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February 6

How many?

My friend and I were discussing the rather obscure topic of The Year of the Dolphins when we came upon the rather obscure subject of the dolphin-human ratio. So, to determine that, can anyone tell me how many dolphins there are in the world (all kinds, including Orcas. etc.)? Thank you. 99.226.39.245 (talk) 00:03, 6 February 2008 (UTC)

Measuring populations is notorious difficult. Measuring marine popoulations is even worse. Consider for example the current controversy of the whale population and fish stocks. Even our estimate of the human population is a very rough guess and we have far better data then we have for any other animal Nil Einne (talk) 11:31, 6 February 2008 (UTC)

There are almost undoubtedly more humans than all of the whales and dolphins. According to our list of cetaceans there are more than 80 species, and the largest known population is about 3 million for the Pantropical Spotted Dolphin. Most of the species have much smaller population estimates, and the population of many of the species is unknown. If you take the largest numbers possible (90 species, each of 3 million) you come up with the largest conceivable population for all cetaceans of 270 million, or about one quarter of a billion. Since the human population is on the order of 6 billion, the cetaceans if they were the maximum 270 million would be only 1/24th of the human population. (The actual number of cetaceans is probably much smaller than 270 million, of course.)--Eriastrum (talk) 19:06, 6 February 2008 (UTC)

Thank you very much! 99.226.39.245 (talk) 01:55, 7 February 2008 (UTC)

Extreme biology

Re steel munching microbes that live in nuclear reactors and shrimp that live in 95ºC, what's the name of the study given to creatures that live in extreme conditions on earth? Thanks in advance, Julia Rossi (talk) 00:24, 6 February 2008 (UTC)

I'm not sure, but the cretures who live in these conditions are called extremophiles. Hope that's of some help. Zrs 12 (talk) 00:34, 6 February 2008 (UTC)

That's it exactly – thanks for your help Zrs 12. Julia Rossi (talk) 00:55, 6 February 2008 (UTC)

You're welcome. Zrs 12 (talk) 01:00, 6 February 2008 (UTC)

what are these yellow flowers called?

I have lived in the San Francisco Bay Area my whole life and these yellow flowers sprout out everywhere, but no one i know knows what they are called, and neither do i, but we all know about them. does anyone have any idea? they are all over the place.Boomgaylove (talk) 05:35, 6 February 2008 (UTC)

I believe what you have there are Oxalis pes-caprae, often known as Bermuda Sorrel (see article for more info). In case you wondered, I found it using this personal website. Sadly, I am not in fact an expert in the field of California wildflowers :) --Bmk (talk) 07:08, 6 February 2008 (UTC)

Although the California poppy sure is beautiful to see when I'm out on the west coast. --Bmk (talk) 07:13, 6 February 2008 (UTC)

• thank you very much, thats exactly what i wanted. soursob---I KNEW I HAD HEARD THAT SOMEWHERE! apparantly tehyre not california wildflowers though. =( hmm i actually am kinda fond of em, except that out wildflowers are nicer but less common. —Preceding unsigned comment added by Boomgaylove (talk • contribs) 07:36, 6 February 2008 (UTC)

Can I give you a friendly warning about these plants, I had some in my garden in southern Spain and they are the most pernicious weed I have encountered. They propagate by seed and worse by tiny bulbules attached to the main bulb so if you try to dig them up these bulbules fall of and form dozens more plants. I had to regrettably turn to chemical warfare to control them. Enjoy them where they are. Richard Avery (talk) 08:05, 6 February 2008 (UTC)

If you need to get rid of them manually, wait until winter. Digging out oxalis then usually means the bulb is contained. After that it crumbles into bulbules as Richard testifies. Julia Rossi (talk) 08:35, 6 February 2008 (UTC)

They are definitely a terrible invasive plant in coastal California. You should make every effort to rid your garden of them. I live in central coastal California and believe me, I know!--Eriastrum (talk) 19:11, 6 February 2008 (UTC)

They're considered a noxious weed in Australia. Pity, really; they look very pretty. Another one is Patterson's curse, which looks absolutely magnificent when it invades a whole 1,000-acre paddock. -- JackofOz (talk) 21:50, 6 February 2008 (UTC)

Thermochemistry

For homework, I was given the following problem: The carbon dioxide exhaled in the breath of astronauts if often removed from the spacecraft by a reaction with lithium hydroxide: 2LiOH(s) + CO2(g) => Li2CO3(s) + H2O(l) Calculate the work involved (in joules) when 7.20g of LiOH(s) reacts with 4.16L of CO2(g) at 1.00 atm and 25.0 degrees C. Assume ideal behaviour for CO2. Is the work done by the system on the surroundings, or the other way around?

I used ideal gas law to find that there's 0.17 mol CO2 initially, which, through stoichiometry, I determined to be the limiting reactant. But what do I do next? I know that work=-P*deltaV, so would I say that the change in volume = -4.16L, and so that the work = 4.16L*atm? I have an issue with this because the surrounding doesn't cause the CO2 to dissipate. —Preceding unsigned comment added by 76.68.246.134 (talk) 06:37, 6 February 2008 (UTC)

Yes. 1atm = 10⁵Nm^-2 and 1Litre=10^-3m³ for the answer in Joules. That would be the work done by the LiOH. What you've calculated is the work done on the air (the surroundings) by the LiOH - that seems to be the same as the work extractable (by a piston perhaps) from the system.. Hope that is right and helps.87.102.74.24 (talk) 20:17, 6 February 2008 (UTC)

Scientific reason for men or women higher%?

In the world’s population , is the % of men greater or women? And in case of any of the possibilities what is it’s scientific reason except the genetic basis of 1: 1 possibility of XX or XY.Moreover if the % of any of these two is greater and the same fashion prevails for the incomming 20-40 years, will it not lead to unbalanced human population and if so what will be the most dramatic result of this change?--Mike robert (talk) 08:07, 6 February 2008 (UTC)

The article on sex ratio discusses this in some detail.--Shantavira|^{feed me} 08:32, 6 February 2008 (UTC)

Water freezing point and supercooling

Hi, I posted an unanswered question in the Supercooling talk page ("Can be supercooled"). Can someone please help? Gil_mo (talk) 09:06, 6 February 2008 (UTC)

In short, there's no good reason to redefine the freezing/melting point of water based on achievable supercooling effects. All that would accomplish is to move (and vastly enlarge) the area of ambiguity. Explaining that water freezes at 0°C except for sometimes in controlled environments is tricky, yes. Contrast this, though, with saying that water freezes at -42°C except for natural environments where it has this pesky problem of pseudofreezing at 0°C. This similarly holds for superheating, freezing vs melting points, and other such issues. — Lomn 17:43, 6 February 2008 (UTC)

Melting and freezing point are statistically defined. That is, they refer to the phase transition between most probable macrostates in a thermodynamically random sample. If you control the randomness (by cooling really fast), you can achieve less-likely macrostates, and I believe supercooling is an example of this phenomenon. SamuelRiv (talk) 17:53, 6 February 2008 (UTC)

I'm more confused than I was to start with, since both replies seem quite ambiguous. What is "most probable"? Isn't the freezing point measured under lab conditions, i.e. by taking pure clear lab water (not pond water), cooling it in a most clean container until it freezes? If the answer is yes, then in that case the water would freeze at minus 42 celcius. Gil_mo (talk) 18:01, 6 February 2008 (UTC)

In its basic formulation statistical mechanics looks at "most likely states" from the perspective that every microstate is equally probable. That means that any potential barrier to crystalline freezing, as occurs in ice, that would require a seed molecule, is ignored. So you are effectively assuming infinite randomness of initial distribution. This can be formalized mathematically, and should create a precise definition of melting and freezing points. You can likely do the same thing with supercooling if you change the "all microstates are equal" axiom, but that would be a lot less useful from a real-world perspective. SamuelRiv (talk) 18:23, 6 February 2008 (UTC)

I'll repeat my answer from there: We got taught that although melting point is well defined, because of the above "freezing point" is in fact not well defined, period. therefore, there are such things as melting point microscopes for analysis; nobody makes a "freezing point microscope". Even the article I found on "Freezing point determination" depends on, if you read it, actually measuring the melting point Gzuckier (talk) 19:46, 6 February 2008 (UTC)

Thank you all. Gil_mo (talk) 07:49, 7 February 2008 (UTC)

A Gulf Stream in the Pacific?

The Gulf Stream takes warm water to the north and helps in making the weather of west Europe and East North America warmer than the same latitude in Asia; I want to ask the following:

See the effect of the Gulf Stream

• Why isn’t there a similar stream in the Pacific?
• Could such a stream exist (or did exist) in the Pacific? Maybe due to global warming?
• How far would the effect of such a stream extend inland (if it’s the same magnitude as the Gulf stream)? E.g. would the effect of such a stream give Magadan a similar climate to Helsinki?

-DelftUser (talk) 10:37, 6 February 2008 (UTC)

Japan Current

There is such a current. See the article Ocean current. The north-flowing warm current in the Pacific can't get through the narrow Bering Strait, so its effect is different. It seems to miss the Sea of Okhotsk, too, being deflected by the Kuril Islands. Pity, that. Stupid Kuril Islands. I'm sure Magadan would be a lot more temperate if the current got in there. --Milkbreath (talk) 15:08, 6 February 2008 (UTC)

So it has to do with geography and not climate! Indeed pity, thanks a lot. --DelftUser (talk) 09:44, 8 February 2008 (UTC)

minimum molecular weight of colloids (IV fluids)

what is the minimum molecular weight of colloid IV fluids? what is the maximum MW of crystaloids? what is the basis of such classification? if it is based on capillary permiability, what about charged molecules? some books say more than 30000: but, what is the mw of mannitol? i am confused. please help me

dr_sutharshana —Preceding unsigned comment added by 222.165.153.46 (talk) 11:15, 6 February 2008 (UTC)

physics

circuit diagram of an opto-electronic lamp system

by tusiime fiona —Preceding unsigned comment added by 82.206.143.13 (talk) 14:11, 6 February 2008 (UTC)

I'm not sure what you want exactly, but one of the links within Optoelectronics may help. --Bmk (talk) 16:39, 6 February 2008 (UTC)

Hair and nails

As our Hair and Nails dead?How can it grow?...usman khan —Preceding unsigned comment added by Usmanzia1 (talk • contribs) 14:14, 6 February 2008 (UTC)

Yes, both hair and nails are 'dead'. They both grow as new material is added at their bases, pushing the hair or nail out. TenOfAllTrades(talk) 14:32, 6 February 2008 (UTC)

most things which you can cut off your body and not scream are 'dead'. Gzuckier (talk) 19:37, 6 February 2008 (UTC)

And on the off chance that the question is just badly formatted, there's also this. GeeJo ^(t)⁄_(c) • 20:03, 6 February 2008 (UTC)

K2, the most difficult mountain in the world?

I've heard many times that the K2 is the "most difficult mountain to climb" in the world, more than mount Everest. Is that true? If it is, why is that? (topographic prominence doesn't seem to be a factor) --Taraborn (talk) 14:24, 6 February 2008 (UTC)

K2 is much steeper, much windier, much more prone to avalanche, and requires significant technical skill. Everest, by contrast, is technically pretty simple - only the Khumbu Icefall (which paying climbers cover on ladders when roped up) and the Hillary Step (which is roped) pose much of a technical challenge - the rest is just a horrible icey slog (made dangerous largely because of the horrific effects of altitude). K2 has all those same altitude problems, plus is a technically difficult and terribly unpredictable hill. See this for more info. -- Finlay McWalter | Talk 14:37, 6 February 2008 (UTC)

Excellent response, thanks. --Taraborn (talk) 14:54, 6 February 2008 (UTC)

Probably the only reason Everest is considered so difficult is because so many Americans used to like the appalachains try to climb it.. don't they realize that Everest is neither the highest point on earth NOR the tallest mountain from its base? :D\=< (talk) 16:59, 6 February 2008 (UTC)

"Mount Everest is the highest mountain on Earth, as measured by the height of its summit above sea level." Also list of highest mountains -- MacAddct  1984 ^{(talk &#149; contribs)} 17:29, 6 February 2008 (UTC)

Chimborazo_(volcano)#Farthest_point_from_Earth.27s_center ... wtf does the level of the oceans have ANYTHING to do with the highest point? :D\=< (talk) 20:14, 6 February 2008 (UTC)

Because most humans tend to live their lives in the space between the oceans and the sky, only occasionally going under water, which makes the ocean level a convenient and reasonable reference point when considering humanity's relationship with mountains (or with those parts of mountains that are not under the ocean). -- JackofOz (talk) 21:43, 6 February 2008 (UTC)

I'll be impressed when someone climbs Olympus Mons -- MacAddct  1984 ^{(talk &#149; contribs)} 17:44, 6 February 2008 (UTC)

Bah. Olympus Mons is a piddling five-degree slope and you'd be under one-third Earth's gravity. I've had walks in the park that are more difficult. I won't be impressed until someone does the climb without supplemental oxygen. TenOfAllTrades(talk) 19:01, 6 February 2008 (UTC)

:D\=<, the thickness of the air is based on its hight above sea level. The bulge of both sea level and the atmosphere near the center of the Earth are due to the centrifugal effect. The only things about hight that effect the difficulty of a climb are the distance you climb (hight from the base), and the thickness of the atmosphere (hight from sea level). Why would it matter how far you are from the center of the Earth? — Daniel 00:56, 7 February 2008 (UTC)

Homework HELP (DO NOT GIVE ANSWER)

"How much energy must be added to a 2-kg piece of aluminum with a specific heat of 900 J/(kgoC) to increase its temperature from 10 degrees Celsius to 50 degrees Celsius?"

How do I solve the above problem? At first I thought I used the forumla enthalpy change=final enthalpy-initial enthalpy, but that wasn't right. Please help!!! DO NOT GIVE ME THE ANSWER!!!--AtTheAbyss (talk) 14:48, 6 February 2008 (UTC)

No, that's not the formula that you need. There's another one that gives an explicit relationship of the variables mass, specific heat, temperature and energy. Just apply that formula, it's a trivial problem. --Taraborn (talk) 14:53, 6 February 2008 (UTC)

Wait is the equation Joules/(Kg)*(Degrees in Celsius)?--AtTheAbyss (talk) 14:57, 6 February 2008 (UTC)

Nevermind I figured it out. Thanks anyway though. --AtTheAbyss (talk) 15:01, 6 February 2008 (UTC)

I meant the one that said Heat=mass*specific heat*change in temperature, if that's of any help now. --Taraborn (talk) 15:02, 6 February 2008 (UTC)

yeah it does. The answer is 72,000 right?--AtTheAbyss (talk) 15:05, 6 February 2008 (UTC)

Yes, it is. --Taraborn (talk) 15:06, 6 February 2008 (UTC)

Thanks mate. I owe ya one. --AtTheAbyss (talk) 15:13, 6 February 2008 (UTC)

You're welcome :) --Taraborn (talk) 19:40, 6 February 2008 (UTC)

Watch out for the problems where there is also one or more phase changes, such as starting with ice and winding up with steam. Edison (talk) 16:10, 6 February 2008 (UTC)

Albumin and 11-year sun cycle

A friend of mine says that in the 1930s a correlation was found between human Albumin levels and the 11-year solar cycle. I can't find anything about it. Does anyone have any information on that? Bubba73 (talk), 18:20, 6 February 2008 (UTC)

My friend sent me this

Lowered human immunity may also be a consequence of solar activity, according to Solco W. Tromp, director of the Biometeorological Research Center in the Netherlands. Over 30 years of research, using blood data from 730,000 male donors, led Tromp to the conclusion that the blood sedimentation rate varies with the sunspot cycle. Since this rate parallels the amount of albumin and gamma globulin, resistance to infection may also follow the lead of the sun. (Freitas, Robert A., Jr.; "Sunspots and Disease," Omni, 6:40, May 1984.)

Has this been verified or refuted? Bubba73 (talk), 19:32, 6 February 2008 (UTC)

A link to read. Bubba73 (talk), 19:38, 6 February 2008 (UTC)

ailments due to marriage in close relations????

what if I marry a girl whose father's maternal grandmother & my grandfather were real brother and sisters,then what health hazards we both can face??? —Preceding unsigned comment added by 117.99.5.120 (talk) 18:54, 6 February 2008 (UTC)

You are referring to a second-cousin marriage. See cousin couple which specifies the genetic risk for first-cousin marriages. The genetic risk for second-cousin marriage will be less. -- kainaw™ 19:40, 6 February 2008 (UTC)

Is this not a "first-cousin-once-removed marriage?" —BradV 22:37, 6 February 2008 (UTC)

Nope. The grandfather and grandmother are siblings. Their children are cousins to each other. The next generation of children are second cousins to each other, the next third cousins, and so on. The "removed" comes in between people not of the same generation relative to a common ancestor. -- JackofOz (talk) 22:44, 6 February 2008 (UTC)

They're not the same generation. Her great-grandmother was sister to his grandfather. They're second cousind once removed. --Trovatore (talk) 22:48, 6 February 2008 (UTC)

Oops. You're correct, Trovatore. I misread it as "whose maternal grandmother", not "whose father's maternal grandmother". That makes the questioner and the girl's father second cousins; and the questioner and the girl herself second cousins once removed. -- JackofOz (talk) 23:02, 6 February 2008 (UTC)

Ok, so they're even further than second cousins. The common ancestors are the OP's great-grandparents and the girl's great-great-grandparents. I believe that makes the consanguinity around 2%. —BradV 23:45, 6 February 2008 (UTC)

You yourself do not face any health hazards, it would be your kids. If your shared relative had a rare recessive allele to a nasty disease there is a 50% chance that it will be passed on each generation. There is always a chance that you both carry the disease allele (for you ~13% chance for her ~7% chance). Your kids would have a small chance of inheriting two of the disease alleles (one from each of you). Knowing that, you can calculate the probability of your kids inheriting two of the hypothetical alleles. David D. (Talk) 19:45, 6 February 2008 (UTC)

Why would they have different chances of having the allele? :D\=< (talk) 20:10, 6 February 2008 (UTC)

Different number of generation. Read the question carefully, it's only his grandparent but her great grand parent who were siblings. David D. (Talk) 21:39, 6 February 2008 (UTC)

(Edit conflict) To froth: here's why:

Common ancestor -> the girl's great grandmother -> the girl's grandmother -> the girl's father -> the girl.
Common ancestor -> the boy's grandfather        -> the boy's parent       -> the boy.

• The probability of the girl inheriting a given nasty gene from the common ancestor is 1/2⁴ = 1/16 (~7%)
• The probability of the boy inheriting a given nasty gene from the common ancestor is 1/2³ = 1/8 (~13%)

To the original questioner: We should not be giving genetic counseling here on the refdesk. If you have any specific worries about marrying the girl, please consult your doctor. --NorwegianBlue ^talk 21:54, 6 February 2008 (UTC)

Why are Britney and Jamie Lynn Spears both pretty, while their parents are both extremely ugly?

How is this possible? 64.236.121.129 (talk) 21:31, 6 February 2008 (UTC)

Hybrid vigor could account for it, also known as heterosis. David D. (Talk) 21:41, 6 February 2008 (UTC)

Not to mention the fact that "prettiness" is only partly determined by genes. - Nunh-huh 21:57, 6 February 2008 (UTC)

64.126... Your comment about the celebrities' parents are obviously subjective as there is no standard of "prettiness" or "ugliness". Which are you by the way, pretty or ugly? Check with mirrior mirror on the wall...  ;-) --hydnjo talk 22:02, 6 February 2008 (UTC)

Possibly dominant and recessive genes? (is that the proper terminology?) Ilikefood (talk) 22:18, 6 February 2008 (UTC)

It's the right terminology but it doesn't apply here. Something as complicated as "beauty" is not controlled by a few Mendelian characters. --24.147.69.31 (talk) 23:02, 6 February 2008 (UTC)

Plastic surgery and airbrushing could account for it. --Carnildo (talk) 22:56, 6 February 2008 (UTC)

Right. Remember that the "pretty" ones here have been largely made to be so (it helps that they are young). Britney in particular makes this level of gauze fairly obvious these days—compare how she looks on the cover of tabloids to the way she looks when she's being presented by her label. Personally I think both Britney and her sister look very plain—take away the makeup, the money, the lights and the fame, and they're no different from many of the girls who went to my high school, unremarkable, couldn't pick them out of a blond crowd. But of course tastes differ. --24.147.69.31 (talk) 23:02, 6 February 2008 (UTC)

Apparently Britney's and Jamie Lynn's Dads didn't think their girlfriends were too ugly to make them their wives. Your question is based on the premise that these ladies "are extremely ugly"; that's an opinion, not a statement of fact, and the real question is "why do some people think they're ugly but others don't". -- JackofOz (talk) 00:05, 7 February 2008 (UTC)

"Too ugly"? I would just like to point out that it's possible for one person to think another is ugly and still want to marry them. As to any specific people, I absolutely have no comment! --Anon, 00:26 UTC, February 7, 2008.

Right, right. All very correct and good. Eye of the beholder and all that. But when the argle-bargle dies down, we all wanted to have those medium-hot high-school honeys at the time, it's undeniable that the nubile BS had a certain trailer-trash, jailbait schwing factor, and her folks are enough to make a freight train take a dirt road. I always thought it was just a lucky roll in the genetic crapshoot. --Milkbreath (talk) 22:33, 7 February 2008 (UTC)

By some strange law of probability that crapshoot seems repeatable when you compare the early Courtney Love and her dad. ; ) Julia Rossi (talk) 10:14, 8 February 2008 (UTC)

good eye makeup. look at any beauty star in a paparazzi shot without makeup, you wouldn't give them a second look. Gzuckier (talk) 15:52, 8 February 2008 (UTC)

Of course, you have to take into account that Britney's mum is much older than Britney. And the way Britney is going, in about 5 years her mum is the one who is going to look better. As for the general consideration, my answer to this, as to so many other things, is that it is "regression to the mean". Britney was VERY good looking to begin with, and talented, that is why she became famous. Now when we compare her with others, we have to remember that she was chosen from amongst millions to begin with, so that of course she looks better. She is not a good example to use when looking at how kids look better or worse then their parents. This is the answer to a lot of questions of this kind. For example: why are sequels to films so rarely as good as the originals. Well, look at it this way. For a film to be in the running to get a sequel it must have been a big success to start with. So maybe such films are already in the top 10 % as far as quality is concerned. Now, even if the quality of films was an entirely an arbitrary and random process, then we should find that films of exceptional quality would be followed by sequels of inferior quality. Another example. Why do very tall people marry people who are shorter? And why do geniuses marry people who are less intelligent? It’s commonsense really, isn’t it?

There is no reason to posit causative agencies when the effect may be nothing more than a statistical artefact. Regression to the mean. Once you know how it works, you will see it operating everywhere. Myles325a (talk) 06:41, 11 February 2008 (UTC)

One reason why you think they are pretty is because they are famous. It is the same reason why people like name brand products over generics. Another reason is you have never seen either one first thing in the morning. When you do see them they are on TV with a professional make-up job.cris

Determination of chloride in sea water

Hi. I'm currently in an AP Chemistry course at my high school. We received a lab that we ourselves have to write the procedure for. The purpose is to determine the percent of chloride in sea water samples. The materials we are given are: 1 ml pipette, test tubes, graduated cylinders, beakers, analytical balance, NaCl solid, silver nitrate solution (unknown concentration), distilled water, potassium chromate solution (unknown concentration, and sea water samples with unknown concentrations. I know that this lab will b a titration- using silver nitrate as the titrant, and potassium chromate as the indicator. My question is- without knowing the molarity of the titrant how is it possible to conduct this experiment and yield resuluts that are accurate?Is there a way I can determine the molarity of the potassium and silver solutions? —Preceding unsigned comment added by 76.214.199.203 (talk) 21:50, 6 February 2008 (UTC)

Why don't you use the NaCl solid and distilled water to make a known concentration of salt water? Then, use that to determine the concentration of the sodium nitrate. Finally, use that knowledge to determine the concentration of the unknown sea water. (EhJJ) 00:40, 7 February 2008 (UTC)

Silver Chloride is pretty much insoluble in water. Add excess AgNO3, you get solid AgCl. Wiegh it. n=m/M and you know the moles of Chloride! —Preceding unsigned comment added by Shniken1 (talk • contribs) 02:11, 7 February 2008 (UTC)

storms

How can a series of synoptic weather maps be used to predict the future location of a low pressure area? —Preceding unsigned comment added by 24.90.241.2 (talk) 21:54, 6 February 2008 (UTC)

Extrapolation.--Shantavira|^{feed me} 13:54, 7 February 2008 (UTC)

Catalase

Hi there, I've got a couple of questions of Catalase not answered int the article. Since the reaction it catalyses is primarily between the H202 molecule and the Fe2+ ion, and Catalase has four Fe2+'s, does catalase have four active sites? Also, although Catalase has an optimum of around 7.0 apparently, is there a larger range over which the pH is effectively optimum? Thanks, James —Preceding unsigned comment added by J.Lillington (talk • contribs) 21:58, 6 February 2008 (UTC)

I don't know about this enzyme but generally enzymes do not have an active site per metal centre, so no there are probably not 4 active sites. I would guess there would be 2, this is a 'normal' case where two metals are needed at an active site. One is oxidised the other is reduced (I think this is the 'norm' anyway). Some times enzymes have a metal centre that is not involved in the reaction at all but this is normally Zinc (d10 atom and is redox inactive). As for activity in pH, http://www.ualberta.ca/~edtechpd/documents/activity_probes_experimentenzymeaction_boora_v1.pdf on page 8 there is a small graph of this. I'm sure there are better graphs than this though...Shniken1 (talk) 23:21, 6 February 2008 (UTC)

Catalase is constructed of four identical subunits, so I think it's a safe bet it has four active sites. As for the pH, the value given in the Catalase article has been changed so many times (without changing the citation!) that I have no idea what it should actually say. I've looked on the google scholar, but found a lot of conflicting information (a lot of studies were also on different catalases). Someguy1221 (talk) 23:19, 6 February 2008 (UTC)

The BRENDA enzyme database points to a JBC paper [1], which gives a pH optimum of 7.5 for Escherichia coli catalase (note that catalases from other species may have different pH optima). Looking at the pH vs. activity graph (Figure 6, black circles), there's little change in activity between 6 and 7.5. It would probably be most correct to say that catalase has a broad pH optimum, centered around pH 7 or so. -- 128.104.112.12 (talk) 00:00, 12 February 2008 (UTC)

23.5°

Hello. I know that Earth's ever-changing axial tilt is 23.439281°. However, according to my school textbook, Earth's axial tilt is 23.5°. Assuming that Earth is on a 23.5° tilt, why are the latitude distance between the North Pole and the Arctic Circle, Earth's axial tilt, and the most northerly latitude where the Sun's vertical rays reach on the Summer Solstice all 23.5°? The figures may be approximate. Thanks in advance. --Mayfare (talk) 22:13, 6 February 2008 (UTC)

Does this maybe have something to do with precession? —BradV 22:40, 6 February 2008 (UTC)

I don't believe precession is relevant here. Rather, it's the geometry of the Earth's tilt relative to its orbit about the Sun. Assume for illustration that the axial tilt is 0°. In this case, the North Pole is the point at which the Sun never rises above the horizon (assuming a point-source Sun) and the Equator marks the arc where the Sun's rays fall vertically. Right? Now let's add the Arctic Circle and the Tropic of Capricorn, without adjusting the axial tilt. The AC is an "arc" at the Pole, and the ToC an arc directly over top of the Equator. Next, let's bump the axial tilt up to 5°. Now at mid-winter the North Pole is 95° off the angle of the Sun's rays, making the Sun-on-the-horizon limit (90° off the ray angle) at 85° latitude. This becomes the line we define as the Arctic Circle. Similarly, at the summer solstice, the Equator is -5° above the ray angle, making the Sun-directly-overhead limit at 5° latitude -- what we define as the Tropic of Capricorn. This 5° relationship (or the 0° relationship in the simplified example) exists because the axial tilt defines other parameters you're asking about. — Lomn 23:44, 6 February 2008 (UTC)

On a marginally-related-at-best note, I would caution you to beware of false precision when claiming that you "know that Earth's ever-changing axial tilt is 23.439281°." As you've noted (in the phrase!), it's changing, and 8 significant digits are unlikely to be correct. Measurable nutations cycle in as little as 6 days. — Lomn 23:51, 6 February 2008 (UTC)

The Earth wobbles, and wobbles.--Shantavira|^{feed me} 08:16, 7 February 2008 (UTC)

Evaporation of sea water

If there were no rain and if all the rivers on earth were to stop flowing to the oceans for ONE day, how much of sea water would evaporate? How much would the sea level lower? 128.163.80.161 (talk) 22:22, 6 February 2008 (UTC)

Without rain there would be little or no evaporation, as the atmosphere would quickly reach saturation. The article Water cycle says that a total of 505,000 km³ of water falls as precipitation each year, which would be the same as the total annual evaporation. On an average day then there is a total of 1,383.56 km³ of evaporation. I don't know what percentage of that comes from the ocean, but I imagine it would be in the order of 90%. —BradV 23:03, 6 February 2008 (UTC)

If we taken the premise of the question as actually possible I would imagine a lot of water would start being lost to space. Water is a VERY good green house gas and the earths temperature would increase significantly and the water molecules may get hot enough to be able to escape the earth.Shniken1 (talk) 23:10, 6 February 2008 (UTC)

Following on from the first response. If there is 1,383.56 km³ of evaporation, and the water surface of the earth is approximately 361,132,000 km² (from Earth), then the average lowering of sea level will be 1383.56/361132000 = 3.83e-6 km, which is 3.83 millimeters.--Dacium (talk) 23:23, 6 February 2008 (UTC)

Thank you all!128.163.174.150 (talk) 23:20, 7 February 2008 (UTC)

NEWTONS LAW 1 AND 2 QUESTIONS FROM THE PHYSICS MAGAZINE GUY

Hey,it`s Me The Physics Magazine I`ve got some questions for you. the unbalanced force required to accelerate a 2.0 kg mass at 4.0m/s is a 6.0 n b.2.0 n c 8.0 n d 16 n a force of 10.n applied to a given mass accelerates it at 1.0 m/s.the same force applied to a mass one-half as great would produce an acceleration of 1.0 m.s squared 2.0 m.s squared 0.50 m.s squared 4.0m/s squared a certain net force causes a 10.kg mass to accelerate at 20.m/s squared.the same force will cause a 5.0 kg mass to accelerate at 9.8m/s squared 10.m/s squared 25 m/s squared 40.m/s squared. a 30 kg child exerts a force of 100 n on a 50 kg object.the force the object exerts on the child is 0.0n 100n 980n 1500n if the mass of an object is decreased,it`s inertia decreases increases remains the same if the net force applied in the direction of motion to a certain object on a horizontal fritctionless surface is doubled,the acceleration of the object is halved doubled unchanged quadrupled a car whose mass is 2000 kg is accelerated uniformity from rest to a speed of 15m/s in 10.s on a level highway.the net force accelerating the car is 2000n 3000n 20,000n 30,000n if the sum of all the forces acting on a car is zero,the car must be at rest may be at rest must be moving at a constant speed must be accelerating which of the following is equal to one newton kg.m/s kg.m kg.ms 2 kg/ms 2 if the magnitude of the gravitional force of earth on the moon is f,the magnitude of the gravitional force of the moon on earth is smaller than f larger than f equal to f there is also a series of questions,about the asteriod apophis,which set to hit the earth on april 13,2029. a force of 10.n appiled to a given mass accelerates it at 10 m/s squared.the same force to a mass of one half as great would produce an acceleration of 1.0 m/s squared 2.0 m/s squared 0.50m/s squared 4.0m/s squared a certain net force causes a 10.kg mass to accelerate at 2.0 m/s2. the same force will cause a 5.0 kg mass to accelerate at 9.8 m/s squared 2.0 m/s squared 0.50 m/s squared 4.0 m/s squared a certain net force causes a 10 kg mass to accelerate at 20.m/s squared.the same force willcause a 5.0 kg mass to accelerate at 9.8 m/s squared 10 m/s squared 25 m/s squared 40m/s squared a 30 kg child exerts a force of 100 n on a 50 kg object.the force the object exerts on the child is 0.0n 100n 980n 1500n if the mass of an object is decreased,it`s inertia decreases increases remains the same if the net force applied in the direction of motion to a certain object on a horizontal fricionless surface is doubled,the acceleration of the object is halved doubled unchanged quadrupled a car whose mass is 2000 kg is accelerated uniformity from rest to a speed of 15 m/s in 10 seconds on a level highway.the net force accelerating the car is 2000n 3000n 20,000n 30,000n if the sum of all the forces acting on a car is zero,the car must be at rest may be at rest must be involving at a constant speed must be accelerating which of the following is equal to one newton kg.m/s kg.m kg.m/s squared kg/m.s squared the weight of an apple is closet to 1n 9.8n 19.6n 980n on the surface of a distant planet a 5kg mass weighs 20n.what is the acceleration due to gravity on that planet 0.25m.s squared 1m/s squared 4m/s squared 15 m/s squared the unbalanced force required to accelerate a 2.0 kg mass at 4.0m/s squared is 6.0n 2.0n 8.0n 16n —Preceding unsigned comment added by Yeats30 (talk • contribs) 23:49, 6 February 2008 (UTC)

Please don't yell at us, Physics Magazine Guy. Maybe try to make your question a bit more readable? And did has anyone established if this magazine is real yet? --Emery (talk) 00:02, 7 February 2008 (UTC)

Changed post to lowercase - much easier to read. By the way, this looks a lot like homework. —BradV 00:13, 7 February 2008 (UTC)

Thanks BradV and, how did you do that! --hydnjo talk 03:02, 7 February 2008 (UTC)

If you're on something unixy, pasting the post into "perl -ne 'print lc'" will lowercase it. --Sean 14:55, 7 February 2008 (UTC)

What I actually did was less impressive. I copied the text into OpenOffice and used the change case feature. —BradV 21:26, 7 February 2008 (UTC)

Indeed, it is. It's a direct copy and paste job from here. TenOfAllTrades(talk) 01:05, 7 February 2008 (UTC)

Thanks TOAT for your vigilance and researching. --hydnjo talk 02:53, 7 February 2008 (UTC)

(edit conflict) Wow! PMG, shame shame. What physics magazine copies homework? Haha. Anyway, consider formatting the values in LaTeX mathematical notation using the tags <math>...</math>. It would be much easier to read. (By the way, don't cheat! You don't learn anything that way.) Zrs 12 (talk) 01:21, 7 February 2008 (UTC)

Yay Zrs 12! Thank you for your honest assessment. --hydnjo talk 02:39, 7 February 2008 (UTC)

To be honest I'm kind of disappointed. Up until now "Physics Magazine Guy" has been pretty careful not to let us know we were doing his homework. —BradV 02:58, 7 February 2008 (UTC)

For shame indeed. Not even the barest attempt to reformat the copied homework problems - a magnificent lack of effort. I second Zrs 12 - learning how to do the problems yourself will be much more rewarding, not to mention much more efficient!! --Bmk (talk) 07:06, 7 February 2008 (UTC)

On the other hand, Physics Magazine Guy, I encourage you to come back here with specific questions about problems after you've tried them yourself. Or ask your teacher for extra help. --Bmk (talk) 21:28, 7 February 2008 (UTC)

I second that, BMK. However, PMG, we are here to help, but not just blatantly give answers. Zrs 12 (talk) 03:11, 8 February 2008 (UTC)

You're right... I searched last time and had a look at the site and haven't yet found where the previous question on dropping a penny and a Mexican hat came from. I guess what happened is he/she gave up trying to be sneaky after it became clear everyone was ignoring him/her anyway Nil Einne (talk) 06:37, 8 February 2008 (UTC)

February 7

Tornados in the American South - why?

Tornados in the American South - why? Why do severe tornados occur in the Southern USA in about 5 states (Arkansas, Tennessee et al) and seemingly nowhere else in the world? Here in Australia, at about the same latitude in the Southern Hemisphere, and around the same land size, we get what we call “willy willies”, and they could hardly lift a paper bag off the ground (Think of the breeze blowing the plastic bag around in “American Beauty” and you’ll get the picture.) Is God punishing the South for some reason? Myles325a (talk) 00:15, 7 February 2008 (UTC)

See Tornado#Climatology and Tornado climatology. --Anonymous, 00:30 UTC, February 7, 2008.

Also see Dust devil to understand why willy willies are so different from tornadoes. --Allen (talk) 07:33, 7 February 2008 (UTC)

They're attracted to trailer parks? Meanwhile, also see our Tornado Alley article.

Atlant (talk) 18:42, 7 February 2008 (UTC)

I know you were just joking, Atlant, but we do have an article on tornado myths. This edit is more comprehensive, but unfortunately contained mostly copywrited information. Many of these myths were dispelled during the Super Outbreak of 1974. -- MacAddct  1984 ^{(talk &#149; contribs)} 19:25, 7 February 2008 (UTC)

If I remember rightly, Britain has more tornadoes per square kilometre per year than Tornado Alley, it's just that they're a lot bigger in the states. -mattbuck (Talk) 02:39, 10 February 2008 (UTC)

Batteries heating up

I bought a cheap portable fan yesterday which operates on two AA size batteries. I noticed after operating it for about 10 minutes that the batteries became red hot.They worked okay in a torch that I used them in previously, so I don't think they're defective. I have only seen this once before, in a TV remote control, in which the batteries heated up and died. The next set worked fine and no problems since. As to the fan, I let the batteries cool and they worked but the problem repeated. Is the fan likely to be the problem or the batteries? LuckyThracian (Talk) 01:06, 7 February 2008 (UTC)

Neither. Anytime you draw large current (usually when powering motors) the batteries will heat up, a lot. It might be possible that the fan is drawing too much current because parts of its motor winding is shorting out, but this is unlikly.--Dacium (talk) 01:41, 7 February 2008 (UTC)

Thanks, Dacium. I don't have much savvy on matters electrical so I don't understand how a motor can control what current is drawn. LuckyThracian (Talk) 01:51, 7 February 2008 (UTC)

Any time you ask an electrical device for physical movement, you're going to use relatively big power. AA batteries can light a few LEDs or beep a peizo element till the cows come home, but a motor is a whole nother animal. In fact, if you stop the motor with your hand, the battery sees basically a length of copper wire to ground and will heat up pronto. Dacium is right that you can expect the batteries to get pretty warm (read "hot"), but I would say that "red hot" is too hot (I know that that was an exaggeration, but, still). Rarely is a non-rechargeable battery bad in such a way that it gets hot, although your anecdote about the remote control seems to be that. It's more likely to my mind that the fan is poorly designed or defective. --Milkbreath (talk) 02:17, 7 February 2008 (UTC)

Well, they became literally too hot to hold (if not red)! Okay, so the fan is likely the problem. What I can't understand is why the motor's defect affects the batteries. If it ran slowly or not at all it would make sense to me, but to run at the right speed and heat the batteries? Is it that the inductive coils in the motor determine the rate of rotation of the shaft by their length and force the batteries to discharge at an excessive rate? LuckyThracian (Talk) 02:40, 7 February 2008 (UTC)

What sort of motor is it and how big is the fan? Does it say what power rating it is? Most likly any batteries you put in it are going to get hot (do you have a thermometer?). Batteries are usually used for low current, but a fan motor is high current. If the motor is defective, it will draw excess current. A motor is basically a coil of wire. If the motor did not spin, a huge amount of current would just flow through the wire (this is why you never stop the fan spinning with your hand and hold it there, as the motor will burn out as large amount of current is flowing). As the fan spins up a back emf forms and reduces the current draw. If the motor is defective (in that some of the windings are shorted out) then the back emf will be reduced and the resistance of the motor will be reduced and excess current will be drawn, which heats the battery. Personally I don't think you have anything to worry about. I would imagine the fan needs quite a lot of current and batteries getting hot is normal.--Dacium (talk) 02:54, 7 February 2008 (UTC)

The fan's only a tiddler with plastic casing and "blade". It's made in the shape of a standard desk-top fan but it's only got an 8cm diameter fan-blade and stands about 18cm in height. I was just intrigued by the heating effect - I only paid $3.00 for it and the motor is just the sort you'd find in a lot of small appliances, about 4cm long. Thanks for your time..I'm going to read up on EMF etc. This seems to be one of the hardest things in applied science to get one's head round. LuckyThracian (Talk) 03:21, 7 February 2008 (UTC)

You took some good steps trying to figure this out, by testing the batteries in a tourch and by noting that the fan only cost $3. Some other questions to ask are, did the fan ever work well, or is it only with these batteries that it draws too much power? Normally, I'd suggest trying different batteries, but considering how cheap the fan is, and that it is likely to be no good, and how expensive batteries are these days, I'm not sure I'd bother trying new batteries. --Gerry Ashton (talk) 07:57, 7 February 2008 (UTC)

Here's how to think about the current consumed by an ordinary DC motor: The motor, when spinning, also acts like a generator, generating a voltage that opposes that flow of electric current that the batteries would normally cause. (This is called a "counter EMF".) But the generator isn't 100% efficient so if the motor is running on (say) 3 volts and turning n RPMs, the generator only manages to generate (say) 2.5 volts. That leaves 0.5 volts to flow through the resistance of the motor's copper windings.

What this means is that a free-spinning motor draws relatively little current because its virtual generator manages to generate a counter EMF that pretty-closely approaches the voltage applied to the motor. But as you add load to the motor and the motor turns more slowly, the output voltage of the virtual generator also drops, and there's more voltage left to appear across the resistance of the motor. Stop the motor dead, and the virtual generator output stops entirely; the motor now draws current equal to V/R and the batteries die quickly.

Your fan is probably putting a pretty heavy load on the motor and so the motor is turning a lot more slowly than it would turn if it were not loaded at all.

Atlant (talk) 18:38, 7 February 2008 (UTC)

As mentioned earlier, there might be a short in the motor, or the motor and fan might have excess friction. Does it spin freely without the power on, or does it take some effort to turn it? Small batteries have operated a portable cassette recorder for quite a long time, and it has a motor. I personally would measure the current draw and compare it to the amp-hour rating of the batteries. If they are getting too hot to touch, they will probably be discharged in minutes rather than hours. Edison (talk) 01:12, 8 February 2008 (UTC)

I was off-wiki for a couple of days and just read the further comments. Thankyou all for your assistance. LuckyThracian (Talk) 04:25, 11 February 2008 (UTC)

Olympus Mons climb

Based on an earlier discussion here, what could an interplanetary mountain climber preparing to climb Olympus Mons expect? Off the top of my head I'm thinking lava-flow, dust-storms, drastic changes in temperature from night to day... The air is less breathable there than on Everest, I'm assuming? What kind of gear would such a climb require? Does such gear exist? Wrad (talk) 01:09, 7 February 2008 (UTC)

The atmosphere of Mars is predominantly carbon dioxide; at mean surface level the pressure is a little under 1% of the atmospheric pressure on Earth. At the peak of Olympus Mons – 27 km above Mars' mean surface level – the pressure is even lower: one-tenth to one-twentieth the pressure at the base of the mountain. In other words, the air isn't breathable at the base or the peak of the mountain; it's pretty much a dirty vacuum. Even if the pressure were high enough, the carbon dioxide would kill you. To breathe anywhere on Mars you're looking at a spacesuit.

The 'climb', such as it is, would at least be easy. It's a long hike from base to summit (close to 300 km) but it's not a difficult trek. The slope (typically less than five degrees) is extraordinarily shallow. (For comparison, parts of the climb up Everest are at 50 degrees or worse.) As an added bonus, you get to do the whole climb under gravity that's only a third as strong as Earth's. Now, you might have some tough climbing if you decided to explore the crater/caldera complex at the heart of Olympus Mons. There you've got craters and canyons with sheer drops of thousands of meters. TenOfAllTrades(talk) 01:32, 7 February 2008 (UTC)

because of the atmosphere (or lack of one) duststorms probably won't be a factor. Nor will the weather, as there is little to transfer heat away from you. If you have a suit that survives on the surface it shouldn't be a problem on the summit.--Dacium (talk) 01:44, 7 February 2008 (UTC)

Five degrees isn't as shallow as it sounds -- about a nine percent grade, which is a bit of a slog if you're biking it (on Earth) for more than a mile or two. But I agree it's shallow for straight up the mountain. --Trovatore (talk) 01:46, 7 February 2008 (UTC)

For bicycling, perhaps five degrees isn't shallow, but for hiking, it's easy enough. I don't consider a slope "steep" until it reaches about ten degrees. --Carnildo (talk) 21:11, 7 February 2008 (UTC)

Actually, "Mars ... has the largest dust storms in the Solar System". So large, in fact, that they can cover the entire planet, although I believe at least sometimes the summit of Olympus sticks out the top. Confusing Manifestation(Say hi!) 03:36, 7 February 2008 (UTC)

Perhaps a pressure suit of the grade used in aircraft would suffice for the Martian atmosphere. Retarius | Talk 03:46, 7 February 2008 (UTC)

I would be most worried about the radiation - at it's lowest level, it's not too bad, but if a solar flare hits (small ones occur every few days on Mars, and bad ones every few weeks), or even worse, a solar proton event, you can get cooked pretty good, although only the latter would be likely to kill you on the spot - the rest would probably just shorten your expected lifespan by a lot. And there's unfortunately not a lot that you can do, unless there's a nice deep cave handy (unlikely). --Bmk (talk) 06:58, 7 February 2008 (UTC)

"Largest dust storms" is quite misleading. A Martian dust storm may cover a huge fraction of the planet, but the thin atmosphere means that the dust is equally thin. It would be more accurate to compare it to an overcast day or a light fog than to an Earth duststorm. --Carnildo (talk) 21:13, 7 February 2008 (UTC)

Lava flows are not a risk. Olympus Mons has been extinct for a long, long time. Algebraist 10:20, 7 February 2008 (UTC)

(The same goes for the rest of Mars; Mars is thought to be entirely inactive, geologically. --Bmk (talk) 18:01, 7 February 2008 (UTC)

Mars is actually quite similar to the Moon (Earth's Moon, that is) in many respects. Thus, the gear used for the Moon landings would certainly work on Mars. Solar radiation is definitely a threat; however, there are warning systems for solar flares / CMEs so taking cover seems possible. One would certainly need a pressurized transport vehicle of some sort: to hold supplies, to house the communication equippment, and, most important, to change the spacesuit (or at least the diapers) every few hours. I do not know if such a vehicle would provide a sufficient protection from the Solar radiation, but it probably would provide some protection at least. (Note: ISS is not a good example, its orbit lies within the Earth's magnetoshere so the conditions there are quite different). Note also that Moon EVAs took less than 8 hours each, on every mission so far (Apollo 11,12,14-17); I don't think one can (or should) design a suit that would last much longer, for it probably will be very, very cumbersome and uncomfortable. Cheers, --Dr Dima (talk) 14:09, 7 February 2008 (UTC)

Hmm, with such low gravity, would the fall into one of those canyons of a 1000 meters kill you? How far could you safely fall? Snorgle (talk) 16:39, 8 February 2008 (UTC)

Martian gravity is about a third of Earth's, so a rough estimate is that you can survive a fall three times higher. --Carnildo (talk) 21:21, 8 February 2008 (UTC)

A 1000 meter fall on Mars would result in you hitting the ground at a higher velocity than a similar fall on Earth. Earth atmosphere prevents you from accelerating indefinitely. The terminal velocity for a human on Earth is 50-60 m/s, so most of the 1000 m fall on Earth you move approximately at that constant velocity, until you hit the ground. Mars atmosphere OTOH is far less dense, so the terminal velocity on Mars is higher. Neglecting Mars atmosphere effect altogether, your vertical velocity after 1000 m fall would be about 80 m/s. --Dr Dima (talk) 07:22, 9 February 2008 (UTC)

Device to locate devices

Is there a device that can scan and locate electrical devices (cell phones, tape recorders, PCs - whatever) running near it?217.168.0.55 (talk) 04:44, 7 February 2008 (UTC)

You could try looking around in Technical Surveillance Counter-Measures; many of the devices designed to sweep for listening devices could be applied to many electrical devices. I think Nonlinear junction detector is a particularly cool one (and probably the best answer to your question that I've found). --Bmk (talk) 06:39, 7 February 2008 (UTC)

Actually, after reading more, it seems that it is kind of impractical, and difficult to use. --Bmk (talk) 06:41, 7 February 2008 (UTC)

I personally am looking forward to the day when every object I own is tagged with an RFID tag and I can just walk around the house with a scanner to find my glasses. --Sean 15:02, 7 February 2008 (UTC)

But can you find the scanner without your glasses ? Gandalf61 (talk) 15:19, 7 February 2008 (UTC)

Most of us just depend on our spouses (etc.): "Honey, where'd I leave my glasses?" "Top of your head, dear!"

Atlant (talk) 18:27, 7 February 2008 (UTC)

properties of electromagnets?

can a bar magnet be turned into an electromagnet? would an electromagnet discharge its electricity to any conductive material that was grounded? and if so would there be a way to insulate the electromagnet so as to keep the electric charge and still have increased attractive forces?

Automatedlearner (talk) 06:02, 7 February 2008 (UTC)

You may want to read a bit about what an Electromagnet is. The magnetic field of a bar magnet (or ferromagnet) is basically produced by the magnetic fields of unpaired electrons in the bar; it's actually quite complicated, and it involves phenomena on many different length scales. The magnetic field of an electromagnet is generated by electriccurrents (not charge; an electromagnet need have no net charge to produce a magnetic field). As for whether a bar magnet could be turned into an electromagnet, the answer is...sort of, but probably not in the way you're imagining. Any conductive substance carrying an electric current produces a magnetic field, and is therefore an electromagnet, so you could use a ferromagnetic material to form an electromagnet. May I ask why you want to know? You seem to have something specific in mind. --Bmk (talk) 06:48, 7 February 2008 (UTC)

A bar or horseshoe shaped piece of iron or steel becomes an electromagnet when one or more turns of insulated wire are wrapped around it and electrical current flows through the wire. A strong electromagnet typically has a great many turns, perhaps in several layers. If a bar magnet were used to wrap the wire around, then the effect of the electromagnetism might add to or subtract from the magnetism originally present. A bar magnet would typically be steel or a "hard" ferrous substance which retains a portion of the applied magnetic field when the current is turned off. The electric current is a property under normal conditions of the wire wrapped around the bar of iron, not of the iron itself, so unless there was a short of the wire to the bar, it would make no difference whether the bar was grounded. An electromagnet can be made by wrapping insulated wire wrapped around an iron bar and connected to a battery (with suitable construction to avoid overheating or electric shocks) and with no ground connection whatsoever. An "electric charge" sounds like you have static electricity in mind, so please note that it is a current of electricity through the windings, not an electric charge, that creates the electromagnetism. Edison (talk) 01:07, 8 February 2008 (UTC)

How to select marker bits for data communication

Hi friends!, I have posted it under Science and computing section too. Since this type of question isn't common in this discussion room, I'm unaware of where to ask.ok I'm doing a master project in SDR using vlsi-fpga. Well, now the main issue is that I use some predefined values infront of the data stream. Data from codec is 32-bits(Lch&Rch). I place few bits as marker in front of this audio data to denote the reciver the starting point of my data since data has to be exactly placed in lch and rch of the codec. a single bit reversal or mis-match causes serious noise.Now what happens is that data bits sometimes happen to be the marker value and mimic the marker. So the reciver when tuned on, considers that data bits as marker and starts processing from that point.so next to this action, all info becomes useless. No matter it helps if i increase the marker bits!. Simply it adds overhead only!...Is there anyway tat using a special marker can help in receiving the data without these problems?...Any other new ideas if you think, please suggest me...Thanks —Preceding unsigned comment added by Balan rajan (talk • contribs) 06:53, 7 February 2008 (UTC)

Is your SDR Software defined radio? You will have to have some extra in your data stream to detect if you have got into an error state or not. Perhaps a cyclic redundancy check or parity. If you slip a bit or gain a bit you will have lost sync as well with lots of noise as a result. In some systems there is an extra out of band method to indicate the start of words, or there could be a superfame that contains data in a particular order. Then you have to align your superframe (eg in E1) There will also have to be a way to see if you have slipped a bit in that too. Graeme Bartlett (talk) 09:11, 7 February 2008 (UTC)

YEs, I am doing a project on SDR only. You are correct. there are very possibilities that the bits might slip or gain when sampled in the receiver unit. But how does a CRC check may gonna save this?. My intension is not the error correction or detection. Because I consider that a perfect synchronization will not generate any errors upon receiving except the medium which may generate noise. But however I will use digital modulation. So I guess I can avoid those noises easily. I couldbe wrong, but for now, I believe that I need a way to sync my pulses at the start. Is there any idea of using marker bits?...Any relevant article or information you suggest?....Thanks —Preceding unsigned comment added by Balan rajan (talk • contribs) 13:38, 7 February 2008 (UTC)

You could insert some simple logic in the data path coming from your codec to block the marker value. For example, if your marker value is #FFFFFFFF, then the logic could change all instances of #FFFFFFFF coming from the codec to #FFFEFFFE. This is unlikely to have an audible effect on the data, assuming that #FFFFFFFF corresponds to maximum amplitude. Then, when your receiver sees #FFFFFFFF, it knows that it cannot have originated from the codec so it must be a marker.

If you are not allowed to tamper with your data at all then the solution will be more complex, but it can still be done. You would need to use an escape sequence rather than a single marker value. --Heron (talk) 08:35, 8 February 2008 (UTC)

Thanks!...One bit slip in data is under tolerance... and it's not a CAA project :-) —Preceding unsigned comment added by 122.164.50.218 (talk) 05:50, 9 February 2008 (UTC)

biology

brieftly explain how concentration and temperature can influence the results of a clock reaction. —Preceding unsigned comment added by Mabetoa (talk • contribs) 10:43, 7 February 2008 (UTC)

There are various kinds of clock reaction. See chemical clock.--Shantavira|^{feed me} 13:56, 7 February 2008 (UTC)

Minimum amount of useful sleep?

First off, I just want to make clear that I'm not seeking medical advice. So let's say I set my alarm clock for 7am. However, I wake up at 6:30 because the phone rings, or there's a loud noise outside or whatever. It is worth going back to sleep for such a short period of time, or am I better off just getting up? What if I wake up 15 minutes before the alarm goes off? What's the minimum amount of time of useful additional sleep can a person get? --24.249.108.133 (talk) 16:20, 7 February 2008 (UTC)

Short periods of sleep can be very beneficial. See our article Power nap.--Eriastrum (talk) 16:36, 7 February 2008 (UTC)

I can tell you anecdotally that when such a thing happens to me, I often dream in that short amount of sleep between 6:30 and 7:00. This suggests that I am having REM sleep, which some theories consider a part of memory consolidation. Thus I would hypothesize that this small amount of sleep can be beneficial. I would also venture to say that the usefulness of the short sleep period may relate to the degree of wakefulness achieved during the interruption. I have seen bed partners wake up for very short amounts of time, appearing responsive, then fall immediately back to sleep, apparently deep, and not remember it in the morning. I have also been awakened and found myself unable to fall back asleep. Where you were in the sleep cycle when you wake up may also have a bearing on the answer to your question. I think the shortest answer to your question is probably, "it depends..." Tuckerekcut (talk) 16:39, 7 February 2008 (UTC)

I wouldn't say some theories consider REM sleep a part of memory consolidation, there is enough evidence from animal and human studies to state this as fact. --Rwst (talk) 18:02, 7 February 2008 (UTC)

I would disagree, to this day sleep physiologists disagree as to the purpose of dreams, non REM sleep and REM sleep. Scientifically, a fact is merely an undeniable observation that needs to be explained. Wisdom89 (talk) 18:37, 7 February 2008 (UTC)

Even minimal amounts of sleep like microsleeps can be physiologically significant. The question in your case is if you are able to fall asleep again in such a short period of time. If you need to go on without too much sleep, I can recommend the caffeine nap cited in powernap, specially if you suffer from jet leg or need to regulate abruptly your sleep pattern. Mr.K. (talk) 19:54, 7 February 2008 (UTC)

Regarding the statement above that dreams can occur, indicating REM sleep, during end-of-the night brief sleeps, there was a very funny radio play on National Public Radio in which someone was hitting the "snooze" button repestedly to get additional napping and having vivid dreams, the end of each incorporating whatever the commentator or newsman was saying when the radio came back on (dreams can swerve abruptly to incorporate environmemtal stimuli in a vain effort to maintain the sleep state). Edison (talk) 00:58, 8 February 2008 (UTC)

Disowning our distant relatives.

I realise that by definition this isn't really science, but I was hoping some biologists would have an answer. Is there a dominant creationist position on the other members of the homo genus? Is there an explanation commonly given for the remains? AlmostReadytoFly (talk) 18:18, 7 February 2008 (UTC)

My guess would be that most creationists would refuse to accept one of the following 1.)That they are our extinct ancestors (just as much as they do not accept apes, monkeys and humans evolved along parallel lines) 2.)They aren't as old as the carbon dating techniques used tell us. Wisdom89 (talk) 18:34, 7 February 2008 (UTC)

Those that reject the fact of evolution may often use the vague and undefined term "kinds". Something I've just thought of, even usage of the biological classification system is acceptance of evolution through biological and genetic relationship to other species. -- MacAddct  1984 ^{(talk &#149; contribs)} 18:55, 7 February 2008 (UTC)

Elaboration: Also, creationists assert that every living animal existed at the same time. So they may not deny that Neanderthals existed, but they will deny a common ancestor with homo sapiens (or any species, for that matter). -- MacAddct  1984 ^{(talk &#149; contribs)} 19:02, 7 February 2008 (UTC)

Taxonomy (biological classification) existed long before any theory of evolution (Linneaus was a creationist, of a sort). Evolution means you believe the taxonomic tree is fluid and related; creationism implies that you do not, that you believed in "fixed kinds". That the kinds should look similar, for a creationist, simply implies they were fashioned by the same hand. Just pointing that out. That a "fixed" or creationist view would have held on for so long even among imminent biologists (who were in many cases not wed at all to Biblical literalism) makes more sense when you think about how biologists interacted with the idea of species—not as some sort of flexible collection of all life, but as a real marker of difference between very different types that, as far as they could tell, always "bred true" to their type no matter what. It's wrong, but it's not nonsensical. --98.217.18.109 (talk) 00:25, 8 February 2008 (UTC)

Wisdom89, I must correct you. Humans ARE Apes. See, Great Apes. 64.236.121.129 (talk) 19:23, 7 February 2008 (UTC)

Good catch, that was actually just semantics on my part, but thanks for the correction ; ). My point was that creationists deny common ancestry, or the ancestral gene pool, and therefore disavow organisms sharing extinct ancestors - in this case it would be an extinct ape. Yes? Wisdom89 (talk) 19:28, 7 February 2008 (UTC)

Actually, when they get close enough looking to humans, most creationists argue that they are humans. Neanderthals simply had some sort of bone disease and scientists are cherry-picking the data to make it seem as if there were a group of them living together for longer than the real age of the earth. — Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 20:52, 7 February 2008 (UTC)

Oh, that's right, Lucy just had a really bad case of rickets -- MacAddct  1984 ^{(talk &#149; contribs)} 21:03, 7 February 2008 (UTC)

talk.origins has a nice table on the different classifications of different finds by different creationists. --Stephan Schulz (talk) 21:14, 7 February 2008 (UTC)

My impression is that you can't paint the beliefs of all evolution-deniers with the same brush. Being ideologically obliged to refute easily verifiable facts (e.g., that some stars are more than 6000 light-years away) has unsurprisingly led them to a variety of creative interpretations of the facts on/in the ground. --Sean 21:21, 7 February 2008 (UTC)

Don't you know? God made the stars with the light sticking out! --Carnildo (talk) 21:29, 8 February 2008 (UTC)

Calculating the speed at which pressure travels

If I open a long pressurised tube on one end, how long does it take for the pressure to change on the other side of the tube? I realise the answer will be a function of the length, diameter, initial pressure, viscosity, tube roughness and such, but I'm having trouble finding an equation to use.

For example, if a 100 metre long tube is filled with pressurised air to a pressure of 5 bar, and one end is opened, how long does it take for a noticable change to occur on the other side (apart from the pressure wave of course, which will travel at the standard speed of sound).

Thanks in advance. -- Ec5618 19:40, 7 February 2008 (UTC)

I think you're looking at it the wrong way. It's not the pressure that's traveling, it's the substance itself. I would suggest reading into fluid dynamics -- MacAddct  1984 ^{(talk &#149; contribs)} 20:07, 7 February 2008 (UTC)

The speed of sound is the rate at which pressure changes propogate through the medium. Dragons flight (talk) 20:21, 7 February 2008 (UTC)

• You seem to have a pretty good idea of all the variables involved already; I would add that your particular definition of "noticeable" change is also going to affect the answer. You have correctly noted that the pressure wave travels at the speed of sound. We can be reasonably confident that nothing will happen faster than the sound speed, so one possible answer is that with a sufficiently good sensor, you'll see some effects starting at one sound-propagation time after the other end opens.

We can also put a lower bound on how fast the tube will reach atmospheric pressure. Unless you have some fairly unusual circumstances, the air exiting the tube at the open end won't travel faster than the sound speed. When the fluid velocity reaches the sound speed, you'll have a shock wave at the exit and you'll get "choked flow". —Preceding unsigned comment added by JohnAspinall (talk • contribs) 20:44, 7 February 2008 (UTC)

If you want to go farther, you might be able to find that someone has already done the experiments or written the computer models that could give you a more comprehensive answer (say, pressure as a function of time). This kind of question is fairly common in modelling the safety of things cooled by forced heat transfer. For example, a reactor safety engineer might ask what happens when a pipe carrying the high pressure and temperature water cooling the reactor, breaks? How long before heat transfer to the pipe is lost? Try searching for "reactor safety" and "blowdown experiment".

If you are really ambitious (and have the programming chops), you could write a simple computer model yourself. If the pipe is long, compared to its diameter, a one spatial dimension model is probably pretty good. You will end up with coupled first order hyperbolic PDEs in three state variables such as density, velocity and enthalpy for example. The classic text for all this stuff is "BirdsFoot". JohnAspinall (talk) 20:26, 7 February 2008 (UTC)

Tandem genes

I saw a special about how they are now specially breeding dogs to meet specific needs. One thing they talked about is tandem genes and how these repeating ACTG's are constantly repeating. They mentioned how it is these genes are repsonsible for physica traits at least they say when they change them there is a change in the physical appearance (i.e. the snout will be turned up or down, same thing with the tail. My question is how do they know which part of the repeating code to change and what method do they implore to cause the changes to take effect? Also a quick side note, supposedly there is a small change or difference in the repeating act's that is changed I am not sure if the location on the chromosome and which chromosome strand the tandem genes are located on make a difference or have an effect with the physical appearance. —Preceding unsigned comment added by 67.127.175.202 (talk) 21:36, 7 February 2008 (UTC)

It's unclear if you mean tandem repeats in a gene or tandem genes. As far as breeding is concerned they would use the phenotype so they would not need to know the specific DNA sequences that are being selected (as breeders have always done). Or are you impying these breeds are being genetically engineered? —Preceding unsigned comment added by David D. (talk • contribs) 22:42, 7 February 2008 (UTC)

I just did a quick google and you do mean tandem repeats. Here is a nice discussion on the topic. David D. (Talk) 22:47, 7 February 2008 (UTC)

I believe the breeds were being genetically engineered. How would that change the situation of the approach taken to change the repeats, which part of the repeats would be changed? Would it be a possibility that somewhere in the hundreds of repeats a piece of the code was not a repeat or the same? —Preceding unsigned comment added by 67.127.173.111 (talk) 19:00, 9 February 2008 (UTC)

Sounds like they know the effect that different numbers of repeats have on various breeds. Genetically engineering the desired number of a repeats in a specific breed it will speed up the breeding process dramatically rather than having to wait for a natural variant in the repeat number. I don't know enough about the specific function of the tandem repeats to know if having a insert that is not the same as the repeats would have a dramatic effect or not. David D. (Talk) 22:38, 11 February 2008 (UTC)

is eating potato skins unhealthy?

Is it unhealthy to eat the skin of, say, a baked potato?

Thank you! —Preceding unsigned comment added by 212.51.122.26 (talk) 21:44, 7 February 2008 (UTC)

Assuming the potato has been washed prior to baking, no. --LarryMac | Talk 21:47, 7 February 2008 (UTC)

Actually, green potato skins have glycoalkaloids, a toxin. See: Potato#Toxic_compounds_in_potatoes David D. (Talk) 21:49, 7 February 2008 (UTC)

wow, those two seem like pretty opposite opinions! So, which is it? Can we have a reference for the former? The fact that thiere is a toxin in it doesn't mean anything, there's also gold in my dog's feces. The question is 'how much'. So is eating a potato unhealthy? —Preceding unsigned comment added by 212.51.122.26 (talk) 21:58, 7 February 2008 (UTC)

Note: green potato skin does not equate to baked potato skin most of the time. As to how much, who can say, every potato has a different concentration. David D. (Talk) 22:15, 7 February 2008 (UTC)

In the section that David D. linked, it specifically says "The National Toxicology Program suggests that the average American consumes at most 12.5 mg/day of solanine from potatoes (note that the toxic dose is actually several times this, depending on body weight). Dr. Douglas L. Holt, the State Extension Specialist for Food Safety at the University of Missouri - Columbia, notes that no reported cases of potato-source solanine poisoning have occurred in the U.S. in the last 50 years and most cases involved eating green potatoes or drinking potato-leaf tea." (emphasis added). It also states that the glycoalkaloids are broken down by high heat. Baking involves high heat. And it states the differences between the amounts of those compounds in wild and farmed potatoes, so your question of "how much" has been addressed.

Original research time - 1) I have eaten more than my fair share of baked potato skins in my life, and I'm still typing nearly 50 years on. 2) Some people make an appetizer of "potato skins" which are mostly devoid of potato, but full of cheese and bacon. It's those last two that are going to kill you, not the potato skin. 3) I could stop at the supermarket on my way home and buy redskin potato salad, which is made with chunks of potatoes that have their skin still attached. It is not likely the supermarket would be selling me toxic food. --LarryMac | Talk 22:08, 7 February 2008 (UTC)

Dietitians might recommend against eating baked potato skins because of the concentration of fat. They might also recommend against eating potatoes at all, or at least limiting their ingestation, because of the starch content. But it would probably depend on the eater's dietary and metabolic circumstances. -- JackofOz (talk) 22:13, 7 February 2008 (UTC)

Fat? in potato - is this from added butter perhaps?87.102.118.73 (talk) 13:55, 8 February 2008 (UTC)

[Edit conflict]Yes, it is safe to eat potato skins. If you read the link David D provided above (in the Potato article), there have been no reports of potato poisoning in the US in the past 50 years. It seems that it is even safer if you store them in the dark (as light exposure can lead to increased glycoalkaloid concentration), and avoid green or spoiled potatoes, and always get rid of sprouts on the potatoes. It is even safer if you cook them (which, of course you would - who eats raw potatoes?). The Solanine article is a bit scary-sounding (solanine is the glycoalkaloid in potatoes), but the citation, found here, indicates that potatoes are perfectly safe to eat if you take routine precautions. If I were female and pregnant, I might avoid potatoes just to be on the safe side, since there have been some (inconclusive) indications of increased risk of birth defects. All this being said, nothing you find on this page, or anywhere else on wikipedia should be mistaken for reliable medical information. In short, I am a physics nerd having a little fun on wikipedia, not a toxicological expert. --Bmk (talk) 22:23, 7 February 2008 (UTC)

Good chance is that no one in the US eats green potato skins intentionally. David D. (Talk) 22:33, 7 February 2008 (UTC)

It is reasonable common to eat potato skins in other parts of the world. Personally I never peel potatos anymore or for that matter most vegetables. One of the reasons why it is a good idea to keep the skin on is because vitamins tend to be concentrated on the layer just under the skin so when you peel of the skin you are usually peeling of part of this layer as well. As others have stated, unless the potato is starting to green it will usually be fine. Nil Einne (talk) 06:15, 8 February 2008 (UTC)

Which is why potatoes are often peeled as the solanine is concentrated right near the skin as well. Note also that potatoes are commercially bred to minimize solanine levels. Rmhermen (talk) 23:21, 8 February 2008 (UTC)

Drugs and GI motility

So i've heard that opiates cause constipation. I was wondering why this is so because i thought opiates activated the parasympathetic nervous system, which increases G.I. motility. Also, i have been told coffee increases G.I. motility, and i know caffeine stimulates the parasympathetic nervous system which would decrease G.I. motility. Thank you very much for your time! 24.88.103.234 (talk) 22:31, 7 February 2008 (UTC)

One of the major opioid receptors, mu, located in CNS results in decreased GI motility. Wisdom89 (talk) 22:34, 7 February 2008 (UTC)

Thanks! Anyone know anything about the coffeee? 24.88.103.234 (talk) 17:12, 8 February 2008 (UTC)

It's been known for sometime that caffeine does have an effect on the GI system - The only effects that I can remember off the top of my head is stimulation of gastric acid secretion in the stomach (by increasing hydrogen Ion secretion from the stomach mucosa) and increased smooth muscle contractility. This link might be useful. [2]Wisdom89 (talk) 03:00, 9 February 2008 (UTC)

Which was the LCA of plants and animals?

So that's the question. When did the last common ancestor of plants and animals live, and what kind of form was it? Finally, if one were to list plants, fungi, protozoa, protists and monera in order of decreasing closeness to Animalia, what would it be like? Thanks. -- Leptictidium (mammal talk!) 23:13, 7 February 2008 (UTC)

I don't know the answer to the first question. But the second... choanoflagellates, which are protozoa, are thought to be more closely related to animals than are any other extant non-animals. But except for them, fungi are more closely related to animals than are any of the other groups. Monerans are more distantly related to us than are the other groups you named. As for plants and protists and protozoans, similar answers could be given, but I think the best way to understand the relationships is not to try to list these non-cladistic groups in order of relatedness, but rather to look at a phylogenetic tree and understand which groups these words refer to. --Allen (talk) 01:31, 8 February 2008 (UTC)

Actually, I think I may have made up that use of the word "non-cladistic." What I should have said is that the groups "protozoa," "protists," and "monera" are paraphyletic. --Allen (talk) 01:40, 8 February 2008 (UTC)

February 8

Does cheap alcohol get worse hangovers?

I have heard, for many years. from a variety of sources about how a good liquor doesn't cause hangover, and how if you consume cheap liquor you will get a hangover the next day. Is it really true? If so then why is it that? What is it about a well made liquor that makes the consumer less susceptible to hangovers? Thanks --Spundun (talk) 03:16, 8 February 2008 (UTC)

I initially thought that it was some stray methanol or something like that, that made it unhealthy, but the article Hangover doesn't even mention methanol. --Spundun (talk) 03:22, 8 February 2008 (UTC)

Really wierd,I was just looking at this article :D. It sort of does mention it:

In addition, it is thought that the presence of other alcohols (such as fusel oils), by-products of the alcoholic fermentation also called congeners, exaggerate many of the symptoms (cogeners may also be zinc or other metals added primarily to sweet liqueurs to enhance their flavor); this probably accounts for the mitigation of the effects when distilled alcohol, particularly vodka, is consumed instead. Other alcohols would include methanol i think.Shniken1 (talk) 03:27, 8 February 2008 (UTC)

Ahh, I just search for methenol and didn't find anything, thanks for pointing this out. So I guess thats it then? --Spundun (talk) 03:57, 8 February 2008 (UTC)

AFAIK, hangovers are caused by a slew of factors. First is the effect of the normal metabolic products of ethanol, specifically acetaldehyde poisoning. This effect will be the same for all qualities of drink, unless there is either already acetaldehyde or acetate in the beverage, or there is some compound in the drink which competes with the normal ligands for alcohol or aldehyde dehydrogenase. (Mmm, flagil beer...) This process utilizes NAD+, thus leading to a relative state of hypoglycemia, which in normal individuals will be very quickly remedied, but may nonetheless result in fatigue. Second, is the dehydration caused by diuresis via ADH suppression. Again, this effect will be the same with any quality of drink. Third, and this is where quality comes in, there are impurities in the beverage. Impurities include congeners, which are impurities coming from the processing and fermentation of the drink. The amount of congeners has less to do with the quality of beverage and more to do with type. Unflavored vodka, for instance, and distilled spirits have fewer congeners than simple fermented products like wine or beer. If I am being vague on explaining exactly what a congener is, it's because it's pretty much a catch-all term for various sugars, glycosylated compounds, metals, and organic junk that either taints or flavors your brew. However, congeners are not the only impurities present. There are also things that can form in wine and spirits after they have been opened, they are not immune to chemical activity after shipment. To go much more into this might constitute original research, but suffice it to say that in a perfect world, I would be sure to evacuate all carbon dioxide from my open bottles before storage. Looking back on this (probably partial) list of hangover causes, only one (the congeners) would have much of anything to do with price, and only then within certain classes of alcohol (one couldn't compare the hangover index of a riesling and a bourbon with respect to price). I suspect that if there is a relationship between price and hangover for certain types of alcohol, it has more to do with the expense than the quality. One does not do shots of maduro tequila, though I'm sure they would be very smooth. Tuckerekcut (talk) 17:53, 8 February 2008 (UTC)

My experience in this field is more on the practical research side rather than with the theoretical aspects, but the usual saying of those who should know is that the darker the alcohol, the more savage the hangover. The very worst is dark rum and brandy, and the most forgiving is the colourless vodka. And yes, it is the thousands of OTHER chemicals in the brew that irritate the system and cause the bad effects. Some drinkers aver (and I am one of them) that you won’t get a hangover on vodka. I also have noticed that red wine is a lot more brutal than white. It’s kind of commonsense really, but there is a good Scientific American article about it from the 1980s. Incidentally, one of the most poisonous of all brews is the famous absinthe (the original, which I don’t think is being produced anymore. Apart from a high alcohol content, it also has wormwood as an ingredient, a poisonous hallucinogen. This little number might just be the worst of those that have been sold legally. Wood alcohol will blind people, and the stuff the Russians and others concoct in illegal stills will do that and more. Myles325a (talk) 06:08, 11 February 2008 (UTC)

The dangers of Absinthe have actually been historically exaggerated. Someguy1221 (talk) 06:27, 11 February 2008 (UTC)

Permille

How is permille pronounced? Is it like per mill? I ask because this would be very confusing as per mL is commonly said as per mill and would be used in very similar contexts....Shniken1 (talk) 03:30, 8 February 2008 (UTC)

Per/ml (Permill) is kinda the colloquial way of pronouncing it - 1/1000 - I'm fairly certain that Permille is pronounced per milly - as "mille" means 1000. Wisdom89 (talk) 03:42, 8 February 2008 (UTC)

Actually, scratch that - mille is pronounced "mill" [3] Wisdom89 (talk) 03:43, 8 February 2008 (UTC)

duration of human pregnancy?

what is the mean and standard deviation of human pregnancy lengths?

I want to do the maths so I can go to my sister's city (a far trip) with 90% certainty that I will be there early enough for the birth. --Sonjaaa (talk) 04:54, 8 February 2008 (UTC)

Here's one source that says the mean for pregnancies that end in spontaneous labor at a hospital in India is 272 days, s.d. 9 days: [4]. Most other sources seem to give the due date as 40 weeks (280 days) after conception, and our article on pregnancy says that Sally Tracy says that 90% of births occur within two weeks of the due date. --Allen (talk) 05:25, 8 February 2008 (UTC)

Just to complicate things, some sources measure pregnancy from conception, others from the last period. I have also been told that "second babies are usually early", but no-one has ever been able to tell me whether that means that the median falls while the mean stays the same, or that the mean falls, but they can't be bothered to use a different distribution for bigravidity so they use one they know is inaccurate. Bovlb (talk) 06:25, 8 February 2008 (UTC)

Also, even if you determine the mean and standard deviation, I suspect that they might not characterize the distribution sufficiently. A lot more babies are born three months early than three months late. Bovlb (talk) 06:27, 8 February 2008 (UTC)

I don't think you need a mean - I imagine your sister will have a due date, which tells you her "individual" mean. A non-representative sample of my family agrees with the "two weeks either side of due date" window mentioned above, with first babies typically arriving after due date and second babies typically arriving before. In the UK, if a baby is not born by two weeks after due date then delivery is often induced. Gandalf61 (talk) 11:02, 8 February 2008 (UTC)

Which possibly explains why "second babies are usually early" :-) I know my own mother lied to the doctors about her due dates with later babies, since she knew they would induce if she overshot the date by too much. Or perhaps that's just my mum. Rather annoyingly, she then forgot when her actual due dates were, so we can't work out how late/early we were as guidelines for the future. 130.88.140.112 (talk) 14:43, 11 February 2008 (UTC)

Yes, (OR here) a number of mums choose a due date to suit them (to avoid or encourage induction etc); dates based on cycles can be inaccurate if the woman's cycle is anything other than very regular, and scan due-dates are based on average foetal measurements and thus are usually issued with a "+/- 5 days"-type proviso. On top of that, even if you get a precise due date, each woman has a different relationship betwen delivery/due date. eg. "I'm always early". "I'm always late" etc etc. Babies come when they want to. But if you have 4 weeks up your sleeve, then two weeks either side of the due date is your best bet. If less time, err on the side of late: at least then you won't miss meeting the baby. Gwinva (talk) 03:06, 12 February 2008 (UTC)

Just found this thread, hope you are still reading... 90% of pregnancies deliver within 2 weeks either way of the EDD (estimated date of deliver, or "due date"). That's still a window of almost a month to have a 90% chance of being there. --Ginkgo100^talk 03:50, 15 February 2008 (UTC)

Identify this Hibiscus

Which species of hibiscus is in this picture?

http://en.wikipedia.org/wiki/Image:Hibiscus1.jpg —Preceding unsigned comment added by 202.124.215.123 (talk) 08:24, 8 February 2008 (UTC)

Now THAT'S a pistil! Maybe you already guessed it's Hibiscus Rosa Sinensis or Chinese Hibiscus. Looks like they have frilled edges on the petals. Julia Rossi (talk) 10:05, 8 February 2008 (UTC)

Common corpse perception

There's a common idea that a corpse is noticeably heavier than when it was a living person. Tried cadaver/corpse/body but nothing – unless missed it. Is there any truth in that? Julia Rossi (talk) 09:49, 8 February 2008 (UTC)

Philip Marlowe says "Dead men are heavier than broken hearts", but I don't think he means they actually weigh more, they're just difficult to move around as they are an awkward shape (no handles) and don't make any attempt to help you. 163.1.148.158 (talk) 10:17, 8 February 2008 (UTC)

As a nurse of some decades I have had, unfortunately, to deal with corpses and this myth is of long standing. In my experience there is no evidence to show this to be true, I have never experienced any patient that felt heavier after death. What is often surprising is the weight of a limb or a head when the patient is dead - or unconscious - and this this may have led to this idea. You use the word 'noticeably' in your question which implies subjective assessment. This may be one of those self fulfilling myths. Perhaps a friendly morgue technician will be by in a while to give us some scientific evidence. Richard Avery (talk) 11:31, 8 February 2008 (UTC)

Perhaps its like a child that does not want to be picked up, it seems heavier beacause it is no longer supporting any of its limbs and is flopping around (when you move it, not on its own ;-)) 161.222.160.8 (talk) 18:52, 8 February 2008 (UTC)

I couldn't find any part of the decomp process making it heavier... The last time I heard of it was from a nurse who trained then left many years ago. I'm with the idea that an unconscious body is awkward and cumbersome to lift on its own as above, and kids are wise to this for sure. When people express the impression that a corpse is "so much heavier" it's often in connection with how many it takes to carry the coffin yet no-one likes to admit that it's the coffin making the difference! There;s a lot of subjectivity out there. : )) Thanks all, Julia Rossi (talk) 23:40, 8 February 2008 (UTC)

planetary orbit

has the planets in our solar system ever been perfectly aligned in orbit?

I would assume it was possible, since unless two planets are exactly in phase (eg the angle between them never changes), then eventually they ought to align at some point. It may take longer than the age of the universe, but theoretically it should happen. -mattbuck (Talk) 11:39, 8 February 2008 (UTC)

As the orbital elements are (assumed to be) real-valued quantities, there will never be "perfect" alignment (i.e. it's not impossible but the probability is 0). So there are only points in time at which they are very close to perfect alignment.

Now "perfect alignment" could mean several different things, e. g. that they are (or are closest to being) on a straight line or being in a straight line if projected onto some plane (e.g. Jupiter's orbital plane; the two things are not the same because the orbital planes of different planets are inclined against each other (also remember that the inclinations and the longitudes of the ascending nodes change over longer timespans)), or that they are within an angle as small as possible if viewed from the sun.

If we ignore the inclinations (because they are relatively small) as well as eccentricities and changes in orbital periods, we can make an estimate the time until they are aligned within an angle φ (as seen from the sun) in the following way:

The two outermost planets, Uranus and Neptune, have a conjunction every 172.7 years, a time which we call T_u. Saturn has a conjunction with Neptune every T_s = 36.2 years, Jupiter every T_j = 12.8 years, Mars every T_ma = 1.90 years, Earth every T_e = 1.01 years, Venus every T_v = 0.618 years, Mercury every T_me = 0.241 years. The alignment of the three outermost planets within an angle φ can statistically be expected after a time of (2*π/φ)*T_u. For all planets and a small angle φ (so small that even the innermost planet will have made a total revolution while the outermost passes the angle) this is (2*π/φ)⁶*T_u. If the angle is 10' = 1/6 ° = 10*π/(180*60) then the time is 1.75*10²² years - it has never happened. Icek (talk) 11:45, 8 February 2008 (UTC)

Actually, we can't assume it has never happened. Sure, the universe has only been around for 1.3*10¹⁰ years, and the solar system for 6*10⁹ or so, but without knowing what the initial conditions of the solar system are, we cannot say for sure that it hasn't happened and won't happen before the solar system is destroyed. Sure it's very very unlikely, but... -mattbuck (Talk) 12:05, 8 February 2008 (UTC)

http://www.abc.net.au/science/news/stories/s122109.htm Gzuckier (talk) 15:49, 8 February 2008 (UTC)

Now it's possible...when Pluto was a planet, it wasn't, because Neptune and Pluto are gravitationally synchronized (if I remember correctly...i think it's a 3:2 orbital ratio). -RunningOnBrains 16:36, 8 February 2008 (UTC)

I started to mention this, but started second-guessing myself. It's not that it's impossible when accounting for the orbital resonance (Pluto and Neptune must still cross paths) but it is highly restrictive in terms of where in the Solar System such an alignment could occur. However, even with that restriction, it's not clear to me that the alignment itself is any more restrictive than adding an arbitrary additional planet to Icek's math would be. Neptune and Pluto still align every X years, and it's just a matter of tacking that onto the MVEMJSUN requirements outlined above. — Lomn 17:14, 8 February 2008 (UTC)

Twisted transistors

I am doing engineering but I'm finding quite a bit of trouble to work with the damn transistors. Can anyone drop some good learning materials or something?Bastard Soap (talk) 11:14, 8 February 2008 (UTC)

What aspect of transistors is giving you trouble? And is it transistors in general, or is your difficulty presently limited to bipolar junction transistors or field-effect transistors/MOSFETs?

Atlant (talk) 12:34, 8 February 2008 (UTC)

Are your problems more along the lines of biasing the transistors, or soldering them? Edison (talk) 00:57, 9 February 2008 (UTC)

My problems are in calculating the currents and voltages in transistor circuits, which states should you assume them to be, that sort of things.Bastard Soap (talk) 15:57, 9 February 2008 (UTC)

Then you probably want to take a look at our article Bipolar transistor biasing. Also relevant are Common source, Common drain and Electronic amplifier. We can probably give you better help if you ask a more specific question, and specify the exact circuit you are trying to deal with. SpinningSpark 16:49, 9 February 2008 (UTC)

More common corpse perception

Similar to a previous question, "Common corpse perception", are there any reports of dead bodies becoming lighter? I once heard that a dead person is 39 grams lighter than when alive, and that this was somehow evidence of the soul (it leaves and less weight) 195.194.74.154 (talk) 13:03, 8 February 2008 (UTC)

ps: I'd like to meet a "friendly" morgue technician. Thus far, only Tru Davies seems friendly. 195.194.74.154 (talk) 13:04, 8 February 2008 (UTC)

Corpses definitely become lighter over time as fluids evaporate, various gases are formed and exit the body, and insects chow down and leave.

Atlant (talk) 13:06, 8 February 2008 (UTC)

See Duncan MacDougall (doctor) for the story of a doctor who 'proved' that the soul weighs 21 grams by weighing patients before and after death. AndrewWTaylor (talk) 13:16, 8 February 2008 (UTC)

MacDougall actually weighed six of his patients while they were dying, which is a bit creepy. He also did "control" experiments on dogs. This page at Snopes.com gives a summary of MacDougall's research methods. As our article on MacDougall says: "Although generally regarded either as meaningless or considered to have had little if any scientific merit, MacDougall's finding that the human soul weighed 21 grams has become a meme in the public consciousness". Gandalf61 (talk) 13:28, 8 February 2008 (UTC)

counselling

counselling has become popular, in all aspects of society, discuss this new trend, citing examples from the work place —Preceding unsigned comment added by 196.202.194.10 (talk) 14:02, 8 February 2008 (UTC)

This reads suspiciously like a homework question, which we won't do for you. What aspects of the counseling article do you find confusing or incomplete? We can assist with specifics. — Lomn 14:30, 8 February 2008 (UTC)

Gamma Radiation's effect on matter

When gamma rays pass through something like lead. The lead absorbs some of the radiation. What does this turn out as? Heat? Can gamma rays heat matter? 64.236.121.129 (talk) 14:29, 8 February 2008 (UTC)

Our article on gamma rays notes that three specific mechanisms occur, largely depending on the energy of the gamma ray. In all cases, though, it serves to ionize the matter it interacts with, often with additional lower-energy radiation produced in the process. Per the second law of thermodynamics, such interactions must result in heat, and thus matter can be heated by gamma rays, but this is not the primary mechanism. — Lomn 14:35, 8 February 2008 (UTC)

So the matter it touches, becomes radioactive? But that very same article says they use gamma rays to sterilize medical equipment, kill bacteria off of stuff, etc. But if gamma rays makes things radioactive, then that means all the stuff they are trying to clean with gamma rays becomes radioactive too. 64.236.121.129 (talk) 16:14, 8 February 2008 (UTC)

It means they tend to give off x-rays, but mostly just when they're being irradiated. They don't stay very radioactive afterwards. 81.174.226.229 (talk) 16:27, 8 February 2008 (UTC)

There's a distinction to be drawn between becoming radioactive and being irradiated. Gamma rays cause the latter, not the former. While the high-energy release is sufficient to mess up life processes (irradiation), it's not sufficient to mess up the fundamental atomic nature of matter (radioactivity). That's why it's safe to use as a sterilization process on non-living stuff. — Lomn 17:10, 8 February 2008 (UTC)

I wish the article on irradiation made that distinction a little clearer. It doesn't actually state that objects don't become contaminated or radioactive. 64.236.121.129 (talk) 18:31, 8 February 2008 (UTC)

So then the effect is mostly heat right? If you were to shoot a strong gamma laser at something... lets say a vehicle or a house, would it blow up? 64.236.121.129 (talk) 17:15, 8 February 2008 (UTC)

No, because there's no such thing as a gamma-ray laser (yet), and because there's no available source of gamma rays that strong, other than maybe a nuclear bomb (in which case the house would be blown up, but not by gamma rays).

The actual reason gamma rays are harmful to living things is that they are ionizing radiation and they can destroy molecules by breaking chemical bonds. If a DNA molecule in a cell is damaged, that can cause radiation poisoning or cancer. If a gamma ray hits some inanimate object, nothing spectacular will happen. —Keenan Pepper 17:36, 8 February 2008 (UTC)

Well first of all, I know gamma lasers or gasers, don't exist yet, but they are entirely possible. Next, I question your conclusion on inanimate objects. We have concluded that gamma rays will heat up matter, so there should be some effect I think. 64.236.121.129 (talk) 18:22, 8 February 2008 (UTC)

You could presumably heat things significantly with a gamma-laser of sufficiently ludicrous power, but you'd need a lot to overcome gamma-rays natural tendency to go straight through objects without noticing they're there. You'd do much better to shoot them with something they'll actually absorb most of. Algebraist 18:45, 8 February 2008 (UTC)

Exactly. If you want to blow stuff up, gamma rays are a nonsensical choice. Radiation damage is important for some applications (computer chips in satellites come to mind), but it's usually invisible to the naked eye. If I take a brick and subject it to the most intense gamma source on Earth for hours and hours, it might heat up a few degrees, but afterward it'll still be an ordinary brick. The only permanent effect the gamma rays will have is creating invisible microscopic defects in the crystals. —Keenan Pepper 19:25, 8 February 2008 (UTC)

To continue this, and use an example in a similar vein, a visible-wavelength laser will be far more effective than a graser because most materials won't pass visible wavelengths but will pass gamma rays. Note that laser cutting is well-established in the visible and near-visible wavelength range. Sci-fi likes applying grasers because it's usually accompanied by materials too tough for ordinary lasers to affect. — Lomn 19:34, 8 February 2008 (UTC)

So what kind of electro magnetic radiation heats stuff up the best in laser form? Just regular lasers? 64.236.121.129 (talk) 19:40, 8 February 2008 (UTC)

Anything that's fully absorbed by the material in question and minimally absorbed by the transmission medium (air). Get into a vacuum and you can chuck out the second concern. However, lasers are significantly inferior to other lower-tech devices when it comes to simply heating an object. Their energy is far too concentrated to be effective in this regard. A laser, for instance, could burn through your hand -- but a candle will warm your entire hand. — Lomn 20:23, 8 February 2008 (UTC)

That didn't really answer my question. 64.236.121.129 (talk) 21:17, 8 February 2008 (UTC)

Well, "regular lasers" is rather vague, and I'm not personally up on all the specifics. It's a matter of wavelength and energy, though. Gamma rays are too high-energy for efficient energy transfer. Radio waves are too long-wavelength. So a graser and a raser would both be poor choices. A red laser would be good (for a laser), as it penetrates air well and is absorbed quickly by most materials. Is it best (for a laser)? I have no idea. And then there's that massive "for a laser" caveat, as all lasers are relatively lousy heating elements. — Lomn 21:38, 8 February 2008 (UTC)

You really have to pick a substance before asking what will heat it up best. If you want to heat up organic matter very quickly, use a good carbon dioxide laser in the infrared band. If you want to heat up water very quickly, a maser in the microwave band does a nice job. And as you can tell with your own eyes, plenty of common substances absorb very well in the visible wavelengths. Someguy1221 (talk) 21:45, 8 February 2008 (UTC)

See Active Denial System. Gandalf61 (talk) 10:56, 9 February 2008 (UTC)

Wind loading

Im trying to find information about wind loading, I have to produce a banner that is 4 metres high by 3 metres wide, the banner will be attached to some poles (havent decided how many) but the overall thing needs to be heavy enough to not get blown over by the wind but light enough to be moved by hand by people. —Preceding unsigned comment added by 194.164.82.35 (talk) 15:25, 8 February 2008 (UTC)

i don't have any hard data, but that's going to be really unwieldly. suggestion: cut a lot of vent flaps into it, litle partial circles like 10 cm in diameter, to let the air through. Gzuckier (talk) 15:46, 8 February 2008 (UTC)

So that's what those holes are for. You learn something new every day, eh? 206.252.74.48 (talk) 16:07, 8 February 2008 (UTC)

Mass death of forest tent caterpillars

I live on (in?) Long Island, New York and every 10 years or so, during the spring, we get a population explosion of disgusting forest tent caterpillars (Malacosoma disstria). Then after a few weeks, they all suddenly die. It's almost as if a virus spreads through them all, causing them to ooze, shrivel up, and die. I guess it's possible that a pesticide was applied, but I don't think it was. Are there any known infections that would cause this? -- MacAddct  1984 ^{(talk &#149; contribs)} 15:25, 8 February 2008 (UTC)

There's maybe something here[5] in the article. Julia Rossi (talk) 02:37, 9 February 2008 (UTC)

Why is 98 degrees uncomfortable?

Why do people often find it uncomfortable when it's 98 degrees out? Since normal body temperature is 98~ degrees and all. Bellum et Pax (talk) 15:29, 8 February 2008 (UTC)

because your skin likes it to be cooler so it can unload the heat more efficiently. beside, your skin is lower than 98 degrees. Gzuckier (talk) 15:44, 8 February 2008 (UTC)

Remember that you generate body heat too, and need to get rid of it. 81.174.226.229 (talk) 16:15, 8 February 2008 (UTC)

It's 98.6 degrees to be more exact. 64.236.121.129 (talk) 17:13, 8 February 2008 (UTC)

98.6 is blood temperature; not skin temperature (except perhaps in very intimate places).--Shantavira|^{feed me} 17:40, 8 February 2008 (UTC)

When did I say 98.6 degrees was skin temperature? 64.236.121.129 (talk) 18:24, 8 February 2008 (UTC)

Normal human body temperature ranges over several degrees Fahrenheit. 98.6 is false precision. -- BenRG (talk) 20:55, 8 February 2008 (UTC)

Wow, I had no idea 98.6 F was just an exact conversion of 37 C. --Allen (talk) 06:48, 9 February 2008 (UTC)

Yup, and human body temperature fluctuates during the day, and the normal set-point temp. from the Hypothalamus is different for everybody. Mine, for instance, is 97.1 F. Wisdom89 (talk) 07:16, 9 February 2008 (UTC)

Oh, and we also wear clothes. Add the sunlight that is usually present at that temperature, as well as the usual humidity, and the body may very well react as if it was in a state of 150F with no clothes, no sunlight, and no humidity. Clothes keep in the heat that is already in the body, sunlight adds extra heat to the body, and humidity prevents us from sweating much in order to cool us down...and you've got an uncomfortable situation. I just hope I slightly overcalculated on the global warming scenarios, or we could be dealing with an average of approximately 180F of maximum temperatures that the body thinks it feels like annualy where I live. Just some random speculation. Hope this helps. Thanks. ~AH1^(TCU) 18:46, 9 February 2008 (UTC)

Light

I am really confused. If light is a wavelength of the electromagnetic spectrum, then I guess that it is atoms nudging each other in the air. So how on earth can it travel through space? I must be thinking something wrong. (please use short words)KarateKid101 (talk) 16:26, 8 February 2008 (UTC)

Light is not atoms bumping...actually, that's sound. Light (and all parts of the electromagnetic spectrum) are little packets of electric and magnetic vibrations called photons, and they can travel without a medium. For sound, the medium is air (or a wall or any other object you put your ear up to). For ocean waves, the medium is the ocean water. Light is the only wave in nature that doesn't need a medium. Hope this helps! -RunningOnBrains 16:43, 8 February 2008 (UTC)

(edit conflict) This is a great question - it's one that kept scientists in the 19th century very busy for a long time! Before electromagnetism was well understood, scientists only had experience with waves that travelled through stuff - ocean waves travel on the surface of water, sound waves travel through air, waves could travel through stretched ropes (like a jumprope), etc. However, it wasn't clear what Transmission medium light needed to travel through - it didn't seem to depend on any stuff to travel like other waves did. For a while, the best theory available was that there was some mysterious invisible stuff everywhere in the universe that they called the Luminous aether. After lots of careful experimentation and argument, it was proved that there was no aether. So what's the answer to your question? Light is a displacement in the electromagnetic field. If you haven't studied electromagnetism before, it's a tricky concept to grasp at first. The electromagnetic field is a vector field defined everywhere in the universe. Charge cause the electromagnetic field to be non-zero. When you wiggle charges back and forth, it causes a disturbance, or displacement in the electromagnetic (EM) field, which then propagates (travels outwards). And that's essentially what light is. It doesn't need any air, or atoms to travel. Cool, eh? I hope this helped to answer your question. --Bmk (talk) 16:49, 8 February 2008 (UTC)

It's the Luminiferous aether, not luminous. Algebraist 16:52, 8 February 2008 (UTC)

And it wasn't proved there wasn't any aether, it was just proved that if there was an aether, it was indetectable, and thus could be disregarded or not believed in safely. Big difference. --98.217.18.109 (talk) 17:11, 8 February 2008 (UTC)

You make a good point, but in this case, I disagree - since the aether was defined as the medium through which light propagated, and several experiments showed that there was no such medium other than the electromagnetic field, I'd have to say they did prove it didn't exist - but it's a minor point, and really just a sematical question. --Bmk (talk) 19:32, 8 February 2008 (UTC)

Unless you're talking about experimental error, in which case, of course, they could not have actually proved the lack of a luminiferous medium - they merely demonstrated the lack thereof to a high degree of certainty. I guess you could also say that light may be affected by the hypothetical aether, but so weakly that it is as of yet undetectable. --Bmk (talk) 19:35, 8 February 2008 (UTC)

Hello? Lorentz came up with his beautiful contraction equation by showing that if the medium contracted along with the transmission then there would be no way for someone to measure it. It could still be a medium, it just wouldn't be detectable. There were many definitions of the aether—taking one of them as canonical does its own historical injustice. It was the string theory of its day, and it came in many, many flavors. --98.217.18.109 (talk) 17:44, 10 February 2008 (UTC)

Light is the only wave in nature that doesn't need a medium.

Except gravitational waves. —Keenan Pepper 17:18, 8 February 2008 (UTC)

Shouldn't there be a non-medium-requiring wave to correspond to any particle or chunk of matter flying through space, per the de Broglie hypothesis? --Allen (talk) 17:35, 8 February 2008 (UTC)

Rofl. Leave it to the reference desk to think "please use short words" means "explain advanced and obscure physics to me". :-P -RunningOnBrains 19:13, 8 February 2008 (UTC)

Good point. I apologize. —Keenan Pepper 19:16, 8 February 2008 (UTC)

Sorry... I figure since you'd already answered the original question using short words, it would be okay to branch out to other, related questions. --Allen (talk) 19:51, 8 February 2008 (UTC)

Not criticizing...just funny. -RunningOnBrains 20:01, 8 February 2008 (UTC)

Cool. So how about it then? Can it be said that medium-less waves aren't the province of a few special cases, but rather a broad category, of which light is just one example? --Allen (talk) 20:32, 8 February 2008 (UTC)

Yes - see wave–particle duality for general concept and electron diffraction and neutron diffraction for specific examples. Gandalf61 (talk) 10:46, 9 February 2008 (UTC)

Show me the light!...for photosynthesis

Ok, I may have asked this before so pleaze forgive as I either don't remember the answer or never got one. Plants photosynthesis in sunlight, right? But can they photosynthesize in artificial light, for example lightbulbs, candels, LEDs... I was told yes but every plant that I've seen kept indoors has died if it has no sunlight. xxx User:Hyper Girl 17:20, 8 February 2008 (UTC)

See Grow light. also, please consider using the add a question link instead of editing the whole page --LarryMac | Talk 17:24, 8 February 2008 (UTC)

LarryMac, how can you tell? Think outside the box 17:29, 8 February 2008 (UTC)

from my watchlist. If somebody edits or adds a section, then I can click on a li'l arrow to go directly to that section. If somebody edits the page, I use the diff link to see what was changed. Also, I believe that it helps prevent edit conflicts, but I could be wrong. On topic, consider also the easily found stories of people arrested for "indoor cultivation". --LarryMac | Talk 17:35, 8 February 2008 (UTC)

Yeah, well, it might help if there was an "add a question" link. What the thing actually says is "+". Easy once you know, but... --Anon, 21:55 UTC, 2008-02-08.

"After reading the above, you may ask a new question by clicking here." But it is below the fold these days, so perhaps not obvious. 130.88.140.112 (talk) 14:34, 11 February 2008 (UTC)

Regular light bulbs and tubes just don't make enough light for most plants. For example, try shining a flashlight on a bright sunny day, and you'll see little or no difference. On the other hand, if you open a blind to an otherwise darkened room in the middle of the day, you'll see a big difference (and might not even notice any more light if you turn on a lamp). Even most grow lights need to be within a few inches of the leaves in order to get healthy growth. --SB_Johnny | ^talk 17:55, 8 February 2008 (UTC)

Photosynthesis also says that the wavelength of the light matters. Friday (talk) 17:58, 8 February 2008 (UTC)

Very true, the wavelength does matter, but visible light produced by a light bulb would be 400nm to 700nm - all visible wavelengths and thus, yes, you could maintain plants without direct sunlight artificially - although it might be less efficacious. Wisdom89 (talk) 19:00, 8 February 2008 (UTC)

Printing a full-scale map of the Earth.

I'd like to print a full-scale map of the Earth, I figure with a laser printer 10,000 sheets (and the equivaelnt amount of paper) only costs a couple of bucks (not hard to store, either, the same as 2 very large 5000 page volumes), so it would be (in real size) like a 1:10 000 scale map, not that large to store, a few bookshelves should do.

But that just Doesn't make Sense, because you'd need thousands of square miles of paper, am I being unreasonable after all? —Preceding unsigned comment added by 212.51.122.27 (talk) 17:52, 8 February 2008 (UTC)

Yeah, you must have miscalculated. 10,000 8.5"x11" sheets is nowhere near even one square mile. --Allen (talk) 18:06, 8 February 2008 (UTC)

Perhaps you can satisfy your map lust by just visiting Eartha in Yarmouth, Maine?

Atlant (talk) 18:08, 8 February 2008 (UTC)

My calculations say you need over eight quadrillion sheets of 8.5x11" paper for this project. --Allen (talk) 18:10, 8 February 2008 (UTC)

I feel someone should point you in the direction of Borges's On Exactitude in Science vis-à-vis the possible point of such a project. Algebraist 18:38, 8 February 2008 (UTC)

Wait -- is this a full-scale map or a 1:10000 map? Because the original question uses both numbers, and that's a factor of 100 million when you get down to sheets of paper. — Lomn 19:27, 8 February 2008 (UTC)

I think that is where the confusion is coming in. I'm assuming he wants a full(complete)-scale 1:10,000 map. -- MacAddct  1984 ^{(talk &#149; contribs)} 19:42, 8 February 2008 (UTC)

My impression was that they wanted a full-scale map, and were suggesting that a full-scale map, stacked into reams of paper, would only take up as much shelf space as a 1:10000 map laid flat. --Allen (talk) 19:54, 8 February 2008 (UTC)

• Ah, I think I get it. I bet it was a hyphenation problem. "Full-scale map of the Earth" (where "full" unambiguously modifies "scale") was a mistake for "full scale map of the Earth", with "full" modifying "Earth". --Anonymous, 22:02:08 UTC, 2002-02-08.

OK, so a complete map of the earth at 1:10000 scale -- Earth, with a mean radius of about 251 million inches, has a surface area of about 8e17 square inches. A 1:10000 scale map is still a surface area of about 8e9 (8 billion) square inches. That's about 85 million sheets of 8.5"x11" paper.

Now for storage: 5000 sheets of paper (a standard box of copier paper) measures about 17"x11"x8", or about 1500 cubic inches. 85 million sheets of paper means 17000 such boxes, for about 15000 cubic feet, a cube of paper about 25 feet to a side. — Lomn 20:15, 8 February 2008 (UTC)

• flash* REPLACE TONER CARTRIDGE *flash* -mattbuck (Talk) 01:59, 9 February 2008 (UTC)

Am I missing something? Where are we talking about that 10k of paper + colour laser printer + toner for 10k whole page colour sheets costs $2? Nil Einne (talk) 13:06, 9 February 2008 (UTC)

Square Mercator map

• The equator is around 40,000 km. Scale that by 10,000, you get 4 km. Assume we'll make a square map 4 by 4 km (Mercator projection or whatever). That will be about 12,000 by 20,000 A4 or letter-sized sheets, i.e. 240 million sheets, or close to half a million reams. You'd need quite a bookshelf for that... ;-) Choose another projection, and you'd manage with a bit less... --Janke | Talk 17:54, 9 February 2008 (UTC)

A minor point: The Mercator projection can't be used to map the entire world onto a finite amount of paper. One could choose a latitude range (as implied by Janke with the word "square") or use another projection that can handle the task. Pallida  Mors 20:50, 9 February 2008 (UTC)

Digestion

Approximaetly how long does it take for food to get digested? (i.e. starting from ingestion to egestion?) Thx —Preceding unsigned comment added by 82.46.27.191 (talk) 19:03, 8 February 2008 (UTC)

This varies from individual to individual - the entire digestive tract is roughly 25 feet from mouth to the anus - non digestible material takes roughly 25-36 hours to move this distance. Wisdom89 (talk) 19:16, 8 February 2008 (UTC)

According to the Mayo Clinic, while excretion of undigested material usually begins within 24 hours, it can take up to 72 hours for it to be completely eliminated [6]. And there's a very interesting 70-year-old TIME magazine article here, detailing the time to digest (stomach only) various foods, which should give you a good indication of how much the time it takes to start "eliminating" varries with the content of your meal. Someguy1221 (talk) 19:24, 8 February 2008 (UTC)

On that note, how does the stomach manage to keep one type of food longer than another type? Isn't it all pretty well mashed to a paste by the time it gets in there? --Bmk (talk) 19:37, 8 February 2008 (UTC)

You can probably use a strainer example to visualize how the various food types are "singled out". Imagine mixing chewed meat, mashed potatoes, and a glass of milk in a bowl. Then, you pour the whole mix in a strainer. The milk (and various other liquids) would flow right through. The potatoes would take some encouraging, such as agitation with your hand or a stream of water, but they would slowly make their way through the strainer holes. The meat, not being nearly as soluble or finely divided, would be left in the strainer. Here is where the chemical process in your gut comes in handy, by breaking down the proteins slowly so that eventually it, too, makes its way through the strainer. Tanthalas39 (talk) 21:14, 8 February 2008 (UTC)

To exit the stomach and pass into the intestines, food has to pass through the narrow pyloric sphincter. It passes much more quickly once it has been reduced to liquid or thin paste. ike9898 (talk) 16:32, 10 February 2008 (UTC)

Milk actually takes a while to leave the stomach. Not sure why, but I remember being told as a child that the stomach turns it into something resembling cheese. *shrug* Someguy1221 (talk) 21:56, 8 February 2008 (UTC)

Ever seen a baby burp a while after being breast-fed? ;-) --Janke | Talk 18:16, 9 February 2008 (UTC)

Yes, several times today in fact. It looks like cottage cheese because that's exactly what it is; cheese is just digested milk, after all. Also, baby poop (before solids are introduced) smells exactly like bad cheese, and looks like yellow cottage cheese. And despite all this, I still eat cheese. :P --Ginkgo100^talk 04:04, 15 February 2008 (UTC)

Cheese is traditionally made with an enzyme from cow's stomaches, rennet. Nowadays a vegetable or mold substitute is sometimes used. Rmhermen (talk) 23:01, 8 February 2008 (UTC)

Helicopter Physics

I just saw a U.S. Coast Guard helicopter fly by my window (I have no idea why, this place is landlocked), and it was flying so low that it was level with me on the 8th floor of a 20 story building. I was wondering what is the advantage of flying so low that outweighs the disadvantage of being so close to buildings. A strange theory popped into my head that the air is denser near the ground, thus generating more lift and thus more speed, but I think that is BS. Any ideas? 206.252.74.48 (talk) 19:48, 8 February 2008 (UTC)

The air is slightly denser closer to the ground, but as a practical matter it makes no difference whether the chopper is at your window or five hundred feet further up. (Air pressure declines by about three percent every thousand feet of altitude: [7].) When any aircraft is quite close to the ground ground effect lift comes into play; this effect is only appreciable within a blade-length or so of the ground.

There may have been mission or training requirements that dictated the pilot's choice of altitude, but it wasn't because of thicker air. Maybe your neighbor is an Al Qaeda operative and the Coast Guard was checking him out. TenOfAllTrades(talk) 20:00, 8 February 2008 (UTC)

That's what I thought. Now that I think about it, there is an airport near-by, maybe he had to fly low to keep out of airspace normally used by passenger jets. I wish I knew what he was doing, I've never seen a military helicopter around here before. 206.252.74.48 (talk) 20:38, 8 February 2008 (UTC)

The U.S. Coast Guard isn't part of the military (except when it is, like the U.S. Merchant Marine, during a war). The Coast Guard patrols and protects on navigable waters (some lakes and rivers) as well as blue water operations so you needn't be near the ocean to see them. Rmhermen (talk) 22:37, 8 February 2008 (UTC)

The Coast Guard sure as hell is in the military. Military of the United States lists it as a branch and United States Coast Guard (which you linked to) starts with the sentance "The United States Coast Guard (USCG) is a part of the military of the United States...". And then there is this nice little page on the US military home-page. There was even a dude who received the Medal of Honor for being in the Coast Guard (granted, he was taking part in an operation in Guadalcanal, but still). 83.250.205.56 (talk) 20:48, 9 February 2008 (UTC)

Out of curiosity, what city are you in that you saw this helicopter? —Preceding unsigned comment added by 138.29.51.0 (talk) 14:26, 9 February 2008 (UTC)

Schaumburg, IL. 18:42, 9 February 2008 (UTC) —Preceding unsigned comment added by Chris16447 (talk • contribs)

sky digibox

hi all, we have a sky digi box but no service (after a long dispute over a bill, and we wish to no longer use sky) i have tried to 'tune' in a tv channel into freeview to use the box but alas to no avail, i have two of my three children looking at me as thou i am a hopeless father who can not get them the CBBC channel, the third cares not as he only eats, sleeps, poos and giggles (sometimes all at the same time) can anyone help, a poor tired father of three? Perry-mankster (talk) 19:58, 8 February 2008 (UTC)

If you want Freeview you need a Freeview decoder attached to an ordinary (good quality) TV antenna on your roof. You don't get Freeview from a satellite dish using a Sky box. Buuuut a new free service is scheduled to be launched this year - Freesat. It will carry free channels (BBC, ITV, some other stuff, but not everything you get on Freeview). It seems like your current equipment should be able to receive that, but you don't need a viewing card and don't need to pay Sky anything. They're not super clear when exactly they're starting up, only saying "Spring 08". It will carry CBBC, so your kids can watch Charlie and Lola, but won't carry Five, so they can't watch World's most gruesome sexchange mishaps 2. -- Finlay McWalter | Talk 21:22, 8 February 2008 (UTC)

thank you finlay, bloody sky, what have the roman's sky ever done for us? think i might have an old decoder up de loft (sounds painful){mrs mankster has just reminded me about the HUGE fukin' spider that lives in the loft... about time the kids went outside and played}, you think it would work? - i'm not talking to a disgruntled sky worker by any chance?Perry-mankster (talk) 23:07, 8 February 2008 (UTC)

Not all areas can receive Freeview (check the Freeview website)). Cheap set-top boxes are just as good as more expensive ones, and they all handle the tuning automatically, so as long as the reception is good they are simple to set up, though on every tv I've tried, the scart plug has to be pushed in very firmly and wiggled until you get a picture.--Shantavira|^{feed me} 08:23, 9 February 2008 (UTC)

thanks shantavira, will check out coverage, i too have seen v cheap decoders, so might just go for that optPerry-mankster (talk) 10:12, 9 February 2008 (UTC)

Electromagnetic pulse effects on storage devices

According to the Wikipedia article, an electromagnetic bomb would fry (in order from most damage to least damage) integrated circuits, transistors, vacuum tubes, and inductors. My question, which the article says nothing about, is, what would be the effect of an electromagnetic bomb on storage devices like hard drives, flash drives, DVDs, etc.? —Lowellian (reply) 20:36, 8 February 2008 (UTC)

It'll vary depending on the medium. Magnetic storage like a hard drive is absolutely vulnerable. Physical encoding like a DVD or CD is impervious to EMP. Flash memory, as electronic storage, is most likely vulnerable, though it's been a while since I dealt with the specific mechanics that make flash work. — Lomn 20:58, 8 February 2008 (UTC)

I'm not entirely sure, but my guess would be flash and hard drives would be permanently disabled. Flash drives use integrated circuits and hard drives are adversely affected by magnetic fields. Wisdom89 (talk) 20:59, 8 February 2008 (UTC)

How about a practice of doing a daily or weekly backup of critical data to a flashdrive or outboard hard drive, and storing it along with a transistor radio, calculator, and other useful electronic gadgets in a metal box? The question is how much shielding the Faraday cage would have to provide. Is the metal storage cabinet in an office sufficient, or would an old office safe be required, or a box welded out of 1 cm steel? A data room could be maintained in a shielded room by a business enterprise, with opto-isolation and internal UPS. Edison (talk) 00:55, 9 February 2008 (UTC)

Another question: does the metal casing of a typical external hard drive form an adequate Faraday cage? —Lowellian (reply) 01:15, 9 February 2008 (UTC)

The casing almost never encloses the drive electronics, and there are wires leading from the electronics to the read/write heads. I'd expect the data on the platters to survive EMP effects -- it takes a very powerful magnet to erase a hard drive -- but replacing the electronics is a non-trivial operation, and replacing the heads requires opening the case in a cleanroom. --Carnildo (talk) 03:17, 9 February 2008 (UTC)

Nitrocellulose underwear

Would it be possible/practical to make explosive clothing out of nitrocellulose? --67.185.172.158 (talk) 21:10, 8 February 2008 (UTC)

The article has a story about a chemist who made his apron explosive by spilling nitric acid on it. I have a feeling that it's not so much "explosive" but more "highly flammable" and you'd just end up with burned skin. -- MacAddct  1984 ^{(talk &#149; contribs)} 21:40, 8 February 2008 (UTC)

Sounds like Mythbuster's episode on the farmer's exploding pants. Rmhermen (talk) 22:29, 8 February 2008 (UTC)

You would need to combine the Nitrocellulose paper/material with other compounds in order to make it an explosive. Macaddct is correct - it would just be flammable and burn. In the laboratory I constantly use nitrocellulose membranes for western blotting and I've experimented with applying a flame - it simply burns rapidly. Wisdom89 (talk) 22:39, 8 February 2008 (UTC)

Smokeless gunpowder (and old nitrate film) is nitrocellulose. When ignited in open air, it will burn ferociously, but not explode. Confined - BOOM! (Personal experience... ;-) --Janke | Talk 18:00, 9 February 2008 (UTC)

The questioner wouldn't be Lorena Bobbitt by any chance? Clarityfiend (talk) 19:49, 9 February 2008 (UTC)

February 9

Is it possible to hide somewhere on Earth

or is it all prety much surveilled —Preceding unsigned comment added by 212.51.122.27 (talk) 00:24, 9 February 2008 (UTC)

I'm not entirely sure we are aware of every piece of surveillance technology the governments of the world have at their disposal. My guess would be that, yes it would be possible - There are high profile people currently in hiding who have yet to be found despite our best efforts. The next question is what are the tools we have in our arsenal? Thermo imaging, infrared, satellite etc..etc..Perhaps someone who has more expertise in engineering and physics could field this one. Wisdom89 (talk) 00:36, 9 February 2008 (UTC)

I spent some time in Alaska and know for a fact that it is a very good place to hide, at least in the country. There are no addresses and in some places no good maps to show where things are. And that's in the US! Wrad (talk) 00:40, 9 February 2008 (UTC)

The presence of lack of maps doesn't mean somewhere is easier or harder to hide. All you have to do is meet one person in Alaska who knows who you are and the whole thing is up, even if there is no address. --98.217.18.109 (talk) 00:51, 9 February 2008 (UTC)

Some people have managed (ok, I'm tired of linking) to stay hidden for a long time even with the most technologically advanced nation in the world trying to find and kill them. The earth is a big place; some areas are linked up with heavy technological surveillance, but most are not. Even with those that are, the ability to use disguise, forgery, the help of confederates, etc., make it possible to elude capture for a long time. Is it possible to hide? Obviously yes. The biggest problem is not, I would argue, technological surveillance, but social networks being linked to economic networks and things like that; it's hard to get a job, to open a bank account, to earn money in any real way, etc. without leaving some trace of yourself. --98.217.18.109 (talk) 00:51, 9 February 2008 (UTC)

It is my understanding that countries like the USA have the ability to photograph any spot on the earth above the ground within some time period. However, the presence of electronic surveillance doesn't mean you can't hide. Just because it is possible to photograph you, doesn't mean they can find you - it's a data processing problem. The police need to know which video camera footage to review. --Bmk (talk) 06:25, 9 February 2008 (UTC)

Right, but aerial photography only helps you so much. If you were hiding right now, would aerial photography help find you? Probably not—because you're probably indoors, and from that high up, anyway, most people look pretty much the same anyway. --98.217.18.109 (talk) 17:15, 9 February 2008 (UTC)

Some manage to evade capture for many years. See Victor Manuel Gerena for example.Mr.K. (talk) 06:40, 9 February 2008 (UTC)

Then there is also the man with a US$50 million bounty on his head who we believe is still alive and the US has been (supposedly) very, very actively hunting for the past 6.5 years but is still MIA. BTW, about the satellites, it isn't just a data processing problem. Whether the resolution of current spy satellites is good enough that even a human could recognise a face is unclear, the article suggests it isn't although it's impossible to know what spy satellites are truly capable of. However they may not even be theoretically capable of it if I understand the article correctly. Spy drones are probably a far better bet here. Also it doesn't matter if you can recognise faces if you never actually see the face because it is hidden all the time... Nil Einne (talk) 13:00, 9 February 2008 (UTC)

All we've ascertained from satellite photos is that it's not on the roof! Algebraist 13:27, 9 February 2008 (UTC)

Do we have a space station orbiting the moon?

Do we have a space station orbiting the moon?

(Just to make sure, my understanding is that we don't have one on the moon, and we don't have one either obiting nor on Mars. Is that right?)

Thank you! —Preceding unsigned comment added by 212.51.122.27 (talk) 00:37, 9 February 2008 (UTC)

We have artificial satellites orbiting the moon, but not since Apollo 17 in 1972 has a human orbited the moon. The next planned human mission to the moon, at least so far as the U.S. is concerned, is Orion 17. It took 8 years to plan and achieve a human landing on the moon with the Apollo program of the 1960's, but with 21st century technology and the lessons learned, it is expected to take 13 years from the 2006 announcement of the program until the first mission tentatively scheduled for 2019. Edison (talk) 00:40, 9 February 2008 (UTC)

Sure it will take longer, but it will also be much more expensive! :) --Sean 16:07, 9 February 2008 (UTC)

Minor nitpick. Orion 15 is planned as a moon landing. APL (talk) 17:03, 9 February 2008 (UTC)

It's actually quite difficult to orbit the moon for long periods due to lunar masscons. — Lomn 01:37, 9 February 2008 (UTC)

(The article is at Mass concentration.) --Allen (talk) 03:06, 9 February 2008 (UTC)

The International space station is the only space station in existance, and its orbits earth, far below the moon.--Dacium (talk) 06:25, 9 February 2008 (UTC)

ok. what is "existance"? —Preceding unsigned comment added by 212.51.122.26 (talk) 13:39, 9 February 2008 (UTC)

A common misspelling of existence. Algebraist 15:12, 9 February 2008 (UTC)

How in the world can we have satellites orbiting the moon and I not have know about them? What satellites? And doesn't the presence of the Earth play hob with an unattended lunar orbit? --Milkbreath (talk) 17:19, 9 February 2008 (UTC)

Not sure who you include in "we", but current satellites in orbit around the Moon include SELENE (Japan) and Chang'e 1 (China). There may be others. Gandalf61 (talk) 18:05, 9 February 2008 (UTC)

B12 and Folic Acid Masking

If you see someone with Pernicious Anemia which unbeknownst to you is due to a vitamin B12 deficiency, and you give them a folate supplement, their anemia will resolve. Will they still have homocysteinuria?

--142.157.61.48 (talk) 04:39, 9 February 2008 (UTC)

Homocystinuria is usually caused by an inherited genetic disorder in an enzymatic pathway - but yes, if a person does not receive enough B-12, then they can develop an increase in homocysteine in the blood and urine. However, if you give someone folate supplements it will NOT resolve pernicious anemia - as both B12 and folate are required for the synthesis of thymine. Wisdom89 (talk) 05:20, 9 February 2008 (UTC)

Parts of thr skull?

Where is the "orbit and anterior cranial fossa" located? —Preceding unsigned comment added by 207.5.224.47 (talk) 04:56, 9 February 2008 (UTC)

The orbits are the recesses that contain your eyeballs. We have a whole article on the anterior cranial fossa, which lies over the orbits (the bottom of the anterior cranial fossa consists of a bone that is the top of the orbits). - Nunh-huh 07:05, 9 February 2008 (UTC)

Why is a car moving in a circle at a constant speed said to have accleration?

it's not homework, just something i found in the maargins of my physics textbook. ^^; —Preceding unsigned comment added by 202.156.88.207 (talk) 07:21, 9 February 2008 (UTC)

Acceleration is a change in velocity, which is both a speed and a direction. So if the car is changing direction, it is accelerating, if not in the non-scientific sense. You may be interested in centripetal force. Someguy1221 (talk) 07:48, 9 February 2008 (UTC)

Also vectors Nil Einne (talk) 13:15, 9 February 2008 (UTC)

The natural world: snails

What are snail offspring called?Issi5690 (talk) 10:09, 9 February 2008 (UTC)

Snail life cycles vary from species to species, but it's typically egg, hatchling/larva, tiny snail (uh, not a scientific term ;-) ), adult snail. Sea snails have the additional stages trochophore and veliger (both actually considered types of larva) before adulthood. Someguy1221 (talk) 10:15, 9 February 2008 (UTC)

These are termed as trocophore larvas.--Mike robert (talk) 17:06, 9 February 2008 (UTC)

Bob, Jemima, or, more famously, Brian, but really, pretty much any name the parents like. Except, I hear that modern snail parents have an irrational aversion to calling their offspring "Snoop Doggy Dogg" on the basis that it's too silly (although Snoop Dogg is apparently acceptable). --Dweller (talk) 12:45, 12 February 2008 (UTC)

thermoacoustic refrigerator

hi friends,

i m trying to model the thermoacoustic refrigerator as given in the link:

www.kettering.edu/~drussell/Publications/ThermoDemo.pdf

in this article it is given that a fundamental harmonic is to be established in the resonator(quarter wave) tube and then the power of the speaker is to be increased to such an extent that a second harmonic is barely audible.i m unable to recognize that a second harmonic is heard.rather the incident sound is so high that it is impossible to hear any other sound.any friend with some knowledge on waves.help me.

regards, sam. Reveal.mystery (talk) —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 10:32, 9 February 2008 (UTC)

The article you point to gives 385Hz as the fundamental, right? So the second harmonic will be at 770Hz. This is slap bang in the centre of the human hearing range so you should have no trouble hearing it unless you are stone deaf. I suspect that the problem is more likely that you are not used to picking out harmonics from a composite sound. This can be quite difficult for many people. If you know any piano tuners, ask them to listen, they will be able to do this exercise with ease. If you can't find anyone from the music world to help, you will have to solve the problem with expensive technology; audio spectrum analyser is the instrument you need.

By the way, 100W speakers can generate high sound pressure levels. You would be advised to use ear protection while doing this. SpinningSpark 18:26, 9 February 2008 (UTC)

sir, thank you very much for your answer.if you went through the article .you must have read that there is a need of a thermocouple in it.i live in a remote place,so no thermocouples with me. i m trying to measure the temperature with a metal pin inserted in the resonator such that it touches the stack at a point which is expected to get colder.and then a labrotory thermometer touching it.i am not sure about its working can any one help.

regards sam Reveal.mystery (talk) —Preceding comment was added at 05:10, 10 February 2008 (UTC)

Books on science history

Hi! When I was little I read a set of volumes of books called "Stories of Science" (it was a Hindi translation actually). It gave detailed and fascinating historical accounts of how various discoveries and inventions of science were made and what the people involved went through, and the even the politics involved. I don't have those books any more. Can anyone suggest a similar book(s) that gives an interesting, historical account of the stories of science? Thanks a zillion :) ReluctantPhilosopher (talk) 15:35, 9 February 2008 (UTC)

Wow - historical accounts of the stores of science - the only problem here is where to start. In no particular order:

• Anything by John Gribbin or Adam Hart-Davis.
• Dava Sobel has written several books recounting the history behind scientific achievements - I can recommend Longitude and Galileo's Daughter.
• The Great Arc by John Keay - an account of the Great Trigonometric Survey.
• If you like autobiographical accounts, James Watson's story of the discovery of DNA in The Double Helix is very readable, as are Richard Feynman's Surely You're Joking, Mr. Feynman! and What Do You Care What Other People Think?
• Arthur Koestler's excellent book The Sleepwalkers, about the history of astronomy.
• Isaac Newton: The Last Sorceror by Michael White.

Gandalf61 (talk) 16:06, 9 February 2008 (UTC)

I second the Double Helix suggestion, as it shows how vital beer is to the scientific enterprise. The Making of the Atomic Bomb gives a lot of good social/historical background to early nuclear physics work. --Sean 16:09, 9 February 2008 (UTC)

Alright, thanks a lot :) ReluctantPhilosopher (talk) 17:09, 9 February 2008 (UTC)

• (ec)Cosmos by Carl Sagan is a great read. Particularly good on Kepler and Tycho Brahe. His telling of the story of Hypatia is also unforgetable. SpinningSpark 17:11, 9 February 2008 (UTC)

OK I'll read that, thanks :) ReluctantPhilosopher (talk) 17:17, 9 February 2008 (UTC)

More suggestions:

• The World of Gerard Mercator by Andrew Taylor.
• Brunelleschi's Dome by Ross King.
• Chasing the Molecule by John Buckingham - the origins of organic chemistry.
• The Book Nobody Read by Owen Gingerich - fascinating account of tracking down the remaining copies of Copernicus' De revolutionibus orbium coelestium; an unusual angle on a slice of the history of astronomy.
• For accounts of contemporary science, try Sequence: Inside the Race for the Human Genome by Kevin Davies and Roving Mars, the story of the Mars rovers Spirit and Opportunity, by Steve Squyres.

Gandalf61 (talk) 17:54, 9 February 2008 (UTC)

The Day the Universe Changed by James Burke (also a TV documentary). --Milkbreath (talk) 18:17, 9 February 2008 (UTC)

Thanks, fellas. ReluctantPhilosopher (talk) 17:53, 10 February 2008 (UTC)

Difference between a penny and a penny.

What is the difference between a penny and a penny? Thank you! —Preceding unsigned comment added by 79.122.70.107 (talk) 16:16, 9 February 2008 (UTC)

It is 0d in old money, 0p in new money and 0¢ in American money. SpinningSpark 16:23, 9 February 2008 (UTC)

This question doesn't make any cents. —Nricardo (talk) 16:34, 9 February 2008 (UTC)

ROFL XD ReluctantPhilosopher (talk) 17:08, 9 February 2008 (UTC)

No, really. It doesn't. Are we missing something? Wisdom89 (talk) 17:58, 9 February 2008 (UTC)

Penny, a penny is a unit of currency in several different countries. There are a number of online currency conversion tools that can compare the various values of different pennies. IF that's what you're asking.--VectorPotential^Talk 18:44, 9 February 2008 (UTC)

This one seems to have everyone foxed and the OP has gone away but I think this may have been the question and it does actually get a mention in our article Cent (United States coin). SpinningSpark 21:37, 9 February 2008 (UTC)

Uh, there is no difference between a penny

ok, I'm the OP -- I was just interested in what kind of answers you would give. In fact, you have given answers in terms of a pun, materials science, and finance (currency). But not mathematics (the difference [ie if you subtract the latter from the former] is "zero") or Grammar (the word's place in the sentence - as the first or second object of the preposition "between", perhaps inflection falls at the end of a sentence too...). Surprisingly, no one gave the answer that I was expecting people to give: "Nothing" -- there is no difference between a penny and a penny. —Preceding unsigned comment added by 79.122.91.85 (talk) 23:37, 9 February 2008 (UTC)

Identity_(philosophy) is interesting. --Allen (talk) 23:48, 9 February 2008 (UTC)

Isn't the answer "One of its legs is both the same"? AlmostReadytoFly (talk) 01:03, 10 February 2008 (UTC)

Because vests don't have sleeves. 82.44.115.41 (talk) 22:38, 11 February 2008 (UTC)

trivial querry...

Please tell me why High Tension electric cables(overhead) buzz?? A conspicuous very much audible buzz is found below such a cable..
LONGBOW001 (talk) 17:21, 9 February 2008 (UTC)

It is the magnetic field generated by the current in the cables causing either other cables, or nearby metal parts (in the pylons etc) to vibrate. The note will be twice the frequency of the ac power system. As this is 60Hz in the US and 50Hz in Europe, the audible note will be 120Hz or 100Hz respectively. You might also hear the noise of arcing in damp weather when there is tracking across the high tension insulators. SpinningSpark 17:54, 9 February 2008 (UTC)

See Mains hum. —Keenan Pepper 19:32, 9 February 2008 (UTC)

Corona discharge is a strong component of the buzzing noise. It is not really arcing, but rather the ionization and breakdown of the air around conductors, especially at transmission voltages and particularly around sharp points or sharp edges, where the potential gradient is the greatest. Edison (talk) 20:37, 9 February 2008 (UTC)

Odd-looking moon tonight...

Looking out of my window as I drew the curtains this evening, I noticed the crescent moon in the sky. I don't normally spend a lot of time looking at the moon, but tonight's moon is strange. Despite it being a crescent moon, I can still see the entirety of its face. The proportion of it which should be fully in shadow is actually slightly brighter than the surrounding sky and shows up clearly against it - dark grey on black, to put it simply (I know the sky isn't *really* black - but near as dammit). I live in Northern England, if anyone from my part of the world wants to have a look out at what I'm talking about (it's still doing it now as I type this)...

What's going on? I can't recall ever seeing a moon like this. Unless I just haven't been paying attention (taking the moon for granted?) for all these years. --Kurt Shaped Box (talk) 18:44, 9 February 2008 (UTC)

You can see the "dark" part of the moon in reflected earthlight. This effect is not very noticeable in this country but increases towards the equator. When I was in Oman, this effect was very obvious in the clear desert air. SpinningSpark 18:55, 9 February 2008 (UTC)

Ah, hear we go, I knew there had to be an article on this, I just couldn't find it for the first post - Planetshine SpinningSpark 19:08, 9 February 2008 (UTC)

Hi. Isn't it Earthshine? Thanks. ~AH1^(TCU) 19:09, 9 February 2008 (UTC)

If you look carefully, you will see that Earthshine is a redirect to Planetshine and doesn't have an article of its own. SpinningSpark 19:13, 9 February 2008 (UTC)

Yeah, that's precisely what I'm seeing! Thanks very much, guys. So, is this a particularly common phenomenon? As I said, I don't recall ever noticing it before (the article is nonspecific). --Kurt Shaped Box (talk) 19:18, 9 February 2008 (UTC)

(edit conflict)Oh. Well then, just out of curiosity, could Light pollution sometimes be intense enough to radiate to the moon and be reflected back to Earth at detectable levels? Thanks. ~AH1^(TCU) 19:20, 9 February 2008 (UTC)

The effect is there all the time, um, correction, it is there all the time near the New Moon. On the other half of the moon phase cycle the Full Moon is facing the night side of the earth and therefore gets no reflected sunlight. The reasons we don't often notice it are 1)our weather, 2) relatively high latitude and 3) light pollution. And no, light pollution cannot cause the effect, it is many stellar magnitude (can't be bothered to actually calculate anything) below the reflected sunlight. SpinningSpark 19:27, 9 February 2008

Another and more picturesque name for the phemomenon is Old moon in the new moon's arms (that's also a redirect to Planetshine). It is very common for it to be visible when the moon is a thin crescent, but only when the sky is also dark, and when it's a thin crescent it's mostly in the day sky, not the night sky. --Anonymous, 01:08 UTC, February 10, 2008.

Earthshine is more apparent when the Moon is a crescent because night vision is better preserved. With a nearly-full moon, the eyes do not become more sensitive over time because there is no need to do so. --Bowlhover (talk) 02:31, 10 February 2008 (UTC)

colour of sky

Hi. I'm just wondering, what is the colour of the average clear sky on Earth during the middle of the daytime excluding the colour of the sun and clouds and moon and dark areas and haze and terrestrial objects and aircraft and contrails and lightning and halos and all other objects' colours in the sky other than the average colour of the daytime sky itself, in HTML? Thanks. ~AH1^(TCU) 19:07, 9 February 2008 (UTC)

There is a HTML colour named "SkyBlue" which looks like this but I don't know whether that corresponds to the actual colour of the sky. The HTML code is 87 CE EB. SpinningSpark 19:19, 9 February 2008 (UTC)

The sky is blue, but the exact shade varies enormously with the time of day and the angular distance from the sun. The blue is deepest at 90 degrees from the sun on a line drawn through the zenith. There is more information at Rayleigh scattering and diffuse sky radiation and the links from that page.--Shantavira|^{feed me} 19:23, 9 February 2008 (UTC)

What Shantavira said; and also note that when you ask for the color "in HTML", you're really asking for its representation in the sRGB color space. —Keenan Pepper 19:28, 9 February 2008 (UTC)

By the way, you get the prize for todays' most difficult to parse sentence. SpinningSpark 19:40, 9 February 2008 (UTC)

I think this belongs to the Computing Desk. Visit me at Ftbhrygvn (Talk | Contribs | Log) 15:31, 10 February 2008 (UTC)

February 10

copper sulfate and potassium hydroxide

what happens when you add copper sulfate and potassium hydroxide together, and why it produces the result? —Preceding unsigned comment added by 220.238.205.237 (talk) 04:14, 10 February 2008 (UTC)

This question reeks of homework. Do it yourself, or if you really need to, enter your question into Google like I did and read the answer. I'm often surprised by people who take the time to ask things here, and wait, when they could get the answer themselves in about 60 seconds if they'd try. Pretty weak... dw —Preceding unsigned comment added by 24.86.250.218 (talk) 07:35, 10 February 2008 (UTC)

Assume good faith. Thanks. Wisdom89 (talk) 07:48, 10 February 2008 (UTC)

If this is a homework question, then there are very few things you'll have to ask yourself in order to answer it. The first one is, will anything present react with anything else? Potassium doesn't react with sulfate or copper, so what about the other two combinations? Nope. If there's not going to be a reaction, then your teacher is obviously asking whether anything will precipitate out of the solution. In other words, what combination of ions isn't soluble, if any? If you have trouble figuring that out, it's better to tell us why, instead of just asking for the answer. That way we can teach you how to find the answer. ;-) Someguy1221 (talk) 11:49, 10 February 2008 (UTC)

Wait...I thought the formation of a precipitate was a reaction? --Emery (talk) 21:45, 10 February 2008 (UTC)

I don't consider it a chemical reaction since there is, formally, no explicit chemical change. Someguy1221 (talk) 00:17, 11 February 2008 (UTC)

I would have guessed a possible product would have been potassium sulfate - obviously the KOH would dissociate - although K2SO4 is insoluble in basic solutions. Wisdom89 (talk) 21:51, 10 February 2008 (UTC)

Ah, but will the solution still be as basic when all is said and done? Copper can syphon off that hydroxide pretty effectively. Someguy1221 (talk) 00:21, 11 February 2008 (UTC)

DNA replication

I realize this probably requires a lot of education to understand, but I was hoping for a summary. I know all the steps of DNA replication that I have read from various overview sites: helicase splits DNA; RNA primase inserts starter nucleotides; DNA polymerase adds complementary DNA nucleotides; ... a lot of gap filling ... and viola, a copy of DNA. My questions are: where do these various helpers (helicase, RNA primase, DNA polymerase, exonuclease, ligase) come from? Are they just sitting around waiting for their turn? What is telling them when to move into action? How does step 2 know when step 1 is done, and so on? Are there any links to better overviews of this? Thanks! — BRIAN0918 • 2008-02-10 05:42Z

Like many processes ocurring in the cell DNA replication is basically the result of chaos. The right enzyme just happens to be at it's required position at the right time. It might feel a bit odd a first, but when you realise that there are countless copies of each of these enzymes present within the cell it al starts to make sense. They don't " know " the order in which they work either. It's simply impossible of the enzymes you listed to do their jobs before the other one has finished (or at least started working). So in other words, yes they are just hanging around ...well bouncing around the inside of your cell nucleus untill they can do their job. PvT (talk) 11:11, 10 February 2008 (UTC)

At all times during a cell's life (except right after replication starts) there is protein complex called the origin recognition complex that is bound to the replication origins. These not only bind to DNA, but also to helicase and a couple other protiens. Once parts of the complex have been phosphorylated by the appropriate kinases (which are activated by cell-division promoting factors) the helicases are directed by the complex to open the DNA. Primase then binds to helicase and adds primers where there is room. Then uh, yeah, topoisomerase and DNA polymerase come in somewhere...Since many of the ligases and polymerases (as well as helicase) are involved in DNA repair, it's likely at least some of the machinery is around all the time (not that it's not known, merely that I don't know). Anything that isn't would likely have its genes activated around the same time as the origin binding proteins. I have a textbook I could email you that contains as detailed a description as I've ever seen of replication, and it may answer your questions. Drop me an email and I'll send it to you, assuming you can handle a 90mb attachment (and me, as well, as I've never tried sending anything that big). Someguy1221 (talk) 11:41, 10 February 2008 (UTC)

fuzzy control of dc to dc converter

In the implementation of a fuzzy controller of a dc to dc converter it is found that the input variables to the fuzzification level are the values of the error(difference between the output voltage of the converter and a reference voltage) and the change in error(difference between the error at k^th instant and the error at the (k+1)^th instant. I need to know why this is so. Also the error range was between -1.0 and 1.0. Why? I will provide here the link to the ieee paper that contained this article : ieeexplore.ieee.org/iel3/41/13741/00633467.pdf Please also mention how the hardware implementation of the paper is to be done. I am in urgent need of an answer since I have a review exam in college tomorrow. I will be grateful to you. Thank you for the help. —Preceding unsigned comment added by 59.89.20.119 (talk) 14:08, 10 February 2008 (UTC)

Sassafras wood - safe to burn in fireplace?

A friend told me that the fumes from sassafras wood are toxic when burned in a fireplace. Neither Google nor Wikipedia confirms this, although a product of the tree taken internally is forbidden by the FDA. —Preceding unsigned comment added by 24.127.124.38 (talk) 15:37, 10 February 2008 (UTC)

Hi. I'm not sure about your actual question, but I heard that sassafras was banned in coca-cola because a cancer-causing agent was found in it. However, I think you should wait for a more detailed answer. By the way, coca-cola used to have coca and kola. Hope this helps. Thanks. ~AH1^(TCU) 16:24, 10 February 2008 (UTC)

Safrole is the toxic element in Sassafrass. This is skirting the edges of Wikipedia's ban on medical advice, but I would think that fumes of any burning wood are toxic, if only because of the carbon monoxide released. A properly-functioning fireplace should be able to safely burn pretty much any wood. --Mdwyer (talk) 23:38, 11 February 2008 (UTC)

Pure nucleic acid

Is it possible to extract pure DNA/RNA, and if yes, what properties does it have? I presume it displays all properties common to acids, but more specifically: is it a liquid? What color, viscosity, etc.? - Sikon (talk) 15:58, 10 February 2008 (UTC)

It is certainly possible and is done routinely in molecular biology labs. I believe pure, dry DNA is a white solid. Thinking of it as an acid may be thorwing you off a little. DNA and RNA have more in common with other polymers than they do with acids you are more familiar with. ike9898 (talk) 16:13, 10 February 2008 (UTC)

(Ec) It depends on whether the DNA is in solution or precipitated, and how long the strands are. (A solution containing plasmids a few thousand bases in length is going to have a much lower viscosity than one containing strands of genomic DNA millions of bases long.) DNA alone is a white solid—not a liquid. Extraction and isolation of DNA is very easy; if you'd like to prepare a crude DNA extract you can actually do it in your kitchen. This link has instructions and photographs.

DNA and RNA are routinely isolated in the laboratory. The classic method is phenol-chloroform extraction followed by ethanol precipitation, but there are a number of other techniques in our article on DNA extraction. Google is your friend here— search on keywords like DNA extraction protocol or RNA extraction protocol and you'll get dozens of relevant hits. TenOfAllTrades(talk) 16:19, 10 February 2008 (UTC)

All of the above comments are absolutely correct - However, just one note, any DNA/RNA that you purify, whether it be plasmid DNA, genomic DNA or the various RNAs, will be contaminated with protein. There are methods routinely employed in laboratories to extract the purest and highest grade nucleic acid possible, but it's never 100% efficient - even with commercial kits available. As for the properties, well, the nucleic acids tend to like slightly alkaline conditions and dissolve somewhat readily in such solutions. In solution, plasmids adopt several different physical conformations, genomic DNA is a mess, seriously, and RNA tends to form secondary structures (since it's predominately single stranded). Wisdom89 (talk) 18:00, 10 February 2008 (UTC)

A popular home DNA purification is that of banana (see this). It uses easily obtainable products, and you should be able to substitute isopropanol (rubbing alcohol) for the 95% ethanol. -- Flyguy649 ^talk 22:55, 10 February 2008 (UTC)

Please help me understand some "cookbook" chemistry

I have a procedure that I follow like a recipe, but I would like to better understand what is actually going on. The procedure involves using performic acid to oxidize a sample; this part I understand. When the oxidation is complete, I add hydrobromic acid to the solution and it turns bright orange. This is the part I want to understand. I don't really care why it turns orange, but I do want to understand what the HBr is doing. Is it somehow 'stopping' the reaction? After this step, I remove all the reagents by rotovap. Is the step in question somehow making the reagents volatile so they can be easily removed? ike9898 (talk) 16:09, 10 February 2008 (UTC)

Yes, the hydrobromic acid reacts with – and thereby inactivates – the performic acid to stop the reaction. (I'm not certain what the products of that reaction are, but I suspect they're all volatile: formic acid, water, bromine.) As you suggest, excess hydrobromic acid will evaporate completely, as it's just a solution of (volatile) hydrogen bromide gas in water. TenOfAllTrades(talk) 16:38, 10 February 2008 (UTC)

Jellyfish

Hi. See my question on Talk:Jellyfish#Invasion. I want to see the article if there is one on nemoura but I din't know the spelling. These jellyfish are invading off the coast of Japan and damaging the fishing industry. Thanks. ~AH1^(TCU) 16:30, 10 February 2008 (UTC)

I think you might be looking for Nomura's jellyfish. TenOfAllTrades(talk) 16:40, 10 February 2008 (UTC)

Viviparous (common) lizard

Here's a poser for someone who knows about lizards:

Last night, after dark, I met some friends in Staffordshire, UK, and we spotted a Viviparous lizard on the concrete path. It's about 1½" (4cm) long. It had presumably been basking, as it had been a sunny day, but as a heavy frost was forecast, we thought it was probably at risk where it was, so we rescued it. It is now in my kitchen (right), in a bowl with some water, moss and some leaves. It seems perfectly happy, but I'd welcome some advice on the best way to look after it, and where and when to release it. The weather in Britain at the moment seems to be relatively warm during the day, but more frosts at night. Anyone have any knowledge of this sort of thing? Tivedshambo (talk) 21:21, 10 February 2008 (UTC)

I suggest you put it back. They are very hardy and will be more bothered by a plastic bowl and lack of insects than a spot of frost.--Shantavira|^{feed me} 08:28, 11 February 2008 (UTC)

That's a nice picture. I don't have any answers for you - but would it be okay to use your photo in the Viviparous lizard article? --Kurt Shaped Box (talk) 08:58, 11 February 2008 (UTC)

Are you sure it is a viviparous lizard?! It sure doesn't look like one to me. Looks more like a smooth / common newt actually (see, for example, this page ). Please anyone knowledgeable in British fauna clarify this one! Kindest wishes, --Dr Dima (talk) 10:25, 11 February 2008 (UTC)

I'm pretty certain it's reptilian, not amphibian. The skin was too dry, and amphibians don't tend to bask as the skin dries out (thanks to David Attenborough on TV last night for teaching me that!). I'll release it back into the wild as the do seem to be more hardy than I'd suspected - it just came as a surprise finding one in February. A sign of climate change perhaps. Feel free to use the picture - that's what it's there for! Tivedshambo (talk) 12:36, 11 February 2008 (UTC)

Viviparous lizard has very clearly visible scales covering its body (see, for example, this page ). The photograph you provided is quite high-res, yet I can't see any scales. Bottom line: I think it's a newt. --Dr Dima (talk) 14:51, 11 February 2008 (UTC)

You may be right - I'll tag the photo to state this. Either way, it is now back in the wild. Tivedshambo (talk) 07:42, 12 February 2008 (UTC)

colon cancer

Who first discovered colon cancer?Jafra girl (talk) 21:55, 10 February 2008 (UTC)

Cancer itself has been known since antiquity, though not by that name until Hippocrates and Celsus. The Wikipedia article on cancer says "The first known surgical treatment for cancer was described in the 1020s by Avicenna (Ibn Sina) in The Canon of Medicine." This probably involved the removal of an external, visible tumor, since surgery as we know it only came in during the late 19th century with the advent of anesthesia and infection control. An early anatomist who conducted human dissection and autopsies was Ibn Zuhr (Avenzoar), working in Spain in the 12th century. We can suppose he might have seen colon cancer, it being not uncommon, but no occidental, if you will, before him dissected human remains. You have no doubt noticed that I haven't simply provided a name; that's because I don't know, but whoever it was didn't so much "discover" it as "describe" it medically. People have known about cancer all along. --Milkbreath (talk) 12:21, 11 February 2008 (UTC)

Orkney Isands

What is the scientific origin of the Orkney Islands, and what kind of islands are they? 96.244.11.56 (talk) 22:42, 10 February 2008 (UTC)Lea Jackson

February 11

Melting points of ice in cold

We're experiencing bitterly cold windchills where I live, and it got me thinking: when salt is applied to ice, it removes the ice because it lowers the melting point. So let's say that I have some calcium chloride salt that is effective in temperatures as low as -25°F. Now let's also suppose that the temperature outside is 0°F, but the windchill is -40°F. Will the salt work? --Emery (talk) 01:43, 11 February 2008 (UTC)

As far as I know, it shouldn't make it stop working. As you can tell from reading the article, wind chill is merely an apparent change in temperature, caused by changing the rate of heat transfer. It does not actually lower the temperature of a substance any more than still air would, it just does it faster (it only lowers your body temperature further than still air because cooling air has to fight with your body's heat-generating metabolism). Someguy1221 (talk) 01:56, 11 February 2008 (UTC)

He stole my answer! Just kidding. Someguy is absolutely correct. Wisdom89 (talk) 02:02, 11 February 2008 (UTC)

To say the same thing another way: wind chill does not describe a temperature; it refer to a temperature as an expressive way of describing a rate of heat loss from your body. --Anon, 03:40 UTC, Feb. 11.

"Perceived cold" is a good way of describing it methinks. Wisdom89 (talk) 03:41, 11 February 2008 (UTC)

Orbits

Assuming you have a spaceship with an engine that can provide one gravity of continuous thrust, what's the minimum orbital period you can manage for orbiting Earth? --12.169.167.154 (talk) 01:51, 11 February 2008 (UTC)

Unfortunately, I don't think the question is well-formed. If you launch your spaceship from a point above the Earth's surface (so that the gravitational acceleration is slightly less than g) you will accelerate at an increasing rate, past escape velocity, and break any orbit. As long as you can produce continuous thrust, in fact, you will always be able to break out of any orbit - orbits only require an initial velocity. Anyway, you might be able to find what you're looking for if you note that for stable orbit, Gravitational acceleration must equal centripetal acceleration, or $GM/r^{2}=v^{2}/r$ and the period $T=1/2\pi \omega =r/2\pi v$. SamuelRiv (talk) 03:04, 11 February 2008 (UTC)

The question makes sense if you realize that it's not asking about an orbit in the usual sense of a freefall path, but one where the spacecraft is thrusting continuously downward, but is moving fast enough that it does not collide with the Earth. I have seen the term forced orbit used for this, although it doesn't seem to be known to Wikipedia.

As Samuel noted, in a conventional orbit $GM/r^{2}=v^{2}/r$. Assuming that the orbit is not so high above ground level that diminution of gravity is a significant factor, the left-hand side is simply equal to 1 gee. So if we thrust continuously downward at 1 gee, we double the total acceleration and therefore double the value of $v^{2}$. So the speed is greater by a factor of $sqrt2$ and the period is smaller by the same factor. The answer is just about an hour. For a more accurate number, do the math based on a realistic value of $r$.

--Anonymous, safely at ground level, 03:52 UTC, February 11, 2008.

Force+chair

1. I can lift my own weight. (empirically tested at gym with weight machine)

2. I can lift the weight of the folding chair in my room. (again, tested it)

3. I can lift the chair's weight combined with my own (tested at gym again)

4. I can not lift the chair while standing on it.

Why? I understand that if I did manage it, I would be levitating, and I think it has something to do with...by lifting the chair, I'm pushing down ONTO it with an equal amount of pressure from my legs, neutralizing the lift. Is that right?

Thanks76.118.184.59 (talk) 02:23, 11 February 2008 (UTC)

Yes. Because the amount of force with which you lift the chair is equal to the amount of force with which your feet press against the chair, the net force on the chair and you is zero, and you don't move. Wrad (talk) 02:32, 11 February 2008 (UTC)

But see cartoon physics. --Milkbreath (talk) 04:11, 11 February 2008 (UTC)

"Perceived cold" is a good way of describing it methinks. Wisdom89 (talk) 03:41, 11 February 2008 (UTC)

You meant to put that under #Melting points of ice in cold, right? --Anon, 03:55 UTC, Feb. 11.

heh, yep, slip up - thanks for pointing it out. Wisdom89 (talk) 04:57, 11 February 2008 (UTC)

You could always use a pulley to reverse the direction of the applied force.--Shantavira|^{feed me} 08:32, 11 February 2008 (UTC)

Yea, but the pulley needs to be attached to something which is fixed relative to the ground, and that thing is in effect holding up both you and the chair. --Spoon! (talk) 13:15, 11 February 2008 (UTC)

I have always found such levitation quite easy- while I am dreaming. Edison (talk) 03:23, 12 February 2008 (UTC)

What is Adjunctive Therapy and how does it work?

What is Adjunctive therapy and how does it work? Also, how does it apply to animals, especially exotics, and how does it effect them? —Preceding unsigned comment added by SBlondie8967 (talk • contribs) 04:49, 11 February 2008 (UTC)

Adjunctive therapy, according to the National Institute of Health is "Another treatment used together with the primary treatment. Its purpose is to assist the primary treatment." [8] For example: giving glycoprotein IIb/IIIa inhibitors to someone who has had angioplasty. The angioplasty is the primary treatment, but the IIb/IIIa inhibitors help improve the effectiveness of the primary treatment and are thus considered adjunctive therapy [9]. I'm not sure how to respond to your second question about animals, as I imagine that it would be the same or very similar is in humans. (EhJJ)^TALK 19:25, 11 February 2008 (UTC)

Can you think of any major new organs or adaptive behaviours which evolution might throw up in the next few million years?

Some researchers believe that the Cambrian explosion may have been due to the sudden development of vision. Organs for hearing similarly affected life on earth in profound ways. There are now countless methods whereby creatures walk, fly, mate, live and so on. But are there any other possible major developments that we could second-guess and say: “Here is another organ or sense or way of getting around or maintaining an existence that evolution has not yet found”? Can you think of anything, or do you think that basically nature has no more tricks up her sleeve. Myles325a (talk) 05:56, 11 February 2008 (UTC)

I doubt there will be anything that will create a new Cambrian explosion, but the ability to detect harmful radiation might be useful after humans have irradiated the planet. — Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 06:54, 11 February 2008 (UTC)

Evolution will continue so long as life exists on this planet. Nature is certainly not done. In my opinion it's really not feasible to infer what other adaptations, phenotypic changes, or speciation events might occur in the next million years. Humans most likely will not survive that long. However, if forced to make some kind of a projection, human beings will not be around to observe any major changes. Allelic frequency changes will continue to occur, and new species of plants will continue to emerge, but other than that, I doubt we'd see much. Wisdom89 _{(T / ^C)} 07:52, 11 February 2008 (UTC)

For either genetic drift or natural selection to result in anything you would really consider "evolution," there would probably need to be some manner of reproductive isolation to arise (stir and let cool for 3000 generations). I don't see this as likely in a stable world. Someguy1221 (talk) 08:03, 11 February 2008 (UTC)

An organ capable of breaking down and expelling radioactive material/heavy metals from the body would be a useful adaptation - as would the ability to emit EMP (to defend oneself against those pesky wild, predatory nanobots). --Kurt Shaped Box (talk) 08:55, 11 February 2008 (UTC)

Who is to say that the nanobots won't evolve resistance to EMP? Advanced nanobots can evolve in just one generation, but nature takes a much longer time. Let's hope we don't invent anything like that. 206.252.74.48 (talk) 14:37, 11 February 2008 (UTC)

Is this a reference to Star Trek the Next Generation by any chance? Wisdom89 _{(T / ^C)} 20:48, 11 February 2008 (UTC)

I don't watch Star Trek, so no. Nearly every scientific thing ever discovered seems to be featured on that show, so it's hardly a coincidence. 206.252.74.48 (talk) 16:59, 12 February 2008 (UTC)

WHEELS!!

Eventually humanity will adapt to pavement, as rollerbladers have done... Wheels FTW! —Preceding unsigned comment added by 79.122.115.170 (talk) 08:40, 11 February 2008 (UTC)

I saw the future on TV once. It was land squid. --Kurt Shaped Box (talk) 08:48, 11 February 2008 (UTC)

Kurt Vonnegut's Galápagos posits that the best adaptation for everyone would be for the human brain size to shrink back down to a less troublesome size. --Sean 14:37, 11 February 2008 (UTC)

File:ATPsynthase labelled.png

ATP synthase

But there is the problem of biological wheels being nigh impossible. But there is a clever work-around in the book The Amber Spyglass. I think humans are more likely to develop cup-holders and storage pouches for snacks. We may also eventually secrete petroleum, which will solve all our problems, right? 206.252.74.48 (talk) 16:37, 11 February 2008 (UTC)

Biological wheels are nowhere near impossible- they're quite common, albeit on a small scale. See Flagellum. Friday (talk) 16:52, 11 February 2008 (UTC)

Anyway, it's not the wheels that are the hard part, but the axles! :) --Sean 18:27, 11 February 2008 (UTC)

Not really, see the structure of ATP synthase. It has a protein axle (gamma subunit) that connects the two wheels (F0 rotary motor and the F1 catalytic core) One difference is that the wheels are stationary and the axle spins but the general idea is there from a structural perspective. David D. (Talk) 22:23, 11 February 2008 (UTC)

AIDS

Are we any closer to a cure for AIDS than we were 25 years ago? —Preceding unsigned comment added by 195.188.208.251 (talk) 10:29, 11 February 2008 (UTC)

That's a very possible maybe. There have been some promising studies, although no absolute proof that an HIV cure or vaccine has been developed yet. HIV vaccine describes some of the research in this area, though I'll admit it's not the greatest article. There is also this research program that has (apparently) successfully cured HIV infected mice during the ~40 day duration of the animal testing. Interestingly, that press release completely leaves out about two thirds of what that treatment entails, although those two thirds may have been thought up only after that very old press release was made. There have also been treatments tested in humans that successfully lowered the viral load of infected individuals, though the true impact of such treatments is yet to be seen (I also don't have a link for the treatment I'm thinking of, offhand). Someguy1221 (talk) 11:03, 11 February 2008 (UTC)

I saw some information about this at this link --Dweller (talk) 13:35, 11 February 2008 (UTC)

Military Tattoos

I don't know if this is a big public misconseption but I think it is a common thing for military units to all get tattoos. And, at least here in Aus, you cannot donate blood if you have tattoos. And I would suppose that militaries around the world would use blood transfusions very regulary.

So...can people in the military donate blood? I have seen this happen in movies and such (Pearl Harbour and Band of Brothers comes to mind) but do they (now) enforce the same rule of no donating if you have tattoos? If not why not? (I can't think that where they get their tattoos from is any more sanitary than the general populution). If they do not allow the donating where do they get the blood from?

Shniken1 (talk) 12:44, 11 February 2008 (UTC)

Why wouldn't they let you donate blood if you have tattoos? I have never heard of any such rule in the U.S., so I think this is unique to where you are from. 206.252.74.48 (talk) 14:33, 11 February 2008 (UTC)

The UK National Blood service also has restrictions based on tattoos and piercings [10]. It's possible (probable, in my opinion) that the military have their own rules regarding who can donate. Travel to malarial areas would also be an issue affecting the military. 81.174.226.229 (talk) 14:44, 11 February 2008 (UTC)

From the American Red Cross ([11]) guidelines for deferral of donations:

Wait 12 months after a tattoo if the tattoo was applied in a state that does not regulate tattoo facilities. This requirement is related to concerns about hepatitis....

Acceptable if the tattoo was applied by a state-regulated entity using sterile needles and ink that is not reused. Only a few states currently regulate tattoo facilities, so most donors with tattoos must wait 12 months after tattoo application before donating blood. You should discuss your particular situation with the health historian at the time of donation.

I have seen other jurisdictions with a similar deferral period (12 months) following a tattoo or piercing. As noted, the chief concern is about diseases – particularly strains of hepatitis – that may be transmitted via improperly-cleaned piercing or tattooing equipment.

In wartime, and while experiencing severe blood shortages, it is conceivable that blood-collecting agencies might relax some of their deferral criteria. I cannot comment on how or when this may have occurred in the past. TenOfAllTrades(talk) 14:57, 11 February 2008 (UTC)

RD stress

(See my associated post at the talk page) How often do periods of RD angst occur and how long do they tend to last? I'm depending on you bespectacled intelligent folk to derive some cast-iron objective criteria for determining when these periods are, and then generating some lovely charts and graphs to map it. To help you, I'd suggest that posts to the talk page proliferate at these periods. I'm looking forward to some very informative and comforting responses. If you do really well, you might even prompt me to reestablish the neglected thread of the week award. --Dweller (talk) 13:05, 11 February 2008 (UTC)

You'd better re-establish that reward. In a bizarre coincidence I just discovered it today and was wondering if it will ever come back. 206.252.74.48 (talk) 16:23, 11 February 2008 (UTC)

One thing I agree on.. looking at the dreaded 'discussion' page is a sure sign that things are getting bad or going to get bad soon. The thing has 'bad vibes'>87.102.79.203 (talk) 19:15, 11 February 2008 (UTC)

Looking for northern lights

I have vacation time at the end of August. I decided that I'd like to use it to go see the northern lights. Any suggestions on where to go? I'd want to go to a rather metropolitan area. Tromsø appears to work - but I don't know if it is far enough north. -- kainaw™ 13:32, 11 February 2008 (UTC)

Have you been keeping an eye on http://www.spaceweather.com/ ? There's a wealth of information there, and the site will send you an email (for free) or a phone call (for cash) every time something interesting is happening in the sky. TenOfAllTrades(talk) 15:05, 11 February 2008 (UTC)

One thing to keep in mind is that it will be summer up there, and thus the sun will be shining for most of the night, effectively making the northern lights impossible to see unless you stay up very late. Being in a city won't help much either, as city lights caan block all but the most startling northern lights. If you're lucky and you do your homework, though, you might be able to see them. Wrad (talk) 15:15, 11 February 2008 (UTC)

Tromsø in August is absolutely beautiful, but it's not the place (or time) to go to for watching polar lights - at that latitude, the sun sets for an hour or two in August, but you don't get to see a dark night sky - it's more like a prolonged dusk immediately followed by the dawn. If you can brave the weather, visit Tromsø in December or January for spectacular polar light displays. In August, you probably have better chances at Patagonia (although I don't know if that is far enough to the south) -- Ferkelparade π 15:30, 11 February 2008 (UTC)

Basically, seeing the northern lights is all about probabilities, and by going in the summer and staying in a city, you are drastically decreasing those probabilities, approaching impossibility. Wrad (talk) 15:35, 11 February 2008 (UTC)

Thanks. That all makes a lot of sense. I have seen the lights in Norway before (Bardufuss is the phonetic spelling of whatever city I was in - I don't know the Norwegian name). That was in February and I was on top of a mountain above the snowline. I guess my best bet is to try to head south instead of north. I've noticed on astronomy sites that you can see the band of the Milky Way in August if you head south as well. Now, it is just a matter of deciding where to head to. -- kainaw™ 16:06, 11 February 2008 (UTC)

Two points. First, in terms of being where the aurora is, it's not your latitude that matters, but your position in relation to the magnetic pole. Therefore the aurora borealis can be seen farther south in Canada than in Norway. This particularly matters in summer since the lower latitude in Canada means you get more darkness at night. I haven't looked into the question of where in Canada is best to go, and for the southern hemisphere I have no idea. I also note that if you get too close to the magnetic pole, the aurora dimishes again (hence the term "auroral oval"); but this isn't likely to be a problem in practicce.

Second, we are currently nearer the bottom of the solar cycle (2006) than the top (about 2012). There should be much better auroras available if you wait a few years.

--Anonymous, 22:22:22 UTC, February 11, 2008.

Should I be the smart-ass who points out that you can't see the Northern Lights from the Southern hemisphere? No, I shouldn't, carry on. Mad031683 (talk) 16:56, 12 February 2008 (UTC)

re:thermoacoustic refrigerator

as mentioned earlier im working on thermoacoustic refrigerator for demonstration.in my final experiment my results were not that good as mentioned in the article.rather i m unable to interpret the results please help:

1. room temperature:25 cel {these are temperatures of cold end of stack) 2.temperature inside the resonator:27 cel 3.temperature reduced by 1 cel in 1 min at 385Hz freq and length of wave was 92: 26 cel 4.temperature reduced by 1 cel in 1 min at 385 Hz freq and length of wave was 92:25.5 cel 5.further temperature became constant at 25.5 cel for next 10 mins.

is the temperature reduction due to the stack.or it is due to a push of external air(at 25 cel ) into the resonator. ive used the function generator: http://www.edn.com/contents/images/di2409setup.exe

kindly help, regards sam Reveal.mystery (talk) —Preceding comment was added at 14:03, 11 February 2008 (UTC)

Vacuum in space

Who figured-out/proved that space is mostly empty between physical objects? In particular, that "the heavens" are not full of air like our own atmosphere? Note that I am specifically *not* talking about luminiferous aether or any such medium for EM radiation; just air. Thanks. --Sean 14:29, 11 February 2008 (UTC)

I don't know that this discovery can be attributed to a single person. In the early 17th century Francis Godwin wrote The Man in the Moone in which his hero travels to the Moon in a chariot towed by trained geese - so Godwin clearly believed that interplanetary space was filled with air [12]. By the late 17th century Robert Boyle was experimenting with the properties of a man-made vacumm and conjecturing that the interstellar medium could be a similar vacuum. I imagine that an evolving understanding of the implications of Newton's law of universal gravitation and Newton's laws of motion in the late 17th/early 18th centuries convinced scientists that interplanetary space must be mostly empty, otherwise the planets would quickly lose energy and spiral in towards the Sun. I don't know whether Newton himself ever explicitly pointed this out. Gandalf61 (talk) 16:31, 11 February 2008 (UTC)

Before that, Aristotle (and those who followed him) would not have countenanced the idea that the heavens might be full of air. For him, the cœlestial realm was utterly and profoundly different from the terrestrial/sublunary, cœlestial objects being made of æther. Algebraist 17:09, 11 February 2008 (UTC)

Bœnus pœints for þe use of archæic ligature! SamuelRiv (talk) 21:32, 11 February 2008 (UTC)

Um, doesn't that change the pronounciations completely? Such as it being pronounced "bee-nus peeints"? —Preceding unsigned comment added by 206.252.74.48 (talk) 21:56, 11 February 2008 (UTC)

Depends what century you're in. Originally, œ had the value [oi̯], but this had shifted to [e] by the middle ages. But what do I do with these bonus points? Is there a prize of some sort? Algebraist 23:42, 11 February 2008 (UTC)

The discovery of the barometric formula was a clue as well. Icek (talk) 15:47, 12 February 2008 (UTC)

plastic beads

How are solid plastic beads made? —Preceding unsigned comment added by 71.100.0.31 (talk) 15:36, 11 February 2008 (UTC)

This may be of use (http://www.wisegeek.com/what-is-plastic-extrusion.htm) perhaps? ny156uk (talk) 19:04, 11 February 2008 (UTC)

The material is probably sprayed into a cooling medium. The size of the droplets controls the size of the produced beads.

Atlant (talk) 20:14, 11 February 2008 (UTC)

But how do they get the eyes for the thread? David D. (Talk) 22:29, 11 February 2008 (UTC)

Well, I agree that any that are basically prismatic are probably extruded. Pierced spheres, I don't know about; I could imagine compression molding followed by tumbling for flash removal.

Atlant (talk) 23:36, 11 February 2008 (UTC)

Solid beads are different from pierced beads. pierced beads are extruded pipe or tubing that is cut and then heated until the edges melt and disappear. The spray thing with molten plastic would be like how lead shot is made by pouring liquid lead into a container that has holes at the top of a tower and as the droplets fall they turn into spheres and solidify before hitting the ground. Maybe plastic is done the same way. 71.100.0.31 (talk) 01:27, 12 February 2008 (UTC)

Big-Bonedness

Is there such as condition as being 'big-boned'? --Ouzo (talk) 15:57, 11 February 2008 (UTC)

Yes, ICD9 278 covers the many variations of obesity. If you are referring to conditions in which the bones themselves are deformed and larger than normal, see the ICD9 710 to 739 range. -- kainaw™ 16:11, 11 February 2008 (UTC)

Thanks for the link. ICD-731 listed as Osteitis deformans describes what I'm looking for (articled as Paget's disease of bone). --Ouzo (talk) 20:46, 11 February 2008 (UTC)

Chemistry helper software

Hey everybody. I'm looking for some kind of (simple!) chemistry software, preferably for Mac OS X or Linux. I'm not quite sure what functionality I need, except I need it to help me draw Lewis structure diagrams. By 'help' I don't mean that it should do any kind of actual work (i.e. I want to place everything myself to learn) but I'm tired of using drawing programs! I found a huge list (and another similar one) of chemistry software for OS X, but I want something pretty small and simple (and free) since I'm just starting out. Also, I figured to ask here rather than at the computing reference desk, since the science geeks are over here! Thanks in advance. -- Aeluwas (talk) 16:23, 11 February 2008 (UTC)

Category:Chemistry software has a list of ones that have Wikipedia entries. Molecule editor has external-links to the homepage of many standard ones (including ones with no WP page). BKchem, ISIS/Draw (Windows-only), and XDrawChem are all free and make it easy to do nice organic structures and save or export them in standard graphics formats, without a steep learning curve. DMacks (talk) 19:10, 11 February 2008 (UTC)

I remember using 'chemdraw' on a 'very old' (68000 processor mac) - no idea what it is like now but at the time it was very simple to use.87.102.79.203 (talk) 19:09, 11 February 2008 (UTC) My god that's expensive for what you get - maybe 'xdrawchem' is the free alternative. Good luck. The price of 'chemdraw' is simply outrageous.87.102.79.203 (talk) 19:13, 11 February 2008 (UTC)

There's a very deep academic discount, but if something that's free suffices, that's even cheaper still:) DMacks (talk) 19:20, 11 February 2008 (UTC)

Hmm, thanks guys. I've looked through a couple of these, but haven't found anything that does what I need (i.e. drawing simple lewis structures). I'm sure they'll come in handy later, though. I'd like something to help me create pictures like these (the ones on the left). -- Aeluwas (talk) 12:42, 12 February 2008 (UTC)

Oh sorry, it should be trivial to take a program that does line structures and make it do lewis structures. Maybe you could e-mail some of the free software people and ask if their software can do lewis structures as well. I found http://www.acdlabs.com/educators/cincinnati.html quote:

ACD/ChemSketch is ACD/Labs' chemical structure drawing and visualization application for the Microsoft Windows (95, 98, NT, & 2000) operating system. The software enables you to draw virtually any chemical structure within the scope of your imagination and provides the ability to add chemical structures and drawn pictures, such as lab equipment, Lewis structures, bond ....

it does a lot more as well - here's the main page http://www.acdlabs.com/download/ Note I've never used this program myself.(looks good though) 87.102.81.140 (talk) 13:26, 12 February 2008 (UTC)

Seems to be what I'm looking for, thanks! Way more advanced than I need at the moment, but I suppose the more advanced functions will come in handy soon enough as well. :) -- Aeluwas (talk) 16:31, 12 February 2008 (UTC)

Juxtacapillary (J) receptors

I randomly found this article. It claims that these receptors "sense" oxygen levels (actually it isn't clear from the article how). But I found no mention of them in the Internal senses section of the Sense article. Is that an oversight or is the J receptors article misleading? Rmhermen (talk) 16:56, 11 February 2008 (UTC)

There are literally thousands of chemical receptors like that. Calling them all "internal senses" would be unwieldy and pointless. It is unclear whether the concept of "internal senses" itself is meaningful. --169.230.94.28 (talk) 22:13, 11 February 2008 (UTC)

I can't recall from memory regarding their exact nature, but the stub seems to describe a mechanoreceptor response, not chemical. I could be wrong about that, but this is what I understand from the wording in the article. Wisdom89 _{(T / ^C)} 22:18, 11 February 2008 (UTC)

Using the Hall Effect to Find the Speed of a Flowing Ionic Liquid

Hi, can somebody please give me an indication of how to go about measuring the speed of an ionic fluid using the Hall Effect. Is there any way of doing this theoretically i.e. without simply calibrating the meter by measuring the Hall voltage of a certain liquid at various speeds and plotting a graph?

90.241.222.228 (talk) 17:05, 11 February 2008 (UTC)Shauno

You could just treat the fluid in the same way as an electric current (knowing the charge carriers) as long as you know the magnetic field strength..

There are numerous problems with this - including ion-pairing (reduces effective charge amount) , shielding by the fluid of the magnetic field (reducing effective field strength) and maybe electrode polarisation as well as the physically resistive effect of the charge polarisation..

So simply - you'd need to calibrate.

You could try to build up a model using all these factors (if relevent) - and use that.. (Beyond me though)87.102.79.203 (talk) 19:05, 11 February 2008 (UTC)

• The Hall Effect is when charged particles (in your case, the ions of your ionic fluid) move perpendicular to a magnetic field, they experience a force in the third direction (i.e. perpendicular to both the fluid velocity and the magnetic field). Now if you allow the ions to collect at the edges of the fluid channel, eventually an electric field will build up that will oppose the motion of more ions in that direction. A simple theoretical approach would be to use the equilibrium: force from electric field balances force from Hall effect to find the linear coefficient relating velocity and voltage. JohnAspinall (talk) 19:07, 11 February 2008 (UTC)

Bouncing Squash Balls

If i knew the volume of a squash ball and the temperature, could i work out how high it would bounce from a drop, using gas laws and kinetic energy equations? —Preceding unsigned comment added by 81.151.74.117 (talk) 19:53, 11 February 2008 (UTC)

I doubt it, because most of the energy loss is in the rubber of the ball, and you haven't claimed any knowledge about that factor.

Atlant (talk) 20:13, 11 February 2008 (UTC)

There's an alternative method - ignore the rubber and assume energy loss comes from loss of heat from the gas inside. (this is probably simpler than working out how the rubber deforms and loses energy)

maybe - ignoring the effect of the skin - you could assume that the bit in contact is squashed flat.. - squashing it would cause an increase in pressure and hence an upward force on the squashed bit. Without loss of energy it would bounce just as high.

To take account of the loss of energy you could say that the gas is being heated as it is squashed. If this increase in temperature causes loss of heat to the surrounding then the ball will not rebound as much - however since the heating is related to the rate of change of volume and the pressure you'd certainly end up with a differential equation.

These are the factors..

ʃpressure_t x volume_t dt = energy supplied

Rate of energy loss = k x (T_ball-T_external)

Volume of ball =4/3 pi r³ (1+cos a_t) .. a is the angle of the flattened bit (think this is right see Spherical cap for correct equation also try http://mathworld.wolfram.com/SphericalCap.html (eqaution 9) note the alpha is 90-a the angle I used below . sorry in a rush)

r(1-cos a) = distance of impact (you might need/want to reverse this to get a)

pi x (r sin a_t)² = A_t area of sqaushed bit

A_t x P_t - P_{external atmosphere}= F_t force upwards - note that here I've assumed that the original internal pressure was the same as the atmospheric pressure eg 1atm since I'm ignoring the skin

F_t-mg = overall force upwards (m is ball mass)

Pressure x Volume =2/3 Energy of gas

etc..

There's a bit more work to do here - including the above equations as well as newtons laws of motion I think there is all you need to at least construct a differential equation..(If you don't like differential equations you could use a computer to model this bouncing behavior in small steps of time.)

If you want/need more help please ask.87.102.79.203 (talk) 20:48, 11 February 2008 (UTC)

If you get that far and get stuck the maths reference desk might be your next step. Good luck87.102.79.203 (talk) 20:28, 11 February 2008 (UTC)

(( What follows is irrelevent to the original question but is added anyway 'just in case' .... Alternatively you could ignore any energy losses from the gas and calculated the energy required to flatten a rubber skin - here you might need to decide if there is a gas is in the ball or if the springyness comes entirely from the rubber itself - you could assume that any energy required to bend/compress the rubber is entirely lost - ignoring the bending force the energy is simply the change of length of a part of the skin times the distance it is moved. You might want to assume that the skin is flattenend vertically and does not move horizontally since that simplifies the eqautions..

In practice solid rubber balls bounce because of the springyness of the rubber, but hollow rubber balls bounce because of the springyness of the gas..

As a final option (and easiest) option you could just say that a certain percentage of the kinetic energy is lost on contact - but that wasn't your question.87.102.79.203 (talk) 20:44, 11 February 2008 (UTC) ))

We can do this far more simply. $PV=nRT$. Note that temperature is constant assuming perfect conduction into the outside reservoir (the outside air), as is the number of moles of gas. So $P=nRT/V$, and note that the energy in an ideal gas deformation is exactly $-\Delta U=\int PdV=nRT\int dV/V=-nRT\log V_{i}/V_{f}$. So we now know what kind of change in volume a given amount of energy will induce. Now we have to fudge things a little to make this work, and I don't think this is valid, but with what you are given, it's the only simple approximation I can think of. Let's now assume that the transformation when the ball hits the ground is isobaric - that is, of constant pressure. Then there must be some temperature change such that $V_{f}/V_{i}=T_{f}/T_{i}$, which will result in a heat loss of $\Delta Q=mc\Delta T$. Note there is a compression and then re-expansion of the ball, so we must double our heat loss value to find the total heat lost in the bounce. Find the kinetic energy from $U-2Q$, and you're home. I'm intrigued enough to try plugging in numbers on my own and seeing if this fudge works, so I'll report the results in a later post. SamuelRiv (talk) 21:28, 11 February 2008 (UTC)

The final equation I get is $h_{2}=h_{1}-2T(c_{air}/g)(\exp(-M_{air}gh_{1}/RT)-1)$. Plugging in the relevant numbers gets me a higher height than what I started with, suggesting this equation is wrong. I think my fudge was too fudgey. Back to the drawing board! SamuelRiv (talk) 22:41, 11 February 2008 (UTC)

How dangerous are Moka express machines...

...and other similar cookware that work with pressurized boiling water?Mr.K. (talk) 20:18, 11 February 2008 (UTC)

Moka Express and common pressure cookers have relief valves to prevent dangerous build-up of pressure. The temperatures are only a few dozen degrees above normal boiling point of water, so that on its own isn't a substantially worse scalding hazard than a normal tea-pot. I'd be most concerned about accidentally opening the vessel when it's pressurized...water would flash-boil coffee-grounds go flying, etc. DMacks (talk) 20:50, 11 February 2008 (UTC)

I think that would be difficult to do "accidentally". The pressure will push against the threads, so it should take an awful lot of torque to overcome the friction and unscrew the bottom from the top -- plus the bottom will be very hot, so it's not like you can grab it with your bare hand. Not sure what would happen if you didn't really get them threaded together right in the first place, but my guess is that the water would just bubble out from the joint and no high pressure would ever build up.

It has occurred to me to wonder what happens if the relief valve gets clogged with lime or something. Has anyone ever heard of an actual dangerous explosion from a moka? --Trovatore (talk) 21:01, 11 February 2008 (UTC)

I can't say for certain about Mokas, but the safety valve on my pressure cooker doesn't come into contact with the cooking liquid and isn't even used for steam venting except in failure, so it's not like to get scaled up. AlmostReadytoFly (talk) 09:25, 12 February 2008 (UTC)

Does reading ruin your eyes?

Does reading books, ruin a persons' eyes? If so can vision be preserved by not reading? How about reading on the computer?

Which is worse for vision, reading on the computer or books? --Frsoroad (talk) 23:05, 11 February 2008 (UTC)

Straining in the dark by reading books can be damaging, yes. IMHO, working late at night in front of the computer is more deleterious than reading books in normal warm light. Seriously, using wikipedia in the dark is like staring at white light. Wisdom89 _{(T / ^C)} 23:10, 11 February 2008 (UTC)

A recent article in the British Medical Journal said that idea that "Reading in dim light ruins your eyesight" is a myth. [13][14] Although low light levels can lead to temporary eye strain, there is no evidence that inadequate light while reading will result in permanent vision damage, or so says the article. -- 128.104.112.12 (talk) 23:34, 11 February 2008 (UTC)

Several studies have found myopia to be rare among illiterate cultures, and to increase dramatically in frequency in the first generation of children in those cultures to receive schooling. (See for instance Figure 1 of [15], originally from Morgan RW & Munro M (1973): Refractive problems in northern natives. Can J Ophthalmol 8: 226–228). These observations are widely accepted as evidence that spending a large fraction of ones time during childhood focusing at close distance -- e.g., reading -- strongly increases the likelihood of developing myopia. This conclusion is supported by experiments that have shown that chickens consistently develop severe myopia if they are raised in an environment without anything distant to focus on, or given eyeglasses for the same effect. Chicks, however, apparently unlike many people, only need a brief daily exposure to distant scenes to fully prevent this development of myopia. --mglg_(talk) 01:17, 12 February 2008 (UTC)

I always thought that my chicken tasted rather nearsighted. — Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 02:10, 12 February 2008 (UTC)

Your argument makes perfect sense, mglg. I always did read much more than my peers back in grade school, but even though my lenses are literally an inch thick, I think the rewards outweigh the disadvantages. 206.252.74.48 (talk) 13:36, 12 February 2008 (UTC)

A lot of straining of the eyes will develop bags under them as well. 200.127.59.151 (talk) 13:38, 12 February 2008 (UTC)

HCl Crystal Structure

I cannot find confirmation of this but when frozen does HCl have the same crystal structure as NaCl? i.e. cubic close packed? I assumed that it has this structure because the bond is very ionic, but the proton is very light so this may cause something to happen to the crystal.

Oh and I'm taking about at liquid nitrogen temps ~79 K

Shniken1 (talk) 23:39, 11 February 2008 (UTC)

See doi:10.1038/213171a0. Sounds like some interesting content to add to the HCl article. DMacks (talk) 01:43, 12 February 2008 (UTC)

Thanks for that, it is wierd, it doesn't have HCl written anywhere, hence I couldn't find it. :P (Lesson 1.a try all possible chemical names!)Shniken1 (talk) 01:51, 12 February 2008 (UTC)

Circumcision Controversy

I was just noting today how often this crops up. Why is a minor medical/cultural procedure tinged with so much partisan fervour? Web sites with such fanatical language and claims are myriad. It's not the same for other such things. If one gets an eyebrow piercing there are not fanatical pro and anti camps who will bend logic to their respective ends. Or a pro and anti appendectomy "lobby". I'm guessing it's because it's our "intimate" parts and we hope we have the "right" configuration. I'm not sure if there is any research as to the psychology of circumcision opposition/advocacy, but arrogant opinion is welcome ;-) Fribbler (talk) 23:51, 11 February 2008 (UTC)

Well an appendectomy procedure is designed to prevent the death of the patient. Circumcision is usually just slicing off a bit of someone’s genitals without pressing medical need. Eyebrow piercing would be just as controversial if it was performed on babies who lack the ability to give consent. --S.dedalus (talk) 00:00, 12 February 2008 (UTC)

Edit conflict, ARGH! But as Sdedalus says, the main point is that babies cannot give consent for a precedure that is not needed —Preceding unsigned comment added by Shniken1 (talk • contribs) 00:04, 12 February 2008 (UTC)

Just to clarify: babies don't give consent for ear-piercing, and it is quite common in some cultures that have brought the practice to North America. I don't agree with it, personally, but I don't know of any lobby against it. ៛ Bielle (talk) 00:08, 12 February 2008 (UTC)

I didn't know they did that on babies... But anyway if you don't wear ear rings for a while don't the piercings close up? i.e it is essentially reversable?Shniken1 (talk) 00:10, 12 February 2008 (UTC)

I'm against circumcision myself, certainly in infancy. But then why such vehement pro-circumcision argument? It seems almost like a religious/personal/political type position in that people attach much emotion to their slant without science. Which I believe would generally not favour it. Fribbler (talk) 00:26, 12 February 2008 (UTC)

It has nothing to do with science. It has to do with parents who don't think anyone has the right to tell them they can't have what they see no more harmless than cosmetic surgery done to their kids. Someguy1221 (talk) 00:31, 12 February 2008 (UTC)

To respond to Shniken1, yes, the holes in the ears will close over if left alone, as would the eye-brow piercings referred to by S.dedalus. Both piercings and circumcisions are painful procedures done on infants, when there is no medical necessity to hurt them and no ability for them to give "informed consent". My own vote would be for child abuse, but I doubt I will find many kindred souls in this. (You did ask for arrogant opinions, did you not?) ៛ Bielle (talk) 00:39, 12 February 2008 (UTC)

I did! And agree with you aswell. But I still wonder just why it elicits such emotion. The websites say things like, and I paraphrase for emphasis, if pro: "If you don't get it done your child will be austracised as a FREAK!!!" (in the US I imagine, sure we dont really do it here) and if anti "Your child will be scarred for LIFE!!!" I just wonder if there are reasons for the emotional nature of the arguments. Fribbler (talk) 00:49, 12 February 2008 (UTC)

I think it's not so much a matter of circumcision there as it is that a fair proportion of humans are insane. And wherever a few crazies find an issue to go nuts over, more crazies will go nuts in response. Oh yeah, basic human nature ;-) Someguy1221 (talk) 00:51, 12 February 2008 (UTC)

It's really too bad, for many reasons, but for this one in particular, that User:SteveBaker is no longer active on the Ref Desks. He had, as I recall, very strong, scientific views against circumcision. ៛ Bielle (talk) 01:52, 12 February 2008 (UTC)

My belief is that people are tired of complaining about things that matter, that they decide to complain about something trivial just so they have something to complain about. You pick just about anything (e.g. how to hang toilet paper (there was a RD vote on this!), how much sugar to give to children, fast food, placement of water towers, Star Wars vs. Star Trek) and people will debate it to the end of time. It is mankind's nature to argue and whine and such things. Of course, you can debate whether or not I'm right about that. 206.252.74.48 (talk) 13:48, 12 February 2008 (UTC)

It's an issue of religion and of "the correct way to bring up a baby". That's two sure-fire ways to get serious arguments. AlmostReadytoFly (talk) 09:18, 12 February 2008 (UTC)

February 12

sodium chlorate

what are the specifics of making sodium chlorate? or sodium perchlorate? —Preceding unsigned comment added by Steweydewey (talk • contribs) 01:20, 12 February 2008 (UTC)

Our articles on sodium chlorate and sodium perchlorate describe the synthesis of each. Someguy1221 (talk) 01:22, 12 February 2008 (UTC)

chemistry

magnesium carbonate is added to an added to an iron binding capacity determination in order to a. allow color to develope b. precipiate protein c.bind with hemoglobiniron d. remove excess unbound iron —Preceding unsigned comment added by 72.155.150.73 (talk) 01:38, 12 February 2008 (UTC)

Yes, quite probably one of a, b, c, d is the reason (or maybe a combination of those?). DMacks (talk) 01:40, 12 February 2008 (UTC)

A search eg http://www.google.co.uk/search?q=iron+binding+capacity+determination+magnesium&hl=en&start=10&sa=N suggests it may be 'd'. Who that helps if anyone?87.102.81.140 (talk) 12:55, 12 February 2008 (UTC)

Decrease of Earth’s orbital angular momentum (around the Sun)?

The motion impulse is sustained in case of zero gravity only as a straight line (?) If a turn or curve takes place this will lead to a reduction of the motion impulse. This applied to the motion impulse of the Earth would imply that the velocity of the Earth around the Sun is decreased. This because the gravitational impact of the Sun is such that the straight trajectory of Earth is curved. That is my question respectively my statement. This implies for Earth’s orbit around the Sun, that the radius is decreased. On the other hand leads the Sun’s burning to a decrease in mass and thus also to a decrease in gravitation. And that leads to an increase of Earth’s orbit. The total effect of these two partial effects remains open. Is this sound reasoning? Or can somebody explain me why the orbital angular momentum of the Earth should remain the same during all these millions of years (despite the gravitational impact of the Sun)? 77.57.61.59 (talk) 01:49, 12 February 2008 (UTC)

The Earth is in freefall. It doesn't require any energy input and can go on forever. --Sean 02:42, 12 February 2008 (UTC)

Additionally, the Sun's loss of mass, while existent, is quite negligible. For instance, if the Sun were to completely exhausts its hydrogen supply, it would have lost about 0.7% of its mass. In practice, the Sun won't come anywhere near fully consuming its mass of hydrogen (most of it remains well outside the core where fusion takes place), so something like a tenth of a percent is a better estimate for the mass lost in such fashion. I would expect that solar wind loss is similarly small. — Lomn 14:11, 12 February 2008 (UTC)

Using a 200V machine in a 220-240V country.

A machine has these power specs:
3 phase 200V
50/60Hz
1.6kw

Australia is rated at 220-240V.

If I acquire this machine, is it okay to use?
If not, is there a feasible solution?

Phrased properly: What difference in voltage ratings between a machine and a country is acceptable?
Rfwoolf (talk) 03:02, 12 February 2008 (UTC)

Volunteers on an online encyclopedia are not a suitable source of information for such a question. Consult a licensed professional electrical engineer in your country for advice. That said, the supplied voltage will be connsiderably greater than the rated voltage. This could over stress the insulation and contacts, causing catastrophic failure of the equipment. You might contact the manufacturer to see their recommendations. One remedy would be using a transformer to adapt the machine to the excessive voltage. Another would be to have qualified personnel rewind or otherwise modify it to operate on your voltage. It is surprising that the machine has one rated voltage rather than a range of allowed voltages, since power equipment may see voltage somewhat above or below the "official" supply voltage during actual operation. Edison (talk) 03:20, 12 February 2008 (UTC)

She'll be fine mate. Give it a whirl.Shniken1 (talk) 03:54, 12 February 2008 (UTC)

Does it have a motor in it?Tuckerekcut (talk) 04:50, 12 February 2008 (UTC)

Yes. Rfwoolf (talk) 05:00, 12 February 2008 (UTC)

Standard residential power is single-phase, not 3 phase. I suspect that the motor you are looking at is what we call here (Canada) 208 volt 3 phase. Such motors will not work using 230V single-phase power (which is what will be available in residential buildings in Australia). This motor will be equipped with three conductors (plus ground) instead of two and there will be no way to wire it. As stated above, we are not a reliable source of information, but I can warn you that connecting 3-phase equipment to a single-phase power supply is by no means safe. —BradV 07:02, 12 February 2008 (UTC)

Thanks for all the help. I've only just found out about the 3 phase thing, which I did look up, and now I realise that only certain factories are connected to 3-phase, and we wouldn't have that available, so that puts this issue to bed.
However, for my own education, the question still remains, what difference in voltage ratings between a machine and a country is acceptable? What would happen if the above machine was a 1-phase 200V. Could I use it in Australia which has 220-240V?
Rfwoolf (talk) 07:40, 12 February 2008 (UTC)

This is however an extremely theoretical question since no country has a 200V supply (see Mains power systems) so no one bothers to manufacture equipment for a 200V supply Nil Einne (talk) 09:01, 12 February 2008 (UTC)

I think you'll find that Japan has areas of the country where industrial power is 200V (and residential power is 100V). This diversity (between the low of 200 V and the high of 240 V) is a recurrcing challenge for the equipment that my company designs.

Atlant (talk) 13:11, 12 February 2008 (UTC)

If that device can tolerate such overvoltage, it will work (although it will heat up more)(it also might reduce it's lifespan). If that device cannot tolerate such overvoltage, it will either blow fuse or it will get damaged. -Yyy (talk) 09:57, 12 February 2008 (UTC)

I didn't answer before because I couldn't get my head around what was meant by a voltage in a three-phase system. I was hoping an Australian EE would answer. Our article "Mains electricity#Voltage levels" says that very often loads for 230V supplies will be marked "200V". --Milkbreath (talk) 11:56, 12 February 2008 (UTC)

Have you seen Three-phase electric power, Polyphase system and Three-phase? Nil Einne (talk) 15:39, 12 February 2008 (UTC)

Many large industrial scale electrical devices are built with tapped windings which allow the same machine to be connected to several different voltage levels. The full winding is used when it is connected to the highest rated voltage, and there are taps along the winding to allow it to be connected to somewhat lower voltages. The same motor might be capable of connection to a delta or wye three-phase supply as well. A supplier who has a motor with various taps and connection options needs stock only one motor to handle demands for, say 208 volt or 240 volt supply. Likewise transformers or autotransformers can be used to supply the desired voltage, but this is not a cheap option. If a factory had to install their own transformer because their local utility was supplying them with a higher voltage such as 4,000, 12,000 or 34,000 volts, then it might be quite economical to step the supply voltage down to the quirky voltage required by the electrical device. If a motor is operated on a higher than normal voltage, it may actually draw less current (depending on the type of motor), while it would draw more current if operated at lower than normal voltage. For these motors, low voltage would cause overheating due to high current, but high voltage would stress the insulation rather than overheating the conductors. When only single phase power is available, a phase convertor can sometimes be used to allow the use of a three phase motor. Or a second phase can be brought to the location from the utility's nearest three phase supply point, and the motor could be operated open delta. The most expensive option, and the one with the best results, is to bring in the other two phases. Again, an EE qualified to analyze and design power applications is the best person to advise on this. Edison (talk) 15:24, 12 February 2008 (UTC)

But you'd still have major problems getting the device to work in Australia though wouldn't you? Since three phase power in Australia is of course 415 V not 208 V... Nil Einne (talk) 15:33, 12 February 2008 (UTC)

Strange light

Hello. A few nights ago, I saw a golden sphere in the sky. At first I thought it was a star, but I realized it was moving. Then the light started to dim, and then it disappeared. I don't know what this was. Does anyone have any ideas? Thanks. JetLover (talk) (Report a mistake) 03:32, 12 February 2008 (UTC)

How did you know it was a sphere?Shniken1 (talk) 03:52, 12 February 2008 (UTC)

From my viewpoint, it looked like a sphere. JetLover (talk) (Report a mistake) 03:54, 12 February 2008 (UTC)

See Ball lightning --S.dedalus (talk) 04:50, 12 February 2008 (UTC)

Since this appears to be an UFO I would suggest you look at the page and associated external links. Avoid anything which talks about conspiracy, aliens etc seriously. Look for stuff which discuss which try to explain or suggest logicial possibilities for UFO sightings Nil Einne (talk) 16:02, 12 February 2008 (UTC)

You don't say where you are but a few nights ago, Saturday to be precise, there was an extremely bright sky transit of the International Space Station from west to east at 18.14 hours over southern England. It took about 4 minutes to go from the western horizon to the eastern and it certainly rises as a golden/red colour and sets the same colour but is a bright white overhead. Richard Avery (talk) 09:16, 12 February 2008 (UTC)

time of twilight

is there a mathematical equation to calculate the amount of monutes from sunset to dusk in different parts of the world. for example in NYC how many minutes after sunset will it be completly dark.Yribowsky (talk) 03:49, 12 February 2008 (UTC)yribowsky

I doubt it. I think it depends a lot on landscape. AlmostReadytoFly (talk) 09:51, 12 February 2008 (UTC)

The length of time from sunset until it gets dark - twilight - depends on the latitude and on the declination of the sun. The further north or south one goes from the equator, the longer will be the period of twight. The declination of the sun depends on the season of the year. Therefore in a particular place, the length of twilight will vary throughout the year. To do a mathematical calculation on the length of twilight requires a knowledge of spherical trigonometry.Simonschaim (talk) 13:26, 12 February 2008 (UTC)

Nearest star of spectral class O

What Class O star is nearest to Earth? --Cam (talk) 04:30, 12 February 2008 (UTC)

Zeta Ophiuchi maybe? 458 light years away. Clarityfiend (talk) 06:11, 12 February 2008 (UTC)

Space?

Watching my usual satellite passing over at 0645 this morning, (in Scotland), I was surprised not to be able to any stars. Since I believe that satellites circle 2-300 miles above the earth, what could have been between the satellite and the stars to obscure them. Too high for clouds, or am I wrong? Any ideas please.--Johnluckie (talk) 08:29, 12 February 2008 (UTC)

Are you sure it wasn't simply too bright at the time to see anything else (too much light pollution or perhaps it was dawn?)? You didn't mention what satellite this was but I assume you are referring to a satellite flare rather then simply observing the satellite. Satellite flares can sometimes be fairly bright, for example Iridium flares can sometimes be -8 magnitude which is a lot brighter even then Venus (~-4 i.e. about 40 times dimmer), and Sirius (-1.5) doesn't even come remotely close Nil Einne (talk) 08:52, 12 February 2008 (UTC)

Thanks for this, how do I differentiate between the satellite and it's flare? —Preceding unsigned comment added by Johnluckie (talk • contribs) 09:02, 12 February 2008 (UTC)

Well, the satellite itself would just look like a star moving across the sky in a straight line. A flare is just a flash. —Preceding unsigned comment added by Mattbuck (talk • contribs) 12:12, 12 February 2008 (UTC)

To clarify, a flare lasts a few seconds and you can see it moving during that time. You can look up Iridium flares at Heavens-Above. Icek (talk) 15:34, 12 February 2008 (UTC)

Thanks for these answers. I did see the satellite traversing for at least five minutes as I sat in my hot tub in the garden. It was dawn, I did see one faint star, but I still ask where were the other stars!--Johnluckie (talk) 16:44, 12 February 2008 (UTC)

According to apparent magnitude a non-flaring ISS can still be ten times brighter than any star, under the right conditions. Algebraist 17:30, 12 February 2008 (UTC)

You can look up ordinary satellite passes at Heavens-Above as well (but just now the website seems to be down). Icek (talk) 18:14, 12 February 2008 (UTC)

Golf

At home, I have a golf club that is much lighter than normal. But why does it hit things with the same force as a normal golf club? Interactive Fiction Expert/Talk to me 11:31, 12 February 2008 (UTC)

The lighter club may allow you to swing faster, which can compensate for the loss of mass. Additionally, many modern woods and drivers are engineered with a degree of "springiness" to better hit long drives. Our golf club and wood articles discuss this to some extent. The howstuffworks article on clubs may also be useful. — Lomn 14:05, 12 February 2008 (UTC)

Calculating power use

I am trying to figure out how much power my computer uses in standby mode. I found rates of 1-6 watts on several reference sites. What I can't figure out is how to convert that to kiloWatt hours, the units used on my electricity bill. Watt explains that the time is included in the unit, specifically one joule per second, so does 1 watt mean I have to multiply by 3600 to get the amount of power used in an hour? That gives me an unrealistically high number. It's been so long since I've done this kind of simple physics (ten years!) that I can't remember how to do it, and I am consternated. --Ginkgo100^talk 16:01, 12 February 2008 (UTC)

1 watt is one joule per second. However, no-one uses joules for electricity bills, they use kilowatt-hours. A kilowatt hour is by definition the energy expended in maintaining a power of 1 kilowatt (=1000 watts) for one hour (so it =3,600,000J). Thus if your computer is running at 1 watt (say) it will take a thousand hours (approx. six weeks) to use a kilowatt-hour of electricity. At 6W, it'll take about a week. Algebraist 16:07, 12 February 2008 (UTC)

or to put it another way 1W = 1/1000 (0.001) kWHr if used for an Hour. So 1kWHr of electricity will run a 1W computer for a thousand hours. and a x watt computer will run for 1000/x hours (divide) for the price of 1 kilowatthour.87.102.81.140 (talk) 16:40, 12 February 2008 (UTC)

So in other words I divide by the time rather than multiply. Thanks, I knew I was doing something horribly wrong! --Ginkgo100^talk 16:45, 12 February 2008 (UTC)

Wait... that's not it either... but I will use your formula. --Ginkgo100^talk 16:46, 12 February 2008 (UTC)

Multiply by the number of hours you use it, to get Watt-hours, then divide by 1000 to get kiloWatt-hours. 81.174.226.229 (talk) 16:55, 12 February 2008 (UTC)

Actually it's (watts of computer )x 3.6 x (hours used) to get the number of kilowatthours required —Preceding unsigned comment added by 87.102.81.140 (talk) 17:03, 12 February 2008 (UTC)

Huh? to get from watts to kilowatts you multiply by 3.6? that would cost me over $10000 a month to run one light bulb. 81.174 has it right —Preceding unsigned comment added by Mad031683 (talk • contribs) 17:19, 12 February 2008 (UTC)

Damn SineBot wastes no time. Mad031683 (talk) 17:20, 12 February 2008 (UTC)

No, it's not. You're thinking of Joules. Watts to Watt-hours is a multiplication, which is why they're called Watt-hours.

• If you take Watts and multiply by the number of seconds (i.e. 3600 times the number of hours) you get W.s=Joules.
• If you take Watts and multiply by the number of hours you get W.h=Watt-hours
• If you take Watt-hours and divide by 1000 you get kWh

(I'm IP 81.etc.) AlmostReadytoFly (talk) 17:56, 12 February 2008 (UTC)

Killing a cold virus by Exercising?

[medical question and answers removed.] Sorry, we can't answer medical questions on the reference desk... you'll have to advise your team to see their doctors. --Allen (talk) 17:13, 12 February 2008 (UTC)

Oh, come on. Read this. This was clearly not about medical advice. -- Aeluwas (talk) 17:38, 12 February 2008 (UTC)

Are you crazy? I'm not seeking medical advice. I don't want to get sued. I'm simply asking a hypothetical medical question.

A colleague claims that he was “not feeling well” and running a slight fever on Saturday. By Sunday, his temperature was just over 100 degrees Fahrenheit (38 Celsius). Despite the high body temperature, he went to the gym Sunday afternoon to exercise and workout. Today, he claims that he is much better and now has a normal body temperature. He said he “cooked” the virus (killed it) by exercising. When he exercises, his body temperature rises, and that temperature is too high for the virus to survive. Thus he is cured by exercising at the onset of his cold. Is this plausible? Thanks! Rangermike (talk) 18:14, 12 February 2008 (UTC)

Questions about EMP

Will EMP affect electronics that are turned off? There are electrical signals in the human brain. Could an extremely powerful EMP affect humans at all? 64.236.121.129 (talk) 17:15, 12 February 2008 (UTC)

It is possible for turned off electronics to get a shock from nearby turned on electronics. An overly-simplified way to think of it is to consider dunking the electronics in water. If you put two radios in water, one turned on and one turned off, it is possible that the one turned off could still be damaged. As for humans, I do not know of any EMP tests on humans. I have seen studies on rats - including a good one that had two control groups and tested the rats for three days on maze-learning tests. In general, they find that there is a reduction in brain function following extremely dangerous EMP shocks, but those are repaired over time. It is theoretically possible to do enough brain damage to kill a person (or animal) with EMP. -- kainaw™ 17:39, 12 February 2008 (UTC)

Are all indoor heaters 100% efficient?

If an electric space heater is heating up a room, and is not completely efficient in its method of operation, presumably all inefficiency is lost as waste heat. But if you consider that waste heat to be useful in itself (it also heats up the room), can the heater be said to be 100% efficient (thereby breaking the law)? If not, where did the lost energy go? Thanks. --Sean 17:18, 12 February 2008 (UTC)

Yes indeed. It is 100% efficient. But it doesn't break the 2nd law of thermodynamics. If the goal is to get heat, then the so called "waste heat" is not waste. 64.236.121.129 (talk) 17:22, 12 February 2008 (UTC)

Not quite, if it produces light and sound (like a vibration say), then not all of the energy is heat. Wisdom89 _{(T / ^C)} 17:25, 12 February 2008 (UTC)

What if it wastes energy producing ozone or even X-rays? There is a lot of room for energy "loss". -- kainaw™ 17:30, 12 February 2008 (UTC)

If it produced x-rays or ozone, the person using the space heater would be dead. 64.236.121.129 (talk) 17:34, 12 February 2008 (UTC)

Wouldn't you also have to take the generator into account? Mad031683 (talk) 17:37, 12 February 2008 (UTC)

Why would the user be dead? While X-rays are not extremely common in household appliances, ozone is common in those ionizing air cleaners. I haven't heard of anyone getting killed by using an ionizing air cleaner. -- kainaw™ 17:40, 12 February 2008 (UTC)

Eyeglass prescription relation to 20/20 scale

I've been trying to figure out what my numbers on the 20/20 scale are, and the Snellen Chart doesn't help because I can't see any letters on it at all. My eyeglass prescription is roughly -8 dioptres for each eye. Is there some formula or trick to find out what my eyesight is using this number? 206.252.74.48 (talk) 17:31, 12 February 2008 (UTC)

You can't see anything on the Snellen chart? Are you considered legally blind? -- MacAddct  1984 ^{(talk &#149; contribs)} 18:10, 12 February 2008 (UTC)

Photosynthesis vs photovoltaics

Which one is more energy efficient? Which method derives more energy from a given amount of sunlight? 64.236.121.129 (talk) 17:33, 12 February 2008 (UTC)