Wikipedia:Reference desk/Archives/Science/2009 March 6

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March 6[edit]

Early Lifeforms[edit]

Would early lifeforms have used carbon in any way? Shells like those that form chalk? Part of energy source? (talk) 00:26, 6 March 2009 (UTC)

The earliest life, like all life we know of, would have been built up from amino acids and other molecules involving carbon. Carbon is a key component of all life on Earth and always has been (as far as we're aware). --Tango (talk) 00:31, 6 March 2009 (UTC)
Following EC:Life on earth is based on organic chemistry. That is based on carbon (scroll down on the page I linked to get to the juicy parts). Even Anaerobic organisms fall into that category. So, on a very basic level lifeforms as we know them are based on carbon. (talk) 00:34, 6 March 2009 (UTC)

Right! Sorry for my stupidity. Carbon-based life forms, of course. (talk) 02:25, 6 March 2009 (UTC)

All lifeforms on earth are carbon based.--Apollonius 1236 (talk) 15:57, 7 March 2009 (UTC)
As mentioned above, the earliest life did not have shells - those are actually a fairly late-stage arrival after some billion or so years of proto-life and prokaryotic monerans. Nimur (talk) 06:00, 6 March 2009 (UTC)
Asking stupid questions doesn't make you stupid - quite the opposite, in fact. Had you not asked, you would have continued to be ignorant, now you know. --Tango (talk) 10:31, 6 March 2009 (UTC)
There are no stupid questions. There are questions that beg for stupid answers*, but the above was certainly not one of them. ^_^ Like Tango said... a question that results in a gain of knowledge is always for the good.
* - Example: "Please explain your opponent's ideological viewpoint in a quick sound bite." arimareiji (talk) 14:13, 6 March 2009 (UTC)

Carbon again[edit]

Can graphite go through pyrolysis to become coal? (talk) 02:26, 6 March 2009 (UTC)

I don't think so, but it can apparently get you nanotubes and fullerenes under the right conditions. [1] Someguy1221 (talk) 02:53, 6 March 2009 (UTC)
The name would suggest you might get this Pyrolytic carbon instead. It might depend on what process you are using. Things like pressure, time, temperature etc. can determine what carbon compounds you end up with. For practical applications things like having to wait for a couple of million years or requiring solar surface temperatures might limit your answers. (talk) 04:10, 6 March 2009 (UTC)
What? Coal is graphite. --Pykk (talk) 09:24, 6 March 2009 (UTC)
More like graphite is coal (technically). See Coal. Someguy1221 (talk) 09:32, 6 March 2009 (UTC)
Or even graphite "Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is hard to ignite"

No, it's the other way round - coal can undergo pyrolsis to become graphite (or more often coke). FengRail (talk) 10:51, 6 March 2009 (UTC)

science joke[edit]

I don't get it. Can someone explain? The caption says "Science joke. You should probably just move along." Thanks, flaminglawyer 05:10, 6 March 2009 (UTC)

It is a joke based on Kepler's laws of planetary motion, specifically the second law which states "A line joining a planet and the sun sweeps out equal areas during equal intervals of time." - EronTalk 05:18, 6 March 2009 (UTC)
XKCD often deals with math and science in its punch lines, and fans often don't understand them. If you have access to LiveJournal there is always some sort of discussion (if you can find it among all the other spam) about the interpretation of the joke. (talk) 02:59, 10 March 2009 (UTC)

Atomic Absorption Spectroscopy[edit]

If you're trying to analyze the quantity of iron in some milk, you'd measure the 'absorbance' of the milk at different known concentrations and then plot a line graph. Why is it that milk with no iron concentration registers a small absorbance? Is it a problem with the light source (ie not pure iron), or is a tiny fraction of light not hitting the solution or not being converted? —Preceding unsigned comment added by (talk) 11:02, 6 March 2009 (UTC)

If the atomic absorption spectroscopy shows a small amount of iron, why do you think there isn't any ? (I ask because, whatever other method you used that shows no iron, that might be the method giving the wrong answer.) StuRat (talk) 14:04, 6 March 2009 (UTC)

I don't understand what you mean. If we prepared a solution of milk and we knew for sure that there was no iron in it, and we shone a cathode light made of iron onto it and it still picked up a small absorbance, why is this? —Preceding unsigned comment added by (talk) 09:04, 7 March 2009 (UTC)

I am questioning your assumption that "we knew for sure that there was no iron in it". Iron is very common, and I would expect some contamination (perhaps down in the parts per trillion range) in pretty much everything. A specific mechanism is blood (which contains iron in hemoglobin) in the milk. If you're talking about cow's milk bought at a grocery store, they mix the milk from thousands of cows together at the dairy. Therefore, getting one drop of cow's blood in all that seems almost inevitable. StuRat (talk) 14:21, 7 March 2009 (UTC)
Even air will "absorb" (diffract) a tiny fraction of any given wavelength, let alone milk. For more on the complications inherent in measurement, see absorption spectroscopy. Particularly, take note of how many precautions are needed to make sure that the materials used in the cuvette and/or sample preparation are transparent to light of the specific wavelength the spectrometer uses, and think about whether the proteins and lipids in the milk will be just as transparent, given that they're not transparent in the visible light spectrum. I can't really go farther than that without doing your lab report for you. ^_^ arimareiji (talk) 15:10, 7 March 2009 (UTC)


Would these clouds be considered cumulus clouds? I'm not very smart when it comes to identifying clouds. I mean...they seem pretty poofy to me. ;) Papercutbiology♫ (talk) 13:43, 6 March 2009 (UTC)

Could also be Cumulonimbus cloud it looks pretty dark underneath. I wouldn't be able to tell that from a Cumulus congestus cloud though. Do you know what weather pattern this cloud went with? Did you get a Thunderstorm or rain or was it fair weather? (talk) 14:18, 6 March 2009 (UTC)

It was a fair day, lots of sunshine, and breezy. It didn't rain until the next day...which was pretty unfortunate after having such a pretty day. Papercutbiology♫ (talk) 15:05, 6 March 2009 (UTC)

That would point towards cumulus, then. (talk) 16:41, 6 March 2009 (UTC)
The difference between Cumulus and Cumulonimbus clouds (AKA "Thunderheads") is usually the vertical stack and anvil head on the cumulonimbus clouds. Of course, cumulus clouds may devlop into cumulonimbus type clouds given sufficient lift, and there are likely transitional forms between the two. I am sure there is room for interpretation between the two, but generally I think of Cumulonimbus clouds as more vertical, and cumulus clouds as more horizontal or poofy-rounded. Also, as cumulus clouds tend to be fair weather clouds, it is often clear beneath them. With cumulonimbus clouds, there is often visible virga below them (i.e. streaks of rain) which can be observed from a distance. 19:23, 6 March 2009 (UTC)
Yeah - it's not a Cu.Nim - those have a classic "Anvil" shape - kinda like a mushroom cloud after a big explosion! The big rounded cloud in the photo is a cumulus. There are higher altitude, whispy clouds there that are cirrus or maybe cirrostratus (depending on altitude). Pf course these kinds of descriptions are not hard-and-fast - there are all sorts of in-between possibilities. SteveBaker (talk) 20:47, 6 March 2009 (UTC)
These clouds are far too flat to be cumulonimbus. I think cumulus clouds are present near the centre of the image. On Wikipedia Commons, where I have previously categorised many cloud pictures, I would put that image under the categories Cumulus clouds and Stratocumulus clouds (the flatness of the clouds, fractus-like in some areas, and forming a layer-like structure in the distance hint at this). ~AH1(TCU) 00:36, 8 March 2009 (UTC)

Writing on batteries[edit]

Because I use my digital camera frequently (see Commons:Category:Files by User:Nyttend), I have four pairs of Energizer AA rechargeable batteries: one for the camera, one as spares to carry in the camera bag, and two more to replace those when I'm charging pairs 1 and 2. I'm considering writing numbers on the sides of the batteries, so that I don't put used batteries in the camera and recharge the fully-charged ones by accident just before I go somewhere. Would this be safe? I plan to use a rollerball pen, although since I've not tried writing on them, I don't know if the ink will hold. Nyttend (talk) 16:01, 6 March 2009 (UTC)

I don't think a rollerball pen will get the job done; I would think magic marker is more what you need - the permanent kind, not the water soluble. Neither would be dangerous. - Nunh-huh 16:14, 6 March 2009 (UTC)
I suspect that the ink will hold poorly, but your mileage will vary. (Depending on what else you carry in your camera bag, you may also risk transferring pigment to something valuable.) Whether the ink adheres well or not, the batteries won't be harmed. Per Nunh-huh, a felt-tip permanent marker (Sharpie brand, perhaps) might work better, though even that stuff wears off smooth surfaces if abused.
You might consider the use of a little bit of colored nail polish to identify each battery. (Use different colors or different numbers of dots; I wouldn't try to write out the numerals themselves.) Sally Hansen Hard As Nails polish is reliably durable. (I don't wear it, but I use it in the lab.) TenOfAllTrades(talk) 16:23, 6 March 2009 (UTC)
I'm picturing a dozen rats with exquisite pedicures.... - Nunh-huh 16:26, 6 March 2009 (UTC)
Ha! Sadly, my purpose is much more prosaic. Usually it's to secure and seal glass coverslips on microscope slides. It makes a reasonably hard, waterproof seal. I've always bought the clear stuff though I've considered acquiring different colors to make slides easy to distinguish under conditions of low light and barely-legible handwriting. (Experimental samples will be tagged in Seductive Scarlet, while controls can use Sultry Shamrock.) TenOfAllTrades(talk) 17:21, 6 March 2009 (UTC)
(off topic) As an example of US laboratory health and safety guidelines running amok, when I was in lab they used to make us put "not for human use" on the nail polish we used for sealing slides. I think at one point they even wanted us to get a material safety data sheet for it! --- Medical geneticist (talk) 23:42, 6 March 2009 (UTC)
EC: A Paint marker would work best. In the US they most commonly come in metallic gold. In car part or art supply stores you might find other colors. Also see what you local office supply box has to offer. Shake well before use and make sure to let the paint dry before you use/touch the batteries. (talk) 16:29, 6 March 2009 (UTC)

A Sharpie (marker) should get the job done. They have a fairly fine point, and are permanent, and write on most surfaces. Edison (talk) 18:43, 6 March 2009 (UTC)

I wrap mine with a strip of electrical tape. SteveBaker (talk) 20:16, 6 March 2009 (UTC)
Of all the good suggestions above, I think the nail polish would be best. I'd also be careful to apply it to a surface where it would not be scraped during battery insertion and removal. For rectangular batteries, the side that faces out. For cylindrical batteries, the area surrounding the positive knob. Any debris that flakes or scrapes off and gets inside the camera could ruin it if it works its way into the optics. -- Tcncv (talk) 01:01, 7 March 2009 (UTC)
All these battery marking schemes are not that helpful because you still have to remember which batteries are charged and which are discharged. I use battery cases with 4 little slots that hold the cells (you can get them from places like thomas-distributing dot com). I put charged cells into the cases with the positive end facing upwards, and discharged cells with the positive end facing downward. By the way, that brand of rechargeable cells that you mentioned is terrible. They often crap out after just a few charges. You are better off getting pre-charged cells (available in various brands). Their main feature is near-elimination of self-discharge (that's how they are able to hold a charge while sitting on a store shelf). They sacrifice some capacity to gain that, but it makes them much more reliable. (talk) 06:06, 7 March 2009 (UTC)

How does VIH resist reverse transcriptase inhibitors?[edit]

I've read in the VIH article that this this virus is treated with reverse transcriptase inhibitors. But the article does not explain how the virus can continue to reproduce (and therefore, why isn't AIDS treatable). Can someone help? Thanks. —Preceding unsigned comment added by (talk) 16:54, 6 March 2009 (UTC)

Do you mean the HIV article? On English Wikipedia, VIH redirects to an airport. Nimur (talk) 17:43, 6 March 2009 (UTC)
(ec) HIV/AIDS is quite treatable; treatment of HIV is highly effective - for example, there are no special limits on the lifespan of people who have access to care and have not developed resistance to antiretroviral drugs. Resistance is just one of the limitations of antiretroviral therapy. The articles I've linked can answer many questions. If you don't find what you need, please be more specific. --Scray (talk) 17:47, 6 March 2009 (UTC)
Reverse transcriptase is blocked by either competitive or non-competitive inhibitors (see reverse transcriptase inhibitors). It's kind of trivial that a structural alteration could make an RT resistant to the non-competitive inhibitor, but not so much how a mutation could make it resistant to the "primer blocking" effects of the competitive inhibitors (many of which, as the article describes, act like ddNTPs). "K65R: a multi-nucleoside resistance mutation of low but increasing frequency" Antiviral Therapy (2003) is supposed to describe how this works, but either the publisher's webiste (or my library's) is having some funkiness right now and I can't actually access it. Someguy1221 (talk) 23:47, 6 March 2009 (UTC)

"Reverse transcriptase is blocked by either competitive or non-competitive inhibitors."

That's not correct. The terms "competitive" and "non-competitive" apply to inhibitors of receptors (i.e. receptor antagonists), not enzyme inhibitors. Axl ¤ [Talk] 08:50, 9 March 2009 (UTC)

If you're right, then you might want to tell the editors of Antiviral Research,[2] The Biochemical Journal,[3],[4] and the Biological & Pharmaceutical Bulletin.[5]. Those are just some of the many I found in a quick look for non-competitive HIV RT inhibitors. Is it possible the usage is a little broader? --Scray (talk) 09:43, 9 March 2009 (UTC)
Thanks for pointing that out. You're quite right, Scray. Axl ¤ [Talk] 12:08, 9 March 2009 (UTC)

Clean coal...for real?[edit]

I was reading our coal article - in the vain hope of being able to contribute to our earlier question about the stuff...or at least to learn something for the next time a coal question comes up.

What I read in the article is that the principle ingredients of coal are carbon (well, duh) - and hydrogen. We know that burning the carbon is pretty disasterous for global warming - and even the 'carbon sequestration' tricks the 'clean coal' advocates propose don't look particularly promising. But I wonder if there is any possibility that a true "clean coal" technology could be devised that would extract the hydrogen out of the coal without burning it and making all that nasty CO2 - leaving a pile of purer carbon behind and then using the resulting hydrogen (for example) to power our cars? Obviously the energy you'd get out would be less than if you burned the coal - but it would be a very clean technology - and there is an AWFUL lot of coal down there. I wonder if it would still be economic? I also wondering whether there might be a possible means to extract the hydrogen from a coal seam without digging the stuff up? (Maybe pump something heavier like CO2 down there under pressure?)

Does anyone understand how the hydrogen is bound up in the coal well enough to explain this? (I'm not a chemist - so I need baby-talk for that bit!)

SteveBaker (talk) 22:47, 6 March 2009 (UTC)

The United States Department of Energy has spent millions of dollars on this specific project. See an itemization of over $7million handed out in 2006 here. There are two main issues. First, the hydrogen must be separated. It becomes crude hydrogen because it is mixed with a lot of garbage. Then, it must be refined into quality hydrogen. If you look at the projects involved in the 2006 grants, you will see the same thing over and over - research into refining or purifying crude hydrogen. That appears, from what I see, to be the problem. If you burn crude hydrogen, you will be sending all the pollutants in the crude hydrogen into the atmosphere just like burning coal. -- kainaw 22:58, 6 March 2009 (UTC)
Well, that led to this that explains exactly how it is done. -- kainaw 23:00, 6 March 2009 (UTC)
No - that's the pathway that Arimareiji discusses below - it's still reacting the carbon (in this case with water) and producing CO2 along with hydrogen from the water. I'm asking about whether the hydrogen that's already in the coal can be extracted LEAVING THE CARBON BEHIND. SteveBaker (talk) 02:34, 7 March 2009 (UTC)
Coal, to my knowledge, is more-or-less pure carbon. No appreciable hydrogen in it. Burning it directly gives carbon dioxide, CO2. Hydrogen can be generated if you react that carbon with steam to form synthesis gas (C + H2O -> CO + H2) to serve as fuel. You can further react the CO (carbon monoxide) to get more hydrogen, producing CO2. (CO + H2O -> CO2 + H2) You could see this as analogous to charging a battery - instead of high-energy coal, you now have high-energy hydrogen.
But there's no free lunch. To put it in overly simplistic terms, carbon is high-energy and carbon dioxide is low-energy. You only get the energy difference out of carbon if you turn it to carbon dioxide, regardless of whether you burn it directly or react it to form hydrogen. arimareiji (talk) 23:56, 6 March 2009 (UTC)
@Arimareiji : Yeah - I thought that too - but just go and read our article: coal - there is in fact quite a bit of hydrogen locked up in coal. Hence the question! SteveBaker (talk) 00:55, 7 March 2009 (UTC)
Being 7 months behind in my reading may have paid off, I just read something about this in Nature. Coal can be gasified underground by drilling a well; setting it on fire and adding oxygen; then removing the resulting gas from an adjacent well. The product is synthesis gas (H2+CO) and CO2 which can be used to make all the things syngas is already used for in refineries (diesel oil in this case). This is essentially the same thing as coking, which drives almost everything but the carbon out of coal for use in iron smelting - but in reverse, it leaves much of the carbon in the ground. However, if the output carbon is not sequestered, the process produces twice the amount of greenhouse gas as the straight-out petroleum product. That seems to be the best available technology. Steve, I'll mail you the article and anyone else who wants a copy, drop me a line. Franamax (talk) 02:41, 7 March 2009 (UTC)
Someone could actually get a grant for this now? DMacks (talk) 03:44, 7 March 2009 (UTC)
Again, this is a lot messier than what I was hoping to hear. The hope would be to NOT generate any CO2 and just get at the hydrogen...but it's certainly beginning to sound like it's not possible. Oh well - it was worth a try! SteveBaker (talk) 03:43, 7 March 2009 (UTC)
SteveBaker - from [6], "Carbon, by far the major component of coal, is the principal source of heat, generating about 14,500 British thermal units (Btu) per pound. The typical carbon content for coal (dry basis) ranges from more than 60 percent for lignite to more than 80 percent for anthracite. Although hydrogen generates about 62,000 Btu per pound, it accounts for only 5 percent or less of coal and not all of this is available for heat because part of the hydrogen combines with oxygen to form water vapor."
Franamax - setting coal on fire underground is a very very bad idea; look up the fate of Centralia, PA. Gasification is a sharply different process. arimareiji (talk) 03:51, 7 March 2009 (UTC)