Wikipedia:Reference desk/Archives/Science/2011 August 17

= August 17 =

Ampicillin rash
i want to know the mecanism of the interraction between cytomegalovirus/Ebsein-Barr virus and ampicilling leading to the non allergic rash. thank you. — Preceding unsigned comment added by Pharmaone (talk • contribs) 04:39, 17 August 2011 (UTC)


 * I'm afraid I don't see any information on such interactions at Epstein-Barr virus, or Cytomegalovirus, or HCMV (human cytomegalovirus), or Ampicillin. If this is a personal concern to you, you should see a doctor.  -- Jayron  32  04:50, 17 August 2011 (UTC)


 * I agree with the OP - I want to know the mechanism of this rash, which occurs in almost all children who have acute EBV infection (typically mono) and are given ampicillin (see ). This is a fascinating phenomenon that I have observed (but not caused) many times.  A quick literature search on this topic (which I have done before) was not satisfying - still just vague or weak answers relying on sound reasoning but unproven mechanistically: EBV infection stimulates B cell proliferation, leading to antibodies (especially IgM) directed against the ampicillin, resulting in immune complexes that deposit in the skin and cause a local inflammatory reaction.  Among the reasons this is unsatisfying is that it does not explain why this reaction is so specific to ampicillin.  BTW, it is in no way a request for advice (because an answer requires no knowledge of the person asking, no diagnostic reasoning). -- Scray (talk) 13:03, 17 August 2011 (UTC)


 * The literature is still unsatisfying, so the question is unlikely to be answered satisfactorily here. To reiterate/amplify Scray, the mechanisms are proposed rather than actually empirically studied: as of 2000: "The mechanism by which drugs trigger the development of rashes in patients with CMV mononucleosis is unknown. It is assumed that CMV is likely to be a potential amplifier of drug rashes induced by activation of drug-specific T cells."  - Nunh-huh 17:33, 17 August 2011 (UTC)


 * With reference to that last bit, this paper on drug-specific T cells is interesting: -- Scray (talk) 20:26, 17 August 2011 (UTC)


 * The PMC paper above waits until just the end to deliver the bombshell: "purification of the ampicillin with regard to protein impurities significantly reduces the incidence of the rash in treated patients". They cite quite old papers by two groups that don't sound very certain, though.  Still, it's a pretty straightforward idea - some impurity present in ampicillin, as produced industrially, interacts with the immune system as modified by viral infection.  I'm thinking, for example, it could be a bit of bacterial wall shrapnel that sets off a Toll like receptor.


 * Unfortunately, there is no mention of any attempt to determine whether having the rash improves or worsens the patient's recovery from mononucleosis or other EBV infection, which I'd think it well might. For two decades now I've been waiting for people to get a personalized readout of the body's "internal diagnosis" (in the form of levels of all known cytokines) and to be treated by adjusting this response with bits of cytokine, ligand, or even antibody meant to finesse the pattern of reaction toward that known to be most effective for the medically diagnosed infection.  This would be a very, very crude form of that. Wnt (talk) 04:12, 18 August 2011 (UTC)

Colony of ants solves Travelling Salesman math problem?
I’m thinking of how ants find the shortest, easiest path from nest to food source and use it. What if you separated an ant’s nest and their only food source with a complicated 2 dimensional glass maze. You know, one with millions of possible paths, and all the “easy” options turn out to be duds. Would the ants as they proceed thru the maze on a daily basis, making millions of ant-trips over millions of ant-hours and miles, finally settle on the route that was the shortest, by sheer statistical enumeration? Because if they could, then you could use them to solve many intractable problems in maths like the “travelling salesmen” problem.

The idea is to use ants like an analog computer version of a supercomputer. Each ant’s journey, provided it did more than just follow the leader, must add some data to the ants’ knowledge of the best way there. Has such an experiment ever been done? Coz it should be. You would be using nature as a ready-built computer to solve your probs for you.Myles325a (talk) 06:05, 17 August 2011 (UTC)


 * Yep. This idea is used in ant colony optimization algorithms. —Bkell (talk) 06:15, 17 August 2011 (UTC)
 * By the way, if all you're interested in is finding the shortest distance between two points through a complicated maze, we already have efficient algorithms for that (such as Dijkstra's algorithm). The traveling salesman problem is a bit different from that—the problem is to determine the sequence in which a bunch of given points should be visited in order to minimize the total distance traveled. That is a more difficult problem (or at least, it seems to be, though no one has actually proved that it is fundamentally more difficult; see P versus NP problem). —Bkell (talk) 06:26, 17 August 2011 (UTC)
 * Nitpick: Your sentence is ambiguous with respect to "in order" - if that is read to refer to the points, the problem is trivial. I assume you mean it to read "with the goal of" or words to that effect. --Stephan Schulz (talk) 06:29, 17 August 2011 (UTC)
 * Oh, yes, you're right. Thanks for pointing that out—I did mean "with the goal of minimizing the total distance traveled." —Bkell (talk) 06:32, 17 August 2011 (UTC)
 * (ec)Finding the shortest path through a maze is not equivalent to the travelling salesman problem. Travelling Salesman requires a closed tour that visits all nodes, and is the canonical NP-complete problem. The shortest path problem is squarely in P, as demonstrated constructively by Dijkstra's algorithm and later refinements. That's not to say that ants can't be a good model for solving certain problems. --Stephan Schulz (talk) 06:27, 17 August 2011 (UTC)


 * Natural solutions to optimization problems tend to be some variant of randomized hill climbing, and ant trail optimization is an example of that. Hill climbing by itself isn't guaranteed to find the optimum solution, just a "local optimum" (the top of your hill may not be the highest point in the world). Randomized hill climbing will eventually find the optimum (if you keep trying hills, eventually you'll find the highest one), but it won't necessarily find it quickly, and you won't necessarily ever know that it is the optimum and you can safely stop looking. A brute force search of all possible routes will also solve the traveling salesman problem (there are only finitely many city orders), and you will know that you've found the optimum route when it completes. That's not to say that hill climbing algorithms aren't useful—they are very useful—but merely finding a pretty good route in a middling amount of time, with no proof that the route is optimal, is not the same as solving the TSP in theoretical computer science. -- BenRG (talk) 07:25, 17 August 2011 (UTC)


 * Worth pointing out that solving a travelling salesman problem is not in itself intractable - it can easily be solved in principle by a brute force search. What is hard (not possible, as far as we know, but not proved to be impossible either) is finding an algorithm that can solve any travelling salesman problem with time/effort/resources that are bounded by a polynomial function of the number of cities, rather than growing exponentially with the number of cities. Using an army of a million ants is just like using a million parallel processors - it just reduces solution time by a constant factor of a million. As the number of cities grows, there is a short-term benefit from using a million processors, but this improvement is quickly swamped if the only available algorithms need resources that grow exponentially with the number of cities. Gandalf61 (talk) 08:05, 17 August 2011 (UTC)
 * Intractable in computer science does not mean "impossible", it means "algorithmically hard", usually in the sense that the best algorithms take exponential time. --Stephan Schulz (talk) 11:37, 17 August 2011 (UTC)


 * You might be interested in Physarum polycephalum. 130.88.73.71 (talk) 13:53, 17 August 2011 (UTC)

OP myles325a back live. Thanks to all for answers of a high quality, and far beyond what I was expecting. I had somehow thought that the ant idea was my own, an idle speculation, but it turns out to be a going concern. The Physarum polycephalum article was a real eye-opener - thanks to No 130.88.73.71. Myles325a (talk) 03:45, 18 August 2011 (UTC)

Multiple birth rates over time and in different countries
Can anyone point me to a source that describe changes in the multiple birth rate over time, and in different countries? For example, I'd like to compare the multiple birth rate in China today vs. 100 years ago, and in the US today vs. 100 years ago, and in China today vs. the US today. Our article seems to lack such data. Thanks! Comet Tuttle (talk) 07:18, 17 August 2011 (UTC)


 * Question: Do you mean to include or exclude the effects of fertility drugs ? I ask because these make an absolutely huge difference in the rate of high-multiple births. StuRat (talk) 08:13, 17 August 2011 (UTC)


 * Include, which I hope also makes it easier to find such data. Comet Tuttle (talk) 08:29, 17 August 2011 (UTC)

Quiz
1. Explain the following observations; a)Ammonia forms a white precipitate wiht aqueous manganese(ii) ions, but in the presence of ammonium chloride no precipitate is formed. b)When sodium hydroxide solution is added dropwise until in excess to potassium chromium(iii)sulphate solution, a green precipitate is formed thatdissolves to form a deep green solution. On addition of hydrogen peroxide, the solution turns green to yellowish brown. c)The polarising power of group(ii)elements are much higher thanthose of the group (i)elements — Preceding unsigned comment added by Doctor calvin emma (talk • contribs) 09:11, 17 August 2011 (UTC)


 * No. It is academically dishonest for you to submit our answers for your grade. DMacks (talk) 09:13, 17 August 2011 (UTC)

Lunar eclipse
What is the longest time possible of totality in a total lunar eclipse? 125.235.107.41 (talk) 11:41, 17 August 2011 (UTC)


 * says that the generally quoted figure is 7 minutes 31 seconds (and that the figure varies with time), this value is also given in the 2000 Guinness World Records. claims 7 minutes 40 seconds. An eclipse of 7 minutes 29 seconds is due in 2186. Hut 8.5 13:23, 17 August 2011 (UTC)


 * Those are all values for solar eclipses, not lunar. I imagine that precisely defining "totality" in a lunar eclipse is tricky because (unlike in a solar eclipse) the sun's rays are passing through and being diffracted by the Earth's atmosphere, which is why even at maximum eclipse the moon remains visible.  A NatGeo article from June's eclipse notes that that eclipse's "almost two hours" is near maximum, so "two hours" seems about right, allowing for the combination of Earth-Sun aphelion, Earth-Moon perigee, and Earth-Moon-Sun alignment maximums. &mdash; Lomn 13:30, 17 August 2011 (UTC)


 * The orbital radius of the moon is about 60 Earth radii, so the Earth's shadow at its maximum width is about 1/30 radians of the moon's orbit. But we have to subtract 1 moon diameter (0.273 of an Earth diameter) since we're only counting total eclipse.  So the maximum length of a total eclipse should be (1/30)*(1-0.273) radians = 0.02423 radians.  We also need to account for the angle at which the suns rays reach around the Earth due to the sun's diameter.  The radius of the sun is 0.00464 times the distance to the Earth, so the blur is 0.00464 radians in from either side so we're left with about 0.0150 radians where the moon is fully in the dark.  The synodic period of the moon is about 29.5 days.  29.5 days*(1/2π)*0.0150 ≈ 1.7 hours.Rckrone (talk) 15:45, 17 August 2011 (UTC)
 * Actually, looking at the Lunar eclipse article it answers the question directly. Apparently the longest total eclipse possible is about 107 minutes.  So I undershot a little bit (1.7 hours ≈ 102 minutes).  This may be because I assumed all the orbits are circular, but when the moon is at its apogee its angular speed will be a bit slower which could allow for a longer eclipse.  Also when the Earth is a its apogee, its umbra will be slightly larger. Rckrone (talk) 17:36, 17 August 2011 (UTC)
 * I know you didn't perform any math miracles, but I'm still impressed.. Vespine (talk) 22:50, 17 August 2011 (UTC)

Fruit nutritional components
Hi all,

Does anyone know of components of a fruit which have proven health benefits to humans (or another animal)? I was looking at lycopene but I was hoping for a better example (the studies with lycopene aren't actually so cut and dry). Thanks!

Aaadddaaammm (talk) 16:02, 17 August 2011 (UTC)


 * Well, vitamin C, of course. Looie496 (talk) 16:38, 17 August 2011 (UTC)


 * Resveratrol is found in certain fruits, I believe, but its health effects are actually controversial. Bus stop (talk) 16:48, 17 August 2011 (UTC)


 * Thanks for the answers, but I think I've realised I want to ask a different question. I hope that's OK :P My new question is: why (from an evolutionary point of view) do fruits even contain vitamins? Thanks. Aaadddaaammm (talk) 17:01, 17 August 2011 (UTC)


 * Do you mean, why have fruits evolved containing vitamins, or why have humans evolved to require the vitamins contained in fruits? --TammyMoet (talk) 17:03, 17 August 2011 (UTC)


 * The first one. What advantage does it give the plant? Surely sugar would be enough to keep its seed dispersers happy... Aaadddaaammm (talk) 17:07, 17 August 2011 (UTC)


 * But it's also to the advantage for the plant to keep it's seed dispersers healthy. And from the point of view of a seed disperser, I'd rather eat fruit that provides more of my nutritional needs.  Seed dispersers will develop a craving for those fruits, and only fall back on the plain sugary ones when the better fruit is not available. StuRat (talk) 17:20, 17 August 2011 (UTC)


 * I infer that the OP's revised question is based on this assumption: plants make vitamins to benefit those that consume them. I would strongly consider that this assumption is incorrect.  What we call vitamins are organic substances that we - to a reasonable approximation - must consume in small amounts to survive because our own tissues do not synthesize them.  These same substances are required metabolically, often for the same/similar reasons, in other organisms.  Those organisms will need to synthesize them out of necessity, unless they can acquire them by consuming other organisms or acquiring those substances from commensal/symbiotic organisms.  No doubt some organisms make more "vitamins" than they need as a result of a complex evolutionary relationship with another organism, but I can't think of one offhand.  -- Scray (talk) 17:27, 17 August 2011 (UTC)


 * To simplify what Scray just said: Plants need vitamins for the same reasons that we need vitamins. The reason we need to eat them is because our bodies don't make them as a plant does for itself.  And it isn't just plants we get vitamins from; Vitamin B12 primarily comes into our diet from animal sources.  -- Jayron  32  20:19, 17 August 2011 (UTC)
 * I find this question very perplexing too, if I think too much about it. You might find the article on L-gulonolactone_oxidase interesting. So we used to be able to make our own vitamin C, but we lost that ability. Quite probably (if not certainly)because we had enough vitamin c in our diet from other sources, so we no longer needed to synth it. That makes enough sense to me.. What I can't quite wrap my head around is, how did we need vitamin c BEFORE we started eating it and then it just happens to be in fruit?!  I'm guessing that the answer is that vitamin C is involved in some far more basic biological process then is immediately apparent, but the fact we only LOST the ability to synth it quite recently makes it seem like it's a lot higher level then it is. Maybe.. Well that's the explanation that helps me sleep at night anyway, lol. Vespine (talk) 22:36, 17 August 2011 (UTC)
 * And all I had to do to confirm this was read the vitamin c article again and see that indeed vitamin c has a biological function in plants too, meliorating the oxidative stress of photosynthesis. In addition, it has a number of other roles in cell division and protein modification. Well that settles it then. Vespine (talk) 22:41, 17 August 2011 (UTC)
 * In general, the major vitamin cofactors are exceedingly ancient. Animals, with their long generation times, have more or less taken a time-out from biochemical evolution, evolving more the details of how cells divide labor and respond to the environment than new hard-core chemistry.  With some interesting exceptions, of course!  But I suspect that many of the loose cofactors are much, much more ancient than that.  Look at the structure of your favorite vitamin, then compare it to the nucleosides used to make up RNA.  (For example, riboflavin, molybdopterin, or in your case, compare ascorbic acid to L-ribose)  There's quite often some passing similarity, and yet ... some considerable difference.  I suspect we're seeing relics of the age before proteins, when RNA catalyzed everything, when RNA carried exotic groups to do exotic reactions.  Perhaps in some cases proteins, though replacing almost everything, just couldn't quite manage to get at the fundamental reactions handled by these specialized components. Wnt (talk) 06:27, 18 August 2011 (UTC)

lovaza
What is the benefit of taking Lovaza following cataract surgery? — Preceding unsigned comment added by 68.114.127.128 (talk) 20:35, 17 August 2011 (UTC)
 * According to our article, Lovaza, it's used to lower triglyceride levels. It's not obvious to me why that would be important following cataract surgery. What makes you think there is a benefit? --Tango (talk) 21:11, 17 August 2011 (UTC)
 * Looking briefly on NCBI, I found, which makes it sound like there's some thought that omega-3 fatty acids might help against cataract but definitely no certainty about it. Searching on the web it sounds like some people are using it off-label to try to prevent blepharitis due to claimed antiinflammatory actions of the omega-3's .  To me the evidence seems rather scanty in comparison to most herbal medicines. Wnt (talk) 06:40, 18 August 2011 (UTC)

Does Ramada[n] select against diabetics?
I can't imagine any poor diabetic Muslim in a third-world country being able to survive fasting for a month. Imagine Reason (talk) 21:59, 17 August 2011 (UTC)


 * 1. It's Ramadan. Ramada, AFAIK, is a hotel. 2. Muslims do not fast for a month. They fast during daylight hours for a month. 3. There's plenty of advice on the internet and diabetics & Ramadan - though clearly, equally, it is more challenging for a diabetic. --Tagishsimon (talk) 22:04, 17 August 2011 (UTC)


 * If you follow the Ramadan link, I think you'll find that there are exceptions for those believers with medical conditions that make fasting unwise. If I recall correctly, you are supposed to make up missed fasting days later, when your condition improves, but if it's a chronic condition that never improves, presumably you get a pass.  --Trovatore (talk) 01:53, 18 August 2011 (UTC)


 * I'm an EMT in NYC and last week I had a known diabetic patient who was hypoglycemic because he was fasting for Ramadan. When we arrived at the hospital, there was a least one other patient there for the same reason. -- MacAddct1984 (talk &#149; contribs) 02:11, 18 August 2011 (UTC)


 * I did google beforehand, and I saw nothing that suggests solutions suitable for the scenario I posed. Imagine Reason (talk) 04:14, 18 August 2011 (UTC)


 * It might be better to ask this at the Humanities refdesk - my (extremely shallow) impression is that Islam has a lot of exceptions to rules for medical reasons. Also note that it is famously a dawn to dusk fast only - to me what sounds hardest is that they also abstain from water, under Middle Eastern climate conditions I can't even imagine. Wnt (talk) 04:20, 18 August 2011 (UTC)


 * I can think of a couple ways around it:


 * 1) Presumably medicine is still allowed, so simply drink a "medical rehydration formula", which is essentially Gatorade by another name.


 * 2) Rearranging your sleep schedule so you are asleep during the fasting period would certainly help. Of course, not everyone can do this.  (I wonder if Muslims who work the midnight shift even much notice Ramadan.) StuRat (talk) 06:39, 18 August 2011 (UTC)
 * My friend was in Indonesia (specifically Kalimantan) during Ramadan some time ago. She said that basically the schedule of most of the country changes to accommodate the fast - people work a lot less, many places are closed and not much can be done or taken care of during that time. --Ouro (blah blah) 09:33, 18 August 2011 (UTC)
 * Which is prob'ly one of the reasons why those countries' economies are so screwed up... 67.169.177.176 (talk) 06:05, 20 August 2011 (UTC)


 * See our article on | fasting in Islam. The person with a medical condition is (obviously) not expected to fast. They must instead make on offering of Fidyah. This means feeding a needy person for every fast missed or making a charitable donation. This link suggests 7 euros a day in Germany, Hope that clarifies things a little. Trugster | Talk | Contributions 14:52, 18 August 2011 (UTC)


 * So what do you do if you're both sick and poor ? StuRat (talk) 17:46, 19 August 2011 (UTC)

I hate to break this to you but technically under my definition of fasting. Muslims do not fast in the month of Ramadan. I define fasting as consuming a reduced amount of energy/calory in a 24 hour period and doing so in a prolong number of days. Muslims (under my definition) do not fast, they merely not eat during daylight hours. I call this Vampire Eating habits. Only eat during the "night" time. Ohanian (talk) 23:24, 18 August 2011 (UTC)


 * So at night they drink blood? Is that what just happened in TX? μηδείς (talk) 01:46, 19 August 2011 (UTC)


 * Don't be stupid. Do night guards who work in "vampire shifts" drink blood? Of course not. 139.130.57.34 (talk) 02:10, 19 August 2011 (UTC)

Protein synthesis and Mitosis
How does transcription and protein synthesis occur during mitosis? Clover345 (talk) 22:05, 17 August 2011 (UTC)


 * Sounds like a homework question to me, kid . Sorry. You'll have to do your own work. Dominus Vobisdu (talk) 22:10, 17 August 2011 (UTC)


 * Please don't refer to people using words like "kid", it is condescending and therefore makes you look like a jerk. I don't know whether this is a homework question, but in any case I don't think a pointer to our Cell cycle article is out of place.  It gives some sketchy information, and a web search for "protein synthesis during mitosis" will find a lot more. Looie496 (talk) 02:03, 18 August 2011 (UTC)
 * Point taken. I'm sorry, Clover, and thanks, Looie. Dominus Vobisdu (talk) 08:05, 18 August 2011 (UTC)


 * Please see Mitosis. 64.134.230.200 (talk) 01:36, 19 August 2011 (UTC)