Wikipedia:Reference desk/Archives/Science/2010 November 11

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 11

Home Solar Power.......Need Help

I have recently made an out building into a chicken coop and needed electricity during the winter. It was not cost effective to run hard line out there from the house, so i went with solar. I bought a 15 watt solar panel, a deep cycle marine battery with a regulater, and a two plug in power inverter. Got it all hooked up and running just fine. So here's my problem...currently i have a 10 watt flouresnt bulb thats on a timer for only a few hours during the night. I would light to put a red 50 watt heat bulb in there and leave it on all night? How do i find out what would be the max wattage of buld i can run with the current set up, and for how long? I have looked every where for a "conversion chart" without sucess. I'm new to this solar thing and need help? —Preceding unsigned comment added by Kright19 (talk • contribs) 03:37, 11 November 2010 (UTC)

No conversion needed, watts are watts. If your solar panel is 15 watts, and suppose it gets light for 8 hours a day, you'll have 15 watts*8 hours=120 watt-hours available. If you need 50 watts of heat then you can run that for 120 watt-hours/50 watts=2.4 hours. If you include the florescent bulb then it's 120 watt-hours/60 watts=2 hours. That said there is a complication: inverters waste energy, i.e. they are not 100% efficient. Their efficiency seems to run from 50% to 90%, if we assume 75%, then from your 120 watt-hours available, you'll only be able to use 90 watt-hours. On top of that the battery also is not fully efficient. My suggestion: Instead of using solar power to make and store electricity, store the solar heat directly. You have a number of ways of doing that. One idea is a tub of water on a pole with a u shaped pipe in a loop at the bottom of it. Next use mirrors (even aluminium foil on some plywood will work) to shine a lot of sun near the bottom of one side of the loop (not at the bottom, a little above it, and only on one side of the loop). Convection will circulate the water for you - you don't need a pump. Then use this warm (maybe even hot) water during the night to keep the temperature up. If I did not answer your question please let me know. Ariel. (talk) 03:53, 11 November 2010 (UTC)

It's also worth remembering that a 15-watt solar panel isn't actually going to put out 15 watts except under some fairly ideal conditions. (I have an off-grid cabin in the woods where we use a couple of solar panels to run lights and the odd laptop; the stove and refrigerator are propane, we use wood for heat, and we have a small generator that we only fire up for power tools — or when the weather's been cloudy for several days in a row.) You can expect the sun passing behind a small cloud to cost you up to half your power output; light, uniform overcast can take you down to a third of your rated output or less; dark cloud and rain can leave your panel dribbling out just ten percent of its nominal capacity. You will also suffer a penalty whenever the panel isn't angled to directly face the sun, because the panel will be catching less sunlight. (Up at the cabin, I turn the panels a couple of times a day to follow the sun; one of these years I'm going to build a clockwork system to do it for me....) One more caveat is that even if devices connected to it are turned off, the inverter may be pulling a few watts of its own while on standby, 24 hours a day. In larger systems this parasitic load gets lost in the noise, but for a small system like yours a few watts eats up a significant fraction of your output.

One more formula you might find helpful in planning is this. Battery capacities are often expressed in amp-hours rather than watt-hours; to convert amp-hour capacities to watt-hours, multiply the amp-hour rating by the voltage of the battery (usually 12 volts). For example, a 100 amp-hour (A·hr) 12 volt battery has a capacity of 1200 watt-hours. Worth remembering, too, is that you should aim to exhaust no more than about 50% of the capacity of a deep-cycle battery before recharging; repeated deep or full discharges will shorten the battery life significantly. (So that 100 amp-hour battery should only be thought of as good for 600 watt-hours storage.) Battery performance may also be poorer under cold-weather conditions, and deeply discharged batteries are prone to freezing damage. On the bright side, if your battery and inverter are inside the coop with the chickens (but protected from pecking!) then all of the charging, discharging, and inverter inefficiencies that would show up as 'waste' heat will at least be going into keeping the coop warm.

To sum up — for winter heating use, you're probably going to need significantly more charging and storage capacity than you might predict from the ideal output of your solar panel. Winter gets you less sunlight during the day, at inconvenient angles, and (in many places) more often obscured by cloud. Your battery may not work as well in the cold, and you should try to avoid using all of its capacity if you want it to last. Finally, remember that in a pinch you can always take the battery back to the house and plug it into a wall charger for a day to top it off. TenOfAllTrades(talk) 15:32, 11 November 2010 (UTC)

As an aside, inverters are (as a guess) about 90% efficient. You can get 12V or 24V fluorescent lamps (or even LEDs) from most caravanning shops and chandlers (boat suppliers). It might be more efficient to use the low-voltage lighting rather than mains voltage. However, unless you can use the fluorescents at home, it probably isn't worth the expense of replacing the lamps. CS Miller (talk) 17:32, 11 November 2010 (UTC)

If you want to use the sun for night heating, then you may be better using the solar heating system they have in Tibet I think. The sun-facing wall of a home is painted black and has a layer of glass over it, with an air gap in between. The wall has vents at the top and bottom into the house. The vents are opened or closed to regulate the heating. The massive wall heats during the day and slowly releases its heat during the night. Some book I read once went into a lot of detail about it. Anything massive and painted black, preferably behind glass, should warm during the day and release heat during the night. I expect that fixing any draught is critical. Edit: its a Trombe wall. See also for example http://www.tew.org/development/solar.greenhouse.html 92.15.3.20 (talk) 01:18, 12 November 2010 (UTC)

Water stores heat better than almost anything. So you want something like a large picture window on the south wall, and large black containers of water that stand in the sun behind the glass, with the other surfaces well insulated. 92.24.183.233 (talk) 00:02, 13 November 2010 (UTC)

I question your statement that it is not cost effective to run mains power (120 volts ac) from the house to the coop. How far away did you put your chickens? If they are out of earshot, some varmint or some chicken thief will do away with them. You should be able to set a pole or poles and run wires to the coop, or run the wires direct from the house to the coop, or, depending on local conditions, bury underground wires to get real power out there, rather than trying to run heat lamps off some lame 15 watt solar panel. I have a 45 watt solar panel, with a deep cycle battery and an inverter, and it could not run the load you propose. My grandparents had a chicken house with no electricity. To keep the chickens' water from freezing, they ran a little kerosene heater in the winter next to the watering system. That is another option you might consider. Why do you think your hens need a fluorescent light at night? They should just go on the roost and stay put until morning. If you have a 15 watt panel, then you might figure 4 hours a day at 15 watts, or 60 watt hours. How many hours per day do you need to run the bulb? Discount the 60 watt hours as suggested above for inefficiency in and out of the battery, and that is what your present setup can do. Harbor Freight sells a 45 watt panel, with a battery charge controller, for under $200. Other companies have larger panels proportionately more expensive. Utility power is likely the answer if your house has electricity and your chicken coop is sanely placed. Why would grown chickens need a heat lamp? I am familiar with heat lamps for newly hatched chicks, but not for adults, unless you are in the far north. Is the coop able to be sealed up against drafts in the winter? A 50 watt heat lamp would not cast its beneficial heat very far in any event. Edison (talk) 04:34, 12 November 2010 (UTC)

Diabetes, Insulin, and... mandatory baseline food consumption?

From this article about the disabled Carnival cruise ship: Gina Calzada, 43, of Henderson, Nev., said her diabetic sister, Vicky Alvarez, called her Wednesday morning on her cell phone and started sobbing. She said she has not been able to take her insulin for her diabetes because she is not eating enough. She told Calzada all that she had eaten was some bread, cucumbers and lettuce. "I told her where are the Pop Tarts and the Spam? I thought they brought in 70,000 pounds of supplies," Calzada said. "She said I haven't seen that."

Could someone please explain to me the details of this woman's problem. Why can't she take her insulin? Is she in danger, or just inconvenienced? I don't really understand diabetes... The Masked Booby (talk) 05:28, 11 November 2010 (UTC)

What she describes does not make sense. Not able to take insulin because you don't eat? It's exactly the opposite - if you don't eat you don't need as much insulin. And if she has bread, cucumbers and lettuce then eat it, what's the problem? People pay a lot of money for very fancy, unlimited, food on cruises, and I bet she is upset at not having that. To give the benefit of the doubt, maybe she was told to eat a certain amount to match the insulin, and doesn't know how to adjust it for lower food consumption. And maybe they have a food shortage on board. Ariel. (talk) 06:06, 11 November 2010 (UTC)

There could be a poor translation here. It might have meant "She said she has not been able to eat a much as she wants, because she used all of her own stock of insulin, and has not been given more", or "She said that she ran out of insulin and the only food available [to all passengers] was sandwiches". Given the names involved their first language might be Spanish, however that is a guess, and I don't know if Spanish's structure could make such translation mistakes possible. CS Miller (talk) 17:26, 11 November 2010 (UTC)

An insulin-dependent diabetic needs a baseline dose of insulin (so many units per hour, from a fraction of a unit to more than a unit) as well as bolus doses to prevent high blood sugar when food is eaten (meal bolus) or to lower high blood sugar when it occurs for whatever reason (correction bolus). There is typically a scale provided by the doctor or diabetes educator which tells him to take a unit of insulin for every so many grams of carbohydrate for a meal bolus, or a unit of insulin for every amount the blood sugar was above the target value for a correction bolus. If no food at all were eaten for an extended period, and no insulin at all were taken, the blood sugar might still go high, and bad things might occur. Presumably an insulin-dependent diabetic person stuck on a cruise ship would be measuring her blood sugar several times a day, via finger sticks, whether meals were available or not. If the blood sugar were high, she would likely take insulin. She would probably take basal insulin, if on a pump, or appropriate slow acting insulin at intervals, as her doctor had instructed her. Carbohydrates such as milk, bread, fruit, sugar, glucose (dextrose) tablets, or thousands of other carb types, could be eaten if blood sugar were low. Before 1922 when insulin began to be available, some insulin dependent diabetics lived for years on a starvation diet, wherein they slowly lost weight while keeping the food intake low enough that high blood sugar did not occur. Elizabeth Hughes Gossett is a notable example, a child whose weight decreased from 75 to 45 pounds over a 3 year period on a strict diabetic diet before the advent of insulin, and she lived many decades afterwards on insulin. Some periods, her diet was restricted to 400 calories to avoid high blood sugar. Running out of testing supplies or insulin would be a worry if an insulin dependent diabetic were stranded for a prolonged period. A deluxe cruise ship might well have a medical department with insulin and testing equipment. The account in general does not make a lot of sense. Edison (talk) 04:08, 12 November 2010 (UTC)

Faint glow from compact fluorescent lamp when off

Best seen from the corner of the eye in the dark. What causes it please? 92.29.125.32 (talk) 11:16, 11 November 2010 (UTC)

Phosphorescence from the particles inside the light bulb, much like glow-in-the-dark paint. --Chemicalinterest (talk) 11:40, 11 November 2010 (UTC)

Old black-and-white TVs and oscilloscope screens used to glow after switching off, like that. Cuddlyable3 (talk) 13:00, 11 November 2010 (UTC)

Does that mean it is somewhat radioactive? 92.29.112.73 (talk) 13:18, 11 November 2010 (UTC)

No. shoy (reactions) 14:30, 11 November 2010 (UTC)

Terse. Helpful. 92.29.112.73 (talk) 14:41, 11 November 2010 (UTC)

Except in comic books, most things that glow are not radioactive, and most things that are radioactive do not glow. APL (talk) 14:51, 11 November 2010 (UTC)

OP, the glow does not implicate Radioactivity, but rather the the object is emitting radiation, in this case in the Visible_spectrum. Radioactive materials emit radiation, but emitting radiation does not mean something is radioactive. Hope this helps. SemanticMantis (talk) 15:15, 11 November 2010 (UTC)

As to why it's not fully off: If it only does it for a short time, then it's leftover phosphorescence, but if it does it all the time then you have the light switch on the neutral instead of the hot. Since hot is always connected to the lamp, it's able to draw a small amount of power through it, and out the ground. Besides wasting power, this is also a bit dangerous when you go to change the lamp since it's always energized. Ariel. (talk) 16:25, 11 November 2010 (UTC)

Huh? Whatever you are describing, I don't think it happens in this land of 240 volts and tight electrical regulations. If I remember I will see if it still glows when I pull the plug out tonight. 92.15.3.20 (talk) 19:43, 11 November 2010 (UTC)

So what exactly is causing the phosphorescence? 92.15.3.20 (talk) 19:46, 11 November 2010 (UTC)

Sometimes a fluorescent light is wired incorrectly, and the neutral is switched on and off rather than the hot wire. In such a case, the lamp still has voltage applied to it when it is off, and the electrical field between the hot connection and the grounded fixture can cause it to glow a bit. Edison (talk) 01:26, 12 November 2010 (UTC)

Last night I pulled the plug out of the lamp, so it was completely disconnected, and it still glowed. It had a brighter glow after being unplugged, and must slowly fade. 92.29.120.164 (talk) 14:50, 12 November 2010 (UTC)

Particles and antiparticles - two directions of time

Some researchers have argued that antiparticles are just normal particles travelling backwards in time; positrons are electrons travelling to the past, and so on. Nevertheless, this implies there is an "end of time" from which antiparticles start travelling, just like normal particles start travelling from the "beginning of time". Where is this end of time located? --Leptictidium (mt) 12:07, 11 November 2010 (UTC)

I suppose the Big Crunch is a hypothetical "end of time". But why do you think that "normal particles start travelling from the "beginning of time"" ? Many "normal" particles are much younger than the Universe. The photons in daylight were created a few minutes ago at the surface of the sun. The photons in a artificially lit room at night are even younger. Electrons and positrons can be created in beta decay. And the quarks within hadrons such as the proton and neutron are continuously interacting by exchanging gluons, so a specific bound quark (if such a concept even makes sense) has an incredibly short lifetime. Gandalf61 (talk) 13:04, 11 November 2010 (UTC)

Our T-symmetry article explains that: "although in restricted contexts one may find this symmetry, the observable universe itself does not show symmetry under time reversal, primarily due to the second law of thermodynamics." Not that I understand exactly what is meant by the time-symmetry of particles, but apparently it is something that does not cause entropy to decrease when antiparticles are interacting among themselves.

But I think I see what Gandalf is saying. That one can conceive of the "oldest" (in "reverse-time") antiparticles does not mean that all such antiparticles were created at what would be our "end-of-time" the way that the oldest particles were created at our "beginning-of-time" (are there still any left around from that? What are the oldest "particles" still in existence in our frame of reference whatever frame of reference makes sense?). WikiDao ☯ (talk) 15:51, 11 November 2010 (UTC)

The neutrinos in the cosmic neutrino background were created when the universe was only about 2 seconds old. Red Act (talk) 16:16, 11 November 2010 (UTC)

And would we see a "cosmic antineutrino background" if the universe were time-symmetric to the point of having an "end-of-time" crunch? WikiDao ☯ (talk) 16:24, 11 November 2010 (UTC)

Neutrinos in the cosmic neutrino background that don't interact with anything until a big crunch could arguably equally as well be viewed as being antineutrinos created in the big crunch that are traveling backwards in time. It's not known why neutrinos or antineutrinos would predominate in the big bang or in a big crunch, or what if anything that might have to do with the directionality of time; see List of unsolved problems in physics#Fundamental symmetries and Neutrinos. Red Act (talk) 19:15, 11 November 2010 (UTC)

But neutrinos do interact gravitationally, so you can't view them that way. Ariel. (talk) 19:52, 11 November 2010 (UTC)

I'm not seeing how that would make any difference. What's the difference between a neutrino traveling forward in time along a geodesic of a curved spacetime, and an antineutrino traveling backward in time along that same geodesic? Or are you thinking about the other aspect of gravity, and figuring that how neutrinos affect the curvature of spacetime would be different from how antineutrinos traveling backward in time would affect the curvature of spacetime? Red Act (talk) 20:37, 11 November 2010 (UTC)

Yes, the second one. The neutrinos affect the mases near them, so do interact with things, unlike what you suggested that they don't. Ariel. (talk) 23:18, 11 November 2010 (UTC)

My intent in using the phrase "don't interact with anything" was just to indicate that they don't interact with anything in such a way that the particles can't be clearly said to be the same particles now as at the time of a big crunch. Gravity doesn't affect a particle's identity; particles in the CνB or the cosmic microwave background are considered to be the same particles now as shortly after the big bang, even though the spacetime that their world lines cross is not flat, and even though they themselves have caused some of that curvature.

However, I think there are indeed tough causality issues to try to think through, if you try to consider how gravity fits in with the time directionality (or lack thereof) of particles. Or I could just be full of shit. I'm getting well outside the range of things I actually know, here, so I probably really shouldn't be saying anything . Red Act (talk) 02:07, 12 November 2010 (UTC)

You are confusing a mathematical calculation with reality. The anti-particles are not actually traveling backwards in time! It's just some of the math can be calculated that way, so we try to learn something from it. But the anti-particles are traveling forward in time just like regular particles. And this includes the neutrino and anti-neutrino background. And BTW I believe the actual background is anti-neutrinos anyway. Ariel. (talk) 16:29, 11 November 2010 (UTC)

Is there any reason you believe that the cosmic neutrino background consists primarily of antineutrinos rather than neutrinos? The article doesn't say anything like that. If there's a reliable source that says that, perhaps that should be added to the article. Red Act (talk) 19:24, 11 November 2010 (UTC)

Because the initial conditions are assumed to be neutral, and when you create charged matter from neutral you emit anti-neutrinos. Of course it could be that neutrinos and anti-neutrinos are the same particle, so it may make no difference. Ariel. (talk) 19:46, 11 November 2010 (UTC)

Actually, it's apparently not even known for sure whether or not a neutrino is its own antiparticle; see antineutrino. Red Act (talk) 19:35, 11 November 2010 (UTC)

I haven't actually done the math, so am not too confused by it. ;) (Above: "Not that I understand exactly what is meant by the time-symmetry of particles...")

In any case, the OP may also be interested in our End of the universe article, which gives the impression that "where the end of time is located" is not known, nor assumed to "exist". WikiDao ☯ (talk) 16:49, 11 November 2010 (UTC)

Thank you, Dao, I'm already familiar with that article. All your answers were interesting, but I am most interested in Ariel's. What are the real-world implications of those mathematical calculations? Leptictidium (mt) 17:22, 11 November 2010 (UTC)

Quick introduction here: Anti-particles#Properties of antiparticles (basically to "convert" a particle to an anti-particle you need to reverse a number of properties) and main article is T-symmetry. Just remember that time reversal does not literally mean going back in time. If I'm traveling to the left at 5mph, then if I reverse time I'm traveling to the right at 5mph. So traveling to the right can be considered time-reversal. Ariel. (talk) 18:22, 11 November 2010 (UTC)

That's not really time reversal, except in a Newtonian sense. When you're "going to the left at 5mph", your four-velocity is such that you're mainly heading in the "forward in time" direction, but also heading slightly to the left. If you're "going to the right at 5mph", your four-velocity is such that you're heading slightly to the right, but still mainly heading in the "forward in time" direction. The difference between you going forward in time and going backward in time is really like the difference between the normal you, and a version of you that's made out of antimatter. Red Act (talk) 21:38, 11 November 2010 (UTC)

You're keeping me on my toes :) But it was just an example to illustrate the idea, it was not intended to be exact. Ariel. (talk) 23:18, 11 November 2010 (UTC)

The directionality of time is a deep and difficult topic, and the answers are not yet fully understood; see List of unsolved problems in physics#Arrow of time and List of unsolved problems in physics#Entropy (arrow of time). But my perspective is that if you examine just the events within a region of spacetime within which there is no clear-cut increase in entropy, and within which there is no clear CP violation, it becomes physically meaningless to ask whether the particles involved are "traveling forwards in time" or "traveling backwards in time". Red Act (talk) 18:52, 11 November 2010 (UTC)

The particle-antiparticle duality exists because of CPT symmetry. The CPT symmetry applied twice gives you back what you started with (it's a fancy kind of mirror reflection). Therefore, for any given starting state, there are two possibilities: CPT leaves the state unchanged (it's a CPT-invariant state) or CPT switches back and forth between two states that are duals of each other. In the second case, there's a convention of naming one state by "anti-" prefixed to the name of the other state—for example, electron and antielectron. This is not a universal convention. "Positron" is another name for "antielectron", and the W⁺ and W⁻ are never called anti-W⁻ or anti-W⁺, even though they're CPT duals of each other. Furthermore, it's essentially arbitrary which of the two states gets the "anti" prefix. There's no physical "antiness" property possessed by the "anti" particles.

CPT symmetry includes time reversal (the T), so one could say that the dual states have opposite time directionality. But this is like saying that they have opposite space directionality (the P). It doesn't really mean anything. Particles have no intrinsic time direction to start with, so there's nothing to reverse. And there's nothing "anti" about the particles with "anti" in their name, so you can't single them out as the ones going backward in time. -- BenRG (talk) 22:16, 11 November 2010 (UTC)

For a meaning see the transactional interpretation. But just because particles move forward or back doesn't mean that time has a beginning or an end. (You might say the Big Bang is a beginning, but see also Zeno's paradox) Note for example that a virtual pair is a closed loop... Wnt (talk) 09:24, 12 November 2010 (UTC)

But I was just saying that the particles don't move forward or back in time. (Also, as far as I can tell, the transactional interpretation exists only in John Cramer's head.) -- BenRG (talk) 02:08, 13 November 2010 (UTC)

How much Vitamin D in tin of salmon?

To be exact, a 450g (approximately as far as I recall) tin of wild Alaskan pink salmon. Thanks 92.29.112.73 (talk) 13:23, 11 November 2010 (UTC)

New York State says there are 530 IU of Vitamin D per 3 ounces (85 g) of "Salmon, pink, canned" – or about 2800 IU in 450 g. That would be the equivalent of about 70 μg of Vitamin D. WikiDao ☯ (talk) 16:18, 11 November 2010 (UTC)

Wow, about a week's worth of Vitamin D per 450g tin. 92.15.3.20 (talk) 19:57, 11 November 2010 (UTC)

digoxin

who discovered it and when —Preceding unsigned comment added by 208.104.163.189 (talk) 13:42, 11 November 2010 (UTC)

When someone finds a ref with this information, please contribute to the Digoxin article. DMacks (talk) 14:05, 11 November 2010 (UTC)

According to our article Digitalis_lanata, "Digitalin was not discovered until the mid-19th century by two French scientists Homolle Ouevenne and Theodore Ouevenne. It wasn’t until 1875 that Oscar Schmiedberg identified digoxin in the plant. It was first isolated in the 1930s in Britain by Dr. Sydney Smith." There are no specific citations for these claims, and the wording is somewhat confusing. I have not added anything to Digoxin, will leave that to someone else's judgment. SemanticMantis (talk) 15:57, 11 November 2010 (UTC)

Our Digitalis article has a bit more history of the earlier (than 1800) use of this plant (also known as foxglove). An article (PMID 11601931) in the Annals of Internal Medicine corroborates the description of the 1785 paper by Withering, which I have not yet read. Another extract is Digitoxin, by the way (the former eliminated slowly by the liver, whereas Digoxin is renally cleared). I recall hearing that the crude plant extract was used nearly a thousand years ago by native Americans for the dropsy. It's amazing anyone found a safe use for a drug that has such a narrow therapeutic index. -- Scray (talk) 03:42, 12 November 2010 (UTC)

The reference for Schmiedberg (actually Shmiedeberg) is Archiv f. exper. Patholog. und Pharm. iii 16, 1874 (Pharm, Journ. and Trans [3], v741). -- found on p142 of Plant Analysis Qualitative & Quantitative by G Dragendorff 1884 translated from Pflanenanalyse. Graeme Bartlett (talk) 07:50, 12 November 2010 (UTC)

For French person, Nativelle discovered a secondary glycoside (digitalin) in 1868. Kiliani found another one in 1891. My ref for this A text book of Pharmacognosy by George Edward Trease. 1961. Nativelle would be C.A. Nativelle who is probably notable without an article. Graeme Bartlett (talk) 08:06, 12 November 2010 (UTC)

If you really want Digoxin, a crystaline glycoside discovered by Smith in 1931 who hydrolysed Lanatoside C. also in A text book of Pharmacognosy page 513. This may be this ref: Smith, Sydney: III. "Digitalis glucosides", Jr. Chem. Soc., 1931, 23. 3 Graeme Bartlett (talk) 09:04, 12 November 2010 (UTC)

Memory improvement

Are there any scientifically proven methods of increasing a persons memory and recall abilities? —Preceding unsigned comment added by 140.121.130.67 (talk) 16:01, 11 November 2010 (UTC)

See mnemotechnics.--Shantavira|^{feed me} 16:06, 11 November 2010 (UTC)

The basic answer is that there is no known way to make memory stronger except by taking stimulants or by gaining background knowledge that will allow you to put the things you want to memorize in context. There are, however, some specialized methods that are useful for memorizing lists of unrelated things -- the best known is the so-called Method of Loci. This question comes up on the Ref Desk every so often, most recently in Wikipedia:Reference desk/Archives/Science/2010 June 15#Memory. Looie496 (talk) 17:15, 11 November 2010 (UTC)

R in chemical formulas

Resolved

In chemistry (especially organic chemistry), 'R' is used to indicate an uninteresting side branch/structural group in chemical formulae. Our R (disambiguation) notes this, however it does not indicate what 'R' is an abbreviation for. Could someone update the appropriate articles please? CS Miller (talk) 17:14, 11 November 2010 (UTC)

From "Side chain" ([1]): "The placeholder R is often used as a generic placeholder for side chains, the R historically being derived from radical or rest.". I seem to remember some chemistry textbook actually noting it came from "radical" (should anyone want a reference). But just for now, linking to the article with explanation ([2]) should be enough, I guess..? --Martynas Patasius (talk) 17:54, 11 November 2010 (UTC)

Thanks. CS Miller (talk) 18:37, 11 November 2010 (UTC)

Medicinal use of drugs

Which illegal drugs can be used medicinally and where are they actually prescribed to patients for healing diseases. I once heard about this for rheumatic symptoms. I think it was in the UK or US. —Preceding unsigned comment added by 91.60.249.180 (talk) 18:28, 11 November 2010 (UTC)

First of all, note the important difference between "illegal" and "controlled substance." See Controlled Substances Act for an overview of the legal situation in the United States, and Compare List of Schedule I drugs (US) (which by definition have no accepted medical use) to List of Schedule II drugs (US), which by definition are controlled substances that do have an accepted medical use. Other classes of drugs and controlled substances exist to clarify the "corner cases." The purpose of legal enforcement of controlled substances is that only a licensed, trained, and vetted medical doctor may prescribe a drug for medical use. In the United States, any licensed medical doctor may legally prescribe certain drugs, even if they are (certain) controlled substances. I also added the navigation template below, to help you find Wikipedia articles relevant to other countries. Nimur (talk) 18:56, 11 November 2010 (UTC)

The famous case of this is Cocaine, which was used as a local anesthetic before better ones were invented. APL (talk) 19:38, 11 November 2010 (UTC)

Actually, for a small number of procedures, cocaine is still the local anesthetic of choice; see Cocaine#Cocaine as a local anesthetic. TenOfAllTrades(talk) 21:55, 11 November 2010 (UTC)

Are you thinking of Cannabis (drug) which and medicinal cannabis? Here's a news story about it being used by someone suffering from rheumatism, but it is generally best known for being used by people with multiple sclerosis. _{Can't help dropping in a relevant song}. Oh and there are things like pyrovalerone which is illegal in some countries, but was used as a medicine at first. SmartSE (talk) 22:20, 11 November 2010 (UTC)

Diamorphine (that's medicinal heroin) has been used as a painkiller of last resort (when plain old morphine no longer works) in the United Kingdom; it may well still be used in that context, but I don't have up to date info. Physchim62 (talk) 22:36, 11 November 2010 (UTC)

LSD and MDMA are still interesting to psychiatrists, and ethanol is a good antidote for ethylene glycol poisoning. Wnt (talk) 09:31, 12 November 2010 (UTC)

Morphine comes to mind... Googlemeister (talk) 14:03, 12 November 2010 (UTC)

Also ibogaine and cannabidiol (both better known for medicinal than non-medicinal use, but still Schedule I, lest they cure something) Wnt (talk) 18:50, 13 November 2010 (UTC)

Setting Sun

I'm not sure this is a Science question per se, but it deals with astronomy-type stuff, so I assume it works best here. I currently live some 300 miles due east of where I grew up in the same US time zone. I notice that the sun sets earlier here than it does in my home town. I'm sure it has something to do with the shape of the earth and all. My question is, how far east would you need to travel to experience the sun setting 1 minute earlier than it does where you begain? I know this will depend on the topography (mountains and such), but for the sake of argument, assume the topography is flat. It seems that the sun sets, I don't know, about 30 minutes earlier here than it does where I grew up. Is there a way to calculate that or am I forgetting something very trivial that will cause me to feel like an idiot? Tex (talk) 19:28, 11 November 2010 (UTC)

That depends on your latitude. But, for a rough answer look at the Time zone map. The zones tend to be sixty minutes apart. (Except where they jog from side to side to avoid major cities.) That's the point, actually. To compensate for differences in local solar time.

More specifically, 15 degrees of longitude is exactly one hour. So you could look on a map and figure out how many miles that is for where you live. APL (talk) 19:36, 11 November 2010 (UTC)

You'd need to go exactly one quarter of a degree of longitude, not counting for any horizon effects like tall trees, hills, and so on. In most of Texas, that'd be approximately 25 kilometers, or about fifteen miles. The exact ratio of miles-per-degree-of-longitude varies based on how far north or south you are; here are formulae to help you calculate more exactly. Depending on how accurate you want to be, you should also account for the geoid, since Earth is not a perfect geometric shape (it's neither a sphere nor an ellipsoid). In practice, horizon effects and errors in driving "exactly" due-east will be much larger; so let's say "approximately 15 miles" and not even bother worrying about several decimal places of accuracy. Nimur (talk) 19:42, 11 November 2010 (UTC)

Thanks, guys. That formula looks like Greek to me, so I'll just have to go with the rule of thumb. So, if 15 miles equals to about 1 minute, then 300 miles would be about 20 minutes. That's pretty close to my recollection. That's very interesting. Thank you both! Tex (talk) 20:22, 11 November 2010 (UTC)

Which is why, if you'd been alive 200 years ago, when you moved to the new town 300 miles east and set your pocket watch to agree with the town clock, you'd find that you'd be setting it 20 minutes ahead (presuming that your pocket watch was accurate enough to notice). This wasn't considered a big deal before there were radio stations and railroads, but once the rails were built, it quickly became a big deal. And that's why time zones were invented: to localize the inconvenience to the zone boundaries (which unless you live in a very large country like the US, are likely to follow national borders). --Anonymous, 23:48 UTC, November 11, 2010.

Ships

I know that a square-rigged ship with two masts is called a brig, and with three or more a clipper. Is there a name for a square-rig with only one mast? --The High Fin Sperm Whale 19:56, 11 November 2010 (UTC)

It'd be darned uncommon; but you could make a sort of square-rigged dinghy with a gaff. A lot of ancient longships like Mediterranean Sea galleys and triremes are drawn with single square sails (but these are oar-powered vessels for the most part!). And, of course, a dhow or lateen rig is "square-like", insofar as it is squared (perpendicular) to the keel; but the actual shape of the sail is triangular. I have a sneaking suspicion that the difficulty of using a single square sail is a stability problem, especially if you ever want to sail into the wind. There will be no way whatsoever to beat or tack. That's probably why the primitive Mediterranean oarships could get away with a single square-rig - they had an alternative propulsion source! Nimur (talk) 20:27, 11 November 2010 (UTC)

A longship (think Vikings) typically had 1 square sail on 1 mast. While having oars, Vikings typically used those mainly on rivers. Googlemeister (talk) 20:46, 11 November 2010 (UTC)

A list of different rigs is here[3] but not the one you want. Nor this[4] one. Tends to suggest it wasn't used much. Alansplodge (talk) 14:47, 12 November 2010 (UTC)

Large gaff-rigged mainsail on the sloop Clearwater

Sketch by F.E. Paris (1841) showing construction of a native Peruvian balsa raft

A sloop (left) can be gaff rigged with a square sail. You could also square-rig a raft (right) if need be. WikiDao ☯ (talk) 18:37, 12 November 2010 (UTC)

Backing up the page a little bit, a three-masted square-rigged ship is simply a "ship, or "ship-rigged." A clipper was a highly-specialized form of ship that prevailed for a very short period of time at the end of the age of sail. The third (mizzen) mast on a ship gave the vessel better balance and handling characteristics, rather than contributing much thrust, as it usually had no more than half the sail area of the mainmast to avoid blanketing the main. While brigs and snows required a smaller crew, they were harder to trim and steer. A one-masted square-rigged ship would be very hard to manage, as there would be little scope to alter the center of pressure of the rig with a single mast. They were however, common in Roman times and in the early middle ages - see cog (ship) for details.Also, see the entire Aubrey–Maturin series - once you've read all 6400 pages in 20 books, you'll have absorbed a mass of technical knowledge on the ships of the early 19th century, along with a great deal of fine writing and humo(u)r. Acroterion _(talk) 21:18, 12 November 2010 (UTC)

Moss on Tennis court

Ok the obvious chemical moss killers I can find for an tarmac lawn tennis court are calcium hypchlorite, Jeyes Fluid or Ferrous sulphate. Doing a whole tennis court with any of these looks like several hundred pounds ($400) of chemicals. Anyone know which one will last longer and do least enviro harm? --BozMo talk 22:06, 11 November 2010 (UTC)

This leaflet published by the Royal Horticultural Society has details on herbicides for killing mosses and a list of suppliers. Looking at the list, I'd imagine that acetic acid should be pretty cheap! It explicitly says not to use ferrous sulphate on hard surfaces as it'll stain. SmartSE (talk) 22:29, 11 November 2010 (UTC)

Would pouring household bleach on it work? 92.29.122.31 (talk) 17:45, 13 November 2010 (UTC)