Wikipedia:Reference desk/Archives/Science/2016 January 5

= January 5 =

Fighting fire with fire
When fighting fire with fire, how do they know the right time to ignite the backburn? 2601:646:8E01:9089:5D45:D5AF:855B:E677 (talk) 01:16, 5 January 2016 (UTC)


 * Not a subject expert, but I believe the primary issue in when to ignite controlled burns is the weather. The wind needs to be blowing the right way, towards the main fire, and to be reliable: no sudden changes in wind speed or direction. Aside from that I don't think there's a specific time when it's "right" to start the fire (besides "before the main fire is on top of you" I suppose). The basic idea is to burn fuel with a fire that goes towards the fire you're fighting. Then there's nothing left to burn, and the "bad" fire ideally just dies. --71.119.131.184 (talk) 01:52, 5 January 2016 (UTC)


 * There's the aspect of burning the fuel before the main fire arrives, but there's also an effect of changing the direction the air is flowing. Firestorm discusses cases where fires change air flow patterns.  So, in this case the timing would be more critical, since the wind direction can only be changed while the fire is actually burning. StuRat (talk) 02:32, 5 January 2016 (UTC)


 * My only knowledge of this is from seeing it done on television and I can't see anything online that describes it too well so I'll describe what I've seen from memory. As a fire burns it consumes oxygen and, in the case of large fires, they consume massive amounts. As the fire advances it sucks in the air all around it creating a vortex and the base of the vortex extends well in front of it. The firefighters stand in front of the advancing firewall and wait until they feel the air around them being pulled in towards the fire - which becomes pretty obvious as it creates an increasing rush of wind. At that point they light the fuel (forest litter, saplings, branches etc.), retire quickly and hope that the consumption of all available fuel leaves the fire with nothing to burn and nowhere to go. Needless to say, it's very dangerous, it's only used as a last resort, and it can make things worse.,   Richerman    (talk) 11:18, 5 January 2016 (UTC)


 * Perhaps the best place to start reading is: the United States Forest Service webpage, Managing Wildfires. Also note that some states - like California - have massive state-level organizations (e.g., CalFIRE), and though there is much cooperation, these different organizations sometimes follow different rules and strategic policies for fire management.
 * Federally organized wildfire fighters use backburning, including drip torch crews. For prescribed fires - those that are set intentionally for land management - a specialist who is an expert in forestry management writes up an environmental assessment, and a bunch of paperwork process is required to make sure that the burn will be safe and legal.  At a high level, this process is explained in the Guidance for Implementation of Federal Wildland Fire Management Policy document.
 * Here are a few great resources published by our Forest Service:
 * What the blazes is a prescribed fire?
 * Fire Management Today - a free periodical publication: each issue contains case-studies, technology and science reviews, and the latest and greatest news on federal wildfire management
 * The current issue has a whole exposé on using smart-phone apps and other technology for data fusion to combine weather, aerial firefighter reports and photos, and ground crew information, to make better on-the-spot decisions
 * Training Resources - linking to several short courses, training facilities, and other resources to help promote good fire-fighting policies
 * Interagency Prescribed Fire Planning and Procedures Guide, a detailed technical guide from the National Wildfire Coordinating Group that explains how to plan and implement a wildland fire by intentional ignition
 * Forestry is a big deal, and it's very scientific: you can get an advanced scientific degree in forest management, economics, ecology, and industrial applications. Proper management of natural resources is very important, for ecological and economic reasons; this discipline has therefore developed very rigorous techniques and theory.  For example, here is information from the Forest Management program at my alma mater.
 * Nimur (talk) 15:46, 5 January 2016 (UTC)


 * Thanks, everyone! So from what you told me, when the wind shifts toward the main fire is the right time to break out the driptorch?  (BTW, I'm NOT planning to do any controlled burning on my property or elsewhere -- only highly-trained firefighters are allowed to do it because it's so dangerous, that much I know.) 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 05:36, 7 January 2016 (UTC)
 * Weather, including wind, is only one of many factors that are considered. From the reading I did while browsing the sources I linked, it looks like wind and weather actually rank much lower on the list than other items, like paperwork (!), human factors, resource availability, proximity to roads and structures, terrain, and other considerations.  All of that has a bigger impact than the present wind condition.
 * Even if we consider only the weather factors - it appears that fire hazard prediction (largely based on rainfall statistics and forecasts) play a bigger role than winds when firefighters are deciding course of action. Once a burn plan is decided at the strategic level, wind will make a much bigger difference at the tactical level, e.g. for the firefighters on the front lines.
 * Nimur (talk) 15:50, 7 January 2016 (UTC)

Where can I find a map of average daily temperature range in the US?
I can't seem to find one. Average seasonal range is easy to find but not average range between a day's high and low. Sagittarian Milky Way (talk) 01:30, 5 January 2016 (UTC)
 * At yr.no, you can get graphs of average high and low temperatures per month for a specific place, such as Washington D.C.. The data the graphs are based on is fairly old, though, and probably available elsewere as well. --NorwegianBluetalk 07:07, 5 January 2016 (UTC)
 * That would be a lot of work to make even a rudimentary map yourself. I wonder if there's one already made where it shows average daily range. For instance, the average daily range where I live is around 15°F, it should be more where there's more continentality and/or aridity (when I saw one of those charts for Montana I was like holy crap, it's 90°F in the day and 50°F at night). Sagittarian Milky Way (talk) 07:26, 5 January 2016 (UTC)


 * Occasionally, just occasionally, someone will ask a question like this and get really awesome results.   I created the three images at right about two years ago in my professional capacity as Lead Scientist for Berkeley Earth.  I've now arranged to release these images under CC-BY.  The first image shows the average diurnal temperature range and should answer your question.  Note that diurnal range also has a strongly seasonal component, and these are the annual averages.  The second image is a similar map for seasonal temperature range since you also mentioned that.  (Siberia is a hard place to live, though actually not so bad in the summer.)   The last map shows the annual average temperature.  For the record, I haven't added these images to any articles, so if someone can find some suitable page(s) to add these materials it would be appreciated.  Dragons flight (talk) 10:56, 5 January 2016 (UTC)
 * That's very neat, thanks. I put them in a new article continentality cause I didn't want to mess with the important and image-filled climate, climatology and temperature articles. Others are welcome to think of other articles or see if they want to mess with those three. Sagittarian Milky Way (talk) 18:08, 5 January 2016 (UTC)
 * And the article was redirected back to humid continental climate. It wasn't very good but maybe continentality should redirect to continental climate instead? Humid continental is not very accurate as most of Alaska and Siberia is very continental (Verkhoyansk! 99°F to -90°F) but classified as subarctic climate. Sagittarian Milky Way (talk) 22:33, 5 January 2016 (UTC)
 * Great images. What are those two odd spots of large temperature differences in Poland on the first map? Mountainous regions? Fgf10 (talk) 12:08, 5 January 2016 (UTC)
 * No, not mountains. Basically I don't know.  It is an odd enough blip that when I originally made this map I did go back and double check that this quirk was really in the input data, but nothing there looked crazy.  I don't think it is an error or bad data (though I wouldn't totally rule that out either).  If it isn't an error, my guess would be more variable local weather, but I don't have any really convincing explanation for a weather pattern like that either.  Dragons flight (talk) 12:31, 5 January 2016 (UTC)
 * How interesting! Fair enough, cheers for the reply. Fgf10 (talk) 14:54, 5 January 2016 (UTC)
 * Maybe somebody forgot Poland. --71.119.131.184 (talk) 16:50, 5 January 2016 (UTC)
 * Those dots on Poland are interesting. I think the southern one might be the Błędów Desert, a man-made region of barren sand around a medieval silver mine, which our article on Poland describes as the country's "only desert".  My guess is there's another man-made feature that hasn't been properly credited.  Though I should also note that the area of high temperature extremes is bigger than the feature as marked on the map.  Apparently it had been spreading, though recent efforts partially reversed this.  Come back in a thousand years and I suppose much of Europe may be a double for the Australian outback... Wnt (talk) 18:59, 5 January 2016 (UTC)
 * The file pages say that it's extrapolated from weather stations so if the closest stations to the Błędów Desert one(s) are far away that could make it look very big. Sagittarian Milky Way (talk) 22:33, 5 January 2016 (UTC)

What's with the average daily temperature range in Antarctica ?
(Top chart.) There seems to be very little change for the most part, but one spot has quite a lot. Why is that ? StuRat (talk)

How many viable human DNA combinations are there?
Calculations that I found regarding DNA permutations seem to consider all combinations. However, many of these are obviously not viable humans. What is the total number of DNA combination minus the total number of combinations that would produce deeply disable, brain-dead or dead humans?--Scicurious (talk) 16:55, 5 January 2016 (UTC)
 * I doubt this is a question that can be answered (currently), given that we do not know gene expression or even protein folding into usable shapes well enough or fast enough to make such a determination. We're still figuring out even basics of expression such as epigenetics. --OuroborosCobra (talk) 17:00, 5 January 2016 (UTC)
 * Seconded. However, I will say that the vast majority (probably 99.9999%+) won't be viable. There are many proteins that are absolutely required for life, and it may only take a single base pair change for those to be dysfunctional. A random scramble will almost always result in something lethal. Fgf10 (talk) 17:49, 5 January 2016 (UTC)
 * I agree that the number in incalculable, but would argue that the nonviable mutation rate would not approach 100%. There are vast stretches of DNA in which most mutations would be neutral. Even for critical genes, there are databases full of variant genes (e.g. Online Mendelian Inheritance in Man), not all associated with a disease state. There is a bias towards the presence of a disease state in the databases, since health issues are the likely reason a search was initiated. The number of possible viable mutations and the total number are possible mutations are so vast that ratios are difficult to calculate, especially given that the probabilities have to be weighted since not all mutations are equally probable. additional reading BiologicalMe (talk) 18:31, 5 January 2016 (UTC)
 * Ignore User:Fgf10. The answer is potentially infinite, given non-coding junk DNA. μηδείς (talk) 21:09, 6 January 2016 (UTC)
 * Care to explain that one User:Medeis? You are most certainly wrong, since there are not an infinite number of bases in the genome. Also, take into acoount that 'junk DNA' is mostly not actually junk, but regulatory sequences. Fgf10 (talk) 17:41, 7 January 2016 (UTC)
 * Well, in a way it's all academic, since we can't calculate it. However, in your example, OMID mutations are those found in living humans. Therefore you can automatically say none of the mutations that would cause embryonic lethality are in there. In other words, the most lethal mutations will not be in that database. Furthermore, all those mutations are changes to an established, viable genome. If you were to generate a de novo genome randomly, what would be the changes you get even one working promoter for instance? For a viable human, you don't need one correct sequence, you need thousands. Fgf10 (talk) 18:43, 5 January 2016 (UTC)
 * Although as the previous responses have pointed out it is impossible to calculate precisely, I think we can safely say that there is a practically unlimited number of possibilites for a viable human genome. Even if just 0.0001 % of the 3 billion+ base pairs can be changed arbitrarily without effecting viability, you get over 10^1800 possible combinations, vastly more than can be realized in the lifetime of a billion universes. - Lindert (talk) 11:33, 6 January 2016 (UTC)
 * I agree - the answer is definitely "enough". Enough to make it astronomically unlikely that no two humans will ever (by chance alone) have identical DNA for as long as humanity can survive.  But putting a number to it is an exceedingly complicated question who's answer lies far beyond what we currently know. SteveBaker (talk) 17:50, 6 January 2016 (UTC)
 * Lol, independent variables. You know there's an exception. :) Wnt (talk) 20:38, 6 January 2016 (UTC)
 * Well, my wife and I have identical twin girls...so, yeah, trust me, I know. But I did say "by chance alone".  Identical twins are not identical because the dice were rolled and the one in 10800 chance came up.  They are identical because they started out as a single organism and split in two sometime shortly after formation.   They are, in essence,  a single person who was split in two very early on. SteveBaker (talk) 20:13, 7 January 2016 (UTC)

radio-activity
Is it possible for big storages of fissionable material with high ratios of released-binding-energy-expected per unit volume, to release subatomic reaction energy spontaneously causing unintended destruction ? :-) Thank you — Preceding unsigned comment added by Vijay Chary (talk • contribs) 18:33, 5 January 2016‎ (UTC)


 * I think the answer to your question is "no". Now, many fissile elements are radioactive, so they give off energy through radioactive decay, which can include spontaneous fission. This is why particularly radioactive materials need to be handled carefully. But, you're not going to get a nuclear chain reaction unless you do stupid things with large quantities of material (in which case you may get a criticality accident). Generating a self-sustained nuclear reaction, which you need for nuclear power or nuclear weapons, is actually difficult; a lot of people have this misconception that a nuclear reactor can explode like a nuclear bomb, but this is wrong. The problems with nuclear waste storage revolve around safely storing it while it decays. It would cause "unintended destruction" if not stored properly, but through radiation poisoning, not a big kaboom. --71.119.131.184 (talk) 20:14, 5 January 2016 (UTC)
 * A nuclear reactor can explode like a regular bomb, though. Sagittarian Milky Way (talk) 22:37, 5 January 2016 (UTC)


 * I don't know if the bit " a lot of people have this misconception that a nuclear reactor can explode like a nuclear bomb" is accurate. Of course, this depends on your definition of "a lot", but I would be shocked if this is true when "a lot " means "most people." On the other hand, people believe all sort of crazy stuff and one conspiracy theorists or the other would be delighted to scare people. Denidi (talk) 01:17, 6 January 2016 (UTC)


 * The movie Aliens might have contibuted to this misconception, since the nuclear reactor in that movie did indeed undergo a nuclear explosion once it lost coolant. I wonder if there is any way one could, if foolish enough to do so, design a nuclear reactor where this was actually possible. StuRat (talk) 05:42, 6 January 2016 (UTC)


 * Don't they have military-only designs that use weapons-grade fuel? I'm not up on nuclear physics but 1. It'd be really stupid to design it to go supercritical if the rods were pulled out fully. 2. It's not easy to make a nuclear bomb not fizzle if you've never made one before so unless the containment dome does something wonderful in extending the percent that fissions before it blows itself apart it might not be able to reach a traditional atomic bomb size (14-20 kilotons or so). Maybe you could keep tons of bomb-grade fuel subcritical with enough control rods so if you did a really stupid design like control rods that fall completely out of the fuel at the speed of gravity if the positioning electromagnets fail then maybe you could get another Hiroshima. Sagittarian Milky Way (talk) 16:22, 6 January 2016 (UTC)


 * I seem to recall an almost-as-stupid design where, while the control rods themselves would retard the reaction, the steel tips on the end had the reverse effect, by reflecting particles back into the core when first inserted. Thus, if you inserted lots of rods all at once, you could create a runaway reaction.  I think it just caused a conventional explosion, though.


 * I suppose you could also get a rogue nation, like Iran, building a nuclear reactor designed to generate a nuclear explosion, if attacked, to discourage anyone from attacking (whether due to fallout concerns or the political consequences of causing it). StuRat (talk) 21:19, 6 January 2016 (UTC)


 * That was the RBMK reactor used at Chernobyl among other places, except it was graphite, not steel. And yes, it was stupid; the RBMK reactor is a fairly unsafe design built with the first priority being cheap and quick production of plutonium for nuclear weapons, with power generation as a side effect. After the Chernobyl accident they retrofitted the reactors to remove some of the more dangerous parts of the design, including that. --71.119.131.184 (talk) 21:45, 6 January 2016 (UTC)


 * "A lot" doesn't inherently mean "most", i.e. "a majority". It can just as easily mean a significant minority. ←Baseball Bugs What's up, Doc? carrots→ 06:49, 6 January 2016 (UTC)


 * Look at Fissile material for the difference between fissile and fissionable. Also, check out Natural nuclear fission reactor about a prehistoric natural reactor in Gabon about 2 billion years ago, which was similar to your question. Tobyc75 (talk) 20:24, 6 January 2016 (UTC)


 * This is an exercise in semantics, really. A fizzle yield is not exactly a bomb, but it can separate enough hydrogen to blow up a containment building, and once the fallout is on the way you don't want to be there.  Any storage pond of high level radioactive waste is just waiting for the power to go out, the diesel generators to fail, and they start catching on fire and producing a terrible mess.  So call it a really poorly made, really dirty nuclear bomb, and you're at least technically right. Wnt (talk) 20:33, 6 January 2016 (UTC)

anthropology
If some members of anthropoid 'herds' evolved into proto-humanoid 'tribes', why does the community of anthropologists claim that this actually occurred in south afrika ? :-) — Preceding unsigned comment added by Vijay Chary (talk • contribs) 18:33, 5 January 2016‎ (UTC)


 * I took the liberty of splitting your questions into different sections. Anyway, the generally-accepted view that modern humans arose in Africa is known as the Out-of-Africa theory; that article may be informative. There's a lot of evidence for this. I'm not quite sure what you're asking exactly. Our recent (on evolutionary time scales) ancestors were not herd animals; "herd" has a specific meaning in biology and zoology. Primates, including humans, are generally tribal, living in tribes of between a handful to a few hundred individuals. Humans are believed to have lived similarly before the advent of agriculture. (Dunbar's number might be of some interest.) Also, modern humans are believed to have arisen more in East Africa than farther south, though you might be using "South Africa" to refer to all of Sub-Saharan Africa. --71.119.131.184 (talk) 20:14, 5 January 2016 (UTC)


 * Addressing a couple of possible misunderstandings suggested by the OP's wording . . ..
 * A member (i.e. an individual) never evolves into anything. Evolution happens to populations of many individuals over numbers of generations, whereby the carriers of some alleles ('versions') of genes die before reproducing more often, while carriers of other alleles of those genes die before reproducing less often, resulting in a descendant population with different proportions of the differing alleles (in some cases, the proportion might be zero). Accumulations of such allele differences may eventually give rise to noticeable physiological differences.
 * Very occasionally, more major changes (such as a doubling of a whole gene, a whole chromosome, or even a whole genome) may occur which give rise to noticeable differences immediately, and also result in "surplus" genes that can mutate to take up new functions, which might be beneficial, because the original copies of the gene(s) is/are still carrying out its/their original functions.
 * The reason most (though not all) anthropologists think human (or better, hominin) evolution probably took place in East and/or South Africa is because that's where we've found most of the oldest fossils of likely ancestors or near-ancestors of our particular human/hominin species, Homo sapiens sapiens. This however depends in part on where conditions favourable to preserving and finding fossils exist (fossilisation is a very rare event), and where we've looked so far: more discoveries elsewhere could, and might, modify those presumptions, because that's how Science 'works'. {The Poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 21:29, 5 January 2016 (UTC)
 * I disagree with your final statement, that might have been true 100 years ago, but since genetic studies over the last 30 years I don't believe fossils are the reason, or even the main reason why most anthropologists accept the Recent_African_origin_of_modern_humans model. Our article has some good info about the evidence. Vespine (talk) 00:19, 6 January 2016 (UTC)
 * I concur, but the OP's "anthropoid to humanoid" wording was ambiguous as to whether he was asking about (or even understood distinctions between) Homo sapiens, earlier Homo spp, and other/earlier hominins, and therefore what time frame he was taking about. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 12:47, 6 January 2016 (UTC)

Elements past period 7
With the seventh period of the Periodic Table filled in, is it going to take a massive additional effort to get period 8 elements? Bubba73 You talkin' to me? 20:28, 5 January 2016 (UTC)
 * I don't know who the best person to ask is. For anyone answering this question, please try to focus primarily on ununennium (element 119) and unbinilium (element 120) and not too much about elements 121 and up. Georgia guy (talk) 20:39, 5 January 2016 (UTC)
 * Attempts at those two is noted in our ununennium and unbinilium articles. Extended periodic table is our larger-perspective article on "beyond period 7" possible stability details, etc. DMacks (talk) 20:45, 5 January 2016 (UTC)
 * To get 119 and 120? No. To get anything above that? Yes. Double sharp (talk) 15:30, 6 January 2016 (UTC)


 * The periods of the periodic table are related to the properties of the electron orbits (the periodic table is primarily a tool for chemists, and chemists don't usually care much about what's going on at the nuclear level). The reason heavy elements are unstable meanwhile is to do with the properties of the nucleus (specifically, the repulsion between protons and proton and neutron energy levels within the nucleus). There's no direct link between the two, so synthesizing a light period 8 element shouldn't be much different to synthesizing a heavy period 7 one. It's predicted that period 8 should include some relatively stable elements (where "relatively stable" still means half-lives measured in fractions of a second) in the so-called island of stability. Smurrayinchester 09:45, 8 January 2016 (UTC)
 * The problem with the island of stability is that no one is sure exactly where it is, save that it is around the heavy period-7 to light period-8 region. But if it is at the end of period 7 (around element 112 or 114), then period 8 would be seriously challenging. The current predictions give half-lives rapidly plunging into the microseconds after element 120 for the isotopes we can reach (remember that the superheavy isotopes we can currently synthesize are all neutron-deficient), and nuclides that don't survive a microsecond are not going to make it to the detector with current technology. Already elements 119 and 120 are predicted to be pushing the limits. The borderline of what we currently should be able to do of course has nothing to do with the period divide, but it is coincidentally awfully close.
 * J. V. Kratz incidentally has predicted that the next proton magic number (full proton shell) would be 120, which would very nicely tally with Zagrebaev's prediction that beyond 120 the atoms wouldn't make it to the detector in one piece. Double sharp (talk) 10:25, 8 January 2016 (UTC)