Wikipedia:Reference desk/Archives/Science/2007 September 22

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September 22[edit]

Are there chemicals that will permanently depigment human hair?[edit]

Are there chemicals that will permanently depigment human hair? —Preceding unsigned comment added by 81.99.218.58 (talk) 00:06, 22 September 2007 (UTC)

Yes, but such a chemical would have to be cytotoxic, as to do so one needs to destroy the stem cell niche of the hair follicle. There is not a known chemical that can do that specifically without harming other cells. Similarly exposing your head to high doses of ionizing radiation would permanently depigment your hair. It would probably also give you cancer though. The alternative would be to permanently inhibit the melanogenic enzymes, such as tyrosinase. There are chemicals that can do that in a temporary manner, but doing so permanently, and without serious adverse effects, is not currently possible. So if what you really wish to know is if there is a chemical that can safely and permanently depigment human hair, the answer is no. Rockpocket 01:32, 22 September 2007 (UTC)
You dont need chemicals: you just wait till you are old. It happens naturally! —Preceding unsigned comment added by 212.139.98.210 (talk) 20:21, 22 September 2007 (UTC)
This is being obtuse, but technically, bleaching the hair (normally done with hydrogen peroxide) permanently depigments hair. The hair treated with it will never get pigments back. That is, if you chop off your hair and bleach it, it is going to stay bleached! :) --Mdwyer 05:39, 23 September 2007 (UTC)

Colors[edit]

So, I was reading the question above on colorblindness, and I had a startling thought. You said we don't perceive real yellow, just red + green, right? So if we were to meet an alien with yellow receptors, they could see REAL yellow, and what we call yellow they'd call redgreen (or whatever)? so we never really see Yellow at all (or any color other than red, green, and blue) in the pure forms? After all, people with no green receptors see red+blue for green, right, which looks TOTALLY different... am I on to something here? Kuronue | Talk 00:47, 22 September 2007 (UTC)

In terms of colour perception, it doesn't really matter whether we see "real" yellow when we can perceive it so well using our three types of cones. A yellow cone could certainly provide an alien with a richer yellow hue perception, but they would all still be variations of the same "yellow" that we see (assuming, of course, the same processing system of perception is in place). The reason we don't need a yellow cone is because its redundant to the three that we have. Rockpocket 02:06, 22 September 2007 (UTC)
Yes, but like, someone who is partially colorblind can distinguish between colors, but they look totally different to them. Just because we can distinguish yellow from blue doesn't mean what we're seeing is anything like actual yellow, right? I mean, green looks like brown to people with a defective cone, so maybe some brownish colors to us are actually shades we can't see properly, things like that... Kuronue | Talk 03:01, 22 September 2007 (UTC)
Well, what is "actual yellow"? Its a wavelength of light. Notwithstanding the the "red" receptor actually has its peak sensitivity in the yellow part of the spectrum anyway, the actual detection mechanism is simply a action potential along an axon in response to the detection of a certain wavelength. The information is processed in the parvocellular layer where certain neurons process red-green differences, and others process blue-yellow differences. Its here that we "see" yellow. If an alien had a different cone, then it would fire in response to the appropriate wavelength, but still need to be processed in some manner. Depending on how these inputs are wired, the alien brain could "see" exactly same yellow as we do or it could interpret the wavelength as any pseudo-colour its brain evolved to conjour up. What is likely is that it could use such a receptor to distinguish multiple shades around that wavelength that would be beyond what we can distinguish. I guess what I'm trying to explain is that a fourth receptor type in the visible spectrum doesn't really offer "new" colours - our system evolved to have that well covered - it simply expands the subtles hues within those we already see. Rockpocket 04:27, 22 September 2007 (UTC)

You could try getting your hands on a yellow light - or a white light with a pure yellow filter, as well as two lights with red and green filters - then try illuminating things - you should be able to tell the difference between the things that are yellow for different reasons.. As an aside I remember that some insects can see ultraviolet light - this lets them see patterns on plants that we humans can't see - for instance flower petals look striped to insects87.102.89.127 12:37, 22 September 2007 (UTC)

Right - there are (at least) two "yellow" colours - one is a mixture of red+green and the other is 'true' yellow - light which has a frequency halfway between red and green. Our eyes can't tell the difference - but you can do experiments to see the difference. Put the 'yellow' light through a prism to spread out it's spectrum. Yellow light from your TV or computer monitor will split into two lines (red and green) but true yellow (from a sodium lamp for example) would form a single line (well, more or less). So these two colours look identical to us - but they are NOT the same colour. In order to get an idea how an alien (or your goldfish) would see these colours, we can try some analogies:
  • The analogy of sound: On a piano, you can play two notes 'C' and 'E' together - or you can pick a note midway between C and E ('D'). Does C+E sound the same as D? Nope - not by a mile! But that's the exact same thing as the difference between the two yellows.
  • We see three colours - red, green and blue. Green is a frequency between red and blue. So we can ask: How different is red+blue from a frequency halfway between red and blue? Well, halfway between red and blue we have green. What does red+blue look like? Magenta! So for our alien/goldfish, the difference between those two versions of "yellow" might look as different as magenta and green!!! That's a very powerful indication about how poorly we percieve colour. What I find most mind blowing is the little old lady in England who is a tetrachromat - she sees colours that almost nobody else in the world can see. She works in a store selling knitting yarns and she remarked to researchers how she was much better at matching colours than other people...no surprise if others were 'matching' magenta and green and calling them "the same exact colour". WOW!
I talk about the problems with "yellow" - but the same problems are there with "cyan" (midway between blue and green or a mixture of blue and green?). The third colour pair that might be problematic would be "magenta" - but we have a green sensor so we can tell the difference between red+blue and green. But in general, for colours that are more complex mixtures of frequencies - there are colours like a mixture of red, green and true-yellow that are yet different from the other two versions. Even our goldfish friend can't get the full subtlety - for that you'd need a spectrum analyser.
SteveBaker 15:22, 22 September 2007 (UTC)
Finally, one should mention that there might be people who can distinguish the two yellows by means of having two different kinds of cones for the red colour, one shifted towards yellow or orange. More at tetrachromacy. Simon A. 16:00, 22 September 2007 (UTC)

Special Relativity and Mass Defect[edit]

This was a question that came to me during a physics class. Einstein's special theory of relativity states that as an objects velocity approaches the speed of light its mass approaches infinity, and that increasing amounts of the input energy used to accelerate (eg from combustion of liquid fuel) is converted into matter. The processes of nuclear fusion and nuclear fission produce energy due to the mass defect where the products have less mass than the reactants. However, as the total mass of the system approaches infinity it follows that the mass defect will also approach infinity, which could possibly overcome one of the problems with fast travel and allow us to come closer to the speed of light than if we used conventional fuels. However, wouldn't this also violate the law of conservation of energy (the total energy of the system must remain constant, with mass being recognised as energy according to E = mc2) as both the mass and thrust of the system would increase without any additional input energy?

I only study basic physics, but it would be great if someone could cast some light on whether or not this would be possible 124.183.147.134 01:19, 22 September 2007 (UTC)

  • Short answer: no. There are no such defects in special relativity theory, which has been experimentally confirmed many times. --Sean 02:07, 22 September 2007 (UTC)
Um, I think you might be misinterpreting the word "defect" here. "Mass defect" is not a defect in the theory. --Trovatore 02:19, 22 September 2007 (UTC)
Perhaps I should clarify. The theory of special relativity states that as velocity approaches the speed of light mass will approach infinity (although I'm not sure if this has been proved experimentally). The mass defect is not related to the theory of special relativity, but is observed in nuclear reactions (eg in nuclear fusion two hydrogrens fuse to form a helium, the mass of the helium is less than the combined mass of the hydrogen, and this mass defect explains the energy released). I was wondering what would happen if the two separate situations were combined, as the velocity approaches the speed of light the mass of the system should approach infinity, but if a nuclear reaction is occurring then the mass of the hydrogen and helium will approach infinity, meaning the mass defect of the reaction will approach infinity resulting in the energy produced approaching infinity. If this nuclear reaction was used to accelerate the vessel then it would overcome some of the problems with high speed travel (increasing amounts of energy released from conventional fuels would be converted into mass reducing the effective acceleration and restricting the practical obtainable speeds below that of the speed of light, however if the nuclear reaction produced increasing amounts of energy this would allow the system to continue accelerating at a higher rate) however intuitively it seems to violate the law of conservation of mass-energy... 124.183.147.134 02:47, 22 September 2007 (UTC)
Well, think of it this way. Your spacecraft takes off. Its own mass is an upper limit on how much energy it could possibly generate, ever. That is a very finite value. Therefore, it can never supply an infinite amount of energy. The energy lost in accelerating two hydrogen molecules before fusing them will nullify any increase in energy they will produce thanks to being in a very fast reference frame, relative to whoever is measuring it. Someguy1221 04:56, 22 September 2007 (UTC)
From the point of view of people on the space craft (e.g. in their inertial frame), the fuel isn't moving and hence the mass defect remains constant. Thus from their point of view, the energy they have available to generate thrust doesn't change. However, from an external point of view, it is actually more complicated. Because of time dilation, the apparent rate of the reaction (as measured by an outside observer) would slow down. Hence they would actually be generating less thrust per unit external time as their speed increased. 136.152.153.120 03:42, 22 September 2007 (UTC)
Dear physics student, you may have learned that the mass increases as an object accelerates towards the speed of light. This is true if you're talking about a definition of mass called relativistic mass, which is often discussed in popular works on relativity and sometimes in physics textbooks. Early in the history of relativity, that's what was usually meant by "mass." But it's quite misleading if you start to think about things like nuclear reactions in those terms. Instead, you can use invariant mass, which is more useful for a lot of purposes (it's exactly what you want for thinking about a nuclear reactor on a relativistic spaceship!). Since the 1950's or so, physicists have come to use this definition of mass instead. As you accelerate your nuclear fuel, its invariant mass doesn't increase, and that's what you need to convert to energy. --Reuben 04:03, 22 September 2007 (UTC)
  • Saying that nuclear fusion and fission "produce energy due to the mass defect" is putting the cart before the horse; it reminds me of Feynman's complaint about wakalixes. There is necessarily a mass decrease of E/c2 in any system that releases energy E in some reaction, but that's not why it releases the energy. Chemical power sources work by forming and breaking chemical bonds, and nuclear power sources work by breaking (fission) and forming (fusion) nuclear bonds. There's no difference between them as far as E=mc2 is concerned. —Preceding unsigned comment added by BenRG (talkcontribs) 12:26, 22 September 2007 (UTC)
Right. The mass defect bit of fission, for example, is often used just to calculate the energy released, but it is not a good way of explaining the energy released. And the "energy" released isn't some sort of magical burst of lightning as it is usually shown in little diagrams—it relates to the velocities of the various components expelled from the fission reactions themselves (the fission products and the neutrons). I find a better way of explaining the fission reaction (and calculating much of it) to be in the form of thinking of the two split nuclei as being two extremely positively-charged objects placed right next to each other (just out of range of the nuclear force), and then calculating what the electrostatic repulsion is going to be from each of them. --24.147.86.187 14:16, 22 September 2007 (UTC)

I'm drunk - how to sober up quick[edit]

it's nearly 4am in the UK now and I'm drunk after a night out. I'm meant to be in work at 8am. Is there any way of sobering myself up quickly? —Preceding unsigned comment added by 81.79.171.12 (talk) 02:50, 22 September 2007 (UTC)

Not really, there isn't a whole lot you can do as "there are currently no known drugs or other ingestible agents which will accelerate alcohol metabolism" See Blood_alcohol#Metabolism and excretion. The best you can do is try to limit the damage, see Hangover#Possible remedies. Rockpocket 03:21, 22 September 2007 (UTC)
I suggest drinking lots of water or rehyrating sprorts beverage about once every two hours, which will minimize the hangover's effects. 128.196.149.25 03:25, 22 September 2007 (UTC)
Exercise helped me when I was in the Marines. After drinking all weekend, I'd show up on Monday morning drunk, but be nice and sober after a 6-mile run. I attributed it to sweating out alcohol while pumping more blood through the liver and kidneys where it gets cleaned. Then, it could just be that the time it took to run was enough for me to sober up. -- kainaw 04:54, 22 September 2007 (UTC)
Was the 6-mile run by any chance your punishment for showing up drunk ? StuRat 15:05, 22 September 2007 (UTC)
I also used to run even after wet nights but I was warned that exercising with alcohol in your blood means a serious health risk. I can't remember the details though. Lova Falk 15:44, 22 September 2007 (UTC)
Alcohol induced memory loss ? :-) StuRat 20:17, 22 September 2007 (UTC)
I never had a hangover, because drinking heavily just made me vomit (my body's defense mechanism in action, I suppose). I do NOT suggest that you induce vomiting, however, since that can damage the esophagus and teeth. In severe cases of alcohol poisoning, hospital stomach pumping can help, if they catch it early enough. You might want to call in sick to work, as that likely won't get you fired, but showing up drunk might. You also need to learn not to drink so heavily that you can't function normally (like going to work). Your pores will likely give off alcohol for several hours yet, so even if you clean up you won't fool anyone with a working nose (that's just about all nonsmokers). StuRat 15:05, 22 September 2007 (UTC)
Are you East Asian? Nil Einne 18:24, 22 September 2007 (UTC)
Only in that if you go to Asia and head East you will hit my house in about 12,000 miles. :-) StuRat 20:13, 22 September 2007 (UTC)

When I have a hangover, I usually take a headache pill, drink a cup of hot black coffee, and go out into the fresh air as soon as possible. Staying indoors will make the hangover remain. It is most important to go out into the fresh air and stay there for many hours. JIP | Talk 16:13, 22 September 2007 (UTC)

Bear in mind according to the above link paractemol is suspected of reducing the activity of alcohol dehydrogenase thereby effectively reducing the clearance rate of alcohol from the blood stream. This may mean that you will not suffer such a severe hangover but the alcohol will remain in your bloodstream for longer and so you will remain drunk for longer. Not a good idea if you have to work IMHO. In any case I would strongly recommend the OP do not go to work if they have to drive, operate heavy machinery or carry out any sort of mission or life critical work (e.g. a doctor, police officer) Nil Einne 18:24, 22 September 2007 (UTC)
Good advice. I have never noticed that because none of my (computer programmer), my sister's (teacher), my father's (architect, CEO), or my mother's (architect, city official) jobs fall under the requirements you mention. JIP | Talk 19:26, 22 September 2007 (UTC)
I find that rubbing tiger balm (or other liniment) into my temples/forehead helps with the headache part of the hangover. A friend of mine swears by taking an early morning sauna at the gym or going for a run with his midriff and thighs wrapped in clingfilm to sweat the booze out - though I think someone mentioned on here a while back that this sort of thing doesn't *really* do anything useful in terms of removing alcohol from the blood... --Kurt Shaped Box 19:46, 22 September 2007 (UTC)
You might metabolize about 4 ounces of alcohol in the remaining 4 hours. Sleep, hydration, coffee. You could consider calling in sick (with the "bottle flu" but don't tell the boss that). Edison 03:19, 23 September 2007 (UTC)


If I'm right it's presently 9 AM in the UK now and yesterday's working day is over. Would be nice to hear what happened. Lova Falk 08:04, 23 September 2007 (UTC)

The easiest way to sober up in such a situation is to call in sick the next morning. It's partially true. Don't make a habit out of it, though. --24.147.86.187 15:21, 23 September 2007 (UTC)

matter and anti-matter .[edit]

is the total amount of matter and anti-matter in our universe same ? —Preceding unsigned comment added by Shamiul (talkcontribs) 04:21, 22 September 2007 (UTC)

No, there is far more matter than antimatter thanks to baryon asymmetry. Someguy1221 04:23, 22 September 2007 (UTC)
Well, far more matter has been observed than anti-matter, but the article you linked to mentions that distant regions of the universe may well have large amounts of anti-matter so that there could be equal amounts of both in the universe as a whole. Bistromathic 15:41, 22 September 2007 (UTC)
I read the link in full only after I pasted it here, but now I have another one that might satisfy. Experiments win. Someguy1221 15:58, 22 September 2007 (UTC)
It is now considered very unlikely that a balancing amount of antimatter is somewhere far because at the boundary between the matter and the antimatter region, there should be a violent bright emission of gamma rays, and it is now considered excluded that we would have missed such a thing with our gamma-ray observatories. Hence, the origin baryon asymmetry is considered one of the very big open question in physics. Simon A. 16:06, 22 September 2007 (UTC)
That's very interesting, but I'm afraid most of it went straight over my head! Does this mean that baryon asymmetry should be changed slightly? Does it overplay the possibility of the existence of distant anti-matter? Bistromathic 11:05, 23 September 2007 (UTC)

are there any chemicals that can permanently inhibit the melanogenic enzymes, such as tyrosinase[edit]

are there any chemicals that can permanently inhibit the melanogenic enzymes, such as tyrosinase, stoping the production of melanin, in animals? —Preceding unsigned comment added by 81.99.218.58 (talk) 08:27, 22 September 2007 (UTC)

Link. Someguy1221 15:18, 22 September 2007 (UTC)
Note that none of these permanently inhibit tyrosinase, they simply do so, to a greater or lesser extent, for as long as they are applied. Note they also only work on skin, not hair, as delivery to the hair follicle is an issue. Rockpocket 17:31, 22 September 2007 (UTC)
Generally the only way you can permanently inhibit an enzyme is by irreversibly binding or otherwise destroying the enzyme. This works fine in a static system. However in a dynamic system such as a animal it would I assume effectively be impossible to permanently inhibit the enzyme in the animal because even though you can permanently inhibit what is there at one time, more will be produced. Nil Einne 18:12, 22 September 2007 (UTC)
What's the deal with all these "Is there any way to stop <pigment>?" questions, anyway? Just curious, s'all. --Kurt Shaped Box 19:39, 22 September 2007 (UTC)

Retail trend in America[edit]

20 year ago Home Depot was able to displace local hardware stores by offering lower prices and better customer service. Years went by. Then Home Depot raised its prices, got rid of even minimal customer services like cutting and threading a piece of galvanized pipe. Anything and everything that did not fall within one standard deviation of average got canned. If you needed 4mm x 12mm screws forget it. Only high profit items like stainless remote control barbecue grills and fancy riding mowers now occupy the entrance to the store. My question is are retail stores now looking to stay in business by selling only the icing off the top of the cake and if so where does that leave the consumer who might need a 4mm x 12mm machine screw or a piece of galvanized pipe cut to 2-1/2 ft and threaded on both ends? Clem 12:01, 22 September 2007 (UTC)

Where does it leave the consumer? Up the creek without a paddle I suppose. But seriously, if major stores are starting to offer such a paltry level of service, presumably that opens up the opportunity for smaller businesses to exploit the market niche that does provide what the consumer wants - and then it's up to the consumer to support those stores by shopping there. Or you might be able to find these types of things in stores that specialise as trades outlets. Unfortunately in our first world consumption obsessed societies it seems that fixing or making things yourself has become very unpopular, as its far easier and quicker (and sadly often cheaper) to go down the Home Depot or equivalent and just buy a new one. BTW, is this a 'Science' question? --jjron 13:06, 22 September 2007 (UTC)
Business and consumer science. Clem 18:36, 22 September 2007 (UTC)
It's the law of supply and demand. If there is high demand for one kind of screw - the prices will be good and everyone will stock them. When the demand is low, the volume is low but the cost of the shelf space to stock them is the same - so either the price goes up steeply or they stop stocking them. You'll still find specialty stores that'll sell you those items - but you'll pay through the nose. Here in Texas, there is a vicious turf war between Home Depot and Lowes - and there are WAY too many of these stores for the amount of business they do - sooner or later one of them is going to disappear. The cut-throat nature of their business means that they have to look at everything they stock and to devote shelf space and staff to those areas that are the most profitable. As for cut and threaded galvanised pipe - geez - get a hacksaw and a set of taps and dies and do it yourself - it's not difficult. SteveBaker 14:53, 22 September 2007 (UTC)
In my case I only needed the pipe cutter which cost $120 at Home Depot and $15 at the local flea market, brand new and $50 on eBay, plus shipping, used. For threaded ends I have simply reverted to shopping at my local plumbing supply store which home depot was never able to run out of town since Home Depot had never committed to the full line of plumbing supplies and because they never installed a computer system. All of the accounting is still done by hand and they still use a 1934 cash register without any problem, perfect inventory control, no overstock or understock, and yet a full line of plumbing supplies. How do the do it? They are the real Artificial Artificial Intelligence, Amazon.com Mechanical Turks. Clem 18:51, 22 September 2007 (UTC)
And if what you say is true then those small mom & pop hardware stores with there oh-so-amazing business model will annihilate the Home Depot's and Lowe's of this world. I'm not holding my breath. The problem is that you seem to assume that retail outlets exist for the convenience of their customers - that's not true. They are their to please their stockholders - and that entails pleasing customers only to the degree that you can extract the maximum money from them...if 0.5% don't come to your store because you don't cut pipe threads - and if the 0.5% of the store/staff that used to do that can be switched over to selling garden furniture to bring in 5% more customers - then that's a huge win and not doing it will cause their competitors to get a better stock price and drive you out of business. The Mom & Pop stores (and I use the one near me too) are only able to do what they do if nobody is selling the bulk easy-to-shift stuff more conveniently and at lower prices just down the road. I guarantee that the one near you is holding on by it's fingernails in the face of 'big box' store competition. You may well go to them for the ikky jobs of putting threads on a piece of pipe (taking 10 minutes of employee time to do it and selling at a net loss for $2.50) - but when you need 500' of copper pipe, you'll go to Home Depot because it's 1/3rd the price. This leaves the Mom & Pop store doing only the inefficient, expensive, less-profitable jobs - which will put them out of business sooner or later. That's just economics though...sooner or later, someone will come up with the business model of selling the rare and difficult parts and offering the complicated services at extortionate rates and you'll wind up with two completely separate businesses. This is not unexpected. Gone are the days when every garage sold gasoline AND had a mechanic on duty to fix and repair stuff. Now, a gas station sells gas and jumk food and very little other automotive services. Now we have specialised muffler, lube, tyre and transmission shops that do one job and one job only. Those places don't sell gasoline. SteveBaker 15:39, 23 September 2007 (UTC)
The business I referenced is a speciallty store and sells only plumbing supplies. You acknowledge that the original Home Depot model of a carry everything general hardware store at prices 10% below anyone else with better customer service is evolving into a model of selling only big ticket or high volume items, along with installation and delivery services, as the means of maximizing dividends for stockholders, rather than to serve every Dick and Harry. Clem 00:30, 24 September 2007 (UTC)
What you describe is the classic result of one business (or a small number of businesses in collusion) taking control of an industry. At first, while they are "on their best behavior", to steal customers from the competition and avoid any consumer wrath, everything is great. But then, once they force their competitors out of business, they turn the screws on the consumer to extract the maximum profit. If any other business tries to compete they are likely to temporarily go back to "good behavior" mode just long enough to regain market dominance. Eventually, other businesses know what's in store for them if they try to compete, so nobody ever tries. It would take a new store with even deeper pockets to knock them out of their dominant position.
One hope for the future is Internet sales. That allows low-volume items to be sold without the need for the huge infrastructure of a brick-and-mortar store which would make such sales unprofitable. I'd see if you can find what you need online. StuRat 14:37, 22 September 2007 (UTC)
In many cases online prices are actually higher and believe it or not many companies, especially the ones who sell on eBay, use high shipping charges in place of or together with a restocking fee to guarantee a non refundable profit - in some cases to the point of hilarity where they simply exchange the item price and the shipping charge. Clem 18:51, 22 September 2007 (UTC)
The future is now. Buy commodity items at fairly low proces at Home Depot or Lowe's. Buy weird stuff on the web. The web prices are reasonably low because of web competition, but you pay for shipping. You can find really unusual stuff on the web that is not otherwise available. -Arch dude 16:09, 22 September 2007 (UTC)
BTW this isn't really a science question from where I stand Nil Einne 18:09, 22 September 2007 (UTC)
What do you do for a living? Its a business and consumer science question. Clem 18:35, 22 September 2007 (UTC)
Business science? You mean economics? That's more of a humanities issue IMHO but I don't want to argue this further Nil Einne 18:55, 22 September 2007 (UTC)
Why would you argue it in the first place? Don't tell me you are one of those persons who thinks questions about literature are literary science questions and belong on the science desk instead of on the humanities desk. Ever hear of the Dewey Decimal system? Maybe you should have a look at it first. Besides, if Wikipedia desk question classification were really an objective issue then a Wikipedia neural network bot would make the decision instead of the OP and a whole new basis for classification would therein be created. Clem 19:06, 22 September 2007 (UTC)
Er I don't quite understand what you mean are you talking to yourself? I don't think literature or economics are really science so I don't think they belong on the science desk no. Maybe you do, that's up to you. But apparently I am not the only one. Also, I don't get the relevance of the Dewey Decimal system to the discussion of whether this is a science question or a humanities one. I didn't say it was completely objective issue obviously there are cases when it is unclear but I don't feel this is one of them. (Also just because something is objective doesn't mean it makes sense to develop a neural network for the purpose.) You are free to disagree in any case although I don't get why you're so defensive about this. If you feel it is, fine, it's not a big issue... The biggest advantage is for you not me. When you put your questions in the most applicable desk, you're likely to get the largest number of helpful responses. Nil Einne 19:55, 23 September 2007 (UTC)
Maximizing profit is based on business science whereas serving customers is based on social science. I'm not interested in esoteric or irrelevant opinion but rather a scientific resolution. Aside from that, if you are not knowledgeable as to the Dewey Decimal system or to classification of knowledge in general then you are not entitled to an opinion. Clem 00:57, 24 September 2007 (UTC)

The OP makes the assumption that all mom-and-pop hardware stores were driven out of business by the big-box stores like Home Depot. Not true. While many small shops did succumb, some — usually in rural areas — survived. They did because many of their customers are farmers. Many farmers don't like going to Home Depots, Lowe's, etc. because for the most part the travel uses up a good part of the work day. Also, when they need something, they need it right away, or the farm shuts down — there's no time to order it. At the local shop, if they don't have it, they make it, just like the old days. There exists just such a store in my hometown. It is well into its second century of operation, being owned and operated by the third generation of the same family that founded it (with a fourth generation ready to take over). The store it defies all modern rules of efficient retail design: It's in an old barn-like building that's dusty, has uneven wooden floors, aisles that are way too close together, a seemingly random arrangement of products. But it's always full of customers! Even if farmers can't take the time to travel to the city, city-folk will come to the country to find what they want. — Michael J 19:15, 22 September 2007 (UTC)

In my reply to Steve Baker's 14:53 reply above, I pretty much said the same thing. However, even though there are still nuts and bolts suppliers who have been here for umpteen years they have decided to install their first computer. It will most likely be a replicant of the retail department store systems that existed back in the mid sixties only using modern equipment and software; the death of "inefficiencies" that mean it still has boxes of 4mm x 12mm stainless hex head screws which are not on display, else they would have long since been sold. Clem 19:50, 22 September 2007 (UTC)
The key to a successful hardware business is if you can walk in with a problem and not be quite sure how to fix it, and someone there within five minutes will not only fetch every tool and part you need, but will sketch out a diagram on the bag on how to do the job. ("The PTO coupling on my 1963 Massey Ferguson keeps slipping when I downshift on a grade.") — Michael J 00:53, 23 September 2007 (UTC)
LOL At Home Depot the guy in plumbing is too busy early in the morning replacing and straightening stock and at other times is to busy with other customers while at the self-serve cashier machine "Miss Annoy" keeps telling you to remove the item from the bagging area (your hat, your kid or the store's pet house fly), to put your item in the bagging area or to wait for the attendant while the attendant is busy talking to a co-worker about the dry spot she keeps scratching that has now started bleeding and will require that she take a break to go to the first aide station to get a band aide while you just want to get the heck out of there an figure out how to keep the POT from slipping on your own without risk of defective information coming from the store. Viva La rural America where Home Depots don't grow! Clem 02:10, 23 September 2007 (UTC)
Yeah - OK - so you're arguing that these are terrible places that nobody would ever go to in order to buy stuff if there was a Mom & Pop store nearby...so how come there are new Lowes and Home Depots appearing at every freeway intersection in America and the Mom's and Pop's are going out of business in droves? It's nonsense to keep harping on about these 'deficiencies' (which I entirely agree with you on) - when clearly their business models are vastly more efficient - and they bring in customers. SteveBaker 15:44, 23 September 2007 (UTC)
Lowe's still provides cut and thread service and to stay in business has expanded the line it carries although this might well change. As for Home Depot and Lowe's being on every corner that is but one of many factors like price that such chains try to conquer - proximity to the customer. In areas where the cost of real estate or current ownership prohibits building a new store older less efficient general hardware stores survive on proximity to the customer alone. Who wants to get on the freeway to go to a hardware store two miles away when they can go around the corner and buy the same item at a higher price but save double the difference in price by paying less for gasoline? The question I am asking is whether abandonment of customer need is giving customer loyalty the chance to change. Clem 06:21, 24 September 2007 (UTC)
"Efficient business model" is just another way of saying that they've managed to give the customer the least for his money. Easy to do, if you're willing to spend a couple of years operating at a loss to run the competition out of business. 69.95.50.15 19:53, 24 September 2007 (UTC)

Thrust sea level/vaccum[edit]

Hello

The thrust of the same rocket engine is not the same at sea level and in vaccum, why? The divergent nozzle is adaptable at different pressure?

Tank you —Preceding unsigned comment added by 74.13.154.170 (talk) 13:35, 22 September 2007 (UTC)

I would think the thrust is the about the same.. Maybe because of the added pressure at sea level it is harder for the gas to be pushed out of the engine. Also obviously friction would be greatly increased in an atmosphere, although this wouldn't reduce the thrust it would reduce accelerationShniken1 14:14, 22 September 2007 (UTC)


100% thrust (sea level / vacuum): 1670 kN / 2090 kN (375,000 lbf / 470,000 lbf) 104.5% thrust (sea level / vacuum): 1750 kN / 2170 kN (393,800 lbf / 488,800 lbf) 109% thrust (sea level / vacuum): 1860 kN / 2280 kN (417,300 lbf / 513,250 lbf)

The difference is notable, 25%..... —Preceding unsigned comment added by 74.13.154.170 (talk) 16:04, 22 September 2007 (UTC)

The ejected mass accelerates (The thrust received is due to the change in momentum of the ejected gas as per Newton's second law) due to the pressure difference between the throat of the nozzle and the ambient pressure at the end of the bell. The greater the pressure difference, the greater the acceleration, the greater the exit velocity of burned propellants, and the greater the resulting thrust. Zero is the smallest pressure possible thus any rocket is more efficient (more thrust per unit of propellant expelled)in a vacuum than inside an atmosphere. See http://en.wikipedia.org/wiki/Rocket#Net_thrust and the references provided there for mathematical derivations and formulas. Lazyquasar 03:45, 27 September 2007 (UTC)

Parts of the USA that have a similar climate to Scotland[edit]

Living in England I envy the amount of space people have in the USA - in England land is very expensive and even wealthy people live in small houses on small plots compared with the US.

But in Scotland there is more space, land is cheaper. So if I wanted more space I could in theory emmigrate to the US. But could I achieve the same goal by just moving to Scotland? In many parts of the US the climate is much colder than in Scotland.

So what parts of the USA have similar winter temperatures to winter in Scotland please? And what parts have similar summer temperatures to summer in Scotland please? (These two things are unlikely to be the same places as there is far greater seasonal temperature variation due to the continental climate in the US, and the maritine climate in Scotland). Thanks 80.0.114.206 13:47, 22 September 2007 (UTC)

You might consider the Pacific Northwest, near the coast, particularly Oregon and Washington state. They also are warmed by the Pacific currents, and therefore have a climate similar to England and Scotland (small variation, lots of rain and fog, etc.). See Seattle#Climate for a description of the climate there. And, if you want to include Canada in your list of possibilities, Vancouver Island is a large island warmed by the Pacific version of the Gulf Stream, almost identical to Great Britain in that respect. StuRat 14:01, 22 September 2007 (UTC)
Our article on Köppen climate classification classifies Seattle as type Cfb which is what our article on Climate of Scotland says that region is. This climate is considered unusual in the U.S. though. Rmhermen 14:09, 22 September 2007 (UTC)
Land prices are pretty high around Seattle though. The places in the US with the most temperate climate tend also to be the ones with the steepest property prices. I'm a Brit who lives in Texas - land is pretty cheap (as low as $1000 per acre far from civilisation - more like $15,000 per acre within commutable distances of cities - much, much more in city centers of course). The Texas winter climate is gorgeous - but in the summer, the heat gets rather crazy. My present house (which I designed myself) is on a gorgeous tree-covered 1.2 acre lot - with a view over a nearby lake. But I'm moving down to Austin and I'm probably going to build my new house on a 10 acre 'virgin' lot. There is absolutely no way to do that in England on a programmers' salary. There are a lot of jobs in my particular line of work in California (I'm a Game programmer) - but I can't afford to live there precisely because of insane land prices anywhere within commutable distance of a decent sized city. SteveBaker 14:26, 22 September 2007 (UTC)
Land prices might be high right around Seattle, but I'm sure land can be had cheaply somewhere in the coastal region of Oregon, Washington state, and British Columbia. The search could even be extended to the coastal regions of Northern California and Southern Alaska, which have similar climates. One caution, though, the entire region has some major fault lines, so earthquakes are a possibility. StuRat 14:54, 22 September 2007 (UTC)

Thank you for interesting answers so far, and apologies for not stating the question very well, but what I would like to know are which areas of the USA have a) winter temperatures, and b) summer temperatures, that are similar to those in Scotland. I imagine these would be in a band stetching across the US, somewhere between the cold north and the hot south. I recall seeing in the past climate charts that gardeners use, where the climate is given numbers, and these did have belts stretching from coast to coast. 80.3.44.82 16:24, 22 September 2007 (UTC)

If you want to match both the winter and summer temps, you don't get a band crossing the US, since, as you had noted, there is far more temperature variation within the interior of a continent than on an island. Your only choices are then ocean islands and coastal areas where the temperature is moderated by the oceans. Aside from the area given in the Pacific Northwest your only other choice would be on the Atlantic side. However, since the currents flow south there, not north, you would need to go considerably farther south to match temps with Scotland. Also, since the prevailing winds in the continental US go east, you would need an actual island there, as coastal areas would still be subject to quite high temps in summer, except for those on peninsulas extending well into the ocean. Islands or peninsulas off the coast of the North Carolina and Virginia might work, for example. I suppose you could go as far north as Long Island, New York, and still be close to the climate in Scotland. Earthquakes are less of a concern on the Atlantic side than on the Pacific side, but now you also have to deal with the occasional hurricane. StuRat 17:26, 22 September 2007 (UTC)

Thanks, I did appreciate that the areas for summer and winter temperatures would be different. I aplogise again for not having made this sufficient clear in my oiginal question. Never mind the summer temperatures, what areas or belt across the USA would have similar winter temperatures to those in Scotland? Obviously to the north it will be colder, to the south it woyuld be walmer. Somewhere in between the temperature will be similar to Scotland. Where this belt is, and how wide it is, is what interests me. Thanks 62.253.48.7 13:10, 23 September 2007 (UTC)

It would be more of a U-shape than a band. If you just want to match winter temps, I'd say you'd start at, say Long Island, New York, then go quite a bit south as you go inland, perhaps down through New Jersey, Maryland, Delaware, and Virginia, to North Carolina. Then you would head west, through Tennessee, Missouri, Oklahoma, northern Texas, New Mexico, and Arizona. At this point you would start to get coastal warming and would need to head almost north, through Nevada, Oregon, Washington, British Columbia (Canada), and on to Southern Alaska. Note, however, that those states in the interior will get much hotter than Scotland in the summer (especially in the desert states, like Arizona). To match summer temps, you might start and end at the same places, but arc upwards well into Canada in the interior. StuRat 17:53, 23 September 2007 (UTC)
The influence of being close to the ocean is huge. In Texas, in the winter, the temperature is utterly dependent on the direction of the wind. If it blows from the North - we can sometimes get snow and ice storms. If it blows from over the deserts of Arizona and NewMexico then it can be quite hot - even in the depths of winter. Without the moderating effects of the ocean (which hardly changes temperature at all - and when it does, it does so exceedingly slowly) - you tend to get more wild, unstable weather than you do in a small island such as the UK. So (as others have pointed out) - it's going to be next to impossible to replicate island weather patterns on a huge continent. Even on the coast of the US (where things are a little more stable), weather coming from inland is going to produce different effects from that coming in over the oceans. I'm doubtful that you could find an exact match for Scottish weather at any time of year - yet alone all year round. My advice is to focus on things other than weather - that is a small percentage of life's experience compared to (for example) the total inability to buy decent bacon/beer/strawberries/cheese/...etc in the USA - or the impossibility of buying a dozen acres of virgin woodland with a lake view in the UK. In the end, it doesn't matter much to me whether there is three feet of snow outside - or the temperature outside is above body heat - either way, it's going to be too miserable to go outdoors so I'm going to be stuck indoors or in a car with the heating/cooling cranked up to a bearable level. The relevent number is over what percentage of the year is the weather gorgeous - and for that, your best option is undoubtedly the coast of California - where you can't afford to buy land. So you have to settle (as I did) for someplace like Texas where 50% of the year we have great weather - but property is affordable. SteveBaker 15:12, 23 September 2007 (UTC)

Hello... I'm Frank Necrosis[edit]

What is frank necrosis? How does it differ from plain necrosis? JIP | Talk 16:11, 22 September 2007 (UTC)

The term "frank" usually refers to something that is plainly visible, as opposed to covert (I think that's the medical opposite term...) where they have to go looking for it. Saturn 5 17:29, 22 September 2007 (UTC)
I first heard of necrosis from the Pogo Joe level Hello... I'm Frank Necrosis. The Wikipedia article necrosis gave me a general idea of what necrosis is, but a Google search for "frank necrosis" gave me thousands of results for the exact phrase, all of which are related to actual medicinal research, not to Pogo Joe. So this specific term must have some important meaning in medicinal science, which I am utterly unaware of. JIP | Talk 19:04, 22 September 2007 (UTC)
"frank" = "clinically evident". "Frank necrosis" therefore = "necrosis you can see with your eyes" (i.e. diagnosable clinically, without resort to lab tests) vs. "necrosis" = "necrosis visible in pathology slides". - Nunh-huh 19:08, 22 September 2007 (UTC)
I think I understand. It is obvious there is need to differentiate between necrosis you can see with your own eyes and necrosis you need to do pathological research for. So medicine invented "frank necrosis" as a handy shorthand for the former. And of course, the Pogo Joe level name arose of the similarity between the term "frank" and the first name "Frank". JIP | Talk 19:11, 22 September 2007 (UTC)
"invented .. shorthand" is not quite right; the term frank is similarly applicable to other phenomena, and it's not much of a stretch from the ordinary use of the word. —Tamfang 23:55, 23 September 2007 (UTC)

human eye[edit]

Re: Wikipedia:Reference_desk/Computing#Wide_screen_Vs_Full_screen

Anyone know what the 'human vision aspect ratio' is?87.102.89.127 16:21, 22 September 2007 (UTC)

This link might help you. I just glanced at it and it looked like what you needed.–Sidious1701(talkemailtodo) 17:37, 22 September 2007 (UTC)
It's not obvious how to define the aspect ratio, because the field of view of the human eye is not a rectangle (nor even a rectangle projected onto a sphere). However, the horizontal angle of view is almost 180 degrees and the verticle angle is almost 120, so the aspect ratio in that sense is about 3:2. —Keenan Pepper 17:57, 22 September 2007 (UTC)


We also have peripheral vision, which is complicated to describe and is linked to visual perception, a psychological concept. It may not be possible to measure the aspect ratio without inventing some application-specific operational definitions. Nimur 18:10, 22 September 2007 (UTC)

Thanks87.102.38.119 22:14, 22 September 2007 (UTC)

Our eyes are circular - and I believe the distribution of cells inside is pretty much symmetrical - so in that sense our instantaneous field of view is circular...an aspect ration of 1:1 - but we can (and do) swivel our eyes from side-to-side much more readily than up and down - so our 'stationary head - moving eyes' total field of view is shorter and wider (I don't know the exact number offhand) - similarly, if head motion is allowed as well as eye motion then there is an even stronger 'horizontal' bias - so we can see almost 360 degrees horizontally but considerably less vertically. Add in shoulder/chest motion and that bias gets larger still. But the reason for wanting wide-screen is simply because in most cases, most of the interesting action is not in the sky or the ground close to your feet - the action of visual perspective means that a short/wide screen is a better fit for "where the action is" than a taller, narrower screen which - for the same area - provides less left-right coverage whilst giving more coverage to the relatively useless areas of sky and near-ground floor. Clearly that's not true in all cases - if you are watching a scifi movie about combat in deep-space then a square screen would make more sense - but movie makers know about the shape of the screen and design their action sequences to fit - so it doesn't really hamper them too much in those cases. SteveBaker 14:59, 23 September 2007 (UTC)
You left out the effect of having two eyes whose fields don't entirely coincide. —Tamfang 23:52, 23 September 2007 (UTC)
Or more simply, you might want wide screen because that's what most of the films you'll watch are. It's not exactly your decision. – b_jonas 18:54, 24 September 2007 (UTC)

Black/Dark Outfit and White/Bright Outfit Regarding To The Sun's Heat Absorption[edit]

I heard many times that when we wear black color during daylight will make us hot and sweat more rather that if we wear bright or bright color. This is regarding to common sense that those color (the dark or black ones) absorb heat more than the bright/white ones. Is that true?How is it scientifically explained? Thanks for the explanation

Reno Risanti —Preceding unsigned comment added by 125.161.130.47 (talk) 18:09, 22 September 2007 (UTC)

Email address removed by Nimur 18:11, 22 September 2007 (UTC)

Well the "common sense" explanation does have a scientific answer: dark colors are "dark" because they don't reflect much light — they absorb it. Now it's a bit more complicated than exactly that (since much of the heat energy from the sun comes in non-visible wavelengths, so visible light reflected has a bit more to do with that), but that's basically the essence of it. Now obviously clothing has other factors involved than just color — the type of fabric and cut of it both play large roles in whether or not it allows air to circulate well in it — but if all other things were equal then the color could easily play a large role. --24.147.86.187 18:55, 22 September 2007 (UTC)
You need to look up infrared emissivity--212.139.98.210 21:17, 22 September 2007 (UTC)

mica-porphyrite at Biddlestone NE65 7DT[edit]

WHAT MAKES THIS FAMOUS STONE(USED TO PAVE THE ROAD TO BUCKINGHAM PALACE0 SO RED —Preceding unsigned comment added by 84.92.51.198 (talk) 19:28, 22 September 2007 (UTC)

I assume you mean "is a mica-porphyrite which has a characteristic red colour. This stone, commonly known as red whinstone or Harden Red, is exploited at Harden Quarry near Biddlestone." http://www.northumberlandnationalpark.org.uk/nationalparkmineralsplan.pdf colour coud be due to manganese or iron possibly..87.102.38.119 22:30, 22 September 2007 (UTC)

How much of everything is nothing?[edit]

This question may or may not even have an answer, but I'm curious. What percentage of the universe actually is matter? Not counting energy, just matter. I know that on the smallest micro-scale, the composition of atoms is a very small amount of matter in the form of sub-atomic particles with mostly empty space. And on the grandest macro-scale, stars and planets and other astronomical objects make up planetary systems that are mostly empty, and even more emptiness between stars with a galaxy, and even more emptiness between galaxies, etc. (There is of course interstellar dust, so do count that, but I would think its total volume is negligible.) So in essence, everything is mostly nothing, am I correct? So that is the question in the header, and the reciprocal would be how much actual matter there is. Any guesses? — Michael J 19:29, 22 September 2007 (UTC)

I'm not sure if anything really qualifies as "solid matter" when you think about it:
1) The universe is mostly empty, but the galaxies are full, right ?
2) No, but the solar systems are mostly full, right ?
3) No, but the planets and stars are mostly full, right ? Not when you consider the gaps between atoms.
4) But the atoms are mostly full, right ? Not when you consider the gaps between the electron shell and the nucleus.
5) But the subatomic particles in atoms are mostly full, right ? (I'm not sure on this one, but guess that they are mostly empty too, with just some tiny quarks inside them).
6) But the quarks are mostly full, right ? (I'm not sure on this one, but guess they are mostly empty, too.)
There may be nothing more than singularities of matter (infinitely small points), much like tiny black holes, when we figure it all out as far as we can go. StuRat 20:05, 22 September 2007 (UTC)

I assure you, it's Turtles all the way down. -Arch dude 22:07, 22 September 2007 (UTC)

See Mass of the observable universe. Then again, the population of the Universe is zero. -- Kesh 22:24, 22 September 2007 (UTC)
Because the fundamental particles of matter (quarks and leptons) have no internal structure (as far as we know), they are usually considered to be point-like objects (although "points" that posses certain properties, such as mass, charge, spin etc.). So, in one sense, everything is made of nothing - the "volume" that we perceive objects as occupying at a macroscopic level is entirely empty space, and the fundamental particles themselves take up zero volume. However, at a quantum level, it is not possible to say for certain where particles are, how many particles there are (see virtual particle) and even what space itself is (see quantum foam) - so the question "how much space does matter really take up" becomes more or less meaningless. Gandalf61 10:25, 23 September 2007 (UTC)
The fundamental particles are merely statistical measurements of position - you can't put a 'size' on them. If you can't meaningfully talk about the 'volume' of an electron. What you can say is that there is a 99% chance that the electron will be within some volume of space - and that's a kinda-sorta representation of how 'big' the electron is - but if you pick an 80% confidence instead - you get bigger electrons. In some sense, every electron is everywhere in the universe at the same time - at some non-zero probability. So either the universe is 100% full or it's 100% empty or anywhere inbetween. It's your call. SteveBaker 14:49, 23 September 2007 (UTC)
This isn't really important, but 99% confidence is a bigger electron then 80% confidence. — Daniel 00:18, 24 September 2007 (UTC)
No, it's the other way around. StuRat 16:22, 24 September 2007 (UTC)
People are fond of saying that the inside of an atom is mostly empty space, but that's not true. In order to make it mostly empty, as opposed to entirely or not at all, you have to apply a double standard, saying that the quarks in the nucleus occupy space while the electrons don't.
Now, maybe there's still a sense in which matter is mostly empty space. The mass density of a white dwarf—which consists of atoms packed as closely as they can be packed—is around 106 times that of a star, so perhaps one can say that the sun is around 99.9999% empty space by that token. Also, the mass density of the sun divided by the ordinary-matter density of the observable universe is about 10−31, so maybe you can say that the universe as a whole is 99.999...999% empty space, in a certain sense. -- BenRG 12:17, 24 September 2007 (UTC)
Using that argument, can't we extend it to a black hole, which has infinite density at the singularity ? Therefore, anything at less than an infinite density is completely empty, by comparison. StuRat 16:22, 24 September 2007 (UTC)
You could just compare the density of the galaxy or whatever :large construct you want to examine to the density of household materials, like water or air. – b_jonas 18:52, 24 September 2007 (UTC)

Phase shifting[edit]

May be a stupid question, but I cant get my head round it. If you frequency modulate a sine wave onto a carrier, then change the phase of the resultant by 90 deg, then discriminate the phase shifted signal, would you get he original signal back but phase shifted by 90 deg? Pleas help its driving me nuts--212.139.98.210 20:10, 22 September 2007 (UTC)

no, because the frequency is determining the demodulated output, phase shifting has no effect on this. It will only effect it if your modulating frequencies are close to the carrier frequency, or the frequency shift you use is tiny. Just imagine you have a FM radio. You step back about a quarter wavelength away from the station (75cm) you get a 90° phase shift. The sound is only phase shifted by a few nano seconds, no where near 90 degrees for an audio frequency. Graeme Bartlett 01:31, 23 September 2007 (UTC)
Ah but imagine the fm spectrum: each sideband a has amplitude and phase. If you were to change the phase of all the sidebands by 90deg, what effect would that have on the discriminated signal? —Preceding unsigned comment added by 88.110.17.120 (talk) 12:54, 24 September 2007 (UTC)

finger-licking[edit]

Hi. Why do some people lick their fingers when they read a book, newspaper, pick things up, etc? It's unnesecary and dangerous. For example, they could swallow foreign germs or poisons, spread their own germs to other people, etc. Besides, why don't they just secrete saliva just in front of their lips, and touch that? At least it's safer. I've been pondering this question for years, and so far I've gotten no answer. Why don't they wash their hands instead if they want them wet? Is it to ensure the person doesn't get a papercut, to be able to hold onto the paper easier, to avoid an unpleasent sensation caused by the excessive friction, because other people are doing it, or because it's simply a bad habit? Why do some people do it and others don't? Which places have a higher percentage of people who do this? Does looking up articles on the Internet prevent them from needing to lick their fingers because of the relative lack of paper, or do they just lick their fingers before touching the keyboard or mouse? Do they do it unconciously or voluntarily before flipping a page? Are there higher benifits or risks when performing this procedure? Are there any animals (other than homo sapiens) who have individuals who do this? Do people who do this overall lick more often than people who don't? A few years ago I observed someone doing this, and I tried to ask them why some people lick their fingers, and the subject said they don't have time to answer. Is it because asking such a question is rude in some way? Is there an article on this? Thanks. ~AH1(TCU) 22:43, 22 September 2007 (UTC)

Well normally licking your finger is to get your finger to 'stick' to the page so you can flip it easily. Hygine wise i'm sure it isn't particularly bad for you, providing your have generally good personal hygiene. I would expect it is a 'learned' thing...so if your parents/close friends/family do it then you might subconciously pick up the habit and do it yourself. Kangaroos regularly cover their body in their own saliva by licking/spitting on themselves and working it in - though they do this to cool themselves down in the heat. Your propose 'secrete saliva' idea is pretty odd - it's i'm sure marginally better but why would you go to that much effort just for something that is so simple and (in reality) pretty darn safe. People seem to be developing an almost obsessive fear of germs (there'll be a word for it somewhere). ny156uk 22:58, 22 September 2007 (UTC)
Mysophobia. 152.16.59.190 00:39, 24 September 2007 (UTC)
I'm pretty sure it isn't dangerous, or at least not any more dangerous than the many things humans do. We're able to put up with most germs and the like because we have immune systems and all that. As for doing it, sometimes it makes it easier to pick up a page, especially if you have been flicking through a lot of pages. Washing your hands is overkill—you want a small amount of moisture on the finger pads to get a little more friction when dealing with paper, not a wet hand. --24.147.86.187 23:24, 22 September 2007 (UTC)
I use a slightly more hygienic method of spitting very lightly on my fingers to moisten them. This avoids putting your fingers in your mouth. —Preceding unsigned comment added by 88.109.137.161 (talk) 01:07, 23 September 2007 (UTC)
There are fingertip moisteners on the market, like Lee's Sortkwik. They are usually greaseless, non-staining, and modern ones have antibacterial properties, as well. People who handle a lot of paper often use either that, or rubber finger covers (similar to Finger cots). --Mdwyer 05:32, 23 September 2007 (UTC)

If the corner of each page is discolored, though, don't do it lest you end up like the dead monks in The Name of the Rose/The Name of the Rose (film).

Atlant 14:25, 24 September 2007 (UTC)

Calculations with uncertainty values[edit]

I learned that when I am multiplying two measurements with uncertainty values (±), the uncertainty in the final answer would be the sum of the measurements' relative uncertainties.

eg. (a±x)(b±y)=ab±(x+y)


I need to calculate the area of a circle, and my radius has an uncertainty value. I need to square this radius, which would actually be (r)x(r) Does my uncertainty double, or do I just keep the uncertainty value of one radius? ---Zealz 23:44, 22 September 2007 (UTC)

Your formula for multiplication is not right! You can find a table at propagation of uncertainty that may help. Are you dealing with fractional uncertainties, like 5m ± 20%, or absolute values like 5±1 m? --Reuben 23:51, 22 September 2007 (UTC)
the fractional uncertainty of the radius ---Zealz

\frac{\Delta X}{X} = \frac{\Delta A}{A} + \frac{\Delta B}{B} is the same thing as what I typed ---Zealz 01:09, 23 September 2007 (UTC)

Yes, I see... the formulas from the article are quite wrong for Gaussian random variables at least. I don't know where those come from. For Gaussian-distributed random variables, you want (σX/X)²=(σA/A)²+(σB/B)². --Reuben 02:47, 24 September 2007 (UTC)
I suggest you just multiply the minimum and maximum values to find the range. For example, if your circle has radius 10 ± 1, your radius ranges from 9 to 11. Thus, the area ranges from 81p to 121p. This can be written as 101p ± 20p. If you find it troubling that the base area of 101p is not what you get when using the base radius of 10, you can alternatively write the answer as 100\pi \frac{+21\pi}{-19\pi}. StuRat 01:50, 23 September 2007 (UTC)
I'm not a mathematician, but calculating the error seems pretty straightforward from the formulas at Propagation of uncertainty. Assuming that the radius is r_0 \pm \Delta r_0. Since you said that the error is a fractional value of the radius itself, \Delta r_0 = e r_0 (so if there is a five percent error, e=0.05). Going by the formula from Propagation of uncertainty, this is true:
\frac{\Delta X}{X} = \frac{\Delta A}{A} + \frac{\Delta B}{B} + \frac{\Delta A\cdot \Delta B}{A\cdot B}
(the one you quoted was just an approximation, according to the note). Substituting X for r_n, \Delta X for \Delta r_n, A and B for r_0 and \Delta A and \Delta B for \Delta r_0, we get:
\frac{\Delta r_n}{r_n} = \frac {2 \Delta r_0}{r_0} + \frac{\Delta r^{2}_{0}}{r^{2}_{0}}
Substituting \Delta r_0 for r_0 e, and doing some rearranging we get:
 \Delta r_n = r_n (2 e + e^2)
There's your new error. If your fractional error before the squaring was e, then the new error is 2e + e^2. Assuming I haven't done anything extremely stupid, which is always probable. I'm not a mathematician, as I said (which I'm comfortable with, since this isn't the mathematics part of the desk :P) --Oskar 02:25, 23 September 2007 (UTC)
By the way, e^2 will be very small, so simply doubling the error will be a good approximation. For instance, if the e=0.05, then 2e + e^2 = 2*0.05 + 0.05^2 = 0.1025 or 10.25%. That's very close to simply doubling the error for an answer of 10% --Oskar 02:29, 23 September 2007 (UTC)