Wikipedia:Reference desk/Archives/Science/2014 March 30

= March 30 =

Frog tails
Tadpoles and juvenile frogs have tails, adult frogs don't. Do these tails contain bones? How exactly are those tails lost, do the bones vanish or is it that the rest of the body grows backward so the bones become part of the spine? If the bones vanish, how is this accomplished? 95.112.194.18 (talk) 09:33, 30 March 2014 (UTC)


 * Frog doesn't answer that question precisely, but I suspect that some of the references in that section do so. --ColinFine (talk) 10:44, 30 March 2014 (UTC)


 * This abstract mentions that the tails do not have any kind of skeleton to them (i.e. no bony or cartilaginous skeleton). In fact, the very first sentence mentions that tadpoles lack vertebrae for most of their body length. Matt Deres (talk) 12:52, 30 March 2014 (UTC)
 * In this picture of a mostly translucent tadpole, you can really see how rudimentary their skeleton is. It's also worth noting that the degeneration of the tail appears to be key in developing the strong back legs characteristic of frogs; it's only when those tail muscles shrink away that the legs really begin to bulk up. Matt Deres (talk) 12:56, 30 March 2014 (UTC)


 * This is certainly true for tadpoles, but those pictures on wikipedia of juvenile frogs suggest the tail may well have bones. 95.112.194.18 (talk) 13:59, 30 March 2014 (UTC)


 * Could you specify which pictures you're looking at? You can link them without posting the picture in full by putting a colon : between the square brackets and the word "File" like this File:Haswell's Frog - Paracrinia haswelli tadpole.jpg . Incidentally, the so-called Tailed frog does not actually have a tail at all; the confusion comes from the uniquely shaped cloaca forming a kind of rudimentary penis, and it also has no bones in it. Matt Deres (talk) 15:20, 30 March 2014 (UTC)


 * File:Juvenile_Frog_with_tail_top_view_%281%29.JPG but i think I have seen more pictures (which I can't find again right at the moment) where the apperence looks even more bony. Could still be non-bony tissue, though. 95.112.194.18 (talk) 16:18, 30 March 2014 (UTC)


 * Hmmm, according to and, Megophryidae have supernumerary vertebral centra in their tails that ossify and serve as muscle attachment sites.  It could be interesting to go through the taxon and see if this is truly an evolutionary reversal as the authors suggest.  In any case, "In all four, the larval tail skeleton undergoes massive reduction, with vertebrae apparently degraded by the action of osteoclasts, leaving only the coccyx and ossified hypochord intact." Wnt (talk) 15:59, 30 March 2014 (UTC)


 * I came to think about this question because I was thinking about a (far future) way to do tissue engineering and looked for examples where nature removes bones. 95.112.194.18 (talk) 16:18, 30 March 2014 (UTC)
 * Not at an individual scale, but nature has slowly taken my tailbone. In the "far future", we'll almost certainly better understand the steps it took, so could replicate them viably quicker, and tweak where needed. Of course, in the "far future", maybe every house will simply have a biological Game Genie, growing tails like changing shirts. In the "far future", nature will have removed all of our bones the old-fashioned way.


 * Also, I met a frog with a tail last summer. The frog was about four inches, the tail about one. Didn't notice whether his legs were skinnier than they should have been. If I see him again (somehow), I'll check. InedibleHulk (talk) 17:20, 30 March 2014 (UTC)


 * When I said "far future" I was thinking in terms of medical advance, on example of HIV treatment that is 1/2 to 1 human life spans. (At the time it was detected it was even against the then current dogma that DNA is always translated into RNA and not otherwise. Now we do have effective means to prevent outbreak, and ways to really cure the infection are in the pipeline. 95.112.194.18 (talk) 19:39, 30 March 2014 (UTC)
 * The discoverers of Reverse transcriptase received the Nobel prize in 1975. HIV wasn't even discovered until 1983. 75.41.109.190 (talk) 23:23, 30 March 2014 (UTC)
 * Dogmas don't vanish instantly when disprooven. 93.132.153.222 (talk) 14:23, 31 March 2014 (UTC)


 * I was just thinking the other day about how utterly 'alien' and 'other' a frog's metamorphosis actually is. I mean, it's something that we all see and hear about from an early age, so I don't suppose that we tend to think too much about it - but all this growing of limbs and organs, absorbing some other parts and changing shape so dramatically while living free in the outside world is very strange indeed when compared to many of our fellow vertebrates. --Kurt Shaped Box (talk) 00:09, 31 March 2014 (UTC)


 * not as alien as you might think. Humans embryos not only resorb their tails, but use apoptosis in other crucial places, such as separating the fingers and unifying the halves of the palate. Wnt (talk) 00:38, 31 March 2014 (UTC)


 * When you consider what's going on inside a chrysalis, the tadpole-frog transformation seems pretty tame. Matt Deres (talk) 01:32, 31 March 2014 (UTC)


 * Things that happen inside a chrysalis, or to an embryo in the womb seem more 'unremarkable' to me. For some reason. --Kurt Shaped Box (talk) 21:20, 31 March 2014 (UTC)

need help on this
can any real scientists help me with this? no one here seems to know....

(I have removed the text of this 'question' as a possible copyvio. You can see the text here [//pastebin.com/idhreXds] from lines 640 to 695 i.e. the entirety of chapter 4 except the header. Nil Einne (talk) 04:04, 9 April 2014 (UTC)) 

— Preceding unsigned comment added by 86.6.96.72 (talk) 10:05, 30 March 2014 (UTC)


 * You are conflating a whole load of different phenomena which happen to be about time. In particular, there is no connection between the adjustments needed for the Gregorian calendar (which are simply because the period of the Earth's rotation on its axis doesn't divide the period of its rotation about the Sun; and the Julian approximation to it was not quite accurate enough) and relativistic effects. The idea that when you pass the speed of light you can travel backward in time is speculation, and unrelated to the twin paradox. And if you eat of the fruit of the tree of knowledge of good and evil, you will surely die --ColinFine (talk) 10:48, 30 March 2014 (UTC)


 * I missed the question amongst the nonsense. But the answer surely rests with the difference between Passover, Westerm easter and Eastern easter.  And a nanosecond is 10-9 seconds.  --DHeyward (talk) 11:54, 30 March 2014 (UTC)


 * As many physicists have pointed out, the distinction between past, present and future is only a stubbornly persistent illusion. Count Iblis (talk) 14:24, 30 March 2014 (UTC)


 * No doubt in the future we will be enlightened and no longer believe this illusion. :) And I think I can guess the species of the apple of knowledge, though I might be wrong. :)  Wnt (talk) 14:55, 30 March 2014 (UTC)


 * The Einstein clock thing is interesting though: apparently the time dilation from the different amounts of gravity under general relativity exactly cancels out the time dilation from the relative motion of the equatorial observer?  But... isn't that only from one point of view?  Hmmm... Wnt (talk) 15:03, 30 March 2014 (UTC)


 * That is obviously incorrect. For one thing, Earth's rotation is slowing down (see tidal acceleration).  Even if your statement were true today, it wouldn't be true next year, nor would it have been true in the past.  --Bowlhover (talk) 18:37, 30 March 2014 (UTC)


 * It only appears at first glance to be a surprising coincidental numerical relationship between Earth's gravity and its rotational velocity that would make there be no net time dilation between two clocks attached to the Earth's surface at the equator and a pole. But it's really not a coincidence at all.  The needed relationship between Earth's gravity and angular velocity at points along its surface is provided automatically by the Earth being in hydrostatic equilibrium, which isn't a particularly surprising phenomenon.  As the Earth's rotation slows down due to tidal acceleration, thereby reducing the time dilation effect due to rotational velocity, the Earth will automatically bulge out enough less at the equator due to maintaining hydrostatic equilibrium that the time dilation effect in the opposite direction due to gravity will be reduced by the same factor, resulting in there continuing to be no net time dilation.  Red Act (talk) 23:53, 31 March 2014 (UTC)

The OP needs these numerical corrections: The OP's interest is Calendar building which has always been the effort to fit integral (non-fractional) numbers of time periods to observed astronomical cycles, an effort which can be dated back over 2000 years ago when an unidentified Hellenistic craftsman chose to file teeth in bronze gearwheels to make an Antikithera mechanism. The little sense I can make of the OP's words "26,000 earth years around galaxy" is that it is an unclear reference to the Great Year or period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years, known to Plato who called it the "perfect year". Any new claim to have "drawn a replica watch of earth's correct time" employing Einstein's relativity would have to show verifiable calculations of Time dilation incorporating the Lorentz factor


 * $$\gamma = \frac{1}{\sqrt{1 - v^2/c^2}}$$ to impress any real scientist. Of course a Pendulum clock does run slower at the equator than the poles, and there have been several experimental confirmations that Einstein was right about time. 84.209.89.214 (talk) 18:35, 30 March 2014 (UTC)


 * To be clear, here's a note to Nature referencing that according to a 1966 paper Cocke has also shown that, in so far as the Earth assumes the shape of the geoid (and weak tidal fields can be neglected), its entire surface is an “equal time” surface. Also see  (not sure it's a good source, but it sounds coherent).  I haven't physically laid eyes on the original paper, but I think it's a settled point - and an interesting unity of special and general relativity.  If a rotating geoid actually lays out a frame of equal time passage, the shape of planets and stars is not just a funny happenstance of rotation and gravity, but says something more fundamental about the shape of spacetime. Wnt (talk) 00:52, 31 March 2014 (UTC)
 * I think it's because the time dilation factor is a function of the potential (in the weak-field approximation) and the geoid is an equipotential surface. That may mean that a quartz wristwatch will run at the same rate anywhere on the geoid, but not a pendulum clock, because the gravitational acceleration normal to an equipotential surface isn't generally constant. -- BenRG (talk) 04:19, 31 March 2014 (UTC)


 * Would it be very naughty to steer the OP toward timecube.com? —Tamfang (talk) 04:00, 31 March 2014 (UTC)
 * Better to steer him/her to a hospital, I think. Seriously. -- BenRG (talk) 04:19, 31 March 2014 (UTC)
 * May be the second last sentence here [//en.wikipedia.org/w/index.php?title=Wikipedia:Help_desk&diff=prev&oldid=601894369] is revealing. Then again, if you search that diff, it sounds like OP is the same as the person using the IP earlier this year [//en.wikipedia.org/w/index.php?title=John_W._Allen&diff=prev&oldid=592493302] so there are 2 hypotheses here. Nil Einne (talk) 12:52, 31 March 2014 (UTC)


 * The simple point here is that there is no particular reason why the amount of time the earth takes to travel around the sun (which is what we call a "year") should be some exact multiple of the time it takes to rotate around it's central axis (which is what we call a "day"). Actually, it would be rather surprising if that really happened - if the earth did happen to rotate exactly 365 times during one orbit, then that would be too much to be a coincidence and we'd have some rather serious explaining to do.   But it doesn't - the earth actually rotates 365.256363004 times in one year...a very inexact number!  It would be very painful for our calendars if the start of a new year gradually moved each year.  This year, it might be midnight on Dec 31st/Jan 1st - next year it would be about 6:09am (and 9.76 seconds) on Jan 1st, then on the following year, it would be a little after 12:18pm...and after just a few years, it would be into the following day - and after a few decades, our seasons would be noticably shifted relative to our calendar...and so on.  It would be a mess!


 * So what we actually do, is to pretend that the year is really 365 days long and wait until the "true" start of the year is off by an entire day - then stick a "leap" day into the calendar to fix it. This results in a leap day every 4 years - but even that isn't accurate enough to last over millenia - so to keep things straight we have to miss out a leap day every 100 years.  So, although 1900 is divisible by 4, it wasn't a leap year.  Even that isn't quite right, so every 400 years we break the 100 year rule and once again, we have a leap year...which is why the year 2000 was a leap year even though it was divisible by 100.


 * However, even that complicated rule isn't good enough because that would only work if the year was 365.2525 days long and (as I said) the true length is 365.256363004 days. So eventually, we'll have to add an extra leap day to get things back on track again.


 * So this is nothing to do with Einstein or any of the other complicated things you've been thinking about. It's merely that the Earth doesn't happen to rotate an exact number of times for each orbit.  Other planets have the same kind of problem, Mars has an orbital "year" that's 668.5991 martian "days" long - so people living on Mars would need a leap year every two years, an extra leap year on every year that ends with a '9' and another extra leap year every century.  On the other hand, Venus rotates very slowly - it has a "day" that's almost exactly half the length of it's "year" (a two-day year!) - but the rotation rate is also not exact - so Venusians would need to skip a day rather than adding one - and the anti-leap year would happen every 10 or so years.


 * Slightly complicating matters, the rotation rate of the Earth isn't exactly the same from one year to the next. That's taken care of by the introduction of a "leap second" once in a while.  The interval between them varies and it happens without much impact on people's daily lives.  Most people don't even know it happened.  The last one happened on June 30 2012.  But things like the position of stars in the sky and the time signals broadcast by GPS satellites would be impossible to track without this occasional "fix" to the system.


 * SteveBaker (talk) 13:01, 31 March 2014 (UTC)


 * I agree with nearly all of what Steve writes above, and his figure of 365.256363004 days is correct for the sidereal year that he accurately describes, but the aim of our leap year system is not to match this "year", or even to match the "mean tropical year" of 365.24219 days, but to match as closely as possible the average time between March equinoxes (thus keeping the spring equinox in the northern hemisphere as close as possible to March 21st), this "year" being approximately 365.2424 days, so we probably won't ever have to add the extra leap year that he mentions.   D b f i r s   17:10, 31 March 2014 (UTC)


 * A calendar based on the sidereal year of 365.256363004 Earth rotations will drift out of sync with the seasons at the rate of about one day every 72 years, so that's no good solution. Providing a link to Gregorian calendar instead of an unreferenced impromptu lecture gives readers a well written (grammatical) description of "our" calendar. This works best by inserting leap days before currently accumulating drift exceeds half a day, not an entire day. Both 365 and 365.256363004 are exact numbers but only the former is an integer; the latter is quoted from measurements by Simon et al. and such a precise value should not be quoted without noting the change in the mean solar day since the 19th century (it's increased by about 0.2ms/86400s). With that correction, I quote it as 365.256364. Although the following is not the observed case, I see no fundamental reason why some other liveable planet not unlike Earth should not have a synchronous orbit about its Sun i.e. its "year" period be a multiple of its own rotation "day" period, the only surprise then being the convenient simplicity of its inhabitants' timekeeping. 84.209.89.214 (talk) 20:02, 31 March 2014 (UTC)
 * As you suggest, it's not exactly 365.25 days per year, so the extra-day-every-four-years doesn't totally fix the problem. That's why we have the additional correction that years ending in 00 and not divisible by 400 are not leap years. ←Baseball Bugs What's up, Doc? carrots→ 20:37, 31 March 2014 (UTC)


 * If it hasn't been mentioned already, the Universal Time article gives a detailed explanation:

"* UT1 is the principal form of Universal Time. While conceptually it is mean solar time at 0° longitude, precise measurements of the Sun are difficult. Hence, it is computed from observations of distant quasars using long baseline interferometry, laser ranging of the Moon and artificial satellites, as well as the determination of GPS satellite orbits. UT1 is the same everywhere on Earth, and is proportional to the rotation angle of the Earth with respect to distant quasars, specifically, the International Celestial Reference Frame (ICRF), neglecting some small adjustments. The observations allow the determination of a measure of the Earth's angle with respect to the ICRF, called the Earth Rotation Angle (ERA, which serves as a modern replacement for Greenwich Mean Sidereal Time). UT1 is required to follow the relationship


 * ERA = 2π(0.7790572732640 + 1.00273781191135448Tu) radians
 * where Tu = (Julian UT1 date - 2451545.0)


 * UTC (Coordinated Universal Time) is an atomic timescale that approximates UT1. It is the international standard on which civil time is based. It ticks SI seconds, in step with TAI. It usually has 86,400 SI seconds per day but is kept within 0.9 seconds of UT1 by the introduction of occasional intercalary leap seconds., these leaps have always been positive (the days which contained a leap second were 86,401 seconds long). Whenever a level of accuracy better than one second is not required, UTC can be used as an approximation of UT1. The difference between UT1 and UTC is known as DUT1."

Count Iblis (talk) 17:40, 31 March 2014 (UTC)


 * Yes, Gregorian Equatorial Relativity is quite complicated. 5 working models have been constructed that replicate all of the factors that you bring up in your original question.  There is an article about the contraption found Here.  Take any available seat and solve for X. 186.93.131.249 (talk) 22:00, 31 March 2014 (UTC)
 * The above post by 186.93.131.249 containing misleading links is disruptive. 84.209.89.214 (talk) 23:08, 31 March 2014 (UTC)
 * It doesn't violate these guidelines :) Count Iblis (talk) 01:43, 1 April 2014 (UTC)
 * ...and the correct link for disruptive would be WP:VAND, "link vandalism". OTOH, this does not apply in its fullest strictness to talk pages. (WP:RD is organized like a talk page.) ooze 06:06, 1 April 2014 (UTC)

Free floating arctic ice cap - what happens?


Graphics like the one at show a sometimes much reduced polar ice cap during the summer, which remains attached to Greenland and the Canadian Archipelago. Suppose that global warming this or some future summer sunders this connection completely so that the entire polar ice cap is untethered to any land. Does it


 * (a) act the same as ever, since land so distant can't possibly transmit a force through cracked and moving ice for hundreds of miles?


 * (b) start to randomly drift south like any iceberg, some of which are very large after all?

I have this weird horror-movie scenario of a vast but much reduced raft of ice, loaded with starving, desperate polar bears, abruptly washing up on the shores of Scotland, but hopefully that's just stupid. :) Wnt (talk) 15:24, 30 March 2014 (UTC)


 * Some scientists are predicting the Arctic ice will entirely disappear by 2015. They do have a word for ice that attaches to land but I forget what it is; one of the implications of it becoming unattached is more Arctic methane being released. Raquel Baranow (talk) 15:46, 30 March 2014 (UTC)


 * Did you mean fast ice? CambridgeBayWeather (talk) 01:08, 31 March 2014 (UTC)

A better indicator is aectic ice volume. It's very thick along northern canada. The ice cap isn't going away any time soon. The same cranks that told us there would be no snow in winter in the U.S. by 2010 like to scare up the ice stories. We will know when there is a believable ice free summer when shipping companies and cruise lines start offering northwest passage trips. As for ice, it flows constantly and is quite variable in direction, volume and speed. Polar bear habitat and numbers are not in danger. --DHeyward (talk) 04:52, 31 March 2014 (UTC)


 * I've added a link to a time lapse of the ice that is in the article. I'm not entirely sure how to interpret it though.  Definitely on the year by year time scale the ice seems to flow around pretty freely; it is "gooey" and seems to stick to Canada.  Looking at it I almost wonder if winds keep it pushed over to the Canadian side so that no matter how little is present it always ends up there.  But at the same time... there are parts of westernmost Canada where a band of open water cuts it off, and then it really gets moving fast; and in the 2010 photos that band of open water seems to cut halfway across.  So as dynamic as it is in slow motion, I'm still not sure it wouldn't get much more dynamic in a short term. Wnt (talk) 09:35, 31 March 2014 (UTC)
 * It's pretty difficult to interpret density/area because of things like melt puddles on top of ice versus open ocean. And yes, it flows a lot.  Sometimes out of the Bering sea and sometimes out into the North Atlantic.  Here's what the ice thickness is like.  --DHeyward (talk) 21:15, 31 March 2014 (UTC)
 * Thanks - good link! I truncated the stuff after the last / for some more data, such as an animation .  There's probably a lot more on there somewhere.  Anyway, looking at this, the thickness pattern, the way the animations move, the wind directions over time, I get the feeling there's a continuous tendency of wind to go over the pole toward the Canadian/Greenland regions where the ice tends to stick, which is pushing the ice tight against the land and stacking it up.  Until something changes that, I'm getting the feeling that even in a massive melt scenario, the Canadian edge will be the last to go. Wnt (talk) 21:00, 2 April 2014 (UTC)

Hbv indirect transmission
Are there any cases of HBV being transmitted through indirect means such as through contact between breaks in the skin and contaminated surfaces, in particular wet surfaces such as swimming pools? — Preceding unsigned comment added by 82.132.216.12 (talk) 18:13, 30 March 2014 (UTC)
 * This link from the American Cancer Society] says you can't catch HBV from surfaces like toilet seats, swimming pools or hot tubs, or even from sharing food utensils. Vespine (talk) 22:39, 30 March 2014 (UTC)

realization of the pleura...
I've already a week looking for something that will help me to understand what is it the "pleura" but till now I've no found nothing. Of course, I've read the article here too. I would like to know any realization or any explanation that will help me to understand what is this membrane, how does it work, and what does it look like... I looked for in YouTube but I didn't find something helpful for me. Here is the last resort. 5.28.159.100 (talk) 22:07, 30 March 2014 (UTC)
 * Did you click through to serous membrane? Mesothelium? Epithelium? Tissue? Might help. InedibleHulk (talk) 22:15, 30 March 2014 (UTC)

There is a simple description (better than our own article) and diagrams here. It says "The pleural lining has two layers: the visceral (inner) layer is next to the lung and the parietal (outer) layer lines the chest wall. The pleura produces fluid that lubricates the space between the two layers, this allows the two layers to slide comfortably over each other as we breathe in and out". Anyone who has had inflammation of the pleura (See:pleurisy) will tell you that it makes breathing very painful - which illustrates what it does when it is working properly. Richerman   (talk) 22:33, 30 March 2014 (UTC)


 * A good place to start is our article on the Pleural cavity. RomanSpa (talk) 22:34, 30 March 2014 (UTC)


 * As pleura redirects there I'm assuming that's the article the OP has read. Richerman    (talk) 22:39, 30 March 2014 (UTC)