Wikipedia:Reference desk/Archives/Science/2007 October 29

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October 29

Batch experiment for denitrification endpoint in wastewater treatment

I am told the endpoint for denitrification in biological wastewater treatment can be determined by a batch experiment. What is the step-by-step procedure for conducting such an experiment and are there electronic sensing techniques for obtaining the same information in a continuous fashion? Thanks Thinkaboutlife 03:43, 29 October 2007 (UTC)

Gas formation at extreme low pressure and temperature

This question about wind at the miscellaneous desk spinned off into extreme planetary circumstances, with the planet so far from its star (if any) that it receives no heat (well, of course there is no absolute zero for anything). So I looked up the freezing point of helium, which is 1.15 K at 66 atm. Which would mean that even at extreme low temperatures, there would still be an atmosphere (however thin) of helium because of the vacuum surrounding it. But what about other gases? I guess I'm asking about the bottom left corner of the phase diagram (now why didn't I learn about that at school?), so extreme low pressures or a vacuum. But the article doesn't deal with that extreme. Let me start with one extreme:

• Would uranium be gaseous in outer space?
• And on above planet, at, say, an extremely low 1 Pa, what would be the boiling points of the various elements? The graph at the article doesn't go below 0.1 atm (= 10,000 Pa). And then at 10 Pa, 100 Pa, etc?

I suppose the atmosphere (which has no wind - the point of the original question) would be built up in layers consisting of the various elements with Helium sitting at the top. DirkvdM 07:18, 29 October 2007 (UTC)

On a phase diagram, you will notice that water is liquid at 1 atmosphere and room temperature. However, we also observe that water will evaporate from lakes and puddles. This is because even though the substance is naturally a liquid under those conditions, some fraction will spontaneously change into a gas through a process described by the vapor pressure. This is true for all substances. Uranium, like most metals, is naturally a solid in the limit of zero temperature and zero pressure. However, at all temperatures above 0, some small fraction of atoms will spontaneously turn into a gas and escape since there is zero ambient pressure. For most solids, the rate at which this occurs is neglible not only compared to human experience, but also compared to the age of the universe. In other words, the amount of time before satellites "boil" away in the vacuum of outer space is truly astronomically large. Dragons flight 11:52, 29 October 2007 (UTC)

Another way to think about that is that the concept of 'temperature' is really only a statistical average of the speeds of all of the molecules in the material. Even at fairly low temperatures, some molecules will be moving quite quickly (although the majority are not). Those few fast moving molecules may have enough kinetic energy to escape the surface no matter what. So all things with temperatures above absolute zero (which is to say: "all things" since absolute zero is unattainable) will lose molecules at some rate. But the statistics of the thing mean that the rate will be exceedingly slow at low temperatures because the probability of molecules having enough energy to escape becomes very low indeed. At higher temperatures that probability increases and evaporation will happen to a much greater degree - and finally, at the boiling point of the material, all of the molecules have enough kinetic energy to shake themselves loose and escape to form a gas. SteveBaker 14:06, 29 October 2007 (UTC)

Broad spectrum antibiotics

I know that Penicillin is a broad spectrum antibiotic, but was wondering if all antibiotics ending in cillin are broad spectrum. I couldn't find the answer here on Wikipedia or online, so thought I would ask here. Thanks. Jeffpw 08:52, 29 October 2007 (UTC)

Penicillin is not a broad spectrum antibiotic. It covers a relatively narrow spectrum of organisms, and is useless in Gram negative infections. In fact, most of the "-cillin" drugs were developed in order to find drugs with a broader spectrum than penicillin. You will find more details in the penicillin article, which lists narrow, moderate, and extended spectrum penicillins. - Nunh-huh 13:13, 29 October 2007 (UTC)

Drop dead on the Moon

If you'd drop a dead body on the Moon, what would happen to it? Would it decompose? DirkvdM 09:43, 29 October 2007 (UTC)

It depends on where you drop it on the moon. If you drop it in the dark side, it'll freeze and if you drop it on the sunny side, it will fried. 58.109.93.128 10:23, 29 October 2007 (UTC)

Hmmm .. I assume "dark side" means the far side of the Moon, i.e. the side facing away from Earth, which gets just as much sunlight (two weeks on, two weeks off) as the side facing Earth. I blame Pink Floyd. Anyway, a similar question has appeared on the RD in Nov 2004 here> There is also a response on Ask Yahoo here. General consensus seems to be that there would be some decomposition due to the presence of anaerobic bacteria, as well as dessication and slow weathering as a result of temperature changes. Gandalf61 10:39, 29 October 2007 (UTC)

Actually, on the album someone says "There's no dark side of the Moon, really." but then goes on to say "As a matter of fact, it's all dark.". Which is another bit of nonsense. DirkvdM 11:48, 29 October 2007 (UTC)

Not at all; it is dark. With an albedo of .12, it's only as bright as worn asphalt. We probably think of it as bright because there are no clouds or atmosphere to shade it from the direct sunlight. Matt Deres 16:40, 29 October 2007 (UTC)

The albedo of worn asphalt is only slightly lower than that of bare soil on Earth (fresh asphalt, on the other hand, has an albedo of just 0.04). But what I meant was is that half the Moon is lit by the Sun and therefore not dark. But SteveBaker gives yet another interpretation below. DirkvdM 09:11, 30 October 2007 (UTC)

Over eons, the top several meters of the lunar regolith are stirred up via the action of micrometeorites, through a process known as lunar gardening (wow, a red link). Since there is no appreciable atmosphere on the moon, even dust flecks the size of sand grains will leave tiny impact craters (since they are moving at several km/s). Over the very long term (i.e. many tens of millions of years) such micro impacts would ultimately grind the body down to nothingness. Dragons flight 10:50, 29 October 2007 (UTC)

Ok, looks like it's a race between the bacteria in the body, dessication and being bombarded to bits. I suppose the lunar gardening is the slowest process. How much will the bacteria consume before the body is dried out and the bacteria die too (or become dormant at best)? Also, which bacteria would do this? By far most bacteria in our bodies are benevolent, but would they start decomposing the body after it dies? DirkvdM 11:48, 29 October 2007 (UTC)

Oh boy, there are some confused answers here! Let's try to clarify things a bit...

• The term "dark side of the moon" refers to the side of the moon that is never seen from earth. In this context, the word "dark" is as in "Darkest Africa" - it means "unknown", not "lacking sunlight". The far side of the moon is just as sunny as the near side (and it's not even unknown anymore - we have lots of photographs of it). However, there are places in some craters on the moon that never see sunlight where things stay perpetually frozen. The length of a 'day' on the moon is what we'd call a "lunar month" - about four weeks.
• Since either freezing or baking to the point where it would kill bacteria would be unlikely to take more than a few hours (the temperature in the sunlight is enough to melt lead). I'm pretty sure that bacterial action is a non-problem in something as thermally conductive as a corpse.
• So unless this body is tucked away on the edge of one of those very steep-rimmed craters, it would alternately freeze for two weeks then cook for two weeks. I'd say that dessication/mummification would be the most immediate effect (that's what happens to bodies left on cold/dry mountaintops) - but it's hard to know for sure. There is no oxygen - so the body wouldn't combust in the heat - but it would drive out all of the water.
• As for being bombarded by meteors - that could happen eventually - but it would be a very improbable event. There are no more meteors (per square mile) hitting the moon than there are entering the earths atmosphere. The reason the earth isn't pockmarked like the moon is because the air burns up the smaller meteors and the craters created by the larger ones get eroded by wind & rain and subducted by continental drift - where on the moon they stay intact indefinitely. Look up into the sky on a dark night - how many meteor streaks do you see? Do you think one of them would hit you if it didn't burn up? Well, the odds are about the same on the moon...a little less actually because the earth's stronger gravity is going to pull them more towards the earth than the moon.

SteveBaker 13:52, 29 October 2007 (UTC)

• "... the temperature in the sunlight is enough to melt lead" - huh? This page says the moon gets up to 123°C, and our article says lead melts at 327°C. How would lead melt on the moon? --Sean 14:34, 29 October 2007 (UTC)

I was about to make the same point as TotoBaggins - sunlight on the Moon is definitely not hot enough to melt lead. Granted that 123^oC is still too hot for most bacteria to survive, but for hyperthermophiles such as Strain 121 it is just right. I agree that bacterial decay won't be a significant factor for our Moon corpse, but I don't think we can rule it out completely. Gandalf61 14:40, 29 October 2007 (UTC)

Well actually, without air - the temperature depends completely on the reflectivity/emissivity of the object (it's ability to shed heat by radiation) - the moon rock has an albedo of 0.12 - meaning that it only absorbs 12% of the incoming sunlight and reflects the rest away so the moon itself stays relatively cool. Darker objects will get a lot hotter. But I meant that figuratively rather than literally. I apologise, I should be more careful. SteveBaker 18:13, 29 October 2007 (UTC)

Steve, you've got albedo backwards in this paragraph. An albedo of 0.12 means that it reflects 12% of the light, so it absorbs the majority. -- Coneslayer 19:59, 29 October 2007 (UTC)

Steve, seriously, it's not an issue of "maybe it will be hit by micrometeorites", but a certainty. Objects below about 1 cm in size never get hot enough to leave visible streaks in the sky, but the population mass density of space debris peaks at about 100 microns, and the rate is about one micrometeorite impact per km^2 per second. The Earth aquires some 50,000 tons of space dust per year. And yes, as astronauts discovered, the entirety of the lunar surface is well-mixed to a depth of several meters by the action of meteorite impacts over tens and hundreds of millions of years. Dragons flight 15:32, 29 October 2007 (UTC)

Yeah over a very long period of time, the body will be bombarded to nothingness - but we're talking in the millions of years range. Let's examine your statistic of 50,000 tons of material arriving per year - it sure sounds like a lot - but only if you don't do the math. That 50,000 tons is spread more or less evenly over the 500 million square kilometers of the earth's surface. That means roughly one kilo per 10 million square meters. That number must be about the same for the moon - so if our corpse covers 1 square meter of the lunar surface, it's getting an average of one ten-thousandth of a gram per year of micrometeorite bombardment. Even at the speeds of micrometeors - that's hardly going to shred it to pieces anytime soon. Sure, it might get unlucky and get hit by a 10 kilo monster...but the odds are vanishingly small. SteveBaker 18:13, 29 October 2007 (UTC)

Using the rate of 1/km² or 1/1,000,000 m², and assuming a person's body has about 1 m² of exposed surface on the top side, it would still take, on average, a million seconds for a micrometeorite to hit. That's 11-12 days. So, to be completely destroyed by micrometeorites would take a long time. It would be a shriveled mummy long before that. Also, from how high was the body dropped ? If dropped from Moon orbit it would splatter into tiny pieces immediately, at least if it hit rock. Terminal lunar velocity into a deep pile of Moon dust might leave the body largely intact. StuRat 18:32, 29 October 2007 (UTC)

As there's no air resistance, there's no terminal velocity. I agree that dust would be a less destructive landing surface than rock, but my understanding from the Apollo missions is that the regolith is pretty firmly packed -- which would make the impact destructiveness thing almost entirely a function of initial height. — Lomn 22:04, 29 October 2007 (UTC)

The terminal velocity of a dropped object is still finite: it's equal to the escape velocity (for the Moon, 2380 meters per second). The only way to get something moving faster is to actively propel it. --Carnildo 23:44, 30 October 2007 (UTC)

That... seems unlikely (though I'd be interested to see a writeup on it, most TV stuff is written assuming an atmosphere). Apart from that -- initial conditions other than zero velocity, even without active propulsion, can easily lead to an impact at higher-than-escape-velocity speeds. Not that that's really either here or there.

The 'dropping' was meant in more of a figurative way. Btw, for a dead body, nothing can be considered terminal anymore. :) DirkvdM 09:11, 30 October 2007 (UTC)

Peak Coal

What is peak coal? 58.109.93.128 13:24, 29 October 2007 (UTC)

Peak coal is detailed in the article on Hubbert peak theory. Lanfear's Bane | t 13:32, 29 October 2007 (UTC)

Jehovah's Witnesses & Marriage

Do Jehovah's Witnesses believe and or support marriage to other religions. The reason I ask this question is I am not a Jehovah's Witness and am engaged to one and her father isn't in support at all of us. The rest of his children are married to a Jehovah's Witness. His brother isn't one and is married to one. Any help would be appreciated.

Thanks,

(email removed per instructions at top of page) —Preceding unsigned comment added by Timfreidag (talk • contribs) 14:47, 29 October 2007 (UTC)

• In most religions, getting the blessing of your fiancee's preacher, and then getting the preacher to perform the ceremony, is a sure-fire way to overcome this obstacle. Of course, you and your fiancee should be prepared for the possibility that the preacher is also intolerant of interfaith marriages. --M@rēino 16:33, 29 October 2007 (UTC)

Surely not! Surely religion is all about tolerance? If his brother is married to a JW, surely it would be possible for you? He may be using his faith as an excuse if he is not happy with his daughters choice of partner. (That's not that I am saying there is anything wrong with you, I am just hazarding a motive for his actions). Lanfear's Bane | t 16:54, 29 October 2007 (UTC)

You’d probably get much more knowledgeable answers if you moved this question to the Humanities reference desk, or perhaps the Miscellaneous reference desk. Indeed, I think the Science reference desk may be the worst of the reference desks to post this question to. As a general rule, the more that people are into science the less they’re into religion, and vice versa. MrRedact 18:36, 29 October 2007 (UTC)

The policy of Jehovah's Witnesses is to marry within the JW faith. Marrying someone outside JW may be enough to be dismembered. Graeme Bartlett 00:41, 30 October 2007 (UTC)

I think you mean "disfellowshipped" :-) --Trovatore 00:43, 30 October 2007 (UTC)

No, No, those folks can get real uppity, I think he was right..;-)) —Preceding unsigned comment added by 86.4.189.9 (talk) 08:56, 30 October 2007 (UTC)

Alcohol - on the verge of anaebriation!

If I have a few glasses of wine and start feeling light headed, what is happening in my brain to make me feel like that? Thanks. —Preceding unsigned comment added by 88.144.1.100 (talk) 16:04, 29 October 2007 (UTC)

We have an article specifically on the topic of Effects of alcohol on the body. Friday (talk) 16:05, 29 October 2007 (UTC)

Twin prop aircraft

after flicking through the "What is the name for this kind of aircraft, and why don't we make them?" post, I was thinking. Everyone dismissed the tail rotor on a transverse twin prop aircraft as pointless, but if you did have both props spinning in the same direction and a tail rotor to counteract any net rotation, would rotational manoeuvrability not dramatically increase with charge over the speed and hence thrust from the tail rotor, possibly allowing extremely sharp turns to be made, even at low speeds? ΦΙΛ Κ 16:28, 29 October 2007 (UTC)

The problem in most helicopters is that the tail rotor consumes continuous engine power for no useful purpose. On a twin rotor/propellor craft you can run the rotors in opposite directions to counteract the rotation and have more engine power to spare. You can still manouver by pushing more power to one rotor than the other. In the few (mostly Russian) helicopters that have Coaxial rotors that rotate in opposite directions, they can be shorter, more compact and turn faster than the usual kind. However, there are severe problems with these designs too: the additional complexity of the design, the problems of air turbulance between the blades as they pass each other adds vibration and there is a risk that in extreme situations one rotor might flex and hit the other. Having the two rotors spaced well apart helps that - and that's exactly what the CH-47 Chinook does. This solves most of the problems with coaxial rotors and gets rid of the tail rotor - but your back with a much bulkier design. Incidentally - one generally wants to place the two rotors fore-and-aft rather than left-and-right in order to keep a more streamlined fuselage - the exception being in tilt-rotor designs where obviously a fore/aft configuration wouldn't allow you to tilt the rotors forwards to become propellors for forward thrust. There was an experimental helicopter out there a few years ago that used a turboshaft engine to drive the main rotors and took the ject exhaust from the engine and sent that back to a vectored thrust nozzle in the tail that took the place of the tail rotor. This is a wonderful solution - but suffers from one lethal problem. If the engine fails, then your normal autorotational landing option is gone because in the absence of any tail-thrust, the helicopter would spin like a top. I don't know whether they ever solved that - but you don't see helicopters built like that - so I guess not. Then there is this thing: Piasecki 16H and Piasecki X-49 - which also doesn't seem to have taken the world by storm! SteveBaker 17:52, 29 October 2007 (UTC)

A few points..

1. I'd contest that moving power from one rotor to another in twin prop rotor wing aircraft would provide any significant turning force at all, as to provide a force comparable with that of cutting power to the tail rotors in a helicopter, you would have to stop one of the rotors, which isn't really a possibility, whereas with the tail arrangement I suggested, you could have twice the turning force experienced by cutting power to the tail rotor.
2. In the turboshaft exhaust arrangement you mentioned assuming the rotors and engine were not disengaged when power was lost, the turboshaft's compressors would surely continue to drive air through the tail pipe at a velocity which would allow the aircraft to remain stable, even if a hard turn was required by the pilot as well to further maintain stability.

ΦΙΛ Κ 22:23, 29 October 2007 (UTC)

1. Even assuming that holds, what happens if you have to turn the other way? You've got to mount an even bigger (and still completely unnecessary) tail rotor to counteract two main rotors working in concert. On the other hand, with a standard counter-rotating prop arrangement, all you have to do to generate yaw is vary the pitch of the blades. Same power to both rotors the whole time, and no power wasted on a tail rotor.
2. I don't get your point. If the engine fails, what's powering the compressors?

Anyway, I think it's fairly clear that twin-rotor craft have no need for a tail rotor. It's extra weight, complexity, and power loss for no operational gain. Even if it somehow improves maneuverability (a claim I doubt, and the utility of which I doubt -- more on that), twin-rotor craft tend to be heavy-lift craft where maneuverability is not a priority. Getting back to why the supposed extra maneuverability of a super tail rotor is useless -- think of a helicopter as a motorcycle and the tail rotor as the front wheel. When maneuverability matters for a helicopter in combat conditions, it's at high speeds. Helicopters, like motorcycles, make high-speed turns by banking, not by steering. A tail rotor doesn't even provide a meaningful assist, because while it may affect the direction the nose is pointed, it won't affect the helicopter's inertia. The ability to spin like a top is not a highly prized attribute of helicopters. — Lomn 02:30, 30 October 2007 (UTC)

To explain my second point, the moment of inertia of the blades, the same thing that would cause the craft to spin if power was lost.ΦΙΛ Κ 14:15, 30 October 2007 (UTC)

ΦΙΛΚ misunderstands how helicopters work. They don't "cut power" to the tail rotor in order to turn - they alter the collective pitch on the tail rotor blades. (That's how come they can turn both left AND right! :-) SteveBaker 03:37, 30 October 2007 (UTC)

True, I know very little of workings of a helicopter and was really just making assumptions. But just to say, using the mothod of tail rotor speed variance to steer, you could steer both ways, one way by slowing it down, the other by speeding it up.

You absolutely can, it's just that pitch variance is a far better solution. — Lomn 14:34, 30 October 2007 (UTC)

Theoretically - you might - but not in practice. The tailrotor is driven from a set of gears from the main rotor so that as the main engine throttles up and down, the tail rotor automatically maintains the correct amount of correcting torque. There is no way to speed it up...although I suppose you could slow it down with some kind of clutch mechanism - they don't do that in practice (at least not on any helicopter that I'm aware of). SteveBaker 17:02, 30 October 2007 (UTC)

So just to clarify, twin engine airplanes often do not have counterrotating props. The increase in efficiency is offset by the cheapness of the identical engines on each side (and on single engine models). --DHeyward 05:54, 30 October 2007 (UTC)

Yes - airplanes - because the orientation of the engines to the line of flight would induce roll - not yaw - and roll is easier to stabilise because you've got wings and ailerons and a large amount of rotational drag and a huge moment of inertia along the roll axis because of those big wings and the big heavy engines (not to mention fuel tanks) stuck way out from the centerline. Those things don't work anywhere near so well for the yaw induced by lift rotors in a helicopter or tiltwing. However, the effect of engine torque isn't negligable. Some single-engined aircraft were notable for being able to roll much more sharply in one direction than the other. I'm thinking of the Sopwith Camel as an example. It's Clerget rotary engine actually rotated with the propeller(!) and had a huge moment of inertia. The heavy spinning engine and the short-winged/lightweight biplane design enabled the aircraft to turn much more quickly to the right than to the left - a feature that experienced pilots used to their advantage. However, it killed a lot of novice pilots - so it was a mixed blessing at best! SteveBaker 12:10, 30 October 2007 (UTC)

It still is problem with most light twins with non-counterrotating propellers and that is what makes their safety record less than singles. It's said that it's safer to land a single with no engine than a twin with one because Vmc induces a roll higher than stall speed and with no warning. Some airplanes had Vmc close to stall speed and the asymmetric thrust meant that the airplane was never coordinated and one wing stalled earlier. Vmc + stall = rolling/flat spin close to the ground. Very bad day. —Preceding unsigned comment added by DHeyward (talk • contribs) 13:51, 30 October 2007 (UTC)

Eh? If one of your engines has stopped - it scarcely matters whether it was contrarotating or not! SteveBaker 16:58, 30 October 2007 (UTC)

Actually it matters quit a bit. P factor will induce a rolling moment on one side more than the other. It is why there is a different L/R Vmc in non-counterrotating engines. Minimum controllable airspeed depends on which engine goes out and it's killed a lot of pilots. --DHeyward 05:47, 31 October 2007 (UTC)

Barriers beyond a Planck Length

Even with a Grand Unified Theory uniting all the forces under an overarching Quantum Gravity (allowing us to observe phenomena beyond a Planck Time and beyond a Planck Length), will it be possible to directly study the nature of singularities such as those of a black hole or the infinitesimal "place" we all came from? If we can observe beyond a Planck Length but not all the way to a singularity, what is the next barrier? —Preceding unsigned comment added by Sappysap (talk • contribs) 17:34, 29 October 2007 (UTC)

Even with the GUT at our fingertips, observing beyond plank length or plank time will remain impossible. The present inability to do this is not a defficiency of modern physics, but a necessary consequence of quantum mechanics. And while we know that quantum mechanics and relativity disagree with one another, a meta theory to correct this issue will not change presently known laws of physics. This is precisely because we know why they disagree. Quantum generally assumes gravity to be irrelevant, while relativity generally assumes space to be smooth (ok, there are a few other technical details). These are very valid assumptions for short range and long range interactions, respectively, but neither holds at a singularity. So, don't let the thought enter your head that an inconsistency in modern physics will allow future alteration of the present laws true outside a singularity; they won't (we'll still be figuring out the consequences of those laws, but the laws pretty much stay the same). Now, you might be asking yourself what the point of figuring out singularities is if we can't actually peer inside of them. The answer is that even unobservable interactions can have very measurable macroscopic consequences. There are questions that can't really be answered by physics right now, such as whether a singularity can exist without an event horizon, or what actually happens to a particle that impacts a singularity (it might produce an observable event). Further, if we have an accurate model for what might happen within a singularity, we can develop an model of the big bang that goes further back in time, perhaps making predictions about early distributions of various particles that may have presently observable consequences. Someguy1221 18:33, 29 October 2007 (UTC)

Among theories that attempt to unite quantum mechanics and general relativity, and which are sufficiently well-developed to make some inference about singularities, most tend to eliminate the traditional notion of a singularity entirely and replace it with some sort of quantum fuzziness. For example, in string theory, the core of a black hole becomes something colloquially resembling a tangled ball of twine (no joke). Dragons flight 19:37, 29 October 2007 (UTC)

Remove Blood Stains

What is the most effective way to remove small amounts of human blood stains from clothes (in particular, white cotton) ... preferably with common household products ... and not something unlikely to be found in a home ...? Thanks. (Joseph A. Spadaro 19:13, 29 October 2007 (UTC))

90° water and washing powder in a washing machine will get rid of all the blood stains even on white. Keria 19:31, 29 October 2007 (UTC)

Yes, don’t use hot water! --S.dedalus 19:59, 29 October 2007 (UTC)

Yes, 90 Fahrenheit and not Celsius. Sam Blacketer 20:01, 29 October 2007 (UTC)

Hydrogen peroxide 3%, applied to the item when it's dry. Wait until it's stopped bubbling, then rinse it out. Repeat as necessary. Make sure you don't splash it around, and wash it off any skin that it touches -- it won't burn you quickly, but it will burn you if you insist. Also it may degrade the fabric somewhat. --Trovatore 20:15, 29 October 2007 (UTC)

Sard wonder soap rubbed on wet and then soaked works well. But not once it has been washed in Hot Water. Graeme Bartlett 00:45, 30 October 2007 (UTC)

Spit contains various enzymes. I don't know if any of those would help break down blood. But even if it is just the water in it that helps, it's something you've always got handy to remove a drop of blood right after it landed on the cloth. DirkvdM 09:30, 30 October 2007 (UTC)

I work in a hospital and regularly end up with blood on my uniform. Hydrogen peroxide works wonders. No visible traces left. I'm not sure what the reaction does on a chemical level (does it destroy forensic evidence?), but on a macroscopic level I've not found anything better for removing blood from clothing. 152.16.16.75 10:32, 30 October 2007 (UTC)

The hydrogen peroxide worked perfectly. Many thanks. (Joseph A. Spadaro 04:19, 31 October 2007 (UTC))

Although modern detergents can remove blood stains at moderate washing temperatures, have you tried just soaking the (freshly stained) article in cold water. seems to work 4 me!

Why does blood do that?

Why does blood become hard to remove when heated? What is going on there that is different for other stains? Dragons flight 00:31, 30 October 2007 (UTC)

I imagine it has to do with the blood being composed of proteins. My best guess (dunno why exactly) is that the heat denatures the proteins which then bind with the clothing material and each other forming a interconnected "fabric-protein mass." With this explanation, I would guess other stains with proteins probably behave similarly but they aren't as noticeable because the proteins are clear. I wonder if the iron ion (which with the iron binding amino acids gives the blood the red color) has anything other than a passive role in the staining. Would be nice if someone with more knowledge could speak up on this issue. 71.226.56.79 04:47, 31 October 2007 (UTC)

How can we remove cooked on blood

How can blood stains that are fixed by hot water be removed? DOes peroxide work on these too? Graeme Bartlett 00:45, 30 October 2007 (UTC)

Kinetic Batteries

Would it be possible to put some kinetic powered batteries (like the ones in watches/torches) in an mp3 player, so as that it no longer had to be charged/required batteries? —Preceding unsigned comment added by 78.147.220.128 (talk) 20:18, 29 October 2007 (UTC)

Possible, yes, but probably not feasible. MP3 players have significantly higher power usage than wristwatches, and probably benefit less from natural motion. As for torches/flashlights, my (admittedly limited) experience with them has been that a large assembly is needed to generate power (much larger than a typical MP3 player) and that you're not getting much battery life out of a lot of very intentional shaking. — Lomn 21:17, 29 October 2007 (UTC)

The power draw for my particular mp3 player seems to be about 40 milliwatts. (A single NiMH AAA battery will run the device for about 30 hours.) Note that the power consumption will be higher for a device based around a hard drive rather than flash memory. For reference, this document from the MIT Media Laboratory notes that the typical output from a self-winding watch mechanism is on the order of 10 microwatts, but that up to about 1 milliwatt can be generated if the arm bearing the watch is vigorously shaken. In other words, the design would have to be scaled up substantially to operate a music player. That document does discuss other ways to extract energy from human body motion, however. TenOfAllTrades(talk) 21:58, 29 October 2007 (UTC)

Still 33 milliamp isn't that much. I wonder if a little dynamo could be used. Surely those shake torches use more than 40 milliwatts. Some of them have 10 milliamp 5 volts over each of 9 or more diodes!--Dacium 03:43, 30 October 2007 (UTC)

Sure; some other options are discussed in the article that I linked. TenOfAllTrades(talk) 03:56, 30 October 2007 (UTC)

Surely the OLPC XO-1 laptop is an existence proof that a kinetic power source can work for an MP3 player; if you can crank a laptop computer to operate it, you could certainly crank the far-lower-power MP3 player to operate it.

Atlant 11:53, 30 October 2007 (UTC)

Yes - but there is a VAST difference between vigerously cranking a geared generator and just kinda picking up random motion from your body (which is what a self-winding watch does). The OLPC needs to be cranked fairly hard for five or ten minutes in order to give you an hour's worth of computing. An MP3 player would certainly need a lot less than that - but (as has already been conclusively shown) that's still a lot more than you get from incidental motion. SteveBaker 17:48, 30 October 2007 (UTC)

Certainly. I think the limitation here is one of marketability. It seems to me that it'd be hard to sell a CrankPod that is three times the size/weight of its competitors. I started to say "but doesn't need batteries" or "but doesn't need charging", but that's not really true. You've still got a battery (with any of these solutions), and you've still got to charge it -- you're just changing the charge method from a plug to a crank. — Lomn 14:32, 30 October 2007 (UTC)

Vacuum Sealers - for commercial use

There doesn't seem to be much information on Vacuum packing, I'm trying to vacuum pack food for PACKAGING purposes, i.e. to post or transport to places, and when I try my useless home vacuum packer the food just doesn't last when I *know* that it should. The food's outright growing mould after 2 days. I have a sneaking suspicion that the vacuum doesn't hold and that the uesless vacuum bags actually breathe air (permeability) and I need to invest in one of those $4000 ones that will do the job properly! Anybody aware? Rfwoolf 20:33, 29 October 2007 (UTC)

Even if you remove all the air there are still anaerobic bacteria and yeasts that will decompose your food. There is probably some oxygen left after you suck out the air, a domestic vacuum cleaner cannot create a very low pressure. And there would still be oxygen dissolved if the product was exposed to air, or had pores. Vacuum packaging will still have to sterilise the food by some means, or have some otherway to stop unwanted growths. Graeme Bartlett 00:50, 30 October 2007 (UTC)

The article on Tetra Pak might be interesting to you. --Mdwyer 15:26, 30 October 2007 (UTC)