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October 21

Metric

The Fisher information metric is understood to describe infinitesimal changes in the Kullback-Leibler divergence. However its quantum analog, the Bures Metric, is understood to describe infinitesimal changes in the Bures distance, which is defined with reference to the Fidelity, and not the Quantum Relative Entropy (the quantum analog of the KL divergence). What is the reason for this breakdown in analogy?

Has a metric describing infinitesimal changes in the QRE been studied? Does its behaviour differ from the Bures Metric? — Preceding unsigned comment added by 144.82.191.250 (talk) 10:51, 21 October 2013 (UTC)[reply]

Just linking some of the terms above for reference: Fisher information metric, Kullback-Leibler divergence, Bures metric, Bures distance, Quantum relative entropy. -- The Anome (talk) 11:21, 21 October 2013 (UTC)[reply]

Also Fidelity of quantum states. Red Act (talk) 17:18, 21 October 2013 (UTC)[reply]

Maybe the Mathematics reference desk is a better place for this ... Ssscienccce (talk) 14:27, 21 October 2013 (UTC)[reply]

This is unarguably within the remit of physics. — Preceding unsigned comment added by 86.134.240.24 (talk) 19:45, 21 October 2013 (UTC)[reply]

Regarding the absence of a very well known info on SEXUAL DESIRE on wikipedia

This question is related to sexual desire of males. In the article SEXUAL DESIRE i could not find a very well known fact. It is generally seen that in sexually active active males, the time gap between the ejaculations affects their sexual desire. For example, if a man masturbates or ejaculates regularly(say once a day or once every two days or twice a day) and suddenly stops it, his sexual desire(or what we call libido) increases..It is also observed that the orgasm after a period of abstinence are also intense and getting and erection in a short term abstinence period is quicker..Why does this happen..? And why does wikipedia not mention i under the factors affecting sexual desire ..? I know that males are made to release their sperms once in a while. But why could i not find a reason or mention of it on wikipedia. .. Please give a scientifically proven reason for your answer....many thanks — Preceding unsigned comment added by Ed beerman (talk • contribs) 11:46, 21 October 2013 (UTC)[reply]

If it's that well-known, you should have no trouble finding valid sources on it, and could improve the article yourself. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:42, 21 October 2013 (UTC)[reply]

You are generalizing with no links to any studies. Your statements amount to speculation and can be discarded.217.158.236.14 (talk) 13:24, 21 October 2013 (UTC)[reply]

It is noted (with cite) in Libido#Physical_factors. Libido is one of the concepts linked and discussed in Sexual desire, but I don't understand the distinction between those two concepts...seems like there is a lot of overlap between their articles. DMacks (talk) 15:07, 21 October 2013 (UTC)[reply]

The most relevant article is probably refractory period (sex). Looie496 (talk) 16:05, 21 October 2013 (UTC)[reply]

yes,i have read about Refractory period(sexual)..But this article only deala with the time period after ejaculaion during which it is impossible for a person to get an erection..i am talking about a different thing(although we can relate it to refractory period)...i am asking about the reason that greater the gap between two ejaculations(at least in short run) , higher is the desire to ejaculate ...why is sit so..? — Preceding unsigned comment added by 117.207.94.35 (talk) 17:27, 21 October 2013 (UTC)[reply]

At a guess, I'd imagine that it has at least something to do with the changes in pressure in the ejaculatory system caused by the build-up and release of fluid, but that would be pure unfounded speculation on my part; there are so many mechanisms that could be related to it -- hormonal, nervous (voluntary and involuntary), muscular, vascular, psychological, learned behaviours, etc. etc. that it wouldn't be suprising if it was still an open question. Have you tried to take a look at the medical literature on the topic, e.g. via Medline? -- The Anome (talk) 00:42, 22 October 2013 (UTC)[reply]

Are you sure this is actually true? I usually masturbate (or have sex) around 4 times a day, if I'm busy and not able to, and am aware of this, then what you're discussing holds. On the other hand, sometimes I don't notice, in which case it doesn't make a difference at all. In other words, at least for myself, it seems that if I want sex/masturbation and can't have it, then I want it more- and if I don't really want it and don't get it, then I still don't want it. What you seem to be describing is wanting + not getting = really wanting; but that holds for hunger, thirst, the need for a cigarette, or any other desire. I think the key is where you say "and suddenly stops it", rather than doesn't feel like it- if you avoid satiating anything, again, you're going to want it more.Phoenixia1177 (talk) 04:11, 22 October 2013 (UTC)[reply]

"Oh, no, not again. The creature stirs..." (Momentarily contrasting the desperate intellectual deprivation of the 80s with our fortunate forum, though I think Harry would have missed the sound of a human voice.) Wnt (talk) 05:20, 22 October 2013 (UTC)[reply]

Four times a day sounds like above average frequency for male orgasm. I have heard "Age 20: tri-weekly. Age 40: try weekly. Age 60: Try weakly." So no scientist has published reliable sources looking into the temporal link between getting off and horniness? Amazing. Think of all the studies that could be done with experimentally varying the hydrostatic pressure in the seminal vesicles and seeing how it affects horniness, or just measuring the horniness as a function of the interval from last orgasm, or administering hormones and seeing their effects, whether on rats, monkees or human volunteers. Edison (talk) 04:02, 23 October 2013 (UTC)[reply]

It is above average frequency, I suppose, I've always had a strange fascination with sex. I think, though, as far as the question goes, the focus is too narrow- the same relations hold for most wants. If you miss a meal, you might eat more at your next, or at least think more about it. The main element seems to be having an unsatisfied desire, not anything specifically sexual.Phoenixia1177 (talk) 05:06, 23 October 2013 (UTC)[reply]

'You regularly have it(like you 4times a day) and you suddenly stop it, then you want it more(if you are aware and not having it), this is what i want to say..does the urge to masturbate not really increase if you dont have sex for a,say a week(when you regularly have it)..? are the orgasms after a peiod of short term abstinence not more intense than the usual..? Also it is so common to say that we get a wet dream to release the fluids when the tank is full..Sexual desire is also like hunder or any other biological need.. Now i arrive at two simple questions: When will the sexual desire(or stimuli) be more strong--When you are masturbating fouth time in a day..? Or when you are masturbating after four days Should "time gap between ejaculations" be a factor affecting sexual desire on wikipedia..? If no, Please tell why..many thanks 12:16, 22 October 2013 (UTC)~~ — Preceding unsigned comment added by Ed beerman (talk • contribs)

I would think that the plumbing, hydrostatics and hydrodynamics contribute very little. The main stimuli are psychological and pheromonal. Dbfirs 12:56, 22 October 2013 (UTC)[reply]

I can only speak from personal experience to answer, so bear that in mind. I notice that the more I want sex, the more intense the experience is, and the more I think about it- and the worse it is if I can't have it (I work long hours some days). Some weeks, I get wrapped up in other things of interest and sex is far from my mind (as are things like regularly eating and sleeping), in those cases, I don't really miss it, and, when it returns, it doesn't come back in a "flood", but slowly increases back to normal (hunger and the interest in sleep do the same). On the other hand, sometimes I'm very fixated on sex, in those cases, if I can't have it, it's all I want to think about- in that case, I masturbate more, think about it more, etc. As for when the sexual experience is the most intense: during those times when I am masturbating more frequently, the experience is stronger- since I'm not doing this back to back, but a few hours apart, each experience is equally intense (there is variance, but it is a factor of time of day and schedule more than where the event is in sequence). As I said, I think the major factors in intensity and want is desire and availability- if I really really want sex and get stuck at work for a 20 hour shift, it's very amazing when I finally get home- on the other hand, if I'm at a low period of interest and work a 20 hour shift, when I come home, sex is less of a "yippee!" and more of a "I'm sleepy, but my wife likes sex, so okay".Phoenixia1177 (talk) 05:06, 23 October 2013 (UTC)[reply]

Opportunities for Exploring Comets and Minor Planets

Where can I get information about proposed projects and/or theoretical opportunities of unmanned space explorations?

Is there a list of future "windows" for the exploration of solar system objects?

Launch windows are determined partly by the available propulsion power and the location of your launch facility. If you have an ion rocket and a very light-weight spacecraft and your rocket base is on the equator, you probably have larger windows for visiting every solar system body. Otherwise, you may have smaller or no windows at all.

I just want to see a list of the "ON SALE" (least expensive) days for visiting comets and minor planets. -- Toytoy (talk) 15:14, 21 October 2013 (UTC)[reply]

I think you will need to narrow you criteria; there are over 1 million asteroids and comets known. Rmhermen (talk) 15:43, 21 October 2013 (UTC)[reply]

There must be some useful rules for solar system tours.

If you want to travel beyond Mars, you may need to use Mars as a slingshot. Then you have to look-up the nearest window for Mars at first.

I think there must be many rules and restrictions to narrow down available possible destinations. -- Toytoy (talk) 07:41, 22 October 2013 (UTC)[reply]

See Exploration of Mars#Launch windows. Duoduoduo (talk) 17:43, 22 October 2013 (UTC)[reply]

Also Exploration of Venus#Under study, BepiColombo, Solar Probe Plus#Trajectory and mission, Venus In-Situ Explorer, Venus Entry Probe, Venera-D, Europa Jupiter System Mission, and Titan Saturn System Mission. Duoduoduo (talk) 17:54, 22 October 2013 (UTC)[reply]

I heared a presentation on which asteroids you can visit and bring a sample back. Although there are a lot of asteroids out there the number was small like 5 or 10. First you have to get ride of all with high inclination. The ones which are far out are off limits because of the too high reentry speed. Third is to eliminate all fast spinners. At the end you elimated all but 10 and you end up at the point that OSIRIS-REx and Hayabusa 2 had too look for the same conidates.--Stone (talk) 18:21, 22 October 2013 (UTC)[reply]

The problem is always you can go for venus mars and earth flybys to get to speed and with that you have a lot of oportunities. --Stone (talk) 18:21, 22 October 2013 (UTC)[reply]

Soda pop can exploding when frozen

Why do soda pop cans explode when put in the freezer too long? I've put 20 fl oz plastic bottles of cola in the freezer, but they don't explode. --209.203.125.162 (talk) 17:51, 21 October 2013 (UTC)[reply]

Aren't cans usually full to the top, with no room for the ice to expand, while bottles usually have air in the neck? μηδείς (talk) 17:56, 21 October 2013 (UTC)[reply]

Plastic bottles seem like they can stretch a bit from internal pressure, whereas metal can certainly deform but not as readily to increase volume? DMacks (talk) 19:00, 21 October 2013 (UTC)[reply]

Yes that's it. Soft plastics can undergo a great deal of plastic deformation (no surprise there), while metal isn't as flexible. StuRat (talk) 20:55, 21 October 2013 (UTC)[reply]

However, as I understand, the recent incidents of "dry ice bombs" in LAX were plastic bottles stuffed with dry ice and then capped tightly. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:59, 21 October 2013 (UTC)[reply]

That's because it's easy to put dry ice in a plastic bottle and seal it. If you fill it completely with dry ice, then it will have to pop. For it not to pop would require it to be able to contain a gas at a pressure of about 1000 bar. Count Iblis (talk) 00:26, 22 October 2013 (UTC)[reply]

Which is essentially what makes them work. If you tried the same with a can (somehow, not sure how you'd seal it), you'd probably get a smaller pop, since it would rupture at a much lower pressure. MChesterMC (talk) 08:50, 22 October 2013 (UTC)[reply]

So if the cola inside is frozen, why does it explode all over the freezer? Why doesn't the can just burst open, leaving a frozen cola cylinder ? --209.203.125.162 (talk) 01:17, 22 October 2013 (UTC)[reply]

Not all of the cola is frozen. Enough freezes for it to break the seal, through which the remaining liquid escapes. 81.147.166.89 (talk) 01:31, 22 October 2013 (UTC)[reply]

The freezing process involves the unmixing of the water and the cola ingredients, you get pure ice from which the rest of the cola is expelled. The freezing temperature depends on the concentration of the ingredients, so, when a little ice forms the cola ingredients have been expelled from the ice, the concentration will have increases in the remainder. So the remainder will only freeze at lower temperatures. This means that at some given temperature, the freezing process will stop before everything is frozen. But of course, if the can cannot hold a large pressure it will break open. Most of the contents will be a liquid which then explodes out of the can as it was held under pressure. Count Iblis (talk) 01:35, 22 October 2013 (UTC)[reply]

There are a number of phenomena going on here. The big ones are the liquid freezing from the outside in, forming a rigid container of ice around an ever-decreasing volume of liquid, and freeze distillation forcing dissolved carbon dioxide out of the liquid as it freezes, forming a bubble of high-pressure gas. In a relatively inelastic can, at some point the pressure reaches the point where the ice shatters, the can ruptures, and the remaining liquid and gas spray all over the place. In an elastic bottle, the bottle will stretch as the ice breaks, letting the formerly-dissolved gas join the bubble at the top of the bottle. --Carnildo (talk) 01:45, 23 October 2013 (UTC)[reply]

The can bursts because water expands when it transforms from liquid to solid, unlike many other fluids. I wanted to create a smooth hemispherical dome on the bottom of a Diet Coke can so it would work well as part of a Van de Graaf generator using "found" materials .I had observed that a cola can has a recess at the bottom and that when it freezes, the recessed bottom as well as the top expand out and become convex. I used Diet rather than Regular Coke because the sugar lowers the freezing point. Anyway, after a while the can at about zero F had bulged out at the bottom into a dome with a few rings and the top was deformed outward as well. It was placed bottom up for better observation. I decided to give it another 5 minutes to try and smooth out the dome a bit more with increased interior pressure. When I came back, the poptop had failed and the Coke slurry inside had come out like a rocket, and the can had clearly bounced around in the freezer. The actual instant of failure and resulting rocket action would make a cool Youtube or Mythbusters episode (perhaps motivated by checking the "myth" that Diet Coke freezes and bursts before regular Coke in a deepfreeze or very cold outdoor environment). Edison (talk) 03:46, 23 October 2013 (UTC)[reply]

Meat from unstressed animals

The claim that meat from unstressed animals tastes better is regularly made, but is there any scientific evidence that it is actually true? All the sources that I can find merely assert it without presenting any evidence, or use words such as "people say that...". 86.176.215.115 (talk) 19:42, 21 October 2013 (UTC)[reply]

Science has certainly backed this up. Lack of references may come from generations of our forefathers experience that take this as a given – so our forefathers didn’t require any authority to tell them what they already knew - so that's the origin of "people say that...".

This 'patent' give some of the science bit as background (with refs) to explain the patent:[1]
This link explains why it is important in to the meat industry:[2]

--Aspro (talk) 21:13, 21 October 2013 (UTC)[reply]

The type of food an animal eats supposedly can make a significant difference in taste (I've been told that deer that feed on corn taste a lot better than deer that have to resort to leaves and twigs), so it's not unreasonable to expect that the animal's general well-being could also affect the taste. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:01, 21 October 2013 (UTC)[reply]

That's an interesting point which is worthy of a separate discussion. In short: You know how Coca-Cola did blind consumer market research and tried to introduce New Coke only to find it was then rejected – as not the real thing. I think is a bit like corn feed deer. Some people used to eating domesticated animals I can well imagine, find that the taste of 'farmed deer' more familiar. I myself, prefer what I am more familiar with - i.e., Scottish wild deer. My tasted bud are now getting a bit jaded (alas) by the passage of time but younger members of the family refer to farmed deer, as a bit like funny tasting lamb! In other words, lamb has been slaughtered before it has developed the richer taste of mutton. Farmed deer are slaughtered before they have developed a rich flavor and so like lamb, non have the taste that my hungry mouths around the dinning table associate with meat from a deer hunted on a scottish estate where they feast on a natural Highland diet. But that has nothing to do with the stress that the animal is put through before slaughter. PS. The food the animal eats does has a very big effect on taste - there is no supposing about it.--Aspro (talk) 18:18, 22 October 2013 (UTC)[reply]

You may check out this article.

http://www.journalofanimalscience.org/content/83/2/440.full

If a pig has been scared for too long before slaughter, you may see its meat whitened unnaturally and lose its meat juice. -- Toytoy (talk) 08:09, 22 October 2013 (UTC)[reply]

Cline variation

What is meant when it is said that human variation is clinal not racial? — Preceding unsigned comment added by 70.49.46.102 (talk) 19:54, 21 October 2013 (UTC)[reply]

It basically means that the prevalence of specific human genes and phenotypes generally varies gradually instead of suddenly across geographic regions, making it difficult and arbitrary to try to meaningfully divide humans into discrete races biologically, if you consider humanity as a whole. See Cline (biology). Red Act (talk) 20:10, 21 October 2013 (UTC)[reply]

So essentially it is hard to draw the line where for example black race or white race or asian race starts? But it is easy to do that, we all know what an Asian, or African or white person looks like? — Preceding unsigned comment added by 70.49.46.102 (talk) 20:15, 21 October 2013 (UTC)[reply]

No we don't. There is so much regional variation those terms are almost meaningless sometimes. That of course doesn't mean there aren't' genetic differences between different populations, but they don't necessarily map to the traditional 'human races'. Fgf10 (talk) 20:49, 21 October 2013 (UTC)[reply]

A couple points:

1) It isn't always easy, with people of mixed ancestry.

2) The genes that describe things we think of as race (skin color, hair color and texture, etc.) are only a small number of the total genes. So, you could have Asian genes that control your appearance, and yet have non-Asian genes as well, which don't contribute to your appearance. StuRat (talk) 20:52, 21 October 2013 (UTC)[reply]

It can sometimes work reasonably well as a model to divide people into races, if you only consider the people who live in one geographic area, due to historical immigration patterns from separated locations which have obscured the clinal nature of the genetic and phenotypic variation among humans as a whole. For example, a lot of people arrived in North America from Europe, mainly Northern Europe and Western Europe, during the European colonization of the Americas, and a lot of people arrived in North America from Sub-Saharan Africa during the Atlantic slave trade. People in northwestern Europe and people in Sub-Saharan Africa tend to look rather different, so if you're only considering people who now live in North America, it works moderately well to categorize at least some of the population in North America into "white" vs. "black" races. However, if you take into consideration everybody in the world as a whole, what people typically look like varies gradually if you consider a sequence of populations extending from Sub-Saharan Africa up through northwestern Europe. For example, people from Egypt (in Northern Africa) don't typically look like they came from England or France, but they don't look like they came from Senegal, either; instead, they look very roughly somewhere in between (although the variation is more than one-dimensional). But if you're considering only people who are currently in North America, you aren't taking into account too many people with largely Egyptian ancestry, because there wasn't a large wave of immigration to North America from Egypt in North America's history. Similarly, the concept of "Asian" as a race also works somewhat in North America, because historically a lot of people arrived in North America from East Asia and Southeast Asia, but not as many people arrived in North America from Central Asia or Eastern Europe, so the clinal nature of genetic and phenotypic variations along the populations in between East/Southeast Asia and northwestern Europe is obscured. Red Act (talk) 22:18, 21 October 2013 (UTC)[reply]

This is even further obscured by our limited understanding of history. If a large wave of immigration to North America from South America (or vice versa) occurred before recorded history, we would have no knowledge of the event. --Auric talk 22:38, 21 October 2013 (UTC)[reply]

Archeologists could figure it out, say if the pottery style from one South American tribe suddenly turned up in North America. StuRat (talk) 17:55, 22 October 2013 (UTC)[reply]

Yes, exactly. The Timucua of Florida have as their closest relatives speakers of languages in northern South America. The same path from South America up through the Caribbean was taken by the ancesters of the Taino language and other Arawakan language speakers. μηδείς (talk) 02:26, 25 October 2013 (UTC)[reply]

Thank you very much, that clears the confusion for me! 70.49.46.102 (talk) 01:11, 22 October 2013 (UTC)[reply]

Resolved

StuRat (talk) 02:05, 23 October 2013 (UTC)[reply]

Why are screw propeler more efficient than paddle wheels?

Couldn't well-designed paddle wheels (not just a flat board) be equally efficient? OsmanRF34 (talk) 22:00, 21 October 2013 (UTC)[reply]

Intuitively paddle-wheels seem less efficient because they waste energy lifting water and submerging air. Also, only a portion of the water they do move goes in the proper direction. StuRat (talk) 22:28, 21 October 2013 (UTC)[reply]

Is a screw propeller actually more efficient? They are superior for many purposes because paddle wheels don't work well if the water is not flat, but I would like to see a reference before accepting that there is an advantage in efficiency. Looie496 (talk) 00:09, 22 October 2013 (UTC)[reply]

The advantage of screw propellors is that the direction of flow imparted to the water is parallel to the screw rotation axis. That allows propellors to be made with blades of shallow pitch at the tips, gradually increasing to a more agressive pitch as you move toward the centre. In this way the velocity imparted to the water is the same throughout most of the blade length, even though the tangental velocity of the blade is a lot less near the centre than it is at the tips. Also, the blade tips can be rounded, so that in the last 5 to 10% or so of the blade, the water velocity is gradually brought down, avoiding a large shear, which would waste energy in turbulence.

Paddle wheels have the direction of water flow at right angles to the direction of rotation. That means neither variable pitch nor blade tip tapering can be used. As StuRat said, paddle wheels move some water in the wrong direction, they also move some of it at the wrong velocity, and the large shear at the bottom of the paddles causes much useless turbulence.

The problems of paddle wheels could be overcome to a limitted extent by using co-axial nested paddlewheels of huge diameter, with the inner wheels turning faster, and the very outside wheel turning very slowly. Or by using some sort of linkage to keep the paddle blades vertical. But its never going to be as good as a propellor, with anything like a practical robust assembly. Why would you bother, when a simple propellor does the job. 60.230.213.251 (talk) 00:43, 22 October 2013 (UTC)[reply]

There are various tracked amphibious vehicles which propel themselves using their tracks ("some sort of linkage to keep the paddle blades vertical"). The DARPA Captive Air Amphibious Transporter looks fun. Card Zero (talk) 01:04, 22 October 2013 (UTC)[reply]

besides every movement in a propel contribute to the ship displacement, in the wheel you have to waste energy raising up the paddles over the water surface, plus the wheel weight more and require more space, etc.

Planes have to be very very efficient, so they has “propel like” devices (helices turbofans etc)

Iskánder Vigoa Pérez (talk) 02:13, 22 October 2013 (UTC)[reply]

Actually, the raising of paddles is not a problem. It takes energy, stored as potential energy in the paddles, but it is balanced out by other paddles moving down into the water, which give back their potential energy. Wheel weight also have no effect on efficiency. A high wheel weight just means that the wheel acts as a flywheel, and a flywheel running at constant speed does not consume energy. In any case, propellors have considerable weight too. 60.230.213.251 (talk) 06:17, 22 October 2013 (UTC)[reply]

Hmmm... what if the paddles were made up of some sort of "molecular origami" that was held by some thin, strong, rod, but otherwise had substantial freedom to furl and unfurl in an arbitrary shape by computer command throughout the stroke? If you had the ability to force a succession of, say, cupped parallel planes through the water, might it work better than the screw shape? Wnt (talk) 05:15, 22 October 2013 (UTC)[reply]

Well, as I said above, a paddle wheel cannot be more efficient than a propellor, and any real design will be less efficient because with a paddle wheel the water flow is at right angles to the axis of rotation, whereas for a propellor the water flow is parallel to the axis of rotation. That allows profilling the blade width and pitch along the length of the blade, so over most of the blade, the motion imparted to the water is consistent in the desired direction. Yet shear at the tips is minimised by tapering the blades, reducing turbulence. Have a look at the photo of a modern propellor in the propellor wikipedia article. See how the blade pitch increases as you move to the centre. See how the blade width is taperred of to nothing at the blades tips. You can't do that with a paddle wheel - it has no geometical meaning.

Incidentally, while a paddle wheel can be improved by arranging the paddle blades to remain vertical, that still leaves us with excessive turbulence due to shear at the bottom of the blades. And increased shear at the sides. Again, why go for a complex mechanism when a simple propellor does the best possible job? Also, cupped shaped blades do not alter any of this.

60.230.213.251 (talk) 06:30, 22 October 2013 (UTC)[reply]

I don't think that one can say that either is more efficient, without fixing some parameters. One could fix the impeller area and total thrust, with the Reynolds number being very large. Under these conditions, the impeller that accelerates water over the largest area will generally be most efficient (least total kinetic energy imparted to the fluid per unit time for a given thrust). Since a paddle wheel only effectively accelerates the fluid over the area of a blade, but a propeller does so over the area that it sweeps out, the latter's advantage is kinda obvious. At a low Reynolds number (imagine treacle), viscous drag dominates and adds a significant energy loss mechanism, when this argument does not apply. — Quondum 03:14, 23 October 2013 (UTC)[reply]

Really? The value of computing the Reynolds Number is that it tells you whther or not the flow is going to be turbulent (high Reynolds) or laminar (low Renolds), just from the speed of the fluid past surfaces. You don't want turbulence, it is just a waste of energy. So, paddlewheels or propellors, you want to operate at a Reynolds Number below the transition value. Below that value things are pretty much linear with speed. 124.178.152.227 (talk) 03:31, 23 October 2013 (UTC)[reply]

October 22

Penicillin-producing fungi in the human body

According to its article, Trichophyton interdigitale is a species of fungus that's often responsible for causing fungal infections in humans and other species, and it's also one of the species known to produce penicillin. If wounded (e.g. punctures or cuts), are areas infected with T. interdigitale less likely to develop bacterial infections than areas not infected by the fungus? Or does the fungus produce such small amounts that it doesn't have a substantial effect? Nyttend (talk) 04:57, 22 October 2013 (UTC)[reply]

Well, the effect is apparently more just that the bacteria become resistant [3] but that does suggest there is some real antibacterial activity at some point. Wnt (talk) 05:25, 22 October 2013 (UTC)[reply]

House dust mite - Helping me with this could very well improve my life

Soon i am gonna move to a new place so it's kinda in late, but, is there any actually affective anti-House dust mite (Anti-HMT) Spray that i could buy from the net and spray upon my bed or in the room? something that'l really do the trick? thanks from all heart. Ben-Natan (talk) 09:10, 22 October 2013 (UTC)[reply]

I am not aware of any spray that will kill dust mites AND be harmless to humans. However, there are other things you can do:-

Give the house a really thorough vacuuming with a high-suck vacuum cleaner like the 2kW Volta. Not one those useless litle round robot things. Deep pile carpets and matresses, especially matresses with a top wool layer per American practice, are nice to sleep on but they are dust mites' best friends.
Then, get a commercial cleaning service in to wash all carpets.
Wash the bedroom curtains. — Preceding unsigned comment added by 60.230.213.251 (talk) 09:40, 22 October 2013 (UTC)[reply]
Use fine-weave cotton sheets on beds. You can get special fine weave sheets expressly for this purpose. They work, because the mites hide in the mattress during the day, then come up though the sheets to bite you when they sense your body warmth. With fine-weave sheets they have to walk the long way round.
Before you move in, get a referral to an alergy specialist and have him test you for dust mite response. If you have no response, most likely with normal good cleaning stanards you won't have a problem. If you do have a response, you will need to be extra scrupolous in cleaning until the dust mite poulation falls.
If you are moving into a furnished home, give the matresses away to the needy, and buy your own new. This is always a good idea anyway. All sorts of body oozes collect in matresses, even when they look clean.
Wash the bedsheets each time you do so (should be once each week) with a small amount of eucalyptus oil added with the detergent. The smell's not at all overpowering, most people think its nice, but dust mites hate it. — Preceding unsigned comment added by 60.230.213.251 (talk) 09:43, 22 October 2013 (UTC)[reply]
If you remain concerned, say by itching, have yourself tested again 3 months after you move in.

Lastly, the main problem with dust mites is that they make you itch. So do lots of other things - gardening in short sleaves without gloves, old age causing hormone levels to fluctuate (especially with females, but men too), taking certain presciption medications, alcoholism, and taking illicit drugs.

60.230.213.251 (talk) 09:37, 22 October 2013 (UTC)[reply]

Some of the information given above is bordering on medical advice which we are not supposed to give. You will find information from the professionals on how to deal with dust mites here and here. You will find lots more information if you google "dust mite allergy" Richerman (talk) 13:54, 22 October 2013 (UTC)[reply]

I didn't think that dust mites caused itching - according to [4] there are other mites that do that. A search readily turns up resources like [5] that discuss both physical and medical approaches. Wnt (talk) 14:00, 22 October 2013 (UTC)[reply]

Which echoes my concern about some of the above being medical advice. I think the uncited advice from the anonymous editor above should be removed. Richerman (talk) 14:11, 22 October 2013 (UTC)[reply]

I want to make sure we are talking about dust mites and not bedbugs. Dust mites are microscopic and universal, and the best we can do is to reduce their numbers and the accumulations of their feces, by careful, frequent cleaning. Bedbugs, on the other hand, are large enough to see, and come out to bite people at night and suck blood, and need to be addressed by professionals, as they can cause medical problems. StuRat (talk)

Can dust mites be killed using radiation? It seems to me that irradiating your mattress with intense gamma rays would get rid of them. Count Iblis (talk) 15:48, 22 October 2013 (UTC)[reply]

Right -- just whip out your handy-dandy portable Tevatron and you're ready to go. Or would you prefer a tiny nuclear explosion? Or covering the bed with plutonium, maybe? Looie496 (talk) 16:06, 22 October 2013 (UTC)[reply]

The basic concept of sterilization by irradiation is sound (but men, don't try standing in front of the microwave as a "poor man's vasectomy"). However, home irradiation isn't practical, as it requires handling dangerous radioactive materials. I suppose somebody could offer a service where you bring your items in and they irradiate them, but just putting them in a chamber devoid of oxygen might be a lot safer. StuRat (talk) 16:15, 22 October 2013 (UTC)[reply]

You might say that radiation is used to kill bedbugs ... infrared radiation, as they are heated up. There's a whole little industry of tenting houses and heating them to 130 degrees F, and lesser expedients will apparently work: [6] Wnt (talk) 16:39, 22 October 2013 (UTC)[reply]

Ha, beat me to it. Yeah, insects are prone to dehydration. One way to ensure you're not carrying bugs from your old place to your new oine, for example, is just leave the truck wit all your junk in it parked in the sun for a day or more. So maybe if you just cranked up the heat in the new place as high as possible for as long as possible. This is all conjecture, of course, and note that these guys will probably breed back to the original level pretty quickly. 206.213.209.31 (talk) 17:19, 22 October 2013 (UTC)[reply]

Your thermostat goes up to 130°F ? Is that a Vulcan brand thermostat ? :-) StuRat (talk) 17:52, 22 October 2013 (UTC) [reply]

Damp clothes smell

After getting wet in the rain, I notice a musky smell on my clothes or body, that smells a little like clothes that have been forgotten in the washing machine. What causes this? Is it related to the same process for clothes left damp in the washing machine? --129.215.47.59 (talk) 10:05, 22 October 2013 (UTC)[reply]

See mildew. --Jayron32 11:04, 22 October 2013 (UTC)[reply]

Agreed. Clothes must remain wet for some time for mildew to grow. However, when they dry off or are washed with detergent alone, this doesn't kill the mildew, it simply remains dormant until the next time the clothes are left damp. I find using bleach in the laundry to be the most effective way to kill the mildew. StuRat (talk) 16:19, 22 October 2013 (UTC)[reply]

anaphilaxis and andrenaline

Why when someone needs to inject Epipen for elergy he needs to do it in her knee? why the other place of the body are not for that? If it needs the mussels there are a lot of them in the body, so what is the special in this place?176.13.29.148 (talk) 13:24, 22 October 2013 (UTC)[reply]

The muscles of the thigh (note—not the 'knee') are a large, easy-to-hit target, and one that is easy for most people to reach on their own body. The prinicipal concern with epinephrine autoinjectors like the EpiPen is that one might accidentally hit a vein, thereby allowing a single, concentrated dose of epinephrine (adrenaline) to be delivered straight to the heart. The outer thigh is an ideal injection site, as it contains no large blood vessels. From the manufacturer's web site [7]:

...The outer thigh is the safest site for IM injection as there is minimal risk of injection into major blood vessels or nerves in this area. Intravascular injection (which is possible on the front of the thigh) could lead to acute cardiovascular compromise. Injection into a major nerve (which could occur on the posterior thigh or buttock) can cause significant damage; also, injection into the buttock may not be effective for a severe allergic reaction. Accidental injection into the hand, particularly the digits, can cause serious injury and possibly gangrene....

So, the risk of Bad Things is higher with other injection sites. TenOfAllTrades(talk) 13:40, 22 October 2013 (UTC)[reply]

Looking for articles or references on epidemics due to lack of immunity

Hi all, when European colonists met indigenous peoples in the New World, Australia, and other places, my understanding is that many of the locals there were killed by smallpox and other diseases, diseases to which which the Europeans had an acquired immunity. The story then goes that contact between populations is inherently dangerous, because of this potential for epidemics. Yet as far as I am aware, the reverse did not happen, that is, the colonists did not in turn die of diseases contracted from the natives. Why did one side get sick and not the other? Or is the premise false? IBE (talk) 16:23, 22 October 2013 (UTC)[reply]

There is extensive discussion of this in Diamond's book Guns, Germs, and Steel. DES ^(talk) 16:28, 22 October 2013 (UTC)[reply]

Thankyou - exactly what I was after. I shall take note of the reference, and put it on the to-do list, but I won't be able to do this until well after the thread is exhausted. Can you or someone give me a very quick (three or four point) summary? I am primarily interested to know if the premise is true, and whether it is due to smallpox being a particularly contagious and virulent disease that just happened to be prevalent around at the same time as the contact between civilisations occurred. IBE (talk) 16:40, 22 October 2013 (UTC)[reply]

The article linked to summarizes his arguments fairly well. As to your question, it is generally agreed that there were a number of very widespread epidemics in North and South America after contact by Europeans, and that these were particularly severe because the local populace had little or no immunity to the imported microbes. Going the other way, it has at least been alleged that Syphilis migrated from the Americas back to Europe in a similar way, and that its initial outbreaks were very severe because of a lack of immunity. As to WHY this effect was so much larger in the Americas than in Europe, I don't think there is a general consensus. Diamond asserts that the previous history of Europeans had involved more encounters with initially separate groups, and a much wider East/west span (for all of Eurasia), and a larger variety of domestic animals (often a source of disease) all leading to a more robust set of immunities among the European population. Not all scholars accept his views. DES ^(talk) 16:49, 22 October 2013 (UTC)[reply]

I wouldn't think you'd need to look farther than the relative population sizes of the New and Old Worlds. With more people, there would be more diseases to evolve, and immunity to develop, in the Old World. The differences in population would, in turn, be due to the larger land area in the Old World, and the fact that it has been populated far longer. StuRat (talk) 17:46, 22 October 2013 (UTC)[reply]

According to this article indigenous diseases may have actually started to affect the indigenous population more at the time of colonization. Count Iblis (talk) 20:03, 22 October 2013 (UTC)[reply]

is space what we really see?

Is the outer space really what we know, like we see them in photos and movies? Or is it to human eyes? Will cat or chimpanzees have a different look at it? Is there anything invisible (to us at least) out there? -anand, chennai. — Preceding unsigned comment added by 122.164.37.214 (talk) 16:48, 22 October 2013 (UTC)[reply]

There's dark matter and black holes, although black holes become visible as they swallow matter. Also, all forces are invisible, including gravity, electromagnetism, and dark energy.

And the universe would look only slightly different to eyes that see ultraviolet or infrared. StuRat (talk) 17:36, 22 October 2013 (UTC)[reply]

Actually, no. For example galaxies look very different depending on the wavelength. Eyes can see only a tiny part of the electromagnetic spectrum. One can play with this e.g. with chromoscope. Various kinds of objects can be very faint at the visible wavelengths and very bright in X-rays or far-IR.

Photos, e.g. those colourful ones NASA proudly displays, also are generally different than what we could see with naked eye. The observations are (almost) always designed to solve some scientific problem... for example, a galaxy could be observed at three different wavelengths: 1) narrowband H-alpha 656 nm to probe star formation 2) some broadband observations at optical, like V-band 500 nm 3) infrared K-band at 2.2 micron. One then combines them into a RGB single image, which looks pretty but is very different than one would see with naked eye. The big telescopes do not even have eyepieces--at least normally. Telescope opening ceremonies and celebrations are a different matter, at least the first 8-m VLT had an eyepiece then. 88.148.249.186 (talk) 18:23, 22 October 2013 (UTC)[reply]

I'd call that slight difference. If there were galaxies which only existed in the IR or UV spectrum, I'd call that a major difference. StuRat (talk) 22:21, 22 October 2013 (UTC)[reply]

Cats see things a bit differently than humans do because (most) humans have trichromatic vision, whereas cats have dichromatic vision. Chimpanzees, however, have trichromatic vision similar to humans. Red Act (talk) 18:32, 22 October 2013 (UTC)[reply]

You might be interested in the qualia article. Sean.hoyland - talk 18:33, 22 October 2013 (UTC)[reply]

The qualia problem has bee solved. See Stephen E. Palmer's work. μηδείς (talk) 02:58, 23 October 2013 (UTC)[reply]

Thanks for the name because I don't think I've read anything of his, so I will. I didn't really mention qualia as "a problem", more as a response to the notion that "outer space" or anything is "really" like how animals or machines perceive or represent it. Sean.hoyland - talk 07:51, 23 October 2013 (UTC)[reply]

Palmer's research is in vision science and visual perception. I don't see how that than can "solve" the much wider philosophical questions about what qualia are, or whether they have any objective existence. Qualia (if they exist) are a component of all conscious experience, not just visual phenomena. Gandalf61 (talk) 09:09, 23 October 2013 (UTC)[reply]

Judging from this, Palmer apparently wouldn't disagree with that view. Sean.hoyland - talk 10:04, 23 October 2013 (UTC)[reply]

The Church–Turing–Deutsch principle implies that qualia are computational states. Intuitively this should be obvious from the brain in a vat thought experiment and then considering replacing the brain by a computer that simulates it. Count Iblis (talk) 17:18, 23 October 2013 (UTC)[reply]

But that's assuming a philosophical position, then offering it up as the answer. In other words, it's, essentially, "Assuming qualia are computational states, then qualia are computational states.", anyone who disagrees that that's what they are isn't going to accept any part of what you just said (nor will they find your intuitive/obvious conclusions to be intuitive/obvious). I'm not agreeing, nor disagreeing, just pointing out that most evidence is only evidence if you already assume the conclusion it is evidencing- hence the lack of positive results in philosophy.Phoenixia1177 (talk) 06:07, 26 October 2013 (UTC)[reply]

Feeding habits of the subterranean invertebrata

So... my yard is a thin coating of topsoil over the naturally occurring red clay, varying from dense to essentially rockhard. I've been attempting to improve drainage in one corner, maybe 30 foot square (10 meters square), which involved pulling up the sparse lawn there last fall and doing some digging. The point being that this area has been essentially vegetation free for about a year, baked pretty dry.

During the digging I notice two things. Firstly, down in the clay, maybe up to a foot deep which is as far as I dig, where there is no trace of any organic matter and it's pretty dense clay, I find quite a few earthworms of large size. Not monster movie size, but up there on the upper end of the normal earthworm distribution size. I don't find these guys in the more soil-like layer anywhere, although there are smaller earthworms there in reasonable number. I can see their tunnels horizontally in the clay, without any evidence of their going up into the soil layer. So, what do these big guys eat? You can't eat clay for a living, can you, even if you're an earthworm?

Secondly, back in the soil layer, there are a lot of chafer beetle grubs, the usual kind which infest lawns and eat the grass roots. Like a few per square foot, fat and happy. Mind you, this is bare soil, no turf, the occasional weed is all, and the grubs don't seem to associate with the weeds. There are a lot of maple tree roots in the soil, and they appear to be more numerous where there are roots, but I couldn't swear to it. They're not where the roots branch out into terminal little rootlets, just near the big solid inch thick roots. However, the rest of the yard where the grass is growing into a decently dense lawn, is essentially grub free. ??? Maybe the parents find it harder to lay eggs where the grass is thicker, but my question is, what are these guys in the bare area eating? They don't eat tree roots, AFAIK. I suppose they could eat whatever organic matter is in the soil, but again, I thought grubs didn't do that, they were consumers of grass roots. They're thriving quite well in the absence of any living plants other than the tree roots. ????206.213.251.31 (talk) 17:38, 22 October 2013 (UTC)[reply]

I'm not an earthworm expert, but from your description it seems likely that the large worms are in fact living in the topsoil and you're only noticing their tunnels in the clay because they can't break through and instead are worming along the boundary, perhaps looking for deeper crevices. In the normal topsoil their tunnels would probably collapse more readily and not be as noticeable. My "yard" runs from mixed to very clayey and it seems the ability of the clay to hold shape makes the worm trails there more long lasting and noticeable. Matt Deres (talk) 19:51, 22 October 2013 (UTC)[reply]

Clayey's not a word! You just made that up! μηδείς (talk) 02:56, 23 October 2013 (UTC)[reply]

To be honest, I was surprised when the Firefox spellcheck didn't redline it. Huh, it's redlining both "spellcheck" and "redline", but not "redlining" (or clayey). What a world. Matt Deres (talk) 15:44, 23 October 2013 (UTC) [reply]

The weird part is that what I remembered to be the correct word, clayvey, appears in only a handful of sites around the Internet and isn't coming up in dictionaries I see. Yet there are just enough hits to convince me it is real, hmm... Wnt (talk) 18:36, 24 October 2013 (UTC)[reply]

The mistake you're making is assuming that they stay in place. Both beetle larvae and earthworms are quite mobile. Is it getting colder in there? Those grubs are probably preparing to overwinter and are moving to deeper soil. They only really begin to feed in earnest in spring and summer before pupating and emerging as adults. Those "giant" earthworms are also very likely anecic earthworms (different from the smaller earthworms you found in the grassy soil area) which form permanent burrow networks and only emerge at night to find organic matter (usually dead leaves, but can be anything organic really) which they then drag back to their burrows to feed on. Have you noticed earthworm droppings (looks like a small pile of oozing or granular mud) in the bare area anywhere? If so, those are near the openings they emerge from. -- OBSIDIAN†SOUL 18:27, 23 October 2013 (UTC)[reply]

Cleaning from background radiation

By which means a human body can be completely cleansed from background radiation, including radon exposure? And what actions minimize their effect (perhaps water while taking a shower)? --93.174.25.12 (talk) 19:29, 22 October 2013 (UTC)[reply]

I'm quite confused. Background radiation is the stuff that is, like, everywhere, the radiation that exists as a baseline in all places. It cannot be avoided. See Background radiation which states that it is "ubiquitous". Excess radon exposure isn't really "background", if, for example, you have radon buildup in confined basement areas. If you wanted to minimize your exposure to background radiation, you could chose certain areas of earth to live on (the background radiation is ubiquitous, but not uniform). However, you cannot make yourself live your entire life exposed to literally no ionizing radiation ever. --Jayron32 19:40, 22 October 2013 (UTC)[reply]

Right - there is radiation coming from radon gas in the air, there is radiation from the food you eat and the water you drink, there is radiation from the rocks in the ground and from space in the form of cosmic rays. You could possibly reduce that somewhat by living in a lead-lined box in Antarctica *where atmospheric radon is at a minimum), eating food grown in another lead-lined box. That won't reduce the amount of radiation to zero - because you'd need an infinite thickness of lead to guarantee that.

But it's all a bit silly - we've evolved to live with a certain amount of background radiation - sure, there is a tiny increased cancer risk from background radiation - but eliminating it would come at such a high personal cost as to almost certainly make your statistical chances of dying early larger rather than smaller. There are better ways to spend money to live longer.

That said, if you live in an area with excessively high radon density, it does make sense to install good ventilation systems into your home and place of work.

SteveBaker (talk) 20:47, 22 October 2013 (UTC)[reply]

Is lead itself very slightly radioactive? Card Zero (talk) 21:39, 22 October 2013 (UTC)[reply]

Theoretically. But the observed isotopes of lead in nature do not show detectable levels of radioactivity. Someguy1221 (talk) 21:49, 22 October 2013 (UTC)[reply]

Not just theoretically but actually. We used to spend a fortune on special low radioactive lead for use in the lab. I think it came only from a few very deep mines but this is the only ref I can quickly fine to explain it. [8] Presumable the lead from these very deep mines formed so long ago that the radiation had reduced to very low levels. So yes, even lead give a slight radioactive signature -what ever its age and origin. Yet, to put it into context: my mom's apple pies are very much more radio-active – but too yummy to resist.--Aspro (talk) 22:07, 22 October 2013 (UTC)[reply]

...so they stay warm forever ? Yum. As for the lead, I don't think the lead from deep underground was formed earlier, if you are talking about the lead atoms themselves. However, there might be impurities in the lead ore (other elements) which have short enough half-lives that they significantly decay over millions of years. StuRat (talk) 22:17, 22 October 2013 (UTC)[reply]

What Stu said is right. The radiation is not coming from lead, but from contaminants. I hadn't thought of that wrinkle. Someguy1221 (talk) 22:25, 22 October 2013 (UTC)[reply]

@ StuRat. No, I am not talking about the formation of the lead atoms themselves but the age that they had crystallised and laid as Native metal in that deposit. Petrologist use the age of the overburden to help to attain and double confirm the latest age of the underburden. Thus, native lead from the deep mines exhibit lower alpha emitters – (or so the lead refiners that charged us an arm and a leg for just a few hundred weight told us). P.S. Mom's apple pies often got cold (when she was presumable able to keep them hidden from us long enough for the radiation (thermal?) to die down and they were just as good when cold. In which case I personally preferred a few cloves where as her hot pie benefited from a little aromatic cinnamon. Maybe a chief with a nuff (enough) culinary degrees to get a job as a cooks thermometer would like to comeback on this – as I am still experimenting to reproduce that elusive je ne sais quoi'' @Someguy1221 Now lets get to the 'term' lead. The post above said and I quote “living in a lead-lined box in Antarctica”. One assumes in this context... the common understanding of lead. forth definition. I.e., The stuff we come across every day. No mention, nor suggestion, intonation, et cetera, et cetera, of a practically unobtainable pure lead-lined box . Lets us now wave a 'red flag at a bull' . Tell me where I was wrong in my last post? --Aspro (talk) 14:35, 23 October 2013 (UTC)[reply]

No one was wrong. We were simply using different definitions. Someguy1221 (talk) 20:59, 23 October 2013 (UTC)[reply]

I believe almost all lead on Earth was formed in a supernova long before our solar system formed. Perhaps a tiny amount is produced as a decay product of other elements, but I can't imagine that being much of the total. However, if more radioactive lead isotopes are formed that way, it might be a significant amount of the radioactivity in lead. Can anyone confirm that this is what's happening ? StuRat (talk) 20:38, 23 October 2013 (UTC)[reply]

Oh Gosh! StuRat asks such good questions at times that I wished he concentrated on growing fluffy white butter flavoured pop corn ;-) Supernovas (as far as I understand) don't produce elemental lead. As far as I was taught, lead formation comes about in ordinary stars (think red giants but don't quote me on that). Earth might have arrogated from the detritus of a super-duper big bang but the heavier elements can have come from previous stellar fusion processes long, long, before the star went kapow. Come on Stephen Hawking's -where are you when I need you?--Aspro (talk) 21:47, 23 October 2013 (UTC)[reply]

Ah. As a sea mariner might say after he has thrown-up into the wind “it is all coming back to me now ”. The red giant/super giant forms elements up to the mass of lead. Heavier stuff is what super-dooper nouveau bright sparks are good at doing (they might -in this state- also create some more lead as well but I don't what to be around at such a time, to find out how much)”. [9]--Aspro (talk) 22:37, 23 October 2013 (UTC)[reply]

I don't think so. The longest lived radioactive isotope of lead is lead-205. Its half life of 15 million years is significant, but not enough for it to survive from any novas that provided significant amounts of material to the formation of the Earth. There are a number of papers on lead-205 [10] but I cannot access them at the moment. There are papers that discuss looking for the decay products of lead-205 in nature in order to determine whether it was present in the early solar system, and these papers seem to make the assumption that lead-205 is not itself present. Some groups claim that there is natural lead-205, but present as a contaminant in thallium ores, not lead ores (hypothetically produced by neutrino capture by a thallium nucleus). I suppose it's also possible that some lead-205 may be present as a decay product of more stable radioactive isotopes, but that's just a guess. Someguy1221 (talk) 06:49, 24 October 2013 (UTC)[reply]

A few weeks back I asked about ways to grow radiation-free food. Unfortunately, chemical elements like potassium, which we need for our survival, naturally include a significant amount of radioactive isotopes. The conclusion of the discussion was that it might be possible to produce foods using centrifuges and such to reduce the portion of radioactive isotopes, but it would be very expensive, and would only reduce the radiation somewhat. I do agree that, if it was possible to live a life free of ionizing radiation, then we should. Unfortunately, it doesn't seem to be possible. StuRat (talk)

It's not clear that living in an environment entirely free of ionizing radiation would be beneficial. Good data on the effects of human exposure to low (comparable to background) levels of ionizing radiation are very hard to come by, since the primary endpoints – overall lifespan, change in cancer rate, etc. – take a long time to assess (years to decades), and because any small effects of radiation exposure tend to get entirely swamped by the effects of more potent confounders (genetic and other environmental/behavioral). Moreover, there's obviously no data whatsoever on the effects of significantly-less-than-normal-background radiation exposure, just because it would be so difficult and costly to construct and maintain such an environment.

There is at least some laboratory evidence in model organisms suggesting that low levels of ionizing radiation exposure may be mildly beneficial, conferring some protection against certain types of damage. This stimulating effect, if genuine, goes by the name radiation hormesis; the thinking behind it is essentially that regular low-level challenges from background radiation serve to prime the cell's protective mechanisms and thereby make cells more resistant to additional radiation or other insults. TenOfAllTrades(talk) 22:26, 23 October 2013 (UTC)[reply]

First only use isotopical pure substances best the pure elements. Go and get carbon-12, .... only the non radiaktive ones. Buy the biosphere 2 disasamle it and bring it to a very deep mine building and clean it properly. Fill it with the isotopes you need and start introducing microbes to process the whole stuff to more complex chemical compounds. Algae would be best to start with. After some time you should be able to live in the biosphere 2. All the things you eat should come from inside the biosphere 2 and all what you want to get ride off should be dumped outside.After several years you should be fairly clean. To be 100% save wait one or two generations. A nealy non radioactive human will be at hand.--Stone (talk) 22:31, 22 October 2013 (UTC)[reply]

...and you'd better re-build you biosphere and all equipment using low-background steel. This could get very expensive :) Gandalf61 (talk) 08:28, 23 October 2013 (UTC)[reply]

Even then you're hosed, of course. Even if you start out with perfectly, ideally, absolutely pure stable isotopes, you're still going to get induced radioactivity from occasional interactions withneutrinos. You just can't win. TenOfAllTrades(talk) 21:22, 23 October 2013 (UTC)[reply]

Smog contest: Great Smog of 1952 in London versus today in Harbin, China

Did any scientists do air monitoring in the Great Smog of 1952 in London to see the level of particulates and pollutants?Has any reputable source at least estimated the actual pollution levels, beyond " blinding and deadly pea-soup?" I wonder how it compared to the present smog in industrial areas of China? Edison (talk) 22:49, 22 October 2013 (UTC)[reply]

Prob'ly not -- at that time, smog in London and other British cities was considered commonplace and not something to be too concerned about. It was only in retrospect, after examining the epidemiological data, that the actual harm caused by the Great Smog to the life and health of Londoners became apparent -- which led to clean-air legislation (which wasn't in place before the Great Smog). 24.23.196.85 (talk) 01:33, 23 October 2013 (UTC)[reply]

The CNN report on it says visibility was 100, and yesterday down to 20 - 30 meters. That's much more than during the Great Smog, according to our article visibility could be down to a metre or so... So, assuming similar composition, London was 20 - 30 times worse. They're both grey smog, not photochemical. Ssscienccce (talk) 08:43, 23 October 2013 (UTC)[reply]

My dad tells me that the worst day of the great smog was so thick that you could not see your feet while walking - but at as he travelled in to London by rail the visibility outside was only 50 feet or so because of fog. It surprises me that anyone would even try to travel in this, but evidently many people did by feeling kerbs and looking for lamp posts (road traffic had completely stopped). This makes a comparison of pollution levels difficult, it could well be that the thick natural fog meant that visibility was a lot less for the same pollution level. -- Q Chris (talk) 08:58, 23 October 2013 (UTC)[reply]

At any rate the article now says can't see a person so close that you can hold their hand. Sagittarian Milky Way (talk) 22:42, 23 October 2013 (UTC)[reply]

http://www.iapsc.org.uk/presentations/1206_P_Brimblecombe.pdf (page 7) shows some pollution measurements taken in London at County Hall and gives some interesting background information. Unfortunately, the London and Harbin measurements use very different types of measure making comparison difficult. I was a child in London at the time and remember smog being very frequent in winter. The Great Smog was unusual in its duration rather than in its thickness. The effect on health was well known but, still in the aftermath of the war, other things took priority. Thincat (talk) 23:25, 23 October 2013 (UTC)[reply]

"London-type smog is mainly a product of burning large amounts of high sulfur coal. Clean air laws passed in 1956 have greatly reduced smog formation in the United Kingdom; however, in other parts of the world London-type smog is still very prevalent. The main constituent of London-type smog is soot; however, these smogs also contain large quantities of fly ash, sulfur dioxide, sodium chloride and calcium sulfate particles. If concentrations are high enough, sulfur dioxide can react with atmospheric hydroxide to produce sulfuric acid." [11] BTW, I just about remember the last London smogs in the early 1960s - they don't make 'em like that any more. Alansplodge (talk) 23:34, 23 October 2013 (UTC)[reply]

What is this medical process called?

Be prepared for some extremely unscientific and vague descriptions here.

Step 1. Person has a disease.

Step 2. Person survives the disease, either through doctor intervention or just surviving it.

Step 3. The Doctors use something from his body to cure others in the future.

What am I describing? I feel I've heard of this before, but Google can't find anything of this description. 68.111.166.27 (talk) 23:58, 22 October 2013 (UTC)[reply]

Sounds like antibody therapy, or the related intravenous immunoglobulin therapy. The basic idea is that you take the antibodies that one person has developed against a disease-causing agent and use them to attack that same agent in other patients' bodies. In modern medical science, these therapeutic antibodies are not harvested from human survivors, but from genetically engineered lab animals. The sequence for the antibody is, however, often derived from a human survivor's immune system. Someguy1221 (talk) 00:32, 23 October 2013 (UTC)[reply]

Thank you! 68.111.166.27 (talk) 05:26, 23 October 2013 (UTC)[reply]

There's also polyclonal antibody therapy. Used more often for pathogens, venoms, and poisons. See Antiserum and Polyclonal B cell response.-- OBSIDIAN†SOUL 17:51, 23 October 2013 (UTC)[reply]

October 23

Killed so quickly pain is not registered

Is is really possible to kill someone so quickly their pain receptors will not signal? I assume lasers would do as such; but what about something more conventional?— Preceding unsigned comment added by CensoredScribe (talk • contribs) 01:16, 23 October 2013 (UTC)[reply]

Yes, destroy their nerves faster than the rate of pain. Plasmic Physics (talk) 01:27, 23 October 2013 (UTC)[reply]

I don't know if you'd consider nuclear weapons to be "more conventional", but they can do the trick very well -- someone caught in the actual fireball would be vaporized before even the ion channels can open in the pain receptors, let alone the signal traveling to the brain! 24.23.196.85 (talk) 01:38, 23 October 2013 (UTC)[reply]

I have added a link to ion channel to your post. 220 of ^Borg 05:22, 23 October 2013 (UTC)[reply]

I’ve thought about this in the past and I suspect if a shipping container fell on your head without you “seeing it coming”, you’d be dead before you knew it, or felt any pain.. I think it takes about a second for your pain receptors to really kick in to full swing in your brain. Watch people who break a limb playing a sport, like soccer, it’s not uncommon that they don’t even realize it for a short while. Vespine (talk) 02:59, 23 October 2013 (UTC)[reply]

Isn't that just adrenaline? Sagittarian Milky Way (talk) 12:25, 23 October 2013 (UTC)[reply]

(edit conflict)The sensation of pain is 'created' in the brain in response to impulses from nociceptors. The brain itself though feels no pain, if I recall my anatomy & physiology classes, though the meninges covering it do.[12]

Therefore any action that destroys the brains' function quickly enough should cause no pain sensation.

For example, a gunshot in an appropriate spot (or large enough caliber) that causes brain death should work. There are though examples of people with grave head wounds involving large portions of the brain that survive with surprisingly little disability.[13], 43% brain lost

Vespines unexpected "shipping container" on the head, & being on top of a nuke when it explodes as our IP editor 24.23... suggests, indeed anything that near 'instantly' totally destroys the entire head & brain would seem to be good candidates too. Hand grenades or other explosive held to the head, or a rocket propelled grenade head-shot too perhaps.

This seems to be a rather hard thing to prove (volunteers would seem hard to come by), but I wonder if any tests on animals have been conducted? 220 of ^Borg 05:22, 23 October 2013 (UTC)[reply]

Yes. It is of utmost importance to well run abbatoirs. For hooved animals at any rate, three methods have been shown to work well, provided the operator does what he is supposed to do: a) a "bolt" of the right diameter impact driven into the head to just the right depth and at the right spot. The animal may well suffer though if the operator does not do it at the right point. b) an large electric current into the brain. The device should contain automatic circuitry so that the animal gets instant lights out or nothing at all. c) carbon dioxide asphixiation (used on pigs in some places). It takes up to 10 to 15 minutes or more to kill, but the animal is rendered painlesslessly unconscious long brefore death. The downside is operators may not wait long enough, and pigs recover consciousness with brain damage during the butchering process. That's not good. See the Temple Grandin lectures on YouTube. 124.178.152.227 (talk) 08:14, 23 October 2013 (UTC)[reply]

I have my doubts about that last. CO2 poisoning (not "asphyxiation" but really poisoning; CO2 in high enough concentrations is lethal even if there's plenty of oxygen) sounds fairly nasty to me. Our hypercapnia article says "symptomatology progresses to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death". (They seem to have left out headache — is that a myth?) --Trovatore (talk) 09:01, 23 October 2013 (UTC)[reply]

I suggest you read up on the ways of dispatching pigs. The effect of carbon dioxide is more complex that the article suggest. But the article does include headaches. Small amounts of CO2 just make you breath faster, without any ill effects. For that reason, gas fire suppressant systems, such as Inergen, which work by driving oxygen out of the building by displacemnt with intert gasses, also include CO2 to stimulate deaper breathing so humans can better utilise what oxygen partical pressure remains. At higher concentrations than are used in fire suppression, it can produce the symptoms described in the article. I have experienced a full Inergen dump in a computer room and felt no discomfort whatsover. At really high concentrations, CO2 asphyxiates as the blood looses its capacity to carry oxygen, which the lungs can't get enough off anyway, due to displacement - unconsciousness follows quickly with little or no distress. Note however what I said before - if the animal is not held in a CO2 chamber long enough, the oxygen starvation of the brain WLL produce nasty symptoms if and when it wakes up. The article also does not make that clear. The table of effects in the article only covers low CO2 concentrations experienced for long durations as might be encountered in human activity and you want the person to live. Pigs are dispatched with high concentrations as you want them to die as quick as possible. 124.178.152.227 (talk) 10:24, 23 October 2013 (UTC)[reply]

I should note that the experience of breathing carbon dioxide is readily available to anyone who has just finished consuming a bottle of soda pop, by inhaling from it. What's surprising is that it seems painless in this form, or when breathing from above a container of dry ice, but I've found it can definitely give a soda-pop-up-the-nose discomfort if it is humid (cloudy looking) enough. (I was curious what I was putting the mice through...) Wnt (talk) 15:48, 23 October 2013 (UTC)[reply]

@ IP124.178 I was thinking more of having sensors or electrodes attached to the animal (likely in their brain) to detect if they feel any pain at the instant they are despatched, if that is possible. The CO² thing would seem to fall outside the original question posed by CensoredScribe. I think it's implied that a fully conscious lifeform is suddenly killed without warning. -Δ-220 of ^Borg 09:39, 23 October 2013 (UTC)[reply]

I don't think that would be allowed, unless they use that kind of medicine that works by simply slowing down nerve signal speeds to bearable levels (instead of blocking brain consciousness or getting you high (opiates)), and then figuring out the full no-drug speed. Or for full scientificness, crush the animal's foot and then destroy it's brain before the signal could get there. And time it's nerve speed. Myelinated signals travel at up to 0.1 to 0.15 km/s, so over 340 mph should be unfeelable, even if it started at your toes. Sagittarian Milky Way (talk) 12:25, 23 October 2013 (UTC)[reply]

The Guillotine was introduced for this very purpose but it's still a matter of debate whether it is painless or not see: [14]. Of course, knowing that you are going to be executed is obviously a 'painful' experience in itself. Richerman (talk) 12:51, 23 October 2013 (UTC)[reply]

Supposedly, decapitation was the preferred method for condemned royals, over the other option, hanging, as decapitation was assumed to be as quick and painless as it could get. Common criminals had no say in the matter - hanging was it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:15, 23 October 2013 (UTC)[reply]

Of course it's possible if you have something like a nuclear explosion, but trying to answer this question in a comprehensive way gets into surprisingly deep philosophical problems. Daniel Dennett has devoted a lot of effort to explaining those problems -- see our article on the Multiple drafts model for a brief overview, or http://ase.tufts.edu/cogstud/papers/time&obs.htm for a more extended account, or even better, chapter 5 of Dennett's book Consciousness Explained. The basic point is that if you don't believe in dualism, then there can't be a specific point in space and time at which experience originates. Looie496 (talk) 15:55, 25 October 2013 (UTC)[reply]

Cryogenic neutrons

How low must the temperature become, before free neutrons are electrostatically bound? (Are we talking nanoKelvin, picoKelvin, etc.?) At standard pressure, would a neutron gas convert to a solid or liquid below this temperature? What sort of packing would the solid assume, HPC? Plasmic Physics (talk) 01:21, 23 October 2013 (UTC)[reply]

There are no bound states at zero temperature and standard pressure. Compare to Helium where you also don't have a solid state because the zero point motion would provide enough energy for the Helium atoms to escape. Count Iblis (talk) 01:28, 23 October 2013 (UTC)[reply]

Then what is the minimum pressure required for bound state. Plasmic Physics (talk) 01:39, 23 October 2013 (UTC)[reply]

You'll probably have to be careful defining "bound state". Liquids exist because of inter-particle attractive forces, which could lead to a "bound state": where particles remain in close proximity, even if it is en masse rather than individually. Liquid helium should be regarded as a bound state under this definition, especially as this state occurs at zero pressure and temperature. The context can then be transposed to neutrons (which, for all we know, could exhibit a miniscule van der Waal's force due to the neutron's internal structure (or other slight attractive force). The best approach might be to try to determine the phase diagram, or pressure–volume diagram of a neutron gas at zero temperature. Chances are such information would not be easily determined, though. And as Plasmic Physics subtly suggests, and overall pressure may lead to T–P–V points where two phases are in equilibrium, where one of these phases could be considered to be a bound state – maybe even for neutrons. — Quondum 02:55, 23 October 2013 (UTC)[reply]

Is it possible to predict a lowest pressure boiling point and/or melting point using the highest predicted dipole moment? Plasmic Physics (talk) 22:05, 24 October 2013 (UTC)[reply]

Pin tumbler lock

Europrofile Cylinder set with 2 double cylinders and one single cylinder (left) and the screw to secure the cylinder

Today's main page picture is from pin tumbler lock. I understand that picture and the mechanism well. However I have never understood how locks where you can enter the key from either side of the door work - indeed you can fit two keys at once, although the second key often won't turn regardless.

How does the two sided mechanism work especially given that the key isn't symmetrical. -- SGBailey (talk) 08:20, 23 October 2013 (UTC)[reply]

It's a double cylinder, simply 2 identical tumbler mechanisms, one on each side. See pic, left a single, right a double one. Ssscienccce (talk) 08:52, 23 October 2013 (UTC)[reply]

So if you wanted to, then you could make a double lock with kay A for one side and key B for the other side? I had visions of complex levers actuating the pins. -- SGBailey (talk) 11:21, 23 October 2013 (UTC)[reply]

Escape velocity

Hi,

In this week's "what if? - xkcd" Randall says the following: "However, the weird thing about escape velocity is that it doesn't matter which direction you're going.". I'm inclined to believe him as he's rarely wrong. But how is this? Surely you are more likely to escape from a planet if you are moving directly away from the centre than if you are moving tangent from the surface? Can anyone explain this to me? Thanks! 80.254.147.164 (talk) 10:01, 23 October 2013 (UTC)[reply]

Ditto, have you ever thought about moving towards the planet, and expecting to escape from it? Good luck. The escape velocity must have a vector which is greater then tangential. If the escape velocity is equal to the tangential, then you would have a simulated orbit. Plasmic Physics (talk) 10:21, 23 October 2013 (UTC)[reply]

If the planet has no atmosphere and is not rotating and the escaping object is moving ballistically and its trajectory does not intersect the planet's surface, then its escape velocity would be independent of direction, and is more correctly an "escape speed" - it is simply the speed at which the projectile's kinetic energy plus its (negative) gravitational potential energy is zero. The xkcd article is discussing a hypothetical small non-rotating asteroid, and it says "If you go faster than the escape speed, as long as you don't actually go toward the planet, you'll escape" - which is correct in that context. In practice, planets have atmospheres and rotate and rockets are not ballistic projectiles, so confusion arises when people try to apply the "escape velocity" concept to rocket launches. It makes more sense when applied to orbital mechanics in space. Gandalf61 (talk) 10:31, 23 October 2013 (UTC)[reply]

Even if you throw the body towards the planet, but make a tunnel in the planet for the body to go through, it will escape from the other end of the tunnel - WikiCheng | Talk 12:01, 23 October 2013 (UTC)[reply]

The part about the chaotic orbits of elongated objects is interesting, but I think the article fails when it says you'd have to worry about going into a tumble if you run too fast. Provided you were otherwise accustomed to the weird gravity, staying vertical rather than having periods of fast spinning, etc., your "near orbit" run would not be in a chaotic domain, I think. Wnt (talk) 15:55, 23 October 2013 (UTC)[reply]

A counterfactual example might be helpful here. Suppose it was harder to scape if you started your orbit horizontally. Then you would have to reach a point of maximum altitude and start falling back. at that point you would have to move slower than an object following a circular orbit at that altitude - That must be the case because your orbit would have a smaller radius of curvature even though you were under the same gravitational acceleration. But an object in circular orbit has a speed smaller than the scape speed contradicting our original assumption that your speed was equal to the scape speed. Dauto (talk) 16:03, 23 October 2013 (UTC)[reply]

Here's another way to think of it: The planet creates a well of potential energy. Think of it like a depression in a surface. To "escape" means to have more kinetic energy than the difference in potential energy where you are, and the limit at infinity. Kinetic energy is a scalar; it doesn't matter what direction you're moving (unless, as others have noted, you hit atmosphere, or the planet itself.

Things do get more complicated if there's more than one object you're trying to escape, especially if some of them have mass comparable to yours -- see n-body problem -- because you could lose energy to the system, or even steal energy from it. If the planet is non-homogeneous and rotating, this might possibly have some (small) effect on what's required to escape, and that could depend on the direction.

Responding to Gandalf, I would back off from the "velocity is a vector, speed is a scalar" shibboleth. I don't think actual physicists pay much attention to that; it's just a convenience for high-school physics teachers, who have a better chance of keeping the distinction fixed in the minds of their students if they can use a different word. Certainly there's no etymological basis for it (velox just means "fast", not "fast in a particular direction"), and terms like "high velocity" or the "velocity of light" are used regularly and I would argue correctly. --Trovatore (talk) 04:06, 24 October 2013 (UTC)[reply]

How do mirrors work ?

I've been reflecting on a problem in my head, the details of how an optical mirror reflects light. I'm using a particle model to try to understand. In that model, I believe the basic idea is that photons bounce randomly off a rough surface, and you get white, or they bounce in parallel off a smooth surface, and you get a mirror reflection. However, photons are subatomic particles, and surely all surfaces must be rough at that scale. That seems like bouncing tennis balls off a pile of boulders and expecting them not to go in a random directions.

So, do I need to completely abandon the idea of a photon as a particle here ? Even using a wave model, it's hard to see how a field of boulders doesn't scatter the wave packet randomly. Or does some quantum weirdness apply where the photon behaves as if it was a much larger particle, like in one variation of the double-slit experiment, where each electron seems able to go through both slits at the same time. StuRat (talk) 14:04, 23 October 2013 (UTC)[reply]

Actually, metallic surfaces are rather smooth even at that level due to the sort of metallic bonding (i.e. "sea of electrons") that minimizes the distinguishability between atoms. It's why metals make good mirrors and reflect so well. --Jayron32 14:40, 23 October 2013 (UTC)[reply]

That's not right. Seas of electrons, atoms, and metallic bonds are on a far small scale and have nothing to do with it, as StuRat has come to realise. Metals make good mirrors because they are ductile and easy to polish to a low surface roughness. Glass is not a metal. Everyone knows that in a domestic mirror, a greater amount of light is reflected off the silvering on the back surface, but you get quite a bit reflected of the front air/glass surface too. In vacuum tube colour TV cameras, unsilvered sheets of glass were used to split the light from the lens into 4 paths. It worked because each glass sheet reflected some light as a mirror, and let the rest straight through to the next piece of glass. Coloured film was used to block cyan from the red pickup tube, a magneta blocking film for the green pickup tube, etc. The fourth tube got unfiltered light and provided the luminance signal. As the eye cannot see detail in colour the luminence tube was the best possible, the other three were smaller cheaper versions. If you polish ceramic to a surface roughness less than 30 namometres, it will work nicely as amirror too. I've worked with ceramic pole insulators that you can see your face in. Not all ceramics can be polished that good though - it depends on what's in the mix before firing. We've all seen good reflections in water when there is no wind. Still water makes a good mirror becasue it is a liquid and thus self levelling.124.178.152.227 (talk) 14:54, 23 October 2013 (UTC)[reply]

This is where you need to look at it on the basis that light is a electromagnetic wave. Sometimes you need to consider it as photons, sometimes you need to consider it as waves. The wavelength of visible light is in the range of 400 to 700 nanometres, or 0.0004 to 0.0007 mm. To function as an optically smooth mirror, the surface variation needs to be sensibly small compared to the wavelength or scattering and destructive interference will occur. If the surface roughness is sensibly small compared to the wavelength, there is little time of arrival diffrence between waves and they will reinforce, only in the direction of propagation. Now what is a typical surface roughness of a reasonably good mirror? It's in the order of 30 nanometers or less. Check the wiki article on mirrors. Quite ordinary float glasses have a surface roughness of around 50 nanometers, which can be signifantly improved by polishing. 124.178.152.227 (talk) 14:42, 23 October 2013 (UTC)[reply]

Here you have to take into account the spread of the wavefunction in the perpendicular direction. Suppose you have a particle that moves in the z-direction. Then initially it will be within some area in the xy-plane, so it starts out as a beam with some cross section. By the uncertainty relation, the smaller that initial beam cross section is the larger the uncertainty in the momentum in the perpendicular direction will be, therefore the beam will diverge faster.

When light reflects off a mirror, you have to consider the area of the mirror that is illuminated. If e.g. the light from the source is collimated to a narrow beam then only a small area of the mirror will reflect the light. Each photon starting out from the light source that makes it into the beam will be spread out in the perpendicular direction when it arrives at the mirror over that area. Suppose the mirror is perfectly smooth. Then the reason why the photon would reflect off the mirror in the epxected way is due to intererence of all the possibilities that you have within that reflecting area. Perpendicular to the incident beam, the phase is constant. This means that at the reflecting area oin the mirror you have phase shifts. In the outgoing beam, the phase is again constant accross the beam, and that requires that the angle of the reflection is equal to that of the incident beam but opposite w.r.t. the perpendicular direction.

The narrower the incident beam on the perfect mirror is, the less well defined will the reflecting beam's direction be. You always get an inteference pattern where the central peak correpsond to the "correct direction" but the spread in that peak becomes larger then smaller the beam width is. Then what happens for incoherent light sources is that the interference pattern gets washed out (each photon will have a different interfence pattern), so you won't see inteference fringes, you will see that the reflecting beam diverges. Instead of a small incident beam, you can also use a tiny mirror here. If the mirror is not perfect, you will have the effect of introducing additional phase shifts accross the reflecting area which has the effect of distorting the reflecting beam.

The classical picture of the moving and reflecting particle is only obtained when the beam width is much larger than the wavelength, the so-called geometric optics limit. For perticles like electrons, you have such small wavelengths that you can pretend that the wavelength is zero. But for light you will easily see the effects of it havng a finite wavvelength, and then you get the paradoxical result that classical behavior only arises in the limit that the beam width is infinite, which is actually not classical at all. This is due to the uncertainty realation, if you want to have a well defined beam moving in a particular direction, the uncertainty in the momentum in the perpendicular direction has to be small, but that implies that it must have a finite width.

Example. Take camera with a perfect lens of 5 cm diameter. Photons of 500 nm from a certain direction will have an angular spread of the order of 500 nm/5 cm = 10^(-5) radians. This means that in a picture of an object at 1 km distance you can't resolve detals smaller than 1 cm. So, evewn the most expensive lens with that aperture on a gigapixel camera won't give you perfectly sharp pictures. Count Iblis (talk) 15:35, 23 October 2013 (UTC)[reply]

One thing that can throw you off is thinking in terms of "bouncing" at the atomic/photon level like billiard balls. Rather photons are absorbed and re-emitted by the electrons in the mirror's metal surface. The re-emitted photons interfere to give a coherent image. It gets into quantum electrodynamics I'm afraid. There is always QED: The Strange Theory of Light and Matter which talks a lot about mirrors. 88.112.41.6 (talk) 15:58, 23 October 2013 (UTC)[reply]

The article on Surface Plasmon may be of interest to StuRat and others trying to answer this question.--86.157.138.182 (talk) 14:52, 24 October 2013 (UTC)[reply]

Ammonia to remove mildew from clothes?

Having established above that my clothes and towels are riddled with mildew, I'd like to kill off what I can. A gamma irradiator would be perfect for this, but the one I have access too is way too small and we're not allowed to clean our clothes with it :P Can I use ammonia indiscriminately or would I need to check each items material composition and avoid certain or all colours? I'd like to avoid damaging my clothes and towels. I don't really have the opportunity to hang my clothes outside (I live in an apartment block; I'm guessing that hung outside would UV-treat them, but I guess that also fades the colours). I don't mind using chemicals so long as they don't damage the fabric or my health. --129.215.47.59 (talk) 14:05, 23 October 2013 (UTC)[reply]

Have you tried either bleach or bleach alternative? Ammonia may damage the fabric. --Jayron32 14:36, 23 October 2013 (UTC)[reply]

Before doing either (bleach can damage fabric as well), I'd give it a run through the washer again with hot water and a good detergent to see what comes of it. But yeah, bleach would be the next step; not ammonia. Matt Deres (talk) 15:55, 23 October 2013 (UTC)[reply]

Some bleach alternatives are safer on fabric, and can still have some deodorizing effect. Clorox 2 and OxiClean are two different name brands with different formulations. These are sometimes called "color safe bleach", though I believe that the new term "bleach alternative" is currently more in use. --Jayron32 16:42, 23 October 2013 (UTC)[reply]

...and never use ammonia and bleach at the same time. Mixing the two can produce chloramine and other toxic gasses.--Srleffler (talk) 16:53, 23 October 2013 (UTC)[reply]

I forgot my gym t-shirt for for four days, leaving it (soaked in sweat) for four days in the pocket of my gym bag. On discovering it, it was extremely mildew-ey; I thought it was a gone-er. At a last ditch, I left it in neat white vinegar (the cheapest generic kind the supermarket has) overnight, and then laundered it with other clothes. It's fine, free of nasty odours and with neither mildew marks nor any bleaching. Vinegar is a great fungicide, and supermarkets sell it almost as cheaply as bleach (which lightens, weakens, and damages many things like fabrics which vinegar does not). -- Finlay McWalterჷTalk 18:14, 23 October 2013 (UTC)[reply]

Since vinegar is just weak acetic acid, couldn't I just fill the bathtub with a weak acid and clean a load of clothes at the same time? Since acetic acid is just a weak acid, couldn't I just as well use an equivalent solution of hydrochloric acid? 2.97.26.56 (talk) 04:45, 24 October 2013 (UTC)[reply]

I've found that real bleach can be used without damaging most clothes:

1) Wear junk clothes when doing laundry, in case you get some on your clothes.

2) Run washing machine a bit first, to get all the clothes soaked, then add bleach.

3) Don't use super-concentrated bleach.

The only thing I found that still fades when bleach is used is my black socks. I wash those separately. Also, don't use with "rubber backed" drapes, rugs, etc. Those melt in bleach. StuRat (talk) 19:16, 23 October 2013 (UTC)[reply]

Repotting a Marigold and Inducing Flowering

I visited my parents in September, we had Chinese takeout, the restaurant parking lot was full of brilliant orange marigolds run riot, sprouting from the gardened soil and having spread to the sidewalk and blacktop. I pulled out a single small plant from the blacktop and put it in a vase. The next time I visited it was still in full bloom and had developed copious new roots, so I planted it in a small pot of topsoil, very lightly fertilized it, and dead-headed the blooms. I am quite certain it is a variety of Tagetes, almost identical to the one pictured, just a pumpkin orange color instead. It was doing so well the squirrels were eating it. Since it will frost by Halloween I put it inside in a southern-facing window that gets about six hours of direct sun. I cannot find any advice on how to get it to bloom all winter. (I have a red "geranium" that does so.) Where can I get advice on care and how to induce blooming? Thanks. μηδείς (talk) 21:17, 23 October 2013 (UTC)[reply]

It seems that photoperiodism plays a large part in flowering see:[15], also temperature and access to nutrients [16]. There's also some interesting info at [17]. Incidentally, you seem to be American (sidewalk, blacktop) but talk about 'soil' and not 'dirt'. Do most Americans use both terms? Richerman (talk) 12:22, 24 October 2013 (UTC)[reply]

Yes, Americans say both "soil" and "dirt". Some of us might even make some distinctions in meaning :) SemanticMantis (talk) 13:44, 24 October 2013 (UTC)[reply]

It's a question of attitude. I said soil because the concrete paved area had four square areas left unpaved, filled with nice topsoil, and intentionally planted. Had my nephew started playing in one of them, I'd have told him to get out of the dirt. (One of my undergrad majors was biology with a focus on plant ecology, and I worked for two years in the crop science lab, so I do know all about soil and photoperiodism (I keep poinsettias year-round, and have grown crops of marijuana). I just don't know the facts in this case.) μηδείς (talk) 18:22, 24 October 2013 (UTC)[reply]

I only asked about usage of terms because a lot of times on TV I hear Americans talking about 'dirt' where in the UK we would say 'soil'. We use them pretty much as as in the example you gave. My American cousins (from Illinois) found it confusing at times when they visited England because a lot of times we use the same terms but with a different meaning e.g. back yard, potato chips etc.and as for that line that goes "with kisses on the bottom, I'm so glad I got 'em" - we won't even go there :) Richerman (talk) 21:15, 24 October 2013 (UTC)[reply]

You will definitely hear people who do not know the distinction between dirt and soil, and who will use only dirt, and even people who say "put it on the floor" when they mean on the ground. (THis is very common in NYC, of course.) But for most educated people, if you said "They were doing construction and left the roadway covered in dirt" they will picture a smear of dry earth that needs to be washed away, while if you said, "...covered in soil" they would imagine a pile of fresh earth that will presumably go back in place when the work is done. Or at least I would. μηδείς (talk) 01:43, 25 October 2013 (UTC)[reply]

Using floor instead of ground is common here too - one of my pet hates. Richerman (talk) 04:54, 25 October 2013 (UTC)[reply]

I suspect that it will not work well to keep a marigold ever-blooming indoors. The general natural history of Pelargonium is to be evergreen perennial, while marigolds are (mostly) annuals. The Tagetes article says there are some perennial varieties, but I don't think they are commonly used as plantings in restaurants... Probably the one you got from the blacktop was a volunteer from the previous season's seeds, and they will senesce no matter what you do. Still, the best bet would be to religiously dead head the plant, because it is usually seed completion that sends senescence hormones in temperate annuals. Worth a try though, and little to lose! SemanticMantis (talk) 13:44, 24 October 2013 (UTC)[reply]

Actually, I don't mind if it truly is an annual, I want it to bloom. I read that almost all marigolds except for some specialized hybrids actually are perennials, but they are allowed to die of cold and dry over the winter, rather than being brought indoors in harsh areas. Looking at the way the plants were growing by the restaurant (size and spacing) I got the impression the ones in the soil, which were much larger, and which had obviously not just been planted that season given their wild growth habit, were survived perennials and the smaller plants growing all over were from the previous year's seeds. μηδείς (talk) 18:22, 24 October 2013 (UTC)[reply]

This article [18] seems to say that you can force marigolds to bloom indoors, but it might be hard to access. Most of the stuff I'm finding seems to be about starting them from seeds in the winter, to have them blooming indoors by e.g. Feb or March. For better googling, include the term "force" or "forcing" which is the horticultural term for making plants bloom when then otherwise wouldn't ([19]), along with /marigold indoor bloom/ etc. Finally, you can probably get better answers by asking the same question at e.g. GardenWeb [20]. SemanticMantis (talk) 14:29, 24 October 2013 (UTC)[reply]

Yes, I am familiar with forcing, I did it to my marijuana. Unfortunately the ebsco link you gave simply says you can bring them indoors and says how to pot them from the soil. μηδείς (talk) 20:05, 24 October 2013 (UTC)[reply]

The last link I gave above says about marigolds "Flowers are available round the year. It is a day neutral plant which takes 60 - 70 days from seeding to harvest." I suppose it would be easy enough to keep a succession of them going all year but that's not really what you were asking was it? Richerman (talk) 21:27, 24 October 2013 (UTC)[reply]

Yes, I really would like to keep this plant blooming, it was a really striking color. I believed it was budding again about 10 days after repotting from the vase, when the dastardly squirrels ate some buds off. (Seing it, I banged on the window, but the squirrel only stared at me in contempt, so I ran outside hissing and clicking squirrel obscenities, and brought the plant in.) I am tempted to go get some seeds from the garden shop. Tomorrow I will bring in the geranium I kept in the window last winter. I'll have to post some pictures to wikimedia of my prize Poinsettia. Frankly, I have a very green thumb. I am just curious whether I can expect this marigold to bloom before next spring, and if so, how to encourage (force) it. μηδείς (talk) 22:02, 24 October 2013 (UTC)[reply]

I just found out that 'African' marigolds come from Mexico - how did that happen? Usually when I plant them quite a few get their leaves stripped by slugs and snails. That's our damp climate for you! Richerman (talk) 05:05, 25 October 2013 (UTC)[reply]

You might want to import some Virginia opossums and Raccoons, as well as Skunks and woodchucks. When I was in grade school, these animals were quite rare (they were hunted for food until well after the Depression. Six inch slugs were so common it was suicidal to go barefoot after dark, or lean on a tree without looking first. Nowadays those mammals are very common, and I haven't seen a slug or a slime track in almost 30 years. μηδείς (talk) 05:38, 25 October 2013 (UTC)[reply]

Hmmm, we have enough trouble already with American grey squirrels and mink. I blame the Romans for the snails - they introduced them to Britain as a delicacy. Well, actually, we did have some already but you have to blame someone :). I remember years ago there was a hedgehog in the garden so I started putting cat food out to try and keep around to eat the slugs. Then one night I saw it run straight past a big fat juicy slug to get to the cat food. Richerman (talk) 13:36, 25 October 2013 (UTC)[reply]

So, the "African" marigold is from India in French. (Rose d'Inde, Oeillet d'Inde). Now, snails. The Romans tried to introduce the large "Burgundy" snail, that the French call "gros blanc". Failed. We only have the "petit gris". Which is not all that petit, unfortunately. Itsmejudith (talk) 20:37, 25 October 2013 (UTC)[reply]

cancer evolution

Are cancer cells evolving? They are so successful like adaptive microorganisms. Is that like they have other proteins as accomplices to overlook the mutation? Even when around 95% gene (junk) is evolved to sacrifice bearing mutations, some proteins can't just overlook the mutation. Are proteins that allow the cancer cells enjoy any evolutionary benefits? — Preceding unsigned comment added by Anandh chennai (talk • contribs) 23:23, 23 October 2013 (UTC)[reply]

I believe individual cancer do evolve, or at least adapt, in that they develop a tolerance to specific drugs, because only the least susceptible cells survive and spread. However, it's important to note that Bob's cancer doesn't then jump to Tom, in this evolved form. Tom's cancer starts over again from scratch. So, in that sense, they aren't able to evolve and pass down those mutations, beyond the current host.

Of course, some cancers are caused by viruses, like HPV, and the viruses can evolve. StuRat (talk) 03:36, 24 October 2013 (UTC)[reply]

StuRat is correct. Another difference is that species evolution gives rise to new characteristics and capabilities. This has never been reported as happening with cancer. What happens is that cancer cells turn on metabolic processes that should be turned off. When a small cancer gets going, the cancer cells divide and multiply, increasing the size of the tumour until the distance of inner cells from the nearest blood capillary becomes too great. Then the tumour stops growing because the cells are starved of oxygen and nutrients, and can't adequately get rid of CO2. At this stable starvation phase, the tumour is in no way a threat to the host animal. However, after some time, a tiny fraction of cancer cells in a fraction of tumours somehow turn on something that is necessary in the animal's growth phase, especially in the embryo stage. These cells begin to secrete a substance that causes blood capillaries to grow toward them. So the nearest capilliaries do what they are programmed to do, and penetrate the tumour. The tumour then can begin another growth spurt. It's now this tiny fraction of cancer cells that get the closest blood supply, so they divide and multiply faster than the other cancer cells. 120.145.195.215 (talk) 05:17, 24 October 2013 (UTC)[reply]

It's quite rare, but there do exist cancer cells which have the opportunity to evolve beyond the extent to which they have the time to evolve within one animal, namely, the clonally transmissible cancers. These include the devil facial tumour disease, in which the cancer cells are spread by devils biting each other, Canine transmissible venereal tumor, in which the cancer cells are sexually transmitted, and contagious reticulum cell sarcoma of the Syrian hamster, in which the cancer cells are spread via mosquitos. Red Act (talk) 08:19, 24 October 2013 (UTC)[reply]

WP:WHAAOE: Somatic evolution in cancer. From my brief skim of it actually looks like a damn good article (well, it's well referenced at least, which puts it in a better state than many), although it reads more like a scientific review article than a wikipedia article at present. Equisetum (talk | contributions) 11:07, 24 October 2013 (UTC)[reply]

October 24

Why does the green of afterimages look so weird?

I don't have colorblindness. Sagittarian Milky Way (talk) 00:25, 24 October 2013 (UTC)[reply]

Define "weird". And what "afterimages" are you talking about specifically? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:35, 24 October 2013 (UTC)[reply]

Staring at a compact fluorescent lightbulb for a minute or two, then closing eyes and watching it go greenish teal. It seems too close to ultragreen, which is what green would look like if your red and blue cones didn't work. My monitor's green-blues seem unvivid to me. Which is not unexpected, see the Gamut article. Do I just not look at poisonous tropical frogs and green-blue lasers enough? Sagittarian Milky Way (talk) 05:39, 24 October 2013 (UTC)[reply]

Take a break from the serotonergics, and let us know if it changes :-) --Trovatore (talk) 07:44, 24 October 2013 (UTC) [reply]

Baseball Bugs wants to hide his post
The following discussion has been closed. Please do not modify it.
Typically you should see complementary colors to whatever you were looking it. It could be that CFC bulbs are not pure white. Take the various tests in Afterimage, and if they don't work out the way they're supposed to, you should consider going to an eye doctor for further testing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:53, 24 October 2013 (UTC)[reply]

Note that our Afterimage article is not usable as a medical test, and we're in no position to advise you that there's something wrong with you if your experience of afterimages is different than it says in our sometimes incomplete text. In any case, it doesn't sound like a huge problem :) And yes, I think there is something weird about green afterimages, especially from the Sun, which I'd guess has to do with receptor photobleaching. (The ability of the eye to see light really does get "used up" to some degree in a very short term - it's mentioned in cone cell, vitamin A Wnt (talk) 18:27, 24 October 2013 (UTC)[reply]

I also see a turqoise afterimage when I stared at a filament bulb. Plasmic Physics (talk) 12:35, 24 October 2013 (UTC)[reply]

I theorize that this is because the different types of cone cells recover from neural adaptation at different rates - so the afterimage should in fact go through a series of colors. We're not supposed to theorize here, so I looked for a reference: [21] - this page (seems to be from Dresden Tech psych department) says "As you continue to observe the afterimage carefully, it fades and its color changes slightly. This is because your different cones (and chromatic mechanisms) recover from adaptation at different rates." That could be how you get a color afterimage from a white light. Card Zero (talk) 21:21, 24 October 2013 (UTC)[reply]

Deflection calculation

I'm trying to work out the deflection of a 2kg cube dropped onto a cantilever rod with diameter 16mm and E=200GPa. L=0.6m. So I have I=(pi)(16*10^3)^4/64=3.217*10^9. Then deflection = fl^3/3EI = (19.62)*0.6^3/3*200*9*3.216*10^9=2.27*10^-20m. All calculations are made using SI units. The correct answer should be 15.63mm. I suspect I'm calculating f wrong but I can't figure out how. Clover345 (talk) 17:39, 24 October 2013 (UTC)[reply]

16 mm = 16*10^(-3) m. Count Iblis (talk) 20:31, 24 October 2013 (UTC)[reply]

Also, I think you should be measuring the moment of inertia I about an axis along the centre of the beam, in which case it is (pi)d^4/32, not (pi)d^4/64. So I should be 6.434*10^-9. Gandalf61 (talk) 09:08, 25 October 2013 (UTC)[reply]

Can lungs by cleaned by inhaling a spray of lung macrophages?

In a BBC documentary they showed how after exposure to even mild air pollution you get a lot of particles in your lungs, you could clearly see macrophages busy with cleaning up the mess. But the rate at which they can work is rather limited, it's not sufficient to deal with even mild air pollution if you are exposed to that frequently. I was wondering if one could grow lung macrophages in the lab and inhale a high dose of those when exposed to air pollution.

Count Iblis (talk) 20:44, 24 October 2013 (UTC)[reply]

You wouldn't want to be using other people's macrophages. Acquired immunity. Maybe something like this could be done in the future when the technology and capital were available to give everyone his own clone bank. μηδείς (talk) 21:52, 24 October 2013 (UTC)[reply]

Macrophages tend to do some heavy-duty demolition work. The body would make more if more worked better. Often interventions seek more to turn off inflammation than to turn it on. Macrophages release cytokines^[22] and can mediate fibrosis of the lungs.^[23] (random references, not necessarily the best - you could find many making related statements) Wnt (talk) 02:11, 25 October 2013 (UTC)[reply]

Plugged noses

Why, in general, do noses get plugged and congested, and how does nasal spray clear them? EDIT: I've read the article Nasal congestion, but it lists causes, but not how it actually happens. How do the blood vessels actually cause the blockage? Mingmingla (talk) 23:55, 24 October 2013 (UTC)[reply]

You may find some useful info in Nasal spray. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:29, 25 October 2013 (UTC)[reply]

There are two different things here which might be confused here. Nasal sinuses can blocked, and there swollen blood vessels may play a part, and the nose itself can also be blocked, but that's more likely to be due to mucus (snot). StuRat (talk) 03:19, 25 October 2013 (UTC)[reply]

Swelling of the mucosa lining the nose accounts for most nasal blocking. The mucosa swells in response to infection or allergy to inhaled particles. You may also find nasal polyps worth reading. Most nasal spray contain a mild steroid or some other medication that reduces the swelling. The efficacy of these sprays can vary enormously. Richard Avery (talk) 07:13, 25 October 2013 (UTC)[reply]

Thanks for asking, reminded me of this interesting phenomenon: Nasal cycle. alternating partial congestion and decongestion of the nasal cavities in humans, with a cycle of 2.5 hours. Article could do with some more sources though.

The article about nasal sprays may be emphasizing the steroids too much, I would guess that normal decongestants are more common, these can be pseudoephedrine, oxymetazoline, phenylephrine or xylometazoline. They cause vasoconstriction (narrowing of blood vessels), that narrowing also reduces fluids "leaking" into the tissue, and decrease mucus production. They either cause vasoconstriction directly by binding to α-adrenergic receptors, or in the case of pseudoephedrine do that indirectly by triggering the release of noradrenaline, which binds to the receptor. Ssscienccce (talk) 20:43, 25 October 2013 (UTC)[reply]

October 25

Soil dynamics

Am I correct in assuming that in soil dynamics, if measuring the total stress of any soil, you should multiply everything (sum of rho*h)by g/density of water? Or is this just for saturated soils? Clover345 (talk) 12:02, 25 October 2013 (UTC)[reply]

Mr Frosty cryogenic storage containers - replacing isopropyl alcohol

The Mr Frosty cryogenic storage containers for controlling the rate of temperature change when freezing cells (to 1 C/min) require that the IPA is changed every five uses. Why? What happens during each cycle (we freeze to -80 and the next day to -150 then let the container return to RT). --129.215.47.59 (talk) 19:06, 25 October 2013 (UTC)[reply]

Sooo.... what does the fox say?

http://www.youtube.com/watch?v=jofNR_WkoCE — Preceding unsigned comment added by 24.45.120.97 (talk) 17:40, 25 October 2013 (UTC) (Seriously) — Preceding unsigned comment added by 24.45.120.97 (talk) 17:41, 25 October 2013 (UTC)[reply]