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January 20

What happen to helium in our sun

I know the Sun fuse Hydrogen into Helium and after billions of years eventually it ran out of hydrogen then started to fuse helium into bigger atoms and eventually collapse. What happen to helium in those billions of years? Is it just stay somewhere inside the sun? Or is it broken down to hydrogen again to start out the fusion cycle? 184.97.244.130 (talk) 00:18, 20 January 2013 (UTC)[reply]

Eventually it will become carbon through the triple alpha process.--Gilderien Chat|List of good deeds 00:25, 20 January 2013 (UTC)[reply]

That's not what I'm asking... What happen to Helium in our Sun right now as hydrogen is still abundant.184.97.244.130 (talk) 03:20, 20 January 2013 (UTC)[reply]

Nothing at all. Currently, the Sun is fusing hydrogen into helium. This produces enough energy so that the Sun cannot collapse and become dense enough to fuse helium. Therefore, the Sun is hot enough to fuse hydrogen but not hot enough to fuse helium (yet). Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:46, 20 January 2013 (UTC)[reply]

I am not sure that is correct, Whoop. I'd really like to see some sources and articles quoted. Helium three is being constantly generated and destroyed at this point. See proton-proton chain reaction. There's no a priori reason to assume that certain, perhaps low-rate, nuclear reactions with Helium four are not also going on at this point. Citations are needed. μηδείς (talk) 04:52, 20 January 2013 (UTC)[reply]

While the rate of helium burning isn't strictly zero, it's actually astonishingly close. As noted (and footnoted) in the article already linked by Gilderien, the rate of the triple-alpha process responsible for helium fusion depends on the core temperature to the fortieth power. In a low-to-middling mass star like our Sun, the rate might as well be zero right up until the helium flash. TenOfAllTrades(talk) 05:09, 20 January 2013 (UTC)[reply]

So basically helium is just there without any interaction until the Sun is hot enough to fuse them, correct?184.97.244.130 (talk) 05:31, 20 January 2013 (UTC)[reply]

Yes, it is effectively simply accumulating in the sun as an end product of the hydrogen fusion process at the moment. — Quondum 08:08, 20 January 2013 (UTC)[reply]

Is the helium mostly at the centre, or does it spread evenly throughout the mass of the Sun? I know we cannot see the centre of the Sun, but maybe some simulations have given some hints.--Lgriot (talk) 09:00, 21 January 2013 (UTC)[reply]

How well mixed together the hydrogen and helium are depends on the size of a star. For a small red dwarf, it's all mixed together evenly (which is part of the reason they burn for so long - hundreds of billions of years, compared to a mere 10 billion for the Sun). For the Sun, it's more concentrated in the core. Convection zone and Radiation zone are relevant articles, although they aren't very good... --Tango (talk) 11:29, 21 January 2013 (UTC)[reply]

Thx --Lgriot (talk) 13:35, 21 January 2013 (UTC)[reply]

why is this not used in air?

http://en.wikipedia.org/wiki/Modulated_ultrasound

why isn't this used for near-field communications (like bluetooth etc). is it because radio is so much easier? But radio requires licenses and has limited spectrum, not that this doesn't but i would imagine while no one else thinks to use it it does! :) 178.48.114.143 (talk) 00:22, 20 January 2013 (UTC)[reply]

Lol, I found this: http://www.theregister.co.uk/2012/11/08/ultrasonic_bonking/

“

A Singapore firm is punting ultrasonic sound as an alternative to NFC for short-range wireless communications, pointing out that it works with existing hardware and provides a demo app to prove it.

The software, which is on Google Play and iTunes (search for SSCconnect) in both free and ad-supported versions, allows devices to exchange contact details, URLs, and clipboard contents at the breakneck speed of 275 bytes per second.

”

But in fact this is just iphone hardware. couldn't specialized hardware be a bit better? 178.48.114.143 (talk) 00:24, 20 January 2013 (UTC)[reply]

Take a look at these:

http://alumni.media.mit.edu/~wiz/ultracom.html

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA499556

http://www.cs.ou.edu/~antonio/pubs/conf059.pdf

In particular, look at the data rates they have been able to achieve.

--Guy Macon (talk) 00:53, 20 January 2013 (UTC)[reply]

I suspect one problem would be interference. In other words it would work fine if you were the only one using it, but what happens if you were in a crowd with many people using it. There could also be a problem with phase diffraction from multiple sources. (See also Superposition principle and Circular convolution) ~ It would probably be okay if by "short-range" you mean "a few inches". ~E:(talk) 01:17, 20 January 2013 (UTC)[Fixed header:74.60.29.141 (talk) 01:38, 20 January 2013 (UTC)][reply]

It will also drive your dog crazy. And it provides fairly limited bandwidth at plausible frequencies. --Stephan Schulz (talk) 10:14, 20 January 2013 (UTC)[reply]

oligomers and monomers

--41.203.67.133 (talk)mkm~

what are the differences between oligomers and monomers using equations and mechanisms as a basis for the differentiation — Preceding unsigned comment added by 41.203.67.133 (talk) 01:08, 20 January 2013 (UTC)[reply]

I'll offer you a hint: Consider what the prefixes "mono-", "oligo-", and "poly-" mean. These are all fairly fundamental concepts in polymer science. Assuming the course these homework assignments belong to is a polymer characterization course you probably want to have these kinds of definitions down cold. (+)H₃N-Protein\Chemist-CO₂(-) 02:07, 20 January 2013 (UTC)[reply]

polymerisation

what is the difference between the average degree of polymerization and the extent of a reaction using equations and reaction mechanisms to distinguish between them — Preceding unsigned comment added by 41.203.67.133 (talk) 01:12, 20 January 2013 (UTC)[reply]

Perhaps you should take a look at our article titled "Degree of polymerization". We're not going to do your homework for you, but if there are any remaining points of confusion we can probably help clarify them.(+)H₃N-Protein\Chemist-CO₂(-) 01:54, 20 January 2013 (UTC)[reply]

chemistry [polymer chemistry]

what is the difference between number average molecular weight and weight average molecular weight — Preceding unsigned comment added by 41.203.67.133 (talk) 01:17, 20 January 2013 (UTC)[reply]

You may want to have a look at molar mass distribution. These sorts of definitions are necessary to describe polymers, which are virtually always a mixture of molecular weights. Some methods such as static light scattering are intrinsically weight averaged, since scattering intensity is proportional to molecular weight amongst other things. (+)H₃N-Protein\Chemist-CO₂(-) 01:43, 20 January 2013 (UTC)[reply]

RF interference

An organization I'm in using some wireless devices that use 915 MHz. They recently replaced a wireless microphone and they say that the new one interferes with the other devices. The mike says it can be set to frequencies between 524 MHz and 865 MHz. Could the mike really be causing interference? (I used them together a few days ago and did not experience any problem.) Bubba73 ^{You talkin' to me?} 02:21, 20 January 2013 (UTC)[reply]

The frequency at which it's set isn't necessarily the only frequency at which it broadcasts. See spurious emission. Indeed, devices not made to broadcast RF at all, such as microwave ovens, frequently still do, although at a level that can only cause interference within a few feet (see Radio_transmitter_design#RF_leakage_.28defective_RF_shielding.29). StuRat (talk) 03:41, 20 January 2013 (UTC)[reply]

Microwave ovens are meant to produce RF, though. It's how they cook stuff. And lots of devices use RF at the same or very similar frequencies as microwave ovens. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 05:02, 20 January 2013 (UTC)[reply]

They aren't meant to "broadcast" RF, which is what I said. StuRat (talk) 05:06, 20 January 2013 (UTC)[reply]

WP:OR, but my wireless internet in my house goes a little jinky when the microwave is running. --Jayron32 06:03, 20 January 2013 (UTC)[reply]

To Jayron's point, Obligatory xkcd reference. Zunaid 09:02, 20 January 2013 (UTC)[reply]

It could be a harmonic, so we could try some other frequencies. I once lived in a city where you could pick up an AM radio station on two frequencies - one was half or double of their actual frequency. Bubba73 ^{You talkin' to me?} 04:23, 20 January 2013 (UTC)[reply]

For it to be a harmonic, wouldn't it have to be set to 457.5 MHz, which is outside the given range? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:59, 20 January 2013 (UTC)[reply]

For a 2:1 or 1:2 harmonic, yes, but there could be other harmonics, 3:2, etc, I think. Bubba73 ^{You talkin' to me?} 05:47, 20 January 2013 (UTC)[reply]

Such devices usually oscillate at the transmit freqwuncy (ie there is not internal multiplication), so only integer multiples of the rated frequency is possible - i.e., 1048 MHz, 1536 MHz, etc at the lowest channel setting. Interfering on a sub-harmonic, and relatuonships such as 3:2, 2:3 are not possible. However, radio reciveing devices can suffer from blocking - the receive circuits are overloaded and thus de-sensitised by a strong signal close to the frequency they are tuned to. How close in frequency is determined by the design of the receiver and how physically close and strong the interfering signal is. So the answer is yes - the radio mike could well be interfering, without being in a harmonic relationship. Keit124.178.178.83 (talk) 08:45, 20 January 2013 (UTC)[reply]

Thanks. Bubba73 ^{You talkin' to me?} 14:51, 20 January 2013 (UTC)[reply]

Altitude / temperature

I've hiked the Grand Canyon a few times, and one thing seems counter-intuitive: it's quite warmer at the bottom than on the rim. Consider the following: a) heat rises. b) air is thinner (less dense) at the top; sunlight should therefore be stronger. c) the bottom is in the shade much of the day, whereas the rim is not. ~ So, ~ why is it warmer at the bottom? ~:74.60.29.141 (talk) 02:43, 20 January 2013 (UTC)[reply]

My previous home was on a hill and when I was walking, it was warmer at the bottom, in the valley. I figured that at the top the air warmed by the ground got blown away by the wind, but I don't know if that is correct. Bubba73 ^{You talkin' to me?} 02:56, 20 January 2013 (UTC)[reply]

Basically the lapse rate for temperature is a function of two things: (1) solar heating occurs almost entirely at ground level; (2) the ability of the atmosphere to retain heat is weaker the higher the altitude. The way those factors trade off for something like the Grand Canyon is not so easy to work out, but you should bear in mind that the south-facing canyon walls are very strongly illuminated, pretty much all the way to the bottom. Looie496 (talk) 04:26, 20 January 2013 (UTC)[reply]

I've always understood that the main function responsible for the lapse rate is the adiabatic expansion / contraction of the circulating atmosphere. Note that adiabatic lapse rate redirects to the lapse rate article you linked. I am a bit confused by the article, though. Is the environmental lapse rate the observed lapse rate at a particular location while the adiabatic lapse rate is the predicted rate due to the modeled adiabatic processes which are the major factor? -- 41.177.85.143 (talk) 07:25, 20 January 2013 (UTC)[reply]

Following up, sources such as this give the following elevations:

South Rim (Bright Angel Trail Trailhead): 6,860ft

Colorado River (presumably at the Silver Bridge): 2,400 ft

North Rim (Kaibab Trail Trailhead): 8,241 ft

That puts the South & North Rims 4,460 ft and 5,841 ft above the river. An average lapse rate of 3.5°F/1,000 ft would estimate the temperature at South and North Rims to be 15.6°F and 20.4°F above the temperature down near the river. (Using the dry lapse rate of 5.5°F/1,000 ft would give even greater temperature differences of 24.5°F and 32.1°F.) Googling "grand canyon hotter bottom" turns up a lot of pages stating that the temperature at the bottom is 15°F to 20°F warmer than at the rim, suggesting that the adiabatic lapse rate is sufficient explanation. -- 41.177.85.143 (talk) 11:10, 20 January 2013 (UTC)[reply]

Finally, the questioner should ask themself whether they have ever wondered with equal curiosity why it is cooler on top of mountains, and if not, then why they haven't. It is the same mechanism at work. -- 41.177.85.143 (talk) 11:12, 20 January 2013 (UTC)[reply]

Yes, I realize the same principles apply to mountains, it's just that the difference seems more obvious at the canyon. Plugging numbers into a formula might provide a mathematical description, but not a satisfactory explanation of why higher altitudes are colder than lower ones (given the same approximate latitude). ~:74.60.29.141 (talk) 18:00, 20 January 2013 (UTC)[reply]

The explanation is "expansional cooling" and "compressional warming". When a gas expands it push the surrounding air out of the way (so it can expand) and that requires energy which is taken from the internal thermal energy of the gas, hence the drop in temperature. When a gas is compressed the opposite happens, the energy flows the other way, and the temperature rises. Dauto (talk) 18:19, 20 January 2013 (UTC)[reply]

That explains how an air-conditioner works; but it seems implausible that there would be an energy transference from the rim to the bottom by that means. That would require a pressure differential over time and distance, and the specific air molecules wouldn't necessarily be transferred from one place (low density) to another (high density) where the heat energy is exchanged. ~[Does that makes sense?].

I don't mean to sound unappreciative of the answers, it's just that this question has bothered me for quite some time. I'm sure the lapse rate / adiabatsis explains it, but the underlying thermodynamic principles are still unclear to me. Consider the following hypothetical: given a column of air (let's say 1km) - perfectly sealed within a thermally insulated (vertical) container. Leave it alone for a year or two; when you come back the air temperature at the bottom would be higher than that of the top, by an amount consistent with the related equations — right? ~:74.60.29.141 (talk) 21:22, 20 January 2013 (UTC)[reply]

Feeling warmer in a valley is quite common, but not all valleys are warm. All this talk of lapse rate is misleading you. As Looie496 said in his post, air is hotter nearer the ground because the air is heated by the ground, which is heated by incoming solar radiation. The air both absorbs some of the raditated heat (in both directions), and re-radiates it, in both directions. This is the greenhouse effect, resulting in a band of air at altitude that has the minimum temperature - below the air is warmer as it is close to the warm ground, and above it is warmer due to being above most of the air heat absorption.

Now, think about it. If this was the only factor, and (say) the average ground temperature at some latitude is 20 C, you'd expect the temperature at 1000 m above it to be 13.5 C, applying the satndard lapse rate of 6.5 C per 1000 m (Note that the lapse rates given in a post above are incorrect). Now, assume you are on level ground in a bloody great hole 1000 m deep. Based on the greenhouse effect, which is what causes the lapse rate, you'd still expect the temperature at the bottom of the hole to be 20 C, and the top of the hole to be 13.5 C.

It can't work that way - the temperature of air at the top of a hole cannot be 6.5 C below the surrounding air, because wind and convection will mix it to equality at the top. Any hot air at the bottom will be less dense and try to rise out of the hole, and be replaced with cooler air.

So what does cause the bottom of some but not all valleys, and the Grand Canyon, to be warmer?

The south facing walls get full sun as Looie496 said.
Some of the heat re-radiated off the south walls gets trapped by the other walls - this is a large scale example of the cavity radiator effect, well known to engineers - to find the appoximate temperature of a furnace, drill a small hole in the side - if the furnace is red hot, the hole will appear to be a hotter colour.

Supporting what I've said is the common experience of folk living in the bottom of valleys. Some valleys are warm and some are not. It depends on the alignment of the valley axis vis-a-vis the direction of the sun's radiation, and on whether or not the alignment of the valley axis allows the prevailing winds to penetrate.

Wickwack 120.145.56.251 (talk) 01:11, 21 January 2013 (UTC)[reply]

I'll have to think about this some more (later, its bedtime).. ~:74.60.29.141 (talk) 04:10, 21 January 2013 (UTC)[reply]

Hey Wickwack, can you clarify "applying the standard lapse rate of 6.5 C per 1000 m (Note that the lapse rates given in a post above are incorrect)."? I assume that you are referring to my 3.5°F/1,000 ft which is the standard value quoted in our article and is equivalent to your 6.5 C per 1000 m. -- 41.177.85.143 (talk) 07:05, 21 January 2013 (UTC)[reply]

I never looked at the Wikipedia article, as they are not intended to be trusted as a data source. They are only intended to guide novice readers to references and sources. I got the standard rate 0.0065 C/m (= 6.5 C per 1000 m) for the altitude of the Grand Canyon from a set of standard tables (Turns & Kraige 2007, page 94) I have. Note that the lapse rate is not constant but varies with altitude - at 4000 m it reduces to 1/10th this value, and at 15,000 m it is zero. At greater altitudes it increases at opposite sign, untimately reversing sign again. The value you used in your calcs, 3.5 F / 1000 Ft equates to 6.38 C / 1000 m. That is, you used a value 2% low. This is not significant in the context of the question, but I thought that someone would squawk that I used a different value. I should have explained it better - I appologise for the confusion. Wickwack 124.182.14.231 (talk) 07:55, 21 January 2013 (UTC)[reply]

Thanks. I certainly wouldn't quibble over a one to two percent difference in figures which are only given to two significant digits, but the variability of lapse rate with altitude is something which could have a significant impact on my calculations above. -- 41.177.85.143 (talk) 08:18, 21 January 2013 (UTC)[reply]

I agree that local topography, insolation, and winds can have a large effect on the actual, observed lapse rate, but the standard rate falls between the dry and saturated adiabatic lapse rates and successfully predicts the observed rate at the Grand Canyon itself, so I don't understand why additional mechanisms are needed here to explain what appears to be consistent with the thermodynamic model. -- 41.177.85.143 (talk) 07:38, 21 January 2013 (UTC)[reply]

A coincidence is not proof. I have explained why the lapse rate actually is not the full story, as relying on it alone means that the floor of the canyon, around 800 m above sea level, should have a temperature about the same as the area generally, about 2700 m above sea level, and if it did, there would be a pocket of air above the canyon at 2700 m lower in temperature than the air in the area generally, and that cannot be the case, as Louie pointed out. Wickwack 124.182.14.231 (talk) 08:04, 21 January 2013 (UTC)[reply]

The lapse rate in the Grand Canyon is specifically addressed in this (PDF 1.3 MB) 1965 Journal of Applied Meteorology article. -- 41.177.85.143 (talk) 08:46, 21 January 2013 (UTC)[reply]

Note that this paper, which is about the improved horizontal resolution of a then new satellite, talks about an apparent lapse rate, which the author's data indicates was 10 C per 1000 m at the time of measurement, well above the standard value. The article does not use the standard lapse rate to explain why the canyon floor was warmer, it merely says that there appears to be a significant lapse rate and mentions some reasons why it might be thought to occur at the magnitude that it did. The purpose of the paper was use the Grand Canyon to show how good the horizontal resolution was. Wickwack 120.145.80.46 (talk) 10:38, 21 January 2013 (UTC)[reply]

This PDF link isn't working for me (can't connect to host) but googling "Lawrence E. Stevens The Biogeographic Significance of a Large, Deep Canyon" and looking at the "Quick View" gives a 2012 work which states in section 3.4, Elevation:

Nonetheless, elevation remains an overwhelmingly important ecological state variable due to its strong negative relationship with air temperature and freeze-thaw cycle frequency, and its positive relationship to precipitation and relative humidity. The global adiabatic lapse rate is -6.49 °C/km. Analysis of paired daily minimum and maximum air temperature from 1941-2003 at Phantom Ranch (elevation 735 m) on the floor of GC with the South Rim (2100 m) produces a GC-specific lapse rate of -8.7 °C/km. The >1.3-fold steeper lapse rate in GC is likely a function not only of the dark red and black bedrock color of the inner canyon, but also to aspect. Steep, S-facing slopes in the GCE, particularly those with darker rock color, absorb and re-radiate more heat than do N-facing slopes, which often are shaded from direct sunlight, and are cooler and more humid than S-facing slopes across elevations. Overall, elevation strongly and broadly influences synoptic climate, while aspect exerts strong local control over microclimate and microsite potential evapotranspiration and therefore productivity.

I find it interesting that he does not mention the arid climate as a factor in the lapse rate as the dry adiabatic rate of 9.8 °C·km^-1 is greater than that observed in GC. A paper on the subject written by a climatologist would carry more weight than a passing mention by a biologist, but I'd be inclined to pay more attention to either than to anything said here. -- 41.177.85.143 (talk) 11:03, 21 January 2013 (UTC)[reply]

►The bottom line: the primary principle involved would be adiabatic lapse which relates to air density, which relates to barometric pressure (?). Therefore, the barometric pressure at the bottom is consistently higher than at the top. [?]

Localized topography, azimuth orientation (etc.) primarily accounts for the variety of micro-climate conditions.

~Eric _the OP:74.60.29.141 (talk) 22:04, 21 January 2013 (UTC)[reply]

why when people have fever the feel colder?

seem a bit pardoxic. i had fever today, and i felt cold, anything i wore almost gave no heat. why is that? — Preceding unsigned comment added by 79.176.113.107 (talk) 03:30, 20 January 2013 (UTC)[reply]

Because your bodies ability to sense temperature is out of whack. Your body is not an accurate thermometer, and your general sense of warmness and coolness is not really directly connected to the internal or external temperature. Wikipedia has an article on thermal comfort which is a bit bloated, but has some information. Physiologically, your sense of temperature is wrapped up in your Somatosensory system. --Jayron32 03:35, 20 January 2013 (UTC)[reply]

It's common to swing back and forth between feeling hot and cold, when you have a fever. StuRat (talk) 03:37, 20 January 2013 (UTC)[reply]

My understanding is that a fever is a response to infection in which the body tries to raise its temperature in order to increase the activity of the immune system. It does that by raising the homeostatic "set point", and anything below the set point is going to feel cold to you. Looie496 (talk) 04:16, 20 January 2013 (UTC)[reply]

It's not really that the body's ability to sense temperature is out of wack, but that the thermostat has been reset either by the immune response or the pathogen itself. See Pyrogen (fever). One theory of fever is that whichever agent induces the fever, the pathogen or the body itself, will function better against its opponent with a raised temperature. Many proteins function best within a set temperature range, and leaving that range can have a huge effect. μηδείς (talk) 04:47, 20 January 2013 (UTC)[reply]

Looie496 is right. Your body has a "normal" temperature. When you get a fever, the "normal" temperature rises. Therefore, what originally was at the "normal" temperature is now colder than the "normal" temperature, and consequently feels cold. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:52, 20 January 2013 (UTC)[reply]

For completeness sake, the homoeostatic set-point for temperature is set by the hypothalamus. Fgf10 (talk) 12:03, 20 January 2013 (UTC)[reply]

Fevers occur in reptiles, fish,[1], and even insects.[2] Fever is stimulated by eicosanoids and therefore would seem to be conserved with mammals. [3][4] Amazingly, this means that the fever response dates back almost to the Urbilaterian, maybe further. All this time fever has been a matter of behavior, and only in the most recent times does it control internal temperature directly. What's odd is that Hollywood appears unalterably convinced that people with fever are hot, and must have shown this idiocy in a thousand movies. Don't they get sick in celebrityland? Wnt (talk) 22:46, 20 January 2013 (UTC)[reply]

I think there is a big misunderstanding here. Your body doesn't directly detect the temperature of the air around you.

Let's do an experiment: Touch a piece of metal with one hand and a piece of plastic with the other. Which feels warmer? The plastic - right? But in truth, they are both at the exact same temperature (you can check...use a thermometer!). That's because, what we actually detect is the amount of heat energy that is drawn out of our skin. Metal feels colder than plastic because it conducts heat away from your body very efficiently, where plastic doesn't.

Now, consider Newton's law of cooling: "The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings.".

That means that when your feverish body is hotter (compared to the surrounding air) than it usually is, you lose heat to the environment more rapidly than you normally would...and because "rate of heat loss" is what our skin actually measures, you feel colder because you're losing more energy to the outside world than usual.

When I have a fever, I feel cold because my body is hotter compared to the surrounding air. Seems backwards - but it's not. SteveBaker (talk) 17:25, 21 January 2013 (UTC)[reply]

Check your understanding against Transient receptor potential channel, especially TRPM and TRPV. The proteins act as thermometers, and being in exposed regions of skin which may vary from core body temperature, they can sense a temperature that is influenced by the outside air. Likely someone can remedy my ignorance, but I am having trouble thinking of an instrument that measures heat flow directly. Wnt (talk) 16:55, 22 January 2013 (UTC)[reply]

I think both of you are basically correct. The receptor activity is determined by the temperature of the skin, which is largely determined by the rate of heat loss from the skin (also by the amount of blood flow reaching the skin). Looie496 (talk) 17:08, 22 January 2013 (UTC)[reply]

There is no need to argue - do the experiment. Metal feels cold, plastic feels warm. How can you explain that other than by the fact that we measure rate of heat loss as opposed to temperature? SteveBaker (talk) 21:03, 22 January 2013 (UTC)[reply]

Well, I did do the experiment - and found that you are wrong. I got a thick piece of aluminium (about 150 x 30 x 25 mm), an excellent conductor of heat. I mounted on it two PT100 platinum film temperature transducers, on opposite sides. These are available in very thin forms - the ones I have are about 100 x 10 x 1.5 mm mounted. I got a similar piece of Tufnol, a type of composite filled plastic, moderate conductor of heat, and attached two PT100 transducers to that. I also got a similar size piece of polystyrene, a poor conductor of heat, and mounted two PT100's to that. I connected all the PT100's up to electronics to read the temperatures in deg C and after allowing a settling time they all read the same temperature - 23 C. Then I put two fingers on the top PT100 on the aluminium block, two fingers on the top PT100 of the Tufnol, and two fingers of the other hand on the top PT100. Sure enough, very quickly I felt the aluminium as cold, the tufnol a bit warmer, and the polystyrene as warmest. None of the bottom PT100's changed. But while the top PT100 on the aluminium did not change its temperature while my fingers were resting on it, the top sensor on the tufnol went up 4 C or so, and the polystyrene top sensor quickly went up 9 C. In other words, plastic feels warm not because of a low flow of heat, but because its surface in contact with your skin gets increased in temperature. Wickwack 121.221.216.91 (talk) 14:41, 23 January 2013 (UTC)[reply]

Out of battery detonation

What are the most common causes of out-of-battery detonations in firearms? 24.23.196.85 (talk) 05:45, 20 January 2013 (UTC)[reply]

Human error? ~:74.60.29.141 (talk) 05:48, 20 January 2013 (UTC)[reply]

See slamfire. Zoonoses (talk) 06:04, 22 January 2013 (UTC)[reply]

Do you mean that accidental slamfires are the most common cause of out-of-battery detonations? 24.23.196.85 (talk) 06:13, 22 January 2013 (UTC)[reply]

Isn't slamfire intentional and beneficial, due to its allowing the user to spray shells onto the enemy by simply holding the trigger and operating the pump? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:44, 22 January 2013 (UTC)[reply]

I meant "see slamfire," nothing more. After reading slamfire, you should have the answer to your original question. Zoonoses (talk) 06:49, 23 January 2013 (UTC)[reply]

Electrical conduction

Could somebody please tell me the answer to this, I can't seem to find anything about it in Wikipaedia articles. If I connect an ordinary multi-strand copper wire to a 12volt DC connection, but only get half the strands in the connector, then connect the other end of the cable to a device (like a light for example) but only get the other half of the strands in that connector, how efficient will the power transmission be? Thanks in advance. 124.191.177.1 (talk) 07:21, 20 January 2013 (UTC)[reply]

Assuming that the individual strands of the conductor are not corroded, oxidized or coated in any way, the inter-strand resistance (per metre) between copper strands will be low. Thus, after as short distance (a few diameters of the copper of the wire), the current should be effectively uniformly distributed over the cross-section of the copper. Thus, one could say "about as efficient as using all strands, but with a small added length to the cable". For most practical purposes, this means the effect will be insignificant. — Quondum 07:59, 20 January 2013 (UTC)[reply]

(agreed) ... and it's very unusual to get corrosion or significant oxidation in the middle of a wire if the insulation is undamaged. For wires carrying a high current (for their cross-section), then it is obviously better to connect as many strands as possible, but even one connected strand at each end (and not the same strand) will usually give efficient power transmission, though I wouldn't recommend the practice because the single strand at each end might get hot, and it will act like a fuse wire, burning out at a certain high current. Dbfirs 16:51, 20 January 2013 (UTC)[reply]

Thankyou, the multistrand cable I am using is tinned copper, so I assume this makes no difference to the interstrand resistance.124.191.177.1 (talk) 07:23, 21 January 2013 (UTC)[reply]

~~Tin is actually an even better conductor than copper, so using tinned copper helps. In addition,~~ the tinning prevents oxidation of the copper, so largely prevents the problem of corrosion mentioned by Quondum above. Dbfirs 10:22, 21 January 2013 (UTC)[reply]

Dbfirs: are you sure that tin is a better conductor than copper? I seem to remember copper is a better conductor, and the table at Electrical_conductivity#Resistivity_of_various_materials seems to support this. – b_jonas 16:03, 21 January 2013 (UTC)[reply]

Sorry, my error. I picked up the conductivities from a table elsewhere on the internet and either it was wrong or I mis-read it (the latter being more probable!) In fact pure tin has only one seventh the conductivity of copper. I've striken my erroneous comment above, leaving only the second part that remains valid and is more significant in the situation being considered. Tin does have a higher conductivity then oxidised copper, and bare copper corrodes easily. Dbfirs 22:45, 21 January 2013 (UTC)[reply]

You're right that tin is a worse conductor - only silver is better than copper. But "tinned copper" doesn't necessarily mean literally "copper coated with tin" - it's probably a lead/tin alloy with other metals involved in the mixture. The practical function is twofold - excluding air and thereby reducing the corrosion of the copper - and (because lead/tin alloy is so soft and because it flows into the gaps between the conductors) improving the contact area between the strands and between strands and terminal block. Those two things taken together greatly improve the quality of the contact. SteveBaker (talk) 17:12, 21 January 2013 (UTC)[reply]

If you think about it, even if you get all of the conductors stuffed into a "screw terminal", only the outer strands are actually in contact with the terminal block - so you're relying on inter-strand conductivity to make the other connections anyway. The big problem with only connecting a few of the conductors is the very short distance between the terminal block and the point where all of the conductors meet. It doesn't much matter how short that distance is - the wires can still overheat at that spot and cause problems. SteveBaker (talk) 16:26, 21 January 2013 (UTC)[reply]

The reason why wires are made multistranded is to improve tolerance of vibration and to make the wire easier to install, which usually requires sharp bends. If not all the strands are soldered or clamps at the termination, you have an increased risk of the wire breaking. The reason for the tinning is to improve solderability. Wire intended for screw clamp connection is generally not tinned. Oxidation is not a problem as it won't occur where the strands are under clamping pressure at teh termination, and should not occur within the plastic insulation. Ratbone 124.178.141.66 (talk) 01:12, 22 January 2013 (UTC)[reply]

I agree that oxidation does not normally occur within the plastic insulation, even after 40 years in damp conditions, but it can certainly occur around the clamped wire, and if the clamping is not as firm as it should be, it can spread under the clamp and increase resistance at the contact. I've seen it happen, but I agree that it shouldn't under a really secure clamp. The problem is more serious in telecommunications and data wiring where insulation-displacement connectors are used. Tinned wire is standard in these applications. Dbfirs 08:17, 22 January 2013 (UTC)[reply]

tDCS for insomnia?

According to this article: "I’ve been told that [transcranial direct current stimulation] is handy if you have racing thoughts at bedtime." Have any controlled trials of tDCS confirmed this? If not, with how much confidence can it be inferred given results with TMS? Neon Merlin 08:22, 20 January 2013 (UTC)[reply]

I can't find any details of any such trials. It may be of interest to you to note an article in the Journal Of Psychiatric Research (2013 Jan; Vol. 47 (1), pp. 1-7), which is 'Clinical utility of transcranial direct current stimulation (tDCS) for treating major depression; a systematic review and meta-analysis of randomized, double-blind and sham-controlled trials.' This concludes that there is at this stage no clear evidence for the clinical utility of this method for the treatment of MD, and more extensive trials will be required. ---- _nonsense ferret 14:27, 20 January 2013 (UTC)[reply]

Nuclear fusion to produce phosphorus

What temperature would be required for the fusion reaction ²⁸Si + ⁴He → ³¹P + ¹H (which [jtgnew.sjrdesign.net/stars_fusion.html this site] says is part of the stellar oxygen-fusion chain) by known methods? Could any known fusion reactions produce ³¹P at a lower temperature from isotopes abundant on Earth? Neon Merlin 13:56, 20 January 2013 (UTC)[reply]

You misunderstood what they said. They mean that the Oxygen-burning process has several possible outcomes:

¹⁶O+¹⁶O= ³¹P + ¹H or

¹⁶O+¹⁶O= ²⁸Si + ⁴He

among them. The required temperature is more than 1 billion K. Ruslik_Zero 17:48, 20 January 2013 (UTC)[reply]

Electric current through gases

At normal pressure air or any other gas is a nonconductor of electricity, but at low pressure the gas become conductor of electricity. How does this happen?
In a discharge tube, sparking is accompanied by crackling noise. How this noise is produced? — Preceding unsigned comment added by Want to be Einstein (talk • contribs) 14:02, 20 January 2013 (UTC)[reply]

Non-ionised gasses are not conductive at any pressure, low or high. What makes you think they are conductive at low pressure? Conversely, an ionised gas is conductive at all pressures.
When an electrical discharge occurs, there is local heating, which causes an increase in pressure. The over-pressure travels outwards and thus constitutes a sound wave.

Wickwack 120.145.81.211 (talk) 14:48, 20 January 2013 (UTC)[reply]

Some links you might find useful: Plasma (physics)#Generation of artificial plasma, dielectric strength, and for a more detailed explanation of the mechanism, see Paschen's law. — Quondum 15:05, 20 January 2013 (UTC)[reply]

I have seen that gases become more ionized at low pressure than at high pressure. How a gas becomes ionized at low pressure ? Want to be Einstein (talk) 17:07, 23 January 2013 (UTC)[reply]

Same way as at high pressure. Energy must be supplied to knock electrons off the atoms or molecules. See Paschen's Law, cited by Quondum. Wickwack 121.221.91.193 (talk) 01:47, 24 January 2013 (UTC)[reply]

Hydrolysis of Phosphodiester bond in DNA

When the phosphodiester bond in the Phosphate-backbone of the DNA is hydrolysed by DNAses enzymes, which one of the P-O bond is broken? Dnakid (talk) 17:59, 20 January 2013 (UTC)[reply]

Depends on the DNAse. Deoxyribonuclease I leaves 5' phosphates, whereas Deoxyribonuclease II leave 3' phosphates. -- 71.35.98.191 (talk) 20:24, 20 January 2013 (UTC)[reply]

compressing gas into a cylinder

would a very light-weight "pod" floating on a helium baloon with a line into it, be able to consist of also a battery, light empty canister, and pump, and descend when it wishes by pumping (compressing) the helium (or enough of it) back into the cannister to descend?

Of course, the battery would have to be recharged after a while, but in this way helium could be conserved. The idea is that when it wishes to ascend again, it can refill the baloon from the helium it has just pumped into the cannister.

Would this work? Thanks. 178.48.114.143 (talk) 18:28, 20 January 2013 (UTC)[reply]

Yes, in fact there is a (proposed) aircraft which uses a similar principle -very interesting concept- See "Gravity Plane": http://www.youtube.com/watch?v=0QZ1KzveIic (WP won't allow direct link to YouTube) ~E:74.60.29.141 (talk) 18:56, 20 January 2013 (UTC)[reply]

More directly related to what you're thinking about: Aeros Flight Buoyancy Management - "By compressing and decompressing helium, the density in the ship can be varied as a means to control the ship’s static heaviness."

On a much smaller scale (your balloon) the limiting factor would be the weight of your "pod". ~E:74.60.29.141 (talk) 21:52, 20 January 2013 (UTC)[reply]

A very rough rule of thumb is that you need one cubic meter of helium to lift one kg of craft. That has to include the weight of the balloon itself. SteveBaker (talk) 02:36, 21 January 2013 (UTC)[reply]

What you are describing is "sort of" an aerial version of a Stab jacket, similar principle anyway. Vespine (talk) 05:25, 21 January 2013 (UTC)[reply]

Except that while gas is added from a cylinder to a stab jacket to increase buoyancy, it is vented to decrease buoyancy. It would be as if there was a pump to move gas from the jacket back to the cylinder when less buoyancy is desired. -- 41.177.85.143 (talk) 07:50, 21 January 2013 (UTC)[reply]

In order to link to youtube use this markup in edit: [http://www.youtube.com/watch?v=0QZ1KzveIic gravity plane vidoe] to produce this link: gravity plane video. The video itself is absurd, since the plane is presented as a perpetual motion machine, and its capacity for failure seems unlimited. μηδείς (talk) 07:30, 21 January 2013 (UTC)[reply]

No, that doesn't work. The canister strong enough to contain the helium always weighs more than what that much helium can lift. – b_jonas 15:58, 21 January 2013 (UTC)[reply]

What makes you say that?!? I certainly don't believe it's true. The volume of a sphere is a function of the cube of the radius - the surface area increases as the square of the radius. Since the amount of lift is proportional to the volume - but the weight of the envelope is a function of the surface area. Double the size of the balloon and you can double the thickness of the envelope without changing the pressure it has to withstand. Hence it's always possible (in principle) to build a bigger balloon to make it light enough to fly. (Recall the Mythbusters episode where they made a balloon out of lead foil - and it actually flew!) But the amount of additional pressure required to make the balloon lose altitude doesn't have to be that much - providing you don't need to lose altitude rapidly. From that point of view, it's a plausible machine. SteveBaker (talk) 16:17, 21 January 2013 (UTC)[reply]

The plane in the video is (effectively) powered by compressed air. They say that compressed air is used to create thrust - it's dumped as ballast - and it's used to re-compress the helium so the plane can return to earth. What replenishes that compressed air? All of the energy for the flight is contained in that compressed air...but it's not a perpetual motion machine. That said, the video is confusing...why would this plane require wings? Why folding wings? Lighter-than-air craft aren't magical - they are like up-side-down aircraft. With a regular plane, ascent costs lots of energy, but coming back down again is free. With a conserved-gas lighter-than-air craft, it's the reverse...going up is free, but it takes energy to get back down again. The only "free lunch" comes from venting gas at altitude - effectively switching from being lighter-than-air to being heavier-than-air and thereby getting a free ride both up and down. But venting gas is a problem: Helium is expensive, and it's a non-renewable resource that humanity is rapidly running out of - so simply venting the stuff to get you back down again is not a great way to go. That leaves you with other potential lifting gasses - but they are either rare and expensive (helium, neon), potentially dangerous (hydrogen, methane, ammonia), energy-intensive to produce and maintain (hot-air, steam), only marginally light enough (nitrogen, neon) or nasty green-house gasses (methane).

Recompressing helium at altitude (as suggested by our OP) is a good approach - but it still consumes energy.

I like the idea of using a Rozière balloon - which is a hot air balloon with a helium balloon inside it. If you paint the upper envelope such that one side is black and the other silver. By turning the balloon with the black side facing the sun, the hot air will expand - causing the balloon to rise. Rotate the balloon with the shiney side towards the sun and the hot air can cool. With the majority of the lift coming from the helium, you only need the hot air to provide altitude control. SteveBaker (talk) 16:17, 21 January 2013 (UTC)[reply]

Put thin film solar panels on the blimp and and make the battery life infinite. Have they ever tried acid and metal filings-based buoyancy storage? Vent the hydrogen to go down. Sagittarian Milky Way (talk) 18:16, 21 January 2013 (UTC)[reply]

January 21

Hot water in pan

To thaw a hole in ice on my pond I put a pan of hot water on the ice, and noted that the water in pan the rotated in a anticlockwise motion Why is this? — Preceding unsigned comment added by Johnmyers00 (talk • contribs) 08:30, 21 January 2013 (UTC)[reply]

The most likely reason is that you filled it from a hot tap that generated the rotation as it filled the pan. The Coriolis effect explanation has been shown to be invalid, I think. Dbfirs 10:11, 21 January 2013 (UTC)[reply]

Yeah, the Coriolis effect works on the scale of hurricanes and other major weather systems. Didn't stop this cafe at the equator in Uganda I was once at from putting bowls 10 m either side of the equator, expecting the water to drain opposite ways... Sigh! I guess the movement of the pan while being carried from the tap to the pond would also affect rotation here. Fgf10 (talk) 10:25, 21 January 2013 (UTC)[reply]

I am more curious about what made it rotate at all. If the bottom was heated I would guess convection currents but a pan of hot water on ice should stratify, So why did it rotate? --Guy Macon (talk) 12:14, 21 January 2013 (UTC)[reply]

Yes, if the water was completely still without any "curl" when placed on the ice, I can see no reason why it would gain an overall rotation through convection. It can be difficult to see small rotations in clear water, so perhaps the stratification just made a pre-existing rotation visible. Dbfirs 22:22, 21 January 2013 (UTC)[reply]

Ah, nothing to do with answering the question but if the ice was thin enough to melt with a pan of water then would it not be almost too thin to walk on? The Canadian Red Cross says 15 cm (5.9 in) and Environment Canada, no link but I just checked the manual, says 20 cm (7.9 in). Even at 15 cm it would take several pans of hot water to melt through. CambridgeBayWeather (talk) 13:02, 21 January 2013 (UTC)[reply]

Could've been from the shore. Mingmingla (talk) 17:36, 21 January 2013 (UTC)[reply]

Further south, our recommendations are 4 inch thick ice for foot traffic, 8 for autos, 15 for pickups.[5] Rmhermen (talk) 21:28, 22 January 2013 (UTC)[reply]

The OP didn't say anything about walking on it. And certainly a "pond" does not conjure a picture for me of anything big enough to even consider walking on. --ColinFine (talk) 13:29, 23 January 2013 (UTC)[reply]

I would expect it's a fish pond and the OP was melting a hole in it to allow gaseous exchange to take place to keep the fish healthy. Richerman (talk) 22:20, 23 January 2013 (UTC)[reply]

Battery paradox

So I'm looking for a new wireless mouse and I come across this. Looks good, but the rechargeable battery only lasts a few days according to most of the consumer reviews. Then I come across this, and it purportedly lasts 2 years on just AA batteries alone (it doesn't work on glass though so that's a deal breaker, but I digress). I was under the impression that lithium ion batteries have much better energy density than ordinary alkaline AA batteries do. So what's the deal? Why does the mouse which runs on AA's lasts so much longer than the lithium ion one? ScienceApe (talk) 08:36, 21 January 2013 (UTC)[reply]

Two AA cells are quite heavy for a mouse. I suspect the the Lion battery is much smaller and lighter. Perhaps the manufacturers assume that recharging is not much trouble so they don't put a large and expensive battery in the first mouse. It's also possible that the AA mouse has a processor that draws less power (and perhaps does less processing?) Perhaps someone can check the specifications? Dbfirs 10:06, 21 January 2013 (UTC)[reply]

Energy density Extended Reference Table lists the energy density of both:

Alkaline battery: 1.15 to 1.43 MJ/L

Lithium ion battery: 0.83 to 3.60 MJ/L

So no more than a 2:1 difference one way or the other.

Mice don't typically specify current draw, and the specified battery life is often an advertising fiction. A 20:1 ratio in current draw between different designs is fairly common. So when you factor in battery size, energy density, current draw, assumptions about use patterns, and stir in a few fibs from the marketing department, that could explain the difference. --Guy Macon (talk) 11:16, 21 January 2013 (UTC)[reply]

While not denying battery life figures from manufacturers aren't particularly reliable, if consumer reviews say the battery life of the earlier mouse is only a few days then I would suggest the mouse has a rather short battery life. I've used several AA mice in the past and with rechargeable NiMH battery life is in the weeks to months range presuming decent full charged batteries. I'm of course presuming a more ordinary consumer pattern, not say 24/7 FPS gaming. Nil Einne (talk) 11:40, 21 January 2013 (UTC)[reply]

My guess is that the difference has little (if anything) to do with the batteries. The amount of power a mouse needs depends drastically on how (or "if") it shuts down when you're not moving it. The problem is often that to shut itself down sufficiently to save power when you stop moving it, makes it take a lot longer to wake up when you start it moving again. So if I had to bet, I'd say that the mouse with the significantly lower current draw would have that annoying lag that you get with some cordless mice when you start using it again after a break. Some mice shut down much sooner than others too - that would make a big difference to power consumption. SteveBaker (talk) 15:35, 21 January 2013 (UTC)[reply]

I don't think so. They are made by the same company and have the same power saver features. We're talking about a difference between 2 years and a couple of days too. ScienceApe (talk) 17:46, 21 January 2013 (UTC)[reply]

Performance Mouse MX M950:

Requires 1 AA NiMH rechargeable battery.

Expected battery life is up to 30 days.

http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/12710

Wireless Mouse M510:

Requires 2 AA alkaline batteries.

Expected battery life is up to 24 months (2 years).

http://logitech-en-amr.custhelp.com/app/answers/detail/a_id/17990/

The M510 has a standard laser.

The M950 has a dual Darkfield Laser.

http://www.logitech.com/images/pdf/briefs/Logitech_Darkfield_Innovation_Brief_2009.pdf

From the above, it looks like the M950 uses about twelve times the power that the M510 uses. --Guy Macon (talk) 19:02, 21 January 2013 (UTC)[reply]

You might think the darkfield laser requires more energy, but I own this mouse. It's logitech's other darkfield laser mouse (allows it to work on glass and reflective surfaces) and it has worked for months with just two AA batteries. According to consumer reviews, it has worked for at least 6 months. I would just buy another one, but this one is designed for laptops so it's smaller, I want a bigger one for my desktop. ScienceApe (talk) 21:53, 21 January 2013 (UTC)[reply]

I agree with Guy Macon that you cannot at all relay on manufactuer's claims on mouse battery life. I have an ordinary Microsoft Wireless Laser Mouse 5000 (Model 1058). It runs on two AA cells, and the claimed battery life is 1 year. There is never any noticeable lag after the mouse has been idle, but lag occurs if the battery is flat. Working at home, I mostly use email, Microsoft Word, Excel, and spend a lot of time writing software. All these things are keyboard intensive and from experience I'd say the claimed mouse battery life is comfortably exceeded. But sometimes I accept commissions involving CAD/CAE work, which is very mouse intensive. When doing CAD/CAE all day long, the mouse batteries go flat within weeks. Incidentally, the mouse has a facility to give you an on-screen warning that the batteries are low. This function is totally unreliable. It gives false warnings sometimes, and sometimes the mouse fails without any warning. Ratbone 124.178.141.66 (talk) 01:03, 22 January 2013 (UTC)[reply]

Railgun on the moon

Would it make sense to launch probes to the outer solar system with a railgun from the moon? This is meant in a few years (decades or centuries) after a moon station is built and we have a few people there. I know that it does not make sense to transport all the stuff to the moon built a railgun there and than think it is more effective and cheaper than to launch from earth. Is the speed you can reach higher than what chemical propulsion or ion thrusters can provide?--Stone (talk) 13:35, 21 January 2013 (UTC)[reply]

This has been suggested at least since I was a child (the 60's). I remember illustrations showing how material from the moon could be sent to Earth orbit using this method. Zzubnik (talk) 16:15, 21 January 2013 (UTC)[reply]

I think it's possible - but not economically sensible for that purpose. Between the lack of atmosphere and lower gravity, railguns would certainly be much more effective from the Moon than from Earth. But you've still got the problem of transporting the probe from earth to moon and loading it into the railgun - that might cost more fuel and equipment than would be saved by doing a launch direct from earth orbit. But you could also considering placing a railgun like that in earth orbit or at one of the lagrange points too - and that would be even more effective than building it on the moon.

The only reason (that I could imagine) for putting this machine on the moon would be the possibility of making the machine from materials commonly found there to avoid having to ship them up to Earth orbit. But that would be a much bigger task. Moon rocks contain iron, aluminium, silicon, magnesium and titanium - but not much copper or silver for making electrical conductors suitable for all of those magnets. Aluminum wires are also possible - but their conductivity would be poor. There ought to be materials for making photocells with which to make solar panels. You'd probably want to use superconducting magnets - and the specialized materials needed for that would be even harder to make there. But before any of those things can be done, you'd need massive mining, refining and manufacturing facilities on the moon - and the cost of those things would dwarf the costs of sending probes to the outer solar system from Earth. We routinely send those kinds of probes out there - and the cost is easily accommodated within NASA's budget - but the cost of even one human mission to the moon would be huge.

So I think the first problem is to find money and motivation to build extensive lunar colonies with the infrastructure to process moon rock in large quantities. Helium-3 mining (as fuel for fusion reactors) is a possible reason to do that - and using a railgun to launch helium canisters back to Earth would be a strong motivation to build a lunar railgun. But if it's aimed to get canisters into low Earth orbit, I don't know whether you'd be able to aim it correctly to get a probe into the outer solar system.

So, possible? Yes. Likely? No.

SteveBaker (talk) 16:52, 21 January 2013 (UTC)[reply]

(Multiple ECs) You (the OP) might wish to check out Robert Heinlein's novel The Moon is a Harsh Mistress, in which a railgun – used to transport (metal-jacketed) bulk materials from the Moon to Earth – features prominently. While this is fiction, Heinlein was a trained engineer (he worked on early versions of what eventually evolved into NASA's standard spacesuit, amongst other things) and would have been careful to get the underlying concept and numbers right. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 16:55, 21 January 2013 (UTC)[reply]

Yes, but that book was written almost 50 years ago (1966) - before most of our understanding of practical superconductors and before we had rare-earth magnets. Three years before we had even a single moon-rock to analyze. A modern railgun would be a very different beast to the thing that Heinlein imagined. SteveBaker (talk) 17:03, 21 January 2013 (UTC)[reply]

Really the only hurdles would be financial and technological hurdles. Seems to me that it will be done once we begin colonizing space. ScienceApe (talk) 17:39, 21 January 2013 (UTC)[reply]

A railgun will be built only if it's better than all alternatives, and I'm pretty sure it's not. A space elevator is not yet feasible on Earth, because no known material is strong enough for the cable, but it is possible on the Moon with current technology. --140.180.255.25 (talk) 19:12, 21 January 2013 (UTC)[reply]

Yep, I agree. A space elevator would be an excellent solution for the moon...but then you might want to advance another step and build a Skyhook (structure)...or an Orbital ring...or a Space fountain...or a Lofstrom loop. There are many, many other ideas that become possible without an atmosphere and with sufficiently strong materials. SteveBaker (talk) 21:09, 21 January 2013 (UTC)[reply]

A problem here would be that there are no long term stable orbits around the Moon. All probes orbiting the Moon need to have very frequent course corrections to prevent them from crashing into the Moon due to very strong tidal perturbations from the Earth and the Sun. Count Iblis (talk) 21:46, 21 January 2013 (UTC)[reply]

For a lunar space elevator, you need to put the counterweight at the L1 point, which is sufficiently stable not to need much station keeping. --Tango (talk) 23:10, 21 January 2013 (UTC)[reply]

See mass driver. --Tango (talk) 23:10, 21 January 2013 (UTC)[reply]

I have my doubts that a space elevator would be able to compete with a railgun on the moon for the purpose of launching. Aside from being considerably simpler, cheaper, smaller, quicker on launch and with substantially larger launch velocities, a rail gun should be roughly as energy-efficient. In terms of landing, if super-accurate guidance becomes possible, it could even be used for objects landing on the moon from suitable trajectories. — Quondum 09:23, 22 January 2013 (UTC)[reply]

The trouble with a railgun is that it's much less versatile. The G-forces involved in a railgun launch would make it unsuitable for humans - so it would be a cargo-only thing...a space elevator is a much gentler ride. Also, a railgun needs to release all of it's energy in one monumental "oomph" - making it ill-suited to solar power (which is the only reasonable to make power on the moon) without gigantic numbers of batteries. A space elevator would be easier to power with solar energy.

You wouldn't use a railgun to launch payloads into space, you would use a mass driver which is basically a coilgun, and the acceleration can be controlled. ScienceApe (talk) 16:30, 23 January 2013 (UTC)[reply]

Microphone physically attached on a string

suppose a microphone is physically attached ot a string. it's tiny, assume it weighs close to 0 grams and vibrates freely with the string - maybe it has its tiny battery and just transmits whatever it "hears", via FM or whatever.

Now. What *DOES* it hear? Tee same thing as it would hear if it were NOT freely vibrating on the string, but attached to a fixed point right next to it?

91.120.48.242 (talk) 15:42, 21 January 2013 (UTC)[reply]

It'll certainly hear things - the modes of vibration of the string (being a long, thin thing) will be very different than the modes of the microphone pickup - the string will be highly susceptible to vibrations near to it's natural frequency and to lateral vibrations rather than vertical ones. So for that reason, it doesn't isolate the microphone from all sounds...the string+microphone also has a lot of inertia - so when a high frequency sound hits it, it takes time to get moving. But the super-lightweight microphone transducer is designed to have minimal inertia. So the string might dampen out very low frequency vibrations - but not the high frequencies that we think of as "sound". I doubt you'd hear anything very much different compared to a stationary mic. SteveBaker (talk) 16:56, 21 January 2013 (UTC)[reply]

Thank you, this was the answer. Followup question: does this added weight affect the string much? (I suppose I could check this experimentally, but I'm lazy). 178.48.114.143 (talk) 18:34, 21 January 2013 (UTC)[reply]

Well, it certainly affects it...but "very much" is a value judgement. If you take one a 100' length of one of those 3" diameter ropes they use to tie ships to docks - and attach one of those pin-head microphones that spies use...then "not very much" would be a reasonable answer! On the other hand, if you're talking about a 6" length of thin string and one of those gigantic 1920's radio microphones - then you'd be lucky if it didn't snap the string...so "very much" would be a good description! SteveBaker (talk) 21:04, 21 January 2013 (UTC)[reply]

Disposing of Cooking Oil

There are a lot of specific instructions concerning the disposal of used cooking oil. They seem largely unnecessary to me. Couldn't I just pour the oil outside and let the soil microbes decompose it for me? The oil in question is a blend of soy, olive, and canola oils.70.171.28.155 (talk) 17:07, 21 January 2013 (UTC)[reply]

Sure, you can pour cooking oil outside. Ideally you compost it, in a bin or pile with other kitchen and yard waste (coffee grounds, dead leaves, etc.). If you just pour a bunch of oil on the ground, it can start to smell rancid and attract unwanted pests (opossums, racoons, etc.) SemanticMantis (talk) 17:13, 21 January 2013 (UTC)[reply]

You shouldn't add too much oil to a compost pile; too much fat retards decomposition. Some people claim it can be used to kill weeds in gravel or sidewalk cracks, but I don't know how effective that would be. SemanticMantis (talk) 17:17, 21 January 2013 (UTC)[reply]

You should find out if somebody in your community converts cooking oil to biodiesel; they'd be happy to take it off your hands. -Or- buy a diesel powered vehicle and make your own fuel:[6]:[7] There are pre-fab units (~$1500) that convert 40 gal. at a time. (Or you can DIY):[8] ~:74.60.29.141 (talk) 19:24, 21 January 2013 (UTC) ~ (P.s.: I have used straight (filtered) cooking oil, but this is not recommended for cold climates or when the fuel sits awhile.)~:74.60.29.141 (talk) 19:40, 21 January 2013 (UTC)[reply]

Why not just use as much as you need (which amounts to deposing it in your toilet a day or so later) ? Count Iblis (talk) 21:42, 21 January 2013 (UTC)[reply]

If you deep-fry correctly, little of the oil soaks into the food, leaving you a fryer-ful of used oil for disposal. DMacks (talk) 21:47, 21 January 2013 (UTC)[reply]

I see! When I visit my parents and eat some snacks they prepared, I see one or two such fryers with used oil. I never bother deep-frying stuff myself, I prefer to know exactly how much oil/fats I'm actually eating. Count Iblis (talk) 21:58, 21 January 2013 (UTC)[reply]

There are recycling centers, like this one, in many local areas that may be able to help you. Richard Avery (talk) 22:53, 21 January 2013 (UTC)[reply]

By now there are people who actually steal used cooking oil (e.g. [9]) - that's how far biodiesel has come in just a few years! This is particularly gratifying to see because it's an alternative energy source that has appeared in the hands of the common people, not some guy who owns the hilltops or can afford to build a massive energy project. Wnt (talk) 03:53, 23 January 2013 (UTC)[reply]

Quantum mechanical question. in a physical sense of actual reality (what is true) does the mathematical identity function (==) not hold for objects?

Update: this is a quantum mechanical question. Identity means mathematical identity.

In a physical sense - referring to actual reality/truth - does the mathematical identity function (==) not hold: meaning, ~~you are not mathematically identical to yourself~~ a physical object does not pass the mathematical identity function (is instead =/= to itself). My reasoning is as follows:

- ~~People~~Physical objects, unobserved, do not have exact locations, but instead are probability waves. (per quantum mechanics).

Therefore, when "comparing" ~~to yourself~~ any physical object with itself, ~~you would necessarily find that you are not identical to yourself~~ one would find that the object fails the mathematical test. By whatever means this comparison were to physically occur (per qm):

That is to say, it is not an experimental limit, but a facet of [the physical universe].

Can we, therefore, conclude that the mathematical identity function does not hold for ~~real-life objects~~ in the physical universe? That ~~an atom, or whatever, is not identical to itself?~~ physical objects cannot be considered to pass the equality test with themselves? 178.48.114.143 (talk) 17:21, 21 January 2013 (UTC)[reply]

I don't think it's meaningful or helpful to apply concepts like the identity function to thingstri-as-they-are, rather than things-as-we-approach-them. If you consider any object, and realise that it is a collection of atoms, with quite fuzzy edges as the microscopic level - and then realise that the atoms are mostly space, and the sub-atomic particles that make them up defined only by probability functions, and so on - it becomes clear that the identity of an object, or a person, or anything at all is a matter of perceptual and conceptual convenience, rather than an absolute truth. In order to get through life and not go crazy, we behave as though our architectonic approach to the material world is true. I don't stop and worry if my lunch is 'real' or not; I just eat it.

As to whether the self is real - I strongly recommend Douglas Hofstader's book I am a Strange Loop, which is all about the perception of one's own self, identity and thought processes. AlexTiefling (talk) 17:26, 21 January 2013 (UTC)[reply]

I've updated the question slightly to reflect that I am asking about "physics" (qm in particular) and not philosophy, etc. I'd like a more rigourous answer, though I did not use formalism (equations, etc) in my question, since I don't know it. Thank you. 178.48.114.143 (talk) 18:32, 21 January 2013 (UTC)[reply]

Many people are half bicycle so they don't retain their identity ;-) from Flann O'Brien, The Third Policeman: "The gross and net result of it is that people who spent most of their natural lives riding iron bicycles over the rocky roadsteads of this parish get their personalities mixed up with the personalities of their bicycle as a result of the interchanging of the atoms of each of them and you would be surprised at the number of people in these parts who are nearly half people and half bicycles" Dmcq (talk) 18:43, 21 January 2013 (UTC)[reply]

It would have been useful if you had marked the changes more clearly. I stand by my original answer, though. The term 'identity function' has, to me, only the technical mathematical meaning of a function which maps every term to itself. It has nothing much to with identity in the sense of individuality. But the human self is not a quantum mechanical thing; it exists, if it exists at all, at a much higher level both of size and abstraction. It is in no way helpful to think of macroscopic entities like people as probability functions. In any case, no person exists unobserved: they observe themselves, even when asleep, by means of their motor functions. You're trying to apply the tools of the sub-microscopic world, and of the abstract mathematical world, to large, chunky things which they do not usefully describe. I am not a probability function; in quantum terms I am a highly deterministic averaging-out of billions of billions of very localised probabilities, indistinguishable from a Newtonian entity. Unless someone subjects me to a Schrodinger's Cat test, the quantum world does not affect me perceptibly - even though it may play some part in the brain functions by which I decide what is and is not perceptible. But I'll say it again: I am not a quantum function; I am a strange loop. AlexTiefling (talk) 19:06, 21 January 2013 (UTC)[reply]

Edit: I've now I added the word "mathematical" before every occurrence of "identity" and made substantial and well marked clarificaitons. I only mean the equals function, and the physical universe. I don't care about any other aspect. 178.48.114.143 (talk) 19:41, 21 January 2013 (UTC)[reply]

I'm sorry, but this still isn't really a physics question. It's pure semantics. The word 'self', and all its compounds, conveys an idea of equality such that 'the set of all things not equal to themselves' is guaranteed to be empty. (I expect someone will be along shortly to prove that rigorously with first order symbolic logic.) So however you have defined any given physical entity, that thing (according to that definition) will be identical to itself. But if you stop thinking of that entity in macroscopic, architectonic terms, and start considering the wave functions of all its component particles, not only are you treating it in a way that is not reasonable for any ordinary person - even a professional physicist - you are also ignoring the implicitly inclusive and fuzzy-matching way we identify macroscopic objects.

If, on the other hand, the physical entity you first chose is, in fact, a subatomic particle, then (thanks to Heisenberg's Uncertainty Principle) your initial identification of what and where it is was only ever a well-informed guess to start with. In that case, you may not be able to say later that another, similarly defined particle is definitely the one you had earlier; but at any given point of time, even an electron is itself.

Bottom line: mathematics is not the real world, and trying to make the real world obey mathematical rules leads to headaches. But equally, the real world at the large scale is not usefully described by quantum theory. AlexTiefling (talk) 19:58, 21 January 2013 (UTC)[reply]

I'm not sure I entirely understand the question - but we have an article "Identical particles" which certainly says that at the level of electrons, atoms and such, there is "absolute equality" between all particles of that type. It says: "Identical particles ... are particles that cannot be distinguished from one another, even in principle. Species of identical particles include elementary particles such as electrons, and with some clauses, composite particles such as atoms and molecules."

Furthermore, John Archibald Wheeler (in a concept prominently reported by Richard Feynman in his Nobel Prize speech) suggested that electrons are not just identical - but that there is actually only one of them in the entire universe(!) - bouncing back and forth through time and appearing as an electron when going forward in time and as a positron as it travels in reverse.

I'm not sure this helps!

SteveBaker (talk) 21:00, 21 January 2013 (UTC)[reply]

Wikipedia has an article on that. It's short, but it exists. The One-electron universe. --Jayron32 04:52, 22 January 2013 (UTC)[reply]

The fact that particles don't have an exact location in space is definitely a facet of the universe but that doesn't meant that the particle is not identical to itself. All it means is that exact location in space is not a property of particles. Dauto (talk) 22:31, 21 January 2013 (UTC)[reply]

You're confusing the domains of the subjects you're talking about. It might make sense to say that 1+1=2 is modeled by putting two apples into a sack and asking how many you have, but this isn't the same as saying that addition operates on the apples. On a more deep level, computers don't operate by the rules of mathematical logic; it just happens that logic corresponds really well with what the physics produces. At any rate, such issues aside, you're question either reduces to nonsense or is asking if things can have identity. The latter is not really a physics question, more philosophy. If you'd like to go into this, I'm sure that we can; if I'm reading you wrong, please clarify. (PS, unless this is something you study, it's a confounding area of thought, so I don't mean what I've written as offensive, I think it would give any outsider pause on how to word their thoughts into a question.)Phoenixia1177 (talk) 09:23, 22 January 2013 (UTC)[reply]

common ways to relieve heart palpitations

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

--Jayron32 22:26, 21 January 2013 (UTC)[reply]

Not a request for medical advice. I'm not asking to treat anything, and the problem isn't a medical one. 128.143.1.176 (talk) 07:53, 22 January 2013 (UTC)[reply]

You can see Palpitation and Atrial fibrillation; however, there are sites other than Wikipedia. ~:74.60.29.141 (talk) 19:29, 22 January 2013 (UTC)[reply]

Why do airships exploit lift so little?

Hindenburgs travel at least 90 mph, why not make that airspeed do something useful for once? I might've seen an article about balloon-wings to orbit (with rockets and momentum providing the final boost). What's the article for that? Sagittarian Milky Way (talk) 18:42, 21 January 2013 (UTC)[reply]

Read the FAA's Balloon Flying Handbook. This free text-book will introduce you to everything you need to know about basic aeronautical engineering, aerodynamics, and engineering realities of modern lighter-than-air aircraft. Nimur (talk) 18:51, 21 January 2013 (UTC)[reply]

I now realize that the word lift was unclear. I meant airfoil lift. Sagittarian Milky Way (talk) 20:35, 21 January 2013 (UTC)[reply]

Lift doesn't come 'for free'. If you add a wing - and it produces lift, then it will inevitably add drag - and that slows the airship down or requires larger engines and more fuel...which in turn makes it heavier...so yet bigger engines and yet more fuel.

Furthermore, if you need that lift in order to maintain altitude with your regular payload weight, then you have all manner of new problems that true airships manage to avoid. For example, an airship can hover - it needs very little fuel to travel long distances. If it had to use engine power to create motion through the air just in order to avoid losing height - then it wouldn't be able to hover without falling out of the sky. If you need that wing lift to get it to gain altitude - then you'd need a runway for it to take off an land on. True airships can land and take off vertically - which is vital given how big they are!

If you don't need the extra lift - then why complicate the design and add a ton of drag for no particularly good reason?

That said, airships do gain lift - they just don't have wings to generate it. When the airship needs to gain altitude in a hurry, it can use the elevators on the tail and/or ballast shifting to point the nose up in the air - and in that attitude, that huge body does actually generate lift. I don't recall seeing any of the giant world-war-I era craft doing that - but I've definitely seen the Goodyear Blimp do it.

SteveBaker (talk) 20:49, 21 January 2013 (UTC)[reply]

I take then you're talking about a Hybrid airship Quote: “However, critics of the hybrid approach have labeled it as being the "worst of both worlds" declaring that such craft require a runway for take-off and landing, are difficult to control and protect on the ground, and have relatively poor aerodynamic performance.”--Aspro (talk) 20:56, 21 January 2013 (UTC)[reply]

►"...article about balloon-wings to orbit" → Orbital airship. ~:74.60.29.141 (talk) 21:09, 21 January 2013 (UTC)[reply]

According to Ben Bova, author of "The Great Supersonic Zeppelin Race" (fiction), a Supersonic Zeppelin can be designed so as to not create a sonic boom. The sonic boom limiting the Concorde to over-water flights is considered by many to be a major reason why it failed. --Guy Macon (talk) 23:00, 21 January 2013 (UTC)[reply]

Basically what Steve said. The engineering trade-offs involved make something like that much less efficient than one would imagine just looking at raw numbers. Lift is drag, with its powers harnessed for good rather than evil. Evanh2008 ^{(talk|contribs)} 06:17, 22 January 2013 (UTC)[reply]

However, there is an advantage to putting all your hydrogen or helium into a giant wing, that increases the surface area on the top, which allows for greater collection of solar energy by solar cells placed on the top. There was a flying wing design for a robotic plane that flew for something like 2 weeks that way. StuRat (talk) 06:28, 22 January 2013 (UTC)[reply]

There are some interesting tradeoffs here. If you want to minimize the weight and maximize the lift, you would choose a sphere. Clearly dirigible designers decided long ago that the reduced drag of a cigar shape is worth the extra weight, but they made various length to girth decisions. You do get lift from a cigar shape, but not from a (non-rotating) sphere. Once you add solar cells to the top (or paint it black to get more lift from warming the gas) some sort of a wing shape seems like it would be better, but what shape, and how thick? I am guessing that a flattened long-and-narrow shape like a thick surfboard would be better than the flattened short-and-wide shape I imagine when I hear "flying wing". Or perhaps a flying saucer shape? If everything else was equal, would a flying surfboard get more lift going sideways like a wing? Would it have more drag? Would they cancel or would the lift-to-drag ratio change? There must be a silver surfer or back-to-the-future hoverboard joke in here somewhere... :) --Guy Macon (talk) 05:23, 24 January 2013 (UTC)[reply]

January 22

In time of need, can the Male body metabolize Gynecomastia's Connective tissue?

I'm totally serious with this question. could it be that the body will use it's relevant contents to make needed substances? thanks ! — Preceding unsigned comment added by 79.176.113.107 (talk) 04:03, 22 January 2013 (UTC)[reply]

Your question is not clear. But the body will certainly use the fat reserve in case it need to do so. It does not matter where the fat is accumulated. --PlanetEditor (talk) 04:32, 22 January 2013 (UTC)[reply]

But comrade, i don't talk about Fat tissue, but of Connective tissue. — Preceding unsigned comment added by 79.176.113.107 (talk) 04:48, 22 January 2013 (UTC)[reply]

Fat tissue is a connective tissue. --PlanetEditor (talk) 05:12, 22 January 2013 (UTC)[reply]

oh yes?, because in any occasion, even when i heard physicians (plastic surgeons) speak about this, they always impressed me that the Gynecomastia tissue is of some "special" kind of "Connective" tissue, that cannot be "burn" (Beta-oxidize) like regular fat. (but i ask of metabolism in general).

Connective tissue. μηδείς (talk) 04:40, 22 January 2013 (UTC)[reply]

Breasts are composed of a combo of tissues, but a fair amount of it is fat (in adipose tissue). As such, breast size is substantially reduced when either women or men lose weight. However, too rapid of weight loss could result in sagging skin, particularly in older individuals. StuRat (talk) 14:06, 22 January 2013 (UTC)[reply]

okey, but we know that except fat, also muscle could metabolize by the body. so what about the other lean "Breastish" tissues - can they be metabolize too? — Preceding unsigned comment added by 79.176.113.107 (talk) 01:31, 23 January 2013 (UTC)[reply]

So far as I know, the other tissue is mammary gland tissue, which is indeed not a connective tissue at all but an epithelium. The effect of starvation on them must not be too great, because once food is administered, gynecomastia can then result even in previously unaffected men.[10][11] I suppose this tracks back to the "apparent purpose" of mammary tissue, for feeding, which should go on regardless of food supply. Wnt (talk) 19:27, 23 January 2013 (UTC)[reply]

RNA primer instead of DNA prime

Why RNA primers instead of DNA primes, are used in the replication of the lagging strand? What could the evolutionary advantage of this? Dnakid (talk) 06:31, 22 January 2013 (UTC)[reply]

Maybe because they can be more easily removed when no longer needed? Or perhaps their synthesis requires less energy than for DNA? 24.23.196.85 (talk) 09:00, 22 January 2013 (UTC)[reply]

DNA polymerase 3 only adds 3->5, but RNA polymerase can add where its complement is on the ssDNA. The RNA goes first and it provides that 5 and 3 end. The 3 end for the DNA polymerase to add DNA. It's more complicated than this, but this is the general answer. Smallman12q (talk) 04:15, 23 January 2013 (UTC)[reply]

In a sense the question isn't philosophically valid - evolution doesn't actually need a reason for doing something. Nonetheless, the "design" is often plainly visible - leading to the conundrum that it is very difficult to prove what seems obvious, and we end up with Just-so stories. But - without claiming that this is "the" reason - I will point out that when an enzyme attempts to prime DNA synthesis, every now and then something will go wrong and the primer won't get a chance to extend before it flies off into solution never to be recovered. In that instance it is far more predictable what will happen if it is RNA, which is subject to the continual attacks of RNAse, than if it is a piece of DNA that, in theory, could end up being stuffed into the genome somewhere it doesn't belong. Wnt (talk) 19:27, 23 January 2013 (UTC)[reply]

Why were my questions removed?!

I've asked two questions about biochemistry (one about chloral hydrate, and one about drug-induced amnesia), and both were removed with NO explanation given! Why is this?! 24.23.196.85 (talk) 06:51, 22 January 2013 (UTC)[reply]

They were removed (not by me, but by someone else) as a violation of Wikipedia:Medical disclaimer. --Jayron32 06:56, 22 January 2013 (UTC)[reply]

All right, then let me explain why I asked them: I was NOT asking for medical advice, but researching for a detective novel. 24.23.196.85 (talk) 07:00, 22 January 2013 (UTC)[reply]

I suggest you restore them, and add that bit of info. StuRat (talk) 07:05, 22 January 2013 (UTC)[reply]

I suggest that you don't, as medical advice requests aren't changed by adding sentences which claim that what they are asking for isn't medical advice. --Jayron32 07:06, 22 January 2013 (UTC)[reply]

I had actually typed up a response to the first question, but was hit with an edit conflict when I tried to save the page. I understand why they were removed, but I tend to think that the IP is telling the truth when he says it's for research; I am a writer and my Google search history can be a tad unsettling from time to time. I see nothing in the reference desk guidelines that prevents asking questions related to the biological effects of certain chemicals, but we will stop short of actually advising someone to do (or not do) something hazardous. Evanh2008 ^{(talk|contribs)} 07:12, 22 January 2013 (UTC)[reply]

If this is the same I/P who has asked many Q's for stories before, it should be reasonable to Assume Good Faith that they are, indeed, asking for that reason now. It's only medical advice if they actually intend to do it. StuRat (talk) 07:13, 22 January 2013 (UTC)[reply]

Go ahead, be my guest. Have fun. --Jayron32 07:15, 22 January 2013 (UTC)[reply]

Just like to note that the editor who removed the questions (AndyTheGrump (talk · contribs)) did provide an explanation in their edit summary: Wikipedia does not give advice on how to administer toxins etc. I suggest any further discussion of this belongs either at their talk page or at the Ref Desk talk page. Gandalf61 (talk) 07:21, 22 January 2013 (UTC)[reply]

Bad guys drugging good guys

Two questions that were mistakenly removed as medical advice:

(1) If chloral hydrate is added to spring water (as opposed to a flavored beverage like wine, apple juice, etc.), would the intended victim be able to detect it by taste alone?

(2) What drug(s) can induce temporary amnesia?

NOTE: This is NOT for medical advice -- it's for a modern-day detective novel that incorporates plot elements from Norse mythology, which I've outlined a few years ago but never got around to writing because I realized the project was too much over my head. I intend to come back to it soon, though, when I'm done with the four titles I'm working on simultaneously right now. 24.23.196.85 (talk) 08:49, 22 January 2013 (UTC)[reply]

For (2), see Drug-induced amnesia. — Quondum 09:41, 22 January 2013 (UTC)[reply]

For (1), I tasted chloral hydrate many years ago (I was prescribed it; long story), and I'm pretty sure I'd be able to detect it in just about anything. Imagine something somewhere on the continuum between over-chlorinated tap water and chimney ash. The book sounds interesting, by the way. If you need a beta/proofreader I'd be glad to give it a look. Evanh2008 ^{(talk|contribs)} 09:47, 22 January 2013 (UTC)[reply]

here is a description of the taste. As with anything on the Internet, it may be completely made up. --Guy Macon (talk) 10:58, 22 January 2013 (UTC)[reply]

(2) See retrograde amnesia, date rape drug e.g. roofie. Wnt (talk) 16:43, 22 January 2013 (UTC)[reply]

Thanks, everyone! I don't want to give too much away, but my first question is for a scene near the end, right after an intense firefight where one of the good guys knocks out a main battle tank, when one of the bad guys tries to give him (and the rest of the squad) water with chloral hydrate, in order to put them all to sleep -- but the good guy becomes suspicious and thwarts this. And my second question is for another scene, where another villain (a woman this time) gives the above-mentioned commando a two-component "love potion" (she slips it into his beer while her accomplices distract him) and tries to seduce him -- she almost succeeds, but just as he's about to come to her bed, his memory starts to come back and he runs from her place in just his underwear (but unfortunately for him, not before she takes several compromising photos of him with her and uses them to turn his own girlfriend, a field agent in her own right, against him). For the second question, in particular, I need to know the composition of the "love potion" so that my characters could figure it out. I've decided to make it a two-component drug: one component would be a straight aphrodisiac, to increase the victim's sexual desire (probably some kind of zinc-testosterone complex), and the second component would cause temporary amnesia, to make him forget about his current relationship. So in effect, the potion will make him horny for whichever woman he happens to be looking at/talking to (as long as she's not ugly), regardless of him being in love with someone else -- but she'll still have to do the work as well. :-) 24.23.196.85 (talk) 02:22, 23 January 2013 (UTC)[reply]

Testosterone for an aphrodisiac abuses my credulity - there are lots of men who take testosterone supplements, but while they are said to restore lost libido for some I don't think they are particularly effective in making a man fall for someone on the spot, and also many who take anabolic steroids, with rather less than indifferent results. I tend to give more credit to pheromones, which seem to have potent effects, but an effective aphrodisiac is definitely one of those things the audience will find hard to be persuaded by. Might be tempting to mix up some ideas and add some blur. For example, for the pheromones I recall reading a Santeria formulation in David St. Clair's book "Drum and Candle", in which AFAIR scrambled eggs are poured between the woman's thighs and served to the man in an omelet. To this you could plausibly add some named herbs like Yohimbe, and then hint at more "rare herbs and spices" known only to great obeahs, etc. We might not believe it but we can't be sure it won't work, because the ancients were much better at medicine than people give them credit for, and some of the old herbal preparations yield up new secrets to science every year. Wnt (talk) 03:43, 23 January 2013 (UTC)[reply]

Testosterone injections are known to cause priapism. Perhaps that does or doesn't count as an aphrodisiac. μηδείς (talk) 03:52, 23 January 2013 (UTC)[reply]

Technically it doesn't -- the point is to increase desire (which is not just physical but psychological as well). How about bremelanotide? 24.23.196.85 (talk) 04:59, 23 January 2013 (UTC)[reply]

Thanks for pointing to me to that interesting story. The more memorable keyword is Melanotan. Fun in the sun, bottled, and (terribly wicked) sometimes even sold without dutiful submission to the cartel. Wnt (talk) 17:08, 23 January 2013 (UTC)[reply]

That seems like a good idea too. Also, if it results in noticeable skin darkening (the guy is a typical pure-blood Teuton from Bavaria and has a pretty light complexion), that could also be a clue for the detectives that something is amiss. :-) 24.23.196.85 (talk) 05:08, 24 January 2013 (UTC)[reply]

Experimental Medicine

I remember once reading a story in reader's digest about an experimental medicine that would significantly reduce the need for sleep a person would need, but I threw away the copy of the magazine. Any ideas on what chemical it was? Rabuve (talk) 09:04, 22 January 2013 (UTC)[reply]

Modafinil is a possibility depending on when the article was published.Phoenixia1177 (talk) 09:16, 22 January 2013 (UTC)[reply]

Trip hammer mechanics

How does a trip hammer work? The article has no good picture and I can not figure out myself how it works. Especially the mechanism by which the hammer is released gives me a headache. There must be really big stress and wear on the material. How was this done in historical times, with wood and little to none metal? 93.132.137.91 (talk) 13:30, 22 January 2013 (UTC)[reply]

Have you watched the video in the article? It's fairly clear that there is no mechanism specifically to release the hammer; it just falls off the protruding part of the cam as the cam rises and rotates out from under it. And the article reveals that the earliest trip hammers were around 2,200 years ago, which is well after the iron age. China and Rome (where these hammers originate) both fielded large armies in those days armed and armoured with metal. There wasn't 'little to no metal' at all. AlexTiefling (talk) 13:34, 22 January 2013 (UTC)[reply]

No. My computer can't play videos. That there was iron does not imply that it was cheaply available. My problem with understanding is exactly the moment when the hammer "falls off". Tere must be friction and high forces. 93.132.137.91 (talk) 13:41, 22 January 2013 (UTC)[reply]

As far as I can tell, the iron casing of the cam is sufficiently polished that the friction isn't a big deal. The cam is sufficiently cleverly shaped that it lifts the hammer and then drops it fairly cleanly; it's all in the profile of the cam. And I used the existence of huge standing armies with metal weapons as evidence that metal was plentiful. Whether it was cheap doesn't necessarily matter, but in practice I believe that iron was pretty cheap in both late Republican Rome and early Imperial China. Why would you think otherwise? We have literally tons of iron artefacts from this era, as well as extensive written sources about the relatively casual use of iron. AlexTiefling (talk) 13:54, 22 January 2013 (UTC)[reply]

Accidentally I came across the trip hammer question when thinking about early iron making. The process must have been very labor intensive, first making charcoal, mining and grinding the ore, smelting in a bloomery and then hammering the slag out. The article Obolus mentions the Spartans had rod shaped iron as a currency, so it could not have been all too plentiful.

Back to the mechanical problem. The hammer must be lifted by "some peace of material", and the contact area gets smaller and smaller, until the hammer drops off. So just before that, the area on which the hammer rests must be extremely small, putting large stress on the material. I do believe you that it works, but I don't understand why. 93.132.137.91 (talk) 14:41, 22 January 2013 (UTC)[reply]

(outdent) Because the cam is curved rather than pointed, I think the area under pressure remains quite high until almost the last moment, and then reduces rapidly. So there isn't any part to break off, or anything. Moreover, the cam itself is made of iron, or of wood heavily shod with iron. So even a relatively small part of the whole is still an immense object, not prone to snapping under pressure.

(The Spartan obol appears to have been an anachronism even 2-4 centuries before the first tilt hammers became widespread. It's notable that the Romans were famed for their engineering acumen, constructing the first trans-continental highways, minutely engineered aqueducts, and pontoon bridges that spanned Europe's widest rivers and most notorious maritime straits. Smelting iron on a larger and more efficient scale than individual Greek city states was not a problem for them.) AlexTiefling (talk) 14:53, 22 January 2013 (UTC)[reply]

Thanks, I think the rounded part is what circumvents my understanding problem. And for the iron, I think it simply accumulates over time, as it is not consumed. 93.132.137.91 (talk) 15:27, 22 January 2013 (UTC)[reply]

Definitely try to watch the video on another computer. It certainly helped me understand. And the iron thing is complex: it can be recycled, so the amount of iron in circulation will increase over time. But it it isn't always; the sheer mass of iron artefacts from ancient Roman sites shows that a lot of it ended up in latrines, rubbish pits, ditches, etc. And it also rusts - stainless steel being a much more modern invention - so the iron artefacts we've got are often badly corroded. Even if you retrieved a rusty infantry sword and melted it down to make a hammer-head or something, you'd end up with a lot less iron than had been in the sword when it was new. So the efficiency and breadth of the Roman (or Chinese) industrial economy was still probably a major factor. (I've been down a Roman gold mine, years ago. Those guys were seriously accomplished engineers.) AlexTiefling (talk) 15:31, 22 January 2013 (UTC)[reply]

Related, but somewhat off-topic: does a user without video access see the still image? If so, can that image frame be specified? The current image is not particularly useful (the outside of the building) - a video frame from the operating mechanism could explain a lot: "a picture is worth [many] words". A trip hammer is a remarkably simple mechanism; the article should include a diagram or something. ~Just my 2¢, ~:(talk) 20:02, 22 January 2013 (UTC):modified:74.60.29.141 (talk) 20:21, 22 January 2013 (UTC)[reply]

E.g.: "Diagram of a forge trip hammer". ExplorePAHistory.com. WITF; Pennsylvania Historical and Museum Commission. Retrieved 22 January 2013.

File:Frohnauer Hammer Innenraum.jpg is a low-tech (simple spokes rather than smooth cam to lift). DMacks (talk) 20:16, 22 January 2013 (UTC)[reply]

Requirements of control panel for seismic relay.

Kindly let me know whether an electrical/control panel conforming to Seismic catagory/class III can be used for mounting/installing the triaxial(seismic) relay installed at suitable location for the power supply to plant.

I know that an electrical/control panel conforming to Seismic catagory/class I or II can be used for mounting/installing the above said tripping relay. — Preceding unsigned comment added by Ashutoshsds (talk • contribs) 14:07, 22 January 2013 (UTC)[reply]

You are going to have to be more specific. In particular, you have to specify what standards you are trying to meet. I am pretty sure it isn't UFGS (Unified Facilities Guide Specifications) because UFGS Seismic Design Categories are specified with letters such as A or B, whereas you mention "class III". Are you trying to meet EN (European Norm) standards? IBC (International Building Code)? Something related to the NRC (Nuclear Regulatory Commission)?

Furthermore, the basic earthquake safety standards for electrical control panels have different goals than the standards for seismic trip relays. An electrical control panel that is completely isolated from any possible ground movement would pass with flying colors, but a seismic detector wouldn't work at all under those conditions. Likewise, being solidly mounted to the foundation of a building and thus able to experience full earthquake shaking works fine for a seismic sensor but not for electrical equipment such as circuit breakers that may chatter if shaken hard enough.

In order to get any sort of sensible answer, you are going to have to describe what you are trying to do and exactly which standards you are trying to meet. --Guy Macon (talk) 18:15, 22 January 2013 (UTC)[reply]

Fire Drills

I'm having trouble finding any information on how effective fire drills are at preventing death and injury based on the frequency of the drills. I'm especially interested in whether areas/facilities where extremely frequent fire drills, in addition to false alarms of any type, happen have an increased likelihood of death or injury during actual emergency situations. (The reason being that people might begin to ignore the alarm in certain facilities like a dormitory or office.) Lord Arador (talk) 14:29, 22 January 2013 (UTC)[reply]

Well a quick back of envelope calculation by me indicates it is senseless to have fire drills more than once a year in any place except dwellings where people cook and sleep. The basics are that you have something like a 1 in 2000 chance of dying in a fire over your entire life in Britain for instance, but about 75% of that is at home and half of the lot is because people were too drunk. The rest are split evenly between other buildings, vehicles, and outside. That means you have something like most places doing fire drills the chance of the people dying of a fire per year is something like 1 in 30000, i.e. they lose on average 1/30000 of a year per year due to the risk = about 18 minutes. You should only waste of that order of magnitude or less of their time per year, i.e. have one fire drill a year. Just my thoughts - I'm sure the fire department will say otherwise! Your best bet is have good obvious exit direction notices they'll follow with an alternative depending on where the fire is. Dmcq (talk) 16:27, 22 January 2013 (UTC)[reply]

You're missing the possibility that the reason why deaths are so low in these kinds of buildings is because of fire drills. Stop the fire drills and maybe those deaths would go through the roof. It's like saying "Hardly any drivers die in low speed car accidents - so why should we bother with seatbelts?!". To do a proper study, you'd have to look back to a time before fire drills. SteveBaker (talk) 20:49, 22 January 2013 (UTC)[reply]

The risks would have to go up very fast indeed for that sort of thing to make an appreciable difference and your comparison to driving is totally wrong - if people could keep their speed down then there wouldn't be much point in seat belts. It is up to people who deprive us of a portion of our lives to show that what they have substituted is worth it rather than up to the people who have shown that it probably isn't worth while. And by the way a pet peeve of mine is fire doors on halls - these as far as I can see cause more deaths than they save because people lock them and they are too strong to break through. Saying they should not be locked during a concert is just missing the point of what reality is. Dmcq (talk) 22:31, 22 January 2013 (UTC)[reply]

It also depends on the structure. Pretty much anyone can figure out which way the exit is in a single-story detached house, but some offices and factories are like mazes. It sounds like Lord Arador might be in an environment where they do an excessive amount of fire drills. In such a case it is worth asking whether any time has been spent on fire education. Knowing where the exits are is a Good Thing, but have they been taught about crawling vs. walking in a smoke-filled hallway? About feeling a door to see if it is hot before opening it? How to effectively use a fire extinguisher or fire hose? Have they been told about propping open fire doors? When somebody does prop open a fire door, is there someone who confronts them for endangering everyone? Our article on Fire safety is a good place to start. --Guy Macon (talk) 18:29, 22 January 2013 (UTC)[reply]

In my way of looking at it if you have some people per floor with health and safety responsibilities as part of their job then you can move some of the life costs over to them so it becomes worthwhile spending the time giving them proper training. Dmcq (talk) 22:55, 22 January 2013 (UTC)[reply]

The question I always had, when in school, was whether fire drills mid-winter were likely to kill more children than they saved, since it meant going outside in extreme cold, without a coat. The problem is, kids who got sick and subsequently died weren't likely to have the cause of death listed as "fire drill", so stats would be unreliable. StuRat (talk) 19:58, 22 January 2013 (UTC)[reply]

Having experince as a fire warden in an 18 storey office building, I offer the following OR from my experience:-

When we moved into the building, after a few weeks we had a full evacuation fire drill, with fire brigade signalling turned off. We warned all tenants a few days in advance. It took about 30 minutes to get everyone out and caused significant disruption to city traffic, as the only usuable assembly area was 2 block away requiring a road crossing. About 5% of staff dissappeared. If there had been a fire, 20 minutes evac time would have resulted in quite a few deaths. All fire wardens met later and discused what went wrong, then we held talks on all floors. We did it all again 3 months later, and achieved a full evac in 14 minutes, which is quite good, and we didn't cause traffic disruption. Another 3 months, we did it again, again a good fast orderly evac, 14 minutes. Everybody able bodied went down the stairs on the inside, as they were taught to do (firemen are taught to ascend on the outside). Minders looked after the few folk who were in wheelchairs (Australian practice is to leave folk who cannot walk in designated areas with a minder for communication. The fire brigade is responsible for transporting them out) About 6 months later, we decided to do another drill - this time without warning the tenants, and we included the fire brigade in the drill. Result: A terrible mess. Some people assumed it was another drill and decided to continue their phone calls etc. Others, perhaps triggered by the sight and sound of fire engines, panicked. It took us 35 minutes to get every able bodied person out. A guy in a wheelchair was abandoned. So, what do I think? Ordinary drills with everyone knowing its a drill help the wardens learn what to do, but don't do too many of them. Every firewarden in a multistorey building should experience a full without warning drill - without it they will be overconfident.

It is worthwhile getting external audit people to assist with drills. Fire brigades love doing it. In another office tower I worked in, the auditors used smoke bombs, and they dissabled the public address system, simulating a PA system fault. The result was a complete shambles, because the stupid wardens had not maintained the batteries in their loudhailers and 2-way radios. Wardens learnt a lot that day - not the least because 3 hours of work for 1500 people were lost - company top managers were not amused. Another time the building was left unsecured, so folk off the street could go where they liked. That's bad - very bad.

Floda 120.145.134.18 (talk) 00:23, 23 January 2013 (UTC)[reply]

Very interesting. What do you mean by going down on the inside? Hugging the axis of the stairwell? μηδείς (talk) 02:51, 23 January 2013 (UTC)[reply]

While American buildings tend to only have stairs in the center utility corridor, to avoid taking up valuable window space, in other nations they frequently have one set in the center and more stairs on the outside wall. This has the added advantage, that, during the day, they can be lit with natural light from the windows, if the stairway lighting fails. This approach also increases capacity and thus decreases evacuation time. StuRat (talk) 07:26, 23 January 2013 (UTC)[reply]

StuRat has jumped in without thinking on things he knows nothing about, as he often does. You get buildings with stairs and lifts in a more or less central core, and you get buildings with stairs at the ends. Neither is peculiar to the USA or anywhere else. "Going down on the inside" has nothing to do with that. One evacuates on ALL available stairs of course. And all stairs must, by building code, have battery backed emergency lighting. Any one stair well, per building code, is wide enough so that standard ambulance stretchers can be carried up and down - this makes them wide enough so that 3 or 4 largish people can go down or up side by side together, though that is not the intention. There is a grab rail on the walls (the "outside grab rail") and a banister/grab rail in the centre (the stairwell "axis" if you will -viualise the stairs turning 180 degrees on each floor landing). In Australia, people are supposed to evacuate with their hands on the inside/centre grab rail. This has four advantages: 1) it is a lot safer - people are less likely to trip or fall with their hand continuously on the centre grab rail; 2) it makes for a single-file proceding down the stairs, without fitter (or more panicky) people trying to overtake the slower ones. This actually helps achieve a minimum time evacuation. 3) it keeps the landing doors clear so fire wardens can use them. 4) fire brigade officers are trained to go up the stairs on the "outside" that is against the wall side or "outside" grab rail. In other words, the fire fighters can charge up tye stairs simultaneously with the people leaving, without anybody getting in the way. The building designated fire wardens can also use this clear path. Floda 60.231.240.175 (talk) 10:36, 23 January 2013 (UTC)[reply]

Indeed very interesting. That reminds me of a strange inconsistency with drills: with movies about the military (which is all I know about them) they are always saying "this is not a drill!" in emergency situations. And indeed in recent movies they even indicate when something is a drill. But there isn't an immediate indication with fire drills when it is fake and when it is real. My thought is that the military must know more about drilling than anybody, so if they really do tell people, that would be a good idea for fire drills... (On the other hand there's Sean Baker, though that sounds like the exception that proves the rule) Wnt (talk) 03:25, 23 January 2013 (UTC)[reply]

Anything the military do or don't do has no bearing on civilian practice. Military personell are trained to absolutely obey any order without hesitation and without question. When a platoon member calls "DOWN!", you don't think "Oh! 'down' - I remember doing that in boot camp." You instantly on reflex go flat on your stomach on the ground - or you die from enemy bullets. Civilians don't have that training. If you tell military guys 'Wait in the floor assembly area till I call Go!" - they'll do just that. If you tell civilians to do that, which as a fire warden you will if you know the stairwell is already clogged but will clear in 2 minutes, you'll get most doing what you want, some idiots returning to their desks, and some idiots will think "Stuff you - I'm leaving", and enter the stairwell anyway. And some idiots will want to ask questions or debate the point with you. You need to think on your feet as a fire warden in an office tower. And get folk you can trust guarding the doors if necessary. There's enough people on each floor in large office towers to completely fill 4 or 5 flights of stairs, so wardens need to coordinate and stagger each floor's evacuation, so that each stair well is fully occupied but only just fully occupied, for as much of the evac time as possible. Floda 120.145.189.213 (talk) 11:44, 23 January 2013 (UTC)[reply]

In my school days we could see if it was a drill based on whether the office secretaries were still at their desks, ignoring the alarms. Someguy1221 (talk) 10:50, 23 January 2013 (UTC)[reply]

Another reason, from experience, for doing drills. One time I was working in a customer building, a largish office tower. It was after business hours, and all fire wardens had left for the day, but there were still quite a few women working. Something tripped the fire alarm - fortunately a false alarm. The building went automatically into fire mode: First, the Alarm tone sounded on all floors - and kept on sounding. The airconditioning shut down. A moderately loud humming noise started. Then, we could hear the Evacuate tone sounding sequentially floor by floor. Then Evac tone sounded on my floor. By this time the girls were loking pretty worried, and they were saying to each other, "What should we do." I called out "evacuate immediately of course - via the nearest stairs". Some girls went to the lifts, which of course had automatically shut down. Some girls came with me to a stairwell. A girl got there first, and said to me, with much alarm in her voice, "This door is locked!". At that point I realised what the humming was - this was a building that, when in fire mode, pressurises the stairwells with a huge fan at the top, in order to prevent fire travelling up the stairwells. I tried the door - sure enough it would not open with normal force. So I pushed hard and it opened. I and the girls then proceeded down the stairs. As I got near the door to the next floor down, above the noise of the fan, I could hear a lot of screaming and yelling - staff on that floor obviously thought they were locked inside a burning building. I had some pointed words, about conducting proper drills, to say to the building Management next morning. Ratbone 120.145.189.213 (talk) 12:54, 23 January 2013 (UTC)[reply]

It was daft not having a notice beside the doors warning about that along with any other vital information. Enough people working in buildings do read the notices eventually so most groups would be okay. Dmcq (talk) 17:16, 23 January 2013 (UTC)[reply]

Quite right, though it may be that the pressurisation was excessive. However, if they had held a fire drill, not only would sufficient staff be aware of it anyway, someone would have pointed out the need for signage. It illustrates the two main reasons for holding drills: 1) Teaching people what to do and not do, and 2) discovering what's not right. Ratbone 120.145.160.76 (talk) 01:56, 24 January 2013 (UTC)[reply]

It bears mentioning that the event, in the U.S., that led to widespread fire safety practices in terms of building design as well as even things like "fire drills" is the Triangle Shirtwaist Factory fire. --Jayron32 17:23, 23 January 2013 (UTC)[reply]

Since outsourced to Tazreen Fashion... Wnt (talk) 02:00, 24 January 2013 (UTC)[reply]

Barter prices for iron in ancient and medieval times compared to other goods

I wonder what the price of, say, a pound of iron was back in history in different places, compared to other goods, like grain, wine, copper, silver, gold, shoes, clothes or different kinds of livestock. 93.132.137.91 (talk) 19:07, 22 January 2013 (UTC)[reply]

I doubt that it was bartered very much. It's really only directly useful to a blacksmith, and doesn't make a very convenient medium of exchange. The amount that a blacksmith would give in barter would depend tremendously on supply and demand as well as on the quality of the iron. Looie496 (talk) 19:35, 22 January 2013 (UTC)[reply]

I wonder if you will get better information at the Humanities desk, because there are more qualified historians who would know how to look for such an answer. I assume, for example, that there is much recorded history of trade and merchant transactions, including prices, dating back to the economy of the Roman empire, who were notorious for writing down everything. We've got Roman_economy#Mining_and_metallurgy; Roman_metallurgy#Social_ramifications; those should point you in the right direction, at least! Certainly, data is known about the economies of other historical empires whose records are well-studied. The farther back into the bronze-age and beyond, the harder it is to know with great certainty; but again, the humanities desk may contain more archaeologically-interested contributors who would point you to good resources. Nimur (talk) 19:46, 22 January 2013 (UTC)[reply]

I'm not sure about that. As I have started the question here I would like to see what answers I can get here first, before moving or duplicating the question. 93.132.137.91 (talk) 19:58, 22 January 2013 (UTC)[reply]

(after ec);

I was asking for "barter" because I don't want those studies that try to give values in modern day currencies. Those are frequently in the media, telling that an average worker in some underdevelopped country gets only half a dollar per day, neglecting that he can buy from that, on average at least, enough to make a living for him and his family. Which wouldn't be possible from ten times the income in any "developed" county. So when I said "barter", I meant "what could he get in exchange".

The picture from the article Bloomery lets me guess that the gain from one bloom was at least enough to have a days meal for several people. 93.132.137.91 (talk) 19:52, 22 January 2013 (UTC)[reply]

It might, perhaps, be possible to get an idea of the cost by comparing the barter value of iron objects made by a blacksmith and figuring some kind of cost he'd add for his labor. Horseshoes ought to be a good thing to consider. But money was pretty well established in those times - it's not clear whether they'd still be bartering anyway. SteveBaker (talk) 20:44, 22 January 2013 (UTC)[reply]

Iron was also used to make coins in a number of times and places as was lead, copper, silver, gold. So it may have been more like bullion than barter. Rmhermen (talk) 20:50, 22 January 2013 (UTC)[reply]

From the discussion above (Trip hammer mechanics) it was mentioned that the Obol (coin) represents a certain amount of iron - literally translated as a "handful" of iron rods. From the article: grasp of six oboloi [handful of iron rods] = 1 drachma. I'm not sure what 1 drachma could buy - perhaps a large pizza and a pitcher of beer? ~:74.60.29.141 (talk) 21:05, 22 January 2013 (UTC)[reply]

I don't think that insisting on barter is necessarily more instructive. The Roman Empire had a well-defined currency system, and prices related to it are moderately well-known. If you don't want unhelpful modern-day conversions, just ask the humanities desk for prices in denarii, etc. AlexTiefling (talk) 21:08, 22 January 2013 (UTC)[reply]

OK I see my original question was somehow misleading. So I rephrase it. In different times and locations, especially non-modern (medieval, ancient, iron-age), what kind of living could I buy for me (and my family) if I produced an iron bloom every day, week, month? 93.132.137.91 (talk) 21:30, 22 January 2013 (UTC)[reply]

"55 pounds of grain (1 medimnos) cost 5 drachmas 7" -and- "Greek rowers on triremes in the 5th century also earned 1 drachma/day" : [12] (do the math) ~:74.60.29.141 (talk) 21:35, 22 January 2013 (UTC)[reply]

The problem is determining how much weight ≃ 6 iron "rods", which ≃ about 10 lbs grain, ≃ one day's labor wages, etc. (and what is an "iron bloom" worth?).~:74.60.29.141 (talk) 22:01, 22 January 2013 (UTC)[reply]

It is not only that I am too lazy to do all the math, and it is not only that this would be ill famed original research, but I think that there are (or at least should be) some resources out there on the net from some people who have already done such research (and who have very probably been paid at least indirectly from some money taxed from other people). Anyway, there is probably some already existing knowledge that is easier to improve than to start all over again each by oneself, and based on indirect data randomly found. 93.132.137.91 (talk) 22:22, 22 January 2013 (UTC)[reply]

Right, that "already existing knowledge" is called "history," and it is typically classified as a humanities. The resources out there, on the net and elsewhere, are called "historical documents" and "secondary sources" that regurgitate such knowledge in more digestible forms. And, the "people who have already done such research" are called "historians." This is not meant to sound snarky; I'm trying to be sincerely helpful here: this is a realistic acknowledgement that the best answers for this type of question will probably be found on the Humanities reference desk, because it is full of people who are on the whole better able to find and interpret such resources. Nimur (talk) 22:39, 22 January 2013 (UTC)[reply]

So I will, after some waiting here, repost the question on the Humanities desk. But don't think of me as all too lazy .... if you try a google on "prices historical" you get a real lot of hits about stock market prices reaching back even as far as ten years. But not really what I am looking for. 93.132.137.91 (talk) 22:45, 22 January 2013 (UTC)[reply]

Discourses on Salt and Iron (81 B.C.) is an interesting book about this subject. -- Toytoy (talk) 17:23, 23 January 2013 (UTC)[reply]

Help me identify an insect

Any idea what this is? It's sitting in my bathtub; I live in the woods near Bloomington, Indiana. When I took the photo (which I've cropped from 2816×2112 pixels), a human hair was sitting next to it; when I went back a few minutes ago, the hair was gone despite no other changes; I wonder if it might have eaten the hair. It's almost exactly an inch long. Note that the thing appearing to protrude from the rear of the insect is actually a line on the tub, not a part of the insect. Nyttend (talk) 19:50, 22 January 2013 (UTC)[reply]

As for eating hair, I believe cockroaches will do that, so it's possible this critter did, too. StuRat (talk) 19:55, 22 January 2013 (UTC)[reply]

Looks to me like your basic oriental cockroach. It's not uncommon for them to come out of drains. Looie496 (talk) 20:23, 22 January 2013 (UTC)[reply]

Uggg...time to talk to the landlord, I guess. I wondered about a roach, but (1) I thought cockroaches fled from light, while this sat still although the ceiling light was on for more than a full minute, and (2) I thought cockroaches lived in warmer climates. Nyttend (talk) 21:05, 22 January 2013 (UTC)[reply]

Cockroaches live almost everywhere... they just start approaching the size of small pets when you go into warmer climates. Shadowjams (talk) 15:13, 23 January 2013 (UTC)[reply]

If it's what I think it is, there's no need to talk to the landlord. These are known as "sewer roaches" -- they don't move very quickly, and don't give rise to infestations -- they just occasionally make their way up from the sewer where it's warm. They're nasty because they're large and ugly, but they aren't nearly as much of a problem as the smaller American and German cockroaches. Looie496 (talk) 21:10, 22 January 2013 (UTC)[reply]

I have found that keeping a jug of bleach handy and giving the drain a small splash of it after using the tub or shower keeps them out and also avoids the drain getting smelly. A stopper would also work.

For the Germans and Americans, a combination of Dupont Advion roach bait, Gentrol Point Source IGR Insect Growth Regulator and Harris Roach Tablets works wonders. The Gentrol stops the next generation from growing up, the Advion gives you secondary and tertiary kills (Google it - it's disgusting) and The Harris Tablets are non-toxic (boric acid) and so cheap you can throw one in every drawer and every cupboard shelf, behind every appliance, etc. --Guy Macon (talk) 23:10, 22 January 2013 (UTC)[reply]

Unknown plant

Anyone know? M.t.lifshits (talk) 20:45, 22 January 2013 (UTC)[reply]

Expanded.--Gilderien Chat|List of good deeds 20:49, 22 January 2013 (UTC)[reply]

I'm getting euphorbia vibes, but couldn't say what variant. Looie496 (talk) 21:01, 22 January 2013 (UTC)[reply]

It grows in a pot, and not have irrigation, only rain. M.t.lifshits (talk) 21:24, 22 January 2013 (UTC)[reply]

It certainly has a superficial likeness to Euphorbia characias "Portuguese Velvet",(aka Spurge, Portuguese Velvet) the stems look very euphorbia-like. If you can pull off a leaf stalk and cut or break it, if it is a euphorbia it will have a definite milky sap, CAUTION - this sap can badly irritate some people's skin so take care. Euphorbias are usually drought resistant which this plant seems to be. Richard Avery (talk) 22:54, 22 January 2013 (UTC)[reply]

Thank you very much. M.t.lifshits (talk) 08:42, 23 January 2013 (UTC)[reply]

January 23

Do grass grow?

nip this in the bud

The following discussion has been closed. Please do not modify it.

I mean, no matter how long I spend looking at grass in a lawn I have NEVER seen it grow with my own eyes. Yes there are time lapse photography but if you do not see it grow with your eyes, how do you know if the grass were teleported out and slight longer but identical grass were teleported in to replace it? 202.177.218.59 (talk) 02:33, 23 January 2013 (UTC)[reply]

Because teleportation is impossible, since it violates the Heisenberg uncertainty principle. 24.23.196.85 (talk) 02:36, 23 January 2013 (UTC)[reply]

Clearly, the replacement blades of grass are stored in Russell's teapot. TenOfAllTrades(talk) 02:44, 23 January 2013 (UTC)[reply]

Assuming good faith, you might be interested in epistomology. SemanticMantis (talk) 03:18, 23 January 2013 (UTC)[reply]

I understand that some types of bamboo, which is a grass, grow so quickly you can actually see and hear it (groaning sounds). See bamboo#Ecology. StuRat (talk) 08:46, 23 January 2013 (UTC)[reply]

Why doesn't the sun float away like a balloon?

If the sun is made of helium why doesn't it float away like a balloon? — Preceding unsigned comment added by 82.132.216.9 (talk) 09:05, 23 January 2013 (UTC)[reply]

Helium rises in the Earth's atmosphere because it is pushed up by the air around it. Basically, the Earth pulls harder on the air than it does on the helium, thus the air goes down, and the helium up. There is no such force in space, because there is no air, and because it is outside the Earth's gravitational reach. Also, the helium in the sun is much denser than the helium in a balloon, and there are other, heavier elements in the sun too.

For more information about how and why the sun and the planets move, see e.g. Planetary_orbit#Newton.27s_laws_of_motion and Solar_System#Structure_and_composition. - Lindert (talk) 09:25, 23 January 2013 (UTC)[reply]

It's not true that the sun is "outside the Earth's gravitational reach": the earth gravitationally attracts the sun with the same force as the sun attracts the earth, and the effect is the earth's orbit around the sun. AndrewWTaylor (talk) 12:02, 23 January 2013 (UTC)[reply]

You're right, I stand corrected. What I meant to say was that gasses near the sun are not very much affected by the Earth's field in comparison to other forces which are far stronger. - Lindert (talk) 17:14, 23 January 2013 (UTC)[reply]

I remember several children's science books that used to say that Saturn would "float on water." Here's one, Saturn at the BBC Solar System website. This fact is supposed to be surprising! Saturn is a gas giant; most of the planet's volume is comprised of low-pressure hydrogen, helium, methane, and ammonia - almost entirely in the gaseous state. For perspective, that portion of Earth that is in the gaseous state - what we call our atmosphere - also floats on water! Otherwise we'd have oceans in the sky!

When we talk about astronomical-scale objects, it's important to keep in mind that simple approximations about buoyancy break down, because the simplest approximations of gravity break down. If you ever took an elementary physics course, you may have studied fluid pressure and approximated it using the potential energy relationship, explained in our article as the "local approximation" equation. That equation totally doesn't work over large distances - like when we're measuring things the size and density of planets. For studying these objects on these length scales, the most important effect is gravity, not fluid pressure - so buoyancy is usually not even considered. If you get into technicalities, some scientists actually model the solar wind as a fluid (albeit, as an electromagnetically interacting charged plasma - "magnetohydrodynamics") - so some of the equations familiar to fluid dynamicists do show up, with a lot of adjustments.

And of course, if you study the sun's interior, it will be no surprise that the less dense parts of the sun "float to the surface" of the sun - in a constant cycle of swirling and electromagnetically-interacting convection. You can read about helioseismology to see how we study these enormous masses of constituent gas as they "float around" inside the Sun. If you want to start straying farther from common terminology, you could technically even call the solar wind a special case of "stellar" gas escape - with is a thermally-driven buoyant process: hot gas is floating away into space. Nimur (talk) 16:51, 23 January 2013 (UTC)[reply]

Passing out when hurt and evolution

I've just been wondering about how sometimes, when you get hurt badly (especially when you receive a blow to the head), the brain will essentially just shut off for a while and you will pass out. Now, I know from painful experience with the occasional stupid accident that there is a point where the level of pain becomes unbearable and where passing out and waking up a couple hours later in the hospital is a real blessing, but I'm wondering how this mechanism could have evolved - because it seems rather inefficient and dangerous to me. Let's say you're an early humanoid or an animal, you're happily walking around the steppes, then suddenly you're hit by a falling rock or tree branch or something - you pass out and you're just lying around motionless for a couple hours, being easy prey for any predator who happens to come along. I understand that depending on the type of injury you received you might hurt yourself even more while trying to get away, and in any case you could probably only stumble around slowly after an accident, but at least you could try to get to safety if you didn't pass out, instead of just presenting your edible and tasty body to predators on a silver plate - all of which could be avoided if our brains had some sort of limit for the level of pain we feel. So...has there ever been any research done into that? How could this mechanism have evolved, and what evolutionary advantage (or lack of disadvantage) can there be to passing out?

And just in case it's necessary, let me add that this is not one of those "if evolution is true, then how come we have eyes/giraffes/whatever" questions - I have no doubts whatsoever about evolution in general, I'm just idly curious in this instance. -- Ferkelparade π 11:06, 23 January 2013 (UTC)[reply]

Not every characteristic we have was evolved for some advantageous reason. Evolution often results in things that were NEVER an advantage. A well known example is the routing of the urethra through the prostate gland in male humans. It is an obvious consequence of having evolved from earlier life forms but has resulted in nothing but trouble for men. If humans were designed from the outset to walk upright while carrying things in our hands, instead of being a modification of a pattern for walking on all fours without a load, you can be sure our backs would look a lot different, and not have the current spine design that results in picking up a mere 30 kg weight, well within muscle strength, causing a load of a few tons on a bit of gristle below L4 about 7 or 8 cm across. I suspect that getting knocked out is one of those things - a disadvantage inherited from early life forms that needed a modicum of decision making capability at the mouth end. An obvious solution would be a standby brain somewhere else, or a brain inside the chest, but that is just not possible with the DNA we inherited. Floda 120.145.189.213 (talk) 12:09, 23 January 2013 (UTC)[reply]

A possible explanation:

http://cogprints.org/5046/1/2006_C.A.R_LETTER_Fear_response_of_Opossums.pdf

More info on it:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC506859/

--Guy Macon (talk) 12:23, 23 January 2013 (UTC)[reply]

It probably would have been possible for evolution to develop the enteric nervous system into the main nervous system if that was worthwhile - but having the brain just beside the eyes, ears, nose an mouth certainly looks more efficient to me. Dmcq (talk) 16:52, 23 January 2013 (UTC)[reply]

Most large predators (lions, bears, wolves, etc.) are more likely to notice a slowly-moving prey item than a completely motionless one. In other words, stumbling around slowly is more likely to draw a predator's attention. 24.23.196.85 (talk) 05:12, 24 January 2013 (UTC)[reply]

Another possible explanation is that it evolved in response to fights for dominance. That is, when one person was damaged enough to pass out, this made it clear that the other won the fight, and thus stopped the fight before either was killed. Being able to decide who is in control without actually killing anyone would be an advantage to a small group, which otherwise might have had trouble maintaining it's population. StuRat (talk) 07:01, 24 January 2013 (UTC)[reply]

I'm fairly certain sturat is completely wrong. To my knowledge, it is not the norm for animals in fights for dominance to knock each other into unconsciousness - rather, one side usually backs down or is killed. Anyway, I'd question the very premise of the question, that not passing out is beneficial. I would postulate that during that passed-out period, your body is carrying out some vital life-saying processes without which you would certainly die or suffer permanent brain damage. Someguy1221 (talk) 07:10, 24 January 2013 (UTC)[reply]

He's wrong alright. Note that the OP asked about passing out in response to a blow to the head. In such cases, for humans as with almost any animal, a blow hard enough to knock you out has a high risk of brain damage including permanent damage, and also a risk of death sometime later, eg from blood clots. If you are knocked out, there is an immediate risk of death from loss of control over the epiglotis. We often see in the news media that someone has died from the so-called one punch kill - where someone has punched someone else hard enough to render them unconscious while they are still falling - the loss of the reflex to tilt the haed up and use one's hand as shields means that the victim will strike his head on the ground from the fall. If the ground struck is in fact a small rock or concrete the result is often death. This is not an evolutionary result. Loss of consciousness occurs because the brain simply cannot remain functional under impact. Note that the links provided by Guy Macon, are, if you read them, about syncope, not a response from blows, and are to that extent irrelavent. Floda 121.215.130.102 (talk) 08:41, 24 January 2013 (UTC)[reply]

Curricula/syllabuses for math & science education in secondary education

I'm looking for curricula/syllabuses for math & science subjects in secondary education that are generally regarded as well designed and modern. I'm hoping that the info would be available for free or at low cost. I'm trying to see how the curriculum of our local school district compare to elsewhere in the country (US) and in the world. If particular curricula/syllabuses have a reputation of being biased, unevenly covered, or faddish, I'd be interested to know when doing a comparison.

Any pointers to where I can find the info? Thanks. — Preceding unsigned comment added by 173.49.10.182 (talk) 14:15, 23 January 2013 (UTC)[reply]

Does this meet your needs? If so, you will find other syllabuses on the websites of the English exam boards. There's a list of them here, and the articles have links to the websites.

To explain some of the terminology, you will probably want to search for GCSE and A Level qualifications - GCSE being an exam taken at age 16, A Level at age 18. Students are free to sit an exam from any of the exam boards, though usually the school will choose which exam board to use for all their students in any particular subject. The standard of examinations is very similar between boards, although the exact subjects covered does vary. This is more obvious in the Humanities (one board might cover the Cold War whilst another focuses on the rise of Communism in Russia, for instance) than in Maths and Science, but some differences can be noted. - Cucumber Mike (talk) 15:27, 23 January 2013 (UTC)[reply]

The Chinese "Popcorn" Cannon

http://www.youtube.com/watch?v=lhTdAMWiYeo (demo of a U.S. franchisee of a Chinese popcorn chain)
http://www.youtube.com/watch?v=Ta5jh9VglDw (... their Chinese franchisor)
http://www.youtube.com/watch?v=SRHlEMlfArA (pop rice Gangnam Style)
http://www.youtube.com/watch?v=P0zgZ-m1J3o (an industrial pop rice cannon)
http://www.youtube.com/watch?v=NoMQm2WGM9Q (firing Battleship Yamato's 18" guns!!!)
http://www.youtube.com/watch?v=GBeTvvdBnOk (pop rice Vietnam Style, a very different way)
http://www.youtube.com/watch?v=_MrXFXFGTKo (handmade Indian popcorn, how lovely ...)
http://www.youtube.com/watch?v=B7UmUX68KtE (the correct way of making good ole popcorn)
http://www.youtube.com/watch?v=q1v52f1TrWg (John Madden and his Chinese franchisee)

Is it a good idea to use the Chinese popcorn cannon to pop corn?

Generally, I have only seen people make pop rice using this thing because thanks to today's international trade and advanced agriculture, Chinese people can obtain very cheap popcorn and pop them in the correct "Swedish way". People only use these cannons to pop rice and ordinary corn. Yes, Chinese people certainly know how to use a kettle. It's just milk in China is expensive. Many have to use soybean oil instead of butter.

However, I guess this cannon can be less efficient when it comes to make popcorn because corn is much larger than rice. Therefore, the former cooks much slower than the latter. It takes longer to cook corn using the cannon and it's more likely to burn the corn. I guess this Chinese cannon is good for making popped rice. It may not be a good way to make popcorn.

Is the Indian way of making popcorn a little better? I mean if you use hot salt to cook popcorn (Chinese people use hot sand and syrup to cook chestnuts), the contact surface is increased, cooking temperature is also higher, and popped seeds do not contact the salt (they float to the top) so they are less likely to become charcoal. And the very little salt on the popped corn's surface makes it taste good.

The Japanese video clip clearly shows the before and after samples. I measured the sizes and the popped rice seems to be about 20 times larger than rice. The pressure within the cannon shall be 20 times atmosphere. There must be a practical limit where rice can be popped without breaking apart.

If you put one grain of rice into the cannon. The very limited moisture inside the rice cannot generate so much steam to increase the cannon's pressure so it's not going to pop.

If you fill up the whole cannon with rice. The rice probably contain so much water and finally it may generate too much steam.

There must be a "sweet spot" where so much rice generates so much steam and make the pressure high enough to pop the rice correctly.

I also wonder how could the Vietnamese use hot sand to pop rice. I thought popping rice requires a pressure cooker. Anyway, they are not John Madden. -- Toytoy (talk) 16:14, 23 January 2013 (UTC)[reply]

The "cannon" or pressure vessel contains limited amount of air. Heating it only increase the air pressure a little bit.

To make it easier to analyze. Let's assume the cannon contains ideal gas (PV = nRT) and dried rice. Without water in the rice, if the temperature goes from 300K to 600K, the pressure shall be doubled. The rice is burnt and it's still not going to pop.

Now we add a drop of water in the vessel and restart the experiment. Water shall vaporize and greatly increase the vessel's pressure (forget about calculations). A drop of water generates much steam. Now "n" increases and "P" also increases as a result. I know water vapor is far from ideal gas.

If we add more water, certainly there will be more vapor. "n" and "P" shall be increased greatly. The rice may not pop because in this thought experiment, the rice contains no water. Vapor outside the rice cannot be used to pop the rice.

But you know what I mean anyway. It's just a simplified way to analyze the system.

If rice contains a little moisture. More rice inside the cannon means more water and more pressure when the cannon is heated. So this cannon is quite interesting. If you put to little rice, it's not going to pop. If you put too much rice (or the rice is too wet), it may generate too much pressure.

The only way to guarantee success seems to be watching the pressure gauge. When it reaches a predetermined pressure (probably depending on the type of grain, e.g., short grain rice, basmati rice, jasmine rice, winter red hard wheat, ... something like that), you must open it to pop the grains. I think this is very different from making popcorn the "traditional way".

If you put only a grain of popcorn inside the pan, it's going to pop anyway.

However, I think you must have a minimum amount of rice in the cannon to guarantee a successful pop. -- Toytoy (talk) 17:00, 23 January 2013 (UTC)[reply]

Voltage required to accelerate a proton?

Resolved

How much voltage would be required to constantly accelerate an initially stationary, free proton by say 17 meters/sec/sec for, say 23 seconds? Would a "voltage density" variable be required for the calculation? 75.220.14.192 (talk) 17:12, 23 January 2013 (UTC)[reply]

Well after 23 seconds it would be travelling at 391 m/s, which with KE = 1/2 m v^2 and a mass of 1.67262158 × 10-27 kilograms means it has 1.2785602988599 x 10^-22 Joules which is 0.0007991001867874375 electronvolts over 3325 m is 2.4*10^-7. Hope that helps--Gilderien Chat|List of good deeds 17:42, 23 January 2013 (UTC)[reply]

Yes, that helps immensely. Thanks!

75.220.14.192 (talk) 23:23, 23 January 2013 (UTC)[reply]

Hmmm... somehow I came up with a slightly different figure when I ran through. I think a voltage density is at least implied, though the above way avoids actually calculating it. 1 volt = 1 kg m²/C s². So (electron mass kg/electron charge C) * 17 m/s² = (9.1E-31 kg/1.6E-19 C)*17 m/s² = 9.7E-11 volt/m. To keep that up for 23 seconds, during which the particle moves 1/2(23*17 m/s)(23s) = 4496 m, requires a total voltage difference of 4496*9.7E-11 = 4.4E-7. Wnt (talk) 01:54, 24 January 2013 (UTC)[reply]

Plug in C=1.6E-19eV/V and the proton's mass to get 1.77E-7eV/m. -Modocc (talk) 07:06, 24 January 2013 (UTC)[reply]

The answer should be 0.000798eV/4496.5m = 1.77E-7 eV/m. -Modocc (talk) 07:06, 24 January 2013 (UTC) -Modocc (talk) 07:06, 24 January 2013 (UTC)[reply]

Lifespan of a blackhole

How long does a black hole lasts ? What happens to those clouds and ashes which revolves around the black hole ? Want to be Einstein (talk) 17:27, 23 January 2013 (UTC)[reply]

Hypothetically, all black holes will evaporate via Hawking radiation, so long as their rate of accretion is less than their rate of evaporation. However, there's a nice calculation in that article which shows that even for a black hole which is not adding mass to itself, it's lifespan is something like 40-50 orders of magnitude longer than the age of the entire universe. So, it is unlikely that any black hole will entirely evaporate before the heat death of the universe, which is as close to "forever" as there is. --Jayron32 17:31, 23 January 2013 (UTC)[reply]

So, then we would have a period with a universe containing just black holes, and nothing else of interest ? StuRat (talk) 18:31, 23 January 2013 (UTC)[reply]

Note that the article equivocates, with many "citations needed", about heat death of an open or flat universe, which we think we have. "Near" absolute zero is not "at" absolute zero, if one is willing to consider processes occurring over much longer time scales. I've been rather inspired by the concept of "neutrino nuggets", for example... [13] Wnt (talk) 18:56, 23 January 2013 (UTC)[reply]

Our article Hawking radiation says that "For a black hole of one solar mass (1.98892 × 10^30 kg), we get an evaporation time of 2.098 × 10^67 years — much longer than the current age of the universe at 13.73 ± 0.12 x 10^9 years." And that's based on the assumption that the temperature of the surrounding universe is absolute zero. In fact, for that evaporation process to begin, you'd have to wait for the cosmic microwave background temperature - currently 2.7K - to fall below the innate temperature of the black hole, which is about 100nK (about one thirty-millionth of the current temperature), which is also a process which takes an unspeakably long time.

Pretty much any conceivable matter in the vicinity of a black hole will have fallen into it in a period of time that, relative to these timescales, is effectively zero. AlexTiefling (talk) 17:42, 23 January 2013 (UTC)[reply]

Note that tiny black holes evaporate much quicker and the super-massive black holes in the center of galaxies much slower. StuRat (talk) 18:33, 23 January 2013 (UTC)[reply]

Yes, but with the exception of primordial black holes, which may not exist, no black holes are smaller than 1 solar mass. Black holes form after the supernovae of massive stars, and the star needs to be at least 8 solar masses to undergo this process, creating a black hole of 3 solar masses. --140.180.244.202 (talk) 00:26, 24 January 2013 (UTC)[reply]

There are other theoretical ways to form micro black holes. StuRat (talk) 06:54, 24 January 2013 (UTC)[reply]

...which would indeed evaporate via Hawking radiation in a short amount of time. SteveBaker (talk) 14:13, 24 January 2013 (UTC)[reply]

Sound

What is the speed of sound on the moon?--YanikB (talk) 19:37, 23 January 2013 (UTC)[reply]

The Apollo 17 Lunar Seismic Profiling Experiment Final Summary report yielded V_p = 8.3 ±0.4 km/s below the superficial layers of lunar rock. The atmosphere of the moon is too sparse to meaningfully discuss sound-speed. Nimur (talk) 19:43, 23 January 2013 (UTC)[reply]

There is no atmosphere on the moon - so sound doesn't travel at all. (Well, I suppose you could argue that it travels *though* the moon - as a siesmic wave - in which case the speed would be pretty similar to the speed of seismic waves on earth - which is around 8000ms^-1.) But assuming you mean the speed that sound travels - like here on earth - through the air - then it doesn't travel at all...there simply is no sound. If you are thinking about the speed that sound would travel inside a spacecraft (like the Apollo lunar module) - then it would be the same as the speed in a similarly pressurized vessel on earth. SteveBaker (talk) 19:45, 23 January 2013 (UTC)[reply]

Irrelevant to the question. Free feel to continue discussion inside hat.

The following discussion has been closed. Please do not modify it.

Considering just the earth, we know the speed of sound is faster in water and in solids than in air. Given that, is there a significant difference in the speed of sound, in air at sea level vs. in air high in the Himalayas, for example? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:49, 23 January 2013 (UTC)[reply]

Absolutely yes. That's why pilots of very fast, very-high-altitude airplanes must understand their Mach number very carefully. You may find this section of our sound-speed article helpful. Nimur (talk) 19:55, 23 January 2013 (UTC)[reply]

From Speed of sound:

In fact, assuming an ideal gas, the speed of sound c depends on temperature only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out). Air is almost an ideal gas. The temperature of the air varies with altitude, giving the following variations in the speed of sound using the standard atmosphere - actual conditions may vary.

^{[citation needed]}

Effect of temperature on properties of air
Celsius temperature θ [°C]	Speed of sound c [m/s]	Density of air ρ [kg/m³]	Characteristic specific acoustic impedance z₀ [Pa⋅s/m]
35	351.88	1.1455	403.2
30	349.02	1.1644	406.5
25	346.13	1.1839	409.4
20	343.21	1.2041	413.3
15	340.27	1.2250	416.9
10	337.31	1.2466	420.5
5	334.32	1.2690	424.3
0	331.30	1.2922	428.0
−5	328.25	1.3163	432.1
−10	325.18	1.3413	436.1
−15	322.07	1.3673	440.3
−20	318.94	1.3943	444.6
−25	315.77	1.4224	449.1

Given normal atmospheric conditions, the temperature, and thus speed of sound, varies with altitude:

Altitude	Temperature	m·s⁻¹	km·h⁻¹	mph	knots
Sea level	15 °C (59 °F)	340	1225	761	661
11,000 m−20,000 m (Cruising altitude of commercial jets, and first supersonic flight)	−57 °C (−70 °F)	295	1062	660	573
29,000 m (Flight of X-43A)	−48 °C (−53 °F)	301	1083	673	585

--Guy Macon (talk) 20:01, 23 January 2013 (UTC)[reply]

Very interesting. There is a significant difference in the speed at different altitudes. That's one factor. But thinness affects sound also. Let's suppose I could magically ascend with a boom-box set at some particular volume. As I rise in the atmosphere, would the volume slowly become fainter until there was too little air to sustain sound waves? To put it another way, if the moon somehow magically had an atmosphere whose various altitudes matched those of the earth? Would sound operate the same way as on earth? (I'm thinking the answer is "Yes", but I'm just wanting to be certain.) And what I was really thinking about was not the moon, but Mars, which does have a thin atmosphere, which tends to be very cold. So, given the above info, would sound at the surface of Mars be both slower speed and lower volume? Again, I'm thinking "Yes", but I defer to the experts. 20:14, 23 January 2013 (UTC) — Preceding unsigned comment added by Baseball Bugs (talk • contribs)

Yes, there is a difference in the ability of the medium to efficiently transmit the sound, but this is irrespective of the speed the sound travels. Thinner air doesn't transmit the sound any slower, however thinner air has less molecules available to transmit information, so there is some greater loss of information, hence greater loss of volume at greater distances. --Jayron32 20:41, 23 January 2013 (UTC)[reply]

Sound waves need a medium to propagate - unlike (for example) radio waves. You may recall from High School science class the "Bell jar experiment" - (an electric bell in a glass jar) - As you pump-out the air in the jar, the bell gets quieter and quieter - until you reach a near-vacuum and you can't hear it at all, but you can still see the clapper banging. At altitude, the speed doesn't change, (disregarding temperature), just the volume (intensity) of the wave. ~:74.60.29.141 (talk) 20:43, 23 January 2013 (UTC)[reply]

Yes, I do recall that now. It's been a while. :) OK, so if I'm understanding correctly, for the OP's question about the speed of sound on the moon, assuming he's talking about atmospheric sound waves, would be that if the moon had a measurable atmosphere, then the speed of sound would be a function of the air temperature. As it stands, there is no defineable air temperature on the moon (to speak of) because there is no air (to speak of). ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:54, 23 January 2013 (UTC)[reply]

And I failed to notice the earlier reference to Atmosphere of the Moon, which indicates that technically the moon has an atmosphere, but it's extremely thin. So, supposing that it could transmit sound waves, the speed would be a function of whatever micro-measurable temperature it has, hence it would be very slow; and the volume of any such sound waves would be extremely low. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:00, 23 January 2013 (UTC)[reply]

At the moment I can't find sources for this, but... essentially, you need enough air molecules so that they can "bang into each other" in order to propagate the sound energy. Warmer molecules, being in a more energetic state, (and occupy a larger volume of space) can more easily (and quickly) transfer the sound (motion) to other molecules. [There are equations somewhere, for those who like to do the math] ~:74.60.29.141 (talk) 21:32, 23 January 2013 (UTC)[reply]

As I understand it the speed of sound depends on the density of matter. 5000 m/s in solid, 1500 m/s in liquid and 340 m/s in the air. What is the density of matter at moon ground level?--YanikB (talk) 00:02, 24 January 2013 (UTC)[reply]

Did you read above? The speed of sound in a gas depends on the temperature of the gas primarily. Density has little to do with it. --Jayron32 02:00, 24 January 2013 (UTC)[reply]

I've hatted the majority of this discussion, because it's completely irrelevant to the OP's question. The OP didn't ask about the speed of sound at various altitudes on Earth; he asked about the speed of sound on the Moon. Nimur and SteveBaker already gave the answer, and there is no need to confuse the OP with irrelevant details that are clearly well above his level of understanding. --140.180.244.202 (talk) 05:23, 24 January 2013 (UTC)[reply]

Does this show us something new about African Grey Parrot behaviour?

Apparently, this guy has taught his parrot to drive. Seriously. As I'm sure that most of us know already, African Grey Parrots are one of the most intelligent of birds - but is the one here doing something, in terms of actually controlling and directing the buggy, that we didn't think that they could do already? --Kurt Shaped Box (talk) 23:47, 23 January 2013 (UTC)[reply]

Well, it would be nice to see a peer reviewed source ... this isn't an answer, but just looking at it, my feeling is that if the parrot can be persuaded to stay on that perch, it's bound to mess with the lever. I don't see any sure sign that it is directing the vehicle to a destination - it comes toward the camera in many of the clips, but there is likely a strong selection bias in what we're seeing. It seems like every time the vehicle jiggles, it stops, and the bird is liable to move the lever any which way when it starts again. But... I can't rule out that they really have something there, either. Wnt (talk) 01:35, 24 January 2013 (UTC)[reply]

Please check 2:09 of the video

Does the bird intentionally avoid driving over the pebbles? -- Toytoy (talk) 04:32, 24 January 2013 (UTC)[reply]

It looks that way, but then again as Wnt mentions, it could be selection bias on the part of the inventor. I'd love to know if the parrot definitely gets on the buggy and uses it with the intention of *going somewhere* - which I think would be evidence of something quite significant, as opposed to just (say) going backwards and forwards and spinning in circles at random. As for the bird stopping every few seconds - it's been suggested in the YouTube comments that he's stopping to check where he's going and look on the ground in front, which necessitates (due to limited binocular vision) turning his head sideways and craning his neck. This would be amazing if true. --Kurt Shaped Box (talk) 06:39, 24 January 2013 (UTC)[reply]

See 1:43, where the parrot fails to avoid driving over pebbles. --140.180.244.202 (talk) 08:19, 24 January 2013 (UTC)[reply]

That task doesn't seem beyond the capabilities of an African grey parrot to me. It's not particularly good at it, but may get better with practice. StuRat (talk) 04:46, 24 January 2013 (UTC)[reply]

Note that the inventor is Andrew Gray. Did he change his name to match the parrots ? :-) StuRat (talk) 04:44, 24 January 2013 (UTC) [reply]

Math for astronomy degrees?

Do you have to be good at math to get undergrad and grad degrees in astronomy or astrophysics? Reflectionsinglass (talk) 23:53, 23 January 2013 (UTC)[reply]

Yes, or at least be able to pass advanced math courses. The BA of Astronomy degree from Boston University lists both Differential Equations and Linear Algebra, plus the necessary prerequisites, in their "Recommended" area (I have not attempted to determine their specific nomenclature for graduation requirements). — Lomn 00:10, 24 January 2013 (UTC)[reply]

It depends on what you mean by "good at math". To get an undergrad astrophysics degree, you will definitely need to be familiar with 3rd year physics, including Lagrangian mechanics, quantum mechanics, electromagnetism, and thermal physics. All of these courses require, at the very least, familiarity with calculus and some knowledge of linear algebra, along with the mathematical concepts from the courses themselves. That said, upper-level university math courses are usually proof based, and focus on rigorously proving some theorems at an abstract level. Science courses don't usually require as much rigor or as many proofs, because physical phenomena are more well-behaved than the crazy functions that mathematicians can think of. In this sense, it's not necessary to be good at math in order to do astro. Don't be fooled, however: if you were to take a random astro student and compare his math abilities to that of the average university student, he would be much better. He would certainly have counted as "good at math" in high school, unless said high school was exceptionally prestigious and focused on the sciences. --140.180.244.202 (talk) 00:21, 24 January 2013 (UTC)[reply]

I am not aware of any major accredited university that grants undergraduate degrees in astrophysics. If anyone knows of one, please feel free to post a link to that program; I would be interested to read about it. It is far more common to pursue an undergraduate degree in physics, or math (or even chemistry or biology), and then pursue graduate study in a physics department. Few graduate programs even have an "astrophysics" department; most graduate astrophysics Ph.D. students are rolled into the physics graduate program under the guidance of one or more specialized faculty. Nimur (talk) 00:31, 24 January 2013 (UTC)[reply]

It depends on what you mean by "major", but see [14]. I agree that what you said is a much more common route. --140.180.244.202 (talk) 00:37, 24 January 2013 (UTC)[reply]

Also, Earth and Space Exploration, from Arizona State University. It is worth emphasizing that there is a distinction between astronomy and astrophysics. Nimur (talk) 00:39, 24 January 2013 (UTC)[reply]

(ec) While I'm inclined to agree with your impression, there are at least a few schools that seem to have – or have recently had – an undergraduate program in astrophysics. There are a number of schools and individuals that refer to offering or acquiring an "undergraduate degree in astrophysics". The College of Charleston is one; McMaster University in Canada offers a physics degree with Astrophysics Specialization; UC Berkeley's Department of Astronomy has an astrophysics major; Princeton University's Department of Astrophysical Sciences offers an astrophysics major. (I'll be honest, I was a bit surprised at how many schools actually do have a distinct, degree-granting 'Department of Astronomy/Astrophysics' or similar.) TenOfAllTrades(talk) 00:53, 24 January 2013 (UTC)[reply]

Leicester University has this course, and you will see there is no mention of maths related subjects on that page. It may be lurking in the detail. --TammyMoet (talk) 10:39, 24 January 2013 (UTC)[reply]

Astrophysics "is taught at Oxford as part of the undergraduate Physics degree", with an option for much of the third year (of the three-year course) being an astrophysics project. (Astrophysics is a sub-department of the Physics department.) "Everyone who applies to study Physics or Physics and Philosophy at Oxford must sit the Physics Aptitude Test. There are no exceptions". Try out a sample of that test, including its mathematics components, here. The main target audience for that test would be British 17 and 18 year olds, pretty much all of whom would be studying both Physics and Mathematics, and possibly Further Mathematics, at A-level in the UK equivalent of high school. Less aggressively selective universities may not be as concerned about mathematical aptitude. --Demiurge1000 (talk) 12:15, 24 January 2013 (UTC)[reply]

January 24

USAGE OF DNA PRIMER

CAN DNA PRIMER BE USED INSTEAD OF RNA PRIMER DURING REPLICATION — Preceding unsigned comment added by 14.139.187.146 (talk) 05:43, 24 January 2013 (UTC)[reply]

Didn't you just ask this ? StuRat (talk) 06:45, 24 January 2013 (UTC)[reply]

Neurotheology

Is it secular neurobiological explanation of religious belief or religious attempt to take over science? --PlanetEditor (talk) 07:16, 24 January 2013 (UTC)[reply]

From a quick look at our article, it seems that it purports to be the former, though to me at least it looks like applied hogwashology. Have they thought of looking for a neurobiological explanation for believing in neurobiological explanations for religious belief, I wonder? AndyTheGrump (talk) 07:34, 24 January 2013 (UTC)[reply]

How is it hogwashology? How is your last sentence related to whether or not it's hogwashology? I've read articles by reputable neuroscientists on neurotheology, even though it's a new area of research whose conclusions are often controversial. I don't see how it's a religious attempt to take over science, since it is clearly based on scientific principles rather than religion. --140.180.244.202 (talk) 08:16, 24 January 2013 (UTC)[reply]

Is neurotheology a branch of neurology or branch of theology? --PlanetEditor (talk) 08:19, 24 January 2013 (UTC)[reply]

Since the term originated with Aldous Huxley, I'd be tempted to put it under Philosophy. ~E:74.60.29.141 (talk) 10:14, 24 January 2013 (UTC)[reply]

Displacement of a body on a circular path

This is not my homework question. A body is moving around a circular path, this means it is changing position as well as direction at every instant of time. Is the displacement of the body being changed at every point during its motion on a circular path ? Show your knowledge (talk) 10:20, 24 January 2013 (UTC)[reply]

The displacement is a sine-squared function of time. Plasmic Physics (talk) 10:42, 24 January 2013 (UTC)[reply]

Yes. The displacement increases till the body reaches the other (diametrically opposite) side of the circle and then decreases till it becomes zero when the body reaches its original position. See Displacement_(vector) — Preceding unsigned comment added by 59.145.142.36 (talk) 11:36, 24 January 2013 (UTC)[reply]

Why do electrons emit photon, not other particles ?

When a higher orbit electron comes to a lower orbit, it emits photon. Why don't it emit other elementary particles (like boson or any other) ? What are the possible reasons behind this ? Sunny Singh (DAV) (talk) 10:30, 24 January 2013 (UTC)[reply]

The short (oversimplified) answer is that it is energy that is emitted, not matter. I don't know if this will help with your specific question, but there is a nice page for visualizing this at http://spiff.rit.edu/classes/phys301/lectures/spec_lines/Atoms_Nav.swf (Turn on JavaScript first).

Also see:

http://curious.astro.cornell.edu/question.php?number=85

http://www.ccmr.cornell.edu/education/ask/index.html?quid=257

--Guy Macon (talk) 11:58, 24 January 2013 (UTC)[reply]

"Best" university of natural sciences / math in New York City

Engaging in literary pursuits, I ask for a hint concerning the protagonist of my story: What would presumably be the best / most prestigious college/university in New York City for a very gifted student of mathematics, physics and/or astronomy? --KnightMove (talk) 10:40, 24 January 2013 (UTC)[reply]

I can't myself answer, but those who can will likely need clarification whether you mean right now or at some date in the past. When is your story (or the part of it relevant to the question) set? {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 14:08, 24 January 2013 (UTC)[reply]

(edit conflict) The most prestigious university in New York City overall is likely either Columbia University or Fordham University. The two biggest science/technology schools are Polytechnic Institute of New York University (NYU-POLY) and New York City College of Technology, (City Tech). Columbia School of Engineering and Applied Science as part of Columbia University probably meets all of your requirements: A very highly regarded science and technology school, and a very prestigious university overall. --Jayron32 14:12, 24 January 2013 (UTC)[reply]

Some simple questions

1. Why sunlight appears yellow in color?
2. Is it possible to polarize electromagnetic radiations other than light using Polaroid filter?
3. What is the size of the smallest object we can see through naked eyes?
4. Is it true that transverse waves can only be produced in solids and liquids, but not in gases?
5. What is difference between water wave and water current?
6. Is it true that: "charge * electric field = electric force"? --Britannica User (talk) 10:47, 24 January 2013 (UTC)[reply]

For question 1, see this. For question 3, 0.1 mm long object can be seen by the naked eye (20/20 vision). --PlanetEditor (talk) 11:19, 24 January 2013 (UTC)[reply]

Why do we feel more pain in winter than in summer ?

I have observed this many times that we feel more pain in winter than in summer. Why is it so ? A bit more. We write the name of orbits of an atom as K, L, M, N, etc. Why we not write it as A, B, C, D, etc ? Concepts of Physics (talk) 11:07, 24 January 2013 (UTC)[reply]

I'm sure there's some good logical reason for the second item. For the first, keep in mind that our bodies are accustomed to operating in warmer weather, and our joints get kind of stiff in colder weather. In baseball, the old expression is "bees in the bat handle". In cold weather, if you don't hit the ball squarely, the bat's vibrations can really hurt - way much more so than in warm weather. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:24, 24 January 2013 (UTC)[reply]

Here is a blog post which discusses exactly the same issue. --PlanetEditor (talk) 11:30, 24 January 2013 (UTC)[reply]

With regard to the electron shells, see Electron shell#History and, for Barkla's original use of K and L to name two of them, the third response here. The other shell names are obviously a continuation of Barkla's initial two. Deor (talk) 13:58, 24 January 2013 (UTC)[reply]

Klebsiella pneumoniae

"is a Gram-negative, non-motile, encapsulated, lactose fermenting, facultative anaerobic, rod shaped bacterium found in the normal flora of the mouth, skin, and intestines It is clinically the most important member of the Klebsiella genus of Enterobacteriaceae."

This sounds like it important to have in our mouth skin and intestines. can someone clarify this, please?165.212.189.187 (talk) 13:36, 24 January 2013 (UTC)[reply]

It is unclear what is meant by "important". The most appropriate place to discuss this would be on the article's talk page.--Shantavira|^{feed me} 14:10, 24 January 2013 (UTC)[reply]

Typesetting and the perception of wordy/terse prose

I recently had to switch an unfinished paper from two-column IEEEtran format to AMS. The length went from about 2.2 to about 6.2 pages. (It has 5 equations, 3 lists of variables, and no tables or figures.) Since the AMS template is much closer to what I used as an undergrad, and I was expecting a smaller difference, this means my previous grad-level papers have been a lot longer than I thought compared to my undergrad work.

Have any studies been done on how formatting affects a reader's perception that prose is wordy, concise or terse, or on how much editing and expansion is done to a draft even in the absence of a page-count guideline? Are the effects the same on paper as on the screen? Neon Merlin 14:14, 24 January 2013 (UTC)[reply]

Inner horizon of a supermassive black hole

Hello, The orders of magnitude article: http://en.wikipedia.org/wiki/Orders_of_magnitude_%28power%29, gives as the greatest power the luminosity of the inner horizon of a black hole. Could I maybe get some more info, as I cant find anything in this direction on Wikipedia. TY.DST

@@ Line 537: / Line 537: @@
 Have any studies been done on how formatting affects a reader's perception that prose is wordy, concise or terse, or on how much editing and expansion is done to a draft even in the absence of a page-count guideline? Are the effects the same on paper as on the screen? [[User:NeonMerlin|<span style="background:#000;color:red;border:#0f0 solid;border-width:1px 0">Neon</span>]][[User talk:NeonMerlin|<span style="background:#0f0;color:#000;border:red solid;border-width:1px 0">Merlin</span>]] 14:14, 24 January 2013 (UTC)
+== Inner horizon of a supermassive black hole ==
+Hello, The orders of magnitude article: http://en.wikipedia.org/wiki/Orders_of_magnitude_%28power%29, gives as the greatest power the luminosity of the inner horizon of a black hole. Could I maybe get some more info, as I cant find anything in this direction on Wikipedia. TY.DST