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July 29

Turbojets

The article on turbojets seems to indicate that they are more efficient than turbofans above Mach 2, but it doesn't really give a clear answer. Is that true? --The High Fin Sperm Whale 00:48, 29 July 2010 (UTC)

According to this chart (in the Jet Engine article) a turbojet will be more efficient (measured in Isp) than a turbofan starting at about Mach 1.5. I suspect this is because the turbojet will have a higher average exhaust velocity than the turbofan. A turbofan exhausts a large volume of lower velocity air, but since the thrust has to do with the difference between airspeed and exhaust velocity, the lower exhaust velocity means lower thrust at a high airspeed. The turbojet exhausts a smaller volume of high velocity air, so it maintains higher thrust at a high airspeed.

anonymous6494 02:14, 29 July 2010 (UTC)

Thanks, but the chart does not show turbojets. Thanks anyways. --The High Fin Sperm Whale 02:31, 29 July 2010 (UTC)

For these purposes, you can think of a turbojet as a low-efficiency turbofan - so on that chart, they will lie just below turbofans. For example, the engine that powered the infamous Concorde will have an Isp of around 3000 s at cruising speeds (just over Mach 1). You can verify this for yourself by converting the thrust specific fuel consumption in to specific impulse (the equations are given in our article for a variety of units). In this case, Olympus 593 engines have a SFC of ~1.2 lb/lbf·h - so convert by (3600/1.12), yielding Isp around 3000 s at cruise speed of Mach 1. In reality, the distinction between a turbofan and a turbojet is a semi-subjective distinction about what counts as "low pressure" bypass. There are many engines that could pass for either description. Compare the cartoon diagrams of turbofans to turbojets - as you can see, the big difference is expansion ratio of the bypass flow - and there is not a clear demarcating line between the two. In the extreme case, of course, we can clearly see that a large amount of ducted air is not "jet-like", and you can keep making the bypass ratio higher and higher... at some point you stop bothering with a nacelle and end up with an unducted turboprop (even more efficient! but much slower). Nimur (talk) 03:50, 29 July 2010 (UTC)

What is the lightest/least dense non-porous solid?

So if Aerogel is the least dense porous solid, which non-porous solid has the lowest density? —Preceding unsigned comment added by 71.163.18.235 (talk) 01:51, 29 July 2010 (UTC)

Lithium is the lightest element that's solid at room temperature at 0.53 g/cm³. I don't know whether there are any less dense compounds out there - but I suspect not. SteveBaker (talk) 02:02, 29 July 2010 (UTC)

If we can freeze non-solid-at-RT things, solid hydrogen I think is probably around 0.07 g/cm³. Or at least that's what hydrogen says the liquid is at the melting-point, so probably close? The article specifically about the solid has few physical properties. DMacks (talk) 02:38, 29 July 2010 (UTC)

It's 0.088 g/cm^3 which is the lowest of all known crystalline solids. Dragons flight (talk) 02:44, 29 July 2010 (UTC)

Could you add that with cite to the solid hydrogen, and maybe also hydrogen articles? DMacks (talk) 06:18, 29 July 2010 (UTC)

For this one, we might have to define "porous". Everything would have exactly the same density if it were not for the void-spaces. It just so happens that some solid materials have void-spaces on molecular scales that are defined by crystal lattices; some solid materials have void-spaces on macro-crystalline or polycrystalline scales; some solid materials have void-spaces that are large enough to be filled by air or gas; and so on. One could conceivably build a sturdy steel shell and pump out the air from its interior: would it be fair to call that a low-density material? After all, there would be nothing but steel in it; nothing would be "diluting" its volume or mass. And it wouldn't really be porous. How small of a pore is required before you call a material "nonporous?" Nimur (talk) 04:05, 29 July 2010 (UTC)

It should also be noted that an aerogel is not a material per se. It is a colloid; which is to say it is a type of mixture. As a mixture, it is a combination of multiple materials; aerogel being a mixture of the solid matrix and air. The density of a mixture is dependent not only on the properties of the components, but the proportions in which they are mixed. Pure substances generally have well-defined densities, for example look at the infobox of iron or or sodium chloride or sucrose. However, not being a pure substance, one cannot define a specific density for aerogel in general, only for specific formulations of aerogel. --Jayron32 06:42, 29 July 2010 (UTC)

The Dirac sea perhaps. Cuddlyable3 (talk) 17:59, 29 July 2010 (UTC)

If you could get enough Di-positronium together and crystallize it you would get something about 1000 times less dense than solid hydrogen. However it is too radioactive with too short a life for this to happen in our current technology. Graeme Bartlett (talk) 10:23, 30 July 2010 (UTC)

Airport Runways

I would like to know if Airport Runways are built in one direction taking Earth's rotation into consideration. Are they built East-West? —Preceding unsigned comment added by Shyamlal777 (talk • contribs) 02:17, 29 July 2010 (UTC)

I don't think that the Earth's rotation needs to be taken into consideration, since the atmosphere spins with it. --The High Fin Sperm Whale 02:20, 29 July 2010 (UTC)

A trip to any reasonably-sized airport would disprove "Airport Runways are built in one direction". And even single-strip airparks would be likely to disprove "Are they built East-West?". They're built at whatever directions space allows and that is viable for prevailing weather conditions. Our runway article talks about it in a whole section about orientation. Airplanes care a lot about wind, which can blow in any arbitrary direction regardless of the earth' rotation, though there may be some places that almost always have wind in a certain direction. Weather systems are certainly affected by the earth's rotation on a large scale, but not "rotation -> that's how the breeze goes in general". Rockets and other things that are not relying on air motion for their own motion and that need to move in a certain direction relative to the earth could rely on the rotational boost. DMacks (talk) 02:29, 29 July 2010 (UTC)

Right. Most places have a prevailing wind, actually, and airplanes can take off and land more easily facing into the wind than facing with it or sideways to it. Looie496 (talk) 03:44, 29 July 2010 (UTC)

SImple land geography is a big factor too. Runways have to go where hills and mountains aren't. HiLo48 (talk) 04:28, 29 July 2010 (UTC)

I'm a pilot, and I can assure you that there is no set way that a runway must be oriented. DMacks, Looie496, and HiLo48 are all correct. They are built with the local environment, "normal" winds, etc in mind. Not all runways are the same. Some have [slight] hills in them, so they have a pronounced dip or crest in the middle, some are longer, some are shorter, some are wider, some are narrower, some can handle more weight, and there are some where you take off and land in one direction because there's a mountain on one end. It really depends almost entirely on what the runway is to be used for and where it is. Falconus^{p t c} 05:06, 29 July 2010 (UTC)

Indeed. The airfield just down the road from me (LEIG) is planning on extending the runway: the main consideration was where they could buy the land from (although it's also one of those one-way runways with a biggish hill at one end). Physchim62 (talk) 05:30, 29 July 2010 (UTC)

Other then what's already been said, I think the consequences of the flightpath the runway will impose will also get consideration. For example a runway which means the planes will be largely taking off over water or flat, uninhabited land would generally be preferred over one which results in planes over taking off or landing over houses (meaning when height is not a concern) not just for safety reasons but because planes tend to be noisy particularly when low flying Nil Einne (talk) 07:27, 29 July 2010 (UTC)

Landing flight paths over uneven terrain are avoided if possible because signal reflections can distort the radio guidance beams. See the article Instrument landing system#Limitations and alternatives. Cuddlyable3 (talk) 17:44, 29 July 2010 (UTC)

About CAN networking

Dear Sir, i have a fiat car wit me some days back its stop working , some engineer came and said some one is putted cut in the main network line(CAN Network) bcoz of that its stop start working,now they have rectify that error.Now i want to know that whether dis cut can produce any error in future nd what kind of cut should i make in the networking so that my sub woofer(Amplifier) work properly .

Thanks —Preceding unsigned comment added by Kuks222 (talk • contribs) 02:46, 29 July 2010 (UTC)

The CAN-bus is an automotive network technology. Think USB for a car and it's a close approximation. As such, the repair shouldn't lead to errors down the line. Presumably they replaced a cable and, unless that cable is cut again, that's not a part that's likely to fail any more than USB cables go bad (which is to say, rarely). Of course, a future cut would produce the same problems. As for the subwoofer, as far as I know, car stereos don't use CAN-bus to carry audio signals. They'd be analog speaker wire rather than digital CAN-bus. — Lomn 03:54, 29 July 2010 (UTC)

I'm wondering if the person who installed the subwoofer cut the CAN bus wire, thinking it was the audio line and trying to re-route it to the subwoofer amplifier. In that case, you should make them pay for any repairs necessary. Nobody should have touched your CAN bus to install an amplifier. If the CAN bus is damaged, depending on your particular FIAT model, there may be serious safety concerns operating the vehicle - some engine control units and safety features like brake or airbag controllers may use the CAN for communication. Most cars have a separate CAN bus for critical vehicle systems and "passenger-compartment" things like radios and DVD players; but the information provided is insufficient to know what has been cut. Have a mechanic you can trust analyze the problem, and make whomever cut the wire pay for it. Nimur (talk) 04:13, 29 July 2010 (UTC)

iitmadras

Hi I am from Hyderabad. I want to do my MTech from IITs but my aggregate is less than 60% in my BTech. But in IIT Madras website I saw the minimum qualification is a degree and GATE score http://gate.iitm.ac.in/mtechadm/gelig.php Can I get the admission if my GATE score is good?? —Preceding unsigned comment added by 115.109.194.75 (talk) 12:09, 29 July 2010 (UTC)

why do stocks prices move during the day even when there is no new information!

why is it that even in boring times with no new information, multibillion dollar companies' stock prices fluctuate at least a few percentage points continuously every second or few, all day, every day? For me, it would make more sense for them to stay in a flat line for a few day (or hours, if a piece of news comes unexpectedly) then jump to the new price based on the new information and stay in a flat line until it jumps to a new price due to the next piece of news. But this never, ever, ever happens even within a single day (for the largest companies) let alone for days or weeks. Why is that? You don't get a different price at the gas station every fifth of a second, why do you on the stock market? 84.153.183.42 (talk) 16:31, 29 July 2010 (UTC)

The price does not depend only on the single company, it also depends on the industry group. It also depends on the relative risk between that company and other companies, and between that company and bonds. So other things change, which causes a relative change, which moves the price, i.e. other stuff might suddenly be slightly better or worse. Ariel. (talk) 16:37, 29 July 2010 (UTC)

so? Information changes in the real world second by second, but the gas price isn't updated at the pump that fast. What's the difference? 84.153.183.42 (talk) 16:39, 29 July 2010 (UTC)

There isn't a single, efficient market for gas, there are lots of different gas stations. If I want to buy a share in a company, I will buy the cheapest share on offer. If I want to fill my gas tank, I go to the most convenient gas station and pay whatever they are charging (within reason). --Tango (talk) 16:46, 29 July 2010 (UTC)

Gas prices do actually change every second, it's just the gas stations refuse to adjust the price because it would make people nuts. They do earn and loose money on the changes! They hate volatility for this reason. It's even worse for them - they may buy a truck full of gas for a high price, and the next day prices are lower, and they loose money on all the gas they are storing. And they reverse too, and they hope it works out long term. Ariel. (talk) 17:00, 29 July 2010 (UTC)

There is a constant influx of new information: all the buy and sell orders that are going on. Friday (talk) 16:43, 29 July 2010 (UTC)

Yeah, the price is determined by what people have recently traded it for. When the price fluctuates that means there have been trades and since different people have slightly different ideas about what the stock is worth the price will change. What people are paying in turn affects what other people think about the value. There is also new information all the time in the sense that lots of things can subtly affect the market and people are working very hard to analyze the incoming data and update their valuations. When the stock of some other company goes up, when a new trade agreement gets signed, when a new oil reserve is discovered, that can affect the value, even if the company has little to do with these other industries. There are things happening in the world all the time. Rckrone (talk) 17:13, 29 July 2010 (UTC)

Yes. Reported stock prices are snapshots of continual trading activities. The only way to get a prolonged flat "noise free" price would be for nobody to trade in that stock. Gas (petrol) stations that have electronic price displays can use them to play "gotcha" knowing that different market segments refuel at characteristic times e.g. commercial vehicles on weekdays, private vehicles at weekends. However changing the retail price too often would be counterproductive as bad PR. Cuddlyable3 (talk) 17:31, 29 July 2010 (UTC)

Also, consider some investor who holds 10,000 shares of BoringCo. It has had no news for a month and will have no news for another month. But that investor is also investing in and monitoring ExcitingCo, which you can find 20 news stories on every day. When news on ExcitingCo makes the investor think the shares are going to go up, he may sell 5,000 of his BoringCo shares to invest the money in ExcitingCo instead; and when ExcitingCo announces all their iPads are overheating, the investor may dump it all and invest the money back in safe old BoringCo. Multiply this by many investors and there's plenty of price fluctuation, though all this buying and selling of BoringCo has nothing really to do with news coming out of BoringCo. Comet Tuttle (talk) 18:08, 29 July 2010 (UTC)

This is really a question about human behaviour related to financial greed. That also applies where computers are assisting because humans have programmed the computers. It's all about people trying to gain the tiniest advantage, and then gain financially from it by multiplying that tiny advantage thousands of times. HiLo48 (talk) 19:49, 29 July 2010 (UTC)

Dog repellent

I need to keep dogs away from a part (not very large) of my garden and I'd like to find out if there are some substaces whose smell acts like a deterrent/repellent for them. Obviously not something armful. The best would be a "homemade" substance relatively odourless for humans but as disgusting as possible for dogs. --151.51.156.20 (talk) 18:27, 29 July 2010 (UTC)

I have seen some products sold, though I cannot recall the company. --Chemicalinterest (talk) 19:37, 29 July 2010 (UTC)

Suggestions I've heard include lemon slices, or ammonia, but the latter can make it pretty unpleasant for humans too. And I've had a beagle that decided he liked to eat citrus fruit, along with the million other things beagles typically found attractive. It can depend on the breed of dog, and what it is in that part of your gardent that could attract them. Scent hounds can be attracted to something that seems heavenly to them but quite unobservable by humans. Any human created product has to overcome a scent we can't even detect, quite a big ask. A bit of trial and error may be needed. Can't do a wire fence? HiLo48 (talk) 19:59, 29 July 2010 (UTC)

If the dogs are yours and it's acceptable to have them wear shock collars while outside, you could also bury a wire around the forbidden area and make an invisible fence. Comet Tuttle (talk) 20:06, 29 July 2010 (UTC)

And if the dog is not yours—or you just want to keep things simple—just build a visible fence. --Mr.98 (talk) 13:39, 30 July 2010 (UTC)

Double S(not T)P in one day

If the pressure of the atmosphere gradually increased to double its normal pressure within a day, what would be the effects on human life and industry? --Chemicalinterest (talk) 20:36, 29 July 2010 (UTC)

I think it would still be safe to breath, SCUBA divers breath standard air at that pressure all the time.

The boiling point of water would go up by about 30 degrees C. So your spaghetti would cook a lot faster.

Fires would probably burn hotter and stronger with twice as much oxygen per unit volume of air. You can imagine that both these things would effect large industrial processes like power generation. Not all of them would be able to adapt. APL (talk) 21:10, 29 July 2010 (UTC)

If the boiling point went up, wouldn't spaghetti take longer to cook and not cook faster? ~AH1^(TCU) 00:52, 2 August 2010 (UTC)

Climbing Mount Everest would be a walk in the park. HiLo48 (talk) 21:13, 29 July 2010 (UTC)

Hmm I don't know about your last point. I still think it will be hard to climb 20,000 feet even though you could breathe easily. --Chemicalinterest (talk) 21:49, 29 July 2010 (UTC)

True, but, as mountains go, Everest is apparently quite an easy one to climb. You can basically walk up most of it. The cold, wind and lack of oxygen are the main problems, rather than the physical act of climbing that high. --Tango (talk) 00:15, 30 July 2010 (UTC)

You'd need to put more helium in your Zeppelin, but once you did that it would have greater carrying capacity. APL (talk) 22:14, 29 July 2010 (UTC)

You'd get a lot more horsepower out of your car too - no need for a turbocharger! But even if humans could endure that - I'm sure that there would be abrupt and spectacular decline in animal and plant populations for one reason or another. It's hard to predict exactly what all of the details might be but I would guess that forest fires would be much more common - and insanely difficult to control, more gasses would dissolve into the oceans - and that could change their pH and cause all manner of other nastiness for oceanic life. It's pretty certain that it would lead to total disaster of one kind or another within a matter of months. SteveBaker (talk) 22:25, 29 July 2010 (UTC)

Be sure to check your tire pressure before trying out your new-found horsepower! You'll find it's nearly 15psi lower than it should be. APL (talk) 00:04, 30 July 2010 (UTC)

Not overnight, but eventually you'd get really big bugs. Most insects rely on diffusion (rather than an active circulatory system) to provide oxygen to their tissues and this is a key factor in determining their maximum sustainable size. Increasing the pressure of oxygen will allow insects to evolve large sizes. Dragons flight (talk) 22:43, 29 July 2010 (UTC)

As evidenced by the giant insect fossils found from times in the Earth's past where the proportion of oxygen was much higher, eg. the Meganeura. Not all scientists agree about the role of higher oxygen in allowing large insects to survive, though. (That article gives some details.) --Tango (talk) 00:15, 30 July 2010 (UTC)

Well that's convinced me not to follow through on my evil plan to double air pressure and thus rule the world. -mattbuck (Talk) 19:30, 30 July 2010 (UTC)

Major changes in weather and climate. The amount of solar heat escaping to space would be greatly reduced, so the Earth would get quite a bit hotter and wouldn't cool nearly as much at night. Looie496 (talk) 00:13, 30 July 2010 (UTC)

The troposphere would expand, making the tropopause higher, and thus producing taller thunderstorms, larger hail, more intense lightning, etc. Sea levels would likely initially fall due to higher surface pressure exerted downward (can anybody confirm?). The pressure gradient would likely be greater, making for stronger winds. ~AH1^(TCU) 00:52, 2 August 2010 (UTC)

Liquids are barely compressible, so a 1 atm higher pressure at sea level will have minimal impact on the ocean depth. Googlemeister (talk) 13:48, 2 August 2010 (UTC)

what type of endocytosis is this?

Surely it's not phagocytosis right? These are lung cancer a549 cells, not white blood cells. (Watch the gold particle in the upper left corner of the centre region.)

• File:First capture animation.gif

John Riemann Soong (talk) 22:12, 29 July 2010 (UTC)

Image converted to link. Animated gif was more than 2MB — that's rather large to include inline. TenOfAllTrades(talk) 23:34, 29 July 2010 (UTC)

helium,

How many pounds of helium is necessary to support an object with a weight of 200lbs,utilizing one square meter of material filled with the gas?The height of the object is six feet.What type of material should be utilized to constrain the pressure? The apposing force to the object is water. Thank you Sincerely, Tom Ambron email {email removed} —Preceding unsigned comment added by 75.82.85.84 (talk) 23:08, 29 July 2010 (UTC)

We do not respond by email here at the ref desk -- you'll just have to check back. DRosenbach ^{(Talk | Contribs)} 23:22, 29 July 2010 (UTC)

Do you mean that you wish to construct a balloon with 1 square meter of surface area? This will limit you to a maximum sized balloon based on the surface-area of a sphere (the most efficient volume-to-surface-area structure). If you use a balloon, the necessary consideration is "how many kilograms of helium are needed to inflate the balloon? If the material is inelastic, you can fill it with helium at atmospheric pressure (or the pressure of the water at the depths you are considering). Then you can use the ideal gas law to calculate the mass of helium that will inflate the volume at that pressure. Now the question is whether the resulting density of helium is sufficiently low to provide 200 pounds of buoyant force. I think you need to restate the question - it is not really clear what you're looking for. We can solve all kinds of equations, but when the requirements are unclear, such solutions may be inapplicable. Nimur (talk) 23:33, 29 July 2010 (UTC)

It's simply not possible. Forget the helium, even the mythical vacuum balloon couldn't do it. If you mean that the balloon is a cubic meter, the displaced air weighs only 2.6 pounds. If you mean that the envelope is made of exactly one square meter of material, then the displaced air is only ¼ pounds! A balloon, no matter what it's filled with, cannot lift more than the weight of the air it has displaced.

You may be of the common misconception that helium has negative weight and that the more you cram into a balloon the lighter it gets, I'm afraid that's not true. Balloon lift comes from buoyancy, the same force that causes boats to float. A common analogy is that wood floats, but if you pile enough wood onto a ship, it will eventually sink. APL (talk) 23:58, 29 July 2010 (UTC)

Is there any theoretical particle that exerts negative gravitational force with which we could fill the ballon? —Arctic Gnome (talk • contribs) 01:19, 30 July 2010 (UTC)

No, there is no such particle. Antigravity is firmly in the realm of fiction. As far as exotic matter with negative mass, there is currently no consistent explanation for how such a particle would behave; there is no need for such a particle to play any role in the standard model; and any speculative theories about negative mass or repulsive gravitational force is exactly that - speculative. Nimur (talk) 04:00, 30 July 2010 (UTC)

The anticharm quark exerts negative gravity. --142.104.53.238 (talk) 22:50, 1 August 2010 (UTC)

I don't understand that bit about water. Are you saying the object is underwater? Helium at above atmospheric pressure would be worse than helium at atmospheric pressure, since there is more helium taking up the same amount of space, so it will weight more while displacing the same amount of air/water. The absolute best buoyancy you could get with 1m² surface area would be a complete vacuum (you would need a strong container to hold a vacuum, which would therefore be heavy, but let's ignore that and assume a massless container). Such a vacuum-filled container submerged in water would be able to lift the weight of water displaced by the container. As Nimur says, the best shape is a sphere. The surface area of a sphere is $A=4\pi r^{2}$ and the the volume is $V={\frac {4}{3}}\pi r^{3}$. If we substitute A=1 into the first and rearrange, we get $r={\frac {1}{\sqrt {4\pi }}}$. We substitute that into the other formula and we get $V={\frac {4}{3}}\pi {\frac {1}{(4\pi )^{\frac {3}{2}}}}=0.094\mathrm {m^{3}}$. That is 94kg or 207lb, so you could just lift your object. If we're using helium at atmospheric pressure, rather than a vacuum (which is wise, due to the weight of material required to cope with the pressure), then we have to minus off the mass of that helium, which is about 16 grams (if I've calculated it right - I expected it to be more, but I don't know why), so not significant. If I misunderstood your mention of water and your object is actually just in air, then you don't stand a chance. --Tango (talk) 00:06, 30 July 2010 (UTC)

Instead of using the ideal gas law directly, under standard temperature and pressure, one mole of any gas has a volume of just over 22.4 litres. Nitrogen-14 has a molar mass of 28 grams, oxygen-16 is 32 grams, helium-4 (which is mono-atomic) is 4 grams. Therefore air (80% nitrogen, 20% oxygen approx), has a density of 28.8 grams / 22.4 litre. A helium-balloon has a buoyancy of 24.8 grams/22.4litre or 1.1 grams/litre.

As for the water analogy, imagine an (theoretical) advanced life form that lives on the sea bed. Their density is well above that of water, so they can't swim up. If they want to lift an object to the surface of the water then they can attach a balloon to the object. As long as the object+balloon is less dense that water then it will rise. If the balloon is filled with vegetable oil (900grams/litre) then there is 100grams/litre of lift in water. The balloon still has real mass, it's just that the density is less that water, so it will rise.

BTW, a wooden boat, full of wood, will float, but very close to the water. It will act like a solid wooden object. In fact they were used for demining sea areas during WWII, see Naval_mine#Mine_breaking.

CS Miller (talk) 03:38, 30 July 2010 (UTC)

Sure, but you couldn't keep piling wood on indefinitely. Eventually the weight of the wood would exceed the boat's capacity and the boat would sink. (Once the boat fills with water and the cargo itself becomes buoyant, the comparison to a balloon in air breaks down, of course.) APL (talk) 00:29, 31 July 2010 (UTC)

July 30

in a cell culture medium, pH 7.4, will hydrogen peroxide oxidise colloidal gold?

I incubated a549 cells in 200 micromolar H2O2 for 90 minutes, washed the cells with fresh media and then observed them under DIC. (The cells had already been incubated in the presence of colloidal gold prior to incubation with H2O2.) The results were rather spectacular: an insane amount of intercellular bridges and connections (on all sorts of levels, criss-crossing everywhere) could be found, compared to situations without hydrogen peroxide. Oh was I happy!

But then 40-60 minutes into the experiment, my cells started dying from the bottom of the slide upwards. It was strange -- normally apoptosis is a stochastic event and is a rather random process that increases in chance as time goes by, but here it was like there was an invisible wave of apoptotic death slowly creeping up the slide. Is it nutrient exhaustion? I am sure I sealed the slide with nail polish to prevent evaporation.

A few papers I found said that H2O2 at 200 micromolar shouldn't decrease the viability of a549 cells too much...but they used 24h assays. Maybe in the time frame of a few hours, the H2O2 kills a lot of cells only to have the really mitogenic ones produce lots of viable ones?

Or maybe they are not apoptotic at all? The normal "apoptosis bubbles" were hard to see -- the entire cytoplasm changes viscosity almost -- it becomes very viscous and the cell's "insides" appear to slow down and look very different. Maybe it's the actin polymerising? I wonder if it's because the hydrogen peroxide is oxidising the colloidal gold, producing lots of Au(III) oxide and at the same time, decreasing the pH since Au(III) seems like a strong Lewis acid. John Riemann Soong (talk) 00:06, 30 July 2010 (UTC)

I thought that Au₂O₃ was insoluble, so the Lewis acidity was "locked away". --Chemicalinterest (talk) 11:58, 30 July 2010 (UTC)

Mmm, I didn't see any precipitate, but then again this is colloidal gold, not bulk gold, so Au(I) and Au(III) atoms would remain attached to Au(0) on the nanorod. I believe the sulfide thioether linkages popular for functionalising colloidal gold with are made by having the functionalised thiol precursor bind to the residual Au(I) sites (on an otherwise Au(0) rod) that weren't reduced in the initial manufacture of these nanorods. (Someone correct me if I'm wrong). John Riemann Soong (talk) 13:58, 30 July 2010 (UTC)

Oh it just hit me. According to the thioether article, they can be oxidised to sulfoxides and sulfones. I do pipette most of the old media (containing the nanorods) before I add the H2O2 but maybe I should do a few buffer rinses first? H2O2 won't react with membrane-bound gold rods inside endosomes in cells, right? Are sulfides bound to Au(I) more reactive or less reactive? Do they become more or less nucleophilic -- I mean, the Au(I) should sap some of the sulfide's nucleophilicity, right? (The linkage looks like: (rod)=Au(I)-S-(short alkyl/polyether chain)-COO-. John Riemann Soong (talk) 14:20, 30 July 2010 (UTC)

Also, why is the standard half-cell reaction potential for Au(III) + 3e- ---> Au(0) less than the reaction potential given for Au(I) + e- ---> Au(0)? (The latter has a higher potential than the two electron reduction of hydrogen peroxide in the presence of H+). I'm trying to figure out how favourable gold oxidation by hydrogen peroxide is, and I only spent a third of a semester on electrochemistry. John Riemann Soong (talk) 14:28, 30 July 2010 (UTC)

If bromine can oxidize gold to gold(III) bromide, then H₂O₂ should be easier. Also the colloidal property means it has much more surface area. --Chemicalinterest (talk) 15:12, 30 July 2010 (UTC)

Yeah but for the noble metals, halide compounds are more stable than oxide compounds. I think? Also from gold(III) chloride: "Reaction with reducing agents such as hydrogen peroxide or Fe2+ causes elemental gold to be precipitated from solution." Hydrogen peroxide is a reducing agent??? (My main issue is oxidation of the sulfur linkage -- if the sulfide is attached to an Au(I) atom, will hydrogen peroxide break the Au(I)-S bond, leaving free Au(I) and sulfonic acid? John Riemann Soong (talk) 16:41, 30 July 2010 (UTC)

A common example of H2O2 as a reducing agent is its reaction with NaClO, where it reduces Cl+ to Cl-, itself oxidized to O2. --Chemicalinterest (talk) 19:43, 30 July 2010 (UTC)

Stress Energy Tensor

I don't completely understand this. Why is this used instead of mass in General Relativity? What's the difference? ScienceApe (talk) 00:23, 30 July 2010 (UTC)

Because energy and mass both exert gravitational force; in Newtonian physics, mass is used in gravity calculations. The stress energy tensor (hint: read that article) takes energy and momentum into account; remember that according to General Relativity, gravity is a pseudoforce caused by curvature of spacetime. In most layperson explanations of GR gravity, it is explained that large masses curve spacetime, and that gravity is really just objects moving staight (as objects do), but doing so in curved spacetime. However, it turns out that mass is not the value which describes the curvature of spacetime, the stress energy tensor is the relevent value. --Jayron32 00:38, 30 July 2010 (UTC)

Momentum as well will curve space-time? So if we take an a 1kg object, it will curve space-time more if it's moving at 99% the speed of light? ScienceApe (talk) 01:16, 30 July 2010 (UTC)

Well, yes, but not because of momentum, per se, but because it has more energy, via KE = 1/2 mv². Well, not exactly, but via the GR equivalent at relativistic speeds near the speed of light. Objects moving at a higher velocity have more energy, and thus curve spacetime more than than those which are stationary. Velocity affects energy, and energy is mass. --Jayron32 01:26, 30 July 2010 (UTC)

How does momentum bend space-time? ScienceApe (talk) 01:32, 30 July 2010 (UTC)

How? By inducing a noether current that must be counterbalanced in order to conserve mass/energy/momentum flux. Consequently, some other "thing" needs to either move or change velocity, or else the flux conservation is violated. But Newton tells us that things don't just start "moving" for no reason - we have inertia! A body at rest remains at rest! So, if we want to remain at rest, and also change our momentum, we need to start warping space so that maintaining a constant position yields a change of momentum - ergo, gravitation. The exact geometry of the warping is nontrivial - and requires solutions of the general relativistic equations - but in the simplest case, we see elliptical planetary orbits, - planets that are tracing out an <x,y,z,t> vector path, when in fact all good sense tells us that they should be inertially stationary. Nimur (talk) 04:32, 30 July 2010 (UTC)

In a bit more details on why the tensor includes momentum; its because there are three fundemental conserved quantities in any physical interaction between bodies: energy, mass, and momentum. This is true even in classical physics. So, when two objects interact, even classically, momentum must be conserved. Even under the Newtonian definition of gravity, as two objects interact with each other gravitationally, their total momentum must remain constant throughout the interaction. Think of it this way. If you are a chunk of space rock flying by the earth; as the earth slows you down by "pulling" on you via gravity, the earth itself must speed up by the exact same amount.

In GR physics, its FAR more complex, and requires some pretty advanced mathematics. However, the law of conservation of momentum still cannot be violated. So, any calculation of gravity must take momentum into account. The stress energy tensor itself is described by a matrix of values. It isn't a single number like "mass". It is a tensor, which is a multi-dimensional quantity. If you know what a vector is, you can think of a tensor as a vector on steroids. Where as a vector quantity has two values (origin and direction), a tensor can have dozens of values, which are manipulated via matricies. The stress energy tensor uses four "types" of values (though there are multiple groups of values for some of the types). There is the "energy density", the "momentum density", the "energy flux" and the "momentum flux". Basically, in order to correctly calculate the effect of gravity within a system, say a simple two-particle system, you need to know a) the mass-energy of each object (energy density) at your initial conditions b) the momentum of each object initially (momentum density) c) the mass-energy changes experienced by each object as they interact (or curve spacetime, whatever your perspective) (energy flux) d) momentum changes experienced by each object as they interact. Now, it is even more complex because each location in the matrix isn't a simple number like "three", but rather a complex polynomial which describes, say, the energy density of the entire system in three dimensions (that is, how much mass-energy is at every point in space in our system). This is of course a gross oversimplification, since you actually have to do the math to get the implications here. I can't do the math myself, really, but this is how I understand it as a layperson. Perhaps someone with a better physics background could fix my errors or explain it better. --Jayron32 01:44, 30 July 2010 (UTC)

And just as an addendum, you may want to read Stress-energy-momentum pseudotensor, which is the actual value used in GR. The stress-energy tensor has other uses, but it is not strictly applicable to GR apparently. Again, I lack the math to understand exactly why, but I do read english, and that's what the article seems to say. --Jayron32 02:00, 30 July 2010 (UTC)

Another way to rephrase Jayron's explanation: the stress energy tensor allows a physicist to describe the gravitational interaction of a body in the form of a matrix that describes all the relevant concepts - energy, momentum, position, and so on, in generalized coordinates. The way that the body behaves depends on the mathematical laws that are expressed as degrees of freedom of the system dynamic. In a simple case, like a ball rolling down a hill, the only relevant degrees of freedom are position (x,y,z); and the respective derivatives with respect to time (velocity in x, y, z). These parameters are constrained by Newton's laws of motion - a set of empirically derived relationships between position, velocity, and acceleration due to gravity. General relativity allows the physicist to consider these relationships in a more general way, (hence "general"); part and partial to this generalization is that the position, velocity, and acceleration must be described only in a relative way, and not with respect to any fixed frame. Now, there are lots of relativistic theories, including some that are classical and consistent with Newton's laws - Galilean relativity, for example. But if you make the theory extremely generalized, you can no longer make the relationships simple: "F = m a" is not a general description of a gravitating system, because Force due to Gravity is a sort of "imagined" quantity that Newton invented. (Sure, it mathematically explains the rate and distance at which the moon circles the earth, but it doesn't do a very good job at explaining why the moon keeps magically changing direction instead of flying off in a straight line). So, general relativity seeks to eliminate that unnecessary invention by reformulating the relationships between the free parameters (position, velocity, mass, energy, and so on). The only sensible way to reformulate those relationships and still describe the kind of behavior we observe is to write out a stress energy tensor in a generalized coordinate space. The result is a description of gravity without any "spooky action at a distance" - in fact, the solution to the general relativistic equations that describe a planetary system yield accurate predictions about orbits; and do not rely on any weird spurious "force" of gravity. Gravitation is instead a property of the system - it is a description of the way the masses influence each other. Nimur (talk) 04:12, 30 July 2010 (UTC)

Piper nigrum and alcohol

So I was making steak au poivre the other day, and once the steaks were seared and removed from the pan, the recipe called for cognac to be added to the still-hot pan and the vapors ignited. Quite the impressive show resulted---the flames themselves were only about a foot tall, but the plume of hot air was at least six feet tall. I don't really want to recreate that indoors, but I don't really want to have to find an outside area free of flammables before I can make the dish. I'm wondering if I can skip the flashy vapor-igniting and just cook the alcohol off, though I'm concerned that without that step that some of the harshness of the cognac will remain. I certainly don't want to skip the alcohol both for its deglazing and solvent usefulness. Thanks for the help!72.219.136.28 (talk) 06:37, 30 July 2010 (UTC)

You should be okay to simply cook out the alcohol, if you make some changes. Igniting the flames like that serves two purposes: first, it is theatre (i.e. simply a show); second, it serves to remove the alcohol quickly. Depending on what else you plan on adding to the dish, you may want to significantly reduce the temperature to avoid burning something during the longer cook time. Incidentally, the alcohol never cooks "out" completely. Well, never is a long time, but you catch my point; don't try to just cook out (or flambé out!) alcohol for someone who is intolerant or something. Matt Deres (talk) 13:58, 30 July 2010 (UTC)

My wife (who is French and therefore "correct-by-definition" about all culinary matters) says that you're probably using WAY too much cognac. To cook a couple of steaks "au-poivre", she'd first cook the steaks in cracked soft/green peppercorns with a simdgeon of butter and ground black pepper until they are essentially "done". Then she'd use just one tablespoon of cognac for two steaks - it's a strong flavor and you don't want to overpower the cream and make it bitter. The flames are generally rather unimpressive, particularly because alcohol flames are almost invisible. It's hard to get the cognac to ignite in the pan - so she lights it in the spoon and gently pours it onto the steaks while it's still burning. Don't pour straight from the bottle into the pan! She douses the pale blue flames very quickly by pouring on the cream - then turns off the heat and allows maybe 10 more seconds in the pan to get the cream hot and mixed in with the cognac, pepper and meat juices - and then serves it straight to the table. But you do need to burn off the alcohol - it has to be added towards the end so that the flavors in the cognac don't get destroyed by the cooking - and you don't want to overcook everything else while you wait for the alcohol to simply evaporate off. If you are getting a gigantic and colorful fire - then you may have set the fat from the steaks on fire - and that's "A Very Bad Thing" for both safety and flavor. Since you're going to be serving the sauce from the pan - and you don't want a lot of ikky beef fat in it - if there is a lot of fat in the pan - then remove most of it before adding the cognac. She suggests not cooking more than a couple of steaks in a pan - if you need to cook more then two or three steaks then use a second pan so that you can control everything more closely in that busy half minute at the end of cooking. Also, avoid leaving the steaks too rare with this recipe because the blood in the cream doesn't look appetizing - so limit yourself to medium-rare. The plates you serve onto need to be really hot. She uses a sprig of parsley to decorate (and, I suspect, to meet the "7 ingredients rule" of French cooking that I've deduced from watching her cook!) Because the timing of all of this is so important, she tends to serve vegetables that can stand being a little over-cooked - asparagus is generally her choice - because then she can give full attention to the steaks without having to panic about not over-doing the veg. SteveBaker (talk) 14:32, 30 July 2010 (UTC)

Very helpful advice! I think in the future I'll probably just "cook it out" to use the term instead of the big old show. Mr. Baker, you have a good point about the color of the flame---it was orange, and even though I poured off the excess fat, there was likely still some in the pan. There was 1/3 cup cognac (I used brandy, but anyways) in the recipe, so I think I agree on the sentiment of using too much of it. Not that I really tasted it at all...anyways, thanks so much!72.219.136.28 (talk) 21:13, 30 July 2010 (UTC)

An orange flame definitely indicates that something OTHER than the alcohol was causing the fire. Alcohol flames are notoriously hard to see...and when you can see them, they are pale blue. I think you had a fat fire - possibly exacerbated by the cognac. When a liquid flash-boils because it's hitting fat that's higher than the liquid's boiling point then it causes an 'aerosol' effect that sprays a fine mist of hot oil into the air. If there is a source of ignition (and you handily provided one when you tried to set light to the cognac) - then you have a fat fire, which can be almost explosive. Perhaps you need to turn down the heat and let things cool off a little before you add the alcohol? SteveBaker (talk) 06:06, 31 July 2010 (UTC)

And if you're cooking on a gas range, please make sure you turn it OFF before you start adding combustibles like alcohol! Matt Deres (talk) 14:50, 31 July 2010 (UTC)

Quantum Mechanics Problem

I'm working through a quantum mechanics book and have encountered a problem with one of the exercises and I need a little help. The problem defines a phase flipping operator in d dimensions to be a unitary operator with eigen values +1 or -1. Then, it wants me to show what happens if we take the whole collection of such operators relative a specific shared basis of eigen vectors and average their effect on a a density operator. However, by linearity, this should be the same as applying the average of the unitary operators to the density operator, but since there will be as many +1's as -1's for any eigen |k>; the overall operator appears to average to 0. This does not seem to be the answer the book wants since it says that it should preserve the populations of the density operator, but wipe out its coherencies. Thus, I suspect I am missing something really simple or the book is wrong, can anybody point me to which one of these is the case; if the former, can I have a small hint as to what I am missing. Thank you:) 66.202.66.78 (talk) 09:29, 30 July 2010 (UTC)

Nevermind, being half asleep, it somehow seemed reasonable to average the unitary's, get 0, then apply them; obiviously that does not follow from linearity. Instead, I should obtain that only the diagonal of the density matrix remains:) 66.202.66.78 (talk) 09:39, 30 July 2010 (UTC)

practical consequences of existence

philosophically, existance in an open question. what are the practical consequences of whether I exist? Does it really mean anything for me if in the end it is proved/discovered that I don't? —Preceding unsigned comment added by 92.224.207.77 (talk) 10:14, 30 July 2010 (UTC)

http://plato.stanford.edu/entries/existence/ --Zomzom12 (talk) 13:14, 30 July 2010 (UTC)

Philosophers are a waste of quarks. What is the definition of the word "exist"? Sadly, it's not a very well defined concept. Wiktionary says "to be; have existence; have being or reality". So what is "reality"? Well, again, Wiktionary comes to the rescue with:

1. The state of being actual or real.

   The reality of the crash scene on TV dawned upon him only when he saw the victim was no actor but his friend

2. A real entity, event or other fact

   The ultimate reality of life is it ends in death

3. The entirety of all that is real.
4. An individual observer's own subjective perception of that which is real.

If we discount circular definitions of reality as "that which is real", then we're left with only the last (and still somewhat shakey) definition - and since your own subjective perception of reality is that you exist - it is completely impossible for someone to prove to you that you don't exist. It might be possible to prove to me that you don't exist (Maybe you're an AI program designed to test reference desk response times!) - but that cannot ever (by the very definitions of the words) prove to you that you don't exist. Since it can't be proved - the question of what that might mean for you is entirely moot.

Philosophers love to argue about this circular definition of what words in English mean - but, as I said, they are a waste of quarks and we may safely ignore everything they say.

SteveBaker (talk) 14:04, 30 July 2010 (UTC)

Wow, you are very dismissive of philosophy... Ironically, you yourself are engaging in philosophical argumentation above. Best regards. Zomzom12 (talk) 15:29, 30 July 2010 (UTC)

Ah - but I'm not pretending that anything terribly deep is going to come out of this. I'm merely pointing out that it can only be a matter of linguistics. If these words mean X then Y is true because that's how the words are defined. This is only a discussion about the meaning of words. If I were to define the word "existance" as "Having an account on eBay" - then the conclusions of the debate would be wildly different. Rational debate can only be undertaken when everyone agrees on the definition of the words being used because these are (mathematically speaking) a part of the axioms of the theory you're trying to prove. The big philosophy debate on the nature of existance isn't anything to do with producing some deep understanding of the universe or the human condition - it's just a matter of defining a tricky word. SteveBaker (talk) 05:58, 31 July 2010 (UTC)

Cue the cartoon showing why engineers aren't invited to philosophers' parties. Comet Tuttle (talk) 17:09, 30 July 2010 (UTC)

He was engaging in philosophical argument in order to demonstrate how pointless it is. Philosophy was replaced centuries ago by science, but there are still a small number of philosophers that keep going for no gain whatsoever (well, they get paid, so I suppose that is a gain for them). --Tango (talk) 17:32, 30 July 2010 (UTC)

If you don't exist, how could you have asked this question? Looie496 (talk) 17:13, 30 July 2010 (UTC)

I think that the subject you are talking about is ontology. Ontology may have some ethical consequences. For example, imagine a nearly-perfect computer simulation of a universe with some humans in it. Does their "ontological inferiority" mean that they don't really exist, or do ethical obligations extend to them? Paul (Stansifer) 17:24, 30 July 2010 (UTC)

That doesn't mean we need philosophers to debate it endlessly, we would just need to make a decision. It's no different from decisions that politicians make every day (assigning value to different people's lives) and we don't rely on philosophers for those decisions. --Tango (talk) 17:32, 30 July 2010 (UTC)

There is no word "existance" though it sounds a bit like the British punk band Exitstance. Wikipedia has an article about the metaphysical concept Existence.

Existence is apparent only in terms of interactions with an Observer. Thus a table does not exist to a blind man until he bumps into it. The OP did not exist (as OP here) to us until we observed his/her question. Some practical consequences of the OP existing are that we pay him/her attention and he/she pays us attention. If we discovered that the OP does not exist, which could happen if someone found that the question was posted not by a person but by a random sentence generating machine, it would mean our interactions would change. I might conclude I have better things to do than talk to a machine. The machine wouldn't notice anything except that its battery would eventually run down and probably not be replaced. Cuddlyable3 (talk) 18:36, 30 July 2010 (UTC)

But that example isn't really true. The table does exist for the blind man because it exerts a slight gravitational pull on him - it deflects and absorbs sound waves and thereby alters the acoustics of the room - it also alters the behavior of other people who live in the house - if there is a table, they might eat in that room, and if not then they wouldn't. That too would have subtle ramifications for the blind man, and that change affects him even if he isn't actively aware that the table is there. There is a measurable difference on him because the table is there. So you can't say that it doesn't exist for him.

Because every atom in the observable universe eventually affects every other one (to an admittedly small degree) everything 'out there' interacts with us as observers. Since there are no totally unobserved things, you can't say that anything in the universe doesn't exist for us using a clear black-and-white definition. To make this point about the table not existing for the blind man until he bumps into it, you have to set an arbitrary threshold for how much it's allowed to influence him without it "existing for him". Maybe objects that produce less than 0.0000000001 g's of gravity and reflect electromagnetic radiation at us at less than lumen, etc, etc can be said to "not exist" for us...but that's an exceedingly unsatisfying answer. Nobody is ever going to agree on such an arbitary threshold for "existence". SteveBaker (talk) 05:58, 31 July 2010 (UTC)

Philosophers don't debate it endlessly; they mostly talk about other things. Computer scientists don't talk about ones and zeroes forever, and historians do stuff other than memorize dates. (However, I now wish I'd taken that philosophy class on nothingness in college, since it turns out that there are a lot of different varieties of nothingness, absence, and the void in computer science.) And politicians might benefit from paying attention to what the philosophers have to say! Well, at least humanity might benefit. Paul (Stansifer) 18:57, 30 July 2010 (UTC)

Endlessly does not mean constantly. The debate on the nature of existence hasn't ended, has it? --Tango (talk) 20:45, 30 July 2010 (UTC)

They don't ever seem come to any widely agreed conclusions - so there is no end to their discussions. SteveBaker (talk) 05:58, 31 July 2010 (UTC)

All that money I spent on a philosophy course and what have I learned about? Nothing! Cuddlyable3 (talk) 21:01, 30 July 2010 (UTC)

Take a look at existentialism, consciousness, reflexive self-consciousness, homunculus argument, qualia, and metaphysical solipsism. And...sigh. Metaphilosophy. ~AH1^(TCU) 00:37, 2 August 2010 (UTC)

Misinterpretation of UN population report?

Has the media and the public completely misinterpreted the findings of the UN report "World Population in 2300" (http://www.un.org/esa/population/publications/longrange2/longrange2.htm)?

Here are some quotes:

"Fears that the human race may drive itself to extinction through over-population are challenged by new United Nations figures suggesting an eventual equilibrium as people in poorer countries come to understand the need for smaller families. " http://www.guardian.co.uk/world/2004/nov/06/population.brianwhitaker

"The world's population will stabilize in 300 years to about nine billion people, with an average life expectancy of 95 years, the United Nations predicts." http://www.cbc.ca/world/story/2004/11/05/population_041105.html

All the Report says is that "According to the medium scenario, world population rises from 6.1 billion persons in 2000 to a maximum of 9.2 billion persons in 2075 and declines thereafter to reach 8.3 billion in 2175. The return to replacement level fertility coupled with increasing longevity in the medium scenario produces a steadily increasing population after 2175 that reaches 9 billion by 2300. If the effects of increasing longevity are counterbalanced by fertility, population size remains constant at 8.3 billion from 2175 to 2300 as in the zero-growth scenario (figure 1)."

Does this mean that this medium scenario is the most likely?

Thanks for your help!

Zomzom12 (talk) 12:37, 30 July 2010 (UTC)

I don't see that implication anywhere in the report. SteveBaker (talk) 13:51, 30 July 2010 (UTC)

Thank you for the input. Zomzom12 (talk) 15:30, 30 July 2010 (UTC)

Predicting something 300 years in the future is pretty much impossible. I can't imagine why they would even try. The biggest flaw is usually that they extrapolate existing trends without accounting for changes (not that they could). Another common error is mistaking Exponential growth for Logistic growth. Ariel. (talk) 21:32, 30 July 2010 (UTC)

A world population near nine billion sometime this century and again in 300 years does not imply the population stablizes at that level in 300 years. See also our articles Malthusian catastrophe and population growth. ~AH1^(TCU) 00:28, 2 August 2010 (UTC)

canteloupe

how can you tell when a canteloupe from the garden is ready to be picked?--Horseluv10 13:02, 30 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

http://www.youtube.com/watch?v=11-XzxukFoM --Zomzom12 (talk) 13:11, 30 July 2010 (UTC)

To summarise that video (since Horseluv has previously implied they are confined to a Whitelist that only allows Wikipedia).

1. The cantaloupe will get paler until it isn't green anymore, but rather a more buff-like colour. This will presumably vary between varieties.
2. The cantaloupe will start to smell of melon.
3. The melon will start to separate from the stem, so they no longer look like the stem and melon are all one piece.
4. You will be able to separate the cantaloupe from the stem with very gentle pulling/pushing. If you have to pull properly, or cut the melon off the stem, it isn't ripe.

Anyway, that's what the video says, while showing you so that it's clearer. 86.164.66.83 (talk) 14:52, 30 July 2010 (UTC)

As a onetime seller of the melons, I agree that color change is one sign of a canteloupe being ripe, but the smell of ripe melon is the best indication. Unlike watermelons, the sound when it is thumped does not become deep and dull. Edison (talk) 23:18, 30 July 2010 (UTC)

thanks for the info from the video. i couldnt get onto it. im blocked.--Horseluv10 01:10, 31 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

The video is a great guide for growers to decide when to pick. Smell is the best guide for a consumer to decide which canteloupe to buy, since you can't tell, in the store, what the vine looked like. Edison (talk) 04:14, 31 July 2010 (UTC)

Atomic theory

Atomic theory tells us that valence electrons in an atom are the particles that are mostly involved in many phyisical or chemical activities of substances. In lasers, electrons move from one energy level to another and thereby releasing coherent and monochromatic photons. During chemical reactions,valence electrons move from one atom to another and thereby changing the properties of the substances involved.Duruing charging,substances lose or gain electrons.DOES AN ELECTRON MOVE AWAY FROM ITS MOTHER ATOM WITHOUT ITS MOTHER ATOM COMING TO CONTACT WITH AN ATOM THAT THE ELECTRON IS INTENDING TO GO TO.JUST AN ELECTRON(ALONE) MOVING AWAY FROM ITS MOTHERATOM,POSSIBLY IN A VACUUM. —Preceding unsigned comment added by Mlondo (talk • contribs) 14:37, 30 July 2010 (UTC)

I have added a header separating this question from the one above. 86.164.66.83 (talk) 14:43, 30 July 2010 (UTC)

I think that the electrons separate in a plasma. --Chemicalinterest (talk) 14:58, 30 July 2010 (UTC)

Are you talking about chemical reactions, electrons moving in metals, or lasers? John Riemann Soong (talk) 15:01, 30 July 2010 (UTC)

The OP was asking whether there is an instance that an electron moves away from the mother atom without an ionic bond occurring. I responded by saying that I think in a plasma the electrons are stripped from the mother atom and sort of float around it. --Chemicalinterest (talk) 15:18, 30 July 2010 (UTC)

The OP describes well what happens in a metal conductor. Atomic nucleii rest in fixed positions while electrons can drift in the intervening space. An electric current occurs when electrons move from orbiting one nucleus to orbiting a neighbouring nucleus. Cuddlyable3 (talk) 16:15, 30 July 2010 (UTC)

It does happen in a metal to and is the basis of electrical conductivity; this moving away of electrons from mother atoms without a redox reaction going on. An exception would be electrical conductivity in ionic solutions. --Chemicalinterest (talk) 12:26, 31 July 2010 (UTC)

The OP describes a standard gas-phase ionization reaction: see ionization energy for more details. Physchim62 (talk) 14:57, 31 July 2010 (UTC)

Maybe in cases of positron radiation where the β⁺ particle comes into close contact with an atomic electron? ~AH1^(TCU) 00:10, 2 August 2010 (UTC)

water

Ages ago I saw someone with a glass of water and a weird device with two metal prongs which they put into the water. Then the water started to go grey. I asked them what the fuck they were doing and they said it was putting silver into the water and then they'd drink it for health benefits. What the hell were they doing? —Preceding unsigned comment added by Fdge45y4uwuetj (talk • contribs) 15:01, 30 July 2010

I think it was an electrolytic apparatus. --Chemicalinterest (talk) 15:03, 30 July 2010 (UTC)

What makes you think it was anything other than putting silver into their drinking water? While unconventional, this is not really that weird considering the other weird stuff people consume in the name of health. I would suspect the 'device' was some sort of soluble rod that allowed for easy introduction of silver into the water. --144.191.148.3 (talk) 15:05, 30 July 2010 (UTC)

Here it mentions electrolytically dissolved silver. --Chemicalinterest (talk) 15:09, 30 July 2010 (UTC)

It may well have been exactly what they said. Silver sometimes used as a quack medical cure-all, (Presumably because of its weak antiseptic abilities.) See : Colloidal_silver#Current_alternative_medicine_use

Fun Fact : Overuse of silver 'supplements' can turn your skin blue. See : Argyria

APL (talk) 15:38, 30 July 2010 (UTC)

Fun idea: Argyria turns skin blue where it is exposed to light. Could sitting in front of a slide projector eventually produce a skin tattoo of a photograph? Cuddlyable3 (talk) 16:00, 30 July 2010 (UTC)

What happens when the sun shines on your tattoo? You would need a "fixer" to lock the color in so additional light will not make the whole area blue. --Chemicalinterest (talk) 19:59, 31 July 2010 (UTC)

Seems "safer" to do it topically in a small area...obviously "do not try this", but paint on a solution of some silver salt, expose self, wash off. Essentially make yourself into a photographic plate. DMacks (talk) 19:41, 30 July 2010 (UTC)

Lest you think I'm just proposing bad ideas, the idea of using a slide projector to trigger photochemical reactions that produce an image of what was projected is actually pretty cool! One neat application is DOI:10.1021/ed800170t. DMacks (talk) 19:46, 30 July 2010 (UTC)

After reading your first two sentences and before reaching your third sentence, I was sure they were using one of those portable, unsafe, electric gadgets that you can put in a mug of water to boil it. You plug it into household AC, and it boils the water super-quick. Of course, if you drop the gadget and the two prongs touch your skin, you're then plugged into household AC yourself. Comet Tuttle (talk) 16:57, 30 July 2010 (UTC)

I don't think those "water heaters" have live AC current. If it was just two electrodes, then it would fizzle the water furiously, creating a highly flammable oxyhydrogen mixture. --Chemicalinterest (talk) 21:04, 30 July 2010 (UTC)

I have a humidifier that works like that. It's simply two electrodes directly connect to power, and in the instructions they say to add a little salt to the water. Ariel. (talk) 21:27, 30 July 2010 (UTC)

Silver is antibacterial, so it makes sense that they would want it. --138.110.25.31 (talk) 19:37, 30 July 2010 (UTC)

Well, it doesn't "make sense", because silver doesn't kill billions of bacteria on contact in the way that antibiotic ointment does. Comet Tuttle (talk) 20:09, 30 July 2010 (UTC)

Read medical uses of silver. Even the WHO adds silver ions to drinking water. --138.110.25.31 (talk) 20:12, 30 July 2010 (UTC)

Ok 138.110.25.31! Let's read that article!

At present, there are no evidence-based medical uses for ingested colloidal silver. There are no clinical studies in humans demonstrating effectiveness, and a few reports of toxicity. The U.S. National Center for Complementary and Alternative Medicine has issued an advisory indicating that the marketing claims made about colloidal silver are scientifically unsupported, and that the silver content of marketed supplements varies widely and that colloidal silver products can have serious side-effects to the consumer, including "argyria,... neurologic problems (such as seizures), kidney damage, stomach distress, headaches, fatigue, and skin irritation. Colloidal silver may interfere with the body's absorption of some drugs, such as penacillamine, quinolones, tetracyclines, and thyroxine."

Any questions? WHO does not use it for medicinal purposes. They do sometimes use it to disinfect contaminated water in third-world countries, but in western countries with good public water systems that doesn't apply at all. APL (talk) 00:24, 31 July 2010 (UTC)

Isn't silver poisonous? Count Iblis (talk) 23:06, 30 July 2010 (UTC)

Yes. It is. Alternative medicine fads are often dangerous. APL (talk) 00:24, 31 July 2010 (UTC)

No; silver is not poisonous. It is an unreactive element. Silver compounds are poisonous.Yeah I know--Chemicalinterest (talk) 00:53, 31 July 2010 (UTC)

Elemental silver can cause a number of health problems. The bit I quoted above mentions some of them, the articles mention more. (Besides, if it's so 'unreactive', how's it killing all that bacteria in third world water supplies?)

Please don't post things that you thought up off the top of your head. Especially when the actual facts are so close at hand. APL (talk) 19:29, 31 July 2010 (UTC)

Silver kills bacteria and is therefore useful as a disinfectant/antiseptic. --138.110.206.101 (talk) 01:25, 31 July 2010 (UTC)

Perhaps, a bit anyway. But you don't drink disinfectants! APL (talk) 03:40, 31 July 2010 (UTC)

Silver nanoparticles can be poisonous due to the presence of residual Ag+. John Riemann Soong (talk) 03:15, 31 July 2010 (UTC)

One additional word of caution about colloidal silver and gold is that when it changes your skin color, it does so permenantly. There is no cure and it doesn't fade or dissipate over the remainder of your life. Since there is zero evidence of beneficial effects of putting the stuff into your body - you'd definitely have to be crazy to take the stuff. The antibiotic effects of silver outside of the body are really rather mild - not even a fraction as good as modern antibiotics. SteveBaker (talk) 05:13, 31 July 2010 (UTC)

But don't you want your cells to be all bright and sparkly like these a549 cells? John Riemann Soong (talk) 05:44, 31 July 2010 (UTC)

My opinion is that the disinfectant in colloidal silver is too weak to be of any use in vivo. --Chemicalinterest (talk) 11:02, 31 July 2010 (UTC)

ChemInt, I don't mean to be rude, but no one cares what your opinion is. Not in the slightest. APL (talk) 19:29, 31 July 2010 (UTC)

I don't care. But since I don't know (haven't read the studies), I can only have an opinion. --Chemicalinterest (talk) 19:57, 31 July 2010 (UTC)

I did read a few studies while trying to mediate a wiki-dispute once, and my slightly-informed opinion matches the mainstream view - colloidal silver is utter crap and relies on confusing people with studies that examined ionic silver. Franamax (talk) 21:16, 31 July 2010 (UTC)

Then why would you imagine you needed to answer? I have an opinion on lots of things I haven't got evidence or sources for, but I'm not going to offer it when there are plenty of people offering more informed views. If those people do not present themselves, the second best option is to inform myself so that I can give an actually informed answer with sources. Giving an uninformed opinion is absolutely the last-ditch option when I can't find any information and nobody else has offered anything good and the question has been up for days. And even then, it has to be an opinion that might lead them to greater understanding of the topic, swathed in acknowledged limits. 86.164.66.83 (talk) 01:25, 1 August 2010 (UTC)

Except in burn treatment where for instance "Silver sulphadiazine continues to be the antimicrobial agent most often used in burn care facilities" [1] and silver ions counteract problems with bacterial resistance.[2] Note this is not colloidal silver. Entire sheets of metallic silver used to be used for burn treatment too, and I think there may even still be active research on this. Franamax (talk) 21:12, 31 July 2010 (UTC)

Flossing

I am writing a work of historical fiction surrounding the invention of flossing. The novel begins when the protagonist notices that on some days her teeth are very tight and it's impossible to get the floss between them without breaking it (the floss), while on other days it just glides through with no problems. She sets out to discover whether it's possible/normal for the teeth to cycle through this kind of tightening and relaxation and what it's called. Anyone know? Thanks. --Sean 16:59, 30 July 2010 (UTC)

You ask a good question. It's an evidence-based assertion that occlusion, or the manner in which teeth of the upper arch meet with the teeth of the lower arch, changes ever so slightly throughout the day. Normal physiology dictates that hard tissue join not directly to other hard tissue but rather via ligaments. Teeth are no exception, and they are attached to the alveolar bone via fibers of the periodontal ligament. As such, there is some physiologic mobility to healthy teeth (contrast this to dental implants which, when properly osseointegrated into the jaw bone, fuses directly to bone and exhibits no mobility. So, to respond to your question directly, I cannot say that I've heard of any research on that front, but it's certainly biologically plausible for contact between teeth to shift enough for a layman to detect with a floss test -- I question if the magnitude of change would be enough to tear the floss one day and allow it to pass though, as you described it, a nearly open contact. Moreover, I have a pamphlet that describes the invention of floss, and if you email me and give me a few days, I'll scan it and send that to you. DRosenbach ^{(Talk | Contribs)} 20:23, 30 July 2010 (UTC)

Thanks so much for the thorough answer. I'd never even considered that teeth were held in by ligaments, though that makes sense, of course. Don't bother with the scan, but thanks; I've got enough to go on about the variable tightness issue from here. DRosenbach, I've thoroughly enjoy your dental-themed contributions to these desks over the last year or so. Cheers! --Sean 21:25, 30 July 2010 (UTC)

(non EC-flagged EC) Whew. I can't think of anything that would cause that particular cycle, though hopefully our resident dentist can come up with something. I hope you don't mind me saying this, but that seems like a really bizarre way to start... anything. Seriously - the central problem of the story is why floss sometimes gets stuck? Good luck with the publishers, my friend. :-) Matt Deres (talk) 20:26, 30 July 2010 (UTC)

Oh, I assure you it will be a ripping yarn as we watch our intrepid flosser invent all manner of ludicrous backstories as she outwits the various bureaucratic regimes that stand in the way of her idle wonderings, even when she agrees with those regimes in principle! --Sean 21:25, 30 July 2010 (UTC)

Yeah, when you're heroine is busy being subtle, make sure she doesn't push her luck by gloating in the presence of people who played along with her. That wouldn't make her a terribly sympathetic protagonist. 86.164.66.83 (talk) 23:37, 30 July 2010 (UTC)

... I was actually wondering if this was just an elaborate ploy to circumvent our medical advice policy. "So I was writing a work of historical fiction where my protagonist's foot looks like this. Do you think it's infected?" Does dental advice fall under the desk medical guidelines? Nimur (talk) 23:55, 30 July 2010 (UTC)

It does, but I think this is one of those cases when we can AGF Nil Einne (talk) 11:03, 1 August 2010 (UTC)

Floccinaucinihilipilification? ~AH1^(TCU) 00:05, 2 August 2010 (UTC)

paradoxical redox reactions

Oxidising and reducing power should be a transitive property, right? According to the article hydrogen peroxide: "In acidic solution, H2O2 is one of the most powerful oxidizers known—stronger than chlorine, chlorine dioxide, and potassium permanganate."

Why then does hydrogen peroxide reduce potassium permanganate in acidic solution? Hydrogen peroxide would appear to be less reactive in alkaline solution (what with it being deprotonated and all) yet it would oxidise in alkaline solution? How can an oxidising agent A be a more powerful oxidiser than an oxidising agent B at say, pH 1.5 and yet get oxidised by agent B? John Riemann Soong (talk) 17:00, 30 July 2010 (UTC)

(That section is missing info [3], however this doesn't affect the answer)

Kinetics is the key here when considering products - since the reaction of H2O2 >>> 2H+ + O2 + 2e- is doable by permanganate there is nothing to stop it happening .. in this case it is the faster reaction. So that is what happens.

In fact since it is more thermodynamically favourable: half cell emf of above reaction ~0.2V giving an overall potential of 1.8V (cf the overall potential for the H2O2 + MnO2 > MnO4- + H2O reaction is about 0.2V) it can be expected (but not certainly) to be the faster reaction anyway. (Sf5xeplus (talk) 20:09, 30 July 2010 (UTC)

Additionally there isn't actually anything the permanganate could be oxidised to. Sf5xeplus (talk) 20:20, 30 July 2010 (UTC)

It might not be stronger than KMnO4 in acidic solution though. Reduction for MnO4-- is +0.59 in basic solution but +1.70+1.51 (the article states reduction to Mn++) in acidic solution. H2O2 is +1.78 in acidic solution. As reducing agent its oxidation potential is -0.70. --Chemicalinterest (talk) 00:49, 31 July 2010 (UTC)

The curve of increase in oxidizing power as a result of pH may not be the same for both chemicals. So in an extremely acidic solution (all H+), H2O2 might be stronger, while in a more weakly acidic solution MnO4 might be stronger. Just an idea. --Chemicalinterest (talk) 00:51, 31 July 2010 (UTC)

Also bear in mind that one of the possible reduction products for permanganate, Manganese dioxide, is a catalyst for the (non-redox) decomposition of hydrogen peroxide.77.86.5.67 (talk) 12:05, 31 July 2010 (UTC)

77, it is a redox reaction; specifically, it is disproportionation of 2 O₂^2- into O₂⁰ and 2 O^2-. --Chemicalinterest (talk) 12:22, 31 July 2010 (UTC)

Wisteria

I have grown a number of seed-containing pods. What should I do with them? Kittybrewster ☎ 18:39, 30 July 2010 (UTC)

Kill them. Wisteria is a highly invasive and troublesome plant. If you decide to put it in your yard, you will have to prune it daily. Even then, it will likely spread underground and take over not only your yard, but all yards around you. A lady three houses down planted Wisteria in her yard two years ago. Now, the entire neighborhood has an impossible Wisteria infestation that is not only problematic, but also causing property damage as Wisteria is a strong plant that can take down fences, trees, and crack the foundations under houses. -- kainaw™ 19:40, 30 July 2010 (UTC)

It is hardly kudzu. Kittybrewster ☎ 20:25, 30 July 2010 (UTC)

Out of curiosity, has anybody gotten the neighbor to pay for the damage? Comet Tuttle (talk) 20:07, 30 July 2010 (UTC)

Rylands v Fletcher? Kittybrewster ☎ 20:25, 30 July 2010 (UTC)

Wisteria in the UK is a beautiful slowish growing climber that rarely causes damage if planted in the right place. I have seen several that have been growing close to houses for decades with no obvious dammage. It is not invasive in the sense that it propagates in an uncontrollable way. I'd plant those seeds in the autumn in a gritty loam and see what happens. I have doubts that much will but just imagine - your very own wisterias. Good luck. Richard Avery (talk) 22:02, 30 July 2010 (UTC)

From what I recall reading, even in the UK they cause damage to brickwork, and they do not support their own weight so have to be supported. On the other hand there is an attractive wisteria growing up the side of a building in one of the Inns Of Court in central London. 92.29.119.4 (talk) 22:31, 30 July 2010 (UTC)

We (UK) have some wisteria growing that supports itself, but we do have to prune it back every year to stop it getting too heavy for itself, and too intrusive. 86.164.66.83 (talk) 23:35, 30 July 2010 (UTC)

Here (in the southeast US), Wisteria grows so fast that you can literally watch it grow. Every weekend, I have to trim back foot long vines such that no Wisteria can be seen. It all grows back in just a week - over an inch a day. -- kainaw™ 17:19, 31 July 2010 (UTC)

veneer core plywood

what is veneer core plywood —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 19:19, 30 July 2010 (UTC)

You can find an explanation of the different types of plywood here. Looie496 (talk) 19:24, 30 July 2010 (UTC)

Strange patterns in the water

There is a lake on the University of Nottingham's Jubilee Campus (it's the north one if you want to look on Google Earth) and it has several what I assume are oxygenating bubble jets which cause the water to bubble. When it rains, there is always a disc visible around these jets where the water is a different colour (see picture). Can anyone explain why this would be the case? I'd have thought it might be the jets adding some sort of chemical, but the effect is too clear-cut than diffusion would suggest. I have uploaded a sunny picture for comparison. -mattbuck (Talk) 19:21, 30 July 2010 (UTC)

Heh, I live in Nottingham and spend a bit of time at that campus. How strange. Can't answer your question though, sorry! Regards, --—Cyclonenim | Chat  20:07, 30 July 2010 (UTC)

Possibly a convection cell - oxygenated water forced up by the pumps spreads out a specified distance and then rolls under. that would imply a density difference of some sort, however (either the oxygenated water is colder than the surrounding water or the oxygenation process changes water density). You can see the pattern in the sunny picture as well, if you look closely - it's just more muted. --Ludwigs2 20:14, 30 July 2010 (UTC)

Could be a visible effect from the submerged heat-exchangers in the lake. Nanonic (talk) 20:36, 30 July 2010 (UTC)

Is there something under the disk meaning the water is shallower there? --Tango (talk) 20:47, 30 July 2010 (UTC)

I honestly have no idea. All I know is there are a lot of big koi living in there, and that it leaks because they need to keep topping it up every week. -mattbuck (Talk) 22:10, 30 July 2010 (UTC)

If it's not artificial, it could be some form of natural spring. ~AH1^(TCU) 23:55, 1 August 2010 (UTC)

The upwellings caused by Langmuir circulation are clearly visible

Upwellings can cause a texture on the water surface that give it another colour. This is seen on a larger scale in Langmuir circulation. EverGreg (talk) 07:39, 2 August 2010 (UTC)

Irrational fear

The other day me and a couple of friends were sitting and talking on a park bench pretty late, and the conversation came up about fear and how we all seem pretty susceptible to fear even when we know it's very, very illogical. For example, if you sit and look out into the distance in the dark, you can imagine things there that really quite obviously aren't, and the presence of fear can remain. Is there a term to describe irrational fear, other than just that? Also, is there a term describing when you see something that isn't there (not a mirage, I think you get the point)?

Cheers! Regards, --—Cyclonenim | Chat  20:05, 30 July 2010 (UTC)

Phobia, and hallucination? Looie496 (talk) 20:14, 30 July 2010 (UTC)

Not really what I was looking for. 'Phobia' doesn't quite fit as it's not an inherent fear that's there all the time, it's only there when you're really focusing on what you're actually thinking about! Hallucinations don't normally come across as hallucinations, do they? I mean, people having hallucinations usually think what they're seeing is real. I don't. Regards, --—Cyclonenim | Chat  20:31, 30 July 2010 (UTC)

It sounds a bit like paranoia. --Tango (talk) 20:48, 30 July 2010 (UTC)

For phobia I take your point. For hallucination I don't think you have the word down correctly -- it doesn't imply believing that the thing is real. Looie496 (talk) 20:54, 30 July 2010 (UTC)

Fear of the dark seems to cover this. It is a normal phenomenon, as distinguished from the pathological fear of darkness, nyctophobia. Not great articles, but maybe that's a start? --- Medical geneticist (talk) 20:58, 30 July 2010 (UTC)

Thanks, that does pretty much cover it. What about the phenomenon of actually seeing things that aren't there? I take Looie's point above with respect but it still doesn't occur to me as an hallucination. This only really happens in the dark and it's basically if you stare at some space in the distance your mind wrongly decides that, say, a post by a tree is actually a person. Maybe I'm just overthinking this and it is a form of hallucination, I don't know. Regards, --—Cyclonenim | Chat  22:43, 30 July 2010 (UTC)

Imagination is not just for kids. It's easy to imagine things, and if you are good at it you can even (for a while) believe it. Imagine is often used as a negative word, but it doesn't have to be. Ariel. (talk) 23:25, 30 July 2010 (UTC)

Fear, anger, sadness and love are always irrational emotions but may be based on good cause. Hallucinations may be chemical and don't have to induce fear. Eg seeing a bunch of horses galloping past your right field of vision in your dining room. Kittybrewster ☎ 02:11, 31 July 2010 (UTC)

Also see fear of ghosts and boogeyman. ~AH1^(TCU) 23:54, 1 August 2010 (UTC)

Name this climbing plant?

What is this please? http://img201.imagevenue.com/img.php?image=27784_climbingplant_122_47lo.jpg Thanks 92.29.119.4 (talk) 22:28, 30 July 2010 (UTC)

My guess: Virginia creeper Parthenocissus quinquefolia --Digrpat (talk) 01:48, 31 July 2010 (UTC)

Looks like it. Thanks. 92.15.12.218 (talk) 13:41, 31 July 2010 (UTC)

Silent cars?

Will it ever be possible to have silent cars, and hence no traffic noise? Or is the current noise-level of modern cars as quiet as we can get? I assume most of the noise comes from the tyres and road surface rather than engine noise. Thanks 92.29.119.4 (talk) 22:55, 30 July 2010 (UTC)

While not directly answering your question, I'll direct you to Electric vehicle warning sounds, and ask you to keep in mind that the majority of modern cars are still operating with standard internal combustion engines. --LarryMac | Talk 23:00, 30 July 2010 (UTC)

Personal experience, but it's relevant. When the first Prius cars came out I was at an art festival in the Blue Ridge mountains and whilst walking through a parking lot had the very disturbing experience of a Prius appearing out-of-nowhere into my peripheral vision and then passing me as I walked along. Now - the Prius obviously had been driving through the parking lot at a safe speed and simply passed me as any other car would, but because of its engine design, the only thing I heard was the light sound of tires on gravel. Had it been blacktop, I'd not have heard a thing. That's pretty silent!

Assuming in some alternate reality everyone switches to electric or quiet hybrid cars, though, you're still going to have horns and the occasional need to use them. So if you include horns and aftermarket stereos in your "traffic noise" category, then the answer is clearly "no" regardless of engine noise levels... 61.189.63.171 (talk) 23:35, 30 July 2010 (UTC)

Maybe silent cars of the future will need radar-operated horns to honk and automatic brakes to operate when some doofus or blind person steps out in the street without looking both ways. Edison (talk) 04:12, 31 July 2010 (UTC)

Actually, at high speed on a freeway the dominant sounds are tire and wind noise. Engine noise is there, but it's nearly drowned out by the tire noise. An all-electric car with normal tires is nearly as loud as any other car on the freeway. If cars start using the tweel instead of inflatable tires, they'll be even louder (my company tested this for a military application; the rubber spokes flexing and snapping taughttaut as the wheel turned generated a lot of noise). ~Amatulić (talk) 05:47, 31 July 2010 (UTC)

You mean taut. 92.15.12.218 (talk) 13:23, 31 July 2010 (UTC)

Yes. Thanks. ~Amatulić (talk) 06:02, 1 August 2010 (UTC)

Perhaps for the safety of pedestrians, electric cars should be fitted with external loudspeakers playing recorded or simulated internal combustion engine sounds in synchronisation with their speed and acceleration :-) . 87.81.230.195 (talk) 12:02, 31 July 2010 (UTC)

Or else Good Humor truck jingles, just to confuse all the kids. DMacks (talk) 15:16, 31 July 2010 (UTC)

Need I point out a lot of this is already somewhat discussed in the link LarryMac, the first respondent, provided? Incidentally I don't think people tend to cross on highways, looking first or not Nil Einne (talk) 19:34, 31 July 2010 (UTC)

ZENN vehicles (zero emission, no noise) are said to produce no "noise", but it's difficult for any car to be completely silent unless it integrates some kind of external sound absorption mechanism. ~AH1^(TCU) 23:50, 1 August 2010 (UTC)

July 31

Have cognitive scientists explained why it's tedious to not use pronouns?

Please see thread at

Wikipedia:Reference_desk/Language#Have_cognitive_scientists_explained_why_it.27s_tedious_to_not_use_pronouns.3F

thanks

Andrew Gradman ^talk/_WP:Hornbook 01:44, 31 July 2010 (UTC)

To quote your example from the Language desk: "After Jane Smith ate a sandwich, Jane Smith took a walk, where Jane Smith saw Jane Smith's favorite tree next to Jane Smith's favorite house ..." - I think it's pretty obvious. "Jane Smith" is much longer and slower to say, write or type than "she" and "her". SteveBaker (talk) 05:04, 31 July 2010 (UTC)

I think it's more than that. Try "Jo" for instance. Still more tedious. I think it's because we use pronouns to keep track of people "already" in working memory and we get puzzled at having to introduce 'new instances' of the same person. John Riemann Soong (talk) 06:00, 31 July 2010 (UTC)

Or even just "M" or "Q" or something other than "I", where the letter is meant to be a name. "After Q made James Bond a sandwich, Q took a talk, where Q saw Q's favorite gadget..." --Mr.98 (talk) 13:06, 31 July 2010 (UTC)

Yes - but having established that in most cases it is quicker to use the name once at the start - then use to 'her' and 'he' after that, we have that as a 'normal' way of speaking - so we use that same pattern even though it's no faster in the case of 'Jo' and 'Q'. SteveBaker (talk) 15:33, 31 July 2010 (UTC)

Languages such as Italian ("null subject languages") have an even faster way — once it's clear who's being referred to, you just omit the subject altogether, without replacing it with a pronoun, except for emphasis. Continually repeating the pronoun in Italian sounds as stilted as continually repeating the name would, in English.

Of course it's a bit easier to do that in Italian because it's a more inflected language than English; the verb ending (usually) tells you first-, second-, or third-person, and singular or plural. --Trovatore (talk) 21:41, 31 July 2010 (UTC)

1) After establishing who a personal pronoun represents, one has available a standard set of pronoun versions tabulated below. They are usually quicker to read than the corresponding name version. The name versions for ownership and reflexive seem particularly tedious compared to the pronoun versions. Only the pronoun versions distinguish between nominative and object immediately without the reader needing to look for context.

                  NAME VERSION      PRONOUN VERSION
Nominative        Steve             He
Object            Steve             Him
Ownership         Steve's           His
Reflexive         Steve himself     Himself

2) The first sentence below using names requires some effort at anaphore resolution which is obviated by the second version.

Bob shot Robert K. StJohn-Hollyoaks.
Bob shot himself.

Cuddlyable3 (talk) 23:00, 31 July 2010 (UTC)

3) Personal pronouns can resolve gender ambiguity.
It was Pat's mother that chose Pat's name.
It was his/her mother that chose Pat's name.

Cuddlyable3 (talk) 14:35, 1 August 2010 (UTC)

That's not really an advantage though. Most languages have sexual dimorphism among names for a reason; sexually ambiguous names are exceptions to a trend. Besides, it's usually a problem when you don't know the gender of said person. Pronouns aren't used for these rather trivial "advantages". Some languages use kinship terminology rather than pronouns -- see Vietnamese pronouns. John Riemann Soong (talk) 19:17, 1 August 2010 (UTC)

Speed of lightning

What is the range of lightning speed observed? I'm a bit confused by some documentaries and websites that explain lightning discharge can travel at speeds near from the speed of light. --Email4mobile (talk) 04:04, 31 July 2010 (UTC)

Lightning propagating at near light speed is hard to believe. I can see the progress of a lightning stroke across the sky, and it looks orders of magnitude slower than light should be able to travel through the same portion of sky. There should be some quantitative answers from high speed photography done in the course of lightning research. Edison (talk) 04:09, 31 July 2010 (UTC)

Check out this [4] incredible video. It shows lightning propagating - filmed on a 9,000 frames per second camera - so the lightning is slowed down maybe 300 times. The initial strokes take several seconds to grow in the video - which means 10's of milliseconds in reality. It's hard to judge how high the clouds are in the video - but it's likely to be in the 500 meter-ish range. So 500 meters in maybe 10 milliseconds is 50km/sec or 100 thousand miles per hour. Light travels at 670 million miles per hour - so the lightning bolts seem to be propagating at a very small fraction of light speed. This is a pretty rough calculation though - there is room for maybe a couple of orders of magnitude of error - so maybe at most 1% of light speed? SteveBaker (talk) 05:01, 31 July 2010 (UTC)

Lightning leader propagates at 10⁵ - 10⁶ m/s, or sometimes even slower, see "Lightning: Physics and Effects" by Rakov and Uman. The subsequent "strokes" of lightning (the ones that propagate in the established channel), however, are much faster, sometimes in excess of 10⁸ m/s. Speed of light is 3x10⁸ m/s. --Dr Dima (talk) 05:28, 31 July 2010 (UTC)

You can see that latter effect in the video - once the channel is established, the subsequent strokes along that same path happen instantly - even at 9000 frames per second. I was talking about establishing the initial path. SteveBaker (talk) 15:28, 31 July 2010 (UTC)

As usual, the problem stems from a problem of definition. What do you define as the "speed" of lightning? Lots of complicated things are happening in the course of a lightning bolt. There are electromagnetic waves, that propagate at the speed of light, carrying information about bulk changes in ion distributions. These waves help "prepare" the air mass for the next phase - dielectric breakdown. The dielectric breakdown of air propagates at a difficult-to-determine speed. At every point along an (as-yet undecided) path, the static electric field must be greater than the breakdown-strength of air - something like a megavolt per meter. But that exact number depends on air density and humidity (among other parameters). These values fluctuate on the microscopic scale - and are affected by the breakdown of neighboring regions - so it's a mess of electromagnetic wave propagation and fluid-dynamics. The next phase is that after breakdown, current begins to flow. Just like any electric current, we have both an electromagnetic wave (propagating at the speed of light in ionized air), and we have microscopic drift motion of electrons (and, unlike a copper wire, bulk drift velocity of ions). Every constituent ion of air has a different ion drift velocity - because it depends on mass. So, O^- will drift at a different speed than O₂^- or N₂^- and so forth. The current will flow at the speed of the electromagnetic wave that conveys information along this ionized path (which is still forming as the instantaneous static electric field overcomes the breakdown strength in new areas at the edges of the strike path). Finally, the slowest part of all, is the incandescence - what we actually see. The current releases so much energy that it heats the air. The rate of heating depends on the current strength (which can very from a few hundred amps in a small lightning strike, up to nearly a mega-amp in a giant bolt). The rate of heating depends on air parameters, (density, humidity, and so forth). So when you finally see the "light" of the lightning, the bolt may have already existed for anywhere from a few nanoseconds to a few milliseconds before the air got hot enough to glow. Lastly, the thermal and electromagnetic change that has been building up over these microsecond scales will seem instantaneous to the neutral air surrounding the lightning strike path. This air is not ionized; it has not been affected significantly by the electromagnetic waves or the ionization that has communicated the change of state through the bolt path. As far as this air is concerned, the change from "normal air" in its neighboring region to "ionized plasma with enormous electric current and heat" is "instantaneous". So, there is a rapid shock front - a thunderclap - as the hot air acoustically transfers heat, pressure, and momentum away from the bolt at the sound speed in air (perturbed by pressure and humidity, not to mention rain-drops, which are non-negligible - they are a dense field of acoustic scatterers with dramatically different acoustic speeds, reflecting, dispersing, and attenuating any acoustic energy). The amazing thing about lightning is that it occurs across many orders of magnitude - microscopic voltages between individual ions accumulate (each individual electron charge) and result in a bulk ion concentration of thousands of coulombs of static electricity. Tiny perturbations in air pressure (chaotic variations of nano-meter size) between air particles dictate which air parcel will be most susceptible to instantaneous dielectric breakdown and ionization. Electromagnetic waves travel at near the speed of light in vacuum; and then when the ion channel forms, they travel through that channel much slower (because of the plasma properties); but they still travel through the neutral air at near-vacuum speeds, so there is a complicated interplay there. The rate of heating and incandescence are derived from this massively complex interaction, and the illuminated bolt you see tracing its way across the sky eventually expands at speeds on the order of kilometers-per-milliseconds. Finally, just for the interested reader - transient luminous events associated with lightning, including jets, sprites, and elves, are not well explained. Our physical understanding of the appropriate propagation speeds in sparse plasmas tell us that the jets appear above a lightning strike too soon at too-high an altitude - indicating an unknown form of information- or energy-transfer. The most likely explanation is a nonlinear interaction between weak electromagnetic waves and sparse, ionized plasmas, somehow amplifying the energy and generating a "second" illumination about a hundred kilometers above the lightning strike. These are rarely observed from the ground (though it has been done); but they are regularly observed by satellite. Red Sprites and Blue Jets, from Univ. of Alaska's Geophysical Institute, and Lightning-induced Electron Precipitation from Stanford's Low Frequency radio group both have good descriptions, pictures, and links to active research on lightning physics, including efforts to experimentally verify the relevant timescales for each physical process in a lightning strike. And, the Lightning Research Lab at Univ. of Florida experimentally triggers lightning strikes using rockets - again, attempting to characterize the physical parameters of the strikes, including the ion distributions and speed of bulk charge transfer. Nimur (talk) 17:18, 31 July 2010 (UTC)

The article says that lightning can travel at speeds near 60,000 m/s. While the flow of current can travel close to the speed of light in a lightning strike, the electrons would move much slower than that and the lightning itself slower still. ~AH1^(TCU) 23:47, 1 August 2010 (UTC)

Rechargeable batteries not recharging

Because I take lots of photos, I maintain eight NMH rechargeable AA batteries; at any given time, four are in the charger (although not always plugged in), two are in the camera, and the other two will be backups in the camera bag. Last time that I switched my batteries, I noticed that the ones in the camera and the ones in the camera bag seemed to hold only a small charge; apparently they're older. Today, I charged them, and when they were done, I put them into the camera, taking care to separate them and the other four. It turns out that two of the batteries, when placed in the camera, have only enough energy to produce a "Change batteries" message, even though they've charged all day. Should I assume that they're just too old and past their ability to hold a charge, and thus trash them? Or is there some practical way for me, the non-scientist, to do something useful with them? Finally — it's been so long since I got rid of rechargeable batteries that I don't remember what to do with them; is the trash safe, or is there a better option? I live in a rural area without any realistically-nearby HAZMAT centers. Nyttend (talk) 04:11, 31 July 2010 (UTC)

In my experience, there is a substantial chance that the charger goes bad and not the batteries. You can ask your friends to lend you their charger for a day, and see if the batteries charge better with a different charger. --Dr Dima (talk) 05:42, 31 July 2010 (UTC)

I own Energizer NiMH batteries that are old and although fully charged at the beginning, die within about 4 days because of current drainage. --Chemicalinterest (talk) 11:04, 31 July 2010 (UTC)

Dr Dima, this isn't an option because the other two batteries that I charged don't even cause the low battery indicator to appear, while the four batteries that I had in the camera also work for quite a long time. Nyttend (talk) 11:18, 31 July 2010 (UTC)

If some are older than others, then the older ones may behave as I have stated above. --Chemicalinterest (talk) 11:43, 31 July 2010 (UTC)

Rechargeable batteries should be recycled, but NiMH do not contain hazardous substances like other batteries do. --Chemicalinterest (talk) 11:44, 31 July 2010 (UTC)

I find that my camera seems to require fairly new NiMH batteries and that cells that have been recharged lots of times give a battery low indication almost immediately, but that when they no longer hold sufficient charge for the camera, they can still be used for less-demanding equipment for many more charge cycles. Slower charging (14 hours at 1/10 rating) and slower discharging in low-current applications seems to prolong their life, but eventually they have to go to recycling. Dbfirs 12:40, 31 July 2010 (UTC)

Most probably the batteries are getting older so don't hold a full charge, so won't work in a high drain device like a camera, but would be fine in an alarm clock/remote control or other low drain device. Here in the UK most large supermarkets accept all types of AA and AAA batteries for recycling. Rjwilmsi 16:37, 31 July 2010 (UTC)

Hello most active Wikipedian! I don't normally see you at the desks. --Chemicalinterest (talk) 18:50, 31 July 2010 (UTC)

Hmm, I've never recycled batteries, because I didn't know that they could be. I'll see what can be done about using them in other devices; no reason to get rid of batteries that should work with those things. Thanks, everyone, for the input! Nyttend (talk) 12:59, 1 August 2010 (UTC)

Of course, the link to battery recycling would also be useful. ~AH1^(TCU) 23:41, 1 August 2010 (UTC)

Blu-Ray video files?

I have Sony PMB software, and average graphics card which my Cyberlink video software tells me needs upgrading on a dual core computer running Windows XP. The Cyberlink software is needed to write to my new Blu-Ray drive, because unless there is some sort of upgrade for XP(?) it only "knows" about DVD/CD... —Preceding unsigned comment added by 80.1.80.10 (talk) 06:21, 31 July 2010 (UTC)

Question moved to to the computing/IT reference desk by CS Miller (talk) 09:55, 31 July 2010 (UTC)

difference between taxis and tropism

What is the popular explanation of difference between taxis and tropism in biology? —Preceding unsigned comment added by 113.199.157.152 (talk) 11:34, 31 July 2010 (UTC)

Try the articles on taxis and tropism where this distinction is amply covered. If you have any specific questions, feel free to ask and we'll try to help. --- Medical geneticist (talk) 14:06, 31 July 2010 (UTC)

Working prototypes

How are working prototypes of machinery or consumer goods usually built, without going to the expense of a robotic production line? Supposing I had a cool idea, and I was sufficiently trained/experienced in the relevant science to know that it could work, but I wasn't a master craftsman in all the dozens of disciplines required to produce a working model by hand. If I was working on it by myself, how could I get one built within a realistic budget? I have read the rapid prototyping article, and I think 3D photocopying is ace :-)) but isn't the plastic used by an additive modelling machine too weak for moving parts? 213.122.216.120 (talk) 12:05, 31 July 2010 (UTC)

There are companies that specialise in making prototypes. Or you could try Meccano or woodwork or making it at a different scale that would be easier to make. 92.15.12.218 (talk) 13:27, 31 July 2010 (UTC)

It's normally chiselled from universal matter, obviously you can only make substances for which you know the molecular composition this way, but you don't have to start with machined or mass-produced parts 84.153.192.227 (talk) 13:55, 31 July 2010 (UTC)

See also Reprap#Materials , Fab lab 92.15.12.218 (talk) 14:25, 31 July 2010 (UTC)

Very often, companies will use the 3D printer (aka rapid-prototyper) to make plastic parts to check that everything fits together right and that parts can move as desired without interfering with each other. They may also be painted and assembled to show to marketing departments, etc. Then they may use the plastic version to make molds from which metal parts may be made. There are also 3D printers that can use Direct metal laser sintering to produce metal parts directly. Alternatively, CNC milling machines can automatically make some types of part by 'subtractive' approaches (they carve the part out of a solid block) rather than using additive techniques. Failing that, they may just use an old-school engineering shop to hand machine the parts in small quantities for prototypes using drills and lathes and other traditional tools.

For doing something yourself, commercial 3D printers and CNC machine tools are still hideously expensive. If you are moderately good with your hands, you could build your own RepRap or a three-axis router (I built one of those!). But if you aren't skilled with your hands - then you may have to find a small engineering company who'll make one-off parts in appropriate materials. It's not going to be cheap though. Depending on what you're trying to make, you might be able to get creative with stuff like Lego Technics, Erector-set/Meccano, whatever - or build it from available parts from places like McMaster-Carr who have everything from nuts and bolts to gearwheels, motors, you name it. A lot depends on what you're trying to make. If you've invented a new kind of super-tanker or airplane - then you've got a big problem - but if you've invented a new kind of mousetrap - then it shouldn't be too hard to figure out how to prototype it.

Electronics and computer parts are a whole different set of problems - and again, there are companies that will do that for you - and (if you have the right skills) there are lots of ways to build this kind of thing yourself. If you need a computer-controller, then consider the Arduino range of systems. You can get a computer board for under $30 and program if from your PC...but again, what skills do you have along those lines?

If you don't have the skills to make things yourself and you fancy yourself as an inventor - then you should definitely consider learning those skills. There are plenty of courses at community colleges and such like that will teach you many of these skills and give you access to their workshops and machinery to practice on. I took a welding class like that and was able to use their equipment to do all the welding on a classic car I was restoring. The $200 I spent on the course (plus welding gloves & mask) were well worth it because in the end, I didn't have to go out and spend $2000 on a welding machine - or pay someone else $800 to weld up my car - and now I have a skill that I didn't have before. A lot of basic metal and wood-working skills are easy to teach yourself - just buy tools and potter around in the garage making stuff - and you'll get better at it. Useful shop tools like used drill presses can be bought very cheaply on Craig's list as engineering companies fail in our declining economy.

We could give you a much more concise answer if we had more specific information about what you're trying to build and what skills you have.

SteveBaker (talk) 15:13, 31 July 2010 (UTC)

I kept the question vague because I don't have an invention of my own (yet!). I'm just honestly curious about how prototyping works. Never understood how ideas made the leap from the Eureka moment in the bath, to having a working example that might convince investors it's worth hiring specialist craftspeople or setting up a production line. Guess I shouldn't be too surprised that it's mostly self-improvement plus trial-and-error, if you haven't got money to burn. Thanks a lot for the replies. 213.122.216.120 (talk) 17:43, 31 July 2010 (UTC)

Where I work we've gone through this a few times, and let me tell you when we started we had the same questions as you because we're all software developers and none of us had ever developed hardware.

The first steps are obviously brainstorming and coming up with ideas and sketches. First broad ideas are sketched out on the white board, then the best ones are sketched out in more detail. Our artist likes to use a 3d modeling program to sketch out how things fit together, but he could have used pen and paper without too much more difficulty. If the device has electronics (and if we're designing them ourselves) a draft circuit diagram is drawn at this point. Probably using specialized software, but again, pen and paper wouldn't be too much of a hassle either.

Next, usually a very rough prototype is made to make sure we're not crazy. This was done with scrap wood and everyday tools of the sort that most people already have hanging around somewhere. None of us are what you would call 'carpenters' or 'craftsmen', so this is always good for a laugh! But it also provides the important function of making sure that the basic idea of what we're building is right. (If the device has electronics, a rough draft of the electronics would also be made on a breadboard or something. Or maybe just a rat's nest of wires!)

Finally, if we still thought we were on the right track, we find a local plastics shop and give them our sketches and 3d models. Ideally, at this point you would want the design finalized by someone who knows what the heck they're doing, but we've found this isn't strictly necessary if you're willing to put up with a lot of trial and error. The plastics shops makes us some prototype pieces of the plastics parts. (Using 3d printing if we only want one or two, some sort of molding process otherwise.) We also get circuit boards made. (This is very cheap if you don't mind soldering the bits and pieces on yourself.) Then we spend another fun day putting the pieces together ourselves.

The result is a professional-looking prototype that does what it's supposed to do and if you don't look too closely you can't tell it's held together with superglue!

I'm sure companies that do this stuff on a regular basis have a much more streamlined and efficient process, but I think our experience more closely approximates the 'garage inventor' scenario that you're imagining. APL (talk) 19:55, 31 July 2010 (UTC)

That "streamlined and efficient process" is to find a professor with a vaguely similar research idea and make his graduate students build a prototype for you. Graduate students "know how to build things!" But seriously, there's an important distinction between a prototype that does something useful, and a prototype that is packaged professionally. If you need a quick turnaround with a slick interface, you need to find a good machinist, a good electronics assembly technician, and so forth. They will make a device that looks clean, works smoothly, to whatever spec you ask for. If you care less about presentation and packaging, and are concerned with innovating, then you spend less effort on things like appearance, usability, and reliability - "proof of concept" - to demonstrate that it's worth throwing more resources at a project in the future. Then you find somebody with resources. Nimur (talk) 20:16, 31 July 2010 (UTC)

Plant health question (Podocarpus macrophyllus)

I have a Podocarpus macrophyllus that I bought several weeks ago. It's shaped like a lollipop, with a roughly spherical clump of branches on top of a straight stem. At a glance, it looks green. But upon closer examination the "core" of that spherical clump is largely composed of brown or wilting needles. The outer "layer" all around is dark green or lighter green (new growth). I've never owned anything similar before, and would like to know if this inner browning is a natural part of the growth of the plant, or whether I should be concerned. Any tips regarding pruning would also be welcome. Thank you! 61.189.63.171 (talk) 13:24, 31 July 2010 (UTC)

Is the soil very dry or very wet? 92.15.12.218 (talk) 13:37, 31 July 2010 (UTC)

If the outer layer is, as you say, green with new growth, then the plant is growing. I can't imagine a podocarpus being this shape naturally so it sounds as though it has been continuously trimmed to make it a lollipop shape. I'm thinking maybe the trimming has caused a dense outer covering of shoots that is preventing light and air getting to the centre which has started to die back. There would be cut stems over the surface of the plant, under the new growth, to indicate previous trimming if my idea is correct. If you have new growth then you should not be too concerned, but it is odd. Richard Avery (talk) 07:44, 1 August 2010 (UTC)

Farm Pond Spray Fountain

Would like step by step information on how to construct a spray fountain in a large pond to assist with aeration. What specific parts are needed and how to assemble. ≈≈≈≈ —Preceding unsigned comment added by 198.203.175.175 (talk) 18:48, 31 July 2010 (UTC)

The article Water aeration has some links, or search for "pond fountain spray how to" or similar. Basicially you put a fountain in the pond with a spray nozzle. Note that over aeration can be harmful to plants.

There are literally hundreds of pond fountain options - they will have instructions for installation.Sf5xeplus (talk) 12:41, 1 August 2010 (UTC)

Who coined the term 'fine-tuned Universe'?

Or when? I was horsing around in the web, but couldn't figure out. Twilightchill t 20:52, 31 July 2010 (UTC)

The earliest source I found is 1990 Richard Swinburne Argument from the fine-tuning of the universe in Physical cosmology and philosophy, J. Leslie, Editor. Collier Macmillan: New York. pp. 154-73. Wikipedia has an article on Fine-tuned Universe. Cuddlyable3 (talk) 22:17, 31 July 2010 (UTC)

I think it may have been George Coyne, a Jesuit astronomer who was using the term in talks and publications as early as 1982. Coined by Coyne, heh. Looie496 (talk) 00:58, 1 August 2010 (UTC)

The modern idea of Fine-tuned Universe can be traced back to Leibniz's optimism that "we live in the best of all possible worlds", famously lampooned by Voltaire in his novel Candide in 1759..Cuddlyable3 (talk) 13:08, 1 August 2010 (UTC)

Corner reflector

What is a three surface corner reflector? --The High Fin Sperm Whale 21:20, 31 July 2010 (UTC)

Imagine a hollow cube with three faces removed. What you have is three squares joined along three edges:

        /|\
       / | \
      /  |  \
     |   |   |
     |  / \  |
     | /   \ |
     |/     \|
      \     /
       \   /
        \ /

The deal is that whichever surface an incoming beam hits, it will bounce off again, hit a second surface, then a third - then head back in exactly the exact reverse direction it arrived in. SteveBaker (talk) 21:34, 31 July 2010 (UTC)

Also see Corner reflector. --Cookatoo.ergo.ZooM (talk) 21:38, 31 July 2010 (UTC)

Wait a minute, if a beam of light comes at an angle close to 0 degrees relative to the normal of one of those surfaces, could the beam miss any other surfaces completely and reflect in a non-reverse direction? ~AH1^(TCU) 23:36, 1 August 2010 (UTC)

Well, in an idealized corner reflector, the three surfaces are infinitely large and eventually, either the ray hits another of the surfaces - or it's literally at zero and bounces right back into the source. Of course, real corner reflectors aren't infinitely large - so they don't reflect back 100% of the light. But for most practical purposes, they are highly effective. SteveBaker (talk) 01:51, 2 August 2010 (UTC)

August 1

Question 9, part (d)(i)

http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/008614/RND01/PHY5C_paper.PDF The Right hand grip rule tells me that current is flowing clockwise, which means the electrons are flowing anticlockwise, but apparently that is not correct. Am I missing something?--220.253.172.214 (talk) 01:08, 1 August 2010 (UTC)

The grip rule refers to the field created by moving charges. However, in this case the field is externally applied (i.e. not related to the electrons), and you are asked to explain how the charges move in response to the field (rather than the other way around). If you apply F = qv × B and the right hand rule you'll arrive at the correct answer that the electrons move clockwise in the applied field. Dragons flight (talk) 01:22, 1 August 2010 (UTC)

I don't see how F=qvB is usable here since you are not given values for F, v or B. I also fail to see the correct application of the right hand rule, sorry.--220.253.172.214 (talk) 01:35, 1 August 2010 (UTC)

You don't need the values, just the relationship and signs. In order to move in a circle, F must point towards the center. B points into the page. q is an electron, so it is negative and flips the sign. Given those factors, you use the right hand rule (specifically this) to decide whether clockwise or anti-clockwise v fits the other constraints. Dragons flight (talk) 01:45, 1 August 2010 (UTC)

To be clear, you need ${\vec {F}}=q{\vec {v}}\times {\vec {B}}$, not just F = qvB. Dragons flight (talk) 01:48, 1 August 2010 (UTC)

You don't want or need to use the right hand grip rule - you need the Fleming's left hand rule for motors (again remember that current is in the opposite direction to elecron flow). You have the field, and the force (the force must be directed into the centre of the circle to make the electrons turn) - one of the two directions of current gives a force inwards (the other outwards) - from this you can find out whether the current is clockwise or anticlockwise).Sf5xeplus (talk) 12:35, 1 August 2010 (UTC)

Identical twins and children

Suppose a woman has a threesome with two identical male twins and gets pregnant from this. Is there any way to find out which twin is the father? 68.237.21.90 (talk) 01:27, 1 August 2010 (UTC)

Theoretically, yes. But you'd have to use a more sensitive technique than traditional paternity testing which only looks at a few loci at which the identical twins are almost certain to be identical. There is a certain mutation rate inherent during gametogenesis, so if you had an appropriate "sample" from each of the potential fathers you could potentially identify positions at which the offspring might differ between them using whole genome sequencing. --- Medical geneticist (talk) 01:38, 1 August 2010 (UTC)

How does that work? Why would one sperm from a man have the same mutations during gametogenesis as another sperm from that man? And, if that is the case, why would it be different mutations in an identical twin? --Tango (talk) 01:46, 1 August 2010 (UTC)

The gametes of the two identical twins will contain different de novo mutations. By chance, some of those mutations will be present in the majority of that individual's sperm (while others may be present in only a fraction of the sperm). This is called gonadal mosaicism. If the two sperm samples were sequenced deeply enough using "next-generation" methods, it would be theoretically possible to identify new mutations unique to either of the twins (those would be the positions at which their respective offspring would differ). Then you could just sequence those sites using standard methods in the child. Please note, however, that the OP asked if there was "any way to find out which twin is the father", not whether that method was "practical", "likely to succeed", "admissible in court", or "achievable by the average person". Even though what I've outlined is possible, it would require an extraordinary effort by today's paternity testing standards. --- Medical geneticist (talk) 11:27, 1 August 2010 (UTC)

I'm sorry, but you aren't making sense. You seem to be using "gamete" and "sperm" as if they are different things. Sperm are the male gametes. When you say "gamete" do you actually mean "gonad"? --Tango (talk) 15:10, 1 August 2010 (UTC)

Spermatozoa are the mature male gametes. However, de novo mutations occur in the earlier gametic progenitors (during DNA replication), which is why I called them gametes and not sperm. See spermatogenesis and meiosis. The gonad is the sex organ (testis or ovary) that contains and supports the developing gametes, along with having endocrine functions. There is certainly a difference between "gamete" and "gonad". When we talk about "gonadal mosaicism" or "germline mosaicism", the implication is that there can be gametes (progenitors and mature gametes) gametic progenitors with different genetic compositions -- either chromosomal or at the level of individual nucleotides. In the context of the OP's question, the most likely sample to be analyzed would be the mature spermatozoa as opposed to a testis biopsy specimen, which is why I specified that it would be the sperm sample that would be sequenced in this highly improbable scenario. Does it make sense now? --- Medical geneticist (talk) 18:00, 1 August 2010 (UTC)

No, the same problem exists: if the mutation happens in the production of individual gametes then there will be no correlation between the mutations in different gametes. Without such a correlation, you can't identify the father from new sperm. I think you are trying to say that the mutations happen in the production of gametocytes, not gametes. --Tango (talk) 23:16, 1 August 2010 (UTC)

Point taken. It was sloppy for me to use the word "gamete" to refer to gametic progenitors. However, gametocyte isn't quite right either. The proportion of sperm carrying a given de novo mutation will depend on how early in the process of gametogenesis the mutation was introduced. In order to generate a significant degree of germline mosaicism, the new mutation would have to occur in the primordial germ cell or spermatogonium. If the mutation occurred as late as the gametocyte, there would not be enough affected mature gametes to allow determination of paternity. --- Medical geneticist (talk) 02:31, 2 August 2010 (UTC)

(edit conflict)AFAIK, not with current technology. Children of identical twins have the same genetic similarity as half-siblings (rather than as cousins, which is to be expected as the children of non-identical siblings). While it should be noted that one could find genetic difference between identical twins at the full genome level, genetic fingerprinting and paternity testing use a tiny tiny fraction of the total genome, such that one cannot tell the difference. Remember that the human genome project took over 10 years to complete the first full sequencing of a human genome; and that was just a generalized genome for humans in general. An individualized full genome for even one person is a practical impossibility with current technology.ed note: striking. It appears it has been done, but it is still generally impractical to do for purposes such as this Hypothetically, if you COULD obtain a full genome from the child and both twins, you MAY be able to tell the difference. But that isn't possible under modern methods of DNA fingerprinting. See Twin#Genetic_and_epigenetic_similarity for a (IMHO) altogether too-brief discussion of twins and genetics. --Jayron32 01:42, 1 August 2010 (UTC)

You've blinked and missed the revolution. Sequencing a full individual human genome only costs a few thousand dollars right now, and is expected to drop to less than $1000 in a year or two. (Although I think it's correct that this problem would be extremely difficult even given both full genomes.) Looie496 (talk) 02:01, 1 August 2010 (UTC)

Note that "a few" still means around $20-15 thousand. But yeah, getting cheaper all the time. --Mr.98 (talk) 02:17, 1 August 2010 (UTC)

Part of the reason why DNA fingerprinting is legally admissable is that their is solid experimental backing that it works; there are now millions of successful uses which allow us to say that matching two samples via DNA fingerprinting methods is reliable as can practically be. Full genome sequencing indicates that the current number of published full genomes of individuals runs somewhere in the dozens at the outside; while comercialization in the next few years may increase this number, it is not in any way currently a reliable method of identification, which is what is needed to use it to determine which of two identical twins is the father of a child. --Jayron32 02:33, 1 August 2010 (UTC)

Well, it hasn't been tested in court because of the minimal number of people whose genomes have been sequenced, but I can't imagine it would be seen as unreliable. Basically DNA fingerprinting is sort of like saying two books must be the same because all 20 chapters have the same number of pages. A match based on full genome sequencing is like saying two books must be the same because they match word for word and letter for letter. There just isn't any way it could conceivably give a wrong answer. Looie496 (talk) 06:40, 1 August 2010 (UTC)

Oh, I am with you on that point. However, I am also married to a forensic scientist, so there is also the other end of it. Being reliable for a scientist isn't the same as being reliable to a lawyer. They are overlapping, but not necessarily identical, sets of data... --Jayron32 03:41, 2 August 2010 (UTC)

Where is the center of the universe?

An explosion radiates energy equally in all directions. As the energy loses heat, it decays into matter. The Big Bang was such an explosion, and it created a universe, which continues to expand, after nearly 14 billion years. So one would assume that the center of the universe is empty, since all its matter continues to move outwards, and away from other matter. But I am told that our solar system is at the center of the universe, as is our galaxy, the Milky Way. How is this possible? On the other hand, Penzias and Wilson were able to measure the residual microwave radiation of the Big Bang, in frquency and temperature, at the outer edges of the universe. They found that the values were equal in all directions, within minuscule uniformity. How would this be possible, if some of their measurements were taken from one side of the universe to the other, across its empty center? Or from closer to one edge of the universe than to another, more distant edge? Where are we, in relation to the center of the universe? ---- —Preceding unsigned comment added by Geepod2 (talk • contribs) 01:57, 1 August 2010 (UTC)

The universe has no center; an alternate perspective is everywhere is part of the universes center. The universe does not expand from a single point, like an explosion, it expands from every point, like a rising loaf of bread. One standard analogy is to think of the universe as being like polka dots on a balloon surface. If you draw polka dots on a balloon, and blow it up, all of the dots move away from each other, yet no one of the dots is actually the "center" dot. This is because the universe is not expanding into empty space, it is creating the space itself. The article shape of the universe discusses some of the common theories about the shape of the universe, and many of the best fit shapes are "edgeless". --Jayron32 02:02, 1 August 2010 (UTC)

When thinking on the scale of the universe, Newtonian physics is no longer a good approximation. HiLo48 (talk) 02:21, 1 August 2010 (UTC)

You said you've been told the solar system is at the center of the universe. Whoever told you this is completely off the mark since, as described above by Jayron, the universe has no center. You are probabily better off desregarding anything else that person told you about cosmology. Dauto (talk) 05:55, 1 August 2010 (UTC)

That person maybe meant the Observable universe, since the universe is expanding uniformly and the light has had an equal time to travel in all direction we are of curse in the centre of our Observable universe. Every point is in the centre of the universe observable from that point.Gr8xoz (talk) 10:11, 1 August 2010 (UTC)

The "center" of the universe isn't in the universe at all! Think of it like an expanding balloon, but a 3-dimensional surface on a 4-dimensional sphere instead of a 2-dimensional surface on a 3-dimensional sphere. --138.110.206.100 (talk) 12:54, 1 August 2010 (UTC)

Let's pretend that there are only two dimensions of space for a minute. If the universe were infinite in size, then clearly there is no boundary and nowhere can be called "the centre". But if the universe were finite in size (like a piece of paper) then there is a clear boundary and one can define a central point. The same goes in 3D: if the universe is infinite then there is no centre. If it is finite, there it.

There is an interesting alternative however. Imagine we're back in 2D again. Imagine curving the piece of paper into a sphere. The universe (the surface of the paper) is still finite, but now there is no boundary and so no centre on the piece of paper. Or you could form the paper into a doughnut shape or something even crazier. These "curved back on themselves" model universes are said to have "non-standard topologies".

So what do we think applies to our universe? Well, some cosmologists are working on non-standard topology theories, and there are astronomers looking at the sky for signs that we live in such a universe. If light could go "all the way around", we might be able to see the same star at opposite points in the sky. So far we haven't found any evidence for non-standard topology but we certainly haven't ruled it out. But the "standard model" (our best theory of the universe at the moment) says that either that the universe is infinite, or so huge that each point in our observable universe is so far from the boundary that we can't tell which is the central point. And of course if the universe is finite in size (but much much bigger than the observable universe) then the centre of the universe will not be in our observable universe anyway. Most cosmologists don't think that the universe has a wrap-around topology like in the balloon example, so that's not a good explanation as to why there is no centre in my opinion.152.78.128.149 (talk) 13:51, 1 August 2010 (UTC)

Can you give some examples of cosmologists that seriously think the universe has (or is likely to have) a boundary? My understanding of modern cosmology is that we either live in an infinite universe, or a finite universe without boundary (such as a torus). I've never heard anyone seriously suggest the universe might have a boundary - what would that boundary be like? --Tango (talk) 15:16, 1 August 2010 (UTC)

True. I don't think I've ever heard of anyone considering a universe with a boundary. Having said this, I work in particle physics (I've just started a PhD, so I'm no expert!) and a model that I've looked at proposes that there is a fourth spatial dimension of (small) finite length that is simply a line segment and not compact like a circle. Technically though, it can be formed by orbifolding a circle. This extra dimension thus has two boundaries. But the orbifolding process naturally leads to boundary conditions on the fields that can live in the dimension so that excitations (i.e. particles) travelling into either one of the boundaries are reflected. So a boundary isn't a completely crazy idea if you add some extra postulates (like those boundary conditions) that effectively tell you what happens to things travelling into a boundary. I definitely haven't heard any cosmologist talking about this stuff though. I'm the poster you replied to, despite the different IP! 86.137.169.18 (talk) 15:49, 1 August 2010 (UTC)

Inflation makes a large homogeneous region, but not (necessarily?) an infinite one. I remember one of my undergraduate professors sketching on the blackboard a flat region of space surrounded by a crazy wavy region on which he wrote "here be dragons". That's an accurate if sardonic representation of the present state of knowledge in cosmology. The problem is that you can't experimentally distinguish models that only differ outside the observable universe. If the flat region were smaller than the observable universe then we'd see huge inhomogeneities in the CMBR, so that much is ruled out. But whether the flat region is finite and larger than that is anybody's guess. Compact spatial topologies have the same problem. When people propose that space wraps around, they always have it wrap around on a scale smaller than the observable universe, simply because that's the only way the model can make any new predictions. So far, all testable models of this type have been ruled out, but whether space wraps around on a larger, untestable scale is an open question, and may always be. -- BenRG (talk) 22:06, 1 August 2010 (UTC)

Sure, the inflated region may well be finite, but what would happen at the edge? There would still be spacetime outside it, would anything actually happen when you crossed the edge other than the average density increasing (a lot)? You are right, though, what we are discussing is largely unscientific: by definition, what happens in the unobservable universe is not empirically verifiable. --Tango (talk) 23:24, 1 August 2010 (UTC)

For the universe to have a shape, that "shape" would take place on a "plane" that would be the "boundary" of said universe. The existing space within the boundary would be the universe, and the non-existing emptiness is what's outside the boundary. Since the universe has an age, it must have had such a boundary while it had a finite size early in its life, and the same should be true when multiverses are created. If such a boundary does exist, it would likely be moving faster than light since matter cannot move faster than $c$ but the expansion of space can. The centre of the universe could be considered the origin point of the Big Bang, but that point might no longer meaningfully exist as the universe itself could have moved relative to that point yet there is no outside frame of reference to compare the location of the universe to. ~AH1^(TCU) 23:31, 1 August 2010 (UTC)

I'm afraid that's all nonsense. It just doesn't work like that. When we talk about the universe being a torus (for example) we don't mean a torus embedded in some higher-dimensional space, we're just talking about its inherent shape. It's a little difficult to get your head around, but thinking of the universe as being embedded leads to completely nonsensical conclusions. The big bang does not mean the universe is finite - the universe didn't necessarily start as a point, it could well have been infinite at the time of the big bang and then expanded at all points. --Tango (talk) 23:38, 1 August 2010 (UTC)

To expand on Tango's idea for a bit; the idea of defining the universe as expanding within something has the problem as this merely redefines what the Universe is; as does the idea of "Multiverses". The Universe is, by definition, everything; if you define the Universe as part of everything, then you aren't talking about the Universe, but something smaller. If the Universe is expanding into something, that something is the real Universe and the thing doing the expanding is a smaller subunit of it. --Jayron32 03:39, 2 August 2010 (UTC)

Indeed, well put. I like to define "universe" as what you get by taking your current point in spacetime and then adding every point that is causally connected (two points are causally connected if something that happens at one point can have an effect at the other, which basically means light can travel between them) to that point (which results in the observable universe), and then every point that is causally connected to any of those points and repeating ad infinitum. By that definition, any "other universe" in the "multiverse" can either have no effect on us whatsoever, so we might as well assume it doesn't exist, or is part of our universe. You can then forget about multiverses as anything more than a mathematical convenience. --Tango (talk) 12:05, 2 August 2010 (UTC)

Placebo Questions

I was reading the placebo article on wikipedia and I was wondering a few things...

1. Why does the placebo effect wear off overtime? 2. It also says that a placebo may not always give immediate relief or improvement and the real drug will, why is that? 3. Why does the placebo effect only work in 30% of people? Is it a certain group of people? People that really trust their doctor or people who really think it's going to work? I know the article talks about personality and the placebo effect and says there is no difference in placebo effect based on personality, but does anyone know of any studies that show a difference? —Preceding unsigned comment added by 76.91.30.156 (talk) 08:02, 1 August 2010 (UTC)

Placebos work on the premise that psyhology can affect physiology. There is a wide physiologic range among people, and there is likely a wide psychological range as well. Even physiologically speaking, a common dose of medication is usually referred to as the ED50, referring to the dose at which 50% of drug takers will manifest the effect. (In order to judge the lethal dose, a similar LD50 is used.) And there's a lot of psychology involved in almost everything one does -- numerous studies have shown that people who engage in social interaction, exercise regularly, etc. can be shown to complain of less pain. So there are so many numerous factors involved in things like post-operative pain/sensitivity/complaints. Perhaps that's a start for you. DRosenbach ^{(Talk | Contribs)} 13:05, 1 August 2010 (UTC)

I corrected your ED50 link. Dose thresholds are meaningful where there is a correlation between dosage and effect. There is no consistent correlation for placebos. Cuddlyable3 (talk) 13:23, 1 August 2010 (UTC)

There can be an effect between dosage and effect in placebos, if only insofar as the patient believes that two different placebo pills contain different dosages of the illusory drug... --Jayron32 03:34, 2 August 2010 (UTC)

Computer-controlled cars

I think it might have been in Time Cop; I recall a driverless car that took its occupant to the desired location. Assuming there is no track in the road guiding such a car, could such a system work on the GPS technology we current have, assuming we got vehicular technology up to such a level? Cars would be speeding around and would never crash because the GPS map would know where each car is at every moment. Assuming streets and highways would be off limits for pedestrians (or some kind of sensors would allow for them to be integrated into the GPS map), is such a system possible, or can, for instance, GPS not detect objects to such precise measurements? DRosenbach ^{(Talk | Contribs)} 13:10, 1 August 2010 (UTC)

Yes, it has been done. See DARPA Grand Challenge for an example. The third challenge in 2007 took place on the streets of a disused airbase, although the only other cars were other challengers. 62.56.61.163 (talk) 13:38, 1 August 2010 (UTC)

(ec) GPS satellite navigation can give adequate location precision though safety would require keeping generous spacing between vehicles and provision for signal shadow areas. There would be concerns about the vulnerability of the radio navigation to interference, whether it is accidental or deliberate jamming. The radio controlled traffic lanes would have to be isolated from all other traffic, comparable to creating a new railway system. With central control, traffic could move very efficiently but it would be constricted by the limited number of entrance/exit points. These points would have to include adequate spaces for acceleration, deceleration and queuing. All possible failure modes need study. Cuddlyable3 (talk) 13:42, 1 August 2010 (UTC)

You wouldn't just use GPS — the car itself would have localized sensors to detect other vehicles, walls, pedestrians, dogs, etc. It takes more than GPS to navigate through a real-life environment for fairly obvious reasons (GPS can't tell you when an old lady is in the street). Anyway, this is potentially something out there for the future, though aside from the rather copious technical hurdles involved, and the problematic legal ones — how would such a thing be insured? who is at fault when they crash? make no mistake, there will be crashes, no matter how clever the technology is, because that's how things work in the "real world" — there is also a high psychological barrier to being driven around in such a fashion by a computer.

Getting out my crystal ball, I would suggest that unmanned cars will probably only be used in rather limited situations, like guarding a border fence or a military base, where the conditions can be relatively controlled for and the car itself can defer to a remotely-controlling human in the case of anything anomalous. I doubt they will be used for general transportation, especially since if you want someone to drive you somewhere, it is not that expensive to just hire an actual human being. I suspect automatic transportation for general use would only be used on tracked systems, like subways or rail, where the conditions can be easily automatically limited. --Mr.98 (talk) 14:22, 1 August 2010 (UTC)

(ec) The autonomous vehicle article goes into more detail. Basically GPS is used only for deciding which junctions to take. Each car has short-range LIDAR (IR laser based RADAR) and video-cameras so it can detect what other vehicles are doing, and avoid collisions. There is a car platoon protocol; this allows cars to form convoys. Each car indicates to the car behind that it is about to brake, so that the second car can brake earlier. This allows the separation distance to be less. The lead car decides what speed to travel at and to avoid collisions. If each car communicates its acceleration/braking profile to the others, then the platoon can follow the least capable car, and the separation distance can be very close. Of course, there need to be a way for cars to announce that they are about to leave the platoon; if car in the middle needs to leave, then the car behind it will become a temporary lead and drop back a bit to make some room. The leaving car will then drop back a bit itself, and then leave at the next junction. The car behind will then rejoin the platoon. CS Miller (talk) 14:31, 1 August 2010 (UTC)

An Italian university is scheduled to have a driverless car driving from Italy to China in October. http://www.dw-world.de/dw/article/0,,5829135,00.html Impressive if true - but I thought it was impractical for a human driven car to do the same route due to wars? 92.29.127.162 (talk) 17:11, 1 August 2010 (UTC)

Wars? Between who? The link and my searches don't seem to discuss the route, but mention Siberia and Mongolia. In any case, the obvious route from what's been described would be reaching Russia somehow from Italy (many practical ways) then on to Mongolia and China. There are of course other routes, e.g. [5]. All these options have a variety of safety risks, likely a lot of paperwork & money & time & other facets of bureaucracy and probably a bunch of bribes too (for example you'll probably need a 'guide' to drive in China http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=1780257) so while not for the faint hearted is doable and there must be a resonable number of people who do that sort of thing, i.e. driving from Western Europe to China every year. Nil Einne (talk) 19:18, 1 August 2010 (UTC)

Technically, the Italian car isn't exactly driverless. There will be someone sitting behind the wheel the entire time - they'd never get permission to have an entirely unmanned machine to drive in those places. How many times will he have to take control? Lots, I suspect. SteveBaker (talk) 01:46, 2 August 2010 (UTC)

Audi designed and built a driver-less Audi TTS to do the climb up Pikes Peak at full tilt [6]. Episode 10x08 of Top Gear featured an autonomous BMW doing a full-ball lap of the track [7]. As mentioned by others, such systems won't only use GPS. Some of the other systems that are already in use today include radar guided cruise control, park distance control, lane departure warning, traction control, vehicle stability control, ABS, infra-red and visible light cameras featuring facial, vehicle, pedestrian and road sign recognition, self-parking systems etc. It's amazing how many of the necessary systems are already in place in the (top-of-the-range) cars you can buy today. Zunaid 18:21, 2 August 2010 (UTC)

few question about glycolysis

1)What is the logic of glycolysis?? I mean its main purpose is to provide energy and also it is a multipathway i.e,its intermediates are use in many other pathways... bt do it have any other function other than the above....???

2)glucokinase is synthesized after 2 weeeks of birth. After feeding(insulin) stimulates the glucokinase system. What kind of regulatory mechanism is operational here....??

plz help me by replying fast.....m waiting!!!! —Preceding unsigned comment added by Priyankajoshi7 (talk • contribs) 14:59, 1 August 2010 (UTC)

As a point of netiquette it is generally considered impolite to ask for a quick response; we are all volunteers here. For future reference, please sign your questions and replies by typing in ~~~~. It's to the left of the '1' (one) key on US-keyboards and to the 3 keys right of the 'L' on UK-keyboards, or press the pen-like button on the standard editing toolbar.

Back to your question, bio-chemistry is not my discipline, but our glycolysis article gives some of the other uses of the intermediates, especially the biochemical logic and intermediates for other pathways sections. CS Miller (talk) 15:46, 1 August 2010 (UTC)

What is convergent evolution?

If an octopus and I have a common ancestor who possessed what I might call 'proto-eyeness', by which I mean not eyes themselves, as we know them, but everything necessary to the production of descendants with eyes, then can my own eyes and the octopus's eyes be said truly to have evolved independently, and is there really any such thing as convergence? By analogy (no pun intended), a woman with no formal education but wealth and social connections has three daughters, two of whom go to university. The university degrees did not evolve independently of one another: they are each the result of the mother's wealth and social connections (or 'proto-universitiness'). I mention the third daughter because I know some of our cousins have no eyes. 91.107.28.138 (talk) 20:13, 1 August 2010 (UTC)

Did you read Convergent evolution? A good example: sharks and dolphins share many similarities and look a lot alike. However they are not closely related at all. The converged on many of the same traits because they lived in similar environments and benefited from many of the same adaptations. Friday (talk) 21:17, 1 August 2010 (UTC)

Friday, I did read Convergent evolution. It says of bats and birds that 'their last common ancestor did not have wings'. But I think their last common ancestor did have 'wingedness', or everything necessary for the production of descendants with wings. 91.104.164.37 (talk) 17:04, 2 August 2010 (UTC)

You are describing parallel evolution rather than convergent evolution. --Tango (talk) 23:27, 1 August 2010 (UTC)

The term convergent evolution doesn't carry any implication about causes, it only says that two species are more similar now, with respect to a certain feature, than their ancestors were. It is entirely possible to have convergent evolution at the organism level in spite of divergent evolution at the gene level. In the case that you describe, convergence would result from unveiling of a previously hidden similarity. That isn't how convergence normally arises, in the opinion of most biologists, but if it did, it would still be called convergent evolution. Looie496 (talk) 00:32, 2 August 2010 (UTC)

An interesting recent paper argues that the distinction between "parallel evolution" and "convergent evolution" is artificial and should be discarded. See Convergence and parallelism reconsidered: what have we learned about the genetics of adaptation? Adrian J. Hunter^{(talk•contribs)} 09:28, 2 August 2010 (UTC)

The eyes of an octopus evolved from skin cells. Your eyes evolved from brain cells. They're not modifications of the same 'proto-eye'. — DanielLC 22:47, 2 August 2010 (UTC)

can loud music (esp. prominent electric guitars, drum, bass) kill cells on a microscope slide?

When imaging cells for sometimes up to six hours at a time, I of course take advantage of my laboratory's nifty sound system ;-)

but I want to ask if thundering bass in the same room can affect my experiments? John Riemann Soong (talk) 21:28, 1 August 2010 (UTC)

Sonication usually uses ultrasonic frequencies. It seems very unlikely that audio frequency music would be able to disrupt cell membranes. Nimur (talk) 21:42, 1 August 2010 (UTC)

Well I wasn't thinking disrupting cell membranes, but maybe activating sensitive mechanoreceptors that would set off apoptosis? John Riemann Soong (talk) 22:45, 1 August 2010 (UTC)

I read one paper where apparently sustained exposure to "low-frequency sonication" could kill cells. Would that be in the audible range? John Riemann Soong (talk) 23:09, 1 August 2010 (UTC)

Maybe something like this, this or even this? ~AH1^(TCU) 23:19, 1 August 2010 (UTC)

The first link is from 1932 (!) and the others describe killing cells with ultrasound. Bass and sub-bass are infrasound so I don't think they can kill cells _{(I'm glad off this, although I do get a strange headache after listening to drum and bass)} This paper states that "low-frequency sonication" is of 25 kHz, just outside of our hearing range and the opposite end of the spectrum compared to bass. I think that sonication must also be very loud sound, considering that bats produce ultrasound at 130 decibels but don't drop out of the sky as their cells die. Considering all of this I agree with Nimur that it is very unlikely that loud music could kill cells on a slide. Smartse (talk) 00:45, 2 August 2010 (UTC)

Sound waves have two measures of strength: Their intensity (or amplitude) and their frequency (or tone or note). Both can do damage. High frequency soundwaves are of a higher energy sound than lower frequency sounds of the same intensity, AND louder sounds have more energy. Your hearing can be damaged by high volume infrasound, even if you cannot hear it. Presumably, very high volume, but low frequency, soundwaves could cause damage even on the cellular level. --Jayron32 03:31, 2 August 2010 (UTC)

Yes, but noise-induced hearing loss occurs because the cells that are damaged have evolved specifically to absorb sound energy - normal cells won't be affected. My physics is pretty rusty but AFAIK the wavelength of low frequency music would be too large to interact with something as small as a cell. What frequencies and decibels do you mean by "very high volume, but low frequency" and can you find a rouce to back up your presumption? Smartse (talk) 08:30, 2 August 2010 (UTC)

Personally I would be more concerned about the stability of the optics during imaging than killing cells - excessive vibration could shift or blur your images (how long is each exposure?). However if you are not finding this a problem already it's probably ok - but you should check if anyone else in the lab is doing vibration sensitive experiments, or you might find yourself quite unpopular when they check their images/results. Equisetum (talk | email | contributions) 08:32, 2 August 2010 (UTC)

I usually take time lapse images -- I use a 55-75 msec exposure time but for space constraints (to avoid taking 1 terabyte of data each day) I use a 500-800 msec delay between each capture. Focal drift is always an issue, so I always have to play with the knob now and then, even to stay on the same focal plane (and particles I'm tracking often shift focal planes as well) but I did notice that with music on, I seemed to have to knob more frequently. John Riemann Soong (talk) 14:20, 2 August 2010 (UTC)

August 2

Units of Time

Are there any natural units for measuring time not based on the movements of the Earth?

Like, say you were far out in space trying to communicate to an alien how long a day on Earth is, what unit of measurement could you use that's universal? Are there any longer than the amount of time it takes hydrogen to perform a hyperfine transition? Just curious. 108.3.173.100 (talk) 00:26, 2 August 2010 (UTC)gejl

The most natural unit of time is the Planck time. There's a bit or arbitrariness to do with factors of pi, but otherwise it's something that aliens with similar understanding of physics to ours should share. The Planck time is very short, though, so doesn't answer your second question. The Hubble time is very long, but also pretty fundamental. --Tango (talk) 00:30, 2 August 2010 (UTC)

It's "natural" in a physics-y sense of "being based of fundamental physical quantities". However, it's not particularly "natural" in the colloquial sense of being familiar and easy to recognize. I would also point out that the Planck time has a standard uncertainty of 5×10⁻⁵ which is pretty crappy. This is mostly due to our difficulty in measuring G. By comparison, the best atomic clocks have a precision ~5×10⁻¹⁶ at measuring a second as defined to be "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". If we wanted a really rigorous comparison, I think we would definitely tell them something based on an atomic clock. For a quick and dirty comparison, it would probably make more sense to use a simpler physical process that is easily accessible such as the half-life of a common radioactive decay. Dragons flight (talk) 03:17, 2 August 2010 (UTC)

Assuming the alien can understand multiplication/exponents, is there anything wrong with applying those the tiny units? $\sim$ Lenoxus " * " 00:49, 2 August 2010 (UTC)

Accuracy. As mentioned above, Planck time is only measured accurately to around 5x10^-5 (confirm here at NIST.gov). 50 ppm might seem tiny - but for frequency stability, it's actually really terrible - we've had better frequency-stability technology for literally thousands of years, even using shoddy "oscillators" like pendulums and water clocks. If a clock drifted with 50 ppm of timing error, it would accumulate about a half-hour of error each year. This would definitely become problematic. A modern run-of-the-mill off the shelf digital watch uses a quartz oscillator with an (electronically compensated) accuracy of around 1e-8 (and you can still tell a few seconds of drift per month or so). A modern scientific timing system can achieve many orders of magnitude better frequency stability by using even better oscillators, like atomic resonances or cesium decay rates. For practical purposes, this means that we can trust our clocks accurately enough to synchronize distant electronics and computer systems to a very high degree of precision and accuracy - making possible things like phase shift encoding in GPS and mobile telephones. Better frequency stability in such technologies directly corresponds to higher achievable data rates. Nimur (talk) 15:41, 2 August 2010 (UTC)

The primary unit of time, the second, is now defined using an atomic clock. Atomic clocks don't rely on movements of the Earth, Sun, moon or any other celestial body. Dolphin (t) 02:58, 2 August 2010 (UTC)

...but first you would have to tell the alien which atomic clock to use. To be understood, a message usually implies a particular time base e.g. to demarcate successive words or symbols. See Arecibo message which was an exercise in constructing a message that an alien might be able to interpret. Cuddlyable3 (talk) 18:36, 2 August 2010 (UTC)

A message can contain its own definition of temporal units: "The duration of the transmission of this sentence is one grondlewipple." - since the aliens can directly measure the duration, they now know how long a grondlewipple is. Obviously you'd have to allow for relativity - but that should be a relatively simple thing for the aliens to estimate. SteveBaker (talk) 00:08, 3 August 2010 (UTC)

Precambrian rabbits and natural fossil exposure

A thought just occurred to me on the subject of Precambrian rabbits. Occasionally, natural events like erosion will expose fossils which date from tens of millions of years prior. Given this, couldn't an organism die immediately on top of or next to such a fossil site, after which the whole thing gets covered in sediment, resulting in "distant neighbor" fossils?

To put it another way: Given this small possibility (unless, as is far more likely, it's not a possibility), why is the fossil record so consistent? Why are there (at least) no Triassic rabbits? $\sim$ Lenoxus " * " 00:46, 2 August 2010 (UTC)

Because the experts are aware of this issue and take it into account. The rock the recent organism is fossilised in would be different from the rock the old fossils are in, so you would be able to tell that something had happened. Working out the ages of different layers of rock can be a bit of a challenge, but it can be done (in various ways). --Tango (talk) 00:55, 2 August 2010 (UTC)

As stated by tango, geologists understand the processes by which rock formation and erosion can occur; in fact rocks are often dated by index fossils, which determine their age. Thus, finding a rabbit lying in a rock layer which was immediately on top of a trilobite wouldn't lead people to conclude that the rabbit was really old, rather that the rock layer the rabbit was in was much younger than the one the trilobyte was in. --Jayron32 03:27, 2 August 2010 (UTC)

I had a strong feeling it would be something like that (since that relates to how they're able to tease apart folded strata); thank you both! So, now I'm wondering… has the situation I described ever happened? That is, are there any known "distant neighbors" (where the rocks are obviously quite different, etc)? If not, any particular reason why not? $\sim$ Lenoxus " * " 04:48, 2 August 2010 (UTC)

You'll want to follow the threads that lead from the article titled Stratigraphy, which is the science of reading and interpreting rock layers. Undoubtedly, examples exist of local areas where two non-sequential rock layers lie side by side. I cannot think of one specific example, but that's more a function of there being so many rather than being so few. --Jayron32 04:59, 2 August 2010 (UTC)

The specific term, BTW, for such a situation is an Unconformity. Examples given in that article show pictures of adjascent rock layers which are actually represent gaps of up to 1 billion years. --Jayron32 05:02, 2 August 2010 (UTC)

It does happen that sometimes fossils get into layers they don't belong in. Most commonly it is a case of older fossils getting incorporated into younger rock -- this can happen if the soft rock they are embedded in erodes away, leaving the fossil behind to be covered by younger sediment. It's much harder for younger fossils to get incorporated into older rock. Looie496 (talk) 05:44, 2 August 2010 (UTC)

A closely related phenomenon happens all the time in archaeology. In those cases, you end up with different soils rather than different rocks, but it's still (usually) quite obvious when it's occurred. During a proper excavation, you make note of all visible stratigraphic layers, as well as any and all discontinuities you find. There are a variety of pedological assays you can have done to help out, but for the most part a detailed visual inspection is all that's required. Matt Deres (talk) 14:07, 2 August 2010 (UTC)

Depression Medication

A while back I saw an article that showed which type antidepressant is more likely to work in what type of people. I can't remember the different categories they had for the type of people. Has anyone seen it? —Preceding unsigned comment added by 76.169.33.234 (talk) 05:04, 2 August 2010 (UTC)

That's rather vague, and could describe every single antidepressant; each probably works better in some types of depression than others. You could explore Category:Antidepressants yourself to see if you can dig it up. --Jayron32 05:07, 2 August 2010 (UTC)

The most common types of depression are major depressive disorder and bipolar disorder, and they are usually treated with different types of drugs -- the articles will give you more information. Looie496 (talk) 05:39, 2 August 2010 (UTC)

There's also a list of antidepressants which might be of use. Smartse (talk) 08:48, 2 August 2010 (UTC)

Contact between shaft and bearing

hey i want to know on what basis the contact(clearence,angle)between shaft and bearing(journel,liner) because am installing new roller of shaft dia 320 and my liner is of dia 320, its is a semi spherical(only i have liner at bottom half)??? and why???? —Preceding unsigned comment added by 82.129.222.71 (talk) 09:25, 2 August 2010 (UTC)

There's some basic info here on the hows and whys of journal bearings [8] does yours match any of these types?77.86.94.177 (talk) 12:53, 2 August 2010 (UTC)

It's not clear if the bearing is a Plain bearing - it might be - one reason for only having half a cylinder would be if the bearing was supporting a force that was predominately in one direction - eg a heavy weight - is your bearing of this type? 77.86.94.177 (talk) 15:50, 2 August 2010 (UTC)

Electrolysis

What are the typical values of current and voltage required for the electrolysis of water? In the current industry what power input do they use, is it mostly of national grid systems? Thanks very much--91.103.185.230 (talk) 11:15, 2 August 2010 (UTC)

You need to use DC if you want to separate the hydrogen and oxygen. A minimum voltage would be around 1.5 volts DC. In my experience, 24 volts DC works fine; add some baking soda, sodium hydroxide, or sulfuric acid for the electrolyte. Current might be 100 milliamps. --Chemicalinterest (talk) 12:11, 2 August 2010 (UTC)

The minimum voltage required for water electrolysis is 1.23V (see Electrolysis of water). However the overpotential needed at the electrodes is ~1V (depending on electrodes). Additionally producing the gas at above 1atm pressure also increases the voltage.

The current directly controls how much water is electrolysed per second.

The voltage used therefor will be roughly 2+IR where I is the current, and R is the internal resistance of the electrolysis cell.

Also see http://www.hydrogenassociation.org/general/faqs.asp and this google books Hydrogen fuel: production, transport, and storage By Ram B. Gupta p.162-163

Commercial cells produce work at high pressure. This link http://www.nrel.gov/docs/fy04osti/36705.pdf gives typical figures - there are high and low pressure cells, and electrolyte of KOH is used to reduced cell resistance. As with all processes that use electricity as a feedstock hydroelectric power is common.

Using the wattage figures in the nrel.gov link above you can work out the typical current values using V=~2V after taking into account the efficiency. However note that typical cells are connected in series, not parallel -so the figure may be a sum of the currents going through the cell rather than the supply voltage/current.77.86.94.177 (talk) 12:15, 2 August 2010 (UTC)

Here are some commercial low pressure cells from Statoil : [9] they use ~4000Amps (max) - voltage depends on number of cells.77.86.94.177 (talk) 13:12, 2 August 2010 (UTC)

It depends whether the OP is talking about commercial electrolysis or laboratory electrolysis -- I was talking about the latter. --Chemicalinterest (talk) 14:16, 2 August 2010 (UTC)

Seems like the question quite directly tells you his context... DMacks (talk) 14:41, 2 August 2010 (UTC)

Fennec Hare

Is there any such animal as a Fennec Hare? This page says they are critically endangered, and one has just been born in captivity. However the photo looks like a kitten 'shopped to have bunny ears, and it's supposed to have been born in North Korea. Is this nonsense, propaganda, or maybe possibly true? 213.122.216.120 (talk) 12:53, 2 August 2010 (UTC)

In case you aren't aware, the Fennec fox does exist, but I still very much doubt the authenticity of the article (the misspelling in the URL doesn't fill me with confidence). The "Iperian steppe" doesn't exist, and here is also doubtful. In short: no. - Jarry1250 ^{[Humorous? Discuss.]} 13:21, 2 August 2010 (UTC)

So this was our April Fool's joke in 2009. Amusingly, it inspired a number of would-be conservationists and some additional Photoshopping (try Google Image searching "Fennec Hare"). Here is our April Fool's joke from 2010 - http://www.zooborns.com/zooborns/2010/03/rare-baby-skeksis-chick-born-at-franklin-park-zoo.htmlDeKreeft27 ^[Discuss.] 14:09, 2 August 2010 (UTC)

Keep in mind: Wikipedia has an article on everything: cabbit. Nimur (talk) 16:44, 2 August 2010 (UTC)

That is excellent. Was a baby mystic also born simultaneously to the skeksis? APL (talk) 19:43, 2 August 2010 (UTC)

documentary

Anyone know of a good documentary on bees / wasps / ants? 82.43.88.151 (talk) 13:10, 2 August 2010 (UTC)

This is maybe too specific, but Queen of the trees is about fig wasps and is the best documentary I've ever seen. For army ants, see this BBC page, you should find some other videos on there too (sorry not sure if they work outside of the UK). There have been a couple of recent films about colony collapse disorder which I imagine would discuss bees more generally as well. Smartse (talk) 15:05, 2 August 2010 (UTC)

(ec)Below are links to video documentaries about

bees, sand wasp, Ichneumon Wasp, paper wasp, fairy wasp, ants (old film), and ants (new film). Cuddlyable3 (talk) 15:24, 2 August 2010 (UTC)

So are you vouching for them as being good? (Did you even watch them?) Because I'm sure the original poster can use Google/YouTube as well as you can. They're asking about quality. --Mr.98 (talk) 16:35, 2 August 2010 (UTC)

I do not take it for granted that all videos at YouTube are good and therefore I looked at all of them. Several are by David Attenborough or have National Geographic logo that IMO also speaks for quality. Cuddlyable3 (talk) 18:24, 2 August 2010 (UTC)

Real life lightsaber

In this video, http://www.youtube.com/watch?v=6G8VztSWnVo Michio Kaku describes how to make a real life lightsaber. Of course being the geek I am, I loved it. But are there any problems with his design? Any way to improve upon it? Would 12,000 degree plasma be sufficient to cut/burn through almost anything? What would the plasma look like? Color? 148.168.127.10 (talk) 14:24, 2 August 2010 (UTC)

It would likely function, but you will he holding 12,000 degree plasma in your hands. How thick will the insulation need to be to avoid burning yourself? Remember, his design fills the "insulation" area with batteries - which aren't great insulators. In fact, he doesn't explain how we keep the batteries from melting. In the end, it is a heat saber, not a light saber. -- kainaw™ 15:49, 2 August 2010 (UTC)

The plasma can be bright but composed of very little mass, so it is almost impossible to get burned. A static electricity spark is an example. To make a large amount of matter in the plasma state requires much more energy than a few batteries can supply. --Chemicalinterest (talk) 17:36, 2 August 2010 (UTC)

Then, how will it cut things? Nimur (talk) 18:57, 2 August 2010 (UTC)

Could it be similar to a CCFL? With maybe some colorants? --Chemicalinterest (talk) 17:45, 2 August 2010 (UTC)

Not really. He isn't trying to make something that looks like a lightsaber. He is trying to make a pretty hand-held plasma cutter. From his design, which is poorly shown, the plasma cutter begins looking like a sort of flashlight. Then, a fan blows the arc out from the handle to make the "blade". So, the user is literally holding the handle within an inch of the cutting heat. He could make it safer, but you'd end up with a normal plasma cutter - which already exist and are used every day. -- kainaw™ 17:52, 2 August 2010 (UTC)

We should just come out and say it: the light saber is not an effective design, from an engineering point of view. It was imagined by a filmmaker, because it looks neat, and makes for great special effects. But any small amount of practical consideration invariably yields the same conclusion: infeasible. It has little to no utility as a weapon (if the enabling technologies for a "light saber" existed, they would be better employed to make more efficient weapons or shields). It has little advantage as a tool, compared to existing technologies; and again, if the mysterious fictional technologies necessary to make the saber did exist, they could be packaged in a more convenient form-factor if the objective was a cutting-tool or welding tool. As Kainaw has pointed out, we already have plasma cutters, cutting torches, and so on. What exact advantage would the light saber actually have? Nimur (talk) 19:01, 2 August 2010 (UTC)

Can a plasma cutter bounce energy weapon ammo back at the shooter? Googlemeister (talk) 20:05, 2 August 2010 (UTC)

That is a fictional capability and a fictional scenario. But following my above statements, if a lightsaber could do it, wouldn't it make more sense to build a big array of light-saber "light" and carry it around in front of you? Anyway, we already have a technology that does provide pretty good protection against bullets, projectiles, and so on; what is the advantage of a lightsaber over a solid, resistant light-riot-shield? Nimur (talk) 20:26, 2 August 2010 (UTC)

I disagree Nimur. If we were to have a real lightsaber, and it worked the same way it does in the Star Wars movies, I can see it being very useful. It would be the size of a knife, but have the blade length of a sword, and supreme cutting ability. I can see this being quite useful in combat situations for cutting down doors, walls, obstacles. Sure there are other devices that can do those things, but we're assuming the lightsaber works fine, and it's small so why not? It can be used to start fires, or heat up water which can find some uses. Yes we already have cutters, and torches, but we're assuming the lightsaber works fine right? Well in that case, the lightsaber is smaller, and has a longer blade which makes it more useful as a weapon and cutting device. Yes I'm sure the technologies could be implemented in projectile weapons or shields, but why not have both? ScienceApe (talk) 02:31, 3 August 2010 (UTC)

You missed Nimur's point completely. Assuming the technology exists to make a light saber as understood from Star Wars, it (the lightsaber) would likely be the least useful thing that technology could produce. 218.25.32.210 (talk) 04:48, 3 August 2010 (UTC)

Hematite color change

I have a small bead of hematite. It's has a beautiful dark, shiny gray color and I'd like to keep this color. I've read that hematite can turn red through contact with oxygen though. It's in a plastic container right now. Can I keep it in the open while still preventing this? Should I maybe coat it with a bit of oil like with steel? --85.145.56.218 (talk) 15:20, 2 August 2010 (UTC)

Sensitive gemstones such as malachite or haematite usually have a coating, something similar to furniture polish or wax. This should protect it from air. Unfortunately I don't know the trade name of a suitable product to use.77.86.94.177 (talk) 15:46, 2 August 2010 (UTC)

Looks like you have a product similar to iron(II,III) oxide and want to prevent it from oxidizing to iron(III) oxide. I would recommend keeping it in mineral oil, the same procedure used to store sensitive alkali metals. --Chemicalinterest (talk) 17:38, 2 August 2010 (UTC)

No. Cleaning mineral oil off of a piece of jewlery or a display piece is fantatsically impractical. Instead, why not coat it with some sort of clear lacquer, like clear nail polish... --Jayron32 02:07, 3 August 2010 (UTC)

Wind Erosion on Venus

There's a discrepancy in the first section of the article Geology of Venus. It states

Long rivers of lava have been discovered, as well as evidence of Aeolian erosion and tectonic shifts which have played an essential role in making the surface of Venus as complex as it is today.

but later

These winds exist at high altitudes, but the atmosphere at the surface is relatively calm, and images from the surface reveal no evidence of wind erosion.

Aeolian erosion is just a fancy name for wind erosion, isn't it? Is there evidence of it happening on Venus, or not? I've asked on the article's talk page, but got no response Rojomoke (talk) 15:28, 2 August 2010 (UTC)

I think the clue is in the word "relative". According to the article Atmosphere of Venus, the overall atmosphere of Venus circles the planet in around 4 days, which works out to around 400 km/h, and the article mentions high-level winds of 100 ± 10 m/s (= 360 ± 36 km/h) at altitudes of 60-70 km, in the same ballpark. By contrast, it says that

"the breeze barely reach[es] the speed of 10 km/h on the surface", and elsewhere

"the winds near the surface of Venus are much slower than that on Earth. They actually move at only a few kilometers per hour (generally less than 2 m/s and with an average of 0.3 to 1.0 m/s), but due to the high density of the atmosphere at the surface, this is still enough to transport dust and small stones across the surface, much like a slow-moving current of water."

Bearing in mind that the atmospheric pressure at the surface is about 92 bar (i.e. 92 times Earth's), and that these comparatively low average figures do not preclude occasional gales and gusts, you can probably see that these surface winds are, though "relatively" slow, still capable of erosion. 87.81.230.195 (talk) 17:19, 2 August 2010 (UTC)

That's a good scientific explanation, but it doesn't address the issue - the article contains two contradictory claims, and we need a source, I think, to tell us which is accurate. Vimescarrot (talk) 18:54, 2 August 2010 (UTC)

aspartame

My friend believes that aspartame is in too many things ("everywhere") and is a poison and is only on FDA's GRAS list because of a conspiracy, and that aspartame is somehow making everyone dumber. While an organic food nut, she's also a really nice person who's a musician and is quite influential among my peers. I'm afraid the more orgo terms I use, the more I'll scare everyone. Any suggestions? John Riemann Soong (talk) 16:23, 2 August 2010 (UTC)

Ignore? --Stephan Schulz (talk) 16:26, 2 August 2010 (UTC)

Personally I've found "confrontation with facts" to not work terribly well, because people quickly close their ears up. When talking about potential low-level risks (like cell phone towers, which my mother is kind of afraid of), I generally emphasize that the risks we are talking about here are quite low, to be indistinguishable from other sources of risk, and are a lot safer than, say, the risk one takes when getting into an automobile. I tend to believe that whatever risks aspartame brings, they probably are offset by the risks that come with excessive sugar consumption. (One can argue that this can be accounted for otherwise, and indeed it can, but we don't have many means of enforcing that and we should not let the perfect edge out the good.) The evidence for it being dangerous is not very strong, in the end. Even in the cases of honest-to-god big conspiracies (e.g. tobacco), there were always lots of qualified outsiders willing to question the conclusions. --Mr.98 (talk) 16:34, 2 August 2010 (UTC)

(edit conflict)Aspartame controversy is a pretty comprehensive article that does not delve too deeply into the orgo itself. It covers both sides (i.e., hers too:) and has lots of cites from reliable-sounding sources that are not gov/industry-tied, so it's not dismissable as just more of the same conspiracy she fears. Stephan also raises a good point...I fear that some conspiracy nuts are too far gone to be helped by any amount of fact or logic. They refuse to question what they know because they already have seen the light and it's blinded them. Consider this a formal warning not to push this discussion towards religion. There are obviously lots of reasons why people behave this way...we probably even have an article about the rise and social popularity of scientific ignorance. DMacks (talk) 16:35, 2 August 2010 (UTC)

I agree with Mr.98's point. Low level risks, like aspartame or cell phone towers or living next to high-voltage transmission lines, make much less difference than higher level risks, like riding in automobiles and overeating of trans fats. One should notify the person that their views are out of perspective. If they listen, explain. If they do not listen, ignore what they say. --Chemicalinterest (talk) 17:44, 2 August 2010 (UTC)

Well it's hard to ignore someone who's trying to convert everyone to the cause over fb (quite successfully). John Riemann Soong (talk) 19:52, 2 August 2010 (UTC)

Another very easy approach is to say, "Hey, Wikipedia has a pretty good article on this, that seems pretty balanced. It seems that in the end, the evidence for it being harmful is pretty weak, and that if there is harm, it is basically indistinguishable from the background level of things that happen to people." I've used this for some of the other "controversies" before (like whether Jesus existed as an actual human being, or whether cell phones are dangerous), when the Wiki article is actually good and balanced. It tends to be a way to say, "Hey, this is a tough question, and if we take a balanced view of it, we see it doesn't readily give an unambiguous black or white answer." That's generally the place I try to get such people to arrive at — not so much believing, "this is safe," which it might not be, I don't know, but rather to "oh, this isn't a simple-minded thing, it's a complicated one," which is a lot better than the propagandistic approach in any case, and removes the missionary zeal. --Mr.98 (talk) 20:25, 2 August 2010 (UTC)

"People cannot be reasoned out of a position they did not arrive at via reason". The only response to people who believe in outrageous conspiracy theories is to either ignore them or ridicule them for your own amusement. No amount of actual evidence and reasoned discussion can convince them out of their position. --Jayron32 02:04, 3 August 2010 (UTC)

Human consumption of uncooked cereal grains

Just curious what would be the result of eating uncooked cereal grains (like raw oatmeal, rice or rye). Cooking converts the grains into human usable starches, right? Would the human digestive system be able to get any nutritional value out of raw grain? --70.167.58.6 (talk) 16:47, 2 August 2010 (UTC)

A short answer would be: "Yes it can, but not too well". Cooking gelatinizes starch which makes it a lot more absorbable to the digestive system. Raw grains are not digested easily and the body only takes up a tiny amount of the nutrients. The undigested and unabsorbed nutrients in the grain will go into the intestines and end up just feeding the gut flora, likely causing lots of gas, and then gets expelled from the body more or less whole in the feces. -- Sjschen (talk) 18:03, 2 August 2010 (UTC)

wasp-like insects

Last year when I was cycling on the common I saw these tiny holes in the ground. This was during the summer, and the ground was very dry. Then I saw these flying wasp-like insects going into them. What were they? —Preceding unsigned comment added by CuteLesbianPossum (talk • contribs) 18:29, 2 August 2010 (UTC)

Digger wasps? Looie496 (talk) 18:36, 2 August 2010 (UTC)

It could be any of a thousand different wasps. Many wasp species burrow. For example beewolf wasps and cicada killer wasps. Without knowing more about the wasp in general, we can only say it may be some random species of burrowing wasp. --Jayron32 03:03, 3 August 2010 (UTC)

Queen Ant

When the ants were flying this year, I caught a lasius niger queen because I wanted to start an ant colony. Only today I discovered that you're meant to get them after they shed their wings. So I have a queen who hasn't mated and will never lay eggs to start a colony. She looks sad and vacant most of the time, just sitting in the container with her antenna slowly twitching, except when I feed her a tiny drop of honey on the end of a pencil - then she jumps into life, climbs onto the pencil and happily licks the honey. But afterwards she just goes back to sitting alone in the container. I feel very sad, because she is going to be all alone. Is there anything I can do to help her? I read that the worker ants are meant to feed the queen, but since there are no workers I will have to do it. Is feeding her honey the right food? Rebmetpes27 (talk) 18:44, 2 August 2010 (UTC)

If you know she will never lay, then why are you keeping her? Just release her. --Tango (talk) 19:35, 2 August 2010 (UTC)

Without worker ants to forage for food and protect her, she would die Rebmetpes27 (talk) 19:55, 2 August 2010 (UTC)

Well, she's not going to do a whole lot better in your cage, without a mate. She has basically one purpose in life as she sees it — breed, and lay eggs like mad. That's all she cares about. --Mr.98 (talk) 20:19, 2 August 2010 (UTC)

But she can't lay eggs; she is entirely dependent on me now, and my actions determine her fate. I do not want to kill her by putting her into the wild knowing she won't survive. My question is about how to help her. How can I care for her? What food does she need? etc Rebmetpes27 (talk) 20:43, 2 August 2010 (UTC)

My point is that you have already disrupted her only real purpose in life. She does not care about life itself and probably does not care about death in the slightest. She cares about laying eggs and that's it. I do not think you should feel bad about putting her out to certain death under these circumstances — at least in such a case, she will be food for something else! The queen is not an individual — the colony itself is the "organism," the queen is just the egg-laying part of it. The colony is already dead. (You needn't feel distraught about this — in all likelihood it wouldn't have survived anyway, only some of the new queens end up forming successful colonies. That's how nature — and evolution — works.) --Mr.98 (talk) 01:17, 3 August 2010 (UTC)

According to List of animals by number of neurons, ants have only 10,000 neurons, cats have 300,000,000 and you have 100,000,000,000. The ant has a spectacularly small number - its ten times more stupid than a house-fly, 100 times more stupid than a cockroach. Almost all of those 10,000 cells will be there to process light and pheremone scent and to run basic instincts, feeding, walking, etc. It is basically impossible that she is able to feel happy or sad or anything else for that matter. She's simply obeying a scent and instinct-driven imperative to do whatever comes next in her life cycle - like a robot - and when it doesn't happen she shuts down, conserves energy and waits. You certainly shouldn't feel sad about it. You sealed her fate the moment you removed her from the environment - whether you keep her, let her go, squish her - none of that makes a difference. It's already over for her - she feels precisely nothing about anything. SteveBaker (talk) 23:59, 2 August 2010 (UTC)

I don't care whether scientists think she feels emotions or not, I still want to help her. What foods do they eat? Is honey enough, or do I need to give protein and vitamins and other stuff? Rebmetpes27 (talk) 00:16, 3 August 2010 (UTC)

Googling "ant farm food" seems to indicate that honey and water are OK foods for an ant farm. I doubt the queen by herself can deal with more complicated foods (which are, if I recall, predigested by workers usually). --Mr.98 (talk) 01:19, 3 August 2010 (UTC)

Am I missing something (probably me lacking in knowledge on ants), or couldn't he just go find the queen some mates and put them in the ant farm with the queen? Ks0stm ^(T•C•G) 02:52, 3 August 2010 (UTC)

Probably not. Ants can generally recognize their own nest by smell (else, how would ants from nests of the same species find their own nest), and may kill the queen from a different nest as an intruder. It also may depend a LOT on the specific species of ant as to what their reaction would be, but it may not go well for the queen... --Jayron32 02:59, 3 August 2010 (UTC)

Fluid balance - production of water by the human body throu metabolism

I'm puzzled how exactly does the human body produce water as stated by our Fluid balance article "In the normal resting state, input of water through ingested fluids is approximately 1200 ml/day, from ingested foods 1000 ml/day and from metabolism 300 ml/day, totaling 2500 ml/day" Can anyone explain this? 89.72.128.27 (talk) 19:41, 2 August 2010 (UTC)

Water is a byproduct of breaking down simple sugars during cellular respiration. Dragons flight (talk) 19:51, 2 August 2010 (UTC)

Simply put, when you take a molecule of sugar like C₆H₁₂O₆ - and add six O₂ molecules to extract energy, you end up with six CO₂'s (which you expel when you breathe out) and six H₂O's which add to your water "input". SteveBaker (talk) 20:44, 2 August 2010 (UTC)

Silicon Bakeware

I am trying hard to find out what the symbols on some new silicon bakeware mean. I have used search engines and looked all over this site's main pages, archives, and reference desk. The best thing I've gotten so far is my own account here! Seriously, though, I would like to suggest that a "chart" section be added. With more and more technology and international cooperation in just about every field, there are more and more symbols being used. I find them from clothing labels to my new bakeware. There are three different circles with the universal "do not" slash accross them. I do not have any idea what the pictures inside the circles are so, therefore, don't know what I'm supposed to avoid. I think charts like this can be found in paper encyclopedias, and would be very usefull to many people. (posted on behalf of User:Designed4Him from his talk page) —  Hamza  ^{[ talk ]} 20:57, 2 August 2010 (UTC)

I've never seen something with "just logos" like that...there's either wording with it or a separate printed note about them. What we would need for an article (or to even answer a question like this:) is to actually see the symbols. No idea how standardized these are, but could have a gallery like at Hazard symbol. DMacks (talk) 02:04, 3 August 2010 (UTC)

at a guess (from glancing at the net) they would be warnings not to use knives, not to place the bakeware on direct heat, and not to use abrasive cleansers. those appear to be nonos for silicone. --Ludwigs2 03:55, 3 August 2010 (UTC)

Tipler Cylinder

Why would an infinitely long Tipler cylinder allow time travel, but not any spinning object? Is there more to it than just making a strong enough gravitomagnetic field?

Why couldn't this be done with regular electromagnetism? Why would general relativity only apply to gravity?

While I'm at it, the Tipler cylinder page mentions a conjecture Stephen Hawking made, but then says he proved it, so it would be a theorem. Should I change it? — DanielLC 22:19, 2 August 2010 (UTC)

Of course, there is the problem of building an infinitely long object... --Jayron32 02:01, 3 August 2010 (UTC)

Regarding your second paragraph: general relativity and gravity are the same thing. Possibly you could do this with electromagnetic fields, since they gravitate. You can't do it with electromagnetism in a gravity-less universe because the lack of closed timelike curves is already built into the spacetime background. A closed timelike curve is a distortion of spacetime, and spacetime distortions are gravity. Regarding the other two paragraphs, I'll have to guess. Third paragraph: the abstract of Hawking's paper (which is all I've read) says "This shows [i.e., proves] that one cannot create closed timelike curves with finite lengths of cosmic string." I think a rotating cylinder falls under his definition of cosmic string. But he also says that this only suggests (doesn't prove) chronological censorship, which he defines as the hypothesis that "the laws of physics do not allow the appearance of closed timelike curves". He might simply be saying that, although he's proved this result starting from general relativity plus the averaged weak energy condition, he hasn't proved it about the real world. But I'm not sure. First paragraph: as Tipler mentions, there are closed timelike curves in the Kerr vacuum that describes a spinning black hole, but in that case the CTCs are behind the event horizon. So the question is really whether you can have CTCs that aren't inside a black hole. Tipler's infinite cylinder has infinite mass, so perhaps you could say that the Schwarzschild radius is infinite and therefore all the weirdness of that geometry is technically inside the event horizon. When you reduce the cylinder to a finite size, the Schwarzschild radius becomes finite but all the weirdness is still confined. But I'm even less sure about that. -- BenRG (talk) 03:33, 3 August 2010 (UTC)

From my understanding of General Relativity, it's all just what happens if you think of gravity as an accelerating reference frame. If an electron falling to the Earth from gravity isn't really accelerating, why would an electron falling to a proton be? Electromagnetism and gravity seem to otherwise follow the same principles.

If it was just gravitomagnetism that caused the closed time-like curves, any object would work, so long as it spins fast enough. 67.172.112.226 (talk) 05:11, 3 August 2010 (UTC)

What sort of mood disorder is the following?

Does there exist/is there a name for a type of mood disorder where a depressive period is caused afterwards by a period of happiness. Like, for instance, if someone were to hang out with friends for a while, feeling really happy, and then aftewards go home to find themself in the opposite mood. Not necessarily reacting to the fact that they had to leave, but rather like some sort of a strange emotional balance out? Does that sort of thing ring a bell to anyone? 68.160.243.61 (talk) 22:57, 2 August 2010 (UTC)

We aren't allowed to offer medical advice - and in particular, we're not allowed to offer a diagnosis. If you (or whoever you might be referring to) is concerned, see a doctor. Our Mood swing article suggests some possibilities. SteveBaker (talk) 23:41, 2 August 2010 (UTC)

There are several disorders that might feature behavior like this: manic depression, certain forms of schizophrenia, a number of neuroses. This is also a fairly normal reaction to stress, a normal part of development in adolescents and young adults, and a typical response to certain life events. Normally no diagnosis would be made unless the behavior is consistent over a long period of time, unrelated to overt biological and environmental factors, and in some way damaging to health or well-being of the person involved, and that decision would need to be made by a qualified therapist (because it is next-to-impossible to diagnose someone with whom you have an close relationship, and completely impossible to diagnose yourself). --Ludwigs2 23:50, 2 August 2010 (UTC)

Manic depression is often called bi-polar disorder, and it sounds like what you are describing. Ariel. (talk) 03:40, 3 August 2010 (UTC)

August 3

How to attack ceramic capacitor to solderless breadboard?

Ceramic capacitors are very small and have no wire legs, so how are they usually connected to a solderless breadboard? I could solder some wires on to form legs, but is that the usual solution? ----Seans Potato Business 01:05, 3 August 2010 (UTC)

No wire legs? I take it that you're using surface-mount components, then...? In principle, there's no technical reason not to solder legs on to them for breadboarding (the usual cautions about being careful not to overheat the component while soldering apply). But honestly, you can probably save yourself a fair bit of time and frustration (and possibly some slightly singed fingers) by investing in a few handfuls of assorted small ceramic capacitors with leads. They're pennies apiece if you can find a suitable store; they'll look like the brown one in the upper right corner of the top photo accompanying the capacitor article. (Hint — you're looking for a shop that has a wall of unpackaged electronic bits in little trays and drawers; a good place to look is near a university with an active electrical engineering program.) TenOfAllTrades(talk) 01:57, 3 August 2010 (UTC)

Right - the fact that it's potted in ceramic has nothing to do with the fact that it's packaged as a surface mount device. Potting and packaging are related but different parts of the mechanical design of electronic components. You can buy ceramic capacitors in all sorts of different packages. (I guess in the specific case of capacitors, "potting" is probably not even exactly right. Unlike other ceramic potting (e.g., for an IC), the dielectric layers in a cap are super-thin - they're probably CVD'ed, sputtered, or grown as an epitaxial layer). Nimur (talk) 03:25, 3 August 2010 (UTC)

What benign medical conditions are easily misdiagnosed as a deadly incurable condition?

For a short story I’m working on I’m looking for a chronic benign condition which is often misdiagnosed as a lethal, incurable condition. To fit the needs of the story, the lethal condition should also be typically relatively non-debilitating for a few months to a year. This should be the kind of mistake which could actually be made, even with analysis by a specialist and a variety of tests. Thank you for helping me make my writing as scientifically accurate as possible. --S.dedalus (talk) 02:42, 3 August 2010 (UTC)

[10] suggests Aortic dissection - which can be mistaken for heartburn. Dunno that it would still be mistaken after specialists and tests had been done though.

[11] suggests that strokes in people under the age of 45 are misdiagnosed as a bunch of relatively mild diseases.

SteveBaker (talk) 02:55, 3 August 2010 (UTC)

Thanks Steve, but I'm actually looking for benign conditions which could be misdiagnosed as deadly ones. A traumatic but fortunate turn of events to be sure! --S.dedalus (talk) 03:03, 3 August 2010 (UTC)

I'm not sure there is anything that meets all your conditions. If there is something that is "often" misdiagnosed, specialists quickly become aware of it and get more careful with their diagnoses. The closest thing I'm aware of is that benign forms of prostate cancer are pretty frequently misdiagnosed as aggressive forms -- but at the stage where this can happen, even the aggressive forms are still treatable. Looie496 (talk) 04:17, 3 August 2010 (UTC)

Your best chance is to just go with a technical error. True story - when I was 22 I blew out my right knee's ACL in a basketball game, but didn't realize it (thought it was just a sprain). The swelling went away pretty quick and I got on with my life. 3 months later I went to see an orthopedic specialist because that knee had some persistent swelling in the rear. He ordered an MRI, after which he informed me I had cancer in the lymph node(s?) in my knee. A second opinion revealed the blown ACL (and the first doctor to be an idiot), but for a full 72 hours my entire family thought their otherwise healthy 22 year old son was dying of KNEE CANCER. Bizarre. 218.25.32.210 (talk) 04:56, 3 August 2010 (UTC)

Interesting problem with AM Radios...

I wasn't quite sure whether or not to post this in the Computing Reference Desk, since it seems too low-tech for that page. Anyway, here goes.

I live in a 3,000 square foot 2-story house that's on a lot that's about 90 feet wide by 120 feet long. (From me looking out my window, but my sense of perspective is sometimes very off). The hill that our house is on is about 325 feet about sea level, and it slopes down gently to river level (I don't believe it's sea level) over the course of just over a mile. The town overall gets fairly decent AM reception on most local channels. However, since a week or two ago, the AM reception in our house's lot has completely disappeared. Whenever we are driving home from anywhere and we have the AM radio on, the radio works fine as we are driving down the road, but all of the channels go from clear to static (over the course of 10 feet or so) right as we pull into our driveway. This is the same for any other AM radio that is on our lot. FM works just fine, and so does any other sort of wireless communication except AM. The local AM channels also work on the properties of the 30+ other houses on our street. It's almost like there is an "AM black hole" that encompasses our property. I thought that it might have been our wireless router (which we had repositioned the antennas around the same time this ordeal started) causing the trouble, but the other members of my household (one with a ham radio license) believe this is not the case. It is nothing severe (it's not like we are in a place where the only way we get news is from AM stations), but it just seems a little strange. Could there be anything (electronic or geological) that is causing interference with the AM band? Any insight (be it professional or not) would be greatly appreciated. Hmmwhatsthisdo (talk) 04:18, 3 August 2010 (UTC)

Brand name drugs vs generics

I read the wikipedia article about generic drugs, but I am having a hard time understanding why a generic drug can really differ from the brand name. I have customers who use all generic drugs and don't have any problems or complaints with any of them. But those same people, when switching from brand to generic on certain drugs have a problem. An example would be generic Wellburtrin XL, both the 150mg and 300mg. Its a widespread problem. Almost everyone complains about it, not just one or two people. So I know there is a real issue. There are a few other drugs out there that really seem different than the brand name. I'm convinced it's not just in the head of my customers because they use other generics with no problems. Since the FDA regulates all generics and tests them also and I'm sure by now they have heard about it and would have done something if there was a chemical difference, what could be an explanation to the problem? —Preceding unsigned comment added by 76.169.33.234 (talk) 04:59, 3 August 2010 (UTC)