Wikipedia:Reference desk/Archives/Science/2013 March 4

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March 4

where does dried water (molecules) go to?

His bath mirror is covered in humidity - he opens a hot fan towards it - it banish. where have the water molecules went? thanks ! 79.183.98.234 (talk) 01:42, 4 March 2013 (UTC)

the water molecules evaporate, which means turn to steam, and then go into the air. 86.101.32.82 (talk) 01:45, 4 March 2013 (UTC)

Agreed. You may wonder why you can't see the steam (water vapor). Well, if the droplets are small enough, if becomes invisible. In fact, there is water vapor in the air all the time, called humidity. It's only when it forms bigger droplets that it becomes visible, and forms visible clouds. StuRat (talk) 02:05, 4 March 2013 (UTC)

It should be noted that "steam" in common parlance can refer to water vapor and also to the mist formed above boiling or evaporating water. Water vapor is invisible; mist or fog is visible under normal conditions. 75.164.249.10 (talk) 04:35, 4 March 2013 (UTC)

To be clear: water vapor (evaporated water) is invisible (it's a colorless gas). Condensed water may form droplets - but then it's not water vapor. -- Scray (talk) 05:55, 4 March 2013 (UTC)

At what point does a water-in-air liquid aerosol become distinct from a water-and-air gas mixture. Plasmic Physics (talk) 06:23, 4 March 2013 (UTC)

At the point where there ceases to be an identifiable phase boundary (my god, is that a horrid article) between the liquid droplet and the surrounding gas. -- 71.35.110.219 (talk) 06:32, 4 March 2013 (UTC)

That just rephrases my question into: at what point does there cease to be an identifiable phase boundary. Plasmic Physics (talk) 00:33, 5 March 2013 (UTC)

You can think about it this way: Take a spoon full of sugar (or salt) and place it in a glass of water. Wait for a while, or if you're impatient, heat and/or stir it. You'll find that the sugar (or salt) dissapears. Where did it go? It dissolved into the water. The same thing happens with water and air. The water "dissolves" (evaporates) into the air in much the same way the sugar dissolved into water. And you can also speed up the process by heating the air or by stirring the air (e.g. by using a fan), or both. -- 71.35.110.219 (talk) 06:29, 4 March 2013 (UTC)

As I recall from science class long ago, the term "dry" is relative; there's actually a thin layer of moisture on pretty much everything, even "dry" objects. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:58, 4 March 2013 (UTC)

Really, even on lithium tetrahydridoaluminate(1-)? Plasmic Physics (talk) 09:54, 5 March 2013 (UTC)

Yes indeed -- that's why there must always be a thin layer of oil in between this stuff and the thin layer of moisture around it, to keep it from starting a fire that nothing can put out. 24.23.196.85 (talk) 03:19, 6 March 2013 (UTC)

Self-defense question

Can a woman of average (or somewhat greater than average) strength stun a man, even briefly, by hitting him on the head with an umbrella as hard as she can? Can she do the same to an attack dog (or at least deter it from ripping out her throat)? Thanks in advance! 24.23.196.85 (talk) 04:54, 4 March 2013 (UTC)

The first would depend on the umbrella - the standard cheapie unbrella you buy for a few dollars is made of thin alloy tubing and is simply not heavy enough and rigid enough to even raise a bruise. However, it might be possible to find and umbrella strong enough - I haven't seen one. The second obviously depends on the dog. Most sizeable dogs who can be a threat simply have stength and reacion speed that few humans (male or female) can defend themselves. If you pretect your face, any dog with half a brain will simply go for the tendons at the back of your knees and bring you down, and then spring round for another attack while you are still falling. The best way to defend oneself against a threatening dog is the same way that you can handle a mugger though - show confidence and no fear. Both like easy targets, but a vicous dog is more difficult. In any case, in my experience, many women (who have strenth and speed under normal circumstances not dissimilar to men) simply freeze under sudden threat, or panic and do something stupid. (Some men will do that too) Wickwack 58.169.246.228 (talk) 05:39, 4 March 2013 (UTC)

This gal works for the SOE, so she won't freeze or panic -- but she's normally unarmed. 24.23.196.85 (talk) 06:21, 4 March 2013 (UTC)

I didn't know Sony Online Entertainment employees were so tough. But perhaps you really meant the Slavko Osterc Ensemble, in which case I suggest hitting the dog with her euphonium might be more effective than an umbrella. SpinningSpark 23:36, 4 March 2013 (UTC)

(EC) Probably not. The mass is too low, the length is too short, and the fabric provides a cushion. Now, if you put a mace ball at the end of the umbrella, and reinforced the shaft, then you might have a reasonable self-defense weapon. As far as existing umbrellas go, some have pointy tips, so could possibly be used to poke an attacker in the eye. StuRat (talk) 05:41, 4 March 2013 (UTC)

Thanks! So, she should poke that Gestapo fink in the eye, then? 24.23.196.85 (talk) 06:21, 4 March 2013 (UTC)

Yep, a direct hit to the eye ought to stun anyone, especially if she manages to puncture it. If she knows about the danger ahead of time, perhaps she can sharpen the tip, specifically to make it a better weapon. StuRat (talk) 06:26, 4 March 2013 (UTC)

If your heroine really needs to kill the attack dog, a knee drop on it's chest will do a lot of damage very quickly. Google that . 124.191.176.117 (talk) 07:18, 4 March 2013 (UTC)

I would say good luck to any human who thinks they can poke an attack dog in the eye, with an umbrella or any other thing. What do you think the dog will do, just stand there and take it? The reaction time of any decent dog is far quicker than that of a human. For the same reason, she would have buckley's chance of doing a knee job to a dog too. A good knee job ought to to kill a dog, but the dog will dodge. And if you just poke it in one eye, you'll just enrage it, so that it will now go for the kill instead of just disabling you. There are two ways of defeating a dog without an overt weapon such as a gun or spear: 1) Prevent it from approaching by using something like a large shovel with a sharp edge or garden rake with sharp prongs, with a handle at least 2 m long; 2) spray its eyes and nose with some sort of serious irritant. Kerosene based fly spray would do, but that would not have been carried by anyone unless they were in an area subject to flies, such as Australia. Maybe you could think of something else that is not an overt weapon. Maybe you could have an scenario where she throws a couple of darts (as in the dart board game) but that seems too difficult to me - she'd have to score a first time bulls-eye in both eyes, otherwise the dog is not incapacitated, but enraged.

Poking an ordinary man in the eye seriously will stop him. But a Gestapo officer? I don't know what training they got, but any two-bit policeman or soldier will not be stopped by eye-poking.

Wickwack 58.169.246.228 (talk) 09:23, 4 March 2013 (UTC)

As in the advice to discourage sharks by punching them in the nose. If you think poking a dog in the eye would be difficult, imagine punching a shark in the nose, underwater. From what I've read about alligator wrestling, the idea is that although you can't possibly keep their jaws from crushing you, it's not impossible to keep their jaws opening if you can get a good grip on them when they're closed. I suspect the same may be true of dogs, although I've never been anxious to do research. Gzuckier (talk) 21:48, 5 March 2013 (UTC)

A punctured eyeball is certainly a more serious irritant than kerosene sprayed in the eye. It would be difficult to do that to a dog, but if the dog is lunging at you and doesn't consider the umbrella to be a weapon, you have a better chance. StuRat (talk) 16:20, 4 March 2013 (UTC)

A more serious injury long term, but kerosene will temporarily blind both eyes, thereby immediately disabling the attacker, whther human or dog. An eye totally destroyed by poking/stabbing will not disable as the attacker still has the other eye fully functional. It would stop your average mugger, but not a dog, and not a trained policeman or soldier - they are trained to get the upper hand even when injured. I expect the same would apply to a Gestapo officer. Wickwack 124.178.41.155 (talk) 00:40, 5 March 2013 (UTC)

If we're talking about standard predator behavior, then any serious (painful) injury should be enough to persuade the attacker to look for easier prey, as risking ones life for a meal rarely makes sense. With that in mind, can these dogs really be trained to continue to attack, even after sustaining such a serious injury ? How would they so train them, since this would require seriously injuring them (or perhaps just making them think they were) ? Also, having one eye punctured ought to cause both eyelids to close, reflexively. I doubt if the other eyelid could be opened quickly after. StuRat (talk) 01:08, 5 March 2013 (UTC)

oh that part's easy; you just teach them that they can't lose, and that the only option is to press the attack and that they will always succeed. you let them win every encounter, starting as a pup, and gradually move up in intensity of painful striking back at them, but letting them always win in the end; maybe even really put the hurt on them if they do back off from attack. you wash out the ones who do figure out that they can run away, but with the rest you end up teaching them that backing off is not an option, and keeping up the fight will always win. training attack/fighting/security dogs is mainly a task of teaching them to believe the lie that the universe is built on logical and ethical principles and if they stick to what you taught them, nothing bad can happen. much like teaching kids, or soldiers, or kid soldiers. See also the legends regarding hassan the assassin Gzuckier (talk) 21:48, 5 March 2013 (UTC)

Interesting -- in Nazi Germany, did they use concentration camp inmates as live targets for dog training? 24.23.196.85 (talk) 03:24, 6 March 2013 (UTC)

The instinct/desire to win any fight is inbuilt in dogs. You don't have to train them to it, so much as use training to enhance it for military attack dogs. In police dogs (for which the desire is to bring down and restrain villains, not damage them), part of the training and screening is to eliminate dogs from doing unnecessary damage. It varies with breeds - with labradoors, this instinct is greatly suppressed; with put bull terriers, this instinct to win at all costs is enhanced. Regarding damage to one eye closing both eyes: You must have funny eyes. While rding a motorcycle some years ago, with 1960's style biker glasses, a small stone flicked up by a car bounced off my checkbone and entered my right eye, rendering it temporarily useless. I had no trouble at all keeping the other one open, I can assure you - driving a motor cycle at speed while blind is just not an option, even for a second. Fortunately the doctor was able to save my eye. Wickwack 120.145.159.132 (talk) 02:00, 6 March 2013 (UTC)

But you must admit that evolution would not favor the desire to continue fighting, when you risk your own death (or injury to the point of precluding reproduction) by doing so. Why would this not apply to dogs ? StuRat (talk) 18:41, 6 March 2013 (UTC)

How about a cane gun or a swordstick disguised as an umbrella? 196.214.78.114 (talk) 13:16, 4 March 2013 (UTC)

WWII secret agents in British boys' comics of the 1950s and 60s generally carried a pot of pepper to deal with guard dogs. Whether they actually carried these, I have no idea. Alansplodge (talk) 13:19, 4 March 2013 (UTC)

The mailman once sprayed my dog with what I imagine would be official government approved antidog pepper spray for mailmen. It wasn't a full blown attack, just sort of hesistant stalking behavior. I was urging the mailman to spray him, of course, since it's important for dogs to learn the proper lessons regarding the impersonal adverse consequences of misbehavior, rather than just raw obedience. Anyway, the spray bothered him surprisingly little; he just sneezed and grudgingly backed off, giving the mailman an "I'm ready if you are, buster" look the whole time. I firmly believe had it been a serious attack, he'd have taken no notice of the spray (he wasn't an aggressive dog, just one of those territorially defensive barker types). after the acute episode, the mailman succeeded better at solving the chronic problem, with the other solution to similar problems; bribery. A milkbone every time the dog "caught" the mailman was adequate to buy his permission to pass, although suspiciously and with grumbling. (of course, another aspect of serious security dog training is to teach them that strangers offering food are never to be trusted). Gzuckier (talk) 21:48, 5 March 2013 (UTC)

Is it her own umbrella? If so perhaps she could have one like this, maybe supplied to her by the SOE, it would likely be less incriminating than a cane gun or swordstick if discovered, although I don't know if suitable materials would have been available at that time to make it without increasing the weight excessively. Equisetum (talk | contributions) 13:32, 4 March 2013 (UTC)

Actually, it turns out their premium model is made from steel and aluminium, so the materials would have been around. Equisetum (talk | contributions) 13:37, 4 March 2013 (UTC)

She can certainly hit him with the handle on the temple and plain knock him out. It may not be reliable, but it's not implausible, either. --Stephan Schulz (talk) 15:25, 4 March 2013 (UTC)

Given the weight of the whole umbrella is given by the website as less than a kilogram, their pretensions of use in self defence is optimistic to say the least. I certainly would not expect it knocking anyone out. To have any hope of doing so, she would have to make a pretty vigorous large swing, like wielding an axe. A Gestapo agent would see it coming and simply duck or parry it with a hand. I should think that in this respect you should consider Gestapo offcers the same as policemen. That is, you either knock him out or blind him first time with complete certainty, or he will retaliate, violently. The pepper idea is the best so far. Wickwack 120.145.200.139 (talk) 15:47, 4 March 2013 (UTC)

Every time I have killed a dog that was attacking me it was by shoving the tip of the umbrella down its open mouth, and then a left knee drop to the chest while pulling its head down to the right with the umbrella in its gullet. Sheesh, that's just dog-defense 101. μηδείς (talk) 18:12, 4 March 2013 (UTC)

And just how many dogs have you killed? Just one maybe? None? Dog attacks actually are not very common. And what sort of dog was it? Miniature poodle? Chihuahua? Or some poor old tottering dog just about ready to drop dead with old age? Wickwack 124.178.41.155 (talk) 00:27, 5 March 2013 (UTC)

ROFL. This makes my month in terms of comedy. Unintentional or not. Any post that begins with "just how many dogs have you killed".... Shadowjams (talk) 01:04, 5 March 2013 (UTC)

"And just how many dogs have you killed?" Well, duh, every one I have had to use this method on. As for the ones who haven't needed killing--I can think of one, a smallish German Shepherd--a swiping blow to the head that transitions into grabbing the bitch by the scruff, lifting her enough so she loses purchase with the front legs, and then a rolling side toss followed by full body compression on the upper torso works wonders. (A swift punt return will always work on toys; but I like chihuahuas.) Of course, your results may vary. μηδείς (talk) 01:26, 5 March 2013 (UTC)

Well, come on, how many then? So you have killed every single dog you had to kill - Zero most likely - you haven't needed to kill any. If you think you can bash a german shepherd that doesn't regard you as friend, you are simply living in fantasy land. It will have its' jaws clamped round your forearm before you can move it even half way. That's why police use them to bring down violent crims. Wickwack 121.215.74.126 (talk) 02:06, 5 March 2013 (UTC)

Wickwack, you so crazeh. I said smallish. μηδείς (talk) 02:17, 5 March 2013 (UTC)

Enjoyed the video clip. You still haven't said how many you killed. Must be none. And that smallish one you didn't need to kill - an untrained puppy who thought you were a friend eh? Not an attack trained dog. Wickwack 124.178.62.87 (talk) 02:49, 5 March 2013 (UTC)

I wonder whether suddenly opening the umbrella in it's face (especially if it's one of those spring-loaded ones) might surprise the dog for long enough for one to escape or something? I could easily imagine that even trained attack dogs have never seen something jump in size so abruptly...kinda like the defense a puffer-fish puts up to deter predators. Even if the dog doesn't run off, I could imagine it grabbing the umbrella and tossing it around, ripping it to shreds for long enough to allow it's owner to get away.

But I can't imagine an umbrella doing much physical damage to either dog or human...for all of the reasons given above. But Google "SOE unarmed combat training" - and you'll see several references to declassified documents about exactly the training they went through and the techniques they would have mastered. I bet you could find something interesting and surprising that your heroin can do against the enemy if she's been through the SOE unarmed combat classes. Another thing is that you describe "a woman of average (or greater than average strength)" - several sources for the SOE indicate that they selected only the most physically capable individuals - and then trained them to be better, so "average" isn't possible - and "greater than average" should mean *MUCH* greater than average. (I'm thinking: a stiletto heel dug into the knee and scraped hard down to the ankle, followed by that old saw, the knee to the groin and then garotting with her headscarf.) SteveBaker (talk) 21:47, 4 March 2013 (UTC)

There's a reason groin hits and eye gouges are banned in every professional fighting sport... cause they work a little too well. Shadowjams (talk) 22:40, 4 March 2013 (UTC)

It's not because of their effectiveness so much as the possibility of causing permanent damage. SpinningSpark 23:34, 4 March 2013 (UTC)

Far from my field of expertise, but I believe professional boxers hammer away at the other guy's eye with the intent of opening up a cut in the eyebrow area, the blood coming down and interfering even slightly with vision being a big impediment to the other guy.Gzuckier (talk) 21:48, 5 March 2013 (UTC)

They tend to be related, but that's a good point. There's two practical pieces to self-defense... physically stopping an attack (tazers seem to be really good at this, if you can penetrate heavy clothing, can hit on the first shot, are within close range, etc.) And then there's the deterrent effect. The fact that if you get hit by a bullet you could die is a powerful incentive to avoid situations where you could be hit by a bullet. There's something to be said for that notion. Groin hits and eye gouges I tend to think of in the "stop the attacker" category, but obviously also in the permanent injury category. Spinning has a really good point on this... although, i think that if you get a thumb in your eye or a knee in your groin, the long term damage is secondary to the immediate pain. Shadowjams (talk) 01:01, 5 March 2013 (UTC)

She'll definitely kick him in the balls before poking his eye out with the umbrella (which comes with a sharp tip as issued, specifically for contingencies like this one). But she won't have time to choke him with her scarf, because other Nazi thugs will arrive and she (and her partner) will have to climb out of the third-floor window onto the cornice in order to escape. Thanks, Steve! 24.23.196.85 (talk) 06:14, 5 March 2013 (UTC)

You'll note (if you followed up on reading the SOE 'dirty fighting' stuff) that the SOE started out in designing their course by looking at all of the rules for boxing and wrestling and deliberately teaching their operatives to break every one of them. This makes good sense for two reasons: One is that the rules were designed to prevent serious and permanent damage or death - the other was that trained fighters may well have been trained with boxing or wrestling as an art and would be less likely to expect illegal moves from their opponents. It's right there in the book! SteveBaker (talk) 16:06, 5 March 2013 (UTC)

One last suggestion. Having a sharpened tip on the umbrella might make it obvious that she has a weapon. If she has a rubber cap on the end, which makes it look innocuous, she could then remove that cap at the first sign of trouble (perhaps by holding it on the ground, and stepping on the rubber cap with her shoe). StuRat (talk) 06:20, 5 March 2013 (UTC)

Ya stu, maybe if the weapon's concealed it will be less illegal! Shadowjams (talk) 13:03, 5 March 2013 (UTC)`

Who said anything about legal. And where do you that bans sharpened umbrellas? Rmhermen (talk) 14:36, 5 March 2013 (UTC)

(Or inspects them!) SteveBaker (talk) 16:06, 5 March 2013 (UTC)

Incidentally, it is certainly possible to kill someone with a specially prepared umbrella. There was that Bulgarian dissident - Georgi Markov who was killed with an umbrella by Francesco Gullino (codenamed "Piccadilly") while walking across Waterloo bridge in London. It was rigged to inject a tiny platinum/iridium micro-pellet containing ricin into his leg! This kind of "for real" spy stuff is right out there in James Bond territory! However this technique wouldn't help our brave SOE heroin because Ricin takes up to a day to kill - and I doubt that WWII engineering was up to creating the required micro-pellet anyway. A second victim of the micro-pellet umbrella survived (Vladimir Kostov), so it's not the most reliable technique! SteveBaker (talk) 16:06, 5 March 2013 (UTC)

Hey, they used that plot point on "The Americans" the other week. Gzuckier (talk) 21:48, 5 March 2013 (UTC)

Right, I could issue her an umbrella that doubles as a concealed, silenced 22-cal rifle -- but that's not my intention, since her primary mission is to gather intelligence (and smuggle Jewish refugee kids out of the Reich), not to ambush German troop convoys or snipe at Wehrmacht officers. Thanks anyway! 24.23.196.85 (talk) 03:31, 6 March 2013 (UTC)

A final point is that in real life, it's surprisingly difficult to knock somebody unconscious. As I boy, I fell head first five feet (1.5 m) onto an asphalt playground, fractured my skull and was in hospital for three days vomiting continuously, but remained conscious throughout. I've seen a friend get hit on the side of the head by the full swing of a pickaxe helve (handle) which was being used as a rounders bat, and again, no loss of conciousness but a rather sore head. In films, a small tap is all that's necessary to send someone to sleep for a few minutes, but it ain't necessarily so in the real world. Alansplodge (talk) 18:37, 6 March 2013 (UTC)

It's rather uneven. Those injuries could cause unconsciousness, but are not guaranteed to do so. And, any injury which does cause it, may very well also cause brain damage (as may well those head injuries which don't cause unconsciousness). StuRat (talk) 18:47, 6 March 2013 (UTC)

HIV/AIDS deaths

List of causes of death by rate, sourced to this WHO document, lists HIV/AIDS as causing just under 5% of deaths in 2002. I thought that HIV/AIDS broke down the immune system so that other things, which are normally repelled by the body easily, are instead able to take over. Does HIV/AIDS kill anyone directly? If so, we need to point this out in its article, unless I missed it when reading it. If it doesn't kill people directly, I'm confused: why don't they count the AIDS deaths according to the immediate cause of death (e.g. infection, cancer), and how do they decide which HIV+ deaths are AIDS-caused and which aren't? Presumably they include as an HIV/AIDS death someone who dies of an HIV/AIDS-enabled bacterial pneumonia infection, but presumably when someone with HIV/AIDS shoots himself, they count it as Intentional injuries (Suicide, Violence, War, etc.). Nyttend (talk) 06:34, 4 March 2013 (UTC)

The vast majority of that 5% consists of people dying of HIV/AIDS related diseases. You are correct that the vast majority of HIV patients die from secondary infections. They may still be listed as having died of HIV/AIDS, regardless. There are ways you can die from HIV in an of itself, but they are rare. HIV-associated nephropathy could conceivably kill a person, and AIDS dementia complex can leave a patient as good as dead. Someguy1221 (talk) 06:44, 4 March 2013 (UTC)

• (edit conflict)As you say, HIV causes immune dysfunction that renders the infected person susceptible to a variety of immediate causes of death. When someone has heart failure, they may die from low oxygen in their blood but we count the death as related to heart failure, (e.g.) due to coronary artery disease - and this death could be counted as due to coronary artery disease. In a similar way, if someone dies from Pneumocystis jirovecii pneumonia (PJP) in the setting of HIV infection, the death can be attributed to HIV (because prevention or treatment of HIV would have avoided the PJP altogether). The WHO most likely has a list of proximate causes of death that, when found in persons with HIV infection, would be counted as AIDS-related deaths. -- Scray (talk) 06:51, 4 March 2013 (UTC)

Thanks to both of you. I'd never heard of the topics that Someguy links, while Scray's heart analogy and notes about a potential list made the concept much simpler. Nyttend (talk) 14:39, 4 March 2013 (UTC)

I, too, would expect to see the fact that AIDS doesn't kill directly in the lead of the article - and I don't see it either. Anyone want to improve it? Rmhermen (talk) 15:44, 4 March 2013 (UTC)

I think it's pretty clear already, and should not be overstated. If someone is shot and loses a great deal of blood, resulting in a massive stroke or heart attack, would you (or reliable sources) say prominently that the gunshot did not kill them? I realize that this discussion should probably continue over there rather than here. -- Scray (talk) 16:12, 4 March 2013 (UTC)

In the US (and probably most first-world countries), death certificates allow for listing both an immediate cause of death and an underlying cause of death (as well as other contributing factors). In the AIDS example, the immediate cause of death might generally be an infection, but the underlying cause of death might be listed as AIDS. For US data, the typical database will contain both listed causes, so even though AIDS doesn't typically kill people directly, one can still easily compile statistics on cases where AIDS was listed as the underlying cause of death (or as a contributing factor). For the US anyway, it isn't necessary to make any special inference based on the type of the infection because the doctor / medical examiner filling out the death certificate should have already made that determination and noted it on the form if appropriate. Dragons flight (talk) 16:28, 4 March 2013 (UTC)

Here's an example of a representative US form showing multiple causes of death: [1]. Dragons flight (talk) 17:53, 4 March 2013 (UTC)

Those suggestions are far better than the ones I've seen on actual death certificates. Of course, even those didn't go all the way back to the root causes, which were likely a poor diet and lack of exercise. StuRat (talk) 18:03, 4 March 2013 (UTC)

(EC) Note that multiple causes of death is by no means unique to AIDS. For example, you could have poor nutrition + sedentary lifestyle -> obesisty -> diabetes -> kidney failure, or poor nutrition + smoking -> high blood pressure -> stroke. As far as I can tell, there's no universal way of listing the multiple causes of death. The person filling out the death certificate often seems to just pick one, most likely the last one in the chain, and ignore the rest, which makes us not appreciate how serious the root causes are. StuRat (talk) 16:30, 4 March 2013 (UTC)

I read once that as far as our definitions go, all death is caused by lack of oxygenated blood to the brain, regardless of how that is "caused". Vespine (talk) 03:14, 5 March 2013 (UTC)

Color reproduction

Why is there so much variety in color reproduction on different monitors/tv/displays? Is it a lack of standard, sample to sample variation or something else? bamse (talk) 10:39, 4 March 2013 (UTC)

There are plenty of standards out there (eg CIE 1931 color space) - and I don't think sample-to-sample variation accounts for much of the problem - although that kind of variation does exist. On CRT displays, the age and amount of usage of the tube would dramatically affect the color quality - but that issue has largely disappeared with modern flat-panel LED/LCD/Plasma displays. Lack of adherence to the standards by the manufacturer is one possibility - displays used as televisions are often tweaked to produce a "hyper-real" color space because it looks good in the store where you buy the thing from - but which is nowhere near what it should be. (My new Visio TV has a "STORE DISPLAY/HOME" toggle in the menu that seems to do exactly that!).

But in a lot of cases it is simply that the device is not correctly set up. There are devices that one can buy that use a Tristimulus colorimeter coupled to a small 'black box' that adjusts the video signal into the display to produce the most accurate rendition of color that the device is capable of producing. Our Color calibration article covers some of that.

When I worked at a computer games company a few years ago, we had a guy who would come around once in a while with a colorimeter and set up our monitors according to a common standard so that our artists, designers and programmers would all be looking at the same image brightness, hue and saturation. There are gizmos you can buy that do that adjustment continuously and automatically using a little sensor that sticks onto one corner of your screen.

Some cheaper flat panel displays show a tendency to shift color and brightness depending on the angle you're looking at them at. This poses a serious problem for color quality.

SteveBaker (talk) 14:12, 4 March 2013 (UTC)

Here is anothervrason why sme monitors show different colors: [ http://compreviews.about.com/od/multimedia/a/LCDColor.htm ] --Guy Macon (talk) 15:06, 4 March 2013 (UTC)

Thanks for the replies. So it is mostly a lack of common interest and producers trying to make their displays look "good" by deliberately setting them up incorrectly. bamse (talk) 19:10, 4 March 2013 (UTC)

What would you do if every time you made a monitor with accurate color nobody bought it? I have a Samsung LCD TV that has an "accurate color and brightness" setting for when you get it home and a "make it look good next to the other monitors in a brightly-lit store" mode. --Guy Macon (talk) 19:18, 4 March 2013 (UTC)

Yep - that's exactly what my new VISIO TV has. The "HELP" function for that button says that it's necessary to switch it into "HOME" mode in order to save electricity and to meet the "Low Energy" sticker that the TV has. So depending on which way you set that option, what you see in the store is a TV that's brighter than it would be home - or it's a TV that's less energy efficient than it claims. But truly, this is a minefield - far too many reasons or half-reasons not to follow the standards. In the end, if you need color precision and repeatability - you have to get a colorimeter and an accurately calibrated test pattern generator - and adjust the display accordingly. In most cases, you can get away with just adjusting the gamma-correction settings. Also, many modern displays have settings for different "color temperature" - and others (like my VISIO) has settings that purport to set the TV up better for Movies versus TV shows versus sport. I have no idea what those actually *do* but you know that whatever effect they have isn't making the display follow any kind of color standard.

If you're talking specifically about computer displays, then your graphics card probably has a bunch of color tweaks in it's control panel which can "fight" the controls on the display itself, making accurate color setup an absolute nightmare! nVidia cards (for example) have a "Digital Vibrance" control which basically looks at which of the three color components (red, green or blue) is the largest at each pixel and makes it larger still. This definitely changes muddy-looking pictures into more colorful ones...but it circumvents the intent of whoever produced the images in the first place. SteveBaker (talk) 20:07, 4 March 2013 (UTC)

• Important to this discussion, because of the phenomenon of color constancy, the sort of differences you all are noting usually aren't perceptible unless you have multiple TVs or monitors showing the exact same scene simultaneously; something most people don't have in their homes. For most people, the sort of differences in color reproduction that exist between various display devices just aren't all that noticeable unless you're deliberately training yourself to look for it, or you've carefully constructed a set up to highlight it. --Jayron32 04:54, 5 March 2013 (UTC)

Yes - but right now, I'm sitting in front of three monitors - two of them are nicely color matched, the third has an annoying reddish tinge that I really should take the time to adjust! I disagree that the changes aren't noticable. My son was building a website for a friend of mine - and she's complaining that the soft dark patches he used behind some of the text to highlight it are way too dark...but on my monitor and my son's monitor and tablet, they look great. However, she's right - the screen on her laptop has bad gamma setup and that's why it looks awful. Sadly, many people with poorly set up laptops will view the page, so it does need to be adjusted as a compromise between well-set-up computer screens and those that are a mess. SteveBaker (talk) 15:47, 5 March 2013 (UTC)

True, with two caveats: 1) As noted in the color constancy article, it doesn't hold over all possible ranges of lighting. Some differences show up obviously, and others not so much. It depends a LOT on the specific environments. It is quite possible (and common) to have such a badly tuned monitor that the color problems are instantly obvious to anyone. 2) As you note, you notice some differences because you have the monitors side-by-side, and you're also looking for the difference. Your out-of-tune monitor may (or may not) have been widely noticeable as such depending on a) how out of tune it is and b) if someone had the chance to use it without comparing it to your other monitors. --Jayron32 19:41, 5 March 2013 (UTC)

• Not disagreeing with what is written above, but I'd like to explain why this problem is theoretically unsolvable. When you have a real, physical object, such as a painting, the light that it emits is a product of combining its surface properties with the light that illuminates it. Change the illumination, you change the emitted light. But a computer display always emits the same light, regardless of the illumination. This means you can have a monitor display and a picture that seem to match perfectly, but if you change the lighting in the room, they may no longer match. The history of color-matching technology is a long series of efforts to find the best way of dealing with this fundamental theoretical problem. Looie496 (talk) 16:12, 5 March 2013 (UTC)

I understand your point, but what about non-real objects, such as text or background colors, window decoration, etc? bamse (talk) 20:03, 5 March 2013 (UTC)

I think Looie496 misunderstands the problem. Sure, we can't reproduce the exact wave-front of the actual light coming off a real-world object. But color standards aren't about doing that. They are about ensuring that this web-page design (or whatever) looks identical on my monitor as it does on my customer's. For that to work we need standards and the teeth to enforce them. SteveBaker (talk) 21:01, 5 March 2013 (UTC)

I actually understand the problem very well: I worked as a developer on GIMP for a few years, and dealt with color management at a technical level. It isn't just about monitors and other monitors -- people who are using printers want what they see on a monitor to match what their pictures will look like on paper. There is no way to make that work without calibrating each individual monitor, taking into account the light conditions of the place where it is situated. The problem cannot be solved by setting monitor standards. Some monitors are worse than others, of course, but there is no such thing as an ideal monitor in this respect. Looie496 (talk) 23:09, 5 March 2013 (UTC)

I'm not sure I understand what you're saying. The color appearance of a physical object depends on the illuminant. The appearance of color on a monitor also depends on the ambient lighting (I think it's the color adaptation of the human visual system). The two environments are generally not the same. When you work with color on a monitor, you want it to be in a dimly-lit environment. I think if you want to see what a printed image looks like under a given viewing condition, you apply a suitable transformation to remap the colors. But why do you need to re-calibrate your monitor? --173.49.9.122 (talk) 05:37, 6 March 2013 (UTC)

Monitor to monitor differences are, I would guess, the primary cause. As I write, I have a laptop (HP elitebook 8440p) with an external monitor (HP LA1951g) plugged in, with both screens configured as one extended screen. the monitor and the laptop screen are the same age, with about the same amount of hours of use. obviously, the ambient lighting and graphics processing is the same. I would assume HP intends this monitor to be used with this laptop, at least that's what they're telling my employer. if i put a window that's a particular shade of blue so that it spans both monitors, on the laptop it's a medium blue, I would guess a tad lighter than the typical windows text blue as in the menu on the left margin of this page, but on the external monitor it's a definite turquoise (and the text in the left column here looks dark navy blue, almost black). on the other hand, many colors are indistinguishable between the two monitors. Gzuckier (talk) 18:03, 6 March 2013 (UTC)

Ground penetrating radar and sink holes

Can't they use ground penetrating radar to detect cavities forming under buildings and things to know when a sinkhole is going to occur? ScienceApe (talk) 16:02, 4 March 2013 (UTC)

Yes, but "when" might be tricky.  — Preceding cryptic message added by 74.60.29.141 (talk) 16:28, 4 March 2013 (UTC)

From Ground-penetrating radar:

"Optimal depth penetration is achieved in ice where the depth of penetration can achieve several hundred meters. Good penetration is also achieved in dry sandy soils or massive dry materials such as granite, limestone, and concrete where the depth of penetration could be up to 15 m. In moist and/or clay-laden soils and soils with high electrical conductivity, penetration is sometimes only a few centimetres."

Guess what kind of soil most sinkholes form in (hint: rhymes with "vet"...) --Guy Macon (talk) 16:34, 4 March 2013 (UTC)

Limestone is porous and thus tends to be well drained (hint: rhymes with "Bye"...)! It is due (in part) to the the porosity that the rain water (think about pH of precipitation here) peculating down through the rock that demineralizes it . The hole's are invertible dry for many feet down to wherever depth the water table lays. Constantly saturated limestone would have a high pH and thus not dissolve the rocky matrix in that way (ie. vertically). --Aspro (talk) 12:43, 5 March 2013 (UTC)

Florida sinkholes tend to form where there's a layer of limestone underneath a thick layer of clay. --Carnildo (talk) 02:46, 6 March 2013 (UTC)

And it's an irregularity in that clay barrier that leads to a sink hole beneath it. --Aspro (talk) 20:55, 7 March 2013 (UTC)

The trick would be in knowing when to suspect it, to have the ground penetrating radar used. There might be signs, like a cracked foundation, but you also get these just from normal settling. StuRat (talk) 16:35, 4 March 2013 (UTC)

There are signs, e.g. [2] [3] but the time they take to develop does vary as the case which must have caused this question highlights (although I think it's fairly well established such a sudden development is rare hence why this is involving a fatality is such an unusual case despite the frequency of sinkholes in Florida [4], of course there may have been signs that were missed particularly given the time). BTW, as discussed [5], ground penetrating radar is one of a number of techniques used to assess risk and there is on going research on this [6] and other techniques [7]. However these techniques aren't necessarily cheap and I don't know if they're of much use once you see the signs, by that time the general advice seems to be to avoid the area until the sinkhole develops. The techniques seem to be of greater interest in evaluating risk for insurance purposes or when deciding whether to purchase a property or develop in the area. Note that in the case that probably resulted in the question, it was widely reported someone came to check for sinkholes a few weeks before but didn't appear to find anything. I don't know what they did and I doubt ground penetrating was used but I don't think it's any way certain they definitely would have found something. Nil Einne (talk) 18:11, 4 March 2013 (UTC)

[e/c 3x] Since you're looking for a differential, a gap in "wetness" (soon-to-be hole) should be relatively easy to find in moist soil. (I used to be a field research technician in petroleum exploration). Using a microgal gravitometer survey (with a type of gravimeter) might be better for finding potential sink holes. — Preceding modified for clarity comment added by 74.60.29.141 (talk) 18:41, 4 March 2013 (UTC)

Seismic imaging might be the most practical means of locating potential sinkholes: [8] ←[Where I used to work] 74.60.29.141 (talk) 19:45, 4 March 2013 (UTC)

See also: "What is a Seismic Survey?". Schlumberger. and Thumper trucks. ~:74.60.29.141 (talk) 20:08, 4 March 2013 (UTC):~

Considering it been estimated that there are about on average 17 sink holes opening up everyday in the US, suggest to me that some sort of Seismic tomography could be adapted easily to suit this focussed type of survey. The stuff we saw being used on TV was probably all they had available. Yet, whack a metal plate on the ground with just a sledged hammer with a transducer pick-up several yards away and it can record the reflection from subsurface cavities many feet down – not rocket science and it can be done with equipment to be found in labs across the US. The seismic shocks from just a large concrete braking hammer drill (the type they use for braking up road beds) travel several hundred feet. A purpose built portable seismic tomatography unit would make such surveys affordable and may pay back the insurance companies many times over for their investment -(why should the house-holder or government pay for it, it is the insurance company that is quoting and receiving the premium).--Aspro (talk) 13:12, 5 March 2013 (UTC)

Water and radar don't mix. Is there wet soil above the limestone formations? Yes. Therefore it won't work on a large scale (e.g. aerial or satellite survey). On a small scale it can be done as a radar with sufficient power can penetrate the moisture layer. Sailsbystars (talk) 19:26, 7 March 2013 (UTC)

Does Helium-2 jump off the ledge, or is it pushed?

Has anybody tried changing the "impact velocity" of the Proton–proton chain reaction to see if excess energy makes deuterium more likely?

If this was found not to be the case wouldn't it mean that deuterium is produced purely by diproton decay rather than by the decay of an excited proton? Hcobb (talk) 18:14, 4 March 2013 (UTC)