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August 9

Mosquitos

If a mosquito can spread malaria and West Nile virus, why can't it spread AIDS? 99.245.92.47 (talk) 00:52, 9 August 2008 (UTC)

Because the HIV is digested by the mosquito. Unlike the other viruses and mosquito-borne parasites, HIV hasn't evolved the mechanism to avoid the insect's stomach. See here.--Lenticel ^(talk) 02:23, 9 August 2008 (UTC)

Botany(project topic)

Good day Pls I want to know growth of garlic (Allium sativum) is affected by temperature variables of 28 degree and 37 degree.When grown in Bauchi,North West of Nigeria;West Africa and also, method of observing this changes Thanks —Preceding unsigned comment added by Rukima (talk • contribs) 01:07, 9 August 2008 (UTC)

This sound like an interesting topic. I assume that you intend to do long-term growth experiment. This will be feasible for you only if you can create two environments (such as small greenhouses) that are identical except for temperature, and you can control the temperature. Equipment to control the temperature at 28 and 37 degrees in Bauchi for enough time to grow your plants may be difficult, especially since you will need to control the relative humidity to avoid a second independent variable. According to the internet, the temperature in Bauchi often rises above 27, so you will need a cooling system: this raises the expense of the experiment beyond the amateur level. (A heating system is a lot cheaper.) Alternatively, you might try to do a respiration experiment whereby you somehow grow the plants for an hour inside two small glass jars and measure the oxygen content inside the jar, at two different temperatures. Good luck! -Arch dude (talk) 14:07, 10 August 2008 (UTC)

Obstetricians

what classes do i need to take in high school to give me a head start to become an obstertrician? —Preceding unsigned comment added by Goals101 (talk • contribs) 02:53, 9 August 2008 (UTC)

Obstetrics is a specialty within medicine. Medical students don't choose their specialties until they've already had a few years of med school, so if by "head start" you mean for getting into an obstetrics program, then you should focus on the same classes you would to get into a good college with a strong science program. First college, then med school, then obstetrics. If you are looking to actually start learning about obstetrics, then I would suggest taking sexual education classes and perhaps even getting EMT-B (or better yet EMT-P) certified. You may also be able to volunteer at an obstetrics ward at a local hospital if you're lucky. --Shaggorama (talk) 04:31, 9 August 2008 (UTC)

Different medical schools have different requirements, so be sure to check the website of the college you intend to enter. Generally, high-school courses in science (especially biology), math, and other analytical subjects are more useful for a medical career than art-related courses. --Bowlhover (talk) 07:00, 10 August 2008 (UTC)

Conservation of linear/angular momentum

How is it that someone is able to walk? I mean, when you push against the surface of the earth, you're really applying a torque, and thus giving the earth angular momentum rather than linear momentum. So where does a person's linear momentum come from? I've given this some thought, and the explanation I came up with is that we don't gain linear momentum, we gain angular momentum; basically, we push against the earth with one foot, and the rest of our body rotates around our ankle, which makes some sense. But this explanation doesn't seem to work in all cases. Consider a car, how is its momentum conserved? Well, I would say that when the wheels of a car push against the earth, the angular momentum lost by the earth is transfered to the car's wheels. Everything seems to make sense, until the body of the car is considered: where does it's linear momentum come from? Finally, let's say someone jumps against a wall, while the earth gains angular momentum, the person in question gains linear momentum. How is this possible? Thanks in advance. —Preceding unsigned comment added by 76.68.246.7 (talk • contribs) 04:28, 9 August 2008 UTC

Good question.

What you have to remember is that a body has angular momentum when it is revolving around an external point, as well as when it is rotating around its own center. For example, the Moon has angular momentum due to its rotation around the Earth. Well, if you press horizontally against the Earth with your foot, or you press horizontally against a wall, or a car presses horizontally against the Earth with its tires, you or the car are putting yourself/itself into motion around the Earth. You are revolving around the Earth's center and that gives you the angular momentum to offset the angular momentum that your torque applied to the Earth.

If you jump vertically off the Earth, then you are in a non-rotary motion and you are acquiring linear momentum, and you are giving the Earth the same momentum in the direction that is downward for you. And real-life movements are a combination of the two cases, as a car rolls over hills and valleys and irregularities in the road, and your body moves up and down with each step.

--Anonymous, 07:00 UTC, August 9, 2008.

Angular momentum of an object can be seen as the sum of the linear momenta of all its particles. It's just a handy way of describing thing going around in circles, but angular motions of systems can always be seen as linear motions of particles. (Until one starts talking about quantum "spins" and such, and nice people don't do that.)

Hitting a wall is a force to the brick but a torque to the earth.

Torque (twisting force) is a linear force applied at a (linear) distance. Pistons push on the crankshaft (a "circular" lever) which twists more circular levers until the last ones, the wheels, push on the ground. It's all linear if you look at it closely.

How do you walk? First you have to start falling over, then move your feet under you to keep you from doing it. Saintrain (talk) 13:41, 9 August 2008 (UTC)

Triceratops vs Tyrannosaurus Rex

With their features and body parts, which do you think will win in a fight between a Triceratops and Tyrannosaurus Rex?MachaLeague (talk) 09:31, 9 August 2008 (UTC)

You say "will," which implies future, so I'll go out on a limb: a tie, since they're both extinct. For another opinion, see The Truth About Killer Dinosaurs. (They think it'd be a tie, too.) OtherDave (talk) 11:29, 9 August 2008 (UTC)

I'd probably say Tyrannosaurus as a 'trained' predator, whereas Triceratops were herbivores. That said, Triceratops may have had experience in defending itself when confronted by a predator. I don't really know. —Cyclonenim^T@lk? 12:16, 9 August 2008 (UTC)

God, you guys looovvvee being literal-minded, don't you? --98.217.8.46 (talk) 13:30, 9 August 2008 (UTC)

I can't speak for anyone else. I was having fun with the future tense, but I did post a link to help answer the actual question. And I signed it, too. OtherDave (talk) 17:07, 9 August 2008 (UTC)

I'd point out that this is not purely a theoretical discussion. Both the Triceratops and Tyrannosaurus lived in the Late Cretaceous (68 to 65 million years ago), with overlapping ranges (e.g. both were found in what is now Montana). If we operate under the assumption that the Tyrannosaurus was an active hunter (as opposed to being a scavenger - see Tyrannosaurus#Feeding strategies), one can conclude that there likely has been numerous clashes between the two. Indeed, the Tyrannosaurus article notes "A Triceratops was found in Mexico found with bite marks on its ilium. These were also inflicted by a tyrannosaur and they too appear healed, indicating active predation by the tyrannosaur." (And survival of the incident by the Triceratops, I might add.) This is also mentioned extensively in the Triceratops article. One might surmise that such "fights" generally went the way of most predator/prey encounters. A fraction of the time the predator will win the "fight", bringing down the prey. However, the majority of the time either the prey escapes, or the predator decides it isn't worth the hassle and gives up. Usually the predator will only go for the young, the elderly and the weak. Normally you wouldn't see a predator take on a healthy adult prey - it isn't worth it, as there will probably be opportunities for an easier kill later. I seriously doubt that most encounters would be the epic showdowns normally depicted in fiction - it's not worth the risk to the Tyrannosaurus. (Be honest, if your steak fought back you'd probably just order the fish, even if the resulting clash would have made for good cinema.) -- 128.104.112.147 (talk) 20:40, 9 August 2008 (UTC)

Movies and TV aside, "fights" almost never happen between different species. The closest you'll get is a back-and-forth encounter like this: http://au.youtube.com/watch?v=LU8DDYz68kM

Predators and prey both have a vested interest in avoiding fights. Out and out fighting to the death is "stupid" (i.e. not evolutionary advantageous) behavior. If the predator even gets slightly injured, it's chances of getting more prey and competing against healthy predators drops to almost nothing, and it will probably die later. In other words, as the IP above said, predators only attack prey that they think will not fight back. If they prey starts to fight back, the predator will get out of there (as demonstrated in the video--the lions get chased around by the adult buffalo, while trying to avoid the adults and get the the calf, which is not putting up a fight). In the example of the Triceratops with healed bite marks, the fact that the bite is on the hip bone is telling. All the defenses are on the head, so the Triceratops was most likely running away when it was bitten, not fighting. Dinoguy2 (talk) 23:48, 10 August 2008 (UTC)

Pollution and cycling

Have there been studies of the impact on the respiratory system of riding a bike in the city? Thanks. 190.244.186.234 (talk) 14:23, 9 August 2008 (UTC)

Any particular city in mind? I don't think it matters what form of exercise you're doing, just how much of it. With the Beijing Olympics, the authorities are saying the pollution is only a risk for events lasting over an hour (the marathon, for example), so if you're in a city with similar pollution levels to Beijing, just ride your bike for less than an hour, and you should be fine. --Tango (talk) 15:21, 9 August 2008 (UTC)

Found this but not much more.

"even when account is taken of effort (a cyclist breathes on average two to three times as much as a motorist), the cyclist emerges as the victor of this comparison" (quoted in Cycling: the way ahead for cities and towns). (1996)

The thing I'm more worried about is all the fine particles. I sometimes ride behind buses in their thick black smoke. Fourty-five minutes twice a day. The article has got some real scare stories too and it talks about Australia and Europe that are not nearly as polluted as South American capitals. Any more links? 190.244.186.234 (talk) 19:38, 9 August 2008 (UTC)

Supertime

What would it mean to physicists if a second dimension of time were discovered ? [1] 69.157.227.243 (talk) —Preceding undated comment was added at 15:59, 9 August 2008 (UTC)

The first dimension of time as I understand it is the interval between one event and another or speed as we know it. As I understand it the change in this interval between repeated occurrences of events is the second dimension of time called acceleration. But then I've never slept in a Holiday Inn. —Preceding unsigned comment added by 71.100.162.249 (talk) 16:18, 9 August 2008 (UTC)

You do know that's garbled nonsense, right? 79.66.38.215 (talk) 17:12, 9 August 2008 (UTC)

It could have some interesting effects. I'm not sure exactly, but I think it would make time travel possible. The same as you can use a second space-like dimension to change your direction along a first space-like dimension (without having a slow down and stop momentarily), the same is probably true of time. I'd have to dig out my GR notes to work it out properly. --Tango (talk) 17:32, 9 August 2008 (UTC)

In one dimension there are two discrete directions which you can identify with past and future. In two or more dimensions there's a continuum of directions and you can't make that distinction any more. It's hard to see how such a universe could have a second law of thermodynamics or anything associated with the second law, like biological evolution. The one-dimensionality of time is almost its defining characteristic. -- BenRG (talk) 18:37, 9 August 2008 (UTC)

The other time dimension could be compact, like the extra dimensions in (some versions of) string theory, so it's hardly noticeable on an everyday scale. I'm really not sure of the details of how that would work. I'm not sure what the 2nd law of thermodynamics has to do with evolution, but that's not really important, an extra time dimension would mess with causality, and that's going to mess with everything. Time machines and temporal wormholes and things usually work in such a way that you at least have local causality, it's just globally that things get mess up. This would mess it up locally as well, which is asking for trouble! Could be interesting as a purely intellectual excercise, though. --Tango (talk) 19:11, 9 August 2008 (UTC)

It's not a new idea, there's been some real research into it. I haven't read much of it yet, but it's there. --Tango (talk) 19:14, 9 August 2008 (UTC)

Centrifugal Sorting of Saturn's Rings

The rings around Saturn are believed to consist mainly of pieces of water ice and a small amount of other substances. The material varies in size from dust-like particles to lumps the size of a small automobile. (See "Saturn" in Wikipedia.) There are probably individual atoms and molecules in the rings as well.

The rings vary in the brightness of the light they reflect from the sun. Each ring has the same brightness all the way around it and across its width. There are also gaps between some of the rings. Various theories have been advanced to account for the differences in brightness and the gaps.

The brightness variation suggests that the various rings are comprised of different material. My theory, which I have not seen elsewhere, is that the material in the rings has been sorted by centrifugal separation. (Think of a centrifuge.) Impurities in the water ice would give pieces of it a different density and color.

I conjecture that the densest material appears in the outermost rings, with decreasing density of the material in rings progressively closer to the planet.

Some of the gaps are caused by moons and moonlets clearing their orbit of small-size material by gravitational attraction. Other gaps, perhaps, are due to the fact that there is no material with a density that will place it in the gap.

The centrifugal separation would have taken place regardless of how the rings were formed.

The rings are comprised of an estimated 93 percent water ice. But the ice would not be pure. There would be many kinds and strengths of impurity. This would account for the large overall width of all the rings together

The differences in density of the impure ice particles would probably be small; but over millions of years, sorting would take place.

Material that contains no water would take its place in the rings. These rings would probably be at the outer and inner edges of the ring structure because the density of the material might be considerably different from that of impure water. —Preceding unsigned comment added by 67.150.190.122 (talk) 17:11, 9 August 2008 (UTC)

The centrifugal sorting may have worked together with other causes that have been suggested for the formation of the rings.

AndMe2

67.150.190.122 (talk) 16:30, 9 August 2008 (UTC)

It's an interesting hypothesis! Are the planets in our solar system in order of mass or density? DMacks (talk) 16:51, 9 August 2008 (UTC)

No. See Table of the largest objects in the Solar System. --Tango (talk) 17:38, 9 August 2008 (UTC)

Er yeah, I'm aware of that. It was a continuation of poster's thought experiment, giving him an opportunity to do some actual science and test his idea (make hypothesis, use it to make predictions, check if those predicions agree with reality). If centrifugal sorting worked on "dust particles orbiting a planet", it would likely also be evident in "planets (really big particles) orbiting the sun" (that latter having been taking place for eons longer that Saturn's rings). So if not, it means hypothesis isn't true (or needs to be adjusted to account for this new data). DMacks (talk) 05:33, 10 August 2008 (UTC)

I don't think that's likely. An object's orbit depends only on it's velocity, position and the mass of the central object (assuming there is a big difference in the masses, as there is in the case of dust orbiting Saturn), density doesn't come into it. A centrifuge is very different from orbiting dust - particles of dust don't interact with each other much, the various things in a centrifuge do, and that's why density becomes a factor. The gaps are caused by resonance with the moons, I believe. --Tango (talk) 17:38, 9 August 2008 (UTC)

What if the rings formed in a gas-rich environment? Then they would be particles in a fluid. Would there be a centrifugal effect in that case? Just asking as I have no idea. Franamax (talk) 19:58, 9 August 2008 (UTC)

I'm just guessing now, but I expect if there was enough gas to make a difference, the orbits would just decay and the rings would crash into the planet. Even if they didn't, I think it would only the difference in density between the gas and the ring matter would be significant, so you would get one ring at the bottom of the gas made up of heavier stuff and one at the top made up of lighter stuff. It's an extremely hypothetical situation, though, I don't think you would ever have things orbiting in dense enough gas for it to be significant. --Tango (talk) 21:28, 9 August 2008 (UTC)

Well presumably the gas would be orbiting with similar velocity, so I'm not sure I see the mechanism to crash the rings, since there would be no significant drag in that case. Given a sufficient gas component though, there would be a mechanism to transfer momentum between the solid particles similar in a way to actual collisions between the particles themselves? If they're building a new planet anytime soon, I guess we should try that out. :) Franamax (talk) 01:30, 10 August 2008 (UTC)

Hmmm... I hadn't thought of the possibility of the gas being in orbit, I was thinking of it being like an atmosphere. I honestly have no idea what would happen in that case... --Tango (talk) 02:55, 10 August 2008 (UTC)

This is very interesting and suggests to me that the rings around Uranus may be similarly governed. —Preceding unsigned comment added by 79.76.242.64 (talk) 23:03, 9 August 2008 (UTC)

What STD can be transmitted through oral sex?

Which is the most common? Mr.K. (talk) 18:39, 9 August 2008 (UTC)

Well firstly particularly for the 'most common' bit, it'll be helpful if you specify what & who you're referring. The partner performing oral sex on the genitals of a female partner? The partner performing oral sex on the genitals of a male partner? A male receiving genital-oral sex from a partner? A female receiving genital-oral sex from a partner? (The sex of the performing partner doesn't tend to matter for obvious reasons.) Something else? The rates tend to vary a bit depending on what and who. But to answer the first part of your question simplisticly, I don't know of any STD that can't be transmitted via oral sex. Logically there's no reason an STD won't be transmitted via oral sex unless the STD doesn't infect and/or can't be passed via the mouth/oral region. Of course, STDs which only infect a local area will only generally infect the area they are passed to be it the oral region or the genitalia region. According to this [2] HPV is perhaps the only one which isn't that much of a concern when it comes to oral sex (but it can be transmitted in rare instances) and herpes is the most common (but that probably has a lot to do with do with how common it is in the general population and the fact it tends to be lifelong with occasional flareups). Nil Einne (talk) 19:27, 9 August 2008 (UTC)

I'm not so sure HPV isn't much of a concern. According to this, "A recent study conducted by Dr. Maura Gillison at the Johns Hopkins Oncology Center furthered the premise that HPV is linked with certain types of oral cancer." --71.185.73.240 (talk) 04:18, 10 August 2008 (UTC)

Chlamydia [3]. Franamax (talk) 00:46, 10 August 2008 (UTC)

I remember reading a while back that oral gonorrhea was on the rise amongst U.S. and U.K. teenagers. I can't seem to find any statistics that list STDs by type of infection, however. Horselover Frost (talk) 04:05, 10 August 2008 (UTC)

Educational videos in psychology

Where can I found a source of real case studies in psychology Q! Ĩ am trying to find videos of patients with some sort of mental illness or descriptions of a disorder with plenty of examples. Mr.K. (talk) 18:40, 9 August 2008 (UTC)

That would be cool. *adds name to MOAR list* --mboverload@ 19:09, 9 August 2008 (UTC)

Check out www.learner.org. They have many videos on demand that you can watch for free. The videos they make are often shown on PBS, because I specifically remember watching one of their videos on TV about schizophrenia (sp?). You might have to navigate that site for a while, but I'm sure you'll eventually find their archieved psychology videos.--El aprendelenguas (talk) 22:17, 9 August 2008 (UTC)

You'd be surprised what you can find on youtube. My interests lie more in [neurology], but still I'd suggest you run searches on youtube with the titles of conditions in which you are interested in or experiments you would like to find documentation of. --Shaggorama (talk) 13:59, 10 August 2008 (UTC)

Academic, corporate and free researchers

These three are probably closely entagled with each other. However, I would like to know how much researchers work in an academic, corporate or free environment, where is the money, and, in terms of patents and publications, how productive they are.Mr.K. (talk) 18:42, 9 August 2008 (UTC)

Generally speaking, money and often patents are in corporate, publications are in academia. But that's very generally speaking...it varies among the different areas of science, and a famous academic who becomes head of some huge non-profit research center would make more (esp. in honoraria) than an entry-level BS in some company. DMacks (talk) 20:38, 9 August 2008 (UTC)

This varies quite a lot country-by-country. For example, in 1995, in the USA around 17.5% of all researchers were in higher education (as opposed to government or corporate work), whereas in Japan it was more like 36.1%. However in the same period Japan spent only 75% of what the US spent on higher education R&D. Productivity varies a lot per country as well. Some countries, practically all of their research goes into industry or government sources (like China), whereas some are almost all government (like Russia). The OECD has tons of statistics about this sort of thing. If you only care about the US case, the NSF keeps very detailed statistics about how money is being spent and what comes from it. --98.217.8.46 (talk) 15:31, 10 August 2008 (UTC)

Automobile bumpers

Why do cars don't have a bumper car-type rubber bumpers? Mr.K. (talk) 18:49, 9 August 2008 (UTC)

Because cars need to absorb the energy of a collision, and thus need to bend and break to absorb it. We could make cars that would not be damaged in a collision, but at the expense of damaging the human inside instead. Crumple zone, bumper, Car crash. Any car with a bumper-car style bumper would not even be legal to drive in any first world countries. Any car produced today with no crumplezones and a completely rigid frame and bumper would probably not pass the safety requirements in many countries. --mboverload@ 19:04, 9 August 2008 (UTC)

In simplistic terms, this is achieved by controlled weakening of outer parts of the car while strengthening the inner (passenger cabin) part of the body --mboverload@ 19:15, 9 August 2008 (UTC)

Because SPEED does the matter. With the highest speed of rubber bumper car can't even kill a man, but the speed of car on the road makes much higher impact. Even we can found material in the future to adsorb collision energy, the static velocity of the people in the car may kill them anyway....NINJAW —Preceding unsigned comment added by 124.120.200.29 (talk) 07:05, 10 August 2008 (UTC)

As above, Speed matters: the energy to be absorbed goes up withthe square of the collision speed. Another important point: you can in fact build a bumper that can absorb and release all that energy, but it will make the vehicle unacceptably large and unacceptably heavy, thus ruining the gas milage. -Arch dude (talk) 13:34, 10 August 2008 (UTC)

In part, because Ronald Reagan directed the massive weakening of the United States vehicle bumper standards when he became president, so now your car costs a few dollars less but can suffer several thousand dollars worth of damage when tapped by another car attempting to parallel park. See Talk:Volkswagen Golf for some background on this.

Atlant (talk) 19:37, 14 August 2008 (UTC)

Control group in statistics

In statistics, it is considered necessary to have a control group (placebo group). However, in some situations (heart surgery, smoking and cancer, etc) a control group is not possible. How can I deal statiscally with these cases? Mr.K. (talk) 18:50, 9 August 2008 (UTC)

You might try the Mathematics desk for this question. Also, maybe a bit more detail. What sort of data do you have in mind, and what sort of questions do you want to ask? --Allen (talk) 19:01, 9 August 2008 (UTC)

In medical research it is unusual for the control group to be untreated, since it would be unethical to not treat a group of people. Trials are usually done comparing two different treatments (one established and the other new). The other option is to test the new treatment on people that have exhausted all other treatment options, so in the absence of the trial, they wouldn't be treated anyway, so there is no ethical dilemma in not treating half the patients (at least until the treatment is shown to work). --Tango (talk) 19:24, 9 August 2008 (UTC)

The short answer is that you cannot deal with them statistically, so you must use other means. In more detail: when you do a proper, controlled trial, you choose half the subjects randomly, and put them in the treatment group, while the other half go in the control group and get a placebo. ONLY when you have assigned subjects to groups randomly can you say that the treatment was the cause of any difference between the groups. In ALL other cases, the experiment itself does not show causation, although you may infer this if you have strong reasons for doing so anyway.

For example, if you do a smoking trial, and somewhat unethically, you order half the subjects (chosen randomly) to smoke, and the other half not to, you can say that any increase in diseases (or beneficial effects) in the first group were caused by the smoking. If you take the two groups from among the populations of existing smokers and non-smokers, the results do not necessarily show the effects of smoking. There could, for example, be socioeconomic differences between the two groups causing different health outcomes. Even so, the second group can be used like a control group, and likely confounding variables such as income can be corrected for. When you assign the groups randomly, that is called a randomised trial, otherwise (I think) it is just called non-randomised.

In trying to deal with confounding variables, you can simply include them in your model, with regression analysis. For example, instead of being dismayed at the effect of income in the non-randomised smoking study, you can record it for each subject, and find the best equation that relates smoking, income, and life expectancy. This requires that the researcher anticipate these possibilities, and collect the data in the first place. The ideal is to collect data on several indicators, and randomise for the rest.

In any case, all inferences depend on the scientific method, which most importantly includes debate within the whole scientific community. In the case of medical research, one of the key aspects of debate is that conclusions about cause and effect must have a plausible mechanism. Thus, even if you did a randomised trial and your results showed (by pure fluke) that homeopathic medicine worked, scientists would remain skeptical. It's been emotional (talk) 18:27, 11 August 2008 (UTC)

With the current flood of medical data, control groups are being formed for research using existing data. It is easy to find large groups of people who are not treated, but have a rich medical history. For example, if I wanted to do research on a drug to control HbA1c levels, I can get a large group of people who have had their HbA1c labs performed over the last few years and had no treatment and compare them a group I'm now forming to take a new treatment. I can also include the control group in my study to show how they responded without treatment before the study and with treatment afterwards. At this time, medical data is a growing field of study. So, most researchers do not use existing data. In areas where there is a strong effort to collect medical data, researchers are using the data for, at a minimum, forming a hypothesis for study. -- kainaw™ 18:38, 11 August 2008 (UTC)

Caffeine timing and sleep

If I want to fall asleep by 12:30 am, what time of day do I need to stop having caffeine? NeonMerlin 19:49, 9 August 2008 (UTC)

My experience says that caffeine sensitivity varies wildly between people both in terms of length and powerfulness of effect. I personally need about 6-8 hours for a large amount of caffeine, but I've known other people with other timing. Magog the Ogre (talk) 19:58, 9 August 2008 (UTC)

Concurred...it's very variable (see Caffeine and maybe Caffeine and healthCoffee and health for general info). I can down 4-6 cups and go to sleep within an hour, but I'm a heavy coffee drinker and am usually sleep-deprived. DMacks (talk) 20:35, 9 August 2008 (UTC)

(fixed link) DMacks (talk) 21:54, 9 August 2008 (UTC)

Well the half-life of caffeine is 9-11 hours, according to our article. It depends on how quickly your body absorbs the caffeine and how good your liver is at breaking down the stuff. —Cyclonenim^T@lk? 00:21, 10 August 2008 (UTC)

It definitely varies by person. I recommend experimenting on yourself. By trial and error, I found that for myself, if I stop drinking coffee before 3pm I usually won't have trouble falling asleep at 11pm. ike9898 (talk) 17:36, 11 August 2008 (UTC)

Space-time equation

Since space and time are relative, could scientists ever come up with an equation to turn time into space and vice-versa ? 69.157.227.243 (talk) 20:08, 9 August 2008 (UTC)

The long answer: almost anything is theoretically possible, given how little we know about the nature of the universe, and the possibilities that may exist.

The short answer: no: the two are completely different measures. Magog the Ogre (talk) 20:24, 9 August 2008 (UTC)

I don't know about "completely different measures." See Spacetime. --Allen (talk) 20:41, 9 August 2008 (UTC)

I'm not sure what you mean... an equation describes something, it doesn't do anything. Space and time are distinct (it comes down to a minus sign in the appropriate places), but are closely interlinked. You can come up with a new co-ordinate system that combines the usual space and time co-ordinates, but you'll always have one time-like and three space-like co-ordinates. Interestingly, within the event horizon of a black hole, time becomes space-like and the radial space direction becomes time-like, but that's not really time and space swapping round, it's just a technical thing. --Tango (talk) 21:33, 9 August 2008 (UTC)

Yes, I suppose I didn't quite read the question carefully. The answer is actually yes, they can be interchanged, but not in a practical way. By traveling at an extremely high rate of velocity (i.e., very close to the speed of light), one can essentially skip the time in between. This is time dilation. One could theoretically travel to the other side of the galaxy and back in a few minutes, and millions of years would have passed back at Earth. This would of course require astronomical amounts of energy.

This might not be the pretty solution you're looking for, but I don't know what else you might want: it's not like scientists could just remove a triangular piece of space. Magog the Ogre (talk) 02:50, 10 August 2008 (UTC)

That's not really interchanging space and time, it's just interchanging the rate at which you travel through each. --Tango (talk) 02:57, 10 August 2008 (UTC)

I thought the whole point of talking about "space-time" is that they are just properties of the same stuff, dimensions within the structure of the universe, and that our manner of perception creates the duality. I feel like your question is similar to asking if you could interchange between surface area and depth. Is my understanding of spacetime that far off? --Shaggorama (talk) 14:46, 10 August 2008 (UTC)

The whole point of Einstein about spacetime is that when you try to measure space, you are also making measurements of time, and when you try to measure time, you are also making measurements of space. This itself is not very surprising, except when you throw into this bit, relative mix the fact that there are a number of key invariants, things that aren't relative, like the speed of light. Then there are important consequences. It is a geometrical argument about the structure of measurement and its consequences. It's quite clever. But it's not "space and time are exactly the same thing and you can change one into another" or anything like that. It's that space and time are, quite logically and not mysteriously, inextricably linked to one another and there are practical consequences of that. --98.217.8.46 (talk) 15:21, 10 August 2008 (UTC)

Recent Horrible News!

Recently I've gone through an article of NASA where it was stated that the Earth will be annihilated in 2012. Is it so truely? Is there no way to escape it? Anyone to answer is thankfully welcome.117.201.96.57 (talk) 20:04, 9 August 2008 (UTC)

No, it's completely false, despite claims by some (e.g., An Inconvenient Truth) - where did you read this, and did you truly find it plausible? Magog the Ogre (talk) 20:18, 9 August 2008 (UTC)

An Inconvenient Truth does not claim the Earth will be annihilated in 2012. I'm sure you were joking, but someone not familiar with the movie might not realize that. --Allen (talk) 20:22, 9 August 2008 (UTC)

Yeah, I was kidding (sorry, too much Glenn Beck on CNN anymore). Magog the Ogre (talk) 20:25, 9 August 2008 (UTC)

Actually, I've read these news on the Magazine 'Science Reporter'. Thank you all, for answering. I am relieved from a tension now.117.201.96.57 (talk) 20:27, 9 August 2008 (UTC)

The Reference Desks have already had two discussions on this matter; see [4] and [5]. --Bowlhover (talk) 20:32, 9 August 2008 (UTC)

An article by NASA? That sounds unlikely... was it actually from NASA or was it from some random person claiming that it was NASA that had originally said it? If the latter, they are simply lying. It's just a load of crackpots talking nonsense. --Tango (talk) 21:35, 9 August 2008 (UTC)

I'm with tango. I'm challenging you to produce this article, as I'm sure we'd all love to read it. --Shaggorama (talk) 14:40, 10 August 2008 (UTC)

None of the feature article descriptions of Science Reporter that I looked at (January 2008 - August 2008) had any mention of the alleged 2012 apocalypse. Which issue was it in? Confusing Manifestation(Say hi!) 23:31, 10 August 2008 (UTC)

Comet of Sodom

Look at this : they found the bits and pieces of an asteroid that destroyed the Sodomites in 3123 BC. [6] Explain this one ! San Francisco watch out! 69.157.227.243 (talk) 20:36, 9 August 2008 (UTC)

What do you want explained? An asteroid hit an ancient city, people at the time didn't understand what had happened and assumed it was the wrath of god and, after a few rounds of Chinese whispers, it got written down in a book that eventually became part of the Old Testament. Doesn't seem at all odd to me. There is no reason to believe it actually had anything to do with the residents of the city being particularly sinful. --Tango (talk) 21:39, 9 August 2008 (UTC)

I wonder if "March 31, 2008" explains this one? I think we have more to fear from people who don't use all the facts at hand and look for excuses to justify their biases than from comets:) But even today, otherwise-intelligent people forget (or willfully ignore if it suits their agenda) that correlation does not imply causation. Stock market went up the other day just after I drank coffee, but I'm not gonna sink my life savings on Wall Street and head to Starbucks to make myself rich. DMacks (talk) 22:38, 9 August 2008 (UTC)

From the article: "Dr Hempsall said that at least 20 ancient myths record devastation of the type and on the scale of the asteroid’s impact, including the Old Testament tale...." Emphasis mine and mine alone. -- MacAddct  1984 ^{(talk • contribs)} 22:40, 9 August 2008 (UTC)

Ummmm, there is no mention of any "bits and pieces" being found. The article is about working from half of a 4-inch clay copy of a 2.4 thousand year old clay tablet to pinpoint the hour, 5000 years ago, of an observation that lasted no more than 10 seconds.

Meteorites have impacted Earth many times. How about this and this and this and this or any of these? It happens because of gravity and chance. Saintrain (talk) 23:17, 9 August 2008 (UTC)

Asteroids of the size mentioned in the article, however, only strike Earth once every 80 000 years. If an asteroid "more than half a mile across" really did wipe out Sodom, the incident would be the only major impact event in human history that we know about.

An impactor usually creates a crater twenty times its own diameter, so a half-mile-wide asteorid would create a 10-mile-wide crater, one that should have been discovered long ago. It's also interesting that the article claims the asteroid's impact released energy "equivalent to 1000 tons of TNT exploding", which would imply it was much less energetic than the Tunguska event. A realistic figure would be 50 000 million tons. --Bowlhover (talk) 06:25, 10 August 2008 (UTC)

OK, yeah, glad to see I'm not the only one casting a skeptical eye on this (I've seen other junk articles from timesonline, btw). A piece of pottery talking about a meteorite from 2300 years beforehand, before there was writing, while there were no accurate measurements around? I suppose it is possible (the Semites had a sick amazing oral tradition), but it seems highly unlikely - along the lines of Atlantis. Magog the Ogre (talk) 02:57, 10 August 2008 (UTC)

As Macaddict and Magog tO, there may be the impeccably si-ick oral traditions that leave our media in the shade with feats of memory making silicon valley look primitively mechanistic but when it comes to the causal connections, there's magical thinking to consider. Julia Rossi (talk) 10:01, 10 August 2008 (UTC)

I can't find my mistake

I want to find an equation for the final velocity of an object that is dropped from a height h (not assuming g remains constant), but the answer I keep getting is wrong.

${\vec {F}}=m{\vec {a}}$

${\frac {GM_{e}m}{{\vec {r}}^{2}}}=m{\vec {a}},$ G is less than 0.

$d{\vec {v}}={\frac {GM_{e}}{{\vec {r}}^{2}}}dt,dt={\frac {d{\vec {r}}}{\vec {v}}}$

$\int _{{\vec {v}}_{0}}^{\vec {v}}{\vec {v}}\,d{\vec {v}}=\int _{-(r_{e}+h)}^{-r_{e}}{\frac {GM_{e}}{{\vec {r}}^{2}}}\,d{\vec {r}}$

${\frac {{\vec {v}}^{2}-{\vec {v_{0}}}^{2}}{2}}={\frac {GM_{e}}{r_{e}}}-{\frac {GM_{e}}{r_{e}+h}}$

${\vec {v}}={\sqrt {2GM_{e}({\frac {1}{r_{e}}}-{\frac {1}{r_{e}+h}})+{\vec {v_{0}}}^{2}}},$ where G=gravitational constant, re=radius of the earth, Me=mass of the earth, and h=height the object was dropped at.

Everything seems right, but the final answer's imaginary: somewhere I've made a mistake with a negative, but I don't know where. Please help, and thanks.

Edit: I'm considering down (i.e. towards the surface of the earth) as positive. —Preceding unsigned comment added by 76.68.246.7 (talk) 23:25, 9 August 2008 (UTC)

Why have you said that G is less than zero? It isn't. G is positive, and you need a minus sign in the second equation. Those cancel out, though, so won't affect the final answer. Next, why are the limits on your integral -r_e and -(r_e+h)? Where did those minus signs come from? The radius of the Earth is a positive number. I think making those limits positive will fix your problem. --Tango (talk) 00:09, 10 August 2008 (UTC)

Sometimes G is considered negative and the minus sign in the second equation is ignored, it doesn't make a difference, people have different preferences. As for the limits in the intergral, they're negative because I'm considering the downwards direction as positive. In other words, the initial position of the object is -(r_e+h) because the object would need to travel a positive distance (r_e+h) to reach the earth's centre. Notice that change in displacement is a positive number (h), but if I treated the limits as positive, the change in displacement would have been negative.

To better illustrate this, consider the object as undergoing a uniform acceleration (down is positive). In this case, v=2aΔs, v=2a(r_f-r₀), and because r_f is 0, this equation wouldn't make sense if r₀ was positive.

You can't both take G as negative and down as positive, that's self-contradictory. Gravity is directed towards the center of the Earth and hence the force of gravity must have the same sign as "down". Dragons flight (talk) 01:47, 10 August 2008 (UTC)

Exactly. Gravity acts to reduce distance, which is why there's a minus sign in Newton's universal law of gravity (or, equivalently, G is taken as negative, although I've never seen that). If you measure distance backwards, you'll have to get rid of that minus sign. --Tango (talk) 02:13, 10 August 2008 (UTC)

Well, if down is taken as positive, then r would be negative, and so G (or Newton's universal law of gravity) would still have to be negative, right?

Edit: Of course, r^2 is still positive, my bad. Thanks. —Preceding unsigned comment added by 76.68.246.7 (talk) 03:10, 10 August 2008 (UTC)

I think it's best just to keep G as positive always and add in minus signs where you need them. Changing the sign of a physical constant to suit your co-ordinate system just seems confusing to me... --Tango (talk) 03:30, 10 August 2008 (UTC)

August 10

Herbivores and omnivores in same species

Are humans the only species in which some members are exclusively herbivorous and others aren't? NeonMerlin 00:20, 10 August 2008 (UTC)

Some cats are omnivorous. There might be other species whose diet is modified based on the availability of food. − Twas Now ( talk • contribs • e-mail ) 01:27, 10 August 2008 (UTC)

all humans are omnivorous, very few people have never eating plants or meats. even if many people choose to permanently eat both or either. i.e. most muslims know what pork tastes like, they've tried it, and many are made to try it so they can identify it.^MY♥_INchile 03:07, 10 August 2008 (UTC)

Careful, you don't want a fatwa. I strongly suspect that as most muslims live in countries or communities where Islam is endemic, pork simply isn't available, and the social penalty for eating it is severe. —Preceding unsigned comment added by 86.128.192.207 (talk) 17:40, 10 August 2008 (UTC)

Well, I know dogs are omnivores and can live on vegetarian diets or on mixed diets, as humans can. I imagine there are other species for which this is true too. I have a suspicion the same is true for pigs, but I can't find a reliable looking source either way right now. 79.66.38.215 (talk) 04:57, 10 August 2008 (UTC)

Clearly example is pyrhana, there are 2 types seperately (omnivore and herbivore)....Ninjaw —Preceding unsigned comment added by 124.120.200.29 (talk) 06:59, 10 August 2008 (UTC)

Note that being an omnivore isn't really a question of choice, it's a question of biology. Limiting yourself to a certain diet doesn't make you any less of an omnivore, even if it makes you a vegetarian. -- Captain Disdain (talk) 09:23, 10 August 2008 (UTC)

Also mosquitoes- the males are exclusively herbivorous and the females exclusively drink blood. Nadando (talk) 23:51, 12 August 2008 (UTC)

Wet wipe marker

i need help trakcing down sources for wet wipe markers, also known as chalk in or fluorescent markers, you know they ones they use on the outdoor menu displays at restaurants, that look like chalk but wont get all messy, yeah those. theres a bunch of alleged sources here, but i can't find them on their own, would anyone care to help?^MY♥_INchile 00:38, 10 August 2008 (UTC)

I'd try staples. --Shaggorama (talk) 14:37, 10 August 2008 (UTC)

I assume you mean Staples Inc., a US-based office supply store, not staple (fastener), a small metal clip used for holding paper together. I'll note that any major office supply store would be able to help the original questioner. -- 128.104.112.147 (talk) 19:37, 10 August 2008 (UTC)

Thank you for clarifying my comment. My phrasing was pretty confusing, and I'm sure no one would've understood what I meant besides the two of us. --Shaggorama (talk) 21:36, 12 August 2008 (UTC)

Density of human blood

Water is 1 gm/cc. what is blood density? please? —Preceding unsigned comment added by 79.76.242.64 (talk) 01:29, 10 August 2008 (UTC)

According to our Blood article its 1060 kg/m³. -hydnjo talk 01:49, 10 August 2008 (UTC)

Thats not much denser than water then!, So 8 pints of blood (the content on the human body) only weighs about 10 pounds? —Preceding unsigned comment added by 79.76.242.64 (talk) 02:00, 10 August 2008 (UTC)

If I typed the right numbers into Google calculator, it comes out to just under 9 pounds, but yes, it's barely more than water. --Tango (talk) 02:16, 10 August 2008 (UTC)

It would depend on whether you mean US or Imperial pints. Anyway, the number is about right. The Blood article says the typical volume in a human is about 5 liters, which would therefore weigh 5 × 1.06 = 5.3 kg or almost 12 pounds. But there'd be enough variation that you couldn't count on the second digit there. --Anonymous, 04:57 UTC, August 10, 2008.

True, I assumed US pints since usually online, if people don't specify, they're more likely to mean US. (I'm British, so it's not that I'm bias in favour of US measurements!) --Tango (talk) 05:13, 10 August 2008 (UTC)

If everything in the universe suddenly doubled in size, would it matter?

Would it be noticeable on some level? Like physical laws changing? I thought like Einstein and realized space is relative so at first I thought no. Then I remembered something- singularities. How could you double the "size" of that without seriously disrupting something? It would probably spawn some new emergent property with disastrous consequences! 0_0 -----Sam Science (talk) 01:38, 10 August 2008 (UTC)

Some formulas for natural phenomena include a parameter that is "squared". If everything doubled, these phenomena would be 4 times as great. That might produce unexpected results. Incidentally, I wonder why "squared" crops up so often in formulas for natural phenomena. An example is e=mc². There are many, many other examples. Why should something be multiplied by itself in natural phenomena? AndMe2 66.52.8.89 (talk) 02:19, 10 August 2008 (UTC)

A special case of this is that if you go from the first to the second dimension (length to area) you multiply lengths so you get squares. --Ayacop (talk) 06:45, 10 August 2008 (UTC)

The simplist way a squared can come up is because a factor appears in two different things that end up being multiplied. First thing that springs to mind is air resistance which is proportional to the square of velocity because velocity affects how many molecules of air you hit and how much energy you hit each one with. --Tango (talk) 02:29, 10 August 2008 (UTC)

With any "What would happen if this changed?" type question, it's important to state precisely what's changing and what's staying the same. How are you doubling the size of everything? You would need to change some physical constants appropriately (reduce the electric constant to increase the size of atoms, amongst other things). You have to make sure the physical laws are still obeyed, for example, ${c_{0}}^{2}\,\epsilon _{0}\,\mu _{0}=1$, (those are the speed of light, electric constant, vacuum permeability, in that order), so if you change the electric constant, you have to change either the speed of light, or the permeability to compensate. If you change everything just right, you wouldn't notice any difference (for example, if you doubled the speed of light, the speed of light measured in terms of the radius of one of the objects you've doubled the size of would be the same). --Tango (talk) 02:29, 10 August 2008 (UTC)

Let's consider what would happen if all objects doubled in linear dimensions without changing any physical constants or other material properties. The Earth is 8 times as massive, but its surface is twice as far from its centre, so the acceleration due to gravity at the surface is 2g. Your body is 8 times as massive as it was, so you weigh 16 times your normal weight. However, your muscles are only 4 times as powerful (muscle strength varies with cross-sectional area). You need 8 times as much oxygen as you do now, but your lungs' surface area has only increased by a factor of 4. Fortunately, the air is twice as dense (due to increased surface gravity) so you only need to breathe at the same rate as normal. But you are moving a chest that weighs 16 times its normal weight with muscles that are only 4 times as powerful. Doesn't sound like a pleasant experience ! Gandalf61 (talk) 10:05, 10 August 2008 (UTC)

It's an interesting interpretation, making macroscopic objects twice as big but keeping atoms the same (and just having more of them), but it's not that simple - if you make the Earth 8 times as massive the internal pressure will increase, increasing the average density and the radius won't be twice as big. To get the radius twice as big, you need more than 8 times the mass. There are also all kinds of other considerations. If the sun is also twice as big, and more than 8 times as massive (much more, I expect, the added pressure will be more significant than with the Earth), the Earth's orbit is going to change. You then need to decide what you want to keep the same - the size of the orbit (or, perhaps double that as well), the length of a year, the orbital velocity? Which you choose will change what to affects are. If you keep the orbital velocity the same, for example, you'll end up with a much closer orbit around a much more luminous star and the atmosphere would probably boil off - so much for the atmosphere being twice as dense! --Tango (talk) 20:43, 10 August 2008 (UTC)

William Poundstone covers this question in great and entertaining detail in Labyrinths of Reason. --Sean 14:37, 11 August 2008 (UTC)

Thremocouple power output

What is it? —Preceding unsigned comment added by 79.76.242.64 (talk) 02:34, 10 August 2008 (UTC)

Take a look at thermocouple and see if that answers your question. Otherwise, you'll need to be more precise about what you want to know. --Tango (talk) 02:58, 10 August 2008 (UTC)

Looked. Doesnt really help. I want to know the typical power output of a typical thermocouple or thermopile as used in flame failure devices. —Preceding unsigned comment added by 79.76.242.64 (talk) 21:12, 10 August 2008 (UTC)

A circuit's power is determined by its resistance and voltage; Ohm's law is a good approximation of the relationship for most materials. To find the power used by a flame failure device, you need to know bothy the electromagnet's resistance and the thermocouple's voltage. The latter is not enough.

I couldn't find any data for a typical electromagnet in a FFD, but hopefully another editor will be more successful. --Bowlhover (talk) 09:27, 11 August 2008 (UTC)

When our "gas log" fireplace needed some troubleshooting, I measured this. If memory serves, that particular thermopile was capable of putting out about 40 mA at some very low voltage. Half the current operated the "pilot light maintaining coil" in the gas valve and the other half operated the "main burner coil" in the gas valve. I took notes; if you really need to know the details, I can probably dig them up.

Atlant (talk) 19:30, 14 August 2008 (UTC)

Upthread, someone provided a link to a typical "large" Honeywell millivolt control valve. The specs for that valve state:

ELECTRICAL DATA: 
Pilotstat Power Unit - Hold-in 15 ma maximum; 
dropout 10.5 to 4.5 ma; resistance 11 ohms. 
Valve Operator - Pull-in 65 ma maximum; coil 
resistance 2 ohms. 

And state that the millivolt thermopile produces about 750 mV open circuit.

Atlant (talk) 21:06, 14 August 2008 (UTC)

Cooking Pasta

Standard instructions for cooking spagetti (and other dry pasta) are:

bring water to a boil, then put the pasta in the boiling water.

Is there any good reason to do it this way, or will it work just as well to put the pasta into cold or warm water, then bring the water to a boil?

Based on limited experiment, I suspect the latter is the case.

Thanks, Wanderer57 (talk) 02:54, 10 August 2008 (UTC)

It makes estimating the cooking time a little difficult, since it depends on how quickly the water heats up. Other than that, I can't see any problem. It's more energy efficient, however, to heat the water in a kettle and then add it to the pan already boiling - kettles heat the water quicker, so there's less time to lose heat. --Tango (talk) 03:01, 10 August 2008 (UTC)

Also, the pasta will tend to clump and stick together during the heat-up. -hydnjo talk 03:18, 10 August 2008 (UTC)

If you add a little olive oil, the pasta won't stick together. AndMe2 66.52.8.89 (talk) 03:25, 10 August 2008 (UTC)

I am not a science type but I am a chef. It makes little difference to the resulting pasta if we're talking about a single serving; a small portion in an amount of water that comes to a boil quickly. However, it makes a big difference if we're talking about a large amount of pasta in a corresponding large amount of water that takes a significantly longer time to come to a boil. What you want is al dente. I donlt know the exact scientific reason why but pasta which soaks for any length of time before coming to a boil doesn't yield al dente pasta. Instead, what you get is mushy pasta (mushy pasta=bad). There is another reason for putting the pasta in boiling water, and this applied to both large and small servings: you need to stir pasta to avoid clumping. putting the pasta in immediately means you're going to be standing over the pot stirring for a longer period of time. Efficiency in cooking matters a lot when you're doing it over and over. By the way, putting oil in pasta water as an inoculation against sticking isn't effective, is a waste of oil and shouldn't be done for a very good reason: the sauce wonlt stick well to the pasta, it slides off. Don;lt use oil in the water, just stir. Some other things you might want to know: always wash dry pasta in water just before you put it in the pot. This takes off the starch (if you put it in a bath you'll see how cloudy the water gets); you can't make good pasta without salting the water (use kosher salt, never iodized); Once your pasta is at the perfect state, and you've drained, add your sauce immediately which cools it down. If you take a bit mass of hot, al dente pasta and let it sit, it will continue to cook and voila, mushy pasta.--70.107.9.159 (talk) 03:47, 10 August 2008 (UTC)

Two thoughts about your practical observations:

1. Do you really come to a rolling boil first, or just gentle boil? A rolling boil could itself help avoid clumping by keeping the pasta moving around. That is, it's more than just reducing the need for "standing over the pot stirring for a longer period of time".

2. If soaking pasta leads to mush but plunging into boiling water gives good cooking, I wonder if the boiling water (nearly) instantly cooks the outside a bit (gelling the starch, or whatever happens when carbs "cook"), and this coating prevents the mushing. Either sealing out too much water or preventing the whole structure from dissolving (it's just a chunk of flour:). Something like searing a steak or blanching french fries?

Dang, now I'm hungry. DMacks (talk) 05:23, 10 August 2008 (UTC)

I second the "don't waist oil in the water" and add don't time it, throw your pasta at the window, wall, fridge or whatever "technique" used to time the cooking. Just TASTE it and soon you'll know exactly when they need, 30 seconds or a minute more to be exactly the way you like. 190.244.186.234 (talk) 05:54, 10 August 2008 (UTC)

Ants climbing trees

Recently while up a ladder to cut a branch off a tree, I noticed ants on the bark of the tree.

Why might ants go to all the work of climbing trees?

The tree was not doing something that might have provided food to the ants, like flowering or dripping sap.

Thanks, Wanderer57 (talk) 03:05, 10 August 2008 (UTC)

Cutting the leaves and collecting them for the nest is what I remember from a documentary. Don't they let themselves fall down with it, too? --Ayacop (talk) 06:36, 10 August 2008 (UTC)

Right at the tips of the branches there may have been herds of aphids being farmed by ants collecting the honeydew. Ants don't seem to know the meaning of distance and will walk a long way for some honeydew. Richard Avery (talk) 06:47, 10 August 2008 (UTC)

There appears to be only one kind of ant that does the cutting: leafcutter ant. --Ayacop (talk) 06:50, 10 August 2008 (UTC)

There are also ants that live in trees. See Acacia cornigera and Acacia drepanolobium--Lenticel ^(talk) 10:33, 10 August 2008 (UTC)

Thanks. I'm in southern Ontario, Canada, a long way from where leafcutter ants or those acacia species are found. I will take a closer look at the tree.

Maybe the ants just went up for the view. Wanderer57 (talk) 16:38, 10 August 2008 (UTC)

How do we know Planck measurements are the ultimate?

For example, how do they know the "smallest" planck length is 10 to the negative 20th power? Couldn't you just divide again? The problem could be scale. If something the size of the universe was trying to measure something on our scale it would be meaningless to observer.- And observed.--Sam Science (talk) 03:58, 10 August 2008 (UTC)

My not very well educated answer is that all quantum mechanics appears to work in multiples of the constant or the constant divided by 2(pi). There is not a single part of quantum mechanics that does not, so far as I can tell. Additionally, it has something to do with the c (the speed of light in a vacuum), and is thus clearly somehow integral to the very nature of the universe. In fact, with e=mc2, were Planck's constant infinitely small, c would be infinitely large, and there would be infinite energy in the universe. Unfortunately, Wikipedia's article on the constant is extremely lacking (Brittanica's article is much better).

Sorry for being so nonspecific. Magog the Ogre (talk) 04:24, 10 August 2008 (UTC)

You're getting confused between the Planck length and Planck constant, I think. --Tango (talk) 04:26, 10 August 2008 (UTC)

Yes but aren't they ultimately related? Magog the Ogre (talk) 04:29, 10 August 2008 (UTC)

In that the Planck constant is one of the constants used in the definition of the Planck length (together with the gravitational constant and the speed of light), yes. --Tango (talk) 04:31, 10 August 2008 (UTC)

Planck length#Physical significance has a thought experiment that tries to explain it. --Tango (talk) 04:31, 10 August 2008 (UTC)

Planck time is the amount of time that light takes to travel 1 Planck length; since a Planck length is the shortest measurable length and the speed of light is the fastest possible speed, 1 Planck time is logically the shortest meaningful amount of time. Planck temperature is the highest temperature at which matter remians matter, so it's the highest meaningful temperature.

It is not true that 1 unit in all Planck units represents the lowest or highest possible measurement. 1 Planck mass is much heavier than all fundamental particles, and 1 Planck charge is equal to the charge on 11-12 electrons. --Bowlhover (talk) 10:36, 11 August 2008 (UTC)

Centrifugal Sorting of Materials

OK. The rings of Saturn were not sorted by centrifugal force. I never quite believed it anyway.

But the discussion has led me to some further thoughts about centrifugal separation.

Assume a mixture of material is being separated in a centrifuge. Is the size of the particles significant in centrifugal separation? Conventional (high school) wisdom says "No". But I am wondering why.

To illustrate, let us say a quantity of glass marbles is mixed with a quantity of steel balls. The marbles and steel balls all have the same diameter. Each steel ball therefore has a greater mass than each glass marble. The mixture is put in a large centrifuge and spun. The steel balls will more strongly resist deviation from motion in a straight line and will push their way between the marbles. The steel balls will thus work their way to the outer edge of the spin path. The inevitable vibration (from imperfect bearings, etc.) would hasten the process. A thin coat of non-sticky lubricant on each ball would also assist by reducing friction as the balls slide past each other. Or for simplicity to establish the basic principle, we could assume there is no friction between any of the balls. (Centrifugal separation of gases avoids most of the friction, I think.)

Now imagine a mixture of glass marbles and lead shot. The marbles are all the same diameter. Each lead shot is the same diameter as other lead shot, but is small enough that it has less mass than each marble. Spin the mixture in a centrifuge. The marbles (having greater mass) will more strongly resist deviation from motion in a straight line Will the marbles work their way past the lead shot to the outer edge of the spin path? If so, the materials will become separated by their density, rather than their mass. Let us assume there is no friction.

I don't have an answer to this. Maybe someone can come up with one.

Andme2 (talk) 07:44, 10 August 2008 (UTC)

see Brazil nut effect. Saintrain (talk) 13:50, 10 August 2008 (UTC)

To clarify, if in the thought experiment you provide you are saying that the marbles and lead shot are the same diameter but different masses, then the brazil nut effect is inapplicable because it is a function of volume and not mass. --Shaggorama (talk) 14:34, 10 August 2008 (UTC)

I read OP that the lead shot were much smaller diameter; the weight of each shot is less than that of a marble. Saintrain (talk) 19:59, 10 August 2008 (UTC)

The effect occurs in spherical particles due to a function of volume, mass, and surface hardness. Volume is a major contributer, but experiments have shown that the other factors can overpower it easily. When the particles get non-spherical, we're in the realm of something physics has not yet been able to model. SamuelRiv (talk) 18:53, 10 August 2008 (UTC)

If we assume there is no friction, then I don't think surface hardness enters into it. I think the solution has to do with the fact that the center of each marble is more greatly spaced from the surface of the marble than is the case with the center of a lead shot. Andme2 (talk) 19:28, 10 August 2008 (UTC)

Brazil nut effect article says the effect is seen in mixtures "containing particles of different sizes but similar density". If particles have significantly different densities then the densest particles (note "densest" not most masive) will settle to the bottom/outside of the centrifuge because the centrifuge creates a pressure gradient. Gandalf61 (talk) 19:55, 10 August 2008 (UTC)

Let's try the Brazil nut effect with the marbles and lead shot. Put a mixture of them in a container and fasten the container on a shake table. Start the shaker.

There is no centrifugal force. But this shake table has a vertical component of motion. That frequently throws the marbles and lead shot upward, after which they fall downward.

This shake table also has a horizontal component of motion. As the marbles and lead shot fall downward, the shake table will exert a horizontal force that presses on the marbles and lead shot in contact with the sides of the container. These, in turn, press on some of the adjacent marbles and lead shot. Some of the lead shot will then be pushed a little way beneath some of the marbles. These marbles will rise in the mixture when all the material settles on the bottom of the container.

Some lead shot also gets pushed on top of some of the marbles during the fall. But these will tend to roll off the marbles when the entire mass comes to rest on the bottom of the container. In time, all the marbles will be on top.

By the way, the horizontal push exerted sequentially by each side of the container, together with the rising marbles, accounts for the convection current. In a cylindrical container, the horizontal push exerted sequentially to all sides of the mass is carried through the mass and meets more or less in the center of the container, where it all cancels out. (This convection current will be most noticeable when the particles are more similar in size and density.)

Now imagine the experiment is done with marbles and lead balls, with all spheres having the same diameter. The horizontal component will shove some lead balls part way beneath some marbles during the fall. But (statistically speaking) an equal number of marbles will be pushed under lead balls. There will therefore be no sorting due to horizontal motion.

To clarify the equal-diameter-spheres situation, imagine that only marbles of equal diameter are used. Some are green marbles and some are red marbles. Obviously there will be no sorting due to vertical motion followed by horizontal motion. There will be no wedging effect of small balls being pushed beneath large balls.

These thought experiments ignore the elasticity of the spheres, and permanent distortion of the lead balls that may be caused during the experiment. Air currents during the fall are also ignored. However, by weeding out extraneous elements, we can see the basic process. Extraneous elements can then be figured in later if needed.

Oh, one more thing. I said the force exerted by the shake table has a vertical component and a horizontal component. If these are exerted simultaneously in a curving manner, there will be a centrifugal force. This will be slight and has been treated as an extraneous element. But a special shake table could be built in which these forces are not exerted simultaneously.

Andme2 (talk) 22:57, 10 August 2008 (UTC)

Eucalyptas Tree,nor Cal

Greetings.

We have a stand of rather tall Eucalyptas tree in our yard.

We live in Carmel Valley,Ca

Just recently r deck in the back by the stand is getting bombed with PURPLE droppings,,looks like bird poooooooop, but it is a berry color..!!!

Not trying to stop it, just would like to know what the heck is really going on,,?

Regards.............and................Thanks --Ddemos (talk) 09:04, 10 August 2008 (UTC)

Is it mulberry season where you are? Julia Rossi (talk) 09:51, 10 August 2008 (UTC)

Bat shit is supposedly purple..87.102.45.156 (talk) 13:24, 10 August 2008 (UTC)

or the blackberry season? Richard Avery (talk) 14:51, 10 August 2008 (UTC)

Richard is onto it. Obviously, birds like to hang out in your grove of trees. It's the time of year when berries, cherries, wild grapes, and all that are all ripening, which birds love to eat. And, due to their need to constantly be as lightweight as possible, they poop it out nearly as quickly.

Ergo, don't make the mistake that an uncle of ours did: built an arbor to sit under in the summer, planted grapes to grow on the arbor (fast growing, big leaves, etc). Unusable once the grapes started to ripen!!

--Danh, 67.40.167.46 (talk) 23:04, 10 August 2008 (UTC)

Flu like symptoms

As I understand, flu like symptoms are a reaction of the body to a pathogen which arise in the process of immune defense. But how exactly are these symptoms (or what immediately causes them) helping to defend the pathogen? 93.132.159.115 (talk) 10:56, 10 August 2008 (UTC)

There are several symptoms which you are referring to, I presume. Coughing is the mechanism the body uses to clear the trachea of foreign matter, be it fluid or a solid. This is particularly relevent in Influenza and other upper respiratory tract infections like the common cold since the viruses bind on epithelial cells. The remaining symptoms, bar one or two, are more side effects of the infection rather than a method for helping to remove the virus. Fever, for example, is usually the result of pyrogens released by bacteria or viruses. However, such substances are also released by the cells of your immune system. This particular topic is covered in more detail here. Individual symptom pages usually have a mechanism section, so you may wish to try: Fatigue (medical), Sneeze, Fever and Headache. —Cyclonenim^T@lk? 12:16, 10 August 2008 (UTC)

Thank you for the links. The subsection fever#Usefulness of fever was something of the sort I was looking for. Sneezing and coughing are plain enough: coughing tells the nurse your still alive and she can't skip your lunch and sneezing helps distributing the microbes you already have to your room mates (I'm only half joking). The other articles are too general for my question. Also muscle ache is a symptom for which I'm not sure what it's good for. 93.132.159.115 (talk) 20:01, 10 August 2008 (UTC)

Nasal congestion is caused by the inflammation of nasal tissue, which in turn results from large numbers of white blood cells entering infected tissue. It's very beneficial in the nose because that is the main site of infection. --Bowlhover (talk) 10:23, 11 August 2008 (UTC)

The Matrix

What are the references to mdern physics in the movie The Matrix ? 69.157.227.243 (talk) 13:40, 10 August 2008 (UTC)

One of the points of the movie was that the main characters "hacked" the matrix and so could violate it's rules. Among those rules were the rules of physics. I don't think there was any reference to physics in general in the movie beyond the characters capacity to violate fundamental laws such as gravity. If you want to know what physical laws were violated, I'm sure other members of the RD will be happy to list a few for you. As far as "modern physics" goes, I typically take this phrase to mean materials studies, relativity, and quantum mechanics, which weren't referenced in the film (to the best of my knowledge). --Shaggorama (talk) 14:30, 10 August 2008 (UTC)

The Matrix, like most high-budget special-effects-filled Hollywood movies, is a travesty against physics. It's not even internally consistent, though I doubt the effects team had a physicist on board to ensure plausibility. Your only recourse is to suspend disbelief.

I can't recall any notable references to modern physics in the movie either, just plenty of special effects which confound good 'ol Newtonian mechanics. -- 98.26.182.245 (talk) 17:53, 10 August 2008 (UTC)

And, if memory serves, the purpose was to harvest energy from humans. We're pretty inefficient energy sources. Much better to kill us all and burn the corn. Saintrain (talk) 20:02, 10 August 2008 (UTC)

Sorry this is off topic but I can't help: kill us all and burn the corn is one way, burn the corn so we'll die is another (I put your tortilla in my tank) 93.132.159.115 (talk) 20:22, 10 August 2008 (UTC)

There's a web site that reviews movies on how believable their physics are. Wisely, it chooses not to nit-pick the scenes inside the Matrix (since technically as a computer simulation there's no need for it to follow the laws of nature), but it's got a lot to say about the out-of-Matrix scenes. Confusing Manifestation(Say hi!) 23:04, 10 August 2008 (UTC)

They got it backwards. It's implied that the world we live in now is the matrix, and thus what we believe is the laws of nature is really the matrix' physics engine. This would mean that the physics in the matrix would be the same as in the real real world. The movie real world, on the other hand, could vary well have humans as perpetual motion machines, and the people in the matrix would have no way of knowing. — DanielLC 00:16, 11 August 2008 (UTC)

The Matrix is said to be an accurate simulation of late 20th century Earth, so the laws of physics should be the same in the matrix and out of it. The difference is that in the matrix, you can break those laws. --Tango (talk) 01:01, 11 August 2008 (UTC)

Animals

Do animals get zits? If they do can they squeeze them? —Preceding unsigned comment added by 86.128.192.207 (talk) 17:15, 10 August 2008 (UTC)

Yes they do get pimples all right. The fur tends to hide them from view. They could probably make an attempt at squeezing them, but why bother? Squeezing is usually for aesthetic purposes and as noted one can't see the spots. Fribbler (talk) 17:58, 10 August 2008 (UTC)

Umbilical Cord

Do animals have umbilical cords? If so, what do wild animals do with them? Humans usually cut them and tie them up, but of course animals can't do the tying, so what happens? I am just thinking this, because they must have them, otherwise the foetus would not be able to feed inside the mother. I've seen calves getting born, and they just seem to 'fall out', so to speak, totally unattached. Does it just come off inside the mother? If so, why is a human umbilical so long?--ChokinBako (talk) 17:44, 10 August 2008 (UTC)

Yes, mammals are all born with umbilical cords. Mammals are born with an umbilical cord attached to the placenta, which is also expelled from the mother. If left uncut the umbilical cord will "drop off" in a matter of days. Fribbler (talk) 17:54, 10 August 2008 (UTC)

Well, all placental mammals. Not sure what if any analogous structure is present in eggs. DMacks (talk) 18:08, 10 August 2008 (UTC)

See Placenta#Non-humans. There's not a lot of information there, but it answers your question. --Tango (talk) 18:12, 10 August 2008 (UTC)

I can say for certain that i've seen a cow giving birth to a calf and it promptly ate the umbilical cord and spent the next 10/20 minutes cleaning the little calf up. Was very interesting to watch as it gave birth (unaided) in the corner of a field, it was also amazing how quickly the calf could walk - it was only a matter of minutes before it was stable enough to move around without looking like bambi on ice. No idea if eating the cord is common in other animals but I recall hearing that it helped produce extra-rich milk for the baby (though I wonder if that's just an old wives tale).ny156uk (talk) 22:15, 10 August 2008 (UTC)

I can say for certain that I have seen well over a hundred cows giving birth. In my experience, they don't chew on the umbilical cord still connected to the calf (which is a short piece and dries up as Fribbler says). They do eat every scrap of the afterbirth. I believe this accomplishes two functions - remove the smell from the attention of predators and recover the nutrient-rich material. I don't believe that this helps to make the milk extra-rich though, colostrum is always expressed in the first 24 hours of lactation and is available immediately. The nutrients in the placenta probably help the cow recover from her ordeal though, and tide her over for the first while when she only pays attention to her calf and doesn't eat any grass. And yes, the first thing a cow does is lick every inch of her calf. This does two things - free mucus from the calf's hair so that it can start taking it's natural insulating effect; and the rough surface of the cow's tongue has a stimulative effect on the calf, helping to get its circulation going. The continued licking stimulates the calf to start stretching its muscles. Even if the calf is born not breathing, the mother's tongue can stimulate the calf to get started. We of course would jump in, clear the calf's throat of the mucus plug (breathing or not) and rub it with straw. In the not-breathing situation, we were much more rough, hanging it upside-down and pounding on it. Never lost one that way though. (/off-topic rant, anyone wanna see my photos? :) Franamax (talk) 00:36, 12 August 2008 (UTC)

I've also heard that it hides the evidence to keep from attracting predators. DMacks (talk) 04:27, 11 August 2008 (UTC)

It is long so that baby can make some movements inside and does not break abruptly when baby is delivered.

I too remember having seen on Discovery an animal eating placenta. Umbilical_cord#The_umbilical_cord_in_other_mammals is often consumed by the mother.

Interestingly, some fish (shark) do not have placenta. See Shark births. manya (talk) 04:46, 11 August 2008 (UTC)

I don't think any fish have placentas. Only placental mammals do. What's interesting is that some sharks' eggs hatch while still inside the mother, normally eggs leave the mother before hatching. --Tango (talk) 16:52, 11 August 2008 (UTC)

That caught me off gaurd too, but Google does tend to indicate that some sharks develop a placenta. [7] Presumably it is a result of convergent evolution, since sharks and mammals are on very different parts of the tree of life and so must have acquired the ability independently. Dragons flight (talk) 18:49, 11 August 2008 (UTC)

Placentophagy is the practice of eating the placenta. A number of non-mammals are viviparous, and some of these do have placentæ. DuncanHill (talk) 18:15, 12 August 2008 (UTC)

Bismuth tin alloy

I bought some bismuth tin alloy in the form of shot for some magnet experiments. i was expecting it to be strongly diamagnetic, but I dont get any effect with NIB magnets brought close to it. Is Bismuth tin (the alloy) diamagnetic, of does it have to be pure bismuth? —Preceding unsigned comment added by 79.76.242.64 (talk) 20:34, 10 August 2008 (UTC)

I will just mind my own bismuth on this question. Edison (talk) 00:38, 11 August 2008 (UTC)

Maybe thats wise, as you seem to have developed quite a nasty lithp there! —Preceding unsigned comment added by 79.76.242.64 (talk) 02:08, 11 August 2008 (UTC)

The intro of the alloy article tells us that an alloy "usually has different properties from those of its component elements." Even if the alloy were the sum of its parts, you have to consider that adding tin "dilutes" the amount of bismuth present (therefore reducing its effect). At an extreme, maybe even the tin could counteract the bismuth (an extreme case would be perfect cancellation, for example US 5294268 ).

But in fact, the exact magnetic properties of Bi–Sn alloy have been studied (J. F. Spencer; M. E. John (Sep. 1, 1927). "The Magnetic Susceptibility of Some Binary Alloys" (login/subscription required). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character. 116 (773): 61–72. {{cite journal}}: Check date values in: |date= (help)) and the relationship of the ratio of the two metals in alloy to the magnetic susceptibility of the alloy is not simple at all. Not all ratios of the two metals given a magnetic alloy (and even the sign of the magnetic susceptibility changes!). DMacks (talk) 05:01, 11 August 2008 (UTC)

Apologies for not doing more research. The author of this webpage, just like you, tried levitation using the bismuth-tin alloy and failed because the shot was 3% tin. Interestingly though, these people were successful, although the shot they used might have been pure bismuth. --Bowlhover (talk) 22:52, 12 August 2008 (UTC)

Yeah Id seen the second link: thats where I got the idea. But not the first link-- thanks. I thought all bismuth shot would be approx the same composition (ie 1% to 3% tin). How do you know what you are using when shooting those little birdies? —Preceding unsigned comment added by 79.76.184.142 (talk) 00:00, 13 August 2008 (UTC)

August 11

Favored cigarette brands by ethnicity

Does anybody have this information? I'm doing research regarding the effects of racially-targeted advertisements on tobacco consumption. Kenjibeast (talk) 06:51, 11 August 2008 (UTC)

Hmmm. There could be some useful information here. Fribbler (talk) 10:21, 11 August 2008 (UTC)

Not about style of advertising but by volume: "2.6 times as many advertisements per person in African American areas as compared to Caucasian areas" [[8]]. Rmhermen (talk) 13:45, 11 August 2008 (UTC)

There have been a number of newspaper articles lately on the popularity of mentholated cigarettes amongst African-Americans, with brands like Kool and Newport targeting them specifically. The Newport article has a link to a study about brand preferences that looks useful, though it only breaks it down to "White", "Black", and "Hispanic." It's a few years old but it's a good start. --98.217.8.46 (talk) 17:01, 11 August 2008 (UTC)

What's this map projection?

I came across this unfamiliar projection. What is it? It looks like the Mercator, except with Greenland above North America. AlmostReadytoFly (talk) 13:59, 11 August 2008 (UTC)

It looks like it could be a take on the Goode homolosine projection. Fribbler (talk) 14:21, 11 August 2008 (UTC)

That does seem closest, but what the heck is Greenland doing? And Kamchatka? --jpgordon^∇∆∇∆ 00:23, 12 August 2008 (UTC)

sea anemones

how many years do sea anemones live ? thanks —Preceding unsigned comment added by 76.168.205.163 (talk) 17:40, 11 August 2008 (UTC)

From the BBC: "Sea anemones are anecdotally very long-lived, reaching 60-80 years and more. Like other Cnidarians, they do not age, meaning they have the potential to live indefinitely. Most fall foul to predators before a good age is reached. " Link:[9] Fribbler (talk) 17:56, 11 August 2008 (UTC)

(fascintating - does this mean anenomes are immortal?)87.102.45.156 (talk) 18:36, 11 August 2008 (UTC)

No, since they can still be killed. But they are "Biologically Immortal" in that their cells show no signs of ageing. Fribbler (talk) 18:47, 11 August 2008 (UTC)

(sorry to hijack this question) Do Sea anemones have any predators?87.102.45.156 (talk) 19:00, 11 August 2008 (UTC)

And are they the biggest/most complex 'immortals' ? 87.102.45.156 (talk) 19:02, 11 August 2008 (UTC)

(Outdent) Sea Anemones have few predators. Examples include the Butterflyfish and the Sea mouse. As for the largest Biologically Immortal animal, I'm not sure, but the Portuguese Man o' War must surely be up there. Fribbler (talk) 19:12, 11 August 2008 (UTC)

Thanks, I can't believe the 'sea mouse' has slipped me by all these 37 years. Well you're never too old...87.102.45.156 (talk) 19:32, 11 August 2008 (UTC)

Siphonophorae is interesting too - a colony of distinct individuals, unable to function separately, but not a multicellular organism as such. That's two things I've learnt today. (If you have any more please tell..). Thank you very much.87.102.45.156 (talk) 19:40, 11 August 2008 (UTC)

Hi. Please also see the articles turritopsis nutricula, an immortal jellyfish, and immortality. Thanks. ~AH1^(TCU) 00:09, 12 August 2008 (UTC)

Inexpensive sheets of transparent elastic material

For a hobby project, I'm looking for an inexpensive material with the following properties:

• elastic
• transparent (if possible), or translucent (if it's almost clear)
• available as, or can be made into, sheets of about 1 ft x 2 ft x 0.25 in

Basically I'm looking for something like the material used to make "gel" insoles, but I want it colorless and in a larger size. It would be extra desirable if the material can be easily molded into different shapes (it opens up more possibilities). Any suggestions? --71.185.228.156 (talk) 17:46, 11 August 2008 (UTC)

Check hobby shops for the covering for model airplanes. It is very lightweight, very strong, stretchable, and comes in clear or many colors. -- kainaw™ 17:53, 11 August 2008 (UTC)

Thanks for the suggestion. When I said "elastic", I was thinking about elastic as in providing cushioning, not elastic as in stretchable. --71.185.228.156 (talk) 18:04, 11 August 2008 (UTC)

You wan't a 'gel' material (like jelly ?) - how strong does it have to be - water based gels are very common but weak.

I think what you want is a silicon rubber or another elastomer

seach for 'silicon rubber sheet' if that seems suitbale - it should be easily sourceable in the dimensions you specify.

The alternive is a foam rubber.87.102.45.156 (talk) 18:35, 11 August 2008 (UTC)

Not being familiar with water-based gels, I don't know if what I'm looking for is stronger than water-based gels are. If a material is strong enough to be used for insoles, it's strong enough. --71.185.228.156 (talk) 20:39, 11 August 2008 (UTC)

McMaster-Carr describes "Latex-Free TPE": This transparent thermoplastic elastomer has a gel-like consistency to absorb vibration and conform to irregular surfaces. It is super stretchy and has great tensile strength. It is nontoxic and nonallergenic. That sounds more or less like what you're looking for. You can enter "3430" in their search box for the appropriate catalog page, or enter "elastomer" and click around a bit. -- Coneslayer (talk) 18:53, 11 August 2008 (UTC)

or any other Thermoplastic elastomer qv 87.102.45.156 (talk) 18:57, 11 August 2008 (UTC)

(To Coneslayer:) The "Ultra-Elastic Clear Gel Rubber" sounds very much like what I was looking for. Thanks. --71.185.228.156 (talk) 20:39, 11 August 2008 (UTC)

FYI, if you only need a small amount the manufacturers will often be willing to send you a free sample. --Sean 13:45, 12 August 2008 (UTC)

You could also try folding up sheets of saran wrap. --Shaggorama (talk) 22:20, 12 August 2008 (UTC)

Legs on a whale

A while back I read somewhere that occasionally, when they haul a whale out, the fishermen notice that their catch sports vestigial hind legs. Simple question - anyone have pictures? I managed to find images of rudimentary leg bones found inside the body of the whale (which I gather is not particularly uncommon) but as I understand it, the legs in question here are *external*. Anyone able to satisfy my curiosity? Thanks. --Kurt Shaped Box (talk) 18:55, 11 August 2008 (UTC)

Given how tiny whale legbones are, I find this, err, unlikely. However there was a dolphin captured in 2006 with vestigial hind flippers, which sounds more par for the course. --98.217.8.46 (talk) 21:25, 11 August 2008 (UTC)

Have you seen the photo in the 1921 article “A remarkable case of external hind limbs in a humpback whale”? The photo from that article is available on the Internet (e.g. here). In general see the Wikipedia article Atavism and the New Scientist article “The ancestor within all creatures”, 2007-01-15, issue 2586. --Mathew5000 (talk) 00:45, 12 August 2008 (UTC)

Some more on whales and hind-legs at [10]. DuncanHill (talk) 00:49, 12 August 2008 (UTC)

Eeek! So many answers in so short a time. I was going to link Atavism for that link. --Kjoonlee 00:51, 12 August 2008 (UTC)

Thanks very much for the answers. That was exactly what I was looking for. :) --Kurt Shaped Box (talk) 18:11, 12 August 2008 (UTC)

Terrifying. Plasticup ^T/C 17:14, 13 August 2008 (UTC)

How fast will a fishhook rust

This weekend I was fishing in a pond and someone caught a large snapping turtle. When the person realized that the ~25 weight on his line was a turtle, not a fish, he said that he was going to cut the line leaving the hook in the turtle's mouth. Worried about the turtle's health, I argued that we should try to get ahold of the turtle and remove the hook. Everyone else said I shouldn't worry, the hook would just rust and fall out in a day or two leaving the turtle unharmed. Is this reasonable? Slideshow Bob (talk) 19:43, 11 August 2008 (UTC)

I doubt that any fishhook would rust away within a couple of days - unless it was made out of a very reactive metal (which would just be a silly thing to make a fishhook from). It might fall out on its own, or it might not. Depends where it's lodged, really. There is also the risk of the turtle swallowing or becoming entangled in the trailing line. Your friend should probably have reeled the turtle in and pulled the hook out. I occasionally see fishermen accidentally hooking gulls when walking on the seafront, at which point, I run over and implore them *not* to just cut the line and condemn the gull to a likely death. --Kurt Shaped Box (talk) 19:51, 11 August 2008 (UTC)

No, it's not "reasonable" to think a hook made of high-quality steel (the usual material in modern hook manufacture - see Fish hook) will dissolve or rust quickly. The belief that it will has been, to some extent, fostered by advice such as the following, which is copied from a government website. The topic is how to handle a fish that you have caught and are planning to release.

Use long-nose pliers to remove the hook quickly 
without tearing or injuring the fish. 
If the fish is hooked deeply, cut the line and 
leave the hook in when the fish is released.

If someone is faced with a choice between leaving a deeply-embedded hook in a fish and ripping it out, leaving it in is almost certainly the better choice from the point-of-view of the possible survival of the fish. However this does not mean the hook will dissolve or rust quickly. Wanderer57 (talk) 21:51, 11 August 2008 (UTC)

How about cutting off the barb with wire cutters? Preferably, the entire rounded part of the hook should be cut off. Or would the fishhook be too hard for that?

Andme2 Andme2 (talk) 22:05, 11 August 2008 (UTC)

If the hook is accessible, cutting through it is a definite option. A decent pair of cutters will cut through the hooks typically used in inland fishing (unless someone is fishing for very large fish.) Wanderer57 (talk) 22:18, 11 August 2008 (UTC)

One can buy a range of hook cutters at any good tackle shop. DuncanHill (talk) 22:21, 11 August 2008 (UTC)

I'm not sure I'd want my fingers close enough to an angry snapping turtle's mouth to remove a hook. Can anyone comment on whether this would really be a good idea? APL (talk) 02:27, 12 August 2008 (UTC)

Yes, I was definitely worried about how exactly we could remove the hook without the turtle taking someone's finger (we didn't have a hook cutter), but it never got to the point where we had to do something. The line broke before we had a chance to decide what to do, leaving the hook and an inch or so of line in the turtle. Slideshow Bob (talk) 12:06, 12 August 2008 (UTC)

This should not be taken in any way as advice - but if I had to do it, I'd probably let it bite down on the end of my boot (or a piece of wood, or whatever was handy), then use the opportunity to firmly grasp the head from behind and immobilize it (similarly to how I'd hold a gull or large parrot to avoid being bitten). --Kurt Shaped Box (talk) 18:11, 12 August 2008 (UTC)

Hi Slideshow Bob. This is the Science Desk after all, and it sounds like you have access to fishhooks and water ... :-) Maybe try two experiments, with and without salt. Report back! Saintrain (talk) 13:13, 12 August 2008 (UTC)

Zucchini plants with white lines

I planted several Zucchini plants a few weeks ago. I bought them when they were already grown. On the leaves, squiggly white lines have formed. Is this normal? 66.53.216.249 (talk) 22:09, 11 August 2008 (UTC)

Most likely it's Powdery mildew. I experience the same issues with my squash plants in the late summer and fall. Juliancolton ^{Tropical Cyclone} 22:26, 11 August 2008 (UTC)

These aren't spots, but very thin lines. 66.53.216.249 (talk) 22:50, 11 August 2008 (UTC)

Leaf miners? --Sean 13:57, 12 August 2008 (UTC)

Black holes in the solar system?

mooved from the misc desk Julia Rossi (talk) 22:51, 11 August 2008 (UTC)

If uranus was the size of Jupiter, would Jupiter be swallowed to create the largest black hole in the solar system. —Preceding unsigned comment added by 79.76.161.244 (talk) 21:52, 11 August 2008

No. My anus swallows planets with ease. — Twas Now ( talk • contribs • e-mail ) 22:16, 11 August 2008 (UTC)

What are you, 12? --98.217.8.46 (talk) 01:40, 12 August 2008 (UTC)

There are no black holes in the solar system, so if one formed, then it would be the largest. But it takes way, way, way, way, way, way, way, way more mass than is contained in two gas planets to create a black hole. --Masamage ♫ 22:38, 11 August 2008 (UTC)

Actually, there are theories that there are tiny tiny black holes floating all around. To answer your question though, black holes need to be very dense, and uranus is smaller than jupiter, so making it the size of jupiter would make it less dense. -mattbuck (Talk) 23:25, 11 August 2008 (UTC)

Hi. Also, if two gas planets collided, it would still create a massive explosion, but I don't know how massive. Neptune, by the way, is denser than Uranus, and perhaps more massive as well, but I don't remember. A non-mini black hole would have to be more than 2,000 times more massive than Jupiter and Uranus combined, if I calculated correctly. If the sun collided with another star, there might be a supernova, but I don't know if there will be any remnants, and if there are, it's still likely to not be massive enough to create a black hole. Now, the LHC is planning to potentially create mini-black holes on Earth, but those are likely to evaporate quickly (we hope). Hope this helps. Thanks. ~AH1^(TCU) 00:01, 12 August 2008 (UTC)

Theory on tiny black holes heck, aren't we only days away from starting up our own black hole factory? Franamax (talk) 00:05, 12 August 2008 (UTC)

I'm guessing that the mention of black holes "evaporating" was meant in a general sense, but after reading that I'm wondering, if someone does create a black hole, how can they get rid of it?

If you made a micro black hole, you can control it by adding some positive charge, then orbiting some electrons to make a pseudo atom, and then doing a chemical reaction to fix it in place in some material. Perhaps to really elimenate them you would have to eject them from the solar system, but there may be no reason to do so if you can store it completely safely. The main danger might be a neutral black hole that could fall into the earth. But once it grabbed a proton, it whould be charged and then react with something. Electrons may be too hard to swallow in a micro black hole. Graeme Bartlett (talk) 03:17, 12 August 2008 (UTC)

To mix metaphors, a black hole is a bit of a white elephant. Wanderer57 (talk) 00:15, 12 August 2008 (UTC)

Wait a minute. If there is a possiblity of creating black holes, albeit small ones, in the LHC, then why is there not enough mass in Jupiter and Uranus combined for a black hole? There is certainly more mass in those two planets than is available to feed into the LHC. Wanderer57 (talk) 13:15, 12 August 2008 (UTC)

Presumably the poster meant they're not massive enough to make a black hole that wouldn't just disappear right away. --Sean 14:00, 12 August 2008 (UTC)

Or not enough mass to create a black hole through gravitational collapse (see Chandrasekhar limit and Tolman-Oppenheimer-Volkoff limit). If LHC creates micro black holes (big if) then it will do so by the alternative mechanism known as "hitting things together really hard". Gandalf61 (talk) 14:16, 12 August 2008 (UTC)

Okay, thank you. I didn't realize it was that easy to create black holes. So if I drop (say) a fifty pound lead weight from a height onto a big flat rock, I can create a black hole. How fast does the lead weight need to be going when it hits? Wanderer57 (talk) 14:46, 12 August 2008 (UTC)

99.999999% of the speed of light (or thereabouts). Gandalf61 (talk) 14:57, 12 August 2008 (UTC)

Oh. So we would really have to whip it in. Wanderer57 (talk) 17:54, 12 August 2008 (UTC)

Only violent events can form black holes because the forces involved must be enough to overpower electron degeneracy pressure and neutron degeneracy pressure. Collisions at any speed significantly below that of light are not energetic enough.

Even if Uranus had the mass of Jupiter and not just its volume, the gravity between the planets would not be enough for them to collide. From the articles Jupiter and Uranus, the former is at most 5.5 AU from the Sun and the latter is at least 18.4 AU, so the distance between them must be at least 12.9 AU. Using Newton's law of universal gravitation, if both planets had Jupiter's current mass, they would exert a force of 6.4 x 10^19 N on each other. The force between Jupiter and Saturn is 2.6 x 10^20 N, about three times larger, and yet you don't see them colliding at high speed. --Bowlhover (talk) 23:19, 12 August 2008 (UTC)

Deadliest lightning incident?

Hi. Wikipedia says it's either one of two plane crashes, one killing 81 and the other 91. However, I read a book a few months ago that contained a list of deadliest lightning incidents, and it lists one in an Egyptian army fuel depot in 1993 that killed 431 people, if I remember correctly. I don't know where they got the info from, and I couldn't find info on the Internet, but should this be included in an article even though I could only find one possible citation? Thanks. ~AH1^(TCU) 23:51, 11 August 2008 (UTC)

Is it a reputable book? If it's not a comic book or a novel, yes, add the referenced information. We can always check it ourselves. Leave a diff link here, I'll try my local (city) library. Internet confirmation is not required. Franamax (talk) 00:00, 12 August 2008 (UTC)

And on review, you'll need the name and author of the book for the cite (and preferably page number and ISBN ref) - I might not have been clear on that. Franamax (talk) 01:47, 12 August 2008 (UTC)

According to this "Environmental Assessment for Permanent Aviation Fuel Facility" thing[11], that was Dronka, Egypt, in 1994. This is may be the book [12]? It's in some Oil & Gas journal too, but that costs money to see. --Haikon 01:55, 12 August 2008 (UTC)

Oil & Gas Journal costs money to see? Oh, pshaw. List the ref here, just in case one of the legions has a subscription. And remember there's always the WP:LIBRARY if you want to see it yourself. The second link you give looks like a picture-book, so I wouldn't give it huge credibility. The first one carries some definite weight. Adding in the O&G J would nail it down beyond doubt (if it pinned down lighting as the cause). Franamax (talk) 03:34, 12 August 2008 (UTC)

• Hydrocarbon process safety: a text for students and professionals, Clifford Jones, PennWell Books, 2003, ISBN 1593700040 page 53 Ignition of fuel by lightnig
• doi:10.1016/j.jhazmat.2005.05.053 581 deaths railway derailment in Dronka, Egypt--Stone (talk) 11:27, 12 August 2008 (UTC)

Hi. It's the exact same book mentioned here. I could perhaps go to the library to pick it up today. It's a book about extreme weather by H. Michael Mogil is all I remember. Thanks. ~AH1^(TCU) 18:16, 12 August 2008 (UTC)

The Oil & Gas article ([13]) says "One report said the explosion was caused when flooding caused a bridge to collapse on pipelines. Another report said the depot was struck by lightning. About 15,000 metric tons of fuel were spilled," and that there were about 400 deaths. The J. Haz. Mat. article says only "The accident that caused most deaths (581) was a railway derailment in Dronka, Egypt, in November 1994." Hydrocarbon process safety says that aviation fuel and diesel leaked during a rainstorm and was ignited by lightning causing >410 deaths. -- BenRG (talk) 19:01, 12 August 2008 (UTC)

Hi. I have the source details:

• title=Hurricanes, Tornadoes, Floods, Heat Waves, Snow Storms, Global Warming and Other Atmospheric Disturbances
• author=H. Michael Mogil
• ISBN 978-1-57912-743-5
• pub date=2007, publisher=BlueRed Press Ltd., location=New York, NY
• num of pages=304
• info: Egypt; 430 fatalities; Army fuel depot; 1994
• page/chapter which info is located: pg 135, chapter: "Lightning"

please try to include the info in an article, with this and other sources. Thanks. ~AH1^(TCU) 22

25, 12 August 2008 (UTC)

Does the book list the incident as the deadliest lightning strike? According to page 2 of this book, a lighting bolt that hit a church in Brescia, Italy ignited 100 tons of gunpowder and killed 3000 people. --Bowlhover (talk) 00:19, 13 August 2008 (UTC)

Hi. Actually, no, I think it says either since 1993 or 1990. Please add all this info to an article. Change the info in the articles, and GWR isn't considered a reliable source anyway. Thanks. ~AH1^(TCU) 17:47, 13 August 2008 (UTC)

I have contradictory information. According to the "Environmental Assessment for Permanent Aviation Fuel Facility", "Blazing liquid fuel flowed into the village of Dronka, Egypt. The fuel came from a depot of eight tanks, each holding 5000te of aviation or diesel fuel."

According to Ben's source, "'the release occurred during a rainstorm and was said to have been caused by lightning. 420 fatalities reported One report said the explosion was caused when flooding caused a bridge to collapse on pipelines. Another report said the depot was struck by lightning. About 15,000 metric tons of fuel were spilled,' and that there were about 400 deaths."

What does your book say? I've so far added a brief description of the incident. --Bowlhover (talk) 08:19, 14 August 2008 (UTC)

Plate movement and longitude

Suppose you pick two monuments, one in Labrador and one in England. Because the North American plate and the Eurasian plate are moving away from each other, the east-west distance between the two monuments is increasing by about 34 millimetres a year, corresponding to about 1/600 of a second of longitude. My question is, assuming you could measure longitude (under WGS 84) with sufficient precision, after one year’s time would you find that (a) both longitudes had changed by about 1/1200 of a second each; (b) the longitude of the monument in England had stayed the same but the longitude of the monument in QuebecLabrador had changed by about 1/600 of a second; or (c) something else? --Mathew5000 (talk) 23:51, 11 August 2008 (UTC)

Isn't longitude-zero measured from the Greenwich observatory? In that case, the longitude of the monument in England would have changed only to a negligible degree, while the farther one would have changed to reflect the continental drift. Now as to the movement of the other monument from Labrador to Quebec, that would bear a little more investigation... ;) Franamax (talk) 23:57, 11 August 2008 (UTC)

WGS 84 longitude is relative to the IERS Reference Meridian (which is slightly east of Greenwich). I can' tell from our article whether or not it's fixed relative to the Eurasian plate or not. Algebraist 00:02, 12 August 2008 (UTC)

Yes. Reading in the IERS section, the reference meridian appears to be "on the pavement parallel to and northeast of Blackheath Avenue near the northwest corner of the fence surrounding the Pavilion Tea House". I'm not able to determine whether they move that fence every year to compensate for continental drift. :) I also see that "most countries have adopted a version of the IRM for their maps that is fixed to their own tectonic plate as it existed at the beginning of a specific year". So I'm all at sea here, the GPS article doesn't really help although it has some truly impressive mathematics. I know that my own GPS receiver has regional settings and map datums (i.e. WGS84), it also allows a date-time setting but I don't see how that correlates to continental drift rates. I know that I have to keep it on WGS84 when geocaching if I'm to have any hope of finding the cache - but I don't know if WGS84 is adjusted according to the regional settings!

So here's a call for help to any geographers or tectonicists out there: if we build a monument next to the Pavilion Tea House right at zero-degrees longitude, will it still be at zero next year? Will it matter if I'm measuring from it to Labrador, or to it from Labrador (i.e. will my GPS settings change anything)? Franamax (talk) 02:32, 12 August 2008 (UTC)

I don't quite read that part of the Prime Meridian article as saying that the reference meridian is fixed to that particular spot on the pavement, and if it does intend that, the citations don't support it. As for GPS, I believe that GPS is designed to use WGS84 as a "native" datum, and when your receiver is set to a different datum, the receiver is just using a certain conversion algorithm between WGS84 and the other datum. --Mathew5000 (talk) 18:07, 12 August 2008 (UTC)

I was asked to provide input here. I don't have the answer, but think for uses where measured accuracy is so important, I doubt latitude-longitude are used. In the U.S., there are state plane coordinate systems which cover specific areas and are relative to some point or monument marker in that region. I don't think GPS is designed to be that super accurate that 34 millimetres would make much difference. --Aude (talk) 20:02, 12 August 2008 (UTC)

After doing some searching, I found that WGS84 is not fixed relative to any continental plate. According to this webpage:

"A first step towards more consistency between the WGS84 and ITRS took place in 1993 when the complete WGS84 network was recomputed with respect to 8 GPS stations fixed to their ITRF91 position ([18]). This realization is known as WGS84 (G730), "G730" indicates its official implementation on GPS week 730 (Jan. 2, 1994) [...] Further improvements to the tracking station coordinates in 1996, led to WGS84 (G873). This realization consists of 13 sites (NIMA and Air Force sites); only one of them is located in Europe, namely in the UK"

"The main disadvantage of the ITRS and WGS84 lies in the fact that they are global systems. This means that, due to the plate tectonics, the coordinates in the different continents move with respect to each other. For example, expressed in the ITRF2000, the coordinates of Brussels change with about 2.5cm/year."

This suggests that the WGS84 is defined by GPS tracking stations with no compensation for continental drift. As the above users said, many countries/continents define their own datums that are fixed relative to their plates. Europe uses the European Terrestrial Reference System, North America uses NAD 83, while Australia implemented GDA94 (http://www.geoproject.com.au/gda.faq.html).

Incidentally, there is a datum that addresses tectonic movement (http://www.ngs.noaa.gov/CORS/Articles/Reference-Systems-Part-3.pdf). Those are the International Terrestrial Reference Frames defined by the strangely-named International Earth Rotation Service. The ITRF is not fixed relative to the European plate; rather, the combined angular momentum of all plates is assumed to be 0 and drift velocities of stations defining the ITRF are calculated with that assumption. --Bowlhover (talk) 22:47, 12 August 2008 (UTC)

Thanks; that four-part series by Snay and Soler [14] is very good reading, just what I was looking for. I will make some appropriate changes to longitude and other articles. --Mathew5000 (talk) 19:49, 13 August 2008 (UTC)

Glacial compensation by GPS

This question inspired me to ask about glaciers, which move much faster than continental drift. If any location on a glacier has a GPS coordinate assigned to it, this coord would seem to require frequent updates or some way to automatically account for the movement of the glacier. How do GPS units handle this ? (One option is to just exclude any location on a glacier, I suppose). StuRat (talk) 14:28, 13 August 2008 (UTC)

GPS units work just fine on glaciers. There is bedrock beneath glaciers, which does not move (except for continental drift), and in some spots the bedrock is exposed. The coordinates of locations on the bedrock really don't change. The glaciers do move, their coordinates do change. You can measure the movement of crevasses or other features on glaciers, by looking at the change in coordinates to determine how fast the glacier is moving. --Aude (talk) 16:33, 13 August 2008 (UTC)

You seem to be using the GPS to measure movement of the glacier, which is fine, but what about people who want to find features on the glacier, like crevasses. Unless those coords in the GPS unit are updated frequently and/or automatically, a GPS user may say "how far to the crevass ? Just a few more feeeeeeeeeeeeeeeee...splat !". StuRat (talk) 00:39, 14 August 2008 (UTC)

Your question is “how do GPS units handle this” but I think what you are really asking about goes beyond the basic function of a GPS receiver. The basic function is to use satellite signals to calculate latitude, longitude, altitude, time, and usually velocity. It carries on those functions without any “knowledge” of whether it is in a city, in the ocean, on a glacier, or wherever. If a particular GPS unit is able to tell you the name of the street you’re on (for example), that function is a frill: not part of the information supplied by the Navstar satellites but rather information that resides inside the GPS unit — sometimes you have to buy maps separately and load them in the unit either on a card or through a USB port, or the unit may have been sold with certain cartographic information already loaded in its memory. If your unit was designed for use in an automobile, or for use in a yacht, or whatever, then it probably won’t come loaded with detailed information on the features of individual glaciers. --Mathew5000 (talk) 06:44, 14 August 2008 (UTC)

While finding the position is certainly the core feature of GPS, a unit that doesn't put such info in context is of rather limited use. People on land want to know which geographic features are nearby, people in boats want to know which currents, shipping lanes, and ports they are near, and people in planes want to know which mountains, airpots, and national boundaries are in their proximity. You can, of course, take the GPS coords and then look them up on a series of maps and charts, but this can be time consuming, and possibly fatally so, if you are moving at a high velocity while attempting to determine your position relative to important features. StuRat (talk) 17:46, 15 August 2008 (UTC)

If you are working on a glaciers (such as a researcher), you would use recent satellite images as a "map". The satellite images would be referenced in relation to the bedrock. And the glacier is all relative to the bedrock below or whatever is sticking out. The exact precision of the GPS coordinates for this purpose of navigation isn't that important. One might use surveying techniques or something else to be more exact for scientific purposes. --Aude (talk) 10:10, 14 August 2008 (UTC)

I'm not thinking of scientists, but of explorers, adventurers, and mountain climbers, who would prefer to avoid falling down a crevass. Isn't there a GPS/navigation unit avilable for such people that has automatic updates provided for the revised positions of such features ? StuRat (talk) 17:31, 15 August 2008 (UTC)

August 12

MDS , Myeloproliferative Dysplasia.

This question is for Donna Reister-Piper.

Hi Donna, you have been so kind to Gus, who I believe has spoken to you about my father who is suffering from MDS, and is currently receiving treatment using Hydroxy Urea.

We are in Adelaide, South Australia, and Gus is a relative of ours.

My father has had a Bone Marrow biopsy, and lots of blood tests.

I would like to ask you, what information can I provide to you from his case notes that would help you for his case. There are two volumes at this stage, and I would be more than happy to copy and send the information that you need, including blood tests, biopsy results and the like.

I would also be happy to pass any questions on to the Haematologist, if I can not get this information myself.

I happen to work here at the treating hospital the Royal Adelaide Hospital, so I should be able to get most of the information that you need.

Iwould like to express sincere gratitude for your help.

Thank You

Peter Spyropoulos

—Preceding unsigned comment added by Pspyropo (talk • contribs) 02:28, 12 August 2008 (UTC)

Who is Donna Reister-Piper? This is the Wikipedia Reference Desk, I don't think this is where you intended to post that message. --Tango (talk) 05:33, 12 August 2008 (UTC)

It wasn't intended to be private because it starts with "This question is for Donna Reister-Piper". Maybe said person is a Reference Desk contributor? --Bowlhover (talk) 06:23, 12 August 2008 (UTC)

genaral knowledge

Name the bird species which can only eat with its head up side down?59.98.68.47 (talk) 08:10, 12 August 2008 (UTC)

The flamingo? --Bruce1ee^talk 08:26, 12 August 2008 (UTC)

10 books in science

What ten books would you recommend to a social science or philosopher willing to learn something about science? One I have thought of is Lectures of Physics of Feynman, another is Calculus of James Stewart. I want general, complete books, not necessarily with historical value, but more like a thourough manual, covering Maths, Physics, Chemistry and Biology. Mr.K. (talk) 10:32, 12 August 2008 (UTC)

I would strongly recommend Mathematics for the Million, by Lancelot Hogben, and Facts from Figures, by M. J. Moroney as a start. DuncanHill (talk) 11:33, 12 August 2008 (UTC)

I ♥ The Flying Circus of Physics for its accessible treatment of physics in everyday life. --Sean 14:05, 12 August 2008 (UTC)

Feynman is good, but the Lectures are too technical. Try the "Six Easy Pieces" version, or something else by Feynman. 128.165.101.105 (talk) 16:41, 12 August 2008 (UTC)

I would look for a modern textbook written for a college freshman course in the particular subject (Biology, General Chemistry, ect.). The forward of a textbook often describes its intended audience or what sort of course it is designed for. For your purposes, I don't see value in looking for famous or classic names. ike9898 (talk) 17:01, 12 August 2008 (UTC)

I agree: The Feynman Lectures are amazingly well written and incredible to read...if you already know physics. To be honest, I find that they make a pretty miserable textbook. On the other hand, Surely You're Joking, Mr. Feynman! is an amazing book that is a transcript of some narrations that Richard Feynman made. It isn't instructive on the discipline itself, but I think gives some interesting insights into its culture, though I wouldn't take it as a last word. You have to keep in mind, Feynman was a (lovable) weirdo. EagleFalconn (talk) 21:06, 12 August 2008 (UTC)

Fun question! I'd suggest The Structure of Scientific Revolutions by Thomas Kuhn, A Brief History of Time by Stephen Hawking, Neurophilosophy by Patricia Churchland, Philosophy of Natural Science by Carl Hempel, and The Selfish Gene by Richard Dawkins to name a few good reads. Kuhn is an absolute must: go buy that book right now so you can earn the right to use the word "paradigm" in casual conversation. --Shaggorama (talk) 22:15, 12 August 2008 (UTC)

If you want to throw in an easy book, A Short History of Nearly Everything was quite enjoyable for me. --Kjoonlee 02:34, 13 August 2008 (UTC)

I commend your efforts if you intend to use the Stewart book. That is a fantastic calculus book that will not cut corners. The other suggestions thus far have also been great books, but they will provide more of a "philosophical insight" rather than a technical proficiency. I am of the viewpoint that you can synthesize any philosophical opinions you want to have about science with a lot more perspective if you actually get in to the gory details. I would also recommend the Tipler series [15] of introductory physics books ("Physics for Scientists and Engineers"), which are easy to understand but encourage the application of Calculus to basic physics. These books are categorized into three volumes intended to be taught as separate classes - mechanics, electromagnetism, and "modern" physics. Many physics educators debate whether this is an effective classification of physics concepts (they prefer a sort of "holistic" approach), but it has historically been the standard "sequential" way that most scientists are trained. The Feynmann lectures are really very technical; I would recommend them after you already had a thorough grounding in basic college-level physics. You will appreciate them, as well as many of the "conceptual" physics books more after you have the technical rigor. Nimur (talk) 18:07, 13 August 2008 (UTC)

Chemical Equilibrium question

Hi. I've been looking around for a while in the chem section of Wikipedia, but I can't seem to understand a few things concerning the equilibrium of reactions exactly. I was hoping for a simple tutorial, but, then again, there may be no simple way to describe this...

First, a friend of mine who's studying to be a chem teacher told me a simple rule to determine whether two diatomic salts will react or not, saying that the one with the highest electronegativity sticks with the one with the lowest (e.g. CuF + NaCl react to form CuCl + NaF, but not the other way around). Is this true in all cases?

Secondly, for salts that are not diatomic, I would have to calculate the electronegativity of the conjugate base, which, he said, was the geometric mean of the electronegativities of all atoms forming the conjugate base (e.g. for SO₄^2-, the electronegativity χ_SO4^2- = (χ_S¹ * χ_O⁴)^1/5. It seems to me that this ignores the spatial arrangement of the atoms, can it be true nonetheless?

Finally, for any reaction (n_aA + n_bB + ... -> n_pP + n_qQ + ...), with n_i being the stoichiometrical coefficients, how can I find out step by step whether the equilibrium is towards the reactants of the products?

Thanks in advance for your help, Danielsavoiu (talk) 13:08, 12 August 2008 (UTC)

1. Yes generally true.

2. You are right - but the approximation is often good, but not always.

3. See Chemical equilibrium - tables of 'energies' of the individual products and reactants can be used to get an 'energy' change for the reaction - (you need to ue the right energy depending on whether or not the reaction is contained or is open etc) - this may require more explanation so ask if so.87.102.45.156 (talk) 14:29, 12 August 2008 (UTC)

One exception to the first rule of thumb (and probably not the only exception) is where you're dealing with a metathesis reaction (old guys like me will call these double displacement reactions) that generates a precipitate from two soluble compounds. (Formation of a precipitate will pull ions out of solution and drag the chemical equilibrium to that side.) TenOfAllTrades(talk) 14:47, 12 August 2008 (UTC)

@87.102.45.76: Thanks, I had a look, but it's still a bit technical. I do not fully understand the terms entropy, enthalpy and gibbs free energy to be specific. If you could, please provide a description of these terms as for beginners and provide a formula to obtain a final result X whose sign would indicate to which side the chemical equilibrium of the reaction inclines. I presume this X is the difference in Gibbs free energy, but I still do not know how to obtain it. Something to do with bond energies, maybe?

If the gibbs energy is negative then the reaction goes to the right.( If the gibbs energy is 0 then then equilibrium is 50/50 )

Sometimes gibbs energy is not use an helmholtz free energy is used (in a sealed system for instance)

The first paragraph in entropy gives a good introduction to what it is

The very last equation in the section Chemical_equilibrium#Thermodynamics gives a relatiobship between gibbs energy and equilibrium.

Gibbs energies are calculated/estimated from experimental results and from theoretical work - again that is a book in itself.

I'm sorry I can't be more helpful today but I am very sick. Please try obtaining a book introduction on these topics. Hopefully someone else will be able to help you more.77.86.119.155 (talk) 19:53, 13 August 2008 (UTC)

@TenOfAllTrades: Thanks, I did know there would be an exception in similar cases... Danielsavoiu (talk) 16:03, 12 August 2008 (UTC)

1) I would say the most general way to answer this question would be to say that double displacement reactions take precedence (don't worry Ten, new foagies like me still call them that), and after that the rule your friend gave you. By the way, that rule falls under the Hard-soft acid base theory, which is a good place to read up on it. Mind you, both of these rules are generally true in the long term, not the short term. All sorts of crazy things happen long term. HSAB will usually win in the end.

3) The general answer is to compare the stability of the reactants to the stability of the products. This requires what is amorphously called "chemical intuition" which usually actually means "I've seen a lot of compounds and know some general trends." There is the quantitative approach above, but that requires knowing about equilibrium constants, and if you knew what those were it wouldn't be an issue. Its often relatively easy to come up with a qualitative answer, knowing definitively on a quantitative level is usually much harder to do from scratch.

EagleFalconn (talk) 20:39, 12 August 2008 (UTC)

which type of ether used for anesthesia for child in 1954

In 1954, at the age of two-and-a-half, I had an operation at a large hospital in Illinois. The anesthesia used was "ether," and I'm trying to find out which type of ether it would have been. My end goal is find out what the physical side effects would have been following the operation. I've looked at several articles about different kinds of ether on Wikipedia and don't have enough science background to tell the difference or to guess which one would have been prevalent in a major hospital at that time. Thanks for any help. —Preceding unsigned comment added by Abcol4info (talk • contribs) 16:19, 12 August 2008 (UTC)

Diethyl ether is the classic one, used as an anesthetic since the 1850s. If someone says "ether" with no further specification referring to an anesthetic, that's probably what they mean. Other ethers like methyl propyl ether and vinyl ether are also anesthetics, but they wouldn't be called simply "ether". 128.165.101.105 (talk) 16:35, 12 August 2008 (UTC)

Diethyl ether reminds me of an Osprey. -- Coneslayer (talk) 16:45, 12 August 2008 (UTC)

Sometimes when people say ether, they mean petroleum ether. ike9898 (talk) 16:55, 12 August 2008 (UTC)

True, but that's never been used as an anaesthetic to my knowledge. Algebraist 17:10, 12 August 2008 (UTC)

At the risk of violating WP:OR, after anesthesia via ether, you tend to throw up. — OtherDave (talk) 18:13, 12 August 2008 (UTC)

Ditto. Edison (talk) 23:31, 12 August 2008 (UTC)

Empyrean vs. E8

I was curious about the overall shape of the E8. What does it mean scientifcally, and why does it appear to imitate other famous symbols such as the shape in Dante's Divine Comedy ? 69.157.227.243 (talk) 16:48, 12 August 2008 (UTC)

Well, I don't think the "imitation" is very strong in that instance. It doesn't really resemble it in a strict way, other than the fact that it is a set of interlocking circles. Interlocking circles in general have been common symbols for humans for a long time (see, e.g., mandala). But that particular association seems not very specific to me in this case. Personally I think E7 looks more similar to that example than E8, but it's just a coincidence, once again. One might also spend fruitless time wondering by E7 looks vaguely like the cross-section of an atomic bomb. General resemblances between similar shapes likely has no strict meaning other than the fact that they are similar shapes. --98.217.8.46 (talk) 17:06, 12 August 2008 (UTC)

The Dynkin diagram of E8

Piping. Note the resemblance with the dynkin diagram

What you see is a graph, in the sense of dots connected by lines. Graph theory is the study of graphs. When I took a course in it, one thing the instructor insisted on is that graph theory dosn't deal with the shapes, it dosn't deal with how the dots are positioned relative to each other. Jumble the dots around, but as long as you don't break the links between them, the graph stays the same. Certain arrangements, like the one in the picture, can be useful in showing or even proving properties of the graph, but so can E8's Dynkin diagram, which looks decidedly unmystic. :More generally, an advice I heard from a mathematician is to not focus one's attention on the objects, like "But what IS the number five really?" but instead focus on the relationship between objects. That's where the real stuff is. :-) EverGreg (talk) 16:42, 13 August 2008 (UTC)

Fractals resembling natural forms is a much more interesting concept. Plasticup ^T/C 16:49, 13 August 2008 (UTC)

A conceptual problem in Physics

(I could not think of a better name for this problem, if you can be concise, kindly rename)
Problem:
Consider two earth like planets, A and B, a distance of 1 lightyear apart. Also, assume that these two planets are geosyncronous to each other. A string/rope of length 1 lightyear is tied to one of the planets A and a mass, say "x" kg is hanging on the string close to the other planet B. It is certain that no signal can travel from planet A to planet B in less that 1 year, the question is, if I cut the string at planet A, when does the mass start falling on planet B? Also, what constraints have to be kept in mind, and what assumptions have to be made? (for instance, is it possible for the mass to stay in its original place even after the string/rope is cut, as the gravitational pull of the other planet keeps the rope in "mid air"). —Preceding unsigned comment added by Akanksh (talk • contribs) 18:31, 12 August 2008 (UTC)

I wonder what the mass of the string is, also the mass of the mass, also how far above the surface of B the mass is initially. If the string length is exactly the same as the distance between the planets, the mass might be resting on the surface of B to begin with. Also, how stretchy is the string? Wanderer57 (talk) 18:57, 12 August 2008 (UTC)

(I'll be honest. I'm not going to be able to answer your question, even if you answer all of mine. But somebody else might.) Wanderer57 (talk) 18:57, 12 August 2008 (UTC)

This is close to a very common science question. The basic part of the question is: "If I have a string/rod/bar/rope connecting two things that are very far apart and I cut/pull/wiggle/twist one end, why doesn't the other end get the information instantaneously? Where's my Nobel prize for figuring out faster-than-light data transmission?" To put it simply, nothing is perfectly solid. The string is made up of mostly empty space inside of and between atoms. Each atom reacts to changes from the atoms around it, one after another. At best, you can get a change in one end of the string to reverberate down the string near the speed of light. In reality, it will be much slower (when you drop a rope, the change doesn't make a sonic boom as the change travels down the rope). So, the true answer depends highly on the makeup of the string/rope. -- kainaw™ 19:07, 12 August 2008 (UTC)

Rope is made of a bunch of atoms which are electromagnetically bound to nearby atoms. The bonds have a certain amount of elasticity, i.e. they obey Hooke's law, i.e. you can think of them as rubber bands. In the initial setup, the mass on planet B doesn't fall because the bonds in the end of the rope stretch until the restoring force (tension) counters the gravitational force. The atoms a little higher up the rope are pulled down by that elastic force and by gravity, but they don't fall because the rope above them is stretched even more. Eventually you get out of the effective range of B's gravitational field and the remainder of the rope is under roughly constant tension until you get to planet A. Now, when you remove the mass at planet A, the downward force on the nearby atoms will decrease, so they will accelerate upward, reducing the tension in the bonds above them until it starts pushing them downward, and then they'll go down again, and so on, oscillating until they reach a new equilibrium state. But in this new equilibrium state the atoms above are being pulled down less than before, and they will start doing the same thing (before the lowermost atoms have settled down, actually). And so on, propagating along the rope. But the propagation takes time—I think it will happen at the speed of sound in the rope, which I think will be around 10⁻⁵ c, so it could take 100,000 years. At any rate it will take at least one year. The atoms near planet B will continue defying gravity until the ones above them stop pulling upward, which they won't do until the ones above them stop pulling upward, and so on. It's a real life skyhook. (For some definition of "real life", anyway.) -- BenRG (talk) 19:32, 12 August 2008 (UTC)

You've mentioned everything I intended to say, but I'll post a link: http://math.ucr.edu/home/baez/physics/Relativity/SR/scissors.html --Bowlhover (talk) 22:00, 12 August 2008 (UTC)

Perhaps I'm misinterpreting Kainaw's answer, but if you simply pull on the string it wouldn't take any time at all for the guy on the other end to realize it because it's connected. Even if the string is a zillion light years across they would know it the millisecond you pulled on it because all of the string is moving. Now where is my Nobel prize?! ;) --Sam Science (talk) 01:49, 13 August 2008 (UTC)

That is exactly what I was explaining. When you pull on your end, the atoms on your end move. They then (after some time) pull on the atoms near them. Those then (after some time) pull on the atoms near them. This continues down the string until, eventually, the other end of the string notices the pull. It does not happen instantly. It happens, at best, near the speed of light. In reality, it happens slower than the speed of sound. -- kainaw™ 02:08, 13 August 2008 (UTC)

I'm still having trouble with this. When you move something, all of it moves. At exactly the same time. Now I'm picturing the rope already stretched to the max. As tight as you can stretch it without breaking. So if you pull it, the other end also pulls. It's instantly known. Let's say you're at a stoplight in a light year long limo (play along here). If you're in the back seat, you will know the absolute second the driver hits the gas. Instant, faster than light communication! The Nobel prize pays almost two million bucks, right? Now if you'll excuse me for a moment I have to call my boss (it's 2am here), and tell him to shove it. Sam Science (talk) 02:53, 13 August 2008 (UTC)

An actual limo or rope is at most several metres long. Since compression/tension forces travel at approximately the speed of sound, which is a few kilometres per second in solids, it only takes a millisecond or so for you to feel the brakes' effect or the rope pulling back. A millisecond is not long enough for you to perceive, so you believe forces travel instantaneously. As Kainaw and Ben explained, this is only an illusion and sensitive equipment can prove it false. --Bowlhover (talk) 04:09, 13 August 2008 (UTC)

And, in the case of an accident, the deceleration felt by the passengers is designed to be significantly less than that at the point of impact, due to the crumpling of the vehicle. So, the car most definitely does not move as one solid object in this case. StuRat (talk) 14:06, 13 August 2008 (UTC)

One case where the waves in seemingly solid objects are visible is earthquakes, where the p-wave (5 to 8 km/s) and s-wave have measurable speeds much slower than the speed of light (300,000 km/s), but some 20 times the speed of sound (0.343 km/s) in air. This speed is close to the speed of sound in a solid. StuRat (talk) 14:06, 13 August 2008 (UTC)

Note that in your hypothetical limo idea, 1. it would still take time for the signal from the driver's petal to make it to the engine (even if this was fancy electronics the upper limit would still be the speed of light), 2. just because the back of your limo has started to accelerate does not mean the front will have. The momentum will have to go along, atom-by-atom, until the atoms at the front know that anything has moved. You can see this happen on a different scale with long freight trains, where the back of the train is doing something very different than the front of the train (and sufficient "slack" has to be built into the system or else the changes between the different parts of the train would rip it apart—a mile-long-entirely-rigid train would tear itself apart very easily). --98.217.8.46 (talk) 17:11, 13 August 2008 (UTC)

SamScience seems to insist that solid metals move as a single unit, and remains unconvinced by our technical explanations about atomic forces and such. Maybe the easiest way to demonstrate is with a visual example. Consider a piece of sheet metal. Wobble one end of it. The sheet metal, even though it is solid, does not retain its shape perfectly. It takes a while for your wobbling to have any effect on the other end of the sheet metal. In fact, you can very precisely model the motion and the deformation of the metal. Sheet metal will propagate waves slowly enough for you to visually see the deformation. If you switched the geometries around to, say, a steel pipe, you might not be able to see the wobbling visually, but it would still happen. If your pipe / bar / limo / whatever were lightyears long, the propagation delay will not only be measurable, but the acoustic wave will be significantly slower than an electromagnetic wave, and it will damp out and attenuate due to thermal and other losses. This is why when humans built transcontinental telegraph lines, they did not try to send signals by wobbling the wire acousto-mechanically in Boston and hoping that would be able to tap out Morse Code in San Francisco. Nimur (talk) 18:25, 13 August 2008 (UTC)

Self-sacrifice in non-human animals?

Be it a soldier throwing himself on top of a live grenade in order to shield his comrades from the blast, a bodyguard taking a bullet for his president, a random passer-by jumping into the road to push a child out of the path of an oncoming car and taking the hit themselves, or someone running into a burning building to save a complete stranger, human beings sometimes make a spontaneous, conscious decision to potentially give up their own life for that of another (unrelated) individual.

Are we unique in the animal kingdom in that respect? Does science know why we do this? --Kurt Shaped Box (talk) 18:34, 12 August 2008 (UTC)

We have an article on Altruism in animals. Fribbler (talk) 18:35, 12 August 2008 (UTC)

I read the article before I posted here. It doesn't specifically address my query. Unless I'm reading it wrong. I vaguely understand altruism - but the above human behaviour would be akin to a mouse running in front of another mouse (a mouse which it had never seen before) when it saw a hawk diving from the sky with its talons extended in order that the first mouse might be saved. --Kurt Shaped Box (talk) 18:52, 12 August 2008 (UTC)

There are various documented cases of dogs pulling their owners out of burning buildings, and dolphins have been known to protect swimmers from shark attacks. --Shaggorama (talk) 21:42, 12 August 2008 (UTC)

There are some examples from the Altruism in animals article which may cover the "throw yourself on a grenade" type situations. The examples with baboons and vervet monkeys are situations where the animal incurs a risk in order to protect others. If you want a situation where death is assured, as opposed to "merely" increased in likelyhood, honeybees are the classic example. Your common honeybee has a barbed stinger, which rips itself out of the body after stinging. However, honeybees will attack dangerous animals, killing themselves while protecting the rest of the hive. If you want to nitpick about conscious decisions, you'll have to have a good delineation about where consciousness begins in the animal kingdom. -- 128.104.112.147 (talk) 22:54, 12 August 2008 (UTC)

I would contest that worker bees have no choice in the matter. They were born to serve and obey the Queen unto death and have no other purpose beyond this. I doubt that they can even understand the concept that the continued existence of the individual is a good thing for the individual. I wonder if the Queen knows? IMO, for the purposes of this question, the animal must be able to make the decision to either act, run away, or do nothing. --Kurt Shaped Box (talk) 23:08, 12 August 2008 (UTC)

First off, you're falling into the all too common fallacy of thinking that, because she's named "Queen", the queen bee has some sort of command over the hive. In reality, she is as much as a prisoner/egg-laying-machine forced into service to the hive-as-a-whole as a worker bee. At any rate, regarding the second point, there is a huge gray area as to which animal can make deliberate decisions, and which are "merely" following instinct. When a meerkat gives a warning call, is it making some sort of decision, or is it just following instinct? How can we tell? Where does instinct leave off and "consciousness" take over? Heck, when a human polishes off the rest of a jumbo order of fries, is that a conscious decision, or is it merely mindless instinct left over from our hunter-gatherer days? -- 128.104.112.147 (talk) 16:45, 13 August 2008 (UTC)

I don't think rationality or free will is even the issue here. It's impossible to rationally justify any action in a vacuum. You need a utility function or a moral code or a set of axioms of behavior or some kind of starting point. There are no logical tautologies of the form "my best course of action is such-and-such". The reason people want to live is that it's adaptive: people who survive to live another day have more offspring. That's all. It's not because any rational being will automatically desire to prolong its own existence. We instinctively want to live and we rationally want to live; it's the same thing. If we ever build intelligent robots we'll have to give them goals, and there's no reason to duplicate Homo sapiens' crazy mix of selfish and cooperative motivations. We could just make them cooperative, and we could furthermore make them value human life more than their own. And they would. Not because they're stupid, not because they're unconscious, not because they lack free will, but because their goals are different from ours. -- BenRG (talk) 01:17, 14 August 2008 (UTC)

Dear Ben, have you ever heard the expression, there are no atheists in foxholes? I get the impression that you've never been afraid for your life. I don't mean that disrespectfully. It's just that different people have had different experiences. I just think that self-preservation is a little more basic than wanting to stay alive to propagate. The other day, I was backing my car up to an air hose, and about the time I put on the brake, the car next to me started to pull forward. For a moment, it seemed that my brakes weren't working and that my car was going to roll down an imbankment into a tree. I felt fear that seemed very odd to me because I'm not a naturally afraid person. When I realized that the fear was totally unwarranted, I felt even more curious about having the feeling. Why? I still don't have a clue. Anyway, I just think that it is very natural for a person to be afraid to die, and it takes a conscious choice, for whatever reason, to sacrifice your own life for that reason alone. —Preceding unsigned comment added by 98.163.102.226 (talk) 18:12, 14 August 2008 (UTC)

A classic altruism in animals involves one bird sending out an alarm when a predator approaches, aiding the flock as a whole but calling our their own location to the predator. (Note that before you start nitpicking, the question of what "really counts" as altruism in animals is one that has been debated up and down for years by philosophers and zoologists. Let's not pretend we are going to resolve it here. There are many books on the question of altruism in animals, whether altruism itself ever truly exists, and so forth.) --98.217.8.46 (talk) 00:43, 13 August 2008 (UTC)

I wonder if animals really know about death. Through experience, an animal may learn that other animals may injure it and cause pain. And a predator kills other animals, but does it realize that could happen to itself? Andme2 (talk) 02:22, 13 August 2008 (UTC)

Well, they seem to value life, if that means anything. As for "really" understanding death, I doubt most people do... much of our response to death is no doubt instinctual, required so that we don't just blithely walk off cliffs and whatnot. Even a housefly knows that when I'm chasing after it with a fly swatter that it needs to hustle it's ass out of there... --98.217.8.46 (talk) 15:21, 13 August 2008 (UTC)

One creature that doesn't seem to value its own life is the cranefly. I know that I keep raggin' on this species here - but they don't even attempt to move when you approach to catch/swat them. I've seen the local birds just walking around and picking them up from the grass. --Kurt Shaped Box (talk) 15:41, 13 August 2008 (UTC)

I know it's obvious, but plenty of animals risk themselves to protect their young. Pretty much all mammals, for starters. Plasticup ^T/C 16:40, 13 August 2008 (UTC)

I don't know about craneflies in particular but I find it hard to believe any animal has no response to a common prey (our article mentioned birds often eat them). No response to being swated is easier to understand, if it's not a frequent threat or associated with something that's a frequent threat, they may simply not recognise it as a threat. The other issue may be that being cold-blooded animals, they may get a bit 'dopey' in the winter (I'm presuming you live in a temperate country) or otherwise temperatures outside their optimal clime. As an example, mosquitos in New Zealand even in the summer are rather easy to catch (there are few or no mosquitoes during winter, they can't survive). However before you think mosquitos are dopey easy to catch things, try living in Malaysia for a few months. Nil Einne (talk) 19:09, 13 August 2008 (UTC)

Here in England, the craneflies come out (in their thousands) in the warmth of late spring/early summer, so I don't think that it's a temperature issue. Their primary means of self-preservation seems to be the shedding of limbs when caught. They certainly can't fly away from anything that has the capability to track and give chase when it realizes that it has a mouthful of spindly leg - when they do 'fly', they pretty much go where the wind blows them, wobbling around and crashing into anything and everything. I'm not kidding here - the gulls just glide along at a ridiculously slow pace a few metres off the ground and snap them out of the air in their hundreds. --Kurt Shaped Box (talk) 00:11, 14 August 2008 (UTC)

People have already mentioned dogs pulling owners out of burning buildings. I would go further and point out it's possible to train many animals particularly domesticated ones to do a variety of things. This would include running out a road to save a child for instance (and many dogs know roads are dangerous). Police dogs will generally not hesitate to attack a criminal. I would presume they receive at least some training which teaches them "guns=bad" for example and would often know they are at risk of injury. You may argue it's not the same thing but I would disagree. Much of what you describe above are IMHO likely learnt behaviours. A bodyguard will take a bullet to save the person he/she's supposed to be protecting because it's his/her job and it's the right thing to do since the person they're supposed to be protecting is more important than them. The same bodyguard is probably generally not going to take a bullet to save the life of a homeless person. A soldier is taught about duty, comradeship etc. The same soldier is not going to jump in front of a grenade to save an enemy (he/she or his/her comrades may have thrown the grenade!). A random passerby is quite likely to jump in front of a car to save a child or perhaps 'senior citizen'. Less likely if it's a fit adult. Even less likely if it's someone they despise (e.g. most Americans are not going to jump in front of car to save Osama bin Laden). All these are what we call 'ethical' choices and they are associated with certain behaviour and a big part of it is IMHO learnt (obviously it's partially instinctive). As I've said, you can teach animals similar things. As far as we know, all other animals probably don't have quite the level of detailed thought enabling them learn and react in such detailed ways but they are still capable of learning to react in certain ways in certain situations even if it may cause harm to themselves (and as the pet examples show, an animal which developed a strong bond with an individual may try to protect it even if it wasn't specifically taught to react in that way). Nil Einne (talk) 18:55, 13 August 2008 (UTC)

I'm not going to argue with that. What a good answer (I'm not saying that the others weren't good too). Thanks a lot. --Kurt Shaped Box (talk) 00:01, 14 August 2008 (UTC)

Can a fly, or any other living thing except humans, conceive being dead - not being aware of anything? Perhaps they just live in the present.

A predator may anticipate the movements of its prey in the next few seconds, but may not think at all of the future except for that.

As for a fly moving out of the way of a fly swatter, that may just be instinct. A predator could move toward the fly to seize it, so the fly may instantly flee simply out of instinct. The instinct could apply to things as well. A horse's tail, for instance, may swish toward the fly to swat it, so the fly flees. It may instinctively flee from anything moving rapidly toward it. I don't believe it's a matter of the fly thinking it could be killed.

Creatures that have a memory may anticipate pain experienced from earlier similar circumstances and may flee to avoid pain, but not death.

I think fleeing is either a matter of instinct, or it is from a memory of earlier painful experience. Andme2 (talk) 01:07, 14 August 2008 (UTC)

(Going off on a bit of a tangent) I'm pretty sure that some animals can anticipate the future. To use an example I'm familiar with, Moluccan Cockatoos are notorious for screeching in a tone particularly offensive to human ears when their owners are not in the room in order to attract their attention. The bird will not be ignored and will keep screeching constantly until the owner enters the room. The Cockatoo apparently is taught this from an early age by unwitting owners who lavish attention on it whenever it screeches in order to 'calm it down', treating it somewhat like a human infant. The bird sees that screeching brings its keeper running every time and enjoying human contact and not understanding (or caring) that the human may have other things to do, eventually comes to the realization that 'screech = human will come to hang out with me eventually if I do it for long enough'. Seems to me that the Cockatoo can forsee the consequences of its actions. --Kurt Shaped Box (talk) 01:30, 14 August 2008 (UTC)

The cockatoo is simply remembering past experience. Just as a creature with a memory avoids pain by remembering past experience, it may also seek to repeat pleasure derived in past experience. But if it sees the death of another creature, it may not apply that eventuality to itself.

If a creature does not anticipate its own death (thinks the present will go on forever) it will not knowingly sacrifice its life for others.

Of course, instinct may cause animals to take risks for each other. For instance, a mother animal may defend its young. And a pack of wolves will attack a large and dangerous animal, instinctively aiding each other in the attack.

Or an animal may non-instinctively attack one of its own kind for food, a mate, or pack leadership. (It may also be a coward to avoid pain - that's how pack leadership is given to another.)

But a mother animal or pack animal, acting from instinct, may never think of death occuring to itself when it aids another of its own kind. The same goes for a conscious attack for food, a mate, or pack leadership. Andme2 (talk) 03:58, 14 August 2008 (UTC)

Another thing. I have never seen, in life or in photos, an animal react with horror or aversion when it sees another dead animal. Not even when the dead animal was horribly wounded. The live animal didn't seem to understand what death was. Andme2 (talk) 18:47, 14 August 2008 (UTC)

Completely anecdotal, I know - but if one of my budgies dies in my aviary, the other birds do seem quite 'subdued' whilst the dead corpse is present on the ground. --Kurt Shaped Box (talk) 00:44, 15 August 2008 (UTC)

Teeth Whitening

I have read the essay in Wikipedia regarding teeth whitening but I'm anxious to hear from people who have undergone various proceedures. Do any of them really work? Do the proceedures carried out by Dentists hurt? Do any of the "do it yourself" products really work? Which ones? Thanks, WSC —Preceding unsigned comment added by 75.85.203.191 (talk) 19:45, 12 August 2008 (UTC)

You should ask your dentist these questions. --Shaggorama (talk) 21:39, 12 August 2008 (UTC)

Given that dentists are not very forthcoming about the other side of the effects (such as weakening tooth enamel), and upkeep, try google, do research and take a list of your questions to the dentist to get to the bottom of it. In Oz there's a consumer Choice magazine that compares products so you might find something there or similar. When the dentist offered me (wasn't asked, take note) the whitening system I was impressed with 1) their selling stance; 2) the expense; and 3) the high maintenance of it. It came down to over-servicing in my book because my teeth, not glacial fluoro ceramic white, are white enough. Best of, Julia Rossi (talk) 00:13, 13 August 2008 (UTC)

I've had that gel stuff applied by a dentist ages ago. It didn't hurt. It didn't help my case, though. (I have fluorosis and ended up just needing to get veneers). --98.217.8.46 (talk) 00:39, 13 August 2008 (UTC)

There's a whole range of products available for tooth whitening, which range from quite inexpensive (and ineffective) to very expensive and quite effective. Toothpaste that claims to whiten the teeth would be at the low end, followed closely by over-the-counter gels and gel-strips, then dental treatments like laser whitening. I'd put porcelain veneers both at the top of cost and effectiveness. StuRat (talk) 13:51, 13 August 2008 (UTC)

Veneers are certainly #1 when it comes to whitening, but that's because they essentially build you new teeth out of porcelain. They're not a trivial thing, though. Aside from the cost ($500 a tooth when I had it done—somehow convinced the insurance the cover it), they also have their own other issues—they need to be replaced once a decade or so, and they can crack and fall off if you aren't careful (hard breads in particular need to be avoided, and you absolutely cannot bite your finger nails under any circumstances). If you grind your teeth at night you have to wear a bite guard, because the veneers are not anywhere as strong as your regular teeth. Anyway, just sharing my experience with them—I've had mine for about 9 years now. They look really nice, and are way better than my fluorosis teeth were, but there were many costs. I would not recommend them to people who had not exhausted other options first, as I had. (Oh, and let's not even get into the operation of having them applied, where they grind down your existing teeth first... it's a little horrific, in my opinion.) --98.217.8.46 (talk) 15:32, 13 August 2008 (UTC)

Size of Orbitals?

Hi folks,

I'm going to be teaching an introductory general chemistry class this semester and I've been making lesson plans. I'm at the part where I talk about orbitals, and I have a question I'm not sure how to address. When speaking of the reactivity of electrons, we often talk about the size of the p-orbitals and thats why they are more reactive. But at the same time, I've asked this question before and always been told that size is ambiguous at the quantum level, which I know is crap because in my quantum class we've calculated the expectation value of the radii for some of the orbitals. I guess I'm trying to come up with a good way to answer the question, "But aren't those orbitals (say the 2s and the 2p) occupying the same space? How can two probability areas be occupying the same space? Is the 2p orbital in the 2s orbital?" Any suggestions? EagleFalconn (talk) 20:28, 12 August 2008 (UTC)

Orbital size really is ambiguous (except for nodes), but if you decide what you mean by "size", then it can be answered...you picked an expectation value, probably a probability cut-off beyond which it's too unlikely for you to care. Electrons in a p orbital (compared to s) are mostly away from the nucleus and directional, so they are less tightly held by the positive center and more able to reach out towards something else. But anyway, several orbitals do indeed occupy the same region (even for the usual "fairly likely" location/size/shapes). Overlap allows hybridization, which is a pretty important idea all the way from gen-chem through quantum discussions. Is your class only at the level of "electron filling" and atomic configurations, or have reached as far as covalent bonding? DMacks (talk) 20:36, 12 August 2008 (UTC)

The class hasn't started yet, I'm in the planning phase only. I'm taking something of a non-traditional approach. Roughly, the order I'm introducing topics is

1) Conservation of energy

2) Conservation of mass

3) Define the atom.

4) Atomic structure. Briefly the Bohr model. (about 3 minutes)

5) Wave model at more length. Types of orbitals, filling order by energy, motivation for orbitals existing, why they fill in the order they do, Pauli exclusion, Hund's rule.

6) Kinetic/Thermodynamically stable states

7) Stability of states as applied to chemical reactions.

8) Balancing chemical reactions as motivated by conservation of mass

9) Hybridization

10) Atomic radii/Electronegativity

11) Predicting simple reaction products as an application of hybridization, to motivate Lewis structures.

EagleFalconn (talk) 20:51, 12 August 2008 (UTC)

One problem which has a simple explanation is that the terminology "space" is sometimes mis-used. (i.e. "two electrons cannot share the same space" - this is not correct!) For example, Pauli Exclusion Principle dictates nothing about spatial exclusivity. It strictly operates in the realm of quantum state, which may be related to spatial location, but is not equivalent. So, for example, if someone asks whether 2s and 2p orbitals are "in the same place", you may tell them that they do contain overlapping spatial locations, but they are not in the same quantum state; further, encourage them to understand that in Quantum Mechanics, spatial location is often less important than quantum state as far as determining or predicting the system's behavior - and that is why we do not have well-defined "positions" for so many cases. Nimur (talk) 18:33, 13 August 2008 (UTC)

That's a very good distinction! It helps to keep in mind "could be in the same place at various times" from doing the same thing at the same place and time". You could even use the term "momentum" (no need to call it "angular momentum") to describe the two electrons in different orbitals doing different things (and therefore "different from each other") even if they might be in the same place. DMacks (talk) 18:52, 13 August 2008 (UTC)

In general orbitals that are higher in energy are on average further away from the nucleus. So if your p orbitals are higher in energy than s you can use that.

Two gases can occupy the same space, as can smells, lights you name it. Use an analogy.77.86.119.155 (talk) 19:32, 13 August 2008 (UTC)

Per Atom the outermost electron can be as far as half a millimeter from the nucleus. Edison (talk) 01:17, 14 August 2008 (UTC)

There is a probability of an electron from an atom on Earth being on Mars....but the common diagrams of orbitals describe the 90% confidence level.--Shniken (talk) 14:07, 14 August 2008 (UTC)

I just deleted that sentence from the article since it seems pretty misleading; naturally occurring atoms don't get anywhere close to that size. To the original poster, you have to be a little careful when talking about the expected radius of an orbital. The most likely place to find a 1s electron is inside the nucleus. The most likely radius at which to find it is the Bohr radius. The expectation value of the radius is 1.5 times the Bohr radius (if I calculated correctly). But the electron is actually spread all over the place, as shown in pictures like this, and none of the radii I just quoted accurately captures "where it spends its time". It's also worth mentioning that 1s electrons don't orbit the nucleus in any way shape or form. The only reason they're ever found far from the nucleus is the uncertainty principle. -- BenRG (talk) 16:43, 14 August 2008 (UTC)

August 13

silverback gorillas

Hello,

My friend and I are having a drunken argument about gorillas. He says there's only one silverback, and he turns silver when he becomes the leader of the group, I say its just old age, he becomes silver when he goes grey. What dya rekon? —Preceding unsigned comment added by 86.137.122.244 (talk) 00:33, 13 August 2008 (UTC)

According to our article, you are (more or less) correct. Male gorillas grow the silver hair with maturity (not old age). At about the same time, they leave their troop and go looking for some females of their own. Algebraist 00:41, 13 August 2008 (UTC)

See Harrison Ford for more information. Plasticup ^T/C 16:19, 13 August 2008 (UTC)

Mosquito species?

Which species of mosquito is the most common in Moncton, New Brunswick? I think it's different from the mosquitos that commonly sting me in Toronto, Ontario. I remember the New Brunswick ones as being more abundant and somehow "fluffier" in appearance (from having longer limbs, not from being furry), and I hardly notice when I'm occasionally stung by one in Toronto.--Sonjaaa (talk) 01:51, 13 August 2008 (UTC)

• According to this, there are 32 mosquito species in the greater Moncton area. This doesn't answer your question about "most common", though. --jpgordon^∇∆∇∆ 19:11, 13 August 2008 (UTC)

Welding Smoke

What kind of toxins, chemicals, vaporized metals, etc. are in the smoke produced during shielded metal arc welding? I looked here, but that was only a brief description. I would like specifics, please. Thank you, Ζρς ι'β' ^¡hábleme! 02:32, 13 August 2008 (UTC)

Well, there will be fumes and vapors resulting from combinations of whatever's in the arc area. Metal oxides, droplets of the metals (electrode and substrate) themselves, ozone and notrogen oxides if your equipment or technique doesn't allow for adequate shielding of the weld by the shield-gas, burned bits of flux. DMacks (talk) 03:47, 13 August 2008 (UTC)

(e/c) Basically, everything in the weld rod and the material being welded are present in the smoke. The welding process vapourizes a bit of everything. You need to look at the composition of the particular electrode and the particular metal. Each of these should have a safety data sheet that will have some information. The best course is to ask your local welding supply company for information, they are always happy to provide it. It is very important to evacuate the smoke produced by SMAW or any other welding process if you are doing it in an enclosed space. Franamax (talk) 03:53, 13 August 2008 (UTC)

should I ask them to shave them off or wax them off? —Preceding unsigned comment added by 70.49.159.116 (talk) 04:04, 13 August 2008 (UTC)

Up to you, but either one would likely be preferable to electric-arc methods. DMacks (talk) 04:19, 13 August 2008 (UTC)

Once again, I've scrolled up to this answer to a misplaced post and once again I am convulsed with laughter. Thank you DMacks and all RefDeskers and sorry to the IP - this just really makes me laugh! :) Franamax (talk) 00:58, 14 August 2008 (UTC)

When cabernet sauvignon comes snorting out the nose, it is hard on a computer keyboard. Edison (talk) 01:15, 14 August 2008 (UTC)

Perhaps this should be taken up further then at either of the Humanities or Computing desks? It was Kokanee this time, does that make a difference? It may be disrespectful, but this is bookmark-worthy for me. :) Sorry again to the IP who innocently mis-posted.Franamax (talk) 02:51, 14 August 2008 (UTC)

A recent article in Mother Jones suggests that the big risk is manganese vapor. [16]

Atlant (talk) 19:09, 14 August 2008 (UTC)

Eyebrows

When swimmers shave their eyebrows, how long does it take for them to grow back? Reason why I'm asking is I'm considering shaving my eyebrows off for a cancer fundraiser, however I work in the finance industry and have to see clients on a regular basis. I dont want to look stupid for too long :P —Preceding unsigned comment added by 70.49.159.116 (talk) 03:09, 13 August 2008 (UTC)

I'd take care to shave in the hair growth direction, not against it or you're more likely to have multi-directional regrowth. *_* As for growing time, hair grows faster in summer, so... Julia Rossi (talk) 03:25, 13 August 2008 (UTC)

O rly? Who conducted such an experiment? bibliomaniac15 04:05, 13 August 2008 (UTC)

0.16 mm per day according to this article. The article requires payment but a snippet of the data inside can be viewed via google scholar.--Lenticel ^(talk) 05:18, 13 August 2008 (UTC)

I don't necessarily want to dissuade you from helping cancer patients, but be aware of unintended consequences. Someone I know shaved off their eyebrows as a bar-bet, and afterwards said that he didn't realize how important eyebrows were in keeping forehead sweat out of your eyes. -- 128.104.112.147 (talk) 16:32, 13 August 2008 (UTC)

@Bibliomaniac -- women of course, masterful frequent experimenters in appearance change and their priestesses of wax and pluck, the beauticians. Not this woman, because scientifically, I watch and learn. |;-) Julia Rossi (talk) 23:58, 13 August 2008 (UTC)

Of course, you could use eyebrow pencil to paint on the missing eyebrows, and look like a bizarre waitress from a diner in Tennessee I saw years ago. Edison (talk) 01:13, 14 August 2008 (UTC)

And remains indelible -- Julia Rossi (talk) 03:32, 14 August 2008 (UTC)

Autism-spectrum disorders and evolution

Are autism spectrum disorders a distinctly Holocene phenomenon? If not, how would they have survived the natural and sexual selection of the Pleistocene, given

• the problems that weak or idiosyncratic nonverbal communication would have caused before the development of complex language, in both coordinating a hunt and attracting a mate?
• the tendency toward narrow specialization, when the Pleistocene demanded generalists?
• the difficulty in developing a theory of mind, which would clearly be a prerequisite for Animism?
• the problems that sensorimotor issues would have caused in hunting?

NeonMerlin 04:22, 13 August 2008 (UTC)

Well, the causes of autism are still very much unknown (despite the crackpots who say they've got it all figured out). However, if it is genetic and recessive then it will have no problem passing generation to generation without the need for selective pressures to weed it out. -- MacAddct  1984 ^{(talk • contribs)} 05:35, 13 August 2008 (UTC)

The original poster seems to assume that it's fully or largely genetic. However, if autism has significant environmental components, such as multiple chemical exposures or dietary factors only common to the modern world, then it may have been only rarely expressed prior to the last century or so, meaning there would have been little selective pressure against it. StuRat (talk) 13:27, 13 August 2008 (UTC)

One might find inspiration in the superficially even more difficult question of how homosexuality would be genetically based (e.g., kin selection or whatever—that such a trait would not be selected against if there were some advantage to having one member of your tribe have the specific skills that would come with such a thing). Which is just a way of saying that you needn't imagine all evolution and genetics as being about individuals; the operations of a tribe, for example, can have genetic effects on the individuals within it, obviously. --98.217.8.46 (talk) 15:37, 13 August 2008 (UTC)

The End of the World!

If for some reason the LHC creates a black hole and it does not evaporate through Hawking radiation but instead engulfs the Earth, how long would it take? Will it be slow enough to enable me to see a news broadcast about the impending doom on the other side of the Earth? --antilived^{T | C | G} 04:42, 13 August 2008 (UTC)

Yes. The surface area of the event horizon of 100 TeV mass black hole is much much smaller than the nucleus of an atom. As a result, if such a micro-blackhole can eat anything at all (which is not obvious), then it would be expected to do so very slowly initially. In fact, it would not be surprising if it took years before it got large enough that anyone even noticed such a black hole. Dragons flight (talk) 05:27, 13 August 2008 (UTC)

I would expect it to swallow a charged particle and then the electromagnetic forces will dominate and the black hole will stick to something and not fall forever. Graeme Bartlett (talk) 05:54, 13 August 2008 (UTC)

Are there any theories about an electron-charged micro black hole orbiting a single proton? I guess that would be something like a hydrogen atom with an electron of scalable mass plus a distinction of the quantum properties of the electron and those of its electrical field. 93.132.149.230 (talk) 06:56, 13 August 2008 (UTC)

As the orbiting particle is then heavier than an electron the atom would be like one of those Exotic atom#Muonic atoms? --Ayacop (talk) 08:07, 13 August 2008 (UTC)

If a micro-black hole settled within the Earth and if it began to accrete matter, it would take several thousand years to accrete its first proton. After that, things really speed up and it should swallow the Earth in less than 80 billion years. Plasticup ^T/C 16:09, 13 August 2008 (UTC)

This discussion is taking all the fun out of rampant unsubstantiated speculation.

I'm curious why "it would take several thousand years" for a micro black hole to swallow a proton. Is that because it would have to swallow a lot of smaller stuff first, in order to get big enough to attract a proton?

If a micro black hole became part of (say) a sodium atom, and that atom was part of a grain of salt, and that grain was in a saltshaker with a bunch of other grains, would there be any way to determine which grain contained the black hole?

If that is too tough, how about if 10% of the sodium atoms in a grain contained black holes?

Thanks, Wanderer57 (talk) 17:25, 13 August 2008 (UTC)

Most chemicals are white. You could make no distinction between anthrax and table salt. I'd guess you wouldn't see a difference between table salt and blackholisodium chlorid. But perhaps blackholisodium would chemically act like neon if the negative charged black hole occupies one of the innermost orbits per lepton type without substantially disturbing the electron orbits --- after all, it's a different kind of fermion. 93.132.149.230 (talk) 21:41, 13 August 2008 (UTC)

I'm very uncomfortable with this scenario. On the one hand you're asking that a black hole behave in a fundamentally quantum way (occupying an orbital normally occupied by an electron). On the other hand you're asking that it not decay. I can't make any sense of that combination. I'm happy talking about classical black holes that never decay and take 80 billion years to consume the Earth, and I'm happy talking about quantum black holes, but quantum black holes would decay, because that's what quantum objects do. It's part and parcel of the quantum rules. I don't see how you can strip out that behavior without stripping all the sense from the theory. -- BenRG (talk) 02:03, 14 August 2008 (UTC)

If charge is mediated/effected by photons, which can't escape a BH, can a BH be seen as "charged"? Saintrain (talk) 17:32, 13 August 2008 (UTC)

Yes, a black hole can have charge, mass and angular momentum, but supposedly all other properties get "eaten", according to the no hair theorem. Confusing Manifestation(Say hi!) 23:22, 13 August 2008 (UTC)

My question is, since it looks like the latest from CERN is first beam on 10 September [17], are we going to start a Wiki-pool to predict the date of the last post to the Reference Desk before the black hole swallows the servers? Franamax (talk)

Last admin alive gets to delete the main page. DMacks (talk) 15:32, 14 August 2008 (UTC)

Protein Bending

A couple of days ago I heard about fold it, which is a video game in which you help to fight against cancer and other stuff by bending proteins on your Pc. Very weird. Anyway my question is do we actually have the means of bending proteins if we actually found out their shapes? And secondly which entity of ourselves is concerned with the bending? And are the shapes of the proteins also in the DNA?Bastard Soap (talk) 08:05, 13 August 2008 (UTC)

You do not bend, it's the water molecules that do the bending in reality. The 'video game' probably is a screensaver that only shows a simulation of it. The problem is that with a given protein, if we know the amino acid sequence, we still don't know the 3D form that it takes, especially when interacting with lots of small water molecules. This can be computed but takes much computing power, so you are asked to help by providing your computer for the task.

So, if there were only the protein (whose amino acids are determined by the DNA sequence and possible other transcription processes like splicing) and water, then yes, we would after such a simulation know how the protein bends in such an environment. This is something that could have previous only known by making a crystal of the protein and using X-rays to look into that crystal. Very slow and expensive process, therefore we compute now. The task, however, is complicated by interaction of the protein with other proteins (e.g. receptors) or other small molecules. -Ayacop (talk) 08:17, 13 August 2008 (UTC)

But what determines how the water bends the water? There must be some mean of controlling it, no? 195.158.110.60 (talk) 09:58, 13 August 2008 (UTC)

We have an article on Foldit and we also have an article on protein folding. The screensaver that Ayacop refers to is probably the Rosetta@home distributed computing project. Scientists are not trying to control the folding - they are trying to work out how a particular protein is folded, and what can go wrong in this folding if, for example, one of the amino acids in the protein is exchanged for another one because of an error in the DNA template or the transcription process. Gandalf61 (talk) 10:30, 13 August 2008 (UTC)

The whole chemistry except nanotech is just mixing molecules and let them do their dance, so to speak, we don't have control at the molecular level. Even catalysts are more or less found by chance. --Ayacop (talk) 14:09, 13 August 2008 (UTC)

Each protein has a certain 3D structure that is the result of how its amino-acid chain behaves in (essentially) water. So the 3D structure is in a sense controlled and determined by the sequence (each protein folds a certain way, each different protein folds differently). The trick is that nobody fully understands and is able to predict the 3D structure of some arbitrary sequence. If you could, then you could design a 3D shape by programming the sequence, or could know what alterations to a known protein would cause what changes in shape. DMacks (talk) 14:19, 13 August 2008 (UTC)

Two-stroke engines

HOW CAN ITS FUNCTIONING BE EXPLAINED IN A LUCID MANNER? —Preceding unsigned comment added by Tsm krishnan (talk • contribs) 12:41, 13 August 2008 (UTC)

First, there is no need to SHOUT (typing with caps lock on). Second, have a look at our detailed article, Two-stroke engine. --Bruce1ee^talk 12:55, 13 August 2008 (UTC)

As in lucid dreaming? ---J.S (T/C/WRE) 19:10, 13 August 2008 (UTC)

(in case you're serious) Nah, lucid as in "easy to understand". --Bowlhover (talk) 06:51, 14 August 2008 (UTC)

Have you read our two-stroke engine article? It even has a nice animation to help folks understand. After reading the article, if you still ave questions, please write back!

Atlant (talk) 19:02, 14 August 2008 (UTC)

Heparin suppresion of platelet count

I understand that heparin causes a transitory loss of platelets. Heparin itself has a relatively short biological half-life of 1.5 hours once administered. Does this mean the platelet drop shares the shame biological half-life, or does the recovery of platelet count lag the heparin drop ? If so, what is the time period required for the platelet count to fully recover ? Also, is there any diff between unfractionated heparin and low molecular weight heparin in this regard ? StuRat (talk) 13:16, 13 August 2008 (UTC)

I can't find anything about platelet reduction in Heparin#Mechanism_of_anticoagulant_action. Rather, heparin binds to factor proteins and makes them inactive. --Ayacop (talk) 18:10, 13 August 2008 (UTC)

see heparin-induced thrombocytopenia. - Nunh-huh 18:13, 13 August 2008 (UTC)

Under the "Type I" section it states: "Platelet counts recover even if heparin continues to be administered". However, it doesn't say how long it takes for this to occur. That's the info I'm after. StuRat (talk) 00:33, 14 August 2008 (UTC)

There's no solid number (someone who drops to a platelet count of 75,000 and someone who drops to a platelet count of 100,000 obviously have different amounts of recovery that will be needed), but it's on the order of several days to a week. It's certainly not related to the biological half-life of heparin. It's the same, roughly, as the amount of time it takes to recover from Type II once heparin is withdrawn. - Nunh-huh 01:27, 14 August 2008 (UTC)

Thanks. StuRat (talk) 16:09, 14 August 2008 (UTC)

Need info about penis meds

Have any of those pills and potions that claim to embiggen the penis or increase volume of ejaculation or sperm count actually been scientifically proven to work? I'm not asking for medical advice. I've just seen these products advertised a lot recently. --90.241.191.110 (talk) 14:20, 13 August 2008 (UTC)

No more than a placebo. See penis enlargement. Plasticup ^T/C 15:54, 13 August 2008 (UTC)

If any of them did have any legit scientific proof, you would know about it, as advertising such proof would make their product worth millions, perhaps billions. StuRat (talk) 16:04, 13 August 2008 (UTC)

There could easily be some effective therapies for low sperm count (depending on the cause)- but they'll come from a legit doctor, not a late-night infomercial. Friday (talk) 16:08, 13 August 2008 (UTC)

Also pay close attention to the claim. For example, there are a lot of those "Smilin' Bob" commercials that seem to claim to greatly increase the size of the penis. The actual claim is that an erect penis is normally much larger than a flaccid penis. The claim has nothing to do with the pill itself. -- kainaw™ 16:18, 13 August 2008 (UTC)

That's good advice for any of the shady "supplement" companies out there. Pay very close attention to what they are saying and what they are not saying. Words like "promotes" are meaningless. If a company isn't willing to just come out and say what their product does then they are skirting along the edge of the law and I would be very leary of any company who likes to play those kinds of games. ---J.S (T/C/WRE) 19:14, 13 August 2008 (UTC)

I think that some of the supplements do work to expand the size of the (probably flaccid) penis. But only by causing increased fluid retention in all tissues in general, at some risk to your health. Seems like a pretty dumb tradeoff to me. As noted above, those entertaining infomercials present the smiln' guy saying "oh yeah, it got bigger" - they cut away before "then it turned black and fell off" :). Franamax (talk) 00:43, 14 August 2008 (UTC)

Remember, Enzyte (the "Bob" commercials) is promising "natural male enhancement"; while we all "know" what that euphemism means, what they're literally promising you is completely vague so you will never be able to prove you whether or not you were enhanced in some obscure way after taking their pills. Perhaps your enhancement is that, although poorer, you are now presumably wiser.

Atlant (talk) 18:59, 14 August 2008 (UTC)

My favorite is those commercials that support a product that is assured to "enlarge that certain part of the male body." The tongue? the eyelid? The toenail? I mean no offense, but if you're dumb enough to fall for the rhetoric these companies use, they've earned their money. --Shaggorama (talk) 05:22, 15 August 2008 (UTC)

Measuring age

Is there any way to scientifically prove how old someone is? If so, how accurate is it? To a month? A year? A decade? Not talking about looking on someone's birth certificate.--El aprendelenguas (talk) 21:56, 13 August 2008 (UTC)

Well, there's no way, for example, to determine age closely enough to determine how many of the Chinese girl's gymnastics team are competing illegally. There are a number of ways to estimate developmental age for children. In fetuses and stillborns, developmental age can be estimated from long bone length; in infants and juveniles, dental x-rays are useful; and in older children, "bone age" is often estimated from x-rays of hands, feet, and knees: specific joints tend to calcify at certain ages. But the variability is up to 10% of the estimated age, so someone who is estimated to be 14 years of age may be 12 and a half to 15 and a half years old. - Nunh-huh 22:13, 13 August 2008 (UTC)

(edit conflict) Remembering from my archaeology classes: You can, to various degrees. Certain age ranges can be very accurate, while others aren't. You can look at features such as the plates fusing in the skull and basion bone fusion (I hope I remembered that correctly). Teeth provide fairly accurate age determination (say plus/minus a year or two). The classic example is wisdom teeth (third molars) indicate late teens/early twenties. Beyond a certain point, it's difficult, and you are left estimating using less accurate techniques, such as tooth wear. (This is from an archaeology POV; there may be some "soft tissue" ways). --Bennybp (talk) 22:18, 13 August 2008 (UTC)

Age can be determined pretty well from bones, yeah. Skilled forensic anthropologists like William M. Bass have it down to an art -- it's not entirely exact, of course, but as I recall, they've done pretty amazing things, like correctly determined a victim's sex, age and size from nothing but a small piece of hip bone. -- Captain Disdain (talk) 10:13, 14 August 2008 (UTC)

If you had DNA you could look at telomeres but I doubt the precision is very good. --98.217.8.46 (talk) 22:20, 13 August 2008 (UTC)

With horses, you can look at their teeth[18]. Julia Rossi (talk) 23:49, 13 August 2008 (UTC)

Unless they are gift horses.. DuncanHill (talk) 01:16, 14 August 2008 (UTC)

If they were born after approximately 1946 or so, you can pin it down to within 1.6 years - but you'll need to pull a tooth to check the leftover radiation from atmospheric nuclear tests. [19] Franamax (talk) 00:35, 14 August 2008 (UTC)

And, of course, a person can become younger by walking around the North or South Pole. If he walks eastward in a circle around the Pole, the calendar date will go back by one day each time he steps across the International Date Line. It would not take long to walk in a small circle. By this means, an old man could make himself young again. Hmmm, could that be true? Andme2 (talk) 23:56, 14 August 2008 (UTC)

And that reminds me of the story The Wandering Jew, by Rudyard Kipling, collected in Life's Handicap. It is described by the Kipling Society thus-

John Hay is a wealthy man, driven by the fear of dying. Someone tells him that he who travels eastwards round the world gains a day, and this becomes an obsession for him. He travels incessantly towards the rising sun, in the belief that he is extending his life. Eventually he begins to go crazy, and - to give him some rest - his doctor gives him the idea of swinging above the ground and letting the world rotate beneath him. The story ends with Hay sitting in a swinging chair on the coast of southern India, over a sheet of steel to cut him off from the attraction of the wheeling world, as his brain finally ceases to work

DuncanHill (talk) 00:06, 15 August 2008 (UTC)

A man wouldn't have to be on a swing. He could use a backpack rocket unit to suspend himself over the earth's surface, letting the earth rotate (from East to West) beneath him. Each time the International Date Line passed beneath his feet, the calendar date would go back one day and he would be one day younger. But he would have to wait 24 hours for the Date Line to pass beneath him again, so he would lose a day. Thus, he would alternate back and forth in age, 24 hours at a time. He would become younger instantly, then older again during the next 24 hours. I know the answer to all this. I'm waiting to see if someone else comes up with it. I will post the solution 24 hours from now. (I am not walking around the North Pole, and I am not suspended by a backpack rocket. So I will be 24 hours older then.) :Andme2 (talk) 01:55, 15 August 2008 (UTC)

Communiction with Aliens

My physics professor proposed a challenge to the class:

"Suppose mankind was able to communicate via-radio with an intelligent alien race. It is unknown where these aliens live, what they look like, or their unit of measurement, though we have been able to translate thier language and therefore communicate. What questions should we ask in order to compare their units of measurement for Length, Mass, and Time, with our own?"

After a long discussion, the lcass came up with the following answers:

• Length: "What is the length of one wave of this radio frequency?"
• Mass: "What is the mass of this radio wave?"
• Time: "How long did it take me to ask this question?"

The professor said that our answers for Length and Time were correct, but our answer for Mass was not. However, he did not say why. What was wrong with our Mass answer, and what would be a correct answer to the problem? --Ye Olde Luke (talk) 22:09, 13 August 2008 (UTC)

Well, photons have zero rest mass, so that's your problem there. --98.217.8.46 (talk) 22:15, 13 August 2008 (UTC)

Are you allowed to reference things other than radio waves? You could just ask them what the mass of an electron was, if that was the case. --98.217.8.46 (talk) 22:17, 13 August 2008 (UTC)

Yeah, I'd probably suggest asking them for the mass of something that universally occurs at a certain mass - a hydrogen-1 atom or an electron is probably the easiest, or if you've already established what their unit of length is you could ask them for the mass of a cube of, say, water with sides equal to that length. Photons, as radio waves, don't have a rest mass which makes asking for that at best doomed to a confusing answer. ~ mazca ^{t | c} 22:21, 13 August 2008 (UTC)

(ec)What is the mass of 6.02214×10²³ atoms of ¹²C? should do it. DuncanHill (talk) 22:23, 13 August 2008 (UTC)

The thing is that radio waves are the only things we know that we both have. The aliens might not have discovered the atom or the electron yet, and even if they have, they probably wouldn't call it an electron, or Hydrogen, or water. The class's first attempt at an answer was asking for the mass of an atom, but the professor didn't accept that answer, per the above. --Ye Olde Luke (talk) 22:25, 13 August 2008 (UTC)

Photons have energy, and hence by special relativity they have mass (strictly speaking it is more natural to say that they have momentum, even though their rest mass is zero), but a radio transmission is not a single photon. Rather radio communication works by emitting energy in many directions (with a very large numbers of photons), and each listener recieves only a small portion of the energy in the original signal. Since you have no way of knowing what portion of the total emitted energy the aliens are recieving, you don't have a way of interpreting their response. Dragons flight (talk) 22:26, 13 August 2008 (UTC)

You could always ask the aliens to compute the energy of one photon using E=hf and report the apparent mass calculated by E=mc^2. Asking for the complete calculation would also reveal their unit of energy. --Bowlhover (talk) 22:47, 13 August 2008 (UTC)

Radio technology was discovered before photons, so there is no guarantee that a radio capable civilization would know what a photon was or have discovered Planck's constant. Dragons flight (talk) 23:07, 13 August 2008 (UTC)

Wouldn't the unknown radio Redshift confound the length measurement ("What is the length of one wave...")? -hydnjo talk 23:12, 13 August 2008 (UTC)

So Star Trek was right and everyone speaks English? Or is there some symbolic method of communication developed here?

It seems to me that all your class answers are right, but you would need a serial set of communications to pin it all down. The alien species will presumably know how to measure the momentum of a single photon (rather than mass), maybe that is the missing piece? In any case, I think that for each of your question/answer pairs, you would need to re-transmit something that you predict will yield the equivalent measurement at the other end. Then by each measuring the errors and re-transmitting iteratively, you will be able to converge on a mutual definition. Franamax (talk) 00:29, 14 August 2008 (UTC)

And looking at this again, to repeat, I think your better question #2 would be "what is the momentum of this radio wave?". Anyone else? Franamax (talk) 02:34, 14 August 2008 (UTC)

There are two problems with the mass: red shifts (both doppler and gravitational), and the fact that you did not specify that you want the mass of exactly one photon. The "time" and "length" questions are also ambiguous, since you do not know the relative velocity of the aliens or the difference in gravitational potential. I would ask for all three quantities relative to the same physical phenomenon, the photon emitted by a particular atomic phenomenon, namely the "transition between two energy levels of the ground state of the caesium-133 atom. " (see Atomic clock.) The questions are:

1. length: What is the wavelength of the reference photon?
2. time: What is the frequency fo the reference photon?
3. mass: how heavy isthe reference photon?

For cross-reference, you can ask the same question for several other reference photons. -Arch dude (talk) 03:31, 14 August 2008 (UTC)

It seems to me that whatever your professor considers the "correct" answer will depend on unspoken assumptions that only he knows, making the question rather arbitrary and uninteresting. If you can't assume they know what an atom is, how can you assume they know what a radio wave or a photon is? Or (to be picky) what the concepts of mass, time, or length are? All we really know is that they have some language and own radio transceivers. --Allen (talk) 04:21, 14 August 2008 (UTC)

I suspect that he assumes that the aliens must know what a radio wave is because they can receive them. I personally disagree. They might be able to "hear" radio waves and simply know how to amplify them. They might be using directional antennae to isolate signals, which have nothing to do with knowing the frequency. You could just teach them how to find the values you're looking for. I'd tell them how to find each physical constant, then use Planck units. — DanielLC 16:05, 14 August 2008 (UTC)

You don't need to ask for quantities with units of length, time, and mass, just for any three quantities with linearly independent units. I would first of all ask for the gravitational constant in units of M⁻¹ L³ T⁻² and the vacuum speed of light in units of L T⁻¹, both of which have been known to humans for longer than radio has. Then practically any third quantity would allow you to solve for all units, such as the spectral lines of a substance of their choice in units of their choice. That would avoid having to use the radio signal as a reference, which is problematic because of redshift as people have mentioned. For that matter you could let them choose all three quantities; they understand the problem as well as you and additionally know what data they have available. I agree with Allen and DanielLC that your professor is being unreasonable. -- BenRG (talk) 16:11, 14 August 2008 (UTC)

The illustration on the Pioneer plaque

You might enjoy our article about the Pioneer plaque -- That was an attempt to come up with practical answers for some of these questions.

Atlant (talk) 18:53, 14 August 2008 (UTC)

I have to object to answers that require responses from the aliens - it's very unlikely that we'll get an answer to our question within a human lifetime. We'd want to communicate everything we needed to say in a single communication and hope that a single response tells us everything we need to know.

A reasonable definition for a unit of mass could be "An Avagadro's number of protons at rest in your inertial frame". The standard definition of a second ("the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.") should be good enough for explaining time. Once you've explained time then length can be "the distance a light beam travels through a vacuum in such-and-such amount of time". So our basic units are easy enough.

Some more interesting problems would be describing what you mean by "Left" and "Right", "Clockwise" and "CounterClockwise". You can try sending pictures - but how do you know whether they are looking at them upside-down or mirrored or something? Talking about colours of things would be hard too - we don't see pure colours - we only see the relative amounts of red, green and blue. An entire spectrum of each material from radio to gamma-rays might be needed in order to explain the "colour" of something to unknown alien eyes. Sending pictures (other than diagrams) would be exceedingly problematic if they don't see in visible light because each pixel has to be an entire spectrum - and we don't have "cameras" that work like that.

Even sending simple diagrams would be tough - we don't know that they have the same way of drawing graphs as us - maybe they habitually use polar coordinates or use log axes all the time. Our diagram conventions like the idea that an "arrow" indicates direction is quite meaningless to our aliens who hunted by throwing lots of spikey phthnaaags using a huge polished worchniff and who never invented the bow and arrow. Maybe they use a highly stylised image of the head of some local insect to indicate direction? Maybe the insect was chosen because it walks backwards? Communicating without words AND without knowing what conventions the other guys have is REALLY tough. Perhaps they don't even use two-dimensional images - maybe they do everything in 3D or represent a graph as an animation of a 1D line with time representing the X-axis.

Numbers are things we represent with digits - 123 means 100+20+3. If the aliens work in (say) base 8, we can still talk - but supposing they use sums of consecutive primes or sums of fibbonachi numbers or something instead of sums of powers of 10 as we do? In all the science fiction books ("Contact" is an excellent example) we start off by sending a series of prime numbers - but what if you saw "K KK KKK J KKJ KH KKKH KKJH HKH KKKHH"...would you recognise that this is a series of primes? (It's written in backwards roman numerals with K=I, J=V, H=X). If we saw a system like Roman Numerals without being taught what they mean - would be be able to figure them out?

Understanding what we say could be almost impossible!

It would be interesting to split your class in two - have each half try to think like an alien, then have the two halves send messages to each other and see if you can understand each other. You can't use ordinary writing - you have to invent your own number system - pictures can be screwed with in all sorts of creative ways. I think it'll be REALLY tough to talk at all!

SteveBaker (talk) 00:06, 15 August 2008 (UTC)

If you assume that the humans and aliens can understand each other enough to find out each other's units of measurement, the other difficulties you listed are comparatively trivial. Just reference a few distant quasars and tell the aliens to go from one to the other. That'll establish our concept of clockwise and counterclockwise. Then, tell them to imagine a circle in front of them rotating clockwise. The very top would be rotating to the right; the bottom would be travelling left.

As for graphing issues, the aliens should be able to figure out that an out-of-place marking indicates emphasis, regardless of whether an insect head or an arrow is used. Send a graph showing time versus distance for light, clearly labelling both axes, to make human conventions clear. Use words if necessary.

As for numbers, the most logical number system in electronic devices is binary. Send a list of prime numbers in binary, making sure each number is well separated from the others, and the alien cryptoanalysts would likely suspect binary before anything else. --Bowlhover (talk) 05:48, 15 August 2008 (UTC)

The Big Bang Theory

am bit confused by the big bang theory as logic would have it, something cant come out of nothing, yet this is what is being put forward!i read somewhere that although the universe is expanding, at some point it will slow then contract on its self. if this is the case, does the possiblity exist that at some point the universe will contract to such a point that it will, again? at some point explode outwards? a friend of mine says that the bang radiated out FROM a given point but the materials were travelling in one general direction, not circular. if this is the case, could it also be possible that this universe is made from material from another universe ejected by a huge black hole? My keyboard is playing up some cant find the "tilde" key to end this message!jonathon47 —Preceding unsigned comment added by 82.29.21.231 (talk) 22:37, 13 August 2008 (UTC)

You might want to read Big Bang Theory and Metric expansion of space. And the tilde key is above "Tab". Alternately, you can click the button that looks like and it'll sign for you. --Ye Olde Luke (talk) 22:48, 13 August 2008 (UTC)

Also, you may want to see ultimate fate of the universe. -- kainaw™ 22:52, 13 August 2008 (UTC)

The big bang only says that the universe was in a very hot dense state 13.7 billion years ago and has been expanding since then. It doesn't say that the hot dense state was the beginning of the universe, or that it came out of nothing. That's a combination of overenthusiastic speculation by physicists and misreporting in the popular press. The truth is that nobody knows where it came from, and that's not what big bang cosmology is about (it's about the expansion afterwards). Your friend is incorrect—the bang didn't radiate out from a point and the matter doesn't travel in one particular direction. The book you're thinking of might be A Brief History of Time, which is now very outdated (the cosmology parts, anyway). The location of the tilde varies widely depending on your keyboard layout, and sometimes doesn't even match what's painted on the key caps. -- BenRG (talk) 15:26, 14 August 2008 (UTC)

Let's take this a bit at a time:

• something cant come out of nothing

Why not? The laws of physics become seriously whacked when all of everything is squished into a teeny-tiny sub-microscopic dot. Our "normal experience" is simply not valid there anymore. We're gradually pushing the laws of physics closer to the absolute origin of everything - but it gets tough when things are that compressed.

• i read somewhere that although the universe is expanding, at some point it will slow then contract on its self.

This is the Big crunch theory - and it's not currently what mainstream science believes - but I don't think it's known for sure either way.

• if this is the case, does the possiblity exist that at some point the universe will contract to such a point that it will, again? at some point explode outwards?

That is the Cyclic Universe theory - and it's possible. The trouble is that if everything started as a literally zero-sized dot as big-bang (and indeed big-crunch) theories say - then absolutely no information can pass from one universe to the next. That includes the knowledge that there ever was a previous universe. So it's likely that we'll never know. That's a shame because it's a really nice theory. Perhaps even time gets crunched up and our present universe's collapse to a big-crunch is the cause of the big-bang that started the universe. We simply don't know yet.

• a friend of mine says that the bang radiated out FROM a given point but the materials were travelling in one general direction, not circular.

No - that's definitely not true. But it's not untrue in the way you'd expect. You'd expect me to say "it expanded out like a sphere" but it wasn't just that there was all this big empty space with a teeny-tiny dot in it - then the dot exploded and threw stuff everywhere. That's NOT the present theory. Because mass curves space - if all of the mass is squished into an infinitesimal dot - then space is curved so tightly that space is also squashed into that dot. Time too. So the universe expanded in all directions at once - but space expanded too. But your friend is 100% wrong. There is no "special direction" - we've proven that by looking at how the cosmic background radiation is distributed. This is radiation left over from the big bang. If your friend was right then all of the radiation would be coming from one direction - but it's not. No matter which way we look, the cosmic background radiation is roughly the same brightness. This can only be the case if the universe was all compressed into a dot and no matter which direction we look - we're looking directly towards that dot.

• if this is the case, could it also be possible that this universe is made from material from another universe ejected by a huge black hole?

Well, kinda. Yes. If the universe undergoes a "Big crunch" (and I repeat - that's not what we currently believe) then in it's latter stages, the universe would in a sense become one big black hole. The cyclic universe theory would (presumably) allow this universe to come about from the big-crunch of a different universe. There are lots of speculations in these directions - but because absolutely no information can survive a big-bang/big-crunch scenario - there is no way for us to ever know. So - feel free to speculate - but we can't know for sure.

SteveBaker (talk) 23:04, 14 August 2008 (UTC)

Chemistry and /or biology

I'm not a chemist or biologist, but it seems to me that there are not many questioning these subjects. Anyone say why that might be? —Preceding unsigned comment added by 79.76.229.54 (talk) 23:40, 13 August 2008 (UTC)

Most colleges and high schools in the English-speaking world are not in session yet. Give it a couple weeks and we'll have tons of homework questions here. I particularly like the ones that don't even omit the question numbers. -- kainaw™ 23:51, 13 August 2008 (UTC)

Can you clarify your question? --Shaggorama (talk) 05:16, 15 August 2008 (UTC)

Blood types

Is there an evolutionary advantage for a population to have multiple blood types? Would it possibly protect against some kind of disease making it more an advantage to have diversity? Or is it just something that simply varies among individuals, like hair color? Nadando (talk) 23:55, 13 August 2008 (UTC)

Well in some respects, I think it is advantageous to be AB, but my a insignificant margin. This adaptation means you can "survive" if there is a blood shortage, because you can accept a wider range of blood types from different donors. Also, there is some risks that occur during pregnancy when a woman AO gets pregnant the second time with an embryo growing inside her that has "foreign" receptors on the cell membrane. Maybe this clue will let someone else finish what I'm trying to recall. In general, the only risks I remember are the pregnancy thing, which I don't want to write what I think is accurate. There are plenty of good experts who will read this and help you better. Sentriclecub (talk) 00:05, 14 August 2008 (UTC)

My blood group is at a disadvantage—i'm O- Rh. This means I can give blood to anyone, so it's fairly invaluable to others, but it means i'm in a bit more trouble if I lose 20 or so units of blood. —Cyclonenim^T@lk? 02:19, 14 August 2008 (UTC)

I susoect you are thinking of Rh disease, also known as Rhesus disease. DuncanHill (talk) 01:13, 14 August 2008 (UTC)

I don't think blood types evolved in an environment in which transfusions were an option, so being "able to accept a wider range of blood types" can't be anything to do with evolution. — PhilHibbs | talk 09:32, 14 August 2008 (UTC)

I did always rather think that the sheer number of blood-types is evidence enough of god not existing. Bit of a simpleton reason but I just thought...why? Why would an 'all powerful god make mankind with so many different blood types? I suspect the retort would be that he made one and they mutated, but I still think that we are far far too complex to be 'created' (if I was all powerful and making my own creatures I certainly wouldn't make us as complex inside as we are - why make us dependent on such a set mix of oxygen and other chemicals, why make us able to eat x but not y, etc. etc. Sorry got a little off topic!) 194.221.133.226 (talk) 13:54, 14 August 2008 (UTC)

Diversity is a massive advantage. If some nasty virus appears that attaches to whatever gene produces type-O blood then maybe everyone with type-O dies. Without diversity - it's game over. With diversity, a bunch of people still die - but most survive because they don't have that gene. It's a blip. This is why it's very bad for us to (for example) generate all of our corn from cloned corn plants - there is zero diversity - so the at the first sign of trouble, we lose ALL of our crop.

If there were no genetic diversity then evolution would come to a grinding halt...if everyone were equally "fit" then "survival of the fittest" would fail to produce any change. As the environment changes around us, we NEED that diversity to survive. If something in our environment were to change to favor one particular blood type - then over enough generations, that type would begin to dominate the population and we'd evolve to adapt to that environmental change. If we all had the same blood type and it wasn't the favored one then we'd fail to adapt and do much worse as a result. If the population has a wide range of blood types and they are all equally good - then we're primed, ready to evolve just as soon as the need arises. Same deal with different hair color, eye color - all of those variations help us to evolve and protect our species from being eradicated by virulent diseases.

Even things we consider to be genetic defects are sometimes there for a reason. Look at sickle-cell anaemia - this is a gene that controls the shape of blood cells. You inherit one copy from each parent - it's mostly found in human races that evolved in tropical climates. If both of these genes are "defective", you have a drastically shortened lifespan (maybe 45 years). If only one of them is defective, it happens to confer virtual immunity to malaria. Before we could treat malaria effectively, if you lived in topical regions, it was essential to have sickle-cell prone individuals in society to keep and spread that gene. If nobody had the gene - we'd all suffer from malaria. If everybody had the gene, then everyone would develop anaemia and die early (but not so early as to prevent you from passing the gene onto your children). Only when roughly half the population have it could life continue comfortably in tropical climates. These days, our "environment" has changed - we can prevent and treat malaria fairly easily. Humans are probably evolving to slowly eradicate the gene - but not enough time has gone by for it to completely disappear and there are still MANY cases of sickle-cell disease.

SteveBaker (talk) 22:47, 14 August 2008 (UTC)

Just a note - in the USA and Europe we can prevent and treat malaria fairly easily, however it remains a major killer in Africa. DuncanHill (talk) 22:54, 14 August 2008 (UTC)

Yeah I understand the advantage of diversity, I was more looking for specific examples of blood type affecting fitness. Thanks for the response- nice to see you back SteveBaker. Nadando (talk) 03:05, 15 August 2008 (UTC)

Worker bees can leave. Even drones can fly away. The Queen is their slave.

128.104.112.147's comment in the 'Self-sacrifice in non-human animals?' thread above got me thinking. Now, I'd always thought that the Queen bee was the dictatorial ruler of the colony and the only bee with a form of rudimentary individual intelligence, issuing commands to her army of chemically-stunted-and-controlled, utterly dispensable offspring-slaves from the safety of the bowels of the hive. On more than one occasion, I actually have found myself thinking what a shame it is that the worker bees don't have the capability to realize how badly they're being screwed. :)

So anyway, to my question. Are there any social insect species where the above scenario does apply? --Kurt Shaped Box (talk) 23:59, 13 August 2008 (UTC)

I won't necessarily answer your question but I will point out that since the ultimate goal of life is generally for genes to propagate themselves, it is very much in the worker bee's interest to hang around the hive. They are (I think) 3/4-related to the queen so the best chance of propagating their own particular genome is to hang in there with the queen. The "fly-away-and-be-free" scenario doesn't work out so well for honeybees, since they'd need to organize a group rebellion, in order to have a workable group to handle food collection and storage, defence, etc. Franamax (talk) 00:13, 14 August 2008 (UTC)

Actually, about every 2 or 3 years, the workers DO rebel. If the queen's egg laying declines, the workers raise a number of new queens. The queens in the hive then either go on a killing spree and battle it out to the death with any other remaining queen, or leave, taking a wad of workers with them called a swarm. Furthermore, while the drones live it up during mating season, roaming freely in and out of any hive at will, at the end of the nectar gathering season, they get kicked out of the hive and starve to death. Worker door women stand guard at the entrance to the hive and prevent the drones from returning. So the drones don't have it as well as you might think. The worker bees live on the average about 6 weeks during the height of the nectar gathering season. They literally work themselves to death, flying back and forth up to seven miles to get nectar and pollen. When there is an intruder, I don't really think the workers know they're going to die after stinging. When a bee gets injured, it put's off a stong odor. It's probably a ferimone thing. When the other bees smell that smell, they go crazy. I'm sure it's uncontrollable, having experienced it many times. —Preceding unsigned comment added by 98.163.102.226 (talk) 18:28, 14 August 2008 (UTC)

I am reminded of the story The Mother Hive, in Actions and Reactions, by Rudyard Kipling. In it, a wax moth foments rebellion amongst the more impressionable members of a hive. DuncanHill (talk) 00:38, 14 August 2008 (UTC)

Bees are one of those creatures where thinking about it in terms of individuals makes not a whole lot of sense. I find it easier to consider the entire hive a single organism, since genetically and practically that is how it functions. The worker cannot flee the hive any more than your hair can choose to flee your head.

In any case, I don't think the queen has anything like a "rudimentary" intelligence, and she doesn't "issue orders". Don't confuse the political metaphors we use as applying at all at the insect level. She isn't really a "queen", they aren't really "workers", and they certainly have nothing like the human concept for "freedom". They're little robots at best, doing the only things they are pre-programmed to do. Every member of the hive is like this. All insects are like this. Brains are not where their exceptional abilities lie. --98.217.8.46 (talk) 00:39, 14 August 2008 (UTC)

Yeah - I agree. Bee hives and Ant nests are best considered to be single individuals made up of many sub-units. Just as we humans have semi-independent white blood cells swimming around in our veins. We don't consider those to be separate beings because they can't survive and reproduce on their own - and the same thing is true of individual bees and ants. Calling the lone egg-layer a "Queen" is to antropomorphise the situation. She's just one part of a composite organism. The ways ants communicate and get work done is bizarre if you look at individual ants. They do the dumbest things - but the net result of a bazillion individuals working mindlessly is some kind of hive-brain. An intelligence that lets the entire colony react to problems and deal with them appropriately. It's an "emergent property" of all of that dumb behavior. SteveBaker (talk) 03:53, 15 August 2008 (UTC)

Have you considered that the bees may be right and you wrong in your thinking? Am I a slave to look after my children? Should I resent it? I am here because of all my ancestors and I do what I do because they did what they did. Dmcq (talk) 08:35, 14 August 2008 (UTC)

You might like looking at Polyergus (Amazon ants) for a real case of slavery amongst ants. Do you suppose the slaves are happy or sad about this :-) 08:50, 14 August 2008 (UTC) —Preceding unsigned comment added by Dmcq (talk • contribs)

How are they any more slaves than other ants? They were born in a different colony to a different queen, but it's not like they have any way of knowing. — DanielLC 15:43, 14 August 2008 (UTC)

Well, the normal "purpose" of any animal is to perpetuate it's genes into the next generation. When the "slave" Formica ants work for the "slavemaster" Polyergus ants, they aren't working to perpetuate their own genes - they are perpetuating the genes of the Polyergus and ensuring that future generations of the Formica species will do less well than they otherwise would because there will be more Polyergus around. They are working without hope of earning any payback...work for no pay is either volunteerism or slavery. They clearly don't volunteer - so I'd have to call them slaves. However, ants aren't exactly smart as individuals - the Formica's are captured a pupea and when they hatch, they evidently have no clue that they are enslaved. They aren't under coercion - they could walk away at any time and return to their original colony if they wanted to. So it's hard to tie this to a human analog...slaves who don't even know that they are slaves?! It's dangerous to anthropomorphise. What about the cuckoo? Momma cuckoo lays an egg in another birds' nest - the baby cuckoo has evolved to hatch in less time than it's nestmates and it's instinctive first act after it hatches is to push the other eggs out of the nest - thereby "murdering it's step-brothers and step-sisters". Is this a morally unacceptable thing - or is it merely a clever evolutionary strategy? The more we learn about this stuff - the harder it is to attach values to these kinds of actions. SteveBaker (talk) 03:53, 15 August 2008 (UTC)

August 14

Issue of quantum

mooved from the language desk Julia Rossi (talk) 00:24, 14 August 2008 (UTC)
moved back to the language desk here Wikipedia:Reference desk/Language#issue of quantum DuncanHill (talk) 01:06, 14 August 2008 (UTC)

Since this has been moved forth-and-back, I'll fill in the space with a different question/comment. We often see in the popular media that something or other represents a "quantum leap", i.e. it is a major advance. In the physics interpretation, a quantum is the smallest possible change. Does anyone else note this dichotomy? Franamax (talk) 02:27, 14 August 2008 (UTC)

Yep have noticed -- suggest is mis-used because while it means "very small" people use it to mean radical change better served by "paradigm shift" or something about "giant step for..." etc. when trying to impress. Quantum unfortunately became a buzzword when quantum as theory made a big impression on the public (media) mind. One small sacrifice for accuracy... one big leap for rhetoric? Julia Rossi (talk) 02:57, 14 August 2008 (UTC)

Now there's a good point! If the choices are "paradigm shift" or worse yet, "tipping point", maybe I should convince myself that I'm happy with "quantum leap". Ughh, I do dislike such choices... :( Franamax (talk) 03:03, 14 August 2008 (UTC)

I can't imagine that a speaker would look too closely at the meaning of what they say, intending only to sound important and blind them with science catch phrases. A comparison is when science popularisers use football fields to talk about the universe. It's the dumb or dumber option that gets you, isn't it. Julia Rossi (talk) 03:17, 14 August 2008 (UTC)

Btw, "leap" would be enough in itself really, I can't imagine a little leap. Julia Rossi (talk) 03:19, 14 August 2008 (UTC)

This too-often-heard complaint about the expression "quantum leap" or "quantum jump" is not a good point. First, a quantum leap or jump is not necessarily the smallest possible transition. For example, for an electron in shell 1 of an atom the smallest possible transition is to shell 2, but it could also jump directly to shell 3 or 4 or 5, or for that matter, shell 1,729. Second and more important, the complaint amounts to missing the point of the metaphor, which is that a quantum leap or jump involves an instantaneous transition between states without passing through any intermediate states. The size of the transition is irrelevant. If the price of oil is $100 one week and $130 the next, this represents a change so rapid that it seems as if $101, $102, $103, $104, etc. had been directly skipped over -- as they might be if the price was quantized and intermediate values were not possible. --Anonymous, 03:30 UTC, August 14, 2008.

(e.c.) To me, "quantum leap" signifies an abrupt change from one "state" to another, as opposed to a gradual change through a series of intermediate states. I think of this as an analogy to an electron jumping from one orbital level to another without going through any intermediate state. Wanderer57 (talk) 03:39, 14 August 2008 (UTC)

I'll buy both those positions, if I interpret them correctly, you're saying that a quantum is an indivisible amount. But that can apply to anything: I make bicycles, last year I painted them all black. This year I paint them all blue. We changed over the paint line on January 1st, no bicycles were painted with an intermediate colour. Thus I have achieved a "quantum leap" in bicycle design. I used to put cream in my coffee before carrying it over to the couch. Now I carry the coffe mug and the cream over, then put the cream in (less spillage). There was no overlap in my methods. Thus a "quantum leap" in coffee/cream handling. Doesn't the term then become meaningless? Franamax (talk) 03:51, 14 August 2008 (UTC)

It doesn't sound like we're saying the phrase isn't meaningless. DMacks (talk) 05:00, 14 August 2008 (UTC)

I pour the cream and sugar into the coffee but never stir - because every morning when I wake up, the first thing I want to be sure of is that the laws of statistical mechanics which dictate brownian motion and convection are still applicable - and this is sufficient to reassure me that we still live in a causal universe and I am safe for another day. Well, that is the second thing I need to do, after I check Wikipedia Reference Desk. Nimur (talk) 15:13, 14 August 2008 (UTC)

Just want to point out that "quantum leap" is a phrase from the Bohr model of the atom, not from modern quantum theory, which replaced the Bohr model circa 1925. So aside from being inappropriately applied, the term is also 80 years out of date. -- BenRG (talk) 11:18, 14 August 2008 (UTC)

Re Franamax's point. To me, the change in bicycle color would not "qualfy" as a quantum leap. It's not a dramatic enough change. There were lots of blue bikes around before your new models came out. If you introduce a new coating next year that makes your bicycles invisible and therefore less likely to be stolen, that might more reasonably be called a quantum leap.

If the term quantum leap is used for changes such as paint color, or how you prepare your coffee, I agree the term becomes meaningless. Wanderer57 (talk) 13:57, 14 August 2008 (UTC)

plum tree bark

Are there any poisons in plum tree bark? —Preceding unsigned comment added by 210.55.43.55 (talk) 06:49, 14 August 2008 (UTC)

Dr. Duke's Phytochemical and Ethnobotanical Databases list only several flavonoids in the wood so there is some probability that there is nothing really bad in the bark. If you're thinking about cyanides as per amygdaline, that is only in the seeds, according to Dr Duke. Oh, and that's only concerning humans. Animals/microorganisms may react differently. So please be more specific. --Ayacop (talk) 09:06, 14 August 2008 (UTC)

'pop' sound 11 seconds after a shooting star

Unfortunately I missed the Perseids this year, and I wasn't in a quiet area anyway. When I was a teen-ager, though, I remember standing outside our house watching the perseids with my father and my brother, and we noticed that approximately 11 seconds after each one, we heard a distinct 'pop' sound. It sounded a little like a shotgun being fired several miles away. None of us could think of an explanation for this, so we wrote to Patrick Moore, and he replied saying that it was not possible. I'm not talking about this kind of sound, it was very different. Can anyone think what this might have been? My father was a physics teacher, and my brother and I are both fairly scientific in our ways of thinking, so I really don't think that it was a psychological phenomenon or just a naïve mistake. — PhilHibbs | talk 09:07, 14 August 2008 (UTC)

Could it have been a shotgun being fired several miles away? --Ayacop (talk) 09:13, 14 August 2008 (UTC)

The same time delay after each one? I guess some crackpot could have been trying to shoot down the alien invaders. Seems unlikely though. — PhilHibbs | talk 09:45, 14 August 2008 (UTC)

How sure are you of the time interval? Hearing sounds produced by meteors is not unusual, but 11 seconds translates to a distance of only 3.8 km if 350 m/s is used for the speed of sound. If I remember correctly, the average time interval is more than a minute, corresponding to a distance of >21 km.

Also, did you hear a sound after every meteor? If not, what was the dimmest meteor that you heard? --Bowlhover (talk) 09:54, 14 August 2008 (UTC)

Pretty sure. We timed it by counting at first, I think one of us used a wristwatch. And yes, once we first noticed it we heard the sound after every one we saw. — PhilHibbs | talk 10:09, 14 August 2008 (UTC)

I know 11 seconds makes no sense at all for an object that burns up in the mesosphere, which is 50km up, a distance that the meteoroid should travel in around one or two seconds if it doesn't burn up. Unless, of course, they are making it through the atmosphere to an altitude of around 3.8km and then exploding. — PhilHibbs | talk 10:21, 14 August 2008 (UTC)

I call foul - this is all bogus.

Sound moves faster at higher altitudes and at higher temperatures. 380 ms^-1 is roughly the speed of sound AT SEA LEVEL. - so they could be higher than 3.8km and the sound would still reach you in 11 seconds...but it's not enough to double the altitude we estimated already. These are hot, supersonic objects - maybe there is something odd going on because of that? But it still sounds wrong to me. With the denser meteor showers, meteors come in at a rate of more than one per minute - with a more realistic interval of one minute between meteor explosion and the sound arriving at your ears, it's much more likely that the sound you were hearing was from the PREVIOUS meteor than the one you were actually looking at. But that would make an absolutely solid 11 seconds unlikely - meteors don't arrive that regularly.

Worse than that - even if these meteors were exploding at an unexpectedly low altitude and AMAZINGLY close to your location, they are all different sizes, shapes and masses - there is no way they'd all blow up at the exact same altitude - you'd get a WIDE spread of times, not something as repeatable and precise as 11 seconds - you'd be saying "Oh, somewhere between 10 and 20 seconds". So this makes zero sense.

I strongly doubt that the sound of a meteor "exploding" would be loud enough (they don't so much "explode" as gradually boil away anyway...that's why you get the long trails) - I think you'd have to be hearing sonic booms as they hurtled past. That means that the point at which the meteor started to glow visibly (when you start your timing) would not correspond to the moment when the sound barrier was broken - a cold, dark meteor could create a sonic boom long before it started to glow and be visible. Hence the time when you started your measurement is not related to the moment when the sound was produced anyway - so all bets are off.

The times are both too short and FAR too repeatable. I suspect "observer error".

SteveBaker (talk) 22:05, 14 August 2008 (UTC)

Hold on, sound moves faster at higher altitudes? Below the tropopause, the temperature usually decreases as altitude increases. 350 m/s should be too fast and 3.8 km too high, not the other way round.

I agree that the OP was probably suffering from confirmation bias. This type of bias has nothing to do with insanity or unscientific thinking; the only requirement is for an observer to believe his or her theory.

One more point: if the sound you heard was due to an actual physical effect, you should have occasionally heard the sound without seeing a meteor. After all, some meteors were blocked by obstructions and some were outside your field of view. Did you ever hear a "pop" without seeing its source? --Bowlhover (talk) 03:57, 15 August 2008 (UTC)

Steve? O_O -hydnjo talk 00:44, 15 August 2008 (UTC)

Another thought. Do you live in an 'underprivileged', 'rural' area? If so, have you considered the possibility that some whiskey-enhanced redneck was sat on his roof and trying to shoot down meteors with his 12-gauge shootin' iron? --Kurt Shaped Box (talk) 00:52, 15 August 2008 (UTC)

That's not probable because different observers see different meteors and different numbers of meteors. The length of time one has been outside, eye sensitivity, viewing direction, obstructions like trees, and other factors make it extremely unlikely for two people to see the exact same meteors. --Bowlhover (talk) 03:57, 15 August 2008 (UTC)

Kidney output not in article

What is the normal healthy human kidney output in ml/hr. Not home work I just want to know. Its not in article. —Preceding unsigned comment added by 79.76.203.9 (talk) 10:52, 14 August 2008 (UTC)

Output depends on input. Roughly, the normal range is 1 to 2 liters per day. If we take the average 1.5 L, and divide by 24 hours/day, we get about 63 ml per hour. That's obviously both kidneys. If you want, you can half that for the value of one kidney's output. You may be interested in oliguria, which contains other values relating to the question. - Nunh-huh 10:58, 14 August 2008 (UTC)

Im not looking for medical advice but was just wondering if a total kidney output of 91 ml/hr is considered normal in a healthy human. —Preceding unsigned comment added by 79.76.203.9 (talk) 15:07, 14 August 2008 (UTC)

More than the amount given above could be easily due to ingestion of diuretic food plants like asparagus or rice (there are a many more of them). --Ayacop (talk) 16:06, 14 August 2008 (UTC)

Or by drinking a lot of water. 91 ml/hr = 2184 ml/day is on the high end of normal. Polyuria (which you should look at) has a somewhat arbitrary cut-off of 2500 ml/day. In general, the concern would be for low urine output, not for high output; if high output is noted a urinalysis (to check for urine glucose or protein) will be more useful than quantifying the amount of urine. If you've noticed you're peeing more frequently than you used to, it's probably something to mention to your doctor and let him or her deal with it. - Nunh-huh 18:37, 14 August 2008 (UTC)

CD player -- most common type of fault

What is the most common type of fault associated with CD players that causes them to refuse to read a disc. Is it faulty transport (tracking) or the other electronics? —Preceding unsigned comment added by 79.76.203.9 (talk) 10:57, 14 August 2008 (UTC)

In my experience dirty lenses cause far more read failures than anything else. ~ mazca ^{t | c} 12:04, 14 August 2008 (UTC)

...and you can get lens-cleaning disks to sort that out. However, I have had several CD players that seemed to have worn out and refuse to read disks consistently no matter how much I clean them.--Shantavira|^{feed me} 12:14, 14 August 2008 (UTC)

Ive tried the lens cleaner a number of times: some times it improves matters; sometimes not. If not I then resort to a sharp bang on the case. This more often than not sorts it. What could be the problem as Im getting tired of having to bang it all the time —Preceding unsigned comment added by 79.76.203.9 (talk) 15:11, 14 August 2008 (UTC)

My guess would be some problem with the lens carriage (the part that moves the lens back and forward along the CD) - it could potentially just be sticky or have some bits of debris on it that partially jam it, which would be temporarily solved by banging the case. Giving the player a good squirt of compressed air may well clear some of it out, but it's quite possible that the motor itself has some dust in it, which may be harder to fix. ~ mazca ^{t | c} 17:00, 14 August 2008 (UTC)

My impression, at least in the older players I'm familiar with, is that the analog focus and tracking servos get "out of whack". In these older designs, they're adjustable via trim-pots but you need the manufacturer's service documentation to know which of the half-dozen or so pots to turn and under what operating conditions. But yes, ordinary mechanical failures (like a need for cleaning and lubrication on the sled drive) also take their toll over the years.

Atlant (talk) 18:48, 14 August 2008 (UTC)

Yeah, i'm pretty sure that was the problem with my car's old CD player - it would get very confused in some situations and fail to focus on the correct parts of the CD, just generally spending thirty seconds failing before giving a CD read error. But it was impossible to fix in my case, I ended up "repairing it with a new one". CD players are pretty precision-dependent instruments, and time does take its toll as parts warp and decay. ~ mazca ^{t | c} 20:36, 14 August 2008 (UTC)

Railway locomtive Steam Cycle...

I will have a look around, but does anyone here know of anything specfic thats been written on the software simulation of railway steam locomotives? I'm particualrly interested in what if any mathematical models they use. Sfan00 IMG (talk) 11:22, 14 August 2008 (UTC)

Since steam locomotives became obsolete by the time computer simulations were possible, I wouldn't expect many resources to be put into such models. However, I suppose it's always possible that someone did such a simulation to study trains of the past. StuRat (talk) 17:14, 14 August 2008 (UTC)

UFO sightings

Why world's most UFO sightings are reported from the United States? A quick review of the article List of UFO sightings prove Americans are more likely to see UFOs than people of any other nation. Is there any sociological analysis behind this? Otolemur crassicaudatus (talk) 14:10, 14 August 2008 (UTC)

It doesn't prove anything, unless you are certain that the methodology used to construct the list is free of systemic biases. -- Coneslayer (talk) 14:11, 14 August 2008 (UTC)

However most UFO sightings are reported in the United States. This google search result is interesting. Otolemur crassicaudatus (talk) 14:16, 14 August 2008 (UTC)

There are all sorts of possible reasons, many of which depend on your opinion of the ontological state of UFOs (that is, your opinion of what they may be):

1. Americans expect to see them (due to conditioning by the media, etc.) and thus do see them more often
2. There are better/more organizations to report them to in the USA
3. When an American sees something they don't understand, they report it as a UFO; in other countries, they might just let it go or expect it is something mundane
4. There are more potential UFO phenomena in the US (more testing of military vehicles near semi-populated areas, more weather balloons, more incursions by foreign vehicles, or more aliens—feel free to take your pick)
5. In the USA, there is an existing "market" for reporting on sightings, and no political repercussions for doing so

And so forth. In my uninformed opinion it's probably a mix of the above (though I don't really suspect aliens). If an American sees a funny light on the horizon that zooms off in a funny way, he or she is probably more likely to say, "omg, a UFO". --98.217.8.46 (talk) 14:23, 14 August 2008 (UTC)

Not to mention, you have been reading the English Wikipedia, which is disproportionately contributed to by American editors due to language barriers. If you read that same article in Finnish you will see a different breakdown of sighting locations. Nimur (talk) 15:19, 14 August 2008 (UTC)

Kang and Kodos think americans about ready and would like to serve them. Mwah ha ha ha ha ha ha hah. Foolish earthlings use of military power also more interesting than watching ants. Dmcq (talk) 15:27, 14 August 2008 (UTC)

That idea is much older: The reason that we never meet our 'owners' is that they have no interest in talking with their 'livestock' (The Book of the Damned, given just to show that UFOs were hot in 1919 already. Appears to me a continuation of the parapsychology/occultism hype around 1900). --Ayacop (talk) 17:12, 14 August 2008 (UTC)

From list of UFO sightings, I counted 40 UFO reports within this decade, 13 of which were reported by Americans. Considering that the U.S. is the most populous and second largest developed country, 1/3 does not seem impressive to me. --Bowlhover (talk) 06:07, 15 August 2008 (UTC)

Skin effect in transmission lines

By what circuit techniques can the deleterious effects on pulses of skin effect be compensated in a delay line (transmission line). Not homework I'm just curious how its done in oscilloscopes and if there are other more advanced techniques.--79.76.203.9 (talk) 15:20, 14 August 2008 (UTC)

The most common physical technique is to silver-plate the conductor so the current, forced into the "skin" of the conductor, is flowing in a material with the highest possible conductivity. Otherwise, circuit techniques might include an equalizer or an all-pass filter.

Atlant (talk) 18:40, 14 August 2008 (UTC)

OK As i was interested in circuit techniques (because I cant fix the transmission line itself), the equalizer seems preferable. What sort of equalizer would I need? —Preceding unsigned comment added by 79.76.203.9 (talk) 23:19, 14 August 2008 (UTC)

Use SPICE or something to model your transmission line (or equivalent) and vary the distributed series resistance so you can see the effect of rising skin resistance. Then design an equalizer that nulls that out. You may also find the group delay varying and that's why I suggested an appropriate all-pass filter that is specifically designed to cancel the group delay variance.

Atlant (talk) 23:28, 14 August 2008 (UTC)

OK do you have any details on how I should proceed to model the transmission line skin effect in Spice and then design a compensating network--79.76.203.9 (talk) 00:26, 15 August 2008 (UTC)

Electric Current

electric current is a flow of whatkind of charges? positive charges or negative charges.VaibhavIIT (talk) 15:42, 14 August 2008 (UTC)

See electric current. The answer, by the way, is negative (electrons are negatively charged). -- Aeluwas (talk) 15:46, 14 August 2008 (UTC)

But, notationally, the current direction is treated as if carriers were positive charges: See Electric current#Conventional current. -- Coneslayer (talk) 15:51, 14 August 2008 (UTC)

Well, normally (in metal wires and such). In P-type semiconductors the charge carriers are mostly positively charged holes, while in ionic solutions both positively and negatively charged ions could flow simultaneously. See charge carrier for more. Algebraist 15:58, 14 August 2008 (UTC)

In the electronics industry, the concept used by design engineers is that electricity flows (outside the generating source) from positive to negative. Electronics technicians use the concept that electricity flows the opposite way - from negative to positive. Occasionally, engineers and technicians will argue about this. The technician can always stump the engineer by asking him to explain the operation of a CRT (cathode ray tube). I think engineers have stayed with what was a very early concept, before any knowledge of "holes" and all that. To switch concepts would cause confusion when referring to text and formulas - the engineer would not know which concept was used. Magnetic polarity in motors and electrical equipment would also be involved. Technicians use the concept of electron flow, which is the true way to regard it. The concept of holes moving is ridiculous. A hole is nothing - how can nothing move? However, the concept of holes makes certain phenomena easier for the mind to handle. (Positive ions do not enter into most practical electronic phenomena. It is true that the atoms of a metallic conductor are constantly ionized and de-ionized as flowing electrons enter and leave orbit in the atoms; but the atoms do not move, and this can be ignored for practical purposes.) Andme2 (talk) 02:50, 15 August 2008 (UTC)

Hot water cold water

I seen video on Utube showing hot water freezes faster than cold water in the ice box. Anyone know why that might be?--79.76.203.9 (talk) 15:59, 14 August 2008 (UTC)

Mpemba effect? DMacks (talk) 16:07, 14 August 2008 (UTC)

I have read that water that has been boiled, then allowed to cool, will freeze faster than water from the same source that was not boiled. The reason is that boiling removes dissolved gases from the water; that makes it easier to freeze. Even distilled water may include dissolved gases. Also, water from two different sources may contain different impurities and different amounts of dissolved gases, making a difference in the freezing temperature. (Sea water freezes at a lower temperature than fresh water.) Also, ions in water might make a difference. I have heard of "deionized" water. Andme2 (talk) 19:31, 14 August 2008 (UTC)

It turns out to be a really complicated thing. Stuff like the conductivity of hot water being relatively poor - so the edges and top of the liquid that are exposed to the cold freeze quickly because relatively little heat is being transported from the interior of the liquid. With cold water, warmth from the interior of the liquid is conducted to the outside more easily - so the whole volume pretty much has to freeze at once. At first sight, it looks like the hot water froze first - when in fact, the interior of the ice block is still liquid. Then there is lots of complexity due to whether the hot water has been boiled (driving out dissolved gasses) and the cold water hasn't. There are a TON of complicating factors. It's still cool though! SteveBaker (talk) 03:23, 15 August 2008 (UTC)

Electromagnet

If two 7 oz with 100 wraps of wire electromagnets were repeling each other, what would be the force in newtons? Hovercraft Experts (talk) 16:05, 14 August 2008 (UTC)

Practically zero...they are too far away to affect each other and there's no current flowing through the wire. Or did you forget to include some information while copying what looks like a homework problem? Our article about Electromagnets has lots of equations to help you. DMacks (talk) 16:10, 14 August 2008 (UTC)

You need to specify the core material,the current, the geometry, and the distance between magnets for there to be any meaningful answer to the question. Edison (talk) 03:13, 15 August 2008 (UTC)

The End Of The World as we know it!

Inspired from a previous question, what is theorized about charged micro black holes? If they were able to chew up planets or stars we would have seen suspiciously small black holes in space, too small to have been collapsed under there own gravity. But what if we could produce micro black holes with a half life of thousand years, would it be possible to create totally new materials? The article on exotic atoms doesn't mention anything like that --- well, myons have a half life of 2 microseconds, not enough to exploit the chemical properties of myonic atoms. But I miss any note that myons and other fermions don't share orbits with electrons. 93.132.156.107 (talk) 20:17, 14 August 2008 (UTC)

Even if we did have stable micro-black holes that somehow created them, nearly all exotic particles (ie other than proton/neutron/electron and some neutrinos) are just inherently unstable with respect to those, so even if (somehow) a micro-black hole allowed us to produce muon-orbited atoms, say, it wouldn't make them any less massively unstable. ~ mazca ^{t | c} 21:15, 14 August 2008 (UTC)

You misunderstand. His question is whether a charged micro-blackhole could itself substitute for an electron or proton, thus giving rise to "atoms" with different chemical properties. Dragons flight (talk) 21:51, 14 August 2008 (UTC)

Ah, thanks for clarifying. In that case I'd still suspect it would be unlikely due to instability - assuming the theory of Hawking radiation is correct, a micro-black hole small enough to substitute for a subatomic particle would have a lifespan measured in tiny fractions of a second. ~ mazca ^{t | c} 22:17, 14 August 2008 (UTC)

That's a false conclusion. If you compare the lifetime estimate from Hawking radiation to Schwarzchild radius there is a substanitial population of hypothetical black holes with masses from 10⁷ to 10¹⁶ kg where the event horizon is smaller than 1 angstrom (a typical atomic size) but the lifetime is from days (at 10⁷ kg) to longer than the age of the universe (at > 10¹¹ kg). Setting aside the intractable problem of how you create or find a 10¹⁰ kg black hole in the first place, they would appear to be the right size and relatively stable. Dragons flight (talk) 23:30, 14 August 2008 (UTC)

Are your numbers with respect to charged or uncharged? 100 TeV is not 10⁷ kg by far. So to become heavy enough to be stable it would need too much time, wouldn't it? --Ayacop (talk) 08:17, 15 August 2008 (UTC)

Thanks for your answers. As I understand, a micro black hole that is to last in the range of seconds would need a mass > 10⁸ kg and that makes it quite unsuitable to exploit chemical properties of any material it may build. But, say, if a 100TeV MBH manages to swallow just one electron and gain its charge, would the formula for hawking radiation still be the same? I think it can't go on evaporating, keeping the charge, nor could it loose charge gradually. So I guess it would have to spit out the electron in a non-continuous process. Is it that way? 93.132.140.20 (talk) 07:15, 15 August 2008 (UTC) (Sorry, this should have gone to the end of the section 93.132.140.20 (talk) 07:35, 15 August 2008 (UTC))

But would a black hole of that size produce appropriate amounts of strong & weak nuclear forces to hold the bulk material together against it's own gravitational field? Could we get such a hole into a state where it has a positive charge equal to exactly the desired number of electrons? As a practical matter, it seems pretty intractable. SteveBaker (talk) 00:13, 15 August 2008 (UTC)

We are talking about "atoms" that have the same weight as mountains, and it is the charge that strikes you as implausible? Forget everything else, there is no material on Earth that could support that weight and keep a 10¹⁰ kg atom from falling into the core of the Earth. Dragons flight (talk) 04:14, 15 August 2008 (UTC)

It looks like any useful massed black hole would decay too quickly. So if you had a 1000 H mass black hole, does theory predict it will decay in a tiny fraction of a second? Or could it get stuck in a level where decay was too improbably to happen? Graeme Bartlett (talk) 05:02, 15 August 2008 (UTC)

Causality

Problem:
First, let us assume a hypothetical scenario, the earth orbits around the sun and it takes light about 8 minutes to travel from the Sun to the earth (this is not the hypothetical part), following this, let us say that by some unexplained phenomenon, the Sun were to disappear all of a sudden leaving a void in it's place and it would take 8 minutes for a species on earth to figure out that the sun is missing, if they were to depend on light for that information. We also know from the general theory that even the gravitational waves in space-time shall travel at the speed of light and hence the path of earth shall be a conic section for 8 more minutes after the Sun disappers, then it shall start moving tangentially to the conic section.
The question is why can't gravity be an instantaneous force, i.e. how would causality be effected IF gravity was an instantaneous effect? because it really doesn't have to matter if the species can see or not see the Sun, as seeing does not imply the Sun's existence, so even if the light from the sun would still be coming, the gravity would tell us that the Sun is missing, and no causality would be broken. Also, can this problem be modifed in order to suggest the breaking of causality? because in no way can I think the effect of gravity can take place before the Sun has disappeared.
Aah! The simultaneity is the issue, there would be a frame of reference in which the laws of physics act in a manner that Earth changes it's orbit before the Sun disappears. Sorry, I got the answer myself, (the laws of physics should hold in ALL frames of reference), but an interesting question nevertheless, open to discussion too. Maybe someone might have an interesting insight. Aks... (talk) 21:54, 14 August 2008 (UTC)

Asking "what if" with an utterly inconsistent thing like this cannot lead to any kind of a consistent answer or even meaningful speculation. We know gravity isn't an instantaneous effect precisely because everything else would end up being inconsistent if it were. It's kinda like asking "What would the world be like if all of the rules of arithmetic were absolutely normal except that 2+2=7 ?" - the answer is...what? There can't be an answer. SteveBaker (talk) 00:26, 15 August 2008 (UTC)

I believe the question which I put forth was not what if, but why? As far as I understand, the general theory predictions about the speed of gravitational effects came about due to the loss of causality if it were infinite. Hence, even before tests were done, it was suggested that Gravity was NOT instantaneous. Hence, the issue is what were the problems in causality that suggests a limited speed. Therefore, the question is not irrelevant, as there has to be an underlying inconsistency if the physicists believed it was instantaneous. To put it in your way, the question is if all the rules of arithmetic were normal, and we did not know what the value of 2+2 was, why couldn't it be 7? what would lead you to believe that it is NOT 7. Quoting SteveBaker "We know gravity isn't an instantaneous effect precisely because everything else would end up being inconsistent if it were.", what are those inconsistencies? I believe the inconsistencies came before the idea that the gravitational effects are not instantaneous, hence the inconsistencies must have been due to that instantaneous effect assumption. Aks... (talk) 09:34, 15 August 2008 (UTC)

Uses of propane vs. uses of natural gas

Why is it that in residential uses propane has become specialized for use in portable applications (e.g. some barbeques) while natural gas is used in fixed applications (e.g. stovetops)? Seemingly, propane would be the best overall gas since its energy density is higher than that of natural gas, but obviously there must be other effects in play. Thanks --Colonel Cow (talk) 22:03, 14 August 2008 (UTC)

As far as I'm aware, propane - as a pure substance that has to be derived sequentially by cracking of oil - is substantially more expensive to produce than raw, methane-based natural gas which is extracted directly in a near-usable form from gas wells. In terms of camping-gas stoves, for instance, the predictability of a pure fuel combined with the maximum energy-to-weight ratio is worth the extra expense, but when you're piping the substance to houses or power plants, the lower cost of natural gas more than outweighs the lower energy density. ~ mazca ^{t | c} 22:20, 14 August 2008 (UTC)

Propane is heavier than air - natural gas is lighter. This is very important - you don't want your basement filling up with unburned cooking gas! Also, if there are any small leaks in the gas pipeline, natural gas doesn't pool in underground puddles ready to explode at some inopportune moment as propane would. Instead it drifts up into the air and is soon diluted. But for barbeques and such propane is easier to liquify than natural gas - so you get more of it in a cheaper cylinder - it also produces more energy per kilogram - so you don't need as much to cook your food and that makes it better for portable applications. SteveBaker (talk) 00:37, 15 August 2008 (UTC)

(ec)Is natural gas lighter than air? I have made soap bubbles with it, and they sink in air. It also pools in a cooker hob if the gas ring is left on unlit. DuncanHill (talk) 00:51, 15 August 2008 (UTC)

Yes - sure it's lighter than air - it's mostly methane which weighs about 0.7 kg/m³ versus air at 1.2 kg/m³ (our article Natural gas agrees with me - which is always a bonus!). But perhaps it's not sufficiently light to lift the weight of the (heavier than air) soap in the soap bubble? Hmmm...you get maybe 30cc's of gas in a bubble about an inch across - so with a density difference of 0.5 kg/m³ you've got about 15mg of lift...the wall of the bubble is very thin (our article says 25 nanometers) - so with a surface area of maybe 20 cm² and a thickness of only 25nm - your bubble should weigh 0.0005 mg - it should have PLENTY of lift! I don't know why it wouldn't rise. Are you SURE you have natural gas and not propane? SteveBaker (talk) 03:17, 15 August 2008 (UTC)

Many homes in the U.S. use propane for heating. See this map on which dark blue indicates counties where propane has 25% or more of the market share for home heating. The article from which the map comes says that in 2005, propane accounted for roughly 6% of residential heating. Another chart shows how the 7 quadrillion BTUs of energy for home heating are divided; according to this, propane accounts for nearly twice the quads of electricity, and 70% of the quads provided by heating oil. — OtherDave (talk) 00:49, 15 August 2008 (UTC)

Wikipedia discusses these heating gases under "propane", "natural gas", and "butane". These articles give lots of information but (in my opinion) are rather confused write-ups. They need editing. But my thanks to those who did the write-ups for taking the time to provide the info - they knew their subject but undoubtedly were not professional writers. Andme2 (talk) 01:08, 15 August 2008 (UTC)

More important than the "heavier/lighter" than air question is the fact that propane can be stored in liquid form at normal ambient temperature, allowing a huge amount of energy to be stores in a small tank at fairlty low pressure and without the extreme cooling needed to keep natural gas/methane a liquid. Edison (talk) 03:11, 15 August 2008 (UTC)

August 15

While I'm reminded of Moluccan Cockatoos

What adaptations does this species have to prevent brain injury and whiplash whilst doing this for extended periods of time? Yep, it's another strange bird video I found on YouTube... --Kurt Shaped Box (talk) 01:24, 15 August 2008 (UTC)

Though I don't have any special knowledge about parrots, our article says they're prone to behavior disorders. And judging from the title of the video, the owner thinks this individual has a behavior disorder... so I'd say there's no reason to assume the species has any such adaptations, at least not based on this video. --Allen (talk) 04:27, 15 August 2008 (UTC)

Woodpeckers

Why don't they get a headache?--79.76.203.9 (talk) 01:39, 15 August 2008 (UTC)

Have a read of this article. It explains it all far better than I ever could. --Kurt Shaped Box (talk) 02:25, 15 August 2008 (UTC)

Dunbar's number and the autism spectrum

Do people on the autism spectrum have a lower Dunbar's number than average? NeonMerlin 03:22, 15 August 2008 (UTC)

Drawing on the articles' section Alternative numbers, the Dunbar number is actually a measure of sizes of community networks, more than a measure related to individuals. Since dunbar developed his theory, there's been notable advances in Network theory which casts doubt on his extrapolation from community to individual. For instance, a group of 150 people can be quite close-knit even if each person knows only 50 others. A few highly connected individuals may be all that it takes.

When it comes to autists, it's my impression that their sensory and cognitive difficulties present difficulties in making and maintaining social interaction with individuals, for instance in picking up non-verbal cues, but they do not generally have some memory deficiency that makes them loose track of what they've learned about individuals. So I'd say that if the Dunbar number had made sense ascribed to an individual, the answear to your question would be no. EverGreg (talk) 08:47, 15 August 2008 (UTC)

about 20 dec 2012

i have come to known through some research that on 20 dec 2012 the sun ,moon earth &ablack hole would be exactly in a straight line , will this cause a huge damage to our earth by effecting its magnetic field ,, please tell me about it as i am very keen to known about it —Preceding unsigned comment added by 210.214.18.51 (talk) 05:12, 15 August 2008 (UTC)

See 2012#Metaphysical_predictions. --Allen (talk) 05:14, 15 August 2008 (UTC)

Always remember this: if you read about an imminent apocalypse but don't hear it mentioned every day in the news, don't believe what you're reading.

It's interesting that the crackpot whose "research" you read mentions magnetism. The Moon has a very weak magnetic field, so it wouldn't affect Earth much regardless of its position. Black holes emit Hawking radiation and their accretion discs emit high-frequency radiation, but these have a negligible effect on Earth at interstellar distances.

Magnetism from black holes is certainly even less of a factor; the magnetic field weakens with the square of the distance initially and with the cube of the distance later on. To give an idea of how distance affects magnetic strength, consider that Magnetars are the strongest known sources of magnetism; at their poles, their magnetic fields are as strong as 10 billion Tesla. According to magnetar, "It has even been said that at a distance halfway to the moon, a magnetar could strip information from a credit card on Earth." That requires about 0.1 Tesla (if you trust Mythbusters), so half the Moon-Earth distance manages to reduce a magnetic field from 10 billion Tesla to 0.1 Tesla. At 1 light year, the magnetic field is between 4 x 10^-17 T and 7 x 10^-25 T. By comparison, Earth's field is ~4 x 10^-5 T, and the closest black hole is 1600 light years away.

The Sun is quite a different story. Its magnetic field is much stronger than Earth's, and solar flares often disrupt radio communication on Earth. However, there's no reason to believe the Sun would become more deadly when it's in alignment with the Moon and a black hole; these bodies have little effect on it.

You might also be interested in reading the answers to these questions about 2012: [20] [21][22]. --Bowlhover (talk) 08:22, 15 August 2008 (UTC)

There is no mention of a black hole there. Anyway, be assured that these (and all the other) predictions are complete nonsense.--Shantavira|^{feed me} 07:12, 15 August 2008 (UTC)

pH correction

How do we correct the pH of Reverse Osmosis permeate without increasing the TDS? —Preceding unsigned comment added by Knitcon (talk • contribs) 05:20, 15 August 2008 (UTC)