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March 10

Why have two units, like Calories and Joules?

Why the redundancy? Wouldn't science be better off with just one? I understand that some duplicity is possible since difference geographical regions use different units. But, for example, in food packages, you have both side-by-side, although they can be converted unequivocally. --Scicurious (talk) 00:13, 10 March 2016 (UTC)

Some people use one unit, others use the other, so why not do the conversion for them ? StuRat (talk) 00:23, 10 March 2016 (UTC)

Some people use one unit, so, why not drop the other and impose this one on them?

And some people confuse cal and kcal. This is a further reason to drop cal/kcal. --Scicurious (talk) 00:33, 10 March 2016 (UTC)

Being off by a factor of 1000 means it's not a mistake people are likely to make. (If you eat a meal with 1000 kcals, it would be hard to imagine it has only 1, or a million.) StuRat (talk) 18:39, 10 March 2016 (UTC)

George Washington scolded Congress for failing to do anything about the chaotic weights and measures in the early US. Nothing ever changes. Jc3s5h (talk) 00:37, 10 March 2016 (UTC)

I went searching for sources to cite for that... I found that President Washington mentioned uniform weights and measures in the First Annual Message to Congress on the State of the Union (1790). This was notable enough to mention on NIST's Presidential Measurements Timeline. Nimur (talk) 04:44, 10 March 2016 (UTC)

If you made a food product for sale in the US, and dropped listing calories (if that was allowed), in favor of Joules, then your sales would drop off. That's reason enough not to do it. StuRat (talk) 00:38, 10 March 2016 (UTC)

It isn't allowed; the FDA mandates specify "calorie labelling". There are similar rules throughout layers and layers of federal, state, and local bureaucracies. The switch to another unit would have to be promulgated by hundreds of agencies, and they'd have to do it at the same time to avoid the nuisance of labelling in multiple units. It *could* be made to happen, I suppose, but there's have to be a good reason to go to all that trouble. So we don't even have to get to the point where "Joules" winds up confusing Americans. - Nunh-huh 05:00, 10 March 2016 (UTC)

The question is more about why sciences deal with two units that mean the same, than about practical aspects. But I see what you mean. It would only work if all implemented it at the same time. Scicurious (talk) 00:40, 10 March 2016 (UTC)

The calorie is a unit of heat, whereas the Joule is a unit of work. They both have units of energy, so there's an equivalence between them, but they were both natural for their own purposes at the time. --Trovatore (talk) 01:51, 10 March 2016 (UTC)

Why do you assume "sciences" deal with both units? In my field we're standardized on SI and would get a scolding from the editor if we submitted a paper using calories instead of joules. (Unfortunately we then have to translate when talking to members of the U.S. public, but such is life.) Shock Brigade Harvester Boris (talk) 05:00, 10 March 2016 (UTC)

Within the scientific community, isn't metric the standard? It's the general public that uses the customary system. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:50, 10 March 2016 (UTC)

See previous discussion about the use of "parsecs" and "lightyears" instead of kilometers (or gigameters or terameters) in astronomy. Scientists frequently use units that are neither SI nor even metric in their specific fields. However, if they needed to figure out the amount of the luminous flux of a star that reaches the earth from a distance of 100 lightyears - you can bet that the very first step in their calculations would be to convert 100 lightyears into meters. Furthermore, if the distance to the star was initially measured by the redshift method, the result of that calculation would probably have been expressed in meters and then converted to lightyears "for convenience". The point being that while there is a "convenience" factor to talking about lightyears (because in astronomy, time and distance are intimately related) - everyone knows that the SI system is the underlying stratum upon which everything is built. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

Calories and joules are both "metric". Calories are not SI. --Trovatore (talk) 08:03, 10 March 2016 (UTC)

The scientific community would use the joule. To the general public, "calorie" was already established, and "joule" sounds like "jewel" (or "Jewel" for that matter). ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:00, 10 March 2016 (UTC)

That's ridiculous - not everyone speaks English. Don't you think that "feet" and "inches" might get confused in other languages? The entire point of SI (System International) is that it transcends language barriers. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

Thanks, as always, for the unwarranted personal attack. Last I checked, this is the English Wikipedia. Whether other countries use calories or joules, I wouldn't know. But I note that caloría is used in Spanish, while the other unit is called julio, which normally means a month of the year. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:16, 10 March 2016 (UTC)

The question (which we are indeed answering in English) is about scientists...not "English-speaking scientists". Science is an international effort - cross-border (and cross-language) communication being a huge part of what most scientists have to do. I've never heard of anyone being confused between "Joules" and "Jewels" - it's pretty clear from context - and if your argument is that words that sound like other words shouldn't be used as units of measurement then I'd ask how many feet long my feet are and how many yards wide my yard is, how many pounds (force) do I pound my nails in with and...well, let's just get a second opinion about the second shall we? Your responses, are not well thought through - they are frequently incorrect. This time seems to be no different. SteveBaker (talk) 20:16, 10 March 2016 (UTC)

SI snobbery is unbecoming. All systems of units are essentially equally good. The conversions between them are trivial; you just have to use good integration testing to make sure they get done right. --Trovatore (talk) 06:22, 10 March 2016 (UTC)

No - not all units are equally good. Having a standard way to make big units and little units from standard ones, for example. I have no idea how many hogsheads there are in a firkin or teaspoonfulls there are in a cubic mile. But I know immediately how many micro-joules there are in a mega-joule or how many gram centimeters there are in a kilogram meter. Furthermore, the relationships between derived units like the joule and the underlying kg.m².s^-2 base unit is very clear. The BTU, on the other hand, requires you to know how much energy it takes to raise one pound of water through one degree Fahrenheit - which makes it really insanely difficult to use BTU's to calculate (say) the amount of rocket fuel you need to get to the moon where raising water temperatures are not involved. Then we get into the abbreviations of units being a mess...the confusion that some idiots introduced between the calorie and the kilocalorie is a terrible error - and SI units forbid that kind of crap - but what is the standard abbreviation for "a million BTUs"? It can be MBTU, MMBtu or mmBtu? All are allowed - but what about a million feet? So I'm sorry, but it's complete bullshit to say that no system of units is better than another. That's clearly, blindingly freaking obviously not true! So please stop propagating this untruth. SteveBaker (talk) 14:49, 10 March 2016 (UTC)

I'm going to say THE TRUTH again. No set of units is better than any other.

You have no idea how many X are in a Y. So what? You can look it up. If it's something you do a lot, you'll learn it. --Trovatore (talk) 18:21, 10 March 2016 (UTC)

But why should I *have* to look it up? We can (and indeed have) designed a system that makes it entirely clear without having to look it up...or do pointless arithmetic to convert from one set of units to another. See my response below about trying to divide the width of a window into three parts using a stupid imperial tape measure. Even though I know the conversion - it's a pain in the butt to have to do it - and I'm very likely to make a mistake entirely BECAUSE of the stupid units problem. Sure you can memorize a bunch of random numbers and you can search online if you don't happen to remember how many grains are in a pound - then haul out a calculator to do it - but why on earth should you have to do such an incredibly stupid thing when there is a very well tried and tested system that the WHOLE of the rest of the world now uses? (er, except Liberia, and Myanmar). SteveBaker (talk) 20:43, 10 March 2016 (UTC)

Why should you have to? That's like saying, why should you have to have both a flat screwdriver and a Philips. You don't have to. But if you don't, you'll have trouble tightening screws of the other sort. Do you feel entitled to demand that people provide only the screws that fit your preferred screwdriver? --Trovatore (talk) 22:52, 10 March 2016 (UTC)

Sure. In my home workshop I have sets of flat, philips and torx screwdrivers - and about three dozen ball-tipped allen wrenches (metric and imperial) in my collection of tools (I also have some 'security by obscurity' robertson, triangular and other oddly shaped ones). I am also capable of operating in the realms of feet, yards and miles as well as SI units. However, when I'm building something new, I don't ever use screws with slotted heads - they strip too easily, and if the screwdriver slips out of the screw (which happens easily) it can gash your hand. I used to only buy philips-headed screws because, although they still strip - it's not as bad as flats, and the tool doesn't slip out of the screw. This has been the case for about the last 40 years - until just six months or so ago when DIY stores suddenly flooded with torx screws. Since Torx is vastly better than philips, I'm now actively "deprecating" my stock of philips screws and replacing with torx whenever possible. So, yeah - I can cope with flat-head screwdrivers - and with hogsheads, firkins, katals, pyrons, mireds and gilberts. But those are all obsolete. Yes, can still use them if I must - but no, I'm not going to use them for new work - especially if it's in the realms of engineering or science. But I have to recognize that while my car is made of torx bolts and screws - my laser cutters use allen and my house appears to use philips. I haven't seen a slotted screw in anything other than antique furniture for quite a while - and I like it that way! SteveBaker (talk) 14:51, 11 March 2016 (UTC)

The story of my 'conversion' to Torx (and problems related to that) are described in a medium.com story I wrote. SteveBaker (talk) 14:51, 11 March 2016 (UTC)

That's like saying that no system of mathematical notation is better than any other, or no programming language is better than any other. In reality, some are inherently less error-prone than others because humans don't work from formal specs; they rely to a large extent on cognitive abilities that haven't changed much in 100,000 years. And some are better because they are more widely supported/understood. -- BenRG (talk) 20:59, 10 March 2016 (UTC)

OK, look, I didn't literally mean that there were no system-specific advantages. That isn't the point at all. I assert that any inherent conveniences of any particular system are relatively minor. I also assert that trying to shame people into conformity with one preferred system just to avoid some potentially inconveniences is a bad thing. --Trovatore (talk) 22:52, 10 March 2016 (UTC)

Tell that to Mars Climate Orbiter or the Gimli Glider.... The sooner we get rid of non-SI units, the better. Fgf10 (talk) 08:07, 10 March 2016 (UTC)

Point of clarification: the Gimli Glider was caused by confusion due to Canada switching to metric. One could argue that it wouldn't have happened if Canada had stuck with imperial units. clpo13_(talk) 08:12, 10 March 2016 (UTC)

That's a point, but the more important point is that the testing was inadequate.

Same exact thing for the Mars Climate Orbiter. There's not a thing wrong with either set of units. There's not even anything necessarily wrong with using one set of units in one module, and a different set in another; it admittedly introduces more opportunities for error, but with correct testing procedures, you would find them. If you don't do the integration testing, there are all sorts of other errors you can miss that are not units-related. --Trovatore (talk) 08:31, 10 March 2016 (UTC)

Yes, I agree the Mars Climate Orbiter failed because they didn't test it properly - and because someone wasn't sufficiently clear in the specifications for interfaces between subsystems. It could equally have happened in an entirely metric environment if one subsystem used kilometers and another meters. However, we can find plenty of other cases - some potentially far more serious than either the MCO or the Gimli Glider incident. The US had for years used "grains" for weighing dry medicines...the abbreviation was 'g'. When imported bulk pharmacuticals from Europe started to turn up containers marked in grams ('g'), the US FDA insisted that they be re-labelled with 'gr' as the abbreviation for grams (a really, truly, classically stupid reaction to the problem!) Then grains stopped being commonly used and grams went back to being labelled 'g'...so there was ANOTHER change-over period while that was sorted out. What could possibly go wrong? Fortunately, one grain is 0.064 grams - so you're comparing grains to milligrams and there wasn't MUCH chance for an error in practice. But stupid things like that have the potential to cause tremendous harm. SteveBaker (talk) 21:28, 10 March 2016 (UTC)

The calorie was a base unit of thermal energy, the joule a derived unit of mechanical energy (kinetic, gravitational, electric). In the 19th century it was discovered that, using the proper conversion factors, mechanical energy and thermal energy could be converted into one another, keeping their sum constant. This meant that the joule could be applied to thermal energy too and made the calorie obsolete. It's no longer used, except for food. When talking about food, people for some strange reason stick to an irregular unit, even those people who have used SI units or their precursors for two centuries now in other fields. Maybe it's because there is a lot of pseudo-science in the food industry. In Europe, food is labelled in both kilocalories and kilojoules.

Not all scientists use SI. Some use cgs, which uses the erg as unit of energy. Both systems are equally good (and so is the FFF system), as both use conversion factors of 1 between combinations of base units and their derived units. 1 erg = 1 g·cm²/s², just as 1 joule = 1 kg·m²/s². This means there are no strange numerical factors in your formulas. The imperial or US customary systems don't: 1 btu ≠ 1 lb·ft²/s², 1 lbf ≠ 1 lb·ft/s² (using another unit of length instead of foot doesn't help). For the same reason the calorie is unwanted. PiusImpavidus (talk) 13:43, 10 March 2016 (UTC)

A it's heart, the original idea was that FFF is identical to SI except in the choice of the base units. It still uses milli and mega and the concept of having three fundamental base units (mass, length and time) that SI standardized. SI (as a concept) works just fine if you change the definition of a meter or a second (both have indeed changed since the inception of the system - the kilogram is about to go the same way). The point of SI is to define a system where we clearly understand that meters, kilograms and seconds are the fundamental things and derived units like joules are merely convenient shorthands that don't introduce new constants.

After the FFF system was first (jokingly) proposed, people have subverted it by talking about "BTU's per foot-fathom" (see our article on FFF) - which clearly puts FFF back into the realms of stupid antiquated systems where the derived units are not simply defined in terms of the base units. You can't tell how many BTU's are in a firkin fathom-squared per fortnight-squared (which would be the 'pure' FFF unit of energy) because you need to know the specific heat capacity of water and the definition of a foot and a degree farenheit in the FFF system to do that.

In the SI system, you know - without looking it up or memorizing weird constants that the number of joules in a kilogram meter-squared per second squared is exactly 1. You know that because the system defines derived units in terms of base units in a clear and unambiguous manner. How many joules is a pascal per cubic meter or a newton per square meter? I hardly ever need to do those conversions - but I know the answer is 1. How many BTU's is one atmosphere per cubic foot or one pound-force per square foot? Good luck with that! SteveBaker (talk) 15:13, 10 March 2016 (UTC)

What is at the heart of the misunderstanding of the SI-versus-imperial debate is that the pro-imperial people are only arguing that the foot, the pound and the second are just as good and useful as the meter, the kilogram and the second as "base units". I don't have any argument that the choice of base units is arbitrary in both SI and imperial - and one is as good as the other.

BUT that's not why SI is popular among scientists. It's for many more reasons than that:

1. Unit multipliers are the way that you abbreviate big and small numbers. SI defines a standard set of these: kilo, mega, giga, tera for big things. cent-, milli-, micro-, nano- for small things. There is no such thing as a kilo-foot in imperial - there could be - but there isn't. You have to convert feet into miles - which is a pain because you have to memorize the stupid conversion factor. Same deal with pounds, ounces and tons - these are all measures of mass - but they suck because there are more stupid conversion factors to memorize. If you're dealing with the more common units, you can maybe memorize quite a few of them - but the conversion from a grain to pound is not going to be tripping off the tongue if you don't use grains routinely.
2. Derived units. SI defines all 'convenience' units in terms of the base units. Joules, Pascals, Watts - all of these things are nothing more than abbreviations. A "joule" is merely a shorthand way of saying "kilogram meter-squared per second-squared". So you can have equations like F=m.a and so long as m and a are in standard units, F will come out in standard units too. In imperial units, 'force' will be in pounds-force (lbf) - and computing pounds-force from pounds (er pounds-mass I guess) and feet per second-squared requires you (bizarrely) to know the standard value for the force of gravity at the surface of planet Earth. Not so great if you're on the moon or something!
3. Standard abbreviations. What is the abbreviation for pounds-force? Well, you get to choose! lbf, lb_f or, if you prefer, just 'lb'...er...wait...run that by me again? The abbreviation for the standard unit of force is the same as the standard unit of mass? OMFG! What could *possibly* go wrong?!
4. Physics-based definitions for the base units: This is actually a fairly new thing for SI units - and we're not done with it yet. But the meter and the second are defined in terms of physically reproducible experiments. The kilogram still isn't - it's definition is "the mass of a specific lump of metal that's stored in a building just outside of Paris". The meter used to be defined as "the length of a specific lump of metal that's stored in that same building at such-and-such temperature" - but no longer, it's the distance that light travels in vacuum in some specific tiny fraction of a second (about 3 nanoseconds)...and the second is defined in terms of the amount of time it takes some specific atom to vibrate some ungodly number of times. This is important because the building with the standard meter in it could get hit by a meteor impact and we'd have no way to know how big a meter is anymore. The kilogram is going the same way - and probably it'll be redefined as the mass of some specific number of carbon atoms within the decade or so. How is the "foot" defined? Well, currently, it's defined as some exact fraction of a meter...which is pretty much an admission of defeat on this point! We long ago stopped defining the second as 1/(24x60x60) of the time it takes the Earth to make one revolution...which is just as well because that keeps changing. However, all of the funky old units are now defined in terms of the SI units...so SI has won that particular war and you 'imperial units' fans have to give up here!

So - the argument about SI versus imperial isn't about whether the foot is better than the meter. It's about having a consistent set of units with clear ways to make bigger and smaller versions, with clear derived units without wierd and changing "constants" like the gravity of the planet or the speed it revolves, with clear and rigorously defined abbreviations. Once we fix the kilogram, we'll be able to make instruments to measure things without having to calibrate them against copies of copies of copies of the lump of metal in Paris. We have atomic clocks that keep perfect time because by definition they are perfect. That's why scientists use SI - it's nothing to do with the convenience (or otherwise) of the three base units.

My one significant problem with SI is that kilogram doesn't have an un-prefixed name. We should really have gone with something like the french word "Grave" (which means "one kilogram") so that we wouldn't have a base unit with a prefix. There is pressure to make that change - but it probably won't happen. SteveBaker (talk) 15:43, 10 March 2016 (UTC)

SteveBaker (talk) 15:43, 10 March 2016 (UTC)

My hat off to you sir, hardly seen it argued better before. Fgf10 (talk) 15:55, 10 March 2016 (UTC)

@SteveBaker: I had thought a kilogram was "the mass of 1 liter of pure water, i.e. a cubical volume of water 10cm on a side (1000 cubic cm) at standard temperature and pressure." I've always thought it was a damn convenient way to convert quickly between volume and mass for a liquid. Weights and volume conversions in cooking become a snap too (most liquids you cook with — raw eggs, milk, alcohol, even oils — are near enough in density that 1kg=1L is a good approximation. Imperial units have a similar convenience: 1 fluid ounce of water is approximately equal to 1 ounce in weight, so a pint of water is about 1 pound. ~Amatulić (talk) 05:42, 12 March 2016 (UTC)

They say, "a pint's a pound the world around", but the last time I was over there, it was only about 90p. Which may give you some idea how long it's been.... --Trovatore (talk) 06:05, 12 March 2016 (UTC)

The physics-based definitions are important, but not by any means unique to SI. Most customary units have been redefined in terms of the SI ones anyway, so they are implicitly just as physics-based. The "admission of defeat" thing is silly; you're still using (almost exactly) the unit you were using before.

The rest of it is all essentially about minor conveniences. Sure, things are more systematic, and there are times that that saves you ten seconds or so of looking stuff up. The ten seconds don't really accumulate; if you're going to do something repeatedly, you will build the conversion factor into whatever you're doing. --Trovatore (talk) 18:29, 10 March 2016 (UTC)

Powers of 10 are handy for scientists, but they are not very good human-oriented measurements. There's nothing inherently better about the meter vs. the yard, or the kilometer vs. the mile. And decimeters are both too large and too small, and centimeters are too small, for humans to relate two. The foot and the inch are much more relatable. That's part of the reason the metric system remains mostly a curiosity in America, outside of the scientific community. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:21, 10 March 2016 (UTC)

Powers of 10 are NOT the point. Powers of 2 or 12 would be just as useful - arguably more so. I already said that meters versus yards isn't important. But "decimeters are too large or small"...???!!! What for? If I need to measure things that fit into the bed of my 2'x4' (60cm x 120cm) laser cutter - approximately - then feet are far too big for any kind of useful approximation and inches are too small. A decimeter is actually the perfect size for that (although, personally, I'd think in centimeters). That feet and inches are "more relatable" is utter BS. When putting up a curtain rod last night, I needed to divide the width of the window in three. My wife handed me her "sewing" tape measure that has only feet, inches and some random-looking number of tick-marks between the inches. Is that tenths? Eighths? Who knows? OK...look carefully - ah - it's 16ths. OK so I have 8 feet, 7 inches and 11 sixteenths of an inch. Great...what's a third of that? I can't do (8x12+7+11/16)/3 in my head - certainly not while balancing on the top of a ladder! Oh crap - go off to my workshop, grab a metric/imperial tape measure, OK 263.4 cm. I can do 2634/3 in my head - it's 87.8 cm. Hooray.

It's just what you grew up with. I went to school in the UK right on the cusp of the metric introduction - so I was taught both systems. I "think" in metric and imperial with utter ease and have no more problem thinking in either set of units. Neither is more convenient as absolute distances - I don't "prefer" an inch or a centimeter - but I *do* prefer the SI system. The only reason it's not popular in the US is because it's not popular in the US.

You can't deny the value of the four points I described above - you just can't. You're down to pathetic arguments about the "relatability" of ONE of the base units - and you can't even back that up with anything more than a gut feel. If the metric base units were hard to relate to - don't you think there would be pressure in (say) France or Germany to use feet and inches? I don't see that. All I see is pressure in the USA to convert the last major country on the planet from an antiquated system to something a little more modern. The fix for your "relatablity" issue is to teach children the metric system in school as their PRIMARY units of measurement. Within a generation, the pressure to dump the old fashioned units would be overwhelming. SteveBaker (talk) 20:09, 10 March 2016 (UTC)

Your vulgar personal attacks defeat any points you may raise. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:16, 10 March 2016 (UTC)

So you've run out of counter-arguments? OK. SteveBaker (talk) 20:47, 10 March 2016 (UTC)

No, I stand by what I said. What you said has become irrelevant. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:49, 10 March 2016 (UTC)

Huh! That's an interesting debating style. I'm not sure "You upset me, so you must be wrong" is one of the ways to convince people...but it's your call. SteveBaker (talk) 21:06, 10 March 2016 (UTC)

Vulgarity doesn't upset me. It merely diminishes the one who uses it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:13, 10 March 2016 (UTC)

I don't want to get into this discussion too much but when people talk about "powers of" are they referring to the Base (exponentiation)? If so, I think the key point which often seems to be missed is that decimal is the system almost universally used nowadays with a few limited exceptions like in computing science. Other systems were used in the past but we've almost universally settled on 10, perhaps because we humans have 10 fingers or toes. Easier divisions may mean duodecimal (12) would be a better base and as SB I think has said binary (2) also has advantages. But as much as we can imagine how much better it would be if we humans generally had 12 fingers or we'd stuck with some other way of counting or whatever but sadly that didn't happen.

In other words, like it or not, decimal has become the natural system to most humans regardless of any possible flaws or better alternatives. This is the case even for nearly all users of imperial/US customary users. When something is 10 decimal or 130 decimal inches, pretty much everyone writes it as 10 inches or 130 inches, not a inches or aa inches. Maybe the later will be written as 10 feet 10 inches or 3 yards, 1 foot, 10 inches but never a feet a inches. The fact that we don't really have a symbol other than the letters of the English/latin alphabet for any bases beyond 10 is a sure sign of this. And as SB has said, I'm guessing even for many normal users it took longer to convert the 130 decimal inches into yards, feet and inches then it ever should a similar metric unit conversion.

If people using imperial/customary units were actually using a different base universally then it may make more sense, but they're not. In fact as SB has said and the yard-foot-inch example has shown, it's not like the bases used are consistent in the units they use anyway, so they can't.

Nil Einne (talk) 21:14, 10 March 2016 (UTC)

If metric was so wonderful, we would have adopted it already. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:17, 10 March 2016 (UTC)

But, um, we have? Nil Einne (talk) 21:29, 10 March 2016 (UTC)

Where appropriate. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:35, 10 March 2016 (UTC)

Which is nearly everywhere. As mentioned above and below, I use SI nearly everywhere. The only places I may not use SI are time (I do use the second, but also the minute, hour day etc) and temperature (I normally use celsius rather than Kelvin which while making now difference in terms of magnitude, is different in terms of absolute values) and for units in space (I do use the lightyear etc on occasion as it's a useful unit). Oh and I normally use PSI for tyres because that tends to be what the meters and data book displays by default and I don't do any calculations. (Most meters can actuall change to kPA but the unit used here is actually fairly arbitary so I don't really give a damn. I wouldn't likely use PSI were I actually calculating something.) If I was a pilot I may be forced to use feet but I'm not and I'm pretty sure your not a pilot either so it's largely a moot issue. Since I'm not a pilot, when I do fly I tend to view the SI flight information units. And frankly, the main reason why pilots still use feet seems to have more to do with tradition and the risks of switching over. If I were navigating or in charge of a ship I may use nautical miles but I'm not and again I suspect you're not either. (Although this, along with time and celsius as temperature is perhaps one of the few units where there's a reason to keep using it.) I do see any reason to use inches, yards, ounces, pounds, Fahrenheit etc etc and there are probably over a billion people like me, definitely more than those using inches, yards etc. (Although possibly even more do have some usage of other units.) In other words, where appropriate is "nearly all the time". Nil Einne (talk) 17:53, 12 March 2016 (UTC)

You're choosing to use it for your own reasons, but generally it's non-standard in America. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:05, 12 March 2016 (UTC)

P.S. It's perhaps worth remembering that even for people like me who almost never has any need to use non SI for most units (except when reading something written by someone who doesn't use SI and the limited non SI) and frankly only have a vague idea on the conversion for even some more basic units like inches, pounds etc (and I'm pretty sure I'm better than my younger brother who's doing a PhD in engineering); it's not like we don't deal with the problem of inconsistent bases.

Time is one of the few areas which hasn't properly changed and for various reasons probably isn't likely to change any time soon. As SB has said, when I'm going between other units it's trivial (worst case you make an order of magnitude mistake which you'd normally pick up). Working out how long 518 seconds let alone 572782 seconds is annoying and I at least have okay mental maths. Sure I can pull up a calculator on my computer in a few seconds if needed but this doesn't mean it isn't still annoying. In fact since I sometimes specify stuff in milliseconds when scripting for various reasons, even within the units it's obvious how much simpler it is.

Nil Einne (talk) 21:29, 10 March 2016 (UTC)

Yes, the world needs a wristwatch with a decasecond and kilosecond hand! Sadly, the rotation rate of the Earth isn't some handy power-of-ten seconds - but it was never a good choice as a basis for time because it doesn't spin or orbit at a sufficiently uniform rate and we have to fritz around with leap-seconds. Certainly for fractions of a second, you're forced into SI because there don't seem to be imperial units of time less than a second. As a programmer of video game graphics, ruled by a 16.667 millisecond frame time, a millisecond starts to seem like a long time, and microseconds are a useful unit. Most of the time, an inch is close enough to 25mm and a foot is more or less 30cm...the rest don't generally impinge much on my daily life. When I need precision, as a user of Linux (or Cygwin under Windows or BSD under OS-X), I install the wonderous command-line "units" program - which can happily tell me how many oersted furlongs there are in a gilbert (20,116.8!) - and 'bc' which is a command-line calculator that can provide 100 digit precision and work in base 37 if you want it to. I have a similar program to 'units' on my phone - but most of the time, Google does the job easier (it doesn't do oersted-furlongs though). But for most work, doing things approximately in your head is strongly desirable - and for that, it's hard to beat SI. SteveBaker (talk) 15:15, 11 March 2016 (UTC)

I think the reason why Calories (note distinction from "calories", even though they are almost written "calorieinch

s"!) hang on with food is pretty obvious: they're not practically convertible with anything else. A few biodiesel geeks excepted, you don't burn food in your furnace, and you sure as hell can't make it using kilogram weights and a high cliff (excepting if they land on something with tasty meat). So you're asking the whole dieting world to change its units to something they don't know, sentence themselves to a lifetime of multiplying any figure they ever learned in their life by 4 point something in order to compare it to what they're reading on the label today to see if this is a higher- or lower-calorie equivalent, all based on a theoretical correspondence with a unit of heat that they by and large wouldn't know how to do calculations with even if there were any relevant calculations they needed to make. This reform is not going to happen until the days when the consumers are shackled to tracking robot devices that tell them what people of their class and health status are allowed to eat or not, and when it happens it will be an internal update in the software that the consumers don't have the right to reverse engineer even if they had the inclination or mental capability to do so. Wnt (talk) 13:30, 11 March 2016 (UTC)

There are two problems with the calorie - as used for foods and diet plans. Firstly is the horrible mixup between calories and kilo-calories - and second is the problem of what exactly is being measured, and how. The problem is to know how much energy an average human being will extract from one serving of some food or other, you have to either submit some poor experimental subject to having their poop and pee and sweat and breath measured while sitting in a tank of warm water - or you have to kinda guess by measuring their CO2 production. That's a horrendous ordeal to go through for every change in the shape and size of a gummy-bear or every one of the (allegedly) 57 flavors of Cambell soup. So what they actually do is to use a 'bomb calorimeter' and burn the food to ashes to get it's "true" energy content and make assumptions about the efficiency of a typical human gut.

So it's not just that the numbers aren't convertible into other units - it's that we're not even measuring the thing we're claiming that the number represents.

There are few other units that suffer from that kind of issue - perceptual sound and light levels are another - the pain scale - that kind of thing.

Since the science behind what is being measured is so flakey - it's perhaps just as well that we define a special unit and use it (more or less) only for that one purpose. Hoping that when someone decides to build a car that runs on gummy-bears (oh, trust me, there are nut-jobs out there who are thinking about it as we speak!), they don't try to use the calorie number on the packaging label.

I do recall at least one case of confusion caused by the calorie versus the kilo-calorie - and that was when someone claimed that drinking cold beer cause your body to burn more energy in maintaining body temperature than the beer itself contained - so beer must be a good diet food. As expected, the label on the beer bottle said something like "200 calories" and the math done on the bodily cooling was done with joules and converted to proper SI calories and came up with the answer 3,600 calories to warm a bottle of beer to body heat. So on the face of it, drinking beer will be an extremely effective diet!

SteveBaker (talk) 15:33, 11 March 2016 (UTC)

It see arbitrary what unit of energy something is expressed in. I like kilowatt-hours. Edison (talk) 02:42, 13 March 2016 (UTC)

Do Americans still buy their petrol (gasolene) in gallons? There are 20 fluid ounces in a pint, so a pint of water weighs 1lb 4oz. Then there are eight pints in a gallon - a gallon of water weighs ten pounds. The US gallon is a little smaller, but if you divide it into eight I think the weight of water would be more than one pound. Metric is not very well organised - for example the base unit of area is (unsurprisingly) the are, although everyone deals in hectares. And let's not forget that imperial units are conveniently related to parts of the body - a foot is, well, a foot, and when I was working in the market, if I didn't have my yardstick handy I could measure a length of cloth from my outstretched hand to my nose. The stock market doesn't bother with decimals - it's more convenient to quote prices in halves, quarters, eighths and sixteenths. An important feature is the mid - price - the average of what traders are buying and selling at. So if they're buying at 32 and selling at 33 the mid - price is 32 1/2. Simple. 5.150.93.133 (talk) 12:16, 13 March 2016 (UTC)

Yes, Americans still use US gallons for gasoline (and water, milk, paint, pretty much any bulk liquid). In the US there are 16 fluid ounces in a pint, Eight pints in a gallon. The old british system was yet more confusing with 16 ounces in a pound and 20 fluid ounces in a pint. SteveBaker (talk) 04:00, 14 March 2016 (UTC)

Hence the old expression, "A pint's a pound the world around." Our American world, anyway. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:27, 14 March 2016 (UTC)

Clinical engineering

How difficult is it to become a hospital clinical engineer if you have a degree and work experience in civil engineering but plan on doing a postgraduate degree in biomedical engineering? 2A02:C7D:B907:6D00:801E:EA0C:2468:72D9 (talk) 05:13, 10 March 2016 (UTC)

See Clinical engineering. If you have an inventive mind and you like engineering, then this role could be right for you. You will need excellent technical knowledge and also good communication skills to work with patients and understand their needs. To get into this job you will need a relevant degree in physics or engineering. To work in the English NHS you will then need to apply for the postgraduate NHS Scientist Training Programme. - See more at: [1] AllBestFaith (talk) 15:20, 11 March 2016 (UTC)

Field engineers

Which types of engineers work in the field and away from desks/cubicles the most? 2A02:C7D:B907:6D00:801E:EA0C:2468:72D9 (talk) 05:24, 10 March 2016 (UTC)

I'd go with Civil_engineer. 196.213.35.146 (talk) 06:21, 10 March 2016 (UTC)

Why is that? And any sub-disciplines of civils in particular? 82.132.237.203 (talk) 07:45, 10 March 2016 (UTC)

Military engineering has most distance form desks/cubicles id say. But its hard to tell because Engeneers typically become specialists in their job and thus its much more dependent on what job you take then what branch of engeneering you pick at start. --Kharon (talk) 08:38, 10 March 2016 (UTC)

When it comes to things like dams, bridges, roads, etc. the engineer has to spend a lot of time on site. Sure he's given the contractor the specs but he has to make sure they are implemented properly. New dams are not likely to be built anywhere near your office. You spend a lot of time in the field and often this is in the boonies - further than is practical to commute - so you may even live on site for weeks/months at a time. 196.213.35.146 (talk) 12:25, 10 March 2016 (UTC)

Here is an example in the news. The engineers are based in Italy and the project is in Iraq. http://news.sky.com/story/1657170/mosul-dam-humanitarian-catastrophe-warning 196.213.35.146 (talk) 12:30, 10 March 2016 (UTC)

The Field engineers that spend most of their working lives in the field must be the Farm “farm laborers”. They engineer fields, turn the soil, transplant cauliflower when the rain and sleet is flying horizontal, ensure Monsanto earns a fortunes by spaying Roundup here there and everywhere, harvests the wheat all night under the harvest moon. In fall (autumn), they become arborists by cutting hedges and relaying them. Their hydrogeological skill are employed when clearing drainage ditches. Living on a farm they probably don't have access to the internet, so in their free time they are probably out in the garden tending to their lettuces, rhubarb, tomatoes and kohlrabi. Then perhaps get into a bit of Environmental Bioengineering by turning over their compost heaps from time to time. Compared to a graduates fresh out of agricultural collage they shine brighter than the midday sun and they are out in it -come all weathers – in the field. To appreciate their many skills, one one has to communcate with them. In the UK that means knowing a little bit of Polish, in the US of America a working knowledge of Hispanic and Google Translate on the mobile helps. Remember, with out their skills, will would starve.Where as, a civil engineer gets upset when his green wellies get muddy.--Aspro (talk) 20:31, 10 March 2016 (UTC)

No way! A company calls a "field" a defined area of customers. An engineer who maintains projects and problems occuring at the customer site might also be called a field engineer.[2] This is an engineer who travels. --Hans Haase (有问题吗) 12:52, 12 March 2016 (UTC)

Electric utilities send mechanical, civil and electrical engineers into "the field" at some point in their careers. They check field conditions, draw up plans for additions or modifications, and create "as-built" drawings. The electrical engineers might test relays or test transformers and circuit breakers. At other points in their careers they might stick to the office, creating general plans and budgets for system expansion.Edison (talk) 02:48, 13 March 2016 (UTC)

Energy content of water and carbon dioxide

I know that water and carbon dioxide are both energy-poor compounds, the end products of the oxidation of high-energy, organic compounds. Water and carbon dioxide do not burn. I was intrigued, however, when I read that carbon dioxide can react with water to produce carbonic acid, an exothermic reaction. I read on a website (I think it was by Harvard) that carbonic acid is lower in free energy than carbon dioxide, I suppose the way that carbon dioxide is lower in free energy than oil. I asked my biology teacher about this last part, and she said that of the two, water has more energy, but seeing the Harvard website gave me a different impression. I have also found Wikipedia's article, water-fueled car, and it is plain to see that water has a very low energy content. However, you can burn water; you just can't do it in oxygen. Water burns in fluorine, suggesting it must contain some chemical energy. So I was wondering: which has more energy - water or carbon dioxide? I was also wondering what else reacts with water (besides fluorine). Is there any other way to obtain chemical energy from water (using a different electron acceptor)? Finally, I was wondering if anyone could tell me more about the dissolution of carbon dioxide in water to form carbonic acid. I have references that specifically say this is an exothermic reaction. Does that mean that if I dissolve some carbon dioxide in water, the temperature of the water will increase (assuming I don't use dry ice, which is very cold and would cool off the water)? Will the temperature of the water drop when the carbonic acid breaks down into carbon dioxide and water again?162.40.215.36 (talk) 05:39, 10 March 2016 (UTC)

The reaction of water and fluorine doesn't necessarily mean that the water gave off energy, it could also be the fluorine. Note that pure sodium (not sodium chloride/table salt) reacts violently with water, but, again, the energy released may well come from the sodium. A more rigorous way to think about it is that the reaction products have less binding energy than the reactants. StuRat (talk) 06:46, 10 March 2016 (UTC)

Yeah - this is a common idea among the water-fuelled car crazies. The reactant with the abundance of energy in it is what we call "the fuel". So if you add fluorine or sodium into the water, the "fuel" is the fluorine or the sodium - not the water. So, yeah - you could make a sodium-fuelled car (which happened to need a tankful of water to make it work) - but that's no different than an old-style steam car that uses coal or wood as the fuel and needs a tankful water to make it work. The problem with both of those things is that we don't have cheap, abundant (and definitely not renewable) sources of elemental fluorine or sodium. You'd have to put a LOT of energy into the system to make either of those products - and that would by far exceed the energy you'd get back from reacting it with water. Sodium is extracted from salt by electrolysis, and fluorine from potassium fluoride, also by electrolysis. So rather than going the roundabout route of using the electricity to produce one of those lethally dangerous chemicals, then transporting and storing them under horrific hazmat conditions - why not just use the electricity to charge the batteries of an electric car?

The carbonic acid thing is somewhat more interesting. I'm not a chemist - but you should note that very little CO2 combines with the water - even under pressure. So you'd need a truly, insanely, vast amount of water and CO2 to produce any significant amounts of net energy - and with such huge quantities of reactants, the temperature rise would likely be too small to measure, let alone exploit as a source of power. This is clearly a non-starter. Note that so little of it forms that it wasn't until 1993 that anyone was able to show that carbonic acid even exists as a pure compound - and that claim wasn't confirmed until 2011!

Both water and CO2 are common byproducts because they are the lowest energy state of the chemistry that produced them. It's like burning some logs in a fireplace and then expecting to extract heat by doing chemistry with the resulting cold ashes the next day. Even if there is the tiniest amount of energy to be had via the carbonic acid route, for any practical use, you need a much denser fuel. If you wanted to run a vehicle on water and compressed CO2, you'd get more propulsion by using the pressure of the CO2 to drive a pneumatic motor and build a small over-shot waterwheel to drive the wheels as the water flows out of a gigantic water tank on the roof! (And in that case, the water and CO2 aren't fuels, just ways of storing gravitational or pneumatic energy.)

SteveBaker (talk) 14:18, 10 March 2016 (UTC)

I don't disagree with the logic, but it actually is possible to extract some heat by doing chemistry with cold ashes. Wood ash is highly alkaline -- many "folk" technologies relied on dissolving wood ash in water to get a rather potent base. Looie496 (talk) 15:23, 10 March 2016 (UTC)

To put some numbers here, I calculate the heat of reaction for the H2O (l) + CO2 (g) -> H2CO3 reaction to be -20.3 kJ/mol. That's exothermic, but still 2 orders of magnitude lower than a typical combustion reaction (propane is ~2,000 kJ/mol). The other problem is that the equilibrium constant for this reaction is small (our article says 1.7×10⁻³). So only 0.17% of the carbon dioxide that you put into the water actually reacts to form carbonic acid, while the remaining 99.83% either dissolves in the water or just sits there. COULD you run a car this way? I doubt that the energy that you would get out of it wouldn't even move the mass of equipment, water, and CO2 required to run it, much less move a car effectively. shoy (reactions) 14:57, 10 March 2016 (UTC)

For the last bits, see Carbonic_acid#Chemical_equilibrium and perhaps Ocean_acidification. SemanticMantis (talk) 15:18, 10 March 2016 (UTC)

Hi, me again (different IP address). Some great answers here. I was under the impression that fluorine was a stronger oxidizer than oxygen and so water really was the electron donor (fuel) in this reaction. Is that not true? To be fair, though, I also read that it takes energy to produce the fluorine, so you can't use it to fuel a car anyway. I really wasn't interested in water-fueled cars, just curious if water has any chemical energy in it? It doesn't have any at all? Just gravitational energy? Also, I really appreciate your answering my question about the dissolution of carbon dioxide in water. I especially liked the bit about confirming the existence of carbonic acid. Could someone provide a reference for the heat of reaction? I thought it released more energy.174.131.45.84 (talk) 15:42, 10 March 2016 (UTC)

You can't talk about chemical energy that way. There's a reason chemists use change in enthalpy, change in free energy, etc, when they report the results or models. It's because that's what you can measure. Even in the case of gravitational binding energy, this is also just a change in energy (specifically the difference between "current state" and "exploded to infinity"). Any time the reactants in a chemical reaction have more energy than their products, this change is called a release of chemical energy. There is still energy inside a water molecule in the form of electrical, nuclear, and gravitational bonds (. You can define water molecules as having zero "chemical" energy but that would be totally arbitrary, and not to mention the energy inside a water molecule changes with its environment. Someguy1221 (talk) 02:56, 11 March 2016 (UTC)

See Le_Chatelier's_principle and here [3]. There's also a nice animated graphic in this [4] related discussion. SemanticMantis (talk) 16:01, 10 March 2016 (UTC)

I couldn't find a direct reference for the heat of reaction for the formation reaction, it was calculated using Hf data from Perry's Chemical Engineers' Handbook. shoy (reactions) 16:30, 10 March 2016 (UTC)

As far as your use of the term "fuel", that's a bit misleading. While we don't normally think about the oxygen in the air as fuel, it really is every bit as much fuel for the reaction as whatever gets oxidized. It's just semantics that has us not call it that. (Kind of like we don't normally call people animals, although we obviously are, from a scientific POV.) StuRat (talk) 18:36, 10 March 2016 (UTC)

Distinct types within a species

I am trying to find out if there is a term for what might be called "intra-species morphological differentiation"; in other words, distinct forms or types within a species such as worker vs. soldier ants, etc. (?) --2600:1004:B002:C399:C9B7:34:47D9:C78D (talk) 18:10, 10 March 2016 (UTC)

Perhaps you mean Polymorphism (biology) (or "castes" for ants specifically). Sean.hoyland - talk 18:31, 10 March 2016 (UTC)

The term "breed" is used for domesticated animals, though it's apparently kind of loosely defined. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:06, 10 March 2016 (UTC)

What it's called can depend a little bit about where it comes from, and whose sense of the words you are following, how much of a stickler you are, etc. Fortunately I have a very reliable source hand from which I will quote - The Insect Societies by E.O. Wilson, p. 136:

"Polymorphism is defined in a special sense in the social insects as the coexistence of two or more functionally different castes within the same sex. The castes must be stable during one or more instars. ... Most commonly it denotes noncontinuous genetic variation within a population, and as such it is especially well entrenched in the literature of genetics. Consequently Mayr (1963) has proposed the alternate term polyphenism for nongenetic variation of the sort seen in the caste systems of social insects."

Now, it is important to note that many castes are actually not genetically controlled. Certainly not in the bumblembees, nor in queen determination of honeybees, but there is genetic control in the Melipona [5] and in many other clades. Understanding the interplay between genetic and environmental cues in caste determination in specific species and groups remains an active area of research, regularly appearing in Nature [6] and new results appearing as recently as last year [7]. So, if you are referring to social insects, "caste" is a fine word used by experts in the field. Polymorphism is more general, but do watch out for polyphenism, and the fact that you don't want to necessarily imply genetic control when it isn't there. SemanticMantis (talk) 19:14, 10 March 2016 (UTC)

Hmmm, interesting distinctions not clearly explained in articles Polymorphism (biology) and Polyphenism (Too bad I have "retired" from WP editing) -2600:1004:B002:C399:C9B7:34:47D9:C78D (talk) 19:59, 10 March 2016 (UTC)

I think it's ok. The first sentence of polyphenism clearly says arising from a single genotype, and lists social insect castes as a prominent example. The third paragraph of polymorhism explains that sometimes it means a genetic basis and sometimes it doesn't. I have shoe-horned a linked "polyphenism" into the intro, that should help a little. SemanticMantis (talk) 20:17, 10 March 2016 (UTC)

Ring modulation

Is ring modulation just a way of saying that a circuit implements convolution? I think that's what the article is saying but it's not totally clear to me. For the purposes of this question, I don't care about the fact that a real-world heterodyne of this sort may fail at accomplishing mathematically perfect convolution. Thanks, SemanticMantis (talk) 18:54, 10 March 2016 (UTC)

Yes that is what the article says. But real life heterodyne, eg guitar tuning, is additive, not multiplicative, in the time domain. The spectral content of that result is the same as the sum of the input spectra signals, the time domain waveform looks as though it is the average frequency, with an amplitude envelope at the difference in frequency, for equal amplitude signals. Greglocock (talk) 19:56, 10 March 2016 (UTC)

Thanks! I had also missed some of the back-and-forth between time and frequency domains. So ring modulation is multiplicative on the time domain, and convolutional on the frequency domain, which is sort of backward from the way I first came across these issues (that time convolution is simply multiplication on the frequency domain). SemanticMantis (talk) 20:20, 10 March 2016 (UTC)

Heterodyne means different frequencies (literally same power). Whereas homodyne means same frequency. Amplitude Modulation can be achieved by adding two signals and then passing the resultant through a nonlinear process. Also observe the Beat frequency page. Greg is correct though obscure.--31.109.183.147 (talk) 01:33, 11 March 2016 (UTC)

See also single-sideband modulation. --Hans Haase (有问题吗) 12:56, 11 March 2016 (UTC)

March 11

Merge request

Standard enthalpy of formation and Standard enthalpy change of formation (data table) are two articles that are on the exact same thing. I suggest merging those two into one article. Someone please do it! 146.151.96.202 (talk) 02:10, 11 March 2016 (UTC)

The right place to make this suggestion is at the top of the two articles. See Template:Merge. (I've done it for you.) Add a further explanation on the talk page (of Standard enthalpy of formation) if you think it would be useful. --69.159.61.172 (talk) 02:25, 11 March 2016 (UTC)

Underwater vortices

3 related questions: (1) Are there locations on the continental shelf where strong horizontal vortices occur underwater (similar to the rotor effect of a mountain wave, but underwater)? (2) If (1) is yes, then do any predatory fishes take advantage of these to catch prey? (3) If (1) is yes, then how much of a hazard are these to divers? 2601:646:8E01:515D:3C06:A9A7:4EC1:51F0 (talk) 03:12, 11 March 2016 (UTC)

1) I wouldn't expect anything similar to a mountain wave, since water, unlike air, isn't very compressible. So, it doesn't behave like a spring. However, underwater vortices are possible for other reasons, like the collision of two currents. StuRat (talk) 03:19, 11 March 2016 (UTC)

https://en.wikipedia.org/wiki/Category:Whirlpools These often go to the seabed, eg Corryvreckan. Greglocock (talk) 09:28, 11 March 2016 (UTC)

But are there whirlpools with a horizontal axis of rotation? That's what I'd love to know. 2601:646:8E01:515D:3C06:A9A7:4EC1:51F0 (talk) 11:48, 11 March 2016 (UTC)

Compressibility is irrelevant to rotor, since the air velocity is much smaller than the speed of sound (see Mach number). Have you read Strait of Gibraltar#Special flow and wave patterns? --catslash (talk) 12:12, 11 March 2016 (UTC)

Yeah, that definitely looks like the right conditions for horizontal vortices! Are these in fact observed in the Gibraltar? 2601:646:8E01:515D:5537:81A4:208D:1E74 (talk) 11:47, 12 March 2016 (UTC)

Nitrogen narcosis

Is it true that to an outside observer, the symptoms of nitrogen narcosis look similar to those of severe drunkenness? And, what do you do if your diving partner has nitrogen narcosis and is unaware of it (but you don't)? 2601:646:8E01:515D:3C06:A9A7:4EC1:51F0 (talk) 03:17, 11 March 2016 (UTC)

If diving at depths and durations which can cause nitrogen narcosis they really should be breathing "air" with less nitrogen, such as trimix (breathing gas), or even Heliox. If they took the wrong tank and are breathing normal air, switching tanks might help. They might switch to their backup tank if it's likely to have the proper mixture of gases, or perhaps use your backup tank otherwise. Surfacing immediately would not be a good idea, as it might cause the "bends". You might signal the surface to send down a replacement tank, if switching to the backup tank will not allow for full decompression time. StuRat (talk) 03:23, 11 March 2016 (UTC)

Your diving instructor will teach you what to do, when you undergo your diving training. Given this plus your previous question, I certainly hope you aren't trying to learn how to dive based on asking questions online, because that's a really good way to kill yourself. --71.119.131.184 (talk) 07:19, 11 March 2016 (UTC)

No, I'm not -- I'm doing this for book research. 2601:646:8E01:515D:3C06:A9A7:4EC1:51F0 (talk) 09:18, 11 March 2016 (UTC)

That's good. Taking training might still be worth considering, as you'll probably learn a lot more than you will asking non-experts questions. If you're working with a publisher, you should ask them whether they can help you with research. --71.119.131.184 (talk) 18:36, 11 March 2016 (UTC)

Floaty but sturdy material?

In Deadly Duck, flying crabs drop yellow bricks that float on the surface of a pond yet block ducks who weigh considerably more than normal ducks, having guns built into them. They don't even budge. And don't splash when they land. Real life is quite different from Atari life, but is there a somewhat similar material in this world? Something light in gas but heavy in liquid? Or light vertically but heavy horizontally? Most of me thinks no, but technology is sometimes astounding, especially lately. InedibleHulk (talk) 03:30, March 11, 2016 (UTC)

The title made me think of Pykrete, but there's incompatibilities with other parts of your description. Ian.thomson (talk) 03:34, 11 March 2016 (UTC)

Still astounding, though. And pretty close. I'd be scared if there was a perfect match. I'll have to check out some video to get a better idea. Thanks. InedibleHulk (talk) 03:43, March 11, 2016 (UTC)

Many videos out there of shooting and smashing it, but I'm not seeing floating. Probably too boring for modern audiences. Shooting a brick with a rifle does next to nothing, almost like how the duck's shots do absolutely nothing. InedibleHulk (talk) 04:00, March 11, 2016 (UTC)

Yeah, I don't think that a brick sized chunk would necessarily float (unless maybe you put some helium bubbles in there or something), but they were going to build an aircraft carrier with the stuff, so it can float... At least as well as steel does. Ian.thomson (talk) 14:15, 12 March 2016 (UTC)

The right combination of light bubbles and heavy pellets, in some sort of foam, perhaps. InedibleHulk (talk) 05:36, March 13, 2016 (UTC)

Sounds like you are talking about a substance with a different gravitational mass than inertial mass. AFAIK, so far, we haven't found any such substance. StuRat (talk) 03:39, 11 March 2016 (UTC)

Maybe for the best. InedibleHulk (talk) 03:43, March 11, 2016 (UTC)

Note that the outriggers on a trimaran must be more dense than air and less dense than water, so that if they are up in the air, they push downward, but if submerged underwater, they push upwards. In this way, they provide stability and keep the trimaran from capsizing. StuRat (talk) 03:53, 11 March 2016 (UTC)

That's rather cool. Still drifts if you push it, though. InedibleHulk (talk) 04:00, March 11, 2016 (UTC)

An anti-rolling gyro might at least takes the oomph out of the duck's waves. InedibleHulk (talk) 04:09, March 11, 2016 (UTC)

Doesn't this just require an object of low density (lower than water) but high mass? A brick-sized block of hardwood would fload, but the woood would probably be too heavy for a duck to move. (Whether a woodchuck could chuck it is a separate matter). Iapetus (talk) 21:07, 12 March 2016 (UTC)

The mass needs fit into a space about half the height of the duck (and the width of a crab). That's the trickiest part. Should've mentioned it sooner. InedibleHulk (talk) 05:33, March 13, 2016 (UTC)

Cost of Gorilla Glass

Approximately how much does the piece of Gorilla Glass found on most phones cost?

I found this cost breakdown of the iPhone[8] but unfortunately that only provide a total cost for the whole display unit. But at least it shows that the cheapest display unit is $36.09 and thus the cost of the Gorilla Glass is somewhere below there. Johnson&Johnson&Son (talk) 15:52, 11 March 2016 (UTC)

According to this source [9] one display worth of gorrilla glass will cost $3. Or roughly 1/240 monkey's (£500) :) — Preceding unsigned comment added by Polyamorph (talk • contribs)

If you're trying to buy small quantites of Gorilla Glass, for hobby applications, you can email the sales team at the address published on their brochure.

Specialized engineered products - especially custom-made parts - are usually subject to volume pricing, and contract negotiations. That means the price might change based on who you are, where you are, when you need it, how much you're buying... so it's unlikely that you can get a very accurate price estimate without actually talking to the people who sell the part. Nimur (talk) 16:35, 11 March 2016 (UTC)

Large manufacturers never respond to these kinds of queries, so I've learned to respect their time and my own time by not sending such fruitless queries in the first place. Johnson&Johnson&Son (talk) 04:08, 12 March 2016 (UTC)

That's simply untrue; I linked directly to the sales team's contact information. They exist to sell stuff to real customers!

If you'd rather order through a wholesaler, McMaster-Carr sells raw material, including Gorilla Glass. McMaster is pretty expensive, but they carry lots of high-quality materials, and they will happily sell small volumes and will fill single-item orders. Nimur (talk) 04:30, 12 March 2016 (UTC)

Approximately very cheap in mass production. Cheaper than Sapphireglass i guess but then this Gorilla Glass is likely also less weight. Ofcourse for obviouse reasons these prices are very secret. Who would still pay 700 $ for his smartphone if he knew it's completely produced in china for less then 100 $? --Kharon (talk) 13:22, 12 March 2016 (UTC)

logarithmic decay instead of exponential decay?!!!

I am working in a new company where one of our products' shelf-life appears to be modelled more accurately by logarithmic decay (R^2 = 0.994) then exponential decay = (R^2 = 0.93). The logarithmic regression equation gives our product quantity as y = -A * ln(t) + B

This is *so* confusing. I have never seen this type of decay before. I don't know how to model it. For example, I know exponential decay comes from first-order kinetics, and can be modelled through a half-life. How can I model what's going on in logarithmic decay? What kind of kinetics is going on? Yanping Nora Soong (talk) —Preceding undated comment added 16:05, 11 March 2016 (UTC)

The equation you give implies that you started with an infinite amount of substance. I'm guessing that was not actually the case. --Amble (talk) 16:17, 11 March 2016 (UTC)

No, it assumes you start with some surplus (B) and that you decrease over time? (-A * ln(t)?) Yanping Nora Soong (talk) 16:40, 11 March 2016 (UTC)

If A,B>0 and t is time then at t=0 you get infinite goodies, and in some finite time (exp(B/A)) you get negative goodies. Here is plot from wolfram alpha of y=-2logx +3 [10]. Maybe you mean something else? If so please clarify what you mean. SemanticMantis (talk) 16:49, 11 March 2016 (UTC)

We don't start with an infinite amount of substance but we do start with a lot -- on the order of 4-5 million light units at week 0. (We're using a luminiscent anti-human reagent). We use calibration standards to correct for the estimated amount of detected protein as the reagent degrades. (i.e. it's a self-correcting assay). It's a pretty resilient assay up until 6-12 months in the fridge. We'd like to increase this shelf-life further though. Yanping Nora Soong (talk) 17:16, 11 March 2016 (UTC)

Your model predicts an infinite amount of substance at t=0, when in reality you have a finite amount. That makes it a terrible model for the data (including a point at t=0, R^2 = -∞!), so talking about the kinetics that could give rise to such a model is putting the cart before the horse. --Amble (talk) 17:57, 11 March 2016 (UTC)

I started at a timepoint of t=1. Yanping Nora Soong (talk) 18:18, 11 March 2016 (UTC)

I'm skeptical that it is actually logarithmic -- power law decay is much more commonly encountered. The typical cause of weird shelf-life distributions is inhomogeneous variance -- a situation where failure is caused by a number of different mechanisms that each has its own distinct time constant. You could get logarithmic decay if you had a situation where dy/dt ~ 1/y -- that is, the rate of change of a quantity is proportional to its reciprocal. I've never encountered anything like that, though.Looie496 (talk) 16:24, 11 March 2016 (UTC)

I did a power law fit first. The regression fit is 0.97, worse than the logarithmic fit. The shelf-life was modelled with data spanning 25C over 13 weeks. I'm going to look at the refrigeration data to see if the shape changes. Yanping Nora Soong (talk) 16:36, 11 March 2016 (UTC)

What are you talking about? I mean it really could matter whether these are puppies or cans of soup or something else entirely. Its not so strange that a log model might have a better best fit than exponential or other families of functions. You do have to understand the limits of your model though, and you have to acknowledge that the fit of the model by itself can't explain anything about underlying mechanisms. For example if we make the reasonable assumption that by shelf life you mean that time is the independent variable in your equation, then a log model means infinite product at time zero but also negative products after some finite time. The fact that these are both unreasonable doesn't have anything to do with the fact that a log model fits the data well. It does mean that while you may be free to interpolate, that any extrapolation based on this model is very dicey indeed, because extrapolation could predict infinite or negative goods.

In general, think more about Post hoc ergo propter hoc and Cum hoc ergo propter hoc, and overfitting. Maybe a touch of Texas sharpshooter fallacy. I can fit a log line very well to a crease in my palm, but it doesn't mean anything. A simple reason a log model might fit better over a limited sample even when exponential is expected could have to do with outlier_(statistics) and signal to noise ratio. Also keep in mind that the difference in R^2 you quote originally is rather small, or at least could be considered small in many contexts. Finally, if you want to do this more seriously, look into using something like the Akaike_information_criterion, and look into using a more flexible family of curves, perhaps the Weibull_distribution, see e.g here [11] for an application of Weibull hazard distribution to shelf life. SemanticMantis (talk) 16:41, 11 March 2016 (UTC)

We're talking about a time scale of 26-104 weeks here. This is a biomedical product, not a plastic thing that's trying to biodegrade on a beach. The interpolation period is perfectly fine for the timescale needed to model our shelf life. It is simply a matter of trying to fix the chemical issue that is causing shortening of our shelf-life. For example, is this is a big clue that our degradation of our immunoassay reagent (or one of its components) is tending to zero order kinetics, in that case, there is some sort of catalytic surface (not very surprising, we have lots of solid phase reagent, magnetic linkers, etc.) being saturated, etc. Yanping Nora Soong (talk) 17:05, 11 March 2016 (UTC)

Ok, then I think my general advice still applies: the fact that the log model fits better than others you tested can't tell you anything about the underlying process. It could suggest something to look into, and that would be Looie's proposition of dy/dt ~ 1/y, which I've also never seen in the real world, and is probably unreasonable for any real-world goods. A more likely explanation is that there is no underlying process that makes this a log decay. If there were such a process, it would lead to negative goods. The fact that log decay fits slightly better than power law is probably just a fluke, but I don't know anything about the quality control, sample size, precision of data, etc.

Talk to you supervisor. If this is biomedical goods then they can afford to do it right. Guessing at models and then drawing loose implications is not doing it right. Have you even tried a two-parameter model? Or one with five parameters, or five hundred? In this case, I suspect doing it right would involve a careful model selection process that uses delta AIC or similar model selection techniques to select across a range of models that have various structures and numbers of parameters. If you did that, then you might be able to use the nature of the model to help you understand underlying factors leading to too-short shelf life. But that's just about model selection, and doesn't leverage any of the chemistry. Conceptually, knowing what the stuff is and knowing chemistry should also help :) SemanticMantis (talk) 17:26, 11 March 2016 (UTC)

No, I am doing this because we (namely I) are trying to pick up any possible heterogeneous surfaces that could be degrading the reagent in our assay. We're trying to send our product into scale-up (pre-industrial-scale testing) very soon. God, we don't even have MATLAB, I really wish we did. This is a product that is about to be sent out into the real world. That is, the most we are trying to do is tweak the buffer and change the choice of casein vendor or something. We have to release the product by May 1st or risk possibly scrapping the entire immunoassay. My supervisor is a veteran and there are unexplained problems with this assay for some reason that were plaguing her team for months before I joined three weeks ago. So the big question I have is: Is logarithmic decay a sign of partial zero order kinetics? That's all I'm trying to do. I am well aware there could be multiple things going on. I am not interested in the other decay modes going on. I am well aware that is possible. All I am interested in is whether there could be a mix of decay modes, one of them being zero-order kinetics. I see that there is a -A "linear decay slope" in the decay model, which seems to hint at zero order kinetics, which seems to hint that maybe we should look into this further. That's all I want to clue my supervisor in to. Yanping Nora Soong (talk) 17:31, 11 March 2016 (UTC)

GNU Octave is a free alternative to MATLAB, incidentally. Tevildo (talk) 21:47, 12 March 2016 (UTC)

Our immunoassay is a mix of several reagents, all of which are needed to work for the IgM antibody of the particular virus we're working on to be detected. (We also use calibration standards). Thus, if they decay at different rates, this would explain the heterogeneous decay profiles. Modelling this is not the issue. It is not wanted. However, if there is zero-order kinetics going on, I'd (hopefully we at some point) definitely like to address that, because eliminating or mitigating this destructive catalytic surface, whatever it is (it could be one of our own reagents) could help shelf life. Yanping Nora Soong (talk) 17:42, 11 March 2016 (UTC)

I looked at the fit of the curves before I judged them. The power law fit was definitely worse. 0.97 was a very generous R^2 value for it considering that I would have judged it to be 0.85 or lower. The exponential decay fit was basically ignoring a huge part of the data. Let's talk about the error here: the error in the logarithmic fit is several dozen times less than the power law fit or the exponential fit. — Preceding unsigned comment added by Yanping Nora Soong (talk • contribs) 17:27, 11 March 2016 (UTC)

You have to be careful with the r^2 values. You can't just convert the hypothesized function to a linear function, do the linear regression, and calculate r^2 values - that gives misleading results. Bubba73 ^{You talkin' to me?} 02:39, 12 March 2016 (UTC)

Hmmmm. Let me see if I have this straight. First order kinetics implies a rate constant of -A, which is multiplied by the concentration of the reagent, i.e. an exponential decay with a half-life, total rate written in the form of -A e^-kt. Zero order kinetics implies a rate of -A, which is not multiplied by the concentration of the reagent. Your observation implies the overall rate of decay is -A/t, and the concentration of product (by which I mean reactant...) is -A * ln(t) + B, so the "coefficient" assuming first-order kinetics would be -A/t divided by this, i.e. -A/(-A * t * ln(t) + B * t), or 1 / (t * ln(t) + C * t) where C = B/A. Question: would it make sense to look at second-order kinetics? What if the fluorophore interacts with itself, for a rate of -A times the concentration squared... sigh, but what's the concentration? Our article says that these reactions have "a half-life that doubles when the concentration falls by half" - that makes sense. There are some graphs here. My guess is that the second-order kinetics comes close to a logarithmic decay than first-order, and you already didn't have numbers that much worse for first order, so... Well, anyway, I'm not very confident of what I'm saying here, so I better cap my pen at this point. Wnt (talk) 05:03, 12 March 2016 (UTC)

Free energy "model" as mathematical (formulaic) inspiration

It occurs to me there is another class of physical equations that uses the logarithmic decay profile -- e.g. the Gibbs free energy equation in relation to the equilibrium constant. The Gibbs free energy is allowed to be negative and the equilibrium constant is allowed to go to infinity. Except I'm trying to figure out how this would apply to my problem, since the variables with the Gibbs free energy equation uses temperature, not time.

Also this is product development -- we're not trying to develop a rigorous academic theory, we're just trying to fix some problems with shelf life and develop a working model. If we can help our customers (hospitals, hospices, etc.) keep our product 3-4 months longer, that will help us sell more product and that will also help them too. A working model -- to diagnose chemical decay -- is all we need. Yanping Nora Soong (talk) 17:10, 11 March 2016 (UTC)

• Free energy equation: dG = -RT ln K
• Enthalpy form: dH = -RT ln K + TdS
• My equation: P = -A ln(t) + B

So in this case, we can draw a similarity between the constant RT and my "A" constant, and "TdS" and my "B" constant, and "dH" and my amount of product at any one moment. And the equilibrium constant variable somehow shares a mathematical similarity with my time variable. I'm really confused and I don't know if the mathematical similarity is superficial here. Yanping Nora Soong (talk) 17:23, 11 March 2016 (UTC)

Two comments. First, there is no substantive difference between an R² of 0.93 and one of 0.99. They are both extremely good fits, and cannot be used to legitimately choose between models. In fact, an R² of 0.99 essentially never occurs unless there's a model misspecification causing the independent variable to be tautologically equivalent (or almost so) to the dependent variable. So if I were you I would look to see whether the way you've entered the data leads to the estimation of a tautology rather than a predictive relationship.

Second, time t is measured on an interval scale and not a ratio scale; taking the logarithm of the independent variable assumes it is on a ratio scale. That is, the choice of a value for the initial time period is arbitrary; instead of calling it t=0, you could have called it t=1 or t=837 or whatever. In a valid specification an arbitrary choice like that would have exactly no effect on the fit. But with the log specification, it will affect the fit. Loraof (talk) 17:48, 11 March 2016 (UTC)

Two reagent model, one decomposing the other

So here's a thought experiment. Say the luminscent (AE ester) reagent is decomposing zero order, on the surface of one the other reagents, probably solid phase reagent S, which is decomposing more slowly.

Thus, the AE ester, which we call E, is proportional to the amount of the exposed surface of the solid phase reagent S, [E]' = -k1[S]. But S is decomposing first order, through the equation we all know y' = -k2y. Thus ln [S] = -k2t + C.

But then [E]' = -k1[S] = -k1 e^(k2t + C) = -k1 Ce^(k2t), thus E would be described by the equation E = -k1*t * Ce^(k2t). This is not the equation I get, which is E = -k ln(t) + B

Are there any good alternatives? I'm really trying hard here.

Yanping Nora Soong (talk) 18:15, 11 March 2016 (UTC)

Well, you've now answered one of you bolded questions above: log decay is not indicative of partial zero-order decay kinetics. Consider that lots of things will fit better than the log model. Our problem in model selection, contrary to common misunderstanding, is not to simply maximize R^2 or some other notion of goodness of fit. That is actually really easy, all you need to do is throw more parameters at it and presto, your goodness of fit increases! Rather, our goal in model selection is explain things reasonably well and for the right reasons. In this manner, we can hope to learn something about cases that we cannot directly test, extrapolate, and possibly even reveal mechanisms. In this light, the Gibbs free energy thing is just wacky. Why would that have anything to do with this? I mean maybe it does but if so, you haven't explained it, and I think you're just looking for logs. The second approach is much more sensible. That is a good way to go about this: you've now shown what it would look like with two species, one with zero-order decay and one with first order decay. What would it look like if you had three species with zero, first, and second order decay kinetics? What about four? How well can those models be tuned to fit? These are more systematic approaches to your problem. As it stands, I think you're far too vested in that one log fit, which I think all of us here are telling you is probably a red herring. If you just want an better family of functions that won't give you nonsensical answers, look at the Weibull distribution I linked before. That's not mechanistic either, but it will almost certainly be less wrong. SemanticMantis (talk) 21:03, 11 March 2016 (UTC)

Because your probe is fluorescent, there's all sorts of weird possibilities involving quenching (fluorescence). Self-quenching, background phosphorescence that might activate and destabilize the fluorophore via FRET, etc. Self-quenching involves the fluorophore colliding with itself, which is why I mentioned second-order kinetics above. I haven't really investigated these things, but you might find a mathematical model for them with some research (not here or here really) - honestly, just search self-quenching fluorescence or something and from your work on this you'll probably recognize the useful hits better than I can. Note from the second reference how strong these effects can be - you can literally get more fluorescence from something labelled with fewer fluorophores because of some type of self-interaction. Wnt (talk) 10:57, 13 March 2016 (UTC)

March 12

Interrupted Dreams

Sometimes Im having a really good dream, then I have to get up and go to the toilet. When I get back to bed, I cant get back into my dream. Why is this?--31.109.183.147 (talk) 02:07, 12 March 2016 (UTC)

Lucid dreaming is the process of being aware of your dreams as they happen and potentially controlling their content. If you could remember your dream, maybe by writing it down immediately, then perhaps you could get back into it. StuRat (talk) 03:52, 12 March 2016 (UTC)

As a person who occasionally experiences lucid dreaming, though, I have this advice to give you: lucid dreaming is NOT restful, in fact when you wake up from a lucid dream you might feel like you didn't get any sleep at all. 2601:646:8E01:515D:5537:81A4:208D:1E74 (talk) 11:45, 12 March 2016 (UTC)

I have absolutely know of no source besides our articles already linked, as well ass the main one, dream. But my experience is that if I actually have to get up out of bed, negotiate my way to the toilet, make the proper motions, wipe, and flush, then get back to bed, the "train of thought" is gone. Whereas if I wake up and roll over and go back to sleep, it is much more likely the dream will continue.

As for lucid dreaming, with me it usually only occurs in unpleasant dreams, where I can tell myself "this is a dream" and the direction of the dream will become less troubling (e.g., I am being chased through a building by a bear > I am walking through a natural history museum) but I still can't actively choose the direction or outcome. μηδείς (talk) 17:47, 12 March 2016 (UTC)

I didn't read our article, but the area of lucid dreaming actually is likely helpful to your question. In particular, the obvious question in response to your question is "how do you know?" This isn't being facetious but is actually an important issue that Sturat has hinted at above. Are you sure you're remembering exactly what you dreamed after you went back to bed? Unless there's something really unusual about your sleep and dreaming, if you have enough experience and knowledge about how dreaming works, you probably recognise it's quite likely there are many more dreams than you remember. (Notably it seems you're a lot less likely to remember your dream if you don't wake up soom after or when it's happening.) And even for those few dreams you do remember when waking up, unless you write them down or try very very hard to remember them long term, you probably won't. And in fact, you can even be sure if you memory of what you dreamed is correct. In other words, it's difficult for you to be sure your dream didn't continue since maybe it did you just don't remember it happening particularly if you slept for a while afterwards. And even if you by some magic do remember all the dreams you had after you went back to sleep, you'd need the same magic or some other method (like writing it down which unfortunately may either help or disrupt you dreaming the same thing) to be sure you're remembering the first dream you're trying to get back to. Again I didn't read our particular article but I know lucid dreaming does deal with this memory problem and suggestions as to how those who want to experience lucid dreaming should deal with it. Nil Einne (talk) 18:11, 12 March 2016 (UTC)

To come at this from the opposite way: on a number of occasions I've woken up remembering a dream that took place in a non-real location, and with the definite impression that I've dreamt of being in the same dreamed locale before. However, that impression might actually be only a part of the dream I've just had. (Keeping a Dream diary might be a way of obtaining proof of such recurrences, but I choose not to do that.)

I suspect that such dreamed impressions might be common: for example, H. P. Lovecraft wrote stories utilising the idea of voluntary return to a dreamed location, the Dream Cycle.

I myself have on several occasions been able to return to and continue a dream, but usually when deliberately daydreaming during the day rather than when in bed at night. This doubtless borders on the lucid dreaming mentioned by others above.

I fully sympathise with the OP in his frustration at being unable to return to an interesting 'immersive drama'. I suspect quite a few fiction writers began by continuing such 'unfinished stories' in writing. {The poster formerly known as 87.81.230.195} 5.66.243.108 (talk) 23:27, 12 March 2016 (UTC)

This is pure anecdote, but while almost all my dreaming follows the same pattern as the OP (i.e. once you wake, you can never continue it), I have on occasion only half-woken up, remained groggy for a few minutes, and then gone back to sleep and either continued the dream or repeated it. I have even on one occasion continued dreaming despite waking up otherwise fully. Iapetus (talk) 21:24, 13 March 2016 (UTC)

Does any one know?

Hi friends ,where i can get a carbon-ceramic matrix,air interface film coefficient.i want to use it to solve one disk brake static thermal simulation.please guide me 112.133.223.2 (talk) —Preceding undated comment added 08:33, 12 March 2016 (UTC)

You made that up all by yourself :D? --Kharon (talk) 13:03, 12 March 2016 (UTC)

See Heat transfer coefficient for our article. Unlike the thermal conductivity, the heat transfer coefficient isn't a property of the materials, but depends on the geometry of the system and the characteristics of the airflow. Tevildo (talk) 14:11, 12 March 2016 (UTC)

Wind mill blades efficiency

How is the most efficient number of blades determined. I can read that 3 blades is the 'most efficient' for fans, what about windmills or propellers? Is it as simple as 3 blades is 'usually most efficient (moves the most air), or are there other factors? Thanks if you can help? — Preceding unsigned comment added by 94.210.130.103 (talk) 11:52, 12 March 2016 (UTC)

Old-fashioned windmills - for grinding corn - generally had an even number of blades for balance. If one was damaged and had to be removed, the opposite one could also be removed and the mill operate temporarily with just two. If you had three blades, and lost one of them, it was unbalanced and useless. 109.150.174.93 (talk) 12:41, 12 March 2016 (UTC)

Ofcourse there are other important factors like material-, production-, assembly- and maintenance-costs. In Engeneering the approach is often not from perks like "moves most air" or "generates most energy" but instead if one additional blade is worth its investment, efford and potential trouble. --Kharon (talk) 13:00, 12 March 2016 (UTC)

It is not just about efficiency, but practicality that determines the number of blade. All engineering is an assemblage of compromises. Take a wind turbine. A single bade has the utmost efficacy of capturing the energy from the wind and it requires the least amount of material in its construction. Yet the strains on the tower and bearings etc, take there toll – requiring more costly maintenance. Two bladed turbines have better balance but create a resonances in the supporting tower. Three bladed mitigate much this, but cost more... yet have a longer life span. So at present, it appears that three bladed wind turbines demonstrate the best compromise, which in the long run produces cheaper megawatts over the economic lifespan of the turbine, compared to other configurations. P.S. More blades does not mean the more capture of available wind energy.--Aspro (talk) 13:33, 12 March 2016 (UTC)

We have Wind turbine design#Blade count although it's largely unsourced. Nil Einne (talk) 14:33, 12 March 2016 (UTC)

Another factor is that with more blades, each can be lighter, making it easier to handle. StuRat (talk) 15:48, 12 March 2016 (UTC)

It's a matter of defining "efficiency" since it depends on what you're trying to efficsh. In engineering, you can be trying to minimize various things such as weight or maintenance cost, thus narrowly defining "efficiency". In economics, you add up all the costs, because cost is what you're trying to minimize, which makes the question, "What is cheapest?" Jim.henderson (talk)

User:Jim.henderson is exactly correct. The optimal thermodynamic efficiency might not provide the optimal economic value proposition.

If we want to formalize this problem so that we can apply engineering methods to find the most efficient solution, we must define a cost function that meaningfully accounts for all of our subjective ideas about what makes the system "better." The cost function can be a composite of all sorts of diverse items, like material use, energy cost, dollar value, risk, and so on. Defining that cost function is typically the most difficult part of the problem: it requires deep understanding of many totally different disciplines, and requires an ability to turn fuzzy subjective ideas into quantitative decisions. These kinds of problems are formally studied as industrial engineering, process optimization, and related disciplines.

If all you care about is thermodynamic efficiency, we can direct you toward some great books on wind turbine design. Start here: How do wind turbines work? from the Department of Energy. At a high-school science level, we can say that more blades are more efficient at harnessing energy, but only if there is a lot of wind; more blades are heavier, so if the wind is slow, the extra efficiency isn't enough to make up for the extra weight. From there forward, additional detail requires a very abrupt transition into some really hard problems in fluid mechanics and statistics. We have an article on wind turbine design, §blade count; but if you want the real math, you'll have to grab one of the books listed in our section on "Further Reading."

Nimur (talk) 17:38, 12 March 2016 (UTC)

Single blade propellers are the most efficient, by the usual definition, but they have a lousy power density. In the case of wind the incoming energy is 'free' so the usual definition of efficiency is misleading, your goal is to extract the optimum energy from the windstream, taking many other factors into account. Greglocock (talk) 22:12, 12 March 2016 (UTC)

You just need one blade for harvesting energy to produce electricity. But wind turbine designs are not just about the energy efficiency. Llaanngg (talk) 22:38, 12 March 2016 (UTC)

It's a trade-off between the number of blades and the height of the tower. If you have a lot of short blades, you have a complicated and fault-prone hub - if you have fewer blades then they have to be longer and that means building a taller tower. SteveBaker (talk) 03:42, 14 March 2016 (UTC)

Eczema herpeticum

What is the mechanism by which herpes and eczema can interact to cause a systemic infection? Surely, if a localised area of eczema was infected with herpes, the infection would only remain there. 82.132.212.108 (talk) 12:42, 12 March 2016 (UTC)

STDs and alcohol

It's often argued that sex involving alcohol is more likely to transmit stds because it causes poor judgement, people are less likely to use condoms and it's More likely to be casual but could it also be argued that alcohol weakens the immune system hence increasing std transmission risk? 2A02:C7D:B907:6D00:8911:F3BA:77F4:29CB (talk) 13:34, 12 March 2016 (UTC)

Not an answer to the question
The following discussion has been closed. Please do not modify it.
Dear anonymous. It could be argued that alcohol weakens the immune system. However, lets stick to the most likely. Loss of judgement due to alcohol. The effects Ecstasy and Cannabis appear to have a more lovey effect on couples, who will tend to seek out any contraceptive barriers that may be readily available in respect of their lovey feelings toward each other. Alcohol has the thumbs down. Maybe this is because because alcohol depresses the outer cortex of the brain wherein our higher intellect is situated. Cannabis and ecstasy enhances it. The instance of STD has been coming down in resent year. Do you think that that is because teenagers have all of a sudden changes their ways?! Drink a bottle of Bourbon every day, for long enough and ones immune system may suffer but a teenagers metabolism appear not to get get going until a half bottle has entered the blood stream. The cheaper option to alcohol these days, is illicit drugs and politician should wise-up and rationalize the drug laws so that all drugs are properly controlled. --Aspro (talk) 14:09, 12 March 2016 (UTC) I'm hatting this. Your text has nothing to do with the question asked and is mere proselytizing. Take it elsewhere. Matt Deres (talk) 17:54, 12 March 2016 (UTC)

Our article at immunosuppressive drug and immunosuppression do not mention alcohol, but this piece by the NIH says "In both males and females, alcohol exposure suppresses immune responses..." and "An overwhelming amount of evidence reveals that both acute and chronic alcohol exposure suppresses all branches of the immune system, including early responses to infection and the tumor surveillance system..." with several links and citations. Matt Deres (talk) 18:02, 12 March 2016 (UTC)

C4H10O

Hey,

I try to answer for this question:

$A{\xrightarrow {E}}B{\xrightarrow {F}}C{\xrightarrow {HClorZnCl_{2}}}D$

A is an isomer of C4H10O.

Find A, B, C ,D, E, F.

I know that C most be alcohol & I also find 4 isomers of C4H10O but not sure how should I find solution to this problem.

thanks. — Preceding unsigned comment added by 31.210.177.225 (talk) 15:06, 12 March 2016 (UTC)

Think of a structure (or maybe several possible ones) of what C could be (you say you know it's an alcohol--not sure how you know this, but assuming it's true...); there are only a few isomers of 4-carbon chemicals that have that functional group). If that is C, what would the structure of D be? Note that not all alcohols react with HCl. So now you have some ideas for A and some ideas for C, you just need to figure out some intermediate that looks like the partial conversion. For example, if A has the OH on C2 and B has the OH on C1 instead, what are ways you know to get "OH on a primary position" and what are ways you know "to get OH off a secondary position"? Or pick an isomer you think A could be and list all the things you can make from it in one step (various E/B possibilities). Which, if any, of those B can you transform by one step into any of your C possibilities (the F method). That is, either work forwards-and-backwards and find the middle, or work from one end and see how close you can get to the other. DMacks (talk) 15:21, 12 March 2016 (UTC)

I know it because I learned that only alcohol reaction with HCl and Z_nCl...it seems to be so hard...I don't know. I will ask my teacher on Monday. Best.

I fixed the formula and spelling for zinc chloride. DMacks (talk) 18:10, 12 March 2016 (UTC)

I want to make this comprehensible, besides I'm getting rusty on my own chemistry... a quick search for alcohol "zinc chloride" gets this helpful demonstration [12] (well, I can't view the video but the text tells me a classroom exercise) There they use 1-butanol, 2-butanol, 2-methyl-2-propanol. (Note butane = 4 carbons with 2 H per carbon plus two more on the ends = C4H10, and 1- or 2- butanol adds an oxygen under one of the hydrogens. 2-methyl-2-propanol has three CH3s and an OH linked to a central carbon, again C4H10) Anyway, the tertiary alcohol in the demonstration reacts immediately; the secondary alcohol reacts after 6.4 minutes, and the primary alcohol doesn't react. So we know that C is the secondary or tertiary alcohol. Now D, we are told, is the alkyl chloride produced by an SN1 reaction from whichever C is. That leaves us to riddle out what isomerizations you can do to C4H10 in two steps to end up with one of these... Wnt (talk) 16:35, 12 March 2016 (UTC)

Now that we know ZnCl₂ is an alternative for HCl, it makes sense to assume that C would be an alcohol. With only "HCl" as the original question, it could easily have been alkene or alkyne, etc. Lucas' reagent is a great demonstration of the reaction of (and reactivity difference among) various alcohols that Wnt notes. There's one more isomer of the original than the three already mentioned (but 4 is not a lot of choices anyway). Note that there are several possible answers I see, even restricting the range of reactions to SN1/SN2/E1/E2 and simple reactions of alkenes. That sounds like how much you have covered so far in your class?--knowing "what you know" would help us keep from steering you into reaction topics you have not yet learned. DMacks (talk) 18:10, 12 March 2016 (UTC)

Did the question actually say "HCl or ZnCl2"? Or did it say "HCl/ZnCl2"? The second would mean HCl and ZnCl2, i.e. Lucas reagent. I don't know what to do if it's the first. Wnt (talk) 21:24, 12 March 2016 (UTC)

March 13

Hand-thrown projectiles

Both cricket balls and baseball balls are quite similar in size and weight (about 5 ounces) whereas modern hand grenades can be as much as three times heavier (1 pound in the case of the M67). In the case of the balls controlability/accuracy and velocity seem to be the criteria that are emphasized, wheras hand grenades need to be light enough to throw far enough so as not to endanger the thrower but also heavy enough to be an effective weapon, a grenade with a too small explosive payload will not do worthwhile damage to the target. Accuracy is of course also an important criterion. From many news media images it seems that stones used by rioters tend to range from fist sized up to about half a brick (BTW have people who design police helmets and shields studied this topic?).

If maximum range is the main objective, is it possible to figure out in terms of human anatomy/physiology/ergonomics an optimum size/weight for a hand-thrown projectile? Roger (Dodger67) (talk) 09:21, 13 March 2016 (UTC)

There must be some literature on shot - putting and discus - throwing. Discus is an Olympic sport and maybe the other is as well. 5.150.93.133 (talk) 12:03, 13 March 2016 (UTC)

Do javelins count? The world record (before a redesign in 1986 reset the standard) would appear to be 104.8m. Rojomoke (talk) 12:18, 13 March 2016 (UTC)

Good point! When I formulated the question I quite forgot about the shape of the projectile as a factor, and of course aerodynamics is important. Are there any reliable records for distances that baseball or cricket balls have been thrown? Roger (Dodger67) (talk) 12:46, 13 March 2016 (UTC)

When I Googled the term farthest thrown baseball, it pointed me to our article at Glen Gorbous. With a six-step running start, he managed 135 m (445 feet). When I Googled the term farthest thrown cricket ball, the results point to a YouTube video claiming 132 m, so essentially the same as a baseball. When I Googled the term farthest thrown object, it pointed me to the Aerobie. If you're interested, you can perform similar searches here by using the same sort of terms as I did. Matt Deres (talk) 13:07, 13 March 2016 (UTC)

This question from last year has some useful references. The Aerobie record was beaten in 2005 with a traditional boomerang (472.2 m), but I'm not sure that such devices count as "projectiles". The 132 m figure for a cricket ball was obtained by Roald Bradstock (a javelin thrower), who claims a large number of (unofficial) distance throwing records. Tevildo (talk) 13:49, 13 March 2016 (UTC)

I'm quite surprised that the ball records are so much further than the javelin. I think we should discount objects such as the aerobie, boomerang, frisbee, etc. because they rely on aerodynamic lift and fly like aircraft, rather than a ballistic trajectory. I found a claimed golf ball throw of 170 yards, by Roald Bradstock - https://recordsetter.com/world-record/world-record-for-throwing-golf-ball/7349 -- Roger (Dodger67) (talk) 13:53, 13 March 2016 (UTC)

The farthest discus throw is 74 m (81 yards),[13] so the discus is clearly far heavier than whatever the ideal weight is. --Guy Macon (talk) 20:37, 13 March 2016 (UTC)

Yes, it has been figure out in terms of human anatomy/physiology/ergonomics. See :The accuracy of throwing hand grenades. as a function of their weight, shape and size. However, this was done back in the early 1970's and considering the modern US diet, general health an life expediency is now falling behind other countries in the last 45 years, these figure may need to be readjusted down by an ounce or so.--Aspro (talk) 13:24, 13 March 2016 (UTC)

Thanks Aspro, that's an interesting article. Roger (Dodger67) (talk) 13:56, 13 March 2016 (UTC)

Don't let the creamy center of the general population fool you, though. Athletes, soldiers and regular people who just want to throw things as far as they can have much more in the way of sport science and fancy supplements (many of which are perfectly legal) than their grandparents did in the "milk, steak and barbells" day. It's just the middle class of moderately fit, moderately busy folk that's shrinking. Readjust up an ounce or so, I say. InedibleHulk (talk) 09:51, March 14, 2016 (UTC)

Note that hand-thrown objects can go faster and farther if a longer lever arm is used, in the form of an "atlatl", in the case of spears and darts, or a "cesta", in the case of a jai alai ball. A bow and arrow also uses only human muscle to propel the projectile, but differs in that the energy is put into the system when the bow is strung and pulled back, not when released. A crossbow/ballista goes even further, when a crank is used to pull it back, and a catapult/trebuchet extends the concept by using many people to pull back on the bent board or lift a counter-weight into position, to arm the device. StuRat (talk) 18:56, 13 March 2016 (UTC)

That's why the World War II era German grenades were mounted on a stick to allow the heavy end get up some decent momentum before being released. SteveBaker (talk) 03:37, 14 March 2016 (UTC)

The Islamic Penal Code of Iran gave a handy guide to the dimensions of stones to throw in lapidations: The size of the stone used in stoning shall not be too large to kill the convict by one or two throws and at the same time shall not be too small to be called a stone. AllBestFaith (talk) 19:46, 13 March 2016 (UTC)

How can a stone be "too large to kill in one or two throws", unless they mean it can't be lifted and thrown at all ? StuRat (talk) 20:15, 13 March 2016 (UTC)

I think you've misunderstood Amnesty International's? English translation of the rule. It seems clear if you take the whole paragraph that what it means is that the stone should not be too large, such that it will kill a person in one or two throws. And should not be too small such that it would not be could a stone. (Both of these are easily debatable definition at the borderline but what they are trying to say doesn't seem that hard to understand. They want a stone that is big enough such that it will be called a stone. But which is small enough such that it's unlikely to kill a person with one or two throws.) Nil Einne (talk) 20:37, 13 March 2016 (UTC)

Yes. The thinking behind Islamic Hudud stoning is that no individual executioner can be identified, rendering it impossible for the victim's heirs to demand compensation (see Diyya) or demand death of the killer (see Qisas). AllBestFaith (talk) 21:44, 13 March 2016 (UTC)

Interesting question! stackexchange has a similar question. The Quixotic Potato (talk) 01:38, 14 March 2016 (UTC)

Did technical methods - technical levels of application and use are been determined a physical and chemical properties of all substances?

Did the maximum temperature of the burning – flaming of substances as also and the maximum heat capacity of substances are always been depended on the technical methods – technical levels of application and use of these substances?--83.237.192.54 (talk) 11:50, 13 March 2016 (UTC)

Did all are always been depended on the levels of complexity of technique? (Did the levels of complexity of technique are always been decided all)?--83.237.192.54 (talk) 11:50, 13 March 2016 (UTC)

How it (did) been in respect of electricity and gases in particular of natural and inert gases, if work body of any electricity did always been a electromagnetism and work body of all gases did always been a pressure?--85.141.237.179 (talk) 15:54, 13 March 2016 (UTC)

It is well known that electromagnetism of all gases including natural and inert gases is always considerably small irrespective of the valence of these gases, especially in comparison with electromagnetism of electricity, is it right?--85.141.237.179 (talk) 16:25, 13 March 2016 (UTC)

One possible reason why your questions are not being answered may be that we don't understand them. Try writing them in Russian and then machine-translating them. Robert McClenon (talk) 01:32, 14 March 2016 (UTC)

I believe that may be what they are doing. The Russian Wikipedia has a combination RefDesk/Help Desk here. I would suggest the user try asking their questions there. Matt Deres (talk) 02:26, 14 March 2016 (UTC)

In total, did a natural gases as also and all gases really always had a small technogenesis than always had electricity?--83.237.198.62 (talk) 10:26, 14 March 2016 (UTC)

Distance updates due to expansion of the Universe

Due to constant changes in galaxies' distances from Earth amid Universe's expansion and redshift, is it neccessary to specify the date of measurement each time it's mentioned? Something like "1 billion light years from Earth as of March 13, 2016". Why academic sources don't specify that and do not seem to update the distances? Thanks. 93.174.25.12 (talk) 19:21, 13 March 2016 (UTC)

The rate of expansion of the Universe is estimated to be between 60 and 80 (km/s)/Mpc and does not add significantly to the error in recent distance estimates. The value of the Hubble constant is estimated by measuring the redshift of distant galaxies and then determining the distances to the same galaxies (by some other method than Hubble's law). AllBestFaith (talk) 20:03, 13 March 2016 (UTC)

Agreed. It would be a bit like saying the distance from New York City to London varies with the date, due to plate tectonics. It does, of course, but the amount is insignificant unless you look at it over very long time frames, like millions of years. StuRat (talk) 20:13, 13 March 2016 (UTC)

I am reminded of the joke that goes along the lines of: a janitor at a museum is told a dinosaur fossil is 100 million years old, and a week later he excitedly tells visitors that the fossil is 100 million years and a week old. --71.119.131.184 (talk) 23:44, 13 March 2016 (UTC)

That's a lot like the old joke where a teacher is telling children visiting an observatory that the temperature at the heart of the sun is "millions of degrees"...but forgets whether that's centigrade or fahrenheit. A crusty old physics professor who's listening at the back clears his throat loudly and says "Kelvin". SteveBaker (talk) 03:31, 14 March 2016 (UTC)

Would it be possible to have a SEM at home?

Ok, just because I'm curious. Would it be possible to have a scanning electronic microscope at home (regardless of price and space)? I think there would be some problems due to electric energy consumption and/or preparation of specimens.--Carnby (talk) 20:31, 13 March 2016 (UTC)

I took a glance at a few SEM manuals, and they seem to take normal house phase/voltage at a few tens of amps. DMacks (talk) 20:56, 13 March 2016 (UTC)

See the article Scanning electron microscope. The equipment is advanced for a home installation since it includes a vacuum chamber, high voltage supplies and a dedicated display. Biological specimens that are non-conductive usually need to be prepared with a conductive coating, e.g. of sputter coated metal. This video explains the basics. AllBestFaith (talk) 21:29, 13 March 2016 (UTC)

If your pockets are deep enough, sure, you should be able to use a SEM at home. If DMacks is right, power shouldn't be a problem, and even if it is, I'm sure it would be possible to buy an external generator.

As for specimens, that really depends on what you want to look at. If it's conductive, then you can look at it easily. If not, then it's trickier. Poorly conductive samples can be looked at briefly, but will quickly charge up and become invisible. Sputtering generally requires some serious equipment, so sputter-coating may be difficult to do at home. Then again, a quick search reveals that people have actually made sputtering machines at home, so I guess even that is not out of the question.

In any case, you'll generally want to put a SEM in a very clean environment. If you have a spare room to put it in, you should consider installing additional air filtering and adopting basic cleanroom protocols (a gray room to put on a cleanroom suit already goes a long way), though you that's not really a requirement. Whatever you do, always wear fresh disposable gloves when interacting with the sample chamber. I had to use a SEM that wasn't located in a cleanroom, and one of the big issues was carbon deposition. Any number of sources can contaminate your sample chamber with carbon, and it will get attracted to the areas of the sample you're looking at (especially at high beam intensities/high magnification). It's really annoying to see your sample turn black in a matter of seconds! You can mitigate that to some extent by keeping everything really clean.

Another major problem you might face in a home setting is vibration. That's no biggie at low magnifications, but if you want to image structures of tens of nanometres, it'll ruin your day. If possible, try to have some separation between your SEM and its vacuum system; the pumps introduce a lot of vibration. If you live near a busy road, vibrations from traffic may even be a problem. --Link ^(t•c•m) 21:53, 13 March 2016 (UTC)

Would think that a industrial SEM would draw most current when pulling a vacuum – in order to reduce the waiting time. After that, a few hundred watts should be sufficient. I'm normally weary of thing that I see on Youtube but this feller claims to have built one. [ https://www.youtube.com/watch?v=VdjYVF4a6iU DIY Scanning Electron Microscope] At first I was doubtful that he could pull the necessary vacuum inside a bell jar but he goes onto explain he uses both a mechanical and diffusion pump. His apparatus looks clean (no sign of organic oils). For something like this one would need to thoroughly degrease and then depend upon silicon grease only. His solder joint appear clean of flux (any oversight like this can slow down degassing and pulling a hard vacuum). His electronic units are also housed in nice 19 inch racks. So in this case, I think he has indeed built a home SEM. As to your second question about preparing specimens. Inorganic materials etc., may not cause a problem but biological specimens can create all sorts of challenges. Yet, for any one with the know how to build a working home SEM, it should not be beyond their skill to use the same basic set up for physical vapor deposition. As for clean room - I'll send my wife around. Vibrations... 2 to 4 am is a vibration free time. - Don't know, what the current price for SEM images are today, but if one costs ones free time at xx dollars per hour, a lab may be able to do the job more cheaply than messing about building ones own – but hey – to have ones own SEM must be very satisfying. So in answer to your question: It is possible to have a scanning electronic microscope at home.--Aspro (talk) 22:26, 13 March 2016 (UTC)

Does woman can have an erection in her clitoris if she looked in men?

Does woman can have an erection in her clitoris if she looked in porn (without touching there), like what happens sometimes to men who watch porn? 93.126.95.68 (talk) 23:51, 13 March 2016 (UTC)

See Clitoral erection. Tevildo (talk) 23:54, 13 March 2016 (UTC)

When watching heterosexual erotic videos [14], men may be more likely than women to objectify the opposite-sex actor. There are reported differences in brain activation to graphic sexual stimuli, with men showing higher levels of amygdala and hypothalamic responses than women. AllBestFaith (talk) 00:58, 14 March 2016 (UTC)

According to 2013 research conducted at McGill University, both men and women become sexually aroused at similar rates when viewing sexually explicit videos. Cullen³²⁸ Let's discuss it 01:12, 14 March 2016 (UTC)