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November 28

Nasal cauterization

When I was quite young I underwent a few treatments of nasal cauterization. I don't remember much about them except that they turned my nose a deep shade of purple that needed to be washed off later (?). What method of cauterization was this? Would it have hurt? (I don't remember—I was quite young, just the purple nose remains in my memory and the notion that it was cauterization of some sort.) --24.147.86.187 (talk) 04:52, 28 November 2007 (UTC)[reply]

Its all a bit vague, but here's some possibilities:

The purple stuff was an antiseptic, not a cautery agent
Whatever the purple stuff was for, the only thing I can think of that might fit the description is potassium permangenate (KMnO₄). Once upon a time it was used as an antiseptic agent, and as I recall it also has some caustic properties, and so may have been used as a chamical cautery agent.
Chemical cautery is most often performed with silver nitrate (AgNO₃). Phenol is another popular agent. Not usually very painful.
Electrocautery is painful.
Cryocautery is only mildly painful
If the method they were using was considered painful, its more than likely they used some local anaesthetic prior to the procedure.

Mattopaedia (talk) 05:59, 28 November 2007 (UTC)[reply]

So mine is electrocautery eh? Unanaesthetised it felt someone's trying to poke a hole through the middle of my nose. --antilived^{T | C | G} 10:57, 28 November 2007 (UTC)[reply]

Also, silver nitrate is a lovely shade of grey, but might conceivably look purplish depending on your skin colour and your memory. Check out this picture; I could see someone calling that "purple". Matt Deres (talk) 11:53, 28 November 2007 (UTC)[reply]

I am not a doctor, but I've been used/abused/experimented on by many. Many invasive procedure (meaning that you've been opened some place you shouldn't be open, or that they are going to open you, etc) start with "Scrub area thoroughly with Iodine solution". Betadine is a common brand for such. The solution is a reddish-brown, and under some light, it might look purple. -SandyJax (talk) 15:52, 29 November 2007 (UTC)[reply]

Electrochemistry

what is the difference between Formal and standard reduction potential? —Preceding unsigned comment added by 59.163.146.11 (talk) 11:22, 28 November 2007 (UTC)[reply]

Standard reduction potential is the reduction potential at 25^oC, 1M concentration of both anion and cation. Formal reduction potential is the actual reduction potential at whatever specific conditions you're concerned with. Someguy1221 (talk) 15:23, 28 November 2007 (UTC)[reply]

Brain activity: reading vs TV

What are the differences in active areas of the brain or general brain activity between watching TV and reading a book/article? Have McLuhan's hot and cold medium any basis in brain activity as I think he claims? What are the resulting differences between watching TV or reading for 4 hours a day? Keria (talk) 12:29, 28 November 2007 (UTC)[reply]

The brain has different centers for processing images and text. Each activity thus stimulates a different part of the brain, though invariable there will be some overlap. - 131.211.161.119 (talk) 14:47, 28 November 2007 (UTC)[reply]

whey protein

I wasn't sure if this should go in science or misc., but here goes: How many servings of whey protein should I have a day? When should I take it (morning and night, before working out, after, etc.). Should I drink it every day, or just the days I work out? All help would be greatly appreciated. --MKnight 9989 13:51, 28 November 2007 (UTC)[reply]

The answers to your questions could depend on a number of factors, such as your age, gender, current diet, exercise regime, training goals, medical conditions, etc. Your best bet is likely to speak with a physician, dietician or athletic trainer. Our article on whey protein also has several external links which may be able to provide some insight. (EhJJ) 14:36, 28 November 2007 (UTC)[reply]

I'll probably ask my doc, but I'm 17 and weigh approx. 140lb. I want to be reasonably strong (I'm enlisting in the USMC after highschool, so I want to be able to survive boot camp), but by no means do I need to have arms a foot in diameter. I usually take in 2000-3000 Calories a day. --MKnight 9989 14:45, 28 November 2007 (UTC)[reply]

I'm sorry if I gave you the impression that we would be able to answer your question if you gave us more information. Rather, at the Wikipedia Reference Desk, we can not give you medical (including dietary) advice. We are usually more than happy to aid your understanding of a concept or interpret information that you do not understand (in fact, one of the main reasons this reference desk exists is to find which Wikipedia articles need improvement), but we can not give you regulated advice. Essentially, think of us as volunteers at your local library. I would never even think of asking my librarian for medical, legal or (perhaps especially) body-building advice (I've never met a "built" librarian, but they could be out there). Some of us may be doctors or lawyers (I, for example, am a medical student), but law (and Wikipedia policy) prohibits us from giving you medical or legal advice online. Good luck! (EhJJ) 20:17, 28 November 2007 (UTC)[reply]

We may decide not to answer the question, but whether we do or not, it won't be because it's medical advice, since it involves neither diagnosing nor treating a medical condition. Perhaps we should simply change our prohibition to "we don't give advice". - Nunh-huh 20:20, 28 November 2007 (UTC)[reply]

As far as I'm concerned, you or anyone else is free to tell him whatever you'd like, but I wouldn't listen to it relating to my personal health. Do you know how tall he is? What if I told you he's 4'10" and 140lbs. Is your advice different from 6'2" and 140lbs? What if he has phenylketouria or any number of other health conditions? Now, I have no problem providing information but I don't feel comfortable providing specific instructions to him. That said, I did point him to our whey protein article and it's external links plus said that he's probably best of talking with a trainer. Was there something wrong with that? (EhJJ) 21:31, 28 November 2007 (UTC)[reply]

No, the only thing you've done wrong is suggest that advice on nutritional supplements is medical advice. If it were, thousands of health food store clerks would be in shackles. Not all advice with medical implications is "medical advice". - Nunh-huh 22:37, 28 November 2007 (UTC)[reply]

Well, I hope it's OK to direct you to the National Institutes of Health's recommendation, contained somewhere in here. I don't think it specifically mentions whey protein, but it's the amino acids that are important. Someguy1221 (talk) 20:51, 28 November 2007 (UTC)[reply]

Chemicals Released while burning...

Hi,

I have read through your articles about Chrome and Nickel Plating, they helped answer my question on how plating is done and the chemicals involved therein but the one thing I have not yet found out is if there are any chemicals (especially piosonous ones) released when an item plated in either Chrome or Nickel is burnt in an open flame. For instance a grill on a fireplace/Barbecue. The companies that I have spoken to that do the plating say that although they have never done any tests themselves they do plate for a certain brand of Barbecue and have never heard of any issues.

Your assistance is much appreciated, Tyron —Preceding unsigned comment added by 41.243.189.182 (talk) 14:01, 28 November 2007 (UTC)[reply]

Chrome or nickel plating is safe enough for cooking on even in an oven or barbeque. The chemicals used in plating are toxic, but of your new product is well made and washed it should be safe for cooking. There would be limits to a safe temperature to heat it to, and once the grill is left outside and it rusts, the plating could come off in sharp fragments that will be nasty to eat. Graeme Bartlett (talk) 20:10, 28 November 2007 (UTC)[reply]

In terms of toxicity, I would care far more about soot from the fire. Icek (talk) 20:46, 28 November 2007 (UTC)[reply]

Do you know what the temperature limit that it could be burn to would be? As an open flame can reach at least 400°C. Jet (talk) —Preceding unsigned comment added by 41.243.189.182 (talk) 05:59, 29 November 2007 (UTC)[reply]

The articles Chrome plating and Electroless nickel plating might be of help. shoy (^words _words) 17:13, 29 November 2007 (UTC)[reply]

Nickel has the sentence "Nickel is reacted with carbon monoxide at around 50 degrees Celsius to form volatile nickel carbonyl". So if CO comes into contact with hot nickel a poisonous gas is formed.Polypipe Wrangler 08:23, 1 December 2007 (UTC)[reply]

N-glycosylation

Can someone point me to one or more methods I can use to identify the sugar residues on the N-glycosylation sites of a viral protein? I considered using specific enzymes (endo-proteases?) to cut the outer residues in order to find out the attached sugars, but that would be quite a laborious process. Has anyone got a better idea? - 131.211.161.119 (talk) 14:45, 28 November 2007 (UTC)[reply]

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF) is one such technique. 142.20.217.152 (talk) 22:01, 28 November 2007 (UTC)[reply]

How would I know which masses are from the protein and which ones come from the glycans? Would this mean a lot of preparation to obtain a suitable sample to put in the mass spec? - Mgm|^(talk) 23:11, 28 November 2007 (UTC)[reply]

There are many published articles that describe methods for analysis of oligosaccharides such as this one. One approach is to use a glycosidase to cut off the oligosaccharides and then use some form of chromatography to isolate the oligosaccharides prior to mass spectrometry. --JWSchmidt (talk) 00:37, 29 November 2007 (UTC)[reply]

I'm not sure why this article didn't show up on my pubmed search, but at first glance it appears to be just the sort of thing I'm looking for... Thanks to both of you for your input. I'm still open to more ideas, though. —Preceding unsigned comment added by 131.211.161.119 (talk) 08:30, 29 November 2007 (UTC)[reply]

Thermodynamics of heating your house

What's more energy efficient?

turning the heat down to 58ºF every evening and turning it back up to 68ºF in the morning
not turning it down too much so that it doesn't have to re-heat the whole house from scratch every morning

This is a practical question of mine. Basically we have the heating set to go down to 58ºF every evening starting at 10PM, and then at 6AM it is set to rise back up to 68ºF. Is this an optimal way to do things (assuming that we want it at 68ºF during the day and not freezing at night)? It seems like it has to do a lot of work in the morning to raise the temperature again—is it better to keep the temperature a bit higher so that it doesn't have as much work to do? Is there a more optimal heating solution? Surely one of you science geeks will have a good answer for this. ;-) And though I know it sounds like a textbook homework question, it isn't—I don't do homework anymore, thank goodness. --24.147.86.187 (talk) 15:27, 28 November 2007 (UTC)[reply]

If you have a very simple furnace, it will necessarily require more energy to keep the house warm at night than to cool it up in the morning. Over the course of the night, the house will release, say, X units of heat into the environment when the furnace is off. So the furnace has to generate X units of heat during in the morning. If you leave it on at night, the house will initially be losing energy at the same rate. But hot things lose heat energy faster than cold things (my simplest way of putting Newton's law of cooling), so the house will lose more than X units of heat over the course of the night, so the furnace will have to generate more energy overall to keep the house warm. This could be complicated by a furance that can run at multiple "speeds" as with many new gas furnaces. Such a furnace would have a different energy efficiency for the two situations (ie, it would waste a different percentage of energy heating a warm house or a cold house). Someguy1221 (talk) 15:39, 28 November 2007 (UTC)[reply]

Interesting. Well, it's not a new furnace at all (it is quite an old boiler) so it is probably the case that turning it down and up again in the morning is the better approach. Sigh. --24.147.86.187 (talk) 03:33, 30 November 2007 (UTC)[reply]

Trust the mass on a bottle label?

I often purchase small amounts of relatively pure chemicals, usually 50mg or so. I need to make solutions of these chemicals at a known concentration. The thing I have never been sure about is whether chemical supply companies take care to put as close as possible to 50mg (or whatever is on the label) into the bottle. You see, life is easier if I can assume that the right amount is in there, and I can add water directly to the bottle to disolve it and make my solution. If I have to transfer it, inevitably I won't be able to recover some from the bottle or the weigh paper, and additionally my balance isn't the best. What do you think, is the stated mass very close to the actual mass in the bottle? ike9898 (talk) 15:31, 28 November 2007 (UTC)[reply]

It's going to depend, a great deal, on the particular product and the particular supplier. Usually you won't be getting shortchanged, but the margin over and above the label amount can vary. How precisely do you need to know the quantity and concentration? Is there some sort of assay you could perform (spectrophotometric, etc.) on the stock solution to determine its concentration to an acceptable precision? TenOfAllTrades(talk) 17:12, 28 November 2007 (UTC)[reply]

Concurred with TenOfAllTrades: customers would make a hell of a noise if they often found themselves paying for something that wasn't all there. When you say you "need to make solutions of these chemicals at a known concentration", does that mean you have to hit a pre-set (specific) concentration, or you need to be near some value and also know exactly what it is? The latter is much easier, since you can make and then assay. Or else you could weigh the full bottle, then dissolve in the bottle (so you don't lose material) and transfer into another container. Wash the bottle, reweigh it, and now you know the tare and hence the exact (to your instrumental ability) amount of stuff in the solution (you lose a diluted drop or two rather than a few grains of pure material). DMacks (talk) 17:32, 28 November 2007 (UTC)[reply]

I wouldn't be able to assay afterwards because this solution is supposed to be the analytical standard. I like the idea of weighing the bottle before and after. ike9898 (talk) 18:53, 28 November 2007 (UTC)[reply]

I suppose this goes without saying, but if you're getting your chemicals from a single supplier, you probably only have to weigh one bottle once and then use that as your tare in the future. Obviously, that would depend on how accurate you need everything to be, but if it was essential, I'd presume you'd have a more precise scale for weight and not need to ask! Matt Deres (talk) 02:40, 29 November 2007 (UTC)[reply]

The mass of small reagent vials from the same lot usually vary on the order of a few milligrams unless they are specifically matched. ike9898 (talk) 15:04, 29 November 2007 (UTC)[reply]

Power lines, and electric shock

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Hot stick

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If you put one hand on a power line, you won't get shocked right? If you put two hands on the power line you still won't get shocked right? But if you put your two feet on the power line, then put your hands on another power line parallel to it, you will get shocked then right? 64.236.121.129 (talk) 16:37, 28 November 2007 (UTC)[reply]

You can get a shock from touching one power line, if you're in good electrical contact with the earth ("grounded"). -- Coneslayer (talk) 16:44, 28 November 2007 (UTC)[reply]

What if you are standing on a brick? 64.236.121.129 (talk) 16:49, 28 November 2007 (UTC)[reply]

It depends on the electrical conductivity of the brick. I would guess that that might depend on whether the brick is damp. -- Coneslayer (talk)

Don't most shoes have rubber soles? Wouldn't that prevent grounding? Also if you are hanging from the powerline what would happen if you were hanging from one hand, and two hands. 64.236.121.129 (talk) 17:01, 28 November 2007 (UTC)[reply]

Also aren't powerlines covered in some kind of rubber usually? Wouldn't this prevent shock? 64.236.121.129 (talk) 16:50, 28 November 2007 (UTC)[reply]

According to Overhead powerline#Conductors, most overhead power lines are uninsulated. -- Coneslayer (talk) 16:56, 28 November 2007 (UTC)[reply]

You should certainly consider them to be uninsulated, even if they might be insulated. The power company guys certainly think this way: the only time they think it's safe to touch a power line is after they've clamped big grounding cables onto it and proven that the line is then grounded. Before that, they strictly do all their work with their hot stick.

Atlant (talk) 17:56, 28 November 2007 (UTC)[reply]

Yes although there is a fairly recent development for LV OH cables called semi-insulated cable. This means they dont trip the breaker when they momentarily touch together. But I wouldnt advise any one touches them. In fact the answer on higher voltage cables is that it is a waste of time insulating them as youre going to be dead before you touch them, and most of the electric field will still be from the outside of any 'insulation' to earth (because of the capacitive divider effect).--TreeSmiler 01:54, 1 December 2007 (UTC)[reply]

Oh, look: we didn't have an article on hot stick yet. I've stubbed one out; help me fill it in! (And somebody tell Rockpocket.) —Steve Summit (talk) 01:33, 29 November 2007 (UTC)[reply]

You ONLY Get shocked if you bridge the gap between two large differences in voltage. One hands or two hands or one hand and one foot on the same power line will have NO result, as long as no other part of your body is touching something else with different voltage potential like the Earth, another power line, etc. Shoe rubber is a fairly unreliable insulator, unless you are wearing something specifically designed to protect you from shock. Disclaimer: DO NOT TRY THIS AT HOME TO PROVE ME WRONG --Jmeden2000 (talk) 17:55, 28 November 2007 (UTC)[reply]

This is where I get confused though. The current is still passing through you if you are touching the power line with limbs touching the same power line right? Or... maybe it isn't. So how come a bird doesn't get shocked by this, but a bird can get shocked by a lightning bolt hitting it, when it is flying, and isn't grounded. 64.236.121.129 (talk) 21:16, 28 November 2007 (UTC)[reply]

If you were made of aluminum, you'd have a problem. As it is, though, your resistance hand-to-hand is about 50,000 ohms. So, worst case, if you stretch out your arms and grab the line, your 50,000 ohms will be in parallel with about a meter of aluminum as thick as a pool noodle at roughly zero ohms. I wouldn't advise doing that, though, because I'm not sure what role skin effect plays at very high voltages in a case like this. I'd keep my hands close together. I think you'd feel the induced current from the 60-cycle (or 50) field as an unpleasant whole-body sensation if the voltage was high enough.

When a bird is hit by lightning, it's because it was unlucky enough to have been in the path of the leader when it flashed over. The bird becomes part of the conductor, which is a line of ionized air between the cloud and the ground or between two clouds. --Milkbreath (talk) 00:53, 29 November 2007 (UTC)[reply]

Power lines (the high voltage ones at least) do not have electrical insulation because electrical insulators also tend to be good heat insulators and it's essential that these lines remain cool. They also have to remain flexible and there are a bunch of other constraints on them that make insulation impractical. SteveBaker (talk) 19:53, 28 November 2007 (UTC)[reply]

(edit conflict) Read Ohm's law and alternating current. They are pretty straightforward, but alien to everyday affairs. Once you get them under your belt, you can answer these questions yourself.

Whether you get shocked or not touching a bare conductor will depend on many things, principally the voltage. High-tension lines can have more than million volts on them. The rule of thumb for arc distance in dry air is 10,000 volts per inch, so a million volts will jump 100 inches, or about eight feet. If something more conductive than air enters that zone between a high-tension line and ground, like YOU, for instance, the arc will see you as a shortcut to ground and use you as part of the path. Think how cool you'll look with a blue arc as big around as your arm entering the top of your head and incinerating your Air Jordans on the way out. Your wafer-thin shoes would present no obstacle to that kind of power. Even the best insulator has a breakdown point, and the current would be able to pass through the air around the soles, too.

Another thing is that even if you could approach a million-volt line without being near ground, like in a balloon, the line is going to want very much for you to be at the same potential as it is, and it won't wait for you to touch it to accomplish that. The power line repair guys use great big gloves and a long wand to draw the arc that causes, mostly because they want to live through the experience.

A lot of things are dangerous, but you can get away with messing with them sometimes. Bears, for instance, or ex-girlfriends, or cliffs. Electricity has its own agenda and its own rules, and you get one chance not to screw up. --Milkbreath (talk) 20:02, 28 November 2007 (UTC)[reply]

A bird can perch on an uninsulated electric wire and not get shocked, because no current flows through it, because there is no place for the current to flow to.

An ungrounded human can do the same, for the same reason.

There are several ways a human can be ungrounded:

being in a balloon or helicopter
jumping in midair
wearing rubber-soled shoes (though as noted above, their insulating properties vary)
standing on something insulated, like a wooden bench (though again, the insulating properties vary)
standing in the basket of an insulated-boom cherry picker

And, there are also several ways for a human to be grounded, and these are why electric shocks are possible (and rather common, among the careless):

being barefoot, especially while standing on concrete or in water (or on a brick)
accidentally touching something else grounded, like a water pipe
being in a bathtub
accidentally touching someone else who is grounded

And, not only do the insulating properties of various materials differ, but the amount of insulation you need obviously depends on the voltage you're worried about. For "ordinary" household voltages, you can engage in risky behavior and not get electrocuted too much of the time, because (for example) a good pair of tennis shoes will usually withstand 120V. (Although I'm not sure about the 220V that's common in Europe. Can you tell there's some OR here?) But when you get up into the high hundreds of volts or more, the rules are rather different, and unless you know exactly what you're doing and are very careful and use all the right equipment, you can easily get not only a lethal shock, but also electrocute innocent bystanders who try to rescue you by grabbing your energized carcass, or incinerate them in the fire your charred carcass starts.

Finally, there's the matter of inrush current. Even if you're perfectly ungrounded, when you touch an energized wire, there's a relatively small, instantaneous flow of current which brings you up to the potential of the wire. The bigger you are, and the higher the voltage is, the larger this current is. So I think there's a voltage at which the birds are fine, but a human would get a painful (if not fatal) shock from the inrush current. —Steve Summit (talk) 00:13, 29 November 2007 (UTC)[reply]

There is also the field problem. Even at low frequencies, polarized molecules like water can be moved by electric fields. They move more at resonant frequencies like in the microwave oven (think what happens to food in a perfectly insulated plastic box. Put a metal fork in that plastic insulated box and you'll really see what electric fields can do, but I digress.) IF the voltage is high enough and the person close enough, this movement can damage internal structures of living organisms even at low frequencies and without even touching the wires. Birds actually die before landing on these wires. I have only read about the bird deaths occuring in South American transmission lines but even in North America, it appears birds find the very high tension lines to be an unpleasant experience and seem to stay off them. A cool video is to watch how they repair remote high tension lines by helicopter. They first electrically attach the helicopter to the wire and there is usually a three foot arc when the pole gets close. --DHeyward 07:09, 4 December 2007 (UTC)[reply]

Cool Video of guy touching high tension wires after being delivered by helicopter --DHeyward 07:18, 4 December 2007 (UTC)[reply]

Future of Everyday Travel

Is there a reasonable possiblity that there will be Sky Highways in next 30 years? Meaning flying cars or hover crafts. Is it possible to use solely solar power to fuel these crafts or that would be impossible? --WonderFran (talk) 16:47, 28 November 2007 (UTC)[reply]

It's another one of those things where when engineers say "It'll be here in 5 years", it'll probably be here in less. When they say "It'll be here in 20 years" they mean "I have no idea at all when it'll be here - if at all". So, yes, we'll have sky highways within 20 years!

But seriously - the fuel requirements for a flying vehicle are unlikely to ever be as good as they are for a ground vehicle - because you have to generate lift as well as overcome friction and drag. With the pressure to make more fuel-efficient transport, using flying vehicles seems wasteful. Having said that, the ability to travel in a straight line to your destination, the fact that there is more space up there (so no traffic jams) could override that - and I suppose we could get our lift from balloons instead of using motors.

There is also the safety issue. If you have a fender-bender - or any kind of an accident at 30mph on less - or if your car craps out on you on the freeway - you aren't going to die. You'll probably walk away without a scratch. At 10,000 feet, any problem at all will probably be fatal. The people who are building these things say that they'll have multiple redundant engines and that kind of thing - but I've seen cars on the road with TWO of those 'skinny spares' on them driving at 70mph! I've met people who actually wore out a skinny spare bald because they drove on it for 10,000 miles! What happens when your flying car is that poorly maintained?

As for solar power - there simply isn't enough area on the roof/hood/trunk of a car to capture enough energy to propel it through the air at the kinds of speeds that we are used to. The best solar cars go slowly and have interiors that are stripped down to basically being bicycles with supports for the solar panels. No amount of clever engineering can cover for the fact that there simply isn't enough area. Then what about driving in overcast conditions - or at night? At best, you might have a 'Solar Hybrid' that runs on batteries that can be recharged from the sun with a gasoline or hydrogen engine as a backup.

But I doubt we'll see flying cars in our lifetimes. SteveBaker (talk) 19:50, 28 November 2007 (UTC)[reply]

The NASA Pathfinder could fly on solar power, and the Zephyr could even store enough energy to fly through the night (but they had to strip out the pilots to make them light enough, though). Maybe Solar Impulse will change that, but I'm not sure if this will ever be, well, safe (or economical, or not a pain in the ass). And in addition to all of the speculations on what fantastical yet-to-be-invented-inventions we'll all be using in the future, remember that it was once speculated that there'd be an autogyro in every American garage by now. Someguy1221 (talk) 20:31, 28 November 2007 (UTC)[reply]

Well, yes - but you wouldn't describe an amazingly flimsy plane with a wingspan bigger than a Boeing 747 and a top speed similar to a bicycle that can only fly in calm air with no rain as "practical"! There is a really fundamental problem here - in order to have enough solar cells, you need HUGE wings. In order to get off the ground with so little power, the plane has to be super-lightweight. Super-lightweight with HUGE wings means two things: Obviously, it's going to be very, very fragile because you can't afford the weight to make it strong. Secondly, it's going to have a very low "wing loading" and planes with low wing loading are extremely vulnerable to turbulance. These are not characteristics you want for a mass-produced civilian plane - but what's the alternative? Even 100% efficient solar cells wouldn't gather enough power to do this properly - so there is a really fundamental limit. Increasing the area increases the weight - but increasing the weight increases the power requirement which forces you to increase the area. There is no way out of that! SteveBaker (talk) 21:43, 28 November 2007 (UTC)[reply]

I'll just maintain that "pain in the ass" = um, all of what you just said ;-) Someguy1221 (talk) 21:56, 28 November 2007 (UTC)[reply]

I agree - but some things are just not meant to be. There is this blind faith that science can always improve things and make magic happen - but sometimes there just isn't. We MIGHT someday make solar cells that are 99% efficient and we MIGHT make stronger, lightweight materials - but the wing-loading issue is still there as is the fact that it's never going to fit into an urban environment with 200' wings. These are all pretty fundamental problems that put practical solar powered cars and aircraft permanently out of reach. Sadly, these incredibly flimsy machines give the public an altogether different idea - which is a shame. 100% computer controlled (but gas-guzzling) helicopters are probably the closest we'll get to flying cars - and those are going to ALWAYS be a lot more expensive than a mere ground-car - and given that we need to be driving fuel consumption DOWN, not UP, that's not a smart way to go. Perhaps hydrogen-filled, hydrogen-fuelled, mini-zepplins might work. SteveBaker (talk) 22:16, 28 November 2007 (UTC)[reply]

A minor nitpick: According to the second law of thermodynamics, solar cells are not going to be more efficient than 96% (the temperature of the solar radiation is about 5780 K, the ambient temperature for an aircraft at least about 220 K). Icek (talk) 22:38, 28 November 2007 (UTC)[reply]

Solar cells are not heat engines. The Carnot efficiency limit does not apply. There are technical and physical challenges to achieving high efficieny, but that is not one of them. Dragons flight (talk) 01:36, 29 November 2007 (UTC)[reply]

Eh - I think you are both wrong. Or maybe you are both right...I'm not sure which! The second law doesn't only talk about heat - it actually says that you can't convert 100% of heat into work - which includes electricity - so the second law definitely says you can't be 100% efficient...or at least it would apply if solar cells converted heat into electricity - but they don't. What solar cells are doing isn't converting HEAT into electricity - they are converting LIGHT (electromagnetic waves) into electricity. Photons knock electrons out of the silicon. However, they certainly can't be 100% efficient. Some photons pass right through the silicon, some reflect off the surface, others don't have enough energy to produce an electron so they turn into heat. SteveBaker (talk) 04:04, 29 November 2007 (UTC)[reply]

The Carnot efficiency limit does apply. Else I could simply surround the heat source usually used in my Carnot engine with a vacuum and solar cells. Light does have a temperature. If it's monochromatic, the temperature is zero, being analogous to mechanical energy. If it has a Planckian spectrum, it has the according temperature. Icek (talk) 11:45, 29 November 2007 (UTC)[reply]

Temperature (yes, sort of), but it's not a closed system. The Carnot limit is a statement about entropy conservation in closed systems. Not to mention that at no point is the solar cell in thermal equilibrium with sunlight anyway (compare to the cycle of a heat engine where the operating fluid itself varies in temperature from the high to low temperature). Yes, there are physical limits to the efficiency of solar cells. Some even relate to temperature (e.g. the spontaneous recombination of electron-hole pairs), but a solar cell is simply not a heat engine. Dragons flight (talk) 16:37, 29 November 2007 (UTC)[reply]

The Carnot limit only needs a warm reservoir - the incident radiation (or the surface of the sun if you like to view it like that) - and a cold reservoir - the surrounding air or whatever; no closed system is needed. It's a very general statement about entropy, and does not depend on the details of the energy conversion, as far as we know. A relevant Wikipedia article: Exergy. Icek (talk) 17:56, 29 November 2007 (UTC)[reply]

I think the Carnot efficiency applies, but not quite in the way you suggest. Solar radiation at the Earth's surface is actually more like 100°C: that is, an object at that temperature cannot be heated by sunlight because it emits as much radiation as it could absorb. However, radiation that is streaming in a particular direction (rather than suffusing an enclosed space) cannot be said to be in thermal equilibrium with itself (because it does not have appropriately random velocities), so it does not have a true thermodynamic temperature. This is good: it means that the Carnot restriction only operates on the source temperature, and we get your 96% number instead of something pathetic like 17%. But I'm not entirely sure that Carnot applies at all; a heat source in a vacuum is also not in thermal equilibrium (because it has not equilibrated with the vacuum), so it may have more free energy than the corresponding equilibrium situation with the same "temperature" (of the object). --Tardis (talk) 18:26, 29 November 2007 (UTC)[reply]

How did you come up with 100 °C? The greenhouse effect can occur in macroscopic solid objects as well, and I doubt that you couldn't get more than 100 °C. Anyways, that's beside the point, the solar radiation does in no sense have such a low temperature. I don't quite get what you are trying to say: Even if a solar cell was enclosed within a sphere or bubble of gas of a temperature of 5780 K, the solar cell would work as long as its temperature is kept low enough. Icek (talk) 22:24, 29 November 2007 (UTC)[reply]

100°C comes from the solar constant (I used 1kW/m² for sea level) and the Stefan-Boltzmann law. The greenhouse effect can only happen if the (say) glass is not at the same temperature as the contents, which again means that you do not have a single object in thermal equilibrium with itself, so its temperature is not well-defined. My point was that the solar radiation (here, away from the sun) does not have a temperature at all, for similar reasons; I'm not sure what your statement about a solar cell in an oven is supposed to establish. --Tardis 17:36, 30 November 2007 (UTC)[reply]

My statement about the solar cell surrounded by a thermal radiator was a response to your statement that the radiation does not have appropriately random velocities/momentums ...

You are defining temperature by the power of the radiation/equilibrium temperature of an object, I am defining it by the spectrum of the radiation. But however you put it, the Carnot limit with the spectrum-defined temperature does certainly apply. Icek 20:52, 30 November 2007 (UTC)[reply]

SteveBaker made some excellent points about efficiency, but there's more than just that. Flying cars exist; and if you paid me enough I would design a custom one for you. But most flying cars still need to take off from airports. How are you going to get to the airport? For a flying car to be practical it would have to be VTOL, that is, take off vertically from the top of your house. This adds considerably to the complexity of the aircraft, and therefore its costs. It also takes a lot of energy to take off vertically. And the safety concerns addressed above also are important: if a car's electrical system totally craps out, meaning the spark plugs aren't firing, the driver can pull to the side of the road. General aviation aircraft with internal combustion engines have totally redundant systems: dual magnetos with dual spark plugs in each cylinder, completely independent of one another. This is true of every system in an aircraft; safety through redundancy. It makes them very expensive. You could buy a flying car, and afford to operate it, if you were filthy rich, but in order to have an air highway system lots of people would have to be able to afford it. moink (talk) 02:50, 29 November 2007 (UTC)[reply]

Ok it wouldn't be as Zipadidooda but mini Zeppelins are relatively safe and fuel efficient, no zipping around though. Keria (talk) 09:20, 29 November 2007 (UTC) Maybe a blimp is a more appropriate term. Keria (talk) 15:32, 29 November 2007 (UTC)[reply]

The difference between a blimp and a zepplin is that the zepplin has a rigid structure where a blimp is held in shape purely by the pressure of the gas. The original name "blimp" comes from a British term for a particular kind of barrage balloon (designed to prevent enemy planes from flying low over cities) called a "B-type Limp Balloon" (limp as opposed to rigid). This got shortened to "B-limp" and the rest is history. I wonder what became of the Alimp?

Anyway - the cool thing about hydrogen as a lifting gas is that it's cheap, renewable and provides more lift per cubic meter than helium. You can also use it to fuel your motors - so you have this ENORMOUS gas tank and as you consume it, you are forced to gradually lose altitude such that you are always on the ground LONG before you run out of fuel...a handy built-in safety thing since a Blimp without engine power can be exceedingly dangerous! But more interestingly, the fact that you'd continually be using and replenishing your lift gas would go a long way to avoiding the key problem with hydrogen balloons - which is that oxygen can slowly diffuse into your tanks and if too much accumulates: KABOOM! With care, that could be completely avoided here since you can consume hydrogen AND the dissolved oxygen in your engines and always refill with pure hydrogen - so the oxygen levels can never build up to a dangerous degree so long as the vehicle is used reasonably regularly. A practical machine would use hydrogen fuel cells to make electricity and use electric motors to drive the thing around. When you "park" it at home, sensors could monitor the oxygen levels and when they approach the danger level, start the hydrogen fuel cells to consume it safely - putting the 'spare' electricity into your home or back into the electrical grid.

The huge problem is the size of the things and the top speed. Unless we're going to have HUGE parking lots - we'd need ways to tether and stack them. Also, 'runaway' blimps would be a serious matter in strong winds. SteveBaker (talk) 20:44, 29 November 2007 (UTC)[reply]

What happens during the cooking process (and what are those black bits)

So when you slap a piece of meat on the grill, it usually comes off the grill in some shade of brown, with black lines wherever it touched the grill. My general understanding of what happens when stuff is heated up is as follows:

1)various condensation reactions occur, releasing water 2)H2 gas comes off and burns, leaving unsaturated carbons behind. (this is why aromatic/carbon-rich compounds give a sooty flame - there isn't enough H2 given off to facilitate the burning of the carbon itself)

My theory is that those black strips are essentially carbon/aromatic compounds that form from the protein on the surface of the meat. If so, wouldn't those black bits be carcinogenic? Maybe it's not the consumption of red meat itself that causes cancer, but the consumption of those black bits. If so, would cooking on a surface that doesn't leave black bits be healthier/no cancer? (I also notice a shitload of powdery, black residue on the bottom of oven-cooked pizzas)

thoughts? 18.60.12.185 (talk) 20:14, 28 November 2007 (UTC)[reply]

Start with Browning (chemical process) --Mdwyer (talk) 20:20, 28 November 2007 (UTC)[reply]

And then hit The Straight Dope. -- Coneslayer (talk) 20:28, 28 November 2007 (UTC)[reply]

For some of the black products, see polycyclic aromatic hydrocarbon. Icek (talk) 20:54, 28 November 2007 (UTC)[reply]

Eating just before bedtime

Many people believe that eating before bedtime would increase weight gain. My thoughts are that (calories in) = (calories out)and that what matters is how many calories you consume in a day, not when you ingest them. Is there a physiological reason why eating at bedtime would increase fat/weight gain? Are there references available to explain this?

David Winkelaar —Preceding unsigned comment added by Davidwinkelaar (talk • contribs) 22:24, 28 November 2007 (UTC)[reply]

As far as I know, the thinking behind not eating big meals before bedtime is that the digestive system slows down significantly while we are asleep..however, it is often easier to sleep after having a big meal as the body diverts energy to digesting the meal (until you actually fall asleep!) GaryReggae (talk) 22:34, 28 November 2007 (UTC)[reply]

The process is (assuming you're not on the Atkins diet): Sugar enters your body. Sugar that your body needs is put into the blood and taken up by cells. Sugar your body doesn't need is turned into glycogen. When your sugar starts running low, your body converts that glycogen back into sugar (glucose, specifically) so your cells can use it. Glycogen is simultaneously being converted into fat. When you start running low on both sugar and glycogen, your body could just start burning that fat, but instead it decides to be a whiner and make you hungry so it'll get more sugar. The idea is that by eating at night, you increase the proportion of sugar intake that gets converted into fat, calories that your body would rather leave be and make you eat more than actually eliminate. If you actually make sure to balance your calorie intake with exercise, this won't be a problem, as your body will have no choice but to consume the fat once the glycogen runs down. Someguy1221 (talk) 22:59, 28 November 2007 (UTC)[reply]

Machine lubrication oil contaminates kitchen...

Yesterday, my special needs brother cut open a full can of general purpose lubrication oil (for machines and weaponry) in the kitchen, causing it to spray all over the kitchen counters and on a lot of our dishes and cookware. The label on the can says that it's toxic and should not be used on or come in contact with any surface used to prepare food.

My mom seems to think that a simple washing of everything will correct the problem, but I fear otherwise. My question is, what materials must be thrown away and which ones can be cleaned? The oil contaminated things made of glass, metal, wood, plastic, and rubber, as well as metal cooking implements with wood or plastic handles and non-stick pans. It also got on sponges and dish rags.

If any of these things CAN be cleaned, should I use any methods beyond dish soap and water?

Thank you. --69.207.99.230 (talk) 22:41, 28 November 2007 (UTC)[reply]

At the risk of offering something that may sound like medical advice, I agree with your mom. Soap and water will clean the stuff off of hard surfaces very well. Depending on the fabric, a good detergent should also be able to get it out of many cloth items. While motor oil must (in today's climate) be labeled as "toxic", it's not like Arsenic or Plutonium or anything.

For peace of mind, though, you'll want to discard any contaminated food. And if the oil soaked into anything porous (such as wooden cooking implements), you may want to discard them as well, because you probably won't be able to get all the oil out, and the odor and discoloration will be unpleasant even if the contamination doesn't kill you. —Steve Summit (talk) 23:28, 28 November 2007 (UTC)[reply]

Thanks. My boyfriend told me that the oil would be absorbed by and thus ruin all things that are plastic, but I don't know if he's being paranoid or not (one of the plastic things covered in oil belongs to him). He might just be looking for an excuse for my mom to replace it, though. Unfortunately for me, now I need to do the dishes... —Preceding unsigned comment added by 69.207.99.230 (talk) 23:38, 28 November 2007 (UTC)[reply]

Plastic tends to be nonpolar, just like oil, and there are some polar substances which can more-or-less permanently attach themselves to and/or intermingle with plastic molecules. You can notice this with some plastic cookware, especially those ubiquitous semitransparent food containers -- they eventually get discolored by some of the foods they come into contact with. (Oily foods reheated in the microwave are definitely the worst. I've seen this happen both with spaghetti sauces containing tomato products and beef or sausage oil, and Oriental foods containing chili oils.) But while this could be a problem in your situation, I doubt it would happen noticeably unless there were also heat involved. If after a good detergent wash, the plastic thing in question is still slippery or smells like oil, then it may be indelibly contaminated, but if not, it's probably fine. (But far be it from me to intervene in this heaven-sent opportunity for the bf to guilt-trip you, if that's how the stars have aligned here...) —Steve Summit (talk) 00:33, 29 November 2007 (UTC)[reply]

If you are looking for something stronger than dish soap, then I would recommend Simple Green. It is essentially an industrial strength degreaser, but also non-toxic, so unlike most comparable products, it would be safe to use on food surfaces. We use it in a variety of applications around our lab. It is sold in some grocery stores and most hardware stores. Dragons flight (talk) 01:09, 29 November 2007 (UTC)[reply]

Clearly the stuff can't be that toxic. People handle things lubricated with that oil all the time - it gets onto their hands and - yes - people do eat without washing their hands and they don't get sick as a result. I'd toss out things made of wood or cloth just because you'll never get them clean. Anything that's made of plastic or metal - run through the dishwasher on it's hottest/longest cycle. Anything that's metal or plastic that won't fit into the dishwasher, wipe off the excess oil then scrub down with some detergent - washing up liquid will be fine. SteveBaker (talk) 01:25, 29 November 2007 (UTC)[reply]

Just to reiterate a basic point... go ahead and clean the stuff you can (wipe off, then wash, etc.) and then use your brain. Look at the stuff that got splattered and ask yourself whether it looks, smells, and feels like it did before or whether it is different. If it's different: toss it. Blowing twenty bucks on some replacement Tupperware is a pretty small price to pay to avoid even a potential problem. In other words, why risk it? Matt Deres (talk) 02:51, 29 November 2007 (UTC)[reply]