Wikipedia:Reference desk/Archives/Science/2008 July 13

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July 13[edit]

The other week someone said that the African grey parrot was probably the most intelligent dinosaur ever[edit]

Does this also mean that the African grey is also the most advanced dinosaur species that ever lived and therefore the pinnacle of the evolutionary line? —Preceding unsigned comment added by 84.70.123.255 (talk) 01:37, 13 July 2008 (UTC)

Uh, no. Intelligence does not indicate "advancement". (Humans are just as "evolved" as the housefly—evolution doesn't have an "end point" other than fitness for a given environment. We have great brains; dogs have great noses. We're all great.) And parrots are not dinosaurs, though birds are related to them. And even if there was some sort of very intelligence dinosaur, it would mean nothing about whether they were a pinnacle of an evolutionary line. --98.217.8.46 (talk) 02:09, 13 July 2008 (UTC)
Actually birds are descended from dinosaurs and many scientists do indeed consider them as "dinosaurs". From "Bird", "Most paleontologists regard birds as the only clade of dinosaurs that survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma." The term "non-avian dinosaurs" is sometimes used to distinguish the traditional "reptilian" dinosaurs from birds. Axl (talk) 16:34, 13 July 2008 (UTC)
Everybody knows they are descended from dinosaurs. We're descended from little rat like creatures too but they don't call us "rats". The point is though that a bird is not a dinosaur—they're mutually exclusive categories with a little bit of overlap. --98.217.8.46 (talk) 19:47, 13 July 2008 (UTC)
No, Axl is correct. Some paleontologists do consider birds, dinosaurs. According to Phylogenetic nomenclature, reptiles are a paraphyletic group. They can be monophyletic by adding birds. So not only are they dinosaurs, birds are also technically reptiles. ScienceApe (talk) 22:42, 13 July 2008 (UTC)

Well, in Cladistics, they could also be considered lobe-finned fish as well. 24.77.21.240 (talk) 18:27, 13 July 2008 (UTC)

In Cladistics, birds are also bacteria. I think the debate over whether birds are dinosaurs is more usefully seen as linguistic than scientific. --Allen (talk) 04:47, 14 July 2008 (UTC)
E coli are consuming the food in my fridge! Oh wait, it's me. Gzuckier (talk) 19:33, 14 July 2008 (UTC)

Also, note that "pinnacle of the evolution line" is not a valid concept and indicates you do not understand evolution very well. 159.14.240.230 (talk) 22:25, 13 July 2008 (UTC)

Danger of downed wires during a flood[edit]

I'm currently taking a course on swiftwater rescue and although my instructor had a bit to say about utility control during massive flooding, he couldn't give me much of an answer to the following:

A city has undergone massive flooding. Rescue boats are floating down streets effecting searches and rescues. The grid is still up, as evidenced perhaps by street lights, but there are downed wires contacting the flood waters. How much of a safety radius needs to be kept from such wires?

I understand that the conductance of water increases with salinity, so perhaps sewage overflow or brackish water would make conditions more dangerous, but as a rule of thumb what ought to be a safe distance from such downed wires? Normally, the safety radius for downed wires on the ground is the full span of the length of wire (one pole to the next, the radius the wires could potentially swing) but I feel like the safety radius of wires in the water must be different. A referenced answer would be appreciated, but I'll take math guestimates to get this started. --Shaggorama (talk) 02:24, 13 July 2008 (UTC)

If the wires are in constant contact with the water, they should be pretty safe. Electricity takes the path of least resistance to ground, that will be straight through the water, people floating on top should be perfectly safe, there is no reason for the electricity to go through them. The danger would be with wires close to, be not in contact with or in intermittent, the water. A person standing ankle deep in water that touches a wire would probably to more badly hurt than one standing on dry ground - the rubber soles of your shoes will insulate you a bit normally, but if you're in water, that won't happen and you'll get the full force of the electricity through you (it's probably not a significant difference, though, it's dangerous enough without the water and you can't be worse than dead!). I think staying the same distance as you would normally (far enough away that it can't touch you) should be fine - it would have to be a very unusual situation for the electricity to pass through water to you and not just go straight to ground. --Tango (talk) 02:38, 13 July 2008 (UTC)
It would be hard to specify the required "safety radius." It is not true that "electricity takes the path of least resistance to ground." Electricity takes all paths to ground, with the current in inverse proportion to the resistance of the path. So there would ge a gradient of current intensity around a live wire, with the dimensions hard to calculate. People have shocked fish out of the water with relatively low current and voltage [1] [2] (don't try this). The current should be stronger closer to the wire, but there might be enough current to stun the person in the water quite a diftance away. Also a wire at one location could liven a poorly grounded metal object, like a chainlink fence, barbed wire, a metal roof, gutters, or siding producing quite a high voltage at a remote location. Operating a boat and doing rescue in floodwaters with live wires down could be pretty hazardous. If the rescue crew had to extend a pole to poke something or hook something, it would be a good idea to have a fiberglass pole which did not conduct electricity rather than a metal one, because the voltage at two locations several feet apart could be substantially different. If the 4000 or 12000 volt primaries were live on top of the utility poles, the transformers on the poles could send 240 volt electricity to submerged meters for a long time, boiling the water without blowing a transformer fuse, even if the fuses/breakers in the building popped. Utility crews working along with the rescue crews to open poletop switches and kill the power might be a good idea. A couple of switches should suffice to kill a large area. Edison (talk) 13:37, 13 July 2008 (UTC)
The reason I asked for a "required" safe distance is because OSHA often makes safety mandates to that effect. For instance, there are required safety distances for operating in the vicinity of charged wires on the ground as well as overhead clearance for high voltage lines (I can't remember which regulation it is that makes these prescriptions). --Shaggorama (talk) 04:41, 17 July 2008 (UTC)

My potato question[edit]

Since there are already two potato questions recently, here's another:

  • Disclaimer: This is a question involving electricity powerful enough to kill you. Unless you know how to take appropriate safety precautions, do not try to experiment with this yourself.
  • Context: A really cool art installation at ThePowerPlant (if you're ever in Toronto, go to HarbourFront) consisting of cut out package fronts of everything from pantyhose to board games. Artist was Laura someone, orange light, trust me, it was cool. One package caught my eye:
  • The thing: A boxtop abour "The Glowing Potato" or something. This was something from the 60's that plugged into normal power and promised that you could stick a potato on it and make the potato glow.

This sounds not unreasonable to me, since the potato would have a resistance. I'm posting this here to see if anyone has ever heard of the device; and for ideas on how to actually construct one. AC or DC? Stepped-down voltage? There was no picture of the actual device on the package, but it did promise to make a glowing potato. so it's part of the North American cultural heritage :) Help is appreciated. Franamax (talk) 04:30, 13 July 2008 (UTC)

(Fixed your external link; I hope I modified it correctly.) --Bowlhover (talk) 05:15, 13 July 2008 (UTC)
You can make an electric pickle with household voltage but that has a goodly amount of ions available because of the pickling. Most links I see about potatoes were about potato batteries. Rmhermen (talk) 04:49, 13 July 2008 (UTC)
Webpage about electric pickles: http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/pickle.html
Since the light produced is due to excitation of the sodium ions, would a salted potato produce a similar effect? --Bowlhover (talk) 05:15, 13 July 2008 (UTC)
Hmm, maybe it was a pickle. There was an awful lot to look at in those three 10-foot rooms, everything went right around the ceiling. I thought I already knew about the pickle, but they do both start with "P". I guess I'll start with a pickle, then try the higher vegetables ;) I'll try soaking a potato in salt water - in fact, maybe that's the trick, does osmosis come into play? If a potato can be a battery, then could there be some ion exchange that gets the sodium in there?
I'll have to track the art installation down again and check outside to see if the instructions are on the back of the box :) This only makes me curiouser, though I feel sure now that I do have to try that pickle. Thanx! Franamax (talk) 06:19, 13 July 2008 (UTC)

question about baseballs and wind resistance[edit]

moved to mathematics desk.

Why? It's a physics question, not a purely mathematical one. --Bowlhover (talk) 07:33, 13 July 2008 (UTC)
I tend to agree, no point starting a war over it though.. also it's a good idea to link to the moved question.
Like this:
Wikipedia:Reference_desk/Mathematics#Question_about_baseballs_and_wind_resistance —Preceding unsigned comment added by 87.102.86.73 (talk) 16:30, 13 July 2008 (UTC)

Atoms[edit]

Hi! Where can I get a 3-dimensional picture of the atomic orbitals? I wish to see how they co-exist? —Preceding unsigned comment added by 116.68.74.189 (talk) 13:52, 13 July 2008 (UTC)

Does the image at the top of our article suffice? Angus Lepper(T, C, D) 14:24, 13 July 2008 (UTC)
Also later in that article is a table of all ones used for the ground-state of all known elements. DMacks (talk) 15:48, 13 July 2008 (UTC)
The Orbitron tends to be my personal favorite --Bennybp (talk) 15:26, 13 July 2008 (UTC)
See Atom There was a recent report "Physicists Create Millimeter-sized 'Bohr Atom'". Science Daily. July 1, 2008.  of mad scientists exciting an electron such that the poor thing was forced into an orbit around the nucleus creating an atom with a diameter approaching one millimeter, many orders of magnitude larger than the typical atom. No fancy orbital, just a circular orbit like a Bohr atom. The electron followed the circular orbit, like a planet around the Sun, for a few orbits. Edison (talk) 04:32, 14 July 2008 (UTC)

What I mean is, how can I get a picture of ALL the orbitals together in an atom so that I can see how they co-exist. Every picture I have seen depicts each orbital separately and singly. I want to know how they can all be together- for example, both 2Px, and 3Px are along the same axis with the same bilobed shape. Won't some regions coincide?? And they are also supposed to have different energies, but if it coincides at portions, how can that be? —Preceding unsigned comment added by 116.68.74.243 (talk) 16:10, 14 July 2008 (UTC)

This applet allows you to display any one at a time, but you can fix the axis-scaling so that (for example) you can see the different radial extent of each px. Didn't see a way to overlay them (maybe print a few out on thin paper and hold 'em up with a bright light behind, or save to a graphics-format file and overlay them in GIMP or Photoshop?). DMacks (talk) 17:02, 14 July 2008 (UTC)

High temperature changes on the human body[edit]

What are the effects of rapidly changing temperature for a person, assuming the temperatures reached are not in themselves too extreme? Consider a person in a hot tub, going outside in the snow or any such scenario. Does it have health benefits or side effects?Bastard Soap (talk) 15:28, 13 July 2008 (UTC)

This type of a shock is likely to cause a rapid heart rate and high BP spike. Those could certainly be harmful to someone in poor health. I suppose advocates of this argue that it exercises the cardiovascular system and thus keeps it strong, but I'd think it safer to stick with more traditional forms of exercise. StuRat (talk) 17:11, 13 July 2008 (UTC)

A good example is someone with hypothermia getting put into a hot bath to try and reheat their body. Really, really bad idea, it'll burn like crazy. For the record, in that situation, the best thing to do is slow-heat the body, i.e. blankets, very luke warm water etc. — CycloneNimrod  Talk? 17:40, 13 July 2008 (UTC)

A better example (or at least a more common one) is the Sauna. You heat up in a room between 80 and 100 deg Celsius, then you cool down fast, with a cold water shower, dunking in a cold pool, or, indeed, rolling in the snow (careful, it hurts like hell). It is supposed to have many health benefits, including a strengthening of the immune system. As far as I'm concerned, it actually feels really good and relaxing... --Stephan Schulz (talk) 17:58, 13 July 2008 (UTC)
When it comes to snow, you can minimize discomfort by making sure that the actual surface under the snow (if the snow isn't deep) is even enough and doesn't have things like sticks and stones poking up under it. Those can smart. Another thing is to make sure that you're not rolling on pieces of ice. Typically, on a sunny day the surface of a snow bank melts when the sun shines on it, but when the sun goes down and the temperature drops, it freezes -- so you can have a lot of soft snow under a hard frozen cover. Your weight will break the cover, but that ice isn't going to do you any favors. Of course, even soft snow is going to be a bit of a shock after the sauna... but it's a pretty great feeling. Here in Finland, where this kind of stuff is our bread and butter (I just got out of the sauna about an hour ago myself) there's a general understanding that jumping right into cold water or snow after coming out of the sauna is not a good idea if you have any kind of heart trouble -- you should cool down a little before you do so. -- Captain Disdain (talk) 23:40, 13 July 2008 (UTC)
Elderly Swedes have told of getting in the sauna, then running naked out into the snow and hitting each other's naked bodies with bundles of switches (arboreal, not electrical). Sounds nuts, but they lived to a ripe old age. Edison (talk) 04:25, 14 July 2008 (UTC)
Oh, the switch thing is a Finnish classic as well. -- Captain Disdain (talk) 09:15, 14 July 2008 (UTC)
Yay Finland! I got to experience a savusauna (smoke sauna, it has no chimney) when I visited. The switches are for use inside the sauna, they take off the sweat and let you heat up even more. It was so hot my eyeballs seemed to be glazing over. Then right out and into the lake. Awesome experience, one of those "if it doesn't kill you, it will make you stronger"-type things. Franamax (talk) 21:24, 14 July 2008 (UTC)
That's just about the best kind of a sauna you can experience, so lucky you. Sauna deaths are probably not unheard of, but I'm pretty sure they're exceedingly rare... though not for lack of trying! Those guys are just nuts. -- Captain Disdain (talk) 01:27, 16 July 2008 (UTC)

Two-liter bottle (PET) adhesive[edit]

What would be good options (the less toxic the better) for sticking together two-liter bottles made of polyethylene terephthalate? Thanks - Qatter (talk) 16:21, 13 July 2008 (UTC)

could you be more specific in how you want to stick them and what strength the join needs to be..
Meanwhile how about sticky tape or duck tape?87.102.86.73 (talk) 16:26, 13 July 2008 (UTC)
Epoxy adhesives, which mix together two chemical, work well for applications where a strong space-filling adhesive is needed. Edison (talk) 04:27, 14 July 2008 (UTC)
polyethylene is pretty slippery stuff; epoxy might not be the best. i think something solventy would be better. can't say what though. i have tried to glue one of those clearish/cloudyish big plastic storage tubs (which might be polyethylene) together with cement for vinyl pipes from home depot, the kind labelled for all kinds of plastics, and it wasn't great. sure didn't penetrate, like i hoped solvent would. Gzuckier (talk) 19:30, 14 July 2008 (UTC)
Why not just use some form of plastic weld? If you can use just the right amount of heat to partially melt the plastic without puncturing the bottle, then this might be stronger than most glues. Adding more of the same material, partially-melted, will increase the strength. Unfortunately, it is not easy to get just the right amount of heat, but if you have spare bottles, you could experiment until you get it right. Some soldering guns have plastics tips for this type of "welding". Dbfirs 18:49, 16 July 2008 (UTC)
hmm; a heat gun, maybe with a funnel output, a rheostat, and a supply of "welding rod" of the appropriate plastic...Gzuckier (talk) 19:36, 16 July 2008 (UTC)

Body weight[edit]

I have some questions about body weight. Let's assume an average healthy adult male in America (thus, using pounds and not kilograms).

  • (1) Why is it exactly that when you weigh yourself several times within the same day, you will get several different readings? What exactly contributes to those differences?
  • (2) How wide of a discrepancy would be the "expected norm" in these different readings? I assume being "off" by 1 or 2 pounds is normal, but being "off" by 10 pounds is not. Is there some general expected norm?
  • (3) Is there a particular time of day when one's body weight will always be the lowest ... when would that be ... and why ... (for example, just after you wake up, just before you go to bed, right after working out, right before working out, right before eating, right after eating, etc.)? In other words, if one always wants to weigh himself at the lowest point in the day, when should that be?
  • (4) What is a healthy and appropriate amount of weight to lose in a given time period? That is, it is healthy to lose perhaps 1 or 2 pounds a day, but not 20 or 30 pounds a day, I assume ... is there some standard? Thanks. (Joseph A. Spadaro (talk) 18:35, 13 July 2008 (UTC))
1. Food and water must be a big factor, both intake and excretion. Clothes you wear also make a difference (i.e. are you wearing shoes?) — CycloneNimrod  Talk? 18:52, 13 July 2008 (UTC)
Defecation and urination are indeed going to be big factors in how much you weigh at any time. Fribbler (talk) 18:56, 13 July 2008 (UTC)

4. You have to take in about 3,000 calories less than you need to lose a pound of weight. Since the recommended daily intake for a man is 2,500 calories, it's clearly not healthy to try and lose a pound a day. Losing a pound a week (400 calories a day) would be a serious (hard work) diet, and you should see a doctor before you try anything like it - they could say if your plan is healthy.--64.231.9.30 (talk) 22:18, 13 July 2008 (UTC)

  • (3) There is no answer that could possibly apply universally as each individual is, well, individual. The best strategy to monitor weight trend is to pick a particular time of day that would be least influenced by any of the usual stuff, say upon awakening and after voiding (if appropriate) naked and before breakfast. Record that weight with a 0.1 pound resolution digital scale and if your goal is to lose weight then keep the data in whatever form highly visible to yourself (and importantly, to others :-)
  • (4) So, WP:NOR be damned, (this isn't an article after all), two pounds per month is an appropriate challenge for either gaining or losing weight. Now, looking around at all of the information here, it should be obvious that two pounds per day (or per hour) is easily acheivable but, we're not talking about that, we're talking about "usually", so if you drop a six pack before rolling out of bed well then that's your "usual" and so go with that, consistency is the most important thing. Oh , and I think that 1 or 2 pounds a day under standard conditions would not be healthy but 1 or 2 pounds a week seems reasonable. -hydnjo talk 04:14, 14 July 2008 (UTC)
I would expect your lowest body weight to be after you wake up in the morning, defacate and urinate, and weigh before eating or drinking anything. Clearly a pint of liquid refreshment weighs about a pound, and whatever you eat adds to your weight until you defacate and urinate. Any salty food should cause water retention. 2 pounds variation would not be at all surprising, just based on personal experience. Edison (talk) 04:21, 14 July 2008 (UTC)
Another factor in getting different weights could be an innacurate scale. If you are using a spring scale, for example, those tend to have readings which vary dramatically based on humidity, since they can "stick" if used in the bathroom after a shower. StuRat (talk) 04:27, 14 July 2008 (UTC)

An anonymous (well, mostly) poll and invitation:[edit]

Step right up and "weigh-in" RDers, c'mon now, this is one of the least serious polls in which to participate!

If you are trying to gain weight then increment: ..................................... #0
If you are trying to maintain weight then increment: .............................. #1
If you are trying to lose weight then increment: ..................................... #4
If you are not trying to consciously control your weight then increment: ... #1
If you are not understanding WTF is going on then don't dare touch this: .. #43
Results (update #5): The folks not knowing WTF is going on seem to know it all!
Logging out and polling as an anon if of course just fine. -hydnjo talk 04:47, 14 July 2008 (UTC)

(Original research warning...) I've been taking data on this very question and I find that my weight varies over a range of about two to three pounds each day. And this stands to reason: Drink a 16 ounce glass of water and you've just "gained a pound". Eat a meal and you've "gained" another pound. Later, use the toilet and you lose most of that "gain". Go for a long walk, run, or bicycle ride, sweat out 16 ounces of sweat, and you've also "lost" a pound.

In other words, small changes don't matter. This variation can, to some degree, be mitigated by weighing yourself at the same time of day each time you weigh yourself, perhaps in the morning after you've voided your bladder and defecated. But even then, only pay attention to the long term trends (unless you're like me and are doing it just to collect interesting data for later use in an encyclopedia).

Atlant (talk) 12:32, 14 July 2008 (UTC)

My point regarding the use of a high resolution scale was to at least eliminate that variable. So, we all seem to agree that the best strategy to monitor a weight trend is to do what we all said (AM, after voiding (if appropriate), and before eating or drinking anything (unless it is a standard amount each time-in my own case it happens to be 8 ounces of a medicine). Now, given all of our collective wisdom, we seem to acknowledge that there is day-to-day noise in the data however, over several weeks of daily data, a trend can be inferred. I've been taking this data on myself for well over 20 years and am confident of its usefulness. -hydnjo talk 15:30, 14 July 2008 (UTC)
Note that the surface on which the scale rests also has an effect on the reading. My spring scale gives my weight as 130 lb on a ceramic floor and 136 lb on a carpeted floor, for example. --Bowlhover (talk) 07:58, 15 July 2008 (UTC)

Thanks to all for the above discussion. It was very helpful and useful to me. Thanks a lot! (Joseph A. Spadaro (talk) 15:22, 16 July 2008 (UTC))

negative effects of cooking gas[edit]

if someone were to have a faint leak, so that they could smell the gas, and as a result decided to air it out, but continued to smell it faintly, would inhaling it -- I AM NOT ASKING FOR LEGAL OR MEDICAL ADVICE -- be harmful? Ought they to leave the room? —Preceding unsigned comment added by 82.120.227.196 (talk) 19:10, 13 July 2008 (UTC)

This seems to imply that it's not a good thing to doCycloneNimrod  Talk? 19:38, 13 July 2008 (UTC)
The biggest danger of a gas leak is not inhaling it but that it is VERY flammable. You ought to call the gas company (or maybe even the fire department) and get it fixed NOW. See Natural_gas#Safety. --98.217.8.46 (talk) 19:40, 13 July 2008 (UTC)
Continue airing it out, get out of the house, call your local emergency gas leak number. If you're in the UK, this is a good guide. Call 0800 111 999 from outside your house, which should have the windows open, the gas switched off, etc. If you're elsewhere, I'm sure there are local guides and numbers. 79.66.54.186 (talk) 19:42, 13 July 2008 (UTC)
The negative effect is that your house might explode!. Leave the house, use your neighbor's phone to call the gas company. APL (talk) 20:00, 13 July 2008 (UTC)
Obviously, I second what everyone else says about the danger of explosion, and you do need to get out of the house. However, to answer the specific question asked, natural gas is not toxic (according to Natural gas, anyway), the only danger from inhaling it is that you may not be inhaling enough oxygen and could asphyxiate. However, if there's enough gas in the room for you to be concerned about being poisoned, there is enough to warrant getting out of there, so it's purely academic. --Tango (talk) 21:15, 13 July 2008 (UTC)
Also, for the record, if the odor is really really faint, then the amount of gas present is probably tiny. Natural gas is odorless, so compounds are added after the product is refined to assist in detection of leaks. These compunds, often thiols (AKA mercaptans) are so pungeant that we detect them in units of parts per BILLION! For instance, let's say the gas you were cooking with was propane odorized with ethanethiol: the LEL for proapane is 2.1 * 10^7 ppb, but you can detect the odorant at quantities as low as 2.8 ppb. If we call > 10% of LEL our danger zone, you could detect the gas by smell and still have a safety factor of 1 million! Neat huh? Yay technology!
Obviously, you should still play it safe and call the utilities or fire department. Depending on where you live, if you are positive the leak is small, it may actually better to minimize ventilation (close windows) before leaving the house if you know help will arrive soon. Natural gas is heavier than air and will collect in pools which helps detection if electronic gas detectors are used: if the house gets ventilated, the explosive hazard is minimized but it becomes much more difficult to pinpoint the source of the leak. Again, this is ONLY if you know help will arrive soon, you know what detection capabilities they have and you think the leak is small. You don't want to fill up your house with gas. --Shaggorama (talk) 22:03, 13 July 2008 (UTC)
I think there's an error in your calculation - we can smell the odorant at 2.8 ppb *of the odorant*, but the odorant isn't 100% of the gas, obviously, so you need a higher concentration of the gas in order for the odorant to be high enough. I'm not sure what proportion of the gas is generally odorant, but it's quite small, so the safety factor is nowhere near a million. And I would advise against trying to keep the gas in to aid detection - let the experts worry about finding the leak once they get there, don't take any risks. --Tango (talk) 23:03, 13 July 2008 (UTC)
If the natural gas is at a high enough percentage of the air in the structure to explode, clearly the explosion, fire, and structure collapse could have devastating effects. But humans expel methane under the covers while they sleep, and I have never heard of anyone dieing from exposure to small amounts of it. If you report a possible gas leak to the gas company and/or the fire company, they should be able to test for the presence of it. Methane is actually odorless; an odorant (butyl? mercaptan) is added to make it detectable. Edison (talk) 04:12, 14 July 2008 (UTC)
I tried calculating the concentration of propane indicated by the lowest perceivable concentration of its odorant, ethyl mercaptan. Estimates of ethyl mercaptan's odour threshold range from 0.01 ppb to Wikipedia' figure of 2.8 ppb, so I abandoned this approach.
This paper indicates that around 40% of elders cannot detect the odorant at a level associated with a concentration of propane at the Department of Transportation`s safety limit, which is a fifth of propane`s LEL. Three of the 110 subjects could not even smell the ethyl mercaptan when it was at a concentration that would indicate a risk of explosion. So even if the odorant is barely perceivable, the risk of not taking further steps to remove propane is very small, but not negligible. --Bowlhover (talk) 09:10, 14 July 2008 (UTC)
Is there such an odorant as butyl mercaptan? (O Captan! Mercaptan!). Edison (talk) 19:05, 14 July 2008 (UTC)
butyl mercaptan says it "is used…as an odorant for natural gas". DMacks (talk) 19:09, 14 July 2008 (UTC)
So is the answer above wrong which talks about ethyl mercaptan, or are they used together, or do different gas companies use different odorants? Or is it propane versus natural gas? I would assume they have different detectability levels, which would also affect the analyses. Edison (talk) 17:39, 15 July 2008 (UTC)
I think it's at the discretion of the manufacturer what chemical they use as odorant, so long as the added odor meets certain government standards for threshold detectability of the gas. Go to a local camping supplies store and buy the cheapest small bottle of propane there and compre its odor to the most expensive brand: strong probability the cheapo smells worse. --Shaggorama (talk) 12:20, 16 July 2008 (UTC)

Blood types: who is my father[edit]

Who is my father?

Can an O+ and an AB- get an O+ child?PK LAINE (talk) 20:02, 13 July 2008 (UTC)

I don't think so, no. To be O, you need to get the O allele from both parents. Someone that is AB has an A allele and a B allele, so they can't have an O allele to give. There is a table on ABO#Inheritance which shows the possible inheritances. The + part is fine, though, you only need one parent to be Rhesus positive for you to be. Of course, there is always the possibility of random mutations and what have you messing everything up, so the blood groups not matching isn't 100% proof that they aren't your biological parents, but it is unlikely. Note, AB- is a very rare blood type (1% or less of the population, depending on where you are - see Blood type for a table), so you may want to double check you've got that right. --Tango (talk) 20:21, 13 July 2008 (UTC)
See also hh antigen system -- there is a tiny chance that both mother and father could have the recessive h gene, and the child could come up hh (the Bombay phenotype) which means he would have O blood regardless of the rest of his genotype. --Trovatore (talk) 20:37, 13 July 2008 (UTC)
I've also just read in the ABO article that AB expresses less strongly than A or B individually, which I think means AB people are sometimes detected as O. That suggests that it's possible that, in fact, both parents and the child are AB, although that also would be very unlikely. --Tango (talk) 20:43, 13 July 2008 (UTC)
The answer is yes, for a wide range of reasons. If you're concerned about the identity of your biological mother and father, I suggest you speak to your parents and to your doctor. Any answer we provide here is apt to be imcomplete or misleading. TenOfAllTrades(talk) 01:13, 14 July 2008 (UTC)
There was a woman who was told that her true biological child could not be her actual child. It turned out that she was a Chimera with her ovaries possessing different DNA than her blood would imply. There are also cases of hospitals accidentally switching blood samples and reporting erroneous results. Just saying. Edison (talk) 04:07, 14 July 2008 (UTC)
We used to test our blood types in high school biology, but they stopped doing it when students were going home with difficult questions... Plasticup T/C 12:57, 14 July 2008 (UTC)
I've heard that claim before but I suspect it may have more to do with fear of infectious diseases rather then children finding out their parents may not be who they thought they were (although I'm sure it was somewhat of a problem). Nil Einne (talk) 18:35, 14 July 2008 (UTC)
I find it quite believable. One of the major concerns in any medical study involving large-scale blood typing or DNA testing is dealing with the fact that about 20% of the subjects cannot possibly be the children of their supposed fathers. --Carnildo (talk) 22:05, 15 July 2008 (UTC)

Conductive napalm? Railgun + conductive flammable liquid = long range flamethrower?[edit]

Regarding railguns, could it be possible to fire a flammable liquid through it? Are any flammable liquids conductive? ScienceApe (talk) 22:38, 13 July 2008 (UTC)

Wouldn't firing a flaming liquid at very long range with a large ratio of total volume to surface area effectively cause it to cool down too rapidly to be of any use? --98.217.8.46 (talk) 03:10, 14 July 2008 (UTC)
I guess it depends on the flaming liquid, but napalm doesn't cool down very quickly, it's quiet tenacious. ScienceApe (talk) 18:57, 14 July 2008 (UTC)
Right, but it's usually not going very far or at very high speeds, and it's not usually kept in a long thin stream. If you change the characteristics around it'll radiate heat differently than how it does when used in bombs or flame throwers. --98.217.8.46 (talk) 20:47, 14 July 2008 (UTC)
Liquid Sodium etc are flammable/conductive - unfortunately liquids tend to spread out as they travel because they have no integrity - maybe this would be a problem.87.102.86.73 (talk) 10:50, 14 July 2008 (UTC)
Liquid sodium, interesting. Maybe some kinds of gasoline/sodium mixtures might help make it conductive. Yea, in order to make a good flamethrower the liquid has to be a thick gel, this would keep it cohesive. Napalm is actually a thickening agent. ScienceApe (talk) 18:57, 14 July 2008 (UTC)
Napalm is actually a thickening agent. Good, I'll remember to put it in my pudding. Mac Davis (talk) 23:33, 14 July 2008 (UTC)

This page: [3] document that using this idea to propel ships has been considered several times. Basically, the underside of the ship follow the same schematics as a railgun, moving conductive seawater. More info may be found in the Magnetohydrodynamics article. So basically, it's possible in principle. The use of a plasma instead of a liquid may be more interesting though, as there's ways to keep that together. EverGreg (talk) 21:26, 20 July 2008 (UTC)

Ultraviolet light[edit]

So if you go to Ultraviolet, you'll see it only explains how humans deal with ultraviolet light. The only other animal this could possibly apply to is non-feral pigs as they tend to be hairless.

So one wonders, what about other creatures. Are reptile scales any good protection against UV light? It would seem likely they are. What of bird feathers, animal hair, fish scales, dolphin/whale/seal skin, insects and other anthropods, etc.? The Talk:Ultraviolet looks abandoned. Well, is this information somewhere else on Wikipedia that someone knows of? William Ortiz (talk) 23:03, 13 July 2008 (UTC)

Certainly. Scales, feathers, and hair are all good protection from UV light. Additionally, just wearing clothes will protect you from UV light as long as it is fairly opaque. Whales and other marine animals live in the water where the water itself protects them from UV light. You might also wonder about pigs and hippos. They have melanin in their skin (just like us), and also use mud to help protect them. ScienceApe (talk) 23:45, 13 July 2008 (UTC)
Eumelanin, much more so than phaeomelanin, is the principle mechanism of UV protection in skin. Many, many animals have eumelanin in their melanocytes or melanophores in skin and scales. Moreover, hair, feathers and exoskeletons contain much melanin also. The role of melanin in UV protection is highly conserved throughout the animal kingdom. Rockpocket 02:59, 14 July 2008 (UTC)
Cats can get sunburn, at least white cats can. Their ears are particularly vulnerable, if I recall. 79.66.54.186 (talk) 17:35, 14 July 2008 (UTC)
The bridge of the nose and light coloured noses are too of both cats and dogs. Tattooing is sometimes used to try and prevent this although I don't think it's that effective [4] Nil Einne (talk) 18:27, 14 July 2008 (UTC)
Our cat is an albino. As you can imagine, this is a pain for her and us during the summer months. Lots of sunscreen required. If only she liked the stuff... — CycloneNimrodTalk? 15:46, 16 July 2008 (UTC)

Why is it that light colors which reflect heat make people vulerable to sunburn while dark colors which absorb heat protect from sunburn? William Ortiz (talk) 22:38, 14 July 2008 (UTC)

It isn't exactly "heat" that causes sunburn. Dark eumelanin absorbs UV, which means there is less of it around to damage the unprotected cells underneath. Light coloured phaeomelanin can't absorb UV as well, so more of it damages the skin cells underneath, which results in sunburn. Interestingly enough, darkly pigmented skin appears to reflect UVB and UVC better than lightly pigmented skin. It appears that scattering by melanosomes with high relative refractive indices plays a major role in this. Rockpocket 01:20, 15 July 2008 (UTC)
I can't lay my hands on the ref but I have read that the mechanism of melanin protection is that the cell accumulates it and tows an umbrella of melanin into place to shield the cell nucleus as a specific response to UV radiation. I'll try to chase that down if anyone wants, 'tho I'm not exactly sure where to look anymore. Also, pigs definitely do get sunburn if you leave them out in the sun, Yorkshire pigs anyway (pink-white skin + I can't believe we don't have an article on Yorksies!). Franamax (talk) 07:20, 15 July 2008 (UTC)

Right, it isn't heat that causes sunburn. It's UV light. You can wear a thick winter coat on a hot summer day, and you won't be sunburned because the coat will block UV light. You'll pass out from heat stroke though. ScienceApe (talk) 17:14, 15 July 2008 (UTC)

That's right. It's not the reflection of heat that is important here, it is the relection of light. Specifically, lighter coloured clothes would reflect light (of all wavelengths including UV) onto the wearers face making them more vulnerable to sunburn. Jdrewitt (talk) 19:54, 16 July 2008 (UTC)