Wikipedia:Reference desk/Archives/Science/2008 June 7

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June 7

Stones in trees in Yellowwood State Forest

Regarding the new Wikipedia article about Yellowwood State Forest, is it possible the stone simply sat down on saplings and waited for them to grow? --77.125.94.96 (talk) 01:17, 7 June 2008 (UTC)

That's impossible. If a large boulder was weighing down a sappling, there is no way it would have been able to not only grow, but be able to support the weight of the rock, especially if it was just starting to grow.--十八 01:43, 7 June 2008 (UTC)

In any case it seems to me that it's just as unlikely that the boulder walked over and sat on a sapling as it is that it climbed a fully grown tree by itself. SpinningSpark 00:59, 8 June 2008 (UTC)

Phobos (moon)

I have a book on Mars with me that says if Phobos survives the Roche limit and does not break up, the moon will blast a crater over 100km across on Mars. How is the crater's diameter calculated given the object's velocity and volume?--十八 01:45, 7 June 2008 (UTC)

Just to let you know, this smells a little bit like a homework question. But answering your question straightforwardly, I would imagine that the crater's diameter is calculated given the object's velocity and mass (not volume) based on the energy that would be delivered to the regolithic substrate, this latter mostly based on theory investigated by experiments conducted by curious physicists tossing projectiles into things that resemble the Martian regolith. --arkuat (talk) 09:21, 7 June 2008 (UTC)

The article Impact crater might help. SpinningSpark 10:12, 7 June 2008 (UTC)

[1] has some information, for Earth at least. --Fangz (talk) 11:20, 7 June 2008 (UTC)

Thanks, I found this site through the site you provided which works fine. Also, to answer Arkuat's speculation, it's not homework per say. I'm writing a research paper and I wanted to calculate which parameters would have to be taken into effect for the crater to be over 100 km in size, as stated in the book (as it just gave the figure, not the calculations, or even the parameters, involved).--十八 00:54, 8 June 2008 (UTC)

Sorry for my speculation, I ought to have edited it out before posting. arkuat (talk) 05:46, 8 June 2008 (UTC)

Hi. This simulator has impacts for other planets, but it's a bit oversimplicified, and uses Marvin Martian as its theme. Thanks. ~AH1^(TCU) 13:57, 7 June 2008 (UTC)

Threshing and winnowing?

In agriculture, what is the relationship between the activities of threshing and winnowing? What I mean is, are they:

• exclusive either-or activities, two different ways of accomplishing the same purpose (that is, if you thresh, you do not need to winnow, or if you winnow, you do not need to thresh) OR
• both required activities that do not accomplish the same purpose (and if this is the case, does threshing have to come before winnowing, or winnowing after threshing, or does the order not matter?)

—Lowellian (reply) 01:49, 7 June 2008 (UTC)

The latter (and the former). Threshing means bashing the grains to get the chaff (seed-coats, bran) off the grain (what later gets ground up into flour). Winnowing means throwing the resulting mixture (separated, but still mixed in a heap) into the wind or water, to make a bunch of chaff floating away on the wind or water, and a heap of grain sinking in the wind or water. I'm guessing the confusion arises from modern-tech agricultural combines that do both jobs with one vehicle. --arkuat (talk) 06:38, 7 June 2008 (UTC)

Hybrid car mileage

Why do hybrid cars get better gas mileage in city than highway tests, when no others do? NeonMerlin 02:20, 7 June 2008 (UTC)

On the highway, a major energy loss is to wind and road friction, losses not addressed by hybrid technology (and hybrid generate most of their electricity during braking, which doesn't happen much on the highway). In the city, energy loss is during braking and idling. Hybrids recovery energy during braking, and shut off the gas engine during idling. Perhaps others have more technical answers, but I think of it in terms of primary energy loss and how it can be recovered.Scray (talk) 03:20, 7 June 2008 (UTC)

Interesting answer. I had always assumed -- without giving the matter much thought, until now -- that it was simply that batteries can't make a car go 60 mph.

So, Scray and I are both interested in others' more technical answers! -- Danh, 70.59.116.253 (talk) 22:54, 7 June 2008 (UTC)

Scray basically is right, there is not much to add. Electric engines are highly efficient, but the energy ultimately has to come from the IC engine. If you need continuous high energy output, your IC engine will run either way. The primary advantage of the electric engine is in energy recovery during braking and idling. And yes, batteries can make a car go any reasonable speed - this just depends on the dimensions of the engine. The first few land speed records were all obtained with electric cars (although the fastest one was only 65 miles per hour). --Stephan Schulz (talk) 23:35, 7 June 2008 (UTC)

I was under the impression that a big part of the gain comes from using a smaller ICE. An ICE large enough to provide sufficient peak acceleration is inefficient when you're not accelerating; with a hybrid vehicle the electric motor provides extra acceleration and you can get away with a smaller ICE, which leads to better efficiency even on the highway. Someone else will have to say whether this makes sense, since I know nothing about cars, but Hybrid electric vehicle#Benefits seems to back it up. -- BenRG (talk) 23:47, 8 June 2008 (UTC)

ICEs have a certain RPM at which they are most efficient. In hybrids, since the ICE is only generating electricity, it always runs at the most efficient speed. Even when accelerating on the highway, the ICE is still operating at peak efficiency. --Theeldest (talk) 20:11, 13 June 2008 (UTC)

A possible method for superluminal travel

I thought that if there is a warp in space, the area doesn't change, but the warp is curved. So, if anybody could travel straight forward in a warped area without being pulled to the center of gravity, the distance will be cut and superluminal travel may become possible. Can you please tell me is this method possible? Please reply!!! —Preceding unsigned comment added by Superwj5 (talk • contribs) 08:02, 7 June 2008 (UTC)

• Have you read the article on dark energy and especially the section on negative pressure yet? If not, I'm afraid you'll have to rephrase your question in simpler terms. --arkuat (talk) 09:11, 7 June 2008 (UTC)

• You might find the article Alcubierre drive interesting (but highly controversial) and also most the scientific papers cited in that article have links to online preprints. Another of our articles that you could look at is wormholes. SpinningSpark 10:20, 7 June 2008 (UTC)

• Much as I would like to have FTL travel (preferably in my lifetime), Einstein tells us that any form of superluminal communication will break causality - i.e. you can get next weeks lottery numbers today. Given that choice, I vote for a proper sequence of cause and effect.... --Stephan Schulz (talk) 13:41, 7 June 2008 (UTC)

  As long as you have local causality, things should be ok, and space warping techniques usually don't involve travelling faster than light locally, just faster from the perspective of the rest of the universe. Just losing global causality means what people usually call "time travel", is it really so bad to have a universe which allows for time travel? --Tango (talk) 13:34, 7 June 2008 (UTC)

  Yes! Nature abhors a time paradox... --Stephan Schulz (talk) 13:30, 7 June 2008 (UTC)

  Time travel doesn't necessarily involve paradoxes. --Tango (talk) 16:43, 7 June 2008 (UTC)

What you describe sounds similar to a possible method of time travel I read about (superluminal travel and time travel are very closely related) involving cosmic strings. I believe there were two orbiting each other and as you went round them in a particularly way, you got back to where you started from before you left. I don't remember the details, but it sounds vaguely like your idea. If wouldn't work with regular matter, it needs to be a cosmic string. --Tango (talk) 13:34, 7 June 2008 (UTC)

Many of these methods are summarized at Time travel# Time travel to the past in physics. Clarityfiend (talk) 18:54, 7 June 2008 (UTC)

Reduce voltage drop through a diode

I'm making a solar-powered microcontroller device using 5 0.47V 100mA max solar panels in series, feeding through a 7660 to double the voltage to power my IC (Atmel ATTiny13V) and my RF transmitter. According to the datasheet, I need 2 diodes in series from the 7660's output. That's 1.4V drop already, which is way too high for my purpose. I've switched to Schottky diode but that's still over half a volt lost. What are some ways to further reduce this loss? I've looked at synchronous rectification but have no idea what parts are available for drop in replacements for my diodes; I've also thought of using a transistor with the base and collector connected together, will that work? --antilived^{T | C | G} 08:50, 7 June 2008 (UTC)

Why do you have to use that device in particular? There are heaps of dc-dc converters out there for all kinds of different voltages. You would be better off selecting a device for the voltage you want to deliver, see for instance [2], rather than jump through hoops getting this one to do what you want. The one you have picked seems to be specifically for generating a negative rail from a positive one and can also co-incidentally do voltage doubling. Basically, it is not the best chip for the job. A quick Google search or a look through an electronics component catalogue will get you lots more to choose from. SpinningSpark 11:00, 7 June 2008 (UTC)

Availability is one thing, that device being instantly available is a huge plus. The one that you've linked to is a regulator not a voltage converter and therefore unsuitable for my use. Inverting voltage and doubling voltage are based on pretty much the same principle anyway so it's not unusual to see both functionalities on the same chip. --antilived^{T | C | G} 11:54, 7 June 2008 (UTC)

Actually, I think you will find that that device I pointed you to is a switching device rather than a linear regulator, it is just made to be pin compatible with linear regualtors of the 78xx series. However, your complaint is justified because it is step-down rather than the step-up you need. Sorry, my bad. Try this one [3]. I know inverting and doubling can be done with the same device, but neither of those things is what you really need. Availability - you are in New Zealand right? Try here [4]. SpinningSpark 13:59, 7 June 2008 (UTC)

No that's still not suitable for my use. My input voltage (from the solar cells) is only 2.35V max, and will almost certainly be lower than that during most of the day. I only need 20mA at the most so a device that can supply 2.5A is quite an overkill for me. --antilived^{T | C | G} 23:06, 7 June 2008 (UTC)

I'm not sure if this is an intelligent answer, but have you considered biasing the voltage? I know it is a solar cell of some description to generate electricity, but to power an IC, maybe putting the voltage drop amount across the diodes is a solution? Adamd1008 (talk) 20:41, 10 June 2008 (UTC)

United States Of America

Q:When is the national blonde brownie day celebrated in the U.S —Preceding unsigned comment added by 117.194.193.239 (talk) 12:28, 7 June 2008 (UTC)

See here: Wikipedia:Reference desk/Miscellaneous#United States Of America - Copied over there as this is the science desk. Regards, CycloneNimrod ^talk?_contribs? 13:16, 7 June 2008 (UTC)

Cancer stage vs grade

Is there a difference between the terms grade and stage with respect to cancer classification? --Seans Potato Business 17:17, 7 June 2008 (UTC)

The stage refers to the invasive ability of the cancer. The grade refers to how similar the tumor is to the surrounding tissues. See Cancer#Classification. Regards, CycloneNimrod ^talk?_contribs? 17:48, 7 June 2008 (UTC)

I think some clarification might help: Stage is the degree to which the tumor has invaded, not its ability to invade (a very aggressive tumor, with high ability to invade, can be detected at an early stage, i.e. before it has actually done much invading). Grade is determined by comparison to benign (surrounding) tissue, but is actually the dissimilarity relative to normal tissue (high grade means very different from normal).Scray (talk) 20:08, 7 June 2008 (UTC)

Scray is correct. A common saying in pathology helps one keep the two straight: "grade the tumor, stage the patient". --David Iberri (talk) 00:00, 8 June 2008 (UTC)

Stopping earth quakes

We have articles on weather control and asteroid deflection, but are there any proposed methods on stopping earth quakes? Is it possible to do this? ScienceApe (talk) 17:33, 7 June 2008 (UTC)

It's really not feasible since we can't stop plates from colliding with each other. Regards, CycloneNimrod ^talk?_contribs? 17:49, 7 June 2008 (UTC)

We had a discussion of this last year. See Wikipedia:Reference desk/Archives/Science/2007 October 11#Controlling earthquakes by setting them off. Algebraist 18:59, 7 June 2008 (UTC)

Well, there's fiction about it: the novel A földrengések szigete by Fehér Klára. Also in fiction, the Little Prince regularly cleans his volcanos so they don't have violent eruptions. – b_jonas 09:52, 9 June 2008 (UTC)

I know of no proposals for stoppng earthquakes, short of waiting for the core of the planet to cool. However, stopping earthquake damage is straightforward: earthquakes do not kill, buildings do. —Preceding unsigned comment added by 67.131.66.162 (talk) 18:16, 9 June 2008 (UTC)

Indeed, we even have an article on that: earthquake engineering. – b_jonas 19:10, 10 June 2008 (UTC)

Phenylketonuria

I have todo a 15 page essay on Phenylketonuria, and i need alot of research from this site, do you know where i can find 15 PAGES of INFORMATION including, pictures, graphs and websites that my science class can visit

--Katiesorfleet (talk) 17:38, 7 June 2008 (UTC)katiesorfleet

Phenylketonuria is a good start. That's the only article we have on it, otherwise just use Google. Regards, CycloneNimrod ^talk?_contribs? 17:50, 7 June 2008 (UTC)

Specifically, look at the sources at the bottom of Phenylketonuria. Like any other encyclopedia, you should not be using Wikipedia as a research paper source; you should using to get a general overview of the subject. Paragon12321 (talk) 21:17, 7 June 2008 (UTC)

Why is LSD illegal?

? ScienceApe (talk) 19:07, 7 June 2008 (UTC)

Well, the risk of a bad trip comes to mind. For other reasons you might want to read about the effects in the LSD article. - Dammit (talk) 19:12, 7 June 2008 (UTC)

According to the DEA, because it has "a high potential for abuse and serve[s] no legitimate medical purpose" [5], Someguy1221 (talk) 19:14, 7 June 2008 (UTC)

So same as alcohol and tobacco right? ScienceApe (talk) 02:53, 8 June 2008 (UTC)

I agree on tobacco (no redeeming qualities) - if it came to market today it would never get approved (so I can only surmise it is vested interests including farm lobbies and addicts that sustain the business). Alcohol in moderation, however, appears to have some benefits like reducing heart disease. Scray (talk) 03:29, 8 June 2008 (UTC)

Meanwhile marijuana, which does have a legitimate medical use and less of a danger from abuse than alcohol, remains illegal. I'd agree it's all a matter of when it was introduced. Those drugs introduced early on were accepted while the latecomers are seen as dangerous: "Those damn kids with all their pot, it makes me so mad, now light my cigar and get me my whiskey !". StuRat (talk) 18:26, 8 June 2008 (UTC)

Marijuana's initial illegality had a lot more to do with keeping wood pulp prices up than it being considered dangerous. Matt Deres (talk) 02:02, 9 June 2008 (UTC)

(ec) Because legislators in whatever jurisdiction it is you're talking about have made it so. In many jurisdictions, this is required by the UN Convention on Psychotropic Substances (full text). The preamble to that treaty states that it was passed to safeguard public health. Presumably they were thinking of flashbacks and Hallucinogen persisting perception disorder. Algebraist 19:18, 7 June 2008 (UTC)

I wouldn't say tobacco has no redeeming qualities, since studies have shown that nicotine is good for the brain. Just that the risks tobacco introduces far outweighs the benefits. --Wirbelwindヴィルヴェルヴィント (talk) 02:56, 9 June 2008 (UTC)

Toothpaste toxicity (fluoride)

There's a warning label on every tube of fluoride toothpaste that states that the poison control center should be contacted in case more toothpaste is swallowed than is used for brushing. This is because fluoride, the active ingredient in most toothpaste designed for adults, is toxic and can cause acute sickness or death if taken in sufficient concentration. Of course, almost nothing is entirely safe (even drinking too much water too quickly can prove fatal), and warning labels are notoriously overcautious. We've all swallowed toothpaste now and then with no ill effects. How much toothpaste would have to be ingested in order to induce fatal fluoride toxicity in an average-sized (say, 170 lb.) adult? —Preceding unsigned comment added by 66.215.224.253 (talk) 19:51, 7 June 2008 (UTC)

Maybe you should read fluoride poisoning. Anyway, there's no warning label on my tube of fluoride toothpaste. --Heron (talk) 20:24, 7 June 2008 (UTC)

Looks as though the probable toxic dose is about 5 mg/kg (many sources). Given your example of a 77 kg (170 lb) adult, that would be about 385 g. Labels of toothpaste I see list fluoride ion content around 0.14% w/v (0.14 g/100 mL, or 1.4 g/L), so 385/1.4 = 275 L (35.75 gallons). That's a lot of toothpaste!Scray (talk) 20:32, 7 June 2008 (UTC)

So we're looking at the thirty to forty gallon range - wow. Thanks, Scray. I guess the warning label is decidedly overcautious after all. According to the toothpaste article, ingesting too much toothpaste can cause minor digestive upsets such as nausea and vomiting, so I suppose someone has ingested enough of it in the past to suffer some discomfort, but it isn't anything serious after all as the packaging would imply (and Huron, most brands do include such a warning label on the box the toothpaste comes in or on the tube itself, as the aforementioned article will confirm). Stupid warning labels. —Preceding unsigned comment added by 66.215.224.253 (talk) 20:57, 7 June 2008 (UTC)

Umm isn't it 385 mg, which is 0.385g? At that level it'd only take 275mL, or roughly 2 tubes of toothpaste to reach the toxic dosage. --antilived^{T | C | G} 23:33, 7 June 2008 (UTC)

Yes, I think you're right. However, our article says the lethal dose is about 70mg/kg, did Scray drop a 0? What are the many sources? Or does toxic dose differ from lethal dose? --Tango (talk) 01:08, 8 June 2008 (UTC)

My deep apologies - and thanks to 66.215.224.253 for catching my gross slip of the prefix (i.e. I jumped from mg to g). I should have said 385 mg (not g) of fluoride, which then equates to about 275 mL of toothpaste, or a little more than 2 "family size" toothpaste tubes as the toxic dose. The lethal dose, about 14 times that (5 vs 70 mg/kg) would be about 30 large tubes of toothpaste. So, spit don't swallow, and don't worry about the fluoride unless someone comes up with convincing evidence that lower doses are toxic.Scray (talk) 01:30, 8 June 2008 (UTC)

This is all, of course, assuming it would be a adult that ate the toothpaste, which seems highly unlikely. If it were a young toddler, the lethal dose would be much more feasible. Paragon12321 (talk) 04:24, 8 June 2008 (UTC)

Wouldn't it be just as unlikely for a toddler to swallow a propotional amount of toothpaste, say 3 large tubes, as for an adult to swallow 30 ? Also, wouldn't they get ill from things other than fluoride (like the artificial sweeteners) at lower quantities of toothpaste ? StuRat (talk) 18:18, 8 June 2008 (UTC)

Well, I checked the label and the box, and they do advise supervising children under 7 to "minimise swallowing". I took that to mean that adults can guzzle as much of the stuff as they want. Looks like I'll have to limit myself to 2 tubes a day in future. --Heron (talk) 17:40, 9 June 2008 (UTC)

Using that logic, if a yellow flashing traffic light means "proceed with caution", what does a green light mean ? "Proceed with reckless abandon ?" :-) StuRat (talk) 05:05, 11 June 2008 (UTC)

There are other dangers to eating toothpaste and excessive fluoride other than death. If you eat toothpaste as a child you will develop dental fluorosis, which, while not at all life-threatening, is pretty lousy, and requires a lot of expensive dental work to correct. (So says someone who has a full upper set of veneers thanks to extreme fluorosis—$500 a tooth, to be replaced every 10 years or so, and an unpleasant procedure). --98.217.8.46 (talk) 01:33, 10 June 2008 (UTC)

applied sciences

Why is it that a physicist can become an engineer but a biologist cannot become a doctor? —Preceding unsigned comment added by Clover345 (talk • contribs) 20:47, 7 June 2008 (UTC)

Biology is a very different job than medicine. There's a difference between knowing how a cell works and knowing what to do if something is wrong with it. Generally, no one dies if a biologist makes a mistake. Paragon12321 (talk) 21:15, 7 June 2008 (UTC)

There is a difference between theoretical knowledge and practical skills. A physicist knows the theory behind engineering, so can probably design a nice new bridge, say, but they couldn't pick up a welding torch and make it. Likewise, a (human) biologist knows all the theory about how the body works, but they can't just pick up a scalpel and start cutting bits out of it. Knowing the theory is a good start and would certainly help you in a related applied job, but there is more to learn before you can actually start doing it. --Tango (talk) 21:20, 7 June 2008 (UTC)

I agree with Tango, though I bet a lot of physicists would have some learning to do before they could design a bridge. But being trained in biology would still be a giant head start if you wanted to become a doctor. I went to a small college with no official premed program, so most aspiring doctors majored in biology. --Allen (talk) 21:25, 7 June 2008 (UTC)

A physicist would have to get more training in the laws of physics as they apply to the field of engineering or his particular field of engineering before he could be successful as an engineer, or at any rate, if he didn't know enough about the laws of physics as they applied to engineering, he couldn't become an engineer, period. Even if he impressed someone with his credentials, he wouldn't last long at the job. There's nothing to stop a biologist from becoming a doctor, if he goes on to study the principles of biology as they apply to the human body (arguably a greater narrowing than that from physics to engineering, requiring greater specialization; remember, biology is the study of all that is alive, from bacteria to plants to ecosystems, and the correlation between "knowing how it works" and "knowing how to fix it" is much less in biology than in physics). Furthermore, because doctors deal literally with matters of human life and death, it is required in most places that they go to medical school, get a license, etc. Anyone who wants to become a doctor has to meet those requirements, regardless of prior training. A biologist would doubtless have an easier time than someone from an non-life sciences background in some aspects of medical training, but it's still necessary to get training in the field in order to go into the field. Diagnosis, administration of medication, surgery, psychiatry, and bedside manner are aspects of the medical field with little or no parallel in the field of biology as a whole, and many of them are crucial for any doctor to know. In short, medicine is a very demanding specialty that requires much knowledge that biologists simply don't possess - unless they go on to study medicine. 66.215.224.253 (talk) 21:27, 7 June 2008 (UTC)Aletheia—Preceding unsigned comment added by 66.215.224.253 (talk) 21:27, 7 June 2008 (UTC)

Let's also not generalize all physics here. A theoretical physicist is going to have a lot less at hand knowledge than, say, a physicist who specializes in materials science, when it comes to going into engineering. String theory does not tell you much about how to build a bridge; even a fairly generalist physics education does not tell you much about the properties of materials, of specialized techniques, of technologies. --98.217.8.46 (talk) 19:10, 8 June 2008 (UTC)

One difference to consider is that biological organisms are so complex that you really can't predict things very well from first principles. You could have the complete genome of an organism and be utterly unable to predict how many eyes it's going to have or how to treat its diseases. Most human-made -- i.e. engineered -- things are simple enough that you can understand them from the ground up in a way that biologists and doctors might never be able to. --Sean 01:23, 9 June 2008 (UTC)

A physicist may well be able to figure out how to design a bridge, but no engineering firms hire physicists as bridge designers. ike9898 (talk) 20:30, 10 June 2008 (UTC)

Synesthesia

Is there a type of Synesthesia involving smells? —Preceding unsigned comment added by 71.32.207.35 (talk) 23:13, 7 June 2008 (UTC)

This article mentions sound-odour synaesthesia. But it says that it's rare. Fribbler (talk) 23:50, 7 June 2008 (UTC)

I think its rarity can be explained in the context of the cross-activation hypothesis for the Neural basis of synesthesia, as the olfactory cortex in humans is relatively well isolated from other sensory cortex areas. --Dr Dima (talk) 06:26, 8 June 2008 (UTC)