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.
Does yerba mate have any caffeine? If not why does it seem to have that effect? —Preceding unsigned comment added by 63.165.5.103 (talk) 00:34, 11 December 2008 (UTC)[reply]
The article you linked seems to have quite a detailed answer: Mate contains xanthines, which are alkaloids in the same family as caffeine, theophylline, and theobromine, well-known stimulants also found in coffee and chocolate. Mate also contains elements such as potassium, magnesium and manganese. Caffeine content varies between 0.3% and 1.7% of dry weight (compare this to 2.5–4.5% for tea leaves, and 1.5% for ground coffee). Mate products are sometimes marketed as "caffeine-free" alternatives to coffee and tea, and said to have fewer negative effects. This is often based on a claim that the primary active xanthine in mate is "mateine", erroneously said to be a stereoisomer of caffeine. However, it is not chemically possible for caffeine to have a stereoisomer, and "mateine" is an official synonym of caffeine in the chemical databases.76.97.245.5 (talk) 01:10, 11 December 2008 (UTC)[reply]
It's also addressed in the introduction section of caffeine. – ClockworkSoul 00:17, 15 December 2008 (UTC)[reply]
is there a way to keep a plant or seed alive fo a couple months without letting it grow? —Preceding unsigned comment added by 76.14.124.175 (talk) 00:49, 11 December 2008 (UTC)[reply]
Seeds can remain viable for a very long time indeed. Our article seed hibernation mentions seeds which have grown into plants after ten thousand years or so of hibernation. Algebraist 00:53, 11 December 2008 (UTC)[reply]
so you have to freeze the seeds? —Preceding unsigned comment added by 76.14.124.175 (talk) 01:21, 11 December 2008 (UTC)[reply]
I think that's not necessary. As long as you store it in a clean, cool, dry and dark place then the seeds should be indefinitely dormant. Basically you don't want to trigger germination due to moisture and sunlight and avoid spoilage from fungi and bacteria.--Lenticel(talk) 01:58, 11 December 2008 (UTC)[reply]
Yea, just refrigerate them in a dark container. Freezing could actually damage seeds from tropical plants that aren't adapted to such conditions. StuRat (talk) 04:08, 11 December 2008 (UTC)[reply]
What's the application of laser cooling? Is it only able to cool atom? Could it cool molecule? And do they provide data about the coolest temperature reach for each atom? Thanks for your responses. roscoe_x (talk) 01:19, 11 December 2008 (UTC)[reply]
I was fascinated to learn today that Steven Chu, who won a Nobel Prize for work on laser cooling, is the leading contender to be Barack Obama's Secretary of Energy. What a 180° turnaround from the current attitude toward science in the Executive branch! --Sean 21:07, 11 December 2008 (UTC)[reply]
Crystallisation esp. seen in ice... what is the magic of the hexagon?[edit]
The chemistry of crytallisation is the usual topic but what about the physics? Especially seen in Snowflakes and on the poles of Saturn but also seen to create exotic type forces when freezing water (such as expanding its own mass without external reactions and creating linear faces). The stuff on snowflakes and Saturns poles... although non-solids convecting will form hexagonals naturally filling out the available space... what is going on with the hexagonals in snowflakes or on Saturns pole where there is ample space to be some random shape? Although the hexagonal pole of Saturn is peculiar, not even crop circles have a patch on snowflakes. Is this hexagonal a manifestation of the genetics of non-living items? How does a crystal create a smooth face over an area and how does a crystal without boundaries in size create a hexagon in an open space? If somebody travels through space and time, will they use a hexagonal stargate? Are some liquids actually a sub-viral life bound in a hexagonal skin? ~ R.T.G 02:00, 11 December 2008 (UTC)[reply]
I don't think anyone has adequately explained why snow flakes have so many shapes. The water vapor, it is said, condenses on a dust particle and the shape initially established grows. I think there is a theory that impurities in the water vapor establish the original shape. Some information might be obtained if a snowflake can be grown on a solid particle of known size and shape and extremely pure water vapor is supplied for the growth material. "Snowflake" and "Wilson Bentley" in Wikipedia provide interesting information, photos, and leads to other information about snowflakes. —Preceding unsigned comment added by 98.17.46.132 (talk) 02:53, 11 December 2008 (UTC)[reply]
Yeah, the pictures I was talking about are on Wilson Bentley who learned a method to photograph snowflakes in detail. Although possibly related to hydrogen bonding, a ball is similarly related to a ball park. Look at the pictures close up, they are nothing unusual but they are amazing every time, symmetry across distances based on a hexagon much larger than a hydrogen bonded molecule and also the pole of Saturn is probably bigger than the Earth itself. Hey, its not random at all!! ~ R.T.G 03:05, 11 December 2008 (UTC)[reply]
Snowflake growth is actually fairly well-understood. Different combinations of humidity and temperature favor different growth patterns (growth from corners vs. growth from faces vs. growth from edges, linear growth vs. branching growth, plates vs. rods, etc.). On a molecular scale, the six-fold symmetry comes from the hexagonal lattice of ice; on a macroscopic scale, the symmetry continues because as the snowflake forms, it moves around within the cloud, exposing all parts of of the snowflake to a given environment at the same time. --Carnildo (talk) 23:34, 11 December 2008 (UTC)[reply]
are some snowflakes of unusual shape. At first glance, a few of them do not even seem to be hexagonal - but they are actually irregular hexagons. —Preceding unsigned comment added by 98.17.46.132 (talk) 03:14, 11 December 2008 (UTC)[reply]
Honeycomb (see Honeycomb geometry) might shine some light at the phenomenon. I assume you already did read Crystal, Crystal habit and Crystallization. Crystal shapes depend on the material (see the Insulin crystal pix, no hexagon) but hexagons are pretty efficient shapes, so it's not surprising or magic to encounter them in nature. 76.97.245.5 (talk) 15:28, 11 December 2008 (UTC)[reply]
Another strange hexagonal snowflake form obstructing the reference desk Honeycombs are not surprising in an enclosed space such as the pattern of convection also seen in rock at the Giants Causeway but this doesnt cover snowflakes and the poles of Saturn which exhibit hexagonals in free form as though you just dropped something and it landed in the shape of a crop circle. Although it is not covered exactly, the best I can gather from what is available, regarding the snowflake, is that perhaps two molcularly bonded which are theoried to form a six sided shape, might grow around one single one to form a huge hexagon but this would not sufficiently describe the scale of it or the intricate yet intricately symmetrical patterns and even this goes no ways toward explaining the enormous Saturnian pole which exists in the fastest flowing wind known (12000 km per hour i think). One thing that is interesting regarding the hexagonal in particular is the fact that snowflakes and the Saturnian pole form themselves in a free flowing wind. I doubt there is much to explain some crystalline forms but they are simple and amazing. Would love to study them if there was anything to go on but seems like pretty pictures only. Wonder do snow flakes form hexagons in a weightless vacuum? ~ R.T.G 23:28, 11 December 2008 (UTC)[reply]
For more information on the cause of the different shapes flakes take, check out this excellent graphic, which is the last slide in a gallery of incredibly detailed images of snowflakes. --Shaggorama (talk) 07:47, 12 December 2008 (UTC)[reply]
Great pics Shaggo, especially numbers 1 to 4. I have trained up on machining steel and can't get over how some of the details are symetrical, just as though machined to high spec. The missing link between fractals and organisms I reckon or the gene pool of Gaia. ~ R.T.G 14:30, 12 December 2008 (UTC)[reply]
Well, kinda. The symmetry is a consequence of the entire snowflake having been formed gradually by a sequence of additions of material - each "arm" gets pretty much the exact same sequence of temperature, pressure and humidity changes - and hence they all change in more or less the same way. But look closely at the image at right - it's really not all THAT symmetrical. It has blobs in more or less the same places - but the sub-branches have different sizes and complexities. SteveBaker (talk) 04:22, 14 December 2008 (UTC)[reply]
At the place where the tips fork into three (picture on black), theoretically... the molecule in the middle fluctuated some force from each supposed molecule corner (Hydrogen bonding says two water molecules will form a hexagon hence corners), long enough to attract more water to link to each branch tip, with identical force and reacting identically all the way along the snowflake. Possibly but only as a sign of relatively immense linear forces eminating the six corners of the original bond. If the molecule in the center were compared to the size of the Earth, how powerful would a bolt of lightning need to be to be attracted to all six forks at one instant? I am sure it would be well out in space and the fact that it is never a pure hexagon but always symmetrical shows something in connection with something. And it at least proves that ice is bonded by an active and symmetrical force rather than an absent heat. ~ R.T.G 05:58, 14 December 2008 (UTC)[reply]
Assuming mankind either explores other solar systems or perfects terraforming within this system, how much larger than Earth could a planet be before it caused serious problems for the human colonists? And could a planet with a core of low density materials such as lithium or aluminum be much larger than Earth but have normal gravity? Since Ringworlds and Dyson spheres are unphysical even with advanced nano-materials, would a pressurized sphere of hydrogen gas be capable of making a terraformed "Earth" with normal gravity, but on a much larger scale? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 02:57, 11 December 2008 (UTC)Trevor Loughlin (talk) 02:59, 11 December 2008 (UTC)[reply]
One possibility for living on a planet with higher gravity is to live some distance under the surface, where the gravity would be significantly less. Unlike the Earth, though, such a planet must not have a molten core. StuRat (talk) 04:02, 11 December 2008 (UTC)s[reply]
I guess it's possible - but the technology for digging that deep doesn't remotely exist - and remember that you'd have to start all of that constuction - as well as build things like solar power plants on the surface of the planet - so much of the work involved would still be high-g.
As for alternative construction approaches - RingWorlds and Dyson spheres are indeed problematic for all sorts of reasons. You didn't mention the other fictional star-encompassing idea from the book "The Smoke Ring" it's sequel "The Integral Trees" (an awsome piece of imaginative world-making - and actually rather more feasible than "RingWorld"). But why bother - if you have the engineering skills and the raw materials - then just make spinning cylindrical mini-worlds - each a few kilometers in diameter and a few tens of kilometers in length (think "Rendezvous with Rama")...you could make them in stable solar orbits - in vast quantities (if needed) with none of the theoretical issues you'd have with the more exotic designs. Your pressurized sphere of hydrogen would be an interesting concept - but I don't see why you'd choose hydrogen versus a big pile of asteroids. SteveBaker (talk) 06:00, 11 December 2008 (UTC)[reply]
Considering it is a hypothesis, why couldn't it be entertained?96.53.149.117 (talk) 06:06, 11 December 2008 (UTC)[reply]
I think the idea behind using hydrogen is that it is lower density so you can get a larger surface area without having the gravity be too strong for humans to live there. I'm not sure how well that would actually work, anyone want to do the calculations? What would the pressure be like in the centre? The more hydrogen you have the higher the density would be, so there may be a practical limit on how big such a "planet" could get (obviously it would become a star at a certain point, but there may be a limit before that). There is also an issue with the pressure needing to be at least a certain value to keep the shell from collapsing in on itself (that would depend on your choice of building material, of course), it may well turn out to be an over-constrained problem. --Tango (talk) 14:24, 11 December 2008 (UTC)[reply]
Much more serious is the question of how you'd construct it! If you start with a ball of hydrogen - the depth into the ball at which the surface could be suspended by the internal pressure would be pretty deep down - and you'd have to somehow blow away all of the hydrogen outside of your surface in order for it to be supported by internal pressure alone. If you plan to build the 'shell' first - and then fill it with hydrogen, how do you keep the thing suspended against it's own gravitation before you pump the hydrogen in? If it's strong enough to stay put before the hydrogen goes in - then why did you need the hydrogen in the first place? Since the hydrogen acts much like the star at the center of a dyson sphere (both in terms of gravitation and pressure - although in the case of the star, it's photon pressure) - you'll have the exact same stability problems as a dyson sphere...which is known to be fundamentally unstable. So I don't think this 'design' can work. SteveBaker (talk) 17:58, 11 December 2008 (UTC)[reply]
How about this: You pump hydrogen in from who knows where (a nebula, maybe?) and use the reactive force from the pumps spaced around the shell to hold it up as you build it (sure, the hydrogen you pump in before it's finished will escape, but that's not a problem, you just pump in more). I don't think there's a problem with stability because there isn't a massive star at the centre that you need to keep central so it doesn't matter if the whole thing moves about a bit, in fact, you probably want it to orbit a star. --Tango (talk) 18:55, 11 December 2008 (UTC)[reply]
I had a better idea! You start off with a small sphere of steel (or whatever your 'crust' will be made of) - maybe a few meters across. You bring it close to the star and set it spinning. Pretty soon it's molten from the heat of the star. Now, you take a tube made of something that won't melt at that temperature and insert it into the sphere of liquid steel - pushing it in from the stationary point at the 'north pole' of the spinning sphere. Now you pump hot liquid hydrogen (you're going to need a LOT of pressure!) into the center of the sphere through your tube - and simultaneously add more steel into the molten sphere. As the hydrogen enters, it inflates the steel sphere like a soap bubble - and you can control the thickness of the 'crust' by altering the rate at which you add metal or the rate at which you pump hydrogen. When your sphere is large enough - you have to tow it out to the orbit you want it at (very carefully because you don't want it to pop(!!) and then wait for a few millennia for it to cool down (you could actually tow it further out so it would cool faster). As the iron and hydrogen cool - they'll both shrink - so you'll have to keep on pumping hydrogen into or out of it to keep the pressure at the designed level. (NO - I really don't think this would work - the stability issues are still problematic.) A gigantic steel soap bubble! SteveBaker (talk) 20:19, 11 December 2008 (UTC)[reply]
You may have problems with tidal forces making it asymmetric, you wouldn't get a perfectly spherical bubble. As long as it is close, though, it will probably work well enough. I'm also unsure how molten steel would behave in a vacuum - you may have to work quickly to prevent it boiling off. I don't see what stability issues you would have, though, it's just a balloon, balloons have been pretty stable at every birthday party I've been to. --Tango (talk) 21:41, 11 December 2008 (UTC)[reply]
We can avoid the worst of the tidal issues by picking an outragously hot star and doing our construction a nice long way away from it. Balloons (at 'human scale') are stable because they are entirely a matter of air pressure fighting elastic forces in the envelope. For our planet-sized bubble - we also have gas pressure - but instead of elastic forces to counter it - we have gravity. (There is no possible material that would be strong enough to keep the thing together with elastic forces at the size of a planet. The trouble with that is that the force of pressure only cares about the volume of the container - and the pressure will be more or less equal everywhere - no matter how the envelope moves relative to the high density gas at the core. However, gravity is different - it's an inverse square law. So if the dense core of our gas ball should ever move away from the center by a teeny-tiny bit - the side of the envelope that's now a bit closer will be attracted more strongly and the side of the envelope that's further will be less strongly attracted - so instead of the situation sorting itself out - it gets worse. So this is an unstable equilibrium...and that's never a good thing. For enthusiasts of the Larry Nivan "Ringworld" series - you'll have noticed that in later books he had to invent huge rocket motors for his ring that would fire to keep it perfectly in balance. This is the same problem - and it's the (sad) reason why Dyson Spheres, Ringworlds and now Bubbleworlds are not likely to be sustainable. It's a shame because this makes a great story. You fly nickel-iron meteors in from outer orbits - let the the sun melt them for you to make your crust. Any rock you are left with you keep for decorative features like mountains and fijords. Icy cometary stuff can be boiled into steam (do we really need hydrogen? Well - if so, we have to make a big solar-powered electrolysis cell to get hydrogen from the water (and keep back some of the left-over oxygen for atmosphere - and also keep some water for your oceans. Everything you need is right there. But the time involved is crazy - and the stability problems are (I believe) gonna kill the project. SteveBaker (talk) 23:40, 11 December 2008 (UTC)[reply]
Pressure won't be constant it will be higher nearer the centre. If one side of the shell moves towards the centre both gravity and pressure will increase. At first, gravity will increase quadratically and pressure linearly (I think), so it's unstable, but beyond a certain point that will change because the gas is becoming less and less spherically symmetric as the shell moves and sooner or later you can no longer reasonably model it as a point mass. With your model, you eventually get the highest pressure point being at the surface, but that doesn't seem plausible to me, the pressure must surely overcome gravity at some point. While gravity at the surface (which is what's important) may not be constant, it's going to stay within certain bounds as long as the external influences do. Even if it is too unstable, you can just have taps strategically placed around the shell and release hydrogen in order to push the shell in the opposite direction (like a balloon flying round the room when you let go) - you would need some way to replace the hydrogen, but if you managed to get that much to start with, surely you can find some more. --Tango (talk) 00:12, 12 December 2008 (UTC)[reply]
Exactly...the linear increase in pressure with depth versus the square-law increase in gravity is what ensures that the structure won't be stable. When it moves off-center, there is no restoring force - only a force that tends to push it even more off-center. Hence the structure is doomed without some kind of active control system (big rocket motors basically). SteveBaker (talk) 13:36, 12 December 2008 (UTC)[reply]
But what I'm saying if that it's only linear vs inverse-square for small displacements, after that it becomes something more complicated that I imagine will set up a restoring force. The question is how extreme the variations in surface gravity will be by that point. And you don't need rocket motors, as I said, you can just use the pressurised gas inside the shell for thrust. --Tango (talk) 13:46, 12 December 2008 (UTC)[reply]
The core of a planet is almost always going to be made up of heavier elements because they sink down to the centre over time. The only way the core could not contain lots of iron is if there wasn't much iron on the planet at all, which would mean the colonists were very limited in resources for building. You could get a planet quite a bit larger than Earth without too much trouble, though - while the extra mass increases gravity, the extra distance from the centre reduces it so surface gravity only increase linearly with radius (assuming constant density, which isn't quite true, so it will be a little more than linear). That means you can get double the surface area of Earth with only 41% more gravity, which is probably survivable (especially with the advanced medical technology that will almost certain exist by the time we have the technology necessary to reach other solar systems). --Tango (talk) 14:24, 11 December 2008 (UTC)[reply]
Well, there are also other considerations, such as how gravity will affect no only the density of the atmosphere, but on its composition. Higher gravity planets will tend to "hold on" to different gasses at differing ammounts, further complicating the 'livability' question.... --Jayron32.talk.contribs 14:30, 11 December 2008 (UTC)[reply]
Indeed, there are all kinds of things to consider, most of which will depend on far more than just the size of the planet - distance from (and type of) the star and the presence of life will probably have a greater influence on the atmosphere than 41% extra gravity. --Tango (talk) 16:48, 11 December 2008 (UTC)[reply]
Start with and existing gas giant such as Jupiter. Send the construction robots down to the correct depth and build an expandable shell at that depth. The robots themselves are gigantic drigibles supported by heated hydrogen. Then, gradually remove the gas from above the shell by launching it at escape velocity. We have lots of energy available for this effort: just fuse some of the hydrogen. The only theoretical problem I can see is where to get the material with which to build the shell. -Arch dude (talk) 02:25, 12 December 2008 (UTC)[reply]
That doesn't work though - your robots swoop down with a 10km x 10km chunk of 1km thick 'crust' material...what do they nail it to? They can't just let go of it because it'll just fall to the center of the 'gas ball'. Until you have the spherical shell 100% complete, it won't hold pressure - so it'll just collapse. That being the case - how can you build the shell? My proposal to start with a liquid 'drop' of steel and to gradually inflate it like blowing a soap bubble solves that problem completely. SteveBaker (talk) 05:33, 12 December 2008 (UTC)[reply]
You can hold the crust up with balloons filled with hydrogen (they may need to be quite large balloons, since Jupiter is mostly hydrogen anyway, to it's only a slight lifting gas, or you would need to heat it which requires energy, although with some kind of heat exchange system it wouldn't need too much). Then, once you've eliminated the gas above the shell, the pressure can hold it there. Your glass-blowing style method sounds cool, but would probably be much more difficult to achieve - this method is actually possible with today's technology (almost), if we only had the resources available to devote to it. --Tango (talk) 10:36, 12 December 2008 (UTC)[reply]
Consider the moment before the last piece of crustal material is bolted into place...at this moment the ENTIRE crust of a large gas-giant is being held up by balloons?!? We're talking trillions of tons! Now when the last piece is bolted in place - the structure is still not self supporting (because it relies on a pressure differential from the gasses inside the planet versus outside - and your "outer" atmosphere is still there. So with balloons holding up your entire planet your next step is what?....Oh yes - remove the outer atmosphere. Oh - but wait - the buoyancy of those balloons is all that's stopping the crust from collapsing! So as you pump away the upper atmosphere, your balloons will start losing lift...although admittedly you won't need as much lift. Anyway - imagining a reasonable thickness of crust (a kilometer maybe?) - consider the amount of Hindenberg-sized balloons it would take to support a Jupiter-sized crust containing 6 x 1010 cubic kilometers of steel! (8 grams per cc - so 8000kg/m3 - 8,000,000,000,000 kg per cubic kilometer - 480,000,000,000,000,000,000 tonnes for the entire crust. The Hindenberg could lift 3,000 passengers and 160 tons of freight - let's call that 200 tonnes. So you'll need 2,400,000,000,000,000,000 Hindenbergs. At 8 billion tonnes per square kilometer - every square kilometer of crust will need 20 million Hindenbergs to support it during construction - each with a volume of 200,000 cubic meters! Oh - but wait - that was a hydrogen balloon in a dense oxygen/nitrogen atmosphere. You have a hydrogen balloon in a mostly hydrogen atmosphere - so you have to heat the gas in order to get any lift...MANY more balloons - and some means of keeping them all hotter than the surrounding atmosphere. Good luck with that!
Why use steel? There are far lighter things, and I don't see why it needs to be a kilometre thick, there isn't supposed to be any significant force on the crust (gravity and pressure should balance out) so it doesn't need much strength. A couple of centimetres of carbon fibre or something should do it. Far more feasible than a pump that can operate at temperatures hot enough to melt steel. --Tango (talk) 13:53, 12 December 2008 (UTC)[reply]
Actually, the construction robots are gigantic hot-gas balloons, as I said. What I did not say is that the shell they are constructing is merely an entire shell of joined hot-gas balloons glued together. After we complete the shell, we begin removing the outer atmosphere, and at the same time we gradually increase the tensile strength of the shell by adding more and more kevlar straps. This gradually increases the weight, but this is counterblanced by the gradually increasing pressure differential. -Arch dude (talk) 20:51, 12 December 2008 (UTC)[reply]
How about this, according to Tether propulsion often a ribbon of various material has been unrolled from a satellite and tests show that your average ribbon will last something like five hours per ten kilometers and one built to last for two weeks lasted around 3 1/2 days. Balloons will suck at this game! ~ R.T.G 02:13, 15 December 2008 (UTC)[reply]
I know that heterosexual rapists, some of them, get erections when rape is the form of sexual intercourse. Is this also found in homosexual rapists?96.53.149.117 (talk) 05:32, 11 December 2008 (UTC)[reply]
I'm almost certain they do, rapists rape for the same reasons whether they go for the same gender or not. —Cyclonenim (talk · contribs · email) 08:03, 11 December 2008 (UTC)[reply]
I'm sure I'm missing something here, but isn't it impossible to commit rape (as defined by the OP) without an erection? Zain Ebrahim (talk) 11:02, 11 December 2008 (UTC)[reply]
I think he meant that rapists can only get an erection when sex is non-consensual. Belisarius (talk) 11:51, 11 December 2008 (UTC)[reply]
In simple terms, I think this might also be part of what is being asked. It's layman's guess only, so take it as you will:
There's probably a general consensus that a significant part of rape (perhaps the most significant part), is often the acting out of power or fantasy over another person. As such, the physical act of rape will probably elevate a wide range of bodily systems related to bodily arousal, excitement, aggression, and the like - as best I can recall (layman's information only) these will involve factors such as neurotransmitters and/or hormones (for example, endorphins, or epinephrine (adrenaline)), excitation of the autonomic nervous systems related to bodily arousal) generally, emotional excitement, and so on. The same bodily chemicals and factors are broadly involved in sexual arousal. (See also erection#Autonomic control.)
Again as a layman, the response to these would probably be felt as sexual and physically arousing for the person involved, regardless of the nature or gender of the target they were directed to (see rape of males) -- and regardless even of the gender of the rapist (rape by females exists too, see our article on rape by gender). FT2(Talk | email) 15:01, 11 December 2008 (UTC)[reply]
Why is 1 calorie defined as the heat required to raise the temperature of 1g of pure water through 1 degree celsius from "
"14.5 degree & not from any other temperature"? —Preceding unsigned comment added by 118.95.40.140 (talk) 07:30, 11 December 2008 (UTC)[reply]
Good question. The temperature needs to be indicated since the specific heat of water changes with temperature. Consequently, as our article calorie explains, there are different definitions for different temperatures, and the 15 °C calorie (cal15) is just one of them. But why anybody would want to use just that definition, I'm not sure. To me, the 20 °C definition makes more sense, since that is room temperature. Maybe it's because 15 °C is closer to the average outside temperature in moderate climates. — Sebastian 08:47, 11 December 2008 (UTC)[reply]
To expand on Sebastian's excellent answer; raising the temperature of water from, say, 14 degrees to 15 degrees actually takes a different amount of energy than does raising the temperature from say 20 degrees to 21 degrees. Thus, while we often say that "The specific heat of water is 1 cal/g * deg C or 4.184 J/g * deg C" that is an approximation. The actual value varies depending on the temperature. The correct way to calculate specific heat at any given temperature requires some rather complex differential calculus.
Given that we want the units we measure in to remain constant (having the value of the calorie change based on temperature wouldn't be all that useful) we need to pick a temperature to define it at. The actual temperature we use is rather arbitrary, and for some unknown reason, it was decided that 15 deg C was the choice. The same thing happened when choosing 0 deg C for "STP" or 25 deg C for "standard conditions" for thermodynamics. Since the functions are ALL temperature dependent, we have to keep temeperature constant; but beyond that it really doesn't matter what constant number we choose. --Jayron32.talk.contribs 13:32, 11 December 2008 (UTC)[reply]
True, but not directly applicable in this case. The cited effect has to do more with heat transference rate effects (such as the insulating effects of ice, convection currents, etc. etc.). That is, it depends on how fast or slow the heat is removed from the substance. Specific heat, which is the basis for defining the calorie as a unit, is about the quantity of heat energy actually transfered, not how rapidly that heat is transfered. --Jayron32.talk.contribs 19:09, 11 December 2008 (UTC)[reply]
I'm looking for information on spinal injuries, especially fuzing of vertebrae and conditions requiring this, etc. Got a friend who may need most of their back fuzed, and I'm looking for information on what it involves, what the impact might be long term, and (very much secondarily) what sorts of issues might medically lead to such a requirement. Mostly an article on spinal fuzing, or whatever the correct medical term is.
I can't find a relevant article. Do we have any, and if so what are the title/s? (If we don't, what are the correct medical terms and any suggested resources, for a wider search?)
Well, I was going to recommend the article tilted Vertebral fusion, but that is basically a dicdef and nothing else. Hm. Have you tried websites like WebMD or something like that? Google? --Jayron32.talk.contribs 13:20, 11 December 2008 (UTC)[reply]
This site is quite comprehensive. And this article may be useful. -hydnjotalk 14:41, 11 December 2008 (UTC)[reply]
About 2 years ago I found out that our super markets sell deep frozen duck and I ate up to 4 dishes a week -- excellent stuff! I was crazy about it.
The duck came deep frozen on an aluminium dish and packed airtight vacuumed in plastic. Now and then there were small air pockets and where you could eat all of the duck including skin (there were no bones) from the airless packed, those with air pockets often had not so good a taste and I found the skinny parts frequently tough and non-delicious to impossible to eat. Then the oil price rose and, due to the bio-diesel-madness (I put your tortillas in my tank), the food prices, too. In an attempt to make the inflation not to show, the super markets didn't rise the price but reduced quality. Suddenly they sold other brands, and they were not vacuumed and thus did not only have air pockets but were regularly filled with air. With those, I have to discharge about one third of the duck as inedible. Now that the economy is crashing and the oil price has dropped they sell the same low quality stuff at slightly lower prices.
Now the question: does anyone know how exactly the air renders the duck, and especially the skin, inedible? 93.132.132.239 (talk) 19:53, 11 December 2008 (UTC)[reply]
Probably it allows the moisture to evaporate out of the meat - but it's possible it also alters the rate at which the meat freezes - or there was once something in those gaps that is no longer present which is responsible for the problem. It's hard to know which. SteveBaker (talk) 19:56, 11 December 2008 (UTC)[reply]
What I object to is the poor quality of fruit in the supermarkets. It looks good. They dowse it with insecticide while growing so there are no blemishes on the skin. Some of it is waxed to further enhance the appearance. But it has very little flavor. It is almost always unripe as well, including canned peaches and other canned fruit. Farmers' markets just have supermarket stuff. If you want good fruit you have to grow it yourself if you have the space, not using commercial varieties of fruit trees. America has good meat in the markets, but poor fruit. There is good opportunity for fruit and vegetable stores - what the British call a "greengrocer". —Preceding unsigned comment added by 98.17.46.132 (talk) 21:12, 11 December 2008 (UTC)[reply]
Our article on freezer burn may be of interest to your original question. As to the later stuff, I am not sure the reference desk is much of a place to air your greivances against your local supermarket. --Jayron32.talk.contribs 21:15, 11 December 2008 (UTC)[reply]
It is common for air-packed food to be packed with nitrogen (or some other rather inert gas), not just "air". That is why food will last a long time in the bag, but spoils quickly after you open it. So, you need to know if these are packed with plain air or not. As for fruit, this is America. There is choice. I can buy cheap nasty fruit from Food Lion. I can get slightly better fruit from Piggly Wiggly for about the same price. I can get even better fruit from Harris Teeter for more money. I can spend even more and buy fruit from local farms at the farmer's market (though, there isn't much there other than peaches). I can go broke and get organic fruit from Earth Fare at a cost slightly higher than a new luxury sedan. When I travel to other countries, I am always surprised by the lack of choice. For example, when I was in Norway, you could buy Br0d (bread) - one brand. You could buy Melk (milk) - one brand. You had two choices of cereal: wheat or oat. However, there were at least 30 choices of beers and similar alcoholic beverages. -- kainaw™ 04:05, 12 December 2008 (UTC)[reply]
Hold on, Kainaw, this is plain nonsense. One type of bread? Are you sure that was a grocery store you visited, and not vinmonopolet? You're closer to the mark with regard to milk, the milk market used to be a monopoly called "Fellesmeieriet", now Tine, but there are a couple of smaller competitors. Anyway, Tine do of course produce more than one kind of milk (various levels of fat, several types of fermented milk). And your claim about cereals is also incorrect, regardless of how youdisambiguateit. Where the heck were you, anyway? --NorwegianBluetalk 17:02, 12 December 2008 (UTC)[reply]
As far as I know, I was in a grocery store. It was in Bardufoss (I don't really know how to spell it). I'm not claiming that I disliked anything there. In fact, I spent a lot of time trying to figure out a way to stay in Norway. I worked out a place to stay in Tr0mso. I just had difficulty because every official I talked to said that I had to basically have a job offer before I could stay there. Now, I just can't afford to return because the difference in purchasing power between the U.S. and Norwegian economies is terrible. -- kainaw™ 01:42, 13 December 2008 (UTC)[reply]
Wikilinks: Bardufoss, Tromsø. Bardufoss is tiny (2200 inhabitants), and has a large air force base, and I suppose shops to a large extent would cater for the needs of the military, which might explain the large selection of beers. --NorwegianBluetalk 13:09, 13 December 2008 (UTC)[reply]
On the other hand, in America you pay for such choices. Most of the cost in "name brand" products is to cover the cost of marketing, since there are so many brands to choose from, each brand must distinguish itself by spending gobs of cash on advertising, and thus pass that cost onto you, the consumer. In many cases, "store" or "generic" brand products are made in the same factories as the name-brand foods, but at a lower price since there is no advertising on said products... --Jayron32.talk.contribs 05:37, 12 December 2008 (UTC)[reply]
I don't think these two anons are the same person. One IP looks up to Germany the other US. It seems like a semi-random complain tacked on to me Nil Einne (talk) 10:40, 12 December 2008 (UTC)[reply]
I should point out that how significant the demand for biofuels was the cause of the 2007–2008 world food price crisis is an open-ended question. It definitely doesn't seem to be the only factor and may not have even been the primary factor. (One recent suggestion in the case of corn anyway is that it may have partially been an economic bubble perhaps mostly due to speculation of biofuel demand but even in that case it's questionable if you can really blame it on the demand for biofuels as opposed to the stupidity of humans) Nil Einne (talk) 10:40, 12 December 2008 (UTC)[reply]
Thank you, I think freezer burn is what I was looking for. (And I'm not really interested in fruit as long as there is other food available.) 93.132.146.73 (talk) 10:54, 12 December 2008 (UTC)[reply]
This report [1] talks about using piezo-electrics to extract electrical energy from the footsteps of people walking through the tokyo subway.
Are they truly capturing energy that would otherwise have uselessly turned into sound/heat energy - or are they actually making the people expend more effort in walking?
I kinda suspect at least some of the latter - in which case I wonder whether there is a legality to be answered - if you are making people work for you to generate your electricity - don't you have to pay them minimum wage while they do it? (...well, that last part isn't a science question - so I'd better not ask it here!)
I have seen lame-brained "something for nothing" "free" energy gimmicks for years, like connecting turnstyles, stairtreads or revolving doors to generators, or building little piezo generators into shoesoles. These ideas likely spring from the notion that a generator merely turns effortlessly, without a conservation concept, that it is effectively the prime mover pushing all the motors etc connected to its output. I expect that walking on a surface which extracted energy would be a bit like walking up a slight incline, and that the walker's pulse rate would be a bit higher than on a normal floor, if he walked at the same pace. Edison (talk) 20:03, 11 December 2008 (UTC)[reply]
I guess it depends on what the floor was made of before. If it was a very hard floor that barely moved (concrete, say) and now it has some give in it, then it will be more tiring to walk on (think about what it is like to walk on sand - it takes more effort because the sand moves underfoot). If it already had some give in it (eg. floorboards) then they might be able to add their piezo-electrics without making it harder to walk on. (Of course, I doubt the tokyo subway has floorboards, concrete is far more likely.) As for the legality of it, I doubt anyone thought of such things when writing the laws, but that won't stop a skilled lawyer digging out a 400 year old law that could, under a very warped interpretation, ban such things. --Tango (talk) 20:11, 11 December 2008 (UTC)[reply]
I disagree that a floor with give to it is more tiring to walk on. The spring effect is actually quite beneficial, reducing the impact stress from walking. Dance floors, for example, are almost always made of wood, because dancing on concrete causes pain and injuries. StuRat (talk) 17:03, 12 December 2008 (UTC)[reply]
There is a difference between stress and energy, though. You have to lift your feet higher with each step, which uses more energy. --Tango (talk) 17:16, 12 December 2008 (UTC)[reply]
Not if your feet are partially lifted for you, due to a spring-like effect of a floor that "gives". Sore feet indicate stress on the feet, while sore leg muscles indicate over-exertion of those muscles. StuRat (talk) 05:11, 14 December 2008 (UTC)[reply]
While it's possible that the piezo-electrics may generate some electricity for "free", it's likely to be an extremely small amount. This small amount probably won't justify the cost of installing the system. There may be an exception for places which are "off the grid" and where only a tiny amount of electricity is needed. For example, using such a method to power a pedometer that measures how far you've walked might be reasonable, if the price is similar to a button cell battery. StuRat (talk) 17:08, 12 December 2008 (UTC)[reply]
I believe that Tokyo subway stations are AMAZINGLY jam-packed with people - so there would be an awful lot of footstep-generated energy. So I don't doubt that they can extract a useful amount of energy (they must surely have done small-scale experiments to prove that). My question is whether they truly are (as they claim) harvesting 'waste energy' and turning it into something useful - or whether they are causing the general public to expend more energy as they walk in order to power their systems. I think people would object to being put into a giant hamster wheel in order to generate power for the subway company...is this really any different? SteveBaker (talk) 17:35, 12 December 2008 (UTC)[reply]
I would guess it's just using energy that would otherwise become heat. I still doubt if it's worth the money to install it, though. If you've ever tried the bicycle hooked up to a light bulb, you need to work amazingly hard just to light one bulb, so the tiny amount they get out of a footstep would do far less than that. For argument's sake, let's say they can get 1 watt from each person who walks by, but only while they are on the unit. To get one watt-hour, you would need a continuous stream of people to walk over the one device for an hour.
Now, as for the argument that they're stealing your energy, let me give an example. Let's say some government agency comes and removes all the sod on your lawn because they suspect it may be contaminated with lead. That would be objectionable, right ? Now say they come and take one blade of grass to test it, instead. Who would care ? It's just too little to matter, just like the energy from your footsteps. StuRat (talk) 00:04, 14 December 2008 (UTC)[reply]
So if they get 1 watt from one person walking on the device - then if they cover the entire platform of their subway station and there are 500 people wandering around on the platform - then they are getting a more respectable 500 watts for as long as the platform is occupied. That's not really very much - it would MAYBE be enough to light the entire platform (50 ten-watt CFL's?)...I could see the attraction. Of course we don't know whether 1 watt per person is reasonable. SteveBaker (talk) 04:09, 14 December 2008 (UTC)[reply]
Yes, but if it takes 5000 piezo-electric units to have one everywhere a person can step on the platform, and they cost $10 each to buy and install, and last for 10 years, that would mean $50000 to light a subway platform for 10 years, which could likely be done for less with regular electricity. However, if you're someplace without any electricity service, but with heavy foot traffic, like some locations in a national park, that might make more sense than bringing in electrical lines. Other technologies, like solar power and windmills, might also fill this "off the grid" niche. StuRat (talk) 05:02, 14 December 2008 (UTC)[reply]
But this isn't a hypothetical - they really are installing this stuff for real in Japanese subway stations. To quote from the link I provided up-top: "JR East has been trialing these systems for the past year. They have recently improved and expanded the system by changing the floor covering from rubber to stone tiles, and have improved the layout of the mechanisms to improve energy generation. The total amount of floor-space will add up to around 25 square meters, and they expect to obtain over 1,400kw per day - more than enough to power their systems."...although I suspect a little mistranslation because "1,400kw per day" doesn't make much sense - and if they just mean "1,400kw" then I'm pretty sure that's impossible! However, what is clear is that they've tested it - and it works well enough to go from a trial to an actual installation. But I still don't understand whether these are indeed harvesting waste energy. SteveBaker (talk) 07:19, 14 December 2008 (UTC)[reply]
Ah...here we go: [2] says 1,400kw/sec per day for 25 square meters of high-traffic flooring. 10watts per person when the equipment is new - down to 3.3watts per person after the equipment is more worn out.
At 25 sqm or 5 m x 5 m which comes to about the same size in yd. you'd have to take very short 50 cm steps to get 10 steps in. (Average for Europeans is reported at about 62 cm/step.) Taking the stairs when the escalator is out/ switched off would probably cost you a lot more energy. So, don't sell your exercise bike yet. As far as the economics goes, you are paying for use of the subway's facility, including overheads and the use of their floor. There are many things that you do while using the subway that could be done differently at higher cost. You push buttons to open doors, so the subway won't have to pay someone to open doors for you etc. Now the new floor is going to cost more than just re-tiling the parts that you wore off and paid for with your ticket. You can reasonably expect those increased costs to be charged to the consumer. However, the energy generated will enable the company to buy less power. While price reductions in ticket fare for those savings will probably be too much to hope for, the savings after deducting operating costs for the energy generation system should at least cover some cost increases in other overhead positions. So you could expect the ticket prices to stay stable longer than they would otherwise have. In short you are paid for your "work" by being charged less than you would otherwise have been. Sweat equity at its finest. :-) —Preceding unsigned comment added by 76.97.245.5 (talk) 11:22, 14 December 2008 (UTC)[reply]
Replacing the rubber tiles with stone would cause increased stress on the feet, unless the springback effect of the rubber is duplicated by the new devices. Mechanical energy that would be converted to heat in the rubber tiles could be changed to electricity by the new devices. StuRat (talk) 22:03, 14 December 2008 (UTC)[reply]
Am I reading this correctly ?:
"In respect to the generating capacity per passenger, JR East aims to attain 10W/sec at the start of the experiment and 90% of the initial capacity two months later. The experiment carried out in fiscal 2007 (Jan 19 to March 7, 2008) achieved 1W/sec at the start and 2/3 of the initial capacity seven weeks later. As for the experiment in fiscal 2006, the value was about 0.1W/sec at the start and 1/3 of the initial value three weeks later."
It must mean the generated power per device they've achieved so far is only 1W. That's about what I expected, and it's rather pathetic, as is the rate at which the devices lose effectiveness. They hope to increase it to 10W/sec, but losing 10% of capacity every 2 months still seems to make it unusable. Also, what do they do when foot traffic is too low to work the devices ? Do they have battery backup or use electricity off the grid ? StuRat (talk) 22:03, 14 December 2008 (UTC)[reply]
Vanadium foil is used in cladding titanium to steel[edit]
I found the statement: Vanadium foil is used in cladding titanium to steel. over and over again, but it looks all are quoting the rubber bible (CRC Handbook). Has anybody ever heard of this method? I now that welding steel to titanium is nearly impossible and they do explosion welding friction, welding and many other things to combine the two. A scientific article publishes the results on using copper for cladding, but vanadium is nowhere mentioned except on simple websites or in the introductions of some articles about vanadium which have also only one sentence about it, without source. Thanks.--Stone (talk) 20:33, 11 December 2008 (UTC)[reply]
Thanks! I have to read it when I have access to it on monday. Is there vanadium mentioned in the text?--Stone (talk) 22:26, 12 December 2008 (UTC)[reply]
The article specifically states "The best intermediate metal for welding steel to titanium lining is vanadium," - it also cites additional sources to corroborate the idea. Alternatively, the article discusses silver and other filler metals; it also details two techniques which use vanadium as the intermediary metal. Nimur (talk) 20:45, 13 December 2008 (UTC)[reply]
Perfect!! This is the reference I was looking for!--Stone (talk) 07:09, 16 December 2008 (UTC)[reply]
