Wikipedia:Reference desk/Archives/Science/2008 February 16

= February 16 =

EMP and safe deposit boxes
(Note: I bumped this section down to February 15 even though it was initially posted on February 14 because I asked a whole bunch of new questions on February 15 and I wanted to make sure the questions were answered before this section ended up being archived and that people didn't overlook the section just because it was in an earlier day and assume that the questions had already all been answered.) &mdash;Lowellian (reply) 02:29, 17 February 2008 (UTC)

Would a typical bank safe deposit box form an adequate Faraday cage to protect electronic contents from an electromagnetic bomb? &mdash;Lowellian (reply) 00:02, 14 February 2008 (UTC)
 * Well I can't actually answer the question bear in mind your chance of getting access to your bank safe deposit box during the extreme chaos created by an electromagnetic bomb may be slim Nil Einne (talk) 06:54, 14 February 2008 (UTC)
 * Let's say it's electronics you want to get access to once the chaos calms down, so the question still stands, and I'd still like an answer if someone can give one. Also, your response did give me an idea for another question: would modern automobiles be able to start up after an EMP, or are they so dependent on electronics that they would be unable to do so? &mdash;Lowellian (reply) 12:50, 14 February 2008 (UTC)


 * A modern automobile would almost certainly toast after even a moderate EMP event. As it is, the police are learning to use devices that lay in the roadway and transfer an electrical transient to your car in order to stop you; this substitues (more safely) for the spike strips they now lay across the road to deflate all your tires.


 * A safe deposit box made of metal would probably provide pretty good protection against EMP. It all depends on how tightly the cover seals the box and how good and uniform is the electrical contact between the cover and the box; remember that a Faraday cage only works if the openings in it (including long, narrow slots!) are substantially shorter than the wavelength of the signal(s) you're trying to block.


 * Atlant (talk) 13:59, 14 February 2008 (UTC)


 * According to a recent documentary, you can make a car start after an EMP attack by replacing the solenoid. 206.252.74.48 (talk) 14:16, 14 February 2008 (UTC)


 * Very funny! Remember: after a nuclear attack, look for a car that predates any electronics fancier than an 8-track player.


 * Atlant (talk) 15:46, 14 February 2008 (UTC)

A safety deposit box generally is a thin metal box inside a thicker metal box inside a metal or reinforced concrete vault. This provides three levels of shielding against external electromagnetic fields, and should provide a respectable amount of shielding, but I have not seen figures on the strength of the hypothetical EMP so I could not attempt to calculate the field strength inside and compare it to the threshold for damage to electronics, magnetic media, etc. I'm surprised the folks who sell personal keychain radiation monitors and iodine pills  do not advertise EMP safes for the home, perhaps welded from 1/2 inch ferrous metal. I expect that the avionics and communication equipment on military command planes and bombers are hardened to survive EMP, and they would not get off the ground if they had to be as solid as a safety deposit box installation. Edison (talk) 17:18, 15 February 2008 (UTC)
 * EMP-specific safes? Does that mean that ordinary metal home safes not secure against EMP? If not, then why not? &mdash;Lowellian (reply) 19:14, 15 February 2008 (UTC)
 * Many home safes seem to be plastic and concrete in large part, to deter theft and protect papers from fire. Older office safes are big steel boxes and it seems they would provide a great amount of shielding against external magnetic fields. I have seen nothing so far to convince me than a much thinner metal box would be inadequate. Edison (talk) 20:36, 15 February 2008 (UTC)

Another related question: websites I have seen about using aluminum foil or trash cans to construct Faraday cages usually recommend attaching a grounding wire to the makeshift cage. If, as suggested above, safe deposit boxes and metal safes without grounding wires may form adequate Faraday cages, why would the grounding wire be necessary on these makeshift cages? And does the grounding wire actually have to be stuck into the ground, as in the earth or soil? What if you can't leave the Faraday cage outside the house, then what do you do? (Besides sticking it in the soil of a houseplant vase? *wink* ) (Sorry for all these questions, but I don't know much about electrical physics.) &mdash;Lowellian (reply) 21:36, 15 February 2008 (UTC)
 * Whether a metal container is grounded or not should not affect its permeability to magnetic fields. Dissipating an electrical charge, such as from lightning is a different question. If current flowed through the container from a source to a ground connection, that might actually cause a magnetic field in the interior, if the current density was higher in one side of the container than in the other side. Aluminum foil would provide negligible magnetic shielding, but couod provide shielding against electric fields. I once used a coffee can as a Faraday cage to shield a large speaker magnet from causing distorted color in a TV picture tube. I have seen chicken wire used to provide a Faraday cage around a chamber where human subjects had electrophysiological recording of brain waves during perception experiments. No idea how either of these would fare against EMP. Edison (talk) 02:49, 17 February 2008 (UTC)
 * What about my general questions about grounding? How do you "ground" things inside the house without soil? &mdash;Lowellian (reply) 20:57, 18 February 2008 (UTC)
 * If the plumbing in your house is all-metal, you can ground something by wiring it to a cold-water pipe. --Carnildo (talk) 21:13, 18 February 2008 (UTC)

James Randy and Aliens
Anyone know if James Randy believes in Aliens? Malamockq (talk) 03:09, 16 February 2008 (UTC)


 * From his online bio] I get the idea that he does not believe that sentient technologically superior aliens have flown to earth in UFOs. I can't speculate on whether he thinks there is life, intelligent or not, elsewhere in the universe. Sifaka   talk  03:50, 16 February 2008 (UTC)


 * Yea, the UFO thing is quite a bit different though. It's one thing if he thinks there might be life on other planets, it's another thing if they have actually visited us. Malamockq (talk) 21:51, 17 February 2008 (UTC)


 * You may want to see my somewhat OT comment here Talk:Unidentified flying object (please don't reply there tho) Nil Einne (talk) 17:26, 16 February 2008 (UTC)


 * Well, first, his name is James Randi, with an "i", not a "y". Secondly, to answer your question, it seems that he believes it's likely that there are other intelligent lifeforms out there in the universe, but that there is no good evidence so far that any aliens have ever visited Earth.  For example, he has endorsed the SETI project in the past (see here).  However, knowing Randi, he has probably never stated outright that he "believes in aliens" since he prefers solid objective evidence before making such a claim. --  Hi  Ev  01:28, 18 February 2008 (UTC)
 * Probability speaking, it's far more improbable that Earth is the only planet in our universe to have life, than for life to exist on other planets. 64.236.121.129 (talk) 17:07, 20 February 2008 (UTC)

EMBRYOLOGY
Do you know some tacts to remember the steps of growth that ocurre in human embryo growth during the first 8 weeks? thanks —Preceding unsigned comment added by 201.220.222.140 (talk) 04:41, 16 February 2008 (UTC)


 * There aren't many tactics beyond just memorization. Embryology, Human embryo would help. Also search pubmed.org for reviews on human embryology.  Wisdom89  ( T |undefined /  C ) 04:45, 16 February 2008 (UTC)


 * You can find some embryology mnemonics here. Personally I usually have more trouble remembering the mnemonics than I do the information they're supposed to help you remember. - Nunh-huh 04:47, 16 February 2008 (UTC)


 * I'm in Nunh-huh's camp and despise most mnemonics (although I hate "pneumonics" even more ;-). In approaching topics that appear to need rote memorization, I usually first try to understand terms, how structures got their names, etc. Some examples from embryology might be the origin of the term morula (a bunch of cells resembling a mulberry), why it's called the ultimobranchial body ("ultimo-", last; hence, "last of the branchial pouch derivatives"), etc. Works great for me, but your mileage may vary. --David Iberri (talk) 20:08, 16 February 2008 (UTC)

physics/water barometer
the height of water in a water barometer is measured from the open atmospheric pressure end vertically to the under side of the J tube.

the question is - If the lower u loop end of the J is elongated to about sixty feet, what differance will it make to the barometer?

M.Krishnapillai —Preceding unsigned comment added by 124.43.251.138 (talk) 06:59, 16 February 2008 (UTC)


 * I'm not certain if I understand your question, but I believe that extending the open side of a water barometer will make no difference. Perhaps our article on barometers may help. (EhJJ)TALK 22:32, 16 February 2008 (UTC)
 * You will be measuring the pressure of the air from a different point, Although the extra weight of the air in the tube will largely compensate, the difference in air pressure inside the tube and outside could be due to different temperatures, or humidities, or due to wind, sound etc. Graeme Bartlett (talk) 03:33, 18 February 2008 (UTC)

Cowling nozzle?
Watching mythbusters today, when they tried to make a jet pack with 2 props and cowling, they didnt get enough lift. I would've thought that to get more lift, you could focus the air more by creating more of a nozzle effect, by narrowing the diamter after the prop instead of having it the same all the way down. Is there a technical reason why they couldnt do this? —Preceding unsigned comment added by 59.100.252.244 (talk) 12:53, 16 February 2008 (UTC)

How much elecricity does an solar panal of a sq mts produce.
Hello i am thinking of making a paper presentation on a way of producing power by concentrating mirrors and i want to know how they fare with solar panals .I would also like to know about there efficiency,cost etc.--Man manoj1990 (talk) 13:09, 16 February 2008 (UTC)


 * The article on Solar_radiation contains a number of estimates of how much solar energy arrives at the earth. The article on photovoltaics has a discussion of efficiency. JohnAspinall (talk) 04:54, 17 February 2008 (UTC)

Positive and negative load tests
G'day, RefDeskers. I'm stuck with something. I have come across the phrases positive load test and negative load test with reference to railway sleepers. I'm not seeking to learn the methodology of such tests, this is irrelevant - what interests me is the relevance of the terms positive and negative here. How do both of these tests differ and why the differentiation? If anyone has any ideas, I'd appreciate them. Thanks and cheers! --Ouro (blah blah) 13:42, 16 February 2008 (UTC)
 * Try this paper http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1321&context=engpapers (look at figure 1) - can this be the answer. (the loads are 'moments' ie torque..)?77.86.8.83 (talk) 13:58, 16 February 2008 (UTC)
 * Makes me scratch my head, this diagram you pointed me to... could anyone briefly explain further? --Ouro (blah blah) 14:49, 16 February 2008 (UTC)


 * A railway sleeper somewhat works like a beam in a framed building structure. Such a beam is subjected to pressure (positive) in the top part and tension (negative) in the bottom part.  In a typical reinforced beam the concrety bits cope with the pressure whilst the steel reinforcement takes up the tensile forces.
 * I assume that sleepers, being subjected to 2 point loads at the locus of the tracks, have similar characteristics of positively and negatively stressed parts, which have to be mathematically analysed to provide steel reinforcement in the zones of tensile forces. The article from the Wollongong University seems to indicate that significant tensile stress is measurable in the top part of the middle section of the sleeper.
 * There is a stack of suitable articles under the lemma structural analysis. Prost, --Cookatoo.ergo.ZooM (talk) 01:53, 17 February 2008 (UTC)
 * Goodness me. But thanks for youe explanation, ZooM! --Ouro (blah blah) 09:27, 17 February 2008 (UTC)

Deep space travel - Voyager and Pioneer
Are the Voyger and Pioneer space probes travelling particularly fast? That is, would it be hard, using exisiting, proven technology, to make a similar space probe travel ten times as fast as these probes? ike9898 (talk) 14:33, 16 February 2008 (UTC)

"Voyager 1 is departing the Solar System at a speed of 39,000 miles per hour. Voyager 2 is departing the Solar System at a speed of 35,000 miles per hour." http://www.spacetoday.org/SolSys/Voyagers20years.html

I have literally no idea about this stuff so couldn't say with any authority if faster speeds are possible but i suspect that the pace these things are travelling is not something that is controllable/could be changed in any meaningful way by modern technology design. ny156uk (talk) 14:38, 16 February 2008 (UTC)

Oh and Pioneer details on that page..." Accelerating to a speed of 82,000 mph, Pioneer 10 passed by Jupiter on December 3, 1973. so my assumption about speed is obviously wrong. (http://www.spacetoday.org/SolSys/ThePioneers.html) ny156uk (talk) 14:42, 16 February 2008 (UTC)
 * (ec) Well, let's see. Voyager I is travelling at 17,2 km/s relative to the Sun, Voyager II is supposed to be travelling 10% slower, so say about 15,5 km/s, and Pioneer 11 is travelling at 11,6 km/s, and Pioneer 10 is unfortunately unreachable. Now, say we increase tenfold the speed of Voyager II, giving ca. 150 km/s. As I read, one of the Helios probes reached around 70 km/s, a current record for a man-made object. Deep Impact reached velocities in the low twenties per second. So, we're not quite there yet actually, but ion thrusters promise certain advances. Also, keep in mind that probes tend to rely not only on engines for their speed, but also gravitational slingshots. Hope I helped a bit. --Ouro (blah blah) 14:48, 16 February 2008 (UTC)
 * Voyager can cross the galaxy in like 60 years or something x_X D\=&lt; (talk) 04:52, 19 February 2008 (UTC)

can we reabsorb water from the bladder?
Once urine is in the bladder, can the body reabsorb it if it needs it? Say, if you were dumped into the desert with a full bladder would you be better off to 'hold it' so your body could use it later? 216.77.239.212 (talk) 15:05, 16 February 2008 (UTC)


 * The bladder is unable to reabsorb urine. If the bladder was able to reabsorb what would be the purpose of the kidneys, how could the kidneys control the hydration of the body is the urine was reabsorbed. One of the problems of an enlarged prostate gland is the inability to pass urine at will. This causes a build up of pressure in the bladder which if unresolved will result in back pressure on the kidneys. If you are in the desert with a full bladder it would be more sensible to pass the urine into a container and possibly seek a method to distil the water out for reconsumption. I'm assuming a certain desperation here. Richard Avery (talk) 16:23, 16 February 2008 (UTC)
 * Stillsuits! --Ouro (blah blah) 16:53, 16 February 2008 (UTC)
 * However, some people have survived without water by peeing and then drinking their own urine, yes urine is drinkable but at least it is your own urine. Hope this helps. Thanks. ~ A H  1 (TCU) 17:27, 16 February 2008 (UTC)


 * Though there's only a limited amount of times that will work, of course, without an external water source. --98.217.18.109 (talk) 19:24, 16 February 2008 (UTC)


 * Maybe you should source this as from the little knowledge I have of extreme survival it is a bad idea to drink your own urine. On the impermeability of bladders, apparently there is a rise in cases of ruptured bladders in Europe that goes with the increase of the consumtion of beer and this especially for female drinkers as they have a smaller bladder. The scenario goes as follows: drink, to drunk to feel the need to pee, fall, rupture bladder. So if you drink beer, remember to pee! 200.127.59.151 (talk) 23:38, 16 February 2008 (UTC)
 * Drinking_urine APL (talk) 10:33, 17 February 2008 (UTC)


 * Seems unlikely 200.127, as drunk people with full bladders tend to just wet themselves. 79.66.116.27 (talk) 18:18, 17 February 2008 (UTC)

(unindent) thanks for this info, I wasn't really concerned about getting drunk and deserted in the desert. I did think though that the bladder membrane might be water permeable, which I think Richard answered, afaict. thanks Tim (talk) 00:23, 17 February 2008 (UTC)


 * A source is needed for the claim of females having smaller bladders. I have known females who could drink far more than males without needing to void urine. Edison (talk) 02:41, 17 February 2008 (UTC)
 * I don't know about smaller bladders but here is about overindulging . 200.127.59.151 (talk) 18:48, 17 February 2008 (UTC)


 * toads and frogs can, however. Gzuckier (talk) 01:47, 21 February 2008 (UTC)!

Reverse engineering in baking
I've found a type of bun, sold commercially, that is heavenly. It's cinnamon- and apple-flavoured, and I would like to know how I may proceed to make these on my own. They are awfully expensive - £4 for 8x bitesize. Can one reversely engineer these and find the recipe? Thank you immensely. 81.93.102.185 (talk) 16:53, 16 February 2008 (UTC)


 * Are maybe ingredients listed on the packaging? --Ouro (blah blah) 17:21, 16 February 2008 (UTC)


 * Beyond apple, sugar, apple-and-cinnamon fillings (detailed description) and the next 20 ingredients and E-substances, it doesn't lend much of a hint. I am wondering if actual tests can be done on the bun to show its amount of e.g. flour, eggs, everything. 81.93.102.185 (talk) 17:39, 16 February 2008 (UTC)


 * I guess one could try to estimate the ingredients from the results, but it'd be way more costly than buying them every day fresh. Oh, but if you have the ingredients and e-substances you're not that bad off. --Ouro (blah blah) 17:46, 16 February 2008 (UTC)


 * The proportion of the most basic ingredients (flour, eggs, water, yeast) is reasonably fixed, and a simple Google search for a recipe will yield satisfactory results (different will mostly affect the texture and consistency more than the flavour). A lot of those other ingredients, particularly the E numbers, are there because it's a commercial product - they're stabilisers and preservatives that are needed because it needs to have a factory-to-you time of a week or more. That's the big difference between stuff you bake at home and baked goods you buy from the supermarket - the home baked stuff takes incredible for the first 12 hours or so, but very quickly deteriorates.

I think you'll get nice results just baking a basic bun with the normal basic ingredients. You might find that it doesn't taste appley-enough; if so, try making a reduction from apple juice and using that in place of some of the water the recipe calls for. -- Finlay McWalter | Talk 17:52, 16 February 2008 (UTC)


 * A recipe is more than an ingredients list. I'm no expert on baking, but I believe that the heavenliness (or lack thereof) of baked goods is based at least as much on technique as on raw chemical composition.  No amount of reverse engineering, or mass spectrometry (or whatever) is going to tell you how finely or coarsely the shortening was cut in, or how long the dough was kneaded, or how long it sat between kneadings, or at what rate various amounts of liquids (some of which, of course, evaporated later) were added.  For that, you're either going to have to suborn an employee at the bakery, or do lots of experimenting yourself. —Steve Summit (talk) 19:43, 16 February 2008 (UTC)


 * If the dough and sweet mix are separated in swirls, then the sweet mix will almost certainly contain apple or (even nicer) pear concentrate. Also, using apple varieties suited to cooking helps. I used to bake these. Polypipe Wrangler (talk) 21:22, 16 February 2008 (UTC)


 * You could always ask the bakery for the recipe: they might not consider it a trade secret. Of course, even if they give it to you, it might turn out to require equipment you don't have at home.  [And then there's this hazard. :-)]  --Anonymous, 22:19 UTC, February 16, 2008.


 * You might wish to seek out Saigon cinnamon, since it has greater aroma than other varieties in the baking. One source listed in the article is [The Spice House]. The cinnamon is the essence of the baked good, and compared to premium freshly ground spice, the spices sold in little jars or tins in the grocery store are pale imitations. [User:Edison|Edison]] (talk) 02:34, 17 February 2008 (UTC)

Why do some people turn green when they get sick?
I have searched the internet on this subject and not seen anything of use. Recently my daughter (white, slightly olive coloured skin) was ill and she definitely had a greenish cast to her skin. Our family are curious to know what causes the green colour. She was feeling dizzy so may have had blood drain from her face to the part of her body that needed help. Why is the resulting hue green? —Preceding unsigned comment added by 124.197.36.202 (talk) 20:29, 16 February 2008 (UTC)


 * We discussed green skin on the Miscellaneous desk last month (here and also here), but I guess we didn't consider the illness angle much. —Steve Summit (talk) 21:53, 16 February 2008 (UTC)
 * This confirms your observation in a turn of phrase "looking green around the gills" meaning someone looks like they're about to be sick and google came up with green bile in the erm, vomit, but nothing about the skin's appearance except that it can refer to someone looking pale before they  er (excuse me...) Julia Rossi (talk) 11:56, 17 February 2008 (UTC)
 * FWIW I reckon it is just reduction in blood. If you reduce the red component from skin colours they often turn greenish. --BozMo talk 12:56, 17 February 2008 (UTC)