Wikipedia:Reference desk/Archives/Science/2007 June 12

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June 12

car engine question

At speed, if I was to slam on the accelerator, the engine RPMs increases immediately but it takes several seconds of high RPM for the vehicle to finish accelerating to its new speed. My question is, what mechanical component is between the engine and the drive shaft to allow the drive shaft to actually be accelerated instead of a violent and instantaneous change to the new engine rpm, and how does it work? --froth^t 00:25, 12 June 2007 (UTC)

Er, that sounds like you have things the wrong way around. You either have an automatic (in which case when you slam on the revs, the RPM increases because the gearbox downshifts to a lower gear; then the engine RPM goes up dramatically because the drive shaft is rotating at more or less the same speed as before the shift, but now the engine has to run faster "to keep up with it") or your clutch is slipping really, really badly (i.e. the engine responds to the throttle by increasing RPM [although this isn't instant] and the clutch doesn't have sufficient friction to accelerate the drive shaft at the same rate) - this would be a bad thing. Since you're in the US where hardly anyone knows how to drive a proper car ;-) it's probably the former. --YFB ¿ 00:30, 12 June 2007 (UTC)

See automatic transmission. Friday (talk) 00:58, 12 June 2007 (UTC)

And torque converter. Vespine 01:00, 12 June 2007 (UTC)

The rev's don't increase immediately - the rest of the question rests on that misunderstanding. SteveBaker 02:28, 12 June 2007 (UTC)

I agree - the conceptual issue is due to interchanging "rapid" with "instantaneous" acceleration. Nimur 18:09, 12 June 2007 (UTC)

Well, sort of, but the question would make sense if it was an automatic. If you stand on the throttle, the gearbox will almost-instantly downshift and there will then be a near-instantaneous jump in revs. The several seconds Froth mentions is the car accelerating (with the revs increasing further) after the downshift. Or, as I said, he could have the world's most knackered clutch, but I think he'd be able to smell it if one plate was taking "several seconds" to catch up with the other :-/ --YFB ¿ 02:45, 12 June 2007 (UTC)

My point is that the speedometer is clearly not moving in parallel with the -uh- RPM-o-meter. Obviously the two won't always read the same since there are gears in between, but even with gears, if you're accelerating how can the RPMs hold steady while the speed increases? Does the clutch keep slipping until you're at the right speed? And you're right, I only know how to use an automatic transmission, I hate cars and can barely put up with automatic, but the car is defying me with this stupid question :) --froth^t 14:08, 12 June 2007 (UTC)

The torque converter does allow some "slip", but most of what you're seeing is explainable just by gearing. The other "slack" factor you may see is that your gauges aren't instantaneous either. Generally they shouldn't be far behind, but you never know. Friday (talk) 14:53, 12 June 2007 (UTC)

PS. Also, an auto will take some time to shift. You may notice the rpm increase before it's done shifting. Friday (talk) 14:54, 12 June 2007 (UTC)

RPMs are reported by a tachometer, if anyone cares. --Tardis 17:33, 12 June 2007 (UTC)

To first order, you shouldn't see an acceleration without an increase in revs - if the car is driving at constant speed then the revs will be constant, then when you increase the revs the increase in the speed of the wheels is the change in rpm divided by the gear ratio (approximately - not including assorted other transmission components, overdrive, etc.). So if you keep the revs constant, the only way to increase speed is to change to a higher gear, which will inevitably involve a change in revs anyway due to the engine being unloaded while the gears shift. You'd have a better idea what was going on if you drove a manual, since you have to match the revs yourself on downshifts to make them smooth. I hate automatics. There's nothing to do with your left leg and (particularly in the States where you don't have any bends either) it's too easy to fall asleep at the wheel through boredom. Not to mention the fact that the transmission steals a significant portion of your engine power just to save you using one arm and one leg every now and again. Bleh. --YFB ¿ 22:46, 12 June 2007 (UTC)

With an automatic gearbox you might see a change in speed with only a small jiggle in RPM if it happens to shift while you're accellerating but generally, while you are in just one gear, the RPM and Speed are directly coupled by the gear ratio. One big difference would be with a Continuously variable transmission, it's very possible for the RPM to not change at all over a wide range of speeds. I had a MINI Cooper CVT as a loaner when my car was in for service and it's very strange to drive - as you put your foot down, the RPM's don't change at all until you get up to maybe 60 mph! (Unless you really stamp on the pedal) It's weird, you expect to hear the engine sound change - but it just doesn't. SteveBaker 20:31, 13 June 2007 (UTC)

Asparagus - might as well ask this now...

Has eating asparagus ever been proven to have any beneficial effect on male sexual potency, sperm count or semen volume? --Kurt Shaped Box 01:44, 12 June 2007 (UTC)

Many different cultures consider asparagus to be an aphrodisiac, but that appears more to do with its shape than anything else. By most accounts it makes semen taste pretty unpleasant. Wild asparagus root is used to increase male potency in Traditional Chinese medicine (TCM). According to Traditional Asian folklore medicines in sexual health in the Journal of Urology,

It promotes the production of kidney yin and prolonged use is beneficial for sexual weakness. Even though its greatest value is in its "love tonic" attributes, wild asparagus root is often used in tonics designed to overcome impotence or rigidity on the physical level.

So, If you believe your "kidney yin" is the cause of your "sexual weakness" then an asparagus root "love tonic" may be the treatment for you. However, TCM also advocates the consumption of animal testicles to boost sperm count, so you might want to try those first. Rockpocket 02:04, 12 June 2007 (UTC)

As far as I'm aware, my kidney yin is fine at present. Someone did once told me that my chakras were out of alignment though... --Kurt Shaped Box 22:43, 12 June 2007 (UTC)

Intranasal NSAIDS

Why would applying nsaids for rhinitis (besides aspirin, due to its polyp problems) in a gel or liquid suspension not work?

Do they need to be metabolized in the liver to become active?

Thanks, 24.245.49.243 02:20, 12 June 2007 (UTC)cyanide_sunshine

First of all, you should ask your doctor this question, not a team of pseudo-anonymous volunteers. 1. That being said, the NSAIDS in a gel or liquid suspension might not work for any number of reasons. What active ingredient did you have in mind, if not aspirin? Ibuprofen? 2. I would doubt that most NSAIDs need to be metabolized to become active. In fact, most are hepatoxic. As the Non-steroidal anti-inflammatory drug article states: "Most NSAIDs are metabolised in the liver by oxidation and conjugation to inactive metabolites which are typically excreted in the urine, although some drugs are partially excreted in bile." --Rajah 02:54, 12 June 2007 (UTC)

I don't understand what you said. I know this doesn't work, or else there would be products out there. I was referring to ibuprofen or aleve. Anyways, a doctor a) might not even know this b) I don't need to know c) I don't have rhinitis d) it would cost me 160$ to find out if the doctor did know. Thanks, though.

Careful...a possible, workable thing might not exist on the market solely because no company at this time finds it in its best business-interests to do so. The NSAID page teaches that the drugs are generally absorbed well via GI. Maybe the drug has poor absorption on mucosal membranes? The ibuprofen article suggests that half of the drug needs to be metabolized into a more active form. DMacks 05:19, 12 June 2007 (UTC)

Don't NSAIDS have other effects on mucus membranes than just inflammation suppression? I was under the impression that the upset-stomach side effect of aspirin was due to less mucus, so maybe it would dry the sinuses too much. I think some of the reason is that steroids work pretty well in this application, and work at low enough doses that there isn't much sytemic effect.--Joel 18:39, 12 June 2007 (UTC)

Insect cacoomb? cucomb? ARRRG!!

THIS WORD IS PROPELLING ME PRECARIOUSLY CLOSE TO INSANITY.

Insects can build house-like structres made from various materials; catepillars turn into butterflies inside of this structure.

The problem is spelling it.

cacoomb? cacoombe? cucoomb? cucumb? kacumb?

I do know it is NOT spelled: "coxcomb." This word is either: A) some plant, or B) "a conceited, foolish dandy; pretentious fop."

I appreciate any help with this strangely spelled word. Thank you. --67.177.170.96 05:42, 12 June 2007 (UTC)

Cocoon? Splintercellguy 05:44, 12 June 2007 (UTC)

Erm... Interesting. I don't see how cocoon could ever be mistaken for kacumb. Weird... 124.197.49.64 05:55, 12 June 2007 (UTC)

Ahhh, that's it. Thank you kindly. As for the previous question, it's a process called verbal fronting. If the link isn't red, you can take a look. 'b' is easier to pronounce than 'n' (at least to USA Southerners); therefore most of us pronounce "cacoon" as "cacoombe." It is extremely fustrating at times (esp. when utilizing a dictionary). --67.177.170.96 06:02, 12 June 2007 (UTC)

Do you really pronounce the b? How about in lamb? If in fact you mean the /n/ becomes /m/, I'm still surprised (though less so), because I'm told that in Spanish final m (e.g. in Latin words) is pronounced /n/, and I believe Spanish is not the only language with that habit. —Tamfang 06:21, 12 June 2007 (UTC)

Yes, believe it or not, a majority of USA Deep Southerners pronouce lamb as "lahmmbe" (with a hard labial 'b') and cacoon as "cah-COOM-bh" (with a soft labial b). 'ń' (nat) and 'n' (skinny) are very hard sounds for us to make...haha. If I knew my IPA I would use it, but it's been a while. --67.177.170.96 06:28, 12 June 2007 (UTC)

How about "womb"? ;-) Nah, just kidding. —Bromskloss 08:02, 12 June 2007 (UTC)

That can't apply to all words ending in "-n", can it? How about "cartoon", "moon", "soon", "son", "ton"? — Sebastian 08:04, 12 June 2007 (UTC)

Nope. Only the labial fricitive/stop 'n' changes to 'b'. But, the nasal 'n' is severely deemphasized, as such:

cartoon --> car-TOO-nh (nh = nearly inaudible nasal 'n')

moon --> MOO-nh

soon --> SOO-nh

son --> SUH-nh

ton --> TA-nh

Weird, eh? --67.177.170.96 15:09, 12 June 2007 (UTC)

What is a labial /n/, or a fricative /n/? —Tamfang (talk) 20:18, 29 September 2019 (UTC)

Reverse dictionaries are good for this as well. http://www.onelook.com/?w=*&loc=revfp2&clue=caterpillar+butterfly --Rajah 19:10, 12 June 2007 (UTC)

Maybe there's a confusion with catacomb, the last syllable of which is often pronounced COOM. -- JackofOz 00:04, 13 June 2007 (UTC)

nitrogen in tyres

My car needed some brake repair, and the clerk writing me up looked at the tires and remarked, "Your tires are filled with nitrogen; you need to either use only nitrogen to pump them up, or have the nitrogen removed and fill them with air." What?! How can an intermediate blend of nitrogen be worse for my tires than either 4/5 (common air) or 5/5? —Tamfang 06:25, 12 June 2007 (UTC)

The clerk is mistaken. Mixing compressed air in with the nitrogen will do no harm, but it will dilute somewhat the putative advantages of the nitrogen-only fill. You've either got a poorly-trained clerk, or you've got a clerk who thinks that you're gullible. ("It's not safe for you to mix that dirty, free air into your nitrogen-filled tires. Don't worry though, we'd be glad to top off your nitrogen for twenty bucks.")

Note that benefits of nitrogen for someone who drives under reasonable conditions are probably negligible: [1]. You can get the same improvement in mileage just by regularly checking that your tires are properly inflated. TenOfAllTrades(talk) 08:57, 12 June 2007 (UTC)

I thought the point of using nitrogen was not having to check the pressure. —Bromskloss 09:41, 12 June 2007 (UTC)

It's always important to maintain proper tire pressure. That preserves the handling characteristics of the car and helps prevent blowouts and other tire failures. All the nitrogen does is reduce the effect of temperature on tire pressure, and cars already have plenty of safety margins there anyway. — Lomn 13:34, 12 June 2007 (UTC)

Yes, of course it's important, I just meant that with nitrogen, you might not have to check it as often to make sure the pressure is correct. I see how it could be misunderstood, though. :-) Also, everyone, remember that too low pressure means worse fuel economy, which will cost you more and, more importantly, harm the planet through more emissions. —Bromskloss 14:56, 12 June 2007 (UTC)

More like less importantly since I have far more interest in my saving money than my personal, negligible impact on the environment --froth^t 04:33, 13 June 2007 (UTC)

The business of filling car tyres with nitrogen is a bit of a scam - you certainly have to continue to check tyre pressure. There are arguments that the air seeps out through the rubber more slowly with Nitrogen - but you still have to check them just as often because you still don't want to drive for weeks on a soft tyre until you get around to checking it again. Air leaks out for all sorts of other reasons - none of which are helped by using nitrogen. Find another tyre store - this one is clearly staffed with idiots. SteveBaker 20:25, 13 June 2007 (UTC)

Here I assumed that the purpose was to reduce oxidation of the rubber (from within, obviously, we can't do anything about the outside but helping where you can is better than nothing). —Tamfang 16:12, 14 June 2007 (UTC)

lens

if lens is halh covered ,what happens to image

Even if you cover up one part of the lens, there are other paths for the light to reach the image.

Ah, good question. I think the answer is that the image will get darker, not partially obscured. As you can see in the illustration here, the light emanating from an object can hit any part of the lens and end up on the correct spot on the image anyway. Therfore, if you cover one part of the lens, you will block some of the light, but are still lightrays from the object slipping through elsewhere. That said, some parts will probably be darker than others because a larger part of the lightrays from an object hit the part of the lens that is closest to the object and also because what I said is only true (I think) if you approximate the lens to lie in a single plane (not having anyt thickness). —Bromskloss 07:59, 12 June 2007 (UTC)

(ec) Mostly, not a lot happens except that the image is only half as bright, or more technically, has only half the irradiance. Think about what happens when you half close your eyes. However, there can also be changes in the quality and sharpness of the image, depending on the lens or lens system, due to the suppression or enhancement of aberrations. Also, if the original image is somewhat out of focus, the image with the lens half covered may appear to be sharper, because of the effective reduction in f-number. But usually, you will still see all of the image. The ray diagrams under lens (or helpfully supplied here) may help to explain this. --Prophys 08:07, 12 June 2007 (UTC)

On second thoughts, half-closing your eyes is not a good example, because in fact your field of view does become more restricted when you do that. This is an example of vignetting, which happens when you reduce the area of the lens with a screen or aperture that is not close to the lens, but some distance from it. Then you get partial dimming or even cutting off of the edges of the image. If the aperture is right next to the lens, (technically, at one of its principal planes), then the area of the image is not affected by the area of the aperture. As the aperture is moved further away from the lens, the effect on the area of the image becomes more severe. If the aperture is in the plane of the image, then the area of the image is obviously the same as the area of the aperture. --Prophys 12:51, 12 June 2007 (UTC)

If the covering is some distance in front of the lens, there may be darkening of half of the image more than the other half. For this to work as expected, and cause overall darkening, I would expect it would have to be immediately in front of or behind the lens. To be sure that the only effect is overall darkening of the image, the ideal place for the covering to be is between the elements of the lens, at the nodal point, where the diaphragm, iris, or aperture is in a camera. Waterhouse stops were provided with early cameras. They were metal strips with different size holes in them which could be inserted in the lens. The goal of "stopping down" the lens is not so much to reduce the light going through the lens (the slow film of that era needed lots of light to make a good negative]] , but to restrict the path of the light to the center of the lens, where aberrations were least, and to improve the depth of field. One reason human vision is better in bright light is thet the iris of the human eye similarly "stops down" to keep the light path to the sharper central portion of the visual pathway. Edison 13:12, 12 June 2007 (UTC)

Yes, my mistake, the ideal position for the aperture is the plane through the nodal point, not the principal plane, although in many lens systems there's not much difference. --Prophys 10:00, 13 June 2007 (UTC)

Temperature

If today's temperature is Zero degrees centigrade (0°C), the experts predict that it will be twice as cold tomorrow, how cold will it be in degrees centigrade?41.222.12.91 11:38, 12 June 2007 (UTC)

that question is impossible to answer outside of context. Scientifically, there is no such thing as 'cold', just the absence of heat. You can take away or add heat to a substance, you can't add 'cold' outside of finding a way to remove the heat. -M^ask? 11:48, 12 June 2007 (UTC)

This question could be tackled if you adopt a "relative" stance. Relative to yesterday, when the temperature was (say) 5°C, the temperature has dropped by 5 degrees. So, if tomorrow is going to be "twice as cold", you could argue tomorrow's temperature will be -5 or -10 depending on how you define "twice". So... what was the temperature yesterday? Incidentally, if the problem is supposed to be about difficulties of multiplying by zero (which it isn't currently... it's about lack of information) you can always avoid the issue by working in Fahrenheit or Kelvin or whatever other scale you fancy (take a look here). --Dweller 12:06, 12 June 2007 (UTC)

This sounds kind of like a homework question. If you assume twice as cold is the same as half the temperature, 0°C = 273.15K / 2 = 136.575°K - 273.15°K = -136.575°C. See Kelvin as noted above for more info.--GTPoompt(talk) 12:13, 12 June 2007 (UTC)

You'd get a very different answer in Fahrenheit. If it is a homework question, it's a rubbish one. --Dweller 12:43, 12 June 2007 (UTC)

Doesn't sound like homework, but the same calculation makes no sense in Farenheit. Kelvin is a special scale. --h2g2bob (talk) 17:38, 13 June 2007 (UTC)

The "experts" don't predict that it will be "twice as cold" tomorrow. They predict a specific temperature range; it's some wooly-headed reporter or other commentator who comes up with a claim like "twice as cold", which, as we've seen here, is fairly meaningless. (Me, I'd imagine that "twice as cold" means that (comfortable temperature - tomorrow's temperature) = 2 × (comfortable temperature - today's temperature), but we still get to argue over what "comfortable temperature" is.) —Steve Summit (talk) 13:01, 12 June 2007 (UTC)

Oh, and of course the most likely explanation here is that it's not a homework question, but rather a joke, along the lines of imponderables such as "Why do we drive on the parkway but park in the driveway?". —Steve Summit (talk) 13:03, 12 June 2007 (UTC)

Gargling with salt water

Since dissolved salt in water doesn't stay salt, but splits up into the ions (Na+, Cl-), how does gargling with saltwater (which doesn't contain salt) actually kill bacteria in the throat? The common explanation is that salt causes the bacteria to barf up all their water, but that doesn't make sense if there's no salt in saltwater. — BRIAN0918 • 2007-06-12 12:01Z

Claiming that "salt water doesn't contain salt" is a typical act of pedantry. For all intents and purposes, salt water does contain salt, as (a) its name, (b) its taste, (c) the residue left after evaporation, and most importantly here (d) its effect across osmotic membranes and salinity gradients all attest. —Steve Summit (talk) 12:39, 12 June 2007 (UTC)

You haven't really given an answer. Is it that you have to add more salt than can be dissolved in the water? — BRIAN0918 • 2007-06-12 12:44Z

He was stating that your assumption that salt crystals are required to kill bacteria is a false one. A salt crystal is a stable molecule. It won't do anything. When dissolved (turned into active floating ions), the salt will do its job. --Kainaw ^(talk) 12:52, 12 June 2007 (UTC)

(ec) I'm not sure why gargling with salt water works, either (though I have experienced that it does). But your explanation that it "causes the bacteria to barf up all their water" sounds perfectly plausible to me.

If you add more salt than can be dissolved in the water, the undissolved salt sits at the bottom as granules, and I wouldn't say that the water "contains" it. It's the dissolved salt, of course, that gives salt water its properties (bactericidal and otherwise). —Steve Summit (talk) 12:53, 12 June 2007 (UTC)

I'm getting the feeling you didn't really know the answer and are just restating other people's answers or using circular reasoning (as in your original post). That's fine, I can wait for someone who actually knows. — BRIAN0918 • 2007-06-12 13:11Z

I'm sorry, when you said "The common explanation is that salt causes the bacteria to barf up all their water, but that doesn't make sense if there's no salt in saltwater", I though you meant, "I can understand that salt would make the bacteria barf up all their water, but that doesn't make sense because there's no salt in saltwater." —Steve Summit (talk) 13:21, 12 June 2007 (UTC)

The trick is osmosis, which I think is what Ummit was trying to get at there, somewhere. The cell wall of a bacterium is a semi-permeable membrane, meaning it lets some things (like water) through and others (like sodium and chloride ions) out. When you gargle salt water, water rushes through the membrane in an attempt to equalise the salt concentrations - but, since the salt water contains a lot of salt, and the bacteria contain just a little water, what happens is that, in a sense, the bacteria "barf up all their water". Confusing Manifestation 13:02, 12 June 2007 (UTC)

I'm confused. Why does the water rush out of the bacteria if the water inside the bacteria has less salt. I guess the confusion is what you mean by "equalize the salt concentrations". — BRIAN0918 • 2007-06-12 13:10Z

It's a fundamental principle (which I can't give an explanation for) that concentrations of dissolved substances want to equalize. If you have a higher concentration of solute in region A than in region B, you can equalize them either by adding solvent to region A (perhaps by moving it from region B), or by adding solute (e.g. salt) to region B (perhaps by moving it from region A). But if the regions are separated by a semipermeable membrane, that can pass solvent but not solute, then only the first option is available. —Steve Summit (talk) 13:21, 12 June 2007 (UTC)

Yeah, I just figured that out myself. I'm sure I learned it in one of my chem courses, but I obviously didn't retain that knowledge. I did, however, retain the loans. — BRIAN0918 • 2007-06-12 13:23Z

There is no evidence that gargling with salt water kills bacteria. Period. This is folk medicine (I was taught to do it by my mother also). From the standpoint of scientific medical practice it is a harmless "comfort measure", but do not imagine that it is accelerating your recovery from a bacterial infection-- most sore throats are viral. alteripse 13:27, 12 June 2007 (UTC)

So where does the comfort come from. It does make you feel better temporarily. Why? Tufts says that it actually "washes away the layer of mucus on the throat containing bacteria". Why salt-water specifically? Would sugar water also have the same "washing away" effect? — BRIAN0918 • 2007-06-12 13:29Z

Perhaps a visit from Mr. Placebo? 213.48.15.234 13:41, 12 June 2007 (UTC)

However, in answer to the "how does it soothe" question, I don't know. Some of the possible variables: (1) whether you have been told it is effective or ineffective, (2) warm, neutral or cold temp, (3) tonicity of the the salt (hypo-, hyper-, or normal), (4) solute in the water vs plain water, (5) salt, or sugar, or other solute, (6) how much trouble you invest in the preparation. PS: I do not scorn the therapeutic value of Mr Placebo! alteripse 13:49, 12 June 2007 (UTC)

Gargling with salt water might loosen the mucus in the throat, helping your body cough up or swallow irritating mucus build-up. -- JSBillings 14:32, 12 June 2007 (UTC)

I seriously doubt the comfort in my throat is a "placebo effect". I'll admit could possibly be more like getting a punch in the face to ignore the pain in your toe, but in any case I have no doubt that there is some real, unimagined, effect. Ironically, you could never create a placebo to test the gargled water hypothesis, because by definition, you never know you have taken a placebo. Unless your taste buds are dead, you'd immediately know if you were tasting NaCl or some other salt or not in whatever solution you are gargling. And you'd have to show me that salt doesn't kill bacteria, as I have plenty of evidence from other life forms that tell me otherwise. Of course your argument is not directly about the salt, but about the actual action of gargling with something we may identify as salt water. The question then becomes:

1. At what concentration might be required to affect and produce desirous results (if any)
2. For what duration of exposure may be necessary?
3. What are the effects? Could gargling provoke an advantageous immunity response? Maybe the gargling aids the body in more indirect ways than directly harming the phage(s) or viruses?

Unless you can directly and absolutely say that no concentration works, or that for whatever duration that does work it does more harm than good (and how would you know that?) AND that it doesn't aid or signal the body in some sort of fashion that may help the body in the short or long run, I will continue to take this folk remedy, thank-you-very-much. If it works, the reasons behind why it works are nice to know, but not necessarily important.

P.S. I'd even wager that this does better than the vitamin C remedies you have heard about... I've actually felt I have kept myself from getting a early sore throat by gargling with salt water when I had evidence that I was about to have one. I've also taken vitamin C and wonder why I was taking it because it never seemed to do any good.

Root⁴(one) 04:09, 13 June 2007 (UTC)

This is about as vehement a "don't confuse me with the facts, my mind is made up" statement as we have had here for a while. While I admire your confidence of conviction, you are giving us a textbook illustration of how to defend fraud and quackery. Examples: (1) The false assertion that "imagined" effects cannot be "real". (2) "You have to show me it doesn't kill bacteria (you have to prove it doesn't work)" is the usual line from the quacks for everything from colloidal silver to faith healing. (3) Claiming that irrelevant facts are evidence of unrelated efficacy. I will call your bluff: you have no meaningful evidence that salt water kills pathogenic bacteria in any circumstances remotely relevant to sore throats. (4) Claiming it works better than something ineffective. Gargling might indeed do better than vitamin C; since I haven't heard any evidence that vitamin C accelerates healing of a sore throat, that's not a very strong endorsement. (5) Arguing against something your opponent didn't say: I did not deny that gargling saline "worked" to soothe your throat nor did I tell you not to take it. I called it a "comfort measure" taught me by my sainted mother, and nothing you have said refutes that. Gargle away. alteripse 11:11, 13 June 2007 (UTC)

Ok, yes, imagined affects can be as real as some "real" event, but, you have to trust your senses at some point, otherwise you get into the realm of nonsense existentialist philosophies. However, to give an analogy, I do know about completely "imagined" feelings.. this is why, for a pilot's license, they tell you to trust your instruments, not your feelings -- it is the physics of the airplane you have to worry about, not your body, after all. Of course in that situation, I think the senses are still very real, its just that interpretations of them aren't trustworthy in that context. It all depends on context. If somebody had 7 beers and said he saw some aliens and the performed the infamous anal probe (a la South Park), I'd completely rebuff him. But if I knew him to be generally honest, he told me he was not knowingly under influence of drugs, "herbs" or alcohol, I'd not be so quick to judge. His interpretation of events may be imagined, but he may have experienced a very real event or action. The same may apply here. A very real experience is occurring, as well, as some (arguably) real after-experiences.

The problem is the interpretation of the experiences. My experiences have lead me to believe that gargling with salt water does more than just comfort. You could say the same about a number of old remedies. I have significant doubts that treating an injury with olive oil, cloth, and wine, but it may be better than nothing, and experience probably lead people to choose that treatment over other treatments. I grant I'm talking about a treatment that existed at least 1000 years before the discovery of pathogens... but back in the time when the science of disease certainly had not evolved to what it is today, people only had experience, folk remedies, and their conceptualization of the problems to go on.

However, since we do live in a world where much of humanity's data is readily available, I will take your bluff call. You are right, I don't have any scientific evidence at hand that it kills bacteria or otherwise promote better health in a sore throat. This second point unfortunately is going to be hard to prove or disprove because "promote" and "help" are so vague. But that doesn't mean I cannot find it. Give me a few weeks, and I'll report here or elsewhere. If I don't find evidence, that doesn't mean I should admit defeat, it only means I don't have evidence. But I doubt this will be the case. Yes, I'll restrict myself to reporting previous scholarly research or at least verifiable medical websites. I may throw in some non-medical websites for jokes or jabs.

Root⁴(one) 13:14, 13 June 2007 (UTC)

Thanks for taking my rebuttal in the spirit intended and not as a personal affront. I was afraid I had been too harsh. As you can probably tell, I have an allergic response to medical nonsense even when it concerns harmless things like this because I think people are not critical enough about health claims and few can distinguish between scientific medicine (which has many unsettled questions, areas of ignorance, and "reliable facts" that will some day be refuted) and our own culture's folk medicine. I have no problem with saline gargling for a sore throat unless someone starts misrepresenting what it is and what it does and selling it at a high price. alteripse 17:18, 13 June 2007 (UTC)

I always assumed it was osmosis - water travels through the permiable membrane of the bacterium's cell wall - and it travels from areas with the lowest salt concentration to the highest. Normally that means that non-salty water flows into the cell and keeps it running. When you have very salty water, the membrane forces the water out of the cell - presumably killing it. But for how long and at what concentration? I have no clue. But it's clearly not going to work perfectly or for all kinds of bacteria. SteveBaker 20:21, 13 June 2007 (UTC)

This reference desk, like the world outside, is full of people who are quick to toss out "plausible" (at least to them) medical answers complete with mechanisms that are simply folk belief, fantasy, or pseudoscience, with little ability to tell the difference. A really important aspect of being well-educated is knowing the reliability and limits of your knowledge, and clearly at least half a dozen people demonstrated a limited ability to do that in the paragraphs above. Let's unpack the assumptions in your speculation:

1. That gargling with salt water for a few seconds (less than 30 seconds? maybe 2 or 3 times?) accelerates healing of an infectious sore throat by direct and selective damage to the pathogenic microbes. This, as far as I know, is simply an unproven folk belief. One kind of evidence that would support the premise would be a controlled trial, similar to what has been done for cold research, where volunteers are actually deliberately exposed to a virus that causes a cold or a sore throat, and then controlled research is done on various aspects of contagion, symptoms, resistance, course, and treatment. College students will do lots of things for money, including volunteering for colds. So anyone who can find such a trial can refute absolutely everything I say further here, no matter how convincing my reasoning sounds or how many degrees I have. On the other hand, among the weakest and least convincing evidence is personal testimonial: "I did it and felt better and I am convinced it helped" simply because there are far too many alternative explanations.
2. Some cells, if exposed to environments of markedly higher or lower osmolality, will experience a movement of water across the membrane in the direction of higher osmolality that may damage them by shrinking them or swelling them. A really clear example of this occurs when a drop of blood is dropped into a cc of water. Enough water can move across the membranes of red blood cells to cause them to swell and rupture, releasing red hemoglobin into the water as a clear sign of ruptured cells. Normal saline at about the osmolality of body water contains about 150 mEq Na per liter, or about 0.9 grams of NaCl per 100 ml of water. A teaspoon of salt contains 2.4 g Na, or about 6 g NaCl. How do you make your saline gargle? A teaspoon of salt in 6 oz of water? That would be about 6 grams in about 180 ml, or maybe 4x normal, or maybe about a 3.6% saline solution. Red cells are far more fragile than bacteria, but more resistant to a hypertonic environment than a hypotonic, so we can infuse 3% saline by iv without causing hemolysis.
3. While bacteria are also susceptible to osmolar lysis, they are far more protected than red blood cells, or you wouldn't have to wash with soap-- simple water would kill them. Similarly, it takes sustained exposure to much more than 4x normal osmolality to kill most bacteria. Bacteria have several types of defenses against dehydration by a concentrated external environment, including lower membrane permeability to water than rbcs, ion pumps in the cell membranes, and in some cases even the ability to generate idiogenic osmoles to raise internal osmoality to offset external hyperosmolality. How confident are you that 30 seconds of exposure to 4x hyperosmolality will rupture a lot of bacteria?
4. This assumes that the bacteria causing sore throats are sitting on the surface of the throat just waiting to be engulfed by a tide of hypertonic saline. In fact, if they are causing infection and pain, they are inside the tissue and the bacteria causing trouble will not even get their feet wet from your gargle.
5. Oh, by the way, most sore throats are not caused by bacteria, but by viruses, which are far more resistant to osmolar shock because they don't have cell membranes and cytoplasm, and they are far more likely to have actually penetrated into pharyngeal tissue and won't even notice it's raining saltwater outside.
6. So how about the "saline washes away mucus" hypothesis? If mucus were soluble in saline, your saliva would dissolve it. It isn't and it doesn't. You have to swallow it, spit it out, cough it up, or blow it out your nose.
7. Now, doesn't the "it helps because the warm or cool wet sensation on your inflamed throat is soothing" explanation sound much more attractive? alteripse 00:48, 14 June 2007 (UTC)

Gas cylinders

I have used gas cylinders for years in my work and I have never before noticed the regulator getting particularly cold. Recently I have been using CO2 (which I don't normally use) and letting it run at a rate that is quick relative to what I usually do; in this case the regulator gets very cold and sometimes ices up to the point of not working correctly.

So my question is... which is the difference that's causing this 1) the CO2 or 2) the relatively fast rate? The CO2 in a compressed gas cylinder isn't liquid is it? ike9898 13:20, 12 June 2007 (UTC)

The answer is mostly the rate of release. Any time When you release a pressurized gas, it often gets cold. This can be thought of as a manifestation of conservation of energy at work -- when you compressed that gas, it got hot. (That's why compressors often have big cooling fins on them.)

Some refrigerated trucks are cooled not by mechanical refrigerators, but by the gradual release of pressurized nitrogen carried in a tank underneath. —Steve Summit (talk) 13:25, 12 June 2007 (UTC)

Both 1 and 2. CO2 comes out of the cylinder particularly cold because it is liquified rather than simply compressed, so you have to supply the enthalpy of vaporization to get it into the gas phase. The fast rate will cool it even further, due to the Joule-Thomson effect (which is what Steve Summit is referring to above). When you use a CO2 fire-extinguisher, which is simply a CO2 cylinder adapted for simple and rapid release of the gas, you often get the CO2 coming out as a "snow" of dry ice: not a problem, as the dry ice quickly evaporates to give the gaseous CO2 needed to extinguish the fire, but spectacular none the less! Physchim62 (talk) 13:29, 12 June 2007 (UTC)

Thanks for the Joule-Thomson effect reference, Physchim. (I suspected it was more complicated, but never having studied thermo, I'm weak on the lingo.) —Steve Summit (talk) 15:46, 12 June 2007 (UTC)

The only correct solution to the problem is to change the regulator: with a wider opening between the piston and its seat, you will reduce the Joule-Thomson effect. Your gas supplier should be able to give you advice on this one, although you might wish to talk to their competitors as well, as prices can vary considerably. The minimum information required is

• the desired flow rate of CO2
• the length of time the gas will be flowing for; you can tolorate a greater cooling for an intermittant flow than for a continous flow
• the minimum ambient temperature of the installation

With the first two factors (and a few other parameters which you gas supplier will know), you can estimate the cooling power of the depressurization: with the second two, you can estimate the warming power of the surroundings. You must keep the outlet temperature within the operating range of the regulator, and ideally you should try to keep the outlet temperature below the dew point of the surrounding air (to avoid condensation on the regulator). There are other possible fixes, but nothing which I would really like to recommend on a public forum! Physchim62 (talk) 16:19, 12 June 2007 (UTC)

Thanks for the help, guys. One last point I'm not 100% clear on: In cylinders of many compressed gasses (N2, O2, He2) the gas is NOT liquified, correct? ike9898 17:55, 12 June 2007 (UTC)

Correct. Carbon dioxide is stored liquified, some short-chain hydrocarbons (propane, for example) are stored liquified, but almost everything else won't liquify at reasonable temperatures no matter how much you compress it. --Carnildo 00:17, 13 June 2007 (UTC)

By the way, this problem can happen in scuba diving regulators as well when the ambient water temperature is low. That article mentions adiabatic expansion as the cause. Divers crazy enough to dive in cold environments will usually choose environmentally sealed regulators or other equipment specially designed for cold temperatures. (By the way, I'm in the "crazy enough" category, since I live in Minnesota.) --Elkman ^(Elkspeak) 20:37, 12 June 2007 (UTC)

You might want to try putting heater tape on the regulator. To visualize, when the gas is compressed the collision rate between molecules increases. Energy is lost in the form of heat until the gases slow down and the collision rate is essentially the same as pre-compression. When you let the gas out, the molecules still have the same velocity and they collide with the warm regulator and take energy from it. This speeds up/heats up the gas molecules and cools the regulator. Increasing the surface area/diameter of the regulator pipe will alleviate ice build up as will heating the regulator. --Tbeatty 22:11, 12 June 2007 (UTC)

Gas supply systems that are prone to this cooling problem often have heaters in-line[2] or built into the regulator[3]. DMacks 22:24, 12 June 2007 (UTC)

FWIW, I've used both the in-line (gas-shielded welding) and integrated (in the lab) heater units with CO2 - both work quite well provided you've sized the regulator properly given the required delivery-side pressure and flow rates. -- MarcoTolo 03:09, 13 June 2007 (UTC)

A question of conciousness

Ahoy,

after watching 24 yesterday again, these questions came up again: 1) Do people really instantly go unconscious when hit over the head or neck (i.e. pistol-whipped)? In movies it seems like there is a 100% chance when you hit somebody on the neck that he will go unconscious. 2) There is always some kind of stick with I presume gas in it, which people break into two and then hold under the nose of an unconscious person and he instantle regains consciousness. What kind of stuff is in that breakable bar?

Thanks in advance. Aetherfukz 13:34, 12 June 2007 (UTC)

It is very rare for someone to lose consciousness when hit. It is merely a very bad writer's tool for getting people out of a scene quickly. As for the "stick", see smelling salts. --Kainaw ^(talk) 13:37, 12 June 2007 (UTC)

Well, hitting hard enough would do the trick, don't you think? The problem, as I see it, is hitting hard enough and still not so hard that you kill the victim or inflict more severe damage. Anyway, in Tintin (which I otherwise like very much), they seem to use that perfect amount of force all the time. —Bromskloss 13:58, 12 June 2007 (UTC)

It's more complicated than that, of course. If it's a bad guy, a single hit (of almost any degree) will induce unconsciousness. The good guy, on the other hand, can withstand innumerable blows, with the exception of the one per episode which is necessary to effect a capture so that he can (a) learn the last stages of the master plan from the evil overlord during a "last" interview while terminally imprisoned in his inner sanctum, and then (b) spectacularly escape. --Steve Summit (talk) 15:43, 12 June 2007 (UTC)

I'd think that you'd be more likely to have someone screaming and holding the back of their head, or lying on the floor drowning in a pool of their own blood than to knock them out clean. In any case their hair will at least be matted and bloody after, which seems to rarely happen in movies/tv --froth^t 14:13, 12 June 2007 (UTC)

The effect is based on the idea that you can hit a major artery, cause a sudden increase in blood pressure, and then have the body quickly stop blood flow to reduce blood pressure. Then, the person passes out. That rarely happens. It takes a very exact hit and the hope that the person's body will response accordingly. It takes a hell of a lot of luck to knock someone out with a concussion, which is what the movies tend to make it look like. People get out of car accidents and walk away all the time. --Kainaw ^(talk) 14:26, 12 June 2007 (UTC)

There's a Straight Dope on the knock out question, seems to discard the blood flow theory: [4] -- Madeleine 15:02, 12 June 2007 (UTC)

See concussion. As for sequalae, you may find head injury, post-concussion syndrome, and brain damage useful. TenOfAllTrades(talk) 15:10, 12 June 2007 (UTC)

Thanks for all the quick and very helpful answers! Aetherfukz 15:42, 12 June 2007 (UTC)

In defense of this lame trope, I note that boxers are sometimes knocked out by blows to the head. --TotoBaggins 18:41, 12 June 2007 (UTC)

Typically, they're suffering the effects of a Concussion due to repeated heavy blows to the head. -- Kesh 03:43, 13 June 2007 (UTC)

I agree, it is often a lame plot trick. However, never underestimate the second hit; the hit one takes when one falls and hits his head on the ground. I have seen firsthand someone go unconscious for maybe 2 seconds because his head hit another person's heel on the way to the ground. And yes, the impact was to the back of the head. Root⁴(one) 04:20, 13 June 2007 (UTC)

Of course, how many times does that second hit actually occur? Root⁴(one) 13:16, 13 June 2007 (UTC)

The 'wake up stick' is at least reasonable though - Smelling salts - ammonium carbonate. Used to wake up someone who has passed out or fainted. They contain little white crystals that emit ammonia when in contact with the air. You break the glass in the stick right under the victims nose - the ammonia irritates their mucous membranes and cause an automatic and very sudden intake of breath that is very effective in causing someone to come around if they have passed out for most of the common reasons. SteveBaker 19:58, 13 June 2007 (UTC)

Sicknesses

How were things like strep throat, pharyngitis, yeast infections, sinus infections treated or dealt with three hundred years ago?

The 1728 Cyclopaedia would be a good source for this info (volumes: 1, 2). I couldn't find anything in their entry for Pharynx or Sinus, however, and there is of course no article titled "strep", nor one for "yeast". The hard part is figuring out what these illnesses were called back then. Maybe a medical history book would work better. You may also look at the folk treatments that are still used today for these illnesses as many of them may be much older traditions. — BRIAN0918 • 2007-06-12 15:03Z

I found some of the above under Squinancy, see [5] Part of the difficulty is that they seemed to have conflated what we see as distinct illnesses into groups, so I see Angina included with what we Brits call Sore throat. --Dweller 15:16, 12 June 2007 (UTC)

I was just about to post the same thing. The only thing they really prescribe is for severe cases ("severe" by today's standards?), and that is just to slice and dice your way back to healthiness. — BRIAN0918 • 2007-06-12 15:19Z

"they seemed to have conflated what we see as distinct illnesses into groups" - I think you'll find the truth is the exact reverse of that. We've separated out distinct illnesses from what were once thought of as single conditions. -- JackofOz 23:58, 12 June 2007 (UTC)

Psychoactivity of Coleus?

I recently stumbled upon a section on erowid.org that has numerous reports of people who feel psychoactive effects after smoking or chewing coleus. So I ask: is the coleus plant psychoactive? What chemicals in coleus are psychoactive? How would coleus be classified and what neurotransmitter systems are effected? Are there any health risks or any potential for abuse? Jolb 16:24, 12 June 2007 (UTC)

As I see nothing about it in the article, I'm guessing this is not well understood. As always, we cannot dispense medical advice, but prudence would suggest being cautious in ingesting unknown substances. Plenty of plant alkaloids have psychoactive effects, for what it's worth. Friday (talk) 16:58, 12 June 2007 (UTC)

Is this plant related to khat? Khat, another African plant leaf that is chewed, is a stimulant with some other reported psychoactive effects. The taxoboxes say they are both in the same class (biology), Magnoliopsida; how "related" is this? (My guess is "not closely.") Nimur 18:12, 12 June 2007 (UTC)

Coleus is related to salvia, basil, and mint. Coleus and khat are not related: class Magnoliopsida encompasses a majority of known flowering plants. Cheers, Dr_Dima.

Criteria for Sluggish cognitive tempo

In the Wikipedia article it says: "Sluggish cognitive tempo (SCT) is a descriptive term which is used to better identify what appears to be a homogeneous group within the Predominantly Inattentive Type (ADHD/PI) DSM-IV classification."
Yet in one of the referenced articles, it says: "Many ADD children, although not all, appear sluggish, drowsy, spacey, lethargic, and markedly hypoactive. They fit the criteria for having a sluggish cognitive tempo (SCT)." In this article, the term ADD is used for "the truly inattentive type of ADHD (not simply the subthreshold combined type)". So, apparently, some ADD children do not fit the SCT criteria.
Does anybody know what are the criteria for SCT? Or, if there is no consensus about them yet (because SCT is not part of the DSM-IV), does anybody have a list of criteria for SCT that is in use? Lova Falk 18:19, 12 June 2007 (UTC)

I hope my answer is relevant to you. I googled SCt criteria and looked at some studies and one of the studies that popped up (the link below) seemed to pull their diagnostic criteria from Child Behavior Checklist (CBCL) by Thomas M. Achenbach. I haven't found the actual criteria yet. I also found this paragraph in the same paper which may explain why some ADD individuals o not fit SCT criteria. http://findarticles.com/p/articles/mi_m0902/is_5_32/ai_n6234463

Studies of ADHD subtypes as defined in the third edition of the DSM (DSM-III; American Psychiatric Association, 1980) revealed some differences in the specific attentional dysfunction exhibited by each of the groups. Specifically, children with DSM-III attention deficit disorder with hyperactivity exhibited inattention symptoms characterized by sloppy work and distractibility, whereas children with DSM-III attention deficit disorder without hyperactivity were rated higher on inattention items measuring daydreaming, tendency to become confused, lack of mental alertness, and physical hypoactivity (e.g., Barkley et al., 1990; Hynd et al., 1989; Lahey & Carlson, 1991; Stanford & Hynd, 1994), a cluster of symptoms that has subsequently been labeled sluggish cognitive tempo (SCT). On the basis of these findings, the DSM-IV field trials (Lahey et al., 1994) tested the utility of SCT symptoms for the diagnosis of the inattentive type. Consistent with studies of DSM-III ADD, the field trials found that SCT symptoms were associated most strongly with the DSM-IV predominantly inattentive type (Frick et al., 1994). However, further analyses indicated that the majority of individuals with the DSM-IV inattentive type did not exhibit SCT symptoms, so these symptoms were not included in the diagnostic criteria for DSM-IV ADHD. Sifaka ^talk 22:20, 12 June 2007 (UTC)

Thank you so much for your effort! However, I had also googled, with exactly the same words as you did, and didn't find any criteria. The characteristics of STC are clear for me, but I would also like to know if for instance a child that is sluggish and drowsy in most situations (school, visits to the theatre etc), but who can be much more lively during free play, still can fit criteria for SCT. Lova Falk 18:26, 13 June 2007 (UTC)

Help needed badly

I need to have a lab-sheet for a plant-related experiment (hypothesis, test conditions, results). Failing that, I would greatly appreciate a simple graph of some plant experiment, preferably with context provided.

I need this information badly for a course. If I have ever needed information from Wikipedia, I need it here and now.

~ Flameviper 23:48, 12 June 2007 (UTC)

Er, that would I believe be covered by the notice at the top of this page reading "do your own homework". --YFB ¿ 23:51, 12 June 2007 (UTC)

I'm not asking you to do my homework, I just need a link to an experiment page, a PDF, something... you are human as well... ~ Flameviper 00:03, 13 June 2007 (UTC)

Well, that's disputable. Nevertheless, I got the impression you were asking for someone to hand you a written-up lab experiment so that you could pass it off as your own; I'm not feeling over-imbued with good faith this evening so you'll have to excuse me. How about A comparative study between two citrus rootstocks: Effect of nitrate on the root morpho-topology and net nitrate uptake? --YFB ¿ 00:13, 13 June 2007 (UTC)

Finding scientific papers related to plants is easy if you know where to look. Try [scholar] and pick some topics that you think would be interesting to you. Read the abstracts of the articles that appear and decide if it is relevant. Scientific names of plants will help you more than common ones. Wikipedia is excellent for figuring out the scientific name of a common plant.

If what you are looking for is an experiment you can do yourself, here are two suggestions on two simple experiments to generate the things you are looking for.

Here is a classic plant experiment that usually produces clear results that you might attempt if you are looking for an experiment to do with minimal prep equipment. Set up an experiment that will test whether a plant will transpire more in windy conditions or in still air conditions.

• You should read the article on transpiration
• consider how the area of the plant surface might affect the results
• Think about the design the setup
• You can use a clipping of a plant rather than a whole plant with roots (at least several leaves and a stem for best results)

If time is of the issue more than clarity of results and you have access relatively common lab equipment, you may want to try comparing the percent moisture content of leaves between species, different plants... You will have to figure out a way to remove most of the water from the leaves and figure out how much was lost. Sifaka ^talk 00:15, 13 June 2007 (UTC) You have won an Internet.

~ Flameviper 00:16, 13 June 2007 (UTC)