Wikipedia:Reference desk/Archives/Science/2014 May 13

= May 13 =

light dependent and light independent reactions in photosynthesis
are both light dependent and light independent reactions in photosynthesis so important and are both the reactions/phases performed in a single plant in a photosynthesis? Also, what is the importance of light independent reactions? Also,what is the difference between the two ? — Preceding unsigned comment added by Sumukhmlohit (talk • contribs) 06:05, 13 May 2014 (UTC)
 * Wikipedia has an article titled photosynthesis that covers all of your questions, and probably a lot more. -- Jayron  32  11:43, 13 May 2014 (UTC)


 * For the mathematically inclined, this classic paper gives a brief overview of the most important biochemistry, then stitches it together into a fairly simple differential equation model . There have been updates since 1980, but most of the current generation of simulation schemes (that care at all about photosynthesis) still use this Farquar model at the core. SemanticMantis (talk) 15:45, 13 May 2014 (UTC)

phoebe fledging
How long does it take for eastern phoebes to leave the nest?2601:6:6800:25C:FD70:9B92:89E:8A06 (talk) 15:14, 13 May 2014 (UTC)
 * Eastern Phoebe doesn't answer your question, but it does say that they typically have two broods per year, so that at least puts an upper bound on it. ←Baseball Bugs What's up, Doc? carrots→ 16:22, 13 May 2014 (UTC)


 * According to under the section How do they reproduce, " Though the chicks are able to fly by day 15, they usually do not fledge until day 16 or 18. Both males and females feed the young. The young are capable of breeding in their first year." Bielle (talk) 16:26, 13 May 2014 (UTC)

Building an ice-dam.
Various news reports yesterday are talking about a really seriously bad discovery about the Thwaites Glacier and how it's the lynch-pin holding back many other large chunks of ice in the antarctic:

http://www.washington.edu/news/2014/05/12/west-antarctic-ice-sheet-collapse-is-under-way/

Seems like preventing it from slipping any further would save multiple very large and expensive cities - so it would be worth considering what it would take to hold it back rather than spending the money on sea defenses and so forth.

I was wondering what scale of engineering project it would take to build an "ice dam" to hold back the glacier. Just how big an engineering effort would it take compared to things like the Three Gorges dam? The reports seem to suggest that a 700meter tall ridge was what was holding it back...can we possibly build something strong enough and of similar size to do the same job? Three Gorges is only 150 meters tall...would something that big help at all? How wide would it have to be?

SteveBaker (talk) 15:36, 13 May 2014 (UTC)
 * What would stop the ice dam from melting too? ←Baseball Bugs What's up, Doc? carrots→ 16:22, 13 May 2014 (UTC)
 * I think Steve means "a dam to hold back ice", not "a dam made of ice". Though using the extant ice might help. SemanticMantis (talk) 16:42, 13 May 2014 (UTC)
 * Yes, exactly. Contrasting a (wet) water dam with a frozen water dam...either being made of whatever materials seem appropriate.  Most of what's in a dam is weight - so you could probably make a watertight casing and fill it with ice - and you might not care if it melted...but I don't know whether liquid filled dams holding back solid ice would really work...I think you need something denser than ice to make the dam out of.  The "existing" dam is made of sea water... SteveBaker (talk) 18:47, 13 May 2014 (UTC)


 * I don't think this is something we can asses on the "back of the envelope". There's no replacement for doing the actual force loading calculations and engineering. I'm certain such a thing is theoretically possible, but I have no idea if it is practically feasible. One thought I had was to perhaps reinforce the ice, e.g. with nylon or rebar. The idea is pure concrete shatters easily, but reinforced concrete has much more strength. Also e.g. ripstop nylon has very different properties than "regular" nylon. Of course, this would still weaken as the ice melts, but it might be a cheaper way to stave off disaster for a few decades, perhaps centuies (the "fast" scenario is still ~200 years away...) Imagining that our governments are willing to think and plan and spend money on time scales of centuries it itself rather optimistic :-/ SemanticMantis (talk) 16:45, 13 May 2014 (UTC)
 * The only vaguely possible way I can think of stopping a glacier would be to drain water from the bottom of it. That would slow down the total amount of water reaching the sea. It would still be a huge undertaking. Dmcq (talk) 17:40, 13 May 2014 (UTC)
 * Yeah - I was wondering about that too. The effect of meltwater from the surface cutting channels into the ice, then getting underneath it and lubricating the interface with the rock below is one of the factors that accelerate the flow of the glacier. SteveBaker (talk) 18:47, 13 May 2014 (UTC)


 * I have absolutely no idea if this makes engineering sense, but the "obvious" idea that strikes me is that the plug's integrity should depend on its weight, and the key to keeping it in place might be to put more weight on it. I'd think that that could be accomplished as easily as setting up some pumps and hoses and those awful noisy goddamned snow guns from the ski resorts to spray the meltwater leaving under the glacier into the air over the plug during the colder months, when it should freeze solid.  The problem being... a foul up in planning here would be a Real Big Oops.  (In other news, how hard would it be for North Korea to threaten to nuke the thing wide open today?) Wnt (talk) 18:09, 13 May 2014 (UTC)
 * It would be easy for them to threaten it. They have lots of practice making threats. K ati e R  (talk) 12:01, 14 May 2014 (UTC)

Pykrete is a reinforced form of ice that is stronger, thermally insulates and melts slower. Pykrete walls or dams might bolster the underside of a glacier. There is time to investigate whether pykrete can be formed efficiently by exploiting the Antarctic seasonal thaw-freeze cycle, while “All of our simulations show [the ice] will retreat at less than a millimeter of sea level rise per year for a couple of hundred years..." (Joughin). 84.209.89.214 (talk) 18:39, 13 May 2014 (UTC)
 * Interesting idea! SteveBaker (talk) 18:47, 13 May 2014 (UTC)
 * I meant to mention Pykrete, but forgot, so thanks :) It does seem conceptually very similar to reinforced concrete, and if the wood/fiber component were harvested from the right places, it would also be a form of carbon sequestration. One risk would be altering the albedo so much that the pykrete actually absorbs more heat than ice, which could accelerate melting. SemanticMantis (talk) 19:05, 13 May 2014 (UTC)
 * Yes, the pykrete will almost certainly be darker than natural snow. That is why I speculate use on the glacier's underside only. 84.209.89.214 (talk) 23:15, 13 May 2014 (UTC)
 * The explanation I saw on TV recently is that what's happening is that warmer water is coming up under the ice shelf and eroding it away from the underside. ←Baseball Bugs What's up, Doc? carrots→ 19:14, 13 May 2014 (UTC)
 * Yes, it says that under the high-resolution map in the article linked above: "Warm circumpolar deep water is melting the underside of this floating shelf, leading to an ongoing speedup of Thwaites Glacier". Richerman    (talk) 16:48, 14 May 2014 (UTC)


 * The Wall Street Journal this morning (Saturday, 5/17/14) has an article about a project of building an ice dam at Fukushima to prevent radioactive water seeping into the Pacific. It is still a massive undertaking. It is going to be almost a mile long and 100 feet deep. They call it ice wall. --AboutFace 22 (talk) 16:03, 17 May 2014 (UTC)


 * How about if we focus on increasing friction at the bottom of the glacier, say by drilling holes down to the bedrock, and inserting rods into the bedrock, extending up into the glacier ? I suggest a triangular profile for the rods, not circular, in case they break off and start to roll.  You might want to start where the glacier is moving the slowest, to allow for placement of enough rods to stop it before the first rods are broken off. StuRat (talk) 16:17, 17 May 2014 (UTC)

Why doesn't Huntington's disease burn itself out?
Since Huntington's disease exhibits anticipation due to the Huntingtin gene becoming longer and longer faster and faster with each generation, why does Huntington's disease run in families long-term, instead of appearing in one generation, running in the family for a few generations with symptoms appearing earlier and earlier each generation, and then, after a few generations, causing symptoms so early as to kill the carriers before they reach reproductive age, thus burning Huntington's out of the family line after a certain number of generations? Whoop whoop pull up Bitching Betty &#124; Averted crashes 20:13, 13 May 2014 (UTC)


 * Well, Huntington's_disease says it "does not usually affect reproduction." So, even if your proposed mechanism makes sense, it may well just not work that way, and increased depth of vertical transmission might just not have an effect on onset of syptoms. Also, though this disease is not pathogenic, keep in mind optimal virulence, which describes how agents that are too virulent in their methods of reproduction will indeed tend to go away. Also consider the possibility that it will go away eventually, just not yet. That's the sort of ecological take on it, I can't help with the details of mechanisms of genetic control. SemanticMantis (talk) 21:22, 13 May 2014 (UTC)


 * evilution means maximum discomfort for all living things as long as it doesn't keep one from procreating. hence back pains, bad teeth, common cold and everything. only the most fatal stuff, the ebolas among mutations, gets weeded out fast. blatant OR Asmrulz (talk) 21:37, 13 May 2014 (UTC)


 * I'd say Huntington's disease does burn itself out, in that 7 out of 100,000 is only a little bit more common than rarer syndromes caused by simple point mutations, and in that the "anticipation" demonstrates that it is not genetically stable over time. In order to have new mild alleles coming in all the time, the worst ones must be being removed. Wnt (talk) 21:43, 13 May 2014 (UTC)


 * Point of order: the claims of anticipation are unsourced in both OP's first two wikilinks. If there is indeed solid evidence of progressively earlier onset, we still have to firmly establish a negative impact on fecundity, which is a common proxy for Fitness_(biology) (this does seem reasonable, but very tough to show). If both those features are true, then we would indeed expect that disease to eventually go extinct, along with a certain lineage. However, it's not clear to me that the disease cannot also be the result of spontaneous mutation. If that's the case, a sufficient influx of first-generation carriers could keep the disease persisting in the human population indefinitely. SemanticMantis (talk) 22:25, 13 May 2014 (UTC)
 * If we can prove that onset's getting earlier by generation, do we have to study whether it affects fecundity? Unless it simultaneously causes puberty to happen sooner and breaks down societal impediments to children becoming parents, it's got to reduce fecundity.  Oops, I misread things and didn't realise how slowly the disease acted.  Nyttend (talk) 00:53, 14 May 2014 (UTC)


 * Actually, we know that Huntington's can arise spontaneously through a random mutation. Depending on how you crunch the numbers, spontaneous mutations causing expansion of the 'normal' huntingtin protein's polyglutamine repeats is responsible for anywhere between 0.1 and about 3%  of new Huntington's cases. TenOfAllTrades(talk) 02:05, 14 May 2014 (UTC)


 * Huntington's doesn't burn itself out after a few generations because in Huntington's, "propensity to anticipation is heritable for a number of generations through the male line, [but] it originates at the time of differentiation of the germ line of a male who acquires the Huntington allele from his mother". Red Act (talk) 23:20, 13 May 2014 (UTC)
 * Thanks for digging out that paper - it shows among other things that anticipation in maternally derived cases is 1.35 years and in paternally derived 6.73 years; and that there are indeed juvenile (age of onset <20 years) and even infantile (age of onset < 10 years) cases. The 0.1-3% figure above is sort of irrelevant in that they are looking at what proportion of sufferers had a truly new mutation; but if a mutation were to have no apparent effect (small expansion) then it wouldn't count as a sporadic mutation; rather it would be an expansion in the offspring.  Still, that paper points out that the Haldane approach I was thinking to use doesn't really give accurate results in a rapidly changing society/environment.  What we can be sure of though is that yes, there is at least 0.1% of new mutation, and at least 0.5% lethality (that's roughly the rate of onset < 20 years in the first table) so there ought to be something around 0.5% "churn" through the pool of sufferers, genuinely new mutant alleles added and genuinely lethal mutant alleles removed from the population. Wnt (talk) 05:34, 14 May 2014 (UTC)
 * There's also a little evidence that Huntington's confers some sort of health benefit when people are younger . So it may be a bit like sickle cell anemia where there is a tradeoff. There's probably a lot of this sort of stuff with various mental diseases where humans haven't been around long enough to just get the benefits without any of the down sides . Dmcq (talk) 12:11, 14 May 2014 (UTC)

Reliable biography of Nikola Tesla
I have seen all sorts of nonsense about Nikola Tesla, pro- and con-. Can anyone recommend a sympathetic but not credulous biography? Thanks. μηδείς (talk) 21:14, 13 May 2014 (UTC)
 * Where do you draw the line between sympathetic and credulous? InedibleHulk (talk) 06:04, 15 May 2014 (UTC)


 * Well, one that doesn't embrace crackpot conspiracy theories, but which gives reliable, objective information on projects he's believed to have worked on--basically one that takes neither a pro- nor a debunking stance as a whole. I only ever learned enough electricity to pass Physics for Science Majors 201 & 202 over the summer, then promptly forgot it. So I know there are depictions of him by David Bowie and suggestions he was the basis for Ayn Rand's John Galt, but that's not very helpful or reliable. μηδείς (talk) 17:47, 15 May 2014 (UTC)

Typhoid Mary
How can typhoid fever live for years and years in the same person without ever producing symptoms and without dying off, yet still remain capable of infecting other people? The asymptomatic carrier article mentions how HIV can run for years before causing symptoms, but that's normal for an HIV carrier (get it, and nobody will expect AIDS to start right away), but Mary had the infection for years and years while people around her got it within days of exposure. Her article mentions that Stanford scholars believe that the bacteria hid in macrophages, but it wouldn't seem to me that something that's hiding in another cell would be able to get out easily and start infecting people within a few days. Nyttend (talk) 21:45, 13 May 2014 (UTC)


 * From it sounds like it was hiding on gallstones.   repeats this but suggests other sites also exist, and says the carriers are the entire reservoir of the disease. Wnt (talk) 05:40, 14 May 2014 (UTC)


 * Chronic Salmonella Typhi infection of gallbladder is a well known phenomenon and one of the strong risk factor of Gallbladder cancer. Ruslik_ Zero 14:07, 14 May 2014 (UTC)


 * See Typhoid Mary. Also, an infectious disease might not be entirely dormant, but only produce a rather low level infection, which is either not taken as a sign of disease at all or is taken to be something less serious, like a minor allergy. StuRat (talk) 14:19, 14 May 2014 (UTC)


 * This isn't exactly on topic (so remove this if you'd like), but HSV is an example of something that can become entirely asymptomatic, yet still contagious. (again, if this is useless to your question, just delete this - wasn't sure).Phoenixia1177 (talk) 04:38, 16 May 2014 (UTC)