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December 13

Bleach Reactions

Ive had a mouse(or mouses) crawling around my room lately and i didnt really notice untill i saw one of the buggers the other night. Theres mouse excretions all over the carpet and places where it could hide where its especially concentrated.

Is it safe to spray the carpets with bleach or will this have some kind of reaction with the (presumably small?) amounts of ammonia in the mouse waste and ultimately kill me?

Cheers, kp —Preceding unsigned comment added by 121.220.22.118 (talk) 06:28, 13 December 2009 (UTC)[reply]

Urine + bleach --> chloramines, which are toxic. Probably it will be a small amount if you're cleaning a small spot, but it's still not the approach you should take. Go for an enzymatic cleaner (you can find it in pet stores, as it's used to clean up litter boxes and dog and cat urine or poop stains.) It is more likely to remove the smell, and won't turn your carpet white. - Nunh-huh 07:29, 13 December 2009 (UTC)[reply]

Bleach will oxidise ureas? Ureas already seem oxidised to me ... what will bleach do, convert urea to nitrogen dioxide, carbon dioxide and water? :S John Riemann Soong (talk) 01:02, 14 December 2009 (UTC)[reply]

I thought that since people have been putting bleach down toilets for years, this wouldn't be a problem, but it seems I was wrong. The Chlorine institute says not to mix chlorine bleach with urea or ammonia, and this NJ health factsheet warns about cleaning cat litter trays or diaper pails with it. You could try using borax, which is recommended by many for removing urine[1][2] --Pleasantman (talk) 13:34, 14 December 2009 (UTC)[reply]

Nitrogen Trichloride IED?

Would it be possible to build an improvised explosive device using urine and chlorine based cleaning products? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 13:28, 13 December 2009 (UTC)[reply]

I'm not going to look up how to make a bomb, but: "[NCl₃ is] formed in swimming pools when the chlorine gas used to disinfect the water reacts with nitrogen compounds found in urine, and can be a health risk to people like lifeguards who work continuously around the water. NCl₃ can be formed when chlorine reacts with nitrogen compounds in wastewater treatment plants. The particular danger associated with the formation of NCl₃ under these conditions is that a combination of its sensitive nature and low solubility in water leads to explosive droplets of NCl₃."[3] It's also very unstable, so don't try to make any: Nitrogen trichloride#Safety. Fences&Windows 17:04, 13 December 2009 (UTC)[reply]

Autophagy in bacteria

In eukaryotes specialized organelles - lysozomes - are used to mediate autophagy. Since bacteria lack organelles, they obviously can not take that approach. Even so, are there processes comparable to autophagy that occur in bacteria? Specifically, can a bacteria that finds itself in a low nutrient environment break down it's own proteins and structures to provide a temporary emergency supply of energy? Dragons flight (talk) 13:45, 13 December 2009 (UTC)[reply]

As you said, prokaryotes do not possess membrane-bound organelles. It's a great question. DRosenbach ^{(Talk | Contribs)} 14:21, 13 December 2009 (UTC)[reply]

Yes. Under starvation conditions bacteria will break down, or lyse, their macromolecules, and then many form resistant endospores. Fences&Windows 16:59, 13 December 2009 (UTC)[reply]

Don't suppose you can back your assertion with a reference? I specifically want to know about the consumption of macromolecules as a food source, which I'm having trouble finding references to for bacteria. Simply breaking down macromolecules wouldn't be interesting to me unless they can also utilize the associated energy for other activities. Dragons flight (talk) 21:28, 13 December 2009 (UTC)[reply]

There are tons of research studies on it, just Google "bacteria starvation proteolysis". Here's a recent study: [4]. Fences&Windows 20:42, 14 December 2009 (UTC)[reply]

on average how many pounds of fish are under a square meter of ocean?

On average, how many pounds of fish are under a square meter of ocean? 85.181.144.117 (talk) 14:30, 13 December 2009 (UTC)[reply]

Ocean biomass has some aggregate total mass of marine fish for the entire ocean; you can divide that by an estimate of total ocean surface area. However, fish are not uniformly distributed, so the merit of this average value, at least constructed in such a simple way, is dubious. Nimur (talk) 16:18, 13 December 2009 (UTC)[reply]

Google tells me that in January of this year a team estimated that the total mass of bony fish in the ocean is between 812 and 2050 million tons, therefore between 1.6 and 4 trillion pounds (1.6x10¹²—4x10¹² pounds). Our ocean article gives the surface area of the ocean as 3.6x10¹⁴ square meters. Dividing, you get somewhere around a hundredth of a pound per square meter. The distribution is extremely inhomogeneous though -- the vast bulk of fish are found on continental shelves. Also note that the figure leaves out squid, which might boost the number by 25% or more if included. Looie496 (talk) 16:35, 13 December 2009 (UTC)[reply]

what if you include the mass of all living things in the sea, including single-celled organisms? Then how much is under each square meter of water? 85.181.144.117 (talk) 16:57, 13 December 2009 (UTC)[reply]

[5] gives several estimates for the total mass of living things in the ocean - but the bottom line seems to be between 3 and 4x10⁹ metric tons - so let's split the difference and go with 3.6x10¹²kg - dividing that by the 3.6x10¹⁴ square meters of ocean surface gives us a handy 0.01kg/m². Given the size of the likely errors in our assumptions - this is a very similar kind of a number to the one Looie496 gives above - so you could assume that about half of that mass is fish and the other half algae, plants, etc. SteveBaker (talk) 17:22, 13 December 2009 (UTC)[reply]

Europe and Asia

Where does the boundary between Asia and Europe between Ural mountain and Ural river meet each other? —Preceding unsigned comment added by 113.199.185.146 (talk) 16:06, 13 December 2009 (UTC)[reply]

There is no fixed boundary. See Europe-Asia border and Borders of the continents#Europe and Asia. PrimeHunter (talk) 16:16, 13 December 2009 (UTC)[reply]

There are also several politicized slants on where the border is and where it should be, in both a political and cultural sense. The Caucasus has no shortage of conflict over this - see Dagestan (Invasion of Dagestan (1999)), Ossetia (2008 South Ossetia war), Chechnya, (First Chechen War and Second Chechen War). With such a disputed cultural and political boundary, and in the absence of a clear geographical barrier like a river or coastline, the boundary is very poorly defined and its location depends on who you ask. I think the Ural region has had less conflict over the boundary, historically, but the line is similarly ambiguous. Nimur (talk) 17:09, 13 December 2009 (UTC)[reply]

The border of Asia and Europe is not a political issue.It has nothing to do with the politics.It is purely an issue of geographical nature.So my question was also of geographical nature. —Preceding unsigned comment added by 113.199.157.236 (talk) 03:22, 14 December 2009 (UTC)[reply]

As explained in numerous articles including those linked to I presume, geographically the concept of Europe and Asia is questionable or even meaningless Nil Einne (talk) 11:54, 14 December 2009 (UTC)[reply]

The late Isaac Asimov once referred to "Afro-Eurasia." (existing before the Suez Canal)
:-D
Civic Cat (talk) 19:55, 17 December 2009 (UTC)[reply]

Radon

How do I test for radon in water? I would prefer something I can find in a basic laboratory, if not something I could find in a store. I'm doing a science fair project on it. THX --Richard —Preceding unsigned comment added by 76.230.211.192 (talk) 16:18, 13 December 2009 (UTC)[reply]

[6][7][8] Fences&Windows 16:52, 13 December 2009 (UTC)[reply]

It's a shame that F&W provided no description of those links - the second one is highly applicable and contains an excellent discussion of air/water partitioning of radon, with a method of on-site radon testing of water. -- Scray (talk) 17:35, 13 December 2009 (UTC)[reply]

Hmmm - tricky. Radon is a nobel gas - like Neon or Argon - so simple chemical tests are unlikely to be available. It does form a compound with fluorine to form Radon difluoride - but that sounds like a tough thing to do.

Radon is radioactive - and decays with a half-life of 3.8 days - so you could instead test for the decay product. Unfortunately, the commonest isotope of Radon decays to Polonium - perhaps you could detect the polonium instead - but sadly, the test for Polonium requires fancy spectrographic techniques - which are almost certainly beyond your "basic laboratory". So I think you have to test for radiation. If you can get a hold of one - I'd start testing the water with a geiger counter - if that indicates that the water is radioactive to a higher degree than background radiation - then the odds are very high that it's radon rather than some other radioactive substance. I don't know whether a gieger counter falls within your definition of a "basic laboratory".

Our article on Radon says that tests for radon in air are done using a Lucas cell - but again, that's measuring radiation, not a direct test for the chemical element itself. Our article says that radon test kits are cheap "and in some cases, free" - so perhaps you should talk to the manufacturers of the test kits and see if they'll send you a freebie - if you get a hold of the right person and explain what it's for, they'll probably be very helpful (it's free advertising!). However, I suspect that they are talking about radon in the air - not in the water. Also - if you're doing a science fair - remember that the half-life of Radon is just a few days - so you'll need to get a fresh sample on the day of the fair if you need to demonstrate the testing 'live'. SteveBaker (talk) 17:04, 13 December 2009 (UTC)[reply]

It's not chemically difficult to purify extract and purify polonium, even at very small amounts (isolated microgram quantities from several liters of urine!). Once it's pure, it's easy to quantify by measuring the radioactivity. But it's α, so you need a scintillation counter not a Geiger-counter. If you've got a scintillation counter already though, easier to just monitor radon directly with it instead of waiting for its daughter-nuclei. DMacks (talk) 18:08, 13 December 2009 (UTC)[reply]

Yes - but the radon only hangs around for a matter of days to weeks. The polonium that it decays into is much less radioactive and stays around for years. Hence, if you could easily do a chemical test for polonium, that would be a good thing to do because radon is a noble gas and will be extremely hard to test for chemically. But evidently, you can't chemically test for polonium either. So you're back to testing for radioactivity - and if you're going to do that then you might as well try to deduce how much radon is present from that.

You could presumably take a fresh water sample - measure the radioactivity - then wait (say) 3.8 days (the half-life of the most common radon isotope) - then measure the radioactivity of that same sample again. The amount by which the radiation levels have dropped would be an measure of how much radon was present in the original sample. Doing it that way, you're more directly measuring the radon content because (if present) it's radioactivity should completely dominate all of the other potential sources in the water.

Test kits for radon are easily obtainable - and cheap (http://www.free-radon-test-kits.com/ for example!) - but the problem with that is that the test kits only test the air - not the water. That makes our OP's task kinda tricky. I suppose you could boil away the water and somehow separate out the radon gas (it's really heavy) and then use an airborn test...but it's not clear whether you'd get enough radon from a small enough sample of water to make that feasible on an amateur scale (boiling away even a couple of gallons of water is TOUGH!). The second and third of the links that User:Fences and windows linked to seem to say that there are direct tests one can do on water - but since both are pay-to-read pages, I can't tell what the actual tests entail.

So - our OP has to measure radiation - not attempt difficult chemical or spectroscopic tests. Using the "test, wait 3.8 days, retest approach", you'd get a pretty good idea of the amount of radon in the sample...but that requires that our OP can find either a scintillation counter or a geiger counter or something similar.

I suppose - if you didn't have access to a geiger counter - you could try to McGyver a radiation counter somehow. Maybe get a household smoke detector and (carefully!) remove the Americium radiation source from it - then use the alpha particle detector to measure the radioactivity from the water. If you could pull it off - it would be an amazingly cool science fair project! Googling "homemade Geiger counter" produced a bunch of interesting pages. SteveBaker (talk) 19:26, 13 December 2009 (UTC)[reply]

Again, you can isolate incredibly minute amounts of polonium quantitatively. The problem isn't "no chemical test" (you just weigh the recovered material) but actually doing it on such a small scale. The amount of radon in the air (even dangerously-high levels in a poorly ventilated basement) is really a very small number. See Radon#Concentration units. But isn't polonium's half-life very short also? DMacks (talk) 19:50, 13 December 2009 (UTC)[reply]

Oh - you're right. ²²²Rn (the commonest Radon isotope) decays to Polonium - but all of the commonly found isotopes of Po are long-lived. What I didn't check was exactly which isotope of Polonium you get. Our article says: ²¹⁸Po - which has a half-life of just a few minutes. Decay chain says that the first stable decay product is ²¹⁰Pb - lead. Darn. You can't find that chemically because there will be plenty of regular lead in the water anyway. OK - so definitely you're going to need a radiation counter. SteveBaker (talk) 02:01, 14 December 2009 (UTC)[reply]

5' Cap and Poly-A Tail

Hello. If the 5' cap of mRNA is indigestible by nucleases since it resembles the 3' end, then why is the poly-A tail at the 3' end digestible? Thanks in advance. --Mayfare (talk) 19:36, 13 December 2009 (UTC)[reply]

What is your source for the 5' cap being indigestible and the 3' poly-A tail being digestable? In essence, they need not be digestable beyond being able to be cleaved from the mRNA at their points of attachment, which I am sure they are, or else they would remain indefinately. On second thought, does it really matter if it stays indefinately? The AUG "primer," so to speak, is the point at which translation will begin either way, but I do think the 5' cap is cleaved. DRosenbach ^{(Talk | Contribs)} 21:18, 13 December 2009 (UTC)[reply]

The 5' cap doesn't mimic the poly-A tail, the cap is simply a methylated guanine attached in an odd way. Together they prevent digestion, but there are decapping enzymes (names escape me) which can remove the cap. ~ Amory (u • t • c) 01:28, 14 December 2009 (UTC)[reply]

Aaaaand of course there's an article. 5' cap ~ Amory (u • t • c) 01:28, 14 December 2009 (UTC)[reply]

According to the 5' cap article, "the 5' cap looks like the 3' end of an RNA molecule (the 5' carbon of the cap ribose is bonded, and the 3' unbonded). This provides significant resistance to 5' exonucleases." According to the polyadenylation article, "in eukaryotic somatic cells, the poly(A) tail of most mRNAs in the cytoplasm gradually get shorter, and mRNAs with shorter poly(A) tail are translated less and degraded sooner." --Mayfare (talk) 10:30, 15 December 2009 (UTC)[reply]

Identify species from unusual shell

I found this shell on the east coast of the US (Atlantic Ocean). It is the only one I've found that opens on this side - all others I've found go around the other way and open on the other side. Can anyone identify it? Bubba73 ^{(Who's attacking me now?)}, 22:14, 13 December 2009 (UTC)[reply]

Are there some species that are left-handed? Or is this one a mutation or something? Bubba73 ^{(Who's attacking me now?)}, 23:43, 13 December 2009 (UTC)[reply]

It may be a Lightning whelk. Bubba73 ^{(Who's attacking me now?)}, 00:00, 14 December 2009 (UTC)[reply]

We appear to be missing our article on the chirality of shells, but taking Gastropod shell as an example, most "are dextral (right-handed) in their coiling, but a small minority of species and genera are virtually always sinistral (left-handed), and a very few species (for example Amphidromus perversus[) show an even mixture of dextral and sinistral individuals." --Tagishsimon (talk) 00:37, 14 December 2009 (UTC)[reply]

The times had an article about this a little while ago. Again, snails. ~ Amory (u • t • c) 01:24, 14 December 2009 (UTC)[reply]

And sex. And snakes. Excellent article. --Tagishsimon (talk) 01:55, 14 December 2009 (UTC)[reply]

Stephen Jay Gould has written an essay titled 'Left snails and right minds' about that subject in chapter 16 of his book 'Dinosaur in a haystack: reflections in natural history'. Dauto (talk) 01:49, 14 December 2009 (UTC)[reply]

Thanks, these pretty much tell me what I wanted to know (except for the specific species). (And I've ordered Gould's book.) Bubba73 ^{(Who's attacking me now?)}, 01:51, 14 December 2009 (UTC)[reply]

Resolved

Identified as a Lightning whelk. Bubba73 ^{(Who's attacking me now?)}, 16:07, 14 December 2009 (UTC)[reply]

Hunter-gatherers

Hunter-gatherer societies (such as Africans) were largely peaceful and in touch with nature. They only hunted what they needed to survive, and as a result they didn't cause any extinction. Then the Europeans came with technology and changed everything. Now, as a result of European technology, Africa is one of the most violent regions on the planet, with constant extinction, attempted genocide, etc. Other hunter-gatherer societies were largely peaceful as well, but then they turned violent and destructive once technology arrived. Why is it that technological societies have so much more problems than "primitive" hunter-gatherer societies? --70.129.184.254 (talk) 23:03, 13 December 2009 (UTC)[reply]

I just feel the need to say citation needed! Who told you hunter gatherers were peaceful? Were Africans hunter gatherers? Were they peaceful? Where did you get that they only hunted for survival? Have technological societies mopre problems with violence? Citation needed! Dmcq (talk) 23:19, 13 December 2009 (UTC)[reply]

There is little evidence that hunter-gatherer societies are necessarily more peaceful or more sustainable. You might, for example, take a look at John Keeley's War Before Civilization: The Myth of the Peaceful Savage. There are also some good books (the titles evade me at the moment) on the ways in which indigenous societies in the Americas often did agricultural and earth-works projects that had vast effects on their ecosystems. The overall premise that technological societies have more problems than primitive societies is fairly unsustainable. The problems are often different, to be sure. And we lack much record of much of life in a pre-modern period. But social problems hardly seem to be new, nor would one necessarily expect them to be. --Mr.98 (talk) 23:34, 13 December 2009 (UTC)[reply]

Try also Jared Diamond's Guns, Germs, and Steel: The Fates of Human Societies. While I won't go into details, the gist of the author's thesis is that the differences between societies (especially those which made the transition from hunter-gatherer societies to intensive agriculture versus those which did not) can be laid almost entirely at the feet of differences in the availability of domesticable plant and animal species in various regions. He makes a very persuasive argument that the innate character or characteristics of each region's native peoples had no appreciable effect.

On the issue of the relative peacefulness of hunter-gatherer societies, Diamond notes that in areas with low population densities, if your more powerful neighbour wants your land or hunting grounds, then you can just move further away. In small groups (family groups of hunter-gatherers, or small villages of early agricultural societies) it is possible to every person to know every other person in the group; any violence is directed solely at 'outsiders' and there is a vested interest in (indeed, an evolutionary imperative for) getting along. As you move to higher population densities and larger groupings, there's no way to escape your neighbors, and you have to deal with strangers even within your own society. Both factors lead to increased conflict not due to a change in the nature of the individuals involved, but due to a change in circumstance.

On the issue of extinctions, technologically-primitive peoples lacked the tools to efficiently eradicate entire species or (in general) to generate significant change in the environment. Hunter-gatherer populations were generallly very low-density, making it difficult for them to exceed the carrying capacity of the land. In other words, they lacked the numbers and the tools to render (many) species extinct; it had nothing to do with being 'in touch with nature'. They raped and pillaged as best they could, though they probably didn't succeed in wiping out entire species very often. (One very big exception may be the mammoth and other Pleistocene megafauna. See Quaternary extinction event#Hunting hypothesis.) TenOfAllTrades(talk) 00:58, 14 December 2009 (UTC)[reply]

We have Guns, Germs, and Steel, btw. so watch out... --Tagishsimon (talk) 01:02, 14 December 2009 (UTC)[reply]

(ec) There is evidence that Hunter-gatherers caused the extinction of several sub-species of the Mammoth - so, yeah - they probably caused extinctions. Tribes of modern hunter-gatherers have wars - there is no reason to believe that this didn't also happen back in prehistory. Were they in touch with nature? Probably. So this kind of wishful thinking really isn't true - which means that we can't answer your question because it's based on an obviously false premise. SteveBaker (talk) 01:37, 14 December 2009 (UTC)[reply]

What does "in touch with nature" even mean in this context? APL (talk) 01:40, 14 December 2009 (UTC)[reply]

The Native Americans managed to keep bison alive and thriving for millennia. The Europeans showed up and bison were nearly extinct in a matter of years. That shows that the Native Americans were more in touch with nature than the Europeans. --71.153.45.118 (talk) 01:53, 14 December 2009 (UTC)[reply]

It's certainly true that they didn't destroy the buffalo. On the other hand the Indians had neither economic incentives nor technological means to accomplish the eradication of the buffalo. So it doesn't really tell us anything. I have never killed a T-rex, but that's not proof I love and respect them. I think a good case can be made that many Native Americans did in fact treat living things with greater respect than the typical European settler, but to make that case one needs to look at legitimate lines of evidence and behavior and not impossible counter-factuals. For example, their religious and cultural traditions, their (small-scale) hunting practices, and their response to different hunting practices introduced by Europeans. Dragons flight (talk) 02:19, 14 December 2009 (UTC)[reply]

What does "in touch with nature" mean? You have to define it before you can use it in any sort of arguments at all. As far as I can tell it's nothing more than a feel-good phrase. APL (talk) 17:53, 14 December 2009 (UTC)[reply]

It's also commonly believe that humans were the ultimate cause of extinction of much of Australian megafauna possibly both due to hunting and their use of fire. Our article briefly discusses this and the evidence available and this appears to be even more recent [9]. In any case, it is well accepted that the Māori are responsible for the extinction of the Moa and indirectly therefore of the Haast's Eagle which preyed on Moa and also the Adzebill and other species, although of course they weren't necessarily all hunter-gathers. Holocene extinction may also be of interest. In terms of this 'in touch with nature' thing there is IMHO some suggestion that recent human arrivals were commonly not particularly in touch with nature and it was only with the development of more sophisticated culture and in some cases agriculture that they began to realise they should take more care with what they killed to avoid wiping out species in the area they were living in (which was generally a disadvantage to them). Even then, their limitations in tools etc was also likely a limiting factor. Those humans who were completely inept at taking care of nature were likely to make themselves extinct Nil Einne (talk) 03:28, 14 December 2009 (UTC)[reply]

Head-Smashed-In Buffalo Jump shows that Indians did everything they could to kill buffalo and probably harvested more than they could use at time. 75.41.110.200 (talk) 03:37, 14 December 2009 (UTC)[reply]

And the Easter Islanders were sufficiently "in touch with nature" that they made every tree on their island extinct...two for the price of one! SteveBaker (talk) 05:05, 14 December 2009 (UTC)[reply]

There is evidence that the settlement of polynesia, 3000 years ago, caused mass-extinctions and depletion of resources. From recent archeological studies of the island Vanuatu, east of Australia, we know that giant tortoises and many other species disappeared within the first century after human settlement. Excavated household waste also showed that seashells got progressively smaller over the years, indicating that the harvesting of the seashell population was done in a non-sustainable way. Consider for a moment that these ecological catastrophes were brought on not by consumerism or extravagant cultures but simply by people collecting food to eat. EverGreg (talk) 08:00, 14 December 2009 (UTC)[reply]

The Nazca cut down all their best trees. [10] Then again, they were farmers, so this doesn't count. I note though that the reason for farming is to solve the problem of not having enough food. This leads (without foresight) to the problem of deforestation, but the alternative (population control by letting people starve) is still a problem. Also, problems come in two kinds, those which cause heartache and pain and those which cause interest and fulfillment, depending I think on the learning curve or the condition of flow (psychology). Happy states of flow are I suppose more likely to be found in technological societies, where the idea that "nothing is impossible" is present, while hunter-gatherers are presumably stuck behind a kind of learning cliff which they haven't even thought about scaling, and are highly vulnerable to famine and flood and disease (and war). 81.131.39.3 (talk) 09:11, 14 December 2009 (UTC)[reply]

The reasons for the "primitive people were in touch with nature, modern people are not" fallacy are pretty easy to see. They come from our own deep-seated reservations about modernity, about a desire to see our own problems as part of a kicked-out-of-Eden story. But there is not much evidence for this view at all—it is more poetic and literary than it is historical and literal. What we can take away from this, I think, is not that Native peoples were bad, or that the European way of dealing with life is "the same" as theirs. It is more a deeper quality about how humans interact with their environments in general, and in this sense, the technological ability does have real importance—technology allows us to amplify our more exploitive side quite a bit. "Pre-civilized" nations definitely lacked the MEANS to be as destructive to either themselves or their lands on a scale comparable with the Europeans, for the most part, even if they did not actually lack the WILL to do so. In such an analysis, it is a problem of quantity and not quality of difference. --Mr.98 (talk) 14:58, 14 December 2009 (UTC)[reply]

We had almost this exact discussion last week, here. I suggest you read that. Once again, the question is based on a false assumption. There is plenty of evidence that hunter-gatherer societies caused mass extinctions, usually when moving to a new place where the native large animals weren't used to humans and thus made easy prey. You don't need any technology beyond a spear to kill an animal that doesn't know to run away from you. --Tango (talk) 15:03, 14 December 2009 (UTC)[reply]

Note that Polynesians were not hunter-gatherers, strictly speaking--they practiced agriculture. Same for nearly all Africans. Also for the majority of Native Americans at the time of European contact--at least the contact of European diseases. Pfly (talk) 06:16, 16 December 2009 (UTC)[reply]

I would suggest that when one thoroughly examines oral histories as well as the archeological and other such records, that humans are humans no matter the continent or the society. Tehecnology only allows us to be more efficient in what we do . . . without guns and the like, it may have taken longer to over hunt or over gather, but in the end, we are what we are. Some individuals and some communities may be a bit more sensitive, but at risk of over generalizing, we are what we are. Perhaps there is an element of globalization (i.e. awareness and eco friendly marketing) that can be used to alter our naturally destructive path . . . just some thoughts . . . .

Didn't our hunter-gathering ancestors wipe out the Neanderthals: the first race war?Civic Cat (talk) 20:04, 17 December 2009 (UTC)[reply]

December 14

are imine groups stabilised by base?

My class always seemed to discuss imine in terms of equilibrium (e.g. excess HOH ==> hydrolysis; distillation of HOH and excess amine allows formation of imines), but it seems to me that an imine group would survive in water without being deaminated under basic conditions, whereas hydrolysis would be catalysed by acid. (Ignoring the fact that acid prolly changes the equilibrium by deactivating the amine.)

In neutral solution, assuming equal abundance of HOH and amine, would a C=N bond tend to equilibrate to 50% C=O and 50% C=N? I know the bond energies are different but NH2- is a bad leaving group, NH3 is a decent leaving group (sorta?), whereas HOH is only formed as a leaving group under much rarer conditions and certainly much rarer in base! John Riemann Soong (talk) 00:56, 14 December 2009 (UTC)[reply]

If you know there is a stability difference, it would be silly to assume there is an equal distribution at equilibrium. Thermodynamic equilibrium is the same as the balance of the forward and reverse reaction rates. General equilibrium direction is stated in the very first paragraph of the imine article. DMacks (talk) 14:06, 14 December 2009 (UTC)[reply]

Well yes, but mass action principles often seem to overrule enthalpy considerations. I'm wondering just looking at leaving group principles. John Riemann Soong (talk) 00:49, 15 December 2009 (UTC)[reply]

time/temperature formula

Is there a formula to convert cooking time sufficient to kill pathogens such as cooking chicken for 20 minutes at 170 to the time required to kill all pathogens at a temperature of only 120? 71.100.0.206 (talk) 02:03, 14 December 2009 (UTC) [reply]

Is that degrees Fahrenheit or degrees Celsius? You can't kill all pathogens at all at normal atmospheric pressure (except by burning the food); you need a pressure cooker to do that. Certain temperatures from 140 °F (60 °C) to 180 °F (82 °C), depending on the variety of food, will prevent the growth of bacteria and/or destroy any toxins that might have already been produced by bacteria, over the period of time food is normally held between cooking and serving (no more than 4 hours). Below 140 °F (60 °C) bacteria can grow and the heat can do more harm than good. --Jc3s5h (talk) 02:20, 14 December 2009 (UTC)[reply]

Fahrenheit. I read somewhere that vegetarians cook at 118 deg F so maybe the reason is only flavor? 71.100.0.206 (talk) 02:48, 14 December 2009 (UTC) [reply]

I would not recommend cooking chicken at either 170°F or 120°F. My meat thermometer says that, for poultry to be cooked it should reach a temperature of 190°F, and you're clearly not doing that if you're cooking at a temperature below that. Cooking chicken in an oven would typically be done at 200°C (~400°F) so trying to cook at the very low temperatures you're talking about seems an impossibility. --Phil Holmes (talk) 15:15, 14 December 2009 (UTC)[reply]

The 118°F thing may be a reference to a raw food diet, not an ordinary vegetarian diet, but the number is a little different than what our article says. For cooking meats at a low temperature for a long time, see sous-vide. And I don't want to eat chicken that's been cooked to 190°F. 165°F is plenty. -- Coneslayer (talk) 15:30, 14 December 2009 (UTC)[reply]

200 F sounds way too low, and it would take a very long time for the internal temp to creep up to 190. My old 1981 "Better Homes and Gardens Cookbook" says to roast chickens at 375, under 2 pound chickens at 400, turkey at 375, goose at 350, and foil wrapped turkey at 400. It calls for an internal temperature of 185 in the thigh meat as a doneness test. Edison (talk) 19:54, 14 December 2009 (UTC)[reply]

depurination

Why isn't depurination a much larger problem than it seems to be? I know there's BER, but I mean, a purine glycosidically linked to a sugar seems to be quite problematic, because purine seems to be a good leaving group, and that anomeric carbon is all the more reactive to SN2. John Riemann Soong (talk) 02:50, 14 December 2009 (UTC)[reply]

Also why isn't depyrimidination also a mutation regime? Glycosidic-bonded pyrimidines have a carbonyl at the 2' position, effectively making a 2N-nitrogen an amide (negative charge can be delocalised onto the oxygen) so a pyridine lone pair could be similarly delocalised. John Riemann Soong (talk) 03:09, 14 December 2009 (UTC)[reply]

Scanning for a lost cellphone

Hi, I've lost my cellphone. It might have been stolen (it's now blocked for outgoing calls, just in case) but it's on and I suspect it's in my house. I can call it and I get the "calling" sound in the phone I call from but I can't hear it ringing (if it's in the house, the sound must be off or it's surrounded by pillows or something). It's an iPhone but I think the WLAN is not transmitting when it's not being actively used. Is there any way I can "scan" my house for it using simple equipment, like a small radio? Would it be feasible to call the phone while walking around with a radio to see if I hear interference on the radio? If so, would anything other than a radio (just a small speaker, for example) be more likely to work? I'm of course also looking by conventional methods but I just moved and there's a lot of cardboard boxes it could potentially have fallen into (as well as the possibility that it is indeed not in the house). Thanks! Jørgen (talk) 11:23, 14 December 2009 (UTC)[reply]

It turned up without any scanning. But I still think it was an interesting idea... :-) Jørgen (talk) 19:38, 14 December 2009 (UTC)[reply]

Both wifi and bluetooth have RSSI that indicate roughly how close the transceiver is. If you have set your iPhone to automatically connect with a laptop or something you could maybe do some sort of triangulation, although it won't be very accurate. --antilived^{T | C | G} 23:22, 14 December 2009 (UTC)[reply]

The connection between blonde people and intelligence

I have a question, are blonde people really stupid? I mean, does being blonde affect your intelligence? —Preceding unsigned comment added by RocketMaster (talk • contribs) 13:35, 14 December 2009 (UTC)[reply]

Off course not. It is also not true that the chiken crossed the road to get to the other side. Dauto (talk) 14:40, 14 December 2009 (UTC)[reply]

But it is true that silly people post nonsense in Wikipedia at times. JamesBWatson (talk) 15:39, 14 December 2009 (UTC)[reply]

It's a perfectly reasonable question. Sometimes conventional wisdom is right, sometimes it is wrong. Determining which is the case for a particular piece of wisdom is a job for science, not for assuming it must be nonsense because you've been brought up with the dogma of equality. So, how about we try and actually find some references for the OP? --Tango (talk) 15:57, 14 December 2009 (UTC)[reply]

Indeed: intelligence is a combination of nature and nurture, and part of the nurture is attributable to one's appearance. A number of studies have shown that unattractive children receive poorer treatment from their parents, for example, which could lead to lower educational opportunities. --Sean 16:18, 14 December 2009 (UTC)[reply]

There could also be a case of self fulfilling prophecy. If culture views blonds as dumb, then smart women who do not wish to have such a stereotype may dye their hair a different color, resulting in a higher proportion of "dumb blonds". 65.121.141.34 (talk) 16:24, 14 December 2009 (UTC)[reply]

It is not a reasonable question. There is NO conventional wisdom about blonds being dumber. Just dumb jokes about it. Dauto (talk) 17:40, 14 December 2009 (UTC)[reply]

Perhaps "conventional wisdom" is the wrong term, but there certainly are people that believe blondes have a lower average intelligence. Jokes don't exist in a vacuum. Even if nobody believed it, it would still be a reasonable question. Empirically verifying things that everybody believes to be true is an important part of science. The refusal to even consider that your assumption could be wrong is the defining characteristic of a dogma, and dogma has no place in science. --Tango (talk) 17:54, 14 December 2009 (UTC)[reply]

Are you asserting, Dauto, that you are a master of every single one of the thousands of cultural enclaves that exist in all of the 192 countries in the world and that you are positive that nobody believes this? You're overstating. Please stop; this is the Reference Desk. Tango is correct. Let's find some citations. This link isn't one, but its hypotheses touch on why physical features and intelligence might theoretically be correlated (the claim is that genes set an upper limit for intelligence and that "genetic clustering occurs due to geographical isolation over long periods of time, and continues through inheritance", so you could see how, say, hair color and intelligence might be correlated because one particular group happens to be of a certain hair color and of a certain intelligence range. This is surely controversial but that's something to debunk with a link to a study, not by trying to shout it down). Comet Tuttle (talk) 18:00, 14 December 2009 (UTC)[reply]

We do have a dumb blonde which says "This stereotype (and the associated cognitive bias) may have some negative consequences and it can also damage a blonde person's career prospects. [11]" which I think calls into question the idea it's simply dumb jokes. Conciously the people may say it's a dumb jokes but the study here suggests subconciously at least they are being influenced. I have read of other studies before that have been summarised as "blondes really do have more fun" specifically they've found that people (or women?) who dye their hair blonde start to behave differently and also induce different responses from people IIRC. To put it a different way, as with many stereotypes, whether they have any truth or not, people subconciously at least respond to them. And in fact I agree with Tango here, as with many stereotypes there are certainly people who do conciously believe them to some extent.

And repeating what has been said above, it seems likely to me there will be some influence therefore on the blonde's 'intelligence'. To clarify, I should say I'm not referring to intelligence as defined by some IQ score but more generally in terms of knowledge and other things which make the difference between a 'smart' person and a 'dumb' person. Anyway if other people have lower expectations of that person and therefore the person is not pushed so hard to achieve and is given less opportunities to succeed (the study for example) it seems likely this will often negatively influence their intelligence. And conversely since when the person does have to do something they may have to put in less effort to succeed again that's likely to negatively influence their intelligence. Nil Einne (talk) 19:24, 14 December 2009 (UTC)[reply]

Tango, Equality is not a dogma. You seem to be confusing it with a virtually nonexistent belief that there are no differences between people. Equality is simply not taking one person's observed behavior or intelligence and attributing it to trivial factors such as appearance (i.e. blonde hair) with no non-biased attempt to find any actual evidence of a cause-effect relationship between said blonde hair and the specific behavior or intelligence, thereby wrongly assuming that all people with the same appearance (i.e. blonde hair) are less intelligent then non-blondes. --Itwilltakeoff (talk) 00:17, 15 December 2009 (UTC)[reply]

Equality is dogmatic for some people (like Dauto). Of course it isn't for everyone, for plenty of people it is just an assumption based on evidence, or lack thereof. The difference is whether or not you are willing to consider that it might be wrong. --Tango (talk) 00:53, 15 December 2009 (UTC)[reply]

Also, the Stereotype threat article may interest the OP.

Which leads to the vastly more interesting question of whether or not blondes have more fun. ~ Amory (u • t • c) 01:38, 15 December 2009 (UTC)[reply]

I mentioned the study earlier. I found some mention of it here [12] [13]. I couldn't find if it was published or where, one of the articles links to a press release which doesn't work, I didn't try that hard. Some obvious flaws occured to me when reading this study and when writing about it above which I didn't bother mention but found this which does a resonably job of highlighting them [14]. The second ref and [15] mentions some other studies with more ambigious results and [16] [17] suggests blondes may have more fun, unless they want to get married/settle down. It's apparently also a question which interested Darwin [18] [19] so I guess you're in good company for wanting to know. I also noticed this mostly unrelated thing about improvements in modelling blonde hair and the reasons it's difficult [20] which perhaps SB can help clarify if anyone is interested. Nil Einne (talk) 10:10, 15 December 2009 (UTC)[reply]

"It takes a smart woman to play a dumb blonde." (I don't remember who said that, but check out my search results in this Wikiquote search results).Civic Cat (talk) 20:10, 17 December 2009 (UTC)[reply]

What medicine stops the itchiness inside of nose?

This question appears to be a request for medical advice. It is against our guidelines to provide medical advice. You might like to clarify your question. Thank you.

Responses containing prescriptive information or medical advice should be removed and an explanatory note posted on the discussion page. If you feel a response has been removed in error, please discuss it before restoring it.

-- Scray (talk) 03:05, 15 December 2009 (UTC)[reply]

Irritation

Why does a body part become red when its irritated?Accdude92 (talk to me!) (sign) 14:43, 14 December 2009 (UTC)[reply]

I believe it is a histamine response. The redness is due to increased blood flow to the area. --Tango (talk) 15:06, 14 December 2009 (UTC)[reply]

Yes -- check out rubor. DRosenbach ^{(Talk | Contribs)} 03:10, 15 December 2009 (UTC)[reply]

Faroe Islands tunnels/civil engineering.

What are the main civil engineering companies, or company, in the faroe islands? I mean for instance who builds the most tunnels? —Preceding unsigned comment added by 188.74.72.115 (talk) 16:04, 14 December 2009 (UTC)[reply]

We have a List of tunnels of the Faroe Islands - there aren't that many of them. 75.41.110.200 (talk) 21:57, 14 December 2009 (UTC)[reply]

See the Miscellaneous section. By the way that's a real lot of tunnels for only 49,000 people to use. The Danish taxpayers have spent more than a billion Euros on them and now they want independance[21]. Alansplodge (talk) 23:25, 14 December 2009 (UTC)[reply]

Following a link in the Norðoyatunnilin article (the only one linked in the "list of" page), I find this page: http://www.tunnil.fo/Default.asp?sida=565 . From what I can read from it (Norwegian and Faroese separated some 700 to 1000 years ago, so not much) it seems NCC constructed that tunnel. In general I would expect most or all tunnels on the Faroes to have been constructed by foreign companies. Jørgen (talk) 07:33, 15 December 2009 (UTC)[reply]

Google also gave me this (only part of an article, but one more (or the same) example of NCC building a tunnel there) Jørgen (talk) 07:36, 15 December 2009 (UTC)[reply]

Tail on Human

Could this be true that some humans were born with a tail? This is video of a woman showing her tail note: it is a porn video. with a tail. —Preceding unsigned comment added by 74.14.119.246 (talk) 16:24, 14 December 2009 (UTC)[reply]

Well, who knows about the video—one should never look for reality in porn. But our article on Tail covers the possibility of human tails quite well, check it out. --Mr.98 (talk) 16:28, 14 December 2009 (UTC)[reply]

To put 98's comment in a different way, humans can have tails, but while I haven't looked at the video it's quite doubtful IMHO that the woman in the video really has a tail Nil Einne (talk) 19:21, 14 December 2009 (UTC)[reply]

I watched it and it was obviously fake. --Sean 22:12, 14 December 2009 (UTC)[reply]

Quite so. Martin Hogbin (talk) 11:13, 19 December 2009 (UTC)[reply]

Both my nephews were born with tails - instead of curving inwards, the coccyx curves outwards. --TammyMoet (talk) 18:42, 14 December 2009 (UTC)[reply]

See also our Atavism article. 87.81.230.195 (talk) 21:17, 14 December 2009 (UTC)[reply]

And Human tails and this [22] and [23] Alansplodge (talk) 23:19, 14 December 2009 (UTC)[reply]

Theories vs. laws (Re: Einstein)

Hi. I've been trying to figure why Einstein's theories of Relativity are still widely considered theories and not laws, and how there aren't even aspects of those theories that are considered laws per se. I know there have been discussions about the subject here already. What I want to know is if what I found at the Physical laws article is true (and would therefore explain calling Relativity a theory and not a law):

Physical laws are distinguished from scientific theories by their simplicity. Scientific theories are generally more complex than laws; they have many component parts, and are more likely to be changed as the body of available experimental data and analysis develops. This is because a physical law is a summary observation of strictly empirical matters, whereas a theory is a model that accounts for the observation, explains it, relates it to other observations, and makes testable predictions based upon it. Simply stated, while a law notes that something happens, a theory explains why and how something happens.

So, is this really true? Even if it is, I could argue that certain formulas or concepts within the theories of relativity could be isolated and named "laws", right? PS. I found it very curious to know that Relativity is the only item in the List of laws in science article that is still a theory... 190.157.136.97 (talk) 16:42, 14 December 2009 (UTC)[reply]

This issue has been discussed many times on the RD before. You may want to read those discussions first and then come back with anything that still confuses you Nil Einne (talk) 16:59, 14 December 2009 (UTC)[reply]

Yes, that definition is correct. "Still a theory" is nonsense - a theory is a good as it gets. "Theory" in science doesn't mean "something that hasn't been proven", as it does in everyday usage, since there is no concept of proof in science. Something like "E=mc²" could be described as a law, I suppose, as could "the speed of light is constant". They are simple statements that have been empirically demonstrated. The idea that theories become laws is just not how science works and is generally nonsense spread by creationists trying to discredit the theory of evolution. --Tango (talk) 17:02, 14 December 2009 (UTC)[reply]

For example, the Lorentz transform is a law which governs the composition of velocities in the theory of special relativity. However, this law only describes a small portion of the total class of phenomena which might be explained in a special relativitistic treatment. Compare, for example, how Ohm's law is the simplified governing equation for a more general theory of electrical conductivity and an even more general quantum theory of conductivity. Not only is the theory more complex, but it includes the law(s) as special-case simplifications of the general physics. Furthermore, different theories can support some of the same law(s), as is the case when a simpler theory is a proper subset of more generalized theory. Nimur (talk) 17:50, 14 December 2009 (UTC)[reply]

E=mc² is a law: it is a description of mass-energy equivalence. I suppose we could name it something like "the law of mass-energy equivalence". There are two different theories of relativity "special relativity" and "general relativity". --Jayron32 18:56, 14 December 2009 (UTC)[reply]

Don't forget Galilean relativity. Einstein wasn't the first to theorise about things being relative. --Tango (talk) 18:59, 14 December 2009 (UTC)[reply]

This is a very good article comparing evolution with gravity: Evolution as theory and fact. --Mark PEA (talk) 19:35, 14 December 2009 (UTC)[reply]

Actually, that article is not even a Good Article, much less a "very good article". Comet Tuttle (talk) 19:42, 14 December 2009 (UTC)[reply]

No, no, no! Nonsense. An article can be extremely good in every regard - but if nobody offers it to the WP:GA crew to check out, it'll never become a Wikipedia:Good article. SteveBaker (talk) 01:34, 15 December 2009 (UTC)[reply]

A law is just a theory with a good PR agency.Sjö (talk) 21:06, 15 December 2009 (UTC)[reply]

Yes, in physics at least there is no distinction between laws and verified theories. One problem is that the word 'theory' also includes more speculative theories such as string theory. Unfortunately there is no official system in science to declare theories laws when they are accepted. Martin Hogbin (talk) 11:19, 19 December 2009 (UTC)[reply]

foggy car windows

What atmospehric conditions must there be for a car's window to fog up?Accdude92 (talk to me!) (sign) 20:19, 14 December 2009 (UTC)[reply]

The basic cause is that the glass is colder than the air on one side of the glass. Based on the humidity of the air, there is a dew point (a certain temperature) below which the water evaporated in the air will condense into liquid. If the window is colder than the dew point of the air, water will condense on the glass in very small droplets, which is what makes it foggy. —Akrabbim^talk 20:27, 14 December 2009 (UTC)[reply]

Further to this subject, is there a good, cheap way to minimise the condensation that forms on the inside of a car's windows when it's parked outside during an overcast British winter? My car lacks air conditioning and the windscreen's air blowers (using engine heat to warm cold but humid exterior air) take a considerable time to clear it, as does the rear window's heating element. I have latterly resorted to driving with the side windows half-open for 10 minutes, which works but is no fun in the cold and impractical when it's raining. 87.81.230.195 (talk) 21:12, 14 December 2009 (UTC)[reply]

Clean windows fog up much less than dirty ones. I proved this to a coworker who refused to believe it because it meant that he had to do a minor amount of physical labor. I cleaned the passenger side of the windshield. Then, the next week, I saw him driving down the road leaning over so he could look out the passenger side of the car while the driver side was all fogged up. -- kainaw ™ 21:15, 14 December 2009 (UTC)[reply]

In order to fog up, the window needs Nucleation sites. Basically, in order to change phase from a gas to a liquid, the water molecules need some rough areas to "stick" to first. That's why dirty windows fog up so fast, the particles of dirt provide lots of good nucleation sites. If cleaning the window really well does not work, there are anti-fog coatings and sprays that you can buy at any auto supply store, or the automotive department at your local supermegamart. These are usually surfactants (i.e. soap) that prevents the water from forming tiny droplets. Window fog is essentially lots of little droplets, so by lowering the surface tension of the water, the water forms a thin sheet instead of droplets, and a sheet of water is much easier to see through than lots of droplets are. --Jayron32 21:29, 14 December 2009 (UTC)[reply]

As I remember from my (mispent) youth, a cut potato rubbed over the window helps - also it's not bad if your wiper dies and you want to drive in the rain (Mr. Plod might not approve). Way back in the 60-70's there was a product for the rear window called (I think) GnoMist - a thin sheet of plastic which clung to the screen (like some of those window stickers that aren't sticky), that helped to keep the back window clear, I assume the water did not like forming droplets on the surface. Make a mental note for your next car to get one with a heated front window - my Mondeo is just great in keeping the windows clear. Ronhjones ^(Talk) 21:49, 14 December 2009 (UTC)[reply]

I've never heard of GnoMist, but Rain-X and Aquapel are water repellent products available in the US which are supposed to reduce the amount of fogging on windshields. -- 128.104.112.87 (talk) 00:17, 15 December 2009 (UTC)[reply]

Thanks for the suggestions. I admit I'm not big on car cleaning, but I'll give the insides of the windows a go before my next trip. The outsides of the windscreen and back window are no problem. I think the main inside problem is that in our dank British winters, the car's interior never has a chance to dry out properly. Re getting a Mondeo next time, I prefer for various other reasons to stick with the Corsa (I'm on my third, having had Models A, B and C in succession), and in my now-unemployed state see little prospect of changing or replacing my current one for the forseeable future - I can barely afford to keep it on the road as it is! 87.81.230.195 (talk) 15:20, 15 December 2009 (UTC)[reply]

between large vision acuity

This is possible to say 20/100-1 or 20/200+1? What what does this mean? Is 20/100-1 mean like 20/120 and 20/200+1 mean like 20/170 or so? Doctors can do like 20/x+3 if vision is between 20/200 and 20/300, this do happen.--209.129.85.4 (talk) 22:02, 14 December 2009 (UTC)[reply]

I've never seen visual acuity quoted like that. Where did you see it? --Tango (talk) 22:25, 14 December 2009 (UTC)[reply]

Last doctor's visit one eye is 20/100-1 that's what the doctor wrote.--209.129.85.4 (talk) 22:29, 14 December 2009 (UTC)[reply]

Any changes the one is actually a lower-case L? Jc3s5h (talk) 22:36, 14 December 2009 (UTC)[reply]

For "Left eye"? Opticians usually use "S" (from the Latin for left) rather than "L", but I suppose it is possible. --Tango (talk) 00:49, 15 December 2009 (UTC)[reply]

It could be possible that the numbers are actually separate things. The first number (ex. 20/20 or 20/100) might represent the visual acuity expression, and the other number (ex. -1 or 0.5) might represent the number of diopters that the optometrist has prescribed for corrective lenses. 152.16.15.144 (talk) 00:48, 15 December 2009 (UTC)[reply]

December 15

Why isn't t-butyl (as a carboxylate protecting group) sensitive to base?

It seems to me you could perform an E2 elimination and kick out carboxylate as a decent leaving group .... John Riemann Soong (talk) 00:24, 15 December 2009 (UTC)[reply]

The point of using a t-butyl protecting group is that the t-butyl structure represents an extremely bulky group, so effectively the bulk of this group shields the central carbon atom from attack by a base, therefore any elimination requires significantly higher energy than other smaller groups. Rjwilmsi 23:06, 15 December 2009 (UTC)[reply]

That sounds like a conflation of SN2 and E2 modes of reaction. To answer the original question, I ponder "carboxylate as a decent leaving group"^{[citation needed]}. They are easily ejectable if you can generate a β anion directly (2-haloethyl esters under reducing conditions), but I don't know if carboxyl is able to activate β H for direct deprotonation effectively (E2). Are ethyl esters noticeably less stable to non-nucleophilic bases (compare steric shielding of the β H)? DMacks (talk) 23:14, 15 December 2009 (UTC)[reply]

Boiling water simply by adding kinetic energy?

Is it possible in principle to bring water from room temperature to a boil simply by adding kinetic energy via something like an egg beater? If yes, is it possible given the tools available in the average home, or would you need some serious manufacturing/industrial class hardware? Just curious as I gently stir my morning coffee... 218.25.32.210 (talk) 00:40, 15 December 2009 (UTC)[reply]

In theory yes, but it'd be very impractical. A major problem is heat dissipation. (At some point the water will lose more heat than you are adding to it.) And efficiency. An egg-beater is way too weak ... a major problem is that you'll just end up heating the room air instead. If you completely insulated the boiling apparatus in question, and ensured very little heat flow between the container and the outside environment, and dropped in an agitator, you could prolly theoretically boil it. The heat capacity of water (or any solvent for that matter -- even hexane) is kinda large though. John Riemann Soong (talk) 00:46, 15 December 2009 (UTC)[reply]

Given the right circumstances - certainly. If you take an electric drill with a really blunt wood-bit - and try to drill your way into a small chunk of stainless steel - after a couple of minutes of fruitless drilling, squirt a small amount of water into the area and it'll boil immediately. Now, admittedly - we took the kinetic energy of the drill - and used friction to convert that to heat - but the intermediate step is merely a convenience. The question is really whether you can figure out a way to get from motion to convert directly into heat in the liquid. In principle, it's certainly possible - and with a sensitive enough thermometer you'd certainly be able to measure a small, slow heat increase from a fast electric mixing machine or such like. But as John said - the problem is to get the heat into the liquid faster than it'll lose heat to the environment. So you need to agitate the water as fast as possible to get the heat in faster than it's losing it. You'd want an insulated container...that kind of thing. It's got to be possible though - it's just a matter of figuring out a way to do the experiment. SteveBaker (talk) 01:31, 15 December 2009 (UTC)[reply]

My favourite candidate so far is to use a magnetic stirbar. No moving parts, and you could theoretically seal up the container with lots of insulation, then just apply a changing magnetic field! =D Better yet, drop fine magnetic powder and turn on the field. The big thing you see is surface area. If you do some simple calculations, you find your agitator is adding very little energy (most of the energy doesn't end up in the water, even without the water losing anything). Very fine particles being moved about means more surface area ===> more friction ===> greater heating efficiency. John Riemann Soong (talk) 01:36, 15 December 2009 (UTC)[reply]

Nod, keep in mind that 'heat energy' is for all intents and purposes just kinetic energy on a small scale, IE the energetic movements of atoms unless I was deceived as a child. Unomi (talk) 01:44, 15 December 2009 (UTC)[reply]

An interesting extension is to use something with an electric dipole or that is ionic...apply an oscillating electric field and the molecules vibrate and collide with each other to heat the material. 173.79.45.179 (talk) 05:17, 15 December 2009 (UTC)[reply]

Related: frictional heating from the mixing is an important factor when kneading bread dough mechanically. --Sean —Preceding unsigned comment added by 76.182.94.172 (talk) 01:34, 15 December 2009 (UTC)[reply]

I've been told that a step in the commissioning of a nuclear power plant is to generate steam and produce a few megawatts of power from the turbogenerator without any nuclear power input, simply by running the boiler feed pumps to recirculate the water in the boiler. James Prescott Joule investigated the mechanical equivalent of heat in the mid 1800's. He used a falling weight to spin a paddle in an insulated container of water, and noted how much mechanical work it took to raise a given mass of water by a given temperature.His result was 772.24 foot pound force (4.1550 J·cal-1). He found that 772.24 foot-pounds of work raised one pound of water 1 degree F. His claims were rejected by many scientists, who still like "caloric" theories and did not generally accept conservation of energy as part of their core scientific beliefs, but eventually gained acceptance. See also Mechanical equivalent of heat. I leave as an exercise for the reader how much work one would have to do to raise say 1 liter of water from 20 c to 100 c by manually spinning the paddles, or cranking an eggbeater in an insulated bit of water. If a healthy person can produce 1/4 horsepower for over an hour, where a horsepower is 746 watts or 33000 pound-feet per minute how long would it take at 100% efficiency in the mechanical apparatus and perfect insulation of the water container to get a liter of water boiling? (Today we know that the question basically "boils down" to Joules per second of energy input and the specific heat of water.) Edison (talk) 15:37, 15 December 2009 (UTC)[reply]

Actually this is one case I think where the apparatus would not need to be 100% efficient, since losses in efficiency are caused by things like friction, which would generate that heat anyways. 65.121.141.34 (talk) 16:35, 15 December 2009 (UTC)[reply]

I was assuming no friction outside the insulated water vessel, like in a treadmill linkage , or pulleys to speed up the rotation, or a gear box, and all. Note that .25 horsepower as the human input is also a crude number, so it could be .1 hp or .5 hp for a few minutes, and depends on the fitness of the individual. So would it take seconds, minutes, hours, or days for a hard working person to boil 1 insulated liter of water by mechanical agitation? Edison (talk) 00:40, 16 December 2009 (UTC)[reply]

So with the above caveats, and Joule's figures of 772.24 foot-poundforce of work required to raise one pound of water 1 degree F, an assumed 1/4 horsepower of human effort (8250 foot-poundforce per minute), starting at 70 deg F, neglecting changes in specific heat of water, 2.2 pounds of water per kg, I get 29.2 minutes of hard work to raise it to 212 °F (100 °C). At a more relaxed 1/10 horsepower (74.6 watts human effort), it would take 73.1 minutes. This only raises the water to the boiling point, but does not boil it away. It is interesting that in 1842, when Joule presented his findings, conservation of energy was in doubt among scientists. It took Joule and Helmholtz to lay the groundwork for modern physics, chemistry and engineering in this area. Joule's work was initially denied publication because they saw him as a non-scientist, and they doubted he could accurately measure very small temperature changes. Edison (talk) 20:12, 16 December 2009 (UTC)[reply]

Car windows again

The above question from yesterday reminds me of a related question that I have long puzzled over. Several people have assured me that setting the blowers to cold will clear condensation from the inside of a windscreen quicker than if they were set to warm. This does seem to be true, even though it goes against what I would intuit: shouldn't warm air perform this function more efficiently?--Shantavira|^{feed me} 08:25, 15 December 2009 (UTC)[reply]

The condensation is there because the car is warm inside while it's cold outside. So why do warm blowers work at all? 213.122.69.70 (talk) 08:50, 15 December 2009 (UTC)[reply]

Did you even bother to read the answers from yesterday? Warm blowers work because the problem is cold windows in wet air. If you warm up the windows (by blowing warm air on them), the condensation will get slower and slower until it stops, and in addition, the warm air will evaporate the drops that are already there, because warm air can "store" more water vapor than cold air (and the flow of air helps, too). --TheMaster17 (talk) 09:19, 15 December 2009 (UTC)[reply]

I read the sentence about the dew point, yes, but I didn't know car blowers preferentially heat the windows. The ones I'm familiar with are pointed towards the middle of the car. I didn't know that warm air can store more water vapour than cold air, either - does that reduce the effective humidity, meaning the dew point gets lower? I guess that's the critical piece of information. 81.131.54.224 (talk) 15:24, 16 December 2009 (UTC)[reply]

You may be misunderstanding the advice... if you turn on the air conditioning, it will dry the air and improve evaporation. But even with the air conditioning on, you should have the heater set to warm, so the air that blows is warm and dry. -- Coneslayer (talk) 12:31, 15 December 2009 (UTC)[reply]

There are two effects going on here. The amount of water that the air can hold depends on temperature. Warm air can hold lots of water - cold air, much less. So - when your car is cold, the water in the warm air in your breath hits the cold windshield and cools rapidly. At that point, the water can't stay in the air so it forms as droplets on the windshield. Hence:

The A/C cools the air - but also dries it (it's not an "air refrigerator" - it's an "air conditioner" - it "conditions" the air - removing dust and moisture as well as cooling it down). Drying the air reduces the water content (irrespective of temperature) and without water in the air, there is nothing to condense.
The heater warms up all of the air in the car - but since that air was formerly cold - it didn't have much water in it. So now the car is warm (and dry) and your breath can dissipate water into all of the other warm air in the car which (being dry) is easily able to hold it. Also, the warm air heats up the windshield so that when warm, moist air does touch it, it's not cooling the air down enough to allow the water to condense.

Hence either heating or cooling the car will eliminate mist from the glass. In fact, because the main source of all of this water is your body - simply turning on the fan and replacing the air inside the car with outside air will remove much of the moisture and prevent misting. Just blowing the air onto the windshield will maintain a barrier of drier air and thereby prevent your moist breath from getting in contact with it.

Hence, almost anything you do with the car's heating/cooling controls will help to demist it. However, the airconditioner (on cold) works best because it's literally removing the water - not just moving it around. SteveBaker (talk) 14:44, 15 December 2009 (UTC)[reply]

". . . The main source of all of this water is your body . . . ." Steve, you've been living in Texas for too long :-)! Back here in waterlogged Ukland, the environmental humidity (combined with lack of sunlight) is the principal problem - my internal fogging accumulates during the days I haven't driven, not when I'm in the car and driving - and hence delays my starting out. 87.81.230.195 (talk) 15:30, 15 December 2009 (UTC)[reply]

I disagree - on a cold day, there simply isn't "room" in the air for much water. Even at 100% humidity, there isn't much water in cold air. But the air from your lungs has been warmed and moisturized...so it does add the majority of the water. Your car may fog up when it's warmer inside the car than out - but there has to be some other source of water...perhaps you have a water leak accumulating water in the upholstery or carpet. If so - you need to fix it before you get mold growing in there - it's virtually impossible to erase the stink of mold in a car. SteveBaker (talk) 18:14, 15 December 2009 (UTC)[reply]

Fair point. I'll look for a leak as far as I'm able. 87.81.230.195 (talk) 10:34, 16 December 2009 (UTC)[reply]

Shatika

Resolved

Where can I find more information on Shatika? Regards-Shahab (talk) 09:07, 15 December 2009 (UTC)[reply]

Irrelevant discussion because OP mis-spelled sciatica

My guess would be that the snake oil article would be a good place to start. Keep in mind that these sorts of products are rarely regulated, so their claims of efficacy may be totally fictional. Nimur (talk) 13:16, 15 December 2009 (UTC)[reply]

Don't be too hard here. The product is Ayurvedic rather than allopathic. Sometimes I think we're guilty of judging one culture by another culture's lights. I know that's heresy on a science reference desk, but what the hey. --TammyMoet (talk) 13:51, 15 December 2009 (UTC)[reply]

Oh - yes, we can be that hard! This is the science desk and we don't stick our heads in the sand and say things are OK just because it comes from another culture and therefore we must respect it somehow. That is 100% not how science works - we judge things by the facts - and culture simply doesn't enter into the equation. What you just said is beyond heresy - it's completely f**king stupid.

So - let's do this properly. Let's examine the claims made for the stuff: It says that it "Relieves pain" - OK - maybe. Much of pain is psychosomatic and any placebo can do that. So - yeah - maybe.

But it also says that it cures: Arthritis(Osteoarthritis,rhumetoid arthritis),Spondylitis and Migraine. Pick any one of those: Osteoarthritis let's say. This is a disease that's caused by physical wearing and degradation of cartilage around the joints. Unless this oil somehow causes a magical regeneration of cartilage (something completely unknown in humans) - then it can't "cure" osteoarthritis - at best it might relieve the pain - but they already said it relieves pain in general, so they must be talking about something more specific. We don't say "Tylanol cures Osteoarthritis" - although it does help the pain. Spondylitis isn't even a specific disease - it's a symptom of many possible diseases...curing it would require fixing all sorts of odd problems - none of which seem to be listed?!? Curing migrane would require getting involved with seratonin inhibitors in the brain...this would have to be a substance capable of crossing the blood-brain barrier. Such a substance should be regarded with EXTREME caution! In short - if this stuff did what it said - it would be capable of doing untold amounts of harm too! If you used it to cure your Arthritis and it started leaching into your brain and messing with your seratonin levels - the consequences would be horrific!

Where is the list of side-effects. No change that you do to the body comes without changes elsewhere. If it's curing one thing (say your migrane) then whatever effect it has on stimulating the growth of new cartilage in osteoarthritis would cause who-knows-what joint changes in people who have no cartilage problems to start with!

If this stuff works as advertised - it's lethally dangerous and I wouldn't want to be within 50 feet of an opened bottle! If it doesn't work (as I STRONGLY suspect) - then don't buy it because it's snake-oil.

At best, this is a mild pain reliever - probably more for psychosomatic reasons than anything else. My mother uses 'witch hazel' to relieve her migranes - it's very clear that it's not doing anything but acting as a credible placebo for her - so I'm not going to tell her that it's useless. This stuff is likely doing the same thing.

Sorry - but science CAN discuss these kinds of matter.

SteveBaker (talk) 14:27, 15 December 2009 (UTC)[reply]

Out of curiosity several Shell lubricants contain salicylates (Alexia has the most check Google) and we did sometimes come across people abroad massaging it into arthritic joints apparently with some benefit (obviously, this is not medically safe, but aspirin is a salicylate of course). Conventional analgesics can be absorbed by the skin, and do occur in tree bark etc but as I think Steve's said before the ones which work are sold as medicine and the ones which don't work are snake oil. --BozMo talk 14:46, 15 December 2009 (UTC)[reply]

...and this stuff might (maybe) work as a pain reliever. But that's not all that it claims. It's actually claiming to CURE a wide variety of incurable conditions. If you want a topical salicylic acid (asperin) cream then buy something like 'Aspercreme' - which does contains exactly what you need and is unlikely to add a bunch of other things that you don't need. SteveBaker (talk) 15:22, 15 December 2009 (UTC)[reply]

Just out of curiosity, Steve, do you call your mother really fucking stupid for using the witch hazel? You're a smart guy and I appreciate your knowledge, but that was really fucking rude. Matt Deres (talk) 15:11, 15 December 2009 (UTC)[reply]

As a side note, I do call my mother "fucking stupid" when she fails to read the scientific papers I download for her questioning the efficacy of the various CAM products she likes to buy. I tend to get many thought terminating clichés in return for it, but some people just can't be taught it seems, even the organism from which I'm derived. --Mark PEA (talk) 18:03, 15 December 2009 (UTC)[reply]

No - I don't - but then she doesn't wait for a question about the efficacy of a dubious commercial product on a science reference desk and then tell us we can't answer the question because it's culturally sensitive (and the two asterisks don't stand for 'u' and 'c' - that would be rude). SteveBaker (talk) 15:17, 15 December 2009 (UTC)[reply]

omg!! I've been insulted by the great SteveBaker! That's really made my Christmas! By the way, my rheumatologist told me to take glucosamine for my joints. I always assumed if a qualified medical doctor told me to take a tablet then it would work. Is that not the case now? The original question, by the way, wasn't about the "efficacy" of a product, it was "where can I find more information on", and in that case the correct response should not have been to refer to "snake oil", but to the product website. I guess I'm as guilty as the responder as assuming cultural norms here. --TammyMoet (talk) 16:10, 15 December 2009 (UTC)[reply]

Firstly - I'm fairly sure your rheumatologist didn't say that glucosamine would "cure" your arthritis (certainly not osteoarthritis). Secondly - read our article on Glucosamine...pay special attention to the bits about the results of clinical trials. SteveBaker (talk) 17:22, 15 December 2009 (UTC)[reply]

We mis-understood the question the OP was asking, and devolved into a tangential discussion. Nimur (talk) 21:36, 16 December 2009 (UTC)[reply]

All of you have misunderstood my question. I want information on shatika, which is a problem with the nerves. I do not want information on the herbal remedies etc-Shahab (talk) 16:38, 15 December 2009 (UTC)[reply]

Well, the trouble is, there is no such English language word as "Shatika" - so all we could do was to go by the link you posted. That said - I wonder if you mean "Sciatica" (pronounced "sigh-attic-a") - which is a fairly common nerve condition (which that oil won't cure either!). If that is the case - then read our excellent article: Sciatica. Sadly, we're not allowed to give medical advice - so we may not be able to help you much more than that unless your interest is of a more general nature. If you have sciatica (or anything that you think MIGHT be sciatica) - then you need to consult a doctor. SteveBaker (talk) 17:14, 15 December 2009 (UTC)[reply]

Thanks. Sciatica was what I was looking for. Regards.-Shahab (talk) 17:24, 15 December 2009 (UTC)[reply]

Oh well - it was a bumpy ride - but we got there in the end! :-) 18:09, 15 December 2009 (UTC)

Acetone/Water Mixtures: Flammability

Greetings! Acetone is a flammable liquid. 1 % acetone in water is not flammable. At what concentration (v/v or w/w) are liquid water/acetone mixtures flammable? And at what liquid mixture ratio is the vapor flammable? (everything under standard conditions). I have been searching, but these data seem to be hard to find. Thanks for help! Grey Geezer 09:21, 15 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One type of answer (which leads to more questions!) is "whatever liquid ratios give acetone vapor concentration between the lower flammability limit and the upper flammability limit". Assuming it's actually the evaporating (and rapidly so, given the heat of the flame) acetone that's burning, you need to know the Lower flammability limit. The added water means some of the heat is used to evaporate that rather than acetone (reduces the efficiency of the self-perpetuating flame) and to dilute the air/acetone vapor with water vapor (affects the lean/rich mixture required to burn). I have no idea the specifics for acetone, but those are "one level deeper" into how I understand the issues involved. DMacks (talk) 09:40, 15 December 2009 (UTC)[reply]

Depends on the liquid temparature too. My copy of the rubber company handbook has vapour pressure curves for acetone above mixtures of acetone water but in practice it is going to be tough to calculate, and flash points etc in reality depend heavily on geometry however we try to standardise them. The only help I can think of is that these kind of numbers are easily obtained for ethanol and ballpark acetone might be similar. Cold brandy is hard to burn warm brandy will sustain a flame easily. So brandy at say 20C (and 40 degrees proof which is 20% alcohol is marginal). Guess acetone might be something similar? --BozMo talk 10:06, 15 December 2009 (UTC)[reply]

I would be extraordinarily careful about any attempt to generalize from one flammable liquid to another. The boiling point of acetone is only 56°C, compared to ethanol's 78°C; at room temperature the vapor pressure of pure acetone (nearly a third of an atmosphere) is roughly triple that of ethanol. Meanwhile, the lower explosive limit of acetone (2.6-3.0%) is lower than that of ethanol (3.0-3.3%). What you might try searching on is something like air-water partition coefficient acetone. Google scholar or PubMed will turn up a number of results. I'm not in my office at the moment so I can't get at the journal articles that are hiding behind paywalls, but there are some likely hits there if you're coming from a university with suitable subscriptions. TenOfAllTrades(talk) 16:40, 15 December 2009 (UTC)[reply]

I further searched my question with lower flammability limit but still did not find the answer. It surprises me that this piece of data seems to be nowhere available. If TenOfAllTrades comes up with a number and a reference, I could look myself. Grey Geezer 11:52, 16 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs) [reply]

What are the arm blades of a preying mantis made from?

I've seen videos of the large preying mantises stabbing or slashing open rodents and birds with them. I suppose that they're probably made from a similar substance to the rest of the mantis's exoskeleton, but are they toughened or hardened somehow? Also, does the mantis have to do anything to keep them sharp? --95.148.104.205 (talk) 09:23, 15 December 2009 (UTC)[reply]

It may have been done initially with pun intended, but the proper spelling is praying, referring to the folded arms/prayer-like stance. DRosenbach ^{(Talk | Contribs)} 14:17, 15 December 2009 (UTC)[reply]

AFAIK, "blades" of the grasping forelegs are made of the same thing all insect exoskeletons are made of: chitin + protein matrix + calcium carbonate. Chitin by itself is somewhat similar to cellulose, but the addition of the other two components makes it much more rigid. Now, as far as the sharpening goes, mantises spend really a lot of time grooming their forelegs; but I am not sure at all if that contributes to the sharpness of the spines on the forelegs or is just meant to keep them clean. Anyway, keep in mind that any mantis molts a number of times before it reaches adulthood, and the entire exoskeleton is replaced every molt. --Dr Dima (talk) 10:34, 15 December 2009 (UTC)[reply]

Tree question

I am ok at felling trees in a given direction but I have a tricky one. The tree is on the bank of my moat, and is leaning over the moat by about 30 degrees (slowly falling). The moat is 6 m wide and the main tree truck is about 18m high (most of the canopy is gone so it approximates to just a trunk). I do not want to be fishing a tree trunk weighing a number of tonnes out of a 2m deep moat so I want to fell the tree so that the bottom of the fallen trunk is at a good distance from the stump. If I cut the tree at a given height above the ground how far away from the tree stump will the bottom of the trunk be at impact on the ground? Can I improve this by varying the slope of the cut? Any other ideas on how to get the trunk well over the moat?--BozMo talk 10:17, 15 December 2009 (UTC)[reply]

A photograph would help!

It doesn't matter how high up you cut it - the tree rotates about the point where you cut it until it's pretty much horizontal - and then pretty much falls vertically. If the fibreous wood doesn't break cleanly - then the trunk may even stay attached to the top of the stump and cutting it up higher just makes for a lot more grief - and makes what I'm about to suggest even more difficult. But a lot depends on how clean the break is and how top-heavy the tree is. IMHO, you're not going to get the trunk to fall more than maybe half a meter from the stump, no matter what you do.

If the geometry of the situation is as you say then you need to fell the tree so that if falls at right angles to this 'moat' - cutting it as close to the ground as is reasonable. If it's already leaning by as much as you say - you have no chance of making it fall in any other direction anyway.

If you're right about the dimensions then about 12 meters of tree will be on the far side of the moat with 6 meters dangling in fresh air across the moat. In theory - if the tree were of uniform thickness - the 12 meters out there on dry land would be plenty heavy enough to stop the other 6 meters from falling into the water. However - if the tree tapers strongly then it's possible that the bottom 6 meters will be heavier than the topmost 12 meters - and then the heavier bit might dip into the water - but at least you could loop a rope over the top of the tree and with a modest amount of weight - pull it down so it's horizontal.

Once it's down - if you don't have heavy machinery to haul the trunk 6 more meters until it's all on level ground - then I suggest that you prepare some rollers (maybe some nice round logs) on the far side of the moat for the tree to land on that would make it easier to pull it away from the water. If the tree's trunk is nice and smooth and round - you could probably use a fulcrum close to the water's edge to rotate the tree so that it's almost all on land anyway.

Whatever you do, don't start cutting the top of the tree into logs until the bottom is pulled clear of the water because as soon as you remove weight from the top of the tree - the bottom will be more likely to fall in!

Also, I would prepare for the worst by tying some heavy ropes or chains to the base of the tree a few feet above where you intend to cut it - BEFORE you cut it down - so that if it does end up in the water - you at least have something to haul it out by.

Good luck!

SteveBaker (talk) 14:06, 15 December 2009 (UTC)[reply]

The real worry about tree felling as far as I'm aware is if the tree doesn't just angle over still connected to the stump but breaks away, in which case the base of the tree would come towards you rather than go further over the water. So yes the best you can do is cut it near the base. If you can strip off the branches for the first 6 meters it mightn't be too hard to winch it out after you're finished. Or there may be some heavy canvas or a board you could put down to make it slide over the other bank easier. The only advantage I can see of cutting it higher up is that the bit over the moat will be lighter. Dmcq (talk) 14:21, 15 December 2009 (UTC)[reply]

Yep, its a big Ash and will split violently. But by the time it does the canopy must have momentum away from the bank. Perhaps if I undercut the far side and over cut the bank side second I can get the whip to go the right way. My guess is there is at least six or seven metric tonnes of trunk there though so the sliding bit ain't going to be easy. --BozMo talk 14:50, 15 December 2009 (UTC)[reply]

The base of the tree can indeed kick backwards (because the tree would 'naturally' try to rotate about it's center of gravity - not about the bottom of the trunk) - but if you do it right, you don't cut all the way through the trunk - you leave enough wood there to act as a "hinge" to prevent that from happening - and to give you enough time to shut your chainsaw off and get far enough away from the falling trunk! But that hinge also ensures that the tree rotates about the top of the stump - so that end of the trunk will end up close to (if not still attached to) the stump. When you get it right, that hinge breaks through completely just as the tree gets horizontal. The angle of cut of the "notch" that you cut on the side where you want the thing to fall is what makes that happen. The depth of the cut on the opposite side (which actually brings the tree down) is what ensures that the "hinge" is the right strength. There is an art to doing it right. I suppose the if the hinge broke through before the tree got horizontal - it might slide a little away from the stump - but I can't imagine that being anywhere near far enough to make a difference here. SteveBaker (talk) 14:54, 15 December 2009 (UTC)[reply]

I see lots of trees removed from backyards or parkways near homes, and the tree companies almost never just cut it down and let it fall when structures, fences, or sidewalks are anywhere near. Instead, they strip the tree down to the main trunk and a few main uprights by cutting branches and using pulleys tethereed to the main trunk to lower the branches to the ground. Then they cut the main trunk into short manageable sections which are lowered to the ground by pulley attached to the bucket the cutter works from. It is a few minutes work rather than one big boom. If you cut it down in one or two pieces, you would still need to cut it up for firewood or to go in the chipper. Standard tree removal would be easier than trying to cut up a tree which fell in a water filled ditch. Forget trying to be Paul Bunyan. A tree can spring back and kill the person cutting it. The impact of a large tree hitting the ground can jar nearby structures and knock things off shelves, or crack plaster. YouTube and America's Funniest Home Videos are full of unexpected outcomes of amateur tree felling. Call a professional, which might be affordable if you can afford something which needs a moat to protect it. Edison (talk) 15:07, 15 December 2009 (UTC)[reply]

Indeed - but we're told that this tree is 18meters tall(!) so climbing up it to bring it down in sections would be tricky - and it's leaning at 30 degrees out over a freezing cold moat...so lowering the topmost sections to the ground ain't easy either. Also, operating a chainsaw while balancing 50 feet off the ground in a dead tree over a cold wet moat is a life-threating situation that I absolutely won't recommend! SteveBaker (talk) 15:14, 15 December 2009 (UTC)[reply]

See Cherry picker. Pros do climb healthy trees, but more often the work safely from the bucket. The reach can be quite long, and the 3 foot sections can be lowered individually. 18 meters=18 pieces of wood. No big challenge or drama at any point. Edison (talk) 17:08, 15 December 2009 (UTC)[reply]

The critical question here (and something you don't KNOW the answer to) is whether the top 12m of the tree is heavier than the bottom 6m. If it is - then you need to have it land on a nice thin-but-hard fulcrum - close to the center of gravity of the tree. If you had it balanced perfectly on something like a large log - then the effort to rotate it 90 degrees so it's no over the water anymore would be fairly small - even if the weight of the trunk were many tons. Sadly, you can only guesstimate the center of gravity - so make your best guess and at least minimize the amount of pushing and shoving you'll need to do. Personally, I have a couple of block-and-tackle sets which allow me to haul very large tree trunks over short distances - so even if things didn't come out perfectly, it would still be a do-able job for one guy to get the entire trunk over dry land. But like I said - that assumes that the center of gravity of the trunk is more than the width of the moat from the cutting point. The lower you cut it - the more likely that is to be true. But there is absolutely nothing you can do to make a multiple ton tree jump six meters sideways and avoid the moat! SteveBaker (talk) 15:14, 15 December 2009 (UTC)[reply]

...and all of this discussion is why, if it is important for a tree to fall in a particular place (or especially if it's important that a tree not fall in a particular place) one should seek the services of a professional. The pros have all of the equipment and training to do the job right — and insurance, just in case they don't. Look in your telephone listings under "Arborists" or "Tree removal". A wise man knows when he's in over his head. TenOfAllTrades(talk) 16:08, 15 December 2009 (UTC)[reply]

...to be fair I have used tree surgeons for three of the larger dead trees I needed doing this year but those were ones which would have hit a road or an eleventh century church by our boundary. Aside falling in a moat or killing myself with a chainsaw (and I do quite a bit with a chainsaw myself) the worse case with this one is that I lose a load of firewood. The nearest building is a long way off. There may be some damage to a 900 year old scheduled moat too but that will happen for sure if I leave the tree to fall under its own steam. But Steve is probably right there is no way to get it to jump. --BozMo talk 16:43, 15 December 2009 (UTC)[reply]

If it is cut via cherry-picker bucket in short manageable pieces there is no damage to the ancient moat. I'm sure you are a smart feller and will consult a professional rather than random persons on the internet of unknown qualifications. Edison (talk) 17:20, 15 December 2009 (UTC)[reply]

I'll second that, the only posters in this thread you should be listening to are the ones telling you to get someone else to do it. Yes, you can get the tree to "jump" away from the stump—if the wood is sound you could probably fall it in any direction you wanted, despite the thirty degree lean. Do not pay attention to any of the advice above, those giving it have no idea what they are talking about.—eric 18:42, 15 December 2009 (UTC)[reply]

Its ok thanks. I asked for their advice because I wanted it and I am happy with some of the ideas. Sculpting trees in a town centre is a bit different from a country garden with lots of space and several hundred mature trees in it. But a cherry picker might be able to get there in the summer. --BozMo talk 18:57, 15 December 2009 (UTC)[reply]

EricR & Edison: Those are ridiculous statements. For starters, I have been dealing with trees and chainsaws off and on for about 35 years - and I know my way around a block-and-tackle - and it sounds like our OP has been there and done that too. Since we're both people who actually DO know what we're talking about, the advice to ignore all of this, throw up your hands and run to an overpriced professional is silly. This is a simple matter of physics - and that's exactly the kind of thing the science desk is here to discuss. We have medical disclaimers and legal disclaimers - but no tree-surgeon-disclaimers. I'd like to hear EricR's idea of how you get a multiple-ton tree to fall in the opposite direction to which it's leaning (at a 30 degree angle - over water, no less!) - or to jump 6 meters sideways. That should be good for a laugh. This is fairly elementary physics. Having said that, a Cherry Picker could let you take it down in sections if you can find one that can lean far enough out over the water whilst reaching up that high - and not damage the edge of the moat. SteveBaker (talk) 19:11, 15 December 2009 (UTC)[reply]

Not ridiculous at all, and civility is always appreciated. Edison (talk) 00:27, 16 December 2009 (UTC)[reply]

We certainly have no way of knowing if there is a way to drive a large truck near the tree. Foresters in my town have them in various sizes, small to HUGE with a very long reach. Tree felling is one of the most dangerous occupations, and even people who "have been dealing with chainsaws for 35 years" get killed in large numbers every year. Edison (talk) 20:25, 15 December 2009 (UTC)[reply]

There still remains a difference between the pro and even a seasoned amateur, and there's a potentially wide gap between someone who has 'been dealing with trees and chainsaws off and on' and someone who does the job every day for a living. My grandfather was a shop teacher for a couple of decades, then went on to build and operate a small sawmill and woodlot. He felled, cut, dried, and planed the cedar for my parents' back fence. When the time came to take down an awkwardly placed tree near one of his buildings, he still called a pro.

The pros have the right specialized tools (not just 'close enough'), and years of daily practice. The pro comes with a crew who know the job, and wear the right safety equipment; they're not your buddies from work (long on enthusiasm but short on experience, and who lack any sort of insurance coverage) who are in it for the free beer and pizza afterward. If the job requires really specialized equipment (like a cherry picker), the pro probably gets a discount on the rental. (The pro is also less likely to inadvertantly tip the cherry picker into your moat.) While I certainly would recommend avoiding an 'overpriced' professional (by all means get more than one quote!), I can't emphasize enough the value of real professional experience. TenOfAllTrades(talk) 20:35, 15 December 2009 (UTC)[reply]

Why don't we have tree-surgeon-disclaimers? Bus stop (talk) 20:57, 15 December 2009 (UTC)[reply]

The Schools Wikipedia says "not intended ... to be used in any way as a basis for behaviour" which would include trees... --BozMo talk 22:24, 15 December 2009 (UTC)[reply]

Steve, if it's a simple matter of physics then try this simplest of machines. All i can do here is relate a story about this guy. Teaching a class to professional fallers, he boasted that he could wedge over any tree that had good sound wood. Later, someone spotted a tall cedar, leaning way over backwards, and bet that this was one tree he could not wedge over. It was a set-up, he pulled a couple of high-lift wedges out of his bag and went to work. He would whittle away at the back cut, then tap on the wedges for a bit while watching the top of the tree. He added more wedges—driving some sideways near the holding wood and stacking others to get more lift. After about an hour of pounding on the wedges he had lifted the tree far enough that it fell in the direction he wanted—and won a steak dinner from the class.

Now a second-hand story really doesn't belong on the reference desk, but i hope it illustrates the difference between a professional and someone who, since they know a little bit of physics, thinks they can teach something as dangerous as timber falling. Based on your posts above, it sure doesn't sound like you've "been there and done that".—eric 01:10, 16 December 2009 (UTC)[reply]

There are nonetheless limits to what can be done with wedges, I use them a lot. But in this case the hero of the story would have drowned or died of hypothermia...--BozMo talk 13:07, 16 December 2009 (UTC)[reply]

And for a laugh, don't forget to go on youtube and search for tree felling accidents. I personally would agree that if there is any chance of damage to property, you should seek the help of an expert. Even if you are familiar with a chainsaw, if this is the 1st big tree you are cutting down, they say you learn from mistakes and in a situation when a mistake can be dangerous or expensive, it's better to let someone who has learned already do it. Vespine (talk) 23:48, 15 December 2009 (UTC)[reply]

We don't have tree surgeon disclaimers, but we do point out alternative methods that are sometimes used, and there is no reason we cannot counsel calling in someone with special equipment. What Steve says all sounds accurate if there are no nearby structures that could be harmed by an object weighting many tons falling on it. But many tree fellers have been surprised in unfortunate ways when the saw blade binds and they stick around too long trying to rescue it, or when it kicks back, or when the crown hits and it springs back. The timber industry has about the highest mortality rate among occupations. If you just fell the tree across the moat, it is likely to leave a depression in the other side of the moat when it hits. The portion hanging over the water after felling could be sawed off a few feet at a time in manageable hunks, and fished out by a rope you thoughtfully attached ahead of time. That part of the cutting could await warmer weather, so if you fall in the water is not freezing. Pros have lines, pulleys, and tree gaffs and are comfortable using them, as well as assessing the soundness of portions of a tree if climbing is chosen. They routinely take down much larger trees without drama, in small pieces. They have forestry bucket trucks which can reach a 95 foot working height or a lesser height with some lateral reach. Sometimes hard frozen ground is preferable to avoid ruts. Edison (talk) 00:27, 16 December 2009 (UTC)[reply]

I must admit thinking abut it I'm rather concerned that the poster thought the tree would jump in the direction it was falling rather than being worried about the trunk breaking off and coming back at him. If felling a tree you should have some idea of how the tree might behave as it falls and of possible problems. SO yes I'll add my voice to get a professional. Dmcq (talk) 01:24, 16 December 2009 (UTC)[reply]

Actually I've done a fair number of trees. The end of the trunk always ends up hitting the ground some small distance from the stump in the direction of the tree falling (unless the canopy catches other trees). Getting out of the way is not generally a problem especially as the last bit is always done with a sledge hammer and wedges rather than with a running chainsaw. Spring back is the commonest cause of fatalities with chainsaws though and I haven't done many at any angle. I will upload a couple of photos but its snowing now. --BozMo talk 12:27, 16 December 2009 (UTC)[reply]

That's good. The reason it will end up a little from the tree in the direction the tree falls if it is done right is that the trunk only parts from the stump after it has gone nearly horizontal, so yes as you say the momentum after that point will carry it away from the stump. I'd be surprised if you can get much distance at all that way, but I wonder at what angle one would get the best effect. There might be something about felling trees on the web about it. Dmcq (talk) 14:15, 16 December 2009 (UTC)[reply]

tree is in centre — tree hanging over moat

Here is a view of the tree from the corner of the moat, in high res you can just see ice on the near water. The tree is the obvious central one leaning over the water. Not remotely huge as trees go (about 75cm diameter trunk, so maybe 3-4 tonnes rather than 6-7 above) but still hard enough to lift. The angle at the base is close to 45 degrees and the trunk bends upwards, making wedges implausible even without the water. The moat is deceptively deep. There are quite a few similar trees. --BozMo talk 15:07, 16 December 2009 (UTC)[reply]

That looks nasty. The wood may not be good, bits may fall off, it may get lodged in a trees opposite, there's stuff all around it no nice way to retreat, not nice to clean up the bottom of the trunk so it doesn't get stuck in the moat. It looks to me like everything people warn about. And you've a load of them. I'd take professional advice, though I just had a look at a few videos and they looked pretty scary the precautions they weren't taking. Dmcq (talk) 15:52, 16 December 2009 (UTC)[reply]

Hmmm - a picture is worth a thousand words! Firstly - I did some measurements on your image - and there is no way that the chunky "trunk" part of the tree is three times the width of the water as you first said...it's at best twice as wide - probably less (we can't really see where the bank is opposite the tree - so it's almost certainly wider than I measured). Your estimate of a 30 degree lean angle is probably about right (although it's hard to get a decent vertical cue out of that photo). But also, the curve at the bottom of the trunk that makes it start out over the water almost horizontally makes it hard to cut a proper notch to get the tree to fall exactly the way you'd want - so it's probably going to go down at some non-optimal angle. That really changes things because now there is really no way that the bottom end of the tree can stay out of the water - and a very good chance that the whole thing will end up in the drink. Also, the way the bottom end of the trunk curves is going to be bad news for dragging it out of the water afterwards. Do you have access to a tractor or something? At this point, I think I'd tie some heavy chains around the bottom end of the tree - cut it down and let it fall where it may and then use the chains and a lot of brute force (and a heavy block & tackle or a tractor!) to pull it out of wherever it lands. It's either that or use a cherry-picker and take it down a bit at a time as others have suggested - but the terrain around there looks kinda rough for that kind of machinery to get in there and the lean of the tree and the placement relative to the water will make that be a difficult (and therefore expensive) operation. SteveBaker (talk) 19:30, 16 December 2009 (UTC)[reply]

Fair enough. It was easy to get the height (I can do simple algebra) but the width of the water was a guess and it could be 7m. I do have an Ordnance Survey site map from the listing somewhere. But back to my first idea: what happens if I cut it six foot up and a fair way over the water?--BozMo talk 19:43, 16 December 2009 (UTC)[reply]

Movement of the sun and moon around the sky

So, in the Northern hemisphere, the sun rises in the east, moves in a clockwise direction through the sky (and is at its midday peak in the south) and sets in the west. The moon does the same. Am I right so far? So what happens in the southern hemisphere? Does the sun still rise in the east? Is it at the north at midday? Does it go in an anti/counter-clockwise direction to set in the west (if it sets in the west?)? And what happens on the equator?

In the Northern hemisphere, stars move around the Pole Star - but what direction do they circle in - clockwise or anti/counter-clockwise?

Thank you for helping.81.159.89.69 (talk) 11:44, 15 December 2009 (UTC)[reply]

The cause for all these apparent motions, including star movement, sun rise, and sunset, is Earth's rotation. (The moon also adds a non-negligible extra detail due to its orbit around us, and the Sun also adds a smaller variation because of our orbit around it). But the most important factor here is Earth's rotation. Since Earth's rotation direction is the same everywhere on Earth, the apparent rise of the sun and moon are always in the east; the apparent direction is always the same - counterclockwise if you're facing north (clockwise if you're facing south). In the unique case of polar regions, the midnight sun throws another neat variation, in that the summertime sun never gets low enough to sink below the horizon; but it still "wobbles" in a circular path. The equator doesn't really behave very specially, except that the sun is directly overhead, approximately at the zenith, on noon of the equinoxes. As far as where the sun is at its midday peak, this depends on your latitude and the current season. Nimur (talk) 13:25, 15 December 2009 (UTC)[reply]

edit conflict Because, from a bird's eye perspective of the plane, so to speak, of our solar system, the earth rotates on its axis in a counter-clockwise fashion, the celestial entities (sun, moon, planets, stars) seem to orbit us in a clockwise fashion. Therefor, things rise in the east and set in the west. For one living in the northern hemisphere, solar/lunar "orbits" manifest as short days, with rising and setting occurring south of due-east and -west and the celestial entities don't travel too much into the southern sky. For the same northern hemispherer, summer manifests as long days, with the celestial bodies rising way north of due-east and setting way north of due-west and traveling three sides of the sky (east, south + west). Mid-day, by definition, presents as the sun in the exact middle of the sky in an east-west dimension, but the north-south aspect of the suns position at mid-day will depend upon the time of year (n.b. mid-day here is defined as the time from sunrise to sunset divided by 2). I will not speculate about what occurs in the southern hemisphere, because its quite easy to allow a minor error in calculation to become a tremendous error in conjecture. DRosenbach ^{(Talk | Contribs)} 13:30, 15 December 2009 (UTC)[reply]

Another interesting bit about latitude and the sun's midday position: it's a generalizable rule that the sun is southward in the northern hemisphere and northward in the southern hemisphere, unless you're in the tropics. Between the Tropic of Cancer and the Tropic of Capricorn (those lines of latitude equal to the Earth's angle to the ecliptic), this rule can be broken. At the northern summer solstice, all of the northern hemisphere south of the Tropic of Cancer sees the sun to the north at midday. In fact, at the equator, the expected lengths of day and such get extremely odd: the sun is highest in the sky near the equinoxes, lowest at each solstice. At Quito, Ecuador, the longest day of the year is near the December solstice (no surprise), but there's another maximum at the June solstice, and the minima are in April and August.[24] I expect that shift from the equinoxes is driven by the Earth's orbital eccentricity (the Earth is farther from the sun in June than in December). — Lomn 14:07, 15 December 2009 (UTC)[reply]

It's altogether easier to imagine that you're standing on the surface of a spinning ball - with everything else being more or less stationary! The ball takes 24 hours to spin once. (Which is unsurprising - because that's really what's happening.) SteveBaker (talk) 13:45, 15 December 2009 (UTC)[reply]

They say a picture is worth a thousand words, in this case an animation is even better. Download an open source application called Stellarium (computer program) and have a play. Firstly set your own location and play with the time controls, this will give you "bearings" of where and how the sun rises and sets, and where the stars rotate. Once you have a grip on what you are looking at, change your position to anywhere else in the world, the poles, the equator, anywhere in between, and play again with the time controls. Vespine (talk) 23:19, 15 December 2009 (UTC)[reply]

What happens when you mix hydrogen peroxide and liver?

Biology —Preceding unsigned comment added by 68.146.63.129 (talk) 15:04, 15 December 2009 (UTC)[reply]

In respect to physiology or culinary arts? H₂O₂ will bubble with oxygen release when contacting the blood of the liver (liver is very bloody, as it contains vascular sinusoids). DRosenbach ^{(Talk | Contribs)} 15:20, 15 December 2009 (UTC)[reply]

Depends how the liver is prepared. This is a common high-school bio experiment, so I'll not comment further. DMacks (talk) 17:44, 15 December 2009 (UTC)[reply]

I let myself correct your link, Drosenbach. --Ouro (blah blah) 18:00, 15 December 2009 (UTC)[reply]

I let myself correct your grammar, Ouro. :) DRosenbach ^{(Talk | Contribs)} 19:29, 15 December 2009 (UTC)[reply]

I had to check, what an error! Thank you! --Ouro (blah blah) 17:46, 16 December 2009 (UTC)[reply]

Earth Changes

How valid are some of the predictions in this article? Are they even possible? Are there any notable scientists today who vaildate some of the changes predicted here? --Reticuli88 (talk) 15:40, 15 December 2009 (UTC)[reply]

Not very - though I hasten to say it is a good article dealing well with the subject. The last couple of lines answer most of your question: "Prophecies of Earth changes have been described as a form of scientism, in which terminology and ideas borrowed from science are used to rationalize non-scriptural apocalyptical thought based on visionary experiences. David Spangler, a leader of the Findhorn Foundation spiritual community, described prophecies of Earth changes as an expression of collective fear and anger, rather than as foretelling of actual future events."

Clearly some predications may sometime come to pass; if sea levels rise, if there is a major earthquake or volcanic eruption. But the absence of real scientific underpinning tends to be the give-away. --Tagishsimon (talk) 15:49, 15 December 2009 (UTC)[reply]

How do we know the speed of light is constant?

We can measure the speed of light and observe that it has not changed between our measurements, but how do we know that the speed of light has not changed over the course of time? Or how do we know that the speed of light is not a local phenomenon, resulting in our speed of light being at least a little different then the speed of light in another star system or galaxy? 65.121.141.34 (talk) 15:45, 15 December 2009 (UTC)[reply]

The questions you ask are good ones, and physicists do think about what effect a changing speed of light would have, and whether we could observe such variation. While there is no good evidence of a variable speed of light, we do have an article on the topic: Variable speed of light. -- Coneslayer (talk) 16:23, 15 December 2009 (UTC)[reply]

The deal is that the speed of light is built into so many other parts of physics that the way things like the fusion reactions in stars work would be noticeably different if a different speed of light applied. When we look out at things that are a long way from us - we're seeing them as they were a long time ago. If the speed of light was significantly different than it is today - we'd be able to tell because we'd see things like spectral lines representing the emission and absorption frequencies of common elements being wildly different than they are today - or stars of a particular color having different 'ingredients' than stars of that color that are close to us. That same reason also explains how we know that the speed of light is the same in places a long way from us. I suppose that VERY small changes might somehow sneak by - but it would have to be a rather insignificant difference for it not to be somehow measurable. SteveBaker (talk) 17:04, 15 December 2009 (UTC)[reply]

The speed of light was also measured from a binary star, and no difference in the speed was detected when the star was moving toward, or away from us. I believe this was the first direct evidence of the constancy of the speed light. Ariel. (talk) 07:30, 16 December 2009 (UTC)[reply]

See Michelson–Morley experiment for that. --Stephan Schulz (talk) 08:07, 16 December 2009 (UTC)[reply]

At what distance was the binary star? Would a change of 0.1% per 1,000 lightyears be detectable using that method?

Hold on - this question got derailed in the middle there. This isn't the usual question of: "Is the speed of light independent of the motion of the observer relative to the source?" (Yes, remarkably, it is). That's what you'd use a binary star for - and it's what Michelson & Morley proved. No - this question asks whether the speed of light the same now as it was (say) a few billion years ago - and is it the same here, in our solar system as it is in (say) a neighboring galaxy? Michelson & Morley didn't attempt to show that - and a binary star doesn't help you much with that either. As I said - you really have to look at the secondary effects of the speed of light - comparing the diameter of the event horizon of a black hole to it's mass, for example. As I said before, I'm pretty sure that any change in the speed of light at long distances or in the distant past would produce extreme weirdnesses in the spectral characteristics of distant objects that we simply aren't seeing. So I believe it's fairly safe to say that we don't believe that the speed of light has ever been different or is different in different places. SteveBaker (talk) 03:22, 17 December 2009 (UTC)[reply]

Interpreting life expectancy

If I am a member of a group with life expectancy of 80 years and I am 25 years old, should I expect to leave more or less 55 years? Or does it means that children born today could expect to live more or less 80 years? Or people dying today are on average 80 years old?--ProteanEd (talk) 17:49, 15 December 2009 (UTC)[reply]

Given the development of medicine and technology you might live past one hundred. Given the development of ways to make others suffer, hell knows. --Ouro (blah blah) 17:53, 15 December 2009 (UTC)[reply]

WMDs have been around for decades and, in the grand scheme of things, very few people have been killed by them. I don't think their existence has a significant impact on life expectancy. --Tango (talk) 17:59, 15 December 2009 (UTC)[reply]

Usually life expectancy refers to life expectancy at birth. So it is talking about people born today. If you want more detailed information you need a life table (there are life tables available online for free for various populations) - that will show how long people born at different times can expect to live. Life expectancy increases as you get older because there is no longer a chance of you dying before your current age. So, if life expectancy when you were born was 80 years then you can expect to live longer than 55 years (assuming you are an average members of that population in terms of lifestyle, etc.). Life expectancy for people born now doesn't say much about how long you will live. --Tango (talk) 17:59, 15 December 2009 (UTC)[reply]

Bear in mind that such a life expectancy is the calculated average expected for the group overall. There are always variations above and below the average, and unforecastable accidents (such as terrorist bombs) may or may not have been taken into consideration. The predicted life expectancy of the cadre you are in cannot say anything very definite about your individual life expectancy; a detailed individual health and lifestyle analysis would be necessary for that, and-- Oops! Watch out for that meteorite!! 87.81.230.195 (talk) 19:42, 15 December 2009 (UTC)[reply]

I strongly suspect that terrorist bombs and meteorite strikes are but a minuscule impact on life expectancy. 65.121.141.34 (talk) 19:51, 15 December 2009 (UTC)[reply]

I agree. I wrote this on Talk:Main Page but it's of relevance here:

This is somewhat morbid/grim so don't read if you are uncomfortable with that but as has been kind of hinted at, deaths due to natural disasters can relatively easily exceed death tolls due to terrorist attacks or building fires, and unfortunately relatively often enter into the quadruple digits (look at the earthquakes list for example [25]). Just this year we had the 2009 Samoa earthquake and resulting tsunami (death toll possibly exceeded any single event you mentioned) which occured on the same day as the 2009 Sumatra earthquakes (alone over 1000). And a few weeks ago we had 2009 Jeddah floods which was in the triple digits (and deaths during the Hajj are unfortunately not uncommon). Can't remember if we had Typhoon Ketsana (2009) but that's over 600 if we did (and worse therefore then any other terrorist attack so far bar September 11 [26]). Earlier this year, I'm pretty sure we had the Black Saturday bushfires which again possible resulted in more deaths then any single event you mentioned. As Boz said, the 2004 Indian Ocean earthquake and resulting tsunami is the worst that we've had. Hopefully we'll never exceed that in a long time but unfortunately it could happen, List of natural disasters by death toll is perhaps poignant reminder of that. P.S. Just to be clear, I'm not trying to downplay the impact of terrorist attacks simply pointing out that in terms of deaths, they pale in comparison to many natural disasters

Of course even natural disasters are a small percentage of deaths. In much of the developed and developing world, you much more likely to be killed in an road accident for example. P.S. The events that I didn't name there are the recent Baghdad bombings, the recent Pakistani bombings and the night club fire. Nil Einne (talk) 13:18, 16 December 2009 (UTC)[reply]

And then, of course, there is old age. The vast majority of people in the developed world die of age related diseases. The majority is not so vast in the developing world, but I think it is still a majority. --Tango (talk) 16:58, 16 December 2009 (UTC)[reply]

See actuarial table. I believe the article (and the first actuarial table you read) will answer your question fully. Comet Tuttle (talk) 22:53, 15 December 2009 (UTC)[reply]

Why am I able to see depth in this video?

what is the science behind this please. --Reticuli88 (talk) 18:21, 15 December 2009 (UTC)[reply]

When you cross your eyes and get the images (which are slightly different) to overlap what is happening is one eye is looking at one image and the other eye at the other image and brain is interpreting it as if they are both looking at the same thing. Your eyes seeing slightly different things is one of the main ways we perceive depth (see binocular vision). --Tango (talk) 18:42, 15 December 2009 (UTC)[reply]

We have an article on these of course: stereogram. J kasd 18:48, 15 December 2009 (UTC)[reply]

Do you know where on the internet is there videos of moving stereograms? --Reticuli88 (talk) 18:55, 15 December 2009 (UTC)[reply]

A collection of stereograms can be found here. Scroll to the bottom of the page for 2 animated examples. Pim Rijkee (talk) 22:17, 15 December 2009 (UTC)[reply]

We have one here. It's a pretty interesting one since you can't tell what it is until you cross your eyes. (Besides reading the title.) J kasd 04:32, 16 December 2009 (UTC)[reply]

plastic laminate

what makes up laminating plastic material?are the chemicals safe to use in the home ? —Preceding unsigned comment added by 173.88.240.10 (talk) 18:50, 15 December 2009 (UTC)[reply]

For woodworking, most "plastic" laminate is made of layers of paper bound together with epoxy. The chemicals used to bind this to the surface often have volatile chemicals in them and should not be sprayed without ventilation. If you're referring to the thin, sticky plastic used to cover books and posters, this is usually made of PVC with a layer of adhesive. Laminators using heat to make name badges or other objects may pose a risk if you burn the plastic. There are many ways to use a laminate material, so without more specific uses, the safety can't be evaluated effectively. Caltsar (talk) 17:07, 16 December 2009 (UTC)[reply]

Gallium

Where's a good place to buy gallium online? ----J4\/4 <talk> 19:39, 15 December 2009 (UTC)[reply]

It's available on Ebay. 10 gram lots of claimed 99.9999% pure Gallium have sold in the recent past for $29.11 and 100 g lots for $113 from a UK supplier. Also see Answers.com for the same question. [27] sells it for $1250/kg. Edison (talk) 20:14, 15 December 2009 (UTC)[reply]

But couldn't the sellers on ebay be lying? Also, is gallium toxic? ----J4\/4 <talk> 20:16, 15 December 2009 (UTC)[reply]

Toxicity for the pure element is still indeterminate for skin contact. 65.121.141.34 (talk) 20:34, 15 December 2009 (UTC)[reply]

Sellers on Ebay can always be lying. But if it is someone who sells a lot of similar products and has a very good rating, they are probably not lying. --Mr.98 (talk) 21:23, 15 December 2009 (UTC)[reply]

How would they check? Do gallium buyers generally have the equipment required to test its purity to that level? Vimescarrot (talk) 21:34, 15 December 2009 (UTC)[reply]

I assume people buying 99.9999% pure gallium are probably doing something with it that requires very pure gallium. I have no idea what that would be. If pure gallium were indistinguishable from garbage then they wouldn't need to bother buying pure gallium. Rckrone (talk) 22:02, 15 December 2009 (UTC)[reply]

United Nuclear has Gallium chunks available. Expensive, though—$15/g. --Mr.98 (talk) 21:22, 15 December 2009 (UTC)[reply]

Well clearly a home user is not going to be able to differentiate between 99.9% purity or higher -- though 99.5% purity could cause a significant change in physical characteristics that might well be noticeable. A quick search on Google does show Journal articles referencing gallium used at 99.999% purity, sourced from one of the main chemical suppliers, so I would accept that gallium at this purity does exist. There must be a particular feature of gallium or its extraction that makes it relatively easy to manufacture it at this relatively high purity. For other metals the difference between 99.5% purity and 99.99% purity could typically be a factor of 10 in price. Rjwilmsi 23:17, 15 December 2009 (UTC)[reply]

Do none of you ever bother to read the articles? :-P From Gallium

Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[17] An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling."

&

The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal"

Then there's these in the external links pure Gallium crystals ~99,9999% picture in the element collection from Heinrich Pniok & Price development of gallium 1959-1998. And in the article, I noticed

High-purity gallium is dissolved slowly by mineral acids.

which may or may not be a good way to test purity.

However I have to admit I'm sceptical of these Ebay sellers. You can get a decent idea from feedback but it's far from perfect. Given the prices, I wonder if these people really need such high purity or are just buying it because it's cheap. What are they even using it for? Would someone in a research lab or other place where they may really need such high purity actually buy from eBay? It seems to me they're more likely to buy from an established supplier outside of eBay. Maybe the people know the claims are probably bullshit they just don't care? In other words while it may very well be that purity, I'm don't think we can go solely by the feedback. Taking a look at what else the people have purchased may help, since it may give you a hint what they're likely to be using it for.

Also looking at the feedback, e.g. if it's largely "delivered on time, looks great in my metal collection" or "received today, now I can get started on my perpetual motion machine" I wouldn't trust them to know what the purity is. If it's "just confirmed with mass spec and NAA that it's really 99.9999% purity" [28] [29] ref(yes I know this isn't gallium metal) or "wow I didn't really expect it to be genuine 99.9999% purity but I the results from the X-ray diffraction, SEM, AA, BET surface area, and ICP Spectrometry confirms it is" ref(slightly OT but maybe those will be useful to test the purity tool); well then you can think maybe they do know what they're talking about.

I also came across [30] which may be of interest Nil Einne (talk) 15:10, 16 December 2009 (UTC)[reply]

Southern Hemisphere deciduous forests

Why doesnt the southern hemisphere have more temperate broadleaf decidous forests?

There are some in South America (southern Chile and Argentina), and one deciduous shrub in Tasmania, Australia (Nothofagus gunnii), but apart from that, there isnt much. Whats preventing southeastern Australia (New South Wales and Victoria) from having a deciduous forest? The climate there definitely calls for one...

And what about Argentina, further north in the region between the Parana and Uruguay Rivers, and the Buenos Aires province. The climate there also calls for a deciduous forest, albeit different from that of the more southerly one. We can perhaps draw a comparison between the climate of that region (Parana...etc.) and that of the southeastern U.S. (Louisiana, Mississippi, Alabama, Georgia). Those states are predominantly made up of deciduous forests, with a few pine forests also thrown in. So, why doesnt the southern hemisphere have more deciduous forests? Any ideas...? Thanks! —Preceding unsigned comment added by 201.21.180.57 (talk) 21:21, 15 December 2009 (UTC)[reply]

How would deciduous trees of any kind spread to the Southern Hemisphere? They would have to spread gradually through the tropics from the Northern Hemisphere, and they don't survive in the tropics. So, barring human transport, there's no mechanism by which such plants would migrate to the Southern Hemisphere. --Jayron32 21:49, 15 December 2009 (UTC)[reply]

That argument is not valid, as deciduous forests are found all over the world: the question is, why there are more in the Norhern Hemisphere. First of all, deciduous forests are confined to regions with a temperate climate: that is, a C classification in the Köppen Climate classification. This climate is found in the parts of the southern hemisphere you describe: SE Australia, Rio de Janeiro region. Remember, most of the earth's land mass is on the northern hemisphere; together with the Cf-classification needed for temperate forests, suitable areas are limited. Here you can check the area where temperate forests would grow (if soil conditions are suitable). Not nearly as much as on the northern hemisphere. Another major problem is deforestation, as the Cf climate regions are often places for settlement and have huge urban areas (SW China, SE Australia, Rio de Janeiro region). You can see the impact on this map. Thus, limited landmass, little Cf-climate area and deforestation make for less temperate deciduous forests on the Southern Hemisphere. Pim Rijkee (talk) 22:13, 15 December 2009 (UTC)[reply]

I think the argument is valid, though limited landmass/climate area is probably a more major issue here. Jayron is right that most seasonal trees cannot survive the tropics "as they are", though it's obvious that there was a lot of exchange between hemispheres during the most recent ice age (i.e. subarctic varieties had moved so far south, and the tropics were probably so cool as to allow some of the northern varieties to travel to the south), and probably every cold period previously. Because of the large subarctic landmasses in the north, subarctic varieties of forest trees are more likely to produce successful genetic variations, and thus they will survive better in competition with other plants, preserving more species and higher populations. The southern subarctic varieties don't have as much suitable environment, so they come under more competition from non-subarctic varieties; that is as long as the gene pool isn't rejuvenated by transports from the north. 219.102.221.182 (talk) 06:20, 16 December 2009 (UTC)[reply]

December 16

Nuclear Warfare

How much time does it take for nuclear radiation from a bomb to decay to a safe level? —Preceding unsigned comment added by Cborgen (talk • contribs) 00:05, 16 December 2009 (UTC)[reply]

That's going to depend heavily upon how one chooses to define a 'safe' level — does one mean a level that won't cause acute, fatal radiation sickness, or a level that won't appreciably increase one's lifetime risk of cancer? Those two numbers are going to be rather different, and they're going to heavily depend as well on the yield and location of the bomb. (An air burst will generate less fallout than a bomb detonated close to the ground, for instance.) Finally, do you want to know when it's safe to approach ground zero (the point where the bomb detonated) or just somewhere within a certain radius? Whether one is upwind or downwind of the blast will make a significant difference to one's safety.

All of that pretty much boils down to 'it depends'. You might find the information (and references) in our articles on Nuclear fallout and Effects of nuclear explosions on human health to be helpful, though. TenOfAllTrades(talk) 00:17, 16 December 2009 (UTC)[reply]

There are a number of radiation threats from a nuclear bomb. We might characterize them roughly as so: The first is the pulse that you get from the weapon itself—which will kill you if you are within a certain radius (the size of that radius varies with the yield of the bomb). The second is the radiation caused by short-lived fission products. This is intense (will kill you if you are near it) but relatively short-lived—this is what a fallout shelter is designed to protect you from (if you stay underground for two weeks, you miss most of this). The third is the long-term radiation caused by other fallout. This is the sort of thing that will not kill you immediately, but over the course of living near it, ingesting it, etc., will raise the background rate of cancer appreciably, cause birth defects, etc. How much fallout is created (both the second and third types here) varies with the yield of the bomb, the design of the bomb (some bombs are "dirtier" than others), and the height of where the bomb goes off. --Mr.98 (talk) 00:53, 16 December 2009 (UTC)[reply]

Stars, black holes, and motion...

From an article about a recently re-analyzed black hole - The outermost layers of the star are being siphoned by the black hole. The swirling gas forms a hot plasma disk around the black hole before it disappears, and the process emits a lot of X-rays and radio waves. The part in bold, can we observe that in motion? If Hubble takes a look at that pair and then looks back a day later - can we see a change? a week/month/year later? It's easy for me to visualize swirling masses of plasma being sucked off/out of a star and into the black hole, but I'm VERY curious about the timescales involved. Surely observation of the process-in-motion is possible with instruments, it being only a question of resolution? Are we there yet? Can we watch this happening or is it still the "snapshot" approach? 218.25.32.210 (talk) 08:05, 16 December 2009 (UTC)[reply]

It will most likely be a continuous stream, like in this image (which has a white dwarf, rather than a black hole, but the same concept). I think it is mostly an assumption based on the X-rays - they indicate that it is very hot and there aren't many ways of getting things that hot. Gas spirally into a black hole is one of the few things that can. --Tango (talk) 16:35, 16 December 2009 (UTC)[reply]

The dynamics of accretion disk material can be studied through spectroscopy; the material's velocity gives rise to an observable Doppler shift. See for example Time-resolved spectroscopy of accretion disks in ALGOLS. -- Coneslayer (talk) 16:48, 16 December 2009 (UTC)[reply]

To be clear - we don't have any photographs showing this pretty swirling thing happening. We can only deduce that from other data. Hence, no - the Hubble can't take a pair of pictures and show it happening. A better question is whether the spectroscopic data shows that change. SteveBaker (talk) 17:43, 16 December 2009 (UTC)[reply]

There ARE measurements of radiation from the innermost accretion disk of a BH which indicate that there are enormous velocities involved: the amplitude of the radiation had a frequency of several hundred Hz superimposed. That means that matter circles the BH just above the event horizon several hundred times per second, see eg [31]. --Ayacop (talk) 14:40, 17 December 2009 (UTC)[reply]

Condensation Between Propanoic Acid and 3-Aminopropanal

Hello. How is the main product of the condensation between propanoic acid and 3-aminopropanal named according to IUPAC nomenclature? I think that the aldehyde group in 3-aminopropanal does not react and naming the main product 3-formyl-N-propylpropanamide is ambiguous since the aldehyde group can be on the alkyl chain or the 'amide' chain by the naming alone. Is the main product a double-branched amine or a single-branched amide? Thanks in advance. --Mayfare (talk) 09:15, 16 December 2009 (UTC)[reply]

First you have to figure out the structure (what part(s) react, what the connectivity of the product is), then worry about how to name it. When you have branched-branches, there are specific ways to express what is branched off of what, for example, saying "3-formylpropyl" or "3-formylproanamide" to explain which 3-carbon chain is formylated. Also be careful to use hyphens or parentheses to separate groups "N-propyl-propanamide" means "propyl on N of propanamide" whereas "N-propylpropanamide" sounds like there is a "propylpropanamide" on the N of something else. DMacks (talk) 09:53, 16 December 2009 (UTC)[reply]

Total weight of all insects in the world

If you gathered all the insects in the world together, how much would they weigh in total? --OpenToppedBus - Talk to the driver 11:47, 16 December 2009 (UTC)[reply]

Some background to the question. I've seen lots of sites saying things like "the total weight of insects on the planet is more than all other species put together" or "the total weight of insects destroyed by spiders in a year exceeds the weight of the human population". Last night I heard Johnny Ball claim that for every human on the planet, there are enough insects to equal the weight of seven African elephants. But I can't seem to find any evidence to back any of this up. --OpenToppedBus - Talk to the driver 12:41, 16 December 2009 (UTC)[reply]

Our article biomass (ecology) contains estimates that the total mass of ants is 9–90 times the total mass of humans. I don't know what proportion of insects are ants. Algebraist 13:00, 16 December 2009 (UTC)[reply]

Ant says that ants "may form 15–25% of the terrestrial animal biomass". Algebraist 13:03, 16 December 2009 (UTC)[reply]

And it looks like ants may be about half of insect biomass. So let's say insects are roughly 20-200 times the biomass of humans. Worldwide, an average human is roughly 50kg, so there's 1,000 - 10,000kg of insects for each of us. Even taking the top end, that would still be barely more than an elephant each of insects. So it looks like Johnny Ball was wrong about that last night, as about so much else. --OpenToppedBus - Talk to the driver 14:01, 16 December 2009 (UTC)[reply]

According to this page: http://www.entsoc.org/resources/faq.htm?/print#triv1 there are about 10^19 (10 quintillion) insects in total. Multiply by whatever you think is the average weight. Mytg8 (talk) 14:22, 16 December 2009 (UTC)[reply]

Atoms

why are atoms colourless, despite colour originally containing atoms has colour?

colour or paint is made from various compounds.Molecules combine to form compounds.a moleculeis formed by the combination of atoms.As we know that atom retains its identity throughout chemical change.therefore atoms should have colour —Preceding unsigned comment added by Omkar2510 (talk • contribs) 12:54, 16 December 2009 (UTC)[reply]

Colour comes from the interaction of a substance with light. Exactly how it interacts with light depends on the structure of the material, and in particular on the legal state changes for electrons in the material. These are different for individual atoms, molecules, and crystals. But yes, atoms do preferably emit and absorb light at certain frequencies - see emission spectrum. In that sense, they do have a colour (but one that is different from most of the compounds it forms, and different in non-trivial ways). --Stephan Schulz (talk) 13:39, 16 December 2009 (UTC)[reply]

The OP is claiming that since paint has color and is made of atoms than atoms must have colors as well. I just want to point out the fallacy in this logic with an analogy: Humans have thoughts and are made of cells. Does that imply that cells must have thoughts? Dauto (talk) 14:26, 16 December 2009 (UTC)[reply]

We've got articles on logical error: fallacy of division or fallacy of composition, depending on how you look at it. --Sean 15:34, 16 December 2009 (UTC)[reply]

As Stephan notes, the behaviour of matter can be very different when one compares bulk solids with nanomaterials with individual atoms. Consider gold as one example. What colour is it? Well, obviously it's gold. Take a chunk of it; it's gold. Hammer it out into thin sheets; it's gold. Put flakes of it in your drink; it's Gold...schläger. Makes it into tiny beads a hundred nanometers across, and it's...bright red. Whoops. Take it down to single atoms in a vacuum, and you'd get the sharp absorbance spectrum that Stephan describes. Per Dauto, the whole is often very different from the mere sum of its parts; the behaviour of large numbers of atoms tends to be very different from the behaviour of single atoms. TenOfAllTrades(talk) 14:45, 16 December 2009 (UTC)[reply]

To pick a more commonplace example - carbon is black - right? ... Unless it's a diamond when it's completely transparent. It depends on the crystalline nature of the material - not just what it's made of. SteveBaker (talk) 17:39, 16 December 2009 (UTC)[reply]

See HOMO-LUMO gap. The colour behaviour of a substance is determined by its chemical environment, e.g. electron charge density and the relative energies of various electronic orbitals. John Riemann Soong (talk) 18:57, 17 December 2009 (UTC)[reply]

combined serial and parallel circuits

In a combination of serial and parallel circuits, such as this one, am I correct to conclude that all three lamps shine equally brightly? My reasoning is that a and b/c are connected serially, so both a and b/c should get half of the voltage of the cell. B and c are connected in parallel, so they each get the full amount, thus all three each get half of the voltage of the cell. (I know this might sound like homework, but I am just trying to understand more about electricity and I have no teacher whom I can ask...) Lova Falk (talk) 14:41, 16 December 2009 (UTC)[reply]

I'm not going to answer straight out, but I will ask — how much current flows through each lamp? TenOfAllTrades(talk) 14:47, 16 December 2009 (UTC)[reply]

As far as I understand, lamp a gets twice the current compared to lamp b and c. Lova Falk (talk) 14:55, 16 December 2009 (UTC)[reply]

Assuming that all three lamps are identical, yes. Now, by Ohm's law, what does that tell you about the voltage drop across lamp a versus across lamps b and c? TenOfAllTrades(talk) 15:16, 16 December 2009 (UTC)[reply]

Do I understand correctly that the resistance of each lamp is the same, irrespective of the way it is connected? In that case, the voltage of lamp a should be twice the voltage of lamps b and c. Lova Falk (talk) 16:03, 16 December 2009 (UTC)[reply]

Yes, resistance is an intrinsic property of an item (in basic circuit scenarios, anyway). You could also approach the solution by combining lamps B and C into a single unit BC (via the equation for parallel resistance) and then solve the series system of A and BC. — Lomn 16:16, 16 December 2009 (UTC)[reply]

Bingo. Sounds like you're on your way to a final answer, now. From here (and for more general cases like multiple components in parallel or unequal resistances/loads) you'll probably want to have a look at the formulae and derivations in Resistor, Series and parallel circuits, and Kirchhoff's circuit laws. TenOfAllTrades(talk) 16:44, 16 December 2009 (UTC)[reply]

Thank you! Lova Falk (talk) 17:12, 16 December 2009 (UTC)[reply]

new planets

I have questions after reading http://news.bbc.co.uk/2/hi/science/nature/8414476.stm but don't know where to look in Wikipedia. (1) On a planet five time the mass of earth, what would the gravity be like? What would it be like to walk on the surface? (2) What are the odds of any given planetary atmosphere being breathable by humans? (3) How long would it take to travel to a planet 28 light years away using current technology? Thank you for helping. —Preceding unsigned comment added by 70.29.47.136 (talk) 15:05, 16 December 2009 (UTC)[reply]

At 5 times the mass of earth, the gravity would be 5 times as great, and you'd feel 5 times as heavy. See Newton's law of universal gravitation
Probably not very great. The existance of plants is prerequisite for an atmosphere to be breathable by humans and other animal life. Free oxygen is way too reactive to exist unless a system is actively producing it, and on Earth, it is the existance of plant life that creates and maintains the oxygen in our atmosphere. So, unless plants are already there, there will not be a breathable atmosphere.
24 light years = 2.65 x 10¹⁴ kilometers. So you would just need to calculate the maximum speed of a rocket using current technology, and do the math. --Jayron32 15:33, 16 December 2009 (UTC)[reply]

(edit conflict)Gravity depends not just on the mass of the planet, but also the radius of the planet, and is dictated according to the equation Gm/r², where G is the Gravitational constant, m is the mass of the planet, and r is the radius of the planet. The article seems to conflate size with mass, and gives unclear numbers, so I couldn't say much about what it would feel like there.
Who knows, although probably unlikely. Europa has plenty of oxygen, for example. On Earth, Oxygen came into existence largely as a result of photosynthetic life, which could indicate it isn't likely to occur elsewhere. Oxygen was toxic to early life, so much so that planets with a breathable atmospheres are terrible candidates for extraterrestrial life.
A long time. Voyager 1 is the fastest object that far away at 17km/s, at which rate it would take 493,775 years.

~ Amory (u • t • c) 15:34, 16 December 2009 (UTC)[reply]

The correct formula for the surface gravitational acceleration is Gm/r². Assuming a rocky planet with density simmilar to earth's density you get

g_Planet=g_earth(mass_Planet/mass_earth)^1/3

g_Planet=17m/s²

Dauto (talk) 16:37, 16 December 2009 (UTC)[reply]

Whoops, brainfart. Fixed, thanks. ~ Amory (u • t • c) 17:08, 16 December 2009 (UTC)[reply]

While Voyager is the fastest object made by man, it was not designed solely to travel as fast as possible. I would imagine that if cost was not much of an issue, we could, with current technology, create a much faster spacecraft, capable of at least 1% lightspeed and probably more. That would shorten the trip to the order of hundreds or thousands of years. Not great, but it beats half a million years. Googlemeister (talk) 16:05, 16 December 2009 (UTC)[reply]

Quibble: Not fastest. The Voyager 1 article says: The current speed of New Horizons is slightly greater than Voyager 1 but when New Horizons reaches the same distance from the sun as Voyager 1 is now, its speed will be about 13 km/s compared to Voyager's 17 km/s. Comet Tuttle (talk) 18:02, 16 December 2009 (UTC)[reply]

0.01c would be very difficult with current technology. I think the only technology we have that could do it is an ion drive and we are very much in the early days of ion drives. Rockets would require far too much reaction mass to get up to that kind of speed and would be completely infeasible. Laser propulsion would be a good way to do it, but I don't think anyone has even made a working prototype of such a system. --Tango (talk) 16:48, 16 December 2009 (UTC)[reply]

Probably. Best I could come up with back of the envelope is 0.5%c, and it would be quite the engineering feat to get 10,000 solid rocket boosters into orbit and lash them together so that you have 10 useful stages and a final craft weight of only 10,000 lbs. Also would not be that fun for any human since it would get up to speed in about 20 minutes and people can not pull 4 g (Correction, 4,000 g) for that long can they? Googlemeister (talk) 17:32, 16 December 2009 (UTC)[reply]

Also you'd rocket right past that exoplanet. More likely you'd want to burn half your fuel on the way there, then wait thousands of years, then on approach, your descendants would burn the other half to slow down and reach the exoplanet at a reasonable speed so they could enjoy the visit. Comet Tuttle (talk) 17:56, 16 December 2009 (UTC)[reply]

Is that 10,000lbs the payload mass or the initial mass of the whole craft? Either way, I don't think it's possible. The Apollo mission payloads were about 100,000lbs, I think, and they were only supposed to keep 3 people alive for about a week. A generation ship (which we seem to be talking about) would need at least 50 people and they would need to kept alive (and sane) for hundreds of years, which would require a much greater payload. If you use more realistic estimates of the payload mass you'll find the amount of rocket fuel required would be completely infeasible, even if you could overcome the engineering problems. --Tango (talk) 18:23, 16 December 2009 (UTC)[reply]

Aside from anything else - the news of these new exo-planets only appeared a few days ago. Wikipedia is an encyclopedia - not a newspaper - and while we often do create articles as the news breaks - there is no particular guarantee that this will happen for any given story. That said:

It's tempting to suggest (as others have) that at 5 times the mass of earth, the gravity would be 5 times as great - but gravity gets weaker as you get further from the center of gravity of the planet - so a planet that's 5x the mass of the earth that's made of something very dense (lead maybe) would be smaller than a planet of the same mass that's made of (say) aluminium. Hence the gravity on 'planet lead' would be greater than on 'planet aluminium'. So it's not just the mass - the density matters too. Without knowing both numbers, we have to make a kinda guesstimate that maybe the density of these new planets are similar to earth - and if that were the case, the gravity definitely wouldn't be 5x larger because the planet's diameter would be the cube-root of 5 times (1.72 times) larger. Since gravity drops off as the square of the diameter - we're looking at gravity that's 5/(1.72x1.72) = about 1.7 times more than here on earth. So if you weigh 150lbs here - you'll weigh 255lbs there...that's a lot - but soldiers walk around with 80lb packs on their backs and they seem to manage - so the gravity wouldn't stop you from living there - but it would make life uncomfortable. However, you wouldn't want to have to wear a massive spacesuit or anything like that. But this depends on the density of the planet. If it's lower density than earth, the gravity could easily be earth-normal. If it's even slightly denser than earth - we're in deep trouble!

Free oxygen is unlikely to exist there unless there is active plant life or something somewhat similar. Oxygen is a fairly reactive element and will combine with all sorts of materials in the soil and would probably eventually disappear unless continually renewed somehow. It's possible this happened on Mars where the reaction of oxygen with iron in the soil created the red color...rust. So it's likely that without life, there would be no free oxygen. However, there might be CO2 or water vapor - and you could maybe carry some kind of battery-powered gizmo that would convert CO2 or water vapor to oxygen and thereby survive so long as you have power. Also, we could maybe seed the atmosphere and soil with plant life before we go there (See terraforming) so that there would be a nice oxygenated atmosphere ready by the time we got there. This has been proposed for Mars. So we could use Mars for practice and maybe we could colonize these planets later.

SteveBaker (talk) 17:34, 16 December 2009 (UTC)[reply]

It is very difficult to say what kind of terraforming would be required. Different planets differ from Earth in different ways. For Mars, we need to warm it up and massively increase the atmospheric pressure. For Venus, we need to do the exact opposite. For this newly discovered planet, who knows? Creating the oxygen is probably the easy bit (as you say, we just need to seed the planet with plants), it will be adjusting the pressure and temperature that is hard. As long as the terraforming can be done without people being present, then there is a factor in our favour - unmanned terraforming probes could be sent much faster than the colonists, since the probes could survive much higher accelerations. That should mean that the colonists could arrive to find a nice habitable planet waiting for them having had hundreds of years for a balanced and reasonably diverse ecosystem to develop. --Tango (talk) 18:15, 16 December 2009 (UTC)[reply]

"vascular" headaches

Why is vascular headache an outdated term? The page implies that no headaches are now thought to be related to blood vessel swelling. This is at odds with the page for cluster headache which says "The intense pain is caused by the dilation of blood vessels". 81.131.54.224 (talk) 16:08, 16 December 2009 (UTC)[reply]

The article has no sources and the "outdated" edit was made by an IP with no explanation, so the reason for it is not entirely clear. My understanding based on a quick scan of the literature is that (1) "vascular headache" is no longer an officially recognized diagnosis; (2) the theory that migraine is caused by vascular changes has been called into question; however (3) there is no doubt that some headaches are caused by vascular effects; and (4) the term "vascular headache" is still pretty widely used. Looie496 (talk) 17:53, 16 December 2009 (UTC)[reply]

OK, I'm going to insert your (3) into the article. 213.122.38.14 (talk) 19:31, 16 December 2009 (UTC)[reply]

Don't forget about temporal arteritis -- can lead to blindness. DRosenbach ^{(Talk | Contribs)} 02:53, 17 December 2009 (UTC)[reply]

p-phenylenediamine

does p-phenylenediamine degrade when exposed to air and/or light? if so how much? —Preceding unsigned comment added by 74.65.3.30 (talk) 18:30, 16 December 2009 (UTC)[reply]

Oh yes it does. It goes black! Just like most aromatic amines - air oxidation, a bottle of aniline will be a brown liquid - it's colourless when distilled, as soon as air gets in it starts to turn yellow. The phenylenesiamines are even easier oxidised, which is why derivatives of them are used as developing agents in photography - see C-41 process. Ronhjones ^(Talk) 22:27, 16 December 2009 (UTC)[reply]

CHARGED BLACK HOLES

Hello,

I read and come to know that black holes do have charged and react to external charge, but how not known to me. Can you tell me please. —Preceding unsigned comment added by Harshagg (talk • contribs) 19:03, 16 December 2009 (UTC)[reply]

If you drop something with an electric charge into a black hole - the hole retains that charge...or if something with an electrical charge collapsed to form a black hole - then it could happen that way too. Of course there is the practical question of what we could imagine that was large enough - and charged enough to do that - so the idea of electrically charged black holes is still kinda theoretical. I don't think anyone is seriously saying that we have any reason to suspect they are out there to be found. SteveBaker (talk) 19:08, 16 December 2009 (UTC)[reply]

Steve, the honest answer is that we don't know whether any blackholes out there actually have a non-neglible charge. But I find it perfectly believable that they might have a small but non-negligible net charge. Dauto (talk) 19:47, 16 December 2009 (UTC)[reply]

The problem with black holes having a charge is that, if they can have a small charge, they should be able to have a large charge. Highly charged back holes have naked singularities (see Reissner–Nordström metric). Apparently there is something to do with supersymmetry that fixes this problem (by making higher charged block holes impossible), but I've never really understood supersymmetry. --Tango (talk) 20:36, 16 December 2009 (UTC)[reply]

Somebody asked this before, but I'm not sure I find the answer fully satisfying: Since electrical charge is communicated via photons, how can we detect that the hole is charged? If I drop, say, 10e30 naked protons into the hole, how can I detect this charge? --Stephan Schulz (talk) 20:27, 16 December 2009 (UTC)[reply]

You ask how can you detect the charge of the protons. The answer is 'The same way you can detect the mass of the protons'. The electric charge of the protons don't get destroyed by the blackhole. it becomes part of the blackhole. Dauto (talk) 02:15, 17 December 2009 (UTC)[reply]

Ok, so how to do we detect the mass of the protons? If nothing can escape the event horizon, that includes photons and gravitons. My understanding is that the (virtual) photons or gravitons are created at, or just outside, the event horizon, rather than inside it, but I'm not entirely convinced about how that works. --Tango (talk) 03:24, 17 December 2009 (UTC)[reply]

The event horizon is determined by the condition that the escape velocity becomes the speed of light. Coulomb interaction is mediated by only virtual photons, whose effective speed is not anyhow limited (their propagator is not zero over space-like intervals). So I see no immediate contradiction in probing the electrostatic charge of a black hole. If the charge distribution inside the event horizon were changing, then we (the outsiders) would receive no information on that, as that would be conveyed by electromagnetic waves, i. e. real photons, which surely cannot escape. It would still need some computation (applying quantum field theory in curved spacetime) to prove the relevant part of the "No hair theorem" that the total charge of a black hole is observable, but the charge distribution is absolutely not.—Pt_(T) 06:24, 17 December 2009 (UTC)[reply]

Here is another question. We know that gravity is a weak force, compared to the electrostatic force. So it is conceivable that I have a black hole which is charged to a degree that the electrostatic repulsion is larger than the gravitational attraction. Does that mean that the black hole will start bleeding protons? In fact, does this mean that the even horizon is at different radii for negatively charged, positively charged, and neutral particle? The net force (sum of gravity and electrostatic) is certainly different for each... --Stephan Schulz (talk) 08:16, 17 December 2009 (UTC)[reply]

there is a limit to how charged a black hole can be. the charge to mass ratio is actually way below that of a proton. The reason would be that to push all those positive protons together takes a lot of energy. Somewhere someone here worked out the energy to get a mole of protons in a particular apace. Graeme Bartlett (talk) 09:46, 17 December 2009 (UTC)[reply]

Well, since both gravity and electrostatic force follow inverse-square laws, I should be able to drop protons into a black hole until mass and charge exactly balance out. In that state, the black hole would exert no net force on a proton (but, of course, a lot of force on neutral matter, and an even bigger one on negatively charged particles). --Stephan Schulz (talk) 13:12, 17 December 2009 (UTC)[reply]

Strong gravity is not inverse-square anymore, see Kepler problem in general relativity#Relation to classical mechanics and precession of elliptical orbits: there is an inverse-cube term in the effective potential or, equivalently, a r^-4 term in the force law. In addition, curvature of spacetime modifies the Maxwell's equations including the Gauss's law, which would otherwise give the inverse-square behaviour of electrostatic force. I haven't calculated if things actually still happen to cancel and your idea works, but I doubt it.—Pt_(T) 14:49, 17 December 2009 (UTC)[reply]

If you interpret gravity as a deformation of spacetime, rather than a force, then it becomes clear that it can't be cancelled out. No matter how strong an electromagnetic field is, it can't make a charged massive particle move along a space-like path and that is required to leave an event horizon. --Tango (talk) 15:52, 17 December 2009 (UTC)[reply]

As I mentioned above, if the charge to mass ratio gets too great (I think the charge being greater than the mass in the usual dimensionless units) then you end up with a naked singularity, which is usually interpreted as meaning it can't happen. --Tango (talk) 15:52, 17 December 2009 (UTC)[reply]

how far we go back things become less accurate?

Do we 100% know where the continents were 300 million years ago or is this just a theory. Because The Future is Wild said Antartica was in the equator 300 million years ago, most show Artartica was in SP at that time. Is this right the further we go back in historical time, the less we know. Do we absolutely know if southern Africa was 75 degs. south 200 million years ago, some model shows southern Africa only 55 degs south at that time.--209.129.85.4 (talk) 22:17, 16 December 2009 (UTC)[reply]

We don't 100% know much of anything, when you get down to it, especially something like where the continents were 300 million years ago. We have estimates and projections and simulations and assumptions that probably put us in the right ballpark, but then again, they might be wrong in some major way that we don't know at the moment. I would probably suggest that the issue is not "the less we know" but "the more uncertain our knowledge becomes" the further backwards we extrapolate, but that isn't universally applicable. --Mr.98 (talk) 23:20, 16 December 2009 (UTC)[reply]

The margins of error on things like the positions of tectonic plates do get bigger as we go further back, that is correct, however the error is pretty small. I think there is some disagreement on the details of what happened before Pangea formed, but after that is all seems pretty clear. We have a good discussion of the history of Antartica here. I think 300 million years ago is recent enough that we are fairly sure about it. Africa and Antarctica were both part of the supercontinent of Gondwana 200 million years ago, so they would have been quite close together. About 500 million years ago, Antartica was somewhere near the equator, it moved to the South Pole by around 360 million years ago. I'm not sure what The Future is Wild said, but either you have misunderstood it or they have made mistake - it's probably just a mistake about the time, it's 500 million years ago, not 300. --Tango (talk) 23:33, 16 December 2009 (UTC)[reply]

That said for Antartica to be green again like it was 300 million years ago. No mistakes--209.129.85.4 (talk) 19:24, 17 December 2009 (UTC)[reply]

This didn't say anything about the past, they just said Antartica would be green and hot, and it will be back on equator in 100 million years. I doubt if our article made a mistake on time about Tropical Antarctica.--209.129.85.4 (talk) 19:41, 17 December 2009 (UTC)[reply]

The best information has come from core samples taken by drilling into oceanic plate and examining magnetic alignment. However, oceanic plate is constantly being newly created and the older plate destroyed by the very process that causes continental drift. The further back one goes, the less plate of that age there is still in existence. Past the Mesozoic it is all gone and the information becomes much more sketchy. SpinningSpark 11:45, 17 December 2009 (UTC)[reply]

ICP-Chapter 11 Review-Motion

Please help me with these questions. I'm studying for finals and need to know the answers to these questions.

46 questions

FILL IN THE BLANK

1. The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant ____________?

2. The motion of an object looks different to observers in different ____________?

3. Speed is measured in units of _____________?

4. A moving object does not _______________ if its velocity remains constant?

5. The acceleration of a moving object is calculated by the deviding changes in _____________ by the time over which the change occurs.

6. Two or more velocities add by _____________?

7. The direction and length of a straight line from the starting point to the ending point of an object's motion is _______________?

8. Displacement and velocity are examples of _____________ because they have both magnitude and direction.

9. s=d/t is the equation that defines _______________?

10. The difference between speed and velocity is that velocity indicates the ______________ of motion and speed does not.

11. Because its _____________ is always changing, an object moving in a circular past experiences a constant change in velocity.

12. The SI unit for measuring _________________ is the meter.

13. Accelerated motion is represented by a(an) ___________________ line on a distance-time graph.

14. A constant slope on a distance-time graph indicates ____________ speed.

15. A cars speedometer measures _______________.

16. A car that increases its speed from 20 km/h to 100 km/h undergoes ________________ acceleration.

17. The sum of two or more vectors is called the ____________.

18. A distance-time graph indicates an object moves 20 km in 2 h. The average speed of the object is _____________ km/h.

SHORT ANSWER

19. In the equation for acceleration, a=v/t, how can you describe acceleration if the numerator is negative?

20. Vector addition allows you to add what two quantities for any number of vectors?

21. Distance is a measure of length. What information does displacement give in addition to distance?

22. What types of changes in motion cause acceleration.

23. What is the SI unit best suited for measuring the height of a building?

24. What information does the slope of a speed-time graph provide?

25. a=v/t is the equation for calculating the acceleration of an object. Write out the relationship shown in the equation using words.

26. Bus A travels 300 m in 12 s. Bus B travels 200 m in 12 s. Both vehicles travel at a constant speed. How do the distance-time graphs for these two speeds differ?

27. A child rolls a ball 4 m across a room. The ball hits the wall and rolls halfway back toward the child. Using vector addition, calculate the balls displacement.

28. How is motion described when the velocity of an object changes by the same amount each second?

29. What is the significance of the slope in a distance-time graph?

PROBLEM

32. If you ride your bike at an average speed of 2 km/hr and need to travel a total distance of 20 km, how long will it take you to reach your distance?

33. During a race, a runner runs at a speed of 6 m/s. Four seconds later, she is running at a speed of 10 m/s. What is the runner's acceleration?

34. Explain how velocity is different from speed?

35. Picture a ball traveling at a constant speed around the inside of a circular structure. Is the ball accelerating?

36. A girl walks from her home to a friend's home 3 blocks north. She then walks east 2 blocks to the post office, 1 block north to the library, and 1 block east to the park. From the park, she walks two blocks west to the movie theater. After the movie, she walks 4 blocks south to the pet store. What is the girls displacement from her starting point to the pet store? Where is the location of the pet store in relation to her home? Calculate the distance she walked in blocks.

MULTIPLE CHOICE

1. Instantaneous speed is measured

A) over a very tiny "instant" of time B) at the starting point C) when the object reaches its destination D) over the duration of the trip

2. The slope of a line on a distance-time graph is

A) displacement B) time C) speed D) distance

3. A person drives three blocks north, then turns east and drives 3 blocks. The driver then turns south and drives 3 blocks. How could the driver have made the distance shorter while maintaining the same displacement?

A) by driving north 1 block and east 4 blocks B) by driving back to the starting point by the same route C) by driving east 3 blocks by the starting point D) by driving west 3 blocks from the starting point

4. Which example identifies a change in motion that produces acceleration?

A) a ball moving at a constant speed around a circular track B) a particle moving in a vacuum at a constant velocity C) a vehicle moving down the street at a steady speed D) a speed skater moving at a constant speed on a straight track

5. A car traveling 88 km in 1 hour, 90 km in the next 2 hours, and then 76 km in 1 hour before reaching its destination. What was the car's average speed?

A) 209 km/h B) 63.5 km/h C) 74.5 km/h D) 254 km/h

6. Suppose you increase your walking speed from 1 m/s to 3 m/s in a period of 2 s. What is your acceleration?

A) 6 m/s squared B) 1 m/s squared C) 2 m/s squared D) 4 m/s squared

7. The slope of a speed-time graph indicates

A) acceleration B) direction C) speed D) velocity

8. Speed is the ratio of the distance of an object moves to

A) the motion of an object B) the direction the object moves C) the displacement of the object D) the amount of time needed to travel the distance

9. A ball is rolled uphill a distance of 3 meters before is slows, stops, and begins to roll back. The ball rolls downhill 6 meters before coming to a rest against a tree. What is the magnitude of the ball's displacement?

A) 9 meters B) 6 meters C) 18 meters D) 3 meters

10. The rate at which velocity changes is called

A) acceleration B) motion C) speed

D) vectors

Please please please answer the ones you know(: please and thankyou! you will be of big help to do so. —Preceding unsigned comment added by Kaimorgan16 (talk • contribs) 23:01, 16 December 2009 (UTC)[reply]

The standard disclaimer:

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

applies here. Key phrase "Please attempt to solve the problem yourself first." You'll get better responses if you make some effort to tell us why you're having answering the questions on your own. -- 128.104.112.87 (talk) 23:05, 16 December 2009 (UTC)[reply]

I hid the myriad questions, since we won't be answering them in that form. --Tardis (talk) 23:08, 16 December 2009 (UTC)[reply]

That is far too many questions. You need to actually try and answer them yourself and come back with those ones that you really are stuck on. Try looking up the topics in Wikipedia. For example, question 3 is answered in our article on speed (there is a whole section on it). --Tango (talk) 23:11, 16 December 2009 (UTC)[reply]

Quoth the teacher "Distance is a measure of length" ??? -- Finlay McWalter • Talk 23:49, 16 December 2009 (UTC)[reply]

I'm curious as to what age this would be for. And, the answers are simple and basic - the student not knowing the answers implies that they have not attended class or at least been ignoring the teaching. Wikipedians should not encourage this behaviour by answering the questions. 78.149.247.13 (talk) 10:36, 17 December 2009 (UTC)[reply]

ANNs

There is a very good Excel spreadsheet example of the Perceptron method in the article but the subtitles are incomplete and need additional entries which I plan to remedy shortly. Does anyone know where I can find a similar Excel spreadsheet example of an XOR capable layered ANN and one that displays all of the computations for Backpropogation? 71.100.0.206 (talk) 23:17, 16 December 2009 (UTC) [reply]

ANNs in Excel is easily found via google. This one for instance: [32] I'm guessing that this one could be easily modified to show the underlying computations. EverGreg (talk) 08:35, 17 December 2009 (UTC)[reply]

VBA is easy to find, especially those with a price tag. I'm not looking for a VBA applications program but only an example with the computations for each column at the top as in the Perceptron example. 71.100.0.206 (talk) 17:02, 17 December 2009 (UTC) [reply]

I'd be interested in finding something similar for a radial-basis function, and other AI algorithms. Unfortunately I do not understand or use C. 78.149.247.13 (talk) 11:21, 17 December 2009 (UTC)[reply]

December 17

testicular torsion

what happen if the dead testicle is not removed post testicular torsion? —Preceding unsigned comment added by Reolmadrid (talk • contribs) 03:26, 17 December 2009 (UTC)[reply]

See the "Treatment" section of our testicular torsion article. DMacks (talk) 04:34, 17 December 2009 (UTC)[reply]

Explain why cancer has a genetic code?

Please explain how cancer has a genetic code, accoding to this http://news.bbc.co.uk/1/hi/health/8414124.stm I thought cancer was just the result of unlucky mutations caused by bad environmental things (like smoking, too much sun, sodium nitrate etc). I thought only a proper species would have a distinctive genetic code. 78.149.247.13 (talk) 10:46, 17 December 2009 (UTC)[reply]

I believe you are right about mutations causing cancer; if I'm reading the article correctly, it seems that they're just recording what those mutations are. The mutations are changes to the ~~genetic code~~ genome so the cancer cells do have a different ~~code~~ genome from the healthy cells, but it's not the necessarily the same for ever cancer cell as they are mostly random changes. I believe the hope is that by recording these they can gain insight into which mutations will cause cancer, so the oncogenes I guess. I haven't studied genetics too much so my answer is probably lacking in some way. J kasd 11:33, 17 December 2009 (UTC)[reply]

We have an article on this, gene expression profiling in cancer, and see also oncogenomics. Note also, that a predisposition to some cancers can be hereditary (covered in the cancer article) and so these too, can be detected by looking for the genetic marker. SpinningSpark 12:17, 17 December 2009 (UTC)[reply]

One more article you may want to read is tumor suppressor gene. SpinningSpark 12:22, 17 December 2009 (UTC)[reply]

Your confusion is caused by an unfortunate oversimplification made by the journalist who wrote the article, not the scientists who carried out the research. If you read the article on genetic code, it explains that the "code" is the set of rules used by the cell to translate the instructions encoded in the DNA into the proteins that actually do the work in the cell. The "genetic code" is basically the same among all species, with some rare "variants" described in certain single-celled organisms. This is different than the genome -- the entirety of all the genetic information in a cell -- which differs between individuals, and which can accumulate mutations in different cells throughout the life of the organism. Mutations aren't changes to the "genetic code" but changes in the genome. The article title (and the answer by Jkasd) confuses the distinction between the "code" (which is invariant) and the "genome" (which can be highly variable). Cancer cells still follow the same "rules" when translating the genetic information. They just accumulate mutations that activate certain genes (see oncogene) or inactivate other genes (see tumor suppressor gene). Not surprisingly, they also accumulate a lot of mutations that probably have no effect at all. What many cancer biologists are doing these days is to examine "cancer genomes" to generate catalogs of all the mutations found in individual tumor samples, then to see whether the same mutations keep coming up over and over again in different people. This would give us additional insight into the mechanisms of carcinogenesis, and hopefully point towards effective treatments. --- Medical geneticist (talk) 13:27, 17 December 2009 (UTC)[reply]

computer CD ? DVD

what is the material of construction of CD & DVD ? what is the difference ( Construction) between CD & DVD ?193.188.60.123 (talk) 11:10, 17 December 2009 (UTC)[reply]

According to our article CD, they are mostly made of polycarbonate plastic with a thin layer of aluminum. I believe that DVDs are made of the same materials, the difference being the size of the pits and the format used. See Optical Disc for more general information. J kasd 11:24, 17 December 2009 (UTC)[reply]

A big difference between CDs and DVDs that you can easily notice if comparing the two from the side is that in DVDs the reflective layer is in the middle i.e. there are two layers of plastics on the top and bottom. This is because the amount of information that can be stored depends how close the data layer is to the surface so by reducing the thickness of the protective layer they can increase the amount of information that can be stored. There's some explaination here [33] for example (related to Blurays where the data layer is even closer to the surface). Of course to keep the thickness the same as CDs, they add another protective plastic layer to the top. This also means that the reflective surface is protected from scratches unlike with CDs where it can be scratched (and if it is, you're basically screwed). It also means double sided DVDs are possible (albeit still fairly rare because people don't like switching sides) whereas with CDs they're not compliant with the spec. As I mentioned, this is usually easy to see if you look closely from the side and you can actually differentiate DVDs from CDs in a spindle (useful for example if you have a spindle and you're looking for a specific CD or DVD in a mix or you think you misplace it). Some DVDs particularly recordable ones don't bother to put any coating at the top (or it may not cover the whole top) so you can clearly see the reflective layer is underneath from the top side as well.

Of course DVDs can also be dual layer. This means there are actually two data layers each with a reflective metal layer (one being semi transparent) and a small protective layer in between. See [34] [35] for example (these are recordable but much of the same applies to pressed DVDs.) However they are close enough together that it can be difficult to see from the side. From the bottom however if you look at the spindle you should see two different rings perhaps with a different barcode and maybe even a different description (e.g. L0 and L1). One is for each layer.

Also when it comes to recordable DVDs you they use different dyes from CDs.

BTW because of the different track pitch you also get different diffraction grating patterns in particular, the spacing between the lines is wider with a DVD. This works best with a laser e.g. [36] [37] but as with anything involving lasers please take great care when trying that and make sure you know what you're doing. If you don't, you should be able to see this with an ordinary light although probably not well enough to accurately measure. From memory a small light works well, particularly if it has two or three peaks. For example, I had a mobile phone with a fairly long but narrow LED on top (you can see the LED in this photo, it's the transparent bit between the self potrait reflective button thing and the camera) that could shine different colours, it was interesting to see the different colours that made up these and it was also a good way to compare the diffraction patterns of CDs and DVDs.

Nil Einne (talk) 14:51, 17 December 2009 (UTC)[reply]

Particles And Black Holes, are They the Same Thing?

If a particle has mass, but is a zero dimensional point according to standard model doesn't that mean it has an infinite density meaning it is a black hole? I know that according to some theories like m theory, black holes and particles are remarkably similar,but if a particle has infinite density doesn't that make it a black hole. Black hole evaporate by releasing Hawking radiation, but no one knows for sure wether they completely evaporate into a burst of gamma rays after becoming a micro black whole or wether they reach some stable state and the process stops. If at some point black holes do become stable, could a particle actually just be its stable form? —Preceding unsigned comment added by 74.67.89.61 (talk) 12:20, 17 December 2009 (UTC)[reply]

Those are some interesting questions. Our article on the black hole electron briefly touches on some of these points, including the issue of stability of such (hypothetical) particles. The answer to your final question boils down to, "Yes, that would be compatible with some models of physics." Unfortunately, we don't have now (and may never) have the tools necessary to probe the structure of matter on small enough scales to confirm or refute the presence of tiny black holes inside each 'fundamental' particle. TenOfAllTrades(talk) 13:48, 17 December 2009 (UTC)[reply]

Why does once in a blue moon = 1.16699016 × 10^(-8) hertz?

Says Google.

Why?--72.178.133.37 (talk) 14:04, 17 December 2009 (UTC)[reply]

Because a blue moon occurs on average every 2.7154 years and a year has 365.256363051*86400 seconds. Thus, a blue moon occurs every 2.7154*86400*365.256363051 seconds, or with a freqency of 1/85692999.878958419s or 1.1669564625027745e-08Hz (minor rounding errors may have occurred). --Stephan Schulz (talk) 14:18, 17 December 2009 (UTC)[reply]

I don't understand the hertz though. The article says that the unit is defined as "cycles per second". What is a cycle? I've never heard of that unit.--72.178.133.37 (talk) 14:21, 17 December 2009 (UTC)[reply]

From wikt:cycle - "An interval of space or time in which one set of events or phenomena is completed." --LarryMac | Talk 14:25, 17 December 2009 (UTC)[reply]

So how do you compare frequencies? Because when I think of frequencies, I think of radios (sound), radiation (light), and so forth. They all use hertz? Isn't that a bit impractical? I've never heard of, say, the frequency of some light being described in hertz (or megahertz or any size prefix).--72.178.133.37 (talk) 14:39, 17 December 2009 (UTC)[reply]

You compare them (I'm not really sure what you mean by "how" there). Our hertz article notes, though, that "for historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies". For known speed (in this case, c), frequency and wavelength can be trivially converted, so it's simply a matter of nomenclature. Visible light, for what it's worth, is in the hundreds of terahertz range. — Lomn 14:47, 17 December 2009 (UTC)[reply]
Yes. Hertz is just another name for "1 per second" or 1/s. 440 Hz is the frequency of a sound in concert pitch A. That's 440 "cycles" or "vibrations" of the air going back and forth in one second. Around 100 MHz in the electromagnetic spectrum is FM radio. 550 THz EM is green light. --Stephan Schulz (talk) 14:49, 17 December 2009 (UTC)[reply]
(EC) For completeness: You can transform one into the other through v=lambda * f ([phase]speed = wavelength times frequency). For EM-radiation, the speed is fixed at lightspeed. And the reason why different things (sound, radiation, all things that rotate on an axle) are all described using hertz is that they all are, on some level, the same: A circular process which repeats, so you can count how often it repeats in one second, giving you the hertz value. --TheMaster17 (talk) 15:01, 17 December 2009 (UTC)[reply]

So basically then, you can convert anything that happens every once in a while to hertz? So you can say something like, "my birthday is 3.16887646 * 10^(-8) hertz". Doesn't this get confusing?--72.178.133.37 (talk) 15:02, 17 December 2009 (UTC)[reply]

You can, and yes, it's often completely impractical (as is the Google example that started this). However, odd units and transformations can be useful teaching tools -- you may want to look at the firkin-furlong-fortnight unit system, a system of measurement that exists for little purpose except geek humor. — Lomn 15:08, 17 December 2009 (UTC)[reply]

Although as a somewhat-pedantic note, "every once in a while" is subject to interpretation. Hertz values are most commonly used for things that cycle regularly, without significant variation. Expressing the "hertz of New York Yankees championships" wouldn't have much meaning, because the time between each is variable and not dependent on the other values. Google's use of "blue moon" is something of a middle ground -- the true time between blue moons is variable (thus the value they give in hertz is an approximation), but it's also predictable. — Lomn 15:13, 17 December 2009 (UTC)[reply]

In fact, there are two SI units that are both "1 per second" or 1/s. The hertz is intended for regularly repeating events, like the frequency of a wave, while the becquerel is for radioactive decays, which occur randomly but whose expected rate is predictable. --Anonymous, 21:57 UTC, December 17, 2009.

Wormholes and Blackholes

What is the difference between wormholes and blackholes? --Reticuli88 (talk) 14:55, 17 December 2009 (UTC)[reply]

Wormhole v. Black hole. First sentence of each should clear it up. --Mr.98 (talk) 15:10, 17 December 2009 (UTC)[reply]

If I had a choice, I'd prefer to go thorough a wormhole then a black hole. At least I think so. Obviously once I get thorough the wormhole and find some aliens with anal probes I reserve the right to change my mind Nil Einne (talk) 17:08, 17 December 2009 (UTC)[reply]

Well, it is not even theoretically possible to go "through" a black hole. Think well instead of tunnel. Googlemeister (talk) 17:12, 17 December 2009 (UTC)[reply]

Was wondering how long it would be before someone said something like that Nil Einne (talk) 18:42, 17 December 2009 (UTC)[reply]

Collective Human Mind Connection to the planets Ecosystem

Awhile back I remember reading a wikipage on some Theory on the entire human population mind(s) being connected on some unnamed level with the Earths Ecosystem. Does anyone recall what this Theory is called? Cheers, --i am the kwisatz haderach (talk) 17:09, 17 December 2009 (UTC)[reply]

Sounds a bit like James Lovelock's Gaia theory. --TammyMoet (talk) 17:15, 17 December 2009 (UTC)[reply]

Specifically, his Gaia hypothesis.--Shantavira|^{feed me} 17:17, 17 December 2009 (UTC)[reply]

That was it. Thanks much. --i am the kwisatz haderach (talk) 17:24, 17 December 2009 (UTC)[reply]

Is a hot radiator disrupting my TV's remote control?

I have a tv near to and somewhat facing a hot radiator. Could this be disrupting the infra-red signal from the remote control? The standby light sometimes starts flashing and the tv won't start - I'm wondering if this might be the cause. Thanks. 84.13.35.30 (talk) 18:00, 17 December 2009 (UTC)[reply]

It's very unlikely. Infrared diodes usually send signals modulated by a digital code, so it would be difficult for a steady IR source (even if it radiates at the same wavelength) to interfere. If the emitted IR signal from the radiator is very strong, it might be plausible that it's saturating the receiver diode's front end amplifier, but this again seems unlikely. Nimur (talk) 18:06, 17 December 2009 (UTC)[reply]

Extremely unlikely. The IR used by a TV remote is about 900nm, which is only emitted (as thermal radiation) in considerable quantities by something over maybe 500°C (900nm is only slightly longer than the 700-750nm limit of the visible spectrum, so it needs to be almost red hot). Your radiator won't be anywhere near that hot. An incandescent light bulb will emit far more at that wavelength than your radiator ever could, and TV remotes work fine in rooms light by incandescent bulbs. --Tango (talk) 19:01, 17 December 2009 (UTC)[reply]

silicone or rubber compound used for grips etc...

I am working on a new fly fishing tool that requires a very soft rubber grip (possibly translucent) I have only seen it on a hairbrush handle and nothing else. It like nothing I have ever seen before. Doeas anyone know what type of material this is or what it is called.? It is somewhat clear,very soft , no memory any help would be appreciated greatly thanks Jason ,pennsylvania —Preceding unsigned comment added by 24.229.199.70 (talk) 18:09, 17 December 2009 (UTC)[reply]

It's going to be hard to tell - but if I had to guess: Gel pads are usually made of a Polyurethane-based elastomer...these grips sound kinda similar to a gel pad. SteveBaker (talk) 19:52, 17 December 2009 (UTC)[reply]

following migration routes leading to discovery

Now-a-days hunters still wait along migration routes waiting for the opportunity to kill. Before the gun this was possibly done with bow and arrow or snares where flock were know to land. Even crocs take advantage of the knowledge of migration. Is it possible that the discovery of Greenland came form the following of the Barnicle Goose from Western Europe to Greenland over time of seeing it fly in that direction far out at sea? 71.100.0.206 (talk) 19:54, 17 December 2009 (UTC) [reply]

The discovery of Greenland by whom? Greenland has been settled by various people at various times. The Saqqaq culture settled Greenland in about 2500 BC, and left no written history; near as I can tell, it is unknown why they ended up there, or even where they came from. The European settling of Greenland came in the 10th century by way of the Vikings, doing pretty much what Vikings always did, which is to ride around in boats and find stuff to take. I don't think that there is any evidence that the Viking settlement of Greenland was as a result of following bird migrations. --Jayron32 20:11, 17 December 2009 (UTC)[reply]

Isn't there still controversy over who discovered America or has that been resolved?. American Indians were living on the continent long before Europeans arrived. ... of course I mean by Europeans. 71.100.0.206 (talk) 20:35, 17 December 2009 (UTC) [reply]

Ice in My Freezer "Sublimates". Why?

If I make ice-cubes in the freezer on my refrigerator, the water becomes ice well enough, but after about a months time, I'm only left with slivers of ice at the bottom of the tray. I don't know if the ice is necessarily "sublimating" as I doubt that I'm getting steam in my freezer, but might the ice be going directly to water vapor? If so, why? All other freezers I've had required de-icing while mine isn't capable of keeping ice. Zhatt 22:00, 17 December 2009 (UTC)[reply]

Hmm, hard to say. Did you recently move to a drier climate or something? As a practical matter, though, I can't see it as very important; month-old ice tastes terrible (assuming you have anything other than ice in your fridge), and you should throw it out anyway.

Just by the bye, the verb is usually sublime rather than sublimate. Sublimating is something you do with psychological impulses that you can't ~~admit to yourself~~ oops, I think I got that wrong -- that's repression. You repress desires you can't admit; you sublimate the ones you can't satisfy. Or something like that.. --Trovatore (talk) 22:06, 17 December 2009 (UTC)[reply]

I don't know if it is technically sublimating, but it could be melting and then evaporating. Do you have a thermometer in your freezer (or can you put one there)? You may find it isn't really cold enough. If it is only just below 0°C then it will be very close to the triple point of water. That means water can very easily change between all three common states of matter. The water is always in a dynamic equilibrium, meaning there is always some bits melting, some bits freezing, some bits evaporating and some bits condensing. There should be the same amounts doing each so the total amounts of ice, liquid water and water vapour should stay the same but since your freezer doesn't ice up that probably means it has some kind of dehumidifier, so the bits that evaporate disappear off so there isn't much water vapour there to condense. That means the equilibrium is broken and the water gradually disappears as more bits melt, then evaporate and then get sucked up by the dehumidifier (which will then condense the water and collect it somewhere where it can evaporate out into the air outside the fridge). If you can get the freezer colder, that should reduce the amount of evaporation going on. It should be at least -10°C, probably colder (I can't remember the exact guidelines). --Tango (talk) 22:18, 17 December 2009 (UTC)[reply]

You don't know if it's technically subliming. --Trovatore (talk) 22:35, 17 December 2009 (UTC)[reply]

Yeah... I should have taken the hint when I edit conflicted with you and corrected my spelling... --Tango (talk) 22:56, 17 December 2009 (UTC)[reply]

Actually Wiktionary seems to think they're both acceptable. Subliming is just what I've heard, and I do like that it's a different word from the psych one. --Trovatore (talk) 22:59, 17 December 2009 (UTC)[reply]

Never heard of the triple point, but that sounds like a likely situation. I'll grab a thermostat on the way home and check it out. I'll report back here if I find out anything. Zhatt 23:04, 17 December 2009 (UTC)[reply]

Commonly in the UK snow disappears with the temp well below freezing. I don't know why you should be adverse to labelling it sublimation.--BozMo talk 23:11, 17 December 2009 (UTC)[reply]

The noun is sublimation, the verb is sublime. --Trovatore (talk) 23:15, 17 December 2009 (UTC)[reply]

I wonder if this could be a pondial thing, like orient/orientate? --Trovatore (talk) 23:16, 17 December 2009 (UTC)[reply]

If I'm reading the sublimation article correctly, it seems that sublimation occurs at the triple point. So it would be safe to say that its subliming if what Trovatore described is what is happening. Thing is, on the water article it notes that while the triple point of water is nearly at the freezing point, the triple point is also at a pressure about 1⁄166 of normal sea level pressure. I don't think my freezer is also a decompression chamber. Nor is it on Mars. Zhatt 23:35, 17 December 2009 (UTC)[reply]

@@ Line 732: / Line 732: @@
 ::::::The noun is ''sublimation'', the verb is ''sublime''. --[[User:Trovatore|Trovatore]] ([[User talk:Trovatore|talk]]) 23:15, 17 December 2009 (UTC)
 ::::::I wonder if this could be a pondial thing, like ''orient''/''orientate''? --[[User:Trovatore|Trovatore]] ([[User talk:Trovatore|talk]]) 23:16, 17 December 2009 (UTC)
-If I'm reading the [[Sublimation (chemistry)|sublimation article]] correctly, it seems that sublimation occurs at the triple point. So it would be safe to say that its ''subliming'' if what [[User:Trovatore|Trovatore]] described is what is happening. Thing is, on the [[Water molecule #Triple_point|water article]] it notes that while the triple point of water is nearly at the freezing point, the triple point is also at a pressure about 1⁄166 of normal sea level pressure. I don't think my freezer is also a decompression chamber. [[User:Zhatt|<font color="orange">Zhatt</font>]] 23:35, 17 December 2009 (UTC)
+If I'm reading the [[Sublimation (chemistry)|sublimation article]] correctly, it seems that sublimation occurs at the triple point. So it would be safe to say that its ''subliming'' if what [[User:Trovatore|Trovatore]] described is what is happening. Thing is, on the [[Water molecule #Triple_point|water article]] it notes that while the triple point of water is nearly at the freezing point, the triple point is also at a pressure about 1⁄166 of normal sea level pressure. I don't think my freezer is also a decompression chamber. Nor is it on Mars. [[User:Zhatt|<font color="orange">Zhatt</font>]] 23:35, 17 December 2009 (UTC)