Wikipedia:Reference desk/Archives/Science/2009 November 23

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November 23

Is there a dry lips gene?

If I don't use something like chap stick regularly, my lips quickly begin to look like this http://farm4.static.flickr.com/3506/3965747798_661a9087f7.jpg My daughter is just the same. So is there a gene positively identified for lip dryness? 71.161.45.144 (talk) 00:06, 23 November 2009 (UTC)

It strikes me as improbable that there would be a specific gene that encoded something as specific as this. However, there are probably genes that control the amount of saliva in your mouth and the amount of oil on your skin (which would seem to conflict when it comes to keeping your lips clear). On the other hand, what you eat and how your care for your body are probably just as likely to play a part and that would be culturally determined, rather than genetically. Just out of curiosity - are you a female? In my experience, women seem to have a rougher time with their lips, if you'll pardon the pun. Matt Deres (talk) 04:03, 23 November 2009 (UTC)

Different IP, same OP. Actually, I'm male. You're probably right about there not being a specific gene, although I remember back in high school when we were learning about genes we did a test to see who had the gene that made phenylthiocarbamide (PTC) taste bitter. That's a strange thing that is specifically encoded( the variation in the shape of the taste bud, that is ). 20.137.18.50 (talk) 12:38, 23 November 2009 (UTC)

It's only strange to someone who thinks of biology in a very general sense -- someone who appreciates the finer points of biology recognizes that genetic chapped lip susceptibility is an odd thing, while the presence or absence of certain enzymes or receptors is sort of exactly what biologic variability is all about. I mean, you live in the same region as your daughter -- so you are probably exposed to the same elements: excessive cold + wind, etc. You and your daughter may share a similar skin condition (not in the scientific sense, but in the general sense) such that it is a wider, skin sensitivity to, let's say, excessive cold + wind. If you two don't wear gloves, do you both develop red + tender knuckles? DRosenbach ^{(Talk | Contribs)} 13:05, 23 November 2009 (UTC)

I see how it could be our position on the spectrum of sensitivity as opposed to an on/off gene. I wouldn't assume yet that it's a cold sensitivity since she's 3 and stays inside mostly now and still gets it. Maybe I'll dig the humidifier out of the attic and test the theory that our moisture sensitivity lies outside that of our environment. 20.137.18.50 (talk) 13:30, 23 November 2009 (UTC)

The following is OR but I'm convinced that it is true: lip-lube is literally addictive. If you regularly use it when you don't need it, the natural moisture of your lips decreases, with the results that you see. I personally never use it unless I can actually feel my lips start to get crunchy. Looie496 (talk) 16:26, 23 November 2009 (UTC)

I was going to crack a joke about that comment, but as it stands, I think you're probably right and it's part of the same sort of regulatory feedback that affects our hair (see question on shampooing) and skin. Lip balm is just the tip of it (heh) - the skin cream industry is absolutely immense; I wonder what all those millions of Jergens users would have done a thousand years ago? Cracked and crumpled into dust like that dude in Indiana Jones and the Last Crusade? The more I learn about biology, the more convinced I am that our bodies are smarter than our brains. :-/ Matt Deres (talk) 17:25, 23 November 2009 (UTC)

Although in my experience, using lip balm/chapstick can be part of breaking the pattern that often leads to dry lips. If I lick my lips a lot (particularly when going outside in the cold and wind), that can lead to dry and cracked lips: I assume because I'm licking the oils off. Applying an oily layer every time I feel the need to lick gets me past the stage when my lips are dry and sore (so I don't feel like I need to lick them to sooth them). Once they're comfortable, I can start cutting back on the balm while continuing to not lick my lips. I very rarely use it any more, and I think the regulation must have sorted itself out. 86.140.144.63 (talk) 19:38, 23 November 2009 (UTC)

acidity of dimedone, barbituric acid and acetylacetone

Is aromaticity actually a major reason for why barbituric acid is so acidic (pka around 4)? Because at first I thought it was rather acidic for a dicarbonyl (acetylacetone has pka of around 9) but it appears dimedone has a pka of 5.23 ... which is really surprising. Maybe the "aliphatic ring" factor of cyclic diketones has much more to do with it (the fact that the bonds cannot rotate and thus the carbonyls are more likely to be in the same plane?). In general, does aligning two sp2 centers (initially disconnected) on the same plane actually provide much of the impetus for those "exceptional" C-H bond dynamics more than aromatic stabilisation does? Is it the fact that the ring is heterocylic that explains why the pKa difference bewteen dimedone and barbituric acid is only 1.22? John Riemann Soong (talk) 01:59, 23 November 2009 (UTC)

The article for Baribituric Acid you link above actually explains the acidity of the acid. If you have reason to doubt that explanation, then a source which refutes it directly may be helpful. --Jayron32 04:05, 23 November 2009 (UTC)

I actually just wrote the explanation for that article .... however, I said it was both aromaticity and the dicarbonyl effect without saying what was the relative contribution of both. That's because I'm unsure what is the more significant factor. John Riemann Soong (talk) 04:32, 23 November 2009 (UTC)

Well, what you would need is a non-aromatic but similar structured compound, and/or a one without the dicarbonyl, but otherwise similar. Then you could get a very rough estimate as to the contribution of each part; but it is pretty impossible to completely isolate each effect. The two effects likely work together in a way to reinforce each other such that each in isolation would not sum up to the total effect. --Jayron32 04:35, 23 November 2009 (UTC)

Actually what I note is that dimedone is already fairly acidic, even though its conjugate base is not aromatic! Is it because aliphatic rings already have some aromatic character? Do the two methyl groups cause steric hindrance that makes the ring more planar and less chairlike? The surprising thing is that the two effects don't seem to be synergistic. The aromatic stabilisation appears to only give a pKa drop of around 1.23. Why is this so? Is it antagonistic cross-conjugation effects? John Riemann Soong (talk) 04:41, 23 November 2009 (UTC)

Interesting -- actually the loss of the proton could arguably give rise to antiaromatic system ... do I have the right acidic proton? :S (It's not one of the amide protons?) What would be "nature's way" of remedying this -- simply have one of the carbonyl pi electrons not participate in the system? Perhaps the threat of antiaromaticity might actually stabilise an enamine bond (on top of an enol one)? John Riemann Soong (talk) 04:45, 23 November 2009 (UTC)

Careful with the "aromatic" diagram...the negative charge is on the oxygen atoms outside the ring, not in the ring itself. Acually each oxygen is –1 and the ring itself is +2: enolate makes O^– and (neutral) alkene in ring and each amide in its resonance form makes each of those O^– and N⁺ and neutral enamine gives 3 π in ring. That's 6 e^–...what what enamine (leading to antiaromaticity) are you seeing? Regarding which H is lost, phthalimide has pKa=8.30 (measured in water), which is the most acidic simple imide I can find and more acidic than almost any doubly-enolizeable αH I see. Except acetylacetone with pKa=9 (measured in water). Not sure what conclusions to make, except that WP:V forbids you from making your own analysis of the situation in the article. DMacks (talk) 05:18, 23 November 2009 (UTC)

The interesting thing is that the enolate / carbanion / enamine / amide forms are in resonance, but some resonance structures are possibly antiaromatic, while some are aromatic. IIRC the electron density is concentrated in both the centre of the ring and on the carbonyls (I put dashed lines..., i.e. O is only d-) I might upload a Hartree-Fock calculation at some point. When are carbonyl electrons part of a ring, and when aren't they? The sp2 carbon pi orbital in a carbonyl is usable by an aromatic system, but the pi electrons of that carbonyl don't actually participate? John Riemann Soong (talk) 05:49, 23 November 2009 (UTC)

I'm sorry, I have no idea what you are talking about with the "carbonyl electronic part of a ring", etc. If you do normal resonance of carbonyl, the electrons move out to the O, not in to the C. If the C but not the O is in the ring, the normal resonance makes the electrons not part of the ring. I can't think of any reasonable resonance except the "α carbanion" form that has negative on the ring itself, and there are several resonances that put N⁺ on the ring itself. But more importantly, if you are considering aromaticity, the only way you get a 4n+2 electron count is by having a net +2 on the 6 ring atoms and –1 on each oxygen. All six atoms are not the same in a charge-distribution sense, but the diagram is "net for the whole ring". The logical extension of your idea as you are explaining it is that α deprotonation at C5 of 2,4-cyclohexadienone would be "δ^– on O but mostly –1 on the ring". But I don't think anyone considers that a reasonably good approximation of phenoxide. DMacks (talk) 06:22, 23 November 2009 (UTC)

How does dietary fiber affect absorption of nutrients/pharmacueticals

I was curious of the mechanism of why fiber negatively affects the absorption of some (but not other) nutrients and medications. --68.103.143.23 (talk) 02:47, 23 November 2009 (UTC)

I know that it can speed up the digestive cycle. I'm afraid I don't know more. 66.65.141.221 (talk) 19:23, 24 November 2009 (UTC)

North Africa from the sky

We've been looking at aerial pictures of North Africa and have noticed that, while Egypt and Tunisia are nearly entirely sand-coloured and white, its immediate neighbours, especially Libya but also North Niger, Chad and parts of Algeria, are a magnificent array of colours, including silver and a varied pallete of blues and browns. Can anyone explain what accounts for the difference?

All the best

--77.211.105.58 (talk) 14:16, 23 November 2009 (UTC)

That may depend on your source of aerial imagery. In NASA's famous 'Blue Marble' satellite image series, very nearly all of North Africa is uniformly covered by the Sahara desert, as seen in this image. On the other hand, if you look at the 'satellite' view (actually a combination of satellite and aerial images) in Google Maps, you'll see significant changes in the appearance of the Earth as you move westward from Egypt, through Libya, into Tunisia. Obviously the sands of the Sahara desert don't abruptly change colour at the Egyptian border. Instead, what has happened is Google has licensed aerial and satellite imagery from a number of different sources; the Libyan were collected and manipulated differently than the Egyptian data. It's a matter of choosing different settings for contrast and colour correction. In the Google Maps images, I'd say that the Egyptian colour choices are probably more 'realistic', but the Libyan data set has more contrast and reveals more detail. It's a matter of aesthetic preference, and also of what further use to which you'd like to put the images. TenOfAllTrades(talk) 14:51, 23 November 2009 (UTC)

• That's a fantastic response - thanks a lot, it really helps. --77.211.228.139 (talk) 15:52, 23 November 2009 (UTC)

It's actually really hard to get photos of large areas of the world that have comparable coloration. The trouble being that some photos come from satellites with one kind of sensor - others with another - yet others from aircraft flying at different altitudes. All of that results in different amounts of shifting of the color depending on how much air is in the way. Then, it also depends on the sensitivity of the film or digital sensor, the duration of exposure. Also, on what time of day and what time of year the photo was taken - and whether it was cloudy or clear. In remote parts of the world, the amount of time since the last rainfall makes a huge difference. So all in all, it would be pretty remarkable if these photos ever matched up! That said, many photographic sources will attempt to correct for all of these vagiaries - with varying degrees of success! SteveBaker (talk) 00:15, 24 November 2009 (UTC)

Matter

Is water the only substance found in all three forms: liquid, gas and solid? —Preceding unsigned comment added by Divyam21 (talk • contribs) 16:11, 23 November 2009 (UTC)

No. Pretty much any element or compound can be found in all three forms. Few other than water can be found in all three forms at everyday temperatures and pressures, though. Room temperature is very close to the triple point of water (which is about 0°C), so we see all 3 quite often. --Tango (talk) 16:37, 23 November 2009 (UTC)

Tango makes several correct statements but incorrectly joins two of them with "so". In a zero-pressure environment, no matter how close the temperature was to the triple-point temperature, you would never see liquid water. --Anonymous, 22:15 UTC, November 23, 2009.

Tango surely did not mean we often see all 3 forms at the same time so his comment is valid. Most of us are seldom if ever in a zero-pressure environment so how is that relevant? Cuddlyable3 (talk) 19:01, 25 November 2009 (UTC)

You have missed my point. If we say "A, so B" it means that if A is true, we can always conclude, from that alone, that B is true. In this case A and B are both true but only because there is an additional reason involved, namely that "most of us are seldom in a zero-pressure environment". The word "so" was wrong, and that was all I was saying. --Anonymous, 19:52 UTC, November 25, 2009.

Absolutely not. However, water is one of few materials commonly found in all three states naturally on Earth's surface. — Lomn 16:35, 23 November 2009 (UTC)

Question answered, but to add some fun. The phrase "all three forms" is vague, or incorrect really. There are a lot of forms of matter. Chris M. (talk) 19:19, 23 November 2009 (UTC)

Perhaps the OP meant to ask if water is the only substance found in all three forms naturally on Earth. A Quest For Knowledge (talk) 23:52, 23 November 2009 (UTC)

I"m sure they did, but there are at least four forms found naturally on Earth. Plasma is very common on Earth]. :) Chris M. (talk) 12:32, 24 November 2009 (UTC)

Sulphur can be found in all three states "naturally" on Earth's surface - although it takes a volcano to turn it into a gas. Of course it takes some pretty hot hot-springs to get water into it's gaseous form - steam isn't usually present in most parts of the world! Sulphur melts at 115 degC and boils at 444 degC. Lava is around 700 to 1400 degC and sulphur is commonly found in volcanic regions. Of course it's possible that it may burn before it boils depending on the conditions. Iodine and bromine are other good candidates - but they aren't exactly commonly found just lying around on the earth's surface. Bromine melts at -7 degC and boils at only 58 degC - so it has an even "better" temperature range than water if you're interested in seeing solid, liquid and gas at close to room temperature. SteveBaker (talk) 00:06, 24 November 2009 (UTC)

Also note the subtle distinction between gaseous water vapor and water mist, which is liquid water that has condensed by nucleation. Though it can waft and convect, it is properly liquid water that is being buoyantly lifted. Water mist and true gaseous water vapor can coexist in equilibrium, so the distinction is subtle. Nimur (talk) 01:47, 24 November 2009 (UTC)

which is the acidic amide in uric acid?

Google is being obnoxious. I suspect (from a hint I got somewhere) it's not the amide proton between the two carbonyls. Why not? Help! John Riemann Soong (talk) 16:20, 23 November 2009 (UTC)

Can someone also quickly do an HF-3-21 charge density calculation for me? John Riemann Soong (talk) 16:21, 23 November 2009 (UTC)

Once again, the article on Uric Acid explains this. The acid is diprotic; the more acidic hydrogen is the one on the 6-membered ring, and the second hydrogen is on the 5-membered ring. My guess is that the most acidic proton IS the one between the two carbonyls, but if you have reason to suspect why not beyond "gut feeling" you may have sources which explain so... --Jayron32 21:41, 23 November 2009 (UTC)

Phtalimide's pKa is only 8.3 but uric acid's pka is half that so I suspect it may be a different motif. John Riemann Soong (talk) 22:14, 23 November 2009 (UTC)

Uric acid has many more oxygens and nitrogens that phthalimide, so i suspect that the inductive effect has a whole lot to do with it. The same explanation can explain why perchloric acid is a much stronger acid than chlorous acid. Remember that pKa is a logarithmic scale, so uric acid is about 15000x stronger than phthalimide, but perchloric acid (pKa = -10) is 100,000,000,000x stronger than chlorous acid (pKa = 2), for the difference of two oxygen atoms. --Jayron32 02:46, 25 November 2009 (UTC)

I looked at all the crystal structures of urate salts I could find, and the missing proton is always the one on the 6-ring not between carbonyls.

The simplest explanation I could think of for this proton being the most acidic is that the anion formed has more good resonance structures (4) than the anions from deprotonation at two of the other three sites (3). It doesn't explain why the proton on the same side but on the 5-ring is not lost as the corresponding anion also has 4 resonance structures.

I drew some structures to illustrate my point.

Ben (talk) 18:57, 25 November 2009 (UTC)

muscle metabolism

which metabolic pathway is used in contracting muscles while jogging? —Preceding unsigned comment added by 207.230.204.2 (talk) 19:16, 23 November 2009 (UTC)

See muscle contraction#Skeletal muscle contractions. Looie496 (talk) 19:53, 23 November 2009 (UTC)

How to flatten the pages of damp books?

During heavy rain today the ends of two books in my bag got wet, and now the ends of the pages are not straight but wavey. Does anyone have real knowledge and personal experience of how they can be got back into being straight again? I've just read a few pages about how to dry damp books on the internet - can anyone add anything to that? I have a woodworker's vice that could put a lot of pressure on them - but the internet pages say use a moderate weight. I'm wondering if the vice would be better. 84.13.162.136 (talk) 20:14, 23 November 2009 (UTC)

If you use the vice, ensure that the pressure is even across the book. You really want a book press. I'm not sure why I can't find an article about them on Wikipedia. The main difference between a vice and a press is that the vice just squeezes while the press squeezes with uniform pressure to ensure the binding isn't messed up. -- kainaw™ 23:00, 23 November 2009 (UTC)

Be very mindful of the type paper, ink and coating. Some coatings act like glue and if the pages are closed before drying or exposed to high pressure or heat will stick together forever. Some book stores or print shops may have proprietary techniques for book restoration but the process may cost more than a new copy. 71.100.11.112 (talk) 07:23, 24 November 2009 (UTC)

One of the books is now perfect again, with no sign of water damage. The other book, which had black and white photos on a set of glazed paper pages, has had these pages stick to adjacent pages, as I left it under a lot of weight. With hindsight the best thing to do with the glazed pages would have been to stand the book up with its pages fanned out so that they did not touch until completely dry, and then compress in my vice for a few days to flatten any remaining waveyness. 92.24.40.108 (talk) 12:01, 24 November 2009 (UTC)

Brightest stars in the sky?

I live in an area with a huge amount of light pollution. At best I can only see about one star in the sky at night. About half or more of my sky is blocked by buildings. I am near London, and looking south. Can anyone have a educated guess as to what the star is I can see? I suppose this is complicated by the possibility of a bright "star" actually being a planet. Sidenote - earlier this evening I was in a darker area, and I was surprised to see my shadow cast by the moon behind me, which was not even a full moon! I've never seen that before. 84.13.162.136 (talk) 20:27, 23 November 2009 (UTC)

Right now, Jupiter is particularly bright and generally overhead in the early evening. There are also numerous star charts available across the web that could help you narrow down the candidates. — Lomn 20:36, 23 November 2009 (UTC)

I'd second the Jupiter guess. It's visible during your evenings, and easily the brightest non-Moon thing in the sky right now. If you look closely, does it seem to have a different color? If so, that should confirm it, as would the fact that it probably appears slightly larger than your average star. I live in New York City, so Jupiter is usually the only thing in the sky I can see. As for your side note, cool! Still, it's nothing compared to 400 years ago; back then Jupiter and the Milky Way would cast shadows at night!! ~ Amory (u • t • c) 20:42, 23 November 2009 (UTC)

Sorry, but I don't buy that last bit. I've been out in some very isolated unelectrified parts of the world, and while the Milky Way is spectacular from such a vantage point, it's not going to cast shadows. The full moon has apparent magnitude of -12.6; Jupiter's maximum apparent magnitude is -2.9. Jupiter is one thousand times dimmer! The Milky Way, as a visible band, is ballpark mag 4, another 100 times dimmer than Jupiter. It's not going to cast a discernable and distinct shadow. There's also the problem of soft light. Even if it's dark enough for starlight to illuminate the ground (and I'll buy that), said starlight is effectively evenly distributed. Jupiter may well be the brightest object in the sky under some conditions, but it's less than 10 times brighter than a great many stars. What meager shadows any one would produce would be washed out by the hundreds of other sources of illumination. — Lomn 22:23, 23 November 2009 (UTC)

According to NASA ([1]), Jupiter can't cast shadows, but Venus can. According to Bortle Dark-Sky Scale, the brightest parts of the Milky Way can cast shadows under ideal conditions. While the Milky Way is pretty dim it is very big, so that light adds up (see Surface brightness for a discussion about how the light from extended objects is measured). --Tango (talk) 22:37, 23 November 2009 (UTC)

Lomn: how dark was the area you visited? Did you see the zodiacal light and gegenschein? If the zodiacal light didn't appear annoying bright and you can see clouds as more than holes in the sky, your area probably wasn't as dark as it was 400 years ago. --Bowlhover (talk) 23:23, 23 November 2009 (UTC)

I think, Lomn, you missed the 400 years ago part of my post. ~ Amory (u • t • c) 04:37, 24 November 2009 (UTC)

Thanks, although I really meant in general rather than just recently. And in the past I recall seeing a star in the sky even when its still daylight - would that be Venus? 84.13.162.136 (talk) 21:03, 23 November 2009 (UTC)

Yes, Venus [2] a fortnight ago (and quite regularly). Dbfirs 21:27, 23 November 2009 (UTC)

Jupiter is right next to the moon right now, so you should be able to identify it. If it isn't Jupiter, then it is probably Venus. --Tango (talk) 21:38, 23 November 2009 (UTC)

Right around sunrise and sunset (before, during and after), Venus is generally the brightest thing in the sky apart from sun and moon - so if you can see only one "star" - and if it's around that time of day - the odds are very high indeed that you're seeing Venus. Another surprisingly bright thing you see sometimes at around about the same time of day is the International Space Station - but it's quite distinctive because it's moving so fast. SteveBaker (talk) 23:50, 23 November 2009 (UTC)

What I meant was over a period of years rather than just the last few days or weeks. Unfortunately this has not been answered, so I'm still none the wiser. 92.24.40.108 (talk) 11:22, 24 November 2009 (UTC)

It isn't possible to answer definitively for "a period of years" because the directions of the stars change regularly over the course of a year while the directions of the planets (which means "wanderers") change less regularly (though still predictably). In your described situation and location, the only star-like objects you are likely to be seeing are the brightest star Sirius, which is visible (at night) low in the south during Autumn and Winter, or the two planets Venus and Jupiter, both of which are generally even brighter than Sirius. For many weeks past, Jupiter has been very prominent in the late evening Southern sky, and is therefore almost certainly what you've been seeing lately. In the past (and in the future) you might have seen (or may see) the sometimes-even-brighter Venus, which however is currently visible only in the East before dawn. There are many books, magazines and online sources that can help you keep track of what is visible in the sky: this one, [3], for example. 87.81.230.195 (talk) 12:18, 24 November 2009 (UTC)

To be honest I'm getting sick of hearing about Jupiter. OK, I'll take a few years off work, study for a degree in astronomy, and then I'll have the answer. 92.24.40.108 (talk) 12:52, 24 November 2009 (UTC)

To give you a reasonable answer, we'll need to know a lot more details about WHEN you saw the star, and in what direction. Different stars are visible at different times of the year. I've seen Jupiter, Saturn, Mars, Sirius, and Venus during the evening, and all of them were bright enough and isolated enough to be considered the "brightest star in the sky". --Bowlhover (talk) 16:05, 24 November 2009 (UTC)

Sirius? Jørgen (talk) 12:07, 24 November 2009 (UTC)

Perhaps I can re-phrase the question: what are the top ten brightest stars (not planets) in the sky (viewing from London and ignoring those only seen near the horizon)? Thanks. Edit: I've found List of brightest stars but this does not tell me which are visible from London. 92.24.40.108 (talk) 12:44, 24 November 2009 (UTC)

Most stars will be visible from London at some time of the year. Only those in the far south of the sky will always be below the horizon. I suggest you go to http://www.heavens-above.com, you can say your are in London, enter a time and date, and see what stars are where in the sky at that time from London. Brighter stars are shown as bigger dots and planets are shown in different colours. All interesting things are labelled. --Tango (talk) 13:09, 24 November 2009 (UTC)

Okay, the latitude of central London is about 51°30'N, so any stars between +90° and -51°30' declination will be in the sky at some time. In practice make that +90° to say -47° because stars very low in the sky are likely to be dimmed by atmospheric effects and blocked by obstacles; it doesn't matter anyway for this purpose because there aren't any very bright stars between -45°0' and -52°0' anyway. Stars between +51°30' (or in practice say +55°) and +90° will be visible all the time at night if it is clear; outside that range, the lower the declination the narrower the time window to see the star.

The following table is based on the table of brightest stars in A Field Guide to the Stars and Planets by Donald H. Menzel (my copy is dated 1964). I have used the forms of the names that Wikipedia does. The table shows the 16 stars that can be brighter than magnitude 1.0; Betelgeuse is slightly variable, so it comes and goes from that list. (I have shown its ranking as the book does, which I presume is based on some average brightness.) Of the 16 stars, 11 are in the range of declinations visible from London at least sometimes, and I have numbered these at left, and shown the declination and magnitude for each star.

   1. Sirius           -16°39' decl. -1.42 mag.
      Canopus          -52°40'       -0.72
      Alpha Centauri   -60°38'       -0.27
   2. Arcturus         +19°27'       -0.06
   3. Vega             +38°44'        0.04
   4. Capella          +45°57'        0.05
   5. Rigel             -8°15'        0.14
   6. Procyon           +5°21'        0.38
      Achernar         -57°29'        0.51
      Beta Centauri    -60° 8'        0.63
   7. Altair            +8°44'        0.77
   8. Betelgeuse        +7°24'      variable, 0.4 to 1.3
   9. Aldebaran        +16°25'        0.86
      Alpha Crucis     -62°49'        0.9
  10. Spica            -10°54'        0.91
  11. Antares          -26°19'        0.92

--Anonymous, 23:10 UTC, November 24, 2009.

Thank you Anonymous for your hard work. 78.146.176.198 (talk) 23:21, 25 November 2009 (UTC)

It wasn't hard, but you're welcome. --Anon, 04:34, Nov. 26, 2009.

Terrestrial Leeches - Are they harmful to pets?

I never knew about terrestrial leeches before this week but there seem to be quite a few of them in the yard of the house I just moved into!

They're ugly little things, mottled grey in color and shaped like fat, deformed slug-like crescents less than an inch long.

I haven't been able to identify the species yet. My online searches have not been very productive and I am concerned that they might be harmful to pets.

Are these leeches dangerous to cats or dogs?

Is there a resource that can help me to determine the species? We are located close to the shoreline of San Francisco Bay, if that helps to narrow the focus.

Thanks! —Preceding unsigned comment added by 24.6.75.255 (talk) 21:22, 23 November 2009 (UTC)

The Wikipedia article on Leeches seems to indicate that "land leeches" do not burrow into the skin; and that removal should be easy. this book is listed as the source. IANWEWKATS (i am not whatever expert which knows about this stuff), but that book may be a starting point to look. --Jayron32 21:37, 23 November 2009 (UTC)

Leeches are not good for cats or dogs, just as they are not good for you either. Does your pet have too much blood? You can remove them by sprinkling with salt, or some other irritating substance. If you just try to pull them off it can be very hard, and the wound bleeds for ages. Graeme Bartlett (talk) 11:16, 24 November 2009 (UTC)

Appearance of the moon 2 million years ago

KageTora says that he's been reliably informed that at the dawn of humanity, the Moon was so much closer to Earth that it appeared twice as large in the night sky. Is there any truth in this? Neither of us have found anything great on the Internet. We know the moon is moving away at 3.8 cm per year - suggesting it was in the same place as Earth less than ten million years ago (I'm...unsure if my maths is right there). Obviously, the speed of that movement must have changed somewhen, somehow...so simply working out the distance some given time ago with just that number didn't work. Anyone know what we've missed? Vimescarrot (talk)

This site appears to summarize the issue nicely. Also, your back of the envelope calculations appear to have missed the km-to-cm conversion. 380000 km divided by 3.8 cm/yr is 10¹¹ years, not 10⁷. Addressing "double the size": At the dawn of humanity, certainly not. Doubling the size means increasing the apparent radius by 1.4 (the square root of 2). That means moving the moon in by 30% (based on the reciprocal of 1.4). 30% of the 10¹¹ years from the back of the envelope calculation above is still 30 billion years, double the age of the universe. However, at the time of the moon's formation (assuming the giant impact hypothesis), there's a good chance that, briefly, the moon was double the apparent size it is today. Not that anything would have been around on the thoroughly molten surface of Earth to appreciate it. — Lomn 22:10, 23 November 2009 (UTC)

Actually, 380000 km divided by 3.8 cm/yr is 10^10 years. Moving the Moon by 30%, then, would require 3 billion years, not 30 billion. --Bowlhover (talk) 23:16, 23 November 2009 (UTC)

Given that the interaction that transfers angular momentum to the moon is gravity, and that gravity is an inverse-square force, it's clear that the forces involved have been much larger in the past, and hence that the process must have slowed down over time. --Stephan Schulz (talk) 22:31, 23 November 2009 (UTC)

The process that transfers angular momentum is actually tidal friction, which actually follows an inverse cube law. Also, the arrangements of the continents alters the movement of ocean tides, which in turn affects the rate of tidal acceleration. Probably neither of these factors are significant over a 2 million year period, however. --Bowlhover (talk) 23:16, 23 November 2009 (UTC)

A note as to the title of this thread: the moon formed at 4.5-4.6 billion years ago, about the same time as the Earth.

Switching tacks, the arrangement of the continents, and in particular, the continental shelves, is actually very important as to the recession rate of the moon. The more shallow areas there are that are covered by water, the more friction will result from the tides. So while supercontinents exist, there is much less coastline. In the early Precambrian, higher heat flow resulted in shallower oceans. Awickert (talk) 23:37, 25 November 2009 (UTC)

Edman degradation help!

I'm stuck because I can't find any further overlaps and I don't know what the "trick" is.

trypsin digestion

Ser-Glu-Phe-Ala-Gly-Leu-Ile-Lys ==
Gln-Ala-Gly-Phe-Pro-Tyr-Ser-Gln-Ile-Ala-Gly-Thr-Lys ++ 
Gln-Glu-Phe-Val-Tyr-Arg OO 
Glu-Asp-Phe-Leu-Ala-Asn-Ala-Gly-Pro-Phe-Arg ==

***
chymotrypsin digestion

Ser-Gln-Ile-Ala-Gly-Thr-Lys-Leu-Ile-Ala  ++ 
Ala-Gly-Leu-Ile-Lys-Glu-Asp-Phe ==
Gly-Lys-Gln-Glu-Phe OO 
Leu-Ala-Asn-Ala-Gly-Pro-Phe  == (internal) 
Arg-Gln-Ala-Gly-Phe ++ 
Arg-Glu-Val-Tyr

(Symbols are where I've found matches).

The amino acid is 46 aa long -- that's my other problem; even without overlapping and randomly joining my sequences together I can only get 45 aa.

I've managed to join them some of them up to yield these fragments:

• Ser-Glu-Phe-Ala-Gly-Leu-Ile-Lys-Glu-Asp-Phe-Leu-Ala-Asn-Ala-Gly-Pro-Phe-Arg (19 aa)
• Arg-Gln-Ala-Gly-Phe-Pro-Tyr-Ser-Gln-Ile-Ala-Gly-Thr-Lys-Leu-Ile-Ala (17 aa)
• gly-lys-gln-glu-phe-val-tyr-arg (8 aa)
• Arg-Glu-Val-Tyr (4 aa)

Quite stuck though. John Riemann Soong (talk) 22:21, 23 November 2009 (UTC)

Since you're really stuck, then I'll try to get you un-stuck without doing the whole problem. I find it easier to use single-letter codes. I will refer to your tryptic peptides as T1, T2, T3, T4, and your chymotryptic peptides as C1, C2, ...C6. We know that each of the Tn peptides must be preceded by K or R, unless it begins with P or is the N-terminus; similarly, the Cn peptides must be preceded by W, Y, F, L, or M (but your peptides contain no W or M, so it's really down to Y or F not sure why L is not a cleavage site, but it's been awhile since I "used" chymotrypsin). Your peptides become:

(KR)SEFAGLIK

(KR)QAGFPYSQIAGTK

(KR)QEFVYR

(KR)EDFLAQAGPFR

and

(YF)SQIAGTKLIA

(YF)AGLIKEDF

(YF)GKQEF

(YF)LAQAGPF

(YF)RQAGF

(YF)REVY

I hope you can see the utility of this more compact depiction, with the parenthetical indication of the potential preceding residue. Thus, your intermediate solution would look like this:

(KR) SEFAGLIKEDFLAQAGPFR (T1+T4)

(YF) RQAGFPYSQIAGTKLIA (C5+PY+C1, i.e. C5 plus C1 linked by "PY" from T2)

The C1 fragment must be the C terminus, because it ends in A which is not a chymotrypsin cleavage site. This, plus the fact that the T1+T4 fragment ends in a R preceded by F, indicating that there will only be a one-residue overlap there, suggests:

(KR) SEFAGLIKEDFLANAGPFRQAGFPYSQIAGTKxxx (T1+T4+T2)

(YF)    AGLIKEDFLANAGPFRQAGFPYSQIAGTKLIA (C2+C4+C5+PY+C1)

That's 35aa, with "x" indicating a residue missing because a small fragment was lost after cleavage. So, now you have something 35 aa long, which is 11 shy of your goal, and you know you have to build the N terminus. Your building blocks are T3, C3, and C6; neither C3 nor C6 ends in "SEF", so you may need to assume that was lost as well. That should give you enough to finish. -- Scray (talk) 02:36, 24 November 2009 (UTC)

acetic anhydride isn't symmetrical?

It's really surprising to me -- but one C-O bond length in acetic anhydride is significantly longer than the other C-O bond, when I bring up acetic anhydride with some ab initio calculations. The charge on the carbonyl oxygens aren't even the same. Is it my program, or does this reflect real life? John Riemann Soong (talk) 23:13, 23 November 2009 (UTC)

What aspect of "real life", how good a set of calculations did you do, and what was your initial geometry for the optimization? DOI:10.1021/jp993131z, which scanned a range of geometries and compared with gas-phase structural data, says there are several low-energy conformers, some of which are not fully planar. I don't have a ref for crystallographic/diffraction structure of the solid. DMacks (talk) 04:08, 24 November 2009 (UTC)

Well I initially minimised it with a molecular force field optimiser, which gave me an aplanar structure for some reason (for sterics?) I used HF-3-21G, but I didn't think it'd be that far off. John Riemann Soong (talk) 08:28, 24 November 2009 (UTC)

Again, "minimization" is sensitive to starting geometry...tends to get stuck in local minima near the start rather than making larger changes to get to the global, and the cite I gave notes that there are several local minima with close energy. For example, if you start with the O=C-O-C=O in a "U" shape, you may not ever twist all the way to an elongated conformation, even though that might be better for avoiding O...O dipole-dipole repulsion. And aplanar is not the same as asymmetric (with respect to bond character, charge distribution, etc.) Could have a propeller shape, for example, where one lone pair on the central O is aligned with one carbonyl pi and the other lone pair with the other rather than one O lone pair aligned with both in a fully planar arrangement. DMacks (talk) 17:32, 24 November 2009 (UTC)

I skimmed the article, and there are a whole host of electronic and steric effects here. The energy minima are non-planar, and some calculations give different C-O and/or different C=O lengths. DMacks (talk) 21:58, 24 November 2009 (UTC)