (talk) 12:27, 27 August 2010 (UTC)

You could call it, say, hydridol(II) carbyne, a compound of hydridol and carbyne where hydridol has an oxidation number of 2. Hydridol and carbyne could be some as-yet undiscovered elements. Although a real scientist would know there is no gaps in the periodic table, so they would have to have huge atoms and likely be radioactive. Do whatever you like--178.167.206.113 (talk) 14:09, 27 August 2010 (UTC)

Any plausible superhard material would have a tradename or, at the very least, a nickname that scientists use for it (a bit like "magic acid"). Physchim62 (talk) 14:19, 27 August 2010 (UTC)

You could borrow from the Dune universe some Plaz, a synthetic glass, used for windows (especially in aircraft and spaceships) due to its superior strength, or some Shigawire which is a metallic extrusion of a ground vine (Narvi narviium) grown only on Salusa Secundus and III Delta Kaising. It is noted for extreme tensile strength and used as a recording medium (among other things). Shields (Star Trek) are reportedly generated by replication of an alloy of diburnium and osmium, the hardest alloy known to the Federation. Cuddlyable3 (talk) 15:03, 27 August 2010 (UTC)

From a scientific point of view, there's no way to get anything much harder than diamond using ordinary chemical bonds. The only real possibility for getting a superhard material would be to go to the nuclear level. If I were writing about something like this, I would use quarkonium, a substance made from neutronium by getting the neutrons to share quarks. I think even a particle physicist would have difficulty automatically ruling that out. Looie496 (talk) 15:49, 27 August 2010 (UTC)

It depends on how hard the material should be. There are many carbides, tungsten carbide, tantalum carbide, and rhenium carbide (need an article on that last; cute stuff). And diamond is "carbon carbide", you might say. It is very well plausible that by forming exactly the right matrix of this metal and that metal in just such-and-such a configuration, you can get something that would eat diamonds for lunch, drill bit to drill bit that is. Wnt (talk) 18:43, 27 August 2010 (UTC)

Again borrowing from Sci Fi, Unobtainium, unless you are after the chemical name. 220.101 talk^\Contribs 20:06, 27 August 2010 (UTC)

Is there a specific reason you don't want to make material scientists vomit, are they likely to be a large group of your readers? I second a 'carbide' as they're popularly known to be hard. The first time I saw the word 'unobtainium' used seriously in a novel I just had to laugh. I'm amazed how prevalent it is tho, how lazy does an author have to be to use that!? what's next, "is that hardonium in your pocket or are you happy to see me?" 87.113.180.73 (talk) 02:01, 28 August 2010 (UTC)

Thanks, all - it's being used as an orbital tether, so has to be plenty hard - what I was worried about, I guess, was that the 1,8-Bis(hydridol) part of it might look so silly to a scientist, or even a lay person with some knowledge of chemistry, that they'd be distracted from the story. Adambrowne666 (talk) 05:49, 28 August 2010 (UTC)

Add a footnote that indicates that the compound is fictional. --Chemicalinterest (talk) 11:07, 28 August 2010 (UTC)

An orbital tether should be strong, not hard. The strongest material currently known is carbon nanotubes. Looie496 (talk) 17:16, 28 August 2010 (UTC)

I almost held this one for my special reserve, but my current draft features a world... not in the market for space elevators. So I should mention that if you read space elevator, you'll see that much of the problem meeting the specs involves a) a factor of two safety margin and b) that not every nanotube performs up to theoretical specifications. These two things can both be offset through better design in the future: specifically, if a "splint" travels up and down the tether, which allows the main cable to be broken apart at prefabricated joints, and a device precisely focuses high-frequency microwaves/IR down each and every nanotube at each of these joints, then each one can be tested for flaws. Possibly transitions induced by the electromagnetic radiation could actually repair small flaws in each tube; otherwise, a chip with microactuators could detach a single tube and feed through a fresh replacement. In this way conventional carbon nanotubes, perhaps doped up with a bit of boron and nitride, could do the job reliably. Wnt (talk) 18:31, 28 August 2010 (UTC)

Parallel connection of two sets of batteries

I want to keep a battery-powered LED flashlight on for a few more days. So I plan to add another set of batteries externally in parallel. Is it a good idea for the rechargeable batteries? Will it damage the batteries?

• Internal batteries: 4 * AAA NiMH (4 * 1.2 Vdc).
• External batteries: 4 * AA NiMH (4 * 1.2 Vdc).

I'll just leave the battery compartment open and let the wires from the external battery box touch the internal contacts. The whole thing will then be placed in a big waterproof plastic bag.

I know it's very bad to have mixed-type batteries serially connected because of internal resistance issues. I guess parallel connection of two sets of serially connected batteries shall not be a deadly sin. I just want to make sure it's not going to blow planet earth off its orbit. -- Toytoy (talk) 17:50, 27 August 2010 (UTC)

Parallel connections on rechargeables kills them. What happens is that one battery is slightly less charged than the other, so the first one tries to charge it, it overshoots, and then the second one charges the first, and the current swings back and forth over and over till both batteries are not just discharged, but also dead. This is a big problem for cars when you want to add a backup battery. For cars they usually add a manual cut-over switch. You may be able to solve this with some diodes. Ariel. (talk) 19:45, 27 August 2010 (UTC)

Do you have a citation for that? I'm having trouble buying the thermodynamics of that explanation. While connecting two batteries (of the same chemistry) with different charge levels will cause a current to flow as one battery charges the other, the current will decline as the two batteries approach the same potential, and stop as soon as they reach the same level of charge. I can't think of a mechanism by which the charging would 'overshoot'; it's not as if the wires are pipes full of momentum-laden flowing water.

By my reckoning, the reason one would put a manual cutover switch on an automobile's backup battery is not due to some weird cross-charging effect. Instead, it's so that when you leave your lights on in the car park (or are the victim of some other slow electrical leak), only one battery will go flat; you'll still be able to switch to the other fully-charged battery and be on your way. TenOfAllTrades(talk) 20:11, 27 August 2010 (UTC)

I also find it questionable. Parallel connection of NiMH batteries and various li-ion chemistries is quite common in various situations like for RC usage but also things like for DIY bicycle lights. There are also things like C and D adapters where you can use several AAA or AA in parallel for greater capacity but the price of AAA/AA. You should have relatively matched batteries (i.e. same type, capacity, age and charge state). However charging NiMH in parallel is can be a bad idea edit:particularly if you use a dV/dT method (see [1] for example) edit:but actually any method is a bit risky (see [2]) so you do need some way to disamble them if you plan to charge them in that wayedit:for charging. (It's fine for li-ion types since they aren't charged like that.) Note for li-ion, parallel is even used for commercial laptop battery packs [3]. Edit:[4] also says the same thing Nil Einne (talk) 22:01, 27 August 2010 (UTC)

Battery voltage is not constant, it varies because it takes some time for the chemical reactions to equalize. For example when they sit for a little while the voltage goes up, and if you discharge them heavily it drops, then recovers later. Note: I've never experienced this personally, I'm just writing what I read about a while ago. Ariel. (talk) 22:03, 27 August 2010 (UTC)

That is true (to an extent), but the effects would not cause the 'see-saw' charging that you describe. Consider two batteries with different levels of charge, connected in parallel. The fully-charged battery will start to charge the battery with the lower charge. As a result, the apparent voltage across its terminals will decrease, while the voltage across the less-charged battery's terminals will increase. (Energetic reactants are being depleted from the first battery, and accumulated in the second.) The more-fully-charged battery will continue to charge the less-charged battery until the apparent voltage across each pair of terminals becomes equal. If you cut the cables at around this point in time, there can be a small amount of rebound in both batteries. The potential across the apparently-initially-full battery's terminals will rise slightly, as current is no longer being drawn off, and reactants are no longer being consumed. Similarly, the potential across the other battery's terminals will fall off a bit, as the components inside that battery equilibrate. If subsequently reconnected, a small amount of current will flow between the two batteries, in the same direction as before. The two batteries will eventually fully equilibrate, so that no current flows between them and they will maintain the same potential across their terminals even when separated. The important bit is that the potential across the first battery's terminals will never be lower than the potential across the second battery's terminals, and current will never be flowing back in the other direction. TenOfAllTrades(talk) 22:40, 27 August 2010 (UTC)

The first response above[5] is completely wrong and should be deleted preferably by the poster. Cuddlyable3 (talk) 23:32, 27 August 2010 (UTC)

I agree. What actually happens with unequal cells in parallel is that as one cell's potential falls through discharge, the other provides more of the load current until the potentials are equal. There will be some recharging of the depleted cell once the load is removed, but no significant current swing. Ariel's point about potentials rising after the load is removed is certainly true. This is caused by recovery from polarisation, and it is possible that the cells will recover at different rates, but the cells will not discharge each other to a significant extent. There will be no significant harm done by connecting cells of the same composition in parallel, even if they have different capacities. It would be better if the cells could be separated once the load is removed, but this is not essential. I haven't set up a circuit to test my claims, but I'm convinced that any "swing" would be no more than a brief microamp causing negligible waste of charge. Can anyone find a reference to back this up? Dbfirs 19:13, 28 August 2010 (UTC)

Well, I'm not going to delete it because I got the info from people who actually did it (with car batteries) (it was years ago, so don't ask me for a ref). But I can accept I might be wrong. I'd really like to test it. Does anyone have a multimeter with a data out port? Attach two batteries, and measure the amps flowing between them on one side, leave it connected for several days, integrating abs(amps) all the while. I may buy a new multimeter just for this, but probably not soon. Ideally the batteries would get used occasionally, but I think that would make the measurements of leakage much harder (but would probably give more realistic results). You'd have to measure amps from each battery separately, and integrate only the difference. Ariel. (talk) 02:45, 29 August 2010 (UTC)

Car batteries are usually lead-acid of course, but all types of cell suffer from polarisation. If you ever find details of the test I'd be interested in seeing them. I was thinking about setting up a test myself, though I don't have the equipment to integrate the current. I suspect that the problems are caused by one battery being charged and the other discharged on connection. I've often done this with car batteries, but not left them long enough to see what happens when the discharged one gains charge. There is certainly a considerable loss of total charge when one cell charges another. Dbfirs 18:06, 31 August 2010 (UTC)

If you want to use the internal battery and a similar external battery to keep a light on as long as possible, the optimal solution would be to use one set of batteries at a time, to avoid the more discharged cell from pulling current out of the more fully charged cell. Alternating use might be best, since a cell could recover a bit while resting. I expect considerable energy would be lost in the parallel connection versus the one set at a time use, provided that the drain is well within the current rating of the cells. Edison (talk) 20:28, 28 August 2010 (UTC)

I agree that alternating would be the optimum, but, if this is not convenient, there will be no significant energy loss in the parallel connection if both cells are fully charged at the start. Why would you expect considerable loss, Edison? I agree that there would be some loss if a charged cell were connected to a discharged cell. Dbfirs 21:13, 28 August 2010 (UTC)

3D jumping spider

Jumping spider

Sorry for asking, but this jumping spider die in a small beaker in my lab and dried for an unknown period. It is 4mm in length and I broke a leg and the Pedipalp to get a better Scanning electron microscope 3D image of the Chelicerae. Is there a chance to get a rough estimate where to put it into the classification of jumping spiders?--Stone (talk) 21:08, 27 August 2010 (UTC)

I assume, from your userpage, that you found it in Germany? Smartse (talk) 21:48, 27 August 2010 (UTC)

Right. Right in the middle of Germany.--Stone (talk) 05:13, 28 August 2010 (UTC)

You can just run SEM on anything you want? DRosenbach ^{(Talk | Contribs)} 22:11, 27 August 2010 (UTC)

That is quite awesome! A while ago I took a similar picture of a bee's face with just a cheapy usb microscope, obviously the quality is much poorer. I reckon you should do some close ups of it's eyes and fangs. Vespine (talk) 01:04, 28 August 2010 (UTC)

The instrument is a very old (1960s I guess) and therefore there is no restriction for using it. So I will do some more pictures when I find some time. --Stone (talk) 05:13, 28 August 2010 (UTC)

Memory loss caused by Urinary Tract Infection - UTI

How does a urinary tract infection UTI cause memory loss - What is the actual biological/chemical mechanism?

I searched through quite a number of topics on Wikipedia, but the above information was not provided (searched Urinary Tract Infection, Memory, Memory Disorders, Amnesia). This information should be added to the appropriate articles. JSNC (talk) 21:14, 27 August 2010 (UTC)

Where did you get the idea that UTI causes memory loss? I see no reason why that would happen. Looie496 (talk) 21:51, 27 August 2010 (UTC)

I was just about to ask the same thing. It sounds pretty implausible and google scholar doesn't bring up anything obvious. Smartse (talk) 21:52, 27 August 2010 (UTC)

Don't you remember...it was on the news only last night! Maybe you've had one too many UTIs... DRosenbach ^{(Talk | Contribs)} 22:09, 27 August 2010 (UTC)

I never heard of this one, but it can be found easily enough: [6][7][8][9] I'm seeing mention of delirium and TNF-alpha. Apparently the drug Ditropan for the urinary tract infection can cause memory loss. Good news is that it may readily be reversible. Just one more proof that nothing is impossible in biology! Wnt (talk) 22:36, 27 August 2010 (UTC)

No reference, but I've heard it discussed in terms of elderly people, that a UTI can lead to a high fever and other symptoms of infection, which in turn lead to symptoms of dementia such as memory loss. You treat the UTI, it then looks like you've cured (or lessened) dementia! I've seen it mentioned in this way when discussing the need for vigilant staff at nursing homes, and regular visits by doctors, to catch when a patient is actually suffering from dementia, and when they just need some antibiotics. All made more complicated by many patients suffering from both. 86.161.108.172 (talk) 00:21, 30 August 2010 (UTC)