Wikipedia:Reference desk/Archives/Science/2009 December 24

= December 24 =

Earliest sunset
is there anywhere in the world where the sun can set before local noon? —Preceding unsigned comment added by 97.118.58.208 (talk) 00:08, 24 December 2009 (UTC)
 * Going back to the previous section, perhaps Viganella? Nyttend (talk) 00:13, 24 December 2009 (UTC)
 * Since noon is defined as halfway between sunrise and sunset, you can't have noon be after sunset. Unless you consider the sun being behind a mountain as sunset. Ariel. (talk) 02:20, 24 December 2009 (UTC)
 * That depends on your definition of 'noon'. In my experience, 'noon' is usually held to be synonymous with the midday 12 o'clock in whatever time zone I happen to be in.  In principle, one could have a very short day (near the Arctic circle in midwinter, for instance) and be standing near the eastern edge of the time zone.  Sunrise and sunset could follow in quick succession, and you could be back in the long night before the clock rolls over to twelve.  Using this handy calculator, one can easily confirm this.  Poking around a bit with Google Maps, the village of Pajala in northern Sweden meets the necessary criteria.  On four days this year (19 December through 22 December) the time between sunrise and sunset is only about an hour, and the sunset falls before local 1200.   TenOfAllTrades(talk) 03:03, 24 December 2009 (UTC)


 * If you define "local noon" as "the time halfway between sunrise and sunset", then by definition the answer is "no". If you define "local noon" as "12:00 according to the local time zone", then any place close to the arctic circle and offset far enough from the time zone's meridian can have sunset before noon. --Carnildo (talk) 02:44, 24 December 2009 (UTC)


 * The latter is also true if you define "local noon" as "noon according to local mean solar time" without reference to time zones, due to the equation of time. At the day of maximal equation of time (some 16 minutes), stand sufficiently far north of the arctic circle that the length of the day is less than half an hour. Then the sun will set before noon MST. –Henning Makholm (talk) 06:57, 24 December 2009 (UTC)


 * On the road between Todmorden and Bacup, Lancashire, England, there is a place which is in the shadow of a hill for about 3 months of the year. There is a small hamlet at the foot of the hill which casts this shadow, so this may well qualify as the answer to the question. --TammyMoet (talk) 16:00, 24 December 2009 (UTC)

Returning isolated human and immunity
Suppose we have an ordinary healthy human in his or her twenties who has lived his or her entire life in urban areas. Then, he or she spends three or four years in some kind of complete isolation from physical human contact (for example, an Antarctic research station or a solitary prison of some kind). During that time, he or she has plentiful access to food, water, living space, telecommunications, etc., everything necessary to stay in good physical and mental health. When he or she returns to the city, will he or she be more likely than the average person to catch the common cold or a seasonal flu, or is three or four years not long enough a period of isolation for it to matter with respect to medical immunity?

—Lowellian (reply) 01:46, 24 December 2009 (UTC)


 * No, however they may get a bunch of colds at once (which is probably indistinguishable from having just one), since they didn't get a chance to get them one at a time each year. Immunity in general lasts a lifetime. A person is also never sterile, even if you are not infected with visible illness your environment is full of bacteria, so the immune system never stops working. I think some lab animals are grown completely sterile, but it's quite hard to do. The bio-filter on the Star Trek Transporter would in actually be really bad, if it removed all bacteria from a person. Doing that would cause the immune system to go haywire, and would also cause all sorts of digestive and skin problems. Ariel. (talk) 08:27, 24 December 2009 (UTC)


 * I already know immunity lasts a lifetime and that even isolated environments are not sterile, but that's not the point. It's not what I'm asking, so let me try to clarify. Viruses and bacteria constantly mutate. That person who has been in isolation won't have immunity to any new strains that developed and spread among the human population during those three years. So, another way of looking at the question is, is the rate of new strain development fast enough that the person would be at significantly higher risk of getting sick than people who haven't been in isolation, or is the rate of new strain development slow enough that there would be no appreciable difference given a timespan of only three to four years? —Lowellian (reply) 09:10, 24 December 2009 (UTC)


 * The only way to get immunity to a cold is to get sick. People outside will get sick X number of times. The isolated person will also get sick when he emerges. Basically he's putting off getting sick for a while, but in net will get sick at the same rate as people outside. He's not reducing or increasing his risk, he is postponing it. And actually he might feel sick just once, and handle all the new stuff all at once, while the people outside had to do it one at a time. (Actually, the previous strains may no longer exist much in the wild, and he won't have to deal with them. People in general do not constantly shed viruses. There are only a limited number of diseases where you have chronic carriers.)


 * The rate of mutation of a cold is such that after 3 years there will probably be a new strain - I think it's fast enough that you have a new strain every year, but I could not find hard numbers. Is that your main question? How often does the cold/flu virus mutate to the point that people will get sick again? Ariel. (talk) 09:40, 24 December 2009 (UTC)
 * This year's flu is around for everyone to catch. Last year's mutation of the flu is not necessarily still around in enough numbers for the "returnee" to ever be exposed to it. (Especially true of this year's swine flu) 75.41.110.200 (talk) 14:55, 24 December 2009 (UTC)
 * Indeed. Ariel, your first paragraph above makes no sense. How many times have you caught black death? You weren't around for the first one, so presumably you're due to get in at any time, right? And if you don't have sex until you're sixty you'll catch herpes, the clap and crabs all at once to make up for all the STDs you should have gotten if you'd been having regular intercourse? Nature doesn't just force you to "catch up" somehow to make it all fair and even. What possible mechanism would be involved? Matt Deres (talk) 17:24, 24 December 2009 (UTC)
 * What paragraph are you talking about? Because I was the one who said that: "Actually, the previous strains may no longer exist much in the wild, and he won't have to deal with them. People in general do not constantly shed viruses. There are only a limited number of diseases where you have chronic carriers." Ariel. (talk) 18:11, 24 December 2009 (UTC)
 * My apologies. Your comment that "He's not reducing or increasing his risk, he is postponing it. And actually he might feel sick just once, and handle all the new stuff all at once, while the people outside had to do it one at a time" is what I was referring to, though you did obviously correct yourself in the bracketed comment. My bad. I would normally put the most correct answer in the regular part and perhaps add a parenthetical remark to acknowledge something that was conjecture rather than the opposite setup, but I still should have read your post more thoroughly. Matt Deres (talk) 18:23, 24 December 2009 (UTC)

Still same situation as posed above, but let me try asking this question another way. In a given month, there exists some probability p that an average non-isolated healthy person will get sick with the cold or flu at least once. Suppose the returnee comes back to the city that same month after three or four years in isolation. There also exists some probability q that the returnee will get sick with the cold or flu at least once that month. Is q going to be significantly higher than p? —Lowellian (reply) 00:42, 25 December 2009 (UTC)


 * Imperceptible. There should be a slightly increased probability if you investigated closely enough, but I reckon a sample size of many thousands of subjects would be necessary to show a statistically significant difference in a randomized controlled trial (the best answer medical science can give you). I know of no such study, and anecdotally I've never heard of terrible health problems in returning Arctic researchers, astronauts, Biosphere 2 workers, etc.
 * Crowded humans encounter numerous types of cold and flu virii; infection stimulates the formation of memory B cells against that specific virus. The crowded man simply gets more exposure during those 3 years, so he has more opportunity to develop immunity to the relevant pathogens. However, the number of different cold and flu strains is vast, and I think most of them won't have touched the crowded man significantly enough to give an advantage. Plus, the isolated man still has functional innate immunity (which deals with the majority of infections), and his adaptive immunity from before the isolation is still formidable.
 * For the seasonal flu specifically, it's often a relatively novel strain. In this case, it's even less likely that the crowded man would have had an exclusive opportunity to encounter it in the three year window. - Draeco (talk) 21:30, 25 December 2009 (UTC)


 * The answer is no, you will not be any more likely to catch a cold. There are too many diferent viruses floating around and they mutate too rapidly to make any difference.  Gandydancer (talk) 03:38, 26 December 2009 (UTC)

Mass and Weight Physics
Can someone describe the difference between mass and weight?

When you stand on a weighing scale, is that weight or mass?

I'm just getting confused b/c like for a chemical reaction, a problem can say you have oxygen with a mass of 100g, but is that specific to that much oxygen on earth, or any other planet / in outer space?

thanks. —Preceding unsigned comment added by Legolas52 (talk • contribs) 07:30, 24 December 2009 (UTC)


 * Mass: the amount of matter. Weight: how strongly that matter is pulled by gravity. You are confused because since the easiest way measure how much matter there is, is by seeing how strongly it is pulled toward the earth, this strength of attraction is (was) used to also indicate how much matter there is.


 * When you stand on a weighing scale, the number shown is weight. But, knowing the weight, and the strength of the earth's gravity, it is possible to then calculate the mass. Ariel. (talk) 07:44, 24 December 2009 (UTC)


 * Thanks for your reply! But still, this is what I'm confused by - if in a chemistry problem, you are given a "mass" does it refer to its mass or is it weight labeled incorrectly. Or, moreover, does the scale correct for earth's gravity by dividing by 9.8 m/s^2? —Preceding unsigned comment added by Legolas52 (talk • contribs) 07:59, 24 December 2009 (UTC)


 * Chemistry is almost always concerned with amount of matter, that is, mass. Gravity is not involved at all, except indirectly as a cause of pressure, which does matter chemically. Conversely, if the chemistry problem talks about "weight", it is almost certainly using that word in its everyday usage where it is synonymous with mass. Only if the problem quotes the "weight" in newtons is there reason to even suspect that it means gravitational pull.
 * Practical scales do not explicitly "divide by 9.8". Even scales that work by measuring force (using springs or strain gauges) are simply calibrated in mass units from the beginning, tacitly assuming the local acceleration of gravity wherever the calibration took place. –Henning Makholm (talk) 08:15, 24 December 2009 (UTC)


 * Scales are a common source of confusion here. Although they measure weight, they are labelled in units of mass (kilograms). Strictly speaking, the scale should be labelled with the (non-SI) unit of force called the kilogram-force or kilopond. Your weight is not 100 kilograms, it is 100 kiloponds. Gandalf61 (talk) 09:36, 24 December 2009 (UTC)


 * Whether a weighing scale actually measures mass or weight depends on its construction. Your typical bathroom scale, which measures the amount of force your body exerts on it, actually measures weight. The kind of weighing scale used in a doctor's office actually measures mass. --173.49.78.112 (talk) 18:25, 24 December 2009 (UTC)


 * g and kg are units of mass, and so it is not really incorrectly labelled. Scales measure your mass by directly claculating your weight and assuming a force field of g perpendicular to the plate of the scales. —Preceding unsigned comment added by 92.17.229.48 (talk) 12:23, 24 December 2009 (UTC)


 * Try this explanation out. You have a block of wood.  That block of wood has a specific mass.  If you put it on a scale here on Earth, it will have a certain weight.  That's because the Earth is pulling it down.  Now you take that wood block to the Moon.  It still has the same mass, since you haven't changed how much wood you have, but it's weight is smaller because the Moon is not as big as the Earth and doesn't have as much gravity.  So, the mass is the same, the weight is different.
 * Now, as for chemistry.  What is important is the mass and not the weight.  Since mass is always the same wherever you are, that's the important part for chemistry.  The amount of stuff that you have, the mass, is everything.  What it weighs is not because if you have the same mass of stuff, the reaction should be the same on the Earth as it is on the Moon.  Dismas |(talk) 12:36, 24 December 2009 (UTC)


 * Lab balances I have seen, even in high school, measured mass, by having a standard mass on a slider and the to-be-measured chemical in the pan, perhaps with a standard mass in the other pan. Measured masses would be the same on the Earth or the Moon, where the gravity is about 1/5 as much. The digital gram scale I have in the kitchen, on the other hand, measures weight, by noting the depression of a spring or strain gauge via an electronic circuit. Things would weigh less on the Moon with it. Some analog kitchen gram scales are actually balances, using an eccentric counterweight which rotates under load. Edison (talk) 00:30, 25 December 2009 (UTC)


 * I believe weight is a relative measurement of mass, so while something's mass remains the same, the measurement of its weight can be different depending on the level of gravitational force in the location of measurement. --Neptunerover (talk) 07:29, 29 December 2009 (UTC)

acylation of benzene rings with amino acids
I was told Friedel Crafts acylation would be too harsh of a reaction to do amino acid acylation cleanly (there would be lots of polymerisation), even with the amino group protonated. Are there any alternatives or modifications? A superacid to ensure the proton stays on the amino group? Do I have to protect the amino group? Use thionyl chloride or oxalyl chloride instead of PCl5? (This is in-situ acyl chloride formation.) Use an activated ester? Any help would be appreciated.

Do protonated amines react with acyl chlorides even in protonated form? (A second-order reaction?) Or does the proton momentarily come off, with small amounts of reactive free amine reacting with the acyl chloride at any one time? John Riemann Soong (talk) 16:49, 24 December 2009 (UTC)
 * "Amine + acyl chloride → amide" is often done using glacial acetic acid as solvent. The amine is mostly protonated under these conditions (aids solubility). And the byproduct is HCl, which pushes that acid/base equilibrium even further towards the protonated state, yet the reaction still runs to completion without a problem. DMacks (talk) 05:30, 28 December 2009 (UTC)

Is salt a spice?
Another site, I was reading, it described salt as a "cheap and abundant spice". Is salt a spice?--Idun90 (talk) 17:43, 24 December 2009 (UTC)
 * Not according to our spice article: "A spice is a dried seed, fruit, root, bark, leaf, or vegetative substance used in nutritionally insignificant quantities as a food additive for the purpose of flavour, colour, or as a preservative that kills harmful bacteria or prevents their growth." Dismas |(talk) 17:57, 24 December 2009 (UTC)
 * Salt is not a spice, but it is a seasoning. People often confuse the two terms, but culinarily speaking they are seperate categories of flavorings.  -- Jayron  32  18:15, 24 December 2009 (UTC)

Would this work to generate (small amounts of) electricity?
A bowl-shaped induction coil with a spherical neodymium magnet, suspended so that the whole thing could swing in the wind...or would the effect of having a free-moving magnet flipping pole-over-pole along the coil basically negate any gains? FWIW, I'm not talking about any gains larger than charging a small capacitor and lighting a single LED (as a proof of concept for a fun project). Thanks in advance. -- Kickstart70 T C 18:04, 24 December 2009 (UTC)
 * You would have to make sure the bowl moved, and not the magnet, or the magnet and not the bowl. If both moved together nothing would happen. But otherwise, yes. But you'll have to deal with random voltages and polarities. Use a Bridge rectifier. You'll have best results if you can move the magnet perpendicular to the direction of winding (i.e. across the coils), and not left/right along the length of each winding. So if are using wind, and it's shaking left right, lay the coils on the side. I'm not sure if there is a winding that will let you collect energy from motion in any direction. Ariel. (talk) 18:20, 24 December 2009 (UTC)
 * Thanks, that helps. -- Kickstart70 T C 18:50, 24 December 2009 (UTC)
 * The faster the relative motion, the stronger the magnet, and the more turns in the coil,then the greater the voltage, other things being equal. An iron core in the coil might be better able to generate a useful output. If the magnet is made to vibrate rapidly by some fluttering action that might help to get some voltage out. I've seen a novelty which had a magnet on a spring next to a coil. The spring got bent to one side to a release point, after which it snapped back and vibrated fast for a fraction of a second next to the coil, generating a painful output voltage. Not sure why the magnet in your idea is going to flip pole over pole, from your description, without some sort of blades to catch the wind and turn the magnet. The rectifier mentioned above is needed because a magnet moving toward and away from a coil, or rotating next to a coil, will generate AC rather than DC. The rectifier would decrease the output voltage by a fraction of a volt, a potential problem if only a tiny voltage is generated. Other generators use a mechanical commutator, but it's hard to see how one would work with a magnet just wobbling around suspended in a bowl shaped coil. If current were coming out of the coil to a load, or to charge the capacitor and light the LED, that would tend to oppose the motion of the magnet. Edison (talk) 00:16, 25 December 2009 (UTC)

Any downsides to eating lots of sugar-free candy?
Are there any bad effects of eating lots of sugar-free candy over the holidays? --70.167.58.6 (talk) 18:34, 24 December 2009 (UTC)
 * Well, if it was the only thing you ate, you would die from lack of nutrients. Abce2 | Free lemonade  only 25 cents!  18:36, 24 December 2009 (UTC)
 * There is some research that shows that eating sugar free foods messes with your bodies sense of fullness. i.e. the body no longer knows how to calculate how many calories you ate based on the taste. It's expecting calories based on the taste, but none showed up. So when you eat other foods you will eat more, since it thinks the tongue "calibration" is off. Eating sugar free foods may therefor cause you to gain weight. This is not a settled issue though, for all I know it could have been refuted, I'm going from something I remember. Also, some kinds of fake sugars can cause diarrhea and other effects - you would have to ask about the specific fake sugar you are eating. Ariel. (talk) 19:15, 24 December 2009 (UTC)
 * Not to mention that the larger the quantity of certain sweeteners (sorbitol, other polyalcohol sugars, sucralose, etc.) the likelier that diarrhea will result. The polyalcohol sugars (mannitol, sorbitol, xylitol) are often used in candy, and in addition to causing osmotic diarrhea when eaten in large quantity can actually raise blood sugar, an issue for diabetics. Not so merry. So some moderation is advisable. - Nunh-huh 19:23, 24 December 2009 (UTC)
 * As mentioned at Sugar substitute &, there have been fears of artificial sweeteners being partially carcogenic, but as the evidence has accumulated most initial concerns have reduced. Some countries have banned some which others have not. There is of course a chance that some risks have not been detected yet particularly for new ones although most are usually tested fairly extensively before release AFAIK. And of note, this applies to a lot of substances in sweets and other things you eat and even if the substance is not new it doesn't mean any increased risk would have been picked up yet and significantly many relatively new substances are not well tested if they are 'natural' Nil Einne (talk) 10:39, 25 December 2009 (UTC)

Gene Therapy
Would it be possible today or sometime in the future for gene therapy to turn off cancer cells (tumor making genes) throughout the entire body? Or can gene therapy only work in one designated part of the body, i.e the eyes? —Preceding unsigned comment added by 71.156.64.184 (talk) 18:46, 24 December 2009 (UTC)
 * It sounds possible, but we can't do it yet. It will probably need different therapies for different cancers since it is different genes that need turning off (or on), though. There was some work published recently sequencing cancer cell DNA which should help with the development of such gene therapies. --Tango (talk) 19:05, 24 December 2009 (UTC)
 * I think we just had this question.  DRosenbach  ( Talk 04:47, 25 December 2009 (UTC)

easily transported survival rations
In terms of pure survival it appears that 40 grams powdered potatoes, 15 grams powdered milk and 17.76 grams milled flax seed mixed with water and consumed six times per day along with a daily multiple vitamin tablet is sufficient to provide a balanced diet that includes fiber. How long can such a diet sustain human life without alternate or additional ingredients? 71.100.6.153 (talk) 19:21, 24 December 2009 (UTC)
 * I'm not completely convinced we know about all the microneutrients, but you should read total parenteral nutrition. Are you sure you are getting enough minerals like magnesium? What about EFAs? Did you check that your proteins were complete? Also, the nutrition numbers for foods is not exact - there is a wide variation in real food. You would be in trouble if you happened to have a batch will less of some mineral or other. Ariel. (talk) 19:28, 24 December 2009 (UTC)
 * Did you check the nutritional content of each of these, noting the total against the recommended daily allowances of all essential nutrients? The info is likely to be on the food packaging. There is more to nutrition than carbs, protein, fat and fiber. Would your diet supply all needed vitamins and minerals? To survive for a week or 2 on such a diet might be less of a challenge than to stave off pellegra, scurvy, beriberi or other deficiency disease over months or years. Would your diet provide much fat? Not if it were nonfat milk. Fat has 9 calories per gram compared to 4 per gram for carbs or protein, and something with some fat content would seem to be a desirable calorie dense part of survival rations, especially if weight is a consideration and any climbing, hiking  or hard work is to be done. A very boring diet might dampen spirits, not the best thing when a good attitude could aid survival, which is an argument for variety. Edison (talk) 19:37, 24 December 2009 (UTC)
 * I don't see any salt in that diet either - that would be a problem sooner than anything else. Salt, water and sugar would probably do for a few weeks (although you wouldn't feel too good). If you've got some decent fat reserves on your body then you could do without the sugar, too. --Tango (talk) 19:55, 24 December 2009 (UTC)
 * I understand that the modern thinking is that the optimum amount of salt required is very low, and salt will be in the ingrediants naturally anyway. The recommended daily amounts are achievable goals in salt intake reduction, and not the optimum. I don't think any nutritionist has regarded sugar as an essential nutrient for several decades at least. 89.240.110.255 (talk) 16:11, 26 December 2009 (UTC)

I should have made clear that minerals are generally included in a daily vitamin supplement tablet and that one reason the Irish came to depend so heavily on the potato is that with milk it provides all of the amino acids. So much so in fact that a computer program picked potato and milk combination over egg white. What I am thinking of here is minimum transport weight to disaster areas of maximum nutritional benefit. 71.100.6.153 (talk) 20:33, 24 December 2009 (UTC)


 * A kilogram of fat would provide 9000 calories, while a kg of the instant mashed potatoes I found in the kitchen would provide only 3928 calories. A kg of the ground flaxseed I found in my kitchen would provide 5714 calories (they have 80 calories per 14g serving, and 45 of the calories are from fat, along with 4 g of fiber. Using data for nonfat dry milk from, it has 3600 calories per kg. One ration portion as you described it above, per the figures I found, would provide 157 calories from potatoes, 54 from milk, and 102 from flax, for 313 calories per each of the 6 meals, or 1878 per day. Why would the food providers want to give people 6 tiny meals a day, with all the attendant lining up and washing up?    I also think the recipients might riot after 4 days of mashed potatoes 3 (or 6) times a day. Some variety would seem highly desirable, rather than just looking at maximum nutrient density. Unappetizing food might be rejected even by the malnourished. I read of stranded travelers who were fed macaroni and cheese (liked well enough by most folks) 3 meals a day for a week who came to loathe the idea of ever eating it again. A factory in town was manufacturing the product and donating it to the shelter where the travelers were staying.  Edison (talk) 00:06, 25 December 2009 (UTC)


 * I have no problem with developing a very long list of powdered ingredient combinations and hopefully such a list already exists. Chocolate as a matter of fact was used by the Inca for this very purpose and there are many powders to work with including rice and soy powder. The key is the right amount of each ingredient in one batch for each combination to be divided into three meals or six meals per day. 71.100.6.153 (talk) 11:40, 25 December 2009 (UTC)


 * OK the calories may suffice if you don't move too much. Proteins have all needed amino acids as you point out. However, I think you won't get enough proteins: powdered potatoes have about 10 per cent, and powdered milk about 15 per cent proteins. That will get you all in all 24g plus 14g = 38g protein per day. This is too low, if you believe the rule of 1g/kg body weight per day for normal people, and 1,5g/kg for athletes. --Ayacop (talk) 16:35, 25 December 2009 (UTC)

Below is the result after adding other food sources...

Notice that in this case the program picked egg white and potatoes but added a taste of canned vegetables and about a cup of flax seed. Since potato is considered first and filled the requirement for carbs there was no need to include soy powder or rice as when potato is not included.

71.100.6.153 (talk) 04:08, 26 December 2009 (UTC)

trying to find out about a plant I saw in Mexico
I'd like to attach a picture of a plant I saw in Baja, Mexico. I think it may be a palm, rather than a cactus. Can I attach a picture? —Preceding unsigned comment added by Jeancahill (talk • contribs) 19:30, 24 December 2009 (UTC)
 * Assuming you have the rights to the picture (ie you took it yourself) you will need to upload it to Commons before you can post it on this page. Brand new users do not have the ability to upload directly to Wikipedia but Commons is just as good, pictures there can be displayed on Wikipedia pages (or any other Wikimedia project).  Sp in ni  ng  Spark  20:50, 24 December 2009 (UTC)
 * The alternative is to upload it to Flickr or Imageshack or Photobucket or something similar, and post a link here. Tevildo (talk) 22:25, 24 December 2009 (UTC)

what's with the weird alkynyl-cyclopropane group in Efavirenz?
What is its purpose? Does it get metabolised to something else in the body? John Riemann Soong (talk) 22:02, 24 December 2009 (UTC)


 * I don't know, but I don't think it is metabolised. If you look at the structure-activity relationships of other drugs, such as opioids, then you will also see these alkynyl/cycloalkyl groups in the antagonists (compare nalorphine to morphine; also see naltrexone, naloxone, naltrindole, nalmefene). Here is a ref speculating why those functional groups produce antagonistic effects, and it thinks that it may prevent G-protein coupling to the receptor, so it would be wrong to extrapolate that to enzyme inhibition (as is the case with your ligand). --Mark PEA (talk) 22:18, 24 December 2009 (UTC)