Wikipedia:Reference desk/Archives/Science/2013 April 19

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April 19

Unknown salt water animal

Does anybody know of a salt water creature that is about the size of a coffee bean, is coloured red and black, has fins and lives in the Arctic. I'm not sure how widespread this is but it has been observed on the south coast of Victoria Island (Canada). I've never seen one so I can't really expand on the description. CambridgeBayWeather (talk) 07:12, 19 April 2013 (UTC)

It turns out I missed part of the description. It isn't red and black but clear like a jellyfish. The colouration is inside and the red is what appears to be blood and there is a black spot. Apparently asking a local man who has spent most of his life hunting and fishing was no help as he had never heard of them either. CambridgeBayWeather (talk) 08:00, 19 April 2013 (UTC)

That's not much to go on. Maybe some sort of marine cladoceran? (See the picture of Evadne spinifera in the article. It's too small [1–1.35 mm] to match your description; but there are larger species, though most of the order's species live in fresh water.) Or some type of copepod, many of which live in arctic climes? Deor (talk) 11:35, 19 April 2013 (UTC)

Thanks. I realise that it is unlikely I'm going to get an answer but I thought it worth a try. I did get a bit more information. It turns out there was a range of sizes with the coffee bean being an average but some were as big as 2-3 cm while others were smaller. The fins resembled those of Batoidea. I'm now wondering if it may have been a juvenile fish of some sort given the rage of sizes. CambridgeBayWeather (talk) 16:17, 19 April 2013 (UTC)

Yes, I was going to suggest a juvenile stage, too. They often lack pigment, except for red blood and a black spot. For example, here's a tadpole that roughly matches what you described, although it's starting to get some body pigment: [1]. (I'm not suggesting that what you describe actually is a tadpole, just using this as a juvenile example.) StuRat (talk) 17:27, 19 April 2013 (UTC)

Saltwater tadpoles are called larvaceans. μηδείς (talk) 17:35, 19 April 2013 (UTC)

Clione limacina? Oda Mari (talk) 19:43, 19 April 2013 (UTC)

And that's what it was. Thanks very much. Strange that I've never seen them before or that they only seem to occur in a small area. CambridgeBayWeather (talk) 02:41, 20 April 2013 (UTC)

Resolved

recognizing a flower

anyone can identify me?

Hi, I took this picture in East Talpiot, Jerusalem. Does anyone know which flower it is? --SuperJew (talk) 09:17, 19 April 2013 (UTC)

Without a doubt this is an aloe, but there are many species of aloes and some time will be needed in sifting through the long list to find the identity. Richard Avery (talk) 09:41, 19 April 2013 (UTC)

could it be Aloe vera? --SuperJew (talk) 11:22, 19 April 2013 (UTC)

Jerusalem Tulipusis?165.212.189.187 (talk) 14:29, 19 April 2013 (UTC)

• Looks like Aloe brevifolia, see this picture. μηδείς (talk) 17:32, 19 April 2013 (UTC)

• Hmm, good match on the flower, not so sure on the leaves. Richard Avery (talk) 19:27, 19 April 2013 (UTC)

Agreed they look large, but I believe the flower we are seeing here is a spike from a different plant from the one whose leaves are visible, making size judgment difficult. The OP can simply google image "orange aloe flower". μηδείς (talk) 16:11, 20 April 2013 (UTC)

growing a hair in a petri dish

if you could remove a human hair complete with hair follicle, could you then grow the hair in a petri dish? Horatio Snickers (talk) 10:56, 19 April 2013 (UTC)

Yes - according to our Hair follicle article, people have been doing this since the 1980's. Evidently, some researchers have gone even one step beyond that - according to THIS, scientists at Berlin Technical University in Germany have grown artificial hair follicles from stem cells. If they can keep those alive in-vitro, then I would expect there to be no problems in doing it with follicles taken from a human scalp. There are a lot of links relating to this subject - I suggest you google for "grow hair in-vitro". There is more information in Hair_follicle#Hair_follicles_in_hair_restoration. SteveBaker (talk) 12:12, 19 April 2013 (UTC)

The "Horse hair snake" myth is that a fresh horse hair placed in water will become alive and swim around like a snake, when what is seen is really a long, thin worm. This would be something to control for in trying to "grow" a human hair in growth medium in home experimentation. (Note: I tried this when i was visiting Granddad's farm when I was 5, and it just stayed a horse hair).. Edison (talk) 18:50, 20 April 2013 (UTC)

What is the optimal x-ray balance for sterilization?

How does one figure out the optimal balance between x-ray voltage (kV) and current (mA) to sterilize an object like a shoe ? the radiation has to penetrate leather, it has to have enough high probability to hit the virus, and then to actually kill it. Electron9 (talk) 12:23, 19 April 2013 (UTC)

I don't know how this is really calculated (or experimentally determined) - but one way to do it would be to put a sheet of photographic material beneath the shoe - then adjust the X-ray parameters until "sufficient" radiation to kill whatever it is shows up on the sheet beneath it. Food_irradiation#Dosimetry seems to suggest that this is (essentially) what is done when irradiating food - they use dosimeters to sample the amount of radiation at key points in a load of food.

Incidentally, current and voltage aren't the only parameters - time is another. A short burst of X-rays would be less likely to sterilize something than a long burst. It would also matter whether the shoe could be rotated slowly as it passes through the X-ray beam...shoes sometimes have metal components that would effectively block the X-rays giving organisms a place to hide even from very large doses. In many cases (eg in food sterilization), it may not be necessary to kill 100% of organisms - merely enough to prevent a dangerous level of them from building up before the desired "Sell by" date.

Also, from what I can see, X-rays are used to kill bacteria and mold spores - but not viruses. I could be wrong about that - but viruses don't seem to be mentioned in any studies I looked at.

SteveBaker (talk) 12:52, 19 April 2013 (UTC)

Probably it's not mentioned because it doesn't matter -- viruses can only reproduce in living cells, and their spores generally don't last very long in nonliving matter either. Ionizing radiation should certainly be capable of disrupting the DNA of viruses. Looie496 (talk) 17:11, 19 April 2013 (UTC)

Suppose one powers a rectifier tube like 1B3GT that can sustain 33 kV and 1.1 mA (36.3 W) and most food irradiation seems to be specified to 10 kGy. The aperture is also something to take into account. So how long does it need to be on in order to irradiate sufficiently? Electron9 (talk) 19:12, 19 April 2013 (UTC)

This is an interesting thought experiment - a very simple application that should remind us that radiation biology is more complicated than you'd think. The key articles are absorbed dose, at the hub of the concepts, gray (unit), in J/kg, which can represent either the kerma (physics) emitted from a source, or the absorbed dose. Anyway, 1 kV * 1 mA = 1 W, so the tube above nominally would produce 33*1.1 = 36.3W as stated. Take that times, say, a 1-second emission and you have 36.3 J. If all of this goes to X-rays (certainly not true; you'd have to measure) I think you'd have a kerma of 36.3 J/whatever the tube weighs, which seems pointless; more interesting is that if you can say for sure that the target shoe receives all the radiation (definitely not true) then the quarter-kilogram or so is getting a dose of 120 J/kg or so, which would be a bit more than typical radiation therapy, and maybe 100,000 times more than a chest X-ray, if I didn't foul up somewhere badly. But of course the whole point of X-rays is they don't stop for the shoe, and you'll only get a fraction of that.

Where things get really sticky is that you have to somehow get from Gray (unit) to Sievert, which is a really goofily arbitrary semi-empirical estimate of how much damage radiation does to different kinds of tissue. What kind of tissue is a virus? How much dose does it take to kill it? Radiation_sterilization#Ionizing_Radiation_Sterilization gives some indication that for routine use you only need about 6 Euro cents worth of electricity to sterilize a cubic meter of material, but of course the full efficiency of that doesn't go to the shoe because most of the radiation is wasted on your neighbor's kids ten meters downbeam. I should also note that according to that article 'material properties can be changed' by gamma rays (maybe not soft X-rays so much?) so you would have to be fairly careful not to damage your shoe after all.

On the plus side, at least you're not planning to eat it. :) Wnt (talk) 15:28, 21 April 2013 (UTC)

It may have been better if Wnt had not posted the above. I don't know how much electricity you get in Europe for 6 cents, but in my country you don't get 36.3 J, you get about 1.5 MJ - 41,000 times as much. The most important technical fact to note here is that the OP proposes to use a 1B3GT television EHT rectifier as his X-ray tube. This is designed to convert AC into DC in the 15 to 18 kV range, and has an electrode structure that is completely stupid for producing X-rays - in fact it was intentionally designed to minimise X-ray production. The anode is top hat shaped and completely encloses the cathode. To the X-rays will be produced inside the internal nickel/steel "top-hat" and have to penetrate it. They then have to penetrate the glass, which for these types of tube was normally lead-loaded. So, only a tiny fraction of the X-rays produced (and calculable from the standard X-ray equation) will get out of the tube, but we have absolutely no idea what that fraction will be, and absolutely no idea how much that fraction will change as the tube heats up. We also have no idea about the shape of the emission, except to say it certainly will not be a nice neat spherical emitter like a small light globe, nor will it be a nice simple single fan-shaped beam.

I mentioned above the phrase most important "technical" fact. The real most important thing of course is that fooling around with X-rays is stupid and dangerous, which a high risk of causing deep burns that won't heal, blindness (should a stray undetected beam enter your eye, it may result in no pain but blindness later), and a significant risk of cancer. Don't do it, unless you know so much about it, and have all the right instrumentation, that you would have absolutely no need to post such a question on this forum.

Ratbone 121.221.230.118 (talk) 00:32, 22 April 2013 (UTC)

Well, you've got a point - at the same time, it's the folks like him who vindicate the human dignity of tens of thousands of schizophrenics who believe their neighbors are targeting them with dangerous rays. B) Stir in the possibility that somebody somewhere is crazy enough to try such an attack and maybe you have paranoid people detecting when North Korean drones are actually flying overhead and doing it to them. Who knows? All I know is that working out a BOTE understanding of rads and rems and Grays and Sieverts is more likely to protect than harm in the long run. But enough of ethics, back to the interesting part:

A factor of 41,000 isn't that far off, because that's for a cubic meter, and a shoe is under a cubic decimeter of actual material. The remaining factor of roughly 41 matches the various inefficiencies. The yield of the tube can be measured, roughly, by figuring out how much heat is produced by the tube and if any significant amount is missing; obviously it is not optimal, but irradiation with a proper source is so fast and cheap that even a very bad source could actually do the task - subject to the caveat that yes, obviously, enough X-rays to sterilize something is just millions of times more than you want to be exposed to. Wnt (talk) 21:47, 23 April 2013 (UTC)

Wnt, I assume what you've written is meant as some kind of joke - but we don't know what the OP or any other fool who may be inspired to try it will think. The various inefficiencies cannot be estimated as something like a factor of 41. It will be a lot less than that - but I woudn't even hazard a wild guess as to the order of magnitude, because, as I said, the design of TV rectifier tubes is a design intended to be self-shielding - TV sets are not designed to emit X-rays. Estimating the X-ray output be measuring the heat output and comparing it with electrical input is most certainly NOT possible. If (say) the the accuracy of measuring the electrical input is 2% (a very good but realistic achievement for a home experiment with ordinary commercial instruments), about the best that the heat output is measured to an accuracy of 10% (a very good achievment in a home experiment), you are likely to get heat output apparently anywhere from 88% to 112% of electrical input - clearly totally useless if the X-ray output is orders of magnitude lower.

A most important factor that I mentioned before, is that the X-radiation from such a tube will not be a simple fan beam - it will comprise various beams at widely varing strengths coming out at odd directions. It is more than likely that any home experimenter would, in order to get a decent exposure on a film, will also be subject to another beam he doesn't know about being strong enough and on long enough to seriously hurt him. Shielding the tube with lead is perhaps an obvious thing to do, but he cannot know how to properly do that or how much lead to use.

Ratbone 58.164.237.20 (talk) 23:14, 23 April 2013 (UTC)

What are we doing when we compose?

Possibly a weird question, but I'm sure a couple of people here know where to look. What I'm looking for is recommended reading that will help me understand this idea.

What are we actually doing, or what is our brain actually doing, when we compose music? I can sort of see, when we compose songs, that we start with the rhythm and tones of the spoken word, and then play with those in a way that we call music. And I can sort of see, when we replicate sounds we've heard such as bird song or mechanical noise and play with those, what we're doing there. But when we get an original bit of music just sort of appear in our heads, and can continue to play with that to express mood (for example) or just to expand it and make it interesting, what are we actually doing? Or when we want to compose a fresh piece of music, not based on words, but based on emotion or an idea, what are we actually doing? 86.161.209.128 (talk) 12:40, 19 April 2013 (UTC)

Our Musical composition article talks about this at length - and links to many more articles that contain relevant material. SteveBaker (talk) 12:55, 19 April 2013 (UTC)

Hey mon! We be jammin'! See jam_session 196.214.78.114 (talk) 13:13, 19 April 2013 (UTC)

I wrote a toy algorithm a few years ago, implemented in Java, to compose music. I pre-programmed several chords and preprogrammed several chord-transitions, so the algorithm had a lot of prior knowledge of music (or at least, of western tonal-scale music and conventional chord transitions). I used a random-number generator to provide pseudorandom beats for the melody for syncopation; and a non-random sequence to play chords for the harmony. (This algorithm was an experiment in an extremist interpretation of structure in music theory). I had hoped that my toy program would be able to jam with me, and by tuning or postprocessing the random number sequences, that I could teach it to play jazz improv; but it always created very pleasant, simple ambient music in the style of a carousel or music-box. You can probably find better incarnations of melody synthesis algorithms with additional tunable parameters; these are computer programs intended to mimic human creativity. While my program didn't create anything very spectacularly symphonic, it gave me a lot of insights into the ways that musical parameterization affects the final "experience." And it gave me a lot of insight into the degree to which the final product was limited or defined by the note and chord structures that I had built into the algorithm.

I'll take a look through my bookshelf, because I'm sure I have some music theory books that explain "structure" in a more structured way... if your interest is in the actual sounds and waveforms, rather than in song composition, Physical and Audio Sgnal Processing talks about the theory and practice of synthesizing realistic-sounding musical instruments.

Here are some course-notes on symbolic analysis of music: Computational Music Analysis. Nimur (talk) 13:30, 19 April 2013 (UTC)

Certainly there are plenty of computer-based composition systems that can produce acceptable and original music. I've also played around with Markov-chain systems - fairly simple C++ programs that can be fed large bodies of music (in MIDI-file format in my case) and which can then generate unending quantities of entirely new music in that style. My experience (like yours) is that they fail to produce anything very memorable or moving - but it's pleasant enough for background music.

But I've never found myself humming any of their compositions to myself.

What I take from this is that the actual mechanics of composing music is something that can be substantially rule-based (although the composer may be unaware of the rules and has somehow subconsciously deduced them - much as a two year old child learns how to form grammatically correct sentences just by listening to their parents talking). However, producing memorable, moving, emotional music seems to require a human spark that's not easy to capture or teach. That is clearly something that cannot be taught - or else there wouldn't be just a few handfuls of composers who are thought to be so much better than the rest of us.

The analogy with spoken language is probably no accident. Our brains are wired to do this amazing trick of learning to understand and produce spoken language with absolutely no formal training and no input other than odd snippets of language we can pick up as a child.

It seems highly likely that this same mechanism is what allows us to understand and compose music just by listening to music we hear.

However, not every person who learns to converse fluidly in their native language ever becomes a poet or a novelist - or an empassioned public speaker...which probably explains while everyone can probably be trained to compose music, it likely takes someone with more specific skills to produce music that's memorable and moving.

SteveBaker (talk) 14:02, 19 April 2013 (UTC)

Where I can find these programs that can compose music? 190.60.93.218 (talk) 16:48, 19 April 2013 (UTC)

See Algorithmic composition. Red Act (talk) 17:26, 19 April 2013 (UTC)

Thanks for all this, but I don't think I can have been clear enough (because I didn't fully understand what I was asking for), but I think I'm looking for more of a neuroscience answer? Although I think the algorithm answers are probably also useful, if I can understand them properly. 86.161.209.128 (talk) 19:49, 19 April 2013 (UTC)

We have quite a lengthy article on the cognitive neuroscience of music, and several other related articles. I'm not sure how much they'll tell you, though -- we really don't understand brain activity on the level of composition algorithms. The book Musicophilia, by Oliver Sacks, might also interest you, although it is mainly a collection of anecdotes. Looie496 (talk) 21:01, 19 April 2013 (UTC)

There's no simple answer to this question, since music composition takes many forms and differs among people. Even within a single person there's a big difference between periods of creative inspiration and periods of editing and tweaking. Beethoven comes to mind as someone known for spending a lot of time working out ideas over and over, editing and revising. Sometimes the process of creating the raw material for a work of music goes quickly and easily, like for Richard Strauss's An Alpine Symphony (he described the process as being "just as a cow gives milk"). This was then followed by months of orchestration and editing. And all this was preceded by many years of sketches and abandoned pieces using the ideas later incorporated into An Alpine Symphony. These various processes are quite different cognitively. Then there's issues of musical differences. I would expect the composing of a complex Bach-like fugue would necessarily be quite different from, well, Strauss's Alpine Symphony, which was intended to musical depict scenes and events. There's some neuroscience type info at creativity. And there's plenty of books and articles about the neuroscience of music (like This Is Your Brain On Music), although mostly about listening to music rather than composing per se. Pfly (talk) 16:37, 20 April 2013 (UTC)

What is (or was) the neutretto?

In various outdated popular books and articles, one finds references to a sub-atomic article called the neutretto. According to Wikipedia, the neutretto is a historical name for the muon neutrino. According to this book, the neutretto is an older name for the neutral pion. Yet a third neutretto, apparently, is that mentioned in several newspaper articles from 1948, as having being ruled out after being hypothesized in 1947 to explain a mass defect in heavy meson (i. e. pion) decays.

What was the original "neutretto hypothesis"? Was it conclusively ruled out, or was the 1948 "exclusion" premature, and the neutretto lives on as either the muon-neutrino or the neutral pion?

הסרפד (call me Hasirpad) (formerly R——bo) 18:49, 19 April 2013 (UTC)

The neutretto, as far as I can tell, was a hypothetical particle with neutral charge and substantial mass, proposed in 1938 in this paper in order to explain the mutual attraction between protons (see p. 170). It is now believed that the strong force is responsible for that attraction, and that no such particle as the neutretto exists. The term was frequently used in the following years, though, and perhaps not always with exactly the same meaning. It always meant a neutral particle with nonzero rest mass, but other properties may have varied. Looie496 (talk) 20:56, 19 April 2013 (UTC)

The "heavy electrons" and "neutrettos" in that paper are bosons that are supposed to mediate the nuclear force, which makes them clear precursors to the charged and neutral pions. Here's a paper (surprisingly recent) that unambiguously uses "neutretto" to refer to muon neutrinos -- BenRG 01:24, 20 April 2013 (UTC)

Thank you both, but neither of these "neutrettos" correspond to the "outruled" 1948 neutretto. (One thing seems clear though: neutretto was a generic name for neutral particles less massive than the neutron.) הסרפד (call me Hasirpad) (formerly R——bo) 03:47, 21 April 2013 (UTC)

Note that here (p. 120) a neutretto is defined as any neutral particle who mass is greater than that of the electron and less than that of the of the neutron. (Though the muon-neutrino does not fit this description.)

The neutretto I am interested in is this one: [2]. The description fits a muon-neutrino, but not the fact that its existence is described as excluded. הסרפד (call me Hasirpad) (formerly R——bo) 18:42, 21 April 2013 (UTC)

Balloon Framing

What is the citation for the line drawing image of balloon framing at http://en.wikipedia.org/wiki/Balloon_framing#Balloon_framing? Is it in the public domain? Thanks. — Preceding unsigned comment added by Abqwriter (talk • contribs) 20:23, 19 April 2013 (UTC)

Just click on the drawing and you'll find out -- you're taken to the page for that file, which contains information about its copyright status. Looie496 (talk) 21:03, 19 April 2013 (UTC)

Dam seepage

Does more water discharge/seepage under a dam effect its stability? — Preceding unsigned comment added by 99.146.124.35 (talk) 23:06, 19 April 2013 (UTC)

Yes, seepage tends to cause erosion and thus undermine a dam. This can happen quite quickly with an unreinforced earthen dam (note that our article is about reinforced earthen dams), and much more slowly in a concrete dam. StuRat (talk) 23:19, 19 April 2013 (UTC)

The St. Francis Dam disaster was caused by the dam being undermined by seepage. It was a concrete dam. --Jayron32 00:36, 20 April 2013 (UTC)

Also the Malpasset Dam. 24.23.196.85 (talk) 03:07, 20 April 2013 (UTC)

They're about to spend a ton of money on my local Isabella Dam because of a combination of seepage, construction errors in the late '40s, greater protection against a 100 year flood (won't do jack about a 200 year flood, but we already had two of those in the last century), and a recently analyzed Kern Canyon Fault. A lot of people still seem to think storing water in giant puddles rather than in underground aquifers is a good idea. </soapbox> --jpgordon^{::==( o )} 14:44, 21 April 2013 (UTC)

If you've had two 200 year floods in the last century, I'd question the estimate of the 200 year flood level. It's possible you were just unlucky, but unlikely. Also, the estimates may have been correct, initially, but now need to be revised as a result of global climate change. StuRat (talk) 17:43, 21 April 2013 (UTC)

Rather the opposite here -- global climate change has led to considerably less snow in the Sierra Nevada, in particular on Mount Whitney, which is the primary source of the Kern River's water. This is a case of the USACE wanting to take on a billion dollar project where a quarter billion would likely suffice. They need to fix the seepage; they don't need to raise the dam 16 feet. --jpgordon^{::==( o )} 20:30, 21 April 2013 (UTC)