Wikipedia:Reference desk/Archives/Science/2010 December 24

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December 24

When two metal panels with different work functions approach, what happens?

When two metal with different work functions approach but still is seperate finally, will their surface produce opposite charge (+, and -) when at equilibrium? and will their Fermi levels line up finally?

Another similar case, when a thin oxide is sanwiched by a metal and a semiconductor, if the metal and the semiconductor with different Fermi levels, do their Fermi levels equalize when at equilibrium? --Wkfan (talk) 03:18, 24 December 2010 (UTC)

Why do superstrings "vibrate"?

What causes them to vibrate? Have they always been eternally "vibrating" or does something initially "pluck" the string to get it going? Can they ever stop vibrating? and if so what would happen then? In layman's terms please. (I'm a layman so if these questions doesn't make much sense it's probably because I'm misunderstanding some aspect of the theory :) -- œ^™ 05:17, 24 December 2010 (UTC)

It is better to think of superstring theory as a model used to represent physical reality. Like all models, it is an explanation of reality, and not reality itself. That is, these "strings" are not strings in the literal sense, which need to be plucked in order to vibrate. Rather, the attempt is to represent matter by vibrating strings, insofar as the mathematics of resonance seems to apply to the way in which fundemental particles interact. Using "standing waves" as a model for fundemental particles actually predates superstring theory by some time, for example the Schroedinger equations and wave functions are a much older model used to explain the behavior of the electron cloud in an atom. Superstring theory is in some ways expanding upon these earlier models to a more fundemental level. --Jayron32 05:24, 24 December 2010 (UTC)

A string in a frictionless environment would continue to vibrate forever. They likely existed (and vibrated) since the Big Bang, but all bets are off for what existed before that. StuRat (talk) 06:43, 24 December 2010 (UTC)

Vibration, also known as harmonic oscillation, shows up everywhere in physics. In quantum theories, because of the uncertainty principle, the vibration can never stop completely, so everything vibrates (though this "vibration" is a bit different from what you might think of as vibration in a non-quantum world). String theory is a quantum theory, and because it's possible, geometrically, for string-shaped objects to vibrate, they always do. That property of universal vibration isn't new to string theory, nor is it a particularly important aspect of string theory. The reason it's emphasized in popularizations is that they don't know what else to talk about. Explaining what string theory is really about would be too confusing, so they fall back on showing vibrating violin strings, even though those could just as well illustrate any physical theory from the last few hundred years. -- BenRG (talk) 23:13, 24 December 2010 (UTC)

makeshift loudspeaker

I'm a little confused by this: http://www.youtube.com/watch?v=oGrlz6t28XE

If the sound is being caused by the bottle vibrating, then why is it still making sound when: 1) he is holding it, and 2) when he holds it near the magnet, but not on the table? Thanks. 65.92.7.244 (talk) 08:08, 24 December 2010 (UTC)

At normal frequencies the sound is not from the bottle knocking on the table. The sound is from the bottle directly shaking the air, which causes sound waves that you can hear. Earlier, he ran it at a very low frequency of 5 hz (times per second), which is far too low for you to hear. So what he did is make the bottle knock into the table and you heard a knocking sound each time. Notice how at 5 hz you hear a series of tick, tick, tick, rather than a pure "tone". But at higher frequencies you are actually hearing those tones. Excellent question BTW. Ariel. (talk) 09:52, 24 December 2010 (UTC)

See the Wikipedia article Voice coil.

1. The source of the sound vibration is the wire that is attached to the bottle neck. The vibrations travel through the bottle material at the speed of sound in the plastic. Holding part of the bottle does not prevent other parts of the bottle vibrating.
2. The wire must be close to the magnet to be within its magnetic field for the motor effect to work. The resulting music sound is weaker but less distorted when the bottle is suspended slightly above the magnet so the downward swings of the sound vibration won't cause the bottle to hit the metal plate. Cuddlyable3 (talk) 15:15, 25 December 2010 (UTC)

Heavy luggage in small, light car

Where would the best place be to put heavy luggage (huge bags of books in this case) in a small, light car (Hyundai Atos). I put it in the trunk but it seemed to put tremendous strain on the rear suspension so I was hoping someone with the knowledge on this could help me out. I don't want to break my car but I also want to have the best fuel economy. Would the position of the heavy luggage have an effect on the fuel economy whatsoever? I'm just a student and I need to travel far so that's why I'm so curious as to where to put the bags in order to save money! :O 196.210.239.252 (talk) 11:22, 24 December 2010 (UTC)

For fuel economy I don't think the position will matter much. You use extra fuel because you have to work harder to accelerate the extra weight. But for handing purposes try to balance it evenly front to back, too much weight in the back can severely hurt handling and breaking power, too much in the front is not as bad, but still bad. Also, you will need to add extra air to the tires - besides needing to do it to keep from damaging the tires, this will also help you save money. As for how much air, I can't check the numbers for you right now, but find out how much your car weighs, and how much pressure you normally need, then divide to find pressure/weight, and then calculate that for the extra weight. Ariel. (talk) 11:35, 24 December 2010 (UTC)

Anywhere between the wheels is good. You should avoid putting heavy weights beyond the wheels, as that will cause it to handle poorly. StuRat (talk) 18:08, 24 December 2010 (UTC)

Unladen weight of the Hyundai Atos is quoted as 847 kg. It is a 4-seat car so should be within its limits carrying the equivalent weight of 4 heavy adults. Recommended tyre pressures are 30 PSI front and rear. Do check the car handbook. Cuddlyable3 (talk) 14:46, 25 December 2010 (UTC)

meningiomas (a.k.a. brain tumor;angle tumor)

Periodically I search the internet for any mention of connection between meningiomas (a.k.a. brain tumor;angle tumor)and either estrogen or progesterone receptors. I was surgically treated for such a tumor in 1991. In 1998 I was told of 'recurrence'(that word is significant in my opinion,based on research). I went to Mass Genl for radiation treatment.In making usual/customary rounds for various physical exams, it was the endocrine/ob-gyn doctor who inadvertently and casually mentioned that said tumor in my case had progesterone receptors. She didn't seem to notice my shock when I said 'what?'. "yeah, she said, they see these types of tumors all the time during autopsies, they're very common. They become problematic when they grow too large and progesterone can make one with progesterone receptors grow."

I was prescribed and took progesterone (the so-called "bioidentical good kind from Women's International Pharmacy in Denver, Co.) It was prescribed for reasons not at all 'cosmetic' or superficial. I began taking it in the mid 1980's and contimued taking it after meningioma surgery in 1991. I stopped taking it after I left the informing doctor's office that same day.

While surgeon told me he removed it all, his written record stated that it was "unlikely due to the very vascular nature of the tumor". Ir follows, with some logic I would say, that continuing to take progesterone would cause further growth, hence future problem (these tumors are slow growing). In the late 1990's *Mifeprestone (a.k.a. RU486, the abortion pill;a.k.a. "anti-progesterone") was used in clinical trials to treat meningiomas. I may have misspelled *it. While it met with significant success, there were other strange blocks(of the political and/or greedy types and tones) to making it available to those in need (many with much more frightening alternative choices,if any choice at all). My most recent search (12/23/10 revealed a brief reference to mifeprestone as treatment modality, but required much digging to get to that partial one line reference.

To this day, I cannot find anywhere by anyone any straigtforward, clear mention of this connection as I have described it. I tell every female with whom I cross paths-they 'hear' me with considerable attentiveness; I've written everyone I deem 'should know and disclose'-I know of no response or interest. I have mentioned it to every doctor/healthcare provider with whom I come into contact (most of whom not even visibly moved enough to shrug a shoulder). The kind of empty eyed void or twilight zone experience I have come to call the 'Is it just me? Am I crazy?-game. Or, why isn't 'logic' a required course?

After telling this to my dentist's assistant, she responded by telling me that during a conversation between her mother and Assurant Health Insurance Company, the rep told her mother that she was considered 'disposable'.

Can someone broaden my understanding of this?11:35, 24 December 2010 (UTC)Wastetime4info (talk)

We have a very small article on it Hormone receptor positive tumor. Nothing in the article limits it to breast, but all of the references mention that. Mifepristone may help, but nothing in there mentions cancer. This article seems to match what you wrote - it mentions meningiomas (but I did not read it), maybe it will help you. You can continue searching for articles using this search. Adding meningiomas to the search comes up with lots of stuff. You will not have access to read many of the articles, but your local public or university library probably will have a subscription, so you want to search from there. Ariel. (talk) 12:19, 24 December 2010 (UTC)

Edit: In the article meningiomas I found "Antiprogestin agents have been used, but with variable results." So it could be they did think of it - but it didn't help much. Ariel. (talk) 12:24, 24 December 2010 (UTC)

..and the source used in that article, which you may have already seen says "About 70% of meningiomas express progesterone receptors, while fewer than 31% express estrogen receptors. These observations suggest that progesterone influences tumor growth. A progesterone antagonist such as mifepristone therefore may inhibit tumor growth." This study has something to say about hormonal exposures and risk so it may be of interest if you haven't seen it before. Sean.hoyland - talk 12:47, 24 December 2010 (UTC)

To the OP: background information/observations combined with logic are the first two steps to developing a good hypothesis. However, the field of medicine generally requires more than a good hypothesis to justify treatment decisions (hence, the 'logic' course you mention is not part of the regular medical curriculum). The next step is to generate data that supports or refutes that hypothesis. There seems to have been a reasonable amount of research into whether or not hormone exposures are truly a risk factor for meningioma (see [1], [2], [3], [4], [5], and a meta-analysis of different studies here). The overall result of those studies seems to be that hormone exposure plays a minimal role in the development of meningiomas, if at all.

The next thing you are interested in is whether (based on the progesterone receptor expression in meningiomas) a treatment based on progesterone blockade, using mifepristone (RU-486) would be a good treatment. This is another excellent hypothesis, but one for which there is again no strong evidence. The best I could see was a recent study (here) that looked at long-term effects of mifepristone. The main outcome measures were tolerability and side effects, and I don't think the study was specifically designed to look at treatment outcomes. However, they did mention "minor responses" in a subset of patients (8 out of 28 treated). Altogether, it seems as though (despite the good hypothesis) progesterone blockade hasn't proven to be an effective treatment for meningioma. --- Medical geneticist (talk) 13:44, 24 December 2010 (UTC)

Testosterone levels

Does the Testosterone level in a male human body change after ejaculation? --119.155.10.188 (talk) 11:56, 24 December 2010 (UTC)

Usually, although the extent likely depends on mental health. See PMID 16871136. Ginger Conspiracy (talk) 23:22, 24 December 2010 (UTC)

The PMID reference is about treatment of sexual dysfunction in patients with epilepsy and depression but it does not seem to address the OP's question about change in hormone level after ejaculation. Cuddlyable3 (talk) 21:12, 25 December 2010 (UTC)

So normally would the level increase or decrease in an average human? --119.155.18.241 (talk) 14:50, 25 December 2010 (UTC)

Mercury's mineral status

Is native mercury a mineral? I have a cite [6] to back up my claim that it is a mineral, but nonmineral "uncitedly" states otherwise. Is it a mineral? --Chemicalinterest (talk) 17:28, 24 December 2010 (UTC)

Your reference does not exactly address the question of what is, and is not, a true mineral. According to the mercury article mercury is rarely found as a native metal. I notice your source also lists iron, which afaik, is never found as a native metal. SpinningSpark 18:16, 24 December 2010 (UTC)

I don't know how it is classified, but it is possible to find natural deposits of metallic iron (typically as micron to millimeter sized grains). It can form when iron bearing minerals are heated to high temperatures in the presence of abundant carbon and with very low levels of oxygen. A typical example is when a coal seam is set on fire by lightning or magma intrusion. Not exactly a common scenario, but such things do happen. Dragons flight (talk) 19:11, 24 December 2010 (UTC)

Chemicalinterest wasn't asking whether or not it commonly forms naturally; he was asking whether or not it would be a mineral. According to our article, "A mineral is a naturally occurring solid chemical substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties". So the answer is yes. --T H F S W (T · C · E) 21:06, 24 December 2010 (UTC)

Sorry for being so dense! "A mineral is a naturally occurring solid chemical substance". So I geuss no, if you stick to the rules. However, native copper of gold would be a mineral. --T H F S W (T · C · E) 21:20, 24 December 2010 (UTC)

Where's your citation for the "fact" that a mineral is solid? --Chemicalinterest (talk) 22:21, 24 December 2010 (UTC)

Here. --T H F S W (T · C · E) 22:31, 24 December 2010 (UTC)

THFSW, your reference explicitely states "Mercury, however, is recognized as a mineral even though it does not occur in a crystalline state on Earth". And maybe it does occur in a crystalline state sometimes: Temperatures at higher latitudes are sufficiently low - at least in the winter. Icek (talk) 23:44, 24 December 2010 (UTC)

Your source supports my source. It proves that mercury is a liquid mineral. --Chemicalinterest (talk) 00:40, 25 December 2010 (UTC)

Well, from whatever I posted on simple talk, if correct, that's not the case. native mercury = mineral. Liquid mercury = not a mineral. wiooiw (talk) 07:43, 25 December 2010 (UTC)

Native mercury is liquid mercury. Mercury does not exist in a crystalline state on Earth. Look! What needs to be found out is whether mercury (its status of liquid is given) is a mineral. --Chemicalinterest (talk) 13:07, 25 December 2010 (UTC)

Could we agree that mercury is a mineraloid, and a mineral when it is very cold? Dbfirs 20:40, 25 December 2010 (UTC)

As far as Britannica is considered, Native Mercury is a mineral, but liquid mercury does not fit the definition of a mineral, but a mineraloid. wiooiw (talk) 22:25, 25 December 2010 (UTC)

Huh, I found this and this to be quite useful. It reviews older definitions of "mineral". It appears that Brittcanica uses and older version of the definition, thus really is not a valid source to use. So, liquid mercury is now a mineral? wiooiw (talk) 23:46, 25 December 2010 (UTC)

Well, let's look at the official CNMNC guidelines (my italics):

A mineral substance is a naturally occurring solid that has been formed by geological processes, either on earth or in extraterrestrial bodies (Nickel 1995a). A mineral species is a mineral substance with well-defined chemical composition and crystallographic properties, and which merits a unique name. General criteria for defining mineral species are given below. In practice, most mineral species conform to these criteria, but exceptions and borderline cases inevitably arise, and ultimately each proposal to introduce a new mineral species or to change mineral nomenclature must be considered on its own merits.

Now looking at the official IMA-CNMNC List of Mineral Names, we see that native mercury is "grandfathered", that is its "original description preceded the establishment of the CNMNC in 1959, and [it is] generally regarded as a valid species". The only conclusion that one can draw is that the IMA considers native mercury to be an exception to the normal rule that mineral species should be solid. Physchim62 (talk) 00:08, 26 December 2010 (UTC)

Yes. THFSW's reference stated the same thing, but gave native mercury (a liquid) as an exception to the rule. --Chemicalinterest (talk) 12:21, 26 December 2010 (UTC)

Mercury is much more commonly found as cinnabar. ~AH1^(TCU) 17:55, 27 December 2010 (UTC)