Wikipedia:Reference desk/Archives/Science/2010 January 13

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January 13

Pain caused by discussion of pain or 'medical' issues

(Removed medical question)

I'm sorry but here on the Wikipedia reference desks, we're not allowed to give medical advice. If you are concerned - you should see a doctor. SteveBaker (talk) 00:52, 13 January 2010 (UTC)

I understand that, but I'm not asking for medical advice and I'm certainly not concerned. I just want to know what it is called. Thanks.--80.229.152.246 (talk) 21:21, 13 January 2010 (UTC)

We can't tell you what (if any) medical condition you might be suffering from without offering a diagnosis. If I said "The name of your condition is Antidisestablishmentarianism Histrionics" (I just made that up) then I'd be offering a diagnosis of your condition - implying that I've thought about the symptoms you explained and somehow concluded that you don't have "Supercalifragilisticexpialidocious Syndrome" (I made that up too). This is diagnosis of a condition - and it is STRICTLY prohibited for reference desk contributors - partly because it's dangerous to take medical advice from random individuals on the Internet - and partly because it's illegal to practice medicine without a license in the jurisdiction of most countries of the world. So even if we thought we could probably guess what your condition was - we're not allowed to say anything other than "If you are concerned - please seek medical attention from a qualified Doctor" (which I did). Since some less experienced ref desk contributors are ignorant of this rule, we tend to delete questions that clearly violate the guidelines listed at the top of this page in order to discourage those people from attempting an answer. Sorry - but them's the roolz. Please take any further debate to the "discussion" tab at the top of this page. SteveBaker (talk) 00:14, 14 January 2010 (UTC)

mirrors

if every human that owned a mirror were to place it outside for a day or so, would this reflect enough heat to make a difference in the temperature of the earth at all? Im just thinking that if everyone put out a mirror that is 1 m^2 then that would be 6.7 billion m^2 or 81km^2 ish of reflective surface. —Preceding unsigned comment added by 174.88.21.160 (talk) 03:30, 13 January 2010 (UTC)

There seem to be quite a bit out about "white roofs" (which accomplish pretty much the same thing as a mirror, though not to the same degree) as a way to fight global warming. The point is not so much to cool the whole Earth, but rather to reduce the amount of energy used to air condition buildings. Buddy431 (talk) 03:41, 13 January 2010 (UTC)

Well, let's suppose there are 6.8 billion people. Let's be generous and suppose that every one of us owns a 1 square meter full-length mirror (that can't remotely be true - but let's be generous). There are a million square meters in a square kilometer - so we're looking at a total area of 6,800 square kilometers of mirror (I don't know where you got your 81 square kilometer number from). The surface area of the earth is 510,000,000 square kilometers - so we'd be covering about one part in 100,000 of the earth's surface with our mirrors. Even if we all cunningly stand on the darkest part of the earth's surface and have perfectly shiney mirrors, we'll only increase the earth's albedo by something like a thousandth of a percent - from 0.367 to 0.368 or so. This would "make a difference" - and ought to reduce temperatures - but by a very, very tiny amount.

So you aren't going to solve global warming that way. We've lost close to 40% of the Arctic ice alone in the last 10 years. That's 40% of the 15,000,000 square kilometers turned from bright white shiney ice to dark ocean. The 6,800 square kilometers of mirror don't make even a tiny dent in that amount of albedo change...and that's not counting all of the glaciers, the antarctic and mountain-top ice & snow.

However, there might be other ways to do similar things. After the 9/11 disaster, the US shut down all air travel for a day or two. This resulted in there being no jet contrails in the sky. Since contrails are very white - and therefore reflect light back out into space (not as well as a mirror - but pretty good) - you'd expect there to have been a small increase in air temperatures over North America as a result...and it turns out that there was - and it was quite measurable. So it seems kinda possible that we could reduce global temperatures by spraying water droplets or something similar up into the atmosphere. That's maybe possible - and some scientists are actively discussing this possibility (it's generally known as "Plan B") - however, there are grave concerns that by tampering on such a large scale, we could inadvertently trigger some other major problem that we haven't yet thought of.

SteveBaker (talk) 04:59, 13 January 2010 (UTC)

Contrail#September 11, 2001 climate impact study -- Finlay McWalter • Talk 16:01, 13 January 2010 (UTC)

Fanuc Ac servomotor

How to calculate heat generation in fanuc AC servomotor? and what are the modes and parts of heat dissipitaion? Thanks - kushagra

Please see my response to your other FANUC question below. SteveBaker (talk) 00:03, 14 January 2010 (UTC)

time machine.

whats the latest development in research related to time machine? if a time machine is made will it be able to take us to the past??baba (talk) 10:43, 13 January 2010 (UTC)

See Time travel. Staecker (talk) 14:22, 13 January 2010 (UTC)

There are a few scientist who (mostly for the benefit of low-budget pop-sci programs on the Discovery channel) have toyed around with some fairly 'far out' concepts - typically involving wormholes (which really don't exist) and black holes (which do). These ideas are horribly speculative - and are in any case totally impractical. Aside from them, pretty much everyone agrees that time machines are impossible. Those few unlikely/impractical concepts that are out there almost all state that you'd never be able to go back in time to a point before the time machine was built...which means that nobody is travelling back to any point in our past. Broadly speaking, it's safe to say that time machines don't exist and we're pretty sure that they never will. That said - you could 'fast forward' time and effectively travel into the future merely by climbing into a spaceship and flying at somewhere close to the speed of light. Einstein's relativity theories will then allow you to (in effect) travel into the future...but with no possibility whatever of ever returning. SteveBaker (talk) 18:21, 13 January 2010 (UTC)

Long after I thought I had a grand idea of stating that since we don't have time machines that travel to the past now, we never will, I found that Stephen Hawking made the same statement in his Chronology protection conjecture. I'm writing up a paper on polynomial-time solutions to 3SAT now. So, I expect some famous guys published the same thing last month and everyone has already proven the whole P/NP thing. -- kainaw™ 00:53, 14 January 2010 (UTC)

This man says you can [1] and these [2] say you can't. Doesn't Occam's razor say you should discard the least likely theory first? Alansplodge (talk) 20:16, 14 January 2010 (UTC)

John D. Barrow (_not_ the most conservative of theoretical physicists) presents two arguments against backwards time-travel in one of his books; first, if it were possible, there would be enormous numbers of tourists from the future at important historical events (the Crucifixion, Kennedy's assassination, etc), and such tourists were not observed at the time. Secondly, an argument from economics; time-travellers would put a penny in a depost account in 1900 and collect the interest 2000 years later. This would cause a collapse of the world economy in the year 3900, so the banks would send back their 3900 AD managers to tell their 1900 AD colleagues to only lend money at simple interest rather than compound. But that didn't happen, either. Tevildo (talk) 21:03, 14 January 2010 (UTC)

Both of those problems disappear if you assume time machines can't take you back to before the time machine existed, and that is the case for most (all?) time machines described within the framework of general relativity. --Tango (talk) 22:20, 14 January 2010 (UTC)

Steve wormholes might exist, according to the currently known mathematics they are possible, just no one knows for sure, and about hthe tourists traveling to the past, how do we know that there aren't laws against it to protect the time line.

Fanuc material

If you could please help with the materials used in making the magnets, bearings, front flange, windings, stator, brushes, motor, couplings, swap drives, gaskets, insulation and rotor shell of a fanuc ac servo motor, even non-fanuc would do. Also how do they impact the performance of such motors? Thanks-kushagra —Preceding unsigned comment added by 220.225.125.246 (talk) 10:57, 13 January 2010 (UTC)

I very much doubt that anyone here is going to be able to answer such a detailed question - FANUC motors are made by the Fuji Automatic NUmerical Control company - I suggest you ask at the service department of their web site here: http://www.fanuc.co.jp - however, I very much doubt they'll be willing to tell you such detailed information because end users of these motors generally do not wish to know that - and at best, they'd be passing on knowledge to a potential competitor. This is quite simply an unanswerable question. Sorry. SteveBaker (talk) 00:01, 14 January 2010 (UTC)

Flying Flat Bug

I live in the northeast US and there is a flying flat bug in our office. I can't take a pic of it cuz it won't stand still (divas). But it looks like the shape of a giant tick but with long legs and it looks like a wasp when it flies around. What is it? --Reticuli88 (talk) 17:05, 13 January 2010 (UTC)

Sounds like something in the Hippoboscidae family. --Mr.98 (talk) 17:09, 13 January 2010 (UTC)

Ok, someone killed it and here is the smashed version --Reticuli88 (talk) 17:19, 13 January 2010 (UTC)

It's a true bug. --Dr Dima (talk) 17:45, 13 January 2010 (UTC)

Excellent work! What is it? Don't know! Let's kill it to find out! "What did you do today that makes you feel proud" Caesar's Daddy (talk) 08:23, 14 January 2010 (UTC)

What you just described was called biology until the last few decades. Googlemeister (talk) 14:19, 14 January 2010 (UTC)

Oh my God you've killed Kenny. Cuddlyable3 (talk) 23:33, 14 January 2010 (UTC)

I understand your thought process Caesar, but there are some people in our office who had incorrectly identified the bug as a wasp and were deathly allergic. So, for me, it was a toss between my co-worker's death or the true bug's. If I chose the latter (and it was in fact a stinging wasp), the US Courts will promptly send my butt to prison. --Reticuli88 (talk) 14:04, 14 January 2010 (UTC)

OK, I understand. _{Hmm, thinks why did he call himself 'someone' if he performed such a noble deed? Did he mean co-worker's death or co-workers' deaths? What 'crime' would be committed?} Caesar's Daddy (talk) 14:35, 14 January 2010 (UTC)

Not that it should matter, but I'm a she. And not known for my grammatical correctness. Can't please everyone all the time.--Reticuli88 (talk) 15:18, 14 January 2010 (UTC)

So you're satisfied that someone narrowed it down to any 1 of 80,000 species? You, at least, are easy to please! :) TresÁrboles (talk) 04:03, 15 January 2010 (UTC)

Well if she was worried about it being a wasp, since that was eliminated perhaps that's sufficient Nil Einne (talk) 14:57, 16 January 2010 (UTC)

Average adult vitamin D status of the Maasai people of Kenya?

I am looking for the following epidemiological information:

Average adult vitamin D status of the Maasai people of Kenya? The answer will probably be in units of nmol/l or ng/ml. —Preceding unsigned comment added by 65.112.42.83 (talk) 17:51, 13 January 2010 (UTC)

I've looked all over the web - and I can't find any numbers for this. The biggest study of nutrition amongst the Maasai was evidently conducted by Dr. George V. Mann. Searches of his writings turn up all manner of other statistics - but no hard numbers about Vitamin D. Given that the Maasai live mostly out in the open, on the equator, wear fairly skimpy clothing (your skin makes Vitamin D when it's exposed to sunlight) and exist on a diet consisting of pretty much 100% meat, blood and milk (all great sources of Vitamin D) - it's pretty safe to assume that their Vitamin D numbers will be off the chart. Certainly more than adequate. Their problems come when these people move away from the equator, live indoors, switch to western-style clothing and a more typical "northern" human diet. Their very dark skin pigmentation then limits Vitamin D production and with less sunlight at more extreme latitudes, much less exposure to the sun - and a less meat/dairy-rich diet, they may well need Vitamin D supplements. SteveBaker (talk) 23:49, 13 January 2010 (UTC)

The "cc" rating of a car battery charger

I'm occasionally called upon to recharge the car batteries of hapless elderly relatives' cars. My current, ancient, charger has died, so I need to replace it. Looking on the website of large UK automotive-supplies retailer Halfords (just for example) they have a number of chargers, some of which they describe as "1200cc", some as "1800cc". But they don't say what that cc refers to - I guess it's supposed to be the size of the engine of the car engine? But the chargers are all 4A 12V. Do these "cc" values mean anything at all? 87.113.46.161 (talk) 19:27, 13 January 2010 (UTC)

The size of the battery. Car batteries are wet cell batteries, actually a lead-acid storage battery. The cc probably stands for cubic centimeter, aka "milliliter" and is probably the size of the battery itself, i.e. a 1200cc battery will have 1.2 liters of liquid inside. Just a guess, but that's my best guess. --Jayron32 20:52, 13 January 2010 (UTC)

No Jayron. Halfords say[3] "We sell specific chargers for smaller engine batteries: Up to 1200cc (181701). Up to 1800cc (181735)" i.e that the "cc" values do refer to the engine size. I think that is a silly way to market battery chargers. The data that matter are the maximum current and how the output voltage (nominally "12V") is controlled as the battery reaches full charge. Cuddlyable3 (talk) 21:00, 13 January 2010 (UTC)

Nm. So much for guessing. --Jayron32 21:25, 13 January 2010 (UTC)

I guess they are just trying to be helpful - Joe Public knows how many cc's his engine is - so he buys a charger to match. But it's rather silly - the only possible variable is how long the battery takes to charge. You could use an 1800cc charger to charge the battery in a 1200cc car - or vice versa. The voltage is the same - all that would change is how long it takes to charge and what strategy the electronics use to get the battery charged rapidly. In truth, the fastest way to charge a car battery is using a car. I have a couple of car chargers of various vintages - but the thing I use most is one of those "booster packs" that has a small 12v battery and a VERY slow trickle charger - you leave it plugged in all year long - and when you need it, you hook it up to the car like a set of jumper cables (only without needing another car) and that's enough to get the car started...then you drive around the block for 10 minutes in a low gear and your battery is charged. If the weather is unusually bad - or if your battery or your alternator is a bit 'iffy' then you can unplug it from the wall and toss it into the back of the car and it has enough charge to get you out of trouble a couple of times before it needs recharging. It's small enough and light enough that I can plug it in next to my desk at work and recharge the thing ready for the trip home. They aren't really designed for routine use - they are a "get you out of trouble" thing - but if your battery needs recharging a lot - there is something wrong with either the battery or the charging circuit/alternator in the car. In that case - fix the car rather than spending money on a charger. SteveBaker (talk) 23:21, 13 January 2010 (UTC)

I agree 100% with Steve Baker that the booster packs, sometimes marketed as "Portable Power Stations" (or similar) are very effective for helping out "hapless elderly relatives" (and for starting my own vehicle when I foolishly left the interior light on). They are also useful in the event of a household power failure, and can run a TV or other low-power appliance for a while using a solid-state invertor to generate household voltage. They are, however, significantly more expensive than a basic trickle-charger which can take up to 24 hours to fully charge a flat battery. Dbfirs 23:40, 13 January 2010 (UTC)

Mechanics of cancer death?

Pardon what may seem to be a very obvious question, but...how does cancer kill? Obviously the malignant cells spread throughout the body, but I've never quite understood how the spread of such cells causes death, and cancer doesn't seem to address the subject. Do they overload the circulatory system somehow? Nyttend (talk) 20:22, 13 January 2010 (UTC)

This question has been asked a couple of times before, see

• Cancer (Nov 10, 2006).
• Final cause of death in cancer (Dec 8, 2007).
• How does cancer kill people? (March 11, 2009).

--NorwegianBlue ^talk 20:44, 13 January 2010 (UTC)

Thanks very much; I forgot to look in the archives. Nyttend (talk) 22:20, 13 January 2010 (UTC)

A big thanks to everyone who's ever answered (or asked) the one question I keep forgetting to ask! Vimescarrot (talk) 22:27, 14 January 2010 (UTC)