Wikipedia:Reference desk/Archives/Science/2011 March 11

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March 11

18 year Lunar Perigee effects on tides?

I saw an article yesterday that said in mid-March the moon will be as close to the earth as it ever gets ("lunar perigee"), and that this is an 18 year cycle. Sadly, nothing of the sort is mentioned in Orbit of the Moon. I have two questions: 1) is this true and where on Wikipedia can I read more about it? 2) will this cause record high tides? if yes, what would the tidal variation be between the moon at its closest and furthest orbital positions? The Masked Booby (talk) 00:50, 11 March 2011 (UTC)

The mentioned 18 year cycle is probably a Saros cycle, which governs eclipses. The moon reaches perigee about once a lunar month, but the exact timing with respect to the phase of the moon changes. The Full moon cycle of about a year-and-a-bit would be the closest connection between lunar perigees and the size of tides -- we get the largest tides when the moon is close to us just at a spring tide. The Saros cycle arises from the interference between the full moon cycle and the moon's periodic movement north and south of the ecliptic (which also happens about once a month but again only roughly, due to the precession of the lunar orbit). –Henning Makholm (talk) 02:11, 11 March 2011 (UTC)

Henning has given an excellent response. On a general level do you remember (assuming you are old enough) any 'record' tides 18 years ago when the same circumstances pertained. I don't, and I've experienced more lunar phases than I care to mention ;-) Richard Avery (talk) 07:26, 11 March 2011 (UTC)

Diet theory

As far as I remember body stores excess energy in fat. If I have lost weight by eating less, does it follow that my body has used my fat instead of food, and since there is no fat available I should eat more now and I won`t get fat again? 89.235.211.162 (talk) 01:18, 11 March 2011 (UTC)

As our dieting article states, weight loss usually means that one has lost both fat mass and muscle mass. Could you rephrase your last sentence? It didn't make logical sense to me. I must mention that your questions about this may be deleted, or go unanswered, if you ask questions about your body, because that touches on our no-medical-advice policy — I would recommend asking questions about a hypothetical generic human instead. Comet Tuttle (talk) 01:43, 11 March 2011 (UTC)

Eating is not a medical issue and it is a biology question. I don`t see what is there not to understand. A person eats less. He or she loses weight. Assumption is that weight loss is result of body being forced to use fat to get necessary energy. Would it be healthier if person wouls start eating more, given that there is no more fat reserves to dig in? Will increasing food consumtion result in weight gain or will the body convert all food into energy stright away? 89.235.211.162 (talk) 02:46, 11 March 2011 (UTC)

If a person takes in more calories than they expend, the body will have a net positive amount of "energy" and will store it as fat. If a person takes in fewer calories than they expend, the body will have a net negative amount of "energy" and will respond by breaking down fat stores, then muscle if insufficient fat stores remain. If a person's caloric intake and expenditures are roughly equal, they will remain the same. One of Comet Tuttle's points was that what you (the OP) "should" do is dependent on a whole variety of factors and isn't really in the domain of the reference desk. It is doubtful that you have completely eliminated all of your fat stores, and we don't have any way of knowing whether you have altered your basal metabolic rate in the course of your weight loss (by increasing lean muscle mass, for example), or if your daily activity level has significantly increased (thus requiring higher caloric intake simply to break even). So, whether or not you can "eat more" without gaining the weight back is impossible to answer. The bottom line is that you can simply use a scale to weigh yourself (pick one time of the day and try to be consistent). This will answer your question. --- Medical geneticist (talk) 03:08, 11 March 2011 (UTC)

No, I moved to diffrent town for my studies, the only thing I altered was how much I eat, because I don`t like to cook and was hardly ever hungry. I like the result. However lately I am feeling hungry more often, although I eat as much as usually. Hence I wonder. 89.235.211.162 (talk) 04:21, 11 March 2011 (UTC)

Beware of yoyo dieting: losing weight, then gaining more back. It is the usual result of dramatic dieting and weightloss, because your body adapts to the lack of calories and starts to lay fat down more easily. If you find, in a few months time, you are heavy than you were before the weightloss, the only way to definitely break the cycle of steady weightgain is to not diet. 86.163.4.134 (talk) 09:42, 11 March 2011 (UTC)

I think I understand the logic behind your question. Let me state what I think you meant to ask, then answer that:

"Since we have fixed number of fat cells, if I eliminate all of them by dieting, will it then be impossible for me to gain weight since I no longer have any fat cells in which to store additional fat ?"

OK, the biggest flaw with that theory is that fat cells just shrink when you lose body fat, they don't disappear entirely. They can be removed, via surgery, but not all of them. This leads to the remaining fat cells getting even larger, and having many small fat cells provides for a smoother looking body than a few huge ones. But, if we could theoretically eliminate all of our fat cells, what would happen ? I suspect that you would die, or at least get diabetes, as burning fat is important to bridging long gaps between meals. And, on the other extreme, when you ate a big meal, if it couldn't be stored as fat, would your blood sugar skyrocket ? StuRat (talk) 00:07, 12 March 2011 (UTC)

Incidentally, one reason why you may be hungrier now is that you aren't getting all the nutrients you need. If you had an unhealthy diet, but ate 10x as much as you should have, then you might have managed to get all the vital nutrients just by volume, whereas now, if you continue to have an unhealthy diet, but just eat less, you may have deficiencies, leading you to crave more food. Make sure you have a healthy diet, and this problem should go away. StuRat (talk) 00:13, 12 March 2011 (UTC)

No, I wasn`t aware that number of cells is fixed, I thought body generates new cells and eliminates old cells (to extent, at least). I am acctualy concerned of the effect anonymous poster before you mentioned. So let me rephrase. I believe I am hungry because my body has depleted its fat reserves and wants to get more energy from food now. Up until now I ate as much as I craved, but I am worried that because of whole yo-yo dieting deal my body wants me to eat more than I acctualy need. So should I eat as much as I crave or only a little bit more? 84.52.32.137 (talk) 00:30, 12 March 2011 (UTC)

If eating as much as you craved made you overweight before, I suspect that it would do so, again. But, as I said, the answer to cravings isn't to eat more junk, it's to eat the proper amounts of the right things. StuRat (talk) 01:02, 12 March 2011 (UTC)

I ate what my parents served, not junk, though possibly too much bread, matter of fact I`ve been eating more junk food while losing weight than ever before. I currently eat stuff from all major food groups, mostly salad. So I see your point as valid, but I doubt it applies here (besides I guess lacking specific nutrients would cause cravings for a particular product, which contains them) 84.52.32.137 (talk) 01:26, 12 March 2011 (UTC)

Cravings aren't necessarily that specific. And if you've been eating more junk food while losing weight, that supports the idea that you may be malnourished. Salad is a good component of a healthy diet (although the common iceberg lettuce is almost devoid of nutrients), but you might not be getting enough protein. For that you need meat, dairy, beans, or nuts. StuRat (talk) 06:08, 12 March 2011 (UTC)

But all salad normaly contain dairy products, meat and vegetables. Just because I eat fast food once in two weeks dosen`t mean I am malnorished. I learned what is healthy diet in elementary school, no need to educate me on that. I said it is a theoretical question - assume that there are no other factors than quantity and tell me, if it is wiser to increase food consumtion as much as I feel or increase it by little less 89.235.214.143 (talk) 17:10, 12 March 2011 (UTC)

Increase the quantity a small amount at a time, until you start to gain weight, then pull back a bit, to keep your weight steady. As for your statement that "all salads normally contain dairy products, meat and vegetables", that's not true, many have no meat or dairy products. I suspect that you are getting things like a Cobb Salad, which has all sorts of things in addition to a standard garden salad. Such "salads" may actually be quite unhealthy. Try a garden salad, on occasion, too, and skip the rich bleu cheese dressings in favor of a simply vinaigrette. StuRat (talk) 21:59, 12 March 2011 (UTC)

Any fluctuations and reductions in your weight will probably fluctuate around your normal body weight. ~AH1^(TCU) 02:21, 13 March 2011 (UTC)

In the place where I live it is the traditional understanding of what `salad` means, I buy them ready made at grocery store (as I said I don`t like to cook) and they haven`t gotten down the method of producing tasty salad with any other dressing. But anyway thanks, I don`t know why, but idea of letting it fluctuate around slightly and ajusting as needed hadn`t occured to me. 89.235.214.143 (talk) 02:56, 13 March 2011 (UTC)

I don't like to cook much either, but making a salad isn't cooking. With raw ingredients like "baby cut" carrots, cherry tomatoes, and a bag of spinach, you can assembly a salad quite quickly (I just had one for dinner). I like to rinse the ingredients, then just drain, mix and eat. The only problem I've had is they sell huge bags of spinach which tend to rot before I finish them. Still, I bet a do-it-yourself salad will be both cheaper and healthier than a pre-made salad. StuRat (talk) 09:04, 13 March 2011 (UTC)

monopole

what would happen if you took a bunch of magnets shaped like a pyramid (with one pole at the top point and the other pole at the wide base) and then glued them together with all the top points facing in? —Preceding unsigned comment added by 98.221.254.154 (talk) 02:00, 11 March 2011 (UTC)

Your description of a magnetic "pole" as a point is unfortunately oversimplified. The simplest magnetic moment is inherently described as a dipole. A magnetic "pole" doesn't exist at one specific position in the magnet: it is an effective orientation - a preferred direction - that is built into the magnet. Complex ferromagnets have an effective average dipole moment, and so it's fun to draw this as a "north" pole region and a "south" pole region, but in truth, what you have is an net average orientation of all the individual microscopic orientations that make up the magnet. As such, the "north pole" doesn't exist "at the point" of the pyramid, nor the "south pole" at the "wide base." The entire magnet is polarized. Nimur (talk) 02:14, 11 March 2011 (UTC)

(ec) Their magnetic fields would cancel each other out, and only leave a slight inwards-pointing field in the middle of the faces of the resulting polyhedron, and a slight outwards-pointing field at the corners, or vice versa. Some distance from the compound object (say, two radii from the center) there would be practically no net field. –Henning Makholm (talk) 02:18, 11 March 2011 (UTC)

Ah yes, I didn't actually answer the original question! So, to directly answer what would happen: I can't quite follow the geometry the OP is envisioning, but it sounds like you've got a bunch of magnets oriented so that they want to repel each other. Well, if you squish them together, and maybe glue them in place, the result will be that from far away, you'll have an effectively larger, but weaker, magnet. And if you get really close near any of the individual pyramid-shaped magnets, you will find that your magnetic field is best described as a superposition of several individually-oriented dipole fields. (You might even find a way to mathematically re-represent that as one single higher-order moment, if you're pretty slick with math). Nimur (talk) 02:19, 11 March 2011 (UTC)

It could also be modelled as a superposition of two perpendicular linear quadrupoles, so I suppose it is an octopole. —Preceding unsigned comment added by 129.67.37.227 (talk) 02:41, 11 March 2011 (UTC)

Is it correct to compare a magnetic monopole to a one sided coin? Plasmic Physics (talk) 09:29, 11 March 2011 (UTC)

I don't mean a trick coin where both sides are either heads or tails, I mean a coin with literally only one side. Plasmic Physics (talk) 09:32, 11 March 2011 (UTC)

No. An electron is a "monopole" for charge after all. We have never found one for magnetism, but that doesn't mean it's illogical in the way a one sided coin (in a 3D world) is. Ariel. (talk) 10:00, 11 March 2011 (UTC)

I get the concept of a charge monopole, what would be a correct analogy then? Plasmic Physics (talk) 10:07, 11 March 2011 (UTC)

An electric charge monopole is totally described by its position and its charge magnitude. A magnetic dipole must include, at the minimum, its position, magnitude, and orientation. If you want to try and stretch this analogy, you could say a "magnetic monopole would be sort of like an arrow that doesn't point in any direction." In a sense, a magnetic dipole must be oriented - it's built in to the definition of a dipole to have a vector orientation; and our theory of magnetism requires the elementary magnetic unit to be a dipole. In the same way, if you had an arrow and it didn't point in any direction, ... well, you wouldn't have an arrow anymore. Nimur (talk) 14:47, 11 March 2011 (UTC)

I don't agree with all of the above. There sure is room in our current theory of magnetism for magnetic monopoles. Read 't Hooft–Polyakov monopole. That's why the search for a magnetic monopole is not considered a fool's errand. But they have never been observed and it is possible that they simply do not exist. A better analogy for the meaning of a monopole would be a rug that has been combed down away from a central position. Dauto (talk) 16:03, 11 March 2011 (UTC)

Insofar as you mean magnetic field lines would emanate from a monopole, yielding the hypothetical Gauss's law for magnetism, $\nabla \cdot \mathbf {B} =q_{m}$ - yes, that is how we would mathematically describe as a magnetic monopole, if it exists. And we would draw it on paper the way Dauto describes it. Is there room in our theory for it? Sure, with minor modification of Maxwell's equations, we could trivially add a magnetic monopole term; but to make those modified equations fit with experimental observation of physical reality will be a much more subtle and challenging problem. My tendency is to believe that the magnetic monopole does not exist, and is a contradiction against everything we physically observe about magnets, even if we could write equations to describe what it would hypothetically look like. Future experiment may disprove my belief - you're right that it's not futile (and indeed, is a worthwhile avenue for experimental physicists to pursue); so I'm open to the unlikely possibility of discovery of a magnetic charge. Nimur (talk) 16:35, 11 March 2011 (UTC)

The modified equation's fit just fine with experimental observations. I would like to clarify the point that 't Hooft–Polyakov monopoles are predicted to exist by the standard model of particles, so they are not as fringe as one might think. Dauto (talk) 16:48, 11 March 2011 (UTC)

Shouldn't the q _m be rho? Either that or replace the differential left hand side with integral B.dA ...(sorry i cant use TeX at the time) Dauto, they're not fringe, but many people consider them as one of the many flaws of the standard model. ManishEarth^{Talk • Stalk} 04:04, 15 March 2011 (UTC)

Yes, I could have used "rho", "magnetic charge density," for parity with the conventional notation of Gauss's law in electrostatics. Sorry for my imprecision/incorrect equation. I suppose this begs the question whether hypothetical magnetic monopoles would be continuously distributed "charge density clouds" or discrete elemental charges - a can of worms I don't want to open. Nimur (talk) 16:47, 15 March 2011 (UTC)

Drugs

What affects do drugs have on the mitochondria in humans? How are other organelles affected? Albacore (talk) 02:20, 11 March 2011 (UTC)

Which drugs? We can't even begin to answer the question without specifics. --- Medical geneticist (talk) 02:55, 11 March 2011 (UTC)

Well, uncoupling agents are defined by their ability to (essentially) break down the electrical resistance of the mitochondrial membrane e.g. by acting as proton ionophores, discharging its energy unproductively. Oh, and rotenone works a different way, jamming the electron transfer apparatus. Wnt (talk) 04:42, 11 March 2011 (UTC)

Big rip or Big crunch?

Is it more likely for the universe to end in the concept "big rip" or "big crunch"? — Preceding unsigned comment added by Lightylight (talk • contribs) 04:29, 11 March 2011 (UTC)

Our article on the ultimate fate of the universe notes that current scientific data supports an open universe. That viewpoint is incompatible with a "big crunch", but does not necessarily support a "big rip" scenario. — Lomn 04:38, 11 March 2011 (UTC)

That article also says that the Big Freeze is "currently the most commonly accepted theory within the scientific community". There are a couple of variants of that scenario, depending on whether protons can or cannot ever decay. Gandalf61 (talk) 14:58, 11 March 2011 (UTC)

Zoologist specialising in Lepidoptera, "Busck", active beginning to mid C20?

Hi all,
The usual question: any clues about entomologist with either abbreviation "Busck." or full family name "Busck"? Binomial authority for Ypsolopha querciella amongst a whole lotta others. Google is not being friendly. Sounds Scandinavian, and first name initial may be "A".
Thank you! --Shirt58 (talk) 09:52, 11 March 2011 (UTC)

The "A" would appear to be "August" and his publications are listed at WorldCat. SpinningSpark 11:05, 11 March 2011 (UTC)

A F Braun, Lepidoptera, active mid C20

Hi all - same again. Binomial authority for Parectopa geraniella inter alia. Apologies for being such a bother. --Shirt58 (talk) 10:09, 11 March 2011 (UTC)

Annette F Braun [1], [2]. SpinningSpark 11:34, 11 March 2011 (UTC)

Japanese and Chinese earthquakes

Could there be any connection between the two earthquakes, or are they just coincidence? Thanks. 92.24.186.163 (talk) 14:06, 11 March 2011 (UTC)

As a first-order answer, "no, these are just coincidences." To explain in more detail, scientists have been studying earthquakes for a long time, and there are many theories about triggering earthquakes. There's a certain plausibility about massive geological events (like a powerful earthquake) affecting a geographically distant fault and triggering another earthquake; but unfortunately the data record is not clean enough to make a solid, scientific conclusion. Scientists have also investigated more indirect triggers for earthquakes, such as magnetic interactions between large sections of the Earth's interior; glacier, sediment, ocean/tidal, and other "variable" geological overburden loads, and so on. If you're interested, here are a few historically notable research papers: Earthquakes Cannot Be Predicted (1996); and my personal favorite work on earthquake prediction, Scientists debate new evidence for electromagnetic earthquake predictors (1991). (This paper triggered much heated debate). As you can see, most scientists do not believe there is any geological, seismic/teleseismic, electromagnetic, nor any pattern of animal behavior, nor any "telepsychic" method, that can predict earthquake incidence. But, reputable scientists continue to seek any sort of signals that might indicate earthquake precursors, or solidly indicate that one earthquake triggered a second one. Nimur (talk) 15:16, 11 March 2011 (UTC)

Thanks, interesting papers which I shall read, although the question is if there could be any connection between them, which is a different from asking about predicting them. 2.97.212.204 (talk) 16:22, 11 March 2011 (UTC)

Valid consideration: it's really two sides of the same coin. If Earthquake A causes Earthquake B, then there must be some physical mechanism (like a propagating seismic wave from A that disrupts the rock material strength along the fault-line for B). If there is such a connection, we should be able to observe it - or at least, identify what hypothetical "perfect, noiseless measurement instrument" would be required to observe it. And if we can observe A and measure its effects, we should be able to predict Event B. So the distinction between "A triggers B" and "A allows seismologists to predict B" is fairly moot. This is conceptually described with more rigorous scientific precision in the literature I linked. Nimur (talk) 16:45, 11 March 2011 (UTC)

Not really. Prediction is about things in the future, this is asking about things happening at the same time. In economics or finance, for example, there are series which are random and unpredictable yet which have a relationship with each other - in other words they may show Cointegration or Correlation. You've also forgotten that A and B may both be caused by some other factor. 92.15.24.90 (talk) 19:41, 11 March 2011 (UTC)

Earthquakes mostly are the result of movement of tectonic plates. Japan happens to lay on thee diffrent plates and there have been two previous earthquakes in the same region of China in recent years. If you take a look at maps in articles on both quakes and the ones on earthquake, you`ll see that they appear to be on different edges of Eurasian plate, close to diffrent fault lines and are moving in diffrent directions. It can be a coincidence. Though of course it could be that Eurasian plate has become particulary active. ~~Xil (talk) 21:37, 11 March 2011 (UTC)

To add to the list, there have been a number of large earthquakes in New Zealand lately, including the most recent one in Christchurch, and increased volcanic and seismic activity in Hawaii. One theory I've heard is that the Moon may cause this, by being closer than it has for the last 18 years (I'm not sure if this is true, the question posed a few above this should hopefully provide and answer). Since the Moon causes tides (along with the Sun), in water, and also causes hidden tides in the solid portion of the Earth (in the form of both stress and strain), it's not impossible that the Moon's gravitational effect could trigger quakes. Now, if so, the question would come up as to why it's all in the Western Pacific. Perhaps that region was "ready to blow" for other reasons, and the Moon just provided the spark. StuRat (talk) 23:54, 11 March 2011 (UTC)

The whole region is nutorious for seismic activity. See Pacific Ring of Fire for some statistics ~~Xil (talk) 00:54, 12 March 2011 (UTC)

Yes, but it appears to have increased recently. And I congratulate you on your "nutorious" spelling. :-) StuRat (talk) 00:59, 12 March 2011 (UTC)

There is no evidence of any increase in seismic activity that I'm aware of. Rates of earthquake occurrence appear to be constant since seismograph recordings began at about 1900[3]. Mikenorton (talk) 12:26, 12 March 2011 (UTC)

I mean quite recent quakes, like in the past month. There definitely seem to be more big ones in this time-frame, than for the average month. However, as noted below, some clustering of big quakes is to be expected, even if they are random. StuRat (talk) 21:48, 12 March 2011 (UTC)

I heard on tv two scientists say that earthquakes did tend to cluster together in time, even though they are in different places. 92.15.2.144 (talk) 00:57, 12 March 2011 (UTC)

If they're truly random, then they will show clustering. Mikenorton (talk) 12:26, 12 March 2011 (UTC)

This claim was made on CNN by a geology Prof., and he was referring to the really big quakes of magnitude 8.7 or larger. Such quakes are quite rare, they happen on average every few decades. However, there is a strong clustering that contradicts them being random. So, around 1960 there were 3 such huge quakes witin a period of a few years and we now have two or 3 of them (depending on whether you count the predicted magnitude 8.7 2005 Sumatra earthquake ). Count Iblis (talk) 15:24, 12 March 2011 (UTC)

I heard some reports stating that the 2011 Christchurch earthquake triggered more shocks all across the Pacific Ring of Fire to places as far as Alaska, but it's likely impossible to ascertain the connection. Propagation of quakes along the fault line occurred following the 2010 Chile earthquake. However, the 2011 Yunnan earthquake was likely not tied to the Japan shock, even if it is connected to the aftershock sequence from the 2008 Sichuan earthquake. ~AH1^(TCU) 02:17, 13 March 2011 (UTC)

Changing # of chromosomes in evolution

How do new species arrive that have a different number of chromosomes from their antecedents? I can see how the number could go down, actually, in theory, at least, but increasing-- where'd the DNA come from? Unless one of the already existent chromosomes split in the new species (seems like extremely high odds against that happening while not causing serious problems, let alone fitness) And yet many species of life have differing amounts of chromosomes, so it must happen. 20.137.18.50 (talk) 16:18, 11 March 2011 (UTC)

Polyploid plants can be formed from two monoploid parents, so the number of chromosomes can double in a single generation. Often, rather than suffering decreased fitness, many polyploid plants are quite hardy and robust, and specifically have characteristics desirable for agriculture. Many of our primary crop plants today are polyploid. See this section of our page for examples. There are other ways chromosome number can change, but this is a good place to start. SemanticMantis (talk) 16:32, 11 March 2011 (UTC)

You answered your own question. "It must happen". Which means that your intuition about the odds of that happening is simply incorrect. Dauto (talk) 16:42, 11 March 2011 (UTC)

That doesn't answer the how though, Dauto. 90.195.179.167 (talk) 16:44, 11 March 2011 (UTC)

Thanks, SemanticMantis, paleopolyploidy covers exactly what I was wondering about. Dauto, I didn't mean to doubt that it happens, I only meant to express my desire to understand how it happens, noting my perspective at the time given how easily bad things happen when genes get messed with. 20.137.18.50 (talk) 16:48, 11 March 2011 (UTC)

What makes you think that the splitting would have to mess up any genes? The splitting could happen between genes. There is a lot of non-coding DNA between genes in most Eukaryotes. Dauto (talk) 16:55, 11 March 2011 (UTC)

I don't have any specialized knowledge on the subject, and am glad to have any wrongheaded assumption I have made replaced by fact. 20.137.18.50 (talk) 17:10, 11 March 2011 (UTC)

One thing to bear in mind is that increasing the chromosome number by splitting one, or decreasing it by merging two, chromosomes (see Chromosome 2 (human) for an interesting example of the latter) does not involve creating or destroying any DNA, because differently-numbered chromosomes are not all the same size - indeed, they are conventionally numbered according to size order. When such merges and splits occur, individuals with them may initially still be able to reproduce with "unmodified" individuals because the two sets can still line up well enough: over time, the modification may multiply until modified individuals are regularly mating, and then the modification may, through some advantage, take over through Natural Selection.

Also, genes can migrate from one chromosome to another over generations, and smaller chromosomes may have shrunk by some of their genes having moved to larger ones: in time a chromosome could eventually dwindle away to nothing by this mechanism, again reducing the chromosome number. Some mitochondrial genes have over the aeons transferred from the mitocondria's single circular chromosome (I oversimplify) to nuclear DNA chromosomes, which is one reason why mitochondria can no longer operate as independent living organisms, and it has been suggested that the human Y chromosome (already our tiniest) will eventually disappear in this way (several human male-sex-determining genes are already on other chromosomes).

As others above have mentioned, sometimes the Chromosome complement can double "in one go" through polyploidy (I believe it's happened about 4 times in our own deep ancestry). When this happens the organism has a complete operating genome plus a "spare", and genes in the latter are then available to evolve new genes without losing the functions of the "originals". This could also happen if a single chromosome pair was doubled, or increased from 2 to 3, but sometimes such increases can cause deleterious effects, as in Trisomy 21.

Just as you say, such occurrances are rare, and non-deleterious ones rarer, but the deleterious ones are eliminated by Natural Selection, and there is so much time available over the millions of years over which evolution operates that the rare advantageous ones have time to accumulate. {The poster formerly known as 87.81.230.195} 90.201.110.135 (talk) 21:30, 11 March 2011 (UTC)

Is there an example of a species with a variable number of chromosomes, where at least two of the variations could be described as "healthy" ? StuRat (talk) 23:44, 11 March 2011 (UTC)

Yes, Homo sapiens! This link refers to an individual from China with 44 chromosomes (22 pairs) as opposed to the usual 46, and I am sure I have recently read of a family in Scandinavia with the same count (though not necessarily due to the exact same variation), that I am momentarily unable to find references for. The latter family displays somewhat reduced but by no means destroyed interfertility with 46-chromosome individuals, because, as in my description of the Chromosome 2 merge above, the 2 unmerged chromosomes from a "normal" partner can still align well enough with their corresponding end-linked "double" chromosome to achieve homologous pairing. The individuals with 44 chromosomes are entirely healthy; they merely have the same genes packaged in a slightly different way. I suspect that this sort of variation is more common than hitherto realised (because who has been looking?), and I believe some other species more commonly show variable counts, but can't bring any to mind just now because it's past 5 in the morning! {The poster formerly known as 87.81.230.195} 90.201.110.135 (talk) 05:24, 12 March 2011 (UTC)

Interesting, thanks. StuRat (talk) 05:59, 12 March 2011 (UTC)

That is a great link. Note that the man was actually the offspring of two people who both carried the translocation! So there's already some population out there (though probably very small) carrying this new chromosomal configuration.

What is interesting to consider is that if there are even just a few people like this man, it quickly reaches the point where outsiders are the ones with the "funny" chromosome pattern, in the sense that they'll be less capable of producing offspring with members of the group than they are with one another. Should it happen that group members are sitting on some good genes for some situation, this means that their group might spread out and start to dominate an area, and in this way start to look like a "new species" (though further barriers obviously would need to evolve) Wnt (talk) 07:16, 12 March 2011 (UTC)

There's also Przewalski's Horse which has 66 chromosomes and other horses have 64. It's debated whether it's a species or a subscpecies, partly because it can produce fertile offspring with other horse (sub)species. There's a discussion at the talk page that you might find interesting. I also recall reading about some small animal in the Middle East which had varying number of chromosomes in the same species. It might have been some kind of mongoose or rodent. I'll se what I can find.Sjö (talk) 08:09, 12 March 2011 (UTC)

Not exactly what I was looking for but http://www.talkorigins.org/indexcc/CB/CB141.html mentions the common house mouse and the plant genus Clarkia.Sjö (talk) 08:17, 12 March 2011 (UTC)

There was a similar discussion here two weeks ago, see (refdesk 2011-Feb-28) Chromosome numbers and speciation. Populations with interbreeding members having different numbers of chromosomes display chromosomal polymorphism. This is also discussed in Karyotype#Chromosomal_polymorphism. --NorwegianBlue ^talk 20:37, 12 March 2011 (UTC)

See also viral fossil and insertional mutagenesis. ~AH1^(TCU) 02:09, 13 March 2011 (UTC)

After looking at the link provided by the very knowledgeable anonymous editor, http://www.thetech.org/genetics/news.php?id=124, I am wondering why the 6×6 table is not symmetric. The last column, third last row, should be the same as the last row, third last column, shouldn't it? The contents do indeed look the same to me, but one is crossed out, the other isn't. Why would that be? — Sebastian 19:13, 13 March 2011 (UTC) Never mind; that was a mistake that will be corrected. — Sebastian 03:21, 15 March 2011 (UTC)

Strange breakers on Japanese Tsunami

There is a strange looking video of the tsunami coming onshore on CNN [4] (I can't figure out how to link to the video directly, you need to click on "Witness deals with quake terror" in the video gallery"). The wavefront is showing breakers only over a narrow and very well defined front. It does not seem to be due to the wave passing over an undersea obstruction as the breakers are long lasting and continue to show all the way in. What is the explanation for this? SpinningSpark 16:47, 11 March 2011 (UTC)

I also saw it. My impression is that the ground surface along that "strip" was different from the ground on either side of it - turbulent flow over a rougher surface flanked by less turbulence where the substrate is smoother. It also looked like the depth of the water in that area was only a metre or two so even relatively minor "texture" differences could cause a substantially different amount of visible turbulence on the water surface. Roger (talk) 19:41, 11 March 2011 (UTC)

It may be due to a sand bar. The shallower the water, the closer the waves and the more likely they are to break. In WW2, the spacing of the waves measured from aerial photographs was used to estimate the depth and slope of the D-day beaches using a mathematical formula. I have been unable to find an article about this formula: the nearest I could get is this Waves and shallow water but there may be a better article hiding somewhere. 92.15.24.90 (talk) 20:15, 11 March 2011 (UTC)

(edit conflict, replying to Roger) Yes, that's the obvious conclusion but I remain unconvinced for a couple of reasons. Firstly, the wake behind the breakers is ruler straight and constant width as if it was following a road, yet the effect continues up the beach where there is no sign of any lateral change in colour or texture of the substrate - I am sure that a change from sand to shingle, for instance, would be visible in the picture and such natural features are rarely so unnaturally straight. Secondly, I believe tubulence and/or friction caused by the substrate would cause a reduction in the wave velocity, but this is not borne out by the perfect straightness of the wavefront through the turbulent and non-turbulent sections. SpinningSpark 20:21, 11 March 2011 (UTC)

The type of wave may be a spilling breaker which explains why it keeps frothing for a long time. The second issue is why the white breaking part of the wave seems to keep a constant width for so long. This might be an illusion. The wave may be breaking as the instability in the crest and the resulting turbulence is spreading sideways at some fixed speed. Observed at a beach, such a domino-effect may seem rapid, but the same velocity observed from a helicopter seems small. Especially as we visually measure it not in metres per second but in percentages of the already wide breaking crest. It must also be taken into account that waves with a longer wavelength travels faster, so again our beach-aquired intuition about the forward speed of a wave versus the sideways spread of a collapse may not be correct. EverGreg (talk) 22:24, 11 March 2011 (UTC)

Looking at these videos, what seems striking is that the waves are actually able to move water upward in a given spot for a long period of time. In other words, there's a vast long hump of water with a strong horizontal momentum, so that it can wash right up over an obstacle. So I think we're seeing water that not merely is passing over a submerged obstacle, but which is actually striking an object that projects above the point where its surface was. Even so, it just vaults up over it and moves on. Wnt (talk) 07:10, 12 March 2011 (UTC)

The effect of the water piling up is due to the wave entering shallow water and is a "normal" effect of tsunamis. Unlike normal waves which are only on the surface, tsunami waves occupy the full depth of water. The foot of the wave is slowed by the substrate and the rest of the water piles up on top of it. SpinningSpark 09:07, 12 March 2011 (UTC)

Anyway, my gut feeling from watching the video is that there was an obstacle over a long region, which had slightly different elevations (relative to the tsunami, at least) in different areas; and that only where it extended above some critical threshold did it cause the flow to become turbulent. But that's not an expert opinion. Wnt (talk) 16:34, 12 March 2011 (UTC)

That's what it looked like to me, too. WikiDao ☯ 17:43, 12 March 2011 (UTC)

30 seconds into the video you can see the frothing edge being at an angle with the rest of the wavefront. This would be a sign of refraction caused by different parts of the wave being at different depths. So elevations probably factored into this. EverGreg (talk) 19:03, 12 March 2011 (UTC)

In a way, you can say that elevation not just factors in this, but is the main deciding factor. What complicates the matter is that it's not so much the elevation at the place you're observing, but the whole topography of the ocean floor (at least up to a certain depth) over which the wave has passed before. Shallower waters slow down waves, which bundles them much as an optical (convex) lens does. (In the eighties, there have actually been successful experiments in Norway, where they constructed submerged lenses to focus oceanic water waves into one location, where they could be harnessed. Not sure what became of that.) So the streak you're seeing is basically the same as a light beam. The same happens on a global scale, as you can see in this NOAAH height map (the same we linked to from our article). — Sebastian 19:37, 13 March 2011 (UTC)

Air circulation

What is the name for a large body of rotating air, something like an ocean gyre but in the air? --T H F S W (T · C · E) 19:38, 11 March 2011 (UTC)

A cyclone or anticyclone, depending on which way it is rotating. Looie496 (talk) 19:45, 11 March 2011 (UTC)

Note that the direction of rotation is different either side of the equator. Cyclones rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere and anticyclones do the opposite. The distinction that is not location dependent is that the pressure in a cyclone decreases towards the middle and in an anticyclone it increases towards the middle. Cyclones are also called low pressure cells and anticyclones are high pressure cells. Roger (talk) 19:55, 11 March 2011 (UTC)

Note that an ocean gyre is a more or less "permanent" pattern of circulation, though, lasting many thousands of years, at least, while a cyclone or anticyclone only lasts a small portion of a year. StuRat (talk) 23:25, 11 March 2011 (UTC)

The gyres are propelled by the winds. Specifically, they are propeled by the westerlies and the trade winds. The presence of the oceans forces the ocean motion into the gyre patterns. Dauto (talk) 00:56, 12 March 2011 (UTC)

See Hadley cell and Rossby wave. Roger (talk) 19:23, 12 March 2011 (UTC)

From a meteorological point of view, jet streams are probably a closer equivalent of gyres than synoptic atmopsheric systems. They're more "permanent", so to speak, and encompass a much larger area than lows and highs. They don't rotate, per se, but they do circulate. Juliancolton (talk) 23:25, 12 March 2011 (UTC)

"Quasi-stationary" systems in the atmosphere include the Azores High, Siberian High (winter), Icelandic Low (not year-round) and others. ~AH1^(TCU) 02:07, 13 March 2011 (UTC)

This should be a synch...

There was recently a case where a baby was delivered at the side of the road, by the (non-medical) father, with paramedics on the phone. One thing the paramedics advised baffled me. After the baby was delivered, they said it was important to synch off the (uncut) umbilical cord, to prevent continuing blood flow between the mother and baby. Since no other string was available, the paramedics advised him to use the shoelaces from the shoes he was currently wearing. I can't imagine a less sterile item than those laces, and cringed when I heard that advise. So, my Q is, why is it so important to stop the blood flow immediately, rather than just wait for the ambulance to arrive ? StuRat (talk) 20:26, 11 March 2011 (UTC)

Just by the way, I think you mean cinch. --Trovatore (talk) 20:28, 11 March 2011 (UTC)

Thanks, I wasn't sure how to spell that, as it's not a word I normally use, at least in writing. StuRat (talk) 23:16, 11 March 2011 (UTC)

Why does the shoelace or whatever is used to tie the umbilical have to be sterile? The cord and placenta will be discarded soon anyway and the cord will be cut and properly clamped with a clean clamp when the ambulance arrives. The cord must be shut off asap because if it isn't nothing would prevent the baby's blood draining out through the placenta after it detatches from the uterus, which can happen very soon after the baby is born. Not shutting off the umbilical cord will result in a dead baby within minutes wheras a dirty shoelace might have a slight chance of making the baby ill hours or even days later - the choice is a no-brainer. Sterility is in any case massively overrated as a requirement for people who have normal functioning immune systems. We survived for millions of years without even having the concept of germs or sterility. Roger (talk) 20:43, 11 March 2011 (UTC)

We also survived for millions of years without the thumbs necisary to tie a knot or build a clamp, so shutting off the cord must not be manditory (although it might lower the death rate of baby and mother). —Preceding unsigned comment added by 205.193.96.10 (talk) 21:23, 11 March 2011 (UTC)

Animals bite off the umbilical cord, probably not a method that would be prefered by human fathers. Wouldn`t squeezing the cord shut and waiting for the ambulance work too, though, without creating risk for infection? ~~Xil (talk) 22:18, 11 March 2011 (UTC)

I'm not sure how biting the cord off would help prevent bleeding - it would increase it, surely? You'll probably need your hands for other things. Taking care of the mother and baby, delivering the placenta, etc.. Using a shoelace is the standard advice. --Tango (talk) 22:28, 11 March 2011 (UTC)

Yes, I would think biting off the cord would both cause bleeding and infection, due to all the germs in saliva, and the presumably undeveloped immune system in the offspring. What prevents these things from happening ? StuRat (talk) 23:19, 11 March 2011 (UTC)

I`m just saying that the argument about no thumbs might be invalid, I am not sure how the said animals don`t bleed to death. I believe in olden days they would cut the cord and tie a knot in it, not sure, if it is right, though, couldn`t find any quick information ~~Xil (talk) 00:38, 12 March 2011 (UTC)

As long as the unbilical cord is intact and not bleeding, then there is no route for infection to get it so you don't need to worry about sterility. Anyway, worst case scenario: you have to give the baby a shot of antibiotics. Not a big deal. We do (of course) have an article: Umbilical cord#Clamping and cutting. It doesn't discuss infection, but does discuss the pros and cons of clamping quickly, slowing and not at all (there doesn't seem to be a lot of difference). --Tango (talk) 22:28, 11 March 2011 (UTC)

Starvation and blindness

I have read that starvation can lead to temporary vision loss (and when the patient is returned to his or her regulat diet, the vision problems go away), is this true, and how?—Preceding unsigned comment added by 142.1.253.163 (talk) 21:08, 11 March 2011

If you have a vitamin A deficiency, you can go blind. Clarityfiend (talk) 01:29, 12 March 2011 (UTC)

Yes, people who willingly under go starvaion can and do experiance blindness. Hunger_strike#Animal_rights--Aspro (talk) 23:33, 12 March 2011 (UTC)