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May 13

light dependent and light independent reactions in photosynthesis

are both light dependent and light independent reactions in photosynthesis so important and are both the reactions/phases performed in a single plant in a photosynthesis? Also, what is the importance of light independent reactions? Also,what is the difference between the two ? — Preceding unsigned comment added by Sumukhmlohit (talk • contribs) 06:05, 13 May 2014 (UTC)

Wikipedia has an article titled photosynthesis that covers all of your questions, and probably a lot more. --Jayron32 11:43, 13 May 2014 (UTC)

For the mathematically inclined, this classic paper gives a brief overview of the most important biochemistry, then stitches it together into a fairly simple differential equation model [1]. There have been updates since 1980, but most of the current generation of simulation schemes (that care at all about photosynthesis) still use this Farquar model at the core. SemanticMantis (talk) 15:45, 13 May 2014 (UTC)

phoebe fledging

How long does it take for eastern phoebes to leave the nest?2601:6:6800:25C:FD70:9B92:89E:8A06 (talk) 15:14, 13 May 2014 (UTC)

Eastern Phoebe doesn't answer your question, but it does say that they typically have two broods per year, so that at least puts an upper bound on it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 13 May 2014 (UTC)

According to [2] under the section How do they reproduce, " Though the chicks are able to fly by day 15, they usually do not fledge until day 16 or 18. Both males and females feed the young. The young are capable of breeding in their first year." Bielle (talk) 16:26, 13 May 2014 (UTC)

Building an ice-dam.

Various news reports yesterday are talking about a really seriously bad discovery about the Thwaites Glacier and how it's the lynch-pin holding back many other large chunks of ice in the antarctic:

  http://www.washington.edu/news/2014/05/12/west-antarctic-ice-sheet-collapse-is-under-way/

Seems like preventing it from slipping any further would save multiple very large and expensive cities - so it would be worth considering what it would take to hold it back rather than spending the money on sea defenses and so forth.

I was wondering what scale of engineering project it would take to build an "ice dam" to hold back the glacier. Just how big an engineering effort would it take compared to things like the Three Gorges dam? The reports seem to suggest that a 700meter tall ridge was what was holding it back...can we possibly build something strong enough and of similar size to do the same job? Three Gorges is only 150 meters tall...would something that big help at all? How wide would it have to be?

SteveBaker (talk) 15:36, 13 May 2014 (UTC)

What would stop the ice dam from melting too? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 13 May 2014 (UTC)

I think Steve means "a dam to hold back ice", not "a dam made of ice". Though using the extant ice might help. SemanticMantis (talk) 16:42, 13 May 2014 (UTC)

Yes, exactly. Contrasting a (wet) water dam with a frozen water dam...either being made of whatever materials seem appropriate. Most of what's in a dam is weight - so you could probably make a watertight casing and fill it with ice - and you might not care if it melted...but I don't know whether liquid filled dams holding back solid ice would really work...I think you need something denser than ice to make the dam out of. The "existing" dam is made of sea water... SteveBaker (talk) 18:47, 13 May 2014 (UTC)

I don't think this is something we can asses on the "back of the envelope". There's no replacement for doing the actual force loading calculations and engineering. I'm certain such a thing is theoretically possible, but I have no idea if it is practically feasible. One thought I had was to perhaps reinforce the ice, e.g. with nylon or rebar. The idea is pure concrete shatters easily, but reinforced concrete has much more strength. Also e.g. ripstop nylon has very different properties than "regular" nylon. Of course, this would still weaken as the ice melts, but it might be a cheaper way to stave off disaster for a few decades, perhaps centuies (the "fast" scenario is still ~200 years away...) Imagining that our governments are willing to think and plan and spend money on time scales of centuries it itself rather optimistic :-/ SemanticMantis (talk) 16:45, 13 May 2014 (UTC)

The only vaguely possible way I can think of stopping a glacier would be to drain water from the bottom of it. That would slow down the total amount of water reaching the sea. It would still be a huge undertaking. Dmcq (talk) 17:40, 13 May 2014 (UTC)

Yeah - I was wondering about that too. The effect of meltwater from the surface cutting channels into the ice, then getting underneath it and lubricating the interface with the rock below is one of the factors that accelerate the flow of the glacier. SteveBaker (talk) 18:47, 13 May 2014 (UTC)

I have absolutely no idea if this makes engineering sense, but the "obvious" idea that strikes me is that the plug's integrity should depend on its weight, and the key to keeping it in place might be to put more weight on it. I'd think that that could be accomplished as easily as setting up some pumps and hoses and those awful noisy goddamned snow guns from the ski resorts to spray the meltwater leaving under the glacier into the air over the plug during the colder months, when it should freeze solid. The problem being... a foul up in planning here would be a Real Big Oops. (In other news, how hard would it be for North Korea to threaten to nuke the thing wide open today?) Wnt (talk) 18:09, 13 May 2014 (UTC)

It would be easy for them to threaten it. They have lots of practice making threats. Katie R (talk) 12:01, 14 May 2014 (UTC)

Pykrete is a reinforced form of ice that is stronger, thermally insulates and melts slower. Pykrete walls or dams might bolster the underside of a glacier. There is time to investigate whether pykrete can be formed efficiently by exploiting the Antarctic seasonal thaw-freeze cycle, while “All of our simulations show [the ice] will retreat at less than a millimeter of sea level rise per year for a couple of hundred years..." (Joughin). 84.209.89.214 (talk) 18:39, 13 May 2014 (UTC)

Interesting idea! SteveBaker (talk) 18:47, 13 May 2014 (UTC)

I meant to mention Pykrete, but forgot, so thanks :) It does seem conceptually very similar to reinforced concrete, and if the wood/fiber component were harvested from the right places, it would also be a form of carbon sequestration. One risk would be altering the albedo so much that the pykrete actually absorbs more heat than ice, which could accelerate melting. SemanticMantis (talk) 19:05, 13 May 2014 (UTC)

Yes, the pykrete will almost certainly be darker than natural snow. That is why I speculate use on the glacier's underside only. 84.209.89.214 (talk) 23:15, 13 May 2014 (UTC)

The explanation I saw on TV recently is that what's happening is that warmer water is coming up under the ice shelf and eroding it away from the underside. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:14, 13 May 2014 (UTC)

Yes, it says that under the high-resolution map in the article linked above: "Warm circumpolar deep water is melting the underside of this floating shelf, leading to an ongoing speedup of Thwaites Glacier". Richerman (talk) 16:48, 14 May 2014 (UTC)

Why doesn't Huntington's disease burn itself out?

Since Huntington's disease exhibits anticipation due to the Huntingtin gene becoming longer and longer faster and faster with each generation, why does Huntington's disease run in families long-term, instead of appearing in one generation, running in the family for a few generations with symptoms appearing earlier and earlier each generation, and then, after a few generations, causing symptoms so early as to kill the carriers before they reach reproductive age, thus burning Huntington's out of the family line after a certain number of generations? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:13, 13 May 2014 (UTC)

Well, Huntington's_disease#Epidemiology says it "does not usually affect reproduction." So, even if your proposed mechanism makes sense, it may well just not work that way, and increased depth of vertical transmission might just not have an effect on onset of syptoms. Also, though this disease is not pathogenic, keep in mind optimal virulence, which describes how agents that are too virulent in their methods of reproduction will indeed tend to go away. Also consider the possibility that it will go away eventually, just not yet. That's the sort of ecological take on it, I can't help with the details of mechanisms of genetic control. SemanticMantis (talk) 21:22, 13 May 2014 (UTC)

evilution means maximum discomfort for all living things as long as it doesn't keep one from procreating. hence back pains, bad teeth, common cold and everything. only the most fatal stuff, the ebolas among mutations, gets weeded out fast. blatant OR Asmrulz (talk) 21:37, 13 May 2014 (UTC)

I'd say Huntington's disease does burn itself out, in that 7 out of 100,000 is only a little bit more common than rarer syndromes caused by simple point mutations, and in that the "anticipation" demonstrates that it is not genetically stable over time. In order to have new mild alleles coming in all the time, the worst ones must be being removed. Wnt (talk) 21:43, 13 May 2014 (UTC)

Point of order: the claims of anticipation are unsourced in both OP's first two wikilinks. If there is indeed solid evidence of progressively earlier onset, we still have to firmly establish a negative impact on fecundity, which is a common proxy for Fitness_(biology) (this does seem reasonable, but very tough to show). If both those features are true, then we would indeed expect that disease to eventually go extinct, along with a certain lineage. However, it's not clear to me that the disease cannot also be the result of spontaneous mutation. If that's the case, a sufficient influx of first-generation carriers could keep the disease persisting in the human population indefinitely. SemanticMantis (talk) 22:25, 13 May 2014 (UTC)

If we can prove that onset's getting earlier by generation, do we have to study whether it affects fecundity? Unless it simultaneously causes puberty to happen sooner and breaks down societal impediments to children becoming parents, it's got to reduce fecundity. Oops, I misread things and didn't realise how slowly the disease acted. Nyttend (talk) 00:53, 14 May 2014 (UTC)

Actually, we know that Huntington's can arise spontaneously through a random mutation. Depending on how you crunch the numbers, spontaneous mutations causing expansion of the 'normal' huntingtin protein's polyglutamine repeats is responsible for anywhere between 0.1 and about 3% ([3], [4]) of new Huntington's cases. TenOfAllTrades(talk) 02:05, 14 May 2014 (UTC)

Huntington's doesn't burn itself out after a few generations because in Huntington's, "propensity to anticipation is heritable for a number of generations through the male line, [but] it originates at the time of differentiation of the germ line of a male who acquires the Huntington allele from his mother".[5] Red Act (talk) 23:20, 13 May 2014 (UTC)

Thanks for digging out that paper - it shows among other things that anticipation in maternally derived cases is 1.35 years and in paternally derived 6.73 years; and that there are indeed juvenile (age of onset <20 years) and even infantile (age of onset < 10 years) cases. The 0.1-3% figure above is sort of irrelevant in that they are looking at what proportion of sufferers had a truly new mutation; but if a mutation were to have no apparent effect (small expansion) then it wouldn't count as a sporadic mutation; rather it would be an expansion in the offspring. Still, that paper points out that the Haldane approach I was thinking to use doesn't really give accurate results in a rapidly changing society/environment. What we can be sure of though is that yes, there is at least 0.1% of new mutation, and at least 0.5% lethality (that's roughly the rate of onset < 20 years in the first table) so there ought to be something around 0.5% "churn" through the pool of sufferers, genuinely new mutant alleles added and genuinely lethal mutant alleles removed from the population. Wnt (talk) 05:34, 14 May 2014 (UTC)

There's also a little evidence that Huntington's confers some sort of health benefit when people are younger [6]. So it may be a bit like sickle cell anemia where there is a tradeoff. There's probably a lot of this sort of stuff with various mental diseases where humans haven't been around long enough to just get the benefits without any of the down sides [7]. Dmcq (talk) 12:11, 14 May 2014 (UTC)

Reliable biography of Nikola Tesla

I have seen all sorts of nonsense about Nikola Tesla, pro- and con-. Can anyone recommend a sympathetic but not credulous biography? Thanks. μηδείς (talk) 21:14, 13 May 2014 (UTC)

Where do you draw the line between sympathetic and credulous? InedibleHulk (talk) 06:04, May 15, 2014 (UTC)

Well, one that doesn't embrace crackpot conspiracy theories, but which gives reliable, objective information on projects he's believed to have worked on--basically one that takes neither a pro- nor a debunking stance as a whole. I only ever learned enough electricity to pass Physics for Science Majors 201 & 202 over the summer, then promptly forgot it. So I know there are depictions of him by David Bowie and suggestions he was the basis for Ayn Rand's John Galt, but that's not very helpful or reliable. μηδείς (talk) 17:47, 15 May 2014 (UTC)

Typhoid Mary

How can typhoid fever live for years and years in the same person without ever producing symptoms and without dying off, yet still remain capable of infecting other people? The asymptomatic carrier article mentions how HIV can run for years before causing symptoms, but that's normal for an HIV carrier (get it, and nobody will expect AIDS to start right away), but Mary had the infection for years and years while people around her got it within days of exposure. Her article mentions that Stanford scholars believe that the bacteria hid in macrophages, but it wouldn't seem to me that something that's hiding in another cell would be able to get out easily and start infecting people within a few days. Nyttend (talk) 21:45, 13 May 2014 (UTC)

From [8] it sounds like it was hiding on gallstones. [9] repeats this but suggests other sites also exist, and says the carriers are the entire reservoir of the disease. Wnt (talk) 05:40, 14 May 2014 (UTC)

Chronic Salmonella Typhi infection of gallbladder is a well known phenomenon and one of the strong risk factor of Gallbladder cancer. Ruslik_Zero 14:07, 14 May 2014 (UTC)

See Typhoid Mary. Also, an infectious disease might not be entirely dormant, but only produce a rather low level infection, which is either not taken as a sign of disease at all or is taken to be something less serious, like a minor allergy. StuRat (talk) 14:19, 14 May 2014 (UTC)

This isn't exactly on topic (so remove this if you'd like), but HSV is an example of something that can become entirely asymptomatic, yet still contagious. (again, if this is useless to your question, just delete this - wasn't sure).Phoenixia1177 (talk) 04:38, 16 May 2014 (UTC)

May 14

HCV

If the Hepatitis C virus can survive on dry surfaces for prolonged periods, why is it so rare in developed countries? — Preceding unsigned comment added by 82.40.46.182 (talk) 02:35, 14 May 2014 (UTC)

Even if the virus remains viable, it still needs to get into the bloodstream (probably) to cause an infection. (See Hepatitis C#Transmission.) Even if there is viable Hep C on a surface, and you poke it with your finger, it's not going to do anything (probably, and this isn't intended as medical advice or a guarantee of safety) unless you happen to have an open wound. The principle routes of infection are through blood transfusions (in the developing world) and intravenous drug use (shared needles) in the developed world. TenOfAllTrades(talk) 02:44, 14 May 2014 (UTC)

I posted a comment about environmental degradation earlier: I've removed it, because I've just looked up the appropriate reference ([10]) and been quite shocked by just how slowly -- if at all -- the viruses degrade over time. I wonder how long they can stay viable at room temperature? -- The Anome (talk) 13:08, 15 May 2014 (UTC)

Biochem question

How do (some) living organisms produce primary halides? I'm pretty sure that haloperoxidases can't halogenate anything in the primary position, because they follow Markovnikov's rule. The way I see it, such a primary halide would have to be produced by phosphorylation of a primary hydroxyl group, followed by an Sn1 reaction -- is my understanding correct? 24.5.122.13 (talk) 04:57, 14 May 2014 (UTC)

Anyone? 24.5.122.13 (talk) 06:36, 15 May 2014 (UTC)

Cannabis and lung cancer

It says over here, 1,

"Cannabis also has been shown to have a synergistic cytotoxic effect on lung cancer cell cultures in vitro with the food additive butylated hydroxyanisole (BHA) and possibly the related compound butylated hydroxytoluene (BHT). The study concluded, "Exposure to marijuana smoke in conjunction with BHA, a common food additive, may promote deleterious health effects in the lung." BHA & BHT are human-made fat preservatives, and are found in many packaged foods including: plastics in boxed cereal, Jello, Slim Jims, and more."

The paragraph seems to be contradicting itself. First it says that it has a synergistic cytotoxic effect on lung cancer cells with the food additive BHA, but then it says that marijuana smoke in conjunction with BHA maybe promote deleterious health effects in the lung, so which is it? ScienceApe (talk) 15:45, 14 May 2014 (UTC)

The presumption is that lung cancer cell lines are derived from cells which are present in (normal) lung tissue, and that toxicity in these lung-derived cell lines may suggest a likelihood of toxicity in lung tissue. That is, the idea is that the A549 cells used in the study recapitulate many of the properties of 'normal' lung cells, and so can be used as a model for how lung cells might respond to toxins.

Of course, it's a 12-year-old, primary, in vitro only study that found a modest effect in a non-primary cell line and doesn't seem to have been followed up on...so I'm probably going to go ahead and remove that paragraph from our article as giving undue weight to a source that doesn't meet the requirements of WP:MEDRS. TenOfAllTrades(talk) 16:02, 14 May 2014 (UTC)

Um, there is no "which is it". You've just quoted two synonymous passages. "Synergistic" means "work together". "Cytotoxic" means "bad for cells". So, in the first sentence, it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs" and then in the second sentence it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs." So the two statements are somewhat redundant. They say the same thing. ---Jayron32 02:02, 15 May 2014 (UTC)

I guess my answer wasn't as clear as I had hoped. I think ScienceApe noticed that the first part of the passage dealt with cytotoxic effects on lung cancer cells, whereas the second part suggested a negative effect on (presumably) non-cancerous lung tissue—leading to the question, why would a chemical combination that kills lung cancer be seen as bad for healthy lung? Our text wasn't explicit in noting that the lung cancer cell line was being used as a model to draw conclusions about the (possible) response of healthy cells in an intact lung. Without that crucial bit of context – the inconvenient fact that many of the things that kill cancer cells also are quite good at killing normal cells – it would be easy to see a cytotoxic effect on lung cancer cells as a good and desirable thing. TenOfAllTrades(talk) 03:04, 15 May 2014 (UTC)

The two statements are not synonymous, but how are they (as the OP says) not compatible? —Tamfang (talk) 21:26, 15 May 2014 (UTC)

This study has a really unimpressive abstract. We're talking about 0.2 mM BHA * 180 g/mol = 36 mg/l, and 10 mg/l THC ... these are pretty large amounts. I'm a little unclear on [11] but it sounds like food items never contain that much BHA, and the body hopefully isn't preserved like a product on the store shelf. Tested in one cell line that isn't actually a lung - doesn't have the sort of barrier function you expect a lung to have. It's not a study that proves anything, even at a primary level, about actual smoking. Wnt (talk) 05:42, 15 May 2014 (UTC)

Common sense would indicate that inhaling concentrated quantities of smoke, from whatever source, can't be good for you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:51, 15 May 2014 (UTC)

Common sense has its uses, but its weight in peer-reviewed research is limited. —Tamfang (talk) 21:24, 15 May 2014 (UTC)

Oddly enough, some doctors used to promote cigarette smoking. As for the above, it's always comforting to learn that the research bears out the obvious. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:23, 16 May 2014 (UTC)

Not to quibble, but wouldn't it be more apt to say "A lot of what seems obvious is what has been borne out by overwhelming evidence"? I find that it's a 50/50 over if new research is obvious - and when it is, it's more in a "Looking at it now, yes that was obvious" sense than a "Of course, I said that ten years ago" sense. It's easy to forget how informed we are by a background of research already. (yes, this is terribly off topic, I apologize).Phoenixia1177 (talk) 05:21, 16 May 2014 (UTC)

A lot of us were certain that cigarette smoking was bad for you, long before science dared to report their findings. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:28, 16 May 2014 (UTC)

Perhaps, in that specific case, I have no idea what you believed, nor why - however, as a general principle, research and obvious does not seem to go hand in hand, at first. Usually, after a set number of years, what is obvious, is the common understanding of what was researched. If this weren't true, then the billions of folks that didn't believe what we believe would have to have been exceptionally stupid if it was, indeed, obvious - that they, many times, believed the opposite would seem to indicate much of what we know is not, actually, obvious at all. (Since I am derailing the thread here, I'm going to stop at this post - :-) )Phoenixia1177 (talk) 05:38, 16 May 2014 (UTC)

How do portable (not window) A/C units work ?

1) Do they have a hot air discharge hose that blows out a window ? That's the only way I can picture them working. I saw one had an absurdly inefficient option to heat the condensate to get it to evaporate back into the air (hopefully that's the discharge air, not going back into the room).

2) This type of unit seems like it would be a lot easier to use, if I don't have to remove and replace window screens to place it in spring and remove it in autumn. I'm guessing they are less efficient than window A/C units, and you would also need to drain the condensate, if it can't drip out the window and you don't use the heater option to evaporate it. So, how does the efficiency compare with window A/C units ?

3) Do any just pump the condensate water out another hose, going to a sink or also out the window ? StuRat (talk) 19:19, 14 May 2014 (UTC)

Looks like this page: http://homeenergypros.lbl.gov/profiles/blogs/warnings-about-portable-air-conditioners and this page: http://www.sylvane.com/portable-ac-faq.html - answers most of your questions. Justin15w (talk) 19:28, 14 May 2014 (UTC)

Thanks, good info, although they seem to disagree on the value of a second (fresh air intake) hose. The first source says this increases efficiency by not sucking cool air out of the room, which is then replaced by hot, moist air being sucked into the house, while the second source points out that the need for an extra fan and the lower efficiency of cooling the coils with hot, moist air may negate that advantage. The first source seemed to have numbers to back up their claim that 2 hoses are better, so I tend to trust them.

Interestingly, the unit I looked at at the store made absolutely no mention of hoses, condensate, etc., and the pic didn't show them, either. So, that probably means a single hose, and no window install kit is included, and you have to empty the condensate bucket regularly or get a puddle on the floor. I won't be buying that unit, and probably will stick with window A/C. My window screens are apparently not removable, so I had to cut a hole in them to install my window A/C, which means I can never open the windows again when the A/C unit is out, or be deluged with bugs. StuRat (talk) 21:49, 14 May 2014 (UTC)

You can cut holes through your wall instead, hire a good drill to put holes through a concrete wall. Standard warning be careful there aren't any wires or pipes there. Site the unit outside in the shade and off the ground a bit. The installation instructions should hopefully tell you also to insulate the pipes going through the wall. Dmcq (talk) 12:06, 15 May 2014 (UTC)

In fact here [12] is a nice step by step intro showing the sort of thing required and the various tools needed. Dmcq (talk) 12:19, 15 May 2014 (UTC)

LOL, I'm trying to minimize to amount of work required and damage to the house, not maximize it. StuRat (talk) 12:40, 15 May 2014 (UTC)

Well of course one can always get the manufacturers to do it but it should cost you less than $400 in hire and extra equipment and it would look much better than a great hulking thing on the window. I'm sure you gain on the worth of the house. Dmcq (talk) 13:29, 15 May 2014 (UTC)

The laws of thermodynamics demand that the energy that these things consume as electricity plus the energy they remove from the air as they cool it MUST GO SOMEWHERE...and the "somewhere" clearly shouldn't be "back into the room again"! So there has to be some kind of external hose or something. Using this waste heat to evaporate the condensate seems like a reasonable thing to do - so that may not be that inefficient. After all, some people use swamp coolers to cool their homes - and evaporating water is a great way to get rid of waste heat if the air in the room isn't too humid to start with. SteveBaker (talk) 20:25, 14 May 2014 (UTC)

That's the problem. Unless you live in a desert, hot air comes with high humidity, and dehumidifying is as important of a function for an A/C unit as actual cooling. Also, I find my A/C units dehumidify first, with very little cooling until they get the room humidity down to a reasonable level. StuRat (talk) 21:13, 14 May 2014 (UTC)

Same deal though - if it pulls the water out of the air while dehumidifying it - then evaporates the resulting liquid - then it just humidified the air again! So even if it pulls some kind of stunt to get rid of the water, it still has to vent someplace outside. Those darned conservation laws tell you that if you want to go from air with too much energy and too much water to air with less energy and less water - then there is going to be energy and water left over that has to go somewhere. Doesn't matter how the machine does it - what matters is were the resulting matter and energy winds up. In a household situation - out of the window or down some drain are really the only sensible options. SteveBaker (talk) 15:05, 15 May 2014 (UTC)

I wonder if you could use the temp diff from the coils to the outside air to generate a bit of electricity, to increase overall efficiency a bit. StuRat (talk) 16:23, 15 May 2014 (UTC)

You'd be decreasing their efficiency. If you had a really large radiator where the temperature differential was lower the efficiency could be improved. Dmcq (talk) 11:32, 16 May 2014 (UTC)

You want to maximize the rate of heat flow between the coils and the outside air. Anything that reduces this rate (such as a thermoelectric converter) reduces the overall efficiency of the cooling system. --Carnildo (talk) 00:18, 17 May 2014 (UTC)

Static discharge - where is the charge held and how does it get conducted?

Through what route does static discharge from my person to, say, a tap (faucet)? My skin isn't a very good conductor of electricity right? Where about my person is the static charge being built up when the cause is certain items of clothing? Where are these electrons coming from and wouldn't it end up with an increasingly positive charge? --78.148.110.113 (talk) 22:31, 14 May 2014 (UTC)

You're right that skin isn't a very good conductor, and neither is air, which allows a charge to build up until large enough to overcome that resistance. If you were holding onto a good conductor, say a grounded steel bar, then the charge wouldn't build up. For an example of a person holding a large charge, think of the case where a person's hair stands on end, because of the charge: [13]. StuRat (talk) 22:45, 14 May 2014 (UTC)

See Static electricity. According to http://www.sciencemadesimple.com/static.html electrons are lost from your body to the the material (e.g. wool) and so your body becomes positively charged (click on 'Read more' under 'Where Do the Electrons Go?' and then look at 'Triboelectric series'). When you touch a conductor such as a piece of metal and ground yourself then presumably electrons will then move from the ground to your body to replace those that have been lost and neutralise the positive charge. However, I'm sure someone will correct me if I got that bit wrong :) Richerman (talk) 23:32, 14 May 2014 (UTC)

No, that's pretty much it. --Jayron32 01:59, 15 May 2014 (UTC)

There's a slight subtlety that the conductor you touch must be connected to the ground for you to discharge. My office has doors with a metal handle in an otherwise completely glass door. You can build up a fairly significant static charge over the day, which you don't notice until you press the button for the lift on the way home. MChesterMC (talk) 08:28, 15 May 2014 (UTC)

In that case, if you have more of a charge than the handle, a slight amount of the charge will go into the handle, but since it has nowhere to go from there, once the charge is equalized, the flow will stop. StuRat (talk) 12:42, 15 May 2014 (UTC)

May 15

old steel bike frame compromised due to cold temperatures?

So I live in Minneapolis and I ride an old heavy steel framed Fuji road bike, probably from the 70's or 80's, kind of like this. I left it outside all through the winter, though under an awning so it wasn't covered in snow. It was one of our coldest winters ever, with windchills hitting -20F or worse for weeks. We'd have days when the high temp, not even the windchill, was like -7F. One of my extreme bike enthusiast friends told me that the frame is compromised simply from being that cold regardless of if it was actually exposed to snow/moisture. Is this true? NIRVANA2764 (talk) 13:50, 15 May 2014 (UTC)

Windchill doesn't matter. That's just a measure of how weather conditions "feel" to people. But either way, cold temperatures shouldn't have made a difference. Even if it was cooled below the ductile–brittle transition temperature, that's not a permanent change. Permanent changes in metals generally require high temperatures, not low ones. So as long as there was no load on it, it should be fine. Moisture could cause rust, but cold temperatures would slow rusting, and as long as the paint is intact, that should prevent rust as well. Mr.Z-man 14:36, 15 May 2014 (UTC)

Our article steel doesn't seem to mention it, but steel gets more brittle at low temperatures. See e.g. here [14] for a description. I agree with Z-man that there is no lasting degradation to the frame after being stored at cold temps. But it is possible that e.g. an accident that leaves the frame intact at 70F could crack the frame if it happened at a low enough temperature. SemanticMantis (talk) 14:44, 15 May 2014 (UTC)

So that impact would only damage it if it happened while the frame was very cold? We have sunny warm spring weather here now, but I'm worried about the frame being permanently delicate now that it simply has been very cold for months on end at one point. My friend told me that bumps which used to be fine could now buckle the frame. NIRVANA2764 (talk) 14:59, 15 May 2014 (UTC)

I'm sure it would not be difficult to subject the bike to a few test bumps or torsion without you actually riding it. I have no doubt your bike will be fine. Richard Avery (talk) 15:23, 15 May 2014 (UTC)

• The main issue is that steel shrinks significantly when it gets cold, and if different parts of the bike shrink by different amounts, you could get warping, and conceivably a cracked weld somewhere. But I don't think the risk is very high, given how robust steel bikes are, especially those heavy old Fujis (I rode one for years). If the wheels don't wobble when you spin them, and there is no feeling of vibration when you ride, and no visible damage, I wouldn't worry about it. Looie496 (talk) 16:02, 15 May 2014 (UTC)

• Agreed. I'd inspect all the welds for cracks. If you don't see any, it's probably fine. StuRat (talk) 16:20, 15 May 2014 (UTC)

The great and terrible thing about failure analysis is that on any individual unit, you only get one shot. I think your friend is 100% correct: the bicycle is compromised. That is a very specific word-choice: your friend does not say the bicycle is damaged - only that it is compromised. Statistically, there is a greater chance that it will become damaged. We don't know whether your specific bicycle is actually going to break due to brittle failure until it breaks! If (or when) it does break, we can't know whether it would have broken later - or if it would have withstood the same force - had it never been exposed to the cold.

What we can know is that in laboratory experiments, if we subject steel to cold (or any thermal cycle), then that steel is statistically more likely to yield or fracture. To what extent does this make your bicycle unsafe? Well, that's a very hard question. We'd need to have boatloads of statistics about the design and materials of the bike frame; we'd need data about the temperatures it had been exposed to; and so forth.

So what we can say - at the risk of using a weasel word - is that your bicycle is compromised. We suspect that it has been exposed to a condition that can adversely affect the structural integrity. We don't know how much it's affected. Presumably, we can't find any actual damage, and we won't go so far as to call the bicycle unsafe.

Entire factories are full of specialists who study this problem as it applies to mass production. These people include material science and engineering experts; reliability engineers, operations and supply chain experts, and so on. Not to discredit Richard Avery - but his approach is not really applying the scientific method. You can thump around the bike frame all you like, and you might still find that it is undamaged. But have you actually tested the null hypothesis? Of course not!

If you want to know whether the cold has compromised the bicycle, you must conduct a proper controlled experiment. You need a statistically-valid population (say, many dozens or many thousands of bicycles). You need a test group and a control group. You need sterile laboratory conditions to isolate variables from the independent variable - the thermal cycle; and you need to conduct enough tests to determine time until failure on many bicycle frames (damage the bicycle until they break!) And then you need a statistician to tell you whether we can confidently say that the dependent variable ("damage") correlates to the thermal cycle.

And that's failure-analysis for a steel bicycle frame - a couple pieces of welded steel! Steel is a material whose properties are well-known; the common alloys haven't changed in decades and their thermal characteristics have entire ASME and ASTM handbooks encyclopedically detailing how and when they break.

My bicycle owner's manual, which I've of course read cover-to-cover, has an entire chapter on thermal properties of bicycles with complex parts including carbon fiber. Actually, high temperatures are the worse condition for my bike! If stored above 66.5°C, I'm afraid my bicycle falls "out of specification." I suspect exfoliation of the carbon-fiber from the aluminum becomes problematic. Long before we hit that temperature, the synthetic polymer "rubberized" grips also start to become irreparably melted. Around here, my bicycle rarely gets exposed to freezing conditions.

Now imagine if you mass-produce computers. Suppose, hypothetically, that your computer were mostly made out of metal and glass, but with lots of weird alloys - especially new, "non-hazardous metal" - plus silicon and plastic and fibers and flex circuits - and you want to know whether thermal cycles cause them to fracture. (Hey, people leave their metal-and-glass computers outside in the cold all the time - does that "compromise" the device?) Just imagine for a moment the complexity and the cost of building fully-functional computers, thermal-cycling some of them in hot ovens and ice-boxes for many weeks, and then dropping them on concrete by the thousands, just to see if they break. Only then can you safely assert that you know whether the mechanical parts are "compromised;" and you can confidently advertise an environmental requirement for operating- and non-operating temperatures.

Nimur (talk) 16:29, 15 May 2014 (UTC)

What an elaborate response! What my friend meant is, in layman's terms: it's trashed; don't ride it; permanently beyond repair now that it has at one point been so cold. But others have said that even if it got cold enough that it crossed the ductile–brittle transition temperature it would not be permanent change since there was no weight on it and it's warm now. So, Nimur... would you ride it? :) NIRVANA2764 (talk) 16:43, 15 May 2014 (UTC)

Sure, I'd ride it... but I wouldn't ramp it. Nimur (talk) 21:07, 15 May 2014 (UTC)

Indeed, what a lot of woffle from Nimur. But he is right in saying metalugy of the steels etc that bicylcles are made of is well understood. No permanent change in brittleness will occur. There is another aspect: Steel bicycle frames are made with brazed joints (similar to soldering). Any join involving dissimilar metals is subject to eventual failure if subjected to thermal cycling. The basic mathematical approach to predicting failure is called the Coffin-Manson relationship, after the names of two pioneering researchers. Coffin-Manson mathematics has been used to explain effectively "fatigue" failute in things ranging from aircraft airframes to power transistors. At the root of it is uneven thermal expansion. But if you do the calculation on a typical brazed jointed steel bicycle frame, you'd need 1000's of years of extreme weather to induce Coffin-Manson failure. 121.215.85.7 (talk) 16:56, 15 May 2014 (UTC)

As Nimur suggests, nobody here can assure you that the bike is just as safe to ride now as it was two years ago (or 10, or 20, etc). But consider: how old is the bike, and how many cold winters has it seen? What is the marginal change from just one cold winter? Personally, I'd ride it around town without a second thought. But maybe I wouldn't race it, or take a multi-day solo tour. For a point of comparison, I ride a ~1975 steel-frame Chicago Schwinn. It's seen plenty of temps that low over the past ~4 decades, and it still feels indestructible to me :) SemanticMantis (talk) 19:15, 15 May 2014 (UTC)

I live in a place where we get cold temperatures for months on end. Every winter people put their bikes into cold storage and bring them out again in the spring (around this time of year) and they have no problems. CBWeather, Talk, Seal meat for supper? 00:24, 16 May 2014 (UTC)

Just out of curiosity -- if people worry this much about bikes, why is it seemingly universal practice for states to leave bulldozers, road rollers, and such-like heavy duty equipment lying around in state parks, and even when they care enough to stockpile it in a secure lot they leave it out exposed to the elements? I mean, they don't even keep the snow and rain off them let alone anything else. I'd think if I had a $100k+ machine I'd garage it. Wnt (talk) 16:09, 16 May 2014 (UTC)

I think because of the expense of moving such things on the road. You need to rent special flat bed tow trucks that can lift them onto their bed, etc., and that's pricey. If you've been using it in that park until winter hit, and expect to use it again there next spring, it's cheaper to leave it on the job site. Presumably they are also built to withstand such weather. As far as theft goes, it would be rather difficult to hide and then sell such a stolen big rig. StuRat (talk) 16:30, 16 May 2014 (UTC)

Any bulldozer, grader, loader or any other heavy equipment that is going to be used during the winter will usually be kept inside. On the other hand things like dump trucks that are only used in the summer will be stored outside. For personal vehicles if you want to use it all winter and you don't have the space to build a shelter or you can't afford to heat one then it gets parked and plugged in on a daily basis. If you don't plan on using it till spring then it gets left outside. CBWeather, Talk, Seal meat for supper? 22:40, 16 May 2014 (UTC)

Bipedalism

Why back in dinosaurian times bipedalism in animals was more common and more widespread than now, when there are relatively few bipedal species (especially since small upper limbs of bipedal dinosaurs were of little use)? Brandmeister^talk

This is not true when you consider birds to be bipedal. They are modern dinosaurs. The reason that they are smaller is:

1) To allow them to fly (except for flightless birds, of course).

2) Because oxygen content in the air is less now, making breathing more difficult for huge land animals. (Whales get past this restriction because swimming is far more efficient than walking.) StuRat (talk) 16:15, 15 May 2014 (UTC)

Citing birds they way StruRat did is a nonsense. Birds are a later adaption, and their wings are adapted front legs/arms.

I note that most of the larger lizards around today are partially bipedal. When they want to go fast, the raise up their fronts so that the front legs are hanging free, raise their tails up for balance, and run on their back legs only. The back legs are bigger than the front legs, though the difference is nowhere as extreme as it was for certain types of dinasaur. A leg is not mechanically 100% efficient, having a certain level of energy loss mainly dependent on length and to a lesser extent on mass. So running on two legs is more energy efficient that running on four. Efficiency is not critical for mammals as their pressurised blood system, with 4-chambered hearts, allowing the presure to the limbs much higher than the pressure to the lungs, facilitates vastly better oxygen delivery to the muscles. Lizards can run pretty fast, but they tire extremely quickly due to low body temperature and a simplified low pressure blood system. Some large lizards can run as fast or faster than a man, but at max speed conk out after only 10 meters or so.

Running balanced on two legs also confers a significant manouverability advantage when negotiating complex terrain, as in dodging and going around rocks and plants. I've seen a dog chasing chickens that had had their wing feathers removed (so they could not escape over fences). They could not take off, but they could turn so fast the dog could not catch one, uselessly doing 4-paw slides and colliding with trees. But on open ground with no obstacles, those chickens would have been goners, as the dog has greater stamina.

I doubt that the very small front limbs of certain dinasours were completely useless. These dinosaurs persisted for millions of years, so evolution should have got rid completely of anything useless. When you look at some apparently useless feature on an animal, it's usually for sexual attraction or for courtship rituals/"dances".

121.215.85.7 (talk) 16:35, 15 May 2014 (UTC)

While the question of why the bipedalism was ostensibly more common in animals in Mesozoic era than at present may not be answered in the strict sense, I believe the following factors should be considered. (1). Evolution does not produce perfect species, just "good enough" species capable of occupying an available ecological niche. It so happened, due to the mass extinction, that at the beginning of Paleogene many ecological niches became available; and the surviving land vertebrates were mostly small and nocturnal. A nocturnal biped is a rarity: there is no evolutionary benefit in tripping and falling. The available niches were therefore taken by quadrupeds. The quadrupeds diversified, became active at various time of day, and some of them (kangaroos, humans) did become bipedal. Flightless birds also occupied some of the available niches (see e.g. Cassowary, Ostrich, Moa, Aepyornis for extant or recently extinct examples). (2) Vegetation was quite diffferent in the Mesozoic than it is at present. It is possible that whatever suits velociraptor well wouldn't have suited a jaguar nearly as well, and vice-versa. (3) Bipedalism is not unique to birds, humans, and Mesozoic theropods. Even cockroaches are capable of bipedal locomotion when running fast to escape a threat. (4) The perception of the more common bipedalism in the Mesozoic may be rooted in human culture rather than in real fact. We are best acquainted with the largest terrestrial vertebrates. Indeed, they preserve the best, and draw the biggest crowds to museums and movie theaters. Vast majority of terrestrial species, however, are arthropods, molluscs, and small vertebrates. There are not too many bipeds among those, either then or now. A lot of the smaller Mesozoic animals haven't even left any fossils to work with. Hope this helps. Dr Dima (talk) 17:45, 15 May 2014 (UTC) NB. Velociraptor is actually a bad example: there wasn't too much vegetation where it used to live :) Dr Dima (talk) 18:06, 15 May 2014 (UTC)

• I question the premise of the OP. Per plurium interrogationum the OPs question posits a presumption we have not yet established as true. Do we know for certain that bipedalism was more common in the mesozoic era than at other times? I've seen no evidence that is even true. It may be, I am not saying that it is or isn't true, just that until we've established it as true, it makes no sense to say why it is true. --Jayron32 18:09, 15 May 2014 (UTC)
  • I may be actually wrong, it's just my impression. However, in terms of habitual, constant bipedalism it looks like back in the Mesozoic there were more terrestrial animals with such locomotion, than in modern times. My speculation after 121.215.85.7's reply is that at least partially bipedal manouverability proved to be superior to quadrupedal speed, such as in cheetahs. Brandmeister^talk 18:31, 15 May 2014 (UTC)
    • See, that's the problem. People have all kinds of impressions. Has there been any systematic quantification of the prevalence of terrestrial bipedalism across the eons? If not, then what are we basing this on? The fact that we've seen a lot of pictures of bipedal dinosaurs? Couldn't that just mean that the T-Rex is a popular dinosaur? Could it mean that our museums and artists tend to favor familiar forms, and that they tend to put more bipedal dinosaurs on display than others, merely because they generate more interest, being that humans are bipedal and thus tend to be more interested or attracted to bipedal dinosaurs? There's many ways to interpret your impression, and until we've established your impression as reliably enough confirmed, there's really no point in telling you why it is true; if in fact its truthfulness is an open question. It may be true, I haven't said it isn't. Just that it isn't worthwhile to develop a theory to explain why it is true, if it may turn out later to not be true. --Jayron32 00:54, 16 May 2014 (UTC)
      • Indeed. Given that in any ecosystem, herbivores necessarily outweigh carnivores (after all, carnivores need to eat something), and that triceratops, apatosaurus and stegosaurus species were all quadrupeds, this may simply be a wrong impression caused by the popularity of representations. --Stephan Schulz (talk) 05:55, 16 May 2014 (UTC)
        • What you say is common sense, but it is not always true that herbivores outweigh carnivores at a certain locale. See e.g. this (freely-accessible) paper [15], search for "pyramid". There is a whole section on 'inverted biomass pyramids', discussing how in some cases top predator biomass far exceeds herbivore biomass. When I heard Sandin present this work he had great photos of these shark-dominated waters. SemanticMantis (talk) 14:24, 16 May 2014 (UTC)
        • The relatively high prevalence of bipedalism among terrestrial vertebrates (except mammals) is probably because they can not run efficiently using all four limbs. This is related to the structure of their spines, which could only bend in the horizontal and not in the sagittal plane—good for swimming but not for running. So, the only option if you want to run fast was to use only one pair of limbs. On the other hand mammals acquired a number of adaptations that allowed them to effectively use all four limbs for running. This includes spines that bend in the sagittal plane. Ruslik_Zero 12:43, 16 May 2014 (UTC)

Ruslik obviously has never seen a lizard. When on all fours, their sideways swinging gait is generally quite pronounced. 121.221.156.103 (talk) 02:08, 17 May 2014 (UTC)

an illustration for the standard model of particle physics

Hi!

Could you please check this diagram for errors?

I double checked it, but i'm not a specialist in particle physics and i fear i got something wrong.

---

Mass:

   more than 80 GeV/c^2

   1-5 GeV/c^2

   90-110 MeV/c^2

   less than 16 MeV/c^2

   Massless

---

Spin (small blue circles in the middle):
empty circle: 0
full circle: 1
half-circle: 1/2

---

Charge (external circles):

   positive

   negative

full circle: 1 or -1 respectively
2/3 circle: 2/3 or -2/3 respectively
1/3 circle: 1/3 or -1/3 respectively

---

Participation in interactions:

  Weak force

  Electromagnetic force

  Strong force

Thanks!

P.S. I don't want to replace the standard diagram, this diagram is just an additional illustration.

Zhitelew (talk) 17:12, 15 May 2014 (UTC)

It's a really neat diagram, but it sure isn't the standard diagram. Did you create this diagram yourself or are you following a model from a reliable source?

Reputable publications all seem to use the same diagram - in other words, the standard diagram - to illustrate the standard model. I've never seen your new circular lay-out before - and I've read a lot of physics books - so I wonder if it really belongs in an encyclopedia article.

For example, you might find the diagrams in CERN's eduation resource website FermiLab's education resources page look awfully similar to the present diagrams we use in Wikipedia. It's probably best to stick to the schematic representation that real physicists are actually familiar with. Nimur (talk) 21:36, 15 May 2014 (UTC)

Hi, Nimur. Thanks for the answer!

I made this diagram myself, but there is nothing original in it. I just bended the "standard" table into a circle and replaced numbers with colors. The design of the diagram can be new, but all the science and data are from the same "standard" table. --Zhitelew (talk) 21:59, 15 May 2014 (UTC)

...Right, but what does it mean? Let me clarify: I know about the Standard Model, but let's imagine momentarily that I know nothing, and I'm learning it all from your chart. And, I apologize for nitpicking here... you've made a really nice picture and I can see that it took effort. It's quite artistic and very skillful. But, we're making an encyclopedia, not a graphics showcase... and I think there are important and problematic issues with your diagram as a physics-education tool.

See, I look at this chart, and I wonder why you've apparently plotted it in polar coordinates. I see that particles at larger radius have a larger area on the diagram. What does this represent? Are those particles larger? Are they more abundant? What does "area" represent in this chart? What does radial-distance from the origin represent? Are particles at the center of the diagram "inside", while particles at the outer rim or the diagram "outside" of composite particles?

The chart is circular. It "wraps around." What is the physical meaning of this? I'm going to start making inferences - physically incorrect ones! - "photons are close to tau mesons on the chart, so are they related?" ... And now, on account of a confusing diagram, I've embedded incorrect physics into my understanding of things.

So, you see, there is a reason why all the standard diagrams look the same. Consider, for example, the Periodic Table of the elements. It can be re-drawn in many ways;if you read into it, you'll see that many alternate diagrams do exist. But, except for a small number of special-purpose variants that are made for expert users, most of those charts just serve to confuse science-students.

You might enjoy reading the Junk Charts blog. The authors tear apart a variety of infographics that they find on the internet. Artistic creators can draw lots of neat-looking charts - and nowadays, it's very popular to design an exciting-looking infographic diagram - but what do the axes mean? Does the diagram convey information in a straightforward, accurate way that is easy to interpret? Does your diagram? Or, quoting Mr. Fung more directly:

• What practical question are you trying to answer?
• What does the scientific data say?
• What does your chart say?

So: how are the particles of the standard model related? Does your chart answer this question?

These are tough questions, but if you want an honest and very brief answer, "no." (It is my opinion that) your chart is not the best way to represent the standard model in an encyclopedia article. The standard diagram - as boring as it may seem - has been around for a while, and it's best to stick to that layout, unless you find a reliable physics education source that makes a convincing case otherwise. Nimur (talk) 04:10, 16 May 2014 (UTC)

OP isn't suggesting replacement of extant figures. I take your points, but I think this figure is quite nice. Of course I would personally never think the areas represent anything, but that can be explained in the legend to head off confusion. I actually think the colors and pie chart insets for spin and charge make those pieces of info much more easy to grasp at a glance. That is something that this new chart "says" much more clearly than the ones you linked. So, provided there are no factual errors (which I assume you'd have mentioned), I see no reason why this can't be used to supplement other, more standard graphics in our articles. I also don't think this is WP:OR, insofar as nothing is original except for layout. We aren't publishing a paper book, (WP:Notpaper), and there is no limitation on how many figures can be used to express concepts. I don't share your fear of the graph leading to non-physical notions, but again, a good legend will go a long way in preventing that. SemanticMantis (talk) 15:22, 16 May 2014 (UTC)

I have to agree with Nimur. What is this trying to show? For example reading this graph in the top column you have the Higgs with the Z⁰followed by the neutinos (why no anti neutrinos, they haven't been confirmed as Majorana particle yet) working away from the centre of the circle. Okay they all only weak force and are neutral but they are fundamentally different particles. The neutrinos are seperated from the other leptons, why? From this graph it doesn't look as if the charged leptons and the neutrinos are part of the same family but the neutrinos are asociated with the Higgs. There is nothing fundamentally wrong with graph (besides saying for sure the neutrino is not a Dirac particle like all the fermions) but it can lead people to make the wrong connections.Dja1979 (talk) 19:53, 16 May 2014 (UTC)

Thanks for the critics! I didn't add antineutrinos because (as far as i know) the existence of antineutrinos is not confirmed yet.

Agree. The diagram should better display borders between particles with different spin. This should help against possible wrong connections and accentuate the right ones.

I probably should mark the empty slots with other color. These white spaces only indicate the absence of the particles with corresponding properties, not borders between groups of particles.

By the way, aren't neutrinos fundamentally different from other leptons? Yes, they have the same spin as other leptons, but they have all these unique wired properties like oscillations, extremely low mass, only week interacting etc. Shouldn't we indicate this somehow? --Zhitelew (talk) 20:48, 16 May 2014 (UTC)

spiral periodic table

• This might also be a good question for the Mathematics desk since what you have here is a rectangle transformed into a cylinder looked at from a polar prjection (I may have the terms slightly off.) This works fine if the opposite edges joined to form a cirle actually can be so joined--you can do this with a periodic table with some jiggering. You can't do it with a normal chessboard howver, since pieces aren't allowed to move diagonally acrost the right and left edges in the standard game. μηδείς (talk) 20:07, 16 May 2014 (UTC)

Engineering disciplines

Is there a huge difference between different engineering disciplines other than what they're engineering? For example civil engineers engineer civil infrastructure and aerospace engineers engineer aircraft but do they use the same principles? 82.40.46.182 (talk) 22:38, 15 May 2014 (UTC)

No, there isn't a huge difference in disciplines. At my university the big divide was between civil and all the rest, and in the second year the electricals started to specialise away from the rest. Civil is a bit odd as they often design to code, whereas most disciplines design for function. As such I would expect a mechanical engineer to happily work in aerospace, I think that might be more of a stretch for a civil engineer. If you see a mechie in a civil firm he is likely to be working either on the mechanical systems (lifts, HVAC,plumbing) or as a structural engineer, as frankly the civil guys seem a bit flaky on structural analysis. FWIW I was more or less in the mechanical stream, yet my career includes fairly big lumps of electrical and signal processing. University is NOT about teaching you to do a job, it is about giving you the basic tools and the confidence to be able to teach yourself. As such, if you haven't covered the design of power amps during uni, you know at least enough to find the right book and learn from it (to pick an example that came up for me). For that matter I've worked with engineers who did maths or physics at uni, they taught themselves what they hadn't picked up at uni. Greglocock (talk) 23:40, 15 May 2014 (UTC)

On a day-to-day basis engineers usually work with approximations and simplifications that apply in their field or sub-field, even though these approximations and simplifications are not true in general. An example for electrical engineers would be Kirchhoff's circuit laws. Jc3s5h (talk) 23:53, 15 May 2014 (UTC)

Kirchoff's circuit laws are conservation laws which when properly applied to lumped components are exact, not approximate. 84.209.89.214 (talk) 01:55, 16 May 2014 (UTC)

But the real world is not made up of lumped components. Jc3s5h (talk) 02:18, 16 May 2014 (UTC)

• On the contrary, I find that, other than some superficial similarities, the practices and workings of various engineering fields to be quite different. I'm not sure that the training and/or job requirements of a civil engineer, a chemical engineer, and a biomedical engineer are all that similar, excepting that they all are engineering fields; more like each other than they would be to other jobs like say a school teacher, a chef, or an economist; but otherwise I'm not sure many job skills from one of those fields would transfer well to the other. Someone designing a prosthesis would have a hard time working out the fluid dynamics and heat transfer problems a chemical engineer needs to face, and neither would necessarily be able to do the work necessary to design an automobile from first principles, without being fully retrained for the others job. Certain broad concepts, such as the mathematics background and basic physics principles, may cross over, but I'm not sure much more than that. --Jayron32 00:39, 16 May 2014 (UTC)

Curious. Are you an engineer? Greglocock (talk) 01:54, 16 May 2014 (UTC)

Civil engineering tends to be more about managing people and less on the technical side than say electronics engineering, but there is always a large component of working with other people. All also have to work safely within set constraints, be a bit practical, and be conscientious about keeping to schedule and documenting things. And it seems all have to at least occasionally work long hard and unsocial hours. It is a career for people who want to make something useful in the world. Dmcq (talk) 11:19, 16 May 2014 (UTC)

A military perspective. Mechanical engineers build weapons. Civil engineers build targets. HiLo48 (talk) 01:52, 17 May 2014 (UTC)

May 16

Patterns That Change When Tilted

Hello. I do not know how to best word my question but here is a start. I would like to know the field that is concerned with designing patterns that change drastically in appearance when the paper on which it is printed is tilted so slightly. I am not looking for a specific change in appearance; this is be open-ended. Thanks in advance. --Mayfare (talk) 00:37, 16 May 2014 (UTC)

It sounds like you're asking about lenticular printing. Red Act (talk) 01:13, 16 May 2014 (UTC)

Iridescence also is affected by viewing angle, and diffraction gratings can be used to produce angle-dependent effects. —Quondum 04:45, 16 May 2014 (UTC)

There's also holograms of course. It might help if you could link to an example.--Shantavira|^{feed me} 08:53, 16 May 2014 (UTC)

Is there a method that does not change the properties of the paper? --Mayfare (talk) 11:04, 16 May 2014 (UTC)

Anamorphosis is a sort of optical illusion involving an image that appears distorted from one angle, but is intelligible from another angle. The Ambassadors (Holbein) famously uses this technique. ZMBrak (talk) 13:49, 16 May 2014 (UTC)

Doing this on normal paper sounds difficult - paper is a very bumpy material at microscopic scales - so the orientation of the surface to the eye changes across every fraction of a millimeter across the surface. Hence any straightforward "ink" approach isn't going to work because the orientation of your eye to the surface is uncontrollable. If you're prepared to go with very smooth plastic films and such - then it gets easier. There are printable holographic approaches - and of course metal films like the ones on many credit cards. Simplest of all is to use a lenticular film over a printed image - which is a technology that's been around for 80 years or more. I think we need to understand more about the application for this. SteveBaker (talk) 18:21, 16 May 2014 (UTC)

• I'll suggest moire pattern since that ended up being the answer to a similar question I asked. μηδείς (talk) 18:24, 16 May 2014 (UTC)

In theory paper should be compatible with a diffraction grating - in a really quick search I get [16] which points me at Optically variable inks, Optically variable pigment (whatever the difference is), multi-diffraction grating, pixelgram as (perhaps, I'm not sure) methods of printing diffraction gratings on currency to make copying harder. I don't know how much modification they involve from regular paper though... would be interesting to see more. Wnt (talk) 20:33, 16 May 2014 (UTC)

radical surgery on antarctic ice using lasers

Would a high powered laser be able to amputate the part of the sliding ice, if any, that overhangs into the ocean? I was thinking that would slow the slide of the remaining ice into the ocean, giving us more time to deal with it. I know the ice is very thick and hard to cut with a laser, but the overhanging ice would tend to open up any laser cut further, like when a leaning tree is cut on the upper side with an axe. The power level of such a laser would be immense, im sure, but what would an estimate for that power level be? (So that if 50 or so years from now, such a very powerful laser became feasible.)--(If not much of the ice is currently already over the ocean, the report is that it will be in a few years.) Thanks.Rich (talk) 04:31, 16 May 2014 (UTC)

Methinks high explosives (as used, e.g., for avalanche control) would be much more cost-effective. 24.5.122.13 (talk) 04:52, 16 May 2014 (UTC)

It could depend on location. An orbital laser would have an enormous initial cost but could use natural nuclear power, which is close to free, and once in orbit, there wouldn't be any travel overhead, no matter if it's an antarctic glacier, or closer to populated areas.

A pulsed laser to which ice is opaque would probably be the optimal tool for the job. At high power, it would crack, rather than melt, the ice without much heat transfer.

OTOH, wouldn't it be more useful to cut through cultures of this or that, with a laser that big? Preferably while they're being harvested, for added evulz? - ¡Ouch! (^{hurt me} / _{more pain}) 09:22, 16 May 2014 (UTC)

Hmmm...what kind of orbit is this laser in? If it's a polar orbit, then you won't have much time to do your work in each orbit...if it's in a low equatorial orbit, then it wouldn't even see the poles - and if you put it all the way out in a geosynchronous orbit, the accuracy and focussing issues would be amazingly difficult. Plus, I'm not sure how other countries would feel about a laser out there in space with the capacity to slice through half a kilometer of ice at a positional accuracy down to a fraction of an inch...that would make a really good death-ray! SteveBaker (talk) 18:05, 16 May 2014 (UTC)

Why should we even bother to ask them, when we have the means and the ability to do it unilaterally? But I agree that it won't work for cutting ice (although it CAN work against Iranian nuclear missiles). 24.5.122.13 (talk) 22:42, 16 May 2014 (UTC)

Are you sure of your assumption that overhanding glaciers pull the rest down with them ? Aren't they supported by seawater ? I believe the floating ice shelves act more as a cork, stopping the rest from sliding off the land. StuRat (talk) 06:13, 16 May 2014 (UTC)

I'm puzzled as to why you would want to "deal with it", but anyway a laser would be completely ineffective as the hole it creates would continually fill with water which would block the beam.--Shantavira|^{feed me} 08:45, 16 May 2014 (UTC)

That's why Rich made it "high powered". The water would be blocked out by a bubble (or possibly a jet) of water vapor. Not sure how much power you'd need. Also, this. - ¡Ouch! (^{hurt me} / _{more pain}) 09:22, 16 May 2014 (UTC)

The notion of a destructive laser orbiting the globe would likely be met with very vigorous opposition, and in fact might already be banned by existing treaties. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:28, 16 May 2014 (UTC)

You'd need a powerful laser. If you can't grok the orders of magnitude involved in this problem, then perhaps a more visual demonstration will help build intuition: go grab the most powerful laser you can find, and try to melt a block of ice with it. (Unless you're SteveBaker, who owns a personal CO2 laser cutter - but he knows enough to be careful). Everyone else: good luck. Your ice will melt from ambient room temperature long before you etch away anything. Between the immense heat-capacity of water ice, and the high reflectivity of ice to wavelengths of visible light, and the other inefficiencies related to making laser light, this whole exercise becomes very impractical when you scale it up to iceberg-sized objects. Even if you put the laser and ice-cube in the freezer - so the ice doesn't heat up from the room - and let the laser shine on for days - every time it melts a little bore-hole, the water will re-freeze and seal it up pretty quickly.

For anyone interested in real-world ice boring, you might want to read about the IceCube Neutrino Observatory. Conventional technology that we use for drilling into materials like solid rock does not work on Antarctic ice. (The ice flows into the bore-hole, moving as a fluid; and on contact, the pressure re-liquifies and re-freezes!) So the ice just seals up the holes you've cut. The AMANDA and IceCube projects avoided "drilling" and "cutting" and instead relied on "melting" using a steady stream of hot water - and a very wasteful fossil-fuel plant to generate that water! And here's an awesome review from Schlumberger - the oilfield service company - on "Drilling Through Ice". Nimur (talk) 15:33, 16 May 2014 (UTC)

There are two or three significant problems with doing this. So let's talk a bit about my laser cutter...and then we'll see how this idea extends to cutting a glacier.

1. My laser puts out about 100 watts of energy - no more than an incandescent light bulb. That surprises most people when they see it slicing through a half inch of plywood like it wasn't there! But take all of the heat from a 1000 watt bulb and put it into a beam the diameter of a pencil - and the result will set fire to wood and paper...but it won't cut it. To get it to put enough energy into the material to cut it, you have to focus that pencil-thick beam into something about three hundredths of a millimeter across. When you do that, it'll make most organic materials and many plastics simply "go away"! A light bulb has about 100 square centimeters of area to radiate those 100 watts. But that same amount of energy emitted as a one-square-centimeter beam is 100 times more energy per square centimeter than a lightbulb - but focus it down to 0.03mm and you get about 10 million times as many watts per square centimeter as that light bulb...and that's enough to zap just about anything that absorbs it.
2. However, my laser can't cut metal...even a thin sheet of kitchen foil is utterly impenetrable. That's because the metal reflects almost all of the energy away. Because it's an infra-red laser, it also can't cut anything that's transparent to IR light because the beam goes right through it without the energy being absorbed. There are lasers that can cut metal - but they have to be around 3000 watts and they aren't usually
3. The laser cutter has big fans to extract the smoke and hot gasses produced by the cutting process - and a high pressure air jet that squirts into the slot that the laser is cutting. These are there to remove smoke and debris from the path of the laser beam. Anything like that that get in the way attenuates the beam so badly that it won't cut.

The trouble with slicing through a glacier is that you can't focus the beam thin enough once you're more than a few centimeters down into the ice. So you need VASTLY higher wattages. If I wanted to cut wood with an unfocussed beam, I'd need a 100,000 watt laser rather than a 100 watt device! Those kinds of laser exist...but they are massive, difficult, dangerous, fragile and horrendously expensive! I suppose you could consider dynamically focussing the beam, increasing the depth of the focus into the ice as the beam cut deeper - but focussing is problematic. My lasers focussing lens is made of Zinc selenide with a gold coating that's just 2 atoms thick! That 1" lens costs $300 and is about as hard as candle-wax, so it scratches if you so much as look at it. You can't use just ordinary lenses because if they aren't super-transparent, they get hot enough to melt in very short order! Worse still, if you cut with a focussed beam, the "kerf" (the width of the slot) is about the same width as the diameter of the focal point of the beam...but that's not wide enough to fit the unfocussed beam as it enters at the top of the material. For that reason, I can't cut wood that's more than a half inch thick without getting a much longer focal length lens.

Then the light frequency is a problem. Ice is both transparent and incredibly shiny at optical wavelengths...so you'd need to choose a frequency that the ice would strongly absorb and not be either transparent or reflective.

Finally, as you hit the ice, it's probably going to flash into steam...and you get a LOT of steam from a very small chunk of ice. Where that steam goes is a problem...if it simply drifts up the slot that you're cutting, then it'll absorb laser light and attenuate the beam...or it may condense back onto the sides of the slot...causing liquid water to fill the slot and have to be boiled away again. You'd need to extract the steam as you cut if you wanted to make any progress. Worse still, the steam will drift sideways back along the slot you've been cutting...it'll first condense and then re-freeze...so in all probability, your nicely lasered slot would just fill up with new ice again.

So I don't think a laser is the best way to do this. We know that ice is drilled using hot water jets...and that's probably what you want here. SteveBaker (talk) 17:59, 16 May 2014 (UTC)

I have a hard time believing this could have any chance. I don't think of glacial ice having much tensile strength - after all, deep crevasses are all over the place. Wnt (talk) 15:40, 16 May 2014 (UTC)

And if all the reasons already given don't convince you, also consider that glaciers are constantly moving, and different layers move at different rates, so the hole would move and skew as you are trying to cut it. Therefore, you'd need to be able to cut the whole thing off quickly, so the movement wouldn't be significant. StuRat (talk) 18:06, 16 May 2014 (UTC)

Staged fire alarms

Why don't many public buildings use staged fire alarms? Some shopping malls and airports do but many places still seem to use the "if alarm goes off, evacuate building" method. In the staged alarm, there is a first stage where the occupants of the building are made aware that an emergency has been reported in the building and that people should prepare to evacuate, if necessary. During this first stage, building staff normally investigate the situation and make a decision as to whether evacuation is necessary. Normally this is a very quick process so doesn't delay evacuation significantly, in case it is necessary whilst also avoiding mass evacuatiation and system shut downs, if it is false alarms. The staged alarm can also be used for partial evacuation. So why don't many buildings opt for this staged alarm to minimise disruption in the case of false alarms? 82.40.46.182 (talk) 19:36, 16 May 2014 (UTC)

Why aren't magnets used to make pushing colenoids?

To make a pulling colenoid, you just need an iron core that is pulled by a coil. To make a pushing colenoid, you need plastic attached to the core, more length, and a spring to go back to the original situation. It seems much simpler to make the coil push the core by using a permanent magnet as core, where the coil makes a magnetic field in the opposite direction. Nobody seems to use that option, so my question is: why? I rewrote this a few times but I really can't explain it better than this. Sorry for that. Joepnl (talk) 22:11, 16 May 2014 (UTC)

I've never heard of "colenoid" - do you mean solenoid? I suspect that the article relay might answer, but I'm not sure. --ColinFine (talk) 23:05, 16 May 2014 (UTC)

The reason is strength. If you apply a weak magnetic field (as from a coil) to a soft ferromagnetic material (eg iron), yoy get a weak pull. If you increase the strength of the field, the pull gets roughly proportionally stronger until the iron saturates (it is fully magnetised). Increasing the field even more does not increase the strength of the pull, but it does not decrease it either. Solenoids are generally designed to just saturate the iron - this reliably furnishes maximum strength, even if the current is not a precise amount, without wasting too much electrical energy.

To repell a magnet, the solenoid field has to be less than the permanent magnet field. If the current is a bit stronger than needed for balance, the "push" is cancelled out and the coil will pull the magnet in anyway, as the magnet field is simply overwhelmed. Engineers always strive to make things non critical.

Further, there is a choice of materials to make magnets out of. If a metal alloy, such as alnico (a common permanent magnet material), its going to be a lot more costly than a soft iron and a spring, and the coil field will reverse its magnetisation so that it pulls anyway. Metal alloy magnets are made by subjecting the alloy to a very strong coil, and the magnetisation is always in the "pull" direction. The other choice is a ferrite. The strength of magnetisation of ferrites is way below that of metal alloys.

121.221.156.103 (talk) 02:25, 17 May 2014 (UTC)

(ec) A solenoid exerts a strong pulling force when there is a low Reluctance path for its magnetic field, with a gap across which the force is exerted. Typical magnetic materials are iron or ferrite; they form a small gap and the force direction is the same for either direction of current. Pulling solenoids need a spring or gravity to return them to the no-current position. It is possible to make a solenoid both pull and push a permanent magnet core but this has disadvantages:

• Attainable force is limited by the strength of the permanent magnet, i.e. the Coercivity of its material which costs more than iron. High temperature, mechanical shock, excessive repelling current or a strong external magnetic field can all degrade its magnetism.
• It is less easy to construct the curved low reluctance path from these materials.
• Any loose ferromagnetic particles will attach themselves to the magnet.

Two examples of solenoids in permanent magnet fields are moving coil ammeters and the Voice coil in a Loudspeaker. The direction of force on these solenoids is reversible by reversing the current flow. 84.209.89.214 (talk) 02:51, 17 May 2014 (UTC)

wage slavery around the world

hello, are there stats as to what percentage of (fit) people in a given country derive their livelihood from hired labor (as opposed to self-employment (such as keeping a shop), civil service, subsistence farming etc)? I presume it's roughly two thirds pretty much everywhere, but still? also, what makes the difference between the average worker and the "big" CEO's etc, who are but employed workers like everyone else (a fact of which they as a class always seem to make a big point), yet are hardly wage slaves. I only want to know just how prevalent this model, which afaik is pretty recent (300 years?), has become. thanks Asmrulz (talk) 23:58, 16 May 2014 (UTC)

I think the whole idea that "employee" = "slave" is just completely wrong. There are many highly compensated employees, such as the CEOs you mentioned, sports and movie stars, etc. There are also many dirt poor self-employed people, like subsistence farmers, especially in poor nations. The protest that began the Arab Spring was even started by a self-employed man (Mohamed Bouazizi) who was systematically abused by the government. StuRat (talk) 00:37, 17 May 2014 (UTC)

May 17

University/college life

Could it be argued that university/college life a risk factor for cancer, heart disease etc later in life? For many students, university/college life involves studying for long hours creating stress, drinking a lot in response to stress and also eating unhealthily. Clover345 (talk) 03:14, 17 May 2014 (UTC)

This looks to me like a classic request for opinions, rather than well sourced answers. HiLo48 (talk) 03:28, 17 May 2014 (UTC)

What makes you imagine that spending those years NOT going to college is going to result in less stress, drinking and so forth? If not in college, you're probably going to get a job sooner - and for sure jobs can be stressful. College graduates generally have higher income and better access to healthcare and good nutrition in later life - which is certainly going to have a huge impact on cancer risk...there are a million differences in the long-term prognosis depending on the choices you make - it would be extremely simplistic to take the handful of poorly-correlated-with-college-life factors that you list and ignore all of the other effects. SteveBaker (talk) 03:40, 17 May 2014 (UTC)

fusion as a resource?

sir my question is

why can't we still use the the fusion energy as a sustainable resource?  — Preceding unsigned comment added by 14.96.133.124 (talk) 04:27, 17 May 2014 (UTC)