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

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July 11

aerospace

how to be an aerospace engineer ???? — Preceding unsigned comment added by Sourabh007sak (talk • contribs) 03:13, 11 July 2011 (UTC)

Go to college/university, and study aerospace engineering, which is a subdiscipline of mechanical engineering. --Jayron32 03:15, 11 July 2011 (UTC)

Be sure to heavily emphasize the study of computers, electronics, and software, which are now a significant component of modern aerospace design. Also heavily emphasize the pure sciences, such as physics, chemistry, and mathematics. Aerospace engineering is very broad, so investigate some of its subdisciplines: fluid dynamics; material science; propulsion engineering; control theory; and of course the more broad topics that apply to large engineering projects, such as optimization and operations research. Nimur (talk) 18:35, 11 July 2011 (UTC)

Start by making paper airplanes. StuRat (talk) 17:25, 11 July 2011 (UTC)

Be financially prepared to be laid off when the aerospace project is finished. I recall reading about a former aerospace engineer laid off when the Apollo program was done. He was one of the world's experts on electrostatic.electromagnetic shielding of spacecraft, and the only job he could find was driving a cab. NASA just cycled down from 5000 to 1000 employees at Cape Canaveral. Edison (talk) 19:33, 11 July 2011 (UTC)

A lot of people with an aerospace engineering degree work in a job which is more general engineering. I don't think that fellow would have needed to drive a cab if he would have asked Caterpillar or DuPont if they were interested in a engineer (not specifically a spacecraft static specialist position). Googlemeister (talk) 20:50, 11 July 2011 (UTC)

The Cambrian explosion

Hello.

I've noticed that a lot of scientific papers of the late 1980s and early 1990s spoke of "dozens" of extinct animal phyla that originated during the Cambrian explosion and have since become extinct. On the other hand, recent scientific literature has declared [almost] all of these phyla to be invalid and has reclassified their members into extant phyla.

I would like to know whether this shift in thinking is the consequence of new palaeontological data becoming available, or it is merely an attempt by scientists to make the phylogeny of the Cambrian fauna appear simpler than it really was.

Is the reclassification of members of these "extinct" phyla into extant phyla supported by the data available in the fossil record? If so, what data has become available since the early 1990s? Thank you very much. Leptictidium (mt) 06:03, 11 July 2011 (UTC)

It sounds like you are doubting the integrity of the scientists that did the more recent classifications. Do you have any reason for that? Dauto (talk) 08:52, 11 July 2011 (UTC)

I think the major differences are that cladistics has, more-or-less, taken over, and that we can now use anatomical, genetic and protein markers to figure out phylogenetic trees to get a much better understanding of the tree of life as a whole. Also, we have additional fossil finds that connect different animals and groupings - see e.g. the story of Anomalocaris, which turned from 3 animals into one. --Stephan Schulz (talk) 09:59, 11 July 2011 (UTC)

A large part of what we know about the Cambrian explosion has come from studying the fossils of the Burgess Shale. One of the proponents of the "many phyla" interpretation was Stephen Jay Gould, whose book Wonderful Life summarises the early Burgess Shale research. An alternative and more "conservative" interpretation, based around convergent evolution, has been championed by Simon Conway Morris. The whole area is the subject of ongoing research. Gandalf61 (talk) 10:07, 11 July 2011 (UTC)

Are there any specific reasons the "many phyla" interpretation has lost favour in the last couple of decades? Leptictidium (mt) 10:56, 11 July 2011 (UTC)

I'm not very familiar with the Cambrian explosion fauna, but it could simply be that Stephen Jay Gould's death has removed the most vocal proponent of the hypothesis. Gould literally wrote the book popularizing the Burgess Shale fauna and was also a supporter of what he called "bushiness" of taxonomic families (see Full House for more). Matt Deres (talk) 16:06, 11 July 2011 (UTC)

I'm not convinced that Gould, while extraordinary in popularizing his ideas, was as solid with science. I don't want to say "mountain out of a molehill," but that phrase came to mind. Imagine Reason (talk) 00:02, 13 July 2011 (UTC)

It is important to realize that all of our commonly used classification levels (kingdom, phylum, class, etc) are basically artificial. Evolution shows us tree structures with hundreds of branch points if not more -- picking out one particular branch point and calling it the "phylum" level is rather arbitrary. There is tremendous dispute nowadays about the best way to do that. Even when the evolutionary history of a species is well understood (which is often not the case), it may be quite difficult to map it onto the very limited set of levels that Linnaeus defined. Looie496 (talk) 22:03, 11 July 2011 (UTC)

As we get more details from fossils, the most likely classifications by lineage change. 99.24.223.58 (talk) 23:48, 11 July 2011 (UTC)

Bear in mind that more and more Vendian fossils have come out, giving more reason to suspect a longer timeline. Wnt (talk) 05:31, 12 July 2011 (UTC)

Interesting! Please elaborate. 99.24.223.58 (talk) 18:39, 13 July 2011 (UTC)

Swimming in Jello

I remember a that some university in the Midwest (maybe Minnesota) conducted a study where they compared swimming in water versus various viscous liquids. I think they found that the speeds where the same. Does anyone know the study that I am talking about? I have a reference question (talk) 11:10, 11 July 2011 (UTC)

http://www.nature.com/news/2004/040920/full/news040920-2.html --Sean 13:42, 11 July 2011 (UTC)

Mythbusters also tackled the question in their Swimming in Syrup episode, and came to the same conclusion as the University of Minnesota team, i.e., that swimming in a liquid that was about the same viscosity as syrup, i.e., a bit more viscous than water, resulted in a speed that was as fast as swimming through water, within their judgement of experimental error. However, swimming in a liquid that was much more viscous than water resulted in a speed that was much (28%) slower than swimming through water. Red Act (talk) 13:56, 11 July 2011 (UTC)

I read the above with disbelief until I realised that the syrup was the less-viscous form, not the Golden syrup that immediately springs to mind for readers in the UK. Has anyone ever tried swimming in treacle? Dbfirs 11:52, 12 July 2011 (UTC)

In one sense, half of everyone swam in a liquid more viscous than water when the sperm cell used its flagellum to propel itself through the cervical mucus, a mixture of water (90%) and glycerol in the female reproductive tract. Cuddlyable3 (talk) 10:11, 13 July 2011 (UTC)

what is the palm theory？

what is the palm theory？how to use it？ — Preceding unsigned comment added by Wenwenlover07 (talk • contribs) 12:09, 11 July 2011 (UTC)

Do you mean the Palm–Khintchine theorem? Also, why do you type strange question marks? --Jayron32 12:19, 11 July 2011 (UTC)

There's nothing particularly strange about the question mark. It's just the 'fullwidth' form ([1]) which likely is the default on a Chinese-language keyboard setup, for compatibility with the wider Chinese glyphs: [2]. TenOfAllTrades(talk) 13:13, 11 July 2011 (UTC)

They certainly look strange to me, since that font apparently isn't supported on my PC. StuRat (talk) 17:22, 11 July 2011 (UTC)

There is a literature on Palm theory, but it is very esoteric mathematical stuff -- the study of so-called "Palm measures". Looie496 (talk) 21:56, 11 July 2011 (UTC)

See Point process and Chapter 13 of [3]. 99.24.223.58 (talk) 00:23, 12 July 2011 (UTC)

Breeder reactor

They apparantly make more nuclear fuel than what you put in them. My question is, where does the extra energy come from? If they truely created more fuel, wouldnt they be able to both run for ever and supply fuel for other reactors, so that no new nuclear fuel was wever needed. 92.24.187.78 (talk) 14:19, 11 July 2011 (UTC)

It's not so much that they create more energy than is contained in the starting materials; you're quite right that that would be impossible. Rather, the breeder reaction allows the conversion of stable, heavy nuclei (so-called fertile material) into fissile isotopes which can be used in a reactor. Only a small initial investment of fissile material is required as a source of neutrons to start the breeder process, after that it's theoretically possible to fuel the whole thing with the freshly-transmuted isotopes.

Make no mistake, the breeder reactor is 'consuming' those fertile isotopes; in principle their supply is finite, and eventually even a breeder reactor would run out of fuel. In practice, the fertile isotopes are enormously abundant naturally (at least compared to the naturally-occurring fissile isotopes), and readily-available supplies would last for thousands of years. TenOfAllTrades(talk) 14:43, 11 July 2011 (UTC)

To elaborate a little bit:

The nuclear reactions in a reactor are generated by the fissioning of fissile isotopes. Fissile isotopes are pretty rare in nature. Far more abundant are fertile isotopes, which, after absorbing a neutron, eventually become fissile isotopes.

So let us imagine our reactor fuel that contains 5% fissile isotopes (U-235, in this case), and 95% fertile isotopes (U-238, for example). While the fissile isotopes burn up, a large number of neutrons are generated. Some of these will deposit in the fertile isotopes, and create more fissile isotopes. In this case, U-238 absorbs a neutron and eventually, after a few days of decaying, becomes Pu-239, which is fissile.

Then we use a big chemical processing plant (see nuclear reprocessing) to extract all of the new fissile isotopes from the used ("spent") fuel, and use that to create new fuel.

As for relative abundance, consider the case of uranium, where less than 1% of all uranium in the world is U-235, and the rest is U-238. (There are other fertile isotopes as well beyond uranium-238.) Now if you could turn all of that U-238 into Pu-239, using just some of that initial less than 1% of U-235, that means you'd have nearly 100X as much nuclear fuel as there is without breeding. In reality the percentages are not necessarily that high (you lose some of the material while reprocessing, and the inside of a reactor is a complicated environment), but it's still a pretty impressive amount (the number our reprocessing article gives is +60X). You're not creating "new energy" so much as using a small amount of "start-up" energy to convert the other isotopes into forms that would be useful for producing energy. (U-238, as found in the wild, is not useful for producing energy — it needs to be put into a reactor and slightly changed before that is the case.) --Mr.98 (talk) 15:01, 11 July 2011 (UTC)

The short answer: basically any large nucleus will release energy if you break it up into smaller pieces. The problem is that most of the readily available large nuclei are types that are nearly impossible to break. A breeder reactor converts some of the hard to break nuclei into something breakable ("fissile") so that their energy can be released. Rckrone (talk) 16:54, 11 July 2011 (UTC)

I think that's a little too short and simplistic, personally... --Mr.98 (talk) 21:55, 11 July 2011 (UTC)

The OP explicitly asks where the energy came from. That question has a simple answer: As with all nuclear reactions, the energy released by a reactor comes from the nuclear binding energy of the atoms. Energy was placed in the atomic nucleus during stellar nucleosynthesis, a very long time ago. A breeder reactor is essentially converting a stable nucleus (with lots of energy that's hard to get out) into an unstable nucleus (with the same amount of energy, or even a little bit less energy, but this energy is easy to release). The energy we harness when we fission atoms in nuclear reactors is basically coming from millions of years of stored heat from stellar fusion: the ultimate fossil fuel. Extreme heat and pressure inside a sun caused small atoms to fuse into larger atoms, locking in that energy in a very stable form, embodied by the strong nuclear force. When we split the atom back apart, we're returning the energy into a useful form: thermal energy, which is used to heat water and drive a steam-turbine. Nimur (talk) 23:36, 11 July 2011 (UTC)

Er, they asked where the extra energy comes from. Which to me implies that the confusion is over fertile vs. fissile, and why you end up with more fissile material when you end than when you started. (And the rest of the question, beyond the second sentence, makes that more clear.) I don't think it's a question about the origins of binding energy in general. --Mr.98 (talk) 01:38, 12 July 2011 (UTC)

Large edible leaves ?

I'm trying a low-carb diet, part of which involves making lunch-meat sandwiches using leaves in place of bread. I've been using romaine lettuce. I'd prefer spinach, but the leaves aren't big enough. Is there a variety of spinach with bigger leaves ? Are there any other plants with large, edible leaves ? I seem to recall that stuffed grape leaves are used in Greek cuisine, but do they need to be cooked ? Do we have an article on this topic ? StuRat (talk) 17:19, 11 July 2011 (UTC)

You could try kale, it should be plenty large enough for sandwiches. 108.15.155.91 (talk) 17:36, 11 July 2011 (UTC)

Banana leaves are large and inexpensive. Incidentally, you'd be better off replacing the meat than the bread. Instead of your "lunch meat" of ground up lips, eyelids, and anuses, try tempeh or seitan, both of which are high-protein, have a pleasantly meaty texture, and can be made to taste like just about anything with any of a million different recipes you can find easily online. -- SmashTheState (talk) 18:02, 11 July 2011 (UTC)

If you don't already have a wheat gluten sensitivity, it sounds like seitan would give you one. StuRat (talk) 18:20, 11 July 2011 (UTC)

Banana leaves are large and inexpensive and inedible. --Sean 18:43, 11 July 2011 (UTC)

Yes there are plenty of different varieties of spinach, not just the unappetising stuff that comes in bags. I get different ones from my local Indian food shop. When I used to grow spinach, I used to grow Perpetual spinach which had larger leaves if you let them grow. You might also want to try and get Swiss chard or spinach beet. --TammyMoet (talk) 18:05, 11 July 2011 (UTC)

I rather like the flat-leafed spinach that comes in bags, but it's too small for this purpose. StuRat (talk) 18:21, 11 July 2011 (UTC)

Cabbage has large leaves and is often eaten raw, e.g., in cole slaw. You might also try Napa cabbage - a better shape for rolling or for making "flat" sandwiches. Or other types of Chinese cabbage.

Grape leaves are wrapped around other foods and cooked. I'm told that the big leaves are too tough to use for this purpose and the small ones are probably smaller than you want. Wanderer57 (talk) 18:42, 11 July 2011 (UTC)

Would using the concave region of one or more celery stalks count? Those are very high in fiber, so they go well with meats, and they technically have negative net calories. It might be possible to use the leafy regions of celery, which are just as edible and healthy as the stalks, for one half of a meat-celery sandwich, but appropriately cutting, forming, or deviling the meat might turn out to be more labor intensive. *goes to perform an experiment with the celery, chicken and talapia in the fridge* 99.24.223.58 (talk) 23:06, 11 July 2011 (UTC)

I actually do fill celery with peanut butter (see next question), but lunch-meat doesn't seem like a good fit. StuRat (talk) 00:26, 12 July 2011 (UTC)

Celery filled with cream cheese and paprika on top! YUM! Vespine (talk) 02:35, 12 July 2011 (UTC)

No, with cream cheese you need raisins ! StuRat (talk) 03:54, 12 July 2011 (UTC)

Filling celery with creme cheese or PB kind of defeats the point of celery though. Googlemeister (talk) 13:19, 12 July 2011 (UTC)

For a low-calorie diet, yes, but not for a low-carb diet, where proteins and fats are fine. StuRat (talk) 05:24, 13 July 2011 (UTC)

My celery was too droopy to work well with meat, so I ended up having chicken without any vegetables. I would have been far better off with brazil nut butter. I wonder how long that keeps. — Preceding unsigned comment added by 99.24.223.58 (talk) 04:06, 12 July 2011 (UTC)

Vine leaves are often used for wrapping food in middle-eastern cuisine. --Colapeninsula (talk) 10:25, 12 July 2011 (UTC)

As far as I know, all cucurbits (pumpkins, squash) throw edible foliage, and most cultivars produce huge, durable leaves. Some – especially C. pepo's – are more difficult to handle than a rosebush, but cooking should eliminate most of the spininess (although if you cooked them, you wouldn't really use them in lieu of bread on a sandwich). C. maxima leafs are big enough for three-foot subs, let alone normal sandwiches; as long as you cut out/around the primary vein, which is still a bit sharp, you're good. Juliancolton (talk) 21:01, 12 July 2011 (UTC)

Thanks for all the answers so far. I should have specified that I want leaves which can be eaten raw. StuRat (talk) 05:27, 13 July 2011 (UTC)

Making my own peanut butter

I'd like to pour peanuts (or real nuts) into a machine and have a single serving of peanut butter or nut butter come out. This is because jars of peanut butter either seem to contain unhealthy hydrogenated vegetable oil or separate into a layer of oil and a layer of concrete. I supposed I could use a blender, but that would result in peanut butter all clumped around the sharp blades. So, the machine would really need to have it's own method of ejecting the peanut butter. Is there such a device ? I'm also worried that cleaning it after each use may be too difficult, is there a way to make that easier ? StuRat (talk) 17:19, 11 July 2011 (UTC)

"Peanut butter maker". ~ Mesoderm (talk) 17:21, 11 July 2011 (UTC)

Thanks. How easy are those to clean ? StuRat (talk) 17:58, 11 July 2011 (UTC)

Also, if you don't want to buy the machine, many grocery stores (especially co-ops and places that sell good-quality bulk foods) have the machine there, and you can just take a re-usable container with you to fill up with fresh ground PB. It would still probably be cheaper to use your own machine in the long run (and you don't have to worry about what they are cleaning the machine out with at the store). ~ Mesoderm (talk) 17:24, 11 July 2011 (UTC)

That wouldn't really work for a single serving. If I get more than that, it's going to form concrete between uses. StuRat (talk) 17:58, 11 July 2011 (UTC)

I'm not sure what you mean about forming concrete between uses. I usually get about a pound or so of it at a time, and it keeps fine. ~ Mesoderm (talk) 18:17, 11 July 2011 (UTC)

Also, isn't there an emulsifier they can use in peanut butter that's healthier than hydrogenated vegetable oil ? (Our peanut butter article say that palm oil can be used, but that's also unhealthy.) StuRat (talk) 17:58, 11 July 2011 (UTC)

If you went to a health food shop, no doubt you could find organic peanut butter which would meet your criteria. --TammyMoet (talk) 18:01, 11 July 2011 (UTC)

Are you sure ? They all seem to separate. StuRat (talk) 18:02, 11 July 2011 (UTC)

I've been eating pure peanut butter for decades, and separation is perfectly normal. All you do is mix it up before you eat it. I've never had it turn into "concrete," no matter how long it's been sitting. When you mix it up, it turns back into peanut butter. The whole point of eating pure peanut butter is to eliminate the additives like emulsifier in the commercial brands (and to get rid of the aflatoxin contamination that results from mass production). -- SmashTheState (talk) 18:18, 11 July 2011 (UTC)

And get rid of the salt and the sugar. Bielle (talk) 18:36, 11 July 2011 (UTC)

please. There's nothing about aflatoxin contamination that is intrinsicly associated with mass production when it comes to food like peanut butter which come from a source (peanuts) at strong risk of contamination.

And I would actually expect organic peanut butter is a greater risk then high quality non organic peanut butter given non usage of fungacides and common poor scientific knowledge of many of those involved. (This mentions a study which found something similar although apparently not specifically on organics [4]/[5] and BTW read Andrew Weil before making any accusations of corporate shill.)

At the very least [6] choosing a reputable organic brand who test their peanut butter for aflatoxin contamination as required by the FDA in the US (e.g. [7]) and actually understand what aflatoxin is, how contamination happens and how to reduce* it; rather then some random home made brand who may not be required to test their products and probably don't and may not even be properly aware of the risk or otherwise believe silly things. *reduce is a key word, anyone who claims their peanut butter has no contamination almost definitely doesn't know what they're talking about.

Nil Einne (talk) 15:51, 12 July 2011 (UTC)

There's nothing wrong with emulsifiers like lecithin, found in egg white. Elle _{vécut heureuse} ^{à jamais} (be free) 21:59, 11 July 2011 (UTC)

And does anybody add that to peanut butter ? StuRat (talk) 23:00, 11 July 2011 (UTC)

Yes, emulsifiers are common in peanut butter, and if I remember correctly, lecithin need not be listed on the ingredients. 99.24.223.58 (talk) 00:10, 12 July 2011 (UTC)

OK then, is there a brand of PB which uses lecithin in place of hydrogenated vegetable oil, and doesn't separate ? StuRat (talk) 00:21, 12 July 2011 (UTC)

I'm not sure. Lecithin is a vegetable oil which is usually hydrolyzed, which is like being hydrogenated with enzymes instead of hydrogen. 99.24.223.58 (talk) 01:21, 12 July 2011 (UTC)

Is that as harmful as hydrogenation ? StuRat (talk) 01:49, 12 July 2011 (UTC)

Hydrolysis is not the same as hydrogenation.

To my knowledge, lecithin is not harmful, though I wouldn't swear to that. But really, you should just get over caring about the peanut butter separating. As STS said, you just mix it up again. Alternatively, keep it in the fridge (when it's not separated), and it won't separate. Once you get used to natural peanut butter, you'll never go back. --Trovatore (talk) 01:54, 12 July 2011 (UTC)

I'm certain lecithin is less harmful than its calories, but I'm not sure by how much. Hydrolyzed lecithin is not dangerous in the same way as trans fats, at least not more than about 10% enough to matter, if I remember correctly. Check PubMed for details. 99.24.223.58 (talk) 03:59, 12 July 2011 (UTC)

Why, if there's a perfectly good emulsifier they could use ? Apparently, we need to dig George Washington Carver up, and put him back to work. :-) StuRat (talk) 03:51, 12 July 2011 (UTC)

Emulsified doesn't taste as good, that's why not. Try it; you'll see. --Trovatore (talk) 06:48, 12 July 2011 (UTC)

I had always heard that GW Carver did not invent PB. Googlemeister (talk) 13:17, 12 July 2011 (UTC)

Even if not, he did invent many peanut products, so improving PB would be right up his alley. StuRat (talk) 05:34, 13 July 2011 (UTC)

May be you should consider taking your peanut butter to your local construction supply store and ask them if you could use their paint mixer :). Dauto (talk) 23:47, 11 July 2011 (UTC)

I learned a few years ago that with simple peanut butter (without whatever chemicals are added to Jif that prevents separation), you just have to mix the concrete and oil with a butter knife for a few minutes (an unpleasant experience because the oil always sloshes out) ... but afterward it does keep mixed for months without separating. I don't know how long the peanut butter has to sit in the jar before it becomes separated in the way you describe. Comet Tuttle (talk) 06:31, 12 July 2011 (UTC)

I would like to avoid that unpleasant task. Especially since spilled oil isn't easy to clean up (detergent is required). But my PB seems to require a stir every time I use it (maybe you refrigerate yours ?). And, I can't just stir up a bit at the top, I've found, or the bottom half that doesn't get stirred keeps getting harder and harder, thus the concrete. So, I have to spend 5 mins stirring it each and every time I use it. That adds up to lots of wasted time and effort. StuRat (talk) 05:41, 13 July 2011 (UTC)

OK, clearly you just need practice. It doesn't take five minutes. Thirty seconds if you're slow. Do it where the spilled oil is easy to wipe up, like on a countertop, and don't get it on your clothes.

Use a knife that's long enough to go all the way to the bottom of the jar, and kind of scoop it up from the bottom, so that the oil falls mostly into the hole left behind rather than slopping over the top (it's not just that the oil is messy; it's also that it's an important part of the peanut butter and you don't want to lose it).

Then once you've made your peanut butter and banana sandwich (mmmmm) stick the peanut butter in the fridge, and you won't have to mix it next time. It's really not difficult. --Trovatore (talk) 20:43, 13 July 2011 (UTC)

But if you stick it in the fridge, then it won't spread because it's cold. I suppose I could microwave it, but then I risk releasing nasty chemicals from the plastic jar. Now I need to find PB in glass jars. StuRat (talk) 02:50, 14 July 2011 (UTC)

It spreads fine cold. Of course if you put it on bread that won't hold up to it, like white bread or the sort of allegedly "wheat bread" that has white-bread-like texture, then you'll have a problem. But who eats white bread? --Trovatore (talk) 05:52, 14 July 2011 (UTC)

Surely the oil that comes out of peanuts is groundnut oil? What's the problem with eating that? --TammyMoet (talk) 09:09, 12 July 2011 (UTC)

When the butter is first made, and I would try an ordinary food processor first to see if it works, it is an emulsion, right? So if you want it thinner for spreading, you add water as you mix. You could add oil as well or instead but then it will be a little more high in calories. Just like making hummus, really. Itsmejudith (talk) 16:50, 12 July 2011 (UTC)

Is Coeliac_disease an allergy?

It's clear to me that it's not wheat allergy, but as a "is an autoimmune disorder of the small intestine", does it count as allergy ("a hypersensitivity disorder of the immune system")? Quest09 (talk) 20:01, 11 July 2011 (UTC)

It seems like there is a lot of confusion regarding this question. Doing a quick google I've found lots of pages that say it is an allergy and some pages even say coeliac disease is caused by a wheat allergy, but not many of them count as what I'd call reputable sources and I think that is incorrect. I think this excerpt has a reasonable and concise explanation. (In short, no, there are some similarities but they are different things.) Vespine (talk) 22:38, 11 July 2011 (UTC)

Question about scintilating scotoma

My younger brother is interested in being a pilot for the US Air Force, but he has rare occassions where he experiences a Scintillating scotoma. He says he gets one about 5-6 times a year and they last from 15 minutes to an hour. Does anyone know if that kind of thing would disqualify him from that kind of a position? Googlemeister (talk) 20:47, 11 July 2011 (UTC)

I believe those are far more common than the literature indicates -- I've looked into it because I get them too every so often. I believe that many people get them without realizing it. It's potentially a problem because if the scotoma passes through the foveal area, you get a small blind spot right at the center of vision. Recommending what to do, however, would constitute medical advice in my opinion, so I won't. Looie496 (talk) 21:46, 11 July 2011 (UTC)

I agree that these are probably fairly common, but I am not sure they are always associated with a stationary blind spot. The occular muscles would need to be paralyzed for that to be the case, unless they were very large compared to those depicted in the article. It isn't medical advice to recommend being honest with the recruiter if asked about vision. I would hope military recruiters would have some kind of a guideline on their intake physical questionnaires, but those aren't known for being read very carefully. The frequency does seem to be high, but I recall that my phosphene, which is much more striking and likely to be remembered, was at least twice as frequent when I was decades younger; perhaps because I was getting more exertion. 99.24.223.58 (talk) 22:57, 11 July 2011 (UTC)

The problem is that when a scotoma occurs in the fovea, you can still see things by looking off to the side, but they won't be sharp -- the sharp part of your visual field is roughly the size of your fist held at arm's length. Reading, for example, becomes very difficult. That's the thing that first clued me in that I was experiencing a scotoma -- otherwise I probably never would have noticed. Looie496 (talk) 23:05, 11 July 2011 (UTC)

Wow! I've totally had this and never knew what it was: Thanks again ref desk:) It only happens rarely and doesn't last very long and I don't get migraines, but it's actually made me wonder if I'm having a stroke or something, lol. (i'm mid 30s so didn't think it was likely).. Now I know! it won't bother me so much. Vespine (talk) 02:33, 12 July 2011 (UTC)

I get these painfree migraine symptoms occasionally too. We have an article on their likely cause, Cortical spreading depression, but this Scientific American article is quite good. Sean.hoyland - talk 03:12, 12 July 2011 (UTC)

The majority of that article seems to require a paid subscription. Googlemeister (talk) 16:44, 12 July 2011 (UTC)

I can read it all without a subscription. Try this single page version. Sean.hoyland - talk 16:55, 12 July 2011 (UTC)

I read it and it was interesting. I sent him the link. Googlemeister (talk) 20:36, 12 July 2011 (UTC)

software filter on imageJ/photoshop

I need this for my research, and it would help my lab a lot. Is there a way to apply a software filter or script to remove out of focus objects (and the background) and keep in-focus particles? The particles in question are fruit flies, viewed from the bottom of a vial. We want to count the number of flies that are strictly in the focal plane of the bottom of the vial, and not count the flies not on the bottom (the ones at the bottom are suffering from the effects of cocaine).

I've tried some resources online, but they seem optimised for cells. I was thinking of also "scoring" the flies -- to see how far away from the bottom they are, so the ones at the bottom (the most in focus) would have a strong score, and the ones that are near the bottom have a weak score. Any variety of attacks would help. Thanks so much! Elle _{vécut heureuse} ^{à jamais} (be free) 22:12, 11 July 2011 (UTC)

This question would probably be more appropriate for the Computing desk, but basically I believe what you want is an edge detection filter. Edge detection works by picking out points that have a strong contrast with neighboring points, and that's what you want. Looie496 (talk) 22:33, 11 July 2011 (UTC)

[8] might be a place to start. Cells are diverse enough that if you want to do better, you might need to look at [9], but that might be a lot more work than simply counting the number of background pixels showing through the region at the bottom from one or more side view(s) of the vial instead of trying to use focus blur from a top or bottom view. 99.24.223.58 (talk) 00:11, 12 July 2011 (UTC)

Sounds related to focus stacking, except you only want to keep/extract the focal-plane of one image rather than extract and merge from multiple. DMacks (talk) 01:06, 12 July 2011 (UTC)

The simpler technique is to grab an undergrad, give him some of the cocaine, and order him to count the flies on the bottom of the vial. You'll find the proper amount of cocaine will produce results at 3 Hz. Comet Tuttle (talk) 06:25, 12 July 2011 (UTC)

Fluorescent lights in a brown-out

We recently had a brown-out (reduced voltage to around 83 V versus normal 110-120V). The incandescent and LED lights got dimmer, but still functioned, and even the compact fluorescents were OK, while the traditional (long tube) fluorescent lights went nuts, flashing frenetically. This was quite annoying, as the basement has all fluorescent lights, and that's where the fuse box is, which is where we wanted to go to investigate the brown out. We ended up using flashlights. So, is there a type of long tube fluorescent light which is more tolerant of voltage swings ? StuRat (talk) 23:11, 11 July 2011 (UTC)

Nope, that's one of the trade offs for their efficiency relative to incandescent and low cost relative to LEDs. 99.24.223.58 (talk) 23:46, 11 July 2011 (UTC)

Compact fluorescents with their electronic ballasts are apt to fail and even ignite when the applied voltage drops that low, unless they are the "dimmable" ones which cost several times as much as generic ones. An intentional "brownout" by a US utility usually aims to drop the voltage far less than to some value way higher than the reported 83 volts, which is likely to destroy many motor operated appliances, unless their circuit breakers or fuses open due to the excess current drawn. Computers and TVs are unlikely to operate at that low a voltage. Gas appliances which use an electric igniter typically do not operate correctly either (some gas ovens spew out gas without igniting it, with the possibility of a gas explosion). Personally, I would kill the power to everything but an incandescent bulb, using it or a voltmeter as an indicator of when the power came back on. The utility would typically trip distribution circuits offline if they had central control of the substation. Maybe there was something weird about the local transformer or connections to the residence, like a loose neutral. Edison (talk) 03:26, 12 July 2011 (UTC)

Do you have any sources supporting the use of "apt" there as meaning more likely than not? 99.24.223.58 (talk) 03:37, 12 July 2011 (UTC)

Here. He used the word correctly. Comet Tuttle (talk) 06:22, 12 July 2011 (UTC)

I could be wrong but I think 99 is asking for a source supporting the claim the electronic ballasts in CFLs intended for a 120V/US supply are apt to fail at 83V Nil Einne (talk) 15:58, 12 July 2011 (UTC)

I considered that providing only 83 volts to a 120 volt bulb was comparable to operating it on a dimmer, although modern dimmers remove portion of the sine wave from each cycle rather than providing a full sine wave at a reduced voltage like the "brownout" in question. Some lighting installations I maintain actually use a huge Variac (rotating variable autotransformer) to dim a room full of incandescent bulbs smoothly. Here is a 1995 reference: [10] "First, be sure not to use compact fluorescent bulbs in circuits that have dimmers - they could present a fire hazard in these uses." Here is a 2009 report on a home which, according to fire investigators, caught fire due to compact fluorescent bulbs controlled by a dimmer. An article from 2008 says "Never use a CFL with a dimmer in the circuit, even if it is set (and kept) at the maximum setting. It will keep you at risk of fire, and will significantly shorten the lifetime of the lamp and the dimmer." General Electric advises against using CFLs on a dimmer if they are not labelled as suitable for such, but understandably they do not mention the fire hazard. I've heard numerous recent reports of early failures of CFLs (without fire) when they are improperly used on a dimmer. Compact fluorescents can also start fires if they are used in a fully enclosed fixture, and they sometimes emit smoke and a burning smell, and have discoloration of the base when they fail in normal use at the end of their service life, per [11]. A "normal " end-of-life CFL burnout may result in smoke being emitted for 30 seconds, sometimes sufficient to set off a smoke alarm, per [12], along with popping sounds, flickering of the light, and a charred base. In October, 2010 the US Consumer Product Safety Commission recalled 124,000 compact fluorescent bulbs sold in 2008 because they could "overheat and catch fire" with no statement that dimmers were involved. Edison (talk) 17:49, 12 July 2011 (UTC)

Thank you. Do you believe it is safe to assume that those which have not been recalled are not capable of igniting exterior flammables at end of life or when used with improperly low voltage or with a dimmer switch? 99.24.223.58 (talk) 18:47, 13 July 2011 (UTC)

Apparently, installation in enclosed areas is a major determinant of thermal bulb failure, and more common in compact fluorescents. Make sure there is adequate ventilation to prevent any electric fixtures, bulbs or otherwise, from igniting their buildings. It's just good interior design. 99.24.223.58 (talk) 22:07, 15 July 2011 (UTC)

Metals

I recently found a piece of metal at the beach. My local jewler did a test, his machine said it was 99% SE. What is SE? — Preceding unsigned comment added by 98.77.106.79 (talk) 23:33, 11 July 2011 (UTC)

Se (formatted with a lower-case "e") is the chemical symbol for Selenium; but that seems very unlikely for a piece of scrap metal. (Pure selenium is rarely used in industrial metallurgy, and almost never occurs in nature). Maybe your report is using some more specialized domain-specific nomenclature. Or, it might mean "something else" - for example, if he performs a standard chemical test for gold, silver, or precious metals, the test may simply indicate any other material as "something else." Nimur (talk) 23:43, 11 July 2011 (UTC)

I'm guessing it just means it's a "stainless (steel) equivalent." Ask the jeweler. 99.24.223.58 (talk) 00:00, 12 July 2011 (UTC)