Wikipedia:Reference desk/Archives/Science/2009 March 13

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March 13

Name of a test

What's the test called in Psychology where you give a group of people the same sheet of paper where there is a character description. People are supposed to rate on the scale of 1 to 10 how much it applies to them, but the point is that everybody gives it a really high rating because it includes such generic qualities (like being lazy sometimes, wanting to do good, being pretty smart in relations to some things etc.)? I went to a lecture at the local university when I was around 13 and they performed this test on all the audience and I've been trying to find out what it's called ever since. --BiT (talk) 00:50, 13 March 2009 (UTC)

It's the basis of most palm-reading, tarot card readings and astrology predictions. Cold reading, the Forer effect (also called the "Barnum Effect"), Subjective validation, Cognitive bias...these are all related to this effect. I don't know which particular term psychologists use. SteveBaker (talk) 01:06, 13 March 2009 (UTC)

No, it's not related to palm reading or tarot cards. What you're talking about is the Myer-Briggs test. The test is dependent on how self-aware or honest the test-taker is so some people argue the validity of the results, but the theories independent of that are pretty interesting. --75.34.179.39 (talk) 18:39, 17 March 2009 (UTC)

You might also be interested in Barnum effect. --ReluctantPhilosopher (talk) 13:55, 20 March 2009 (UTC)

Worms in face

Hi,

Just saw a video [1], showing tiny worms crawling out of someone's face.

Just what is this worm?

Thanks PrinzPH (talk) 01:21, 13 March 2009 (UTC)

Bloody hell. It looks like all the guy's whiteheads are trying to crawl out of his face and escape. One of the comments on the video suggests that this condition may be related to eating parasite-ridden seafood - and several others suggest that it is best treated by rubbing cockroach juice into the skin. I'd really like to know more about this myself. There's just something incredibly compelling about videos of other people having parasites removed, isn't there? --Kurt Shaped Box (talk) 02:28, 13 March 2009 (UTC)

My dad knew someone with untreated worms, which he would occasionally pull out of his arm as a form of entertainment. For some reason, that man didn't have a wife or girlfriend. StuRat (talk) 05:19, 13 March 2009 (UTC)

_{Really? I would have thought the man would have had plenty of bait for catching women...} —Cyclonenim (talk · contribs · email) 07:43, 13 March 2009 (UTC)

Stuff like that makes my skin crawl.91.111.85.208 (talk) 13:36, 13 March 2009 (UTC)

The skin does not look inflamed, and the "worms" (and I do think that is what they are) do not seem to be erupting in any consistent way with regard to pores or lesions. The way the gloved hand keeps rubbing the skin just before the worms appear makes me suspect the worms are being applied rather than being brought out from deeper tissue. I'm not familiar with any human parasite that would appear in this way, nor would I expect one to affect the face so diffusely without skin changes. I think it's being misinterpreted. Just my sense of it, not enough info to be dogmatic, but I think Worms on face would be a more accurate heading. --Scray (talk) 00:51, 14 March 2009 (UTC)

I decline to view that video, but aren't there some sorts of flies that lay their eggs on an animal's skin that burrow under the surface, and the maggots feast on the fresh flesh when they hatch? -- Deborahjay (talk) 22:19, 21 March 2009 (UTC)

Pressure ridges in ice

Reading about pressure ridges, I was curious: does this involve strictly cracks, or does it include other phenomena also? The picture to the side I took yesterday at a lake that exhibited pressure ridges (see another picture for what I mean), but it also had an extremely bumpy surface at one edge. Could this be related to the pressure ridges? Nyttend (talk) 01:36, 13 March 2009 (UTC)

This sounds like a question for CambridgeBayWeather. Deor (talk) 01:59, 13 March 2009 (UTC)

I would think that bumpy ice is formed when water leaks up through cracks out onto the smooth ice surface and freezes there. StuRat (talk) 05:10, 13 March 2009 (UTC)

Yes, I've seen that before. Also, especially on the edges while the ice is still forming there tends to be a layer of water on top of the ice, and the movement of the water from wind and currents can cause the ice to form in less than perfect sheets. 219.102.220.90 (talk) 06:35, 13 March 2009 (UTC)

I added to the Pressure ridge article that they are also found on sea ice, probably more common due to the larger expanse of ice, added an image and a link to Commons. Google has some good pictures as well. The effect in the picture is probably created in the way that StuRat and 219.102.220.90 describe. It could also be caused by an stream where the inflow is going over the top of the ice and then freezing as per 219. Strangely enough the effect in the picture is not that common up here. Enter CambridgeBayWeather, waits for audience applause, not a sausage 16:23, 13 March 2009 (UTC)

Perhaps because the freezing process occurs quicker? I'd love to time researching the languages up there some day. 219.102.220.90 (talk) 23:36, 13 March 2009 (UTC)

Formula Unit vs Empirical Formula (Ionic Compounds)

Hello. What is the difference between the formula unit and the empirical formula for ionic compounds? Thanks in advance. --Mayfare (talk) 01:59, 13 March 2009 (UTC)

Aren't they the same? Formula unit and empirical formula seem to be the relevant articles. I think there might be some pathological chemicals which are exceptions, where the ratio of atoms does not seem to make sense based on electronegativities or "expected" ionization states; in those cases, the empircal formula would be the measured ratio of atoms as determined by elemental analysis (e.g. by mass). Nimur (talk) 04:30, 13 March 2009 (UTC)

Something like that, yes - perhaps look into Mercurous chloride or similar. 78.151.212.201 (talk) —Preceding undated comment added 10:31, 13 March 2009 (UTC).

Is there a theoretical maximum upper limit to handgun size?

Recently I've heard about people building revolvers that can fire .600 Nitro Express, .700 Nitro Express, .50 BMG and 20 mm caliber rounds. Most of them have been one-off custom jobs, but the former is actually being mass-produced by at least one company.

So, is there actually any sort of upper limit to how large we can make a handgun? --90.240.240.251 (talk) 05:20, 13 March 2009 (UTC)

Well, how much can you lift with one hand? It's mostly a question of weight and recoil, I would think. The gun has to be capable of being aimed and fired without knocking the wielder off his feet. This would be affected by both the size of the projectile and the amount of propellant. A related factor would be capacity - how many rounds should it carry? More rounds, more weight. Hm. Turns out I have more questions for you than answers! - Eron^Talk 05:27, 13 March 2009 (UTC)

Yes. The limiting factor would probably be human lift strength. If you dispense with niceties like ammo and reloading, and focus on projectile diameter, you could theoretically launch a light-weight bullet the size of a dinner plate. Such a bullet would be of negligible actual use, being severely limited in range, accuracy, and damage, but hey, you'd have the biggest gun. As far as practical guns are concerned, you'll probably find the upper limit already available for purchase in one form or another, depending on your particular value of "practical" (0 = dinner plate). In handgun size, like many other things, bigger is not necessarily better. – 74  07:53, 13 March 2009 (UTC)

Yeah, with these 'big guns' it sounds as though we're already getting into the realms of pistols that could only really be fired repeatedly with any accuracy by a Terminator. Sure, if you needed to take down a fully-grown, angry African Elephant or Rhino at close range before it flattened you, then something like the above might be useful - but a pistol that weighs six kilos is a heck of a lot to lug around in the wilds, on a 'just in case' basis (I think that the standard, tried-and-tested elephant rifles are actually lighter than this!). --Kurt Shaped Box (talk) 19:44, 13 March 2009 (UTC)

According to The Rifle and Hound in Ceylon, which is a bit outdated of course, the obvious solution is to exploit some natives as the carriers for each British man's armament:

• 4 Double-barrled No. 10 bore, "of such power in metal that they weigh fifteen pounds each"
• A No. 10 twelve-grooved rifle (rifled preferred for elephant shooting over smooth-bores, though much disputed)
• A four-ounce single-barrel rifle weighing 21 pounds
• One long two-ounce (bullet) rifle weighing sixteen pounds
• Several smooth bores and fowling pieces (which do not count toward the total armament count)

It's hardly a fair fight for the elephant, with that armament. But a fair fight - "this is a foreigner's notion of the chase; he hunts for the pot; and by Englishmen alone is the glorious feeling shared of true, fair, and manly sport." Nimur (talk) 20:26, 13 March 2009 (UTC)

Hey, it sounds a heck of a lot more sporting than one of those canned hunt jobs. Yep, you can now go to South Africa and shoot semi-tame elephants at point-blank range from the comfort of a Jeep or your favourite hunting chair without having to hump the heavy ordnance around (five shot .600 Nitro revolver - five elephants for the bag?). I can't help but feel that we've lost something along the way. --Kurt Shaped Box (talk) 21:07, 13 March 2009 (UTC)

That sounds really awful. Canned hunting? Where's the sport? "Who would shoot a hare in form? who would net a trout stream? who would hit a man when down? A Frenchman would do all these things, and might be no bad fellow after all. It would be HIS way of doing it." Nimur (talk) 21:20, 13 March 2009 (UTC)

Funnily enough, that quote reminded me of something one of the S.African canned hunt operators said when interviewed by a disapproving Louis Theroux. Basically, he said that this (canned hunting) was something that worked in a South African context, stating that the proliferation of CH ranches in the last decade has been beneficial from a conservation standpoint in the country - as the hunters' considerable incoming funds have allowed tens of thousands of acres of natural habitat to be purchased and protected (by armed guards and 50ft fences!), in a pristine state (as opposed to say, being razed for intensive farming) and also, that by breeding endangered species to be put to the foreign gun and (literally) putting a high price on their heads, a tangible financial interest in ensuring the proliferation of the various species has been created (yaknow, give something a value and The People Will Take An Interest). It's an interesting argument, at least. --Kurt Shaped Box (talk) 03:47, 14 March 2009 (UTC)

I'd think the recoil would be the bigger issue. It would depend on both the caliber and "load". Firing too much bullet would cause a recoil which would make the gun move out of position for the next shot. This would make such a gun less effective than one with a more reasonable size. StuRat (talk) 14:50, 13 March 2009 (UTC)

There are widely varying theories of lethality for various calibers (it seems to amount mostly to situational needs and personal preference). I would posit that the mainstream available guns are manufactured in sort of a "bell curve" of available calibers because those dimensions are best-suited for their lethality. For example, although a Desert Eagle may pack a punch with a single round, as a weapon overall it is probably less "effective" than, say, a Beretta 92 (with a dramatically smaller bullet). As such, few organizations use Desert Eagles (and those who do very likely use it for intimidation-factor, rather than combat effectiveness). This is of course a judgment call based on a lot of estimated factors; but the US Army seems to agree - when it comes to caliber, smaller is better. Nimur (talk) 15:30, 13 March 2009 (UTC)

When it comes to a (non sniper) battlefield situation, the difference in tactical terms between killing and merely wounding the enemy is not particularly great. Either way, you've just shot a man, who has fallen over in the mud and now has two or three of his comrades kneeling around him, trying to plug the holes and stop him from leaking (and also not pointing their guns at you). If he lives, he won't be up and fighting again for a while, if ever again. So, if you don't strictly *need* to kill your enemy with one shot to take him and his cohorts out of the fight, then why not use a smaller, lighter round and benefit from the decreased recoil and increased capacity? --Kurt Shaped Box (talk) 20:01, 13 March 2009 (UTC)

That sounds like a reasonable analysis of conventional warfare, but I'm not sure if it applies as well to the modern terrorist. That is, if they are able to move, a suicide bomber will likely still detonate his explosives, and nobody is likely to attempt a rescue of a suicide bomber, in any case. StuRat (talk) 23:41, 13 March 2009 (UTC)

Kurt: I would expect that armies want more stopping power from a more powerful round. bibliomaniac15 04:00, 14 March 2009 (UTC)

Take a look at the articles on Punt guns and on recoilless guns. Especially the latter, as it explains how to deal with the recoil problem. --Dr Dima (talk) 22:37, 13 March 2009 (UTC)

Traditional "recoilless" techniques are of very limited use in a handgun, where discharging anything behind the gun would prove rather hazardous for the wielder. Still, recoil can be managed by trading off against a different parameter: increasing gun mass, reducing powder load, reducing bullet mass, etc. – 74  02:11, 16 March 2009 (UTC)

The Gyrojet of Man from UNCLE fame fired a rocket propelled slug. It came out of the barrel at quite low velocity, so no recoil to speak of. At least in the Man from UNCLE version, the gun itself was very lightweight (didn't need much strength) and could be mistaken for a toy. 75.62.6.87 (talk) 22:10, 14 March 2009 (UTC)

Toilet seat warmers

Sorry, two questions! The first is about the toilets we have here with seat warmers on them. I've heard in the past about bacteria and parasites that can survive x amount of time after initial contact on places like toilet seats (but probably more often on door handles and the like), and I'm just wondering if seat warmers wouldn't have a significant effect on that, possibly keeping these things alive until the next guy comes. 219.102.220.90 (talk) 06:27, 13 March 2009 (UTC) I've taken the liberty of splitting your double-question into two separate questions because otherwise the answer thread(s) will be horribly confusing! SteveBaker (talk) 10:47, 13 March 2009 (UTC)

Bacteria on things like a toilet seat probably don't die through lack of warmth over a period of hours. But what the warm seat MIGHT do is allow them to multiply - which might be more serious. However, there is unlikely to be much in the way of nutrients - so I suspect there is no great risk. At any rate - as careful (and a little obsessed) as the Japanese are about safety in general - and about toilets (we British would NOT want our toilets to talk to us!) - I'm sure they've tested these things for safety. SteveBaker (talk) 10:47, 13 March 2009 (UTC)

Don't worry; my toilet doesn't talk to me. It has a power freshener, makes a waterfall sound when I sit on it, and sprinkles my anus with warm fluid. 219.102.220.90 (talk)

On a dry, nonporous surface, I suspect that warming will have little effect — and may actually shorten the viable lifespan of any pathogens by hastening evaporation. As well, in addition to warmth and moisture, growth of pathogenic organisms will require a food source — and there's very little for a bacterium to eat on a toilet seat.

In practice, the bacterial counts on a toilet seat are usually quite low, and most pathogens aren't capable of entering your body through the firm barrier of your intact posterior. Surfaces in your home that generally host more bacteria than your toilet seat include: your refrigerator door; kitchen countertop; sinks and faucets throughout the home; kitchen sponge or cloth; dish towels; the typical child's toy...[2]. TenOfAllTrades(talk) 13:44, 13 March 2009 (UTC)

This is slightly tangential, but it's worth saying. In this supposed "era" of energy-awareness and conservation, while everyone is converting incandescent lightbulbs to cold-cathodes to save thirty or fifty watts, people are still finding amazing ways to spend fifty or a hundred (or fifty-thousand) extra watts "warming" toilets and roadways. This reflects dismally on our prospects for energy conservation. Nimur (talk) 15:37, 13 March 2009 (UTC)

Yeah, it's pretty sad, I know. There is a button for "energy conservance mode", but it doesn't seem to change the temperature of the seat at all, so I can't imagine how much energy it saves. Maybe it just turns it off during the wee hours. *cough*. 219.102.220.90 (talk)

Nothing feels more refreshing than sitting on a toilet seat that is actually cold. A warm seat just serves to remind you that other people use the bathroom too. Livewireo (talk) 15:58, 13 March 2009 (UTC)

But it's not quite as refreshing a second later, when you realize that it only feels cold because it's wet. :-) StuRat (talk) 01:43, 14 March 2009 (UTC)

Ah - I understand - so you heat the seat so you can be sitting in a puddle of someone else's pee without noticing that it's wet. Got it. Thanks! SteveBaker (talk) 02:33, 14 March 2009 (UTC)

You get used to it after a while. :) 219.102.220.90 (talk)

Thanks!219.102.220.90 (talk) 03:24, 14 March 2009 (UTC)

Donating bodies

The second question is about body donation. I assume that the laws vary a lot depending on where you live; as you can probably tell from my IP I'm in Japan, but I'm Canadian. I have no idea if they have a body donation program in Japan, but I'm pretty sure they do in Canada. Most of the information on the web is about American medical schools so I'm not even sure about that. Also, if I were to want to donate my body to an institution that was outside of my country of citizenship (assuming I was Canadian, or American if there's no information), would that be possible? Thanks! 219.102.220.90 (talk) 06:27, 13 March 2009 (UTC)

Many countries won't even allow you to donate blood if you have lived overseas in the last (say) 10 years - so there is no doubt that organ donation for medical purposes is going to be impossible in some places. However if you are donating it for research, then I don't see why that would be a problem. You're going to have to find out what the laws are where you live because it's highly unlikely that they'll be the same everwhere. SteveBaker (talk) 10:47, 13 March 2009 (UTC)

• Donating your body to science may be possible, but expect to pay for the transport yourself. The University of Tennessee Body Farm has such a clause.[3] - Mgm|^(talk) 11:30, 13 March 2009 (UTC)
  • The body farm issue has came up before Wikipedia:Reference desk/Archives/Science/2008 October_22#UK BOD. If you just want to donate your body to science (be it for research or practice) I'm quite sure there will be progrms available in Japan. If you wan't find anything you may want to check with universities particularly those involved in medical research and attached to teaching hospitals. Nil Einne (talk) 11:36, 13 March 2009 (UTC)

Are psychological illnesses contagious?

If you spend too much time with aggressive people, for example, does this make you aggressive?--80.58.205.37 (talk) 12:17, 13 March 2009 (UTC)

Well, aggressiveness isn't technically a psychological illness, so the answer to your question below is that it depends on the personality. The human mind has a tendency to mimic others and try to fit in with its situation. OTOH, there are people whose personalities are such that they can at least minimize the aggressiveness of some. (Take, for instance, a good counselor who helps violent youth to try to get turned around all day.)

Psychological illnesses, OTOH, aren't contagious int he sense you can actually catch bipolar disorder, for instance. Being around poeple who are totally bipolar all day can wear one down and cause anxiety-related disorders, though.

But then,t here's also the joke that someone will repeat, so it may as well be me - "Insanity is hereditary - you get it from your children." :-)172.131.176.22 (talk) 12:54, 13 March 2009 (UTC)

Depending how one reads your questions, there are a couple of answers. To the general are psychological illnesses contagious?, I suppose one could point to something like mass hysteria for an instance of a bona fidepsychological condition.

The second question – on aggressiveness – could be rephrased as, are modes of social interaction learned? The biggest part of that answer is almost certainly yes. We tend to pick up and internalize cues for appropriate interpersonal conduct from those around us. TenOfAllTrades(talk) 13:28, 13 March 2009 (UTC)

Yes, I expressed myself poorly. I mean both - are some illnesses - like depression or anxiety - 'contagious'? And are character or behavior traits 'contagious'? —Preceding unsigned comment added by 80.58.205.37 (talk) 13:34, 13 March 2009 (UTC)

I would expect that the more common effect would be that people would attempt to keep their mental illness hidden if they receive negative feedback and not keep it hidden if it is "accepted". This wouldn't apply to severe psychoses, but only to those conditions which are somewhat controllable. For example, someone with OCD who needed to repeat some phrase every time a door is opened could probably repeat it in their mind if they were laughed at whenever they said it out loud. On the other hand, if they were around others with OCD or others who were more accepting of OCD, they might say the phrase out loud. This could give the appearance of "OCD being contagious". StuRat (talk) 14:14, 13 March 2009 (UTC)

I haven't read any research on your question, but it would not surprise me. I have worked in psychiatric hospitals and it was really tough for me to spend so much time every working day with people who feel really bad, who suffer from deep depression or deep anxiety. I think it would have been detrimental for my own mental health if I would have stayed there. Of course, this only goes for those of us who are vulnerable in that way, but that is usually the case with contagious diseases. Lova Falk (talk) 17:11, 13 March 2009 (UTC)

The following article might be helpful, you might not be able to read the whole thing if you aren't a new scientist subscriber, but I seemed to be able to get most of it even when I was logged off.

http://www.newscientist.com/article/mg20126881.600-how-your-friends-friends-can-affect-your-mood.html?page=1

131.111.8.97 (talk) 18:24, 13 March 2009 (UTC)

Well, I suppose that psychological conditions could be passed via power of suggestion, but contagious implies that there is a contagion, i.e. a substance which could carry the dissease with it. I mean, if you get depressed being around depressed people all day, that doesn't mean that there was a germ or virus or something that carries the depression, it just means that the emotional state of the people you hang around with can effect your own emotional state... --Jayron32.talk.contribs 00:06, 14 March 2009 (UTC)

I've heard the word "contagious" used in a more general way quite often, as in "laughter is contagious". Then there are a small percentage of mental disorders which may be directly caused by a contagion. On the other hand, general diseases, some of which are contagious, may also cause some mental problems, such as depression, in some people. StuRat (talk) 00:56, 14 March 2009 (UTC)

See Borna disease. --Arcadian (talk) 05:23, 15 March 2009 (UTC)

UV light to reveal body fluids // cat spray

Two part question: -Use of UV light to highlight body fluids on surfaces as seen in crime dramas: Is there a name for this and do we have an article on it? If not, is there any trick to it, or do you just need a UV lamp and dark conditions? -Would this technique work to highlight "cat spray" (not urine, but the oily, stinky stuff they use to mark territory)?

Maybe you can guess -- a cat sprayed in my basement, and I can't find the exact spot, so I can't do much to clean it up! ike9898 (talk) 14:07, 13 March 2009 (UTC)

That's photoluminescence, and specifically fluorescence, although I didn't locate an article specifically about your application of finding bodily fluids. Another way to find the cat pee is to bring a cat or dog down there, which will immediately locate it for you. Just make sure you don't bring an intact male, or he will feel the need to add his own contribution to the spot. And, while we're at it, why not get the cat in question neutered to prevent a repeat ? StuRat (talk) 14:24, 13 March 2009 (UTC)

Using a dog is a great idea, which I think I'll try tomorrow! As to the neutering, this is what everyone I talk to brings up. Both my cats (males) are neutered and have been since they were adopted as kittens. I have caught one of them spraying a few times over the years. So I don't think it's impossible for a neutered male to spray, just a lot less likely. ike9898 (talk) 14:58, 13 March 2009 (UTC)

A quick skim of some fairly reliable sources supports the notion that neutered males can spray. ike9898 (talk) 21:38, 13 March 2009 (UTC)

Yea, I guess that happens if they are too old when neutered. Another factor in animal spraying is that they all feel the need to spray whenever they smell the spray from another animal. Having two males makes them particularly likely to try to best one another. If you can get all the smell out and use a powerful deodorizer, you might stop a recurrence. StuRat (talk) 23:36, 13 March 2009 (UTC)

See luminol. --Sean 16:32, 13 March 2009 (UTC)

Cat urine definitely fluoresces under a blacklight. No luminol needed, no special tricks: just turn the lights out and the blacklight on, and make a basement sweep. I'm pretty sure that "spray" is just a special case of urine. The lights are fairly cheap, so I would definitely give it a try. - Nunh-huh 16:45, 13 March 2009 (UTC)

Does the urine fluoresce after drying? And, does that happen with dog or human urine as well? -hydnjo (talk) 19:48, 14 March 2009 (UTC)

Yes and yes. The components which fluoresce aren't liquid, so can't evaporate. StuRat (talk) 04:23, 15 March 2009 (UTC)

Update I tried two different UV lamps. Both effectively revealed the location of the urine spots, but one of the lamps made the spots glow much brighter (at least one of these two lamps emits UV in a different range that a "Blacklight" does). Anyway, I cleaned the spots, the smell went away, and then two days later the cat did it again! ike9898 (talk) 21:39, 16 March 2009 (UTC)

That's a cat for you.... Try it one more time: clean it, then crinkle up some tin foil and spread it over the previously affected area. Apparently peeing on tin foil isn't quite so much fun for kitty. Some folk also put double-sided tape on the floor near the area (cats don't like to walk on it) and use citrus scented spray, which cats tend to avoid. - Nunh-huh 21:45, 16 March 2009 (UTC)

I've ordered some pheromone diffusers that supposedly have a calming effect on cats. And some enzyme based cleaner. Wish me luck. ike9898 (talk) 13:50, 17 March 2009 (UTC)

Uranian axis tilt > 90 degrees?

The axis of the planet Uranus is said to be tilted about 98 degrees, i.e., it is essentially on its side and "rolling" through its orbit. Cute simplistic imagery aside, why is it that this value is not rather given as about 82 degrees, that is, less than a right angle? As a somewhat absurd analogy, the axis of the Earth is not said to be tilted at 157 degrees.

I thought it might be because the pole found on the south side of the ecliptic was actually closer to the planet's North magnetic pole, but the diagram in the article suggests otherwise, if I read it correctly.

Why is this convention held? Baccyak4H (Yak!) 15:01, 13 March 2009 (UTC)

I'm wondering if it has anything to do with the polarity of the rotation ("clockwise vs. counterclockwise"). I have to think about this for a while to see whether this actually makes any sense (as the planet revolves around the sun); but it may be a greater-than-90-degree tilt to preserve the correct rotation direction as most of the other planets. Nimur (talk) 15:42, 13 March 2009 (UTC)

Also see IAU/IAG Working Group on cartographic coordinates and rotational elements[4], which explicitly lays out the justification for picking which pole is "north", while acknowledging that this is a matter of preference. "The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system. The direction of the north pole is specified by the value of its right ascension α0 and declination δ0." They do not seem to give the "97.77°" number. Note that the description of Uranian rotation is sometimes given as "retrograde" and sometimes not - so it seems like there is not a total consensus on which pole is "north." Nimur (talk) 15:50, 13 March 2009 (UTC)

In other words, the issue is whether you view the direction of rotation as defining which end of the axis is north. In my opinion that is the sensible thing to do and it means that the axis is inclined by 98°. The IAU/IAG group has the opposite opinion. In that case the axis itself does not carry an orientation so it is natural to refer to it as inclined by an angle less than 90°, i.e. by 82°. You then have to add that the rotation is retrograde. By the way, the same issue arises for Venus and Pluto. --Anonymous, 19:38 UTC, March 13, 2009.

Nimur and Anonymous explanations are correct. I just want to point out that the description of Uranus motion as "rolling through its orbit" doesn't make sense and should be avoided. Dauto (talk) 19:45, 13 March 2009 (UTC)

Looking southward onto Uranus from the north side of the ecliptic, the planet would look more like it's rotating in retrograde motion than not. Venus has an axial tilt of nearly 360 degrees, due to its retrograde motion, but that likely depends on the convention used. ~AH1^(TCU) 22:34, 13 March 2009 (UTC)

I think you were turned the wrong way when you said 360°; it should be 180°, right ? StuRat (talk) 23:29, 13 March 2009 (UTC)

Likewise, many sources list the axial tilt of Venus as a more absurd 177 degrees. The convention seems to be that the "north pole" is that pole which, if you call it north, will present a planet that rotates the same direction as Earth. So basically, depending on your perspective, Venus is either spinning "backwards" (if you accept that it's north pole is the one closest to the orientation of the Earth's north pole) or "upside down" (if you accept that north is defined by the direction of spin). The same logic applies to Uranus, and it really doesn't matter which you pick. Either Uranus has an 82 degree tilt, and turns backwards (i.e. retrograde) or it has a 98 degree tilt, turning in the same direction as Earth... --Jayron32.talk.contribs 00:00, 14 March 2009 (UTC)

Many thanks for the replies. The parity of the rotation makes sense. Baccyak4H (Yak!) 03:56, 14 March 2009 (UTC)

Any difference between brush with a dry or wet toothbrush?

I've noticed a few habits when people brush their teeth. Some put toothpaste on a dry toothbrush and proceed to brush. Others put toothpaste on, then wet the toothbrush with water. And still others wet the toothbrush, put toothpaste on, then wet it again. Is any method "better" than others? I would tend to think the dry brush would have a more abrasive effect since it's not being diluted by water (at least initially before its mixed with saliva). --70.167.58.6 (talk) 16:27, 13 March 2009 (UTC)

A clinical comparison of three powered toothbrushes found that the toothbrush filaments on some toothbrush models may bend slightly when wet. There did not seem to be any effective change in the resulting cleaning capability. Nimur (talk) 16:44, 13 March 2009 (UTC)

Keep in mind that, as our toothbrush article indicates, abrasive is not really what you want while brushing your teeth, as it can damage the enamel. --140.247.250.160 (talk) 19:59, 13 March 2009 (UTC)

I'm one of the wet-brushers (I wet it after, but I'll attribute that to laziness), and there is a clear reason for that, or at least there is to me. Putting a dry toothbrush into your mouth instantly lowers the average saliva level in your mouth (because loose saliva will attach to the brush head) and since most gel toothpastes foam better when mixed with water (as with soaps) wetting the brush keeps the inside of the mouth salivized and facilitates the toothpaste foaming process. I find brushing with a dry brush makes it difficult to distribute the toothpaste evenly among my teeth, as it clumps up and gets pushed to the side when it should be getting mixed into the bristles. 219.102.220.90 (talk) 23:51, 13 March 2009 (UTC)

Volunteering extra information: I have in my possession books published about thirty or forty years ago that were against brushing teeth with toothpaste. Using a dry brush was recommended, and for tough cases, brushing your teeth with salt was deemed the best solution. --Ouro (blah blah) 17:26, 14 March 2009 (UTC)

Breathing dust from cat litter, unhealthy?

When I clean my cat litter, it produces an awful amount of dust. I'm wandering whether it can be unhealthy to breath that dust? --Phenylalanine (talk) 16:48, 13 March 2009 (UTC)

Yes. Don't you know we have an article on everything? See here and also here. Matt Deres (talk) 20:04, 13 March 2009 (UTC)

Virtually any type of dust can cause pneumoconiosis. Certain chemicals (notably asbestos and coal soot) are so problematic that they have special medical terminology just for them. However, the sorts of occupational exposures are usually daily interactions over many years. Short-term exposure to small quantities of dust is probably not harmful, but if you find it aggravating, you can consider wearing a disposable dust mask (our article focuses mostly on respirators, but I'm thinking of simpler cloth or fiber masks like this). They are very cheap, and you can get a lot of uses out of them. Nimur (talk) 20:07, 13 March 2009 (UTC)

It may not be unhealthy but it's definitely smelly!!--TammyMoet (talk) 21:09, 13 March 2009 (UTC)

Thanks to all for the useful information! --Phenylalanine (talk) 22:44, 13 March 2009 (UTC)

Wait, wait! There's more about the smell. -hydnjo (talk) 23:41, 13 March 2009 (UTC)

Adding on to what that article notes, the pine-based cat litter is, unlike the silica or clay, nearly dust-free. It alone has earned the Nunh-huh seal of approval. -Nunh-huh 01:35, 14 March 2009 (UTC)

So how do they get rid of the formaldehyde? Or do they? AFIK pine naturally emits formaldehyde. It's part of the "piney" smell. I googled but there seems to be no mention of that. BTW> There's also recycled paper litter and wheat based litter if you don't want to go with clay. Printing ink has some very nasty chemicals in it, so the ink free varieties should be better. Baking soda helps against the smell. 76.97.245.5 (talk) 08:18, 14 March 2009 (UTC)

Baking soda also fizzes when urine is sprayed on it, and the result of that is that kitty point blank refuses to use the litter tray and pees elsewhere! --TammyMoet (talk) 14:27, 14 March 2009 (UTC)

Re the formaldehyde question: From this site "According to the manufacturers, pine-based varieties are made from recycled shavings, which are kiln dried to remove aromatic oils, and then compressed into pellets." And from the Feline Pine site "Feline Pine® is 100% natural, biodegradable pine that has been heated and pressurized to remove any harmful wood oils." -hydnjo (talk) 19:27, 14 March 2009 (UTC)

Thanks, that explains it. Re.: Baking soda Tammy, cats have preferences. We had one who insisted on a particular brand of cat litter and you can imagine what happened when we moved to a place where that wasn't available! If you mix it in with the litter and don't use too much I haven't had one yet who refused to use the box then, but you never know. 76.97.245.5 (talk) 09:39, 15 March 2009 (UTC)

Toxoplasmosis is aerosolized. --Arcadian (talk) 05:16, 15 March 2009 (UTC)

Molecular bio technique: protein expression?

I'm new to protein expression, and I could use a little starting out advice. I have a human gene that has already been cloned into a pCMV-SPORT6 mammalian expression vector under a CMV promoter; the vector also contains an AmpR selectable marker. The protein involved is a very hydrophobic ER membrane protein that is also post-translationally modified, so bacterial expression isn't really an option. My questions are:

1. Since the vector has AmpR, is there some mammalian (or other eukaryotic) selection agent I can use, or do I have to subclone the gene into another vector that can be used for selection?
2. What types of cell lines are usually used for expression of intracellular membrane proteins?
3. Are there any particular pitfalls, gotchas, or other horror stories that I should know about before I begin? —Preceding unsigned comment added by 69.127.231.186 (talk) 16:54, 13 March 2009 (UTC)

Ampicillin resistance will only be useful for bacterial selection (i.e. propagating your clone). For selection in mammalian cells you'll need something like G418 selection, which will require you to subclone into another vector. You could also try expression using baculovirus-infected insect cells. Choice of cell line probably depends on what's available at your institution (it's usually easy for someone to split some cells for you to start growing) but you may want to find the most physiologically relevant cell type. Lots of people just use chinese hamster ovary (CHO) cells, but if you know what cell type your protein is expressed in, you could try to pick a cell line from that tissue. The ATCC website has tons of info about different cell lines (http://www.atcc.org/Portals/1/Pdf/CellCatalog/Tools_Models.pdf) that you can sift through. The major "gotchas" are going to come in the protein purification step, especially if you have an integral membrane protein that is hydrophobic and post-translationally modified. Good luck! --- Medical geneticist (talk) 18:54, 13 March 2009 (UTC)

M.g.'s response is excellent as always, but I'd add that this answer illustrates the utility of being able to move your gene from one vector to another until you find the right system, and the Gateway system can be your best friend in this situation (no conflict of interest to report!). The "destination" vectors they offer (for a wide variety of host cells) include N- and C-terminal extensions that increase solubility and/or offer tags (like 6His, myc, etc) for purification. Of course, they offer all sorts of selectable markers. Transfers among vectors are isothermal and nearly 100% efficient. Getting it into the Gateway system can be tricky but their tech support is helpful. Hope this helps. --Scray (talk) 00:30, 14 March 2009 (UTC)

It looks like a great system, but the costs are... prohibitive. Unfortunately, we're limping along financially as it is. 69.127.231.186 (talk) 03:18, 14 March 2009 (UTC)

Understood, but don't underestimate the savings one realizes when an experiment works. --Scray (talk) 03:27, 14 March 2009 (UTC)

Need information from an Icarus article

I'm hoping someone here has access to this journal article:

• Zellner, B (March 1985). "The eight-color asteroid survey: Results for 589 minor planets". Icarus. 61 (3): 355–416. doi:10.1016/0019-1035(85)90133-2. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

If you do, I'd like to know if it provides a classification of asteroid 243 Ida, when the spectroscopic measurements were taken, and what pages of the article the information appears on. Thank you. Wronkiew (talk) 17:55, 13 March 2009 (UTC)

Not an answer, but you could always try WP:WRE. —Cyclonenim (talk · contribs · email) 22:35, 13 March 2009 (UTC)

Thanks for the tip. I posted this request at WRE as well, maybe someone has access to the paper there. Wronkiew (talk) 17:13, 14 March 2009 (UTC)

Article obtained, thanks again. Wronkiew (talk) 16:06, 16 March 2009 (UTC)

Evaporation of methanol/water mixture

Hi,

If I have a solution of about 50% methanol in water (plus salts etc), is it possible to differentially evaporate only the methanol, leaving only water? For a bit of background, we're trying to remove this from a frozen cell culture pellet in a lypholyser/freeze drier.

Any physical chemists or anyone know anything about this topic?

Thanks!!!

77.12.3.80 (talk) 18:17, 13 March 2009 (UTC)

Since ethanol methanol has a boiling point of 78.4 64.7°C and water has a boiling point of 100°C, heating it to a temp between those two should cause the ethanol methanol to boil off and leave most of the water. This assumes that nothing else is present, but you said some salts are present, which could alter the boiling point of the water. Also, be careful when boiling off ethanol methanol, as it is flammable. That is, don't let it vent into a lab where there are open flames, but rather do this under an exhaust fan. You did ask about evaporation, though, not boiling. This would work, too, but could take a very long time. The colder the sample, the longer it will take. StuRat (talk) 23:19, 13 March 2009 (UTC)

The OP is asking about methanol, not ethanol. As far as ethanol/water, nuh-uh, it forms an azeotrope. Franamax (talk) 23:30, 13 March 2009 (UTC)

Thanks for the correction, I've updated my post accordingly. As for the azeotrope issue, the next poster seems to have addressed that. StuRat (talk) 00:52, 14 March 2009 (UTC)

Azeotropes generally only occur at certain concentrations and pressures, for example with ethanol-water mixture, the azeotrope forms at a 95% ethanol/5% water mixture (hence, the maximum proof of liquor is usually 190 proof). We do have an article on Azeotropic distillation which discusses special techniques for seperating azeotropes. However, this forum post: [5] indicates that methanol and water do not form azeotropes at atmospheric pressure, which means that you should be able to get pure seperation using simple distillation techniques. this data table of azeotropic data indicates the same; that methanol forms no azeotrope with water. So if you heat the mixture to above the boiling point of methanol, which at atmospheric pressure is about 65 deg C, then you will be able to drive off all of the methanol and leave all of the water (as an aside, due to the fact that water still has a sizable vapor pressure at those temperatures, meaning that while you can leave behind pure water, if you cool and collect the methanol vapor, you will still have water in it... --Jayron32.talk.contribs 23:52, 13 March 2009 (UTC)

There's also membrane separation from what I looked ar earlier trying to find a solution. I think the problem here though is that the OP wants to keep the cell culture frozen, so 65 degC wouldn't do it. If the pellet can be thawed, then wouldn't dilution be simplest? Put the pellet on a filter and pour water on it, eventually there will be cells and water, with all the methanol flushed through the filter. (Just don't shake it at the same time, the methanol will get stronger!! :)

To do it in a frozen state, I think you would need something like a getter for methanol, i.e. some substance that would adsorb or fix the methanol and give it a lower vapour pressure. Perhaps enclosing the pellet in a separation membrane, with a drying agent on the other side? Then the methanol would sublimate and pass through the membrane, while the water stayed in vapour equilibrium on the pellet side. Franamax (talk) 03:35, 14 March 2009 (UTC)

banded krait bite

If bitten on hand by a banded krait snake, would it save life if hand was cut off soon after bite? —Preceding unsigned comment added by 72.160.181.221 (talk • contribs) 18:50, 13 March 2009

Let's hope this is not a medical advice question. If the venom has already entered the bloodstream, it will spread within a few seconds, so amputation is useless. If the krait venom is only in the tissues, it will spread diffusely, and so it's possible that an amputation may actually help. Field Manual 21-76 states clearly that in snakebite situations, amputation is commonly a result of too-late treatment, but it does not mention it as a precaution, in the event of snakebite.

“ The primary concern in the treatment of snakebite is to limit the amount of eventual tissue destruction around the bite area.

A bite wound, regardless of the type of animal that inflicted it, can become infected from bacteria in the animal's mouth. With nonpoisonous as well as poisonous snakebites, this local infection is responsible for a large part of the residual damage that results. Snake venoms not only contain poisons that attack the victim's central nervous system (neurotoxins) and blood circulation (hemotoxins), but also digestive enzymes (cytotoxins) to aid in digesting their prey. These poisons can cause a very large area of tissue death, leaving a large open wound. This condition could lead to the need for eventual amputation if not treated. Shock and panic in a person bitten by a snake can also affect the person's recovery. Excitement, hysteria, and panic can speed up the circulation, causing the body to absorb the toxin quickly. Signs of shock occur within the first 30 minutes after the bite.

”

I can find no references to "preventative" amputation. Amputation is not to be taken lightly, and should certainly not be performed by an amateur; this may cause collateral damage far worse than the original injury. Nimur (talk) 19:12, 13 March 2009 (UTC)

Well it certainly helped Hannibal at his time of need ;-) -hydnjo (talk) 22:59, 13 March 2009 (UTC)

I don't know about preventative amputation for snakebites, but preventative amputation is sometimes used in other cases, such as cancer. StuRat (talk) 23:12, 13 March 2009 (UTC)

In that case, a trained surgeon is present and has a little time to prepare - a krait bite's neurotoxin can kill a bull in under half an hour. A human, weighing an order of magnitude less than a bull, probably has an order of magnitude less time. That's not a lot of time to prep an OR! Nimur (talk) 23:44, 13 March 2009 (UTC)

Our article states that, "There are no authenticated records of human beings having been bitten." Not sure this is the snake one should worry about most. --Scray (talk) 02:05, 14 March 2009 (UTC)

Corneal diseases of less severity than Fuch's Dystrophy

Is there a corneal disease of less severity than Fuch's Dystrophy which has the similar effect of poorly regulating fluid transfer in the endothelium and can result in a reduced cell count in the endothelial layer? I heard of something like "Haltata" but could not find anything on the web or in Wikipedia. For symptomatic relief, I understand this condition can be aided by lubricative moisturizing drops as opposed to actually drying out the eyes with a hair dryer as suggested by Wikipedia's article on Fuch's Dystrophy. —Preceding unsigned comment added by Jaysfive (talk • contribs) 19:55, 13 March 2009 (UTC)

Why the location of the new Russian spaceport?

Russia is planning to construct Vostochny Cosmodrome in the Russian Far East, to reduce its dependence on the Baikonur Cosmodrome for low inclination or geostationary launches. They're planning on locating it in the Amur Oblast (although they don't decide as to where until next year). You would think that the primary criterion for a Baikonur-replacement site would be as low a latitude as possible (Baikonur is at 45°N). The Amur Oblast ranges only as far south as 49°N. On looking at the Russian Far East, there seem to be some rather nicer places to put such a facility: somewhere like Khabarovsk (which is at 48°N and which is near Komsomolsk-on-Amur, Russia's capital of aviation) or the flatlands north of Vladivostok (at about 44°N). Both are well connected to Russia's mainline railway network, and seem to be better situated with regard to weather, power, and supporting industry. The launch tracks from either would still largely pass over water, Sakhalin, and maybe the sparsely inhabited parts of northern Hokkaido. Surely every degree south would save fuel or afford more orbital flexibility. So my question is - what technical characteristic favours the inland Amur basin over these two maritime options? (or is there a political angle I've not considered?) 87.115.143.223 (talk) 20:25, 13 March 2009 (UTC)

Far be it from me to speculate, but there may be some ugly politics associated with launching spacecraft eastbound into the Pacific? Nimur (talk) 20:35, 13 March 2009 (UTC)

That's true, but missile/launcher capable powers are very careful to tell each other when they launch anything even slightly suborbital. No-one is going to mistake a Russian sat launch for a missile. Plesetsk is a former ICBM base (firing over the pole at the US) and no-one gets upset when they see a planned launch (often in a polar orbit) from there. 87.115.143.223 (talk) 20:47, 13 March 2009 (UTC)

I guess my point is not about true operational problems (as you describe, it is easy to avoid those). Most civilians have very little trouble cooperating internationally and making sure that their expensive rockets don't accidentally land where they are not supposed to. However, any civilian space-program always carries an implicit, public declaration of military missile capability for the nation it represents - and so there is a subtle, ugly undertone to any civilian launch (even if it carries the most benign and friendly scientific satellite). The act of launching the rocket is sort of a reminder to everyone: "We can launch something (wink wink nudge nudge) and fly it near/over your territory. By the way, this one is harmless." So, even though the construction of a civilian cosmodrome may truly have no sinister intent (conspiracy theories aside, and ignoring military-civilian collaboration projects) - there can still be political thunderclouds associated with it. Nimur (talk) 22:08, 13 March 2009 (UTC)

(Take a look at Poker Flat. A lot of awesome science is done there. It's about as far from "military" as I've seen, and I've been through my fair share of missile ranges). "The whole idea of tipping a rocket on its side was brand new," said Geophysical Institute Assistant Professor and HEX Principal Investigator Mark Conde. An 800 mile-long horizontal rocket-track on a civilian range which points northward from Alaska? Sure it was, Dr. Conde, sure it was. Nimur (talk) 22:13, 13 March 2009 (UTC)

And (as it's surely scarier to be on the receiving end) there wasn't a tizzy when they fired a Bulova missile from the White Sea at central Kamchatka [6] in November. 87.115.143.223 (talk) 20:59, 13 March 2009 (UTC)

Incidentally I think I've discounted some political issues:

1. invasion from China: both Vladivostok and Khabarovsk are of huge military significance to Russia: they'll defend them long after a dump like Amur has fallen
2. proximity to China (wherein countries get unnerved when rockets get launched very near their borders): the same is true for southern Amur - to get a decent distance from China in Amur they'll have to be at about 51°N - it doesn't seem worthwhile to build so far north, when they have Plesetsk.
3. flooding of the upper Ussuri River (for the Vladivostok option) - well, they're not cheap british housebuilders, so they're smart enough to find a big flat hill :)

87.115.143.223 (talk) 20:39, 13 March 2009 (UTC)

When governments build big things in the middle-of-nowhere provinces, it's often to create jobs where they're badly needed. So that's my guess --Pykk (talk) 20:51, 13 March 2009 (UTC)

Pykk's idea is reasonable. However, I'd think that a priority would be to ensure that no launch tracks passed over any other country, even "sparsely-populated" areas. Rockets leave toxic residue from the fuel downrange; Hokkaido is home to the minority Ainu people of Japan, so sparse population doesn't necessarily count; Russia and Japan are still arguing about those four islands from WWII; and I'm not a launch expert, but wouldn't the launch track tend to head a bit southwards anyway? I'd imagine the priority would be to ensure that you can get the payload into orbit entirely over your own territory and international waters. If that takes a little more boost, so be it. The Russians already have pretty powerful boosters anyway, the biggest in the world I do believe. Franamax (talk) 23:50, 13 March 2009 (UTC)

Rockets don't always go where you want them to either, and not hitting people when a booster fails is an important consideration. SDY (talk) 00:08, 14 March 2009 (UTC)

Thanks everyone; I think Franamax has it. Frankly I really doubt the Russians care very much about the nerves of South Korean and Japanese air defence officials, or the feelings of the people of Hokkaido, but I think they don't want to have to fly through Japanese airspace (and thus have to ask permission, rather than just give notice). As our airspace article notes, there's no real definition of how high a country's airspace goes, but I bet they're factoring in some possible future international agreement that puts it at the Karman line, and they need a few hundred miles of setback to make sure they're above that before they pass over Japan. That's essentially the arrangement at Baikonur; they'd still be ascending when they passed over China and Mongolia, but clearly high enough to be (or to claim to be) out of those countries airspaces. 87.115.143.223 (talk) 12:34, 15 March 2009 (UTC)

X-Z motorized stage

I am looking to buy or build a small motorized stage that can move a small, light weight object vertically ~3 cm and horizontally ~6 cm. This will be part of a micro imaging system. An interface for computer control would be a big plus, but manual toggle switches might work too. I have $1000+ budget, but a short time frame, so it needs to be something that can be bought or assembled off-the-shelf in a hurry. Anyone have any ideas of suppliers for this sort of thing? In the absence of something commercial, I've also been considering hobby items and toys that might be repurposed (e.g. Lego Mindstorms), so that kind of suggestion might work too. Dragons flight (talk) 23:52, 13 March 2009 (UTC)

Lego Mindstorms could EASILY do that - and at a couple of hundred bucks would be well within your budget. If you need to move in X, Y and Z then you'll need three motors (I forget how many you get with the standard set - so you may need to buy an extra. The motors come with 'rotation sensors' so you can figure out how far they've moved. There are also 'bump sensors' that you could place at one end of each 'track' so the computer can wind the motors in that direction until the sensor triggers so it knows where they are at the start of the run. There are 'rack and pinion' gears to translate rotary motion into linear motion.

The biggest issue is going to be precision. You have not said how precise or how smooth it has to move...and that's a HUGE deal. You can gear the system WAY down so it moves very slowly - but there is a limit to precision because Lego gears do not mesh particularly tightly - and there is a certain amount of backlash. There are a few tricks to help that - which we can discuss if you'd like. But if you are expecting (say) 1/10th millimeter precision - then it's going to be hard. 1mm precision is more do-able...but that's the critical factor here. There are HUGE numbers of online resources for Lego enthusiasts (they call themselves "AFOL's" - Adult Fans Of Lego) and there are a lot who have much mechanical/robotics expertise.

Interfacing to the Lego computer is very easy - there are lots of libraries out there to help you do that. It has a bluetooth interface should you want to interface things like keyboards - you can drive it with the keypad on any bluetooth cellphone! It can be hooked to the computer with a USB cable. The programming "language" it comes with is a graphical thing where you essentially draw a flow-chart of sorts. However, the AFOL's have written a C-like programming language called "NQC" (Not Quite C) that enables experienced programmers to work with it and feel right at home.

You'll probably find that the kit you get will be missing some parts you'll need for this project (although you might get lucky). If so then I strongly suggest you go to the http://www.bricklink.com/ site - where AFOL's will sell you any number of super-rare and specialised parts for pretty low $$$. That's MUCH less frustrating than scanning the shelves of Toys'R'Us hoping to find a kit with just the right gear wheel - and then finding you need to buy 20 sets to get the number you need!

SteveBaker (talk) 02:26, 14 March 2009 (UTC)

I have a target speed of ~0.5 cm/s horizontal and discrete steps of 0.5 mm vertically. Bricklink seems quite helpful. I was concerned that the parts in the default set didn't go all that far towards covering my needs. Dragons flight (talk) 04:04, 14 March 2009 (UTC)

I would probably take too long for you, but using a printer or scanner might work neatly. I haven't tried to control a modern printer precisely, but the older dot matrix epsom printers could be sent commands to nudge the roller or print head a bit at a time. Polypipe Wrangler (talk) 21:25, 14 March 2009 (UTC)

This is one of those problems that you can solve quickly or solve cheaply - but quickly AND cheaply is harder. I agree that you could certainly do a MUCH better job by repurposing other mechanism or having custom parts made...but that's either expensive or time-consuming. With Lego, you get cheap AND fast - but at the price of not being able to make a really powerful or really precise mechanism. However, you'll certainly be able to gear down a gear train so where you can reach the horizontal speed and the vertical 'step' size - but the problems will come if (for example) you command the system to go 2cm up and then 1cm down - and if you then expect to be 1cm up from where you started to a precision of within 0.5mm - that's tough because of gear backlash. However, if you've driven 1cm up and now you want to drive another 0.5mm up - I don't think that's a problem because you're going in the same direction.

Because the teeth don't mesh precisely - there are little gaps between the teeth of one gear and that of the next. When you keep driving in one direction, this isn't a problem because everything stays in contact. But when you reverse the motor, it has to revolve a little bit to move the first gear tooth backwards across that little gap. This is 'backlash'. If you have to use a 'train' of (say) six gearwheels to get the speed low enough - each pair of wheels has to move across that gap. Worse still, with really low gearing you have to turn the motor much more in order to cross the gap in the last set of gears. So the computer can't naively just assume that if it turns the motor 100 revolutions in one direction then 100 revolutions in the other - that the output will actually move at all.

Backlash is present in all geared systems - but it's worse with lego because the manufacturing tolerances of plastic wheels isn't very good to start with - and the nature of the geometry of lego (with fixed spacing for the 'studs' that is different from the vertical spacing of the 'bricks'), it's necessary to allow for very loose gearing in order that little kids can make things that actually work! Using a nice set of brass gears would get you much better precision - but making it all work on-time and in-budget would be much harder.

There are some tricks (both hardware and software) to get around the problems to some degree.

Re-purposing some other mechanism is possible - but the effort to integrate it into a system is vastly harder. Sure, the positioning mechanisms on old-style printers is pretty good - but you have to figure out (without documentation) how to drive the motors - and you have to machine custom brackets and stuff. You could even use things like the head positioning motors from an old CD drive - which will get you SPECTACULAR precision - but you'll need to fritz around experimenting because they can't move much of a load. (Incidentally - you didn't tell us how much weight you want this gizmo to move...that's important too!) But the beauty of Lego is that it's all there...the parts all fit together - you can build any geometry you want - and you can have something working in a couple of hours. If there is a problem with it - you can tear it apart and do it again some other way and be done in another hour.

Lego has a lot of parts that you'd find hard to get other ways - things like a clutch gear that slips if it's asked to deliver too much torque - very handy to avoid wrecking things if you're trying to drive something against a hard end-stop - there are pulleys with rubberbands for drive belts - drive chains (like a bicycle chain with plastic chain links that you can snap in and out to change the length) - rack & pinion gears, etc. Lego also has pneumatic cylinders, valves, pumps and reservoirs. There are 3rd party Lego-compatible temperature, pH, pressure and ultrasonic ranging sensors.

SteveBaker (talk) 22:29, 14 March 2009 (UTC)