Science desk
< September 24	<< Aug \| September \| Oct >>	September 26 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 25

database software for idea storage

so lately I have been using GMail to store information that I would like to be searchable. For instance I want to store the name of walmarts Green technology activist so I email his name to myself with some keywords. This is obviously not ideal- is their a piece of software out there already that does something similar? I have a mac and considered creating a text document with names and keyword near each-other and using spotlight but that seems clunky, and possibly unworkable...

Other thoughts??

Ebenbayer 00:46, 25 September 2007 (UTC)[reply]

Hmm, yes there are a variety of programs out there that try to do things like this. Here, for example, is a review of various note taking applications, any of which can likely do something as simple as creating a searchable list of notes and information. --24.147.86.187 01:53, 25 September 2007 (UTC)[reply]

Housing economics

I tried reading Real estate economics and housing bubble but they didn't help much... Construction locally has caused a major surplus in houses, to the point that 90% of the houses in some neighborhoods remain unoccupied, even after a few years. I see it's not desirable to sell a house for less than the value of its land/labor/materials, but prices aren't dropping to an equilibrium as they should (?). What is keeping the houses' prices from dropping? Are the developers (or whoever controls the prices) just holding out until the remaining 90% of houses are eventually bought? Because right now, those houses are sitting debts. HYENASTE 01:30, 25 September 2007 (UTC)[reply]

Obviously the developers want to avoid selling at a loss. Thus they'll hold onto the properties while they consider it's of greater economic advantage to them not to sell, than to sell at a loss. There's some recognised economic principle (that I wish I could remember its name), possibly more based on stockmarkets (or sharemarkets depending where you are) that explains how investors are extremely reticient to 'lock in' a loss; they'll therefore sit on often high-risk loss-making stock for years rather than selling, in the hope that the stock will eventually at least regain the initial value that they paid for it. This is despite the fact that more often than not they'd be better to sell when the stock first starts crashing and invest in something else, even it means an initial loss. Anyway, the real estate you write about sounds something similar.

Also what we don't know is the nature of the investments. It's possible for example that what sounds like a housing glut has been encouraged - either overtly or surreptitiously - by the government from wherever you're from. What often happens is that the government will give some type of encouragement to investors to invest in some particular area of the economy, then back it by guaranteeing them that they won't make a loss. If they do make a loss then the government (read the tax-payers) make up for the shortfall, either through direct bailouts of the investors, or through tax breaks. Thus the investors are encouraged to invest by what is essentially a government backed guaranteed profit - the investors take all the profit, while the government, and therefore tax-payers and society, take all the risk. But we don't really know enough about your particular situation to say for sure what's happening. --jjron 09:30, 25 September 2007 (UTC)[reply]

Intron degradation

Hi

The classic statement that people tend to make is "in one review, someone wrongly said that introns were degraded quickly, and everyone picked up on this and quoted this review for ever". My question is: what was this review? Does anyone know when, where or by whom it was published?

Cheers, Aaadddaaammm 07:38, 25 September 2007 (UTC)[reply]

In lieu of actually answering the question, I'll at least provide some relevant information. This paper (which describes the process near the bottom) suggests the process was barely studied until recently, and that the half-lives of mammalian introns have been measured to lie between 6 and 29 minutes. Someguy1221 07:56, 25 September 2007 (UTC)[reply]

When you say degraded quickly are you referring to the splicing of RNA or their presence in the genome? David D. (Talk) 22:39, 26 September 2007 (UTC)[reply]

I'm talking about the intronic RNA after it's been spliced out of the pre-mRNA. Aaadddaaammm 23:09, 26 September 2007 (UTC)[reply]

I have never heard of the review but a quick search reveal a paper from 1992 (L Qian, M N Vu, M Carter, and M F Wilkinson (1992) A spliced intron accumulates as a lariat in the nucleus of T cells. Nucleic Acids Res. 1992 October 25; 20(20): 5345–5350. ) that states "RNA splicing is a process whereby exons are joined and intervening sequences (introns) are removed in the form of a lariat structure" and cites the following review. Sharp PA, Konarksa MM, Grabowski PJ, Lamond AI, Marciniak, R and Seiler, SR (1987) Cold Spring Harbor Symposia on Quanititative Biology. LII, 277-285. That review sounds like a good candidate.

The claimed first paper on this topic in eukaryotes is titled The stability and fate of a spliced intron from vertebrate cells, published in RNA in 1999. They cite half lives of less than 5 minutes for the intro they studied. David D. (Talk) 04:55, 28 September 2007 (UTC)[reply]

What's the problem with Boltzmann brains?

A couple of weeks ago, Newscientist magazine ran a doom and gloom article about Boltzmann brains.

As far as I can tell, the argument goes something like:

We are typical observers
If we're not typical, then the part of our universe we can see isn't typical
Some time in the future, infinite expansion of the universe will lead to an infinite number of Boltzmann brains popping out of vacuum.
The number of normal brains (like us) is going to tend towards "damn big" but not infinite.
"Infinity" outnumbers "damn big"
Over the course of the universe, they will outnumber us (on average)
Given that we're outnumbered, on average, we can't be typical, therefore all our science falls around our feet in a horrible mess of untypicality!
Therefore the world must end before we're outnumbered because obviously we're typical.

How does that matter to us? Why do we have to be typical for our observations to be useful? Is this something to do quantum wierdness? Human egocentricity?

Did I misunderstand the article?

Article is here, sorry, it's "premium" content.

--203.22.236.14 09:33, 25 September 2007 (UTC)[reply]

The point is that there's a "noise floor" for scientific explanations of phenomena. I like to talk about Han Wavel instead. If your evolutionary explanation of Han Wavel's hotels (a civilization evolved that was capable of providing lemon-soaked paper napkins) depends on events less probable than the random formation of the hotels, then you haven't explained anything. For the same reason, you can't just say "well, the observable universe has amazingly low entropy, but that was bound to happen somewhere." You can't just compound improbability upon improbability; you have to come up with something more plausible than dumb luck. -- BenRG 12:24, 25 September 2007 (UTC)[reply]

No! This kind of argument is complete crap. Let's take this carefully:

We are typical observers - we don't know that. But I'll let that slide.
If we're not typical, then the part of our universe we can see isn't typical - we do know that. Most of the universe appears to be vacuum - we are on a tiny blue-green planet. But, let's let this one slide too.
Some time in the future, infinite expansion of the universe will lead to an infinite number of Boltzmann brains popping out of vacuum. - It's not widely agreed that the universe will undergo infinite expansion...but OK, let's run with this assumption too. If the universe is infinite and if a Boltzman brain is physically possible then there are certainly an infinite number of them. There are also an infinite number of anything else that's physically possible too. Infinite numbers of black holes, infinite numbers of cute little white kittens, infinite numbers of everything.
The number of normal brains (like us) is going to tend towards "damn big" but not infinite. - No. If the universe is infinite then no matter how rare, there are still an infinite number of planets like ours inhabited with people like us. An infinite number of them have internets. An infinite number of those have Wikipedias with reference desks and an infinite number of those have questions identical to this one being asked right now. Infinity is infinite...once you have it, nothing within that infinity can be finite anymore - you either have zero of something or an infinite number of them. You can't cut corners.
"Infinity" outnumbers "damn big" - it does - but the previous premise was wrong - so this is irrelevent to the argument.
Over the course of the universe, they will outnumber us (on average) - Not possible, in an infinite universe there is an infinite number of everything that's physically possible. So averaged over the entire universe the ratio of us to them is infinity to infinity...which could be anything. Check out Hilbert's paradox of the Grand Hotel or Balls and vase problem to get some idea of why this assertion is nonsense.
Given that we're outnumbered, on average, we can't be typical, therefore all our science falls around our feet in a horrible mess of untypicality! - the concept of 'average' is difficult when infinities are involved...but it's irrelevent here because we can't take the fact that we might be outnumbered as a 'given'. There are infinite numbers of both things...you can deduce nothing from that. There are an infinite number of elephants and there are an infinite number of humans - but humans outnumber elephants in the local region of space that we care about. With ants, the opposite is the case. You can't tell anything about the relative proportions of things when there are infinite numbers of both spread out over infinite volume.
Therefore the world must end before we're outnumbered because obviously we're typical. - Nonsense.

These kinds of bogus arguments come about from a lack of understanding about what infinite really means. There can be an infinite number of X's (whatever X is) within an infinite universe. But the distance between one X and the next can also be infinite, or it can be very large - or very small - you don't know. The average number of X's per cubic meter is a completely undefined number - it's infinity divided by infinity - which can be any number you like except (perhaps) zero. So in an infinite universe, the number of Boltzmann brains can be infinite but they might be 1000 billion lightyears apart on the average - and the number of human-like species on earth-like planets can be infinite but they might be 500 billion lightyears apart on the average - so for every one Boltzman brain, there are 8 human planets. We win. But then the average distances could be the other way around - and we'd lose. As soon as you get an infinity somewhere, you have to shut off 'normal' mathematical and logical concepts because they simply don't work anymore. A correct version of your argument (without resorting to infinities) is this:

The universe might be infinite - we don't know.
We believe the universe to be fairly uniform - at least to the scale of galactic clusters.
Within any given volume of the universe, there is a probability P_b of a Boltzman brain spontaneously forming out of nothing. Mathematically, P_b is a spectacularly small number - and the probability of one forming anywhere within the observable universe is close to zero. The number of Boltzman brains that could ever possibly come in contact with humanity (N_b) is therefore overwhelmingly likely to be either one or (much more likely) zero.
Within any given volume of the universe, there is a probability P_h of human-like creatures evolving through normal stellar/planetary formation mechanisms. Using the Drake equation, with our best estimate for the various parameters, we believe that N_h (the number of such civilisations within the observable universe) to be vast. The best knowledge we have says that there is (on average) between 2 and 5,000 human-level intelligent species per galaxy - which makes N_h be a very large number indeed for the observable universe.
So, with the best knowledge we have, normal human-like intelligences VASTLY outnumber Boltzman brains within the observable universe. We can make a reasonable assumption that this is true in the remainder of the universe too...be it infinite or finite.
Ergo, we have nothing to worry about.

SteveBaker 13:56, 25 September 2007 (UTC)[reply]

Well summarized, Steve. Also, I take offense to the notion that a simpler form of self-aware organization could exist. Most of the humans I meet are barely self-aware. Humans are almost the simplest system that can possibly be self aware - whether you compare us to similar biological creatures like chimpanzees, squids, or microbes - or if you compare us to geological or astronomical formations like salt crystals or solar fusion convection cells... To postulate that a simpler system than our biological brain could exist is silly - we are entirely self-organizing, on time-scales of geologic and evolutionary systems. What could be more simple than a system which naturally unfurls itself according to basic physical law? It sounds like the Boltzmann brain is implicitly suggesting that some strange arrangement of hydrogen molecules in interstellar space will ever have the capacity to be "self-aware." In any case, we can barely define what it means to be sentient in the first place, so how can we start calculating statistical distribution of sentience? Nimur 14:37, 25 September 2007 (UTC)[reply]

Firstly I think chimps are probably self aware (minor point) and secondly point out that 'new scientist' typically publishes absolute rubbish - don't mistake it for a scientific journal that will make any sense.87.102.10.190 14:49, 25 September 2007 (UTC)[reply]

Of course - but chimps evolved similarly to us, so it's almost expected that they have a comparable level of intelligence (more or less). They didn't "pop out" due to statistical quantum fluctuation. Nimur 15:01, 25 September 2007 (UTC)[reply]

Firstly, there have been experiments that show that (at least) chimps and dolphins are aware of their own existance. Paint a red dot onto the forehead of a chimp while it's asleep - then wake it up and show it a mirror. It'll notice that the chimp in the mirror has a red dot on it's forehead and (realising that the image is 'self') will try to rub the mark off it's own forehead...self-awareness, I believe.

Secondly, we don't have a clue what it takes to make a system be 'self aware' - we don't even have a good definition of such a thing. We can pretty much assume that our computers are not yet self aware - but we know we could program one to tell us that it is - or to fake the results of an experiment to try to prove it. When the classic 'ELIZA' program was first shown to uninitiated people, they believed it was self-aware. The only reason I suspect that other humans are self-aware is because I make the rash presumption that since you guys seem to be a lot like me - you are probably as self-aware as I am - but in other regards, I have no more proof that you are self-aware than that my dogs are self-aware (I'm pretty sure they are). But I don't have any way to know that some other simpler system than a dog is not self-aware. In the end, I suspect that 'self-awareness' is merely an attribute of a sufficiently complex system.

Thirdly, in defense of the OP - in an INFINITE universe, very complex things can (indeed, must) just pop into existance. If it's physically possible for something to exist - it must do so - and in an infinite number of places and times. Such is the nature of infinity combined with quantum randomness. However, the probability of it happening is so astronomically small, we can say with some confidence that such a thing will (essentially) never happen in any part of the universe that we can observe. SteveBaker 16:59, 25 September 2007 (UTC)[reply]

It's the 'boltzmann brains popping out of the vacuum bit' that concerns me - arising from random fluctuation - without any supporting structure to maintain the 'brain' it will cease to exist as soon as it is made - it's like claiming 'clouds can think' - what?87.102.10.190 14:52, 25 September 2007 (UTC)[reply]

Sure - but in an infinite universe, it doesn't matter how improbable an event is, it WILL happen someplace. So a mechanical brain 1000 miles across...complete with supporting structure can (and indeed, will) pop into existance. Now, whether computation is even possible with tenuous gaseous objects - I doubt - but who says it has to be gaseous. In an infinite universe, an exact clone of you - in a pink space-suit with pale blue stripes - just popped into existance in an infinite number of places and thought "Funny? How did I get here?". Such is the nature of true infinity. SteveBaker 16:59, 25 September 2007 (UTC)[reply]

I disagree with SteveBaker's confidence that infinite sample sets defy the laws of causality and determinism. Nimur 23:08, 25 September 2007 (UTC)[reply]

I tend to slightly doubt that 'things can appear from nowhere' at any probability, (even though that seems to have happened to the universe) - that aside - this is the science desk "Science (from the Latin scientia, 'knowledge'), in the broadest sense, refers to any systematic knowledge or practice.."etc and not the philosophy desk.. Current questions suggest that a philosophy desk would get as much questions as a science desk - maybe we should have one..87.102.23.3 01:45, 26 September 2007 (UTC)[reply]

Precisely what do you mean by "with any probability"? What I mean is that in a truly infinite universe, any event with a probability greater than zero (even if the odds are a Googolplex^{googolplex^googolplex}:1 against) not only can happen - but will happen - and will happen an infinite number of times in an infinite universe. You can't deny that. If an infinite number of opportunities arise for a random event then if the odds of the event happening are greater than zero then the number of times the event will happen on the average is infinity multiplied by the probability of the event - and infinity times any number bigger than zero is still infinity. As for Nimur's scepticism: Determinism and causality are not violated - we merely have to invoke the Schrödinger equation. Since every particle in the universe has a very, very tiny (but definitely non-zero) probability amplitude of being at any point in space, the probability of all of the electrons, protons and neutrons required to make (say) a rather nice grand piano spontaneously appear out of nowhere is non-zero. If it's non-zero then this isn't just some hypothetical wild idea in my head: it is literally true that in the time it's taken me to write this reply, an infinite number of grand pianos have spontaneously appeared in the universe. That's not a joke - it's quite literally true. If we agree that the universe is infinite (which I personally doubt) then there is no way to deny that fact. If the universe is merely finite - then no, the probability of a grand piano spontaneously arising is far too small for it to ever happen. What keeps us sane is the fact that the observable universe (the part that could ever possibly affect us or be observed by us) is not infinite - so our little corner of an infinite universe has the same probability of crazy things happening as a finite universe and we don't have to worry too much about spontaneous piano formation. SteveBaker 13:09, 26 September 2007 (UTC)[reply]

If we've got probability density functions that are non zero throughout all space and an infinite universe then I have to agree with you..

However if I ask what's the probability of something appearing apparently at random and staying there for a meaningful length of time - ie being real then the situation changes - because if we take time to be infinitely divisible then the position of an object becomes fixed about a given point (with a wave equation representing how strongly it interacts with other objects)

Consider a fixed proton - according to a probability density interpretation there is a non-zero probability of it's being anywhere.

However if I measure it's position over time it becomes more and more clear that it has a central point about which it's density function drops off - over infinite time - it becomes more clear that the proton is point like and the 'probability density function' is really equivalent to a 'field strength' with which it interacts with other things.

I think you are just considering moments in time and not taking a 'over all time view'?87.102.32.155 13:56, 26 September 2007 (UTC)[reply]

NOTE if you take time to be infinitely divisible then you don't even need an infinte universe for these unlikely things to happen - as in the 1sec it takes me to press "X" there have been an infinite number of opportunities for odd things to happen - I'm suggesting that only the time averaged situation is meaningful..87.102.32.155 14:06, 26 September 2007 (UTC)[reply]

So, in some parallel universe there is a hydnjo that is one t_P younger than myself :-) and another that is that much older :-( (assuming that time frames are as arbitrary as anything else). And in each case we have a left-handed me, the usual right-handed me and an ambidextrous me. Now, for each of those universes there is a good me and an evil me, a tall me and a short me, a cool me and a dorky me, a smart me and a stupid me etc (I don't know what the dividing interval is for those attributes but it sure makes for a bunch of us). After delving into those myriad universes we can then explore what's going on around two t_Ps, Geesh! - hydnjo talk 23:35, 26 September 2007 (UTC)[reply]

The funniest thing with the Boltzmann Brains article in New Scientist has been the huge number of letters they received saying basically "this is humanocentric rubbish". For weeks they've been printing them, along with comments form the editor trying to defend the article. Almost every letter seems to say "Why assume we're typical? You can't base a theory on that.", and still they come... Skittle 15:33, 29 September 2007 (UTC)[reply]

Pull-top cans

I've noticed a problem with all pull-tops, which is worse on full pull-top cans than on pull-tabs (such as on beer cans). The curved piece of metal acts as a spring, such that, when the last piece breaks off, it launches any food or beverage bits on the tab onto you or the wall or whatever else is inconvenient. How could this problem be cured ? (The workaround is to never completely open it, but that makes it more difficult to access the contents.) Perhaps a different material would be less "springy" or perhaps the seal needs to be weaker near the end ? StuRat 14:36, 25 September 2007 (UTC)[reply]

The difficulty is making it sturdy while closed, and easily-separable when opening it. I would guess that the manufacturers have decided to err on the side of "tightly sealed" rather than "deeply perforated" seals, despite the extra difficulty involved with opening the can. Of course, there's statistical variation in any manufacturing process, so if the seal is overly-perforated for ease of use, there will be many more cans with broken seals. Nimur 14:56, 25 September 2007 (UTC)[reply]

This was described on some Discovery channel program or other about a year ago. It is indeed a tricky problem to manufacture something that's solid enough to keep the food fresh 100% of the time (even one can of rotted tuna could put them out of business). So they have to err on the 'perhaps accidentally harder to open 1% of the time' side. This is greatly complicated by the requirement for the cans to be dirt cheap - and because the machine tools that stamp the groove into the metal lid tend to wear out over time making the precise depth and width of the stamping change gradually over time. SteveBaker 17:04, 25 September 2007 (UTC)[reply]

Pull it most of the way in the usual fashion, and then at the end, pull it sideways so that you're only applying a much-smaller peeling force to the edge of the top. The last bit will detach with a whimper rather than a "dang!". --Sean 15:43, 25 September 2007 (UTC)[reply]

A way I found that works is to bend the lid back and forth at the end, so it breaks due to metal fatigue. You hardly get any spring effect when it breaks, that way. BlindMoglin 19:57, 25 September 2007 (UTC)[reply]

I understand you're not talking about the cans as depicted in beverage can, which is called a 'stay tab'. Are pull tabs still used for beverages in the US? (They aren't in the Netherlands, nor in the rest of Europe afaik.) I used to use Sean's solution. Btw, stay tabs have another disadvantage, namely that an external part is pushed into the beverage, which can be unhygienic, depending on 'where the can has been'. DirkvdM 08:48, 27 September 2007 (UTC)[reply]

Yes, those pull-tabs are still used here in the US, but I don't buy cans with those, because of their unhygienic nature. The cans I'm talking about are used for foods, like canned soup, and the full lid peels back, not into the food. I do use those, but don't like being splattered by the food when the lid breaks off. StuRat 12:54, 27 September 2007 (UTC)[reply]

I don't think we're using the terminology the same way. I took the words from the beverage can article, where the 'stay tab' is the unhygienic one. Or do you mean to say 'pull tabs' are unhygienic as well? DirkvdM 18:55, 27 September 2007 (UTC)[reply]

I've never heard anything called a "stay-tab", that must be British English. I call the unhygienic ones pull-tabs and the OK ones pull-tops. StuRat 00:32, 29 September 2007 (UTC)[reply]

Ah, ok. Like I said, I got the terminology from the article, which I looked up to find out what you meant with by 'pull-top' in your original question. But now I'm confused again. In your previous post you said you still use the pull-tabs (stay tabs) in the US. But surely, they came later - the pull-tops (as you call them) were the originals, right? DirkvdM 10:03, 29 September 2007 (UTC)[reply]

Not from my experience. The unhygienic pull-tabs have been on all canned soda-pop and beer as long as I can recall, while cans of food were mostly opened with can openers until recently. They are now changing many of the cans to have pull-tops. One exception I recall is Pringles canned potato chips (crisps), which came with a pull-top as far back as I can remember. The "splash" problem didn't occur there because the contents were solid. StuRat 16:25, 29 September 2007 (UTC)[reply]

Funny, my experience is just the opposite. I've seen pull-tops for food such as fish (and Planter's peanuts, I believe) all my life, but stay-tabs for beverages only since the early eighties or thereabouts. But an age difference between us might also explain this (am I finally going to find out your age? :) ).

HOLD ON, there are three things we're talking about. The pull-tops, where the entire lid comes off, the pull-tabs, where only a section comes off, and (in the terminology of the article) the stay-tabs, which (as the name indicates) stay attached to the can. Nothing comes off at all, and the reason for their invention was to reduce littering. For example the beverage can article only shows stay-tabs. What would you call those three and which are and were in use in the US?

And again, looking at your original question, I'm confused. Pull-tops for beverages? That sounds like a horribly bad idea. At first I thought you were exaggerating, but if I understand you correctly now, you've got all the reason in the world to complain. To get this straight, you're talking about beverage cans where the entire top comes off? DirkvdM 18:03, 30 September 2007 (UTC)[reply]

If you look at the caption in the picture at the top of that article, it is labeled as a pull-tab, not a stay-tab. That caption must have been added by an American, because we don't distinguish between the two cases, calling them both pull-tabs (I suspect that industry insiders distinguish between them, but the public does not). Note that I consider both to be unhygienic because you are expected to put your lips on the top and side of the can.

And no, I don't know of any beverage where the entire top comes off as a pull-top, only foods. However, many such foods contain liquids, like canned pasta, for example (yes, I know any European will wretch in disgust at the thought of this). The fish containers, like sardines, have another mechanism where you have a metal opener around which you twist and wrap the metal top. I don't believe these typically come entirely off, but stay attached at the end. The containers are elongated so that this doesn't block access to the food. StuRat 15:26, 1 October 2007 (UTC)[reply]

Plastic pull-tops, like on an oatmeal container, don't seem to suffer from this problem. Could such plastic pull-tops be put on aluminum cans economically ? StuRat 13:02, 27 September 2007 (UTC)[reply]

doctor's question

Ordehimaria 16:18, 25 September 2007 (UTC)a doctor's usually contains all of the following items except ultrasonic scaler, high speed handpiece, air-water syringe, alginator[reply]

does it really? —Preceding unsigned comment added by 88.110.206.28 (talk) 00:40, 26 September 2007 (UTC)[reply]

I would go with the ultrasonic scaler. Sounds like dentist stuff to me. --Click me! write to me 07:59, 27 September 2007 (UTC)[reply]

All of those are dental tools: Ultrasonic Scaling (removal of calculus), high speed handpiece: cavity preparation, air-water syringe: AKA tripple syring/triplex (the little water gun/air gun), alginator: A very expensive mixing bowl for mixing alginate (the material used to take dental impressions). —Preceding unsigned comment added by 60.242.173.55 (talk) 08:08, 27 September 2007 (UTC)[reply]

Atomic theory

What is an abundant isotope
A sample of Argon exists as a mixture of three isotopes

mass number 36, relative abundance 0.337%

mass number 38, relative abundance 0.0630%

mass number 40, relative abundance, 99.6%

How do I calculate the relative atomic mass of argon, please?

Lastly how do i states the number of electrons, protons and neutrons in the ion ⁵⁶³⁺

Sorry to bombard you with these questions but they haven't been adequately explained by our chemistry teacher, sorry. --Hadseys 17:18, 25 September 2007 (UTC)[reply]

1. In your q.2 the abundant isotope is Ar40 - it means an isotope that occurs in significant amounts

2. The relative atomic mass is the average atomic mass - now the answer should be clearer.87.102.10.190 17:31, 25 September 2007 (UTC)[reply]

1) An abundant isotope is one that exists in large quantities on Earth. That means it can't be radioactive with a short half-life, because those don't last long. It must either be stable or radioactive with a very long half-life.

2) Do the math: 36×0.337/100 + 38×0.0630/100 + 40×99.6/100.

3) The atomic number is the number of protons and electrons in a neutral atom. If you have an ion, since electrons each have a charge of -1, add or subtract the opposite of that number to get the number of electrons (so, a +3 ion, has 3 fewer electrons, while a -3 ion has 3 more electrons). The atomic weight of an atom minus it's atomic number is the number of neutrons. Your question is messed up, do you mean it has an atomic number of 56 (barium) and a charge of +3 ? If so, we would still need to know the isotope or atomic weight to get the number of neutrons. BlindMoglin 17:33, 25 September 2007 (UTC)[reply]

To amplify point (3) - the atomic number is the number of protons in the nucleus, it's the same for all atoms of that element. The atomic mass is the number of protons PLUS the number of neutrons - for most elements, there is one combination of protons+neutrons that is stable, or at least only mildly radioactive, the others are unstable and either shed protons or neutrons until they become stable - hence (mostly) there is one form of the atom that's stable and abundant and other forms that are unstable and rare - but that's not a hard-and-fast rule. The number of electrons (in a lone, uncharged atom) is the same as the number of protons - but when the atom is electrically charged or in a chemical compound, the number will be different.SteveBaker 17:42, 25 September 2007 (UTC)[reply]

Medical and Scientific effects of high voltage low amperage high frequency electric current on the skin

Please explain in simple terms the way electric current works specifically voltage versus amperage as pertains to devices sold as skin tightening devices. Ellisar —Preceding unsigned comment added by Ellisar (talk • contribs) 18:51, 25 September 2007 (UTC)[reply]

[1] Someguy1221 19:16, 25 September 2007 (UTC)[reply]

It's an interesting analysis they got there…current will go through a high-resistance region instead of around it but "everyone knows" that electricty takes the path of least resistance. And higher resistance for a given voltage and current creates higher temperature but power=I²R and V=IR so power is proportional to inverse resistance? DMacks 19:39, 25 September 2007 (UTC)[reply]

I believe they point they were getting at was that, in whatever circuit the current ends up taking, the most heat is generated in the region of highest resistance within that circuit. Someguy1221 19:44, 25 September 2007 (UTC)[reply]

That takes math: I=E/R. Ohm's law. That's for DC, but the principle is the same. Raise the volts (E), you get more amps (I). Raise the resistance (R), you get less amps. This law is just basic physics, though. The device these doctors use undoubtedly supplies a predictable current, so the law doesn't apply at the tip of their probe. I read the website Someguy linked to, and the electronics part was sound. Everything the current passes through will heat up, but they cool the surface of the skin enough to keep it from burning much. The heating comes from power (P): P=EI. The resistance of the skin is constant for our purposes, and the current therefore depends solely on the applied voltage, so raising the voltage will increase both the current and power linearly. Hope this helps. P.S. My electronics teacher would slap me for using the word "voltage". --Milkbreath 20:48, 25 September 2007 (UTC)[reply]

It's not going to be that simple though - as a part of you gets hotter, your blood supply adjusts to keep the temperature constant - and you start sweating. Since both sweat and blood are excellent conductors of electricity - I doubt you could get enough of a differential heating effect to make a difference. I'm betting this is junk science. I'd be very surprised if it really worked as advertised. SteveBaker 14:59, 26 September 2007 (UTC)[reply]

Pictures of brains by Wernicke and Broca

I have been unable to find drawings or photos of the brains upon which Broca and Wernicke based their descriptions of motor and sensory aphasias.72.75.96.28 21:18, 25 September 2007 (UTC)superiorolive[reply]

electronics project

hi, friends i am in the final year of engineering form electronics and communication field, i will be very thankful to you .if u can help me out in prep the project.. from my side i want to make some project that can highlight my intrest in: 1.communication field 2.electronics fdield 3.robotronics

hope to recive the answer soon and thanks in advance kamran ali —Preceding unsigned comment added by 59.178.114.98 (talk) 21:25, 25 September 2007 (UTC)[reply]

How about a remote controlled robot ? That alone probably wouldn't be very impressive, therefore why not add some intelligence to the robot, so you can tell it where to go (say, the kitchen), but not the path, and it can figure out the path ? StuRat 00:32, 26 September 2007 (UTC)[reply]

How about a bot to filter out all StuRats comments? —Preceding unsigned comment added by 88.110.206.28 (talk) 00:39, 26 September 2007 (UTC)[reply]

Or perhaps a reverse filter for Google, which can only return the sexually explicit web sites which match a given search term. (I get sick of getting all those silly sites listed with cats on them.) :-) StuRat 00:55, 26 September 2007 (UTC)[reply]

How about a remote control moving hand controlled by a glove with tactile feedback? Graeme Bartlett 15:05, 26 September 2007 (UTC)[reply]

How about a non remote controlled robot running wild on its own until its batteries run out. Do you think you can build something that can sense walls and stuff, not crash into windows or any glass, and not fall off the stairs? Does not have to do any work ... if it does move around on its own, you are ahead of Honda. --Click me! write to me 07:56, 27 September 2007 (UTC)[reply]

Prion transmission in food products made from animal tissues: the safety of gelatine and related products

Prions are thought to be responsible for Creutzfeldt-Jakob disease in humans, a fatal and degenerative form of transmissible spongiform encephalopathy. The CJD article says normal medical sterilization techniques do not deactivate the prions, and transmission from contaminated instruments is possible (if not proven). The Prion article says "Prions can be denatured by subjecting them to a temperatures of 134 degrees Celsius for 18 minutes in a pressurised steam autoclave." The similar prion-mediated Bovine spongiform encephalopathy is thought to have been transmitted from processed animal tissues (http://www.defra.gov.uk/animalh/bse/controls-eradication/causes.html) such as meat and bone meal used as a protein supplement in cattle feed, even theough the tissues were steam heated and theoretically rendered sterile in rendering plants.

Web sources of uncertain reliability [2] imply that gelatine production techniques could pass prions right through intact to the consumer, and that only animals known to be healthy should be used for gelatine production (a hard thing to verify). That same websource cites a study saying thatinfected brain tissue was "autoclaved during 1 hour at 134°C or for at least 18 minutes at temperatures of 135oC or 134-138oC. This was not sufficient either to inactivate scrapie- and BSE agents" which were shown to still be infectious inanimal studies.The Gelatine article references a study behind a paywall as to the safety of gelatine. The chondroitin article says "Most chondroitin appears to be made from extracts of cartilaginous cow and pig tissues (cow trachea and pig ear and nose)but other sources such as shark, fish and bird cartilage are also used." Thus one could theoretically seek chondroitin not derived from cattle. My question is: if animal tissues are used in products such as animal tissue derived Gelatine, in collagen casings (related to gelatine)for sausages, or in Chondroitin sulfate which many people as a dietary supplement to treat osteoarthritis, is the processing done at a temperature which would deactivate any prions which might be in the cattle tissue? Edison 22:04, 25 September 2007 (UTC)[reply]

I'm shocked to see such a low temperature for denaturing prions. Richard Rhodes' book on the subject says you basically have to reduce tissue to ash to get rid of them. --Sean 23:45, 25 September 2007 (UTC)[reply]

After the Mad Cow Disease outbreak in the UK I have been avoiding anything which may come from beef including gelatin and soap containing sodium tallowate. For years I avoided milk and milk products also. I'd be interested to know just how much mad cow disease is present in the british herd and elsewhere. 80.2.206.123 23:54, 26 September 2007 (UTC)[reply]

cigarette butts

What are cigarette butts made of. —Preceding unsigned comment added by 124.186.47.5 (talk) 22:12, 25 September 2007 (UTC)[reply]

Cellulose. Have a read of Cigarette_filter#Manufacture. --Kurt Shaped Box 22:41, 25 September 2007 (UTC)[reply]

Tobacco, in my case. Plus hemp paper. And a bit of glue. And some saliva, I suppose. But you probably mean filters. Filthy habit, filter-smoking. DirkvdM 08:51, 27 September 2007 (UTC)[reply]

What exactly is the relationship between muscle contractions (excercise & metabolism), and dilation/constriction of blood vessels (vasoconstriction & thermoregulation) ?

I'm kind-of confused about how vasoconstriction and muscle movements relate to each other, and just how big a role superficial veins have in thermoregulation (as opposed to deep veins or arteries).

It is fairly obvious that muscular activity results --or is accompanied by-- inceased arterial blood flow. Does exercise of skeletal muscles also cause superficial veins to engorge, and if so, is this due to thermoregulation?

Also, how does vasoconstriction cool internal organs, if (supposedly) it is due largely to superficial vein activity?

Thank you for reading this. Pine 23:14, 25 September 2007 (UTC)[reply]

Exercise will cause veins to engorge, largely due the fact that they need to return the blood that has been pumped to the muscles in the arteries. The familar 'pump' that you get from weight training and other high load activities is essentially a result of the extra blood in the muscles. In general any vein transporting blood back from an exercised muscle will engorge, those at the surface may help to transfer excess heat from the body; I don't actually know if there's any variation in the degree of engorgement of the different veins depending on whether or not you need to loose heat though.

I'm not sure what you mean by your last question. My presumption would be that if an internal organ needed to be cooled then you should get vasodilation in order to get more blood passing through the organ so that more heat could be transferred out of the organ. That blood could then pass near the skin surface in order to allow heat to escape. The only possible benefit I could see of vasoconstriction in this case would be to limit the blood flow, and therefore limit oxygen and to a lesser degree nutrient supply to the organ, which may then potentially lead to a drop in metabolic activity, and thus a drop in heat production. But that's a bit hypothetical. --jjron 09:21, 26 September 2007 (UTC)[reply]