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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 [1] 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 [2], 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.

In the Standard Model antineutrinos exist and they have been shown to be different to neutrinos (sorry I don't have the paper).The MINOS experiment was able to produce a beam of neutrinos and then by flipping the horn currents produce a beam of antineutrinos. Nuclear reactors only produce antineutrinos so expriments like Daya Bay only see antineutrinos never neutrinos. T2K and NOvA are using the differences between neutrinos and antineutrinos to find the value of the CP violating phase. So we do know that antineutrinos exist.Dja1979 (talk) 23:09, 18 May 2014 (UTC)

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)

I would say no. Only weak interating is stated by the fact that they have colour charge 0 like all leptons and their electric charge is 0, gravity isn't included in the Standard model so left of this only leaves Weak charge I don't think this needs more explanation (any more than up quarks and down quarks are different, so needing explanation). Oscillations in the charged leptons hasn't been observed yet but it could happen. For example the quarks mix to a lesser extent, so not unique to the neutrino. Low mass; we don't know what generates the mass so it may be important, it may not be, I would leave it for the time being. Dja1979 (talk) 23:09, 18 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 [3] 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)

It looks like they just added this feature to the US $100 bill. It now has a strip on it with images that shift between 100's and Liberty Bells, when tilted. StuRat (talk) 03:15, 18 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)

Weapons in orbit are already banned, but "It's not a weapon, it's weed control!"

...or maybe not; this used to be the article that banned permanent blinding via laser, but right now, "Quoth the browser, '404'." - ¡Ouch! (^{hurt me} / _{more pain}) 10:41, 19 May 2014 (UTC)

To Nimur below, click the xkcd link to have a look at the power I had in mind: more than the YAL, and definitely pulsed, to avoid wasting too much energy into melting ice.

Even more clearly, it'd take a JamesBondVillainesque, KillSatirical, WaveMotionGunnical amount of power. I'd call it an EleventhHourSuperPower but that would be an Incredibly Lame Wave Motion Pun. - ¡Ouch! (^{hurt me} / _{more pain}) 10:41, 19 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)

• I am reminded of Noah of Pontium who, reasoning that the Mediterranean was about to catastrophically overtop the Isthmus of Bosphorus, decided to dig just a little trench a few feet deep to let Mediterranean water slowly leak into the Black Sea, rather than in a flash flood that would kill or drive off millions of inhabitants of the area to their deaths. Of course, if we only had sharks with lasers on their noses, they could get under the glaciers and attack them from just the right point, where nothing could possiblye go wrong. μηδείς (talk) 16:59, 17 May 2014 (UTC)

• You're talking about a massive quantity of water flowing through a narrow channel. That would rapidly erode it. It would last longer, at least, if lined with thick stone. StuRat (talk) 23:30, 17 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)

Because people don't get sued for over-reacting to a potential emergency. As building manager, if you purposefully cause a delay in evacuation and it then turns out that someone was killed, the notion that more people might have died in the stampede to the exits will not matter much to the jury. Nor will it matter if the delay wasn't the cause of the person's death. The risk of being sued to smithereens is way too high. Matt Deres (talk) 13:46, 17 May 2014 (UTC)

In which case what's the reason some buildings do use the staged alarms? Mostly large public buildings such as hospitals, airports, large stations, shopping malls, and large schools or colleges seem to use them. 82.40.46.182 (talk) 20:38, 17 May 2014 (UTC)

It depends on how quickly people can exit the building. With tall buildings like the World Trade Center, it took hours to evacuate everyone, so you had to just evacuate a few at a time, starting with those on the fire floor and directly above, to avoid people being trampled to death. In a place with many exits and not many floors, like a mall, you should be able to evacuate everyone at once. StuRat (talk) 00:23, 18 May 2014 (UTC)

The risk analysis differs between different types of building as well. In a hospital, there is a risk of people being injured or killed by an unnecessary evacuation, which balances the risks of delaying evacuation in the event of a true emergency.--Srleffler (talk) 17:18, 19 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)

I note that the two examples involve very weak forces. The pointer deflection force in a moving coil meter is obviously minute. In order to assure long term accuracy and a deflection linear wrt electric current, the coil field strength is much less than the magnet field. Loudspeakers are notoriously inefficient, typically converting only about 5% of the electrical input energy into sound energy. In order to have acceptable harmonic distortion, the coil field strength is quite small compared to the magnet field strength.121.221.156.103 (talk) 05:00, 17 May 2014 (UTC)

Yes. Linear deflection wrt electric current is achieved by the combination of 1) a return spring whose force obeys Hooke's law with 2) a permanent magnet constructed to give a uniform magnetic field strength throughout the range of motion of the coil. 84.209.89.214 (talk) 13:34, 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)

Can arbitrary and capricious harassment be properly described as "systematic"? I'll accept "systemic". —Tamfang (talk) 06:19, 17 May 2014 (UTC)

And from what I have read, it wasn't even harassment in the legal sense of the word -- just nitpicky law enforcement, and it wasn't so much the nitpicking per se that enraged him, but the fact that it was a woman who was laying down the law to him! In fact, one news report (which may or may not qualify as a reliable source) even claims that he was the one who physically assaulted the woman cop, and that's what started the whole thing. 24.5.122.13 (talk) 06:31, 17 May 2014 (UTC)

I don't think that started it, that was a result of the harassment. And the corruption was such there that nobody could get the proper licenses to operate legally without knowing somebody in the government and/or giving them a hefty bribe. StuRat (talk) 13:02, 17 May 2014 (UTC)

Before we go further... is this actually a science question? Wage statistics are really a matter of economics, or political theory, or history. This question, and its responses, might fit in better at the humanities desk. But we've apparently digressed into a discussion of various people's opinions about the "Arab Spring" - and thus far, nobody has actually connected their diverse opinions back to the topic of wage politics. The topic is fascinating, and I'm sure many of us have strong and well-informed opinions on those topics - but this is not the correct place to have the discussion.

The OP might start informing his question with conceptual backgrounds and factual data by reading about industrial and labor relations; employer-worker relationships, minimum wage in the United States, ... Our encyclopedia contains much information on this topic, as pertaining to the U.S. and other parts of the world.

If the OP actually wants statistics - as they asked for - they might find that the Bureau of Labor Statistics (a branch of the United States Department of Labor - makes the most thorough and complete records available at no cost. Other countries may have similar government agencies. Private-sector and academic research may also exist to provide such data, but is usually available at cost.

If the OP is interested in the perspective that employment and oppression are intermingled, he might find Howard Zinn's influential book, A People's History of the United States, a worthwhile read. It is well-informed and factual; it has been called exemplary and inflammatory. Anybody who is interested in wage politics would do well to read it, even if you do not agree with Zinn's views. Nimur (talk) 18:17, 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)

The Op's not looking for a reference. He's already got his premises, and he wants to see if we'll accept his conclusion. μηδείς (talk) 16:43, 17 May 2014 (UTC)

There probably are stats on life expectancy differences between college grads and non-grads, if we can find them. StuRat (talk) 05:48, 17 May 2014 (UTC)

Except that wouldn't do anything to establish a causative link between college lifestyle and the conditions in question. Snow talk 10:04, 17 May 2014 (UTC)

If you can establish a correlation in two events, and that event A happens before event B, and provide a plausible mechanism by which event A might cause event B, then you have a reasonably strong case for A being the cause of B. Of course, no matter how strong the evidence is, one could always argue that everything is just a coincidence, so cause-and-effect can never be 100% proven. StuRat (talk) 15:48, 17 May 2014 (UTC)

It would be interesting to see alcoholism rate relative to education and income level. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:19, 17 May 2014 (UTC)

1, 2, 3, 4: here, hopefully these will give you something less morbid to think about. :) Snow talk 10:43, 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)

The only way to be stress-free is to be dead. The dead have no problems. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:19, 17 May 2014 (UTC)

So bleak Bugs...do you need a hug? ;) Snow talk 10:43, 17 May 2014 (UTC)

"Life is trouble; only death is not. To be alive is to undo your belt and look for trouble." Deor (talk) 12:56, 17 May 2014 (UTC)

Sure. Not bleak at all. Stress is natural. Dealing with it is how we grow and change. As Dennis Miller once said, "The worst moment of being alive is better than the best moment of being dead." ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:07, 18 May 2014 (UTC)

Your premises are wrong. I don't believe most students study for longs hours, expect before examinations, I don't believe they drink more than school drop-outs, nor that they eat less healthy (why would they, if they are on average wealthier). On the top of that, they smoke less, and are more probable of getting a white collar job. Check [| CDC: Higher Income and Education Levels Linked to Better Health ]. Going to college might not be the be all end all, but going to college definitely is related to a life expectancy of 8-9 additional year. The obvious caveat that correlation does not imply causation, that it might be a common cause elsewhere, blahblahblah, apply, but yes, going to college is good for you. OsmanRF34 (talk) 17:34, 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)

Good sir, this article may be of interest to you, as it details some of the development spearheading research into fusion. Our own fusion power article supplies a lot more of the technical details and the history of research and development, but is not written in the most accessible manner to get at the root of your question. In the broadest possible terms, the issue which prevents fusion from being a viable technology is that, using existing technology, techniques, and materials, we are as yet unable to produce more energy from the process than is put into it. Starting a fusion reaction requires immense amounts of energy and we do not yet have the means to start and maintain such a reaction in a process that allows us to recapture a net balance of energy. Even once this hurdle is overcome, it will be another matter entirely to accomplish the same feat at industrial scale. However, as the first article details, significant funding and resources are still being put into this area of research, so the next couple of decades may bear out to major developments. Snow talk 05:22, 17 May 2014 (UTC)

Someone said "Fusion power is always 50 years away." Bubba73 ^{You talkin' to me?} 05:30, 17 May 2014 (UTC)

Or as I remember the saying, "Nuclear fusion is the energy source of the future... and it always will be." 24.5.122.13 (talk) 06:32, 17 May 2014 (UTC)

Yup, but indeed that's why I stressed the point; the scale of investment has followed a steady ramping up, and for the first time procedures are near or beyond the break-even point, on a small enough scale. That's not nothing. Snow talk 08:20, 17 May 2014 (UTC)

The OP can be assured that all the energy we use came originally from the local fusion generator 84.209.89.214 (talk) 12:58, 17 May 2014 (UTC)

What about energy from fission reactors? Bubba73 ^{You talkin' to me?} 17:13, 17 May 2014 (UTC)

Well, that originally came from remote fusion generators. 24.5.122.13 (talk) 20:07, 17 May 2014 (UTC)

But that's not our local fusion generator. :-) Bubba73 ^{You talkin' to me?} 21:15, 17 May 2014 (UTC)

Then there's tidal energy, and the portion of geothermal energy caused by tidal heating. Since the tides are caused by stealing a bit of the Earth and Moon's orbital energy, and that in turn is caused by massive objects being blown away from each other, we could say that ultimately those energy sources derive from the Big Bang and dark energy. StuRat (talk) 23:24, 17 May 2014 (UTC)

I think we will eventually get there, but I don't know if it will be in my lifetime. Bubba73 ^{You talkin' to me?} 17:12, 17 May 2014 (UTC)

It's pretty clear that fusion power is a feasible thing - it will eventually work and become amazingly important. There are test reactors that already run and produce small amounts of energy - but not enough to be useful - and not enough to cover the amount of energy it takes to run them. The limitation isn't the energy that's available in fusion reactions (the Sun, the starts and hydrogen bombs amply demonstrate that there is plenty!) - it's that containing and harvesting that energy so it doesn't melt the reactor is kinda tricky. One hope for getting fusion working economically is to use Helium-3 as a fuel - but the snag is that the most likely source for the stuff is on the moon - which presents significant problems of it's own! The science is well-understood here - the problems are not so much of a scientific nature as in the raw engineering and control techniques. But, as has been pointed out, progress has been horribly slow - and every ten years there is a new pronouncement about when it'll be ready to use - which always seems to have slipped another ten years into the future.

Humanity can't wait for fusion to come along before we switch away from fossil fuels - and that's a problem. If it's not the immediate solution, then governments and industry can't pump enough money into R&D to solve the problems - so we slip the schedule another ten years every ten years. Those slippages cause disillusion with the entire process - which further dampens down enthusiasm for funding the research. What's needed is a massive, concerted push, but it's not happening.

My hope is that the expanding field of commercial spaceflight will result in more interest in robotic helium-3 mining on the moon. The dollar value of helium-3 would easily support the cost of doing it, but it's going to need a commercial company to do the work, and they are still a little short of the technology it would require. A company with the right tech, funded by a handful of the billionaire tech geeks out there (who well understand the potential gains), could make this happen.

SteveBaker (talk) 13:21, 17 May 2014 (UTC)

I would love to see nuclear fusion as a primary energy source. We know that fusion can release massive quantities of energy, because humans have built hydrogen bombs and astrophysicists have thoroughly described the inner workings of our sun. We know that there are massive quantities of energy to be harnessed! But as an engineering problem, extracting that energy from nuclear fusion - for civil power use - in a safe way - is intractable today, and will probably remain so for the next several decades.

You can scour the web pages of reliable sources like the United States Department of Energy's Office of Nuclear Energy. You can read the Annual Report for the International Nuclear Energy Research Initiative, sponsored by the DOE. If anyone anywhere was making active progress towards harnessing energy from nuclear fusion, there'd be some mention of that work in these types of report. ...But there isn't. Experts who have studied the problem already know that with the technology we have today, we aren't making forward progress towards using nuclear fusion as a safe and reliable energy source.

Decades from now, when new science and technology are known, the story might be different.

On the other hand, there is a job opening for Director for the Office of Inertial Confinement Fusion at the National Nuclear Security Administration... fusion research is alive and kicking for "certain specific applications." Nimur (talk) 18:46, 17 May 2014 (UTC)

I asked something similar at https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2014_January_5#Can_fusion_ever_be_a_real.2C_competitive_power_source.3F Wnt (talk) 19:29, 17 May 2014 (UTC)

Did a kreagenny sleep been real

Did a kreagenny sleep been real if a man been update by genо-modification?--Alex Sazonov (talk) 09:44, 17 May 2014 (UTC)

Can you explain what a kreagenny sleep is? I can find no reference to it, but I do rather like the idea of genetic modification as a kind of "update" ;) ... so maybe there's a patch for my baldness gene that I've been stuck with since Humans '98. Note that mean this nicely - it's a great metaphor. IBE (talk) 11:41, 17 May 2014 (UTC)

Be careful with that kind of update – before you know it, you come acrossone of the irreversible updates, like Girlfriend 3.11 to Wife 95. And don't get me started about the child processes which keep eating up all my resources. - ¡Ouch! (^{hurt me} / _{more pain}) 06:21, 19 May 2014 (UTC)

Probably the OP means cryogenic sleep i.e. Cryonics although I suspect they knew that. Nil Einne (talk) 12:11, 17 May 2014 (UTC)

Assuming that's what he meant:

1) We have been able to freeze and revive small animals, but not humans, as larger organisms have the problem that they freeze too slowly, resulting in ice crystal formation that damages the cells.

2) You couldn't genetically modify an organism while frozen, as that requires gaining access to the cells by a virus carrying the new genes, etc. StuRat (talk) 12:54, 17 May 2014 (UTC)

Now for the distant future: If you've seen transporters, as in Star Trek and SG-1, they would have to work by scanning the body, destroying it, and reassembling it molecule by molecule at the other end. Such a technology would also allow you to genetically modify the copy, and you could keep the original version, as is, too, if you wanted. StuRat (talk) 12:54, 17 May 2014 (UTC)

The supposedly survivable cryosleep state promises to be an ideal staging of a patient for surgical procedures including complex Neurosurgery and Reconstructive surgery because it eliminates the usual constraints of Anesthesia, hemorrhaging or Surgical stress and allows unlimited time for analysing samples, consulting other specialists and for obtaining or cultivating replacement organs. 84.209.89.214 (talk) 13:20, 17 May 2014 (UTC)

We seem to lack an article on cryosleep. Is that just where they lower the body temperature, but not below freezing, so they can do longer surgery, etc., without causing brain damage due to lack of oxygen ? StuRat (talk) 15:44, 17 May 2014 (UTC)

Thanks more for all! Did Yours think that a geno-modification is been a private case to solve the problem of Cryonica?--Alex Sazonov (talk) 14:16, 17 May 2014 (UTC)

Oh Yes! Richard Avery (talk) 07:13, 18 May 2014 (UTC)

Is "swimming is far more efficient than walking" like StuRat says above?

I wonder how is this supposed to work, the lower density of air should make walking more efficient. OsmanRF34 (talk) 17:51, 17 May 2014 (UTC)

What is efficient? Are we talking amount of energy "spent" per unit traveled? Humans evolved with bipedal locomotion as their primary means of conveyance, so it is unlikely that our bodies are more efficient at swimming than walking/running. I mentally compare how far, and for how long I could walk/run or swim before exhaustion, and surely swimming is less efficient. Swimming does however put less stress on the joints because water supports the weight of the body more than being outside of water. Sometimes physiotherapy is done in water for this reason. 92.40.92.10 (talk) 19:15, 17 May 2014 (UTC)

It's certainly an awful lot slower. The world record for swimming 100 metres is 46.91 seconds, but on foot it's 9.58 seconds. If you've ever tried swim as fast as somebody strolling along the side of the pool, you'll know who was most out of breath at the far end. Alansplodge (talk) 19:29, 17 May 2014 (UTC)

A sphere attached to a cable, would need more energy to go forward in water or on a surface? I wonder what StuRat meant. I hope he comes along to explain it. OsmanRF34 (talk) 20:07, 17 May 2014 (UTC)

The main sense I'd think of swimming as "more efficient" is that if you design a quality machine to move across smooth level ground, it should be able to do so using an almost arbitrarily small amount of energy, hindered only by air resistance; but natural walking consumes some significant amount of power in muscle contractions that you'd think could be designed out of the system. By comparison, if you try to automate the process of swimming, no matter what kind of boat and screw you come up with, it's still going to take a certain amount of energy to part the water. That said, nonetheless, the resistance of water really isn't all that much compared to most practical means of land transport; you really have to be to the point of building maglev rails before the hypothetical benefit of escaping water resistance becomes real. Of course in theory, when there is no change in potential energy from elevation, all travel is infinitely inefficient; it is not reversible in any such case and the energy is always lost. Wnt (talk) 21:01, 17 May 2014 (UTC)

I mean an animal evolved for the water moves using less oxygen per unit of distance than one designed for land. This is because the up and down motion of legs is wasteful. Specifically, the energy used to raise a leg is not recouped when you lower the leg back down. Wheels are a lot more efficient on level ground, but unfortunately they didn't evolve for land animals (or for marine animals, either, for that matter). StuRat (talk) 21:19, 17 May 2014 (UTC)

(citation needed) SemanticMantis (talk) 22:02, 17 May 2014 (UTC)

if you want to get from Dover to Calais, then swimming is far more efficient than walking {{no citation neeed}} DuncanHill (talk) 23:06, 17 May 2014 (UTC)

Also, most land is not level, so climbing over hills needs to be figured into the equation. Once again, we don't get back the energy used to climb the hill, when we descend. StuRat (talk) 23:10, 17 May 2014 (UTC)

You don't get back the energy used to overcome drag, whether moving through air or water. The drag is a hell of a lot greater moving through water though... AndyTheGrump (talk) 23:14, 17 May 2014 (UTC)

That all depends on your speed and how aerodynamic/hydrodynamic your shape is. For whales moving slowly, there's very little drag. StuRat (talk) 00:26, 18 May 2014 (UTC)

Citation needed... AndyTheGrump (talk) 00:29, 18 May 2014 (UTC)

On what exactly ? That aerodynamic/hydrodynamic shapes create less drag ? That whales have a hydrodynamic shape ? That drag is less for slower moving objects ? StuRat (talk) 00:57, 18 May 2014 (UTC)

• What's all this beating around the bush? The statement is totally wrong. Swimming is far less efficient than walking or running, because it requires displacing water. The most efficient way to swim is on the surface, with as little of the body underwater as possible. Looie496 (talk) 14:03, 18 May 2014 (UTC)

• If that was the case, why are whales able to hold their breaths for long periods of time during dives, so apparently using it a low rate, while land animals, like elephants, can not ? StuRat (talk) 16:01, 18 May 2014 (UTC)

• I wouldn't be so sure about that claim Looie. Our Backstroke article says "Due to increased resistance at the surface, experienced swimmers usually swim faster underwater than at the surface. Therefore, most experienced swimmers in backstroke competitions stay under water up to the limit set by FINA (15 meters after the start and after every turn)."

You can test some of this by going to the beach, getting knee deep in water, then trying to walk or run. Also, compare speeds of man-made sea surface and submarine vehicles vs. airborne and land vehicles. Viscosity is a b*tch. 88.112.50.121 (talk) 19:36, 18 May 2014 (UTC)

Looie496, displacement of water during locomotion, in itself, does not cost energy, and most certainly is not an argument w.r.t. efficiency, unlike arguments using dynamic and static drag, for example. StuRat, the claim of energy not being recouped is similarly not a valid argument; in walking there are several mechanisms that can move energy around between parts of the body, including conversion between kinetic, gravitation and elastic potential energy, also from one part of a limb to another (e.g. via coupled bands of muscle and connective tissue and momentum transfer). The kangaroo is a prime example that uses up and down motion to improve efficiency of locomotion. Yet, nothing has been said here that effectively counters your claim by showing that that swimming is necessarily less energy-efficient than overland locomotion. —Quondum 21:51, 18 May 2014 (UTC)

Changing energy between different types is also inefficient, resulting in much of it ending up as heat. Ever notice how hot you get from running ? That's wasted energy. StuRat (talk)

Is this a reference desk, or a forum?

I ask, because as yet there hasn't been a single source cited for anything. And without sources, the only answer we should be giving the original question is "we don't know." AndyTheGrump (talk) 16:55, 18 May 2014 (UTC)

I'd say that User:Alansplodge nailed it in the second post - with references. The difficulty here is that the original claim uses the word "efficiency" rather than speed - which opens things up quite a bit. If you just float in the water and let the wind/tides carry you, then you'll obviously use less energy than walking. On the other hand when you look at how few people have managed to swim the English Channel - it's clear that relatively few people can do it - and it's hard. On the other hand, most people who are even moderately fit can walk that distance, and many Marathon runners have run it in times under three hours. So what exactly is meant by "efficiency" here? SteveBaker (talk) 17:06, 18 May 2014 (UTC)

A bit grumpy there Andy! Both Alansplodge and I linked to other Wikipedia articles with relevant facts. Presumably they are well sourced. HiLo48 (talk) 21:03, 18 May 2014 (UTC)

I agree with AndyTheGrump that this thread is not actually treating the reference desk as it is ostensibly intended. Simply throwing in a few links does not make up for unreferenced speculations when they do not substantiate said speculation. —Quondum 21:51, 18 May 2014 (UTC)

Not our best day. The fact is it's a poorly phrased question based off of a poorly phrased claim. Of course whales are more efficient at swimming, and kangaroos are more efficient at hopping. If OP is interested in some specific science, he should try over with a more specific claim and scenario, and recall that Stu often just says whatever makes sense to him at the moment. SemanticMantis (talk) 00:15, 19 May 2014 (UTC)

Here's a source (my PC won't display it past the first page, but it seems relevant): [4]. Seasonal migration distances should be a good indicator of efficiency. Humpback whale#Range and habitat says they migrate 16,000 miles (25,000 km), while land animals generally migrate over much smaller distances, if at all. Some of this is due to blockages created by man on land, but even before man, I don't believe seasonal land migrations were on the same order. StuRat (talk) 16:07, 19 May 2014 (UTC)

The problem is still a matter of the definition of "efficiency" - if it's total energy expenditure to get from A to B then everything depends on the speed at which you need to get there. The drag caused by water dominates the cost of swimming - the energy expenditure is proportional to the CUBE of the speed! For walking or running, the air resistance is much, much less significant and the energy is mostly consumed in the bouncing stride (which is why wheels are such good idea) - the energy cost in running versus walking over some specific distance is fairly similar. Walking 25 miles versus running it in a third of the time in a marathon are both pretty exhausting - but you don't need 27 times as much food that day if you were running rather than walking. Calorie charts for human exercise suggest that the energy cost is almost exactly proportional to your speed...so calories per distance on land is pretty much a constant no matter how fast you go. So, we know that at high speeds, swimming is disasterously energy-draining compared to walking/running. But at very slow speeds, the bouyancy of the water means that you're not lifting your entire body mass up and down with every stride - so swimming wins.

Without a precise definition for "efficiency" - we can't say what the answer is. If "efficiency" is expressed in energy-per-distance-travelled, then maybe swimming very slowly wins - but if it's energy-divided-by-speed, then it's not likely that swimming will ever win. For animals, there are other "costs"...being set up with a body plan for efficient swimming really screws up your ability to climb trees - so an efficient organism might be more like a human where the body design permits slow swimming and faster running as a trade for being more flexible over the kinds of terrain you can cover.

That's why this thread has gone off the rails. We're arguing about the meaning of the terms of the question - because it's vague.

According to the article Locomotion: Energy Cost of Swimming, Flying, and Running Knut Schmidt-Nielsenish that StuRat provided above, fish generally expend less energy swimming than we do walking, and we are more efficient at walking than swimming. --Modocc (talk) 21:59, 19 May 2014 (UTC)

Is sweating (in mammals) secretion or excretion?

The wikipedia articles seem to suggest that the skin carries out excretion, however neither secretion or excretion article specifically states what sweating is. While sweat has left the body, some sources on internet saying that sweat serves to cool body temperature, and therefore sweat is not purely waste and has useful function. Therefore things like feces and urine are waste with no function and therefore are excretions, but sweat is secretion. Much obliged if anyone can sort this. 92.40.92.10 (talk) 18:54, 17 May 2014 (UTC)

The article on sebum says that in hot weather it serves to prevent loss of drops of sweat from the skin. Sebum is undoubtedly a secretion. It seems peculiar to think of sweat as an excretion when it is done only for specific reasons, and when water is scarce is done even at substantial risk to the organism because of its benefits. Wnt (talk) 20:51, 17 May 2014 (UTC)

One could also argue that urine serves a secondary function of cooling or warming the body. When hot, you are likely to drink cold liquids. When cold, you are likely to drink hot liquids. Either inevitably results in urinated warm liquid. It's the temperature difference between the input and output liquid which changes your body temperature. We normally only think about the input side, but the output is equally important to the equation. StuRat (talk) 21:24, 17 May 2014 (UTC)

OK agree. Also just saw that the article sudoriferous gland states that sweat is a secretion. TY. 92.40.92.10 (talk) 22:05, 17 May 2014 (UTC)

@StuRat, I can't agree with your assertion that "It's the temperature difference between the input and output liquid which changes your body temperature", The most significant control of body temperature under normal circumstances is sweating and the subsequent lowering of skin temperature by the evaporation of said sweat. Here in the UK, and elsewhere, people in winter do not heat their beer to keep warm, neither do the vast majority of people drink cold tea or coffee in the summer to keep cool. Some people do these things but not usually for temperature control purposes. (Yes, I have seen the word 'likely' as a cop out) And how the heck does the excretion of urine warm the body? Do you let it run down your leg? Don't do that! it will lose you friends and evaporate, further cooling you. Richard Avery (talk) 07:07, 18 May 2014 (UTC)

If you drink hot fluids and urinate them back out as warm liquid, then the temperature difference between the two warms your body. I was only talking about urine. In the case of sweat, it is designed to lower body temperature by evaporative cooling, which would greatly outpace the cooling process for urine, unless it's a humid day. If you meant to point out that in summer, cool drinks come out both as urine and sweat, that's true, but both come out warm, so the cooling effect is still there, it's just less than the cooling effect of sweat evaporation. And drinking fluids that are not at the ideal temperature for the season certainly happens, yes. Provided that you have sufficient temperature controls by other methods, you need not use this method, too. StuRat (talk) 15:57, 18 May 2014 (UTC)

Why must it be "or?" --Jayron32 23:02, 18 May 2014 (UTC)

May 18

Incandescent light bulb color

The last paragraph of the intro of Incandescent light bulb says "their light color which is almost identical to the sun's spectrum". To me, a traditional soft-white incandescent bulb is distinctly yellow/orange. So what color is an incandescent soft white bulb, and how close to sunlight is it? Bubba73 ^{You talkin' to me?} 01:42, 18 May 2014 (UTC)

That's a misleading statement. See color temperature. The lower the wattage, the cooler the filament will be and the redder the light will be. The higher the wattage, the hotter the filament, and the whiter the light will be (if it was hot enough it would actually turn blue, but I don't think a filament that hot would last long enough to be practical). StuRat (talk) 01:55, 18 May 2014 (UTC)

There is a tendency for manufacturers to make lower wattage bulbs run at a lower temperature, but this is just manufacturing convenience, possibly avoiding very thin filaments. There is no logical connection between rated wattage and filament temperature. The filament will be hotter if it is run at greater than the rated wattage by applying a higher voltage. (Not recommended because it reduces the life of the filament.) Dbfirs 12:36, 19 May 2014 (UTC)

Yes, perhaps I should have added "given the same filament". Of course, a thicker filament would waste expensive tungsten (not sure if that's a significant part of the total incandescent bulb price, though) and a thinner filament would burn out too quickly, as you noted. StuRat (talk) 15:32, 19 May 2014 (UTC)

I think it's not so much about the cost of the tungsten as it is about the balance between bulb life and color temperature. A thinner filament gives whiter light and higher energy efficiency, but burns out quicker. A thicker one lasts a long time, but is redder and less efficient. --Srleffler (talk) 03:20, 20 May 2014 (UTC)

I agree the statement is problematic, I've tried to reword it to more closely follow the source but I think the problem is it's trying to summarise different ideas. The actual article more accurately describes the situation. Incandescents eare close to an idealised black body radiators, but their colour temperature is far lower than the sun. They also don't filter through the atmosphere. They therefore have a fairly continous spectrum and a near perfect color rendering index but their spectrum doesn't match the sensitivity characteristics of human vision and they appear far redder than daylight. Many people seem to prefer these redder than daylight colours, particularly for home lighting, and there's some suggestion of psychological reasons for such a preference for dim light sources (like most home lighting) but either way the preference doesn't seem to be universal. LEDs and fluourescents, even ones with a fairly high CRI still have a somewhat discontionous spectrum, although there's some controversy over how well the CRI matches subjective color rendering anyway. Nil Einne (talk) 08:25, 18 May 2014 (UTC)

My wife also prefers the soft white (yellow/orange) color, but not me. I think that is probably because that is what we all grew up on, for the most part. But to me it makes the colors of things unnatural and it is much harder for me to read my soft white than it is bright white or daylight colored lights. Bubba73 ^{You talkin' to me?} 18:24, 18 May 2014 (UTC)

People certainly look better in soft white. Under harsh fluorescent blues, people look pale and veins tend to stick out. StuRat (talk) 15:35, 19 May 2014 (UTC)

I removed the statement. The claim that the spectrum is "almost identical" to the sun's is simply false, and is not what the source said.--Srleffler (talk) 03:30, 20 May 2014 (UTC)

How long would the TGV take to stop?

Hi, I'm asking this question because I'm curious about using it as a hypothetical to get students talking. How long would a train at top speed take to come to a stop on the Beijing–Shanghai High-Speed Railway, if the brakes failed, and it just rolled to a stop? How long for this one? P.S. I'm editing on a quick break, so if this question is actually answered in the articles, please just abuse the c**p out of me, and we'll all feel a lot better, right? P.P.S. Is it "in" a quick break or "on" a quick break? IBE (talk) 09:51, 18 May 2014 (UTC)

I don't think we can accurately answer using first-principles of physics. But we can inaccurately answer: you can estimate the coefficient of friction by observing:

• at maximum speed, all engine power is expended to overcome frictional losses
• P = F v
• The engine power, speed, and mass for each train can be read out of our article
• Assume that full engine power is used at maximum speed. Assume that frictional losses are identical at all speeds. These are flakey assumptions, but if you understand their limitations, you'll see exactly why the problem can only really be answered using empirical data.

With the above assumptions and about two lines of algebra, the braking distance can be solved using Newtonian kinematics. Nimur (talk) 13:36, 18 May 2014 (UTC)

(EC) Three points. One, I'm pretty sure most high speed, trains, heck most trains have multiple independent braking systems (which are frequently designed to be as fail safe as possible) making complete brake failure (meaning with absolutely nothing in the train trying to slow it down, even if it isn't enough to stop it completely under whatever conditions) difficult. See e.g. [5] [6] [7] SNCF TGV Duplex or even Railway brake#Accidents with brakes.

Two; the time taken will surely depend significantly on the conditions. For example if the train is going a slight incline going upwards it will obviously slow faster than if it's completely level which will likewise take longer than if it's going downhill. (If it's going downhill potentially it may never stop until it either derails or reaches the end of the incline. Of course if it's going uphill it may eventually start going in the other direction, but let's not worry about that.) Similarly a train going at 200 km/h is going to stop fasrer than one going at 300 km/h everything else being equal. I suspect at that level even things like if it's going in to a headwind or tail wind may make a noticable differences. Similarly while high speed trains have gentle curves (as with their inclines) I suspect turning a curve will slow the train more than if it's travelling completely straight.

Three; I'm fairly sure any maglev system will be even more complicated. In many systems I'm fairly sure braking will at least partially come from the propulsion system, but loss of propulsion will often likewise mean a loss of levitation. They are of course designed to fail safe (and some designs may maintain levitation under low speeds) so I guess may have wheels or whatever and so should keep going if this happens (and I guess may have some sort of emergency brakes for when this happens), but it's clearly far from a simple case of 'complete brake failure'.

Nil Einne (talk) 14:09, 18 May 2014 (UTC)

And the fourth point: At high speeds (80 mph or above), air resistance becomes a significant part of the "frictional losses", and that force varies directly with the square of the velocity -- so the assumption that frictional losses are identical at all speeds is completely inaccurate. I've taken the liberty of deleting the first two paragraphs of Nil Einne's response, because they duplicate the following two paragraphs word-for-word. 24.5.122.13 (talk) 00:05, 19 May 2014 (UTC)

(Aside: I was going to joke with Nil, yes, I thought you tended to repeat yourself a bit ;) but I was worried it might come out wrong. I was also assuming someone (probably Nil) would take care of it.) Yes, I do remember reading that about friction - at high speeds it is the dominant factor; at low speeds, rolling friction predominates. Interested people can read about it in Energy - a Guidebook by Janet Ramage [8]. I think rolling friction is proportional to the velocity. However, the square of the velocity (for the wind drag) arises because the vehicle has to get the whole column of air moving - the more streamlined the vehicle, the less the wind matters, as it can just slip through the air. Also, for a long vehicle, the head-on air column matters less proportionally. There will be wind drag along the sides of the train, but that again would only be in simple proportion to the velocity. IBE (talk) 00:40, 19 May 2014 (UTC)

Extra comment: no, I was just reading about friction, and it seems it is constant, and has nothing to do with velocity. IBE (talk) 01:00, 19 May 2014 (UTC)

Propagation of extremely high frequency sound in air

I'm involved in an off-wiki argument with a friend about the "detectability" of sound in air at 11.5GHz. I argue that the attenuation is so rapid that the sound is practically undetectable over a distance of several metres - unless the power level is ridiculously high - enough to obliterate the stones! My friend maintains that such sounds are found in "stone circles" - yes there are other pseudoscience issues that I'm dealing with but for this one I need some help with specific facts and figures. Roger (Dodger67) (talk) 12:13, 18 May 2014 (UTC)

Let me see if I understand this correctly - you're asking if acoustic pressure waves - i.e., longitudinal compression waves - in air - on Earth, with normal atmospheric conditions - carry energy in the gigahertz range?

No. Vibrations at those frequencies are uncommon in air. Even if we include vibrational modes that are uncommonly described as "acoustic waves", we still don't find energy at 11.5 GHz. For example, atmospheric oxygen has molecular vibrations - the diatomic molecule "spring" stretches and wobbles - in the infrared range. We would consider those vibrations as part of the optical spectrum - still not at 11.5 GHz. And, no microphone in the world exists that could detect such motion as a "sound." And these vibrations do not propagate energy between molecules, through the bulk of the air, in the form of a pressure-wave, so these vibrations are very much not sound-waves.

When we consider Earth atmosphere temperatures and densities, we find that the attenuation won't just take place over several meters - it'll take place within less than one wavelength. The wave will attenuate to "negligible strength" within a distance that we can measure in units of inter-molecular distance: i.e., a few microns. (Millionths of a meter!) The energy doesn't propagate.

Let me see if I can dig up a proper but simplified equation to describe attentuation of acoustic waves as a function of frequency. My first instinct is to pull out Bittencourt, Fundamentals of Plasma Physics, which generalizes the wave equation for a fluid to incorporate electromagnetic forces - because without a superheated ionized plasma - the sort of soup-y mess of dense hydrogen you'd find inside the Sun - there's essentially no way to convey acoustic energy at those frequencies. Even plasmas in laboratories or in near-Earth space resonate at much lower frequencies. Even plasmas near Jupiter resonate at lower frequencies.

At reasonable normal atmospheric temperature and pressure, and atmospheric gases, if a compression wave existed at 11.5 GHz, individual atoms would be moving so fast that the electrons would separate from the nuclei. The wave would devolve into a superposition of many oscillations - the atomic nuclei, and the electrons that cannot move coherently at this frequency. (To do so would imply that the atomic nucleus and the electrons have different temperatures). This would cause a separation of charge and would induce an electromagnetic wave. The wave will disperse. We can write an equation to give you the scale length for that dispersion relation, but it appears to require nine pages in my textbook. Bittencourt writes the spatial frequency (wave number) for a longitudinal wave in terms of electron plasma frequency, which is a long equation and would take some time to define.

Long story made short: your friend is either pursuing counterfactual science, or they've mixed up their S.I. prefixes. Acoustic waves do not propagate in the gigahertz range, not at any condition we find anywhere in our solar system outside of the interior of the sun. Nimur (talk) 12:50, 18 May 2014 (UTC)

Not disagreeing with any of that, but perhaps a simpler way of putting it is that the gigahertz range is where microwaves live, and if something did vibrate at that frequency, it would generate microwaves, which could easily be detected. Looie496 (talk) 13:55, 18 May 2014 (UTC)

Thanks Nimur & Looie496. This is exactly what I need. I'm far more familiar with calculations involving electromagnetic energy - I'll do a path loss calculation for a radar without breaking a sweat, but mechanical vibration waves are not my thing at all. I gather that for sound the attenuation v. frequency graph (in air at STP) crosses the fuhgeddaboudit! line well below 11.5GHz. As a radio frequency 11.5GHz is in a band widely used for satellite communication and radars - it's just a bit below the Ku band that most people would come across as it is commonly used for satellite tv transmission. The irony of the whole situation is that both myself and my "opponent" are radio hams! BTW the source of the argument is this video. Watch it at your own risk, I will not accept any responsibility if someone following the link does themself a serious injury due to uncontrollable laughter. Roger (Dodger67) (talk) 14:12, 18 May 2014 (UTC)

I agree with everything said above - but I would just mention that in Ultrasound#Imaging it mentions that: "The potential for ultrasonic imaging of objects, with a 3 GHZ sound wave producing resolution comparable to an optical image, was recognized by Sokolov in 1939 but techniques of the time produced relatively low-contrast images with poor sensitivity." - which suggests that GigaHertz-range audio is possible, although perhaps not through air. Our ultrasound article also says that ultrasound reaches up to "several gigahertz".

The obvious way to debunk your friends' argument is to follow the trail of knowledge back to the source. Where did he find out about this? Go there and figure out how the person who told him knew about it...and so forth. One will inevitably find that either the trail goes cold because some idiot just made this up - or a mistake was made and MHz got turned into GHz somewhere - or that you find how this "fact" was ascertained in some kind of experiment or other. My bet it that it's the first of those things. This is obviously complete B.S. pseudoscience. Very likely someone thought about the reputed "energy" found by people in and around stone circles - and when they thought about how it might be transmitted without anyone being able to measure it, they guessed "ultrasound" and made up a plausible-sounding frequency without thinking about whether it's possible or not.

here, for example is one such site - it mentions stones that it's claimed produce ultrasound - and also block ultrasound (weird!) - and it references a book "Circles of Silence" by Don Robins (Souvenir Press, London, 1985). From what little I could find about it in Google Books, it does make mention of ultrasound - but I couldn't find "GHz" or "gigahertz" in a search of the book. Don Robins also wrote "The Secret Language of Stone: A New Theory Linking Stones and Crystals With Psychic Phenomena" and has made claims that ultrasound is the cause of crop circles. (<sigh> - this isn't looking good is it?!).

Anyway, those claims for stone circles come from something called "The Dragon Project". Digging into that a bit turned up "The Dragon Project and the talking stones." an article in the "New Scientist" journal(!) - which has graphs and stuff in it! Now we might be on to something! That article says that these ultrasonic waves were detected using a bat detector...well, our bat detector article says that these work in the 15 kHz to 125 kHz range. So right there - we're not talking Gigahertz - or even Megahertz - we're in the range only just above human hearing...and far from being hard to detect, a $85 (Amazon.com) detector (or this $26 kit) is sufficient to pick them up.

Now, those graphs of the ultrasonic energy of the stone circles says that the energy is highest in March and November...and I'd bet that March is breeding season for bats. They talk about building a whole series of increasingly sophisticated ultrasound detectors - but there are no details about what frequency range they detected or what intensity levels. The article is full of self-contradictions (eg he says that February is one of the high points of ultrasound levels - when his graph says March).

So I'd have to say, that this was a fairly amateur effort and the results are not accurately reported. There is certainly no evidence that I could find for frequencies up into the Megahertz range - let alone gigahertz...and far from being hard to detect, you can pick them up with a sub-$100 piece of equipment.

SteveBaker (talk) 15:32, 18 May 2014 (UTC)

Hi SteveBaker - The "trail of knowledge" starts with this video - I also linked it in my post just above yours - see my "disclaimer" above. Roger (Dodger67) (talk) 15:43, 18 May 2014 (UTC)

Yes, the guy who posted that is Michael Tellinger - who is a politician, song writer and trained as a pharmacist. I wouldn't put much store by his science credentials, and from all I can find, he's basically just repeating the claims of Zecharia Sitchin. That guy is into the whole "aliens came to earth and played god" thing...and our article about him says "Sitchin's ideas have been rejected by scientists and academics, who dismiss his work as pseudoscience and pseudohistory. His work has been criticized for flawed methodology and mistranslations of ancient texts as well as for incorrect astronomical and scientific claims.". So that just about wraps it up for that trail of evidence! At least the Dragon Project made an effort to some up with something. SteveBaker (talk) 16:59, 18 May 2014 (UTC)

Just a quick comment: any physicist could recognize that a 3 GHz sound-wave would permit acoustic images with high resolution. In the same way, I can recognize that a glass lens whose refractive index were an imaginary number would allow me to build an infinitely-thin camera. But I still can't make one! That's the difference between theoretical physics - in which we crunch the equations just to see what should happen - and experimental physics, where we see what actually happens, then write a better equation to describe it! Nimur (talk) 18:33, 18 May 2014 (UTC)

• There are some great arguments here for why gigahertz frequency sound is impossible. The only nagging problem I have is that our article on ultrasound pointed me to acoustic microscopy, which uses gigahertz frequencies routinely. There are lots of articles that come up in a search for "acoustic microscopy" and "gigahertz"; unfortunately, sampling these, it looks like this is one of those fields you're not allowed to know much about unless you pay or your owner did. Wnt (talk) 15:51, 18 May 2014 (UTC)

There is no air involved in acoustic microscopy - it's all about solids and liquids. See Acoustic microscopy#Sample types and preparation. The highest frequency mentioned in that article is 400MHz - a very long way from 11.5GHz! Also take a look at Medical ultrasonography where "microscopy" is discussed as an experimental technique to examine structures in the eye - the highest frequency mentioned there is 100MHz. The medical article also briefly discusses attenuation in (mostly liquid) human tissues. Roger (Dodger67) (talk) 16:21, 18 May 2014 (UTC)

I invite you to run the search - many snippets mention 1 GHz or 3 GHz. I don't deny that ultrasound attenuates rapidly in air, but the argument about the frequency turning into microwaves should apply in water too, shouldn't it? Actually, this reminds me of an old question that never got an answer about whether materials where slow light travels at the speed of sound are able to convert sound to light or vice versa. It'd be interesting to hear more. Wnt (talk) 19:38, 18 May 2014 (UTC)

I think the suggestion that they would turn to microwaves is simply fishing something out of the air. Given the massively different propagation velocities, even if there was a radiative mechanism (e.g. relative displacement of nuclear orbital charge), it would not be self-reinforcing. This speculation simply does not belong here. —Quondum 20:56, 18 May 2014 (UTC)

Why do not

Why do not womens breasts shrink back after finishing baby feeding?--86.160.193.27 (talk) 12:17, 18 May 2014 (UTC)

Who says they don't? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:34, 18 May 2014 (UTC)

Breast#Hormonal_change covers this pretty well. SteveBaker (talk) 14:26, 18 May 2014 (UTC)

Also, they aren't filled with milk the way a water balloon is filled with water. It not just a bag to hold the milk, it's still fat, tissue and all the other stuff. Mingmingla (talk) 17:32, 18 May 2014 (UTC)

Sunset time and darkness

How long does it take to get completely dark in London after sunset in May? Can you provide reliable evidence for this? 82.40.46.182 (talk) 13:46, 18 May 2014 (UTC)

See Twilight#Duration - Roger (Dodger67) (talk) 14:41, 18 May 2014 (UTC)

Since it's a big city with lots of artificial lighting, it never gets "completely" dark in London. Our article Dusk discusses the various definitions of twilight and sunset. Basically, the definition depends on whether you're talking about "civil", "nautical" or "astronomical" twilight - and the definition is in terms of the angle of the sun below the horizon rather than how dark it actually is. This site (amongst many others) documents the sunset time and the time that twilight ends for each definition of twilight. So for London on 18th May 2014, the sun officially sets at 20:50:28, Civil twilight ends at 21:32:42, Nautical twilight ends at 22:31:21 and Astronomical twilight ends 00:08:09. Which of those you take to be "completely dark" is entirely a subjective matter since it's never going to be particularly dark in or near such a large city - and for any definition based on actual light levels, it's going to depend a lot on the cloud cover, moon phase and whether you are standing in a dark alleyway or on top of a tall building. I suppose the best generic answer is "about 40 minutes" - which is the duration of civil twilight - but in truth, this is one of those "How long is a piece of string" questions. SteveBaker (talk) 14:42, 18 May 2014 (UTC)

The rule of thumb that I use is about an hour. Bubba73 ^{You talkin' to me?} 18:27, 18 May 2014 (UTC)

Observant Jewish people need to know these sorts of things and have precise definitions for them, see Zmanim. The times you're talking about would correspond to Shkiyat Hachama and Tzet HaKochavim. According to chabad.org those times for today, May 19, are 20:50 and 21:42 respectively, so 52 minutes, pretty close to Bubba's hour. --Dweller (talk) 17:15, 19 May 2014 (UTC)

After reading the Zmanim article you linked to, I really wouldn't describe the Jewish reckoning of times pertaining to twilight as involving "precise definitions". The definitions aren't particularly precise given that they involve such vague quantities as the amount of time it takes to walk a mil, the amount of light needed to recognize a person four cubits away, or the amount of light needed to distinguish the blue threads of a tzitzit from the white ones. The Jewish holy books aren't even internally consistent about daylight reckoning, with the Talmud in Pesachim saying there are four mil between sunset and nightfall, and the Talmud in Tractate Shabbat saying there are just three-fourths of a mil between sunset and nightfall. With all that vagueness, it's unsurprising that when exactly nightfall is considered to be depends on which group of rabbis you choose to follow the interpretations of. And even if the Talmud and the rabbis did all agree, it would still just amount to a rather arbitrary set of definitions that only have meaningful significance to the 0.2% of the world's population that follows Judaism. Red Act (talk) 20:36, 19 May 2014 (UTC)

Believe me, by the time the Acharonim finished with the Talmudic definitions, the calculations have become very precise indeed. I appreciate very few people follow these arcane rules, but it seemed a way to answer the question using references, rather than finger-in-the-air speculation, which is, after all, what we're here for. And "52 minutes" is a nice, specific answer, from a proper reference, for the OP. Whatever religion they may or may not follow. --Dweller (talk) 06:56, 20 May 2014 (UTC)

May 19

Games that computers can't play

Computers won't play the games in Brueghel's painting. 84.209.89.214 (talk) 15:02, 19 May 2014 (UTC)

I thought that since this isn't a troubleshooting question, this was a more appropriate forum than the Computing desk.

My question, basically, is are there any games that computers simply cannot play, for whatever reason? Given the right programming, computers can easily play (and win) a game with high complexity, multiple game pieces of varying function, and fine strategy such as chess, and a mathematical puzzle-game like sudoku would probably be orders of magnitude easier for a computer to complete in a fraction of the time. A computer could probably solve a crossword puzzle, given access to information of the sort Watson had when he took down those Jeopardy! champions, though there's obviously very little entertainment value in watching a computer solve a crossword, at least more than once or twice.

What I'm wondering, though, is if there are any games that are simply too complex for a computer to understand and/or put into practice. To come up with a workable definition of "game," I guess it helps to narrow things down. There are certain intellectual pursuits that computers are obviously not capable of (yet?); a computer couldn't compose an essay on Shakespeare, for instance (or at least not one that contains any original ideas), but we wouldn't term that a game. On the other hand, a computer is absolutely capable of analyzing data sets and finding statistical patterns, instances of correlation between different sets, etc. That isn't a game, either, but it is more pertinent to how some board games work. Literary criticism, though, is just a tad more complex, and a bit too abstract.

So I guess we'll impose the requirement of some level of strategy being involved, and a multi-player format, as in chess, checkers, or most card games. Charades has a physical component that makes it hard for a computer to put into practice—though I suppose a particularly language-savvy computer with a large library of pre-recorded gestures might be able to keep up. Drinking games and paintball are similarly outside the reach of computers for physical reasons, but are there games that are beyond computers' capacity for (for lack of a better term) intellectual reasons? Evan ^{(talk|contribs)} 04:25, 19 May 2014 (UTC)

Game complexity may be relevant. Among widely played "chess-like" games, Go has been famously difficult—see Computer Go#Obstacles to high-level performance. -- BenRG (talk) 04:38, 19 May 2014 (UTC)

Despite the plethora of soccer robots, true bipedal soccer robots are still no match for a human. Bipedal robot control usually depends on inverse kinematics, and state-of-the-art algorithms suffer from instability, slow speed (i.e. solutions cannot be computed fast enough), and poor error recovery. These are mathematical problems that present-day computer software can not easily solve, even though there has been a lot of research in this exact topic. To be clear: this isn't a mechanical problem - it's a software problem. The actual moving parts in a bipedal robot are perhaps expensive but they are not very complicated. It is the control algorithms that suffer from numerical instability and computational complexity. A robot with two legs has, in addition to the usual multidimensional kinematics matrix, a branched kinematic chain topology. That means, for example, that the robot doesn't know which foot is on the ground, and which one is in the air. As easy this identification-task is for a human brain, it is a difficult challenge even for a supercomputer. If you can write a software program to answer that question, you've got yourself a solid career as a robotics programmer! Nimur (talk) 05:11, 19 May 2014 (UTC)

There are games that are based on creativity and storytelling, such as role-playing games and perhaps the ultimate, Calvinball. 88.112.50.121 (talk) 10:34, 19 May 2014 (UTC)

Computer game designer Chris Crawford (game designer) distinguished between a competition where a player can only outperform the opponent, but not attack them to interfere with their performance, and a game where attacks are allowed. By this logic a computer can't play a game with you unless it can attack you. 84.209.89.214 (talk) 15:02, 19 May 2014 (UTC)

• Let's be clear that when you ask whether computers could play a certain game, what you are really asking is whether programmers would be able to figure out how to write a computer program that could play the game successfully. There are certain things that people find easy but are very difficult to write programs for. For example the game Who Is This?, in which you show the contestant pictures of famous people doing various things and ask for identification, would be extremely difficult to program on a computer. Another game that would be very difficult to program is Twenty Questions. Looie496 (talk) 15:20, 19 May 2014 (UTC)

This online version of Twenty Questions is actually pretty good with common objects. I got it to "hairdryer" in twenty-two questions. Evan ^{(talk|contribs)} 16:22, 19 May 2014 (UTC)

In Pictionary, I would expect a computer to be very good at drawing pics, as long as it had a pic in memory for the word in question, but very bad at recognizing pics drawn by people. More generally, any game that requires the computer to do visual processing of an image to determine what it's seeing will be problematic. Even Watson didn't do character recognition, but rather they fed it the questions as ASCII code. (I don't imagine it would have been a problem to recognize the consistent, printed text used on Jeopardy, but reading cursive handwriting, etc., would have been more of a challenge.) StuRat (talk) 15:27, 19 May 2014 (UTC)

Of possible interest: mathematical game, solved game. Up until ~2006, no computer was very good at playing angels and devils. But now that some people have done some very difficult math, computers can win easily. So in the field of complex games, it is usually operator/programmer knowledge that limits the computer, not the computer itself. (Sometimes the solution to a game is provably NP-hard, and in a sense, you could say that the restriction is more due to the computer than the operator, insofar as P_versus_NP_problem does not result in P=NP ). SemanticMantis (talk) 15:44, 19 May 2014 (UTC)

Mornington Crescent (game) would make a very good test for a computer - I'd imagine it's the game-playing equivalent of the Turing test. It'd be hard for a computer to join in convincingly, in a way that fulfilled the game's real intent, which is to entertain. --Dweller (talk) 15:50, 19 May 2014 (UTC)

I don't know how I'd judge that a computer had successfully been entertained by playing Mornington Crescent. But I rather think I could write a program to play the game. I think Inform 7 might be well-suited to it - create a map representing the network, so that convincing-sounding justifications and objections can be written on the fly. The new adaptive-text feature could make it refer back to earlier rounds fluidly, too. Allowing it to play with multiple human opponents would be a little more challenging, but not impossible. AlexTiefling (talk) 15:58, 19 May 2014 (UTC)

Sorry, I wasn't clear. The purpose isn't to entertain the computer (let's not go there) but the audience. While the computer could for sure spout random station names, I find it difficult to imagine any kind of programme that would capture the humour behind its pronouncements, including providing new and sufficiently wacky variants of rules, except by means of mixing up a database of old ones, which would fall flat in much the same way (or worse) than an unfunny fan of the game thrown into the programme would do. In short, a computer would be able to play the game alright, but very badly, because, to coin User:Dweller/Dweller's first law of computers: Computers aren't funny. Much. --Dweller (talk) 16:53, 19 May 2014 (UTC)

How German homes are built

I am building a new house and I want it to be made of cinder block, but well insulated. No builders in my area do ICF. I read somewhere that in Germany they make houses out of cinder block, then add Styrofoam insulation to the outside, then cover it with stucco. I would like specific information on how this is done and any problems with it. I am concerned about bugs and ants eating the Styrofoam and also about water or moisture getting behind the Styrofoam and caused mold. ( I am allergic to mold) Is this a problem? Also how is it done, do they put tyvek or a waterproof membrane between the Styrofoam and the cinder block? and how do they attach it to the cinder block? If they have to drill holes does that cause problems with air sealing it? And what thickness Styrofoam do they use?--Interestingusername123 (talk) 05:50, 19 May 2014 (UTC)

I don't know but bear in mind your house will have to be built according to your local building code, which might not have provision for that type of construction.--Shantavira|^{feed me} 07:40, 19 May 2014 (UTC)

Leca Isoblokk is a ready-made sandwich of cinder block and Styrofoam, shown in this video. I found nothing about it in English but you can try asking at your nearest Weber Saint-Gobain plant, found here. 84.209.89.214 (talk) 14:40, 19 May 2014 (UTC)

Note that Styrofoam is both flammable and gives off toxic fumes when it burns, so putting that much of it in a house may make it into a deathtrap. However, given the choice, it might be best on the outside of the cinder blocks, in the hopes that most of the toxic fumes would be released outside the house. A secondary concern is outgassing of toxic fumes as it sits. Since most of this happens when it's new, just letting it sit for a few months before using it in the house should help here. StuRat (talk) 16:32, 19 May 2014 (UTC)

I'd be surprised if German building code didn't ban toxic, highly flammable foam like ordinary styrofoam. After all, we're talking about Germany. ¡Aua! (_Rammstein \ ^Kraftwerk) 07:14, 20 May 2014 (UTC)

I had a house built down here in Texas using ICF (we used "Greenblock") - it comes as a bunch of foam blocks - like lego bricks. Each one has two sheets of foam - held together with two or three pieces of carbon-fibre. They pour a conventional concrete slab, then build the house up out of these bricks - threading rebar down between them. Then they pour concrete down into the gaps between the foam. So the resulting wall is about 1" of foam, 3" concrete and another 1" of foam. Then you put brick or stucco on the outside and sheet-rock and plaster on the inside. It worked amazingly well - the house is incredibly well insulated. If I ever get the chance to have another house built, that's exactly how I'd do it again.

The key here is that there is foam both outside AND inside the concrete. I don't know whether using hollow cinderblock for the core is good or bad. The walls are certainly going to be a lot less physically massive - so their thermal properties will be very different. My house stayed more or less the same temperature through day and night because of the thermal inertia of all of that concrete - plus the two layers of insulation.

Personally, in your situation, I'd use cinderblock - but have them insulate both the inside AND outside of the blocks with an inch or so of fire-resistant foam. (It's not really "stryrofoam" it's denser and not only does it not burn easily, if it does start to melt, it actively suppresses the fire somehow. It's been 15 hears now, so I forget the details.

The tricky part about using two layers of foam is having some way to tie the brickwork (or stucco or whatever) to the inner core - and the Greenblock system solves that with those carbon-fibre pieces that are embedded in the foam. They have tabs inside the foam that you can screw into - which is how the sheet-rock is held up, and how you can hang siding on the outside. There were special metal straps that they used to tie the brickwork to it...I forget how those work. There was also a way to apply stucco to it - but we didn't do that, so again, I don't know.

Definitely a great way to build a house though. It added about 5% to the cost of building it - and our heating/AC bills were about half that of our neighbors with similar sized houses. I calculate that the extra cost paid for itself in 5 years - but bear in mind that Texas summers are ferocious and they high cost of airconditioning is what kept the payback time that short. The CO2 benefits are harder to calculate because concrete manufacture is incredibly bad for generating CO2, I never did figure out what the "payback time" was in terms of carbon footprint - but since the concrete structure should still be viable in 50 to 100 years - I'm pretty sure it's a net win.

I also liked that the house was so quiet - and because the walls and slab formed a continuous piece of concrete, there were very few insects getting into the house.

SteveBaker (talk) 16:59, 19 May 2014 (UTC)

"15 hears" ? That's definitely hearsay then. :-) I'm curious if the outgassing was a problem. Did the house smell like plastic for the first year ? Also, putting holes through the wall for cable TV, etc., can be a bit more work with concrete walls. And if less air naturally flows through the walls, then you might need active ventilation with a fan running all day, and that cuts into your energy savings. StuRat (talk) 17:06, 19 May 2014 (UTC)

No, I didn't have a problem with outgassing...you can see details of their materials as [9]. Making holes in the steel-reinforced concrete walls was indeed a major problem. Our builder mistakenly put the cooker vent three feet away from where the cooker hood was, and he had to get some very exotic drilling equipment to make the new hole. When the house was built, he had a large hole in the bottom corner of the garage (made by putting a length of 4" plastic pipe into the wall before the concrete was poured) - phone and TV lines came in through there as well as power cables, A/C drain hoses, etc. The reduction in air flow was something we were very concerned with, so we had a couple of large fans built into the upstairs ceilings that would pull air out of the house and dump it into the attic. There was enough gaps around door and window frames to let air in whlie it was running. However, since (here in Texas) there is only about a week between needing to heat the house and needing to cool it(!), the airflow through the heating/cooling system was plenty to keep the air inside fresh. On those few days when we didn't need either A/C or heat, we'd have the windows open anyway - so I don't think we needed the vent fans for more than a few days each year. We had heat-pumps for the household heating - things would probably been different if we'd had a different heat source. SteveBaker (talk) 20:20, 19 May 2014 (UTC)

Haven't done this for a while, but in the UK existing brick houses have been insulated on the outside using either flame-retardant insulating foam slabs or rockwool/glass fibre insulating slabs, with fixings going through the insulation into the outer skin of brickwork. The slabs were then covered with glass fibre reinforced stucco (or rendering in UK terms) which provided a waterproof outer layer. Having the insulation on the outside meant the brick structure would warm, giving a lot of thermal inertia, and the dewpoint for condensation would be outside the brick structure. If the building was to be quickly heated intermittently you could perhaps add an internal layer of insulation, but care would be needed to include a vapour barrier and calculate that the dewpoint was somewhere that condensation wouldn't occur or matter. This is to cope with a challenging climate, very variable with a lot of condensation problems in cold weather. Other countries differ. . . dave souza, talk 17:13, 19 May 2014 (UTC)

I was always told not to insulate the inside of a cinder block building, only the outside, becasue the cinder block acts as thermal mass and will hold the heat or cooling that you are putting into the house (basically acting as insulation itself). I'm not sure why you say I should put Styrofoam on the outside and the inside.--Interestingusername123 (talk) 03:45, 20 May 2014 (UTC)

A thermal mass isn't quite the same as insulation. A large thermal mass will tend to delay when the outside temperature makes it to the inside, not stop it. In the case of most masonry, it seems to delay it about an hour per inch of thickness. So, 12 inches of masonry would delay the heat of the day from hitting the interior until about 12 hours later, so the middle of the night, when the extra heat might actually be appreciated. Unfortunately, most homes have maybe half that thickness, so it gets hottest inside some 6 hours after the hottest part of the day, putting it somewhere around 9 PM, when opening the windows to cool the house down might not work yet, since it's still warm out.

I'm also not sure why putting insulation on the outside and inside of the cinder blocks is better than putting a double thickness on the outside. Perhaps each creates a vapor barrier, and that prevents moisture from getting into the cinder blocks from the inside, condensing on the cinder blocks when they are cooler than the air in the morning, and causing mold to grow. I'd expect this to be a potential problem by the bathrooms, if you take showers or baths in the morning, or by the kitchen, if you boil food in the morning. You can create a vapor barrier without foam, however. StuRat (talk) 13:36, 20 May 2014 (UTC)

How does knowing the gene for a disease help you treat the disease?

How does knowing the gene for a disease help you treat the disease? 203.45.159.248 (talk) 07:03, 19 May 2014 (UTC)

As far as I know, it doesn't. It is not the reason why one would want to know the gene for a disease. Plasmic Physics (talk) 08:42, 19 May 2014 (UTC)

It might help if you were developing a drug to target it specifically, or perhaps a corresponding bacteriophage. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:28, 19 May 2014 (UTC)

How is that supposed to work? Plasmic Physics (talk) 09:40, 19 May 2014 (UTC)

I think there's some ambiguity here between sequencing the genome of a pathogen (say a virus or a bacterium) as assumed by Bugs' reply, and knowing the relationship of individual genes in a larger genome which produces a given genetic disorder in that genome's owner. The latter was my interpretation of the question, and I think yours too, but it's definitely ambiguous. AlexTiefling (talk) 09:43, 19 May 2014 (UTC)

Yes, I agree. Although, I wouldn't normally associate a disease with a pathogen. Plasmic Physics (talk) 09:55, 19 May 2014 (UTC)

Why not? Our article disease even lists pathogenic diseases first in its typology of disease near the end of the the lead. AlexTiefling (talk) 10:00, 19 May 2014 (UTC)

Habit - I'm not saying that it's wrong, it's just not my primary go-to. Plasmic Physics (talk) 10:04, 19 May 2014 (UTC)

It can help a great deal indeed. If the exact mechanism of disease development wasn't know before, but becomes more clear after finding the genetic association, you can start far more targeted studies for therapies. Fgf10 (talk) 14:45, 19 May 2014 (UTC)

• Biologists generally dislike the term "gene for a disease", because it is an easily misunderstood way of saying "gene whose malfunction causes a disease". Knowing that a certain gene malfunctions may be a step toward understanding how to cure a disease. In most cases the result of a gene malfunction is either (a) a certain type of protein is malformed and does not work properly, or (b) a certain type of protein is made in quantities that are either excessive or deficient. For any of those mechanisms, pinning down what happens is a step toward figuring out how to deal with it. Looie496 (talk) 14:48, 19 May 2014 (UTC)

• "Gene" is commonly used, at least in everyday language, to refer to a specific allele of a gene; for example, one might speak of the "gene for type A blood". Perhaps biologists are careful not to use the word "gene" this way; but saying "the gene for a disease" or "the gene that causes a disease" (as OttawaAC does just below) is just another example of it. --50.100.193.30 (talk) 03:56, 20 May 2014 (UTC)

If the gene(s) that cause a disease are identified, that can lead to a test for diagnosing the disease. Not all diseases are easily diagnosed, for example mental illnesses like schizophrenia, bipolar disorder, and so on. They can be tricky to diagnose and sometimes it takes years, simply because there's no way to do a test to find the correct diagnosis. And the more quickly a disease is accurately diagnosed, the more quickly the correct treatment can begin. If the genetic basis of these illnesses was more fully understood, the effects on the brain would be known with more precision, and medications that target brain chemistry more effectively could be developed. Some illnesses are developmental problems, meaning the genes are "programmed" to trigger the problem at a certain point in the patient's development, like autism in toddlers. If the genes triggering those issues were known, then testing and perhaps preventative gene therapy could be introduced. OttawaAC (talk) 15:47, 19 May 2014 (UTC)

It is rare, but knowing the gene that causes a disease absolutely can lead directly to a treatment. Figuring out that chronic myelogenous leukemia is typically caused by a mutation of BCR and ABL1 led to the creation of imatinib. Figuring out that cystic fibrosis is caused by mutations to CTFR led to the creation of ivacaftor.

Those are just examples where treatments were developed that target the gene (or rather, it's protein product) directly. There are countless more examples where knowledge of the genes that cause a disease expanded our knowledge of how disease occurs, and led to treatments in more indirect manners. Someguy1221 (talk) 06:15, 20 May 2014 (UTC)

Is it true that RNA helix viruses mutate faster than DNA helix viruses?

And if so, then why does the MMR vaccine (which treats an RNA helix group of viruses) only require one vaccine while the flu vaccine only works for 1 year and even then sometimes doesn't work. Both being RNA viruses, one would assume they mutate at about the same rate. ScienceApe (talk) 15:00, 19 May 2014 (UTC)

I'm not expert in viruses, but I assume this is at least partly due to the fact that the flu is not caused by just one, but an entire family of viruses, the orthomyxoviridae, which typically generate new strains not just by mutating but by recombining with one another. Someguy1221 (talk) 06:19, 20 May 2014 (UTC)

Inconspicuous transport by sea

I was watching some film and they had to smuggle millions in cash from the US to Switzerland and I wonder couldn't they transfer it via a private boat? What's the problem sending a yacht or something else? Range? Inclement weather? --78.148.110.113 (talk) 15:22, 19 May 2014 (UTC)

Perhaps they were worried about being intercepted by the Swiss Navy. Gandalf61 (talk) 15:28, 19 May 2014 (UTC)

I should point out that it could be transferred by land after reaching the European continent. 78.148.110.113 (talk) 16:05, 19 May 2014 (UTC)

The more times they transfer it and cross borders, the more chances they will be caught, by customs agents, etc. Since cash is fairly compact, a private plane would be the obvious method, needing to pass inspection only once. And weather is also a concern for a boat trying to cross an ocean, as is the time it takes. Both work together, in fact, as it takes too long to cross to get an accurate forecast for the entire trip before you leave. And taking a small boat across an ocean is sufficiently rare that it might garner extra attention, particularly looking for drug smuggling or illegal immigrants. StuRat (talk) 16:11, 19 May 2014 (UTC)

It depends on how much money one is transferring. One million dollars in hundred dollar bills is about the size of a briefcase. Thus, a hundred million dollars would require 100 briefcases to transport. This page gives an interesting perspective on the size of large sums of money, from a geometric point of view. --Jayron32 18:19, 19 May 2014 (UTC)

Don't use the train 95.112.250.227 (talk) 19:08, 19 May 2014 (UTC)

Is it true that blood glucose can change your eye prescription if you wear glasses?

^Topic ScienceApe (talk) 15:28, 19 May 2014 (UTC)

[10]< reference. --Jayron32 16:02, 19 May 2014 (UTC)

Creatures with 3 pairs of limbs

There are a lot of mythical creatures that look quite like Tetrapods but with an additional pair of limbs, mostly wings or arms. (Centaurs, angels, pegasus to give just a few examples.

I always wonder how the additional pair of limbs would be attached to the skeleton in a was that is not obviously dis-functional.

So what in real nature comes closest to those creatures, or, to avoid all the answers saying "this is impossible because we have not observed such a thing": if some students would have a joke and fake such a skeleton, working real hard avoiding obvious mistakes, how would that look like?

95.112.250.227 (talk) 18:49, 19 May 2014 (UTC)

Perhaps like this Meganeura. And that has an extra pair of legs and an extra pair of wings over and above what you wanted. Dmcq (talk) 19:34, 19 May 2014 (UTC)

Also try googling "six legged cow" to get some examples. Dmcq (talk) 19:40, 19 May 2014 (UTC)

In vertebrates, limbs come from girdles formed during development. We don't have a page on general girdles, but see pelvic girdle and pectoral girdle. The pectoral girdle developed in bony fish. Here is a paper that specifically discusses evolution of girdles and mechanisms that account for the change in development [11]. In short, a putative six-limbed vertebrate would come from a whole lineage of three-girdled ancestors. This is not a sport that can spontaneously pop up and survive to reproduction, let alone have some advantage among extant tetrapods. In nature, we do have ants with three-limbed workers. They have imaginal discs that allow development of separate limb pairs, but they don't have internal skeletons. Certain Odonata are slightly closer to the pegasus, but they have three pairs of legs and two pairs of wings. I can't think of any animal that has exactly four legs and exactly two wings. SemanticMantis (talk) 19:41, 19 May 2014 (UTC)

With respect to Dmcq's cow comment, here's a science article presenting a dissection of a six-legged goat [12]. From what I can tell, it did not have an extra girdle, and the legs would have been totally useless. SemanticMantis (talk) 19:46, 19 May 2014 (UTC)

I guess the same applies to other creatures mentioned in our article on polymelia (such as Stumpy)? ---Sluzzelin talk 19:55, 19 May 2014 (UTC)

Thanks for the answers so far. I was really thinking about Tetrapods (to be distinguished from quadrupeds), not about arthropods. So the hint to girdles seems crucial. Those polymelia forms look like they are not even good for an additional Eisbein.

But I know that there are additional vertebral notches occurring in nature, either genetically or somatically. Nature does all kinds of "mistakes", so is there anything known about additional girdles? 95.112.250.227 (talk) 20:25, 19 May 2014 (UTC)

The problem with having an extra limb girdle is that it changes the entire vertebrate bauplan. The few genes (HOX being probably the best known) that account for correct rostro-caudal segmentation and development of an animal, in my understanding do not separately encode developmental "commands" like "make an extra pair of lungs" or "make a shoulder girdle here". Rather, by modifying those genes, it is possible to change the developmental "fate" of certain body segments: e. g. have a Drosophila grow legs instead of antennae, or have a duplicate thorax (example here: http://biobabel.wordpress.com/tag/abd-b/). Duplication of a limb girdle in a vertebrate animal would probably result in duplication of some of the internal organs as well. There is no funcdamental reason why this would be impossible, though. In fact, a centaur is supposed to have two hearts, two stomachs, and two pairs of lungs; and a catbus 8 or 10 pairs :) Dr Dima (talk) 21:22, 19 May 2014 (UTC)

For centaurs I was always wondering if they had duplicate precious parts.95.112.250.227 (talk) 21:49, 19 May 2014 (UTC)

I can imagine an evolutionary path (if conditions somehow favored it) where a bird develops longer and longer talons, and shorter legs, until the talons essentially are the legs. At that point it might have 6 "legs" and two wings. StuRat (talk) 22:25, 19 May 2014 (UTC)

• Obviously mythologers were both ignorant of and unconcerned with anatomy. The wings of gryphons are speculated to be the dislocated head shields of fossil ceratopsians Where are the scapulae and musculature going to go for a harpy? Not to mention how is it going to carry the extra weight of the arms? Forelimbs in tetrapods develop cranially in relation to the thorax, hindlimbs develop caudally to the abdomen. Nothing develops medially to the abdomen and thorax. The disruption to the abdominal diaphragm alone would be a lethal malformation. Even how turtles manage to develop their limbs inside their ribcages remains an evolutionary mystery. And four-legged ruminants inevitable have a doubled set of rear limbs, not three pairs of limbs equally spaced. Given the presence of two dorsal fins in the ancestors of tetrapods, there doesn't seem to be any a priori reason why we couldn't have a third arm and leg in the middle of the back, but the purpose that might serve excapes me. I'd actually be surprised if some competent physiognomist hasn't examined the conundrum. Good luck. μηδείς (talk) 02:08, 20 May 2014 (UTC)

Drug tests, "cleansing"

so i have a drug test tomorrow and i bought this strip nc extra strength body cleanser. It contains a 1 fl oz liquid and 4 pills. How long does it last and when should i take it? — Preceding unsigned comment added by 50.185.136.93 (talk) 21:24, 19 May 2014 (UTC)

I added a header so your question appears in its own section. Please use the "ask a new question" button at the top in the future. As to your question: we cannot give you medical or legal advice here, and your question could easily be seen as asking for one or both. I can point you to this site, which seems to have some good information about the various sorts of drug tests, how they work, etc. [13]. Good luck, SemanticMantis (talk) 21:37, 19 May 2014 (UTC)

If any reference is given here, it should be to the Wikipedia article Drug test rather than to a marihuana promotion site. 84.209.89.214 (talk) 23:29, 19 May 2014 (UTC)

I should have looked at our article first. Here is a link from our refs there that might be more reliable than the one I posted before [14]. SemanticMantis (talk) 13:30, 20 May 2014 (UTC)

Efficacy of vaccines

If I got three different vaccines, let me say Gardasil, One against pneumonia, one against flu, in a time span of just 3 weeks, can that negatively affect the efficacy of vaccines? 112.198.90.97 (talk) 07:00, 20 May 2014 (UTC)

Sorry, questions calling for medical advice aren't allowed to be answered here. Please ask a doctor or pharmacist. --50.100.193.30 (talk) 07:25, 20 May 2014 (UTC)

We can't give medical advice, but we can direct you to information published in reliable sources. If you are really concerned about yourself, seek a medical professional. If you are interested in the general topic, here is a recent journal article titled "Long-term health effects of repeated exposure to multiple vaccines" [15]. Here's another one titled "Simultaneous administration of childhood vaccines: an important public health policy that is safe and efficacious" [16]. SemanticMantis (talk) 13:40, 20 May 2014 (UTC)

Identifying a bird

Hello. I found a wounded bird and have called the regional bird sanctuary to take care of it. In the meantime, can you help me identify what species it is? It comes from north-eastern Spain.

Picture of the bird.

Thank you! Leptictidium (mt) 07:22, 20 May 2014 (UTC)

A juvenile common starling, I think, but given that you're in Spain, it might be a juvenile spotless starling instead. 2.220.78.158 (talk) 08:14, 20 May 2014 (UTC)

I concur. http://2.bp.blogspot.com/-slZCKJpTRz0/UNZRTfwqfeI/AAAAAAAANVA/eQKRLw5eAwk/s400/Starlings+feeding.jpg 196.214.78.114 (talk) 09:44, 20 May 2014 (UTC)

Projectile dynamics

With no air resistance and perfect elasticity, the simplest approach would say that a ball thrown ahead without rotation on level ground will perform an endless sequence of identical parabolic arcs, but I feel that the degree of friction between ball and ground would have an effect on trajectories after the first arc. Is this so, and if so what would the effect be? What would happen in the limiting cases of the coefficient of friction being 0 or 1?→86.146.61.61 (talk) 12:38, 20 May 2014 (UTC)

The friction with the ground would induce more spin with each bounce, and accelerating the ball from no rotation or less rotation at each bounce would use up some of the forward momentum, so the parabolas would get narrower with each bounce, but remain just as high, given your assumptions, until the spin was such that the ball matched the ground, so rolled perfectly on it with each hit. Of course, in addition to being impossible in the real world, one set of your perfect assumptions are also inconsistent with each other. If it was perfectly elastic, then it wouldn't deform at all when it hit, and would hit for an infinitely short period of time, and thus there would be no friction, either. StuRat (talk) 13:20, 20 May 2014 (UTC)

Perfect elasticity is the assumption, friction is a "feel" that the OP has. I'm not sure if perfect elasticity leads to zero friction, but if it does, then the solutions to the model would just be identical repeating parabolic arcs forever.

As for the claim that "perfect elastic, then it wouldn't deform" -- that depends on what OP means by perfectly elastic. E.g. if the modulus of elasticity is infinite, then no deformation occurs, and contact time (hence friction) is 0. But if the elastic limit is infinite, then even with a small elastic modulus, some sense of "perfect" elasticity is retained, even with positive contact time and friction. My impression is that "perfect elasticity" usually refers to the sense given at Elastic_collision, in which case, I agree that there is no friction, as that would fail to conserve kinetic energy. SemanticMantis (talk) 13:52, 20 May 2014 (UTC)

I actually meant by perfectly elastic that there was no loss of kinetic energy but that some compression was possible on impact - in which case, I would assume that in the case of non-unity coefficient of friction there was the possibility of momentary ground-contact sliding before the next parabola, which would certainly occur if the coefficient was zero, with the threshold value depending on the initial angle of projection.→86.146.61.61 (talk) 14:22, 20 May 2014 (UTC)