Wikipedia:Reference desk/Archives/Science/2009 August 11

= August 11 =

Does the mass of the earth change with population growth?
Does a batch of newborns add mass to the earth? My feeling would be no, due to the law of conservation of matter. —Preceding unsigned comment added by 12.168.244.134 (talk) 00:07, 11 August 2009 (UTC)


 * No, everything the new organisms are made of was already on the Earth, it is just existing matter being rearranged, nothing is created from scratch. There is some change of mass due to the atmosphere escaping, meteors hitting the Earth, etc. and also some due to energy entering and leaving the Earth as radiation (E=mc2), but that's pretty negligible. --Tango (talk) 00:10, 11 August 2009 (UTC)


 * You are correct. The mass of a newborn had been counted as part of the mass of the baby’s mother before the baby was born, so childbirth results in no increase of the total mass on the earth.   Red Act (talk) 00:25, 11 August 2009 (UTC)
 * Even if all newborns actually came from outer space, the mass addition wouldn't matter as far as the Earth is concerned. The Earth has a mass of about 6x1024 kilograms, and if there were seven billion people alive (there aren't) and they all weighed 100 kilograms (220 lbs), that would only be 7x1011 kilos, which is a paltry contribution. ~ Amory  (user • talk • contribs) 00:45, 11 August 2009 (UTC)
 * A fact which I think is even more counterintuitive which I only really "got" recently is that burning a tree does not decrease any mass either.. The mass of the ashes that are left and the gasses released by the burning actually equals the mass of the tree before it was burned.. I mean I always knew all the "matter" was still there just in a different configuration, but I never really realised that the gas actually had the same mass as the tree. Vespine (talk) 01:06, 11 August 2009 (UTC)
 * Strictly speaking, it is marginally less because some of that mass has been converted into energy (E=mc2 again), but since the speed of light is so enormous it is a negligible amount of mass that is lost (and it is only actually lost when that energy gets radiated into outer space). --Tango (talk) 01:18, 11 August 2009 (UTC)
 * I think E=mc2 only applies to nuclear reactions. Burning a tree is a chemical reaction. (As is growing it in the first place.) Mitch Ames (talk) 11:25, 11 August 2009 (UTC)
 * If you read the article it's quite clear that applies whenever there's a change in mass although as Tango mentioned and I think it's been pointed out before with actual figures the change in mass is negible. See also Reference desk/Archives/Science/2009 February 24 or search more in the archives Nil Einne (talk) 11:37, 11 August 2009 (UTC)
 * It applies to everything. It just says that mass and energy are equivalent. You think of it as energy having mass, if energy is released its mass goes with it. --Tango (talk) 16:30, 11 August 2009 (UTC)
 * Would the mass converted into energy while dismantling the tree roughly equal the energy that was turned into mass by capturing the sun when the plant was growing in the 1st place? Would it be completely incorrect to say that the fire is just years of accumulated sunshine released in a (relative) instant? Maybe not strictly correct but rather poetic way to look at it I think. Vespine (talk) 04:54, 11 August 2009 (UTC)
 * Once, in answering a child's question "Why is the fire hot?", Buckminster Fuller said that the fire was the sunlight the tree had absorbed "unwinding from the log". Deor (talk) 06:15, 11 August 2009 (UTC)
 * Yes, that is a good way to describe it. --Tango (talk) 16:23, 11 August 2009 (UTC)

Howard Hughes Medical Institute
Is the Howard Hughea Medical Institute(tax-exempt) classified as a 501c(3) organization under the IRS tax code? —Preceding unsigned comment added by Bmmillar (talk • contribs) 01:04, 11 August 2009 (UTC)
 * From the Wikipedia article:

Hughes was the sole trustee of HHMI and transferred all his stock of Hughes Aircraft to the institute, in effect turning the large defense contractor into a tax-exempt charity. For many years the Institute grappled with maintaining its non-profit status; the Internal Revenue Service challenged its "charitable" status which made it tax exempt
 * That would seem to imply that yes, it is, despite my paltry knowledge of the tax code. ~ Amory  (user • talk • contribs) 01:11, 11 August 2009 (UTC)


 * No, it counts as a Medical Research Organization, which is IRS code section 170(b). Red Act (talk) 01:20, 11 August 2009 (UTC)

Northern Canada, Anchorage and southern Greenland
Do Northern Canada and Anchorage, Alaska get up to 70s F in summer highs ? Well it is up in the 60 degrees away from equators. Is is possible southern Greenland can get up to 50s F in summer highs?--69.229.108.245 (talk) 02:07, 11 August 2009 (UTC)


 * Anchorage can get to the 80s: 75.41.110.200 (talk) 03:00, 11 August 2009 (UTC)


 * Wow, that's amazing Anchorage have hit 80 F. Thanks 75.41.110.200--69.229.108.245 (talk) 03:02, 11 August 2009 (UTC)


 * As you can see at our article on Anchorage, Alaska, the average summer high is above 60 degrees Fahrenheit, and the record high is 93F, so it seems likely that the temperature often reaches 70F or higher. As for Greenland, Narsarsuaq routinely gets above 60F, see here.- Running On Brains (talk) 03:41, 11 August 2009 (UTC)

Remember that while the summer daylight in these places is less intense than nearer the equator (because the sun is lower in the sky), there are also a lot more hours of sunlight each day in the summer (up to 24 hours a day when you get beyond the Arctic Circle), which partially offsets the weakness of it. "Summer" in climatic terms tends to be short in the arctic, limiting the kinds of plants than can grow there (for instance), but it certainly exists. --Anonymous, 04:16 UTC, August 11, 2009.


 * Even today, in August, Accuweather is forecasting 69°F for Anchorage. A bit chillier in |GL|GL003|NUUK&metric=0 Nuuk, though! Tonywalton Talk 11:45, 11 August 2009 (UTC)


 * Much of the populated parts of Alaska are known for warm, muggy summers. Remember that tundra is basically seasonally frozen swampland; so much of the southern parts of Alaska become quite humid and muggy in the (albeit short) summer months.  Many people are surprised, for example, of the massive mosquito problem that Alaska has; or that cities like Juneau and Sitka occasionally get days over 100 deg F.  As noted, even Anchorage gets a day or two in the 80s or 90s.  Continental Canada has a likely much different climate, as the tempering effects of the ocean don't reach places like Yellowknife or Dawson.  -- Jayron  32  04:54, 12 August 2009 (UTC)
 * According to http://www.weather.com/outlook/travel/businesstraveler/wxclimatology/monthly/graph/USAK0116?from=36hr_bottomnav_business Record high for Juneau is 90F. Sitka is 87F.  Warmer then you might expect, but certainly not over 100F.  Don't forget the impact of a maritime climate for a lot of the cities on the south coast of Alaska.  Also, south Alaska is NOT tundra.  Googlemeister (talk) 13:30, 12 August 2009 (UTC)

Conversions
I saw this information on YouTube. Before the explosion in the engine room aboard the SS Norway, 60,000 liters of water heated up to 500 degrees Celcius in a matter of seconds. How many gallons of water is 60,000 liters? How many degrees Fahrenheit is 500 degrees Celcius?69.203.157.50 (talk) 03:05, 11 August 2009 (UTC)


 * Google is great for these kind of questions, here's the first http://www.google.com.au/search?hl=en&q=60000+l+in+gallons+&meta=&aq=f&oq= i'll let you work out how to do the temperature your self :). Vespine (talk) 03:17, 11 August 2009 (UTC)


 * Well, the question is what kind of gallons you mean. Note that even though Vespine's link is to the Australian version of Google, it gave a result in US gallons.  (At least, it did for me, trying it from Canada.)  If you want Imperial gallons, you have to ask for them explicitly.  --Anonymous, 04:21 UTC, August 11, 2009.


 * 500C = 932F. (Double the C, decrease by 10%, add 32. You can do it in your head, right?) What supposedly caused this temperature increase? What was the starting temp? Where did the energy come from? How many Joules does it represent? Sounds dubious. Was it this incident?  A boiler rupturing and flashing to steam should not cause a temperature rise, and energy does not come to a boiler from nowhere. It normally took over 3 hours to go from cold to full pressure.  Edison (talk) 04:39, 11 August 2009 (UTC)
 * Just for the numbers, i have 125Gj to get that amount of water to 500 degrees, from 0. 30 tons of TNT. I'm bad at numbers tho so that could be way off.. However, i think they've just misreported it, i don't think the water would heated up to that high in a few seconds, i think the explosion and consequent vaporisation of the water took a few seconds. The tempereature was probably right up there just before the explosion. I'd be looking for a failure in the cooling system as the cause. But no doubt on a ship like this, multiple systems must have failed for this kind of accident to occur. warning sytstems, shut down systems etc... Vespine (talk) 05:09, 11 August 2009 (UTC)


 * The very informative NTSB accident report says "About 0637, a boiler ruptured in the aft boiler room ... The boiler contained about 20 tons of water operating at a temperature of about 528º F under a pressure of about 60 bar (870 pounds per square inch [psi])). In the normal atmospheric pressure of the aft boiler room (14.7 psi), the pressurized hot water rapidly expanded in volume about 1,260 times into steam. The expanding steam, mixed with smoke, soot, and debris, swept through the engineering spaces, fatally injuring four engineering crewmembers who were on watch or on duty in or near the boiler room, as well as four other crewmembers who were in the crew living spaces on the starboard side of the Caribbean deck, next to the boiler room". Chronology of the incident says:
 * "0637 - Rupture occurs in boiler No. 23 in aft boiler room. Rupture activates sprinkler system in areas around boiler room as well as smoke alarms locally in affected areas and remotely in wheelhouse. Pier-side Miami-Dade police officer radios report of accident to his command.
 * 0638 - Boiler automation system shuts down operating main boilers, which stops steam turbine generators and causes loss of main electrical power. Ship’s battery-operated emergency systems activate and function as designed."
 * Further on, the report says "Tests of the four safety valves on boiler No. 23 revealed no significant defects, indicating that they probably functioned properly at the time of the accident". The report concludes that "the probable cause of the boiler rupture on the Norway was the deficient boiler operation, maintenance, and inspection practices of Norwegian Cruise Line, which allowed material deterioration and fatigue cracking to weaken the boiler". So sounds like the boiler failed during normal operations and the steam came from the superheated water that was already in the boiler, not from external water heated by an explosion. Gandalf61 (talk) 10:08, 11 August 2009 (UTC)
 * Our article says "Her engines consisted of eight high-pressure, super-heating boilers delivering 65 kg per cc and 500 degrees Celsius, all weighing 8,000 tons". This isn't referring to the accident but if I understand this correctly that is the normal operating temperature. There's a possible source but it's offline. It also says "This move cut down fuel consumption to 250 tonnes per 24 hours. The remaining four boilers and engine room were made fully automated, and operated from either a central control station below decks, or from the bridge", it's not clear if this cut down the operating temperature as well. Nil Einne (talk) 11:31, 11 August 2009 (UTC)
 * By the late 19th century, safety practices in operating steam boilers included periodic internal inspections, to detect the beginning of cracks or failure of internal bracing, and periodic testing of indicator valves and safety pressure relief valves. Boilers and other pressure vessels had to undergo hydrostatic testing, in which it was pressurized way above operating pressure by being filled with water. That way if it burst during the test, there was little or no stored energy to cause the damage and casualties that happened here. If I were investigating, I would wnt to check those tests and inspections. If a boiler had passed a pressure test, and had functioning relief valves, why would it pop like a kernal of popcorn? What was the root cause per the investigation? Malfeasance or incompetence? Murphy's Law? Bad Luck? Shit Happens? If it was a design problem, were there other similar boilers which had to be modified or taken out of service? Also, reports above list both 500 C and 528F, which are far apart as I noted. Edison (talk) 15:49, 11 August 2009 (UTC)
 * The safety board investigation cited above concluded "The National Transportation Safety Board determines that the probable cause of the boiler rupture on the Norway was the deficient boiler operation, maintenance, and inspection practices of Norwegian Cruise Line, which allowed material deterioration and fatigue cracking to weaken the boiler. Inadequate boiler surveys by Bureau Veritas contributed to the cause of the accident." Pressures and temps were normal when it failed. Cracks from fatigue and corrosion extended to .55 inches in a wall .935 inches thick.  Internal inspection or hydraulic testing had not been done recently on the header which failed. Edison (talk) 16:35, 11 August 2009 (UTC)

name of soviet car
File:Beriozka-gastronom.jpg

What is the name of the type of car in this picture? --67.173.155.191 (talk) 04:07, 11 August 2009 (UTC)


 * Dunno. It sort of resembles a ZIL-117 but some differences are visible.  Maybe another model in the same series. 70.90.174.101 (talk) 04:20, 11 August 2009 (UTC)

That would be a Gaz-14 Chaika. Here's a Youtube video that nicely shows the distinctive rear.--Rallette (talk) 10:50, 11 August 2009 (UTC)
 * Oh yeah, the Cadillac clone, the kind that all the big bosses drive. 98.234.126.251 (talk) 03:03, 16 August 2009 (UTC)

Cheap DNA restriction enzymes
To help in finding cheap sites for restriction endonuclease analysis (REA), I'm trying to compose a list of cheap endonucleases for use with my molecular cloning program. I know that, for example, EcoRI and BamHI are examples of relatively cheap enzymes, and therefore preferable candidates for REA. Can someone help me to augment this list? --94.212.39.7 (talk) 07:26, 11 August 2009 (UTC)
 * New England Biolabs's website has a pricelist  Rockpock  e  t  07:45, 11 August 2009 (UTC)
 * It would be a lot of work to deduce the enzymes from that price list. I was hoping someone already had a list compiled or otherwise was familiar enough with the prices to be able to reel them from the top of their head. --94.212.39.7 (talk) 10:47, 11 August 2009 (UTC)
 * Page down to page 7 of the price list. On the left column, starting with product number R0101 are the restriction enzymes. They continue until page 10, with product number R3642 - basically all product numbers starting with "R" are restriction enzyme, restriction methylases and related. A quick glance shows that NEB's pricing for restriction enzymes is relatively simple, with "small" sizes in the $50-70 range, and "large" sizes in the $225-275 range. Different enzymes have different amounts of enzyme in each size, though. Uncommon or hard to purify enzymes may only have 500 units in the small size, whereas commonly used enzymes which NEB expresses recombinantly have 10,000 units in the small size. The cheapest ones are the ones you've probably heard of: EcoRI, HindIII, BamHI, and PstI all come in 10,000 units in the small size. - If you're at all interested in restriction enzymes, it pays to spend time browsing NEB's website. They have a lot more information there than the standard "this is what we sell and this is how much it costs" info. - 128.104.112.100 (talk) 16:15, 11 August 2009 (UTC)

Sorry, I didn't fully understand what you wanted. NEB and other companies generally price their enzymes at roughly the same price, what they vary is how many enzyme units you get for that standard price. Therefore the amount you plan use use is a factor in value for money. 128.104.112.100 is correct, though, in that most of the restriction enzymes are grouped together on that list, so it should be easy to scan down and find the best value for your application. In general, I seem to remember BamHI, EcoRI and XhoI are very inexpensive. Rockpock e  t  16:57, 11 August 2009 (UTC)

Battle excavations
Is it posssible to detect and excavate for example the shields, bones and other artifacts of Greek warriors at the site of Thermopylae? Also, is there a good source on battlefield excavations? 217.25.31.169 (talk) 09:13, 11 August 2009 (UTC)
 * Use "find" for "archaelogy" in Battle of Thermopylae for more details, arrowheads etc have been found there. Don't know about shields - I would suspect any are long gone.
 * Note that you personally cannot do this (ie start digging)- you'll get arrested by angry greeks ! - amateur archaelogy is illegal in all countries.83.100.250.79 (talk) 13:03, 11 August 2009 (UTC)
 * (it might be an idea to move your question to the humanities desk)83.100.250.79 (talk) 13:38, 11 August 2009 (UTC)


 * Amateur archaeology is not "illegal in all countries". Tempshill (talk) 16:10, 11 August 2009 (UTC)
 * Where did that idea even come from? There are probably regulations on where digging is allowed, but anyone can do archaeology, amateur- or professional.  In most places, even digging is okay.  In places where archaeological artifacts are known to exist, a lot of regulations probably exist, but "illegal all countries"?  Really?  .  Nimur (talk) 19:20, 11 August 2009 (UTC)
 * If I remember The Mildenhall Treasure correctly, in the UK, any treasure found that is gold or silver must be reported to the authorities, and the Crown has the authority to confiscate it. Failure to report it is a crime.  But conducting amateur archaeology to look for such treasure (or any other artifact) is not illegal in the UK, as far as I know.  Tempshill (talk) 22:47, 11 August 2009 (UTC)
 * It is more complicated than that. There is a big difference between property intentionally hidden in the ground and property simply lost. That means a random coin found when ploughing a field falls under different laws than a stash of coins found in a grave. I can't remember the details of those laws, I would have to look them up. I think gold (and maybe silver) has different laws to other things found as well. It is all extremely complicated in the UK (other countries probably have simpler laws, I would be amazed if they have more complicated ones!). --Tango (talk) 04:15, 12 August 2009 (UTC)
 * We have a fantastic article on the subject: Lost, mislaid, and abandoned property. There may be some statutes that alter the common law, but I think the basic principles are the same as they always were. --Tango (talk) 04:23, 12 August 2009 (UTC)
 * As long as you have the permission of the landowner, I can't see there being any problems. If you find human remains there are usually procedures to go through and there may be complicated rules about who owns whatever you find, but you amateur archaeology isn't illegal in any country as far as I know. There are archaeology societies made up of amateurs set up all over the place. --Tango (talk) 21:35, 11 August 2009 (UTC)
 * My wife's grandfather was an amateur archaeologist, and he had literally THOUSANDS of carefully cateloged Native American arrowheads. There are parts of the midwest where all you'd need to find one is a garden rake; they are quite literally littered all over the place.  As far as I know, as long as there are no regulations, such as removing artifacts from a national park, and you have the property owners permission, there's little problem with this sort of amateur archaeology.  Now, there may be pragmatic probelms, as noted above, with tripping over say a large gravesite or large cache of valuables, but for little things like arrowheads and potsherds and the like, I'm pretty sure its unregulated.  -- Jayron  32  04:49, 12 August 2009 (UTC)
 * Right, I just would not go out to a famous historical battlefield and look without permission from whoever is responsible for managing it though. The rules might vary in different legal jurisdictions.  Googlemeister (talk) 13:25, 12 August 2009 (UTC)


 * IMHO, you might not find much in the way of artifacts by digging in an ancient battlefield -- ancient warriors were usually VERY punctual about picking up any dropped battle-gear (metals were SO expensive back then, so even hopelessly broken weapons and armor were usually recovered to be melted and remade), so there are prob'ly few weapons left on the field. And what few artifacts the warriors HAD lost, professional archeologists prob'ly found.  (And for the record, I'm NOT being paid by the angry Greek landowners to discourage y'all from digging.) 98.234.126.251 (talk) 03:14, 16 August 2009 (UTC)

European Maple Syrup
Are any of the species of maple tree native to Europe usable for making syrup? --Carnildo&#39;s non-admin account (talk) 09:46, 11 August 2009 (UTC)


 * I think the issue is not the species of tree but the climate. I think Maple syrup is incredibly bitter without the right weather (long cold plus correct timing). I suspect you would have to be somewhere well East in Europe to have a chance --BozMo talk 13:14, 11 August 2009 (UTC)


 * Sugar maples originated in North America. In Europe I have seen some in gardens, parks and even alleys, but I am not aware of any agricultural usage of the tree.  Googling indicates that the European climate is unsuitable to produce any significant yield of syrup, as this requires freezing nights and warmish days for prolonged periods.  Molasses from other sources (sugar beet) were / are used in Europe.    --Cookatoo.ergo.ZooM (talk) 14:52, 11 August 2009 (UTC)


 * So, it appears that extreme cold is bad for sugar maples. How about warm weather?  I'm currently in the Ozarks (Missouri) and there is a lot of sugar maples.  A road nearby is called "Sugar Tree Hill" because the sugar maples there are supposedly extra sweet.  It rarely freezes at night here - just a few weeks in February.  So, I wonder if there are warmer weather sugar maples and colder weather sugar maples (or if the sugar maples here aren't sugar maples at all). -- k a i n a w &trade; 15:07, 11 August 2009 (UTC)
 * Sugar maples can grow in a lot of different places. The suitability of the sap for making syrup is based both on the tree species, and on the climate.  I see no reason why maple species native to Europe could not produce good syrup if grown in the right conditions, or that a sugar maple grown in improper conditions would not give good syrup.  In fact, you can make syrup from birch trees.  Googlemeister (talk) 15:15, 11 August 2009 (UTC)
 * This site describes the European field maple, and indicates that the sap contains sugar, and can be drunk or turned into syrup, but that the sugar content is far below that of the North American sugar maple. As far as climate/weather goes, take a look at this site, but basically, it needs to get warm enough for the sap to flow well during the day, and cold enough (below freezing) to allow the tree to recover at night.  Sugaring season ends when the leaves start budding because of chemical changes in the sap related to bud/leaf production which give the syrup an off taste. Some jerk on the Internet (talk) 18:48, 11 August 2009 (UTC)

There are no native sugar maple trees in Europe. We have plenty of native birch trees in Eastern Europe so we produce birch syrup, it's expensive so it is rare. 87.207.137.5 (talk) 13:51, 17 August 2009 (UTC)

Relativistic Doppler effect-another problem
Relativistic Doppler effect has relativistic abberatition formula
 * $$ \cos \theta_o = \frac{\cos \theta_s-\frac{v}{c}}{1-\frac{v}{c}\cos \theta_s} $$

I just calculated putting $$ \cos \theta_s = 1/x (|x|>1) $$. Then
 * $$ \cos \theta_o = \frac{c-v}{cx-v} $$.

Because c>|v|, the numerator is always positive, so the denominator decides the sign of $$ \cos \theta_o $$. And because |x|>1, and c>|v|, |cx|>|v|, and the sign of x decides the sign of $$ \cos \theta_o $$. If x is positive, $$ \cos \theta_s $$ is positive, and if x is negative, $$ \cos \theta_s $$ is negative, and vice versa. Taking |x| as large as possible, $$ \cos \theta_s $$ comes near 0, that is, $$ \theta_s $$ comes near $$ \pm 90^\circ $$, and still the sign of $$ \cos \theta_o $$ is the same as $$ \cos \theta_s $$. Looking at Relativistic Doppler effect, the direction at $$ \pm 90^\circ $$ comes forward. Hmmm... Like sushi (talk) 11:04, 11 August 2009 (UTC) Sorry, I found a mistake in calculation. Like sushi (talk) 11:39, 11 August 2009 (UTC)

Why is AIDS so Common in Africa?
I was taught that AIDS was spread through gay sex. But the infection rate--last time I checked--was &#8531; in some countries in Africa. It's hard to understand how a disease that isn't airborne could infect that many people.--IndexOutOfBounds (talk) 15:01, 11 August 2009 (UTC)


 * AIDS may be spread by any unprotected sex (gay, straight, bi, tri...). It is rampant in underdeveloped countries due to a lack of education and prevention. -- k a i n a w &trade; 15:03, 11 August 2009 (UTC)


 * A guy can give a girl AIDS, but not the other way around, right? At least, it'd have to involve untraditional sex for that to happen, right?--IndexOutOfBounds (talk) 15:04, 11 August 2009 (UTC)


 * Wow, have you been poorly served by your public health service. Girls can give guys HIV with regular, traditional sex. Both penetrative and receptive partners can transmit and receive HIV. Here's an overview of HIV transmission. Statistically, it is less likely to occur, but it can, and does occur. Keep in mind that there are non-sexual ways to transmit it as well; mother-to-child is a very common mode of transmission in Africa in particular. --98.217.14.211 (talk) 15:08, 11 August 2009 (UTC)


 * I graduated from high school in 2000 and last learned about HIV/AIDS in 1998. So, no, I don't remember everything they told us about AIDS back then, and even if they went into details such as these.--IndexOutOfBounds (talk) 15:15, 11 August 2009 (UTC)
 * It's kind of a big deal, you know, how to avoid getting various diseases. I'm just saying. And it's pretty easy to look up this information. You might as well be posting on here about whether the Earth is flat or not, and then complaining that you went to school a long time ago and can't be bothering to remember such a thing. To think that AIDs is "only spread by gay sex" is an extremely, extremely ignorant thing to believe still. If that's really what you were taught in 2000 (which is not what I was taught in the 1990s), then you were, as I said, seriously poorly served by whomever taught you about public health, STDs, etc. --98.217.14.211 (talk) 16:13, 11 August 2009 (UTC)
 * Just so you know, this is a reference desk where you can ask questions. I'm not a doctor. I have few college degrees, but none of them are in biology or medicine. So, to call me ignorant is (ironically) ignorant.--IndexOutOfBounds (talk) 23:45, 11 August 2009 (UTC)
 * It's not, though. This is considered to be high-school knowledge in the USA. It's basic public health. It's about one step above knowing about how condoms work. Anyway, your question has been answered, many times over. My quibble isn't with you, just that you've been so poorly, poorly served by your secondary school education. (If you had graduated from high school in the 1970s, that would be one thing. But 2000? Come on.) The idea that you've somehow managed to get college education and be so ignorant about this basic, world-relevant, individually-relevant health fact is even more disconcerting, in a way. My degrees are not in biology, either, but one learns just a certain amount by simply paying attention to the world around you. The fact that AIDS is not spread only by homosexuals has been a major public health message since the 1980s. --98.217.14.211 (talk) 02:40, 12 August 2009 (UTC)
 * At least IndexOutOfBounds can admit what he doesn't know. What are you trying to make up for by pretending that you know everything?Ksngdfhg (talk) 03:11, 12 August 2009 (UTC)
 * I think there is a troll with a sockpuppet in the house.  But IndexOutOfBounds is entertaining and I would like to hear where he claims to be from.  And if "IndexOutOfBounds" is busy I wouldn't mind hearing where Ksngdfhg is from.--OMCV (talk) 03:37, 12 August 2009 (UTC)
 * I really feel sorry for your kids, guys. You people can't even answer a simple question without calling someone ignorant? IndexOutOfBounds may have been ignorant about AIDS, but at least he's not stupid. I'm afraid there are no articles on Wikipedia that cover how to answer a simple question. I guess there's nothing that can be said to help you.Ksngdfhg (talk) 03:44, 12 August 2009 (UTC)
 * Well, look at it like this. User:Ksngdfhg's "User contributions" consists entirely of two posts to this thread - and nothing else.  How likely is it that a brand new user arrives at Wikipedia, types in a random string on the home-keys of his/her keyboard as a user ID (possibly the least memorable one imaginable) and heads straight over to the Science ref-desk to stridently support IndexOutOfBounds and does NOTHING else on Wikipedia.  Are you surprised that people accuse this account of being a sock-puppet?  I don't know for sure because I don't have 'check-user' priviliges - but I'd bet good money on it - and so I remind IndexOutOfBounds/Ksngdfhg that sock puppeteering for these kinds of reasons is a serious offense around here...it could easily get you blocked from the site if it becomes a habit. SteveBaker (talk) 12:01, 12 August 2009 (UTC)


 * Are you currently in Africa? I thought we spent enough time and money in America and Europe to stamp out such ignorance. -- <font color='#ff0000'>k <font color='#cc0033'>a <font color='#990066'>i <font color='#660099'>n <font color='#3300cc'>a <font color='#0000ff'>w &trade; 15:10, 11 August 2009 (UTC)
 * Wow. You're a really big troll. I don't think the reference desk is for you. After having to read your comments, I don't think it's for me, either.--IndexOutOfBounds (talk) 15:15, 11 August 2009 (UTC)


 * Also note there is more information in the transmission section of the article on HIV. --130.216.1.16 (talk) 15:10, 11 August 2009 (UTC)


 * You have kind of answered your own initial education. Poor education and ignorance (sometimes willfull) of the facts are a major factor in transmission. See Jacob Zuma and his infamous "shower cure". Fribbler (talk) 15:12, 11 August 2009 (UTC)[
 * As well as Fribbler's comment, HIV conspiracy theories and AIDS denialism have also taken hold in parts of Africa. When political leaders such as Thabo Mbeki and Manto Tshabalala-Msimang are spreading misinformation about how HIV is spread, it's difficult to get the message about safer sex across. AlmostReadytoFly (talk) 15:21, 11 August 2009 (UTC)
 * According to the AIDS article, the primary mode of HIV infection worldwide is through sexual contact between a man and a woman. One possibility being researched as to why heterosexual transmission is more common in Africa than elsewhere is that schistosomiasis, which affects up to 50 per cent of women in parts of Africa, damages the lining of the vagina.  Red Act (talk) 15:35, 11 August 2009 (UTC)
 * I hope IndexOutOfBounds is not seriously offended by comments here. I can remember when doctors genuinely thought that AIDS was mainly transmitted through gay sex, but that was in the 1980s, and much has been discovered since then, and I would have thought that any educator would have updated their knowledge by 1998.    D b f i r s   18:20, 11 August 2009 (UTC)
 * Misinformation is a big part of it. One persistant myth amongst African men is that having sex with a virgin will cure you of AIDS.  I leave it to your imagination as to (a) how such a crazy notion might spread faster than the "don't have sex" message - and (b) the devastating consequences of such dangerous claims. SteveBaker (talk) 18:33, 11 August 2009 (UTC)
 * The Catholic prohibition of condoms is also a significant factor. --Tango (talk) 21:30, 11 August 2009 (UTC)
 * And also the George Bush government funding AIDS awareness campaigns throughout Africa under the specific condition that abstainance be taught rather than condom use. That's such an incredibly irresponsible thing to mandate, it makes me want to scream! SteveBaker (talk) 23:33, 11 August 2009 (UTC)
 * Is it in our best interest for our government to continue spending our tax money on AIDS awareness campaigns in Africa at all? Just asking. 98.234.126.251 (talk) 03:22, 16 August 2009 (UTC)
 * I am not aware of any sexually transmitted disease that is only spread by gay people, only spread by males, only spread by females, or in general only spread by any particular kind of person. Any person can transmit a sexually transmitted disease to any other person, and it may not even involve sex (mishandled medical equipment can also be a vector). Pathogens don't pay attention to what kind of person you are. What is correct is that there was a point at time in which AIDS was statistically more prevalent in the gay community than in the general population in the United States. I don't know whether this is still the case. Dcoetzee 23:26, 11 August 2009 (UTC)


 * Life is a sexually transmitted disease (normally) only spread by hetero-sex. :-) Mitch Ames (talk) 11:26, 12 August 2009 (UTC)


 * The most harrowing thing about the HIV->AIDS epidemic is how human ideologies fan the flames. Be it nationalistic: "This country can't have aids, for it is too great!", religious: "Abstinence is gods way. If you want to have sex, then don't...", or political: "AIDS would be bad for business, any chance of massaging the figures?". Nationalistic denials, abstinence programmes that kill millions in the name of "decency" and political manipulation of pandedemics exacerbate the AIDS problem more than prostitution, drugs, or, as some people believe, "teh geys". Education stops HIV. Proven fact. It's the best weapon we have, and we should use it! Fribbler (talk) 23:55, 11 August 2009 (UTC)

African womens bodies have more sexy curves, but plainer (androgenic) features compared to most Caucasians. The plain features reduce the male protective instinct, so risky behavior by the male partner (promiscuity, unprotected sex) is more likely, but the superior curves make them more attractive just for sex-a lethal combination! Hybridization (Beyonce,Kerri Hilson) could be the solution- a hyper-sexy African body, with paedomorphic European features to blunt male predatory instincts. An alternative would be the breeding of women with prematurely aged andromorphic bodies AND faces using Middle Eastern and South Asian cultural/religious practices, but whilst this might reduce AIDS, the dysgenic effects, along with resulting homicidal/suicidal psychiatric disorders in the males deprived of female beauty, would be too high a price to payTrevor Loughlin (talk) 04:18, 14 August 2009 (UTC)
 * Red Act (talk) 04:31, 14 August 2009 (UTC)
 * It's probably a personal communication from The Future. APL (talk) 12:56, 14 August 2009 (UTC)

Trevor...I have so many issues with your post. 1. Stereotypes are not usually accepted in a scientific article. For every "sexily curved" African woman, there is a "sexily curved" Caucasian, and vise-versa. And, I would like for you to take a video camera and tell any African woman that her features are "plainer" (which, by the way, should be phrased "but more plain") and tape it, then p.m. me the link. Please. 2. I can't believe that you suggested "hybridization" as a cure for AIDS. Exactly how is that supposed to cure AIDS, even if your ridiculous "sex appeal" theory was remotely true? 3. You should be placed in eternal isolation for suggesting "breeding" women, you sexist. 4. There would be no "homicidal suicidal psychiatric disorders in the males deprived of female beauty...." It is ludicrous to think that such ideas would be instantaneous. The gradual shift of physical appearance would be slow enough for the male psyche to suitably adjust. If you will, what was the stereotypical ideal woman in the 1930s? 1950s? 1980s? 2000-Present? I think you'll find that they have changed considerably, without damage to the males. 5. I timeless cliche that you should accept as truth "Beauty is in the eye of the beholder." While one man may find "sexy curves" (which disgusts me to say, due to your racist comment) appealing, while other men may find thin attractive, or muscular, or obese.

So, in summary, you are racist, sexist, incredibly and overly stereotypical, and really quite socially ignorant. :) —Preceding unsigned comment added by Hubydane (talk • contribs) 19:45, 14 August 2009 (UTC)

Electric field strength
Hi, this is a homework problem, but I'm not asking for the solution, I'd just like someone to point out where I've gone wrong please. The problem is:

"Given two point charges of arbitrary same-signed charge q1 and q2, at locations x1 and x2, find the point x between them at which the electric field strength is equal to zero."

What I did was make x1 equal to zero, then made this equality:

$$\frac{q_1}{x^2} = \frac{q_2}{(x_2 - x)^2}$$

Then I rearranged that to get:

$$(q_2 - q_1)x^2 + (2q_1 x_2)x - q_1 {x_2}^2$$

Which is just a quadratic, so then you solve that. The trouble is, the way the problem is given, values for the charges and distances are given (these change every time, it's an online thing), and the answer you check it against is the numerical one for that particular set of values, and mine keeps coming up incorrect. For example, if I have

$$q_1 = 6 \mu \mbox{C}$$

$$q_2 = 4 \mu \mbox{C}$$

$$x_1 = 25 \mbox{cm}$$

$$x_2 = 58 \mbox{cm}$$

Then I get the values of the coefficients in the quadratic as

$$2 \times 10^{-6}$$

$$3.96 \times 10^{-6}$$

$$-6.534 \times 10^{-7}$$

And when I solve that, I get 0.153 m, which I add to 0.25 to get a final answer of 40.3 cm. The given solution for this set of values, however, is x=43.2 cm. I've checked and double-checked my working; could someone help me? --130.216.1.16 (talk) 15:08, 11 August 2009 (UTC)

The x2 you use in your equation is the distance between the charges, not the position x2 from the assignment. —Preceding unsigned comment added by 81.11.170.162 (talk) 15:57, 11 August 2009 (UTC)
 * No, although the symbol $$x_2$$ is used to mean two different values, the distinction is maintained mentally such that that isn’t a problem. The real problem is that there’s a sign error – the expression above should be


 * $$(q_2 + q_1)x^2 + (2q_1 x_2)x - q_1 {x_2}^2$$


 * Red Act (talk) 16:17, 11 August 2009 (UTC)


 * I don't think so. Dauto (talk) 21:44, 11 August 2009 (UTC)
 * The problem is that $$q_2-q_1=-2\,$$. Dauto (talk) 00:34, 12 August 2009 (UTC)


 * Why not take the square root?
 * $$\frac{q_1}{x^2} = \frac{q_2}{(x_2 - x)^2}$$
 * $$\frac{q_1^{1/2}}{x} = \frac{q_2^{1/2}}{(x_2 - x)}$$
 * $$q_1^{1/2}(x_2 - x) = q_2^{1/2}x$$
 * $$q_1^{1/2}x_2 = (q_1^{1/2}+q_2^{1/2})x$$
 * $$x=\frac{q_1^{1/2}x_2}{(q_1^{1/2}+q_2^{1/2})}$$
 * Which is not only simpler than the quadratic but also avoids the secon (spurious) solution to the quadratic. Dauto (talk) 00:34, 12 August 2009 (UTC)
 * Whoops, you’re right! The sign error I showed was my error.  The actual problem was the sign on the $$2 \times 10^{-6}$$, as you pointed out.  Red Act (talk) 04:46, 12 August 2009 (UTC)

helicopter ejection seats
The Kamov Ka-50 was the first helicopter to be designed with a ejector seat, have there been any others with this feature? Googlemeister (talk) 15:10, 11 August 2009 (UTC)
 * The Ka-52 two-seat variant also has the ejector system; I've found no reference to ejector seats in other helicopters. Rotary wing aircraft can already survive many unpowered landings via autorotation. &mdash; Lomn 15:53, 11 August 2009 (UTC)
 * If it also rather difficult to eject from a helicopter since there are rotor blades above you! You have to get rid of them before you can eject, which makes for a much more complex system. They will only be fitted if it is really worth it, which it rarely is. --Tango (talk) 16:39, 11 August 2009 (UTC)
 * What's wrong with ejecting downwards? Vimescarrot (talk) 17:58, 11 August 2009 (UTC)
 * It prevents low-altitude ejections, and helicopters are typically in low-altitude environments. &mdash; Lomn 18:05, 11 August 2009 (UTC)
 * They usually have explosive bolts to blow the rotors off...with the amount of centrifugal force, it doesn't take much for them to fly outwards at a truly spectacular speed!  There have been experiments with ejecting through the floor of the helicopter also - but having large doors in places like that really messes up the structural rigidity of the thing.  The US experimented with them on the Cobra - but I don't think that ever went into production.  Part of the problem is that helicopters generally fly too close to the ground for a safe ejection.  While there are ejection systems that can fling the seat high enough for the parachute to open - those seats have big rockets under them and are too heavy for helicopter operations...they are mostly only used for aircraft that do carrier deck landings. SteveBaker (talk) 18:30, 11 August 2009 (UTC)
 * Thanks for the info! :) Vimescarrot (talk) 21:50, 11 August 2009 (UTC)

Why can they eject foreword, backward or sideways? Or would the brain be scrambled by the G force in some directions more than others?Trevor Loughlin (talk) 04:30, 14 August 2009 (UTC)
 * Well Sideways might work if you designed the seat right, but if you eject forward, the rest of the helicopter might hit you from behind. You can't eject backwards, because most of the helicopter is behind you and you would have to have some way of making it get out of the way of your ejection path.  Probably not a simple matter.  G forces on the person are also a concern since a traditional seat would provide no support for that kind of maneuver.  Googlemeister (talk) 15:28, 14 August 2009 (UTC)
 * I think ejecting sideways could break your neck unless your head is perfectly restrained in the seat. FWiW 98.234.126.251 (talk) 00:11, 17 August 2009 (UTC)

The Moon
I just read about the "Giant impact hypothesis" for the first time. Very interesting. But for that much material to have been blasted off the face of this planet, surely when the NASA guys took photos of earth, they'd have seen something that looked more like Pacman than a sphere? --Dweller (talk) 16:18, 11 August 2009 (UTC)
 * The Earth’s solid crust is relatively very thin, below which there’s a liquid mantle. So an enormous hole like that would get filled in rather immediately.  Red Act (talk) 16:31, 11 August 2009 (UTC)


 * The mantle is a solid! See rheid.  It's like cheese; it moves when you push on it, but it is not a liquid.  Nor is the mantle a sea of magma.  Dragons flight (talk) 23:30, 11 August 2009 (UTC)


 * My boss told me he had heard there was one side of the earth with less dense material (visible on a "gravitation map" or whatever) which could be due to such an impact. I don't know if he was correct or not...  TastyCakes (talk) 16:33, 11 August 2009 (UTC)
 * See: Physical geodesy. --Tango (talk) 16:36, 11 August 2009 (UTC)
 * I'd think that since Earth is geologically active, it would have erased any gravity anomalies long ago. Anything below the crust is fluid and in a state of constant motion (although said "motion" is slower than the speed that glass flows), so density variations would even out pretty quickly.  The crust is constantly being created, subducted, and moved around by plate tectonics, so very few rocks remain from the time of the impact.  --Bowlhover (talk) 22:01, 11 August 2009 (UTC)
 * See also: History of the Earth for a brief note about how the Earth reacted to the collision. The theory is that it became completely molten - which would cause it to quickly become nearly spherical. -- <font color='#ff0000'>k <font color='#cc0033'>a <font color='#990066'>i <font color='#660099'>n <font color='#3300cc'>a <font color='#0000ff'>w &trade; 17:24, 11 August 2009 (UTC)
 * Even without becoming molten, gravity will reshape a body like the Earth back into the near-spherical condition of hydrostatic equilibrium (the IAU's definition of a planet notes that a defining characteristic is sufficient gravity to overcome rigidity and reach hydrostatic equilibrium). &mdash; Lomn 18:07, 11 August 2009 (UTC)
 * Indeed, but a molten planet will reshape quicker. --Tango (talk) 18:30, 11 August 2009 (UTC)

Large population increases rate of evolution?
In a book review, game designer and former physics teacher Chris Crawford cite two writers as showing mathematically that a larger population increases the rate of evolution, even if it doesn't make previously abundant resources scarce. Can anyone here confirm that the numbers work out, whether because they've read the book or because of another source that says the same thing? Neon Merlin  17:54, 11 August 2009 (UTC)


 * It seems pretty obvious - in order to have evolution, you have to have some kind of pressure on the species such that not every individual can have offspring survive into the next generation - and you have to have some source of genetic variation. A larger population means that there are more mutations - more new genes appearing and more combinations of genes showing up.  Assuming there is at least some level of breeding pressure, the increased number of mutations will obviously result in faster evolution. 18:21, 11 August 2009 (UTC)


 * I would think it was more the opposite. Population bottlenecks can cause rapid evolution since any mutations in the few members of the population that survive will inevitably end up in a large proportion of the population. --Tango (talk) 18:29, 11 August 2009 (UTC)
 * It's both. A larger population means there is likely to be a greater number (not necessarily percent) of genetic mutations occurring, so the potential is definitely there.  However, in a small population, all it takes is one particularly persistent mutation to quickly affect the entire population. ~ <font color="#FF0099">Amory <font color="#555555"> (user • talk • contribs) 19:18, 11 August 2009 (UTC)
 * I guess we have to be more careful about what we're saying when we talk about increasing the "rate" of evolution. Certainly having a smaller population would result in a new, beneficial gene spreading more rapidly - but an awful long time could go by without any new, useful mutation showing up.  With a large population, beneficial genes would show up much more frequently - although it would take longer for them to spread everywhere.   But the degree to which that is the case has to depend on exactly HOW beneficial the gene was.  A gene that made you immune to heart disease would spread through the population incredibly quickly - but a gene that helped you survive being struck by lightning could take forever to take hold in a larger population.  When you consider the evolutionary advances due to two or more rare genes that are only beneficial in combination happening to meet as a result of sexual reproduction - the advantages of a large population should be even more significant. SteveBaker (talk) 23:28, 11 August 2009 (UTC)


 * Right point, but wrong example. There is apparently such a mutation in a family from Italy, but it has little chance of being fixed any time soon. People typically die of heart attacks long after their reproductive age, so the selection pressure is fairly minimal. --Stephan Schulz (talk) 00:40, 12 August 2009 (UTC)
 * But! if old people play a big enough part in raising and supporting the children of their family, their longevity could still play a part in selection pressure. This would be analogous to "drones" which alone can't breed or pass their genes on, but they play enough of a role in the "family" of the hive to explain how they evolved. Darwin thought this was important enough to devote a chapter in "Origins" to its study. Vespine (talk) 01:09, 12 August 2009 (UTC)
 * Okay, but that selection pressure is going to be extremely weak. Old people aren't even remotely as crucial to the support of a human family as worker drones are to a colony of ants. Maelin (Talk | Contribs) 01:49, 12 August 2009 (UTC)


 * I disagree. Check this out. And consider this quote, found here:


 * One more distinction between Neandertals and moderns deserves mention, one that could have enhanced modern survival in important ways. Research led by Rachel Caspari of Central Michigan University has shown that around 30,000 years ago, the number of modern humans who lived to be old enough to be grandparents began to skyrocket. Exactly what spurred this increase in longevity is uncertain, but the change had two key consequences. First, people had more reproductive years, thus increasing their fertility potential. Second, they had more time over which to acquire specialized knowledge and pass it on to the next generation—where to find drinking water in times of drought, for instance. “Long-term survivorship gives the potential for bigger social networks and greater knowledge stores,” Stringer comments. Among the shorter-lived Neandertals, in contrast, knowledge was more likely to disappear, he surmises.


 * The above may be peculiar to human evolution, but it is still evolution. Bus stop (talk) 01:59, 12 August 2009 (UTC)
 * Isn't "worker drone" a contradiction in terms? Workers are infertile females, drones are fertile males. Vespine meant "workers" not "drones". (Unless some social insects are very different to the honey bee, which is where my [limited] experience lies.) --Tango (talk) 04:09, 12 August 2009 (UTC)


 * I think the opposite is observed more frequently... Take Darwin's finches, the large parent population on the mainland remains relatively unchanged for a long time. The small island populations on the islands are evolving like crazy. Yes the variable selection pressures have a lot to do with it, one year there is a drought so the seeds are hard and dry, the next year might be wet so there's more food around. But I think the large population does a lot more to "dilute" any evolution that takes place, they said that if any birds made it back to the mainlad, their genes would be diluted into the large population.. ring species is a very interesting topic, not exactly in response to this topic, but related. Vespine (talk) 23:54, 11 August 2009 (UTC)


 * Yes, the main problem with large populations is that beneficial genes don't spread quickly at all—hence the old Galtonian problem of reversion to mediocrity. You don't get quick changes unless there is isolation, and so unless there are strong pressures you tend to get more of the same, on average. --98.217.14.211 (talk) 00:36, 12 August 2009 (UTC)


 * The changes are no more quick when you have small populations, but the stresses are peculiar to that population, thus sending that population in its own direction. Isolation correlates with stresses peculiar to an isolated population, resulting in "peculiar" creatures. Bus stop (talk) 01:40, 12 August 2009 (UTC)


 * I think our problem here is multiple uses of the term "changes". Why don't we say, "the spread of particular mutations." In a population that is very large, individual mutations will tend to have a very small net effect in the overall gene pool—they represent a very small percentage of the next generation's genes. In a small population, they will represent a sizable proportion of the next generation's genes. Over the course of a large number of generations, you'd see that particular mutation in a far higher percentage of the total population in a small group (assuming it is beneficial), than in a large one. I think most people would consider that to be a faster "rate of evolution" in a very colloquial sense, even though the total amount of gene exchange is identical. This is obviously a very crude approach to things. In the end, I think we're all getting caught up on the terminology like "rate of evolution," which is rather ambiguous. A large population will have a higher rate of mutation—that is clear—but the mutations themselves will not spread quickly unless there are very strong selective pressures. --98.217.14.211 (talk) 02:47, 12 August 2009 (UTC)


 * "Faster" and "slower" evolution are subjective terms. Faster is not necessarily better than slower. Populations of the same creature that become isolated from one another will diverge from one another under forces of evolution if the challenges to reproduction and survival are different in their different ecological niches. Species evolve in order to preserve themselves (in an attempt to avoid extinction). Bus stop (talk) 03:07, 12 August 2009 (UTC)


 * You can define the terms objectively in terms of change over time, to be sure. As for their "value" (good, bad, ugly), yes, that's subjective. --98.217.14.211 (talk) 15:17, 12 August 2009 (UTC)


 * What are the advantages of "slower evolution" -- that is, of having beneficial mutations either arise less often or spread more slowly? Neon  Merlin  16:41, 12 August 2009 (UTC)


 * Advantages from what point of view? If we consider it advantageous that parrots be colorful and beautiful than we want evolution to go in that direction. But evolution has no agenda -- apart from survival and reproduction. I don't understand the question concerning slowness or rapidity in evolution. There may be material available on this. I am just ignorant of it. Bus stop (talk) 18:33, 12 August 2009 (UTC)

core not molten
When will Earth's core become solid and what would be the consequence for Earth? --<font face="rage italic" size="4.5" color="LightSteelBlue"> Taxa (talk) 18:39, 11 August 2009 (UTC)


 * The inner core is solid, it's just the outer core that is molten. (The inner core is hotter, but under more pressure, so is solid despite the heat.) The Earth is slowly cooling, so I suppose it is possible that the outer core will freeze eventually. That would have a significant impact on the geomagnetic field, although I don't think it would eliminate the field entirely. I can't find a timescale for that, though - it might be longer than the life of the Sun, so would be moot. --Tango (talk) 18:56, 11 August 2009 (UTC)


 * From what I understand, our knowledge of the thermal conduction properties of the inner earth are very limited. In fact, our best information on the deep earth comes from seismic analysis - which can give a good sound-speed and rock shear properties.  This lets us estimate the rock composition in the mantle - but the error bars are non-trivial.  We also have electromagnetic information, but it's not very conclusive as far as telling us material properties in the earth.  So, from this amalgamation of data, we "guess" what sort of rock is down there, and under what conditions (pressure, temperature, etc).  The next step is to estimate, or measure in a laboratory, the thermal conductivity properties of such a material - again, we don't have a great way of synthesizing molten silica or iron at the temperatures and pressures we expect to find in the deep mantle or outer core, so lab measurements are helpful only as far as data-extrapolation is reliable.  Finally, the thermal conductivity problem can be solved analytically or numerically to estimate the time-constant of cooling.  To my understanding, the Earth is almost in steady-state temperature, with solar energy incidence equally balanced by reradiation into space.  But, with all these "Global Climate Change" scientists redefining what is meant by "Temperature of the Earth" (they usually mean the sea-level average temperature, or the average ocean temperature, or whatever - but they rarely mean the blackbody temperature or the radiation temperature as observed from space) - it's hard to be very sure whether Earth as a whole is "warming" or "cooling".  On geological time scales, we can probably say that Earth is actually cooling, but very slowly; and by comparison to other Earth-like planets that we have measured (Mars, Mercury, and Moon -not really a planet, but who knows what terminology IAU will come out with next-- come to mind).  All of these planets have cooled and appear to have solid interiors as evidenced by weak or absent dipole planetary magnetic fields; but our seismic experiments on the Moon were noisy and weak (so we aren't really sure).  No seismic experiments have been conducted on Mars or Mercury (to my knowledge) so we have very limited understanding of the interiors of those planets.  Each of those three seem to have cooled quicker than Earth - probably due to their smaller size (which means lower thermal mass, and also a greater surface-area to volume ratio).  We can pretty much assume that Earth's interior will also solidify; I would estimate the timescales are on billions-of-years (which means that the steady-state approximation of solar heating will be invalid).  Regarding the consequences - the biggest question is, "what will happen to our dipole magnetic field?"  Mars seems to have greatly weakened and frozen some magnetism into the crustal rock; but Mercury and Moon have a neglible magnetic field.  The dramatic consequences might include the disappearance of the Van Allen belts, exposing the atmosphere to the highest-energy solar wind particles; but this is speculation.  It's worth noting that the most intelligent geomagnetism experts I have talked to about this always preface things by reminding me that we really have no idea why Earth has a magnetic field anyway - something about "hot iron" and maybe some kind of circular, convective motion ... but try to get a straight answer as to why this makes the planet look like a bar magnet - and you just get more questions.  So - maybe a frozen interior will have no effect on our magnetic field... Nimur (talk) 19:32, 11 August 2009 (UTC)
 * Given the long timescales involved, are we going to be rendered uninhabitable by the Sun before this happens? Vimescarrot (talk) 21:47, 11 August 2009 (UTC)
 * The Sun will kill us in about a billion years, so if Nimur is correct and we're talking billions of years then yes, the Sun will kill us before the core cools down enough to be a serious problem (if it will ever be a serious problem). --Tango (talk) 22:59, 11 August 2009 (UTC)


 * The inner core started to solidify 3-4 billion years ago, and in that time ~15% of the total core has frozen. Given that time scale, the sun will almost certainly die before the core could solidify completely. Dragons flight (talk) 23:24, 11 August 2009 (UTC)
 * Is it a linear thing? --Tango (talk) 23:41, 11 August 2009 (UTC)


 * Everything is linear if you approximate enough. ;-)  No, it's not entirely linear.  However, heat flow through the Earth is roughly proportional to the temperature gradient and both the interior and exterior temperature are quasi-steady state, so energy loss is roughly constant (of order 10 TW for the core).  Incidentally, the crystallization front between the inner and outer core is itself responsible for stabilizing the interior temperature, since the boundary must exist at the temperature where liquid and solid core material can coexist (i.e. a phase boundary).  Dragons flight (talk) 23:50, 11 August 2009 (UTC)
 * Everything differentiable is linear if you approximate enough, that being the definition of differentiability (a definition, anyway). I'll except that it is differentiable, though, but I suspect that over the billions of years you are talking about it may not be reasonable to approximate that much. It's not just residual heat involved, most of the heat comes from ongoing radioactivity that will be reducing over billions of years and may be concentrated more in certain layers, which will make the temperature gradient more complicated. The boundary isn't at constant temperature either, as it moves outwards it will decrease since the pressure is decreasing. These, and various other factors that I probably could never think of, mean it is probably far more complicated than a linear relationship. --Tango (talk) 04:01, 12 August 2009 (UTC)
 * Tango, where are you getting 'about a billion years' from? The Sun article says it's about halfway along the main sequence and will enter the red giant phase in about another 5 billion years. Is something likely to happen before that that we need to worry about?AlmostReadytoFly (talk) 07:39, 12 August 2009 (UTC)
 * In our Earth article, the 'future' section suggests that there may be less than a billion years before the effects of increased luminosity of the sun makes the planet uninhabitable. See also '' (borrowed from a discussion on that article's talk page), which certainly gives food for thought. Mikenorton (talk) 08:14, 12 August 2009 (UTC)


 * Nothing that some orbital mirrors wouldn't be able to fix for a few more billion years. Dauto (talk) 22:26, 12 August 2009 (UTC)

esterification of edible alcohols, besides ethanol
So I got some favourable correspondence from a chef, so I'm about to refine my series of experiments. The thing is, being 19, I don't really have good access to ethanol, and I'm tired of borrowing my roommates' beer. Which is a pity, since ethanol is probably an alcohol I could use in excess, and I wanted to try frying pan syntheses of ethyl cinnamate. What are some common food items that contain favourable OH groups for esterification? (And favourable COOH groups too?) Preferably these are compounds I could react in excess (for a noticeable ester smell?).

I was thinking of using tannins, since they are abundant. must I do to get tannin OH groups to react? (If I say, added tea leaves?) Why are aryl OH groups hard to esterify in general? Are there any pleasant tannin esters, anyway? Are there any cooking pan methods to turn compounds into reactive alcohols, e.g. turning spice oils?

Are sugar's OH groups conducive to esterification? What about sweeteners? What about caramelised sugars?

Could I also use enzymes or microbes to produce alcohols besides ethanol, e.g. convert an aldehyde into an alcohol? John Riemann Soong (talk) 19:11, 11 August 2009 (UTC)


 * Depending on your area, possession of ethanol for chemistry is not regulated; you might be able to order it from a chemical supplier like Fisher Scientific: ||BP2818500||BP2818100&pos=12&catCode=RE_SC&endecaSearchQuery=%23store%3DScientific%23N%3D0%23rpp%3D15&fromCat=yes&keepSessionSearchOutPut=true&fromSearch=Y&searchKey=ethanol&highlightProductsItemsFlag=Y Molecular Biology-grade 100.0% ethanol is available for about 25 US dollars per 100 mL. Nimur (talk) 19:54, 11 August 2009 (UTC)
 * (It should be noted - DO NOT DRINK 200 proof ethanol). Nimur (talk) 19:55, 11 August 2009 (UTC)


 * Wow, 200 proof ethanol is really expensive ... couldn't I get it at azeotrope concentration? I imagine that would cheapen things considerably. Or is azeotrope-distilled alcohol (without a bittering agent?) regulated? John Riemann Soong (talk) 20:08, 11 August 2009 (UTC)
 * There are numerous grades available; less pure ethanol may be cheaper. You can search for them or find other vendors.  Of course, if you want to eat any of this stuff, be very careful - impurities in lab-chemistry-grade chemical supply can be extremely toxic - deadly.  Even the 100.0% ethanol, which claims to be very pure, still might have as high as 100 ppm acetone, and other impurities ("probably below the LD50" isn't safe enough for human consumption).  Nimur (talk) 20:12, 11 August 2009 (UTC)
 * In many areas, you can buy 190 proof (95%, the azeotropic ratio) in liquor stores (some places regulate it as any other drinking alcohol, other places are stricter specifically about this one). I'll second Nimur's comment though, that lab-grade chemicals, while they may have a higher % purity than food-grade, may have than smaller amount of contaminant be a more dangerous chemical; food-grade is often lower purity but you know the impurities are safe to eat. Methyl alcohol (probably 70% or 90%, maybe also 100%) is often available from pharmacies. Isopropyl is also, but I don't know of any popular esters of it. DMacks (talk) 21:02, 11 August 2009 (UTC)
 * That's two threads on WP:RD/S about Everclear right now! DMacks (talk)
 * Even if you do, it isn't simple to get 200% proof - this 14-page document is a summary of the rules: . You only need status, power of attorney, federal inspection, tracking systems to account for it down to no more than 1% loss, etc. 75.41.110.200 (talk) 21:29, 11 August 2009 (UTC)
 * Depends on if you get denatured alcohol or not. As mentioned above, you can get "200 proof" denatured ethanol that has ppm levels of acetone/benzene/gasoline/etc. in it which renders it "unfit for human consumption" in the eyes of the government (and anyone who doesn't want to seriously destroy their liver). Denatured ethanol is relatively easy to come by - most hardware stores carry it in the paint department, where it is used as a cleaning solvent and finish component (for shellac and the like). Whether that would be suitable for chemistry experiments, I don't know. -- 128.104.112.100 (talk) 17:32, 12 August 2009 (UTC)


 * I don't know why there's this emphasis on high-purity alcohol. I'll be happy with 25% alcohol.... I suppose I could get cooking wine. but then that would mess up my experiment (it's easiest to notice a difference if there's no smell beforehand -- well except for the smell of distilled vinegar -- and a smell afterwards.) John Riemann Soong (talk) 08:48, 13 August 2009 (UTC)


 * Aryl OH is harder to esterificy than alkyl OH because of the lower nucleophilicity of Ar-OH - caused by delocalisation of the O lone pairs onto the benzene ring - the same effect causes the higher acidity of phenols compared to alcoholes (in general, for the same type of atom, higher acidity = lower nucleophilicity)
 * You can get enzymes to do almost anything - both oxidations and reductions - however for a reduction you'll probably need a reducing agent to 'feed' the enzyme.
 * I think tannin esters would be too involatile to have a smell. For taste see Tannin
 * 83.100.250.79 (talk) 21:04, 11 August 2009 (UTC)

Re -- ppm impurities in lab-grade ethanol ... if you ferment something with microbes, won't they produce toxic ppm byproducts too? I've gotten ethers and acetone all over my hands so many times (what happens when you stay all up all night for a lab report and then come to lab drowsy -- I once dozed off holding a cylinder of 85% sulfuric acid...) that I really think ppm impurities wouldn't hurt me too much. John Riemann Soong (talk) 09:16, 13 August 2009 (UTC)
 * It depends on the contaminant. Nimur (talk) 14:28, 14 August 2009 (UTC)


 * That's one of the "tricks" of distillation - you can't just stick the output of a still into a bottle to get your vodka/brandy/rum. The very first bits that come off and the very last bits that come off contain things like methanol, acetone and ethyl acetate, among others. The distiller needs to separate off those "tails" to produce a drinkable product. (But not too much, as some of the flavor of the beverage is due to trace amounts of these contaminants and other fusel alcohols.) That's one reason given for requiring distillers to be licensed - an untrained distiller could produce bottles of "rotgut" with too high a level of methanol or other toxic byproducts. -- 128.104.112.102 (talk) 20:45, 14 August 2009 (UTC)

How do I get Ajax out of a can?
I called the company's number and they claim it can't be done. They just sent me a coupon for a new can.

However, I have three or four cans that have something left in them, but at some point even banging the can against a hard surface didn't work.

Yes, the company advised me don't keep it in a moist environment. I don't know where else to keep it. I use it in the bathroom; therefore, it goes in the bathroom. My father used to keep and use it in the kitchen (which the company doesn't advise either). I use Lysol there.

I have a can of Comet--a big one--that may soon be in the same situation. I tried Lysol toilet bowl cleaner but all those warnings scare me. Besides, Comet and Ajax are cheaper--if I can use the whole can.<font color="Green">Vchimpanzee ·  talk  ·  contributions  · 19:24, 11 August 2009 (UTC)
 * Can you cut the can? Tin snips ought to go through them (I think it's really just a stiff cardboard can, right?)  Nimur (talk) 20:17, 11 August 2009 (UTC)


 * That might work. Yes, it is cardboard. The oldest one is bent completely out of shape.


 * I was thinking about Acupuncture needles or something. Thanks.<font color="Green">Vchimpanzee ·  talk  ·  contributions  · 20:43, 11 August 2009 (UTC)


 * What is the chemical formula of Ajax anyway? Might it be possible to gently heat the can in the oven to drive off the excess moisture (I've done that with salt when I lived in a damp flat) - or would the heat cause it to decompose and release noxious gases? --Kurt Shaped Box (talk) 13:38, 12 August 2009 (UTC)


 * As an aside, it's probably not good that your bathrooms & kitchen are that humid - you're just asking for mold to grow there. If you have an extractor fan, you should probably turn it on more often than you currently do. SteveBaker (talk) 23:18, 11 August 2009 (UTC)
 * I do have a fan. My father used to use it but I don't.


 * The kitchen may not be that humid, but under the sink it would be.<font color="Green">Vchimpanzee ·  talk  ·  contributions  · 14:26, 12 August 2009 (UTC)
 * Why? There shouldn't be water UNDER the sink!  You need to take this rather seriously - use the fans - and if something is damp that shouldn't be - find out why and get if fixed.  When (not: "if") mold starts to grow in these moist environments, it will prove (a) smelly, (b) hazardous to your health and (c) hard to get rid of. SteveBaker (talk) 17:29, 12 August 2009 (UTC)
 * I'll echo that. The place I lived in when I first left home (one room basement bedsit with no ventilation) caused my clothing to rot on the hanger if not taken out and hung in front of the electric fire every couple of weeks. Wet towels and bathmats would have mould growing on them within a couple of days. I was always getting chest infections too. The place was that damp that the air felt thick to breathe. Oh yeah, there were always silverfish and woodlice skittering everywhere too - after a while, I just learned to ignore them. --Kurt Shaped Box (talk) 21:39, 12 August 2009 (UTC)
 * Apart from keeping your apartment drier you might want to use a zippy bag around your next can of Ajax. Put a bit of baking soda at the bottom of the bag to absorb any moisture that gets in. (Some grains of rice might also work for that.)  Use a slider bag for easier access to your can.  BTW if you live in a place with high air humidity you might have to consider getting a dehumidifier.  For your existing cans I'd demolish them, use a tool to break up the lump. (No, I will not advise you to use a screwdriver like I would, because that's a good way to damage a perfectly good screwdriver ;-)  Store the resulting powder in a container you can seal.  Be sure to wear gloves, long sleeves and eye protection. 71.236.26.74 (talk) 07:07, 13 August 2009 (UTC)

I think I may have exaggerated the scope of the problem. The man at the company that makes Ajax said don't put it under the sink. I'm not aware of a specific humidity problem.

As for other mold in the house, I do have to make sure I frequently wear each pair of my Converse Chuck Taylors which were made in other countries. Those that don't get worn develop a mold problem. For shoes made in the USA, this doesn't happen.

I also had a blazer hanging in my closet that didn't get worn for a long time and needed cleaning.

And it's not an apartment. It's a house.<font color="Green">Vchimpanzee ·  talk  ·  contributions  · 13:38, 13 August 2009 (UTC)

plant intelligence
What is the most intelligent plant in the world? --<font face="rage italic" size="4.5" color="LightSteelBlue"> Taxa (talk) 19:38, 11 August 2009 (UTC)


 * Define "intelligent". Plants don't have a central nervous system, which is really a requirement for any common definition of intelligence that I know of. --Tango (talk) 19:43, 11 August 2009 (UTC)


 * (ec) Define "intelligent". (Wow, Tango had exactly the same knee-jerk reaction as I did!) We really can't answer this question unless you have a specific idea about what intelligence means for an organism with no central nervous system. Maybe you would find tropism helpful - a lot of response to stimuli can occur without "thinking" - so there's sort of a biological Chinese room problem. Really sophisticated behavior might or might not be due to intelligence, depending how you want to define it. Nimur (talk) 19:47, 11 August 2009 (UTC)
 * Response to stimuli. --<font face="rage italic" size="4.5" color="LightSteelBlue"> Taxa (talk) 20:44, 11 August 2009 (UTC)
 * The Venus fly trap? Bus stop (talk) 20:51, 11 August 2009 (UTC)


 * That's only one response to one stimuli in a millisecond time frame limit. What about sequences that occur over broader periods of time? --<font face="rage italic" size="4.5" color="LightSteelBlue"> Taxa (talk) 21:00, 11 August 2009 (UTC)


 * Plants bend and twist to orient themselves to an available light source. Surely that qualifies as intelligence. See auxins. Bus stop (talk) 21:11, 11 August 2009 (UTC)


 * (ec) Not what you're going to want to hear, but isn't, say, the growth of an oak tree over 50 years the result of a bunch of different stimuli? Roots grow around rocks in the ground, branches grow around any obstacles that exist, the acorns are produced at a certain time of the year, and it's all powered by photosynthesis which is 'stimulated' by sunlight.  Tempshill (talk) 21:14, 11 August 2009 (UTC)


 * You guys are overthinking it; the question is flawed. Vranak (talk) 21:45, 11 August 2009 (UTC)
 * To the contrary. Put yourself in the place of a plant. You are in competition with other plants. You have to outwit the competition. If you are a conifer you decide to fill your photosynthesis devices with resin to conserve water so you can live near the arctic circle. You then send seeds aloft which take root and eventually dominate that part of the globe. You are much more intelligent than the plants which go there with no hope that they can survive. --<font face="rage italic" size="4.5" color="LightSteelBlue"> Taxa (talk) 03:34, 12 August 2009 (UTC)
 * I believe a more thorough understanding of evolution and its pathways may inform and improve upon your understanding of putative 'plant intelligence'. Vranak (talk) 15:18, 12 August 2009 (UTC)
 * An individual conifer doesn't make any decisions like that, the resin evolved over many generations. --Tango (talk) 03:45, 12 August 2009 (UTC)


 * Overthinking! Refdeskers. Preposterous! ;-) Fribbler (talk) 23:30, 11 August 2009 (UTC)


 * The brain cactus (Mammillaria elongata 'Cristata' ). --Heron (talk) 10:59, 12 August 2009 (UTC)


 * In years past, the Y-12 Plant in Oak Ridge was crawling with Ph.D.s.  --Sean 14:22, 12 August 2009 (UTC)


 * For any reasonable definition of intelligence, (Like those you would find in an actual dictionary) there isn't an answer. No cognition is involved, quick and complex or otherwise. APL (talk) 19:30, 12 August 2009 (UTC)


 * What about signals (pheromone or something similar) released to inform wasps which kind of parasites it wants to get rid of with the help of the wasps? --131.188.3.21 (talk) 16:50, 14 August 2009 (UTC)

Plants sleeping
Hello, I was wondering if someone could clear something up for me. It seems that most indoor plant growers have their lights on a timer. Is this to save electricity, or do plants do better if they have regular periods of darkness? Will plants that grow in perpetual light grow faster than ones with light and dark periods? Does this depend on the type of plant? TastyCakes (talk) 19:44, 11 August 2009 (UTC)


 * It depends on the type of plant. Some plants undergo CAM photosynthesis, which means that certain chemical reactions prefer to take place at night (although a day cycle is needed to absorb the light for photosynthesis) - and the entire process is more efficient, even though only half of the reaction (day- or night- reaction) is happening at any given instant.  Other plants can perform better if exposed to light for 24 hours/round-the-clock.  Nimur (talk) 19:51, 11 August 2009 (UTC)
 * Oh ok thanks a lot, do you know if there's anywhere I could get a list of plants that fall into each category? I'm mostly interested in things you can eat... TastyCakes (talk) 19:53, 11 August 2009 (UTC)
 * Our article has a section and a list of common CAM plants; these include yucca, agave, many types of cacti (which may be edible), some Sagittaria tubers, and others. Nimur (talk) 20:00, 11 August 2009 (UTC)
 * Hmm ok, so typical vegetables (lettuce, carrots, tomatoes etc) are more successful in constant light? TastyCakes (talk) 20:48, 11 August 2009 (UTC)
 * Supposedly, in Alaska, despite the cool climate, the long summer daylight hours result in comically large vegetables like these. I don't know if this is true in general, but I have seen some very large pumpkins and cucumbers up there. Nimur (talk) 00:41, 12 August 2009 (UTC)
 * Acutally plants do require set periods of day or night. See photoperiodism. Some plants are long day plants who require a set amount of sunlight (a minumum). Others are short day plants. One hormone that matters for plants is phytochrome. It is converted from one form to another in response to sunlight and the ratio is thought to effect photoperiodism. Not sure if this applies to all plants though.  —Preceding unsigned comment added by 76.94.88.196 (talk) 08:55, 12 August 2009 (UTC)
 * Note that photoperiodism is a a bit more complicated the hours of daylight. The older hypothesis is that it's the hours of darkness that really matter. If you give any plant long darkness but a burst of sufficiently bright light (particularly red light) for several minutes every 5 hours or so, you're likely to mimic long day conditions, so a short day plant will not flower. A phytochrome cycles between two forms, slowly converts back to one form (Pr) under darkness (or quickly under far red light) and quickly back to the other form (Pfr) under red light (or normal light). This is mentioned somewhat in photoperiodism and is sometimes called the hourglass model. However even that is a little too simplistic,  gives an idea of some of the more recent research. BTW, some plants are day neutral Nil Einne (talk) 09:54, 12 August 2009 (UTC)
 * some plants will change their behavior at night eg stop photosynthesis or change their scent to atract nocturnal creature like moths. —Preceding unsigned comment added by The mophead (talk • contribs) 18:20, 14 August 2009 (UTC)

Does this sound right to you?
"According to the USDADietary Guidelines, one serving of fruit is equal to one half cup. This measurement is based on fresh fruit cut in typical slices or chunks. Of course, by cutting the fruit into small bits like we do in Fruit2day, we can fit the equivalent of a full serving into a smaller space. That’s why even though a bottle of Fruit2day is only 6.75 fluid ounces, it still contains two complete servings of natural fruit goodness." Imagine Reason (talk) 20:26, 11 August 2009 (UTC)
 * It is certainly true that cutting something into smaller pieces usually allows you to fit it into a smaller space since you end up with less air around the pieces. Whether a bottle of Fruit2day really counts as two servings, I have no idea, but it is entirely possible. --Tango (talk) 20:40, 11 August 2009 (UTC)
 * Could also be somewhat concentrated, having a higher nutrient to volume ratio then 1 cup of fresh fruit would. Googlemeister (talk) 20:46, 11 August 2009 (UTC)
 * Or it may be older and some of the more volatile things might have decayed into less nutritious stuff. But the USDA guidelines are pretty fuzzy.  It's never clear what they mean when they specify stuff like that by volume rather than weight.  Also - which fruit?  I'm pretty sure there are more nutrients in something dense like (say) a peach than in (say) a watermelon.  The watermelon is almost all water - the peach has much less.  Is a half-cup of watermelon enough?  Is a half cup of peach more than you need?  Given how fuzzy those terms are, I'd be very wary of company claims for being significantly more nutritionally dense than "real" fruit. SteveBaker (talk) 23:15, 11 August 2009 (UTC)
 * Very true, the guidelines are kept intentionally simple, but that means they are of limited use. When you start trying to use them for something they weren't designed for, your results will be highly questionable. The guidelines are designed for fresh fruit, so using them for something like Fruit2day is problematic. --Tango (talk) 23:20, 11 August 2009 (UTC)
 * What's the question? "does this sound right?" No, your post sounds like spam to me. "Natural fruit goodness"? No one asking a question talks like this. Vespine (talk) 23:23, 11 August 2009 (UTC)
 * That's a quote from the linked website, it's not the OP's own words. --Tango (talk) 23:42, 11 August 2009 (UTC)
 * I'm not sure the servings can be manipulated as they say. I have had one such bottle and it looks like some bits of pineapple (I had the pineapple banana version). If a small apple is a serving, surely a half cup of it that is equivalent is not filled with air, but small bits of chopped apple? Imagine Reason (talk) 15:32, 12 August 2009 (UTC)
 * There will be air inbetween all the pieces unless you mash the apples up really finely. --Tango (talk) 16:01, 12 August 2009 (UTC)
 * I doubt there's that much air in the guidelines. 6.75 oz. is 6.75 oz. 98.14.222.41 (talk) 17:36, 13 August 2009 (UTC)

elemental isotopes
Is our current scientific understanding of isotopes of heavier atoms such that the % of each stable isotope of an element is even throughout the local part of the galaxy? What I mean is if we were to theoretically travel to a planet 100 ly away which had a surface of 100% water, could we expect to find 99.762% O16, the same as in the water on earth, or are those % dictated by the local star? Googlemeister (talk) 20:55, 11 August 2009 (UTC)


 * The heavier elements are made inside stars - it seems likely that the isotope makeup could differ depending on the nature of the star that made those heavier atoms.  In many cases, an odd-ball isotope of a stable atom will have come about through the decay of heavier, more unstable elements.  Since the predominance of those must certainly depend on the history of the recent stellar neighbourhood - I'd guess it quite likely that there would be wide variation from place to place in the galaxy. SteveBaker (talk) 23:10, 11 August 2009 (UTC)


 * 100ly away, maybe, it might be orbiting a star that formed from the same nebula as the Sun, so would have similar proportions. At greater distances, Steve's points mean I would expect significant variation. The stars that formed in the same area as the Sun will have spread out quite a bit by now, but their distance from the centre of the galaxy should be fairly similar. --Tango (talk) 23:18, 11 August 2009 (UTC)

The isotopic makeup of some gases is different between the atmospheres of Earth and Mars -- I assume the mechanism is that isotopes diffuse into space unequally and in a way that depends on the air pressure and gravity. This difference is one of the ways that it was confirmed that Mars meteorites on the Earth had in fact traveled from Mars. --Anonymous, 23:32 UTC, August 11, 2009.


 * The isotopes behave very similarly, the only difference is mass and that difference is very small. It is more likely that the elements which decay into the different isotopes are behaving differently. For example, Uranium-238 is very heavy so given a chance it is likely to sink to the centre of a planet, but under some circumstances it will remain on the surface which will mean you end up with Lead-206. So, if those circumstances occur on one planet but not on another you'll end up with a higher proportion of Pb-206 compared to other isotopes on the first planet compared to the second. (I chose that example pretty much at random, it might be seriously flawed, but I think the general idea is sound.) --Tango (talk) 23:50, 11 August 2009 (UTC)


 * Except we're talking about light elements found in atmospheric gases, which (except for helium) are formed only by fusion in stars, not by radioactive decay of heavy elements. --Anon, 04:36 UTC, August 12, 2009.

Broken stereo?
I have a stereo system hooked up to my TV, digital converter box, and DVD player. It is at least 15 years old. Yesterday, after we lost power during a thunderstorm (lightning struck pretty close and took out our cable too), the stereo stopped working. Whenever we turn it on, it looks like it works, but then after a second or two, it turns itself off suddenly. Is the thing history, or is this a pretty simple problem to solve? Thanks &mdash;Akrabbimtalk 21:49, 11 August 2009 (UTC)
 * Probably history. Modern consumer electronics are pretty much disposable once the warranties have run out - the cost of repairing them is normally such that it's more cost effective to replace them with a brand new warrantied model. Also after fifteen years parts and service manuals may be difficult to come by. Before you look at repairing, check the price of replacing with an equivalent new unit - if a new one costs $200 and it will cost $100 to repair the fifteen year old one it's really not worth repairing. Exxolon (talk) 22:47, 11 August 2009 (UTC)


 * It doesn't sound easy. Easy things are broken wires and blown fuses - but if it were either of those, it would probably be just completely dead.  As a matter of course, I'd pull the lid off and see if there is anything obvious such as a blackened smudge around a particular component or a wire that looks singed.  The odds are fairly remote that it'll be anything that obvious though.   You might be able to trick it into working by playing with the controls during the second or two it does stay on...maybe if it has some kind of a setup menu, you could get to a "reset" entry or something and reset it before it craps out.   All of these are very long shots though.  In all likelyhood it has a fried memory chip or something.  The computer inside powers up - checks the memory, finds that nothing makes sense and just shuts down again. SteveBaker (talk) 22:48, 11 August 2009 (UTC)
 * I agree, it sounds dead. Turning on for a second or do and then turning itself off sounds like the firmware is fried. It is possible you can reset it somehow, but you will probably have to get a licensed repair firm to do it and they will charge more than a 15 year old stereo is worth. --Tango (talk) 23:04, 11 August 2009 (UTC)


 * Well, if it were merely that the firmware was failing due to some garbage written into its non-volatile memory - then there is one (very bizarre) last-ditch method to try to fix it. Wrap the main unit (minus speakers, etc) in a plastic bag and leave it in your freezer overnight.  (I told you it was bizarre!)   The idea is that this takes the temperature of the electronics down to below their minimum operating temperature - which in some cases will erase the contents of their non-volatile storage.  After a night in the freezer, bring the thing slowly back up to room temperature BEFORE you take it out of the plastic bag in order to prevent condensation onto the electronics.  After it's been sitting out warming up for a couple of hours, plug it in and see if that did anything.  I'd say that the odds of that working are much less than 1%...but if you're desperate - and the unit is going to become landfill anyway...then I suppose it's worth a try!  (I've used this to erase a forgotten password from the BIOS ROM of an old laptop - and, amazingly, it worked perfectly.  But in that case, I was able to freeze just the chip - not the entire laptop.)  SteveBaker (talk) 11:44, 12 August 2009 (UTC)


 * A possible but unlikely scenario is that the amp output has self resetting shjort circuit protection, like my old stereo. If one channel has a short in the speaker wire, the stereo will play for a second then shut off. Try with speaker wires disconnected (use headphones). That failing try Ebay for an equivalent 15 year old stereo. Or for a modern surround sound system. Edison (talk) 15:36, 12 August 2009 (UTC)

Herbicide
Is anyone aware of a weed killer that would prevent plant growth for a month or more? Someone vandalised my garden on the 4th July weekend, using some sort of spray, and even the weeds haven't started growing yet. The spray was applied quite locally: weeds have been growing between the lines of dead plants for a couple of weeks now. The only other thing that I know about it is that it kills what it contacts: some plants were only partially killed, such as a tomato that was mostly blackened but produced a ripe tomato just a week ago. 24.93.116.128 (talk) 21:50, 11 August 2009 (UTC)


 * I don't know about herbicides, but when you mentioned the date, and then the blackened plant, I think of burning. Could there have been fireworks nearby, with someone's rocket coming down in your garden?? You don't say what evidence you used to know it was vandalized then, after all. Of course, I'm not sure if that would have an impact or not.Somebody or his brother (talk) 22:28, 11 August 2009 (UTC)
 * You wouldn't get lines of dead plants from a rocket, would you? --Tango (talk) 23:06, 11 August 2009 (UTC)
 * No, there was no evidence of a rocket (nothing found in the garden), and the plant is withered: it's black now because most of it died. There's an orangeish residue on the ground, as well.  We think that the plants were sprayed perhaps on the 2nd July, but they appeared normal until suddenly withering on about the 6th.  A rocket flying parallel to the ground isn't in question, because we have a fence that's higher than most of the plants in the garden, and its holes are fine enough that a rocket couldn't penetrate.  Moreover, we had about a dozen lines of plants, so you'd need several rockets.  BTW, the same thing happened to our rhubarb and part of a flowerbed perhaps 10m or more away.  I should note that we talked to the local extension agent, who said that the effects sounded somewhat like Paraquat, but that was several weeks ago, before we knew that it would prevent weeds from growing for several weeks.  That article says "It is rain-fast within minutes of application" and "It becomes biologically inactive upon contact with soil".  Would something like this really be able to prevent weed growth weeks later?  Soil tests, BTW, are out of the question due to cost.  24.93.116.128 (talk) 00:57, 12 August 2009 (UTC)
 * If you think it is vandalism then the police might do the soil tests for you. --Tango (talk) 01:36, 12 August 2009 (UTC)
 * A pity that your solution won't work; a day or two after the garden died, we (i.e. my family and I) notified the local police, and the opinion of the officer who came helped to solidify our idea that it was vandalism, but he said nothing about the police paying for it. They've been laying off policemen for budget reasons lately, so I'm sure that there's no money for soil tests.  Thanks for the suggestion, though.  24.93.116.128 (talk) 02:34, 12 August 2009 (UTC)
 * How about your insurance company? --Tango (talk) 03:44, 12 August 2009 (UTC)
 * Seems... unlikely. The problem is the stakes are very low. It's hard to get anyone official interested if the crime is minor (though annoying) and the property loss is low (though very, very annoying). They aren't going to rate this higher than someone spray-painting the fence, even if, to a gardener, this sort of thing rates rather higher (and represents a lot of lost work). --98.217.14.211 (talk) 16:44, 12 August 2009 (UTC)
 * Responding to the original question - there is a product called Ortho Ground Clear that says it will prevent growth for up to a year. It is freely available at most US hardware and home improvement stores, and I'd imagine there are similar products from other manufacturers.  The active ingredients seem to be glyphosate, which also becomes inactive upon contact with soil, and would cause the quick kill of any plants; and imazapyr, which I deduce would be the compound that adds the year long growth prevention.  --<font color="#3EA99F">LarryMac <font color="#3EABBF"> | Talk  12:04, 12 August 2009 (UTC)
 * Glyphosate is a slow-acting weedkiller - it takes at least a week or two before treated plants show visible signs of wilting. For immediate results you need something like Paraquat. AndrewWTaylor (talk) 12:52, 12 August 2009 (UTC)
 * I'm genuinely confused - what is in Roundup that makes plants wilt within a couple hours? --<font color="#3EA99F">LarryMac <font color="#3EABBF"> | Talk  13:52, 12 August 2009 (UTC)
 * Likely a good surfactant that delivers the glyphosate more quickly. I would have just answered this question with "Roundup" in the first place. Specially since I know how to get the Roundup that farmers use, approx 10x the concentration for consumers. Franamax (talk) 16:55, 12 August 2009 (UTC)
 * What a dick move that was! You have my sympathies.  --Sean 14:32, 12 August 2009 (UTC)


 * Poisoning the earth isn't vandalism, it's war. Vranak (talk) 15:09, 12 August 2009 (UTC)


 * There are weedkillers that prevent regrowth for many months. Some examples are simazine and amitrole. These chemicals remain in the soil and are taken up by the roots of any new growth.    D b f i r s   17:57, 12 August 2009 (UTC)


 * Yes but when someone else is treating your garden with simazine? Vranak (talk) 19:41, 12 August 2009 (UTC)

Thermal cleaning of high carbon steel
In our research we need to reduce organic contaminants to a very low level. With aluminum implements, we routinely do this by baking them in air at a few hundred degrees C to force any organic compounds to boil away as CO2 and similar gases. (Note that this is not just about killing microbes, but actually removing their organic residues.)

Now I am trying to do something similar with a new tool that is high carbon steel. However, if I use the same settings as I do for aluminum, the iron in the steel will oxide (essentially causing the tool to rust). Obviously that's no good. Does anyone know how hot one can make steel before it begins to oxide significantly? Dragons flight (talk) 23:41, 11 August 2009 (UTC)
 * Surely a few hundred degrees will be safe? Aren't oven wire racks made out of steel? Unless you are talking about some oven that goes over 400 deg c. I would think 200 - 300 deg would not cause any reaction from the steel.. I suppose you're after something a bit more assuring then someone's opinion. Vespine (talk) 00:06, 12 August 2009 (UTC)
 * Could be oven racks are coated steel? Otherwise they would rust if you washed them.  Googlemeister (talk) 16:39, 12 August 2009 (UTC)
 * Well my oven actually goes to 1000 C, but experimentally, 350 C seems to be too hot for this particular tool. Regardless of people's opinion, I'll obviously be testing it, but it will save me some time if I have a decent idea of roughly where the limit is.  Your comment about ovens is a good one.  It would be rare to see an cooking oven much over 250 C, and I suspect you are right that they use some kind of steel.  Dragons flight (talk) 00:27, 12 August 2009 (UTC)


 * This book (US Bureau of MInes) says that steel gauze heated to 'below bright red heat' has 'no serious oxidation'. Special atmospheres (dry, neutral gases I'd guess) are sometimes used for such purposes. Maybe you can call a sword-making expert? Twang (talk) 07:20, 12 August 2009 (UTC)


 * I don't really know much about it but think you ought to try make a sacrificial anode (I know these are normally for wet lower temp rust). It is possible it is only rusting because you are using a less reactive metal to hold it? Anyway try clamping a bit of zinc to it and heating them together? Otherwise I think you would need more info on the type of steel to guess a temperature--BozMo talk 09:56, 12 August 2009 (UTC)


 * We discussed a boiler explosion on the steamship Norway at this Ref Desk, above. See the "Conversions" thread. The steel of the boiler operated at 538F. Chemical were used to keep oxygen from corroding the steel. So look into techniques used with modern superheat boilers. Boilers with superheated steam can get quite hot. Boiler says the superheat tubes may get to 1600C. Chemical, some of the toxic, may be used to scavenge oxygen. Edison (talk) 15:30, 12 August 2009 (UTC)


 * Just guessing here, but what about acid-pickling the steel instead? Then distilled water wash and mild drying. Franamax (talk) 16:59, 12 August 2009 (UTC)