Wikipedia:Reference desk/Archives/Science/2011 August 1

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August 1

Block erasure

Why can flash memory be read and written one cell at a time, but only erased in blocks? I've read the flash memory article, and it seems that erasure is just a matter of bringing the control gate low and the drain high, which doesn't seem any more complicated than programming the bit. --140.180.16.144 (talk) 00:19, 1 August 2011 (UTC)

It is a different mechanism. Imagine a flash memory made up of buckets of water. You can ask whether any particular bucket is full. You can fill any particular bucket. Or you can pull the "single" bit of string that opens the bottom of a whole block of buckets to erase the block. Obviously it could be done differently, but memory manufacturers have decided that the block erase method is a commercially satisfactory compromise between being unable to erase at all and being able to erase any particular cell. -- SGBailey (talk) 11:40, 1 August 2011 (UTC)

Disulfiram and fetal alcohol syndrome

I had an episode "Choice" going in the background, where a pregnant woman ends up being sentenced to a court-ordered alcohol treatment program to avoid fetal alcohol syndrome. I became curious whether the notoriously unpleasant combination of Antabuse (disulfiram) and alcohol would increase the risk of FAS, and found some references suggesting that acetaldehyde, which is what builds up when the drug is taken to interfere with alcohol degradation, does indeed have teratogenic effects,^[1][2] though one study found that disulfiram didn't make these worse.^[3] All these studies were quite old, and seemed to mark this as a question of some public health importance, yet I'm reading that disulfiram has remained "FDA pregnancy category C" with no information about whether it is harmful or not to pregnant mothers. How is it that this question has never officially been sorted out one way or the other? Wnt (talk) 01:21, 1 August 2011 (UTC)

Prob'ly 'cause it takes a long, long time to do clinical studies in humans. FWIW 67.169.177.176 (talk) 01:43, 1 August 2011 (UTC)

Well, you certainly can't do a proper clinical trial to look for teratogenicity in fetuses - but you can look retrospectively at what happens when the mother chose to take the drug vs. not, with certain pitfalls. Wnt (talk) 01:50, 1 August 2011 (UTC)

Insane to order her to go on antabuse when she could be incarcerated for nine months and given valium to control the withdrawal symptoms. Rather silly premise. μηδείς (talk) 02:00, 1 August 2011 (UTC)

Incarcerated on what charge? I don't think I saw the episode, but the brief description at the linked article doesn't mention any criminal act on her part. --Trovatore (talk) 08:19, 1 August 2011 (UTC)

The question says "sentenced", does it not? μηδείς (talk) 01:45, 4 August 2011 (UTC)

Sorry - this wasn't really a question about the episode, which never specifies what sort of treatment would be given at all. It just got me wondering whether authorities, one place or another, might be causing fetal alcohol syndrome with their forceful efforts to prevent it. Wnt (talk) 17:11, 1 August 2011 (UTC)

popularizing chemistry

I feel that many natural science branches like biology and physics are more popularized than chemistry.Am I wrong?If so, why is chemistry less popularized? Is it hard or something?--Irrational number (talk) 01:26, 1 August 2011 (UTC)

I dunno -- as a chemist, I don't find it hard at all. Maybe it's just that there's not as much earth-shaking basic research (as opposed to the more mundane but more useful applied research)? 67.169.177.176 (talk) 01:37, 1 August 2011 (UTC)

I think that there's a lot more biology being publicly funded than chemistry, which I think of as being done much more by corporations. Public funds encourage researchers to talk up (if not hype) their research to the public, whereas proprietary research tends to be done in secret, and when discussed by company employees, tends to be disbelieved by a skeptical public. Wnt (talk) 01:41, 1 August 2011 (UTC)

Plus, there are negative stereotypes of chemistry being a "dirty" science (as opposed to biology, which is "natural" and therefore supposedly "green"). 67.169.177.176 (talk) 01:45, 1 August 2011 (UTC)

I would be quite surprised if there was any correlation with amount of public funding received and amount of popularization. The areas of popularization are fairly narrow (a handful of sub-questions of each field, even in physics and biology), whereas the areas of public funding are quite broad. Furthermore, it isn't the case that popularizing your particular discipline (say, physics) is going to result in increased public funding for that discipline, as generally speaking most public funding of science goes into a big NSF pot that is then doled out by the NSF administrators and reviewers, not Congress or "the public" to any degree (and let's thank goodness for that!). --Mr.98 (talk) 01:55, 1 August 2011 (UTC)

This is quite an esoteric question - no way to clearly say exactly which part fits in which branch, and so forth. And, it depends what timeframe you look at, what countries you look at, all the problems of cross-field-studies (is astrophysics chemistry? Molecular modelling? etc) Depending on how you choose to divvy up "The Sciences", you'd get vastly different results. A related article, which might serve as a starting point, is Natural science. Personally, I don't think it is related to difficulty; it could relate to trend/fashion, and could relate to the way subjects (for e.g. Degree-level) are constantly being subdivided. I bet there's a bit of Chemistry included in various Quantum mechanics courses, and in a cooking degree. Is a chef a chemist?  Chzz  ►  01:51, 1 August 2011 (UTC)

In the United States, physics started being really popularized initially after WWII, because of its association with wartime weapons. In more recent years its ability to tell stories about our origins (e.g. cosmology) kept it relevant in the popular mind, and the "mind-blowing" aspects of quantum and relativity make for rather heroic (if often misunderstood) narratives. Biology is mainly popularized via discussions of evolution and genetics, both of which are quite popular in that they again tell stories about our origins and our current selves. Genetics has been of popular interest in the US since the 1920s or so, in part because of its connection with eugenics and race and all that, which really touch pretty deep into major American preoccupations. As for chemistry, there just doesn't seem to be as much popular association. In the best of times it is associated with industry and development; in the worst of times, with all of the excesses and downsides of industry and development (pollution, DDT, whatever). The aspects of it that do pertain to origin stories or selfhood quickly become assimilated into other fields (e.g. cosmology, again). Chemistry does not appear to tell very heroic stories about humanity or its place in the universe, though there is no inherent reason it need not. --Mr.98 (talk) 01:52, 1 August 2011 (UTC)

Here in Australia we have a major political leader who has publicly declared twice in the last week that carbon dioxide is difficult to detect because it's invisible, tasteless, odourless and weightless. That he was able to say it twice without embarrassment shows the poor public situation chemistry is in. HiLo48 (talk) 01:58, 1 August 2011 (UTC)

Wait til he finds out about the insidious chemical, dihydrogen monoxide. :-) StuRat (talk) 02:31, 1 August 2011 (UTC)

Common name, "Copious water"; always labelled "use sparingly" ;-)  Chzz  ►  06:54, 1 August 2011 (UTC)

Simplistic answer: Because as far as the environmentalist, organic food and natural health "industries" (both the crackpot and nominally rational varieties thereof) are concerned, chemistry is the Great Satan!(tm). The major selling point for much of food and "natural" medicines and other products advertising is the claim that they "contain no chemicals" and the gullible uneducated public swallow it whole. The chemical industry has simply been totally and utterly crushed in the propaganda war for public consciousness - probably because they never even noticed there was a war on until after they had already lost it. Roger (talk) 11:29, 1 August 2011 (UTC)

Did anyone tell him carbon monoxide, radon, sarin and a number of other substances he probably does want someone to regulate are also odourless, 'invisible' (presuming this means colourless) and tasteless? Nil Einne (talk) 01:36, 3 August 2011 (UTC)

DNA testing of cremains

On a past set of episodes of the show Dexter, the forensics people performed DNA testing on a very small amount of cremated remains and were able to compare its DNA with the DNA from some nearby saliva and determine the two people were related. Is it actually possible to perform any useful DNA analysis on ashes? To forestall a particularly useless type of response seen pretty often on the Reference Desk, I will note in advance: Yes, I am aware that teleplays are works of fiction, and that authors of fiction often write things that are not possible. Comet Tuttle (talk) 02:50, 1 August 2011 (UTC)

Only if the cremation was done improperly. When a murderer splashes gasoline on a body and lights a match, for example, lots of DNA will likely remain. StuRat (talk) 02:57, 1 August 2011 (UTC)

(edit conflict)Doing a google search, I have found private companies that will take your money to do it for you: Here is but one example. However, others debate that this is normally viable in a properly done cremation: This page says that it isn't possible; This page says that it may be possible if teeth survived the cremation process. Neither of those are what I would call scrupulously reliable, but the College of American Pathology at least has a name that sounds credible, and they say that under normal cremation conditions, there is no way to get DNA. Apparently DNA can survive a "few hundred degrees" for a short time; the reference notes the possibility of recovering DNA from building fires, but cremation conditions (in excess of 2000 degrees C for in excess of 2 hours) doesn't leave anything behind. --Jayron32 03:04, 1 August 2011 (UTC)

Great references - thanks, Jayron32! Comet Tuttle (talk) 16:30, 1 August 2011 (UTC)

energy solution

Suppose public land in each County could be set aside and populated with solar farms and energy storage devices to form a giant power grid sufficient to supply all of the electricity needs of the United States and that this could be done for substantially less cost than the 14 trillion dollar deficit. Is there any reason why this could not be done immediately? --DeeperQA (talk) 04:45, 1 August 2011 (UTC)

Sure, you want to clear all of the nature off of the little bits of greenspace we have left? Turning earth into Coruscant doesn't sound like all that great of an idea... --Jayron32 04:54, 1 August 2011 (UTC)

Besides all other reasons, it is a long term solution, in the short term, it would only make the deficit grow. Plasmic Physics (talk) 04:56, 1 August 2011 (UTC)

Sorry, I did not think it necessary to mention that I am looking for scientific rather than financial or contrived reasons. For instance their are plenty of ways to avoid using green space which produces a little be of oxygen and if you can get rid of the deficit budget and opt for a surplus budget then you can solve two problems with one action. Please try again. --DeeperQA (talk) 05:06, 1 August 2011 (UTC)

So, you've invented a magical world where considerations like money and the environment don't matter, and you're asking us to critique it? With infinite resources and no financial or environmental concerns, you could do anything. By your criteria, you could set up a power grid based on hamster wheels if you wanted. Your solar system could be built if you had literally no other concerns at all. Back here in the real world, these concerns are important... --Jayron32 05:15, 1 August 2011 (UTC)

No need to be sarcastic, you could just have said that you don't perseive any scientific barriers, and that all the possible barriers are economical and evironmental in nature. (or something along these lines) Plasmic Physics (talk) 06:13, 1 August 2011 (UTC)

No. What I am asking is that you consider the end results and whether the end results would be sufficient to overcome real world difficulties instead of artificial difficulties such as already mentioned. --DeeperQA (talk) 06:05, 1 August 2011 (UTC)

Okay, how about this... Instead of going to Mars how about constructing such a grid? Would not that be a better project? --DeeperQA (talk) 06:18, 1 August 2011 (UTC)

Better in terms of what? Plasmic Physics (talk) 06:22, 1 August 2011 (UTC)

You name it. --DeeperQA (talk) 06:35, 1 August 2011 (UTC)

...err, I will rule out one: dealing with the aftermath of a giant asteroid hitting the US and blocking the radiation from the Sun. --DeeperQA (talk) 06:38, 1 August 2011 (UTC)

What I mean is, how are you comparing going to Mars against constructing such a grid? I frankly don't know what you want us to tell you. Plasmic Physics (talk) 07:10, 1 August 2011 (UTC)

I can not explain my question further. It seems clear to me that solar offers a global solution to energy needs and that cost can be handled in many ways. That leaves only the question of whether the science and technology at this point in time is sufficient to begin such a project now rather than wait until the only place to live is in outer space. --DeeperQA (talk) 08:25, 1 August 2011 (UTC)

I think if you have all these trillions of dollars available, investing in nuclear fusion would be a more assured long-term solution to energy supply, though there would be a longer delay before the investment paid off. Dbfirs 08:13, 1 August 2011 (UTC)

Obviously you can not create a 14 trillion dollar deficit unless the resources are available to do so and Chernobyl and Fukushima are good reason to avoid conventional fission based nuclear perhaps except for Thorium based fission rectors. --DeeperQA (talk) 08:25, 1 August 2011 (UTC)

If, like you said resources is not an issue, then either a massive scale solar project and colonising space are both possible projects. But, I'm not such what colonising space has to do with the USA's deficit problem. Plasmic Physics (talk) 09:06, 1 August 2011 (UTC)

Except as a questionable expenditure probably nothing. --DeeperQA (talk) 09:10, 1 August 2011 (UTC)

If you're looking to save the US budget by cutting NASA...I got news for you bud: NASA is a drop in the bucket. Its entire yearly budget is less than the military spends on air conditioning. NASA has arguably contributed more scientific innovations than any other organization in the world. There are better things to cut than scientific progress and research that is constantly bettering ALL our lives. How about we cut out some "fraud, waste and abuse"?-RunningOnBrains^(talk) 16:10, 1 August 2011 (UTC)

I agree, like tax breaks, tax cuts and tax loopholes for the rich. --DeeperQA (talk) 07:57, 2 August 2011 (UTC)

However, with electricity too cheap to measure a surplus budget could follow and forever be maintained in absence of perhaps anything except wise Chinese leader. --DeeperQA (talk) 09:13, 1 August 2011 (UTC)

That would be highly optimistic, even if you could do it for free like you said. Plasmic Physics (talk) 10:17, 1 August 2011 (UTC)

What does the US national debt have to do with it? The US government doesn't pay for people's energy. People pay for it themselves. In fact, the government gets a lot of revenue from taxes on energy. --Tango (talk) 11:42, 1 August 2011 (UTC)

The national debt is in the way. --DeeperQA (talk) 16:00, 1 August 2011 (UTC)

How is the national debt in the way? The U.S. is a free-market economy, not a socialist economy, and the government takes no part in the funding or building of industries, including power plants and the electrical grid. The national debt makes not one iota of difference in this matter... --Jayron32 00:34, 2 August 2011 (UTC)

The Manhattan Project gave us a fast track to nuclear power. It was government funded. The TVA project was government funded. Hover Dam project was government funded. The list can continue and is very long. --DeeperQA (talk) 07:55, 2 August 2011 (UTC)

I just did a back-of-the-envelope calculation and came up with a cost of about 10 trillion dollars for enough solar panels to provide all the US's electricity, at current prices. (Don't take that number too seriously, though.) The reason it could not be done immediately is that at current efficiencies, it would require at least 10,000 square kilometers of solar panels, which could not be constructed in a short time. Looie496 (talk) 16:09, 1 August 2011 (UTC)

Current solar technology is crap. They only convert a small portion of the sunlight to electricity, steadily decrease in efficiency, must be cleaned of dust regularly, have no ability to store the electricity until needed, cost too much, must be turned constantly to face the Sun, etc. Improving the technology is the first step required. In the meantime, there are other energy sources which are ready to be built now, such as nuclear reactors built in safe places, like underground in unpopulated areas, rather than above ground, in heavily populated areas, right by active fault lines. With a high enough level of incompetence, any energy source can be made dangerous. StuRat (talk) 16:23, 1 August 2011 (UTC)

Solar thermal energy is not so terrible as all that, but yes, there's a capital cost. Wnt (talk) 17:04, 1 August 2011 (UTC)

better fit?

Does Kepler's 3rd Law of Planetary Motion find a better fit if it is changed from p^2 = a^3 to p^2 = a^pi(3.141593...)? --DeeperQA (talk) 09:55, 1 August 2011 (UTC)

If it did, wouldn't the be stated as such? Plasmic Physics (talk) 10:21, 1 August 2011 (UTC)

Kepler's 3rd Law is already a perfect fit (under Newtonian gravity and mechanics). It follows by a pretty simply mathematical derivation from F=GMm/r² and F=ma. If you want to allow for relativity then just changing the power isn't going to help at all. --Tango (talk) 11:45, 1 August 2011 (UTC)

No, of course it doesn't. The question is what makes you think it should or could? Dauto (talk) 13:02, 1 August 2011 (UTC)

I was thinking only about planetary orbit approximations and not about mathematical derivatives. I see it: 2*G*M*m/r^3 from G*M*m/r^2. Thanks. --DeeperQA (talk) 14:50, 1 August 2011 (UTC)

You should look into the modern derivation of the law - I was just talking about something like it with electrons. While Kepler's third law might once have been determined by observation, we now know that the radius of an orbit is proportional to the square of the angular momentum of the object, and the length of time it takes to complete that orbit (the orbital period) is proportional to the cube. It's not some arbitrary ratio we can just change or adjust; each of these things is the necessary mathematical consequence of other physical laws. Wnt (talk) 17:07, 1 August 2011 (UTC)

You are right. Its called creative thinking (or speculation) which happened before first coffee and was applied out of place. I must have been asking myself how Kepler came up with the law using empirical data before the Calculus was invented. As for going deeper, yes, it is angular momentum that I was looking for to better connect the third law to electron orbits (atoms) but what my ultimate question is, is whether Kepler's third law is (or can be) applied to subatomic partials or are subatomic particles not regarded in terms of orbits? --DeeperQA (talk) 21:57, 1 August 2011 (UTC)

...Which has already been answered. No. Plasmic Physics (talk) 08:55, 2 August 2011 (UTC)

Statistics on Human Penis Size

Most of the charts I've seen look at stats for length or girth by themselves, I was wondering if there was any availible stats on both together. For example, what percentage of men have 6 inches length and 4 inches circumference, etc. 209.252.235.206 (talk) 10:32, 1 August 2011 (UTC)

A sad percentage. So smarr.

I don't know the answer, but have you read "Human penis size"? There are several references. One of them might have your answer. Axl ¤ [Talk] 06:20, 2 August 2011 (UTC)

What is an airlift system

Apparently fish are moved up the Haneji Dam using an airlift rather than a fish ladder. I've seen and understand a fish ladder. What is how does an airlift work? Is it an Airlift pump? If so, don't the bubbles harm the fish? -- SGBailey (talk) 11:33, 1 August 2011 (UTC)

I think "air lift" may be an artefact of the dam's page's Janglish (which also calls a fish ladder a "stared-fish ways") rather than a correct technical term. It may simply be some kind of pumped siphon system; this company has a bunch of fish-sucking equipment including a siphon fish ladder. I can't find specific information about what's deployed at Haneji. -- Finlay McWalter ☻ Talk 13:47, 1 August 2011 (UTC)

Current Control vs. Voltage control

Hello. I am currently reading up on cochlear implants, but had little luck in finding different control mechanisms. What are some advantages of current control vs voltage control (for cochlear implants specifically, but also in general) ?

Many thanks. 114.77.39.141 (talk) 11:53, 1 August 2011 (UTC)

This paper gives some of the answers. --Heron (talk) 17:33, 1 August 2011 (UTC)

Hmm it does answer some of my questions but it doesn't really go into too much depth. Thanks a lot though; i did try to search for these answers and came up very short. 114.77.39.141 (talk) 10:32, 3 August 2011 (UTC)

Resurecting extinct species

Could species like the saber-toothed tiger or the mastodon be resurrected? There are some similar species which could get a genetically modified fetus contained the genome of them.Quest09 (talk) 12:15, 1 August 2011 (UTC)

There has been some talk of cloning up a moa (brief mention) and the Pleistocene Park guy wants a woolly mammoth. Right now we can clone mammals from a living cell: cloning up an extinct animal presents two major additional problems - firstly is getting a viable genome from something that has been dead for hundreds or thousands of years (that's surely easier for recently extinct things like the dodo and the thylacine than for mammoths, never mind dinosaurs), and secondly getting that genome into an egg and getting a clone to take from it. -- Finlay McWalter ☻ Talk 13:19, 1 August 2011 (UTC)

Mammoths have the advantages of being recently extinct as well as having lived in cold areas. Therefore, intact flesh of a mammoth may be found in the Siberian permafrost. However, DNA may still be found in bones and teeth of animals only a few thousand years old, provided they were properly preserved. This usually means they were encased in rock, before decomposition could work it's way into the interior of the bones and teeth.

Also note that finding a surrogate mother can be tricky, for mammals larger than any living today. Perhaps a mammoth could be placed in an African elephant, or a saber-toothed tiger in a Siberian tiger, but a c-section would be needed before the offspring became too large, with "premie" medical care performed after that. Birds are easier, as you only need an incubator for the eggs. You'd just have to guess at the ideal temperature, though. StuRat (talk) 16:02, 1 August 2011 (UTC)

Don't the eggs need to be laid? -- 203.82.81.54 (talk) 20:41, 1 August 2011 (UTC)

Yes: part of the problem of using a surrogate mother of another species is that there is a great deal of interaction between the physiologies of mother and festus during gestation, so by virtue of their being different species, mismatches fatal to a successful gestation are likely, and even if the fetus is successfully born, it likely won't have developed in quite the same way as if it had been gestated in a mother of its own species. Incidentally, the loose term Sabre-toothed tiger covers several families of extinct mammals, none of which were anywhere near as closely related to the modern Tigers as, say, modern Lions. Similarly, Mastodons were not even in the same family as modern Elephants, and Mammoths were in the same family but not either of the same genera, so again the relationships are less close (though genetic closeness is not completely correlated with the "distance" of these taxonomic ranks), and the barriers likely to be greater, than is popularly supposed. {The poster formerly known as 87.81.230.195} 90.201.110.81 (talk) 19:50, 1 August 2011 (UTC)

Interaction between "mother and festus" ? I hate to picture that interaction: [4]. StuRat (talk) 10:46, 2 August 2011 (UTC)

The interaction is limited, though, otherwise offspring with mothers of different blood types would not be viable, and male offspring would be thoroughly messed up by the female hormones of the mother, all being born with female genitalia. StuRat (talk) 10:49, 2 August 2011 (UTC)

Hemolytic_disease_of_the_newborn, and I've read of interesting studies on younger sons having a less comfortable time in the womb than older sons, due to the whole male/female thing (I can't remember enough to find an article though). Do we have an article on the battle between the mother and fetus? And this is all within one species, a species with little genetic variability. This is a completely different scale to the problems with different species, or different genera, or even different families. 86.163.1.126 (talk) 13:16, 2 August 2011 (UTC)

If mother and baby have different blood types, then mixing of the blood may be fatal to the baby. That's as bad as it gets, same species or different. In rare cases this does happen, but obviously most of us survive, due to the placental barrier. I don't understand your "young son"/"older son" comment. Also, for other examples of cross-species reproduction, look at grafting in trees, and hybrid animals, like the mule/hinny or tiglon/liger. StuRat (talk) 13:44, 2 August 2011 (UTC)

Most of us do not survive. I cannot remember enough about the son thing to link to a fuller explanation. Basically, it was found that as a woman had more sons, she was in some sense 'primed' to reject the male hormones (as I recall, I read this years ago), and her womb became a more hostile place for subsequent sons. The whole thing about the battle for resources between mother and child, and the interaction between them that battles at the edge of parasitism, is mainstream. 212.183.128.5 (talk) 15:04, 2 August 2011 (UTC)

The Pyrenean Ibex was briefly resurrected through cloning in 2009. However there are closely related living animals, the DNA was extracted from a living Pyrenean Ibex and the clone died seven minutes after birth due to a defect. Hut 8.5 17:00, 3 August 2011 (UTC)

To clarify, the DNA was extracted before the last member of the species died off. However, they have a problem of no male sample, so they can't easily create a breeding pair via cloning. And, for proper genetic diversity, you'd want many clones, not just 2. StuRat (talk) 17:40, 3 August 2011 (UTC)

Leptinella/Cotula

Hi there,

I am a very keen gardener from Newcastle, NSW Australia. I have no botany training at all, but I am interested in plants (Australian natives in particular). I bought a plant called Cotula purpusilla and I have been trying to sort out whether it is native to Australia or not. On the Wiki pages for Cotula and for Leptinella the information is a bit confusing as to which plants are called what and why there has been a change in the names and whether or not the changes have been accepted or not. And I still don't know whether my plant is native to Australia or not!

Don't get me wrong - I love Wiki! I guess it is just frustrating when the information given seems a bit muddled (in regard to the names). I suppose the other thing that would be really helpful on the plant info. pages would be to ensure that plant's country/state of origin as well as natural habitat is included.

Thanks so much for your time and effort, Fmcrowe (talk) 12:17, 1 August 2011 (UTC)

This page and others (note the correct spelling of perpusilla) indicate that the plant is native to New Zealand. This page says that the binomial name is a synonym of Leptinella pusilla. When taxonomists try to split or combine taxa, the results are often confusing. Deor (talk) 12:48, 1 August 2011 (UTC)

Weedicides

How does a weedicide know which is the required plant and which is the useless, unwanted plant? I asked this to my biology teacher but she too couldn't answer me. ID: (email removed) Name: Divesh Paryani — Preceding unsigned comment added by 41.58.128.95 (talk) 14:42, 1 August 2011 (UTC)

It doesn't. Many weedkillers kill all green plants, but common selective weedkillers tend to have little effect on plants of the grass family. Some crops are genetically modified to be resistant to general weedkillers such as glyphosate. The article on Herbicide might be of some interest, but it doesn't explain the biochemistry of resistance. Dbfirs 15:46, 1 August 2011 (UTC)

Glyphosate kills plants because it inhibits an enzyme involved in amino acid biosynthesis. (Humans and other animals aren't killed by it because we get such amino acids from our food - an option a plant doesn't have.) Glyphosate resistant (e.g. "Roundup Ready") plants, for the most part, have been modified with a different version of the enzyme (usually from bacteria) which isn't inhibited by glyphosate. In the presence of glyphosate, they can use this other enzyme to make the amino acids. Likewise with glufosinate (Liberty/Basta), which inhibits a different amino acid synthesis gene, which is also replaced/supplemented in resistant plants (e.g. "LibertyLink"). Other specific herbicides function the same way. For example atrazine kills most plants by interfering with photosynthesis, but doesn't kill maize because maize has a naturally occurring ability to detoxify it [5]. 2,4-D is a hormone mimic which promotes uncontrolled growth in broadleaf plants, but doesn't affect the hormone system of grasses, due to the natural differences between the two types of plants. There are also herbicides which affect different stages of plant growth. For example, preemergent herbicides inhibit seed germination. They won't affect plants that are already growing (e.g. your lawn, already sprouted crops) but will prevent the weed seeds that are in the ground from sprouting. -- 140.142.20.229 (talk) 20:42, 1 August 2011 (UTC)

(ec) To answer your question, the herbicide doesn't "know". Rather, many herbicides (known as "selective herbicides") are specifically engineered to be ineffective against some desirable plants, or the desirable plants are themselves engineered to be resistant to particular herbicides. We note that glyphosate, sold as "RoundUp", was conceived as a non-selective herbicide (that is, it killed all plants), but that its popularity led to the development of glyphosate-resistant plants such that it can now operate as a selective herbicide. Note also that selective herbicides require specific intentional pairings of appropriate crops and herbicides; one cannot simply use a weedkiller at will with the expectation that it won't harm everything in sight. — Lomn 15:50, 1 August 2011 (UTC)

Some herbicides are absorbed through the leaves of the plant. Those with waxy or narrow leaves absorb less of the herbicide than other plants. It happens that grass is narrow-leaved and most garden weeds are broad-leaved. Thus these herbicides kill garden weeds but not the grass, however, they also kill clover, which may-or-may-not be a weed, depending on your point of view. CS Miller (talk) 21:31, 1 August 2011 (UTC)

It's not really a difference in absorption for grasses, though waxy leaves certainly help survival. See the excellent explanation from 140.142.20.229 above. Dbfirs 22:41, 1 August 2011 (UTC)

I've removed your email address; as you can see, answers will be posted here. I found a couple of articles, one here and also one here that might be useful. --some jerk on the Internet (talk) 16:34, 1 August 2011 (UTC)

Blushing

Hello. My name is Ian, I am vacationing right now in my mother's home city of Moscow and everyone is noticeably lighter here than back in the States, hence this question popping into my head. Because of my descent (mixed Russian-Finnish), I have a very light complexion, and furthermore I blush easily and to the smallest things; even more so, I've noticed, than even other Russians. A problem I have at home in the States is that when I blush it is more noticeable to others and it is often misinterpreted in social situations by my darker American companions. I know blushing is for the most part an unconscious action but is there anything I can do to reduce the frequency or exercise some control over it? My girlfriend advised me to get a tan but that didn't go so well-- apparently I don't tan, I just burn. Thanks in advance, and a happy summer to all! --Ian — Preceding unsigned comment added by 93.94.234.152 (talk) 17:10, 1 August 2011 (UTC)

Blushing is a signal of shame, and so being ashamed of blushing will only make you blush more. So don't be ashamed of it! Be proud of your blushes! Nobody except you really cares anyway. Looie496 (talk) 17:33, 1 August 2011 (UTC)

Wikipedia has an article about Blushing that describes what is known about its causes and possible treatments. You may take comfort (?) in the fact that no animal can blush, only humans do it. Animals don't have anything to blush about. Cuddlyable3 (talk) 17:39, 1 August 2011 (UTC)

"Man is the only animal which blushes ... or needs to." - Mark Twain StuRat (talk) 17:44, 1 August 2011 (UTC)

Well, make-up would do the trick, but you might find that objectionable (perhaps you could paint your face in your favorite team's colors, at sports events). There's also the "spray on tan" chemicals, although I wouldn't recommend them, personally. StuRat (talk) 17:46, 1 August 2011 (UTC)

Certainly a light foundation, as in the sort of skin-coloured make up you apply over your whole face, would reduce how noticeable the blushes were. This is, after all, why women add blusher on top of foundation. While you might find it objectionable, if you're doing it right, with a carefully chosen 'light' foundation or tinted moisturiser, chosen to match your facial skin (not the skin on your hand) and lightly and evenly applied, will be invisible to observers and still mask the blushing (as well as giving a smoother appearance to your complexion). It would, however, be cheaper and more wholesome to come to terms with your blushing and 'own' it as a personal attribute: "I am someone who clearly signals my moods and reactions, rather than disguising them". 86.163.1.126 (talk) 19:07, 1 August 2011 (UTC)

yes but my problem is that I might blush at something random and whoever I happen to be talking to might interpret to mean I am lying or I am ashamed of something relevant to the conversation, where I'm really not, then I have to explain (and might not be believed!), which causes much more embarrassment and fuss. Thanks for the answers (although I'd prefer not to use makeup!); new ones are welcome. --Ian 93.94.234.152 (talk) 00:27, 2 August 2011 (UTC)

Trying to explain away a blush is a case of continuing to dig when you're already in a hole. Really, don't worry about it: that some people blush more than others and some (like you) blush through momentary social embarrassment is well known and understood by other socially competent people, who likely will take no notice or regard it as merely a small component of your overall personality, assuming they even notice in the first place. Those who are so socially retarded as to misinterpret or want to make something out of it - well, why should you care what they think? {The poster formerly known as 87.81.230.195} 90.197.66.109 (talk) 09:42, 2 August 2011 (UTC)

<crank theory> I feel as if the "emotion" of shame is actually just the sensation of vasoconstriction of the left middle cerebral artery, upstream of its supply to Broca's area, thus shutting down (or responding to a shutdown of?) speech. I feel as if I've been able to counter it to some extent by willing vasodilation in the same area, but I've never tried this with the equipment to test, so it might be delusion. I've seen a few people touch that region of their head when experiencing shame; Facepalm is a stylized example (though not to the left). I wonder whether the constriction of one or several arteries in the brain could lead to a shift of blood into the external carotid artery, and from there the face.</crank theory> Wnt (talk) 17:13, 2 August 2011 (UTC)

aspirin

Is aspirin an NSAID? — Preceding unsigned comment added by 99.70.40.100 (talk) 17:28, 1 August 2011 (UTC)

Yes, as our aspirin article states in its lead. Looie496 (talk) 17:30, 1 August 2011 (UTC)

(Keep in mind the `N' stands for NON, and the abbreviation NSAID is used to describe things in terms of what they are not. To paraphrase Ulam, saying Aspirin is an NSAID is like referring to the bulk of zoology as the study of non-elephant animals.) SemanticMantis (talk) 18:17, 1 August 2011 (UTC)

That answer is good enough to not be in <small>s. 64.134.228.55 (talk) 00:56, 2 August 2011 (UTC)

I disagree. The "NSAID" designation identifies a group of compounds that share side effects, mechanisms of action, etc in a manner that is useful. To the extent that the NSAID term is useful, it is quite a bit different from referring to the bulk of zoology as the study of non-elephant animals. So, that answer does highlight a pedantic issue with the term "NSAID", but doesn't really answer the question. I think the choice of font size was appropriate. -- Scray (talk) 01:04, 2 August 2011 (UTC)

That comparison would be non-specious if it referred instead to "non-mammal animals", and if there were only three or four classes of animals. TenOfAllTrades(talk) 03:06, 2 August 2011 (UTC)

This debate is giving me a headache. ;-) AndyTheGrump (talk) 03:08, 2 August 2011 (UTC)

Take an aspirin. Ooops, no medical advice allowed. DON'T take an aspirin. Cuddlyable3 (talk) 09:45, 2 August 2011 (UTC)

That's medical advice, too! --Stephan Schulz (talk) 09:56, 2 August 2011 (UTC)

The ref.desk advises the OP not to take any advice seen on the ref.desk. Cuddlyable3 (talk) 09:27, 3 August 2011 (UTC)

Perhaps something like fish is a slightly simpler comparison. Nil Einne (talk) 01:25, 3 August 2011 (UTC)

Ok, I'll compare an aspirin to a fish then: on average, an aspirin is more likely to be soluble than a fish is ;-) AndyTheGrump (talk) 01:30, 3 August 2011 (UTC)

Instantaneous force

Hi, I'm designing a small plane; I'm working on the landing gear specifically. Suppose my plane is descending at a rate of 30 m/s at an angle of 45 degrees; What is the instantaneous force acting parallel to the ground, the moment the plane touches the ground? (Ask me if you need any extra data). 117.192.212.48 (talk) 18:00, 1 August 2011 (UTC)

I hope you're not designing a real plane, if you think that's a meaningful question. Looie496 (talk) 18:09, 1 August 2011 (UTC)

Planes don't usually land with a 45 degree glide slope but if yours does, its horizontal velocity is 30 m/s. The horizontal component of the instantaneous force on the landing wheels is whatever causes them to skid. Cuddlyable3 (talk) 18:19, 1 August 2011 (UTC)

I know; the descent angle is way too large. I mean to ask this as a simple physics question. I mentioned 45 degrees because the calculations will be easier. 117.192.212.48 (talk) 18:22, 1 August 2011 (UTC)

i want to know the instantaneous force at the time of impact. 117.192.212.48 (talk) 18:25, 1 August 2011 (UTC)

If your landing gear is rigid it will break. You cannot have instant deceleration of either the vertical or horizontal components of the plane's speed. Cuddlyable3 (talk) 18:28, 1 August 2011 (UTC)

We would need to know the mass of the plane (or the weight, from which the mass may be derived). The mass and radius of the wheels is also important, since they presumably will need to be accelerated from no rotation. I agree with the above comments, that descending at 45 degrees at 30 m/s will result in a crater. StuRat (talk) 18:41, 1 August 2011 (UTC)

Forgetting about the 45 degree angle that others pointed out isn't realistic, and assuming that the mass of the wheels are negligible compared to the mass of the plane, its clear without having to do any actual calculation that the instantaneous force acting parallel to the ground is negligible. Dauto (talk) 19:34, 1 August 2011 (UTC)

Yes, the horizontal force acts only to accelerate the wheels from initial skidding to rolling speed. Unless the wheels have a large moment of inertia, the force will be small compared with the braking force subsequently applied. To calculate the average force, you need to know the radius and moment of inertia of the wheels, the horizontal ground-speed at touchdown, and the skid time or distance. Once the wheels are up to speed, the only horizontal force is from friction in the bearings (and air resistance on the plane). Of course, if the brakes are already on as the plane touches down, rubber will be torn from the tyres by the greater friction force. Dbfirs 20:11, 1 August 2011 (UTC)

A simpler question contains the same basic issue: "Two blocks collide at 1 m/s. What is the instantaneous force between them at the moment of collision?" The answer must be that it depends on the mass of the blocks, Young's modulus, etc. The nearest parts of the blocks inevitably must match speeds first, and then transmit this force outward, in quite a complex way. The wheels of a plane add the additional variable that the force of friction is limited and they may slide over the landing strip as they first touch. Wnt (talk) 20:30, 1 August 2011 (UTC)

I think everybody missed the obvious. Assuming the ground is reasonably smooth, the force at the moment the plane touches the ground is zero. See Friction#Laws of dry friction. At the moment the plane first touches the ground, there is no applied load. The load will increase rapidly after contact, however. The speed of the plane is irrelevant.

This wouldn't happen to be a homework question, would it?--Srleffler (talk) 23:12, 1 August 2011 (UTC)

Ah, phoooey - meant to mention that when I commented but forgot. I assume that the "moment of collision" is supposed to be defined as the moment when the force is greatest, not at the moment when the objects first touch. Wnt (talk) 04:58, 3 August 2011 (UTC)

Even before the plane touches the ground a layer of air between them is being compressed. Cuddlyable3 (talk) 01:01, 2 August 2011 (UTC)

Yes, the force builds up gradually over a tiny fraction of a second as the air is compressed under the tyres, and as the weight of the plane comes to be supported by the tyres rather than by the wings. The concept of "the moment the plane touches the ground" is not clearly defined. Dbfirs 06:26, 2 August 2011 (UTC)

I'll make it simpler (No Srleffler this ain't a homework question :P ) . A body of mass 10 kg is travelling on a frictionless surface at a constant velocity of 20 m/s. Suddenly, it encounters a rough surface (say, coefficient of friction is 0.5). What would be the value of deceleration. 117.192.199.186 (talk) 06:35, 2 August 2011 (UTC)

See Friction#Coefficient of friction: "The 'coefficient of friction' (COF), also known as a 'frictional coefficient' or 'friction coefficient' and symbolized by the Greek letter µ, is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together". You haven't given 'the force pressing them together', so there isn't an answer. AndyTheGrump (talk) 07:13, 2 August 2011 (UTC)

Ah, but I have. The mass is 10 kg. The force pressing the surfaces together would be 10* 9.8= 98 Newton. 117.192.199.186 (talk) 07:16, 2 August 2011 (UTC)

You didn't - you are assuming a 1 G gravitational force, which you didn't state. Still, I think you have enough information to answer the question now. What is 10 * 9.8 * 0.5? This is the force. Now what is the acceleration/deceleration that results from applying this force to a 10 kg mass (actually, most of this cancels out, unless I am being even more stupid than usual)? AndyTheGrump (talk) 07:24, 2 August 2011 (UTC)

The OP has not made the original question simpler and has instead substituted an entirely different question. Cuddlyable3 (talk) 09:42, 2 August 2011 (UTC)

It is simpler, but it's also sufficiently different to call it an entirely new question. StuRat (talk) 10:34, 2 August 2011 (UTC)

The missing piece of information in this new question is the assumption that the surface is horizontal, but, taking that as given, the answer is 4.9 m/s/s for the 40.8 metres (approx) that is takes for the block to come to rest. The mass of the block is irrelevant, so exactly the same would apply to an object such as a plane, except that the undercarriage might be torn off and the sudden jerk (rate of change of acceleration) would probably cause injury to anyone not wearing a seatbelt. Dbfirs 00:40, 3 August 2011 (UTC)

So my 'physics from a bloke with a social science degree' was right: 4.9 m/s/s, or g * 0.5. It all cancels out. Actually, I'll have to ask how how you came to the conclusion that the block will ever come to rest, according to the formula you use (yes, I know, the formula is an approximation that doesn't work at the limits etc...) AndyTheGrump (talk) 00:50, 3 August 2011 (UTC)

Yes, you were correct. In the simplification where the coefficient of friction is independent of speed (a good approximation in many situations), the rate of decrease in speed is constant until the instant when the body stops. In practice, static friction tends to be marginally greater than sliding friction so in the last millisecond there may be a slight jerk and a coming to rest marginally before the calculated 40.8 m (I just used v² = 2as with "a" as you calculated - simplified from Equations of motion). In a different model where braking force is proportional to speed, as in regenerative braking, the body never actually comes to rest (in theory). Dbfirs 06:13, 3 August 2011 (UTC)

I have some Astronomy Questions:

1. Is it true the clouds of Venus are mainly composed of sulfur dioxide and sulfuric acid?

2. Is it also true Jupiter is also notable for its turbulent weather (e.g. huge storms, lightning, etc?

Thanks!

Neptunekh2 (talk) 20:27, 1 August 2011 (UTC)

I think the articles you linked cover those pretty well, and if not Atmosphere of Venus and Atmosphere of Jupiter should.

Control-F or Apple-F ("Find" in your browser) are your friends. ;) Wnt (talk) 20:34, 1 August 2011 (UTC)

How much does gravity hold the human body together?

If an astronaut floating in deep space floated into a fictional region where the force of gravity stopped working, would the tissues of his body maintain their structural integrity? I.e., is gravity at all significant in its contribution to holding the body together? 76.27.175.80 (talk) 21:49, 1 August 2011 (UTC)

In reality no. See the article Extra-vehicular activity. In fiction you can make up anything you like including turning off physical laws and having people fall to pieces. Cuddlyable3 (talk) 21:58, 1 August 2011 (UTC)

The above answer is correct, but the reasoning is flawed. There is a significant difference between free fall (which is what astronauts experience, and essentially means that the only significant force acting on a body is gravity) and an absence of the gravitational force. If there were no gravity in Earth orbit, then objects wouldn't stay in orbit—they'd fly off on straight tangents. The attractive gravitational force between an object at 350 km altitude (like the International Space Station) and the Earth is only about 10% weaker than it would be for the same object sitting on the Earth's surface. TenOfAllTrades(talk) 02:55, 2 August 2011 (UTC)

No, not significant. See Gravitational constant, where it says:

The gravitational force is extremely weak compared with other fundamental forces. For example, the gravitational force between an electron and proton 1 meter apart is approximately 10⁻⁶⁷ newtons, while the electromagnetic force between the same two particles is approximately 10⁻²⁸ newtons. Both these forces are weak when compared with the forces we are able to experience directly, but the electromagnetic force in this example is some 39 orders of magnitude (i.e. 10³⁹) greater than the force of gravity — roughly the same ratio as the mass of the Sun compared to a microgram mass.

Comet Tuttle (talk) 22:03, 1 August 2011 (UTC)

I feel the need to clarify: you asked two questions, so the answers are: Yes, the tissues would easily maintain their structural integrity, and no gravity does not have a significant contribution to holding the tissues together. Almost every other force known is more important than gravity at that scale. -RunningOnBrains^(talk) 22:06, 1 August 2011 (UTC)

When you are in free fall you are effectively NOT feeling the effect of gravity form your reference frame. For longer term effects not quite as dramatic as "falling to pieces" there's Weightlessness#Human_health_effects. Vespine (talk) 22:47, 1 August 2011 (UTC)

That's not relevant to his question. Regardless of whether you are in free fall, there is still gravitational attraction between the parts of your body. The OP was essentially asking whether this force was significant, compared to the other binding forces. The answer is "no".--Srleffler (talk) 22:58, 1 August 2011 (UTC)

Assume a spherical astronaut of mass 100kg and a density of 1000kg/m³ (ie. that of water). Those aren't far off the mass and density of a typical person. The gravitational binding energy of that astronaut would then be (by the formula in that article) about 1.4x10^-6 joules, or 1.4 microjoules. According to Orders of magnitude (energy), that's about 10 times the kinetic energy of a flying mosquito. In other words, not much. That's the energy that would be required to break your body completely apart against the force of gravity. Since we don't fly apart whenever a few mosquitos fly into us, we can conclude that there is much more holding our bodies together than gravity. --Tango (talk) 23:21, 1 August 2011 (UTC)

To clarify something even more simple: the force that holds together tissues and other molecular structures is the electromagnetic force (in the form of molecular bonds), not gravity. Gravity holds us on the Earth; it does not hold us together. --Mr.98 (talk) 00:20, 2 August 2011 (UTC)

The body is held together by material in a non-fluid state. If the body were composed entirely of gasses and liquids, it would be far more prone to changing shape and breaking up. To the extent that the body is composed of solids, even if in close combination with liquids, that is the extent to which it can hold itself together. As has been stated above, gravity plays very little role in maintaining structural stability. Bus stop (talk) 02:47, 2 August 2011 (UTC)

A human gets taller after staying long periods in low gravity environments. ~AH1 ^(discuss!) 14:24, 8 August 2011 (UTC)

Geomagnetically Induced Currents

I understand that GICs are a big problem because of long stretches of cables and pipes on a global scale such as telegram/telephone cables, fiber optics, railroad tracks, and oil pipelines across oceans and continents. My question is, in order to stop such a thing why not insert a piece of plastic or some other insulator (maybe every 20 miles or whatever) so that the current won't be conducted through? This can easily be done in oil pipelines for example. So why is't it done? And also does anyone know of any incidents where such a current might have caused an ignition and hence an explosion in a pipeline? Perhaps during a solar storm? Thanks! - Looking for Wisdom and Insight! (talk) 22:34, 1 August 2011 (UTC)

You should read geomagnetically induced current and specifically GIC hazard in pipelines. Dragons flight (talk) 23:14, 1 August 2011 (UTC)

Fiber optics being non-conductive are unaffected by GICs. Cuddlyable3 (talk) 00:36, 2 August 2011 (UTC)

For those conductors which are affected, the questioner's recommendation for a series of zener diodes tied to ground is reasonable, but not optimal. 64.134.228.55 (talk) 00:52, 2 August 2011 (UTC)

I read that article but doesn't really answer any of my questions. Why isn't this optimal? Is this used in practice at all? If not then why not? - Looking for Wisdom and Insight! (talk) 18:20, 2 August 2011 (UTC)

From the article in question:

"The GIC hazard to pipelines is that GIC cause swings in the pipe-to-soil potential, increasing the rate of corrosion during major geomagnetic storms"

Introducing plastic elements into an otherwise all-steel construction is probably more expensive than simply repairing the pipes more often. --Carnildo (talk) 00:52, 4 August 2011 (UTC)