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October 28

Why do flour and sugar store so well?

In a kitchen you can store in not especially well sealed containers kilos and kilos of raw sugar and flour, and they will last for months without problem. But if you leave out something like bread or cake, it won't last nearly so long. It seems to me that the sugar and flour ought to be delicious to the endless armies of bacteria, and it puzzles me how the flour and sugar remain untouched. What's going on there?

Searching through the Ref desk archives, I see some explanations to the effect that sugar is so hygroscopic that it dessicates and kills any bacteria foolish enough to try to eat it, but is this the whole story, and does it cover flour as well? It seems a little unlikely to me. --Gwern (contribs) 00:26 28 October 2010 (GMT)

Perhaps it is the presence of water that differentiates between the two. Bus stop (talk) 00:55, 28 October 2010 (UTC)[reply]

Actually, this might depend on the location, but if you leave flour unprotected for long periods of time, even though bacteria won't bother it much, it's entirely possible that you'll find squirmy little multi-celled animals in it. As for brown sugar, I'm not sure; I don't ever recall seeing actual larvae in it, but I have seen it take on a sort of stringy character that makes me suspicious something has been there. --Trovatore (talk) 01:03, 28 October 2010 (UTC)[reply]

Isn't that just water absorption? John Riemann Soong (talk) 01:19, 28 October 2010 (UTC)[reply]

Yes, a primary reason bread bacteria and fungi will colonize bread before flour (in similar containers) is moisture. If you want to test this for yourself, add a small amount of water to your flour and see if it is still good in a few weeks. Trovatore has a good point about other contaminants, e.g. Flour_beetles. Also keep in mind that dry flour and sugar are highly processed products that have been designed to store well; they are not naturally occurring food sources, and relatively few species have adapted to utilize them as a primary resource. SemanticMantis (talk) 03:33, 28 October 2010 (UTC)[reply]

Well, good flour (that is, whole-wheat flour) is not so highly processed. But it is still very dry. --Trovatore (talk) 04:31, 28 October 2010 (UTC)[reply]

Honey never goes off "Honey, and objects immersed in honey, have been preserved for decades and even centuries" and is used as an antiseptic. Alansplodge (talk) 08:06, 28 October 2010 (UTC)[reply]

Perhaps it does not go off, but it does irritatingly become semi-solid to the point where you can not squeeze it out of the bottle. Googlemeister (talk) 13:54, 28 October 2010 (UTC)[reply]

Honey ought to be supplied in jars[1], not squeezy bottles. Ah, the wisdom of our forefathers. Alansplodge (talk) 14:20, 28 October 2010 (UTC)[reply]

And honey that has crystallized can easily be made liquid again, by heating in a hot water bath for a few minutes. But we stray far from the original question. Buddy431 (talk) 15:02, 28 October 2010 (UTC)[reply]

But is it the sugar content of honey that makes it an anathma to bacteria? The WP article suggests low Water activity (a property of sugar) as one agent. Alansplodge (talk) 18:19, 28 October 2010 (UTC)[reply]

Yes, honey is highly acidic, but not if you dilute it with water. Imagine Reason (talk) 17:49, 29 October 2010 (UTC)[reply]

force

Is gravity ultimately the most powerful force in the universe? --96.252.213.127 (talk) 02:35, 28 October 2010 (UTC)[reply]

No. Gravity is quite weak. See the table in Fundamental interaction and the discussion of its weakness there. It's responsible for some of the gigantic and interesting effects one gets on the solar system and universe level. But it is many orders of magnitude weaker than the other forces — hence a tiny magnet can resist the force of the entire planet's gravity. Gravity can do some amazing things when you have a lot of mass together (e.g. a black hole, or a quasar), but it's very weak as far as forces go. --Mr.98 (talk) 02:44, 28 October 2010 (UTC)[reply]

However, it often gives the appearance of being the most powerful, because it is the most easily observed since it usually works on a much larger scale than the others. --The High Fin Sperm Whale 03:43, 28 October 2010 (UTC)[reply]

Okay that is why I am asking the question... so let me put it this way... will an infinite amount of mass located in the same place make gravity the most powerful force in the universe? --96.252.213.127 (talk) 03:47, 28 October 2010 (UTC)[reply]

The question is meaningless. An infinite mass does not exist. --Anonymous, 03:56 UTC, October 27, 2010.

(edit conflict) An infinite amount of mass is impossible, and the implications of having an infinite amount of mass in one location creates all sorts of problems in the local physical universe. An abitrarily large mass would be possibly discussable, but this is not the same as an infinite mass. Also, it should be noted that General relativity doesn't treat gravity as a force, rather as a pseudoforce caused by the effect of mass warping spacetime. If you consider the mass-warping effects of General Relativity, objects move in straight lines within warped spacetime, which gives the illusion of a force. Under the standard model, forces require particles to carry them. Gravity has no known force carrier particle, which would mean that it isn't a force. There is a proposed particle (called the Graviton), but it unneccessary under General Relativity, and there has been no evidence of its existence. --Jayron32 03:58, 28 October 2010 (UTC)[reply]

What about an infinitely powerful magnet? Nil Einne (talk) 03:57, 28 October 2010 (UTC)[reply]

Could an infinite amount of mass in the form of energy exist in the same place if only for an instant? --96.252.213.127 (talk) 04:12, 28 October 2010 (UTC)[reply]

No, its is nonsensical to speak of infinite energy or infinite mass. Also, per Special relativity, the distinction is meaningless. It does no good to speak of infinities, since the mathematics of infinity makes no physical sense in the real world. One might as well ask what one would do if one had an imaginary mass or something like that. It makes no physical sense. --Jayron32 04:28, 28 October 2010 (UTC)[reply]

I disagree. The universe may well be infinite in extent, in which case the total amount of mass in the universe is presumably infinite. It's only local infinities that cause serious problems. It is possible that even those exist (for example, leptons and quarks are generally taken to be points, in which case their charge/mass/color charge densities are infinite). --Trovatore (talk) 06:03, 28 October 2010 (UTC)[reply]

Point taken. Infinities are fine, it is local infinities which create contradictions. And only certain types of local infinities. Singularities in black holes are zero volume, which means they contain infinite density. This results from infinite curvature of spacetime, which is sort-of-kind-of like infinite gravity. Except, that since gravity isn't a real force, this doesn't generate the sort of problems one would expect from an infinite force. --Jayron32 06:06, 28 October 2010 (UTC)[reply]

Yet infinite gravity can exist in the form of a Black Hole? --96.252.213.127 (talk) 05:37, 28 October 2010 (UTC)[reply]

Black hole physics is pretty peculiar, and it doesn't depend on the existance of either infinite mass or infinite energy. Black holes don't really have infinite gravity; they just have enough gravity to generate an event horizon; essentially enough gravity to warp spacetime so that the curved path that light appears to follow in the standard three dimensions bends so far that it curves inward towards the black hole. But this is not infinite. --Jayron32 05:46, 28 October 2010 (UTC)[reply]

The force would, however, be infinite at the singularity at the hole's center. --Trovatore (talk) 06:05, 28 October 2010 (UTC)[reply]

No, this would be infinite curvature of spacetime, which would mean that local objects would move as though being attracted by an arbitrarily strong force. However, a real infinite force acting on a finite mass would generate all sorts of contradictions, such as doing an infinite amount of work on the object. Locally infinite energy has all the same sorts of problems as locally infinite mass has. This is, yet again, further evidence that gravity isn't a force in the traditional sense, since no other forces (strong, weak, EM) can operate under these sorts of localized infinities. --Jayron32 06:10, 28 October 2010 (UTC)[reply]

Hmm? What about the bare electron, unshielded by its cloud of virtual electron/positron pairs? The gradient (maybe Jacobian) of the electric field there is infinite. (I shouldn't really have said infinite force — what's infinite at the hole's singularity isn't so much force as the rate of change of force.) --Trovatore (talk) 06:15, 28 October 2010 (UTC)[reply]

Yeah, but this, like the black-hole-singularity, is some pretty esoteric stuff. Under normal circumstances, you cannot have a pile of matter with an infinite mass, you cannot impart an infinite amount of energy onto an object, you cannot submit an object to an infinite force. When we say, for example, that a black hole has "infinite gravity" what we mean is that it would take an infinite force to extract an object from inside of the event horizon to the outside. That doesn't mean that the infinite force actually exists, it is a demonstration of the futility of the exercise. You can generate local infinites in any situation with zero volume because zero volume generates infinite density (for the singularity this is a mass density, for the bare electron, this is a charge density). But this is a derived infinity, caused by the peculiarities of zero volume particles. The physical reality revolves around a local zero, which is perfectly allowable and understandable, rather than a local infinity, which makes little sense. --Jayron32 06:29, 28 October 2010 (UTC)[reply]

I would answer "yes". The reason is that all the other forces are self limiting - the strong force by distance, the electromagnetic by self-repulsion (i.e. there is a limit to how strong you can make it before it bursts), the weak force by distance again. But gravity is not limited - the more mass, the stronger it gets. Ariel. (talk) 06:52, 28 October 2010 (UTC)[reply]

Except that gravity isn't a force. It requires a force to counteract its effects, but it is not a force itself. It is identical in this nature to centrifugal force, or other pseudoforces. It is an effect cause by viewing an object moving in a straight line through a region of spacetime which is itself curved. See General relativity. --Jayron32 07:03, 28 October 2010 (UTC)[reply]

Um, no. Gravity is a force - go read any article on force you like. There are four forces and gravity is one of them. And your explanation fails if you consider an object that is stationary relative to the region of spacetime, yet still experiences a force. A pseudoforces is a force that only exists in certain frames of reference, but not in others, in particular it only exists in moving (non-inertial) frames of reference. But gravity exists in all of them, and the frame does not need to be moving. And BTW the General relativity article does not once mention fictitious of pseudo forces. I think you are confusing using the principles and math of a fictitious force (equivalence principle) with actually being a fictitious force. Ariel. (talk) 08:01, 28 October 2010 (UTC)[reply]

Jayron32 is correct - in the context of general relativity, gravity is a pseudoforce, not a true force, because a point body following a spacetime geodesic does not experience a local gravitational force. First sentence of Gravitation#General relativity says "In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force". And Introduction to general relativity says "An observer in an accelerated reference frame must introduce what physicists call fictitious forces to account for the acceleration experienced by himself and objects around him ... Einstein's master insight was that the constant, familiar pull of the Earth's gravitational field is fundamentally the same as these fictitious forces". Gandalf61 (talk) 09:04, 28 October 2010 (UTC)[reply]

Richard Feynman begs to differ: [2]. Gravity can certainly be looked at and calculated as a fictitious force, but it also acts as a regular force, and it most definitely is numbered among the four fundamental forces. And the explanations you posted do not explain why a particle that is not moving still experiences a force. Using a psudoforce was a great mathematical technique, but it doesn't mean it actually is a psudoforce. Ariel. (talk) 19:22, 28 October 2010 (UTC)[reply]

The link you gave doesn't say that Feynman disagreed with the idea of gravity being a pseudoforce -- it merely says that Feynman declined to answer the question of whether it's a pseudoforce, which is very different. Personally, I'm totally with Jayron and Gandalf61 on this one. Gravity only looks like a "force" if you aren't doing general relativity. Red Act (talk) 09:35, 29 October 2010 (UTC)[reply]

Reply to Ariel. :-

Notice that I carefully said "in the context of general relativity". We know that general relativity cannot be the whole story because it is a classical field theory, not a quantum field theory. However, gravity does not really fit into the "fundamental forces" part of the Standard Model either because its hypothetical elementary particle, the graviton, has never been observed. We won't know the true status of gravity until we have a coherent theory of quantum gravity.
You say "a particle that is not moving" - but how do you define "not moving" ? As I said, a point particle following a apacetime geodesic (i.e. in "free fall") does not experience gravity. Geodesic motion is the local equivalent of an inertial frame of reference in GR (although it cannot be extended to a global frame of reference). So, in GR, a point particle that experiences a gravitational force is not following a spacetime geodesic, and is therefore "moving" relative to its local spacetime background. Gandalf61 (talk) 10:20, 29 October 2010 (UTC)[reply]

Sexuality question

Do heterosexual men normally get an erection when:

thinking of a penis?
looking at their own penis in the mirror?

Thank you in advance for any helpful answers,

82.112.147.154 (talk) 04:02, 28 October 2010 (UTC)[reply]

The range of "normal" in terms of human sexual response is VERY wide. What is sexually normal for one person is very different than what is sexually normal for another. Terms like "heterosexual" and "homosexual" are convenient political definitions, but sexuality is rarely a black-and-white issue. What a person finds sexually arousing is highly individual, and subjective to social pressures as well as innate desires. It is highly complex. The seminal (excuse the pun) work in this area is over 40 years old. See Masters and Johnson and Kinsey Reports for the cornerstone works in this area. --Jayron32 04:11, 28 October 2010 (UTC)[reply]

That probably depends on the heterosexual man in question. It probably also depends on their age; the earlier in puberty one is, the more likely one is to be aroused by anything. Some people, no matter their sexual orientation, will become aroused simply by thinking about anything to do with sex. → ROUX ₪ 04:13, 28 October 2010 (UTC)[reply]

I dunno. Do you? But when you are say, 14, you get erections pretty much from random motion of air molecules on your wiener. The curve of a tennis racquet's shape can give you a stiffness problem in about 2 seconds. People often forget about this phase of their lives when they get older, unless they recall some characteristic event or conversation. I recall that, at the age of about 14, I was discussing girls with my (male) pal, and he said that he felt that if he were to be in a girls' changing room and could view fully naked girls, not only would he have an erection, but he would almost certainly have an involuntary orgasm. And I agreed with him. Also, all the boys at our school were checked out medically at one stage, and part of that examination involved the doctor palpating the boy's scrotum to check that development was normal. We knew that this was going to happen, and despite the fact that it would only take a couple of seconds, there were quite a few of us who were concerned that we might get erections from being touched like this, or even thinking about it, and that would mean we were gay. Needless to say, later in life, the fires burn a little less feverishly. Myles325a (talk) 06:03, 28 October 2010 (UTC)[reply]

The answer to the question depends in part by what the question means by "heterosexual". There's a Heterosexual-homosexual continuum, of which two attempts at measuring are the Kinsey scale and the Klein Sexual Orientation Grid. If a man who commonly gets an erection when thinking of penises considers that fact to be a sufficient reason to mark "other sex mostly" instead of "other sex only" in response to the "to whom are you sexually attracted" question on the KSOG, then that man would wind up not being considered 100% heterosexual according to that measure, while still potentially showing up as being mainly heterosexual. One thing Kinsey found is that men tend to be more purely heterosexual or homosexual, with less of a middle ground, than woman are. But there still is a middle ground for men, as well.

And I wouldn't find getting an erection when thinking of a penis to be particularly surprising in an adolescent male, even one that scores as being fairly purely heterosexual. It doesn't take much of a reason for an adolescent male to get an erection. Red Act (talk) 06:16, 28 October 2010 (UTC)[reply]

My theory on why we often can’t run in dreams – is it valid?

Think of that terrible chase dream where you can’t move your legs. A lot of people report dreams like that, but why is it so common? My idea is that it is a consequence of dream time. In dream narratives, the story does not proceed in real-time. If, in a dream, you have to wait for an hour in a doctor’s waiting room, your dream will quickly fill up that time with other events. In other words, dream narrative proceeds much like the narrative of a movie or TV show. What is inessential to the plot is cut out or minimized. In fact dreams are so like stories we tell each other perhaps they are the progenitor of creative story-telling. So dream-time works like story time, roughly lasting as long as it might take for you to tell the story. That means dreams compress time, like narrative usually does. But there are times when this natural order is turned on its head. Sometimes, it takes longer to narrate an event than the event would take to run its course in real time.

Think of those times when you are being pursued by some monster and you feel like you are wading through sticky mud, unable to speed away. Here, the events of what might realistically be a few seconds have crammed into them all sorts of important details each of which might only take a split-second in real time, (how you slipped, what the zombie looked like, where you decided to go etc). In consequence, it takes much longer for the brain to “tell” itself this, than it would to actually just act it out. So in such a case, the action is not speeded up as is usually the case, but slowed down (in order to accommodate all this critical detail). But the “flight to survive” instinct in humans is understandably intense, so the part of your brain that is immersed in the action is screaming: “What the hell’s going on!!??!! Get the HELL out of there!!” And it interprets the slow-down as some catastrophic failure of your body, or the presence of some kind of gooey mud or the like dragging on your feet. (I also have a theory about why so many people dream of being able to fly? Wanna know?)

Do you think I’m onto something? Or just on something? Could I bank on a Nobel Prize? Or is that a dream? Myles325a (talk) 06:28, 28 October 2010 (UTC)[reply]

There's a phenomenon called sleep paralysis that (usually) keeps you from acting out what you do in your dreams. Maybe in the dreams you're talking about, you're actually conscious of that paralysis? --Trovatore (talk) 06:31, 28 October 2010 (UTC)[reply]

Is not being able to run a common theme in most peoples dreams? I've never experienced that, although I have terrible dream recall in general no matter how diligently I attempt to keep a dream journal. I can always walk, run, and hover (not fly though) 82.44.55.25 (talk) 10:45, 28 October 2010 (UTC)[reply]

It's pretty common in my dreams, and a pretty definite result of the aforementioned sleep paralysis; I'm partly awake and my brain is aware that my body is completely unable to move, so it transfers that information into my dream. Eventually I'll wake up, seriously short of breath and almost jumping out of my bed. I see no reason to think it was the more-complicated compressed-time theory put forward.

Also, the Reference Desk isn't here to evaluate your ideas. Vimescarrot (talk) 10:52, 28 October 2010 (UTC)[reply]

I guess my view, as a scientist who has worked on sleep, is that there are already so many ideas about how dreams work that further ideas are not very useful unless they're framed in a testable way. One thing that is completely clear, though, is that physical conditions such as being too warm, breathing bad air, sleeping in a bad posture, needing to urinate, etc, frequently are reflected by the content of dreams. Looie496 (talk) 17:38, 28 October 2010 (UTC)[reply]

Op myles325a back live. From above:

One thing that is completely clear, though, is that physical conditions such as being too warm, breathing bad air, sleeping in a bad posture, needing to urinate, etc, frequently are reflected by the content of dreams.

Someone should have told Freud that. It would have saved him and the rest of us from an enormous red herring. (Like the one that chased me last night and I couldn't move.) No, guys this is not sleep paralysis. I've had that, and you are basically awake when it happens. I'm just talking about nightmares in which time seems to be slowed down. No one has addressed my idea on the inversion of dream narrative time. Looie, it might be difficult to do much in the way of running empirical and falsifiable tests on the content of dreams. The world of Inception is not here yet. There is such a thing as lucid dreaming where the person is aware they are dreaming, and I have often experienced that as well. I invariably shed my clothes and fly off cliff tops. It’s a blast! Myles325a (talk) 23:39, 28 October 2010 (UTC)[reply]

There's something weird about how running is handled by the vertebrate nervous system. Chickens, famously, but also cats^[3] have been observed to run around without control from the motor cortex; as I understand it much is handled not even in the brain but lower in the spine. I don't think the same sort of response has been accomplished in humans - certainly the average quadriplegic takes more than a few prods to start running. I suppose it makes sense, though, since primate locomotion in treetops must be integrated directly with visual maps of the surroundings, which would demand that movements be organized fairly near the visual cortex (for example). Wnt (talk) 04:44, 29 October 2010 (UTC)[reply]

I'll add to the poster's question, without really having done much to answer it, by noting my own peculiar observation from dreams - tripping over an object is the one thing south of the eyes not affected by sleep paralysis for me. So if I dream I trip over an odd terrain I'm immediately awakened by the "compensatory" motion of my legs. Wnt (talk) 04:44, 29 October 2010 (UTC)[reply]

Your dreams might not be sleep paralysis-related. Mine most definitely are. You'd have to find out whose are most common. Vimescarrot (talk) 10:35, 29 October 2010 (UTC)[reply]

Awareness of real physiological states often leaks into dreams; needing to pee is commonly noted to produce corresponding dreams, or if a pet cat jumps on you in your sleep you may dream of being attacked by a monster, and so on. People usually sleep with their legs trapped under blankets. So this is my simple explanation for dreaming of being unable to move your legs: it's because you're unable to move your legs. 81.131.53.127 (talk) 11:40, 29 October 2010 (UTC)[reply]

solar enery storage

Can solar cells be mounted on the top of a car, where the converted electric enrgy is stored in electric cell which can be easily removed and used for domestic purpose? Is there a mechanism by which everyday I can easily remove the charged cells from panel and put discharged cells into panel for solar charging? —Preceding unsigned comment added by 203.199.118.12 (talk) 06:40, 28 October 2010 (UTC)[reply]

Yes, it could be done, but why? If the plan is to use the charged cells to power your car then you will need the charged cells. Putting uncharged cells on your car means your car won't move until the sun has been up for a few hours. If the plan is just to charge cells, why not put them somewhere stationary like a house roof where they can be oriented towards the sun (south if you live in the northern hemisphere, or north if you live in the southern hemisphere.) The roof of your car always points straight up, and that isn't an ideal orientation for a solar panel. Dolphin (t) 06:46, 28 October 2010 (UTC)[reply]

(edit conflict) The problem is that batteries can't really store all that much energy, especially given what a normal house would use in a given day. Plus, batteries have a fairly short lifespan; if you are constantly charging and discharging large storage cells, they need to be replaced frequently enough to make the system too expensive for household usage. A far more efficient system is to use excess solar energy to operate a water pump which fills a retention pond. When demand exceeds supply from the solar system, the water in the pond is sent over a sluiceway to generate hydroelectric power. See Pumped-storage hydroelectricity. --Jayron32 06:47, 28 October 2010 (UTC)[reply]

The amount of energy that could be generated by solar cells on top of a car would be only a very tiny fraction of the energy needed to run the car. It might be sufficient to run a car radio on a sunny day. Solar cells to not store any energy at all, they just generate it. A different type of cell (as in battery) is needed to store the energy generated (or an alternative storage system, as in a hot-water cylinder in a house, or Jayron32's suggestion above). Dbfirs 09:22, 28 October 2010 (UTC)[reply]

Some Priuses have a solar cell on top which is to help ventilate the car when it's parked in the sun so it doesn't get so hot. It was intended to charge the battery (obviously not contributing much) but this was found to cause problems with the radio. (See the article.) There have been addons for cars for a while but these don't work very well [4]. It's been suggested the solar cell may be enough for the AC before (I believe this may have been how the Prius was going to be promoted [5]) but I don't think anyone has done this in practice. Nil Einne (talk) 12:02, 28 October 2010 (UTC)[reply]

Solar cells on top of a car can indeed run the car. See the article Solar car racing which notes recent solar cars crossing Australia at 90 to 100 km/h. Cuddlyable3 (talk) 13:24, 28 October 2010 (UTC)[reply]

Granted, but that is not even close to being the same scenario as bolting a couple of panels to the top of your Taurus. Those cars were designed specifically for that event and are not in wide production. Googlemeister (talk) 14:59, 28 October 2010 (UTC)[reply]

... and they can't cope with hills, or even slight gradients without using their backup battery! Dbfirs 07:49, 29 October 2010 (UTC)[reply]

Is ADD real?

Is it really real? I don't mean to offend anyone by asking this, I just need to know if ADD is as real as a broken bone or a cold. When it shows more red spots in the fMRI images of scanned ADD brains is that due to ADD, or is it do to some other issue that could make it seem like its ADD, but its actually just another correalation? If its real, then why does it not seem to have existed in the past, or even 100 years ago? If anyone knows if it is real, how do they know? And did they get it from an unbiased source that wasn't funded by a pharmaceutical company or had nothing to gain? AdbMonkey (talk) 08:35, 28 October 2010 (UTC)[reply]

I'd say it's definitely real. Whether it's a disorder or not is more a question of interpretation. I'm quite sure it did exist going back as far as you like; it may not have been interpreted in the same way. --Trovatore (talk) 08:41, 28 October 2010 (UTC)[reply]

In extreme cases it certainly is a disorder. APL (talk) 14:25, 28 October 2010 (UTC)[reply]

May I ask what leads you to be certain about it being real? What eveidence leads you to believe it is? What is it that makes you say "Ok, now knowing that, I know it is definitly a real brain thing." AdbMonkey (talk) 08:58, 28 October 2010 (UTC)[reply]

It's essentially defined to be real. Anyone who meets the diagnostic criteria has it, by definition. --Trovatore (talk) 09:04, 28 October 2010 (UTC)[reply]

Here are those diagnostic criteria. It can't really "not be real" as it's basically a description of how some people behave. Some people do indeed behave like that; so it's real. Vimescarrot (talk) 10:47, 28 October 2010 (UTC)[reply]

(edit conflict)Have you read the Attention deficit hyperactivity disorder article and associated articles, like history and controversies? Probably also worth thinking that the world is vastly different from 100 years ago in terms of pollutants, availability of healthcare etc. which may explain part of the increases in diagnoses, although the differences in frequency between the US and UK suggest that pharmaceutical companies may also have something to do with it! Smartse (talk) 10:49, 28 October 2010 (UTC)[reply]

In the past the condition you call ADD was simply characterised as inattention, easy distractibility, disorganization, procrastination, forgetfulness, or lethargy, and teachers and parents would react with negative comments (e.g. "you're irresponsible", "you're lazy", "you don't care/show any effort", "you just aren't trying", etc.). There is nothing new about observing these symptoms (that were certainly seen 100 years ago), the change that has occurred is that they are now classified under particular DSM criteria (see articles here and here) for research and treatment. Cuddlyable3 (talk) 13:14, 28 October 2010 (UTC)[reply]

Ok, well thank you for answering, but I guess this is a hard one to answer. AdbMonkey (talk) 13:35, 28 October 2010 (UTC)[reply]

Let me put it this way. We can define arbitrary parameters and claim it is a condition. So having yellow hair we will call "blonde". It's as real as most anything else, even if there is a spectrum of hair color between yellow and brown or red, and we'd have to argue about where the line should be drawn for someone to be truly "blonde". Now all of that is different than saying that being "blonde" is some kind of disorder, something that should be "treated" (through hair dye) or "cured" or stigmatized or used as an explanation as to why people do certain things (e.g., drive around in red convertibles). Everyone agrees that there is some spectrum of the condition, not everyone agrees it is a disorder, or even a disease, or anything other than the spectrum of normal human behavior, or should be treated with medicine, or what have you. --Mr.98 (talk) 14:06, 28 October 2010 (UTC)[reply]

The study of neurology is still developing. Simply because a problem hadn't been identified doesn't mean it's not real. (Before heart attacks were discovered no one was diagnosed as having one, but people still keeled over mysteriously.)

However, many people claim that ADD is over-diagnosed and/or over-medicated. That's a much more difficult question. APL (talk) 14:25, 28 October 2010 (UTC)[reply]

Maybe what this question is getting at is whether ADD is something identifyably wrong with the brain, for example "too much chemical X in the brain" or "brain region A not talking to brain region B". Given that there are medications that help people with ADD but have different effects on people without it, I would guess that it is a phisical problem in the brain, but I am not a neurologist. —Arctic Gnome (talk • contribs) 15:15, 28 October 2010 (UTC)[reply]

Having an "attention deficit" is probably true of everyone to some extent at least some of the time. But "attention deficit disorder" is not just about having a "short attention span" (although people who have it do have that problem more than is "average"; they also have problems hyper-focusing their attention, ie. have an "attention surplus", at times, too) – the ADD/ADHD subtypes are comprised of clusters of symptoms that seem to tend to appear together in a way that is clinically diagnosable (which is not to say that it is not or cannot be over-diagnosed). I can see how you might question ADD's "reality", OP, if you are just thinking it is a matter of having poor attention and finding someone who will give you speed for that – which is what a lot of people would perhaps like to do, far from all of whom could or should be diagnosed with ADD. Disclosure: I am a case of clinically diagnosed and treated ADD myself. WikiDao ☯ (talk) 17:15, 28 October 2010 (UTC)[reply]

Ok. Yes, I was looking for something that said "Yes, ADD is real, because the brain is different and that difference renders x state." But I guess that person up above is right. It might be more questionable as to how its treated rather, or over diagnosed, rather than whether its real. So my queation now is, the biggest THING about ADD is the ability to pay attention, right? Or you can be so sensory overloaded that you can't decide on something, right? So, but isn't that on a continuious spectrum degree plot thing? So I mean, maybe everyone has this to some degree, but ADDers have it a little more to where its interfering in there lives? Because concentration, or lack thereof affects everyone at some time or another, even if they hardly ever encounter it, right? Its like being forgetful, or being frustrated, or tired, or bored, or talkative, everyone experiences that to some degree, right? So, I'm just trying to figure out... it. Teeny tiny font that everyone can still read: I could have it myself too, but I don't know, I'm trying to understand if my problems arejust me, or my 'ADD'. AdbMonkey (talk) 05:49, 29 October 2010 (UTC)[reply]

You can't answer the small-font question without consulting a doctor, really. Vimescarrot (talk) 10:36, 29 October 2010 (UTC)[reply]

Ok, well, I don't want to consult a doctor, because I have consulted doctorS and they seem to have different opinions. But regardless, I wanted to know what they learn about it. Anyway, wikipedia just seems like its reinforcing what I already know, but thanks. AdbMonkey (talk) 11:15, 29 October 2010 (UTC)[reply]

If you are asking if the pathophysiology is "real" (in the sense that the pathophysiology of say cancer is "real"), well, the Pathophysiology section of the ADHD article says, "The pathophysiology of ADHD is unclear and there are a number of competing theories." (It says a lot more, too, though, which you may want to read;). There have been some brain-imaging studies with, as I recall, some fairly clear results, but which have still not been sufficiently developed to provide a reliable means of diagnosis (as far as I know).

And note that ADD is a "syndrome", which "is most often used to refer to the set of detectable characteristics when the reason that they occur together has not yet been discovered."

On a more personal level, I can definitely recommend the book Driven to Distraction, which was a real revelation to me when I read it (and led me to actually go get treated by one of the co-authors, both of whom have ADD themselves, actually!), though it is perhaps a bit dated now (there have been a few sequels to it, "DtD II" etc...). If you think you may have ADD yourself, AdbMonkey, you should definitely try to be evaluated by an ADD specialist (and I believe lists of them may be given as an appendix to the above book). G.P.'s or your standard-issue psychiatrist are usually not too up on adult ADD (its diagnosis and treatment), I've found. WikiDao ☯ (talk) 13:06, 29 October 2010 (UTC)[reply]

Thank you WikiDao. AdbMonkey (talk) 19:32, 29 October 2010 (UTC)[reply]

np, Adbmonkey! :) (And just btw in case you are interested see also: the Hunter vs. farmer theory ;). WikiDao ☯ (talk) 21:27, 29 October 2010 (UTC)[reply]

O2 effect on metabolism

If a person running in standard atmosphere conditions with a 20% O2 content burned 120 kcals running 1 mile, would the same person performing the same activity under identical conditions save the O2 content was 50% burn more or less kcal from the activity? (I don't think you can get O2 toxicity at 1 atm) Googlemeister (talk) 14:13, 28 October 2010 (UTC)[reply]

You may wish to consider anaerobic metabolism. If this happens then it is relatively inefficient and more calories will be consumed, increased oxygen is likely to reduce that, so more oxygen probably means less calories burnt in a run. Less breathing will be needed too if there is higher oxygen level. Graeme Bartlett (talk) 20:33, 28 October 2010 (UTC)[reply]

Pyrotechnic colorant

I have several questions about this article.

Are sulfates really high-temperature oxidizers? I haven't heard of sulfate explosives yet.
Is carbon monoxide strong enough to reduce magnesium oxide to magnesium?
Sodium bicarbonate reacts with aluminium and magnesium to make hydrogen?
Are barium and strontium chlorides oxidized when heated very hot?

Thanks, Chemicalinterest (talk) 14:26, 28 October 2010 (UTC)[reply]

For 2, you can use an Ellingham diagram to see if this is the case. No, it doesn't look like CO -> CO₂ is able to reduce MgO at any reasonable temperature. However, C -> CO will reduce MgO to Mg above about 2100 C (give or take a few hundred degrees, my diagram's not the most accurate). Buddy431 (talk) 14:56, 28 October 2010 (UTC)[reply]

1,3: yes. 4: depends what you mean by "oxidized" Physchim62 (talk) 18:13, 28 October 2010 (UTC)[reply]

I would assume 2 BaCl₂ + O₂ → 2 BaO + 2 Cl₂ What is the reaction between NaHCO3 and Al? I would assume the bicarbonate has decomposed, maybe even to sodium oxide. --Chemicalinterest (talk) 18:25, 28 October 2010 (UTC)[reply]

Heating the bicarbonate gives off water and CO₂. THe water could react with hot metals to release hydrogen. you may get sodium carbonate formed depending how hot you go. Graeme Bartlett (talk) 20:25, 28 October 2010 (UTC)[reply]

Well, the water would definitely make hydrogen gas. IIRC, the conversion to sodium carbonate happens at a relatively low temperature, somewhere around 200C. The reaction would be 4 NaHCO₃ + Mg → Mg(OH)₂ + H₂ + 2 CO₂ + 2 Na₂CO₃ --Chemicalinterest (talk) 22:24, 28 October 2010 (UTC)[reply]

"Oxidiser" doesn't always mean "explosive". In organic chemistry anyway, we need strong oxidisers to attack or cleave or substitute certain bonds and we definitely don't want explosions. ;-) The issue is that sulfate when reduced either forms sulfur (a solid!) or hydrogen sulfide, a really smelly gas, and sulfur is less electronegative than nitrogen is so it's less likely to form H2S given a certain reducing agent. Nitrate explosives form steam and nitrogen gas when reduced, with much higher explosive velocities. Perhaps sulfates are good oxidising agents but their sulfurous gases make for poor detonation velocities. John Riemann Soong (talk) 06:28, 29 October 2010 (UTC)[reply]

The other issue is that intermediate carbon-nitrogen bonds (single, double, triple) are more likely to form than carbon-sulfur bonds in an explosion. I haven't studied explosive dynamics, but intermediates that give alkenes and ethylene and cause large phase changes will cause some severe shockwaves in pressure. The thing for any sizeable explosion is the generation of pressure and gas -- temperature increases the pressure of an existing gas but you need some good gases in the first place. If there are many pathways to oxidation then many gas products will form, and very quickly. On the other hand, if you use an oxidising agent with only a few routes to oxidation, even if it's strong (the kind of selectivity preferred in industrial, nonexplosive chemistry) then you get "bottlenecks" in gas formation which will result in lower detonation velocities simply because the reaction is slower, despite possibly higher thermodynamic potentials. John Riemann Soong (talk) 06:35, 29 October 2010 (UTC)[reply]

Complement system and antibody-antigen complexes

We recently did experiments regarding these two features of the immune system, but it left me somewhat confused. At one stage we were asked to compare our antibody titre for agglutination of red blood cells, and the titre for complement-mediated lysis. They are different, but I'm unsure as to why. When the amount of antigen outnumbers the antibodies, this serves as a cut off point for agglutination since there are no free antibodies. So why is the titre any higher for complement-mediated lysis? Does complement activate the membrane attack complex and then once the cells are destroyed release the antibody so it can attach to another pathogen, or is it another mechanism? Regards, --—Cyclonenim | Chat 15:03, 28 October 2010 (UTC)[reply]

Two IgG molecules bound to a RBC will not agglutinate; however, they are sufficient to activate the complement cascade (and thus generate a membrane attack complex). -- Scray (talk) 18:32, 28 October 2010 (UTC)[reply]

Tachyons

If a tachyon collided with a normal (not FTL) particle, would it transfer its temporal "momentum" to that particle and thus send it back in time? --J4\/4 <talk> 15:37, 28 October 2010 (UTC)[reply]

No modern, coherent theory exists to explain tachyon interactions with non-tachyons. Here is a paper from 1968 regarding interactions between tachyons: Quantum Field Theory of Interacting Tachyons. Applying the techniques in this paper to an ordinary particle will yield an unphysical result. This is a consistent problem with theories about tachyons. Nimur (talk) 16:57, 28 October 2010 (UTC)[reply]

Another chemistry question

How much beryllium-copper-silver alloy is in a small thermal fuse? --Chemicalinterest (talk) 17:15, 28 October 2010 (UTC)[reply]

The patent Thermal fuse of Kazuhiro Miyazawa gives a example 35mm x 3mm x 0.15mm, so it is not much.--Stone (talk) 19:36, 28 October 2010 (UTC)[reply]

I opened it up and saw nothing more than a spring and some ceramic on the ends. They probably don't want too much toxic beryllium on their hands.--Chemicalinterest (talk) 20:18, 28 October 2010 (UTC)[reply]

I used the material some time ago, but the safety regulations were not that bad. Avoid producing air born particles was the major concern. The small copper spring is the only beryllium containing part in the whole system. The beryllium content is 3% by mass max or 17% by atoms. So there is not much beryllium in that fuse. --Stone (talk) 21:10, 28 October 2010 (UTC)[reply]

I wanted to dissolve the alloy in hydrochloric acid to make the chloride, precipitate the hydroxide, and probably do all that work for a picture for my dear Wikipedia. ;) --Chemicalinterest (talk) 21:30, 28 October 2010 (UTC)[reply]

Geodesic dome garden shed

Would a geodesic dome be a cheap way of creating some storage space in my garden, or would I better using another method? http://sci-toys.com/scitoys/scitoys/mathematics/dome/dome.html What do the critics of geodesic domes in the article suggest as a better alternative? Thanks 92.15.25.142 (talk) 18:59, 28 October 2010 (UTC)[reply]

Probably not, at that scale a ordinary rectangular shed would probably a be a good deal easier to build, and would give you more volume for a given section of ground. APL (talk) 19:28, 28 October 2010 (UTC)[reply]

Our article geodesic dome alludes to their leaking. If you google geodesic dome always leak -wikipedia you'll see plenty of testaments to their propensity to leak, despite the advocates' protests. Comet Tuttle (talk) 19:44, 28 October 2010 (UTC)[reply]

I'm not a critic of geodesic domes (by profession) - but they are complex. As an alternative to a rectangular shed various cylindrical and hemispherical shapes make sense - eg nissan hut/Quonset hut or see http://www.plantmanagers.com/hoop.htm .. using flexible hoops the hemispherical one can be made in wigwam fashion.77.86.42.103 (talk) 12:38, 29 October 2010 (UTC)[reply]

Figuring names out for cells

Before anyone asks, it's for a book. A species that is in the book has a few extra immune cells. These include ones that act like mobile chemical detectors (to trace harmful bacteria and other things in the bloodstream), and then there's what I have termed the otocyte. It cuts harmful cells apart and then the macrophages eat the pieces. I got that from -otomy (to cut) and -cyte. However, since Wikitionary refuses to give those definitions for either of those terms, I've decided to ask here. I'd put it in Humanities, but I figure that cell biologists would be the ones naming things. So, otocyte- good name or psuedoscientific one? Feel free to give one for the chemical-detecting cell too. PS: Might as well just block all school computers preemptively, since every time I try to do something on one without logging in it says that it is blocked for vandalism. PSS: While I'm here, would nickel-neodymium be a sufficient substitute for nickel-iron in the composition of a planet's core? ArchabacteriaNematoda (talk) 20:48, 28 October 2010 (UTC)[reply]

Go to better schools? Nil Einne (talk) 21:35, 28 October 2010 (UTC)[reply]

Even the best schools in the world are home to some of Wikipedia's worst vandals. During my stay at MIT, I often received vandal warnings via the shared-proxy before logging in - User talk:129.55.200.20 records some fascinating vandalism from the Lincoln proxy. MIT Lincoln Laboratory is a federally funded research and development center chartered to apply advanced technology to problems of national security... and to post drinking tips to Wikipedia. Nimur (talk) 22:01, 28 October 2010 (UTC)[reply]

The prefix oto- usually refers to the ear. If you want to refer to cutting, you should call them tomocytes (see tomo-). ---Sluzzelin talk 21:40, 28 October 2010 (UTC)[reply]

I second that. "Otocyte" makes me think of cells that listen for noises inside the body. Which would be interesting, but hard to picture. You'd think cells very roughly 1/1000 the size of the cochlea would detect sounds 1000 times higher in pitch — ultrasonic or higher — and I don't know how far those would carry. I have a fair suspicion cells have some as yet undocumented sense of hearing e.g. in primary cilia, but I won't go so far as to predict a specialized cell type. Wnt (talk) 05:04, 29 October 2010 (UTC)[reply]

There's a reason why it's nickel-iron, although neodymium makes sense among the rare earths. One could in theory assemble a planet out of anything. --Tardis (talk) 22:04, 28 October 2010 (UTC)[reply]

Ah, the nuclear binding energy stuff isn't something I'd considered yet. I thought it was just because it makes a great giant magnetic field. But then again, I'm just a junior in an American high school, I haven't gone into anything that deep. This sort of thing is why the internet is so useful. I often surprise my teachers with random facts that I pull off a page of Wikipedia onto my brain. Thus why I figured I needed Nickel was because it balanced out the magnetic field or some such (seeing as I can't get my neodymium magnets to lift a nickel- although that is more copper than nickle I read). Anyways, thanks for the cell stuff and planetary stuff. ArchabacteriaNematoda (talk) 02:07, 29 October 2010 (UTC)[reply]

I don't see why you "need" some substance in a planetary core, but:

Neodymium is not ferromagnetic. An alloy made from neodymium, boron and iron is.
Ferromagnetism isn't relevant in Earth's core, because the temperature is way too high (see Curie temperature)
Earth's magnetic field is caused by certain convection currents and the effects of the planetary rotation in the molten metal.

Icek (talk) 04:34, 29 October 2010 (UTC)[reply]

The tough part about the neodymium core idea isn't the magnetic field (which is pretty near ornamental anyway) but where does it all come from? I know why Earth has an iron core - because a supergiant star burns down to iron, which is the stablest element toward which all fusion or fission leads. But neodymium is a rare earth - one of many similar elements present as trace components of sands in a now closed mine in the U.S. and a mine in China which recently made the news because its production might be reserved by that country for its own use. Apparently the Japanese are now looking to mine in Vietnam^[6] Anyway, you see why making the core of a planet out of this stuff leads to some pointed questions. Wnt (talk) 05:11, 29 October 2010 (UTC)[reply]

Hey, I should have read that article! Apparently rare earths aren't really that rare, just hard to find in useful ores. Neodymium is actually a little more common than lead. Of course, this is still less common than iron even in the crust, and there's not enough lead to make a core for the planet, but my argument above was still partially defective. See Abundance of elements in Earth's crust. Wnt (talk) 05:16, 29 October 2010 (UTC)[reply]

Possible circuit that shows this particular voltage/current pattern

What kind of circuit will produce this pattern of current ("peaks") for a sinusoidal voltage input? http://i54.tinypic.com/2u61fn9.jpg --Belchman (talk) 21:40, 28 October 2010 (UTC)[reply]

A Zener diode could do something sort of like that. It passes current when the voltage is beyond a threshold (in either positive or negative direction). It looks like there's some hysteresis and some non-ideal behaviors in there as well. Nimur (talk) 21:56, 28 October 2010 (UTC)[reply]

It is very likely a Reservoir capacitor and load behind a full-wave Rectifier. The deformation of the "peaks" and the current between the peeks indicates some circuit between the point of measurement and the Rectifier, probably a transformer or a Line filter.

A transformer would be likely but I do think the current between the peeks should be 90 degree after the voltage, not before as in the picture. Maybe I miss something or the current between the peeks are maybe not the magnetisation current a transformer. Could you describe where you got the measurement?

--Gr8xoz (talk) 23:25, 28 October 2010 (UTC)[reply]

Yes. Sorry for not having said this before. Apparently it was gotten with an oscilloscope and a shunt while measuring the power consumption of a personal computer. The same paper also shows the voltage and current during the analysis of the power consumption of a server. For some reason, the server doesn't show peaks of current; instead it shows two sinusoids (a linear relationship between current and voltage, therefore it can be modelled using a single resistor). I don't know what makes the server so different from the personal computer in its power consumption behavior - maybe some kind of power saving mechanism? --Belchman (talk) 08:29, 29 October 2010 (UTC)[reply]

A personal computer uses a Switched-mode power supply and has no transformer before the first rectifier, the current between the peeks is prbably due to Line filter (EMI-Filter) or measurment errors. It is easy to get disturbances in the measurment when using a shunt.

The server has probably a more expensive Switched-mode power supply using a Power Factor Pre-regulator to minimize the disturbance on the mains see [7]. --Gr8xoz (talk) 09:36, 29 October 2010 (UTC)[reply]

Thanks. Also I have a third picture, where the computer screen of the first personal computer has been turned off. It shows an increase in the amplitude of the current peak and also a delay in said peak - so that the voltage and the current are no longer in phase. What kind of power supply do computer screens (I don't know if it's an LCD or a CRT screen) use? --Belchman (talk) 10:19, 29 October 2010 (UTC)[reply]

Most new displays (typically LCD) would/will have a switched mode power supply. I'm not sure if I've read correctly but if current and voltage are out of phase that would suggest to me that there is an inductor in there - ie it's an old fashioned power supply with the initial component a transformer.77.86.42.103 (talk) 21:11, 29 October 2010 (UTC)[reply]

Thank you!! --Belchman (talk) 16:29, 30 October 2010 (UTC)[reply]

BPA degrade

In this fox "news" article, (citing this article) it states that:

Since BPA degrades in the gut when we consume it, very little gets to our cells.

So does BPA have an effect prior to getting degraded in the gut?Smallman12q (talk) 22:40, 28 October 2010 (UTC)[reply]

I find it a remarkable claim to make that bisphenol A (BPA) is degraded in the gut. Chunky aromatics like that usually go to the liver for degradation, that is they can enter the blood stream. I think the Murdoch media have simply chosen an "expert" who will give them the opinion they want. Physchim62 (talk) 23:24, 28 October 2010 (UTC)[reply]

Why put "news" in quotes? The article referred to was written by John Stossel, and is clearly marked on top as an "Opinion" article-- something that Physchim62's post lacks. Admittedly, "Since BPA degrades in the gut when we consume it, very little gets to our cells" is a paraphrase and not an exact quote, but the claim is completely supported by the linked article in the Sun-- hardly part of the "Murdoch media" conglomerate. Fox News didn't "choose an expert who will give them the opinion they want," as was claimed-- a columnist simply quoted Professor Sharpe as support for an argument. I'm not a shill for either the BPA industry or Fox News (I only get basic cable, which goes up to channel 21...) but the reality is that there is no hard evidence, at least at this point, that BPA is harmful to humans. Why, with no good evidence that I should, would I buy a BPA-free water bottle for $4 when I can buy a regular one for $1?

But, as this is the *Science* desk, the OP was presumably hoping for an answer to his/her question. The linked article says:

Q. What happens if we consume too much BPA?

A. Nothing as far as we can tell.

That seems to be the answer (or at least one answer). If your gut (ha, ha) tells you that this claim is less than completely genuine, perhaps a accurately worded Google search would be a good next step. Kingsfold (Quack quack!) 14:42, 29 October 2010 (UTC)[reply]

"but the claim is completely supported by the linked article in the Sun-- hardly part of the "Murdoch media" conglomerate." Err, The Sun is part of News International - see the News Group Newspapers info at the bottom of the article. Anyway, more importantly, the expert, Richard Sharpe looks as if he should know what he's talking about regarding the effects of BPA, but not necessarily whether it is degraded in the gut. The quote in this section of the article would indicate that it may not be broken down in the gut, as it was found in the urine of 93% of Americans. This paper supports that view, and Physchim62's; rather than being degraded, in monkeys it is linked to glucuronides and excreted in the urine, similar to the way that many drugs are metabolised. (Can't help pointing out the possibility that Dr. Sharpe might not have said it and that The Sun made it up, it wouldn't be the first time.) Because of this I don't think we can really answer your original question, other than to say that a tiny amount will be absorbed into the blood in your mouth. Smartse (talk) 15:38, 29 October 2010 (UTC)[reply]

BPA is correlated with health problems, eg and is found in urine (which means it isn't totally destroyed by the gut), it's also found in other body tissues and fluids.

Richard Sharpe; the source of the claim that BPA does not cause health problems accepts the correlation but suggests that it may be due to people having poor health in general being more likely to drink from BPA containing liquid containers - and the cause of their problems being due to their lifestyle not BPA :

Professor Richard Sharpe, of the University of Edinburgh, said for some people a raised risk of cardiovascular disease and diabetes could simply be down to drinking too many high sugar canned drinks. These people would also be exposed to higher levels of BPA from the lining of drinks cans - but that could be purely incidental. He said more research was needed to tease out the truth before BPA could be labelled as the prime suspect. [8]

At least read Bisphenol_A#Studies_on_humans. The Sun (United Kingdom) by the way is not a reliable source.77.86.42.103 (talk) 15:48, 29 October 2010 (UTC)[reply]

There is absolutely no way for any of the intestinal or salivary enzymes to attack any of the bonds in bisphenol A. Digestive enzymes generally work by hydrolysis of acyl bonds. There is nothing hydrolysable in bisphenol A. John Riemann Soong (talk) 06:59, 31 October 2010 (UTC)[reply]

Wikipedia:Reference desk/Archives/Science/2010 October 28