Wikipedia:Reference desk/Archives/Science/2013 September 3

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September 3

Power Plant Efficiency

Consider a power plant running on petroleum. The fuel has a certain amount of chemical energy and it produces a certain amount of electrical energy. How would I find an estimate for its efficiency? (It doesn't have to be very accurate, I just want to compare it to the efficiency of a car's engine... which I also haven't estimated yet. All I've got so far is the thermodynamic efficiency based on temperature of the furnace versus ambient temperature and I don't think that is going to be a good estimate.) Thank you. RJFJR (talk) 00:32, 3 September 2013 (UTC)

Typical diesel engine generator sets run at about 42 to 45% overall thermodynamic efficiency. You can verify this by going to manufacturer's or dealer's websites (eg Caterpillar) and downloading data sheets for any model of your choice. This applies over the range for small portable gensets to huge power stations. Coal fired and oil fired steam turbine power stations run at somewhat less efficiency, especially older power stations, but the fuel (coal or heavy bunker oil) is much cheaper.

Typical gasoline car engines run at around 22 to 27% thermodynamic efficiency at best throttle setting. Diesel engines in power generation service are considerably more efficient than car engines because 1) they operate at higher compression ratios (typically 15:1 vs 9:1), they do not thottle the intake air, and because they operate at a constant RPM, the design can be optimised for that RPM. Also, turbo charging, which can only be applied to a limitted extent set by detonation on a gasoline engine, can be applied to a diesel engine to a much larger degree limitted only by mechanical and thermal stresses. By recovering heat energy from the exhaust and putting it to use, turbocharging raises thermodynamic efficiency as well as power output. A minor factor: The combustion temperatures in a gasoline engine are higher, especially at part throttle, because the combustion is stochiometric. A diesel engine operates with excess air. The higher combustion temperatures in gasoline engines mean a higher proportion of heat lost to the coolant, lowering efficiency.

On light loads, the efficiency of a diesel engine falls off not as bad as it does for a gasoline engine (because the intake air is not throttled, and because combustion tempertures go down).

However, if a large gasoline engine is designed to run only at a specific optimum RPM, no expense is spared, and is operated by trained personell, its efficiency can approach that of a diesel engine. For example Word War 2 vintage Merlin and Pratt & Witney aircraft engines.

58.170.175.173 (talk) 01:41, 3 September 2013 (UTC)

45% efficiency for a diesel generator sounds high, but are you only looking as far as the output terminals of the generator, and neglecting losses in transformers and transmission and distribution? Edison (talk) 02:16, 3 September 2013 (UTC)

Correct, the figure applies only to the extent of the generator terminals. Losses in transmission and distribution can be any sort of value and I assumed the OP didn't want it included. For example, a genset in use at a mine site will have only simple local distribution, and distribution losses may be only 1% or less. But a municipal power station feeding a state-wide grid will encounter transmission and dustribution losses very much greater. For this reason, electric automobiles recharged from the electricity mains are rarely a global carbon advantage, even though their internal efficiency may be 90% or better, or 80% if you include the losses in the charger. For the figure for gasoline engines I gave, it applies to to mechnical output at the flywheel, and does not include losses in the gearbox and differential. 58.170.175.173 (talk) 02:29, 3 September 2013 (UTC)

Yes, I always cringe when I hear somebody claim that electric cars are pollution free. It's unlikely they have a solar or wind source for the electricity, more likely they are burning coal, with all the pollution that creates. It's similar to how people who buy a baked chicken don't seem to think they are responsible for that animal's death. StuRat (talk) 08:19, 3 September 2013 (UTC)

And even if they do have photovoltaic power, over the lifetime of the car and the solar panels, you should include the energy used to make the solar panels, which is quite substantial, and generally coming from coal fired power stations. Those solar power greenie freaks definitely belong to the same club as your baked chicken friends.1.122.244.100 (talk) 08:34, 3 September 2013 (UTC)

That depends very much on where they are driving (or at least, charging). If they are driving in France, then virtually none is from coal. (About 75% is from nuclear – and I don't think it's useful to repeat the debate about nuclear here – and about half the remainder comes from hydroelectric and other renewables.) If they are driving in Canada, then about 13% is from coal (all fossil fuels together make up about 20% of the electricity mix); nearly two thirds (63%) comes from hydroelectricity. If they are driving in Iceland, then nothing comes from coal, and 99.9% comes from a completely renewable mix of hydroelectric and geothermal power. Not every country in the world is the United States or China. And if one can persuade one's government to be responsible in its choices for new and replacement power plant construction, the electric vehicle can become 'greener' over time—something that can't happen with a fossil-fuel vehicle. TenOfAllTrades(talk) 13:22, 3 September 2013 (UTC)

Regarding hydropower, few countries are lucky enough to use this as a major source. Regarding nuclear, leaving aside the debate about accident safety and waste storage risks, which is largely political/emotional, the problem is economics. For instance, various Australian State power authorities, especially NSW and WA, looked seriously into nuclear power in the 1960's and 1970's. The trouble is, when amortising the costs over the life of the power station and waste management facilities, you need a power station so huge, one power station generates more power than the entire market, or it just isn't economic. The West Australian power authority got creative, and looked at buying essentially a US submarine engine room - that was small enough, albiet not able in standard form to meet civilian land locked radiation leakage standards, but they still coudn't make it pay. So no Australian state went ahead with it. Countries like France, USA, and Japan are fortunate in having a population and thus power market much larger and able to make it pay. In the case of the USA, Britain, and France, making bomb fuel as a "sideline" helps justify the nuclear industry. 1.122.244.100 (talk) 15:59, 3 September 2013 (UTC)

That's a false claim. "Making it pay" depends entirely on how you tax the waste products. The nuclear industry is expected to include the cost of total, 100% cleanup of all of its operating waste and decommissioning costs into the price of the electricity. If the coal/oil/gas powered power plants were required to do the exact same thing (implying capturing 100% of the CO2 and scrubbing out the acid-rain-causing materials - and also returning slag heaps, open-cast mines, water retention dams and flattened mountains to usable land, preventing damage to water tables and earthquakes from fracking and so forth) then they'd be completely priced out of the market and nuclear would look cheap by comparison.

If we had invented nuclear before coal powered plants, there is no way that coal would be able to enter the electricity market. It's purely an historical accident that we allow one industry to do more or less what the heck they like while the other has to be regulated out the wazoo.

SteveBaker (talk) 16:28, 3 September 2013 (UTC)

Indeed, and then you also have the fine dust emissions from coal fired powerstations and from cars with combustion engines which kill large numbers of people. So, while one worries about big nuclear accidents, the largest recent one the Fukushima disaster in which zero people died, worldwide hundreds of thousands of people die prematurely each year from lung diseases made worse by air polution. Count Iblis (talk) 01:19, 4 September 2013 (UTC)

Quibble: If you are going to count premature deaths caused by air pollution in the case of coal, then you also need to count premature deaths due to radiation exposure in the case of nuclear plants. Since many of the emergency workers were exposed to high levels of radiation in Fukushima, presumably some will die sooner than they otherwise would have. I do agree that coal pollution kills more people than nuclear plant emissions, though. StuRat (talk) 07:35, 4 September 2013 (UTC)

Chernobyl caused 31 deaths immediately and added a 2% to risk of cancer for a few thousand more. 10 children died from thyroid cancer and 700 more were affected by it - perhaps 4,000 people will die prematurely (but mostly not VERY prematurely) because of the fallout.

But that's comparable to the 30 deaths per year amongst coal miners in the USA and 4,000 new cases of "black lung" each year in coal mine workers - a quarter of whom will die prematurely because of it. Figures on the number of people who die from shipping the coal and at the power plant itself are not available - but they aren't zero. People outside of the immediate workforce have also died from landslides in the spoil tips (Aberfan disaster for example - where the children of an entire village were engulfed and died) and from waste water dams failing (The Buffalo Creek Flood, for example - where 125 civilians died).

The huge difference is that the mine-workers and people living near to coal mines suffer this death toll every single year - and we most certainly don't have accidents on the scale of Chernobyl even once per decade - so far we've really only had two within first 50 years of the industry.

Worse still, comparing US mining death rates (US coal mines are probably the safest in the world) with a Russian nuclear accident isn't fair. The Chinese death toll due to below-ground mining accidents alone is over 6,000 per year...and the Fukushima accident has yet to kill a single person.

But in any case, the world has more than enough people - but we only have just one atmosphere. SteveBaker (talk) 14:24, 4 September 2013 (UTC)

It is misleading to claim that radiation/nuclear contamination from the nuclear accident at Fukushima resulted in zero deaths. That is the official weasel claim of the Japanese Government, and presumably the source of Steve's incorrect claim that Fukushima has yet to kill a single person. But their culture has embedded a marked tendency to avoid or distort inconvenient truths. And this claim is true in its words but totally misleading. There hasn't been enough time yet for such deaths to show up - it can take 10 to 20 years or more. An article in the Japan Times describes a study done on deaths among elderly residents evacuated from the radiation hazard zone. The size of this zone means that almost all such evacuated residents were not evacuated because of the tsunmai damage alone. The study looked at 328 residents - a very small sample of those elderly residents evacuated. Of these, 75 died, whereas statistically only 28 should have died between the Fukushima event and the study cutoff in March 2013. It is not suggested they died from radiation. The trauma of forced evacuation and a reducion in living standards and quality of life is what did it - but there are still ~47 deaths that would not have occurred had Fukushima not been a nuclear power station. Since only a small sample population was studied, we can reasonably infer that the true figure could be in the thousands. See Mizuo Aoki, Elderly 3/11 nuke evacuee deaths spiked, Japan Times, English Language version, March 28, 2013.

Also, there were news reports of nursing home and hospital patients dying after being left in situ without food or medical care due to hospital staff clearing out thinking that someone from their equivalent of civil defence will come within a short time, and they could also return themselves. Due to chaos and communication mix ups no-one did come in time for some patients.

Apart from the deaths that have resulted from the nuclear accident (not to be confused with deaths due to the tsunami that would have occured even if the power station never existed), you should take into account the impact on vast numbers of Japanese. I happened to visit the doctor a few weeks after the Fukushima event. It was evident that one of the nurses was Japanese. I asked her, just being friendly, if her folks back in Japan were ok. She burst into tears! Crying, she explained that she had just, after several weeks, managed to get her parents on the phone that day. They did not live in the hazard zone and were not evacuated. But their lives were totally disrupted due to power cuts and loss of employment (factories had shut down to conserve power). You just don't get that kind of thing with coal and oil fired power stations.

I do however agree that more deaths are associated with the routine operation of coal fired power stations than with nuclear power stations even when nuclear accidents are counted.

1.122.56.214 (talk) 07:43, 5 September 2013 (UTC)

(unindent) Yes, that's quite possibly true - but even thousands of extra cancer deaths in a once-in-a-couple-of-decades event like Fukushima are tiny compared to the number of affected coal miners.

Another consideration is that global warming itself is causing extra deaths. It seems incredible but a WHO report says that more than 150,000 deaths are caused every year by climate change. If that's true then switching over to nuclear energy would be a winning strategy - even if there were 100 Fukushima/Chernobyl-scale events every year.

SteveBaker (talk) 16:47, 5 September 2013 (UTC)

Scanimation

I'd like to make an article on this.

I don't think it's the same as Scanimate, but maybe is similar to Parallax barrier. It may have another name. Does this article exist already? Are there enough sources? Thoughts and suggestions would be most welcome. Thanks, Anna Frodesiak (talk) 02:42, 3 September 2013 (UTC)

Definitely not Scanimate. I think it is only similar to Parallax barrier in that only certain parts of the horizontal row of the image are seen (but sequenced in time rather than for one or the other eye). This trick is conventional animation with parts of successive frames interlaced and then selectively displayed by the sliding grid-card. Closer maybe to Lenticular printing, except using a screen to control which part is seen rather than diffeent angles around a lens (and relying on visual processing to "fill in the blanks" where the screen is blocking out the image entirely). DMacks (talk) 02:58, 3 September 2013 (UTC)

Your brain is at least 4 times bigger than mine. :) Okay, Lenticular printing is maybe a see also item. So, the next thing is about whether or not it can stand on it's own two feet as an article, or should be a section somewhere. And the other thing is about sufficient sources. Anything non-spammy is about the video scanimate. Thoughts? Anna Frodesiak (talk) 03:12, 3 September 2013 (UTC)

I would call it a Moiré_pattern animation. /slit animation/ also gets several relevant hits on Google, and that search also led me to Zoetrope. So I guess it's a Moiré Zoetrope :) SemanticMantis (talk) 03:25, 3 September 2013 (UTC)

It's not Moire because that implies that the lines in the image and the foreground object are not parallel - and that's not the case here. (And it's definitely nothing to do with Scanimate). It's really just a flattened out Zoetrope. The video says that it's an "optical illusion" - but it isn't that either. It's nothing more than a three frame movie. The images contain three frames of animation (the least you can get away with to generate unambiguous rotation directions) - with the three frames interleaved. The overlaid screen just selects one of the three frames to view while occluding the other two. Nothing particularly special about it. SteveBaker (talk) 16:09, 3 September 2013 (UTC)

US Patent 7151541 is the mother ship, associated with several published books/toys using it (see patents citing it, and work up the tree; there you also have the inventor's name if this item is notable). DMacks (talk) 03:36, 3 September 2013 (UTC)

I think this deserves a small section at Moiré_pattern but not a separate article. Does that sound right? Anna Frodesiak (talk) 05:14, 3 September 2013 (UTC)

For what it's worth, that sounds good to me. It's a very interesting trick, but probably doesn't warrant a whole article. You could ref the patent, and perhaps one of the books that uses it. SemanticMantis (talk) 14:47, 3 September 2013 (UTC)

I disagree. This is nothing whatever to do with Morie fringes. That implies that the two sets of lines (in the image and the overlay sheet) are at some angle to one-another - and they aren't (or at least don't have to be) for this effect to work. SteveBaker (talk) 16:09, 3 September 2013 (UTC)

It has the similarity of using a striped screen moved across another image, with the effect of creating an animation, wherein the perceived image seems to move. In the classic Moiré pattern, the underlying image is usually a regular geometric pattern. This case is not the same as the classic demonstration, in that the underlying image need not be regular or repeating. So, while it not be a Moiré pattern under some (nonexistent) strict definition, that is the closest place. There may be other choices, but nobody has yet made a case for a better place to include information on this technique. SemanticMantis (talk) 16:17, 3 September 2013 (UTC)

Zoetrope already has information about "linear zoetropes" (and the Masstransiscope!) - which are precisely what this is. Putting the information into the Moire article confuses and muddies what that is all about (which is interference patterns). The whole idea of an encyclopedia isn't to just wedge the information in there someplace to avoid "losing" it - but to carefully consider where it belongs. SteveBaker (talk) 18:19, 3 September 2013 (UTC)

I suppose this thing could be added to Zoetrope. But the video linked by the OP is not a linear Zoetrope. In a Zoetrope, each "frame" of the image is viewable on its own, as a complete image. In the OP's video (and the patent, etc), the screen is necessary to fill in the gaps. That is, the "image" underneath doesn't make any sense without the screen. As far as I can tell, that is not the way the masstransiscope works either. It looks to me that in the masstransiscope, each frame is a full image, and the slits just control which image you see at which time. Maybe we do need a new article after all! SemanticMantis (talk) 18:47, 3 September 2013 (UTC)

And here's [1] a picture of the Masstransicope frames. As you can see, they don't require a screen to complete (and also mask) the image, as our current device does. SemanticMantis (talk) 18:53, 3 September 2013 (UTC)

I suppose you have a point about the multiple slits...but it's still nothing remotely to do with Moire fringes. SteveBaker (talk) 19:01, 3 September 2013 (UTC)

Nothing remotely? Have a look at Shape_moiré :) I see no substantive difference between the animations there, and the video that the OP links. Contrary to what you seem to think, moiré patterns aren't required to be made from parallel lines, or even be geometrically regular. It is a generally-used term to describe how the combination of two different layers can occlude and interfere, and give rise to a new pattern that was not present in either layer alone. But, thanks for this discussion, it forced me to dig deeper into WP, and learn a few new things (they apparently use this type of "shape" moiré in marine navigation, to make arrows that change direction, and always point toward the obstacle (our ref at Moiré pattern is sadly broken))! And there's no reason we can't have links to zoetrope and other related concepts. SemanticMantis (talk) 19:44, 3 September 2013 (UTC)

Yep! Nothing remotely. That article you linked to is indeed related to moire fringing - it's resampling the data at a different frequency...not at all the same thing as the animation technique referred to here - even though it appears superficially similar. Mathematically, it's not remotely the same...I'm sorry if you don't understand the distinction - but it's truly not the same. SteveBaker (talk) 20:29, 3 September 2013 (UTC)

You really think the animations at shape moiré and the what the OP linked are completely different? The video the OP links could also be described as sampling at different spatial frequencies, with the phase controlled by position of the screen. Both there, and at shape moiré, we have a striped screen moved across an image. In both cases, the filtering out of some frequencies allows a different image to be seen, that is partially made up of bands from the screen, and partially made up of the underlying image. When the screen is moved, the combined image appears to move, due to changes in phase. For me, that is more than enough similarity to consider them the same, for the purposes of WP classification. The only difference I can see is that, in shape moiré, the underlying image is periodic in one direction. So, if your argument is that, to be a "true" moiré pattern, the base layer has to be periodic in one direction, then I can concede that difference, even if I don't agree with the definition. I As for the rest of the math, you are aware that all the math on our articles is ad-hoc, and developed to illustrate how specific examples work out, right? There is no canonical set of equations that can in general model any given moiré pattern. The whole notion of moiré patterns is a bit subjective, so I suppose it's a bit pointless to argue about what does and doesn't qualify. Still, if you care to show us what you mean by "Mathematically, it's not remotely the same", I'll be all ears (er... eyes :) SemanticMantis (talk) 20:57, 3 September 2013 (UTC)

So what's the verdict? Shall I stub it and see how it develops? Anna Frodesiak (talk) 12:43, 4 September 2013 (UTC)

Your call. Thanks for the interesting post! I tried to explain my perspective as clearly as I could, and in my view, it's a sub-class of a wide variety of moiré patterns. It could go in a section at the main article, or as a stub, maybe moiré animation. I actually only skimmed the patent, maybe there's a better name there? Also, if you can find info on any of the books that use they patent, they may call it something specific like "magic screen" or something. If so, that would be a good redirect. I'm traveling for a few days, but I can work on it next week if you contact me on my talk page with the stub link. SemanticMantis (talk) 14:33, 4 September 2013 (UTC)

Okay, I went with Moiré pattern#Animation. I had absolutely no idea how to describe it. It's an eleven on the horribly-written scale. Anna Frodesiak (talk) 23:55, 4 September 2013 (UTC)

I also usurped this former redirect to Scanimate, and made it into a dab page: Scanimation. I'm not sure if I got it right. Anna Frodesiak (talk) 00:15, 5 September 2013 (UTC)

Teabags and Toothaches

Upfront: I do not have a toothache and am not looking for medical advice, just curious about a folk remedy that I can't seem to find a discussion of. I've seen/heard that if you put a tea bag in your mouth, over a tooth that is infected, that it will draw out the infection- I've heard a number of variations too: it has to be a black tea, needs to be warm and wet, needs to be dry, etc.. At any rate, no matter how much I look, I've never come across anyone debunking this claim, or even discussing it beyond the recommendation, most other common folk remedies are debated/discussed elsewhere. So, does this work and, if so, by what mechanism, and if not, why does it seem to get a free pass. (Note: I'm sleepy and wording poorly, I don't mean to suggest that I think it works because nobody debunked it- I doubt it would do anything but give you a foul taste in your mouth.)Phoenixia1177 (talk) 10:09, 3 September 2013 (UTC)

I would consider that "treatment" a Poultice - "used to treat abscess wounds, where a build-up of pus needs to be drawn out." Also, the caffeine may bring some pain relief. http://www.telegraph.co.uk/news/uknews/1360756/Why-a-cup-of-tea-can-ease-the-pain.html. I personally have never heard of this remedy. 196.214.78.114 (talk) 10:48, 3 September 2013 (UTC)

I'd suggest that one reason this hasn't been aggressively debunked is that, unlike many old wives tales, it's not that old. Many old wives have been around for longer than tea bags. HiLo48 (talk) 11:02, 3 September 2013 (UTC)

(JK) They'd be really really old. At least 110. Teabag#History (Lacks citations.) 196.214.78.114 (talk) 12:29, 3 September 2013 (UTC)

Although not in popular use in the UK until the 1970s (purely my personal recollection but I'm fairly certain). Alansplodge (talk) 12:43, 3 September 2013 (UTC)

FWIW I remember Tetley teabags being available in the UK in the mid-1960s. According to this page they sold 5000 tonnes of them in 1968. AndrewWTaylor (talk) 14:36, 3 September 2013 (UTC)

Well I stand a little corrected, however "In the early 1960s, tea bags made up less than 3 per cent of the British market, but this has been growing steadily ever since. By 2007 tea bags made up a phenomenal 96 per cent of the British market..." [2] This page says that we use 130,000 tons of tea per annum, so assuming a similar consumtion in the 1960s, 5,000 tons would be nearly 4%. Alansplodge (talk) 20:14, 3 September 2013 (UTC)

There could be other interpretations of the story or your question, but I'm taking the brass-tacks question here to be: does Camellia sinensis interfere with damage to teeth by Streptococcus mutans? Looking these two things up online, it looks like this is a question pursued by good students around the world, and classes have actually done some good work with it, summarizing the literature and testing on their own. [3] [4] (though the notion of schoolkids growing up isolates of decay-causing bacteria is slightly worrisome...) The latter experiment makes it clear that ordinary mouthwash is generally more potent against bacteria in vitro, but that first student wiki puts forward an interesting hypothesis that tea catechins could have another effect in toxin secretion. Searching NCBI turns up a number of similar studies from throughout the Middle East. [5] My feeling is that the practice is based in science, but the effectiveness of this specific procedure, or little variations in it, has not really been demonstrated. Wnt (talk) 13:54, 3 September 2013 (UTC)

The reason that these things are not always well debunked (or even shown to be true) is that it takes no more than 20 seconds for someone to come up with a semi-plausible idea like this. Let's say: "Soaking your feet in warm diet cherry coke every night before bedtime is a sure-fire cure for male pattern baldness"...that only took me 10 seconds to think up - and I could spam it to the world and a bunch of people would repeat it as truth...before you know it, it would be on The Dr. Oz Show. But it takes years of careful and expensive scientific study with hundreds of human test subjects to show whether it's true or not. It follows that most of these "old wives tales" will go forever untested.

Imagine a test for the teabag hypothesis. You'd need to take 100 people with toothache and have a third of them use the teabag, another third use placebo bag filled with inert, fake, tea-leaves and another third do nothing. Wait for a week and have them all examined for signs of infection. This is kinda unethical - that's 100 people who really should have seen a dentist who didn't. With all of the statistical work, the coming up with a really good placebo bag, double-blinding the experimenters, crunching the numbers, deciding whether there might be something in it - which might require some follow-up work, and publication - with more people duplicating your experiment to verify the results...the whole thing might easily cost a half million dollars to run just to debunk the myth.

So you cannot use the lack of a complete debunking as some kind of evidence that something fairly obscure like this is untrue.

NOTE: Neither this author nor the WikiMedia foundation either promote or endorse soaking your feet in warm diet soda of any kind - do so at your own risk! :-)

SteveBaker (talk) 15:51, 3 September 2013 (UTC)

The difference though is that folk remedies generally spread when they are found to be effective by a user. Of course, they can spread for wrong reasons - political salesmanship like for the King's evil (though some pricey meat wouldn't hurt there), mnemonic convenience like for the doctrine of signatures. They can also spread because they have some sensible science behind them... even though they don't actually work! But not infrequently they spread because they do work. The world is full of traditional medicines that actually contain useful compounds. It is useful in such instances to keep an open mind either way, neither saying yes nor no as a default. Even placebo is sometimes prescribed by physicians, so why discourage using something with a chance? Wnt (talk) 16:41, 3 September 2013 (UTC)

But most folk remedies don't work - and things like Homeopathy spread like wildfire despite that. Some folk remedies are really dangerous - such as Rasa shastra which purports to cure diseases with helpful metals like mercury and lead - that didn't stop it from becoming popular. Others that are growing in popularity in the US include gold and silver therapies - which can cause Chrysiasis and Argyria. All it takes is for some random idiot to read that silver has antimicrobial properties and to extrapolate from this true fact to the entirely unwarranted conclusion that consuming colloidal silver will cure what ails you - and you may soon find that your skin turns permenantly and irreversably purple. SteveBaker (talk) 18:14, 3 September 2013 (UTC)

The problem is in what "found to be effective" really means. With a single self-diagnosing patient, self-prescribing a preferred folk remedy, there's a whole bunch of problems. It's a condition where straight up placebo effect should be expected to be strong (often bolstered by a good bit of spurious argument from authority, whether from grandma, the internet, or a fringe publisher who mistakenly believes that sharks are immune to cancer). There's also the post hoc ergo propter hoc problem—a lot of symptoms targeted by home remedies will go away (or lessen, or be perceived to lessen) by themselves, purely by time or chance. It's an almost ideal incubator for random psychological reinforcement. TenOfAllTrades(talk) 20:34, 3 September 2013 (UTC)

Homeopathy and colloidal silver aren't folk remedies - they're well promoted modern scams with organized backing, and in the case of the former, formal legal authority to offer "diagnoses" and "medications" and "treatments" not allowed to the average wise-woman. Of course, I recognize that there are plenty of ideas from traditional medicines that are completely wrong, but it doesn't deserve credit for these. (Traditional medicine tends to be particularly good for purposes such as immediate pain relief where the user knows whether a clove or a beaver testicle helped his toothache or not a minute later; and particularly bad at long-term uses like for cancer treatment (I don't remember seeing a single traditional treatment for cancer that worked, and they actually missed treatments like yew bark that they had in their pharmacopoeias) Wnt (talk) 22:25, 3 September 2013 (UTC)

I picked those two examples precisely because they are popular enough to have been carefully tested, so we know for sure whether they are effective or not and can therefore discuss them rationally. Things that a very few people believe are not gonna get carefully examined (for the reasons I explained above) so it's hard to find examples of major screwups. But there is no particular reason to assume that an untested treatment from a modern scammer is any more or less effective than something from the proverbial "old wife". Without research, either one of them could be effective, ineffective, provoke a placebo reaction or could be downright dangerous.

The idea that sticking a clove against a painful tooth will make the pain go away might work well for one person but badly for another. It could have nasty side-effects - maybe the tooth falls out three months after treatment or the patient gets a fatal form of cancer ten years down the line because of it. How would anyone notice that the clove was the problem? Without using modern research methods, you have no idea what you're really doing to the patient - even if it seems to work every time. SteveBaker (talk) 13:33, 4 September 2013 (UTC)

OK - how about this as an example. 20 years ago, grapefruit was a "herbal remedy" for all sorts of maladies. It actually did seem to work - but modern science has since discovered that what's really going on is that this fruit interacts with all sorts of biochemical mechanisms and has truly horrendous drug-interaction effects - magnifying the potential of otherwise harmless doses of other chemicals to do serious damage. (See Grapefruit–drug interactions). If your grandma tells you that grapefruit is good for your allergies - and you happen to take it within an hour of taking some Benadryl...well, let's just say "Don't Do That!". SteveBaker (talk) 13:44, 4 September 2013 (UTC)

It's hard to use this as an example - it didn't seem to be mentioned by Dioscorides or Pliny... after a bit I looked up grapefruit and found it was an 18th-century hybrid. Culpeper's herbal doesn't seem to include it either [6] Now, the first and foremost thing about genuine traditional folk medicine is that it is old - sometimes hundreds of years, often thousands, and the use of a few herbs may have even been shown to date all the way back to the Neanderthals. Now, if I take some other curious entry from Culpeper, say about "goutwort" (which I assume is aegopodium podagraria), well, I don't find much in NCBI but I do see it contains a fair amount of falcarindiol, a COX-1 inhibitor. [7] Now they call it "nutraceutical" Since that occurs in carrots also I suspect that is not the end of what might be found in such a plant (since gout sufferers don't usually extol the virtues of those), and certainly looking just now I didn't make much of an effort; but neither has science, I think. My point though is that I would have pretty high hopes for something from one of the old herbals, but not from a random magazine article that cobbles together some snippets of science to push a superfood. Wnt (talk) 07:30, 5 September 2013 (UTC)

molecular mass and formula mass

I need 5 differences between molecular mass and formula mass .... can anyone help me (139.190.171.116 (talk) 13:08, 3 September 2013 (UTC))

You can read our article on molecular mass (which also discusses formula mass) if you do not feel like, or are confused by, the materials provided by your teacher in class or as assigned for you to read in your textbook. Your teacher is obviously asking something based on what you are learning in class, so it's best for you to use its resources to give the answer the teacher wants. DMacks (talk) 13:24, 3 September 2013 (UTC)

I don't see the mass of the empirical formula (which is, according to google, the definition of formula mass) being mentioned in that article... Ssscienccce (talk) 14:25, 3 September 2013 (UTC)

Is why I softened my statement to focus on whatever terminology and ideas the teacher/textbook used. Without knowing what facts and definitions were given, we're stuck saying "google it, here's what I found" or "our formula mass is a redirect to molecular mass and we don't have a distinct definition according to a reliable source". Neither of those would earn passing marks. If there is a difference according to IUPAC, please add it with cite to the article. If this is just a fuzzy or obsolete distinction, then maybe it's best we don't propagate it at all. FWIW, there are bunches of google hits that formula mass is actually what it means in lay language: sum of masses of atoms in the "formula" (either molecular or not explicitly empirical). DMacks (talk) 14:33, 3 September 2013 (UTC)

Good to know the vagueness of the term wasn't just in my head. ;-) IP seems to originate from Pakistan, maybe it has a more precise definition in the original language... Ssscienccce (talk) 15:17, 3 September 2013 (UTC)

help identify this bug

Hi, can you please tell me what is this creature? found dead in Haifa, Israel

unknown bug

Thanks --Golan's mom (talk) 13:15, 3 September 2013 (UTC)

Upon further examination, I have observed the creature to be a member of a species of insect which may be found in parts of Israel, including Haifa. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:29, 3 September 2013 (UTC)

Intelligence tells me that it is a bug-shaped bug manufactured by the Israeli government. Capable of storing 3.72 terabytes of info. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:29, 3 September 2013 (UTC)

Please refrain from posting jokes, especially before the question has a legitimate answer. Nimur (talk) 14:40, 3 September 2013 (UTC)

Dubious humor aside, my wild guess is it looks like some species of longhorn beetle, but even if that's right it leaves a large field of possibilities... Wnt (talk) 13:58, 3 September 2013 (UTC)

Because of complex politics, Wikipedia's articles about nature, wildlife, and ecology in the Levant are particularly fragmented. I watched passively as our article currently known as Biodiversity in Israel, the West Bank, and the Gaza Strip changed hands between Fauna of Palestine and Fauna of Israel multiple times over the last few years. Personally, I was too embroiled in the war in South Lebanon for me to divert any of my encyclopedic energy to the more noble pursuit of natural science, Everyone suffers when senseless conflict erodes our ability to share and categorize our knowledge freely. Anyway, that page links to a few online databases that might be helpful, but I'm unable to reach any of the servers linked - they may be inoperable, or simply very slow. Still, despite the fragmentary organization, there are dozens of Palestine and Israel "lists of fauna" categories and lists that you can peruse by following the category links on the bottom of that page, e.g. Category:Environment of Israel and Category:Environment of Palestine.

Before we jump to wild guessing about the specimen, we should aim for the kind of procedural study that a proper entomologist would use. Here's a guide to arthropod morphology from the American Museum of Natural History that points out the key features that we should focus on, to aid in classification and taxonomy identification. For example, the lack of a visible external ootheca almost categorically rules out any type of cockroach.

With luck, one of our better bug enthusiasts can help us out narrowing down the species. Nimur (talk) 15:07, 3 September 2013 (UTC)

I appreciate your request to refrain from jokes. Refraining from soapboxing is also good advice. --Onorem (talk) 15:14, 3 September 2013 (UTC)

Sorry. I am attempting to sincerely express that our encyclopedia coverage of this topic is actually degraded by the ongoing political conflict, and despite my intimate familiarity with the region and its biodiversity, I am not able to find great internet links about the insects of Haifa. Nimur (talk) 15:18, 3 September 2013 (UTC)

I went to the MNH site suitably chastened, to see what the professional guide would recommend... actually, it links to a group of articles like this which says first to look at the wings, which we can't see, then "Basically, you're eyeballing your specimens, looking at the differences and similarities. Sort your specimens according to shape, color, number of legs, and any other differences you can discover ... If you are able, for example, sort all the things that appear to be beetles. Next separate the long, narrow beetles from the round beetles. Then take a closer look at the long, narrow beetles and see characteristics that some share, like the same type of antennae or the shape of their wing covers." Which actually more or less matches the ad hoc thought process I'd used here, so now I don't feel so bad. Still a poor substitute for a taxonomic key. But looking one up I get [8] saying that there is no accepted taxonomic key - besides, with no way to properly examine either the wings or the genitals, our possibilities are limited. Wnt (talk) 16:34, 3 September 2013 (UTC)

Additionally, we can rule out true bugs by the mouthparts, and see that there are complete elytra. Together, those suggest a beetle, and the long antennae make longhorn beetle a pretty good pick. Still, it is worth mentioning that very few insects can be identified to species level via a single photo, even with a key and training. SemanticMantis (talk) 16:54, 3 September 2013 (UTC)

Thank you for pointing me in the right direction - before I could just tell Golan that it's a bug ... Looking up the longhorn beetle in the English Wikipedia as well as in the in the Hebrew Wikipeida I have arrived at this great site with pictures of Cerambycidae of Israel, see here to insects of Israel. Thank you! --Golan's mom (talk) 17:59, 3 September 2013 (UTC)

And if I would have to take a guess, I would say that the closest to what we found would be Niphona-picticornis --Golan's mom (talk) 18:12, 3 September 2013 (UTC)

semi permiable membrane

semi permeable membrane (talking in context to osmosis) dont allow solvent molecules to pass through it even if the spm has pores of bit larger size than it is of the solute particles.

The fact mentioned is 100% authentic just i need a satisfactory explanation — Preceding unsigned comment added by Shubhamagrawal1996 (talk • contribs) 15:25, 3 September 2013 (UTC)

There are many biochemical mechanisms that exist to help explain how flow against a concentration gradient is possible; this includes selective permeability and active transport. I wonder how "pore size" is being defined... if we were using molecular physics terminology, we could talk about the atomic radii at the periphery of the pores, and we could describe active transport as a selective mechanism to open and close the pores by converting chemical energy (from adenosine triphosphate, usually) into other forms of molecular potential energy. That energy can be used to apply an electrostatic potential to the periphery of the pore, essentially altering the collisional cross section of the pore in a specific way for each solute molecule. As a physicist, I would now say "the pore aperture is smaller than the solute particle cross-section" - but as a biologist, I can see an equally coherent justification for saying "the pore aperture did not change size, but it no longer permits the solute to pass through it." Nimur (talk) 15:59, 3 September 2013 (UTC)

Biochemical? My interpretation of the question was membranes used in reverse osmosis, like for desalination of seawater. Haven't find an answer though. Reading the question again, I see it says not allowing solvent molecules to pass, not sure if that is what he means, in that case nothing passes?Ssscienccce (talk) 22:55, 3 September 2013 (UTC)

Biology

When there is acidity, why the colour of urine become deep yellow?Is due to high level of urochrome? — Preceding unsigned comment added by Titunsam (talk • contribs) 17:26, 3 September 2013 (UTC)

I don't know the answer, but here are a couple related observations:

1) When I drink lots of water, my urine is clear, presumably because it is quite dilute. This would also tend to make it less acidic.

2) When I take lots of vitamin C (ascorbic acid), my urine is bright yellow. StuRat (talk) 07:26, 4 September 2013 (UTC)

Osmosis, diabetes mellitus, and osmosis

Pick the correct answer to the following question. Write a brief statement explaining why each choice of answers is correct or incorrect.

In diabetes mellitus, because of insufficient insulin production, glucose cannot enter cells. instead it accumulates in the blood plasma. which of the following statements would be true under these conditions?

A. The concentration of the plasma would decrease. B. the osmotic pressure of the plasma would remain the same. C. Water would move out of the tissues into the plasma. D. Tissue cells would swell. — Preceding unsigned comment added by 98.214.102.79 (talk) 17:46, 3 September 2013 (UTC)

Or E. Do you own homework. 82.21.7.184 (talk) 18:23, 3 September 2013 (UTC)

You may want to read the article Osmotic Pressure, as well as Tonicity. Knowledge of those concepts should be sufficient to answer at least B-C. I'm not quite sure how to answer A, as the phrase "concentration of the plasma" is vague and confusing. -- 205.175.124.72 (talk) 00:52, 4 September 2013 (UTC)

The speed of light versus the speed of sound. Which has more for the buck?

Years ago a did an experiment utilizing two multiple speed tape recorders. I read the entire front page of the local newspaper on one recorder, rewound it then replayed, put it on the fastest speed to re-record it. I repeated that process three times. Lo and behold the entire paper was a mere BEEP. That being said leads to the question if you could speed it up say a hundred times it might be possible to fit the entire library of congress into a mere beep? If the science is there/here maybe those beeps I've heard that certain astronomers are listening to,,, actually mean something? Origiman (talk) 21:12, 3 September 2013 (UTC)

Your experiment with tape recorders was employing Lossy compression. Many of the people involved with SETI have PHD's in information technology and related fields. Surely they examine their data with every known compression algorithm in mind.--Digrpat (talk) 22:35, 3 September 2013 (UTC)

Speaking of which, using quantum computing with superposition of states, how much information can you put into a single photon shot out into space? Wnt (talk) 23:03, 3 September 2013 (UTC)

You can store a lot of information in the momentum of the photon, the total amount depends on the distance between transmitter and receiver. This follows from the total number of available quantum satates in a volume V; for a single photon this is 2 V W/h^3, where W is the volume in momentum space, the factor 2 is the spin degree of freedom. To measure the photon momentum with an accuracy delta P requires the measurement apparatus to have a size of hbar/(2 Delta p), so the more information is stored in the photon momentum, the larger the detector needs to be to extract that information. And then we've not taken into account the noise that one has to average out. Count Iblis (talk) 23:27, 3 September 2013 (UTC)

I read that this is actually a problem for SETI, because an ideal compression algorithm renders data indistinguishable from white noise. If we assume that any sufficiently advanced civilization actually encrypts and compresses its communication, which is not a stretch, it makes it very unlikely that we'll even recognize the signal as "intelligent", let alone figure out what anything in the signal means. Vespine (talk) 23:34, 3 September 2013 (UTC)

That is in fact a real conundrum. A similar conundrum existed during the cold war: SIGINT, the interception of enemy signals, was a persistent topic of very advanced research. In many cases, the order to launch (or not launch) nuclear missiles was intentionally meant to appear as white noise, and transmitted at all times, because any other type of signal broadcast to the numerous submarines that were necessarily dispersed across the entire globe would clearly indicate the plan to strike (or equivalently, the absence of a command not to strike). I am still astonished that we survived so many decades without more accidental nuclear launches. The existence of these radio signals may seem like fringe-theory pseudoscience, until you build your own very-long-wavelength, extremely low frequency radio and hear the constant, droning, almost-tonal hissing that's always hovering just below the very-well-studied completely natural noise floor. Nimur (talk) 00:37, 4 September 2013 (UTC)

I doubt it's really that much of a problem for SETI, because SETI isn't likely to be able to detect anything that's not shot pretty directly at us in a narrow beam. Why an ET civilization would go to the trouble to do that, and then encrypt it so we couldn't understand it or even distinguish it from noise, would need explanation. --Trovatore (talk) 02:13, 4 September 2013 (UTC)

I inherited a fantastic book, formerly owned by Ronald Bracewell, called The Search for Life In the Universe, by Goldsmith and Owen (from UC Berkeley and SUNY Stony Brook). It is an excellent, very rigorously scientific analysis of this problem. There are two entire chapters on the motivation and practicality of using photons to encode information, including a brief section on the encoding of meaningful information as "bits" stored among the various physical properties of the photon (using the terminology of 1980-era physics and information theory, which is still pretty current, and I'm happy to say is totally bereft of the more recently popular term "qubit"). Anyway, anybody who is interested in squishing lots of information into a radio photon may find this book an interesting read - whether your goals are the academic pursuit of SETI or if you are more involved in the more worldly engineering practicalities of optical or radio communication. Nimur (talk) 14:38, 4 September 2013 (UTC)

This is not, as suggested above, "lossy compression" per se. That is, there is no theoretical issue with compressing audio like this indefinitely. You're just frequency shifting the data up into increasingly high frequencies, and frequencies can potentially rise infinitely high. To that end, you can in principle encode the whole Library of Congress into a single sub-second audio pulse. Where the problems enter is in practical engineering -- no real device will handle those absurdly high frequencies, and so you won't be able to losslessly reverse the process. CDs, for instance, are engineered for about 22 kHz signals. Any signal above that frequency is fundamentally unidentifiable (and any digital implementation will share a similar hard upper bound). Analog equipment doesn't have that hard ceiling, but practical tolerances will still impose themselves before the audio compression idea gets very far. The end result, then, resembles lossy compression (because you certainly have lost data), but it shouldn't be confused with what is meant by "lossy compression", where even in the ideal case data is voluntarily destroyed. — Lomn 01:43, 4 September 2013 (UTC)

Agree with your analysis with a small quibble. The process as described is not just frequency-shifting; rather the time compression leads to frequency expansion. For example, if the original sound occupied frequency range 20Hz-20kHz,after being recorded at twice the speed, the signal will occupy frequency range 40Hz-40KHz. Thus the analog tape used to record the speeded up sound (and the equipment used to record/read the sound) will require higher physical tolerances to maintain fidelity, as you say. Abecedare (talk) 02:41, 4 September 2013 (UTC)

That's the real issue here. If you had an utterly perfect tape recorder - you could do what the OP suggests without loss. But there is no possibility of ever building anything that perfect. All practical tape recorders (and voice recorders of any kind) have limited bandwidth and limited dynamic range - so at every recording, some of the speeded up information is too high in frequency for the tape recorder to record. When you slow down one of those 2x speeded up recordings to retrieve the original text, it'll sound muddy - when you slow down the 4x, 8x and 16x recordings, that'll get worse and worse - to the point where you won't be able to understand what's said anymore. SteveBaker (talk) 13:23, 4 September 2013 (UTC)