Wikipedia:Reference desk/Archives/Science/2009 May 31

= May 31 =

Determining the Concentration of a Solution
Hello. I want to find the concentration of a copper(II) sulfate solution, using the most accurate procedure. Should I evaporate all the solvent and water of hydration, measure the mass, and calculate the amount of anhydrous CuSO4? Or should I add magnesium until no more can react, filter the residue, dry it, measure the mass, and calculate the amount of copper deposit? If I choose to conduct a chemical change, I must consider percentage yield as a source of error. However, I cannot see anything wrong with a physical change. My teacher, who likes my physical change idea, on the other hand, is more comfortable with a chemical change but I do not know why. Thanks in advance. --Mayfare (talk) 00:24, 31 May 2009 (UTC)


 * The deal with the evaporation method is that evaporation at room temperature will likely only yield the hydrate; and the additional heat needed to produce the anhydrous salt could also cause some decomposition of the sulfate to the oxide + SO3 gas. Plus, the anhydrous salt is likely so hygroscopic that it may start to rehydrate too rapidly to get an accurate mass.  How is this for a third option: since Barium sulfate is both insoluble in water, and does not produce hydrate crystals like copper sulfate does, why not add excess BaCl2 or Ba(NO3)2 to the copper sulfate solution, filter the precipitate, and mass that?  What do you think of that one?  --Jayron32. talk . contribs  00:40, 31 May 2009 (UTC)


 * Maybe you could use an osmometer. --JWSurf (talk) 01:03, 31 May 2009 (UTC)
 * An osmometer can tell you the concentration of all solutes, so could be used, but only if it is certain that CuSO4 is the only solute (which is also true of the evaporation method). Gravimetric analysis was how we did this for first year undergraduate experiments - either by adding a solvent that precipitates the salt, or reacting it as in the question or Jayrons reply. Hydration of the solid is removed by drying for a longer period, and weighing the sample periodically (once the weight stabilises, it is assumed to be dry - drying temparatures are usually not high enough to cause reactions in stable salts). The question of the yield of any precipitating reaction is basically ignored by assuming 100% yield if an excess of reactant is used.YobMod 10:24, 31 May 2009 (UTC)


 * I think if you know that there's pretty much no other solute, you should just evaporate and measure the mass, without heating to dehydrate, then calculate the concentration from there. That way you don't have to worry about decomposing the solute. I think you can safely asume that the solute will be left fully hydrated if you evaporate it at room temperature. 209.148.195.177 (talk) 10:50, 31 May 2009 (UTC)

Particle interactions
While looking at Feynman diagrams, I noticed that all interactions between particles seem to fit into three categories: a vertex with two fermions and a boson, one with three bosons, and one with four bosons. Why are there no other possibilities? I don't think any laws of physics would be violated by a four-edge vertex where, say, a gluon and a quark interact to form a new gluon and quark (though the same thing could be accomplished by two successive interactions). However, there are three-Higgs and four-Higgs vertices. Why are Higgs bosons allowed to compress two steps into one, but quarks and gluons cannot? Why are there no five- or even six-Higgs interactions? Thanks, *Max* (talk) 04:44, 31 May 2009 (UTC).


 * This is an excellent question and the answer is a bit technical, so please bear with me. The best way to understand that is through dimensional analysis. This analysis is particularly easy to make if you chose units such that both the speed of light and the Planck's constant are adimensional $$c=\hbar=1\,$$ (no units). That choice leaves only one unit unspecified and that unit is usually chosen to be a unit of energy given in electronvolts (eV). With that choice of units the lagrangian density $$\mathcal{L}$$ has units eV$${}^4$$. Usually this is simply expressed by saying that the lagrangian ha dimension 4. Now if you look at the kinetic terms (the ones with partial derivatives of fields with respect to space-time coordinates) in the lagrangian you will find out that boson fields have dimension 1 while fermion fields have dimension 3/2. It is easy to see now that all the interaction terms present in the lagrangian have product of fields with total dimension 4 or less, while the hypothetical term you described with two quarks and two gluons would have dimension 5. That means that all the terms actually present in the lagrangian have coefficients attached to them with non-negative dimensions while the hypothetical term you described would have dimension -1. The rule of thumb is: no coefficients with negative dimension are allowed. Why? It turns out that these terms are non-renormalizable. A simple (if a bit too naive) way to understand that is to realize that those theories are actually effective (low energy) approximate theories for an (as yet unknown) theory and that the natural energy scale for the real theory is probabily around the grand unification energy scale (GUT) or higher. That effectively supresses those non-renormalizable terms by powers of $$\left[ \frac{M_{weak}}{M_{GUT}}\right]^n$$, where $$M_{weak}\sim 100 GeV\,$$is the weak scale (the scale of the effective theory), $$M_{GUT}\sim 10^{16} GeV \,$$ is the GUT scale and $$-n\,$$ is the dimension of the coefficient of the lagrangian. Those terms of the lagrangian become effectivelly negligible. Dauto (talk) 15:27, 31 May 2009 (UTC)


 * Thank you; your answer was very clear and helpful. *Max* (talk) 00:08, 1 June 2009 (UTC).

New islands found in aerial/satellite photos?
Have aerial or satellite photos ever revealed any previously undiscovered islands? Neon Merlin  05:47, 31 May 2009 (UTC)
 * Yes. Landsat Island is the only example of discovery by satellite photo. Plenty of islands were first revealed by aerial photograph, including, for example, numerous of the 30000 islands in Lake Huron. An aerial survey of the Georgian Bay Islands National Park area was carried out in the 1920s which "discovered" many new islands. Rockpock  e  t  06:19, 31 May 2009 (UTC)
 * Indonesians could only estimate how many islands their country has, of which 8,844 have been named and 922 are permanently inhabited, until a satellite survey in 2002 found they had 18,306 islands. Or are there more when the tide goes down? Cuddlyable3 (talk) 10:35, 31 May 2009 (UTC)

Relationship b/w focal length and magnification of a lens and of a mirror
This Question was given in our summer assignment. (OK, I know I am not supposed to ask homework question. But i have not been able to crack the question for 2 weeks!) What is the relationship b/w focal length and magnification of a lens and of a mirror? The mirror formula is 1/u + 1/v = 1/f and m = -v/u Putting v = -mu in mirror formula gives 1/u - 1/mu = 1/f or 1/u (1 - 1/m) = 1/f Now is m directly proportional to f or inversely proportional? (Same procedure can be done for lens formula) shanu 07:04, 31 May 2009 (UTC) —Preceding unsigned comment added by Rohit..god does not exist (talk • contribs)


 * As you yourself would have done, m = 1/(1-u*f). Now, looking at this relation, it is clear that m is neither directly proportional nor inversely, but if you plot this function, you can say that m always increases with f, but there is a discontinuity at f = 1/u. It goes to infinity from the left and starts off from minus infinity from the right. Similarly you can do an analysis for the lens formula. Rkr1991 (talk) 08:01, 31 May 2009 (UTC)

Basic advantage of hybrid cars
I don't understand how hybrid vehicles can make sense. Okay, from what I understand, 90% efficiency for the generator is pretty good, and so is 90% efficiency for the motor at converting electricity to mechanical energy. So your generator wastes about 10% of your energy, and your motor wastes another 10% just to get the engines mechanical energy converted/stored and returned into mechanical energy. Also, most early and current production models DO NOT take advantage of solar panels or plug-in as an extra source of electricity. So that leaves what, just regenerative braking to recover more than that 20% of the energy lost? What about highway driving, when regenerative breaking is not going to be used. Didn't some models not even include regenerative breaking? So where does the energy savings come from? It sounds like a bunch of converting the energy into different forms for no reason. Am I missing something here? Is there ANY source of electricity besides the engine/generator itself and regenerative breaking in the basic hybrid vehicle? I don't think popular models like the Prius and Insight come with any solar panels or plug-in options. How do they get better mileage? Just by comprimising power? If so, why not comprimise the power and still use just a gas engine? I have one possible explanation, but I'm not sure--does the electric part have a higher PEAK power, alowing the smaller engine to keep running at a steady power and the electric motor provide peak power? That doesn't work however if you need to sustain maximum power, such as when the car is loaded and climbing a mountain side or long hill at high speed. 209.148.195.177 (talk) 10:45, 31 May 2009 (UTC)


 * Actually, you hit upon one of the disadvantages of hybrids. Regenerative braking means that hybrids actually get BETTER milleage in stop-and-go driving than in highway driving.  If you live in a place where your commute consists mostly of freeway driving, then you will not get much advantage from a hybrid.  Basically, a hybrid gives its biggest advantage at the low end of the gas milleage range, bringing up what is the most inefficient part of one's driving.  They do nothing to raise the "high end" of the milleage range; except that they are usually small, light cars with small engines, so they tend to use less gas than say, a Ford Expedition might.  From an emissions point of view, hybrids are usually better than the average car regardless of what style of driving you do; but from an economic one, if you don't do lots of stop and go driving it will take a long time to recoved the added expense of buying a hybrid in terms of fuel savings.  --Jayron32. talk . contribs  12:04, 31 May 2009 (UTC)


 * This question has come up recently. See Steve Baker's answer here. Dauto (talk) 12:45, 31 May 2009 (UTC)


 * I'll cut/paste that reply here - because I need to expand upon it:


 * The reason the Prius hybrid saves energy is a three-way thing:
 * Gasoline powered engines work most efficiently at one particular speed - perhaps 3,000 rpm. If you push them harder than that - or less hard - then they need more gasoline per unit of energy they deliver.   With a normal car, the number of rpm's you need depends on what gear you are in and on what speed you are going - but it's only rarely turning the engine at the best speed.   In the Prius, the engine only ever runs at this perfect speed - and when the battery is fully charged, the engine shuts off and stays shut off until the battery drains down and needs a recharge.
 * When you push on the brake in a normal car, you are wasting the kinetic energy in the motion of the car to wear down the brake pads and heat up the disks. With a hybrid, the electric motors that normally power the wheels can be used 'backwards' as generators - so you slow the car down by (effectively) using the battery charger to extract energy from the car's motion.  Of course you need conventional brakes too - and this process doesn't work when the battery is already fully charged...but still, it makes some significant savings.  This is called 'regenerative braking'.
 * Because you don't need that peak power from the gasoline engine when you do a (rare) hard acceleration - you can have a smaller engine. The engine only has to be large enough to provide the AVERAGE amount of power the car needs - not the MAXIMUM amount.  Since you (mostly) don't go around accelerating hard all the time - this means that you have a smaller, lighter engine, more fuel-efficient engine - and let the battery provide the power for short bursts of speed.
 * Having said that, hybrid cars are not the perfect thing some would tell you. Most of the reason the Prius gets such good gas mileage is because it's super-streamlined, it's actually not a very fast car and it has relatively poor air-conditioning and such.  If you did all of those things to a conventional car - and DIDN'T have to carry around all of those heavy batteries - you can do just as good as the Prius.  The Prius actually gets rather poor miles per gallon on long freeway trips because in that case, the regenerative braking and the average-versus-peak thing doesn't work out too well - and pretty much any decent car, when driven in "overdrive" or topmost gear will have the engine running at it's most efficient rpm's.   Hence the Prius has no special advantages in that case.  However, for in-town stop/start driving, it works amazingly well.


 * Yep. Re-reading my earlier response (which was mostly about the Prius) - I should add that there are a lot of cars out there that SAY they are hybrids which really are not.  It's pretty safe to say that if the car's gasoline engine is driving the wheels - then it's not really a hybrid.  Some claims for being a hybrid include cars that use the electric power only to improve acceleration - and thereby allow a slightly smaller gasoline engine to be used.  They offer no benefits whatever to drivers who do not floor the gas pedal at every opportunity!


 * It's something of a mystery why the Prius doesn't come with a plug-in option. You can certainly buy these as after-market options though - and I'm told that they work amazingly well.


 * Solar panels mounted on the roof of the car are useless. The amount of energy a solar panel can produce is so tiny that you'd be hardly able to drive a mile after a whole day of charging.  The weight and cost of the panels simply don't make it worth-while.  Moreover - if you wanted solar panels for charging your car - why not leave them at home next to your garage - use them to charge a battery - then recharge your car from the battery?  That way you don't have to carry the weight around with you all the time.  No - solar panels are quite utterly useless for car - worse than useless in fact.


 * The Prius (and presumably Insight too) does indeed suffer badly if you are doing long freeway trips. The battery needs to be continuously recharged - so the gasoline engine runs all the time - and what you have is a decidedly underpowered car that's wasting much of it's limited power in the losses involved with going to the wheels via a generator, battery and electric motor.  EPA estimates are wildly wrong for the Prius - and my 140mph 6.5 second 0-60 MINI Cooper'S gets better practical freeway miles than the Prius.  On long uphill sections, the car may actually limit your speed - I've heard stories of Prius owners who had been doing long freeway runs and then heading up a mountain finding that the car would slow down to 15mph - which is the fastest it's pathetic little gasoline engine can manage uphill and without a fully charged battery!


 * So we have to be careful. Hybrids are a useful way of getting better gas-engine mileage for in-city driving...but electric cars are better still at doing that.  Electric cars don't have the range you need for road-trips, however - and for that a gasoline engine is currently the only solution.  So hybrids are not just hybrid in the technology they use - but also hybrid in the range of applications they can cover.   Personally - I'd love to have a MINI-E (all-electric, 100 mile range, 110mph, blistering accelleration) for my daily commute - and an efficient ~40mpg gasoline-only car for road trips.  The technology for both is available...but trying to cram those two vehicles into one car seems like a relatively bad idea.


 * Incidentally - there are technologies out there to do regenerative braking using gasoline engines. The idea is that when you push on the brake pedal, the fuel supply and spark to the engine would be cut off and valve timing changed such that the pistons of the engine would be used to compress air and any remaining exhaust gasses into a high-pressure storage cylinder.  This would provide a kind of super-efficient "engine braking".  Then, when you need to accelerate again, the compressed gasses would be allowed back into the cylinders under high pressure to get the car moving again with no fuel being injected and no spark provided.  Once the tank is depleted, you start injecting fuel and sparking the plugs again - and the engine runs normally.  With this kind of technology, an efficient, modern gasoline engine could out-perform the Prius even in in-town driving situations.


 * SteveBaker (talk) 17:21, 31 May 2009 (UTC)
 * Well-said. One of the hardest things an automobile manufacturer can do is decide its product-lineup, though.  As Steve Baker points out, the optimal solution might well be two separate vehicles: a short range, super-efficient-for-city-driving minicar, and a long-range, high-mileage-on-freeways midsize or compact car.  However, designing and engineering these vehicles leaves out one important (and incredibly non-negligible) factor - these cars will compete with each other for sales!  Given that a market exists for economic, environmentally-friendly vehicles, an automobile manufacturer must estimate how many people will be able to purchase the cars in question.  Releasing two "eco-cars" will saturate the already small market, and neither car will hit sufficient production volumes to make the economies of scale that allow effective manufacturing.  No intelligent auto manufacturer will release multiple cars of the same type because it will drive them into bankruptcy.   For this reason, the successful hybrid cars are really a sub-optimal car like the Prius - which aims to combine the 80th percentile of the desired features for the 80th percentile of the expected market (or some other marketing-ese voodoo statistics).  These design requirements get kicked back to the poor engineers, who have to figure out how to make a 50 mpg engine fit on to a sleek-looking body, run quiet in heavy traffic, and still handle speed on the highways.  The result is sort of a slapped-together "hybrid", which makes some pretty severe tradeoffs as Steve mentioned above.  So, we have the Prius and the Volt and the Insight.  If your only goal is fuel-efficiency, you are probably best buying a diesel compact, which will darn well beat the Prius in true miles-per-gallon across a wider range of driving conditions (and won't be stumbling up those steep hills).  And lay off the jackrabbit starts - if you're an average driver, something like 10% of your gasoline is used while your car is going zero miles per hour, and 50 or 60% is used during acceleration - which means a piddling 20% of your fuel consumption is actually useful.  Changing your driving habits will save more fuel than changing your car.  Nimur (talk) 19:01, 31 May 2009 (UTC)


 * Well, BMW aren't stupid - and the all-electric MINI-E (if/when it becomes a mainstream product) will certainly be produced alongside the normal 40mpg gas-powered MINI and the diesel MINI/One-D - and all three cars are otherwise pretty much identical (except the electric version is a two-seater - the back seat area being basically full of batteries).


 * Diesel cars are also a very good thing - and they're very popular in Europe. But the legal issues surrounding the amount of sulphur in diesel fuels prevents the good ones such as the Golf and MINI/One-D from making it into the USA.


 * That's one of those bloody stupid regulations where the amount of pollutants coming out of the tailpipe is measured as a percentage of the total exhaust gasses. The consequence of which is that a car that burns more gas and produces more pollutants is permitted when one that burns a LOT less gas and produces a little less pollutants is not!  These kinds of dumb laws are in severe need of re-thinking.  SteveBaker (talk) 20:04, 31 May 2009 (UTC)
 * That's because politicians are rarely scientists or engineers. If we had informed decision-makers, we wouldn't have that situation.  The diesel issue in particular is very frustrating - diesel is easier and cheaper and more environmentally friendly to produce than gasoline.  It has better mile-per-gallon and ton-per-gallon characteristics.  The latter is not brought up nearly enough - it's easy to get a lot of miles-per-gallon by making a very small vehicle, but most of our transportation fuel is consumed by commercial trucking - where the vehicle weight is almost negligible compared to the cargo weight.  Fortunately, most trucks do run on diesel - and if the rest of the automobile drivers realized how much of a cost-savings this is, we would dramatically reduce our emissions and fossil-fuel consumption.  Nimur (talk) 21:02, 31 May 2009 (UTC)


 * I'm not sure that the amount of energy you'd get from solar is as completely insignificant as Steve suggests. Our article on solar car suggests that it's not unreasonable to get 2kw from car-mounted solar panels. According to the electric car article the EV1 consumes 2.7kwh for the equivalent of a liter of gas.  Granted, a liter is not a lot of gas. But if I could park my car in the sun while I'm at work and get four free liters of gas, I would not say that this was "unnoticeable".
 * I also notice that a solar panel is an factory option for the Xebra electric cars mentioned earlier in this thread. APL (talk) 13:56, 1 June 2009 (UTC)


 * I disagree - 2 kilowatts is abysmally negligible compared to your gasoline engine. For every second that you charged your battery, you would get one second of a 2 horsepower boost if you had a perfectly efficient conversion.  In reality, you will get much worse performance.  I doubt this tiny boost would even come close to making up for the excess weight of lugging around a solar panel and battery system.  If you want to store more energy, you need a heavier battery - it's a no-win situation.  Nimur (talk) 14:38, 1 June 2009 (UTC)
 * We're talking about Hybrid-Electric cars. They already have batteries. APL (talk) 15:56, 1 June 2009 (UTC)
 * But those batteries are already being used. They'll have optimised the size and number of batteries based on weight and reducing the amount of time the battery is full but there is still excess energy from the engine/breaks which gets wasted. If you added solar panels without adding more batteries you would just end up wasting the energy sources you already have. --Tango (talk) 18:14, 1 June 2009 (UTC)
 * I agree with Nimur - your numbers are hopelessly optimistic. The Zap Xebra does indeed come with a solar panel roof option - and go take a look at their web site and see what they have to say about it. Firstly, it costs $1,500 (a costly option on an $12,000 car!) so it's not at all cheap.  Secondly - if you read the specs on the panel on the Zapworld web page - it doesn't produce 2kilowatts - it produces 150 watts.  Parking the car in the sun all day for 4 liters of gas sounds reasonable - but you're not getting 4 liters - you're getting a little under a third of a liter.  A third of a liter is 0.07 US gallons - so with gas at around $3 a gallon, a full day of recharging saved you about 25 cents.  So the payoff time for that solar panel on a hybrid car is something like 6,000 sunny days...maybe 30 years in sunny parts of the world!  Certainly longer than the life of either car or solar panel.  But worse - the solar panel weighs 85lbs.  The odds are pretty good that it's actually going to cost you more in additional electricity consumption than it actually provides!  Possibly the only reason people buy them is (as the Zap page coyly suggests) is to "appear even more Green to your neighbors!".  Solar panels are not as good as you think.  Partly that's because they need to be tilted at right angles to the sun's rays to produce optimum amounts of power...and a car's roof is rarely (if ever) at the optimum angle.  Secondly, they are adversely affected by dirt (another problem on a car roof).  Thirdly, they gradually lose effectiveness as they age...so you do have to replace them if you plan on keeping your car for a long time.  Fourthly - when solar panels are used effectively, they are on the roofs of buildings where they are unlikely to be shaded - and tilted towards the prevailing sun direction for the location they are in.  You can't always park in the sun.  There are many cities where above-ground parking is rare - or where you are blocked from the sun by tall buildings - or where there are trees overshadowing you.  On the little 3-wheeled Xebra, adding all that weight to the top of the roof....I'd worry about how much they add to the roll-over risk. SteveBaker (talk) 18:24, 1 June 2009 (UTC)
 * I got the 2kw number from the solar car article. I wonder if that doesn't refer to special super-expensive panels used on solar race cars. Oh well. APL (talk) 19:24, 1 June 2009 (UTC)


 * I will add that there is really only a single main reason: Conventional internal combustion engines are generally fuel efficient only at one particular speed. My vechicle is most effiecient at 90km/hour in its 4th gear. This is when it can achieve 7 litres of fuel per 100km. In every other situation it is far less efficient. When accelerating for example, even at low speeds (from 10km/hour to 50km/hour) the fuel consumption can be 40L per 100km or worse. At high speeds (~110km/hour) the fuel consumption goes upto 14L per 100km. At low speeds (50km/hour) its 11L/100km. The cars are engineered normally around typical highway driving speeds. The reason for this is that you need 4 times as much energy to move a car at twice a higher speed. For example a car that does a trip at 50km/hour could use 1/4 as much energy as a car that does the same trip at 100km/hour speed, because airdrag increased 8x and the speed of the trip only decreased by 1/2. So when the go to design a car, even one for the city, they know that it still needs to be able to travel at 100km/hour some times, so this is where they should make it most energy efficient. This is why for 99.9% of convential cars are fuel efficient at speeds of around 80 to 90 km/hour. You can have you manufacturer modify your car so that it is most fuel efficient around 50km/hour (and get say 7L per 100km out of even 4L V6 engines), but the fuel consumption at high speeds like 100KM/hour would go upto 28L per 100km or worse. Electric cars don't have this problem that internal combustion engines have. The electric motor and work at variable speeds easily. For an internal combustion engine to work efficiently at all different speeds it would have to be capable of dynamically changing many fixed variables such as piston stroke length, value timing, huge changes (order of significance) changes in the amount of fuel injected based on speed, instead of only minor changes. Most engines run fixed stroke, fixed value timing and very little change to fuel injection amounts, then they just vary their speed - even though they can only run optimally at one speed. --Dacium (talk) 06:24, 2 June 2009 (UTC)

How many human beings can Australia support?
I often hear the argument that, while Australia is a vast continent, it is also arid and dry and cannot support much more than its current population of 20 million. (For the record, this argument is usually brought up by people terrified of non-white immigrants.) Is there any truth to this statement? While this is a pretty harsh country, there's plenty of spaces that are green and verdant - Tasmania, for example, is roughly half the size of Great Britain, which has a population of nearly 60 million. 58.161.196.113 (talk) 11:26, 31 May 2009 (UTC)


 * In the global economy, the number of people that the food supplies of a nation can support are largely moot. Much of the food in the U.S. for example is imported from overseas.  There are studies, I suppose, which have been done which indicate how many calories a particular acre of land can produce, and how many calories a person needs to survive; but with the ease at which foodstuffs are moved around the world, assuming that a nation needs only support its own population with its own food growing is kinda silly.  --Jayron32. talk . contribs  11:59, 31 May 2009 (UTC)
 * The united Stated is a massive net exporter of food. Most notably, the US is the largest exporter of rice, but also exports huge amounts of wheat and corn. -Arch dude (talk) 20:17, 31 May 2009 (UTC)
 * Australia also exports large amounts of wueat. See Export Wheat Commission. -Arch dude (talk) 20:20, 31 May 2009 (UTC)

Australia's population per square mile is tiny. It could very easily support millions more people. Yes there'd need to be major developments to boost infrastructure, but there's no reason (certainly not food) why a developed nation such as Australia couldn't have a major increase in its population. Whether or not it is desirable is another question though, and more of a political question. 194.221.133.226 (talk) 12:54, 31 May 2009 (UTC)


 * I understood that insufficient water resources may be the limiting factor in the southern part of Australia at least. Mikenorton (talk) 13:22, 31 May 2009 (UTC)


 * An Australian ecologist (whose name I've forgotten) has argued in a book (whose title I've also forgotten), that Australia is already overpopulated when measured against the maximum number its ecology can support sustainably, which I seem to recall he calculated as 17 million. This low limit, he believed, was due to the unusually impoverished soil of the continent, this resulting from the extermination some tens of thousands of years ago of most Australian megafauna by the Aborigines, thus removing their dung from the ecological cycles. If I manage to remember more (or find the book) in the near future I'll post more references - I'm sure I've seen mention of him on Wikepedia. 87.81.230.195 (talk) 18:23, 31 May 2009 (UTC)
 * Are yo thinking of Collapse: How Societies Choose to Fail or Succeed, by Jared Diamond? -Arch dude (talk) 20:17, 31 May 2009 (UTC)
 * No, definitely wasn't it or him. (I've got some of his other books though). 87.81.230.195 (talk) 02:30, 2 June 2009 (UTC)
 * Cracked it! Tim Flannery, The Future Eaters. 87.81.230.195 (talk) 19:41, 2 June 2009 (UTC)


 * Incidentally, I believe Jayron32's argument does not stand - imported food (and other goods) must be paid for with exports of some kind, whose production ultimately depends on their extraction from the ecosystem, and "everything is linked to everything else". The ability of the USA and Australia to consume two or three times a sustainable share of the planetary ecosystem's production is balanced by the populations of other countries having to subsist on much less. If everybody on Earth had a USA/Australian/UK standard of living, we'd need several Earths to sustain it; an equitable sustainable standard for everyone would be markedly lower, unless the world population was only about 2 billions. The medium-term future is likely to see one or more of: drastic reduction of First World consumption through drastically more efficient technology, or First World economic collapse; mass migrations from the Third World leading to worldwide social collapse; drastic population reduction through famine and pandemics. It's being so cheerful as keeps me going. 87.81.230.195 (talk) 18:42, 31 May 2009 (UTC)
 * A higher standard of living doesn't generally take up more space. You still need to eat the same amount of food. --Tango (talk) 20:22, 31 May 2009 (UTC)
 * It need not (though many rich bastards better-off people do have larger houses than the local norm and eat more expensively produced foods), but currently it usually averages much higher consumption of energy and material resources, and production of pollution and waste. We urgently need to develop technologies giving us the same benefits for less of the aforementioned, and to help the developing nations (e.g. China and India) to skip straight to these rather than replicating the wasteful and polluting methods the "West" went through. 87.81.230.195 (talk) 02:44, 2 June 2009 (UTC)


 * The question requires rephrasing: "How many human beings can Australia support *now*?" Every over population doomsday projection (they go back hundreds of years) has been wrong because the projections assume that population increases but that technology does not. While an ecosystem is finite, the sustainable use to which the ecosystem can be put is variable and a function of technology. Wikiant (talk) 18:47, 31 May 2009 (UTC)
 * There is some balance that has to be met at some point between how much energy it cost you to put into each bit of food you produce. You can desalinate saltwater and grow algae and fungi in vats eventually, but that is going to cost energy.  Someone is going to have to mine and dispose of your fossil/nuclear energy materials or solar panel raw materials and waste.  You can unload some of that cost on to other economies for a while. (We've been doing that as 87. hinted.) But at some point the buck stops.  71.236.26.74 (talk) 06:53, 1 June 2009 (UTC)

Well I guess the simple way to answer this question would be to compare arable land. This list gives arable land in Australia as being the 6th largest in the world. The world as a whole has 325 people per square km of arable land, while Australia has 43. This implies that Australia's population could grow to 7.5 times what is today (151 million) before reaching the average density of the rest of the world. Note that many countries are far above this average and still largely self sufficient agriculturally, India and China have 753 and 943 people per square km of arable land respectively. Were Australia to grow to the same density as China, it would have 438 million people. Of course this comparison is not perfect: there is large variation in the "quality" of arable land in terms of supporting humans. There is also the issue of water, as raised above. It adds another complication and uncertainty, especially for a country such as Australia where there is quite a lot of water but it is nowhere near evenly distributed. TastyCakes (talk) 18:04, 4 June 2009 (UTC)

General Motors EV1
The General Motors EV1 electric cars were leased to customers and later recalled by GM. Why did they lease these unsuccessful test cars to people in California and Arizona where the weather is always very hot? Was it a bad decision? Or did their batteries perform even worse in cold weather?

Only a number of these cars were not destroyed. In a few decades, can we install more advanced batteries to these museum cars and make them usable? -- Toytoy (talk) 13:23, 31 May 2009 (UTC)


 * For one, California (where most of the EV1s were issued) is not "always hot". Additionally, Arizona participants were not issued the EV1s with the most heat-vulnerable battery systems.  At a guess, California was selected largely for the PR opportunities of a zero-emissions car in the most emissions-restrictive state.
 * As for the remaining cars, its highly unlikely that any will be retrofitted and restored to the road. GM has no incentive to do so, as the retrofit and associated certifications will be far more expensive than making current-model EVs.  Museums and other display locations have no incentive to do so, as they don't require roadworthy models for display.  Perhaps a private collector, should he be able to acquire an EV1, might have an interest. &mdash; Lomn 14:01, 31 May 2009 (UTC)


 * The cars were not leased to make money for GM - they were leased as an experiment to see how the EV1 would perform out there in the real world with real customers. This is not an unusual thing to do.  In fact, BMW's MINI division is doing that exact thing right now with the Electric MINI Cooper.  They built something like 500 of these cars and have leased about half of them to customers in the US - in California and New York only.  The lease terms are very like the EV1's and stipulate in no uncertain terms that the cars MUST be returned at the end of the lease - no extensions or right to purchase will be made.  Why?  Well because they want to look at how these cars have survived the ravages of practical driving by real people - and (as with the EV1's) they have no intention of supporting them with spares and maintenance off into the future.  If you want to know how well your design works - there is no point in putting them into 'easy' situations - if you suspect that they'll have trouble in extreme heat - then you should absolutely do your trials in Arizona.


 * No doubt the few remaining EV1's could have new batteries and be made to work - but they are now museum pieces and will probably remain that way.


 * If you want an electric car - you can buy one very easily. At one end of the scale, the ZAP Xebra has been in production since 2006 and is quite affordable ($11,700) - but with only a 25 mile range...you'd better have a pretty short commute!  At the other end of the scale - if you have deep pockets and fancy something a bit more sporty - the Tesla Roadster is a pretty cool car (based on a Lotus body) - it'll go 240 miles on a charge and has a 0-60 time under 4 seconds!  Our Category:Production electric vehicles lists many electric cars that are in mainstream production around the world. SteveBaker (talk) 16:55, 31 May 2009 (UTC)


 * I fixed your category ref, Steve.--Polysylabic Pseudonym (talk) 03:20, 1 June 2009 (UTC)


 * You can install whatever you want into a car body, but the ultimate questions are: will it be prohibitively expensive, and will you be in violation of state and federal regulations for road-worthy automobiles? The answer to these questions turned out to be "yes" for General Motors, which is why the EV-1 program was ended so abruptly.  Though numerous conspiracy theories suggest collusion from the petroleum industry, this is sort of a flimsy argument - cost-effective electric vehicles have been around for a very long time, but are mostly unsatisfactory for the sort of driving we have become accustomed to.  Nimur (talk) 19:20, 31 May 2009 (UTC)

Do owls ever get aggressive with people?
I was just out working in my shade garden, and noticed after a few moments that a Great Horned Owl was sitting on the wood pile about 8 feet away, staring at me. I of course went and got my camera and got some pix from about 12 feet away, which he didn't seem to have any problem with (even with the flash!).

I'm just wondering whether I should worry about working so close to him... it's hot and sunny and I was really looking forward to shady work. My wife and daughter will also be getting home any minute now, and I want to show them. So are owls safe to be near? -- SB_Johnny | talk  15:07, 31 May 2009 (UTC)


 * If you disturb their nest or corner them, they might turn violent, but I can't see why they wouldn't just fly away in other situations if they felt threatened. If they don't feel threatened, there is no point them attacking you, you clearly aren't good prey. Oh, unless they are wounded - wounded animals can be very dangerous. --Tango (talk) 15:12, 31 May 2009 (UTC)
 * Owl talons, especially those of large ones defending their nest can be vicious. Check out Eric Hosking and be careful if there is a nest nearby. Shyamal (talk) 15:23, 31 May 2009 (UTC)


 * No, doesn't seem to be wounded... a couple minutes ago he swooped down onto something, ate it, then lofted himself back onto the pile. I've seen (and shot) baby rabbits near there, so maybe the rabbit nest is under the pile? I'm a bit surprised to see him (or her) hunting at mid-day. We all just went down to see it, and it just stared at us and winked :-). I can't imagine the nest is there... I'm pretty sure he lives in the barn. -- SB_Johnny | talk  15:39, 31 May 2009 (UTC)


 * Well I'm jealous, you're one lucky dude. Richard Avery (talk) 21:45, 31 May 2009 (UTC)
 * Congrats on your winged hunting buddy. It probably got interested by you rustling some leaves.  Since you were successful in helping it to a morsel its strategy paid off.  Be careful with pest control.  You don't want it exposed to any poison.  Great Horned Owls prefer hunting at night (?our article says, shouldn't that be dusk and dawn?) because that's when their prey comes out to play.  That doesn't mean they won't hunt at other times if opportunity presents itself.  They rely on their hearing as much if not more than their vision to hunt.  Some falconry shows have horned owls as show birds.  Enjoy the show. (...and maybe post us some of your pix in the article :-) 71.236.26.74 (talk) 06:42, 1 June 2009 (UTC)

Muscle Contraction question
By the grace of G.od

Rechovot (Israel, 31/5/09

Peace and benediction!

In your article about muscle contraction, you write about "cross-bridge" in the myalin/actin action. It will be helpfull to add a few lines about the "cross-bridge" process.

Thank you very much for your wonderfull web.

Yehudah F. Rechovot, Israel EMT-P learning —Preceding unsigned comment added by Yehudah770 - Mashiach Now (talk • contribs) 19:19, 31 May 2009 (UTC)

I have moved your question to a new section. Nimur (talk) 19:22, 31 May 2009 (UTC)


 * The most appropriate place to make a suggestion for a page would be its specific Talk page, which is likely to be watched by people who are both interested and knowledgeable about the topic. In this case, that would seem to be Talk:Muscle_contraction.  Of course, if you have a clear sense of what should be said, you are also welcome to be bold and edit the page.  --Scray (talk) 19:48, 31 May 2009 (UTC)

Downtown Tokyo
I read the cryptographically written articles Tokyo, Greater Tokyo Area, City of Tokyo, and Special Wards of Tokyo, and I couldn't for the life of me find a clear explanation where "Downtown Tokyo" is, i.e. in wich ward(s) or other subdivisions or administrative regions within Tokyo. When I say Downtown, I mean the cluster of skyscrapers you see when you Google Image Search "Tokyo Skyline". Where exactly are these buildings? 209.148.195.177 (talk) 23:32, 31 May 2009 (UTC)
 * This is probably going to be completely wrong, but I was in Tokyo earlier this year and got the impression that there were actually several different clusters of skyscrapers, or "downtown" areas, dotted all over the city. 58.161.196.113 (talk) 16:13, 1 June 2009 (UTC)

La Défense
Is La Défense basically Downtown Paris? Why is it outside the city limits? 209.148.195.177 (talk) 23:33, 31 May 2009 (UTC)


 * La Défense is sort of in the boonies, actually; it is a business district to the northwest that's the newest of the arrondissements &mdash; although I notice it's not even listed in our article Arrondissements of Paris. As a visitor, I claim there's nothing going on in La Défense to speak of culturally, and it's a long, long walk to anything I'd consider "downtown Paris".  Tempshill (talk) 23:52, 31 May 2009 (UTC)


 * I don't think it's correct to refer to La Défense as an arrondissement; that word refers to the 20 districts that Paris itself is divided into, and unless something has changed recently, La Défense is outside the city limits.


 * Why does this concentration of office towers exist in one suburb? Presumably because urban planners decided that preserving the character of central Paris was desirable but also felt that it was desirable to allow this kind of development, so they passed zoning laws to allow for this.  I imagine the construction of the Montparnasse Tower, which many people disliked, must have been a catalyst for this planning decision -- and yes, look at the Criticism section of that article.  --Anonymous, 00:42 UTC, June 1, 2009.


 * As a visitor I claim La Défense itself is culture going on. It is an expression of Gallic gigantilism, full of bold surprises in 3-D. It is the futuristic movie set that could only be imagined for Alphaville (film) and a landscape for artworks that are superhuman but not inhuman. Why is it where it is? Because the Parisians want to reach for the future without mutilating their heritage, and their solution is that long, long axis joining their arch monuments to triumph of courage and triumph of the brain. Vive la différence! they say having digested the painful lesson of immiscible architectural dichotomies. The tourist sees the Grande Arche from afar and may enter its arena that boasts cafés, restaurants, cinemas, occasional grand shows of sound and light, a shopping mall that never ends and a potent motor museum. Cuddlyable3 (talk) 10:00, 1 June 2009 (UTC)


 * For a parallel in the U.S., see the relationship between Washington, D.C. and Arlington, Virginia. Washington has strict building codes designed to preserve the architectural character of the city, but it is also a major urban center which demands a large, vertically aligned commercial district, like any other major city.  Arlington has become the skyscraper farm for Washington DC much the way that La Défense has become so for Paris, for almost exactly the same reasons.  --Jayron32. talk . contribs  18:41, 1 June 2009 (UTC)


 * Incidentally for both this and the previous question, you'd likely receive a better response if you post the question in humanities or perhaps misc, since they don't really seem to concern science much Nil Einne (talk) 22:46, 1 June 2009 (UTC)