Wikipedia:Reference desk/Archives/Science/2012 November 11

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November 11

Could you collect all the CO2 that a vehicle emits?

How much volume would that have? Can you transform it into a solid form? Comploose (talk) 00:48, 11 November 2012 (UTC)

Yes, it could be transformed into a solid, but the question is whether that would be cost-effective (one method would be to lower the temperature to where it forms dry ice). It could also be stored as a compressed gas. If left as an uncompressed gas, it would take up too much space. Also consider that carbon dioxide tanks pose a risk, as leaking ones could knock the driver out and cause an accident, and you can't smell or see it. StuRat (talk) 00:59, 11 November 2012 (UTC)

But, if you remove the 02 and keep the C, the amount won't be bigger than the gasoline. Comploose (talk) 01:35, 11 November 2012 (UTC)

The amount of energy that would take would be prohibitive. StuRat (talk) 01:38, 11 November 2012 (UTC)

((edit conflict) and network timeouts) Removing the O₂ from CO₂ takes a huge amount of energy--you would have to burn probably several times the amount of gas in order to drive that process as well as the car itself. Both of your proposed products are reasonably high-energy (coal is a good fuel and oxygen strong oxidizer) and your proposed starting material is low energy (already-burned), so it takes even more energy to undo that reaction than you get by burning it. Essentially you are proposing an overall process of that gets economically viable energy from "gas + oxygen to coal + water" conversion. It is thermodynamically correct if I understand the numbers correctly, so at least you would not be violating the laws of nature, but not by a lot, so your overall car efficiency (miles per gallon) will suffer greatly. Coal still has a lot of energy, so you are only getting a small amount of the energy density of the gasoline. Energy density is one of the major problems in various alt-energy vehicles. DMacks (talk) 01:56, 11 November 2012 (UTC)

Hypothetically, you could sequester the CO2 from car emissions chemically, that's what Carbon dioxide scrubbers do on an industrial scale. There are several ways to sequester CO2 in this way, most commonly as carbonates. The problem is how to do that efficiently on car exhaust; the chemistry however is simple and used in other applications for exactly this purpose. --Jayron32 02:23, 11 November 2012 (UTC)

Yes: Top Gear (2002 TV series) has demonstrated this. See http://youtube.com/watch?v=nz-Q-4RUd28. The bit about the Range Rover and the greenhouse is complete hogwash, but from about 2m30s there is some actual science. They show that you can use chemicals to sequester the CO2, like Jayron mentioned. They say that they're using Lime crystals; I'm not sure how accurate that is, but it seems to work. See also Carbon dioxide scrubber. - Cucumber Mike (talk) 12:28, 11 November 2012 (UTC)

If something "increases dopamine receptor sensitivity", is that good or bad?

From a fast research, I could find that morphine, fasting (sexual and food-wise), hypothyroidism, and Electroconvulsive shock do that. But is that a desirable effect or a harm done? Is it reversible? Comploose (talk) 00:55, 11 November 2012 (UTC)

I think it all depends on the context. Consider an analogy with increasing light sensitivity in your eyes. That's good in the dark, but not when it's bright out. StuRat (talk) 00:57, 11 November 2012 (UTC)

There are several dopamine receptors with subtly different effects. It also depends on how and where in the brain you are altering dopamine receptor activity. Looking at some real classes of drugs, MAOIs enhance increase the levels of dopamine at certain synapses, which may treat symptoms of depression. Antipsychotics, on the other hand, inhibit dopamine receptor activity, which may treat symptoms of schizophrenia. So the answer to your question is that whether it is desirable, whether harm is done, and how easily it is reversed is entirely contextual. Someguy1221 (talk) 01:05, 11 November 2012 (UTC)

OK, I see that people can have too sensitive dopamine receptors, in the case of schizophrenia, or not sensitive enough dopamine receptors, in some mood disorders. What happens to two normal cases where one mentally healthy person has more sensitive dopamine receptors than the other? The sensitivity of dopamine receptors is also inversely related to the BMI. Could you say that the brain of thin people works differently than the brain of fat people? If yes, how would a brain with more sensitive dopamine receptors differ? Comploose (talk) 01:21, 11 November 2012 (UTC)

As far as I know, none of those manipulations actually increases dopamine receptor sensitivity. They enhance the effects of dopamine, but that isn't quite the same thing. There are drugs that increase the sensitivity of receptors -- for example, benzodiazepine tranquilizers increase the sensitivity of GABA receptors. But I'm not aware of any such effect occurring at dopamine receptors. Looie496 (talk) 02:54, 11 November 2012 (UTC)

There's a general rule in evolutionary biology (Fisher's geometric model) that very small mutations have a 50% chance of being beneficial. The idea is that biological pathways aren't absolutely perfectly tuned, so if you jiggle them just a little, your odds are 50-50 of jiggling them the right way. However, larger mutations are more commonly bad, and extremely large mutations almost invariably so. The same should usually apply to chemical perturbations (provided that they are strictly regulatory rather than say nutritional in nature). I think. So these various drugs, taken in very low doses, should be very slightly good 50% of the time. Combined with even a vague knowledge of when such a modification is a good thing, the effect of many drugs chosen in this way intermingled, at low doses, should on the average be beneficial quite often. Come to think of it, I would speculate (though I've never seen it expressed this way) that this might be the basis of traditional herbal medicine, at least in cases where there is less specific indication for one particular herb. Wnt (talk) 07:53, 12 November 2012 (UTC)

Liquifying francium

I know that francium has a huge heat of decay. However, I'm wondering that if we could prepare a macroscopic sample, keep it renewed by constant synthesis of new atoms, and have a cooling system powerful enough to ensure that the atoms remain liquid, i.e. conducting away all the heat from radioactivity.--Jasper Deng (talk) 02:07, 11 November 2012 (UTC)

There's information on speculative states of matter of Francium at the Wikipedia article titled Francium. Otherwise, I'm not sure the reference desk's mission would be such as to allow us to sit around and invent things out of whole cloth to speculate about what liquid Francium would look like or behave like if we could collect enough of a sample, which we have not yet. --Jayron32 02:18, 11 November 2012 (UTC)

I don't know how to answer this, but it's answerable. Our article shows an image of 300,000 francium atoms in a magneto-optical trap, as a gas. I think it's possible to cool atoms in traps like this, but I don't know how quickly. I assume it's not easy or we'd have a picture of liquid francium there too. Wnt (talk) 16:15, 11 November 2012 (UTC)

It's worth bearing in mind that 300,000 atoms is not a lot—collected into a droplet, you would have a sphere about 80 atoms (probably around 15 nanometers) across. Under visible light, you're not going to see much of anything, and I'm not sure if a particle that size would even be properly 'macroscopic' in its behavior (you get weird things like melting-point depression happening at these sizes, for instance). TenOfAllTrades(talk) 21:41, 11 November 2012 (UTC)

Now there's a general science question I never thought of. What's the smallest possible quantity of a liquid? (or of a solid?) The article doesn't really say, and melting point depression per se shouldn't prevent you from having one. Wnt (talk) 03:53, 12 November 2012 (UTC)

My question is purely theoretical; what if we got at least nanogram quantities (at least ~2.7 billion atoms) and were able to maintain such a sample? The central question is not what the liquid would look like, but whether we would be able to cool such a sample to keep it liquid.--Jasper Deng (talk) 02:56, 12 November 2012 (UTC)

In that case, it is unanswerable by the reference desk. We provide references here so you can know what people already know about things. This isn't the place for people to speculate about unknowns. --Jayron32 00:06, 13 November 2012 (UTC)

Our choice of 25 °C and 1 atm as standard conditions is rather problematic for Fr: the melting point is predicted to be close to 25 °C, but has a large uncertainty, so it's not entirely clear whether we should label Fr as a liquid or a solid. It's worth noting that a simple extrapolation of melting points would result in Fr being a liquid, though. If the 27 °C value from the Francium article is experimental, then it raises questions like whether the experimenters corrected for the decay heat of Fr, since this value is very close to that of Cs (28.44 °C). Double sharp (talk) 05:51, 15 November 2012 (UTC)

Would dogfighting spacecraft need to bank when turning?

Someone told me recently re: "soft science epic Star Wars, that the space craft bank when they make sudden turns (as in dogfights), and they would not need to do this in a gravity-free vaccuum. It made me wonder tho, coz banking would mean the inertial force was felt by the pilot as one pushing him down on his seat, rather than to the left or right.

So where you need to turn suddenly left and right a number of times in quick succession, a banking pilot would feel each of these as a force in the same direction, not as ones zapping him suddenly now to the right, and then to the left. And the force downwards is one very famiiliar to all terrestial beings experiencing gravity, whereas chiral-specific forces are not.

Perhaps banking in extreme turns would also be less stressful on the craft's structure. Myles325a (talk) 07:24, 11 November 2012 (UTC)

Yes, inertia still exists without gravity, so banking would help the pilot. In fact, you'd want to bank more, a full 90 degrees, while on Earth you want somewhat less than 90, because gravity is also pulling you down. As for stresses on the ship, that would all depend on how it was designed. Of course, if they figure it will bank in turns to protect the pilot, then they will design with that in mind. StuRat (talk) 07:32, 11 November 2012 (UTC)

Of course, a ship that does zero to lightspeed in five seconds might need inertial dampeners, in which case it probably wouldn't matter. (Given that maybe the inertial dampeners aren't 100%, the ship might not "really" accelerate to go up and beyond lightspeed, etc.) Wnt (talk) 16:12, 11 November 2012 (UTC)

As far as human tolerances go, in the absence of aerodynamic considerations it would make more sense in a turn to yaw than to roll; humans can tolerate much higher g-forces perpendicular to the spine than along it.

That said, the whole thing is a little bit silly. Standard dogfighting tactics and doctrine (heck, even movie dogfighting tactics and doctrine) have to be rethought once you're working in no air and no gravity. There are an awful lot of what-if and why-didn't-they games one can play (why are there no missiles in the Star Wars universe? why do such otherwise-advanced craft have to rely on manually-aimed guns? etc. etc.) but I'll leave off with a brief nod to the recent Battlestar Galactica remake. In the new BSG series, pilots facing a bad guy 'on their six' didn't panic; they just flipped end-over-end with their manoeuvring thrusters so they could bring their guns to bear while coasting 'backwards'. TenOfAllTrades(talk) 16:42, 11 November 2012 (UTC)

If you would like to read about why aircraft bank during turns (and they don't always!) - I recommend the vintage Aerodynamics for Navy Aviators (1965), available for free online from the FAA. Combining a bank and a yaw maneuver is called a coordinated turn, and helps keep the aircraft stable. During a dogfight, stable flight is not always desirable, especially with very high-performance aircraft. However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives. This would be even more prominent if current technology were projected forward to guide military doctrine in space: risking manned vehicles in remote areas for minimal strategic benefit would be hard to justify. Nimur (talk) 19:12, 11 November 2012 (UTC)

However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives. What are you talking about? How else is a pilot supposed to kill his opponent? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:32, 11 November 2012 (UTC)

I think Nimur is talking about using long-range AA missiles. A8875 (talk) 22:12, 11 November 2012 (UTC)

Which are easily avoidable/distractable/interceptable etc. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:43, 11 November 2012 (UTC)

I assume it must depend on your point of view. If one military is telling its pilots not to engage, surely the other must be saying "Get as close as you can, and engage those Star Destroyers at point-blank range." Wnt (talk) 03:47, 12 November 2012 (UTC)

"However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives." -- Wasn't this doctrine discredited during the Vietnam War? 24.23.196.85 (talk) 05:40, 12 November 2012 (UTC)

It's a cost benefit analysis. A modern American fighter costs about $100 million. A modern medium-range (20 km) anti-air missile has a cost of only about $100,000. Against older planes, missiles have demonstrated a kill rate over 50% (Falklands War). Against modern aircraft the kill rate is expected to be much lower (e.g. 10-20%), but it is still perceived as more cost effective to launch 5, 10, or even 20 missiles at a target than risk a much more expensive fighter. Of course, there will be tactical situations where your aircraft runs out of missiles and is far from any surface-to-air support, and needs to be able to dogfight, but modern American tactics encourage fighters to avoid those situations whenever possible. Better to have the expensive fighter run away, and wait for cruise missiles or other weapons to destroy the enemy's airbase. Of course it helps that America has recently focused on opponents that generally have much older technology, which makes them easier to kill and easier to avoid. Dragons flight (talk) 20:39, 12 November 2012 (UTC)

"Better to have the expensive fighter run away, and wait for cruise missiles or other weapons to destroy the enemy's airbase." What are you going to do after enemy fighters, missiles, and AAA shoot down those cruise missiles? Besides, as 24.23.196.85 says, the shoot-missiles-at-the-enemy doctrine was totally discredited during the Vietnam War. The only reason air-to-air missiles are any use at all against defended aircraft is that since Vietnam they have only been used against obsolete aircraft. Every air force nowadays knows that cannon and Genies are the only effective method for fighter jets to down up-to-date enemy aircraft. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:08, 14 November 2012 (UTC)

Playing the vintage arcade game Asteroids will give you a very accurate intuitive grasp for the mechanics of dogfighting in space. μηδείς (talk) 17:09, 11 November 2012 (UTC)

The most damage resistant configuration would be to have the main engines fixed in place with several fixed reaction jets for turning. (Think Apollo Command/Service Module.) The pilots would be strapped down to resist the push of the main engines, and wouldn't worry about any other forces. Hcobb (talk) 17:26, 11 November 2012 (UTC)

Great swooping turns in space to face an enemy rather than just rotating with thrusters or reaction wheels would would be be very wasteful of fuel. Lots of sci-fi writers either don't know this or don't care, and maker of space-opera like Star Wars just want pretty dogfight scenes like in World War 1, where biplanes made Immelmann turns and other aerobatic maneuvers, which are pointless in the absence of air. If one is worried about stress on the pilot, he could be in a sphere in the center of the craft which rotates independently of the warcraft, to keep him stable while it spins, and in an optimal attitude for translations. Edison (talk) 21:14, 11 November 2012 (UTC)

Dogfighting in space? Surely if the enemy ship was close enough for it to register on your ship's sensors, it would be close enough to hit with a computer-targeted laser beam? Considering that it's a vacuum, I'd guess that you could probably shoot him from the other side of the solar system if your machine could correctly predict his trajectory, provided that there was nothing in the way. As he could also do to you. --Kurt Shaped Box (talk) 23:56, 11 November 2012 (UTC)

When you come right down to it, there's no reason the pilot has to be actually in the craft; without the extra mass required for life support, a drone space fighter would have a lot better performance, and no worries about the pilot's reaction to inertial loads. Gzuckier (talk) 01:50, 12 November 2012 (UTC)

It may help to have a human nearby, to make decisions with short communication lag. But of course space battles, if any, are more likely to be fought by computers. It's absurd (but dramatic) that the Enterprise waits for the Captain's order to fire ... Now!. —Tamfang (talk) 03:09, 12 November 2012 (UTC)

Particularly when the captain is James Kirk who has this tendency to................. pause............... randomly. Gzuckier (talk) 04:00, 12 November 2012 (UTC)

"[Long-range AA missiles] are easily avoidable/distractable/interceptable etc.": In space at very long ranges, there would probably be some dedicated interceptor missiles which would only have one purpose: to slam head-on into incoming anti-ship missiles or any "fighter" foolish enough to get close. There would be dedicated anti-missile guns, both ship-mounted and in drone spacecraft (which would not be crippled as easily as ship-mounted defenses, should one torpedo actually strike home, and thus have a better chance to ward off follow-up strikes) orbiting the capital vessels. And then, there would be some smaller long-range missiles, not intended to destroy, but to fool and to saturate enemy point defense.

This is not just speculation on my part: many of these exist today in the wet navies of the world: Phalanx / Kashtan CIWS , and manned interceptors guard the capital vessels against both air and surface attack.

"If one is worried about stress on the pilot, he could be in a sphere in the center of the craft which rotates independently of the warcraft": just what I would think but for different reasons. If there is only one fixed "main" thruster, that thruster can be more powerful than a vectoring thruster or different thrusters for different directions. Turning before firing the main thruster could save a lot of mass (and thus, fuel).

"a drone space fighter would have a lot better performance" but from time to time, it has to receive new orders. If the enemy manages to jam the communication, its performance goes out the window. Humans on-board may be more like today's AWACS crews rather than "pilots" as depicted in the movies, but they safeguard against both, runaway AI and obsolete programming.

"Considering that it's a vacuum, I'd guess that you could probably shoot him from the other side of the solar system if your machine could correctly predict his trajectory" which is a big IF. One light-second is ~300,000km, an AU is 500 times that, and that's still a fraction of the solar system. Of course, there are only two options: maneuver from time to time erratically but give your position away each time you do so, or put Newton in control (drift) and remain stealthy but predictable if the enemy did spot you before. Stealth will probably play a very important role in space. Huge vessels are not even close to the optimum in that case.

I liked the Honorverse novels the most. They have some plot devices, including inertial dampeners and gravitic drives, but they are few and far in-between. Weapons include lasers, gamma ray amplifiers(basicaly a more badass kind of laser), and anti-ship missiles carrying disposable X-ray lasers. Defensively, they use small point-defense weapons , ECM and banking maneuvers (they "roll ship" to expose the well-protected top and bottom rather than the more vulnerable sides). And I'm not sure if a Honor Harrington movie could not be as epic as another Trek or Wars movie. - ¡Ouch! (^{hurt me} / _{more pain}) 14:27, 12 November 2012 (UTC)

Weber, of course, devised the technologies of the Honorverse so that his ship-to-ship battles would recapitulate the sense and style of ship-to-ship combat of the Napoleonic era. (Honor Harrington's universe owes a great deal to the world of Horatio Hornblower—right down to her initials.) Weber invented a shielding system that protected his spaceships from attacks coming from above and below, because seagoing ships of the early nineteenth century essentially could not be attacked from these directions by the technology of the day. Weber's fictional spaceships lack shielding fore and aft, to mimic the vulnerability of ships of the line to raking fire and emphasize the strategic value of Crossing the T. Weber's 'ships of the wall' were named after, and deployed in a manner akin to, the ships of the line. His more recent work in the Honorverse has moved into the development of carrier warfare and tactics. While it's all fun, and shiny, and exciting, underneath the scifi gloss it's the Battle of Trafalgar. TenOfAllTrades(talk) 21:15, 12 November 2012 (UTC)

Indeed. I find the battles, strategies, and technology in The Lost Fleet a bit less contrived. But it still is not a bulletin from real life... --Stephan Schulz (talk) 11:22, 13 November 2012 (UTC)

OP myles325a back live. I take it that there is a general consensus that, GIVEN a dogfight situation, yawing and banking would make sense. Whether there need be dogfights at all is outside of this question. We could imagine that these dogfights were arranged as games, and the contestants had to fire guns without the aid of computers, and they fired paintballs, or whatever. The Federation thanks the Space Cadets who beamed in their msgs. Myles325a (talk) 09:26, 13 November 2012 (UTC)

The bottom line is not to worry about the structure as much as about the crew. That's where I think that Weber was wrong too, see below. The article about crossing the T seems to concentrate on steamers rather than Ships of the Line, though. While it does mention that battleships moving "horizontally" can use their full armament while the column moving "vertically" can use only about half their firepower, it does not mention that sailing ships used to be handicapped even more. They could bring hardly any guns to bear on the enemy when they get crossed. - ¡Ouch! (^{hurt me} / _{more pain}) 11:44, 14 November 2012 (UTC)

Side topic: Honorverse

In The Short Victorious War, there is one paragraph where he writes that should the inertial compensators fail, there would be not enough left to analyze the circumstances of the failure. I beg to differ. At a quite tame 500g (compared to Trek and Wars), the crew will surely be destroyed beyond visual recognition, but not entirely homogenized into one puddle. The structure will fail horribly, but given that we can analyze planes which crashed head-on into solid rock, (OR) the quality of the debris will be less of a problem than finding it in the first place.

"Weber invented a shielding system that protected his spaceships from attacks coming from above and below, because seagoing ships of the early nineteenth century essentially could not be attacked from these directions by the technology of the day." To an extent. It allowed for the "wall of battle", which is nothing more than a stack of X "lines of battle." It does allow for "rolling ship" (banking) too, i.e. exposing only the unarmed but well-protected top and bottom to direct fire. To merely mimic the effects of raking fire, it would have sufficed to increase the penetration of the disposable X-ray lasers to a degree where they destroy every component in the line of fire.

Weber postulated ("invented") only very few plot devices. No Alien-of-the-week syndrome (although there are nigh-implausible treecats and insectids), no Particle-of-the-week or Force-field-of-the-week, only gravitic drives, macroscopic wormholes (not as abundant as in Stargate either, more like DS9 on a rarity scale), and limited FTL capability. The most amazing achievement is to write an entertaining sci-fi with ships battles between near-Newtonian ships which basically suck dick at maneuvering compared to other space operas... - ¡Ouch! (^{hurt me} / _{more pain}) 11:44, 14 November 2012 (UTC)

Bicycle wheel question

Hi. A spoke from my rear bike wheel broke the other day and I had to buy a new wheel because the rim had cracked. I was chatting to the guy in my LBS and he suggested that the problem arose because I use a single pannier bag, always on the left. My bag weighs 4kg or so. I smell BS, but what do you guys think? Robinh (talk) 09:05, 11 November 2012 (UTC)

I carry a single bag only on the right for about 4900 km per year (I have two on for the remaining 100 ;-). I do sometimes have broken spokes, but very rarely. I've never had a cracked rim. Normally, spokes break because the wheel is not well-build. I had one wheel where the rim was unsuitable for the angle of the spokes caused by the hub, with spokes literally breaking at the the rim. But the most frequent problem is spokes breaking at the knee due to metal fatigue if there is to little tension on the spokes so that they go through a load-unload cycle on each rotation. So yes, I agree with your suspicion. --Stephan Schulz (talk) 09:14, 11 November 2012 (UTC)

If this guy is in your local bicycle shop why not push him a bit further with his explanation. I won't ask why you didn't ask for a specific explanation at the time ;-). Stephan seems as close to any expert we'll see on here. Richard Avery (talk) 14:20, 11 November 2012 (UTC)

We would also need to know how many miles you put on these wheels. It might be completely normal after all. OsmanRF34 (talk) 18:55, 11 November 2012 (UTC)

(OP) rough figures, 20km per working day for about 2 years, thus about 5000km, comparable with Stephan. Follow-on question, the *new* wheel has developed three very very loose spokes (which seem to be in compression) and I've taken it back to the LBS. The guy said that sometimes new-built wheels take some time to "settle out" (I think that was his phrase) and need retensioning after a few weeks. Is this also BS? Hey, I appreciate your advice here guys, Robinh (talk) 20:11, 11 November 2012 (UTC)

With standard wheels, for a standard city-bike, things should be working much better than that. Unless you are going through a rough terrain with a mountain bike, I would expect less incidents and less strange explanations. OsmanRF34 (talk) 00:25, 12 November 2012 (UTC)

Your LBS chap is bullshitting in all respects. I also have biked to work & shops and back every day, about 15 to 18 km every day for years, mostly carrying laptop, personal stuff, shopping, etc often in unbalanced loads. My rims are aluminium alloy and the bike is a fairly heavy general use bike (ie not racing or mountain). I usually did in about one spoke per one to 2 years. New built wheels never showed any problem. I agree with Stephan that the cause of broken spokes appears to be metal fatigue as early failures don't generally occur. Riding over potholes and curb-jumping increases the probability of spokes failing. If you have broken spokes soon after a wheel rebuild/adjustment, I suggest that you LBS chap is not doing the job right. I take it you do sensible weekly checks on your bike, and immediately after shop servicing? As well as checking brake travel, bearing slop, gearchange action, etc, while you have your bike upside down, give each wheel a spin, and watch the rim pass a frame member. There should be NO visible side-to-side movement in the rim. If there is, spokes have either failed or are just about to, or have been incorrectly fitted. Also, at the shop, while the bike is upside down, or just held off the ground, give each wheel a spin and hold your thumbnail so it lightly hits the spokes. They should all make the same "ping" sound. If they don't, they need attention. I bet if you do this when you go to pick up your bike at the shop, the guy will do one of 4 things: a) Say, "sorry I need to give your bike more attention" (ok), or get his more skilled mate to fix it (ok), get bad tempered (find another shop), or tell you more bullshit, such as "the rim needs replacement" (which may or may not be true, but if it is, why did he not say before?). Wickwack 121.215.11.232 (talk) 00:37, 12 November 2012 (UTC)

In this case I disagree with the "in all respects". Newly build wheels, especially if machine-build (which most wheels are nowadays) will indeed tend to "settle", and will need re-tensioning after a reasonable amount of use (2-4 weeks, if you ride as much or as little as you or I ;-). After that, or if build a master wheel builder to begin with, it should be good for a year or three before it needs attention again. I've changed my back rim after 6 years (~30000km/~20000miles) all-weather riding, but it was not strictly necessary. I just like to have everything about my bike shipshape, and the spokes needed replacement anyways. --Stephan Schulz (talk) 08:36, 12 November 2012 (UTC)

(OP) thanks for this. My daily route is all road/cyclepath, no rough ground at all. Just to be clear, the old wheel's rim cracked after two years' use. The new wheel has not suffered any broken spokes, it was perfectly true when bought a couple of weeks ago (ie no side-to-side motion, I checked when I adjusted the brakes). Wickwack, you say you break a spoke every two years or so, but you don't need to replace the rims as often? Stephan's rims last indefinitely, I think. I guess the old wheel's rim was a lemon (lasting only two years), and the new wheel had poorly tensioned spokes(lasting only two weeks before needing retensioning). How long should a rim last? How often should I retension my spokes? Robinh (talk) 01:06, 12 November 2012 (UTC)

I don't know how long a rim should last. I purchased my bike about 20 years ago. The rims have never been replaced, and they are still perfect. However, I only rode it every day to work for about 10 years staring about 12 years ago, due to changing work address. I still use it for shopping. When a wheel has had service attention, use the thumbnail trick to make sure it's perfect. However, after some use you will get some variation in spoke ping. Repalce/retension spokes if there is visible side-to-side movement of the rims, which in my experience will ocurr roughly once a year or two as I said above. If there is no visible side-to-side movement, nothing needs to be done. That's the rule I've followed anyway. Check each week, but do nothing unless it needs it. Wickwack 121.215.11.232 (talk) 01:54, 12 November 2012 (UTC)

I can't prove it mathematically, but off-center loading, particularly 4 kg at the short distance from the center a pannier is at, seems very unlikely to bust a spoke and crack a rim. Particularly since you are one of probably millions doing this, and no epidemic has surfaced. Thinking as I write, I'd say, cracked rim is likely to be result of rim flexing and metal fatigue. From too much tension in spokes? Too little? Can't decide right this second. Somebody probably will know. How did it crack; parallel to the radius, I presume, as if flexing in and out towards the center in the plane of the rim? Note (of course) that the rear wheel is asymmetrical, the right side spokes being shallower and under higher tension, trigonometry being what it is. If it cracked from flexing side to side, that's another thing entirely. There are various kluges around to construct wheels where the rim is less asymmetric, but I can't think of them right now. Yeah, sometimes new wheels need retruing after like 50 miles or something on that order, but various practices like relaxing twist in the spoke nipple after adjustment, etc. reduce that. Also, of course, one can build a metastable wheel which has the spokes all out of whack but is kept in true by the rim for a little while. Oh yeah, another item, are the spokes 3 cross, 4 cross, or something odd? 36 spokes? My current ride has radial spokes in the front, and radial on the left side of the rear. Which is just me screwing around, since I've never really broken a spoke or rim before or since, other than catastrophically with a pothole or automobile or such. Anyway, this is like the Bible of wheelbuilding. Gzuckier (talk) 02:15, 12 November 2012 (UTC)

• If the weight load on your bike is asymmetrical, in order to balance you will have to have your wheel at an angle to the ground, which is not good. But I doubt that 4kg is enough to matter. Looie496 (talk) 03:27, 12 November 2012 (UTC)

Timeline of chemical elements discoveries

Why it took so long to confirm elements 113, 115, 117, 118? 3 of them has been discovered since 2002 and 2003. God, that is like 10 years! Some scientists (especially if they're old) may be dead after 10 years and never know if their discovery has been confirmed. When I think about this, it just doesn't make sense! Did they already confirm it and the article simply is out of date or is it actually not confirmed? Seriously 10 years is a long long time to me. And if it hasn't been confirmed then how come the article Joint Institute for Nuclear Research, it says "2010 – successful synthesis of element 117"? How could it be a successful synthesis if it wasn't being confirmed?174.20.101.190 (talk) 09:21, 11 November 2012 (UTC)

I think its because almost no one have an equipment to repeat the experiment. Only a few big labs have it. --Ewigekrieg (talk) 11:43, 11 November 2012 (UTC)

Some of the elements have been created in one place and nobody ever tried the confirm it. Why should I spent millions worth of equipment time to verify a experiment? You can not publish such a result, because it is nothing new. If you have the equipment everybody would aim for 119 a leave confirmation of 118 to others. After 10 or 20 years the equimpent becomes better and you can do what the others had to do for the discovery of an element for calibration of your machinery in a few days, weeks or months. --Stone (talk) 12:59, 11 November 2012 (UTC)

Put another way, there is "not a lot of interest" in the scientific confirmation of Element 113, 115, and so on; in this case, I have arbitrarily defined "a lot of interest" to mean "enough interest to justify funding immediate confirmation." These elements have no currently-known practical use; their discovery did not refute any well-established theory of nuclear physics, or enlighten us about subtleties that we did not already know. The production of these very heavy transuranic elements can be described as a sort of incremental advance to the knowledge of nuclear physics. Compare this with the history of the semiconductor, or even the discovery of uranium fission; for many decades, the cutting-edge of pure research into the physics of these materials immediately translated into commercialization and productization. Nimur (talk) 20:02, 11 November 2012 (UTC)

I guess Stone brought a good point. People are naturally thirsty for fame and famous but being the first one to confirm it is something right? It is much harder to try to create a "new element" than to try to repeated an early successful experiment to confirm it. I guess the one who discovered it will gain more fame but being the first one who confirmed it is not too bad either. At least your name will be somewhere in science's history or physic's history for being the first one to confirm it, maybe it is just a brief mention of your name if it is there! Eventually someone got stand up to confirm it.

@Nimur: it can said that that while those discoveries of new elements have no significant impact on science but look at it this way, I'm sure somewhere along the line it will become a crucial tool for us, humans, to understand the universe and perhaps dark matter. It may take until element 119 or 125 or even 150 so on... Great discovery doesn't come easy but we're building up to it. I believe the discovery of any new element now will be another step closer to something BIG, but unfortunately we don't know what it is yet! And yes this is comparable to getting man to the Moon. What is it really benefiting us about getting man to the Moon really? That's mostly the result of the "arm race" between Soviet and US and the pride it gives for being the first to get man on the Moon. I'm sure the cost of getting man to the Moon is significant higher. I wish there is something like "element race" between all the countries in the world to find like the ultimate element. If that happened, I think within the next 10 or 20 years, plenty of new elements will be discover. It is sad that people are losing interest in science compare to the 1940's to 1960's (look at all the feats we have accomplished). That being said in the 1940's and 1960's science discoveries are mainly for war purpose and not for the sake of science. 174.20.101.190 (talk) 20:42, 11 November 2012 (UTC)

And one of question above didn't receive any answer, can anyone answer it? how come the article Joint Institute for Nuclear Research, it says "2010 – successful synthesis of element 117"? How could it be a successful synthesis if it wasn't being confirmed??174.20.101.190 (talk) 20:42, 11 November 2012 (UTC)

Maybe it means that they believe they successfully synthesised it, but it hasn't been confirmed yet. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:28, 11 November 2012 (UTC)

I believe there is something wrong with that assumption. They can't just assume that they actually synthesized it without confirmation. If it is considered as successful then there is no reason to be confirm. What if they were wrong? Who knows? To me that is a false statement.174.20.101.190 (talk) 06:01, 12 November 2012 (UTC)

No, that makes sense. As far as their evidence is concerned, they've synthesised it, but there has been no independent conformation by a different lab. Also remember that with these elements it's not like you get a nugget of them, we're talking a few atoms here, requiring careful analysis of data and statistics to find them. Fgf10 (talk) 07:59, 12 November 2012 (UTC)

Here's a quote from IUPAC about this:

"Discovery of a chemical element is the experimental demonstration, beyond reasonable doubt, of the existence of a nuclide...

The TWG realizes that the term ‘reasonable doubt’ is necessarily somewhat vague... Confirmation demands reproducibility... In the case of the new elements the TWG attaches considerable importance to reproducibility and would indeed like to be able to suggest that no new element should be recognized officially until the data upon which the claim is based have been reproduced, preferably in another laboratory and preferably by a different technique. However, ...it would appear unreasonable to apply such a demand of demonstrated reproducibility in all rigidity. We do not believe that recognition of the discovery of a new element should always be held up until the experiment or its equivalent have been repeated, desirable in principle as this may be. However, we would waive this requirement only in cases where the data are of such a nature that no reasonable doubt is possible (for instance for data with a high degree of internal redundancy and of the highest quality), and under circumstances where a repetition of the experiment would imply an unreasonable burden."

Double sharp (talk) 05:43, 15 November 2012 (UTC)

The TWG is the Transfermium Working Group from the Transfermium Wars. Double sharp (talk) 05:46, 15 November 2012 (UTC)

Good physics simulation sandbox?

Could you recommend me a good physics simulation educational software? Something powerful enough to recreate most of school physics experiments? --Ewigekrieg (talk) 11:56, 11 November 2012 (UTC)

Garry's Mod is a very good physics sandbox based on the Half-Life engine. You might also be interested in Learning physics with the Unreal Tournament engine. - Cucumber Mike (talk) 13:18, 11 November 2012 (UTC)

Visual Python makes it very easy to quickly write a 3D visualization for simple mechanics and electrodynamics equations, like simulating an orbiting planet-sun system, in just a few lines of code. Visual Python is free and open source software; you can find installation instructions at the VPython.org website, including some demo videos. Here is a video demonstrating a for-loop and elementary kinematics. If you want to learn physics and learn simulation programming, a little bit more "structured" format will be very helpful. Here is a (not-free) introductory physics textbook, Chabay & Sherwood's Matter & Interactions (available from the publisher), which is used at many universities to guide the freshman-level university physics course with programming examples. Owners of the textbook have access to online versions of the source-code. Nimur (talk) 18:44, 11 November 2012 (UTC)

Always glad to see free publicity for the family! —Tamfang (talk) 03:02, 12 November 2012 (UTC)

Psychology

What's the difference between social anxiety disorder and avoidant personality disorder? --168.7.231.4 (talk) 18:47, 11 November 2012 (UTC)

social anxiety disorder and avoidant personality disorder has the answer. More specifically in Avoidant_personality_disorder#Differential_diagnosis OsmanRF34 (talk) 18:58, 11 November 2012 (UTC)

Self-help books

What research have psychologists done into the effectiveness of self-help books? 65.92.7.202 (talk) 20:44, 11 November 2012 (UTC)

[[1]] OsmanRF34 (talk) 21:29, 11 November 2012 (UTC)

Richard Wiseman, a psychologist, has written a self help book about self help books called 59 Seconds. I'm a big fan of his. Vespine (talk) 21:43, 11 November 2012 (UTC)

Dogbert would say they are highly effective - provided they sell enough copies. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:06, 11 November 2012 (UTC)

Behavior while drunk/under the influence

To what extent does results expectancy affect one's behavior while under the influence of a substance? e.g Are the impairing effects of alcohol naturally induced, or do they occur as a result of our expectations? Same goes for the reduction in inhibitions associated with particular substances. Ankh.Morpork 22:18, 11 November 2012 (UTC)

That's as broad a question as the Milky Way. Can you specify at least a specific drug? μηδείς (talk) 22:25, 11 November 2012 (UTC)

Alcohol. I live on a desert island and eat some fermenting fruit, having never watched Geordie Shore, what happens next? Ankh.Morpork 22:32, 11 November 2012 (UTC)

(ec) To start with alcohol: Testa et al. (2006) "Understanding Alcohol Expectancy Effects: Revisiting the Placebo Condition" Alcohol Clin Exp Res. 30(2):339–348. As Medeis says, this is a very broad and complex question, even if you limit it to one well-studied compound like alcohol; that article provides a lot of references to get you started. See also Short-term effects of alcohol. TenOfAllTrades(talk) 22:36, 11 November 2012 (UTC)

Given you live on an island with no people, don't worry, none of your symptoms will be socially constructed. Enjoy. μηδείς (talk) 23:31, 11 November 2012 (UTC)

Didn't some philosopher once wonder how many people would fall in love if they hadn't been made familiar with the concept via society? Gzuckier (talk) 02:18, 12 November 2012 (UTC)

Related question... The effect of alcohol placebos is very interesting, though I wonder if it is definitely known to be placebo as opposed to some other (unknown) mechanism of contact high. I remember that there have been instances, falling in with people who were drunk for 15 minutes or more, when I've not merely felt intoxicated and felt less socially constrained, but literally felt unsteady on my feet and observed apparent motion of stationary lights when turning my head due to poor tracking, just as with actual alcohol use. I've wondered if there is some natural transition between internal social/mental states of sobriety and drunkenness that preexisted before alcohol was discovered, and if alcohol is only the most common means by which it is forced. Wnt (talk) 19:44, 12 November 2012 (UTC)

I had that same feeling at a party...turned out it was just a bunch of frat guys kept staggering into me and the lamp was shaking because some drunk girl was dancing with it. DMacks (talk) 03:33, 13 November 2012 (UTC)

Colour black

Hello, is it true, that colour black does not exist in nature? And what about white? Bennielove (talk) 22:20, 11 November 2012 (UTC)Bennie

Are you suggesting those colors are supernatural? Can you clarify your question? μηδείς (talk) 22:22, 11 November 2012 (UTC)

I wouldn't say supernatural. You can not find colour black in nature; I've heard sth like that, but now I'm not sure anymore ... Bennie — Preceding unsigned comment added by Bennielove (talk • contribs) 22:37, 11 November 2012 (UTC)

Black is actually when light is not being reflected, so, it doesn't exist in the sense that it's the absence of light being reflected. OsmanRF34 (talk) 22:43, 11 November 2012 (UTC)

So how is black different to colourless? Ankh.Morpork 22:50, 11 November 2012 (UTC)

There are many caves where, if you go down a certain way, no light penetrates. Is not what we see pure blackness? Also, many animals are black - some species of panther, for example; and cats, dogs, cattle, snakes, you name it. As for white, pick from thousands of different white flowers. -- Jack of Oz ^[Talk] 22:59, 11 November 2012 (UTC)

Those animals still reflect some light, so they are not pure black. StuRat (talk) 07:00, 12 November 2012 (UTC)

Re how black differs from colorless: Wiktionary says only that colorless means lacking color, and one of the definitions it gives for color is Hue as opposed to achromatic colours (black, white and greys). [For example] 'He referred to the white flag as one "drained of all colour".' In line with this, in my experience when people say colorless they mean lacking any hue -- that is, being only white, gray, or black. Duoduoduo (talk) 23:13, 11 November 2012 (UTC)

When my black cat is strongly backlit, I can see that his coat is really dark brown. —Tamfang (talk) 03:01, 12 November 2012 (UTC)

Black and color are both psychological terms. They have to do with human perception, not nature in and of itself. Black is what one perceives when there is no even semi-saturated hue. This is so basic as to be childish. Please read hue and color. μηδείς (talk) 23:29, 11 November 2012 (UTC)

However, "a colourless liquid or gas" is transparent, and lacks all hue. Bielle (talk) 23:31, 11 November 2012 (UTC)

The word black is ambiguous, in that it can either mean the absence of light, or the complete absorption of light. But even within those two definitions, the word light is also ambiguous, in that it can either mean electromagnetic radiation of any frequency, or merely electromagnetic radiation in the visible spectrum. There are no substances, whether found in nature or not, that absorb light perfectly; the blackest material yet created has a total reflective index of 0.045%, which is small but nonzero.[2] Using the "absence of light" meaning of "black", the example of the inside of a deep cave would be a good example of the existence of black in nature, if you take "light" to mean just the visible frequencies of electromagnetic radiation, but in such a situation there would still be infrared radiation, so it wouldn't count as black if you're considering all frequencies of electromagnetic radiation. The sky, as seen from space in a direction other than in the direction of a star, would be a purer absence of electromagnetic radiation, although even then there would at least be the cosmic microwave background radiation. But the blackness of the sky is beat hands down by the blackness of a black hole, which is indeed extremely black. The only electromagnetic radiation coming from a black hole is Hawking radiation, but a reasonable-sized black hole emits far less power per area in the form of Hawking radiation than even the cosmic microwave background radiation. Red Act (talk) 00:27, 12 November 2012 (UTC)

There's no such thing known to science as truly black light, but undoubtedly there is black pigment, especially a blackbody. To confuse you further, blackbodies can glow red hot or white hot --- indeed, to within a small approximation, the Sun is black! (And with that, everybody in Colorado or Washington has to take a toke) Wnt (talk) 04:17, 12 November 2012 (UTC)

My reading of black body is that this is a very useful theoretical approximation: an idealized description that does not occur in physical objects on earth. It even opens with "A black body is an idealized physical body." SemanticMantis (talk) 13:48, 12 November 2012 (UTC)

Well, the taste of maple syrup and the sound of an oboe also lack all hue, but we don't therefore call them white or black or grey. There are different ways to perceive color: from reflective surfaces like coal, from luminous surfaces like computer monitors, through transparent object like rose-tinted glasses, or even without focused dimension, like the red one sees through closed eyelids, or the utter black of an unlit cave. Developmentally we first conceptualize colors as perceived on reflective surfaces, fundamentally the colors of a crayon box, including ROYGBIV as well as white, black, grey, brown, silver, gold, etc., all equally as "colors" and all falling within certain ranges where two slightly different blacks still count as black.

It's only when we gain some scientific or artistic sophistication that we learn there is no way to make black light, that grey and brown lights don't exist in isolation, but only in contrast to brighter or more saturated hues, that the colors gold and silver are identical in hue to yellow and white--that their properties are based on the coherent reflectivity of their surfaces, and painters have to use the trick of painting highlights to portray them. All this requires making finer distinctions and expanding our vocabulary. Simply saying black is not a color, rather than, say, explaining in detail how black is different from green, doesn't achieve that. μηδείς (talk) 18:15, 12 November 2012 (UTC)

See here. Count Iblis (talk) 18:48, 12 November 2012 (UTC)

As it happens, on my laptop the change in display color according to change in viewing angle is just sufficient to counteract the optical illusion so that they actually do look the same color. Wnt (talk) 19:48, 12 November 2012 (UTC)

Regarding lightless caves being perfectly black, see eigengrau. Matt Deres (talk) 17:44, 13 November 2012 (UTC)

Now that's a great link - thanks! But I don't necessarily fully understand. I know that there's a distinction between a "dull black" which I suppose is eigengrau, and a "living black" which perhaps is the darker color the article mentions. But when I'm in a darkroom the "dull black" breaks up into "living black" and light blue speckles, which form various sorts of pulsing wave patterns and phantasms of various sorts (including rehashes of recent visually distinctive and unfamiliar stimuli which take on their own original colors, and simple dreams that remain in blue colors), occasionally tinging into yellow. And then there's a "blacker than black" color which I only very rarely see, usually at right around this time of year, on wet reflective surfaces where contrast is present. So I feel like there's some variety of subjective states... but how to study them with any meaning? Wnt (talk) 05:35, 14 November 2012 (UTC)