Science desk
< November 3	<< Oct \| November \| Dec >>	November 5 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 4[edit]

Why does Gamma cell miss in the pancreas?[edit]

I read about: alpha, beta, and dalta. so where or who is the gama cell there? 213.57.99.33 (talk) 01:27, 4 November 2014 (UTC)[reply]

When you google "gamma cell pancreas" and get 492,000 hits, are none of them useful? μηδείς (talk) 02:35, 4 November 2014 (UTC)[reply]

Why don't you read through them all and tell us if any are useful, rather than expecting the OP to do so ? StuRat (talk) 12:23, 5 November 2014 (UTC)[reply]

The OP found our article on the pancreas, apparently, and wanted to know why it did not mention "gama" [sic] cells. I told him where he could get information pretty much sorted by relevance on gamma cells. Are you suggesting we get paid to read those sources for the questioners? μηδείς (talk) 19:32, 5 November 2014 (UTC) [reply]

Going to Islets of Langerhans is more useful - it tells you PP cells are gamma cells, which secrete pancreatic polypeptide. But it does seem like they get short shrift compared to their more famous siblings, which probably means someone has a chance to discover something really interesting about them. Wnt (talk) 04:32, 4 November 2014 (UTC)[reply]

What's special in "Medical" oxygen?[edit]

what is the reason for the noting "medical" on the bottles? 213.57.99.33 (talk) 04:32, 4 November 2014 (UTC)[reply]

You might be looking to read this: Oxygen therapy --lTopGunl (talk) 04:45, 4 November 2014 (UTC)[reply]

Interesting question. This site says there are concentration differences; I'm not all that convinced. There are definitely industrial oxygen concentrators. Chemical oxygen generators exist for emergency situations (those conceivably could contain different chemical impurities, though apparently not to immediately hazardous levels?) An oxygen bar is different from oxygen therapy. The common thread seems to be legal requirements of prescription and medical device regulation. Wnt (talk) 04:57, 4 November 2014 (UTC)[reply]

BOC Healthcare says that it's regulated as a medical drug and therefore has to undergo more intensive testing during manufacture and bottling than industrial oxygen. SteveBaker (talk) 05:02, 4 November 2014 (UTC)[reply]

The designation "medical" means that the gas can legally be given to patients under medical care. Absence of that designation would mean that the gas is intended for some other use. The exact meaning may depend on what legal jurisdiction you are in, but it indicates a specific combination of:

purity of the gas used to fill the cylinder
testing and certification to ensure that the gas is as pure as it should be
fill procedures (see below)

In some places, there may not actually be any difference in purity between medical oxygen and oxygen sold for industrial use—the supplier may use the same grade of gas, but skip the testing and certification.

Fill procedures for medical-grade oxygen require pumping out the previous contents of the bottle first, to ensure there are no contaminants present. This would not be required when refilling a welding oxygen bottle, for example.

I found this web page informative.--Srleffler (talk) 05:16, 4 November 2014 (UTC)[reply]

One important point is that medical-grade oxygen can contain significant amounts of water vapour, which makes it unsuitable for use at low temperatures (such as in aviation or mountaineering). Srleffler's link gives the details. Tevildo (talk) 10:01, 4 November 2014 (UTC)[reply]

Just to clarify the explanations above: the difference may or may not be with the actual gas itself, the difference is in the certification procedure. That is, it is a difference in how well we can trust that the gas in the bottle is suitable for medical purposes; there's nothing stopping a manufacturer from using uncertified (but identical in every other way) medical grade oxygen for other purposes. --Jayron32 17:24, 4 November 2014 (UTC)[reply]

The sterilization is relevant here? (I mean in case of the Oxygen bottle. I thought maybe it's for strilization, but I don't know if an organism can live in this conditions)213.57.99.33 (talk) 05:25, 5 November 2014 (UTC)[reply]

I recently discovered a case in point: It's common to use oxygen in welding (eg in the oxy-acetylene process) - and it's also commonly used as an "assist gas" when laser cutting sheet metal. In neither case does the oxygen have to be particularly pure. But in the latter case, the sensitive (and hideously expensive) optical parts get wrecked by even the slightest trace of oil. When oxygen is compressed for welding, the compressor that they use employs oil as a lubricant - and traces of that get into the gas. In the welding application, this trace quantity of oil gets burned up without anyone even noticing it - but for laser cutting, they need oxygen that's only ever been pumped with "oilless" compressors to avoid that specific contaminant. You could easily imagine similar-but-different limitations with medical oxygen. SteveBaker (talk) 16:43, 5 November 2014 (UTC)[reply]

What are the odds of being struck by lightning?[edit]

What are the odds of being struck by lightning?Whereismylunch (talk) 05:27, 4 November 2014 (UTC)[reply]

See Lightning strike#Epidemiology. For the US, roughly 1 in 500,000 per year. Dragons flight (talk) 05:47, 4 November 2014 (UTC)[reply]

(E/C) About 1 in 700000 or 1 in 3000, depending on the time frame you're looking at. WegianWarrior (talk) 05:50, 4 November 2014 (UTC)[reply]

Killed by a bolt, or affected by a strike? I've read stats closer to one in 1,000 per lifetime for the latter. I'll look for a ref if we can get a defined question. μηδείς (talk) 03:17, 5 November 2014 (UTC)[reply]

Note that your chances of being struck by lightning will vary dramatically with your location, habits, and occupation. Your chances will be a much higher if you work on cell phone towers for a living (or a dying). StuRat (talk) 12:19, 5 November 2014 (UTC)[reply]

This fellow survived being struck by lightning on at least 7 different occasions. Don't miss the "Statistics" section of the article. --174.88.134.249 (talk) 06:53, 6 November 2014 (UTC)[reply]

If you're the Empire State Building, your odds are quite good. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:53, 6 November 2014 (UTC)[reply]

Human body as a capacitive sensor[edit]

If I understand the principle of capacitive sensor operation correctly, any conductive surface can serve as an extension of a sensor. Does it mean that you can turn your own body into one? If so, how sensitive can it be? Would it be able to detect a handshake or an action of holding a door knob? What about the presence of a person nearby? Also, I wonder if it would be harmful for the human body. — Preceding unsigned comment added by 128.68.216.15 (talk) 11:49, 4 November 2014 (UTC)[reply]

I'll first comment that Capacitive sensor is a pretty bad article -- the only people who will be able to understand it are those who already understand it before reading it. Regarding turning your own body into an extension of one, sure, that could be done in principle, but it would be very difficult to distinguish changes in electric field due to touching something from changes in electric field due to changing the posture of your body. Looie496 (talk) 14:12, 4 November 2014 (UTC)[reply]

The capacitance of the human body is exploited in that classic musical instrument, the Theramin. It is insanely sensitive to body position...even small flutters of the fingers are enough to alter the sound coming out of the thing. SteveBaker (talk) 14:29, 4 November 2014 (UTC)[reply]

Giving the inventor his due, it's actually spelled theremin. --174.88.134.249 (talk) 23:01, 6 November 2014 (UTC)[reply]

The same ability is also exploited by those Touch-sensitive lamps. And proving once again that we have an article on everything, see Body capacitance which discusses the principle. --Jayron32 15:35, 4 November 2014 (UTC)[reply]

Our article on Touchscreen is more readable. Dbfirs 15:43, 4 November 2014 (UTC)[reply]

Fanged deer[edit]

Is the fanged deer of Afghanistan or Africa? This seems to contradict this. Bus stop (talk) 12:30, 4 November 2014 (UTC)[reply]

The "fanged deer" referred to in the first article is actually the Kashmir musk deer if you view the whole press release, a separate species from the water chevrotain. ~Helicopter Llama~ 12:32, 4 November 2014 (UTC)[reply]

See the Tragulidae and the Moschidae, primitive unhorned relative of true deer. μηδείς (talk) 19:09, 6 November 2014 (UTC)[reply]

Thank you both. Bus stop (talk) 23:25, 8 November 2014 (UTC)[reply]

Would an EOD suit really stop bullets?[edit]

I'm not 100% sure this is the right section, but there's a trend of games featuring characters wearing bomb disposal suits and being highly resistant to bullets, as well as explosives. Games I can think of include GTA 5, Payday 2, Metal Gear Solid 2, Call of Duty Modern Warfare 2, which provide at the very minimum high resistance to bullets (The characters in Payday 2 take enormous amounts of ammo to take down) to outright invulnerability in the case of Fatman in Metal Gear Solid 2).

Is this realistic? I can't imagine a suit designed to stop overpressure from a bomb blast would be all that great at stopping bullets? 81.138.15.171 (talk) 15:27, 4 November 2014 (UTC)[reply]

We have an article on Explosive Ordnance Disposal#EOD_Suits, and a much bigger article at Bomb suit and even Advanced_Bomb_Suit -- It looks like there's plenty of Kevlar, foam and plastic in a suit weighing up to 37 kg. While they don't seem to be designed specifically for bullet resistance, it seems reasonable that they would provide at least as much resistance as a bullet-proof vest, and possibly more. I can't find any references at the moment that specifically talk about bullet resistance, but there is some good general info in this article [1] about a US EOD technician. Looking it all over, I'd think the biggest unreality in the games would be the movement speed and agility of characters wearing these rigs. In real life, they would be highly encumbering. SemanticMantis (talk) 15:47, 4 November 2014 (UTC)[reply]

[ec] See Bomb suit and bulletproof vest. According to the latter article, "Armor designed primarily to counter explosives is often somewhat less effective against bullets than armor designed for that purpose", "often somewhat less?" Fowler would have had apoplexy. See WP:WEASEL, although the bomb suit would provide a degree of protection. However, it would be virtually impossible to fight in a bomb suit, due to the severe restriction on mobility and the excessive heat build-up in the suit. Tevildo (talk) 15:52, 4 November 2014 (UTC)[reply]

Maybe because it could depend on the type of bullet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:56, 4 November 2014 (UTC)[reply]

(edit conflict) I pasted your question into the Google searchbar and got Ask people anything about their jobs - SWAT Team Commander (Retired), and he says (after claiming not to be an expert): "...typical bomb squad suits are basically giant bullet resistant vests made from the same materials, but that cover the entire body, not just the torso. As such, they are good at stopping flying fragments and shrapnel common to small explosive devices". The Wellington Sears Handbook of Industrial Textiles by Sabit Adanur (p. 387) says that EOD suits have 16 layers of Kevlar, and The Encyclopedia of High-tech Crime and Crime-fighting by Michael Newton (p, 43) says that 16 to 18 layers should "cope with most threats encountered in urban shooting situations". So there you have it. Alansplodge (talk) 16:08, 4 November 2014 (UTC)[reply]

(edit conflict) For sure they are designed to somewhat protect the wearer against shrapnel - fast-moving chunks of metal - so it would be surprising if there wasn't at least some protection from bullets. So this is all a matter of degree. But the amount of damage someone can take in a video game is INSANELY high anyway. In real combat, one hit almost anywhere on the body is enough to take someone out of combat...except in rather rare cases. But in video games, you can take a whole lot of hits before you start to even slow down. In the face to that lack of reality - why would you be surprised if various forms of protection are over-rated?

These are video games...they are only realistic up to the point where the game designers decide that gameplay would be more enjoyable if it were less so. If they need a 'boss' to fill out a level, or to make some objective harder to reach - and if they have to stretch the truth a little to make it so by giving bomb disposal suits magical protection against bullets, then they most certainly will. (Trust me - I used to work on 1st person shooters in the video games industry - AND in 1st person shooters for serious military training - and I can assure you that there is little resemblance between the two when it comes to these kinds of matters!) SteveBaker (talk) 16:11, 4 November 2014 (UTC)[reply]

What, the U.S. military doesn't have little green boxes with + signs on them stashed around battlefields so their soldiers can instantly heal their wounds? --Jayron32 16:58, 4 November 2014 (UTC)[reply]

And we know from these games that no enemy would be so rude as to take them and use them on their own people. SteveBaker (talk) 16:31, 5 November 2014 (UTC)[reply]

I suspect they would not stand up against armor-piercing bullets. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:13, 4 November 2014 (UTC)[reply]

Depending on the range. Air resistance gradually robs the bullet of kinetic energy, so there must come a point where the suit would be of some value. SteveBaker (talk) 16:31, 5 November 2014 (UTC)[reply]

That's a given. And if you're standing sufficiently far away from a bomb blast, you don't need any special protection. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:52, 6 November 2014 (UTC)[reply]

Stopping bullets with magnetic eddy currents[edit]

Magnets are already used in eddy current brakes on trains, roller coasters and power tools. The brakes induce current to circulate in the rails, and the rails a generate an opposing magnetic force. Would it be possible to use this effect to stop bullets made of conductive material? I am pretty sure the bullets would not need to be ferromagnetic.

9×19mm Parabellum has a muzzle velocity of less than 700 Joules. According to our article, the bullet could travel 1 meter in 2.33 ms, so does that mean to stop it within a 1 meter distance would require an average power output of over 300 kW? I know magnetic force declines with the square of distance, so the peak power would be many times higher. I can instantly see how the power requirements make this impractical, as that's a jet engine's power output to stop a pistol bullet. But I still think in theory a magnet of the right specifications could make the bullet stop dead in its tracks, and also heat it up quite a bit.

Am I correct in this belief? Let's say we want to build one of these, what would be the actual requirements of the magnet and power supply used in this "bullet brake"?--79.97.222.210 (talk) 23:17, 4 November 2014 (UTC)[reply]

Several of your concerns are really not a problem. Rapidly dissipating that amount of energy inside the bullet would suddenly and dramatically raise its temperature, but that does not prevent the process from happening in a few milliseconds. And just like a car's engine is much larger and with far lower peak power capability than its disc brakes, the jet engine comparison is all but meaningless. The bullet would have to travel through a region with a strong, rapidly spatially alternating magnetic field, e.g. a set of neodymium magnets with opposing poles directed at each other across a gap barely wide enough to allow the bullet to pass, with the poles alternating rapidly along its travel. The bullet would have to be made from a material that had a suitable resistivity and ideally not ferromagnetic. As with any eddy current brakes, this would become ineffective once the bullet's velocity was low, but by then most of the braking would have been done. As to the power supply, there would be none: only solidly mounted magnets mounted in a suitable configuration. —Quondum 03:41, 5 November 2014 (UTC)[reply]

If the bullet hits a person, it might still do damage, not due to it's speed but due to it being molten metal at that point. StuRat (talk) 12:13, 5 November 2014 (UTC)[reply]

Depends on the setup. If you use a 100m long tube, with a cascade of powerful magnets, it should not be a problem. If you would try a wall of magnets the bullet can hardly be stopped with it. You would need a very high Deceleration force to brake the bullet from around 300 m/s like above example to zero in 2.33 ms. --Kharon (talk) 12:42, 5 November 2014 (UTC)[reply]

Have a look at the "Fun with an MRI magnet" YouTube video (can't post the link) of a guy throwing an aluminium ball into the cavity of an MRI machine. It looks as if the repulsive force gets greater as the speed of the object increases, so it might repel a bullet. Of course, the momentum has to go somewhere, so it might destroy the magnet. --Heron (talk) 19:44, 5 November 2014 (UTC)[reply]