Wikipedia:Reference desk/Archives/Science/2008 December 31

= December 31 =

Best exercise for endorphins
What's the best type and program of indoor exercise for generating endorphins (and, ideally, continuing to do so for the next couple days)? I have access to a high-end campus gym. Will caffeine increase or decrease the effectiveness, taking into account that it will allow me to work out harder? Also, can I expect a change in endorphin levels to affect my academic performance? Neon Merlin  01:12, 31 December 2008 (UTC)


 * Have you read Endorphin? Lisa4edit (talk) 01:52, 31 December 2008 (UTC)


 * I have, and don't see an answer there. Neon  Merlin  04:24, 31 December 2008 (UTC)
 * I think the whole "endorphin high" is sensationalised by the media. Ask an opioid addict what a real endorphin high feels like, because a bit of running isn't really going to make the difference to your brain that pop-science has made out. --Mark PEA (talk) 14:09, 31 December 2008 (UTC)
 * I agree with Mark and would also suggest that the type of exercise is going to make no noticeable difference how how you feel but how often you take exercise might do. Ideally you will move around at different times during the day. Itsmejudith (talk) 17:56, 31 December 2008 (UTC)
 * Even though I feel that it certainly is sensationalised by the media (you probably wont get a big high every time you exercise) there is truth to the "endorphin high" concept, I my self feel happy and have more energy after I go for a strenuous run or swim and several people I know that exercise said they feel the same way after doing moderate to strenuous exercise. Scientists have also shown, that people who exercise (runners especially) have more endorphins and more anandamide (a chemical that mimics the effects of marijuana) in their blood stream than those who don’t.--Apollonius 1236 (talk) 23:15, 3 January 2009 (UTC)
 * Horizontal folk-dancing? Mattopaedia (talk) 03:46, 1 January 2009 (UTC)
 * Do you mean sex, Matt? I agree. Axl  ¤  [Talk]  12:16, 2 January 2009 (UTC)
 * Absolutely!! It's probably the only form of exercise most people would look forward to the prospect of doing almost continually for a couple of days. ;-) Mattopaedia (talk) 22:19, 2 January 2009 (UTC)

One way to feel the effect of endorphins is to cry (hear terrible news), then eat a bar of chocolate, then jog for 10 mins. Polypipe Wrangler (talk) 04:05, 3 January 2009 (UTC)

I heard the best types of exercise for endorphins are ones that involve endurance and long periods of time working out such as running, swimming and cross-country skiing.--Apollonius 1236 (talk) 18:12, 3 January 2009 (UTC)

As for the question at the end about academic performance, I don't know if any study has been done to test possible correlation between the two. Keep in mind that "academic performance" is a broad area covering a wide variety of totally different skills, including memorization, writing ability, time management, etc. Off the top of my head, I would imagine that endorphin levels would mainly help with the social side of academic life (things like taking part in class discussions), but might actually distract from focusing on the other stuff — from my own experience of "runner's high", I would guess that my memorization ability was adversely affected. On the other hand, if you suffer from any depression, then you're already starting out at a "negative" level, and regular aerobic exercise, along with all the other stuff the experts recommend (a good diet, regular sleep, psychotherapy, etc), is a great way to bring your "happiness level" up to "normal" (whatever that is). $$\sim$$ Lenoxus " * " 15:54, 6 January 2009 (UTC)

Pressure reducing devices in city water mains
My friend works for the water company in my city, and she was telling me about these large machines that they have at certain locations along the water mains pipelines, which reduce the pressure. So, as she says, water enters it at one pressure (she measures pressure in feet) and exits it at a lower pressure. She couldn't explain how it worked, unfortunately, which was frustrating because I can't understand how such a device could possibly work. Wouldn't some other property of the water also have to be changed, as all the various properties are tied together by Bernoulli's law and other such fluid mechanics principles? Cheers, Maelin (Talk | Contribs) 01:42, 31 December 2008 (UTC)


 * A venturi tube? Changing the diameter of the pipe can change the pressure in the pipe, if the net flow of water is conserved.  Also, water pressure will drop as various feeds tap off from the water-main, splitting the flow.  Also, changing absolute elevation of the pipe (such as following the contour of a hill, or just changing the depth that the pipe is buried) can decrease pressure.  Nimur (talk) 01:48, 31 December 2008 (UTC)


 * Reduced pressure zone device isn't explicitly built into the mains to reduce pressure, but does so anyway. (It's there to keep your swimming pool water from flowing back into the line. Lisa4edit (talk) 02:00, 31 December 2008 (UTC)


 * Here are a couple of links that I found here and here that have some diagrams and animations. The basic principal appears to involve a valve that opens towards the high pressure (inlet) side, with some kind of diaphragm on the outlet side that controls the movement of the valve.  As the outlet pressure increases, the diaphragm moves outward and the valve moves towards the closed position.  As the outlet pressure decreases, the diaphragm moves inward and the valve moves towards the open position.  I'm not sure if the same principles apply to large scale devices in water distribution systems.  I'm no expert in this field (not even a novice).  I'm surprised there is not a Pressure reducing regulator article.  (To the fluid mechanics experts out there: Here's your chance to contribute!)  -- Tcncv (talk) 04:02, 31 December 2008 (UTC)


 * There is a pressure regulator article, but it has few details on how they work. --Heron (talk) 18:01, 31 December 2008 (UTC)


 * The basic mechanism is pretty simple: on the low-pressure side, you've got a resevoir that, through a spring or other mechanism, maintains the desired pressure. Separating it from the high-pressure side is a valve that only opens if the pressure on the low-pressure side is below the target pressure. --Carnildo (talk) 23:50, 31 December 2008 (UTC)
 * Kittybrewster  &#9742;  19:06, 2 January 2009 (UTC)

Laser based short sight correction-what is the downside?

 * This probably falls under the category of medical advice. We can direct you to laser eye surgery and cataracts but you should primarily rely on your optician, optometrist, or other medical professional.  If you need a second-opinion, you should definitely stick to trained medical professionals.  Nimur (talk) 04:32, 31 December 2008 (UTC)


 * LASIK may have answers for some of your questions - WikiCheng | Talk 04:34, 31 December 2008 (UTC)


 * Myopia might also help you see clearer (In a purely proverbial sense ;-) Lisa4edit (talk) 04:48, 31 December 2008 (UTC)

Reactivity of Salt
Reactivity of Sodium formate and calcium chloride salt towards water? —Preceding unsigned comment added by HairulanuarMohdzin (talk • contribs) 09:40, 31 December 2008 (UTC)
 * At any normal temperature, the water will dissolve these chemicals. Calcium chloride can absorb water from  a humid atmosphere to make a solution.  Calcium chloride can form a hydrated salt. Sodium formate I don't know about. Graeme Bartlett (talk) 11:48, 31 December 2008 (UTC)
 * The article Sodium formate notes that it is deliquescent - that is, it will absorb enough water from the air to form a liquid solution. (Much like calcium chloride will.) -- 128.104.112.113 (talk) 00:06, 1 January 2009 (UTC)

Time
What is used as the physical point of reference for the time of day? Is it the orientation of the sun and the earth? In other words, if all of the clocks in the world stopped, would they be reset by (for example) saying that it is 12pm GMT when the Greenwich Meridian is directly in line with the sun (i.e. the sun is highest in the sky over the Meridian)? YaniMani (talk) 11:30, 31 December 2008 (UTC)
 * I'm not sure if I quite understand your question but if I do the first parts is answered at International Atomic Time and perhaps Leap second. It doesn't answer what happens if all the 300 clocks in various locations stop but I doubt there is any established contigency since it's so unlikely it's not worth considering. It's probably more likely that the earth will be hit by 3 large asteroids in one day and even that may not be enough to ensure none of the established clocks survive.

And even if that happens there are still other atomic clocks that we could decide to use including many in space. If the earth is destroyed, the question is moot anyway. In the unlikely event somehow every single atomic clock stops working and yet there is still enough civilisation and technology to want an accurate global time standard I'm sure we will work out something but it would surely depend on what somehow cause every single clock to start working Nil Einne (talk) 00:40, 1 January 2009 (NZDT, UTC+13)
 * Thanks. I read them, but I am still not sure what the point of reference used is (they talk about correcting for rotation). I am of course not asking about whether there is a contingency for what happens if all the clocks stopped, it is just a theoretical situation to frame the actual question - i.e. what is the external point of reference that we would use? YaniMani (talk) 11:58, 31 December 2008 (UTC)


 * You have opened a great big can of worms. You'll never ask "What time is it?" again without wondering which time you're getting. When we ask what time it is, we mean civil time, which is really standard time, which is directly referenced to Coordinated Universal Time. In the United States, this time can be found on the air on WWV. The reference for UTC is indeed the Prime Meridian, but the position of the sun is too vague for really good timekeeping. The Wikipedia article on UT says "UT in relation to International Atomic Time (TAI) is determined by Very Long Baseline Interferometry (VLBI) observations of distant quasars." They fiddle with it as needed to keep Easter from moving into August, of course. --Milkbreath (talk) 12:30, 31 December 2008 (UTC)


 * Some further reference. Icek (talk) 16:01, 31 December 2008 (UTC)

When the sun is directly over the Prime Meridian, that should be the setpoint, conceptually, for all clocks, as it in fact was in the late 19th and early 20th century, before other standards such as atomic clocks. I understand that for reasons perhaps having to do with the sensitivities of the French to British standards, or the earth not being perfectly symmetrical, the GPS system places 0 degrees longitude a short distance away from the engraved line in a brass plate which equals the center line of the telescope at Greenwich formerly used for the determination of time. So the sun being directly overhead of one of the historic prime meridians could be used as the synchronizing standard of clocks. Edison (talk) 19:14, 31 December 2008 (UTC)


 * Because the earth's orbit is elliptic and not circular (and other factors), the apparent position of the sun will vary throughout the year if viewed at the same time each day. See Analemma.  -- Tcncv (talk) 04:30, 1 January 2009 (UTC)


 * ...And consequently, the basis for time is not that noon UT is when the Sun is at the zenith at the Prime Meridian; it's the average (mean) time of this event. That's why UT used to be called Greenwich Mean Time.  Note that I said "UT" and not "UTC".  UTC, the time we now use, applies a fine-grained correction to UT; see leap second.  --Anonymous, 08:57 UTC, January 1, 2009.

To answer your question as asked: The definition of time has two components: the length of the second, and a nominal zero point. The current defintion for the duration of a second is no longer related in any way to the movement of the earth or other celestial bodies. The starting point is related to a particular event (actually, a statistical average of multiple events) in the past. Therefore, for purposes of definition, the answer to your question is "no." There is no formal definition of a particular future celestial event as being at a defined time. All future celestial events will have observed times, not defined times. Now to answer your hypothetical question: If by horrible mischance, we somehow lose track of time, How would we reset the clocks? This affects only the zero point, not the length of the second: we can create new clocks that accurately measure the length of the second. This means the new zero point must be agreed upon by convention. Depending on how long the clocks were stopped, teg new agreement might try to relate "new time" to "old time" by picking a particular celestial event that was predicted to high precision with respect to "old time" and agreeing that the event is the reference pont for "new time." But note that this would be a new agreement made by a comitee, and would have no more (or less0 absolute signigicance than our current definition. -Arch dude (talk)
 * Thanks for the correction about noon being subect to a correction depending on where in its orbit about the sun the earth is. Subject to that correction, the transit of the sun and the stars through the crosshairs of the Greenwich meridian could be used to re-establish exact time, down to the fraction of a second. The actual transit of the various stars was tracked each night, down to the fraction of a second, recorded, and used to determine standard time in the late 18th and early 20th century. By tracking many starts, and averaging the transits, the mechanical master clocks which sent out electrical signals on the hour, could be regulated to a fraction of a second., as it was over 100 years ago. Edison (talk) 06:10, 2 January 2009 (UTC)