Wikipedia:Reference desk/Archives/Science/2009 August 7

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.

August 7

UV filters

I'm interesting in finding out if some sunglasses and a camera filter that I have are actually doing a good job of blocking UV light. Is there any easy or cheap way to measure the amount blocked? Any way to tell if cheap sunglasses are actually helping or just hurting or to see if my UV camera filter is doing anything put protecting the lens? Tobyc75 (talk) 02:38, 7 August 2009 (UTC)

Sunglasses in some countries are standards tested and rated, see Sunglasses#Standards, but may depend where you live, and don't know how you'd do this yourself if you live somewhere where they're not. In general, in Australia, the rule of thumb is don't buy them if they're so cheap as not to be standards approved. Re the camera what are you actually wanting the UV filter to do? Try the identical shot with and without the filter on and compare the photos down to a pixel level - but many people (myself included) chiefly use the UV filter to protect the lens itself rather than for any real effect. See UV filter and Photographic_filter#Clear_and_ultraviolet. --jjron (talk) 03:10, 7 August 2009 (UTC)

I bought a Hoya Super HMC UV filter for a camera lens, and inside the package was a paper card with a specially treated dot. The dot changes color when exposed to UV light. Outdoors in sunlight, the dot would change color, and when I put the filter in front of it, it would go back to white. I don't know what the dot was made of, or its wavelength response, or sensitivity, or anything else that would make it a quantitative test. -- Coneslayer (talk) 12:42, 7 August 2009 (UTC)

A fluorescent thing would help - but only proves that a narrow band of uv is being blocked/transmitted in general. A better solution would be a photodiode (light meter) and a filter that you know only allows uv (but not visible)83.100.250.79 (talk) 13:00, 7 August 2009 (UTC)

I don't know that it matters to you - but I recently got a new set of eye glasses - specifically for driving. I asked about photochromic lenses (the kind that change color) and asked if they were able to block UV efficiently. I was surprised to hear that pretty much all normal eye glasses sold through mainstream opticians in the US now have UV-protective coatings as a matter of course...even the glasses that are completely clear! So you don't even need tinted glass - a completely clear lens can be an efficient UV blocker if it has the right coatings. SteveBaker (talk) 17:46, 7 August 2009 (UTC)

In fact you often don't even need coatings - CR-39 which is (probably) the most popular lens material blocks almost all uv itself. It's quite difficult to get a glass or plastic lens that doesn't cut out practically all uv.83.100.250.79 (talk) 23:24, 7 August 2009 (UTC)

UV filters are essential for outdoor photography using film, since film is more sensitive to UV than to visible light, and even the near-opacity of glass to UV isn't enough. Digital cameras are the other way around: they're more sensitive to visible than to UV, and the glass that makes up the lenses is sufficient to filter out the rest. --Carnildo (talk) 23:00, 7 August 2009 (UTC)

Thanks for the responses. Re: the sunglasses, I was actually interested in whether the cheap children's sunglasses did more harm than good, and I'm in the US, so I'm not sure if I've seen any government testing stickers on them. I'd guess that, yes the cheap ones most likely are pretty bad. As for the camera filter, I mostly just use it to protect the lens. It's on a DSLR and I can't see any difference between with and without the filter. Tobyc75 (talk) 23:19, 7 August 2009 (UTC)

As I mentioned above in response to SteveBaker - most optical materials block uv anyway, so your uv filter is probably only protecting the lens (which is a good thing anyway). Don't know about sunglasses - you're probably right. 83.100.250.79 (talk) 23:43, 7 August 2009 (UTC)

The trouble with sunglasses is that the darkened lenses fool people into looking at brighter objects without squinting and the reduction in visible light causes your irises to open wider to allow in more light. So if the sunglasses aren't really good a blocking UV, the result is much more UV entering the eye than would normally be the case if you weren't wearing them. However, at least in Europe, those kinds of sunglasses are supposedly banned. SteveBaker (talk) 03:05, 8 August 2009 (UTC)

Bike gearing

This came up in a discussion about motorbike gearing, but probably easier to ask in the context of bicycle gearing and in a simplified form.

Consider a multi-speed bike with typical front and rear gears, and for convenience express the ratios as FR:RR. Now lets take two gear ratios, say 28 teeth front and 14 teeth on the rear, i.e., 28:14, and 48 front & 24 rear, i.e., 48:24. Mathematically both these ratios simplify to 2:1, which is the easy bit.

For a perhaps less 'artificial' or simplistic example consider ratios of 38:16 and 48:20, which come out to 2.38 & 2.40, which again is mathematically essentially the same.

The question is that while these ratios are basically the same mathematically, physically is there a difference between changing the gearing on the 'bigger' chainring or the 'smaller' chainring, i.e., would these gear ratios require say an identical amount of energy to push them?

I'm thinking in terms of effects due to torque, angular velocity or momentum due to the different sized rings, or other relevant things. Anyone with better knowledge of this than me... Thanks in advance. --jjron (talk) 02:58, 7 August 2009 (UTC)

Torque (rotational force) depends on radius. What is the relationship between number of teeth and the circumference of the gear? What is the relationship between circumference and radius? Based on those answers, you can determine if tooth-ratio is equivalent to torque-ratio. Once you've figured it out yourself, you can check with our gear ratio article for more information. DMacks (talk) 03:24, 7 August 2009 (UTC)

Yes, you are right. what matters here is the ratio so, as you pointed out, 28:14 and 48:24 will lead to essentially the same torque, assuming that other factors such as friction can be considered negligible. Dauto (talk) 04:36, 7 August 2009 (UTC)

From Surely You're Joking, Mr. Feynman!:

“ Near the end of the summer I was given my first real design job: a machine that would make a continuous curve out of a set of points--one point coming in every fifteen seconds--from a new invention developed in England for tracking airplanes, called "radar." It was the first time I had ever done any mechanical designing, so I was a little bit frightened.

I went over to one of the other guys and said, "You're a mechanical engineer; I don't know how to do any mechanical engineering, and I just got this job.

"There's nothin' to it," he said. "Look, I'll show you. There's two rules you need to know to design these machines. First, the friction in every bearing is so-and-so much, and in every gear junction, so-and-so much. From that, you can figure out how much force you need to drive the thing. Second, when you have a gear ratio, say 2 to 1, and you are wondering whether you should make it 10 to 5 or 24 to 12 or 48 to 24, here's how to decide: You look in the Boston Gear Catalogue, and select those gears that are in the middle of the list. The ones at the high end have so many teeth they're hard to make. If they could make gears with even finer teeth, they'd have made the list go even higher. The gears at the low end of the list have so few teeth they break easy. So the best design uses gears from the middle of the list."

I had a lot of fun designing that machine. By simply selecting the gears from the middle of the list and adding up the little torques with the two numbers he gave me, I could be a mechanical engineer!

”

70.90.174.101 (talk) 07:52, 7 August 2009 (UTC)

And the parts in the middle of the spec range are most likely to be available on short turnaround. As I mentioned above, there's a difference between "it's in the catalog" and "you can order it and receive it in a reasonable time". This is what's mean by the "OTS" in "COTS." Nimur (talk) 17:21, 7 August 2009 (UTC)

Naturally, if we neglect friction, the torque onto the pedals of a bicycle needed to drive it forward with a specified force is dependent on just the gear ratio. However, the torque is transferred to tension in the chain and that is inversely proportional to the radius of a gear. Hence, to save the chain it's best to use preferably large cogwheels, as then both the tension and the bending of the chain are minimum. — Pt _(T) 02:39, 8 August 2009 (UTC)

The actual diameters also matter if you're dealing with shifting Derailleur gears. This shift is a change of absolute radius and chain-slack on one gear, not a ratio between two gears, but the goal is a shift of relative ratio. That means if the gear has a large radius, a relatively large change is needed to accomplish a shift of ratio. That is, if you are doing a ratio shift 3:1→2:1, changing gears 30:10→20:10 is a change of 10 whereas 60:20→40:20 is a change of 20. WP:OR says derailleurs and chains are more susceptible to jamming with very large changes. Also, the derailleur needs to take up all the slack, so the larger the change, the larger the derailleur cage needs to be. At the other extreme (small gears), a small change in radius represents a more significant change in ratio, so they need to be manufactured more accurately and precisely. DMacks (talk) 05:09, 8 August 2009 (UTC)

Friction, however, does play a small but noticeable role at the margins, a percentage point or two according to the books I've read on the topic. IN a nutshell, the straighter your chain, the lower the friction; not only does this marginally reduce your pedaling effort, but it also reduces the wear on your chain.--Robert Merkel (talk) 23:09, 10 August 2009 (UTC)

conservation of momentum and heat

Does a system gain momentum when it absorbs blackbody radiation, or when it emits it? Thus even though photons are massless, are they potentially carriers of momentum? (This was never covered in AP Physics really...) John Riemann Soong (talk) 08:41, 7 August 2009 (UTC)

Yes, photons carry momentum (despite their rest mass being exactely zero, the classical formula p=m*v does not hold here). Yes, systems absorbing or emitting electromagnetic radiation in a non-uniform way will gain or lose momentum.

See http://en.wikipedia.org/wiki/Photon#Physical_properties

See also radiation pressure and the Nichols radiometer, which can measure the force imparted by a light beam. AlmostReadytoFly (talk) 10:16, 7 August 2009 (UTC)

Doesn't this mean the Earth is actually gaining and losing momentum just through radiation alone...? Or is it assumed that global net radiation flux (Rnet?) is zero? John Riemann Soong (talk) 11:12, 7 August 2009 (UTC)

It's pretty close to zero, yes. If it were not, it's difficult to see how the Earth could remain habitable over millions of years. Although photons don't have rest mass, they do carry energy. The formula $E^{2}=m^{2}c^{4}+p^{2}c^{2}$ gives the relationship between these quantities, where $p$ is momentum.--Leon (talk) 11:27, 7 August 2009 (UTC)

Well, I mean, does Rnet account for photosynthesis? So all those plant sugars and fossil fuels ... are actually carriers of momentum? It's strange cuz in high school (AP Physics C) they always told me, that excepting tiny particles colliding with the Earth, or asteroids, that as far as momentum was concerned, we could treat Earth as a closed system, with no mention of light as a bearer of momentum.

Momentum ain't energy! Momentum isn't really "stored" per se, and whilst the momentum of the Earth would be changed by this, the momentum of the Earth--bomb system would be constant. But you would be converting energy from one form to another. --Leon (talk) 12:31, 7 August 2009 (UTC)

I also remember solving a few problems about conservation of momentum on a system composed of bound protons and neutrons...(yeah a nucleus). The nucleus underwent nuclear decay, ejecting various daughter nuclei. Since the original nucleus was at rest to begin with, we used this condition to solve for the velocities and masses of some of the daughter nuclei (being given the mass of the original nucleus and the masses and velocities of some of the other nuclei, etc.). Thankfully, the problem was in 2D ... I don't think I could have done it in 3 dimensions without some serious linear algebra. Anyway, I'm wondering whether the methodology is necessarily valid, since 1) gamma radiation is likely to be emitted nonuniformly 2) since fission energy is being converted into kinetic energy, why should the total momentum of the system be still zero? John Riemann Soong (talk) 12:02, 7 August 2009 (UTC)

It's a law of physics that momentum is always conserved. However, kinetic energy needn't be. If bombs are detonated as you describe, the kinetic energy of component parts is increased, but the momentum isn't. Remember, momentum is a vector quantity and if you add up those vectors the result doesn't change. Kinetic energy is scalar, and is proportional to v squared not v. --Leon (talk) 12:31, 7 August 2009 (UTC)

Wait a minute - if light is converted to stored energy through photosynthesis there's no impulse (change of momentum) on the body (tree/plant) it acts on - if there was then the energy would be dissapated as kinetic energy - but it's not - it's stored as chemical energy. - a momentum change would need the light to be reflected.

As for the bomb - yes, think so.83.100.250.79 (talk) 12:08, 7 August 2009 (UTC)

No, a momentum change does not need light to be reflected. Though a certain amount of reflection does occur, incidentally. And there is some impulse on the plant! --Leon (talk) 12:31, 7 August 2009 (UTC)

Well yeah, it's the electrons that gain energy, with the potential to transfer momentum later on? John Riemann Soong (talk) 12:22, 7 August 2009 (UTC)

Yes

(edit conflict)The force on the earth due to light reflection is ~ 50 mega newtons (assuming intensity of 920W/m2 [[1]], albedo of 30%, radius of earth = 3x106m , p=E/c , F=dp/dt )83.100.250.79 (talk) 12:29, 7 August 2009 (UTC)

That's the same as 100 British Rail Class 59 trains pulling together.

Mass of earth ~ 5x10^24kg , F=ma so a= F/m a=5x10^7N / 5x10^24kg = 10^-17 m/s2

change in velocity due to acceleration =at . 1year = ~3x10^7 seconds

So increase in outward velocity of earth in 1 year would be 3x10^7 x 10^-17 = 3x10^-10m/s - quite small..83.100.250.79 (talk) 12:35, 7 August 2009 (UTC)

Hmm, but now take billions of years of cyanobacteria and fossil fuel formation ... also I ask about photosynthesis because it's basically a sort of energy sink, allowing Earth to reach thermal equilibrium while actually stockpiling energy. Thus even if no reflection occurs, the system of Earth's atoms has arguably gained momentum, hasn't it? Also, I assume things like angular momentum, axial tilt, and other planetary parameters could be more sensitive? (Though still not very sensitive to anything man-made ... but I am wondering about variation over long periods of years, after accounting for things like tidal lock effects and such.) John Riemann Soong (talk) 12:45, 7 August 2009 (UTC)

Not really momentum - they have gained energy. If you say convert carbon dioxide and water into sugar (increase in energy) there's no real increase in classical momentum.83.100.250.79 (talk) 12:57, 7 August 2009 (UTC)

Indeed, the earth absorbs more momentum by reflecting and/or absorbing photons on the dayside than is radiated away by thermal radiation on the nightside. The photons exert a tiny net force away from the sun. Gravity exerts a force towards the sun. The net effect is a tiny decrease of the force keeping the earth in its orbit, as if the sun were slightly less massive than it actually is. For orbiting dust particles and solar sails, the radiation pressure is comparable to or larger than the gravitational force due to the sun, and the orbits of these things are significantly different from purely gravitational orbits.

Bullets fired in the air returning to ground

When live bullets are fired into the air (9 gun salute e.g.) are the falling bullets just as deadly as usual, or do they burn up or something? Are blanks used in these kind of displays? —Stanstaple (talk) 17:45, 7 August 2009 (UTC)

It depends on the trajectory of the bullets. If fired at an angle, the bullets can maintain their spin and lethality -- there are many documented cases. If fired strictly vertically, the bullets lose their spin and fall at a much slower speed. The MythBusters covered this in some detail a few years back. As for whether blanks are used in x-gun salutes: it depends on who's doing it. — Lomn 17:52, 7 August 2009 (UTC)

Depends how massive the bullets are. If you use cannon, you might want blanks. If you're dealing with a lighter object like a bullet, you should be familiar with the concept of terminal velocity because of air resistance. Bulkier objects tend to have a larger mass / surface area ratio (due to geometric trends). John Riemann Soong (talk) 17:53, 7 August 2009 (UTC)

see Celebratory_gunfire#Falling-bullet_injuries83.100.250.79 (talk) 18:05, 7 August 2009 (UTC)

Of course! For some reason i'd never figured in the effects of wind resistance- Firing a bullet into the air would be akin to droping the bullet from the apex- makes sense when you think about it- thanks again. —Preceding unsigned comment added by Stanstaple (talk • contribs) 18:59, 7 August 2009 (UTC)

Not quite. If you read the article careful enough, it all depends on whether the bullet keeps its spin or not. If it does, just the terminal velocity after the fall can be fatal. If, however, it starts tumbling on the way down, it will fall to earth harmlessly. Seems whether it will tumble or not is very hard to predict.195.128.250.139 (talk) 21:18, 7 August 2009 (UTC)

There's a saying in Russian (and in Serbo-Croatian too), "Even when you shoot into the air, the bullets still fall on someone's head". 98.234.126.251 (talk) 22:32, 7 August 2009 (UTC)

I like the "Bullets are not greeting cards. Celebrate without firearms" slogan from Macedonia. I wonder - are the people who fire off their guns in joy the same kind of people who shoot their TV set when their football team loses, or shoot their monitor when their PC crashes? --Kurt Shaped Box (talk) 23:00, 7 August 2009 (UTC)

No, no, no! Be VERY careful how you answer this question. Shooting a gun into the air is lethally dangerous - period. Unless you shoot it pretty much exactly vertically - it will have considerably more velocity when it finally comes to earth than if you dropped it from the maximum height it achieves. You can imagine the horizontal and vertical velocities of the bullet as entirely separate things. If you shoot a bullet horizontally (eg if there was no gravity) then only air resistance slows it down - and not by very much...the bullet is (predictably) lethal. When you fire it vertically, it travels to the apex, gradually slowing down because of gravity and wind resistance - and then stops - and falls back to earth with gravity accellerating it and air resistance slowing it down. Because of the air resistance, the bullet is travelling more slowly when it hits the ground than when you fired it. The terminal velocity of a spinning bullet is pretty fast - because they are fairly aerodynamic - and quite heavy for their cross-sectional area...but when the bullet is fired vertically, it slows to a stop and has to flip over...it loses the spin that keeps it stable in flight - and one the way back down again it's tumbling randomly - which introduces a lot more drag and slows it down quite a bit. A bullet that fell back on you would hurt quite a bit - but it wouldn't kill you. Mythbusters found them buried in a couple of inches of dirt. But what gets complicated (and VERY dangerous) is when you fire the bullet at an angle - not quite vertical. The horizontal component of the motion isn't slowed down by gravity at all - and that allows the bullet to keep its spin - so as it goes over the top of the arc, it stays nicely pointed into the airflow - wind resistance hardly slows it down at all and it remains completely lethal - exactly as lethal as if you'd fired it in a straight line over the same total distance. The precise angle at which the spin of the bullet turns into a tumble and it becomes much safer is unknown and would certainly depend on the initial muzzle velocity, the precise shape of the bullet and a whole bunch of aerodynamic complications. However, it is very safe to say that if you fire a bullet into the air - you could quite easily kill someone. There are PLENTY of well-documented cases of innocent people who have been killed and injured by stray bullets at celebrations where people shoot guns into the air. Please don't let anyone convince you otherwise...most of them are oversimplifying a complicated aerodynamic situation. They simply don't understand what's going on in enough detail to explain the problem - so they claim to "know" that it's safe - which it patent nonsense given the number of documented cases of people dying.

Shooting blanks is obviously safer - but even so, there have been people killed by blank rounds too - blank rounds are far from "safe".

SteveBaker (talk) 22:46, 7 August 2009 (UTC)

Paradoxically, if you were going to fire off your AK-47 in celebration of <whatever>, aiming it straight up in the air would seem like one of the most stupid things that anyone could possibly do... --Kurt Shaped Box (talk) 22:56, 7 August 2009 (UTC)

Yep - ironically, perfectly vertically is the safest...(well, safest for humanity in general...perhaps not safest for you personally!) But that requires much more faith in aerodynamics than most people have! The Mythbusters tried quite hard to fire their guns perfectly vertically - but the bullets still landed hundreds of feet away. SteveBaker (talk) 02:59, 8 August 2009 (UTC)

in short bullets shot up into the air do fall down but are less deadly but unlike being fired they are limited to their terminal veliocity

Space-filling models software

Hello, I am looking for free software that allows me to generate atomic and molecular space-filling models. Do you know of any? Thank you. Leptictidium (mt) 20:33, 7 August 2009 (UTC)

try browsing Category:Molecular modelling software for free ones that do what you want.83.100.250.79 (talk) 21:26, 7 August 2009 (UTC)

Nipping out buds of tomatoes

I'm growing some tomato plants. I've read a few times that it helps to remove some of the buds on the plant - could anyone clarify what you are supposed to do please? And is doing this truelly worthwile, or just a myth? I happened to see on tv about farmers growing thousands of tomatoes in a big field. I doubt they do any bud nipping, but also they do not support the plants at all - is supporting the plants and trusses necessary? 78.146.176.224 (talk) 21:09, 7 August 2009 (UTC)

The process of removing the buds/side shoots of tomatoes is called "suckering" (at least that's what I learned it as). The thought is to remove growth that will never amount to much, and get the plant to put that energy into flowering and fruiting. The Wikipedia article isn't too applicable, but if you search the web for "suckering tomatoes" (or similar), you should get a number of sites which discuss it. The reason you stake/cadge tomatoes is to keep the fruit off the ground, and to allow it to dry out more thoroughly. Tomatoes are particularly susceptible to diseases especially fungal ones, such as verticillium wilt and fusarium wilt. Commercial farmers don't prune or stake because it's very labor intensive, and labor is costly. It's cheaper/more efficient to just grow more plants, spray with fungicides, and hope for the best. The analysis is different with a backyard gardener, though. The labor expenditure is not as high with just half a dozen plants, and you'll get a much larger crop. -- 76.201.158.47 (talk) 14:57, 8 August 2009 (UTC)

I have previously grown tomatos only in grow-bags, when the thin stalks do need tying to supports to stop them bending to the ground with the weight of the toms. This year I have grown them in soil for the first time - and I have been surprised to see how thick the stems are, like minature trees. Hopefully they will not need tying to supports. The variety used was Money Maker I think. 78.147.132.206 (talk) 11:52, 13 August 2009 (UTC)

power leakage

Is it true that power leaks away when, for example, a phone charger is left plugged in without the phone? How does this happen? How much energy is wasted? --Halcatalyst (talk) 22:10, 7 August 2009 (UTC)

Even the best phone chargers waste some energy - even if they are not connected to anything - they're mostly better than 90% efficient, and probably waste even less when not charging.

Basically they are Switched-mode power supplys - a type of electronic device - they need some electrical energy to keep ticking over, about the same as an electric clock.83.100.250.79 (talk) 22:23, 7 August 2009 (UTC)

Well, the power doesn't "leak" out of the end of the wire...that's a common fallacy. (If it did, every power socket in your house without something plugged into it would be "leaking" too!) However, because a charger is a transformer - which has a coil of wire on the wall-socket side of things, there could be a VERY tiny amount of current consumed - which would appear as a small amount of heat being emitted by the charger. But unless the charger has an LED on it that's lit up to show that it's plugged in - I think the amount of energy wasted is very small indeed. If you are looking for places where electricity is being uselessly consumed, consider things like TV sets which can be "turned on" with a remote. Anything that can be turned on and off with a remote has to have some circuitry running in order to detect the signal coming from the remote. So when you turn off your TV/DVD/Satellitebox/etc - it's not REALLY being turned off - it's just turning off most of it's functions and hopefully saving energy. However, nothing short of unplugging such devices will truly get them "turned off" completely. SteveBaker (talk) 22:24, 7 August 2009 (UTC)

I've heard wall warts (transformers) tend to take significant amounts of energy even if nothings plugged in. I think the good ones have a way of telling if something is plugged in, and disconnect the circuit nothing is. I know from experience that I have at least one wall wart that tends to get warm if you leave it plugged in, even if the device it's connected to is off. — DanielLC 04:16, 8 August 2009 (UTC)

Cecil Adams did a column on this here. He found the the idea that wall-warts wasted huge amounts of energy was mostly a myth. APL (talk) 04:47, 8 August 2009 (UTC)

Since the wasted electricity is converted to heat, you can get a good qualitative idea of the wastage by simply placing you hand on the charger. For chargers of the same physical size, a warmer charger is wasting more heat. A power dissipation as low as one watt will make a charger-sized object quite warm. My two-watt Sheevaplug feels much warmer than the (much smaller) telephone chargers sitting next to it, so I infer that they are each consuming very much less than one watt. I can save more energy by turning off my computer monitor for five minutes than by turning off all my chargers for one day. -Arch dude (talk) 15:30, 8 August 2009 (UTC)

Surgery recovery time

Suppose someone has had surgery for eye injuries due to a shotgun backfire (see the science ref desk archives section "Shotgun backfiring"), and also for multiple bone fractures and lacerations due to being mauled by a bear. How long must the patient stay in one place before he can be evacuated by plane? Also, how likely is he to have complications that would require follow-up surgery? (No, this ain't no medical advice, it's for my story again.) Thanks in advance! 98.234.126.251 (talk) 22:59, 7 August 2009 (UTC)

Too many unknowns to make a definitive decision. The main fulcrum of the decision to move the patient would be the need for improved care against the possibility of damage caused by the evacuation. Helicopters are frequently used to move seriously injured individuals. What sort of plane had you in mind? A small single engined plane that did not ascend to altitude would OK for early evacuation. IMHO. 86.4.181.14 (talk) 07:24, 8 August 2009 (UTC)

The plane I had in mind was that same Queen Air that had to land in a 15-knot crosswind (see the section "Crosswind landing"), but the pilot knows that there's a surgery patient on board, so she flies low and does her level best to avoid any turbulence. What I wanted to know is, how soon before it's safe to even move the patient? Assume that he had to have (1) the splinters taken out of the scleras and corneas of both his eyes, (2) small tears in both irises repaired, (3) blood drained from inside both eyeballs, (4) a SMALL part of the vitreous humor taken out to remove dried blood, (5) compound-comminuted fractures in both forearms cleaned, aligned, and fixed in position, (6) simple fractures of the ribs repaired, and (7) lacerations sutured on face and body. (Quite a list, huh?) 98.234.126.251 (talk) 10:13, 8 August 2009 (UTC)

That bear must have been fairly close to a largish city, for that level of surgical help to be available to your victim. So why does he have to be moved? If it happens in the back of nowhere, then he'd just have pressure bandages applied to stop bleeding, splints applied to stop the bones moving (possibly those inflatable splints carried by ambulances) and then he'd be evacuated to a place with a large enough hospital to do the actual surgery.

Once he's had the surgery he could be safely moved immediately, by road or air transport, as long as his IV drips go with him. It would be no different than being wheeled through 2 hospital buildings to get from the operating theatre to his ward. But if he had the full surgery close to where the incident happened, why move him?

If moving him is a necessary part of the story, you either need a compelling non-medical reason for moving him, or he'd only be able to get basic first-aid at the scene and need evacuation to be able to get the surgery.- KoolerStill (talk) 14:28, 8 August 2009 (UTC)

Ah, but that's not how the story goes. The story is, at the time that he's got hurt, he's trapped on an island in the Canadian Arctic so they can't evacuate him to a hospital. They can't get to the island by sea or over the ice because the ice is just starting to break up, and the weather is so bad that the Canadian chopper pilots are afraid to fly to the island. The Americans are willing to send help, though, but the island is out of range of American choppers, so they can only get there by plane (the aforementioned Queen Air). Unfortunately the island ain't got no airstrip (only a helipad) and landing on the ice is impossible due to the ice breaking up. And obviously with these kinds of injuries the poor guy needs surgery (not just splints and pressure bandages) within 24 hours at the very most or he could very well be maimed for the rest of his life. So what they do is they drop the surgeon on the island by parachute so he can do the surgery in the field, and then later on when the ice breaks up completely they evacuate him by boat and then by plane so he can get follow-up surgery if necessary. As a matter of fact, I got the story line from the poem "Ice Island" by the Russian poet Samuel Marshak, which was written back in the late '40s, before choppers were in widespread use, so I had to take some creative latitude to make sure that the new technologies are unavailable (I also moved the setting from the Russian Arctic to the Canadian Arctic, and added a love story between the surgeon and the pilot). By the way, thanks for answering my question about how soon it's safe to move the patient -- I see now that I won't have to rewrite that part at all. 98.234.126.251 (talk) 21:13, 8 August 2009 (UTC)

Okay, that surgeon is not going to have an operating theatre at his disposal, nor x-rays to see the broken bones, nor an anesthetist, nor proper aseptic conditions. So he can stitch the worst surface wounds where there are no underlying fractures, remove the shrapnel from the eyes to save the victim's sight (to stop further damage from the eyes moving); then splint him up for evacuation. The compound fractures would take many hours of surgery, pins etc to set, which he won't have the equipment for. And which he'd normally have 3 or 4 assistants for, at least. Those would need to be done at a proper hospital. He'd be okay for several days without the bones being set, as long as he is splinted (to prevent painful movement) and has painkillers and an IV going (for hydration and anti-biotics). Seeing you have a lot of ice, consider using a sled rather than a boat. How does this guy call for help in the first place? - KoolerStill (talk) 22:50, 8 August 2009 (UTC)

How can I tell if a martial arts school is crap?

I know to avoid the ones that guarantee that you'll become a black belt in n years (as long as you keep paying every month), or don't actually do any real full-contact sparring against a resisting opponent, tell you that they'll teach you to be able to beat up six guys at once - every time, or claim ninja movie rubbish like that they have 'ancient secret high-level techniques' that will allow you to kill people with one punch, or levitate/teleport/become invisible using chi magic, or throw fireballs, or move fast enough to catch bullets, etc.

But what else should I look out for, as a newb, before I sign up for training that might be generally poor and ineffective? Sorry if this is in the wrong place, but I think that MA is a sort of science. Wasn't exactly sure where to put my Q. --84.69.218.212 (talk) 23:25, 7 August 2009 (UTC)

It's not really a 'science' in the usual sense of what questions are posted here, but here goes: Word of mouth is wonderful for things such as these, similarly if you can find more about local tournaments then you'll maybe find which 'schools' teach the top performers in your area (a-la Karate Kid). Perhaps find a few local ones and ask if they'd let you come and watch in on a session - most will be receptive if they know you're seriously considering joining. ny156uk (talk) 23:35, 7 August 2009 (UTC)

Well, as a karate brown belt, I'd say that you should seek out a martial arts school that first puts an emphasis on teaching the right moves so that you do them right every time, and then, once you learn the techniques, incorporate them into one-on-one full-contact sparring with your fellow students. It's also highly desirable that the instructor should take the time to personally demonstrate the martial arts techniques to the students, and explain or demonstrate what (if anything) they're doing wrong. It's also generally (but not always) true that small MA schools offer better quality training than bigger ones. And last but not least, if within a reasonable amount of time (say a year or so) you don't see your technique improving in perceptible terms, then you should consider changing your MA school. There might be other considerations too, but I can't think of them off the top of my head. 98.234.126.251 (talk) 23:44, 7 August 2009 (UTC)

It's also a good idea to talk to your teacher and ask him who he trained under - then look him/them up. Beware of the guys who claim to be the only non Chinese/Japanese/Korean/Tibetan/etc. person to ever train in the style (which he learnt after living and fighting alongside Far-Eastern monks/ninjas/mobsters/etc.) - which, of course, no-one else will have ever heard of, because it's so secret and deadly. More than likely, he trained to the point of 'not being rubbish' in something else, watched some instructional DVDs in a couple more MAs, then founded his own made-up MA using all the coolest-looking moves and made himself grandmaster. Likewise, avoid the 'former SAS/MI5/black ops guy' - people who've done that don't talk about it, especially not to sell 'how to kill people on the street with your bare hands' classes out of their garages to teenagers. It should be common sense - but for some reason, a lot of people seem to fall for this Walter Mitty crap when it comes to MAs. There was a guy putting flyers about in my town a couple of years ago, claiming SAS (secret, BATTLEFIELD-PROVEN commando techniques FAR TOO DEADLY to be taught at regular MA classes, etc.) - with the caveat "HARDCORE people ONLY! No women, children or time wasters!" at the bottom. You can guarantee that some people saw those and thought "FUCKIN A! I'M THERE!" --Kurt Shaped Box (talk) 18:59, 8 August 2009 (UTC)

Why not invite the instructors to a no holds barred fighting competition? The winner will be the best fighter and likely the best instructor. Marcus Greene (talk) 23:49, 7 August 2009 (UTC)

I find your second statement unlikely. Many people who are good at something are not great teachers. Many great teachers are not the best at their subject. While I'm primarily thinking of academic teachers here, I don't see why this won't apply to martial arts as well. Indeed if we consider sports, the best coaches were often not the best players, and the best players often fail as coaches. Of course a more significant fact is that I don't see any evidence the OP is particularly interested in learning no hold barred fighting and most importantly, unless you happen to have a large amount of money, the chance you a prospective student will convince many instructors to get involved in such a thing is slim Nil Einne (talk) 09:43, 8 August 2009 (UTC)

We have an article about a bogo-martial-art debunking website, bullshido.net. 70.90.174.101 (talk) 01:26, 8 August 2009 (UTC)

In my 30+ years of martial arts (several art forms to keep me well rounded), I would suggest that you watch the instructor(s) and see how they teach. Are they respectful to the students? Do they bully them? Are they good with both children and adults? What are their credentials (e.g. one of my Senseis is a member of Karate Ontario as well as associations in Japan and the US). One can easily check the vaildity of any Association (like Karate Ontario) via the web and then check out the instructor via the Association). I have had instructors who were very good fighters in tournaments but on the street were useless. I have had instructors who were good all around fighters but could not teach if their life depended on it! A few years ago, my instructor asked me to teach the children's class because he didn't have the temperment for it. I really respect him for that. Gotta watch the egos as well. Some egos are quite problematic. Is the instructor open to learning from anyone? I take the stance that I can learn from anyone if I take the time to learn (I learned a lot even from the children I taught).

Also, keep in mind that different martial arts have different emphasis: karate was developed in Japan and Okinawa to mee the needs of the people there. Karate has an older history/tradition than Aidido (also Japaneese)but not as long a Kunf Fu. By contrast, Krav Maga is an Israeli fighting art that places a very different emphasis on self-defense than does karate, kung fu, tae kwon do or even boxing.

What do you want to get out of a martial art? Shop around and don't be pressured into anything that your gut says to be wary of. —Preceding unsigned comment added by 216.154.17.222 (talk) 19:18, 9 August 2009 (UTC)

At the risk of making an obvious statement - an instructor who acts like Pei Mei around his students is probably more a common-or-garden asshole than a learned martial arts master. One who talks like Master Po is probably just pretentious. You don't need to learn from guys like that to be good. --Kurt Shaped Box (talk) 23:00, 9 August 2009 (UTC)

Who??? Are you referring to this Pei Mei? Nil Einne (talk) 17:07, 10 August 2009 (UTC)

Na, I was talking about this *Pai* Mei. Damn my tyops. --Kurt Shaped Box (talk) 23:27, 10 August 2009 (UTC)

I'd like to emphasize 216.154.17.222's point above; you need to consider what you want to get out of training. Are you looking for a cardio workout? Muay thai can sure give you that. Want to improve flexibility? Many forms of Chinese martial arts (i.e. "kung fu") place a heavy emphasis on that. If you really get into it, it can be a huge time and money investment, so shop around. If you just want to kick someone ass, try Homer Simpson's advice: "First, you gotta shriek like a woman, till he turns away in disgust. That's when it's time to kick some back! Then, when he's lyin' on the ground, kick him in the ribs, step on his neck, run like hell." Matt Deres (talk) 14:03, 10 August 2009 (UTC)

Lead lined coffins

I recently saw a TV programme where a scientist said that he had seen a woman's body who had been buried in a lead lined coffin for 200 year and yet he could still tell that her eyes were blue. Is that level of preservation really possible? Would the body have had to been subject to some other preservation? In the same programme they exhumed Mark Sykes and were able to obtain lung tissue after 90 year (even though his lead coffin was split) so I guess it is not impossible that sure amazing preservation can take place. This article on Snopes suggest that an air tight container wouldn't preserve a body very well, without other preservation techniques being used. If somebody eye colour was preserved for 200 years, I would have thought that they would be in pretty good shape for at least the first few years. Are Snopes wrong? Would lead preserve a body better than an air tight casket made of another material? Bury me in a Y shaped coffin (talk) 23:36, 7 August 2009 (UTC)

Lead lined coffins are expensive, and person buried in them may have also been heavily embalmed - meaning that they are preserved longer.

However, all a lead lined coffin does is prevent worms etc getting to the body - it still will decompose - into a "grave liquor" (aka "coffin liquor" "human soup") - this is well known to archaeologists, and grave diggers who have to exhume remains from old grave yards.

http://www.hpa.org.uk/CDR/archives/CDRreview/1995/cdrr0595.pdf

Completely preserved bodies have been found in wooden coffins buried in the ground and completely decayed bodies in apparently intact lead coffins in crypts. Most lead coffins contain dry bones but some are found to be about one third full of a viscous black liquid (coffin liquor), which contains bones and (sometimes) soft tissues. Well preserved, partially mummified bodies are sometimes found and, very rarely, intact and totally preserved bodies are found that are not even discoloured. (Copyrighted PHLS 1995)

Any bacteria sealed inside any coffin (lead, glass, stainless steel etc) will get to work, provided that they can operate in the absence of air. So just sealing isn't the answer.83.100.250.79 (talk) 16:20, 8 August 2009 (UTC)

A sealed vessel, plus something to stop the bacteria is needed. 83.100.250.79 (talk) 16:24, 8 August 2009 (UTC)

When the lead coffins of candidates for sainthood are opened, it is reported that some are better preserved than others[2]. Preservation is a positive mark towards beatification. The rank ones on their way to decay are said to be "walking." Edison (talk) 19:26, 8 August 2009 (UTC)

Thanks, an interesting example. Do you know if Saint Bernadette's body underwent some kind of preservation treatment before being buried? It sounds as if she was almost completely preserved for 30 years after death, and pretty well preserved at least 20 years after that. Bury me in a Y shaped coffin (talk) 20:14, 8 August 2009 (UTC)

As I understand it no - it's considered to be just a miracle. It's worth noting that the parts 'on display' the head and hands are actually wax. see Bernadette Soubirous#exhumations —Preceding unsigned comment added by 83.100.250.79 (talk) 20:34, 8 August 2009 (UTC)

Is the mind software or hardware?

I have been wondering whether if the electrical activity in the brain stopped just for a split second and was then restored, would your "mind" still be there? (I imagine that "mind" is a concept that is a can of worms, but basically would all of your memory and mental faculties be in tact). I guess that it is a bit like a PC, in that if you turn it off and then back on, the hardware is still there and so is the data on the hard drive, but any running software is gone. So is the mind software or hardware? Has anybody ever recovered from a complete cessation of electrical activity in the brain? Bury me in a Y shaped coffin (talk) 23:46, 7 August 2009 (UTC)

I think the important question here is how is memory physically stored in the brain? Is it some chemical or electrical state that needs to be actively maintained like RAM, is it more physical changes in the ways the neurons behave like hard disk storage, or is it physical changes in the way the neurons are linked together like chip architecture. I have no expertise in neuroscience, but I think the answer is first that it's not all that well understood, and second it's probably a combination of a lot of these things. There seems to be a fair bit of information on Wikipedia about this stuff although I'm not really sure where a good place to start is. The memory article talks about the different kinds of memory. I think it's safe to assume that sensory memory (which lasts less than half a second) is probably not facilitated by any permanent physical changes in the brain. Meanwhile neuroplasticity talks about how the brain can over time rewire itself in response to experiences. Rckrone (talk) 00:45, 8 August 2009 (UTC)

It would take a library to address all of the issues you brought up so let's grimace and push those aside. I think the core of what you're asking is "are pathways hard-coded in physical structures, or are they volatile?" It's a tough question. The brain isn't a digital circuit, it's chemical. Neurotransmitters metabolize, unused enzymes build up or break down.. The problem is, brains don't just stop working for a split second. The chemicals that are there are ionized and produce current.. how do you plan to neutralize them? Are they just going to disappear? Well they're critical to the functioning of the brain.. you might as well have asked whether a bullet ripped through your skull for just a split second would cause permanent damage. .froth. (talk) 01:41, 8 August 2009 (UTC)

Electroconvulsive therapy rather thoroughly disrupts normal brain functioning for a fraction of a second, which is fairly similar to what you are asking. There is a lot of electrical activity going on in that case, unlike none as in your question, but the electrical activity that’s going on during that instant is a far cry from what would normally be happening in the brain. The immediate short-term effects of electroconvulsive therapy are confusion and loss of short-term memory, but the confusion goes away, and long-term memories are largely retained. Red Act (talk) 02:39, 8 August 2009 (UTC)

As best we understand it (which is not great), long term memory is in 'hardware' - hard connections that grow between neurons. Short term memory is 'software' - electrical signals circulating around the brain that holds the information until neural connections can fill in and make the memory "permenant". This is kinda backed up by the fact that people who have accidents and lose consciousness often lose all memory of the incident - presumably because the software short term memory disappears (just like losing RAM memory in your computer if you turn it off). SteveBaker (talk) 02:50, 8 August 2009 (UTC)

Try mind, electroencephalogram, coma, and brain death. When awake, the brain always has electrical activity, there's no such thing as electrical activity stopping for a "split second." During anesthesia, loss of consciousness can be associated with a flatline on EEG (though this may be more reflective of the limited sensitivity of EEG as opposed to actual complete electrical inactivity). When brought back to consciousness, the "mind" is unaltered. Complete loss of electrical activity on EEG is sometimes used as a criteria for determining brain death. The brain death article references the case of a man who was declared "brain dead" but later recovered. The references cited in the article indicate that he had no cerebral metabolism on positron emission tomography scan shortly after an injury, though this is not quite the same thing as declaring that there is no electrical activity. He apparently remembers hearing the doctors say that he was dead, so presumably his short term memory (and therefore electrical activity) were working normally. As a hand-waving answer to your questions, it seems as though the brain structures (hardware) are what enable the mind (software) to run and that memories can be written to short-term RAM (as with SteveBaker's analogy) or long-term ROM to be accessed by the mind when needed. --- Medical geneticist (talk) 03:22, 8 August 2009 (UTC)

Thanks to everyone for the input, I have been reading around this subject a bit (including the articles suggested above), I have also found the following of interest: Information-theoretic death and Cryonics#Premises_of_cryonics. Bury me in a Y shaped coffin (talk) 09:53, 8 August 2009 (UTC)

As I think of it, the 'brain' is the hardware (like RAM, hard drive) but 'mind' is software. When we first 'boot up', most mental activity is crude ... but as the hardware gets more input, chemical pathways are established that eventually causes 'mind' - or self-awareness at least - to pop into existence.

Most people aren't conscious of the first few years of their life. Perhaps that is the period before the 'ignition' of mind. At that moment we become aware of the existence of our memories.

Primitive software, like machine language, then assembly language, is still very close to the hardware. But as time goes by, the software is increasingly abstracted from the hardware. Scripting languages are very far away from the underlying hardware. Clearly the software could rise to higher and higher levels of abstraction, while still running on the same hardware. It could be the same way with mind.

What does the program consist of in a computer? A varying pattern of energy levels spread across many transistors. Is the *pattern* made of electrons? No. It is the changing relationship between the electrons!! Which weighs nothing ... it's a complete abstraction! Yet, the program 'works' ... and so does the mind.

Certainly the mind 'ceases running' when the brain is badly damaged. But, like the program, the mind never tangibly existed. So in some sense, it never goes away. Twang (talk) 09:06, 9 August 2009 (UTC)

I don't buy "ignition", if you mean a discrete moment when a child's mind fundamentally changes. I don't remember any events at age 3, but I believe I did remember them when I was 4 (the time of my oldest accessible memories). My guess: as we learn how to learn, our internal language develops, and eventually the encoding of new memories is no longer compatible with that of the oldest memories — but there's no transition, just as (we assume) there was no sharp transition between Latin and modern Spanish. —Tamfang (talk) 04:26, 11 August 2009 (UTC)

'Ignition' may not have been the best choice of words (is 'launch' better?). Because there's a period 'before' without recoverable memories and a period 'after' with recoverable memories, there must be a threshold. It may not matter whether it's quick or not. Is this experience 'private' and ineffable, or could it actually be observed? I don't know of any serious work. (I'm trying to be practical and stay away from metaphysics questions like 'is there mind before there's memory'.)
You may be right: it may be that our personal primitives are slowly massaged into better and better conformity with our sense data without any transition. But I suspect there comes a day for most of us when we first understand that there's an 'I'. That *might* be the day when memory kicks in. Twang (talk) 06:18, 11 August 2009 (UTC)

Complete cessation of brain electrical activity is the standard medical criterion for death. ECT doesn't cause a cessation of electrical activity, only a disruption. In principle it might be possible to cause a very brief cessation, followed by a return to life, by giving a single large DC stimulus -- but it would be a very tricky thing to do. There are some species of animals that can survive freezing, which involves a complete cessation of electrical activity. There are hopes that such a thing might eventually be possible with humans, but it isn't yet.

Most neuroscientists believe that there are two kinds of memory in the brain, long term memory which is encoded by structural changes, and dynamic memory which is encoded by ongoing electrical activity. Disruption of electrical activity, for example by a seizure, would clear the dynamic memory, but leave the long term forms intact. So in the OP's terminology (which is not standard), there are both hardware and software forms of memory -- at least we think there are. Looie496 (talk) 05:05, 11 August 2009 (UTC)