Wikipedia:Reference desk/Archives/Science/2011 March 29

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March 29

Rendering Equations

I've been trying to lean how to render equations instead of having to ask. Why doesn't this render png? On my browser it appears as html.Bugboy52.4 ¦ =-= 03:34, 29 March 2011 (UTC)

${\text{Work}}=F_{av}\times d={\text{2Wd}}$

How about this:

${\text{Work}}=F_{av}\times d={\text{2Wd}}\,\!$

Courtesy of Help:Math#Forced PNG rendering. DMacks (talk) 03:48, 29 March 2011 (UTC)

What about

Failed to parse (syntax error): {\displaystyle \text {E}=\text {mgh}=0.1\times980\times10^{−2}=0.98\text {erg}}

Its not rendering, what am I doing wrong? Bugboy52.4 ¦ =-= 03:53, 29 March 2011 (UTC)

The minus sign in your "-2" is not an ordinary minus sign, it is some sort of fancy dash. The math mode parser does not know how to handle it. If you use an ordinary minus sign, it will render:

${\text{E}}={\text{mgh}}=0.1\times 980\times 10^{-2}=0.98{\text{erg}}$

Looie496 (talk) 04:22, 29 March 2011 (UTC)

Someone please copy this to WP:VPT so the developers know about it. 99.2.149.161 (talk) 17:30, 29 March 2011 (UTC)

The developers will tell you that the TeX parser is fully compliant - and that this behavior is correct. You have entered invalid syntax that is not a valid equation. Unicode (and therefore MediaWiki and its TeX parser) specifies a different interpretation for − and - though the glyphs look similar in most standard Windows, *nix, and Mac fonts. (Consider reading the characters in a hex editor). Read about character duplication in Unicode, which is slightly technical. Nimur (talk) 19:41, 29 March 2011 (UTC)

A test where E. Coli is not exceeding 3/g ???

Under Australian legislation, ready-to-eat meat products must not have E.coli exceeding "3/g"
But it doesn't specify what the unit of measurement is, 3 what???
3 Colony-forming_units?
3 single Bacterium?
^{I have contacted the Food Authority and they will come back to me within 10 days. I have also contacted laboratories but their sales people don't know.}
220.244.35.181 (talk) 05:02, 29 March 2011 (UTC)

Based on this I think it means 3 single Bacteria (per gram). Ariel. (talk) 07:04, 29 March 2011 (UTC)

Thanks, I did come across that paper, but I'm afraid it's no clearer - it doesn't state what test it uses - the test could use a different scale altogether. I'm not a food scientist (or any scientist for that matter) but it was impression that meat products can have thousands if not millions of bacteria - it seems absurd to me that you'd only find "3" micro-scopic bacteria of E. coli on a single gram. 220.244.35.181 (talk) 09:27, 29 March 2011 (UTC)

Reading this [1] report, it seems it may be common to give the number in log10. So "3" actually means "10^3". That's still not a lot though, maybe it just puts a cap on the required measurement sensitivity. If you had say 20 bacteria per gram, you may have had to incubate them for a long time before you could detect them, while a thousand bacteria per gram can be detected just in time to stop a meat shipment. But this is just my speculations. EverGreg (talk) 12:51, 30 March 2011 (UTC)

What percentage of the atoms in our bodies were born in the hearts of dying stars?

Based on this table detailing the Chemical makeup of the human body, what percentage of our atomic composition (not mass) was created as a result of the death of stars? Flaming Ferrari (talk) 06:03, 29 March 2011 (UTC)

It's almost impossible to speculate. Just about any element lighter than iron can be created by Stellar nucleosynthesis; heavier elements than iron are thought to arise from supernovae. However, given all of the various ways that a star may "die"; even if we just consider supernovae, a large percentage of all elements are likely scattered from them, even small elements like hydrogen, so just about any of the atoms in your body could have come from "dying stars"; and since two atoms of the same element and isotope are literally indistinguishable, there's no telling where they came from. --Jayron32 06:23, 29 March 2011 (UTC)

This sounds like a homework question to me. I'd guess that the instructor means for you to figure that everything but hydrogen "was created as a result of the death of stars". So, that's 90% of the mass of a human, but you can do the math to figure out the "percentage of our atomic composition" (which I assume means by count of atoms). Since hydrogen is the lightest element, the count of hydrogen atoms should be considerably more than 10% of the body. If you want to do the math here, we'll check your work. StuRat (talk) 07:16, 29 March 2011 (UTC)

A homework question where the lecturer refers the students to a Wikipedia table? Things have gone downhill since I left academia five years ago! --TammyMoet (talk) 07:57, 29 March 2011 (UTC)

They may have found that on their own, but don't know how to get the answer to the HW question from it. StuRat (talk) 08:55, 29 March 2011 (UTC)

Wikipedia has come on a lot in five years. We hope. Itsmejudith (talk) 16:16, 29 March 2011 (UTC)

A significant part of the Lithium also originates from BBN. Count Iblis (talk) 14:06, 29 March 2011 (UTC)

True, but lithium (and helium, the other major non-radioactive elemental product of Big Bang nucleosynthesis) have no known biological function, and are present in the body in negligibly trace amounts. TenOfAllTrades(talk) 14:29, 29 March 2011 (UTC)

Maybe you should count everything heavier than (or at least as heavy as) lithium and at least as light as iron, because it is hard to think of a supernova's exploding shell as a heart. But then again, most stellar nucleosynthesis takes place when most people would not say the star is dying, but the supernova does, so maybe you should count everything heavier than iron. But don't supernovae synthesize some proportion of light elements, too? Does anyone have a good idea what that proportion may be? 99.2.149.161 (talk) 17:49, 29 March 2011 (UTC)

There's the issue of when elements are created, and also when they are released. Even if somewhat heavier elements are created before the death of a star, if they languish in the star's core, they aren't available biologically. From my experience with sloppy homework (and test) questions, it wouldn't surprise me a bit if the instructor is conflating those elements created by a star's death with those released by it. Unfortunately, with such sloppy questions, figuring out what the instructor really meant to ask is often the most difficult part of the problem. StuRat (talk) 18:09, 29 March 2011 (UTC)

part 2

A.mohammadzade let me ask this again ,as all know the huge part of our body contains water and the protein which made our meat is made of hydro carbon .Calcium element is about 15 percent and iron is in our blood and so zinc and Natherium ,... The first interstellar cloud which made sun and solar system might had hydrogen and helium so the last effects of dust came from novas and supernovae mixed to this cloud and the nebula had some thermodynamic conditions to made water and chemical matters , hydrocarbons made in earth specially condition which made the life .and first nebula did not be able to produce carbon and oxygen , which made 23percent of earth mass and 21%of air ,and several metals and silicates in earth crust are oxidized .

I want you my friends not to say died star for super novae they made life and they are absent in sky and send pulses and notice: Some body used to say something about the black holes but I prefer to say about super novas , the first one shows death and being mystery the second one is about the life and being alive .it had send oxygen and carbon ,so calcium and iron here to made our life(akbar mohammadzade)

 :--78.38.28.3 (talk) 04:08, 30 March 2011 (UTC)

I moved this from your new post on the same topic. It should all be kept together. StuRat (talk) 04:21, 30 March 2011 (UTC)

gas heat

my furnace is AC ready but has no AC hooked up to it. my repair guy said i have to clean that part too. how do i do that? — Preceding unsigned comment added by Wdk789 (talk • contribs) 07:03, 29 March 2011 (UTC)

When you say AC do you mean Air Conditioning or AC electricity? Ariel. (talk) 07:08, 29 March 2011 (UTC)

Air Conditioning — Preceding unsigned comment added by Wdk789 (talk • contribs) 07:17, 29 March 2011 (UTC)

So you have a point where the A/C unit will tie in to the duct-work of a forced-air gas furnace, and need it cleaned ? If it's a matter of cleaning out a duct, I'd use some kind of a mop in the open end. I'd use it dry to get the dust out. Wear work clothes and a dust mask while you do this, or you may be in for a coughing fit. Also, turn the furnace off shortly before you do this, as the duct-work might be hot where it connects. Note that there are companies that clean ducts, if you don't want to do it yourself. StuRat (talk) 07:22, 29 March 2011 (UTC)

Could you fit a model V12 or W16 onto a motor scooter and make it really work?

See, this is a real-working model V12: http://www.youtube.com/watch?v=0V_2v-ol1EU

And this is a W16, intended to be a 1/5th scale model of the Bugatti Veyron engine: http://www.youtube.com/watch?v=-DijdisWkAE

Are the horsepowers divided by their scales? Therefore, if the W16 has 1001 HP, would the fully-working 1/5th scale model have 200.2 HP? If so, how well would a 200.2 HP engine work on your everyday commuter motor scooter?

Regardless, what kind of ride would you get by putting those miniature versions of the Über engines into a motor scooter? What would your top speed be from there on out, as well as the acceleration, noise and fuel mileage? --70.179.169.115 (talk) 07:54, 29 March 2011 (UTC)

I don't know if the simplistic approach to working out the horsepower is right, but even if it is, since the engine is three-dimensional you'd want the inverse cube, which is 1/5th times 1/5th, making 1/25th the horsepower. Wait, or do I mean 1/5th times 1/5th times 1/5th (1/125). It will be disappointing, anyway. 213.122.57.127 (talk) 08:31, 29 March 2011 (UTC)

It would be the cube of 1/5, since the engine displacement volume is related to horsepower. So that would be 1/125th of 1001 HP, or approximately 8 HP, if it worked. However, internal combustion engines aren't very scalable (unless you change the number of cylinders along with the scale). So, while a 3 cylinder engine with that displacement might work well, a 16 cylinder engine would probably barely run, because all those moving cylinders would increase friction relative to the 3 cylinder engine, but without the displacement needed to overcome it. Of course, there are other things to change, too, such as the compression ratio and revs per minute, to get better performance out of the smaller engine. StuRat (talk) 08:47, 29 March 2011 (UTC)

Neutron star matter, on Earth

So let's say some Star Trek like genius, in the 53rd century AD, creates a technology that can grab neutron star matter without it decaying in any way. So the United Federation of Planets decides to go grab some, and transport it back to Earth.

Once at Earth, the matter is released as-is into the Earth's atmosphere. What would the reaction be? of:

1. The Quark-gluon plasma at the center (density: ~6-8 trillion pounds per teaspoon)
2. The crust (density: ~10 thousand pounds per teaspoon, and ten billion times stronger than steal, at least at the immense pressure on the neutron star itself).

Magog the Ogre (talk) 17:16, 29 March 2011 (UTC)

Some potentially useful discussion along similar lines was discussed not too long ago, though it doesn't address your question directly. --Mr.98 (talk) 19:09, 29 March 2011 (UTC)

Oh, neat. From what I can see, regarding the thickest of the matter:

• If it were to remain in this neat sci-fi vessel we have, and not explode, it would barrel a whole to the center of the earth, sucking massive amounts of matter in its wake, and surely causing earthquakes, volcanic eruptions, and all sorts of other havoc.
• If it were released suddenly into the air, it would be the equivalent of a nasty nuclear bomb; however, given that it would keep exploding for a good time, it quite likely could destroy all life on Earth.

For the less dense stuff: maybe just a really big explosion that could kill a lot of people? Magog the Ogre (talk) 20:47, 29 March 2011 (UTC)

At STP, what is the predicted density of a neutron gas. Does a neutron gas have a theoretical triple point? Plasmic Physics (talk) 03:23, 30 March 2011 (UTC)

There isn't any predicted information like that. Neutronium is a term which was coined, conjecturally, for such standard conditions neutron-based matter, but no known substances exist, and there isn't a lot of reliable prediction for what it would look like if it did. The Wikipedia article actually covers this well, at least in noting that no one seriously considers it a likely form of matter, except in some very exotic conditions. The other type of neutron matter, known as Neutron-degenerate matter literally cannot exist at STP, as it requires the literally astronomical pressures in a neutron star to exist. If that matter were to be brought to STP, it would rapidly convert to normal (proton-electron-neutron) matter of some sort, likely mostly hydrogen, deuterium, and helium. --Jayron32 05:21, 30 March 2011 (UTC)

I don't really know what ot make of your answer - I googled "neutron gas", and one result described a low density neutron gas produced for the purposes of a projectile target for a particle physics experiment. For clarification, I'm not refering to degenerate states of matter, but simply a bulk sample of neutrons in a closed container with movable walls. The result did't answer my questions, if you were going to ask. Plasmic Physics (talk) 12:08, 30 March 2011 (UTC)

While I'm at it, here's another one: since neutrons have no atomic orbitals, is there any substance that can contain such a hypothetical gas of neutrons, wouldn't the gas simply diffuse through the walls of the container within a matter of hours? Plasmic Physics (talk) 12:13, 30 March 2011 (UTC)

Hypothetically, neutrons would not be subject to intermolecular forces, since they are both neutral and extremely hard (i.e. nonpolarizable). In other words, they aren't subject to even London dispersion forces, generally held to be the weakest of the common Van der Waals forces regulating the formation of non-gasseous phases of matter. If we were to consider a bulk gas composed of nothing but neutrons which was also at atmospheric densities, there are literally no forces at all which could act, at any temperature, even infinitessimally close to absolute zero, which could cause the neutrons to form a condensed phase. So, there would literally be no triple point, because there are no forces acting to cause neutrons to attract to one another. Collecting low-temperature neutrons like this to even make such a gas is likely impossible; but even if you could it would never be anything but a gas. --Jayron32 13:02, 30 March 2011 (UTC)

The neutrons are made of quarks, right? Quarks have charges, right? Would that make the neutrons slightly polar? So, if the temperature brought within a picokelvin above absolute zero, wouldn't they form transient atractions to one another? Plasmic Physics (talk) 13:12, 30 March 2011 (UTC)

I was about to say no, but reviewing Neutron#Structure_and_geometry_of_charge_distribution_within_the_neutron, it seems that very recent research suggests that there is a non-uniform charge distribution within a neutron, implying that they would be subject to something akin to London dispersion forces, so perhaps at such tiny temperatures (femtokelvin? attokelvin) there may be some time when induced charge seperation could generate a condensed, low-energy, low-pressure form of neutron matter; akin to a neutron liquid or neutron solid. The problem is, we have no reliable way to predict behavior at that level; at the distances that would be required for such tiny forces to work, the electromagnetic force, which would be responsible for solid or liquid formation, is actually much weaker than the nuclear forces which regulate things like quark interactions and internucleon interactions. In other words, at the distance you would need to bring many neutrons together in order to have them be attracted enough to form anything like a condensed phase of normal atomic matter, the situation is so drastically different than even for the smallest atoms. Consider that Hydrogen has a van Der Waals radius of 120 pm; this is the roughly scale of the minimum interatomic distances present in a condensed phase. The Wikipedia article on the neutron doesn't contain any information on its size, but this document calculates a radius of about 1 femtometer, or roughly 1/100,000 the radius of a hydrogen atom. So your hypothetical neutron solid would, once again, be under the influence of forces other than the electromagnetic force, which is sorta the definition of degenerate matter in the first place. In other words, low-temperature neutronium solid wouldn't be a solid under the normal definition of a solid, insofar as it obeys the odd laws of physics regulating degenerate matter rather than that of normal matter. So, once again, there is no hypothetical "normal matter" condensed phase substance composed of neutrons alone. There may be a neutron gas, but it will not condense to form solids or liquids which resemble, in any meaningful way, a real solid or liquid. --Jayron32 14:02, 30 March 2011 (UTC)

The neutron is "supposed" to have a Neutron electric dipole moment according with theoretical models, but that moment is so small that no experiment has ever been able to detect it. Dauto (talk) 19:21, 30 March 2011 (UTC)

Ok, I believe you, there is only one phase in the classical sense for a neutron gas due to the lack of interaction taking place however, interneucleon forces may or may not cause a condensate like phase to form (degenerate matter). What about my other question, concerning its diffusuability through solids? Plasmic Physics (talk) 23:47, 30 March 2011 (UTC)

There is such a thing as a neutron reflector but their efficiency has limitations. Dauto (talk) 01:01, 31 March 2011 (UTC)

What did the retired US Air Force nuclear missile commanders tell the National Press Club?

What's the most reliable summary of this? Specifically I am looking for something with the number of retired officials confirming the incidents, whether there are any incidents reported that vary substantially from the typical report, and the date ranges for each of the incidents. 99.2.149.161 (talk) 17:36, 29 March 2011 (UTC)

That article describes a book, written by a space alien enthusiast. It seems he read about, or attended, a September 2010 press conference, where a retired Air Force officer did make explicit reference to extra-terrestrial life.

But overall, this is just a space-alien enthusiast, who read about, and then created a mangled and contorted version of, a much more benign press version of reality; and then added several generic, probably totally-fictional stock-descriptions about extra-terrestrial encounters. In the 1940s and 1950s, as the threat of nuclear war became real, military brass set up loads of early warning systems: RADARs and other aerial surveillance systems. The plan, part of the Mutually Assured Destruction strategy, was to monitor the sky for anything that looked like an incoming bomber or missile - and if we saw one, we'd blow away the Soviet Union with a full-scale missile strike. (Obviously, this was a bad idea)..

Now, as anyone who has ever used technology of any kind can tell you, electronics have "glitches" sometimes. RADARs often report false-positives - "glitches" - noise, due to electronics and atmospheric effects. (When a RADAR picks displays an unknown dot, it is an "unidentified flying object", right?) So, as the NORAD and SAC commanders and strategists realized that their RADARs had glitches, they realized that they couldn't sustain a "fire all missiles" response to every little static-noise burst.

Our space-alien enthusiasts gladly pick up on Project Blue Book: the Air Force systematically studied UFOs, and then decided to close all further investigations - well, let's step back and read that one more time. After years of policy that required escalating every static noise burst to the President so he could decide whether to nuke the Russians, the Air Force finally realized that there was such a thing as electronic noise, and that not every RADAR pulse was actually an enemy aircraft or missile (or extraterrestrial space-ship). The presence of "UFOs" required bringing our nuclear response to a reasonable level. Nimur (talk) 14:32, 30 March 2011 (UTC)

Is that a fair characterization of what took place at the National Press Club? Is it true or not that "several" retired USAF officials said that they had personally witnessed nuclear ICBMs deactivating at the same time that UFOs were being reported above ground at the same facilities? If so, exactly how many officials and how many separate incidents were there? Over what time period did these incidents occur? Is it true that such incidents have also been reported by former USSR officials? I am baffled that even UFO enthusiasts do not seem to be following this story as closely as I'd expect them to. I just want a reliable summary. 99.2.149.161 (talk) 21:19, 30 March 2011 (UTC)

Here are some more links of interest: video, Socio-Economics History Blog, VeteransToday.com. And [2] might be excerpts from one of the organizers of the National Press Club event. 99.2.149.161 (talk) 02:03, 31 March 2011 (UTC)

What experimental recreational drug am I thinking of?

Resolved

I remember reading a news article a year or two ago (I think) about a company that was trying to create a recreational drug that would get you high, but without side-effects, and with an antidote that you could take should you need to become sober quickly. Does anyone know what I'm thinking of? A Quest For Knowledge (talk) 17:41, 29 March 2011 (UTC)

Nevermind. I found it.[3] A Quest For Knowledge (talk) 20:03, 29 March 2011 (UTC)

Identify my skull

Could anyone help to identify this skull (assuming it is a skull). It was found in rocky hills in Oman; the absence of obvious front-facing eyes is puzzling; it's very light and has what look like air pockets, so possibly a bird? Thanks for any help! Henry^Flower 18:07, 29 March 2011 (UTC)

• 
  side view
• 
  bottom view
• 
  rear view
• 
  eye socket remnant?
• 
  brain case
• 
  the nose

If it lacks eye holes, are you sure it's a skull, as opposed to some other bone ? StuRat (talk) 18:12, 29 March 2011 (UTC)

Not at all sure, no. :) On the other hand, I have no idea what other bone it could be; it is basically round and hollow, with a hole at the back which looks like a spinal cord would go through it; and there might have been an eye socket in the broken part (though then the eyes would have been looking to the side and slightly backwards. Henry^Flower 18:17, 29 March 2011 (UTC)

Yes, it's a skull (you can see the distinctive suture lines), but we'd need more pictures to be sure of what exactly it came from. Based on the general roundness, size, and the area it was found, I'm thinking it's a species of monkey. Matt Deres (talk) 18:57, 29 March 2011 (UTC)

(EC)I can't help with ID, but I think you're on the wrong track with the "lack of eyes" idea. Keep in mind that your specimen is highly damaged, whatever it is. Look at this raccoon skull:[4], and this gerbil skull [5]. Basically, these animals' eyes are well outside the main brain-case enclosure. It could be that what you have is a similarly shaped skull, and the thin bits of bone arch that surround the eye socket have broken off. It's hard to tell from your pictures, but I think the side view may show remnants of such bones. SemanticMantis (talk) 18:59, 29 March 2011 (UTC)

Yes, it's definitely a skull, and definitely very badly damaged -- you really only have a small part of it. It looks to me to be a mammal skull, from a pretty good-sized mammal. One possibility may be a dog. Looie496 (talk) 19:09, 29 March 2011 (UTC)

If there are any teeth left, a close shot of those might be very helpful. Googlemeister (talk) 19:41, 29 March 2011 (UTC)

The round hole at the front made me think of some sort of anteater, something like this doesn't look too dissimilar, has a similar "lack" of obvious eye holes. Having a quick look it seems like there are anteaters in Oman. Vespine (talk) 23:11, 29 March 2011 (UTC)

Hmm well, ok, i'm wrong about the anteater in Oman, seems like they're only in south america.. How about armadillos ? Vespine (talk) 23:21, 29 March 2011 (UTC)

That's the back, so the hole is for the spinal cord. StuRat (talk) 23:18, 29 March 2011 (UTC)

Aaah! Yes, i was looking at it wrong, sorry... but anyway the links I posted show that lack of "obvious" eye holes are not necessarily a problem. Vespine (talk) 23:22, 29 March 2011 (UTC)

I'm really curious now! I don't think it looks rodent, canine or rabbit, what other "common" animals are there in Oman? Vespine (talk) 23:25, 29 March 2011 (UTC)

It would help to know what kind of soil or rock strata it was found in. then we might have an idea whether we're trying to match with a modern (familiar) animal or something else. Also does it seem to be actual bone or rock,as in fossil?190.148.134.128 (talk) 00:32, 30 March 2011 (UTC)

also what is front or back seems at this point to be conjecture.190.148.134.128 (talk) 00:56, 30 March 2011 (UTC)

It's light and has air pockets, i think it's obviously bone, not a fossil. The main problem I think is the OP has not given a good frontal photo showing the nasal area and the jaw structure on the underside photo is badly out of focus, these areas in particular would probably reveal a lot more unique detail. Vespine (talk) 01:02, 30 March 2011 (UTC)

I'm trying to find fauna local to the region but not much luck. There's an awesome feline called a caracal but the skull looks very different, as does a local wolf, hyena and several antelope or goat like animals. I don't think it's a bird or a a lizard, or a rodent, my guess is some sort of mammal but I'm really stumped without some better photos. Just for clarification, you do mean Oman the country on the Arabian peninsula, not some other town somewhere like Paris Texas or something. Vespine (talk) 01:18, 30 March 2011 (UTC)

The nasal area is missing, as is most of the upper jaw. This is really just the back of the skull, and not even all of that. Looie496 (talk) 03:07, 30 March 2011 (UTC)

Thanks for all the ideas! In answer to a few points:

- SemanticMantis, your point about the eyes seems to be along the right lines - the racoon skull is quite similar. Presumably not an actual racoon here in Oman, though there must be something similar.

- I've added a few more photos showing the (probable) remnants of the eye sockets, inside, and what's left of the front/nasal area.

- For what it's worth, this page has photos of various animals from the author's travels (mostly in Oman).

- It's definitely bone, not a fossil. It was in a rocky desert area, altitude about 500m.

Even if we can't identify it for certain, at least is slightly less of a mystery to me now. :) Henry^Flower 03:24, 30 March 2011 (UTC)

AH, I see now. In the first out of focus photo I actually thought those might be tooth socket remnants but it's obvious that whole upper jaw area is worn away.. I take back what I said about it not being a rabbit or rodent, in fact, if you use your imagination, it could be a rabbit, or maybe more likely a hare, if you look at a picture like this and use your imagination to deteriorate the missing parts, it's not extremely dissimilar. Vespine (talk) 04:54, 30 March 2011 (UTC)

My guess would be a Mustelid but without an indication of size it's very hard to be more specific. If it is clearly too big to be a Mustelid I would change my "vote" to Canid. Roger (talk) 12:51, 30 March 2011 (UTC)

I don't think it's a rabbit: the spinal cord hole in the rabbit skulls I've seen is in the base (the head sitting on top of the body); I imagine a hare is the same. This one has the hole in the rear of the skull, which would seem to imply a more horizontal body posture, which in turn would fit with the idea of a weasel-type thing. The skull (or rather the bit I have) is about 7-8cm, so maybe something a bit bigger than a pine marten. Henry^Flower 16:46, 30 March 2011 (UTC)

If I can get a bit nosy: what in the world were you doing in Oman? I can't think of any reason whatsoever to be a tourist in that country. Unless you live there, which also seems unlikely to me. Magog the Ogre (talk) 17:02, 30 March 2011 (UTC)

See Tourism in Oman. Are you confusing Oman with Yemen perhaps? Looie496 (talk) 17:20, 30 March 2011 (UTC)

Didn't they used to be the same country? Regardless, I can't imagine traveling halfway around the world to a part of the world quite hostile to westerners (of which I am one), to go touring in the middle of the desert. Then again, I live in the US, so maybe that will cause some differences. And to each his own (maybe Oman has a great industry I don't know), but I still don't understand why someone else would do it. Magog the Ogre (talk) 19:54, 30 March 2011 (UTC)

We're way off topic here, but the two are quite different. Oman is a country with 2.7 million inhabitants and a per-capita GDP of about $14,000. Yemen is a country with about 22 million inhabitants and a per-capita GDP of less than $1000 -- i.e., one of the poorest countries on earth. Oman is politically stable and welcoming to westerners. Yemen is a hotbed of turmoil and a dangerous place to visit. Looie496 (talk) 20:50, 30 March 2011 (UTC)

What a strange turn the discussion's taking! Looie of course is entirely right. I'm off for the Muslim weekend now, but will be back on Saturday in case there are more thoughts. Henry^Flower 03:35, 31 March 2011 (UTC)

carbon-dioxide atmosphere

I have a long list of questions for an idea that I've been thinking about. But I will stick with the first because it may negate the rest. I only mention this because this question surely seems nonsensical... Assume that a lot of carbon dioxide was added to the Earth's atmosphere. Along with this, there would be extensive global warming. So, it is safe to assume sulfer dioxide would be be produced in excess. Is there a point at which excessive heavy gasses (ie: carbon dioxide and sulfer dioxide) would settle to the lower elevations on Earth and the lighter atmosphere consisting of oxygen and nitrogen would float above that? Obviously, there would be a mixed area. I'm really asking if oxygen can be pushed up higher than it is now due to heavier gasses in the atmosphere - or, will the oxygen remain where it is and just mix with the heavier gasses? -- kainaw™ 19:51, 29 March 2011 (UTC)

We have many different gases in the atmosphere now, and they generally seem to mix rather than form distinct layers. Yes, the concentrations of the various gases does vary a bit by altitude, but, other than the pressure differences, the air on the top of Everest is basically the same as at sea level, because winds continuously mix them up. I'd suspect that winds would be even stronger on a hotter Earth, since heat differences drive winds, so this "mixing bowl" effect would remain. StuRat (talk) 20:32, 29 March 2011 (UTC)

It's because the atmosphere is clear to a lot of radiation, which is then absorbed by the ground thus bottom heating the atmosphere and preventing stable stratification. If the atmosphere was opaque to most radiation, stable stratification could be a possibility. —Preceding unsigned comment added by 92.20.201.71 (talk) 20:57, 29 March 2011 (UTC)

Well, the atmosphere does show quasi-stable stratification, but the strata are relatively thick: troposphere, stratosphere, ionosphere, etc. Within the troposphere there is very extensive mixing due to the fact that solar radiation heats it from the bottom -- this mixing rapidly undoes any separation that may start to arise from differences in density. Note that there have been epochs of geological history when CO2 concentrations were up to 100 or more times higher than today. Looie496 (talk) 21:26, 29 March 2011 (UTC)

One might consider that even with all the lower level mixing there is a surprising degree of stratification.for example ozone being triatomic oxygen O3 is way up there, in the mesosphere if I remember correctly.and we all know how important that is. I don't know what you're theory is but you might pursue it further.190.148.134.128 (talk) 01:21, 30 March 2011 (UTC)

Hi there, i just fixed up 128's reply, please don't manually indent your replies but instead use : at the start of your contribution (have a look at the other replies to see how it works). A manual indent has a different function in wiki formatting. Vespine (talk) 01:27, 30 March 2011 (UTC)

Thank you "vespine". I must explain that I am a really old guy and the computer is a new tool to me. I have no idea what "manual indent" means because I don't speak computorese. you're probably quite young and can't imagine how this can be possible because you probably have grown up with a computor. It sounds to me that you're saying I must read the other entries and agree with them, but I can't believe that. I'm not trying to be a smart ass. please tell me what I did wrong in plain english.190.148.134.128 (talk) 02:22, 30 March 2011 (UTC)

"Manual indent" means starting a line with spaces. If you want a line to be indented in Wikipedia, you should start it with a series of colons, such as "::::::". (I have fixed your previous line.) Looie496 (talk) 03:02, 30 March 2011 (UTC)

And, just to demonstrate:

                      this is a manual indent.

We do use that, but not when we just want regular text, it's reserved for special things. For example, it's sometimes used to make diagrams. StuRat (talk) 03:19, 30 March 2011 (UTC)

It should be noted that in high enough concentrations, carbon dioxide does settle, see Lake_Nyos#The_1986_disaster for an example of what happens when it does. However, this is quite a different scenario from atmospheric carbon dioxide. Essentially what happened at Lake Nyos was a bubble of pure carbon dioxide was "burped" out of the earth; this CO2 had very little mixing with the atmosphere, and so it suffocated the entire region. Atmospheric CO2 accounts for less than one part per thousand (see Atmosphere_of_Earth#Composition). According to Hypercapnia (the medical term for too much CO2), severe effects on humans don't set in until 10 kPa, or about 10% of the air, though minor effects set it at lower concentrations. Even assuming that some medical problems set in at 1% CO2, that would still require there to be 30X as much CO2 in the atmosphere as there is now. Even at those concentrations, there is sufficient circulation in the troposphere to assure complete mixing, even in the face of gravitational seperation. --Jayron32 03:33, 30 March 2011 (UTC)

According to scale height, each gas has its own scale height above 100 km due to diffusion. Wnt (talk) 03:39, 30 March 2011 (UTC)

Yes, but there is a big difference between what happens way up at 100 km and what happens in the much denser, and much more well mixed, troposphere... --Jayron32 03:45, 30 March 2011 (UTC)

Thanks for the answers. It appears that stratification is inhibited by heat that radiates from the planet surface. So, to get stratification to work well, radiant heat must be limited. Low-level greenhouse gasses will assist in two ways. First, they will reflect much of the solar radiation before it reaches the surface. Then, they will absorb and reflect heat before it reaches very high into the atmosphere. I think that studying temperatures on Venus will help me get a good idea of how well that will work. -- kainaw™ 12:15, 30 March 2011 (UTC)

Superallowed beta decay.

Superallowed transitions seems to be defined as those between members of an isotopic spin multiplet.

How could a beta decay not be between members of an isotopic spin multiplet? Since it is a weak interaction surely the number of quarks and hence total isospin will be conserved? So what is the difference between allowed and superallowed transitions? —Preceding unsigned comment added by 92.20.201.71 (talk) 20:29, 29 March 2011 (UTC)

OP: Is it just that nuclear spin doesn't change? In which case how is a superallowed transition different from a pure fermi transition? —Preceding unsigned comment added by 92.20.201.71 (talk) 20:46, 29 March 2011 (UTC)

You stated "the number of quarks and hence total isospin will be conserved?". That's not true. The total isospin can change. Dauto (talk) 21:00, 29 March 2011 (UTC)

up and down quarks both have I=1/2. I don't understand. —Preceding unsigned comment added by 92.20.201.71 (talk) 21:05, 29 March 2011 (UTC)

What don't you understand? We might be able to explain if you let us know. Dauto (talk) 02:14, 30 March 2011 (UTC)

Ok so my understanding was that nuclear isospin multiplets all had the same I and different values of I₃. And that beta decay acted essentially as the creation/annihilation operator I^±. And that since the operator I^± cant get you out of the spin multiplet, all beta decay must be between isospin multiplet states. This appears to be in contradiction with the above statement I was troubled by about superallowed states, and your statement that I can change. So I'd be glad if you could help me grasp the nature of my misunderstanding. Thanks. —Preceding unsigned comment added by 92.20.201.71 (talk) 02:34, 30 March 2011 (UTC)

Let me state upfront that my specialty is with particle physics, not nuclear physics. Your understanding is approximately correct and that's why beta-decays that violate the principle you describe must pay a penalty and will be less probable than naively expected. You must keep in mind that unlike weak isospin, isospin is not an exact symmetry. Dauto (talk) 04:08, 30 March 2011 (UTC)

What kind of beta decays are the ones that break the symmetry? Is it just beta decay which changes a quantum number other than I₃, such as when the neutrino and beta particle make a spin triplet and nuclear spin changes? Sorry, I may be asking tedious questions as I only started nuclear and particle this year so I do not have a condensed understanding of the subjects. —Preceding unsigned comment added by 92.20.201.71 (talk) 20:05, 30 March 2011 (UTC)

I don't remember the answer to that specific question off the top of my head and solving it right now feels too much like homework. You need to get a good book about nuclear physics. As I said, my specialty is high energy physics. But I can explain to you without going into too many details why superallowed decays are favored. Basically, in a superallowed decay the nucleons in the parent and daughter nuclei have similar wave functions so there is a lot of overlap between their wavefunctions and all that needs to happen is the transition between a proton and a neutron or vice-versa. In a non-superallowed decay the form of the nucleon wavefunctions of the parent and daughter nuclei are different and their overlap may be quite small suppressing these decays. Dauto (talk) 00:56, 31 March 2011 (UTC)

ingesting radiation

I am confused as to the reporting concerning the dangers of the current Japanese Radiation problem.

To my very basic knowledge it will be really bad to ingest any radioactive substance even on a small scale as it will spit out beta,gamma or alpha for a lifetime which would harm the body's cells . Hence absorption into the body is the real danger, this will occur via the food chain or inhalation.

I am not sure if the media reporting is referring to "safe" levels of radiation as "safe if you do not ingest/breath it in" in other words the level is safe "at a distance" outside of the body.

In a similar way you can say that Americium in a smoke detector is at a perfectly safe level but if you ate it it would be very bad for you as you are then having a permanent amount of Americium absorbed into your body. —Preceding unsigned comment added by 2.97.155.22 (talk) 21:32, 29 March 2011 (UTC)

It is important to distinguish between "radiation" and "radioactive substances". Radiation reduces very quickly with distance so the radiation being emitted by the reactors in Japan is only potentially harmful for the people working on them. The big risks are associated with radioactive particles escaping, since they can travel great distances and, as you say, be ingested. The big fears at the moment are with water outside the reactors that has been found to contain radioactive particles. As for the media, they usually don't know what they are talking about. They talk about both radiation and radioactivity, but don't always distinguish between them. --Tango (talk) 21:55, 29 March 2011 (UTC)

EC, See Sievert and Gray (unit). Your understanding comes from the fact that ionising radiation has zero risk when the source is at a sufficient distance. However, a suitably small amount of even a potent alpha source, can still be safely consumed. Basically when the scientists say it is safe, it is safe. —Preceding unsigned comment added by 92.20.201.71 (talk) 22:03, 29 March 2011 (UTC)

What happens to you if a radioactive substance gets into your body depends on a lot of things, not just its nuclear properties but also its chemical and biological ones, and mode of administration. For example a very tiny amount of plutonium in your lung is very likely to give you lung cancer. However it might not harm you if you ate it, because it's poorly absorbed (no warranty on this! I will not be responsible for anything that happens to you). See plutonium#toxicity.

Similarly iodine-131 is extra dangerous because of its tendency to concentrate in the thyroid gland, and strontium-90 because it is chemically similar to calcium and is incorporated into bone. --Trovatore (talk) 22:05, 29 March 2011 (UTC)

You are correct that most descriptions of "safe" radiation are about acute exposure, not chronic. Acute exposure is the kind of radiation that'll give you radiation sickness — it's most of what this chart is about. Unfortunately, for 99% of the people concerned, this is not the kind of radiation hazard they are going to be exposed to, because very high levels of radiation are quite rare and usually quite localized (e.g. right around the reactor). The chronic risks are from elements with long half-lives and corresponding low energy radiation, but when ingested can cause a lot of internal damage over time.

Why is this distinction not usually made? Ignorance, probably. Mixed with that lovely impulse by the scientists and engineers to assert that the general public is worried about nothing. But also because discussing chronic exposure requires a lot more specificity about the particular risks you've got in mind, and frankly even the experts are often very poor at breaking these down into separate issues. As Trovatore points out, it really depends on the substances in question and how they get into you. Some radioactive substances through some pathways flush out of the body with no harm. Some deposit themselves in your bones or thyroid or what have you, and can do a lot of damage.

I would not be comfortable if it was just the media telling me it was safe — it is clear that most journalists do not even begin the know what "safe" and "dangerous" means in the context of radiation. I would parse very closely the statements by officials and engineers — they often will say things like, it is safe for you to be in an area, but don't eat anything that grows there. There are also complicating factors — being exposed to radon gas by itself, for example, will have very little effect on your long term lung cancer risk. But if you smoke a cigarette in an area with high amounts of radon, you end up with all sorts of compounding factors and your risk goes up by a huge amount. --Mr.98 (talk) 22:21, 29 March 2011 (UTC)