This is an old revision of this page, as edited by Scsbot(talk | contribs) at 02:16, 6 August 2009(edited by robot: archiving August 2). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 02:16, 6 August 2009 by Scsbot(talk | contribs)(edited by robot: archiving August 2)
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 2
Genetic divergences between humans and clowns
I've heard that the DNA of humans diverged from that of clowns much more recently than with other primates. Is that the case? If so, around what time did human and clown DNA begin to diverge, and is it possible that a human/clown hybrid could ever be produced?--99.251.239.89 (talk) 00:11, 2 August 2009 (UTC)[reply]
My brother was a clown in the Ringling Bros. and Barnum & Bailey Circus for a while when he was in his 20’s, and now he has an office job and is more than half way through getting an MBA. So my brother appears to be some sort of clown/human hybrid. So hybridization definitely is possible. Red Act (talk) 01:18, 2 August 2009 (UTC)[reply]
My brother has produced an offspring, actually, with a fully-human female. It’s too early to tell the extent to which the offspring will exhibit clown vs. human phenotypes. Red Act (talk) 15:19, 2 August 2009 (UTC)[reply]
Guys, we have no idea about the sincerity of the original poster, but it's best practice not to start making joke answers until the question has been correctly answered. (See the Content and Tone guidelines). To the original poster - if there is any confusion at all, let's clear it up. Clowns are comic performers, but they are genetically human; there is no genetic divergence. Nimur (talk) 16:28, 2 August 2009 (UTC)[reply]
Sorry for my lack of humor, but if we all start clowning around on the Reference Desk, things will rapidly devolve from "helpful resource" into "another internet forum full of idiots." Nimur (talk) 16:29, 2 August 2009 (UTC)[reply]
I figured there was next to no chance that this question wasn't a joke question. To the original poster – if this question wasn't intended as a joke, my apologies for not taking your question seriously. Red Act (talk) 17:09, 2 August 2009 (UTC)[reply]
Reliable sources should be provided for the claimed humanity of clowns. They do not, in general look or act like most humans. More clowns fit in a small car, for instance, than would be possible for normal humans. Edison (talk) 00:46, 3 August 2009 (UTC)[reply]
Good point. I would also like to know where mimes fit in. Are they clown-human hybrids or a separate species altogether? How many mimes can fit in a tiny car? – ClockworkSoul02:34, 3 August 2009 (UTC)[reply]
I dunno - the tangled sentence structures used in the simple-english article make it quite a bit harder to understand than the regular english version! SteveBaker (talk) 00:57, 3 August 2009 (UTC)[reply]
Calculating size of projected image
How do I calculate the size of image a projector can project, given the distance from the projector to the screen, and the focal length and f-stop of the projector's lens? I have a projector with F = 2.41 - 2.66 and f = 18.17 mm - 21.81 mm. Can I calculate the projected image size from these numbers or do I need more information? (the projector in question is the Acer P1266) Thanks in advance! — QuantumEleven12:32, 2 August 2009 (UTC)[reply]
The f-stop does not affect the image size, only its brightness. To calculate the image size you need to know the source (a DLP chip I believe) size S. Then image size S' = S x F/f. Your projector has a zoom lens that can optionally increase S' to 1.2 S'. Note: in some modes the whole DLP chip may not be active. Cuddlyable3 (talk) 13:06, 2 August 2009 (UTC)[reply]
Ah-ha - thank you! The data sheet does not give a source size, but it gives a throw ratio, which, according to this, is the ratio of screen width to distance. They give a throw ratio of 1.6 to 1.9 (via a zoom lens, I presume), but they quote a screen size of 62" (1.58 m) at 2 m distance, which gives a throw ratio of 1.27. What am I missing? — QuantumEleven21:58, 2 August 2009 (UTC)[reply]
Seeking a ray-diagram of a toroidal lens
Cannot find one of these on the internet anywhere. If you put a toroidal lens up to your eye and looked through it, would you get a wide-angle field of view like a crude fish-eye lens? The only picture I could find of a toroidal lens is here http://www.isuzuglass.com/g_p.html78.147.244.14 (talk) 14:23, 2 August 2009 (UTC)[reply]
Do you mean a full toroid (geometry), or just part of one (a section)
In the first case the effect is like that of a cylindrical lens off axis - but rotated about the centre line of the eyes view direction.
In the section case the lens will distort images so that the aspect ratio is not preserved since the curvatures are different. (plus other distortions ie a point source will have a non-circular image of confusion)
I think the page that the OP linked to is a translation, and so uses an unfamiliar term for what is better known as a truncated f-theta lens. The name means that the displacement of the scanned beam is the product of f (the focal length) and theta (the deflection angle of the beam). I found a picture of one here, from Melles Griot, and it has some nice ray diagrams. Apparently, the view through a non-truncated (i.e. round) F-theta lens is like that through a fish-eye lens but with less distortion. The "toroidal" lens that the OP mentioned, though, is designed for one-dimensional scanning so would have a uselessly small aperture in one direction. You would just see a bright line, I guess. --Heron (talk) 18:57, 2 August 2009 (UTC)[reply]
Just to add a little bit more - the page (possibly translated) mentions that the "toroidal lenses" are... "It is used in the equipment such as a laser printer, a fax or a copier that incorporates a printing mechanism of a scanning laser beam." - in my experience such lenses have curvature in one direction, and infinite or very large curvature in the other - if the laser beam has finite width the large curvature aspect (at right angles to the scan) might be used to get a smaller laser spot (this is a guess) - and would be a good match for the description "toroidal".
I was assuming that when "fish eye" was mentioned it meant "very wide angle" rather than the type of distortion .. my apologies about that..83.100.250.79 (talk) 19:17, 2 August 2009 (UTC)[reply]
Oh, wait. I've just read an earlier post by the OP and realised that he is not looking for an f-theta lens. He has read the proximity fuse article and wants to know what the "toroidal lens" mentioned there looked like. I think that the lens mentioned in that article is unrelated to the Isuzu "toroidal lens" that the OP found on the web. The proximity fuse lens was, possibly, actually doughnut-shaped. There's not much point in speculating on what you would see by looking through one of those, since they weren't designed to create an image. --Heron (talk) 19:04, 2 August 2009 (UTC)[reply]
Actually I think a toroidal lens (two radii of curvature, not a donot) of the type used in scanners/laser printers - would work to capture a plane of light (roughly) - though maybe a concave version would be better. I can't see a optical donut shaped lens having any use..83.100.250.79 (talk) 19:23, 2 August 2009 (UTC)[reply]
The plot thickens. I've just found evidence that the proximity fuse lens was actually a Perspex ring that formed part of the nose cone of the missile. It was curved around the axis of the missile (obviously) to give it a 360° view, but it was also curved at right angles to that to focus the light onto an internal photocell. Thus it was almost doughnut shaped, and not the sort of thing you would want to look through. --Heron (talk) 19:56, 2 August 2009 (UTC)[reply]
I found that too, but couldn't make 100% sense of it - to me it would seem sensible to have a conical mirror in the middle of the torus reflecting light from the edges (perpendicular to flight) down onto a photocell - possibly that's what it means when it says "and to have the focal axis at any point around the lens lie on a conical surface" - possibly this type of lens could be used to make a 360degree angle lens - I think the image would be projected onto a disc (ie a circle with a circular hole in the middle) - so with the conical mirror - it might be possible to make a 'fisheye' type wide angle lens - 83.100.250.79 (talk) 20:10, 2 August 2009 (UTC)[reply]
To the original questioner - it seems to me that technically a toroidal lens should be convex, however using the same principles a similar type of lens could be made that was concave - speaking from experience I know that some laser printer lens of this type (the scanning lens) are concave, so maybe it doesn't matter if the lens is concave or convex for it to be called a toroidal lens (as long as the general principle of different curvatures remains) - coupling this with the info. given above it looks like a toroidal lens might (in principle) have a fish-eye like effect - though only in the way the image is distorted (rather than having the 180 degree view that people like me associate with fish-eye lenses) I'm assuming that the term 'fish-eye' includes at least some widening of view angle, as well as a particular type of edge distortion.
Its the shape of the lens in an optical proximity fuze that I'm curious about. I imagine that it would focus the light from 360 degrees onto a small disk-shaped photocell. Perhaps it is shaped like an invercone on a light meter. 89.242.100.18 (talk) 22:48, 2 August 2009 (UTC)[reply]
I think quite possibly you're right - though I'm not sure that the invercone uses exactly the same principle - it appears to be opaque and use light scattering inside a almost torus shaped thing - I don't know exactly how an invercone works though.83.100.250.79 (talk) 00:16, 3 August 2009 (UTC)[reply]
Is it some textbook that you’re seeing the in? That does seem problematic. By the formula for integration by parts, those two integrals would be the same only if was the same before and after the process, which for an ideal gas, amounts to the temperature being the same before and after the process, which is not generally the case. Red Act (talk) 20:39, 2 August 2009 (UTC)[reply]
However, the article also says "However, P does not remain constant during an adiabatic process but instead changes along with V". In other words, taken on their own, both W=int(PdV) and W=int(VdP) are incorrect. --Phil Holmes (talk) 10:39, 4 August 2009 (UTC)[reply]
The correct equation is more clearly written as . At the point in the adiabatic process article where the integral is needed, it is already known that the pressure can be expressed purely as a function of volume, specifically, , where , and are constants. So there’s no point in showing the pressure as being a function of both volume and temperature. Red Act (talk) 13:45, 4 August 2009 (UTC)[reply]
Thanks for lot of discussions.let me say that i found the above stated question in a competetive examination file and both int(vdp) and int(pdv) are in option.please help now.
218.248.11.214 (talk) —Preceding undated comment added 16:20, 4 August 2009 (UTC).[reply]
OK, so it sounds like the real question is given that the work integral is one of or , how do you know which one of the two is correct?
I presume you’re familiar with work in terms of a force applied through a distance, i.e., ? You can kind of derive the correct work integral from that.
Suppose you have a piston of area in a cylinder full of gas, with the cylinder/piston system surrounded by a vacuum (it’s an idealized situation). Let be the length of the cylinder up to where the surface of the piston is. The pressure on the piston varies with , i.e., it’s a function . The pressure on the piston is force per area, so the total force on the piston is . As the piston moves, the work performed on (or by) the piston is . But is how much the volume of the gas changes when the piston is moved by , i.e., . So by considering the pressure to be a function of the volume instead of the distance , you can instead do the integral as .
The cylindricality of the container in the example above isn’t important. You can always think of the change in volume of a more general container as being equivalent to a series of adiabatic processes, in which one little piece of the container, with area , is moved by a distance . The force in that area is still , so the work done by that little movement is still , which is still . If you add together enough little changes in container shape that way using arbitrarily small little areas, you can get arbitrarily close to modeling any smooth change in container shape. Red Act (talk) 17:22, 4 August 2009 (UTC)[reply]
Lost in space during an EVA
What happens if during an EVA an astronaut floats off into space, beyond the reach of any mechanical arm? Is he or she doomed? It would be a horrible and drawn out way to go. Why do astronauts not seem to have safety lines connecting them to the airlock door so that they cannot spin off into space? 78.147.244.14 (talk) 15:16, 2 August 2009 (UTC)[reply]
I think they usually are tethered to the craft. You sometimes see them removing their tether and attaching it to a different bit as they move around. --Tango (talk) 15:54, 2 August 2009 (UTC)[reply]
Since the Challenger accident, NASA has done risk-reduction by tethering astronauts during all EVAs. They also eliminated the Manned Maneuvering Unit from EVAs. In the event of serious trouble, the Shuttle Orbiter can fly using the Reaction Control System thrusters for small jumps to pick up a stray object or astronaut. See the history section for the MMU, and the Space Shuttle Orbital Maneuvering System. The hardest part would be tracking the astronaut, whose RADAR cross section and thermal signature are both fairly small; visual contact is difficult because cameras and windows do not face in all directions - so once the astronaut is beyond a (very short) critical distance, the shuttle pilot will not know which direction to fly to recover him (even if that distance is within achievable range and is within safe orbit tolerances). Nimur (talk) 16:13, 2 August 2009 (UTC)[reply]
I don't think the voice radios have directional antennas suitable for location and range detection. (I don't think that functionality is usually needed, so they don't waste mass budget carrying up such equipment). By very nature of being omnidirectional, the voice radio antenanas (on the Orbiter) preclude tracking. It's possible that the shuttle carries a standard set of radio gear, though, and with a sufficiently smart engineer, a direction-finder can be rigged up; but I'm guessing that the Space Shuttle doesn't have that feature ready for use in a standard flight equipment setup.
This news article indicates that NASA is engineering a next-generation EVA radio - a digital, S-band packet system, which will be used for voice, data, and telemetry - but there's no indication of direction-finding capability. I'm looking for more technical briefs on the radios from official NASA sources. Nimur (talk) 19:29, 2 August 2009 (UTC)[reply]
Here is NASA's SBIR solicitation for digital EVA radios; if you have any ideas for how to build a low-power, directional antenna array, you can submit your business plan and research proposal... Nimur (talk) 19:31, 2 August 2009 (UTC)[reply]
I'd think some kind of flashing light Flashing astronaut locator from a bicycle shop would work as well as radio direction finding, unless the person has gone over the horizon. There's no pesky visual obstructions like hills up there. 67.117.147.249 (talk) 20:56, 2 August 2009 (UTC)[reply]
Of course - but it's a matter of range. How far away do you expect to be able to locate the lost astronaut? Also, as I mentioned above, the views are limited to where windows or cameras are mounted. Nimur (talk) 21:09, 2 August 2009 (UTC)[reply]
With a bicycle shop LED strobe, it should be possible to see the astronaut 10 miles away from the shuttle. It would take a long time to drift that far. As for which direction, the lost astronaut should be able to see the shuttle and say which direction he is from it, allowing the thrusters to be used to translate the shuttle to his location. Edison (talk) 00:41, 3 August 2009 (UTC)[reply]
The problem with things like flashlights is that they are very directional - the flashlight shines where you point it - but not much anywhere else. The same is true of the lights on the backs of bicycles. The hapless astronaut is highly likely to be spinning - so the odds of something bolted onto his suit being of any use is rather low. He might have it in his hand - but unless it is tethered to him, the odds are good that he won't.
The issue of the range of vision out of the spacecraft windows might not be such a big deal - the shuttle and space station both have robot arms that are covered with cameras that can be panned and zoomed - so it would be possible to slowly scan the region around the region he vanished from. The astronaut is likely to be in radio range for a LONG time - so whenever he can grab a view of the shuttle, he can say "I'm behind you at about 10-o-clock and above at about 3-o-clock and give everyone a good idea of which way to look.
I guess the biggest determining factor in the likelyhood of saving the astronaut is his speed. If he just missed a footing, the amount of velocity he'd pick up might be of the order of a few centimeters a second - every move the astronauts make on EVA is covered by at least a couple of cameras. It would take a LONG time for the eagle-eyed EVA watchers on earth to lose sight of him - and swivelling a camera in the direction he vanished out of sight in ought to allow them to get a decent fix on his speed and direction within at most a couple of minutes - by which time he's probably still somewhere in the vicinity of one of the shuttle's wingtips. The could aim the arm camera at him and read off the joint angles to get a very good fix on his direction. Once they have a good fix, it doesn't matter that they lose sight of him because his future trajectory is very predictable...and again, he'll be able to see the shuttle for much longer than they'll be able to see him - so he'll be able to say "you need to aim a bit to the left and a bit up". It would be dramatic - but far from certain death. SteveBaker (talk) 00:48, 3 August 2009 (UTC)[reply]
Astronauts are always tethered to the ISS (the last planned EVA from the Shuttle was during STS-125) during an EVA. But in the unlikely case somebody floats away untethered, a jetpack like device called SAFER is attached to the spacesuits. The astronaut deploys a hand controller from near the bottom of the backpack and can thrust himself towards the nearest structure. anonymous649402:07, 3 August 2009 (UTC)[reply]
I was under the impression that the 'SAFER' unit was only being used by the ISS personnel - due to the fact that the ISS could not be manouvered as the shuttle can in order to rescue someone in the event of a disaster. However, I presume the issue comes up when the shuttle is docked to the ISS too (undocking is presumably a time-consuming process)...and since that's pretty much all the shuttle will do from here on until it's scrapped - they may have switched over to using SAFER in all EVA activities. Also, while astronauts are generally supposed to be tethered at all times - there are times when they have to move the tether from one location to another when an accident could potentially occur. It's really unlikely though - the astronauts are well aware of the dangers and you can be pretty sure that their focus will be entirely on the job while they do those kinds of things. SteveBaker (talk) 14:04, 3 August 2009 (UTC)[reply]
If the limitations of joint mobility were not too great, a slowly spinning astronaut should be able to cancel all spin and orient himself in any chosen direction without the use of thrusters. The moves necessary are known to divers, gymnasts, and cats. A battery powered rotary tool might be used as a gyro to turn or to cancel spin. The station should be able to turn on external illuminants or strobes and be visible a l-o-n-g way off. A radar target would not add much mass to the EVA suit. NASA tested on the Shuttle a soccer ball sized robot which would be able to carry a rescue line to a drifting astronaut. A fisherman would be able to cast a strong lightweight line to a considerable distance in space; a "rescue line caster" should be able to target and fire a rescue line, perhaps with a large net at the end. In sci fi stories, spacemen might throw tools or valve off oxygen in the opposite direction to cancel motion and cause drift within range of a robotic arm. How would he acquire motion away from the ISS in the first place? Maybe he jumped off for some reason, and the tether broke or was not fastened. Maybe a pressurized pipe broke loose while he was in its way. Pipe whip can be an awesome propelling force if liquid shoots out an el at the broken end, until the attached end also breaks. Such an event could leave the drifting astronaut stunned and unable to help. Edison (talk) 19:05, 3 August 2009 (UTC)[reply]
Conservation of angular momentum assures us that the astronaut cannot use 'joint mobility' alone to stop the spin. Divers, gymnasts and cats can only do it because there is gravity and air resistance. In a weightless vacuum, he has to impart a spin in the opposite direction to something else...using an electric drill or something might work so long as it can be run continuously at very high RPM - when it slows down again as the battery expires, the astronaut would start to spin as the drill slows down - eventually ending up with PRECISELY the same amount of spin he had at the outset when the battery finally dies. You'd have to get the drill up to speed and then let go of it. Sadly, even that won't actually work because the electric drills and other power tools that astronauts are provided with have internal counter-rotating flywheels precisely so that they DON'T transfer angular momentum to the user. They also don't keep spinning indefinitely - they are programmed to do a specific number of rotations, delivering a closely specified amount of torque and then stop. So that's not likely to work as a means to stop yourself from spinning. You could cancel the spin by accurately tossing two masses in opposite directions...but the manual dexterity, timing and 'feel' for the amount of mass/speed required to do that seem daunting in a bulky space-suit...most likely, he'd end up making matters worse. SteveBaker (talk) 23:40, 3 August 2009 (UTC)[reply]
reduce CO2 by 89%: gross or net?
I read that world CO2 emissions need to be reduced by 89% to prevent unrecoverable disaster. Is this the figure for gross or net emissions? (Unless the rate of removal is expected to fall, the gross figure will of course be less intimidating.) NeonMerlin21:24, 2 August 2009 (UTC)[reply]
I got the figure from a university newspaper and don't have the original source or the details on what harm would and would not be averted. NeonMerlin22:09, 2 August 2009 (UTC)[reply]
It probably meant net emissions from human activity (i.e. something like CO2 emissions from fossil fuel burning plus deforestation plus cement production minus reforestation, etc.) Dragons flight (talk) 23:04, 2 August 2009 (UTC)[reply]
I don't understand your use of the terms "gross" and "net" in terms of CO2 emissions - these are economic terms relating to income taken before or after deductions. What 'deductions' are you thinking about here? I presume that the intended meaning in the article you read is that the annual tonnage of emissions must be 89% of what it is today...that meaning is pretty clear, although "unrecoverable disaster" is not and the number '89%' (why not '90%') seems suspiciously exact for such a fuzzy statement! But this isn't a percentage emission rate issue - the issue is of the total tonnage that's up there. It would take a much smaller cut performed today than the same cut taken in 20 years time.
The CO2 that we emit is likely to persist in the upper atmosphere for perhaps 10,000 years (Greenhouse_gas#Global_warming_potential). So the amount of CO2 we can safely add each year without ever reaching this mythical "point of no return" is 1/10,000th of the total CO2 amount required to hit the point of no return in any given year.
The problem is that we aren't sure where this point of no return is. There are things like the melting of the arctic ice which appear to have already passed the point of no return...as the ice melts, shiney white ice is replaced by dark green water - which absorbs more heat than the ice - which melts more ice. There is no return from that - but the consequences are not so very serious on the scale of potential disasters we expect. However, other systems like the Clathrate gun hypothesis have an unknown trigger point - but consequences that are probably "game over" kinds of event.
It's generally agreed that between 4 and 5 degC of temperature increase will put us past the point of no return - and that every 100ppm of CO2 we add will push the temperature up by around 1 degree. We've added 50ppm in the last 30 years - 25 ppm of which happened in the last 10 years. So if we merely held our emissions to the present level, we'd add 400ppm in 160 years - and that would probably push the global temperature up into the "point of no return". But if we made a 90% (or 89%!) cut in our emissions starting today, we'd still reach the point of no return in 1600 years - and remember that we have to emit at a rate that'll give us 10,000 years.
So the best guess estimate is that we have to cut emissions by about 98% to gain stability. Nobody believes that's possible - society and technology simply can't change that fast. Most authorities are working to give us 100 years of breathing space before we hit that 4 degree mark in the hope that technology (and our understanding) will improve over that time - and with a sizeable 'safety margin' because we know that we have a measure of uncertainty about some of the 'planet killer' effects like the Clathrate gun. But even a 2 or 3 degree rise is insanely bad - that's enough to annihilate an enormous number of major coastal cities, inundate valuable agricultural land, wipe out huge numbers of animal and plant species, etc, etc.
The sad fact is that there is no believable amount of change that will prevent all of the bad consequences...in a very real sense, we've left it too late. If the world had capped emissions at the 2000 levels at the first Kioto accord - we'd have twice as long to think about it. If people had listened 30 years ago and capped levels then - we'd have had many hundreds of years to deal with it. The best we can do at this late stage is to slow down the rate as fast as is reasonable, cross our fingers and hope that a technological miracle comes along before we hit too many of the irreversible barriers.
But with the three major contributors (US, China, India) still growing their outputs at a prodigious rate, with weak response from the US, polite words but almost zero actual action from China and a downright, blatant refusal to cooperate from India - we're in for a very rough ride. Politicians are used to reacting retrospectively to problems...when a couple of bridges collapse in the US, we rush out a program to check and reinforce our bridges...no amount of pleading about the height of the levees outside NewOrleans was effective - but after the city is flooded out, the politicians rush to spend money building them up. But the nature of the CO2 crisis is that if there is enough CO2 in the atmosphere to cause a disaster, then there is literally no action we can take to 'fix' it. It'll take 10,000 years for the planet to recover naturally no matter how much action the politicians take. We have to take action before anything really bad happens - not one day later!
You are oversimplifying. Carbon dioxide residence time is a complex issue because carbon dioxide emitted into the atmosphere will first mix into the oceans and biosphere on a short timescale (100 years), which reduces the remaining atmospheric burden ~70%. Further reductions occur as carbon dioxide in the ocean is converted to calcium carbonate minerals which has a geologically long time scale (100,000 years). (See: [2]) If one believes there is a magic number above which the atmosphere must not rise, then that initial dilution allows one to emit more carbon slowly than if you emit it all quickly. Also, one can maintain stable carbon dioxide concentrations in the 450-550 range while still having an appreciate emissions footprint even 300 years hence [3]. Eventually, those numbers need to trend towards zero, but we can envision emissions scenarios that give us hundreds of years to fully eliminate fossil fuels without truly running off the rails. Of course, even the optimistic scenarios depend on being able to cut ~50% this century (rather than growing by +200%, which seems to be the do nothing answer). Dragons flight (talk) 00:13, 3 August 2009 (UTC)[reply]
In Steve's defense, given the complexity of the subject - which science itself has not yet fully grasped - it would be difficult not to oversimplify at less than textbook length. 87.81.230.195 (talk) 04:31, 3 August 2009 (UTC)[reply]
May I also add that the first shots are being fired from the gun right now?[4] And there's also the permafrost gun, don't forget that one.[5][6][7] We just need tenths of a percent of the excess carbon stored in frozen soils to be released as methane and we don't have to worry about improving gas mileage, at least until the methane stabilizes to CO2 over the next few hundred years. We will have warm summers (and winters). And if the permafrost release triggers the ocean clathrate release, we might get the final answer quite soon, as in our great-grandchildren who don't happen to live in low-lying areas will know exactly how well we did. Franamax (talk) 09:05, 3 August 2009 (UTC)[reply]
If the gun is being fired, so far it is coming up blanks. Methane concentrations now are 30 ppb below the most conservative of the IPCC projections made circa 2000 (and 70 ppb below the most frightful ones). Existing climate simulations have been assuming that methane would increase significantly faster than has actually been observed. Yes, the possibility of methane feedback is a real concern, but with a half-life of only ~12 years and levels that remain inexplicably lower than expected, I think it would be premature to panic about this. Dragons flight (talk) 09:42, 3 August 2009 (UTC)[reply]
Firstly, the signs that some clathrate deposits might be melting are very recent - this may literally only have started during the last 9 months or so - and perhaps only in a small part of the oceans - and it might yet prove to be some other issue entirely. Secondly, while Methane has a fairly short half-life, it traps 70 times more heat than CO2 while it's there...so it has the scope to be a nasty problem that would happen quickly. The nature of the feedback would be to dump an enormous amount of methane into the upper atmosphere - which could produce a sudden and violent change in surface temperatures...far too fast for humans to adapt to. Admittedly, with a half-life of 12 years, the methane problem would abate within 25 to 50 years...but that's more than enough time to trigger all manner of other nasty problems. Also, when the methane disappears, it leaves behind both CO2 and water vapor - so when we say it's "gone" - that doesn't mean that the problem it left behind is over and done with. SteveBaker (talk) 13:49, 3 August 2009 (UTC)[reply]
Most of the clathrates are buried too deep to melt for at least a thousand years even under the most drastic global warming projections, and that's a scientific fact.98.234.126.251 (talk) 01:51, 4 August 2009 (UTC)[reply]
They're just reporters, how often do you think they get things right in matters of science? Besides, they're not even American reporters, they're European reporters -- so it's also likely that they have a vested interest in pushing for CO2 limits that will hinder America's economic growth so they could compete with us economically (which they can't otherwise). 98.234.126.251 (talk) 01:32, 5 August 2009 (UTC)[reply]
I strongly recommend that you actually read the articles Clathrate gun hypothesis and Methane clathrate -- they clearly state that most clathrates are buried very deep under the seabed and will not melt for at least a thousand years. While the Arctic clathrate deposits may melt sooner, they're only a very small portion of the total clathrate deposits -- so even if they do, they won't make a catastrophic impact on global warming. Here's the relevant quote (from Archer):
Most deposits of methane clathrate are in sediments too deep to respond rapidly, and modelling by Archer (2007) suggests the methane forcing should remain a minor component of the overall greenhouse effect.[10] Clathrate deposits destabilize from the deepest part of their stability zone, which is typically hundreds of metres below the seabed. A sustained increase in sea temperature will warm its way through the sediment eventually, and cause the deepest, most marginal clathrate to start to break down; but it will typically take of the order of a thousand years or more for the temperature signal to get through.[10]
OK, so dinosaurs roamed the earth for about 200 million years. First question is - why didn't they evolve to achieve intelligence like humans did in a much shorter period of time? Then I've been thinking about what would happen if SETI find aliens, or we become spacefarers and meet like-minded curious aliens, or they make their presence known because they have been waiting for us to achieve space travel... these aliens would presumedly come from far older civilizations and be far more 'advanced' than we are, given the age of the universe. Well, if dinosaurs did nothing for 200 million years, why is there a common presumption that aliens would have done any better? Sandman30s (talk) 23:16, 2 August 2009 (UTC)[reply]
Evolution isn't a straight line. You don't "evolve enough" over time and get some kind of prize (in this case, intelligence). It doesn't go towards any particular ends, and high, high-levels of intelligence, like humans have, are expensive and for most species unnecessary for their survival. You could easily say, humans have been around for awhile now, why haven't we evolved to achieve wings or giant horns on their heads? It's also worth recalling that though humans at at the top of the food pyramid now, we were quite scrawny and desperate for a good deal of known human history. While its true that in the long run, having lots of brains allows a species to become quite powerful, in the short term being able to adequately reproduce and protect your young is all that is really necessary, and there are plenty more direct ways to do that than having a gigantic frontal cortex.
The presumption about aliens is that if an alien had the capacity to reach us, they probably have much more advanced technology than us, because we don't really have any real prospects of being able to get across the vast, VAST distances of space in any reasonable amount of time. If something has managed to get over to us, it is probably more advanced than we are. --98.217.14.211 (talk) 23:23, 2 August 2009 (UTC)[reply]
There is some empirical evidence that dinosaurs were getting smarter (or more precisely that the relationship between brain mass and body mass was moving in a direction that favors intelligence in modern analogs). In general fish are less intelligent than reptiles, which are less intelligent than mammals, which are less intelligent than primates, etc. The evolutionary developments that led to human intelligence probably progressed through 100s of million of years, and not just the few million years of homonids. With respect to alien civilizations, I would also point out that a lot of the achievements of humanity are associated with the cultural preservation of knowledge and not intelligence per se. As species we biologically evolved almost not at all in the last millenia, but at the same time we have gone from the dark ages to space flight through the accumulation of knowledge. Regardless of their biological potential, an intelligent society with a million years of recorded history will almost certainly have accumulated far more knowledge than we have achieved in our few thousand years. Dragons flight (talk) 23:33, 2 August 2009 (UTC)[reply]
It is theorized that a great asset of modern humans has been grandparents. That of course necessitates life-spans long enough for 3 generations to be alive at once. The benefit of this is the knowledge that can be passed down from grandparents. Sounds quaint, but it is a scientific theory. You can read mention of it in this article. This is the relevant section:
"One more distinction between Neandertals and moderns deserves mention, one that could have enhanced modern survival in important ways. Research led by Rachel Caspari of Central Michigan University has shown that around 30,000 years ago, the number of modern humans who lived to be old enough to be grandparents began to skyrocket. Exactly what spurred this increase in longevity is uncertain, but the change had two key consequences. First, people had more reproductive years, thus increasing their fertility potential. Second, they had more time over which to acquire specialized knowledge and pass it on to the next generation—where to find drinking water in times of drought, for instance. “Long-term survivorship gives the potential for bigger social networks and greater knowledge stores,” Stringer comments. Among the shorter-lived Neandertals, in contrast, knowledge was more likely to disappear, he surmises."Bus stop (talk) 22:19, 4 August 2009 (UTC)[reply]
The comparison between Dinosaurs and Humans is false. Dinosaurs were (are if you include Birds) a Superorder successively divisible into 4 Sub-orders, numerous Families, many Genera and very many Species (see Taxonomic rank), whereas "Humans" is defined narrowly as a single Species (Homo sapiens) and most broadly as a mere Genus (Homo). A "fairer" comparison would be between Dinosaurs and Primates, the Order to which Humans ultimately belong. As Dragons Flight broadly said, the Primate Order is thought to have arisen as long as 85 million years ago, so one could say that it took the Primates at least 83 million years to evolve "intelligence" (depending on your definition of it): equally valid might be a comparison between Dinosaurs and Eutheria, the Infraclass of non-marsupial mammals to which Primates belong, which is at least 125 million years old.
Since evolution is not directed, but in large part contingent on varying external pressures, it says little to observe that one lineage acquired some new characteristic or notable improvement in one (such as intelligence), more "slowly" or "quickly" than another. In line with .211's observations, high intelligence didn't evolve in Dinosaurs over a long span because it wouldn't have been immediately advantageous in the prevailing conditions. It did so in Primates and in particular Humans because their conditions happened to favour it - this may have involved some low-probability coincidences in the preceding evolution of a series of traits (e.g. binocular vision, opposable thumbs, arboriality as a preconditioner for bipedalism, unusually complex social relationships) which, when combined, happened to make the evolution of intelligence more easy. 87.81.230.195 (talk) 00:57, 3 August 2009 (UTC)[reply]
I haven't got a good explanation for it but I recently read that becoming warm blooded was a necessary step in developing the brain beyond a certain point. So high intelligence in lizards is unlikely, even if the dinosaurs were not wiped out. Vespine (talk) 01:08, 3 August 2009 (UTC)[reply]
I believe there is evidence that at least some dinosaurs were warm-blooded (See this for a great summary of the arguments). Look at it this way: We know that birds are warm-blooded - and we're pretty sure that they appear to have evolved from feathery dinosaurs. Is it so unlikely that dinosaurs FIRST became warm-blooded THEN became birds rather than vice-versa? I'd argue that you need to be warm blooded in order to be able to fly (at least at the body size of birds) - hence things had to happen in that order. Ergo - there were almost certainly warm blooded dinosaurs. Either way, you can't rule out intelligence by ruling out warm-bloodedness because the latter is unproven. Furthermore - dinosaurs were not reptiles - relating what they could or couldn't do to modern lizards is simply not a valid thing to do. It's even possible that they DID become intelligent - at least to some degree - after all, there would be little or no evidence remaining of any kind of civilisation after all this time. We've only gained recognisable signs of civilisation in the last 5,000 or so years - we'd be very unlikely to spot signs of intelligence over such a small window.
As for the presumption that aliens would be intelligent...I don't think we do make that assumption. The most common argument that aliens must exist is the Drake equation. It contains a term fi that expresses the probability of life becoming intelligent. Plugging different numbers into fi gets you different probabilities that there are aliens out there who might be able to communicate with us. Most people have estimated that term at 1% - a few pessimists put it at 0.1% - some optimists put it at 100%. However, the total number of alien civilisations that are likely to be out there depends on so many unknown parameters that it's all just guesswork.
Steve: while your points about the likelihood of (some) dinosaurs' warm-bloodedness (though cold/warm-bloodedness is a rather crude and outmoded dichotomy) and the possibility of any evidence for dinosaur high intelligence being missed are valid, it is simply not true to say that "dinosaurs were not reptiles." Our Dinosaurs article's taxobox, for example, gives their classification as -
I agree with your point that modern-day reptiles are not fully representative of all that the Reptilia ever were and potentially could be, but bear in mind that, as well as "lizards," the rather impressive Crocodilia are also reptiles not too distantly related to Dinosauria, and that the majority of palaeontologist now interpret Birds as being, not merely "evolved from feathery dinosaurs," but actually to be dinosaurs, within the suborder Theropoda, though there is some dissent (some to the effect that instead, some dinosaurs are actually descended from birds) and many disagreements over the fine details. As is fairly well known, some birds such as Crows and Parrots can exhibit significantly high intelligence, to the extent of making and/or using tools and appearing to, not merely mimic, but actually to comprehend (and controversially, to rudimentarily use) human speech. 87.81.230.195 (talk) 04:24, 3 August 2009 (UTC)[reply]
Yep - I agree with all of that - I was somewhat oversimplifying for the sake of brevity. Indeed, the terms "warm blooded" and "cold blooded" are not completely explaining what's going on...however, the remark I was contradicting used those terms and I felt it better to reply in kind. Whether we call dinosaurs 'reptiles' and whether birds are indeed dinosaurs (and therefore 'reptiles'!) is mostly a matter of naming. The big prehistoric beasts that we think of as "dinosaurs" are certainly more closely related to birds than they are to lizards. Hence, there is no particular reason to assume that their metabolism resembles lizards more than they do birds. Hence (as I remarked before), the fact that lizards are not particularly intelligent does not prevent dinosaurs from being intelligent...and I agree that the relatively high intelligence of some birds leaves open the possibility of fairly intelligent dinosaurs. If you go with the idea that dinosaurs (or at least the therapods) are descended from birds - then the case may even more strongly be made. 13:07, 3 August 2009 (UTC)
Except that most dinosaurs had very small brains relative to their bodies. Only some of the most bird-like ones ("raptors" and the like) are comparable to (certain) modern birds and mammals in this respect. Not to the smartest birds and mammals either, as far as I remember (vaguely).--91.148.159.4 (talk) 19:40, 3 August 2009 (UTC)[reply]
But like the OP, .4, you're somewhat 'cherry picking' by implicitly comparing "most dinosaurs" (downplaying an alleged minority that were more intelligent) with the small minority of the mammals that have "intelligence like humans" in the OP's original phrase. Also, one cannot simply equate brain size (or better brain/body size ratio) with intelligence across Classes: the architecture and possibly more subtle workings of reptile/dinosaur/bird brains are different to those of mammalian brains, and studies of extant reptiles/birds suggest that a reptile with a given brain/body ratio is more intelligent (insofar as one can measure it) than one would expect in a mammal with the same ratio.
I think Steve and I are arguing somewhat past each other, but I can't agree that we should leave popular misconceptions exemplified by "The big prehistoric beasts that we think of as "dinosaurs" . . ." unchallenged. Bigger bones are preferentially preserved and easier to find, and big animals are disproportionally impressive, leading to sample bias and naive-observer bias, but in reality the majority of (Triassic/Jurassic/Cretaceous) dinosaurs in terms of both species and absolute numbers were probably smaller than, say, humans, and many (e.g. this) were tiny, just like a lot of their extant examples/descendants (e.g. this). In an encyclopaedic context we should surely endeavour to promote the more accurate picture? 87.81.230.195 (talk) 21:03, 3 August 2009 (UTC)[reply]
I'm not sure that's true. I recall reading a recent paper that argued that Mesozoic ecosystems were much simpler than modern ones, because niches normally filled by small animals today were often filled by large animals' offspring back then. The interrelations with vegetation were also less fine and less complex. Furthermore, not all dinosaurs were giants, but what appears to be the immense stupidity of their gigantic representatives surely somewhat discredits small and medium-size dinosaurs as well; the former would often evolve from the latter, too. To be a little crude here - we have elephants, they have sauropods. Finally, the claims about dinosaurs' brain/body ratio I remember did not, in fact, apply only to giants; few of the small and medium ones could actually compare to Troodon and Oviraptor. Even these, being the "brainiest", were close only to modern flightless birds such as ostriches (Martin, Introduction to the study of dinosaurs, p.243, p.262) (i.e. to some of the least intelligent modern birds), and may actually have been even worse than them, according to some [8].
As for the brain/body ratio - a citation of the studies you have in mind would be useful here (I'm afraid there's quite a shortage of similar studies, and I'd be surprised to find one). In the sources on dinosaurs that I've read, the brain-to-body ratio thing was accepted as a more or less adequate criterion, and I can't help but thinking that the differences you stress can't change things significantly, considering the immense differences in proportions we're talking about. I'm rather reluctant to believe that modern birds have managed to achieve a noticeably higher brain efficiency (intelligence-per-brain-size ratio) than mammals, but even if that were true, it may be connected to flight-related pressures on size and these certainly don't pertain to dinosaurs. Worse still, it would be much more surprising if the same thing were to hold true of the (non-avian, cold-blooded) reptiles we know; these are just plain primitive, very difficult to compare with any mammal at all, and I fail to see why mammals' brains would have become less efficient (in terms of size-to-intelligence ratio) than theirs. Yes, the crocodilians are impressive compared to other reptiles, but not really impressive compared to anything warm-blooded. --91.148.159.4 (talk) 21:32, 4 August 2009 (UTC)[reply]
The aim of evolution is survival and reproduction. From an evolutionary point of view, intelligence is of no particular value. Dinosaur intelligence might not have been their greatest asset -- again, from an evolutionary point of view. Bus stop (talk) 22:00, 4 August 2009 (UTC)[reply]
Sure. The whole issue is discussed because the initial asker was contemplating the possibility of sapient dinosaurs. And ultimately, because for some reason intelligence seems to be of some value from a human point of view.--91.148.159.4 (talk) 22:12, 4 August 2009 (UTC)[reply]
Wing contact on landing
The question on crosswind landing above reminded me of a rough landing experience I had at SFO. It's been a while, but I believe the flight was a Boeing 767. We were arriving in windy conditions. At roughly 10 or 15 feet from touchdown, the plane tilted violently to the extent that the tip of one wing almost certainly was momentarily lower than the landing gear. The pilots recovered and we landing without further incident; however, if it had happened just a few moments later in the approach I easily could have envisioned the wing tip clipping the ground.
So, my question, how common are incidents like this? And, how bad would it have been if the wingtip really had made contact? It certainly made an impression on me at the time. Dragons flight (talk) 23:18, 2 August 2009 (UTC)[reply]
Well, if the wingtip touched the ground, the result would certainly be a major disaster - the plane would get a violent jerk in the direction of that wing and would probably cartwheel and break up. I have no idea how common it is for a wing to dip alarmingly low on approach - but I don't think there are many cases where it happened close enough to the ground to cause a crash. I don't know how you judge what happened - from the perspective of a passenger, even quite gentle manouvers seem rather violent...and you have no way to know how low that wingtip really dipped. Your estimate for the plane's altitude may also be 'off'. People tend to assume that the markings painted onto the runway are similar in width to road markings - but they are MUCH wider...that makes you think you're lower than you really are. If it's any comfort, aircraft have inherent stability when they get closer to the ground - there is a "ground effect" which increases the amount of lift under the wing the lower it gets to the ground. If one wing starts to dip low and the other raises up then the down-going wing will gain extra lift and the up-going wing will lose lift - that tends to level the plane out. The closer that low wing gets to the ground, the stronger this effect becomes. Even far from the ground, the fact that the wings on the plane have 'dihedral' gives it some degree of inherent roll stability...but ground effect is pretty powerful. SteveBaker (talk) 02:10, 3 August 2009 (UTC)[reply]
"Certainly" is too strong. See [9] - last year, an Airbus A320 hit the ground during a crosswind landing. The pilot managed to turn it into a touch-and-go landing, but the touch involved parts of the aircraft that should not really touch anything... --Stephan Schulz (talk) 02:48, 3 August 2009 (UTC)[reply]
Runways at SFO
Yes, it is possible I misjudged the height, but I don't think I would have done so by a large amount. SFO has an over water approach (image at right), and we had already reached the land/runway when this happened and were only moments away from landing. Dragons flight (talk) 03:24, 3 August 2009 (UTC)[reply]
I'd say too that it wouldn't necessarily be a disaster. Wings on large jets have a good degree of flex, so my first thought would be that the wing would "bounce". Especially so if it was a sideways roll as opposed to a "tilt-and-slew-down-and-to-the-side", which would tend to drive the wing into the ground. Now, as to Stephan's linked video clip, that's just plain crazy. I'd like to read the incident report on that one, as in, why did the pilot even make that approach? (And Df, I think there are FAA reports you can search to see if your own flight got listed as a near-miss type of incident). Franamax (talk) 08:08, 3 August 2009 (UTC)[reply]
That Hamburg incident in the video DID involve a wing strike, with slight damage to the winglet and leading edge. That means there would have to be an investigation. I've looked on the German aviation authority website and not been able to find a report. Perhaps at 16 months it is too soon. - KoolerStill (talk) 11:35, 3 August 2009 (UTC)[reply]
ID an integrated circuit (IC) manufacturer?
Hi, not really science, but I reckon the people best able to answer my question will be most likely to be watching this desk.
Can anyone here ID the logo of an IC manufacturer? Too hard to photograph, but the logo is a nice, distinctive italic capital T, with an additional stroke to make it also look like a capital F. An oblique 3/4 circle encloses the top of the logo The logo has a circle which cuts the upright of the T/F below the lower horizontal bar of the T/F. Incidentally the chip in question is an MC 34063.
--Polysylabic Pseudonym (talk) 23:36, 2 August 2009 (UTC)[reply]
These are the manufacturers of the MC34063, which is a switching voltage regulator. It sounds like you might be mis-interpreting the Texas Instruments logo as an "F" (it's really a map of Texas). Take a close look at this Texas Instruments SN7400 and see if it's the logo on your chip. Nimur (talk) 01:30, 3 August 2009 (UTC)[reply]
Definitely an italic capital T modified to make an F. No serifs. Is there a cheap knock-off manufacturer with initials TF? No hint of a texas map outline, no hint of an i -203.22.236.14 (talk) 02:00, 3 August 2009 (UTC)[reply]
There are literally a dozen companies that sell that part. "Fantastic Technologies"[10] are the only ones who have F & T as their initials...but I can't find pictures of any of their chips to see what they might stamp onto them. What kind of package is the chip in? That would help to narrow down the list of suppliers. SteveBaker (talk) 02:23, 3 August 2009 (UTC)[reply]
They resell, but do not manufacture, the MC34063. As you can see, they're vendors of an ON Semi version (and maybe a Motorola version - but I doubt that's a stocked part, since Motorola Semi is now Freescale, and they're not making this part). There really are only four manufacturers for this part. (One of the most important things to realize in hardware design is that "presence in the catalog" does not mean "part actually exists and you can order it"). Experience and a bit of "hunch" is necessary to sniff out a real part from a catalog-only part. Nimur (talk) 05:32, 3 August 2009 (UTC)[reply]
Great set of sites Nanonic! But can't find it there either. The logo looks a lot like the Fairchild logo, but with the top of the F extended to the left. --203.22.236.14 (talk) 04:10, 3 August 2009 (UTC)[reply]
