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January 6

Chameleon colour change

Chameleon says that they change colour by adjusting the spacing between guanine crystals. Is it known how much energy that process takes, is it conscious or unconscious, and does it "hurt"? -- SGBailey (talk) 07:51, 6 January 2017 (UTC)[reply]

I looked at the reference in that article in National Geographic, which mentioned Michel Milinkovitch; searching PubMed I found relevant papers at [1] and [2]. Part of this pathway is familiar - the red and yellow pigments are pteridine (biopterin and sepiapterin) which occur widely in nature. Pterins are named for being isolated from butterfly wings, but they are chemically related to guanine which forms the other part of the system and forms part of DNA's structure. The way that the red and yellow pigments are distributed within cells is also familiar - we have much the same in melanocytes when getting a suntan, though not so quickly. Redistributing granules in cells is familiar from neurons, which are distantly related to melanocytes, e.g. retrograde transport. It's not something normally at the level of physical sensation, I would say. The change in structural color was induced in the lab by mechanical pressure or osmotic pressure, but I didn't quickly notice an explanation of control by the nervous system. It's probably something moderately interesting.

The first paper explains though that there are two species of chameleon, one of which redistributes granules to create green color by a combination of yellow + structural blue; the other uses structural green for the same shade. I think you could make an argument that if this were an exceptionally tiresome or painful process, you wouldn't have one species circumventing some of the shade changes and the other not (well, that's sort of weak). And of course you can make an ad hoc argument that a well evolved species shouldn't feel pain from doing what it's designed to do. (human childbirth is a notorious exception from that, but I take it to mean that humans are not a well evolved species, but something relatively new with massive increases in head size) Neither of these are really very persuasive though; ultimately you would need to do more studies. Wnt (talk) 12:54, 6 January 2017 (UTC)[reply]

Clarification please When the OP asks is it "conscious or unconscious", did they perhaps mean "voluntary or involuntary"? DrChrissy ^(talk) 20:17, 6 January 2017 (UTC)[reply]

I have not been able to find a direct study on the energetics of colour change but it appears that up until 2009, this had not been studied - see here[3]"Whether there are significant costs of colour change remains to be demonstrated but could be tested by, for example, comparing physiological performance or fitness of individuals exposed to uniform backgrounds (minimal colour change) with those repeatedly exposed to diverse backgrounds (frequent colour change)." DrChrissy ^(talk) 21:00, 6 January 2017 (UTC)[reply]

So nothing really conclusive, but I thank you for your insights. -- SGBailey (talk) 22:29, 6 January 2017 (UTC)[reply]

If, as it says here they use it to signal their intentions to other chameleons, I would presume it would be under their conscious control for that purpose. Richerman (talk) 16:38, 8 January 2017 (UTC)[reply]

January 7

Talc containing asbestos

I know from Talc#Asbestos link that talc shares source locations with deposits of asbestos. Big name talc products like, say, Johnson & Johnson, are sold in China. Could talc sold in China from such a company contain asbestos? Is talc sold in China from China talc sources? Is talc and asbestos having co-locations a global geo-thing? Thoughts? Anna Frodesiak (talk) 00:05, 7 January 2017 (UTC)[reply]

Asbestos can be white, so if ground into a powder it might look like ground talc. Also, if the same company makes both, they could confuse bags of each, as happened with PBB. See Polybrominated_biphenyl#Michigan_PBB_contamination_incident. StuRat (talk) 04:09, 7 January 2017 (UTC)[reply]

Apparently there have been accusations of asbestos contamination in Chinese talc products [4]. Some point to more lax oversight of talc mining and testing in China, as compared to the US or the European Union. Someguy1221 (talk) 04:16, 7 January 2017 (UTC)[reply]

Holy moly, Someguy1221. I'm switching to corn starch. Thanks. Anna Frodesiak (talk) 08:04, 7 January 2017 (UTC)[reply]

Hi StuRat. I do doubt that J&J would mix those up and sell pure asbestos in bags for baby bottoms. And I seriously doubt US J&J talc would have any asbestos, but do worry a bit about possible lax regulations elsewhere. Hopefully it all comes from the same sources and factory and some is just sold here. Thanks for the feedback. Anna Frodesiak (talk) 08:04, 7 January 2017 (UTC)[reply]

Here is a good article on this topic. StuRat (talk) 16:03, 7 January 2017 (UTC)[reply]

Interesting, Stu. Getting ovarian cancer from talc looks unlikely. It is asbestos that worries me. So, it can be made in China, maybe packaged here, sent to US, all very safe. Here, what are consumers buying when the package says J&J? The same bags stuff shipped to US? Same source sans extra expense for step to remove bits of asbestos? Different, cheaper, higher-asbestos concentration product? Maybe even fake J&J? I know what companies do. They sit around tables and weigh out costs of cheaper processes/product, likelihood of harm, chance of getting caught, cost of lawsuits, potential for loss of sales due to harmed reputation, etc. It's the bottom line that matters to them, not baby lives. So, considering the amount of other products they sell in China, would they dare let asbestos into their talc? Not in US. But elsewhere? Big pharma commonly has drugs banned in the West, then markets them heavily in other nations instead. So, in this case, asbestos, would they dare (gamble)? Anna Frodesiak (talk) 21:47, 7 January 2017 (UTC)[reply]

According to Bloomberg, the sole source of all Talc for J&J Baby powder products is Imerys Talc America, a mining company with mines in nine countries, including the United States, and not including China [5]. Someguy1221 (talk) 21:55, 7 January 2017 (UTC)[reply]

Hi Someguy1221. US source, eh? Thank you kindly for that info. Anna Frodesiak (talk) 04:53, 8 January 2017 (UTC)[reply]

There is a bit of a "no true Scotsman" factor here in that if talc contains microscopically sharp fibers, it's not talc. There is certainly a chemical and mineral similarity between the two. But not all forms of "asbestos" are thought to be hazardous, and asbestos isn't that hazardous (the hazard really is exaggerated a bit for profit, I mean, people used it routinely without thought for decades and the number of people with cancer still wasn't astronomical). On the other hand, talc itself is not really all that safe - it's still ground rock that the body cannot deal with except by physical clearance which may or may not be feasible. (I'm thinking mostly of the lungs - the ovarian cancer seems like almost a red herring, since short of the idiot addicts and dealers who together manage to make it intravenous, it shouldn't usually get that far inland) See [6] for some incidental review of various horror stories like a kid inhaling a large amount of talcum powder at two and having interstitial lung disease at ten. There are a lot of gradations between "safe" and "unsafe", really. Wnt (talk) 02:09, 8 January 2017 (UTC)[reply]

Thank you so much, Wnt. That really puts my mind at ease. :) Anna Frodesiak (talk) 04:53, 8 January 2017 (UTC)[reply]

If you're considering corn starch as an alternative, we should probably do a comparison of the two. One possible disadvantage to corn starch would be if bacteria find it edible, perhaps generating odor. If you try it out and this isn't a problem, then the only other disadvantage I can think of is if it's more expensive. StuRat (talk) 16:35, 8 January 2017 (UTC)[reply]

I really don't want to know how long you're going w/o showering and also you could look online for a price comparison before posting nonsense.--TMCk (talk) 22:13, 8 January 2017 (UTC)[reply]

Hi --TMCk. I'm not sure what you mean. Anna Frodesiak (talk) 01:11, 9 January 2017 (UTC)[reply]

StuRat, good point. I thought of that, that maybe cornstarch on bodies, but especially in beds and cribs could attract odd bugs and things. It is, after all, sprinkling food all over the place. :) As for price, talc is expensive in China. Corn starch is peanuts at around .75 c US a pound. Anna Frodesiak (talk) 01:11, 9 January 2017 (UTC)[reply]

Why sprinkle either on beds or cribs ? StuRat (talk) 05:05, 9 January 2017 (UTC)[reply]

Hi StuRat. Hot weather! It makes everything nice and soft and comfy! :) Anna Frodesiak (talk) 14:36, 9 January 2017 (UTC)[reply]

Since those are used to absorb moisture, I am guessing that sweaty sheets are the problem. That could indicate high humidity, which can be a problem in other areas, like causing mold to grow. I suggest using a dehumidifier and/or an air conditioner to keep humidity down. StuRat (talk) 18:17, 9 January 2017 (UTC)[reply]

Afterburner

Is it true that fighter jets (and in particular the F-16) actually use less fuel in low afterburner (20% or less afterburner) than they do at maximum dry thrust -- in other words, that when you go past maximum dry thrust and into afterburner, the total fuel flow actually goes down before it goes back up? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 10:02, 7 January 2017 (UTC)[reply]

Probably not. Afterburner involves dumping more fuel into the exhaust of the main engine. As such it can't affect the burn rate in the main engine. However, it is conceivable that for a given overall thrust at some speed a lower main engine burn+some a/b might use less fuel than the main engine alone. It is certainly true for some aircraft. What source do you have for this claim? Greglocock (talk) 10:25, 7 January 2017 (UTC)[reply]

Not an actual source -- I was flying an F-16 mission in FSX, and when I turned on the first stage of afterburner (out of I don't know how many) from full dry thrust, the fuel flow went down from 7000 to 4000, so I decided to ask because it didn't seem right. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 13:53, 7 January 2017 (UTC)[reply]

It makes some thermodynamic sense. It is more efficient to add heat to a gas that is already hot. Thus, the exhaust can be made hotter than that which can be allowed pass through the exhaust turbine blades making the whole power unit operate more efficiently. But the more fuel pumped into the after burner, the less mile to the gallon one gets for every incremental increase in thrust. These simulators, model the actually performance fairly accurately so it could be true. What we really need is a ex F-16 pilot that has flown the physical aircraft.--Aspro (talk) 17:17, 7 January 2017 (UTC)[reply]

Ahem. It is more likely that the Air Force will release a detailed official report on the mysterious UFO events at Roswell than that they will release classified aircraft performance data for airframes that remain in service. You could ask anyway! Nimur (talk) 20:38, 7 January 2017 (UTC)[reply]

Following up on this: AviaLogs purports to host a valid, but old, 2003-vintage F16A/B Block 10 & 15 flight manual... but they, too, do not have the performance charts. Now, I don't consider AviaLogs a reliable source - they host all sorts of wonky and weird obsolete manuals even for easy-to-get airframes like the commonplace Cessna 172. In any case, they purport to host this flight manual for the F-16, but I strongly doubt that it is authentic; and even if it were authentic, the important information (including fuel flow rate, along with the entire performance chart appendix) is not included.

Here's a much better and reliable source: a 100+ page book hosted on NASA's technical report server - Effect of Operating Conditions and Design on Afterburner Performance, (1956), (which is clearly punched "declassified.") I tend to believe that this report, hosted by NASA, is actually authentic, although it is some sixty years old and predates the F-16 (...and NASA, for that matter!)

Nimur (talk) 19:15, 8 January 2017 (UTC)[reply]

Try running full afterburnerand timing how long it takes to run out. If you haven't got drop tanks should be less than ten minutes. Otherwise you are being gamed. Greglocock (talk) 20:09, 7 January 2017 (UTC)[reply]

Indeed. This is game physics. The apparently-realistic nature of the game is for entertainment value and it is not an actual model of real aircraft physics. If the designer of the game, or the aftermarket aircraft mod, decided that it would be more fun or just simpler to inaccurately model fuel-flow (or anything else), they'd model that item inaccurately.

Real aviation-grade simulators are way more boring than Microsoft Flight Simulator. For one thing, you don't need any graphics, because the primary purpose of a flight simulator is to be safer and cheaper than flying while wearing a view-limiting device.

Here is a real, actual, non-certificated aviation training device: the Garmin 400W/500W Series Trainer. (It's free, it's quite old, and it only runs on Windows... but a real G530 costs more than your computer and a real G1000 costs more than your car, so... give the free simulator a try first!) Notice that its flight dynamics model assumes a zero-mass, zero-inertia airplane with infinite fuel. Can you fly that model-airplane solely by reference to the simulated instrument? That's the purpose of the simulator! The take-away message is that you, simu-pilot-in-command, must be familiar with the limitations of your simulator. What does it do accurately? What does it do inaccurately? What stuff does it just not simulate at all?

It's great that you're thinking about the fuel-flow, even in FSX - but if your aim is extreme realism, what you really really should do is placard the simulator's fuel-flow gauge INOP and ignore it. Or even more realistically, for the F-16, why didn't your maintenance wing ground this aircraft?

Nimur (talk) 20:38, 7 January 2017 (UTC)[reply]

According to the Standard Aircraft Characteristics the F16 mission profile for combat is 1 minute on (full) afterburner, all the rest is a/b off! That'd make for a very looooong game. Greglocock (talk) 03:08, 8 January 2017 (UTC)[reply]

Well, I had already tried full afterburner during the takeoff, and the fuel flow was something like 50,000 (which sounds right) -- but in lowest afterburner the fuel flow was only 4000 and on maximum dry thrust it was 7000, which certainly doesn't seem right. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 04:35, 8 January 2017 (UTC)[reply]

I'm well aware that our question stems from a flight-simulator scenario, but... this kind of attention to detail during the simulator suggests that we have no ordinary gamer. We're looking for a "realistic" answer to this question. We have a true learning-opportunity.

"That doesn't seem right..." "What's it doing now..." These phrases are literally the textbook examples of things you do not want to be saying in the cockpit. If your equipment is INOP, placard it, ignore it. Immediately. Continue to fly the aircraft safely. Fix it later when you're on the ground. If the INOP equipment was required for safe flight, you are now in an emergency, so declare one and proceed.

The hardest part of an inoperative gauge is admitting that you can not trust its data. Once you decide to ignore that possibly-wrong information, the rest is easy!

You didn't get all the way to flying the simu-F-16 without completing some precursors, have you? Review your basic knowledge about partial panel operations. Is the fuel gauge required for safe continuation of the flight? What does your checklist or standard operating procedure say you should do when you have low (unknown) fuel remaining? Aviate, navigate, communicate, so fly the aircraft, select a suitable safe destination, and simu-radio back in with the "minimum fuel" advisory. ... Or, simu-radio in with a declared emergency. You get to decide.

If you think, for some reason, that combat aircraft are flown in a more cavalier fashion, or that the privileged few who get to fly F-16 "ignore" a minor problem, you are mistaken. A malfunctioning combat aircraft would be grounded until fixed. Even something so minor as a "weird reading" on the fuel flow gauge would ground most military aircraft. The last thing you need, in an air-combat situation, is an unreliable piece of kit up front.

Now, is a fuel-flow gauge always a groundable problem? Heck no. Not for all aircrafts, not for all operations. In the Cessna 172, the pilot manual specifically calls out that fuel readings are inaccurate in some cases: depending on your kit, the fuel flow gauge may have a digital X mark to indicate a measurement failure; the fuel quantity "indicators should not be relied upon for accurate readings..." during certain normal flight operations. Even the "low fuel" annunciator, which is a great way to scare your passengers, can be flakey in some aircraft with particularly sloshy fuel tanks. On other aircraft, like the Citabria, you just have to know that you've got as much fuel as you put in when you took off, minus the precise amount of fuel that is no longer in the tanks, because the fuel gauge is, well, "in an airworthy condition" and that's all you need to know! But those kinds of caveats get called out in the approved flight manual. Does an equivalently-specific advisory exist for the military jet you're simulating, explicitly allowing you to continue safe operation while one of your cockpit instruments is misbehaving? I hope not!

Nimur (talk) 17:39, 8 January 2017 (UTC)[reply]

With respect, you miss reason. With Roswell there was nothing mathematically concrete to expose. Many contractor defence workers may be asked to sign a non-disclosure upon leaving their employ (or suffer a lose of severance pay) preventing them for reviling competitive know-how. In some cases like Corona (satellite) the technology was classified but algorithms are math and in the free world ( US?) algorithms can't be classified, patented nor copyrighted. Algorithms are what these simulators run on and they are free as in beer (Well perhaps not if you buy this book as it costs but look it up on Amazon and the algorithms are there). So the by-pass air has more than enough oxygen to support combustion but it does not lose velocity (momentum) by having to drive the exhaust turbines! So dry stage plus a wet stage combo could produce more thrust than the dry stage alone under certain flight conditions. Which is what I was saying!
You say “A malfunctioning combat aircraft would be grounded until fixed. Even something so minor as a "weird reading" on the fuel flow gauge would ground most military aircraft” really? In war-time do you think you can phone through to the enemy and say “ hold up a moment -we have a few problems to fix”. No they fly anyway (within reason). A fighter may only be delivering a few air to ground missiles but it happens in civilian aviation were they are delivering passengers (men women and children) even if the the aircraft is not 100% Gimli Glider (fuel management problems).
“If your equipment is INOP, placard it, ignore it.” would that have helped the crew of Air France Flight 447? We are talking about complicated aircraft here and you're making it sound as simple as flying a little single engine piston aircraft like my brother did in the Air Cadets (he had not passed his road driving test at the time). So far from convinced. Hope you don't turn out to be a professional airline pilot. If you are, tell me with which airline so that I can fly on a different carrier. Mean that seriously. About the only thing I agree with is don't try to fix a problem in the air. --Aspro (talk) 21:08, 8 January 2017 (UTC)[reply]

Citation needed, you say? Yes, a "weird reading" on a gauge will absolutely provide enough reason to ground a military (or a civil) aircraft. Refer to MIL-HDBK-516B, Airworthiness Criteria, §8.3.1.2, Fuel System: "Verify that adequate crew station information is available to notify the flight crew of the system operating conditions." In other words, if the fuel system indicator is broken, the aircraft is unairworthy. This is a general guideline and it comes from a handbook published by the United States Air Force, hosted on their website, and it provides numerous additional references, including civil regulations, "Part 23" of the FARs. For example, 23.1337 specifies requirements relating to fuel flow indicator malfunctions. An aircraft for which "fuel system information and status" is incorrectly reported to the required flight crew is malfunctioning and probably is not airworthy - for civil or for military use - until appropriate maintenance action is performed and the aircraft is determined to be airworthy. Real airplanes in real combat get a lot of preventative maintenance to make sure they stay airworthy - but if something breaks, combat pilots don't intentionally operate them while the aircraft are broken.

To your point about Air France 447: a contributing factor was a failure to ignore a malfunctioning piece of equipment. The flight director (a thing on the cockpit panel) presented incorrect indications that may have "led the crew to believe that their actions were appropriate, even though they were not." That's not my opinion: it's the official statement by the government investigators who published the final accident report. Specifically, read about the "unreliable speed indication" procedure, and why the flight crew failed to use it. Yes, a wrong indication on a gauge up front was a contributing factor to that tragic accident. The flight crew's continued use of the unreliable reading also contributed to the tragic outcome.

To your point about road-driving, I am not aware of any requirement for an airman to pass a road-driving exam. Why would that be relevant? In fact, with appropriate preparation, one may solo an aircraft at a quite young age: "You are eligible if: You are at least 16 years old. If you plan to pilot a glider or balloon, you must be at least 14 years old." Very young people can fly aircraft, provided that they meet the stringent requirements to the complete satisfaction of their instructor. In fact, this is specifically outlined in chapter one of the official textbook: "The FAA has adopted an operational training concept that places the full responsibility for student training on the authorized flight instructor. In this role, the instructor assumes the total responsibility for training the student pilot in all the knowledge areas and skills necessary to operate safely and competently as a certificated pilot..."

As far as flying with me... don't worry, I won't be flying you around any time soon... at least for today, the weather is quite bad - low level wind shear and gusts up to 60 knots... so I'm content to stay down today and read all about airplane safety stuff! Consider it a hobby of mine!

Nimur (talk) 23:07, 8 January 2017 (UTC)[reply]

Thanks for providing a reference which backs up what I said. You say “a contributing factor was a failure to ignore a malfunctioning piece of equipment.” no it wasn't a malfunctioning piece of equipment. All an' every one of their six pitot tubes froze up. A multiply failure for which your idea of “placard it, ignore it” doesn’t apply. With the benefit of hindsight, one might say – Well, rely in the GPS ground speed! But as the investigation showed they where trained by Air France to go with the flow – the majority indications. “The hardest part of an inoperative gauge is admitting that you can not trust its data. Once you decide to ignore that possibly-wrong information, the rest is easy!” They where operating five flight computer systems all at the same time. So if all six air speed indicators show zero? And all the three pilots were all qualified... and it is so easy -so you say- and yet the plane still crashed? Your reference also points out that in the September (page 218 a Flight Operations Telex (FOT) of 9 September 2009 recommending, at the next recurrent training course, a session on the simulator at high altitude in normal and alternate law including: 'Manual aeroplane handling, Carrying out the UNRELIABLE SPEED INDICATION / ADR CHECK PROC procedure.' (their emphasis not mine). So the flight manual doesn't tell everything – just like the Bible. Just like that passenger flight that had a complete all engine flame-out due to volcanic dust at the very time it was far too low over the sea to go through the lengthy restate procedure, so the pilots really earned their salary on that flight by performing a short -cut that wasn't in the flight manual. These are complex craft and requires a couple of hundred hours of intensive training before one can become even second pilot. Pointless debate.--Aspro (talk) 00:51, 9 January 2017 (UTC)[reply]

Unknown plant

How is this greenhouse plant called?--Sascha GPD (talk) 11:29, 7 January 2017 (UTC)[reply]

Looks a lot like tobacco to me. Looie496 (talk) 14:01, 7 January 2017 (UTC)[reply]

Not tobacco. If you blow up the image and look carefully you can actually see the green peppers - so it is capsicum. Wymspen (talk) 14:40, 7 January 2017 (UTC)[reply]

Agree it looks like a capsicum, probably impossible to confirm specific variety with any certainty, but maybe bell pepper based on size and shape of the unripe fruit. SemanticMantis (talk) 17:35, 7 January 2017 (UTC)[reply]

Two nations divided by the same tongue. What the Americans call a bell pepper is just called a pepper on this side of the pond. Wymspen (talk) 11:21, 8 January 2017 (UTC)[reply]

I think the American designation is better. We haven't had these things very long; I think I was about 12 (1970?) the first time I saw one in London. Now there's a bewildering variety of the things and we can still only call it "a pepper". Alansplodge (talk) 22:34, 8 January 2017 (UTC)[reply]

If we need to distinguish, we can always call them sweet peppers (or I have also heard salad peppers) - and we do tend to call most of the hotter varieties chillies, or chilli peppers. Most of them also have their own distinct names (eg. Jalapeño). Wymspen (talk) 12:35, 9 January 2017 (UTC)[reply]

Building a snowman when conditions are not optimal

I was taught to build a snowman by creating 3 large snowballs: The snowballs were started by packing together a small amount of snow with my hands, and then rolling that pack through snow that was lying on the ground. Doing so would cause the small snowball to grow. Do this long enough, and eventually a large enough snowball to make snowman was yielded.

This approach is fine, except for when the snow doesn't stick to itself. When faced with such, I often just gave up because the initial pack would not hold or because growing the inital pack took too long. However, we (me and my snowball throwing friends) did discover that the snow that had collected on vehicles often packed together better than the snow that collected on the ground.

Reflecting on that observation makes me wonder what or if there are steps I could take to make unsticky snow more sticky. I'm wondering what factors aid snow in sticking to itself. If I am dealing with snow that is not sticking to itself, are there any practical steps I could do to make the snow more sticky?

68.96.10.72 (talk) 17:17, 7 January 2017 (UTC)[reply]

Packing quality of snow is mostly due to temperature. See here [7] from some discussion, we also have snow ball and snow man. I suspect the snow on cars was better for packing because it was warmed slightly due to the vehicle (car gets solar heating, may have had residual heat when snow fell, etc). If you want to pack snow that is difficult to pack, three things will help: 1) you can apply more pressure, 2) use bare hands to give it some heat (both described at ref above) or WP:OR 3) bring out a spray bottle filled with warm water and spray a small patch before you pack it. Hope that helps, SemanticMantis (talk) 17:33, 7 January 2017 (UTC)[reply]

I was also going to suggest wetting it, but I would use a hose. Wear rubber gloves so your hands don't freeze. Note that the snowman will freeze into ice. StuRat (talk) 19:00, 7 January 2017 (UTC)[reply]

Thanks! The spray bottle had occurred to me, but [8] was a great reference on the matter. Others are welcome to continue, but I have my answer 68.96.10.72 (talk) 19:09, 7 January 2017 (UTC)[reply]

Ah, there is snow and there is snow. Living where to do, I would have imagined you get the fluffy stuff that should makes great snow balls and the more you roll them the bigger they get. Maybe however, your getting the fine floury ice crystals (if you live at an Hillbilly altitude in the Blue Ridge Mountains) that don’t lend well to rolling snow balls. Just go out side and look at is it. Is it fluffy or fine and floury. If floury, move to a better US location. Unless you live in a hilly area where it is great for skiing down hill on. Or am I taking the piste?]].

What is this "snow" you people speak of? I have been living in Los Angeles all of my life and have never seen it "snow" during either of our seasons (wildfire season and mudslide season). :) --Guy Macon (talk) 07:56, 8 January 2017 (UTC)[reply]

This article covers the history of snow in LA in some detail. The last major snowfall was in 1949, and the last snow of any sort was in 1962. Tevildo (talk) 10:46, 8 January 2017 (UTC)[reply]

~~Interestingly, those exact years are remembered here in northern England for heavy snowfall that lasted for months.~~ Dbfirs 12:10, 8 January 2017 (UTC)[reply]

You're sure you're not talking about 1947? 1949 had record high temperatures. 5.150.92.20 (talk) 12:23, 8 January 2017 (UTC)[reply]

Oops! Sorry, it was 1947, so there isn't the coincidence/link that I thought I saw. The summer of 1949 was indeed hot. Dbfirs 13:06, 8 January 2017 (UTC)[reply]

Being LA, you don't even have to roll your own.[9] DMacks (talk) 10:56, 8 January 2017 (UTC)[reply]

I know you are being factitious, @Guy Macon, but there are snow sports 2½ hours from Santa Monica beach. LongHairedFop (talk) 11:29, 8 January 2017 (UTC)[reply]

Or facetious, even. 5.150.92.20 (talk) 12:08, 8 January 2017 (UTC)[reply]

Hmmm. After years of dealing with conspiracy theorists and pseudo-scientists on Wikipedia, I think I can do a fair imitation:

Ha! As clearly shown in these references[10][11] that "snow" is FAKE! In Los Angeles, you can even order up a bunch of "snow" with real penguins!![12] --Guy Macon (talk) 14:57, 8 January 2017 (UTC)[reply]

As DMacks alludes to: If one hasn't seen snow in LA, you obviously aren’t getting invited to the right parties. Nor had a snowball. Ho Ho.--Aspro (talk) 16:25, 8 January 2017 (UTC)[reply]

January 8

Euginic is base from correct evoltion science?

If no, can explain why is wrong science? If yes, what evoltion scientist think about discrimation base from euginic? Sorry for bad English. --Curious Cat On Her Last Life (talk) 08:50, 8 January 2017 (UTC)[reply]

No, because it entirely overlooks the effects of genetic defects arising from spontaneous mutation -- effects which are amplified by inbreeding. (Also the reduced resistance of an inbred population to infectious disease, kind of like what we're seeing right now with bananas.) To be honest, though, these effects were not fully understood when eugenics started out -- so it's more precise to say that eugenics are not so much "flat-out wrong" science as they are outdated science. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:36, 8 January 2017 (UTC)[reply]

We have an article on eugenics. Historically, the problems with eugenics were that A) People assigned to genetics traits that are not genetic in origin, such as criminality or poverty, and B) People who have promoted eugenics are frequently mind-bogglingly racist or otherwise so bigoted their decisions have nothing to do with actual science. I'm sure there are scientists (of evolution and otherwise) who would support the elimination of clearly deleterious genes through either genetic engineering, selective abortion, selective fertilization, or voluntary non-reproduction. Genes for diseases like tay sachs or Huntington's, which are not believed to confer any advantage to the carrier. But given that research ethics is such an integral part of modern science education, I doubt many would support involuntary means of getting rid of these genes. You can read about some of this at History of eugenics#Modern eugenics, genetic engineering, and ethical re-evaluation. Now, this is very different from the original idea of Eugenics. Back in the early 20th century, there was some Nietzshean fantasy of creating more perfect humans through eugenics, rather than simply eliminating a handful of rare deleterious mutations. And as I said before, back when these ideas were young, this lead to totally unscientific things like the Holocaust, or limited American attempts to get rid of poverty through forced sterilization, which suspiciously looked like attempts to get rid of black people (see: Eugenics in the United States). Someguy1221 (talk) 09:29, 8 January 2017 (UTC)[reply]

Well, how do we actually know that there is no genetic component whatsoever to criminality??? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:36, 8 January 2017 (UTC)[reply]

We don't know even now. The problem is, that didn't stop people from trying to get rid of it. Someguy1221 (talk) 09:47, 8 January 2017 (UTC)[reply]

We don't. But we know that environmental factors are more significant hence the U.S. violent crime rate is 5 times higher than other developed nations. TFD (talk) 11:08, 8 January 2017 (UTC)[reply]

Additionally, "crime" refers to a whole host of activities, the only completely unifying factor being that the authorities have forbidden them and set specific types of punishment for those who commit them. I think its extremely unlikely that murder, trespass (which isn't a crime where I live, but is in some countries), libel, and watching videos in places the copyright notice says you shouldn't could all have the same genetic cause. (Unless it is simply a genetic propensity to not always obey rules). Besides, even if there was a genetic propensity to any of these activities, it would probably be linked to things that you wouldn't want to breed out of the population. Iapetus (talk) 14:11, 9 January 2017 (UTC)[reply]

^{[Citation Needed]}. Our article on List of countries by intentional homicide rate says that you are wrong. It is higher than most, but not five times higher. According to our article on Sex differences in crime, men account for 80.4 percent of persons arrested for violent crime, so we know that genetics plays a very large role. --Guy Macon (talk) 15:10, 8 January 2017 (UTC)[reply]

Correlation does not imply causation. --Stephan Schulz (talk) 21:41, 8 January 2017 (UTC)[reply]

That is by far the worst application of the "correlation does not imply causation" argument I have ever seen. Do you think that perhaps committing violent crimes reaches back into the past and causes you to be born male? Or perhaps some third factor causes you to be born male and then 20 years later causes you to commit violent crimes? --Guy Macon (talk) 01:50, 9 January 2017 (UTC)[reply]

Neither. But I believe that it is well possible that a third factor (our historically evolved society with its gender-stereotyped roles and education) causes males to commit more violent crime, without this necessarily having anything to do with XY vs XX chromosomes. --Stephan Schulz (talk) 02:02, 9 January 2017 (UTC)[reply]

Eugenics in all its misanthropic interpretations depends on belief that human character determinism by the genetics of sexual reproduction should be directed by intervention. However when Androcide i.e. systematic male Gendercide occurs, as in July 1995 in the Srebrenica massacre, the misandronist perpetrators are disputing some Casus belli but their act carries no eugenic rationale; their aim is to vanquish the victim group, not to change it genetically. I take this opportunity to commend the above reply by Someguy1221 for his well-thought reponse that concisely gives both historical and ethical perspectives to the OP's questions. Blooteuth (talk) 15:34, 9 January 2017 (UTC)[reply]

Well, cultural factors is probably^{[citation needed]} the explanation, but you might argue physiological characteristics (e.g., testosterone makes you prone to confrontation). I guess you could do some comparison with the ratio of male/female propensity to violence in (say) Sweden (where traditional gender roles have almost disappeared) vs. Spain (ok, that choice comes from a stereotype, but still). Tigraan^{Click here to contact me} 16:05, 9 January 2017 (UTC)[reply]

Comparing countries with reduced gender roles vs where they are still more closely ingrained may be a useful exercise but I think it's quite qustionable to claim they have "almost disappeared". Sure they may be significantly less than in many other countries but see e.g. [13]. Consider also that it's only recently that some toy stores have tried to avoid presenting toys as being for girls or for boys [14] [15], way too recent to be relevant to the crime rate. Likewise these sort of things [16] are still an oddity. This may seem a minor thing, but on the other hand, it may also be an indication of how early gender roles are part of the social fabric.

And I've chosen my words carefully here, whether you believe there is a very strong genetic component to some of these differences so they aren't likely to disappear, or it's mostly cultural/learnt but such a fundamental part that it's very hard to remove especially in an internationalised world is beside the point namely that for whatever reason these are still there even in places like Sweden. As mentioned, this doesn't preclude some analysis from the differences but still care needs to be taken into reading too much into the results considering that we know such roles still exist to some extent. Especially since violent criminals tend to be outliers, even more so in a place like Sweden.

And once you start to look at the details, there are obvious complications. Switzerland was mentioned below, an obvious thought is that as as established below, there is a difference between conscription etc between males and females. (Even considering the average physiological differences which I think many would accept are significantly of genetic origin, is the lowest standard needed for males higher than the highest standard some females can achieve? Even if this is the case, males who can't achieve the standard often aren't exempted but made to do something else.) And Switzerland is also the place where one canton didn't allow women to vote on certain issues until 1991. Yet despite that, in many ways the situation for women was likely generally perceived as better than, giving a random example, in Pakistan where women have been able to vote since 1947. But how do you decide what cultural differences in the roles and rights of men and women could be affecting violent crime rates?

Nil Einne (talk) 05:05, 10 January 2017 (UTC)[reply]

User:The Four Deuces may have been thinking of gun-related homicides: "According to United Nations data, a person is 4.5 times more likely to die from gun violence in the United States than Italy [the next highest G8 nation]. [17] Alansplodge (talk) 20:28, 8 January 2017 (UTC)[reply]

Guy Macon, it is true that the U.S. homicide rate declined from 5 to 3.9, while some developed countries have seen an increase. So the list shows Canada at 1.5, France at 1.2, UK, Germany and NZ at 0.9, Switzerland at 0.5 ans Japan at 0.3. 5X is historically accurate and usually quoted. But lets not miss the issue: the differences can be primarily explained by environment rather than genetics. The Swiss, who are mostly French and German, have a 50% lower homicide rate than France or Germany. Alansplodge, gun-related homicides are only one of the factors in making U.S. violent crime rates higher. TFD (talk) 22:29, 8 January 2017 (UTC)[reply]

That would be the same Swiss that by law require every home to contain a loaded machine gun, right? Yet somehow they have a lower rate of gun-related homicide that genetically-identical neighbors. So that argues environment/culture. On the other hand, of the homicides and other violent crimes committed in Switzerland, the vast majority are committed by males, just as is the case in all other nations. So that argues genetics. The thing is, there doesn't appear to be any genetic difference in violence between races or ethnic groups. Those differences are primarily cultural. --Guy Macon (talk) 02:00, 9 January 2017 (UTC)[reply]

Contrary to NRA propaganda, Switzerland very much does not require every home to contain a loaded machine gun. It requires reserve soldiers in a certain age range to have their service gun (which is usually an assault rifle, which is not, by most definitions, a machine gun) stored securely at home. In particular, it is stored unloaded, and the very limited ammunition supply is stored separately in a sealed (as in tamper-proof seal) container. --Stephan Schulz (talk) 02:09, 9 January 2017 (UTC)[reply]

You are somewhat out-of-date. Several years ago, the Swiss changed the law to allow reservists who live no more than X km from an approved armory to store their weapons at an armory outside their home. Such armories are available in most cities. I don't know how many people have taken them up this new option (it is probably still true that most weapons are stored at home). Also, the official guidance is that service weapons should not just be locked but disassembled in the home with the barrel stored in a separate part of the home from the other components to make theft and misuse more difficult. Both the armory option and recommendation that weapons be disassembled speak to the fact that service weapons are intended for national defense, but are not generally anticipated to be used in personal self-defense. Dragons flight (talk) 08:12, 9 January 2017 (UTC)[reply]

Thanks for the update. I primarily remembered my brother in law's joy at finally being able to return the rifle when he passed some age mark a few years back. --Stephan Schulz (talk) 09:57, 9 January 2017 (UTC)[reply]

Indeed. Alansplodge (talk) 22:35, 8 January 2017 (UTC)[reply]

Eugenics is not really as dead as people like to say - after all, cousin marriage is still prohibited, on rather scant evidence, in many areas. More dramatically, abortion law often carries an exception for rape or incest, which seems like quite a crude way to estimate the psychological burden for the woman but would appear to have a eugenic motivation also. There are also eugenic aspects to the sperm donor industry, and I'd hazard a guess that the eugenic potential of computer dating sites, and their proprietary algorithms, is likely unrivalled in history.

That said, the idea of eugenics is still not merely stupid but palpably counterproductive. A monoculture can work well in the short term, but a changing environment requires access to a broad gene pool. With the present level of ecological disruption, we see hybrid species forming all over the world - killer bees, hybrid West Nile carrying mosquitoes that bite humans and birds alike, and many other invasive species with hybrid roots. This should be a tip-off that organisms are casting about far and wide for new genes to deal with new environments. In the case of humans, of course, there are no other species to work with, but there is a broad gene pool in Africa. As a result we see "Recent African origin of modern humans" migrations of Homo erectus, then Homo heidelbergensis, then Homo sapiens. In each case, evolution has gone back to the deep end of the gene pool to pull out a new species. One of my many crazy ideas is that evolution could do this again relatively soon; that "Pygmies" such as the Twa have superior thought-to-mass ratios and would inevitably be selected for in any sort of interstellar dispersal. In any case, it should be clear that a program of rigorous eugenic purification is only a road toward irrelevance and perhaps even extinction. Wnt (talk) 16:00, 8 January 2017 (UTC)[reply]

"This should be a tip-off that organisms are casting about far and wide for new genes to deal with new environments"? That would suggest that evolution is driven by some sort of intelligent plan - which, I'm sure you know, is not how it works at all. Richerman (talk) 16:58, 8 January 2017 (UTC)[reply]

It's difficult to talk about evolution without it sounding that way, similar to how we say "the Sun rises" versus "the Earth rotates so that the Sun becomes visible at our location". It can be done, but it's painful and time consuming. StuRat (talk) 17:04, 8 January 2017 (UTC)[reply]

Well that may be so, but I think the statement above is a step too far for a science reference desk. Richerman (talk) 17:17, 8 January 2017 (UTC)[reply]

@Richerman: Oh, to be sure, I was speaking in a colloquial and, in my opinion alone I suppose, colorful style. Nonetheless, the "breadth of the net" so to speak with which organisms "cast about" is indeed potentially modifiable by selective mechanisms. For example, the SOS response in bacteria allows individuals to decide on a higher mutation rate in the hope (speaking only poetically, sure, bacteria don't hope) that the potential adaptive benefit outweighs the clear and present danger. There are other claims of adaptive mutation... these are generally seen as dubious, yet I continue to suspect that the phenomenon of DNA methylation is not merely a short term or even short term transgenerational form of epigenetic inheritance, but also maybe a method of designating genes for preferential mutation, even preferential types of mutation. But in the present situation, behavior might be more amenable to modification: organisms exposed to an unusually broad range of landraces in a disrupted environment might choose to discriminate less in seeking a visibly similar mate, for example, causing the degree of genetic diversity within each local population to increase, and permitting a more rapid reassortment of available genetic material. Assortative mating and disassortative mating are only extreme approximations, after all, and that behavior is as much the decision of the individual as anything can be. Wnt (talk) 18:54, 8 January 2017 (UTC)[reply]

One problem with eugenics, or any system where people "pick winners", really, is that people are prone to make bad selections. In the case of sex selection, many places may pick disproportionate numbers of males, messing up the fabric of society. Or we may choose the tall, until people become so tall that it causes medical problems. Or we may choose the thin, resulting in people with inefficient digestive systems, and mass starvation when food supplies are low, and overuse of land for farming at normal times. Even supposed defects, like autism or bipolar disorder seem to produce individuals with extraordinary abilities. StuRat (talk) 16:47, 8 January 2017 (UTC)[reply]

You may enjoy reading about plant breeding and animal husbandry and artificial selection. Maybe inbreeding depression or a hybrid vigor. Also related are genetic diversity, founder effect, and sexual selection. SemanticMantis (talk) 17:49, 8 January 2017 (UTC)[reply]

Vancouver cold this winter

Why has Vancouver in Canada been cold so far this winter? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 18:08, 8 January 2017 (UTC)[reply]

'Cause of the Jet Stream. Latest jet stream weather chart for Vancouver Island. Oh, and before any one says that ain’t cold. It is in comparison that Vancouver normally benefits from the Pacific winds that bring both warmth and a hell of lot of winter rain. Don't understand why Bigfoot bothers to live there in such a terrible climate. --Aspro (talk) 18:27, 8 January 2017 (UTC)[reply]

To amplify a bit, the jet stream tends to divide warm and cold air masses, as a result of the thermal wind relation. Unfortunately our thermal wind article isn't very good.

Cliff Mass discusses the recent situation for your area in a blog post here although it focuses more on the "what" than the "why." You could try following up with Cliff in a blog comment or by email. Shock Brigade Harvester Boris (talk) 18:41, 8 January 2017 (UTC)[reply]

There is an idea of "warm oceans, cold continents" that has been floating around a few years [18]; I remember seeing it had been gaining a bit more traction lately but it is still by no means widely accepted. Wnt (talk) 19:08, 8 January 2017 (UTC)[reply]

Don't know if this is an over simplification but when the jet stream is overhead, it drags bad (or severe changes of) weather along with it. Of-cause, we all know that there is no such thing really as 'bad weather' just the wrong clothing. Suitably fitted, the OP will be as snug as a bug in a rug. --Aspro (talk) 19:22, 8 January 2017 (UTC)[reply]

Or, a better way of putting it is, what's bad weather for the trucker can be good weather for the farmer. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:44, 9 January 2017 (UTC)[reply]

Maybe it's not related, but New Zealand has been experiencing an unusually cold and windy summer since mid-December. Swimming pools are noticing a reduction in attendance. Akld guy (talk) 21:11, 8 January 2017 (UTC)[reply]

What are these little spikes on the beach?

I was at a beach recently (on the Atlantic Ocean) and saw these little spikes all over the edge of the water. This one is probably just under 1" but most are a bit smaller. What is it? — Rhododendrites ^talk \\ 21:05, 8 January 2017 (UTC)[reply]

We have an article on Lanice conchilega or the Mason Worm that cements sand grains together like this. What part of the world do you live in and maybe we can home in to the actual critter. Also, as you have a camera maybe you can dig one up a photo it.--Aspro (talk) 21:20, 8 January 2017 (UTC)[reply]

Umm....======> ? --Stephan Schulz (talk) 21:28, 8 January 2017 (UTC)[reply]

I assume he means to photograph the part currently below the surface. StuRat (talk) 21:36, 8 January 2017 (UTC)[reply]

I parsed "one" as referring to the camera. Damn grammatical ambiguity! --Stephan Schulz (talk) 21:47, 8 January 2017 (UTC)[reply]

The picture was taken in Rhode Island, USA (geotagged if a map is helpful), but I don't live near there so can't go back to dig. :/ — Rhododendrites ^talk \\ 21:39, 8 January 2017 (UTC)[reply]

Hmmmm. That mason worm might just be it! this picture I found when googling looks awfully similar -- just without the top part. That's pretty far from my theory -- that some kind of organic material in the ocean froze and accumulated with the outgoing tide... or something. :) — Rhododendrites ^talk \\ 21:59, 8 January 2017 (UTC)[reply]

Had a similar question about things found on the beach a short while ago. Mysterious beach blobs and the OP got confirmation from emailing the images to Scripps Institution of Oceanography. Don't be shy! Email them today. At low tide there is little point in keeping their tentacles out and displayed. P.S. That is a high quality image. Without it being so crisp and sharp I wouldn't have had a clue as to identification for something so very small. It is clear enough to discount File:Type I fulgurites Florida 1.jpg etc. --Aspro (talk) 22:20, 8 January 2017 (UTC)[reply]

January 9

Alcohol-based hand sanitizer

Does alcohol-based hand sanitizer lose alcohol content to a significantly degree over time? If so, is it known how fast alcohol content is lost? In a half-used bottle of hand sanitizer, does the existence of a significant volume of air-filled space in the bottle increase the rate of alcohol content loss? --100.34.204.4 (talk) 04:44, 9 January 2017 (UTC)[reply]

If left open, then yes, the alcohol, being more volatile, will evaporate first. But the amount of air in any portion of a sealed bottle won't hold much of the total alcohol volume as partial pressure. I suppose continuously opening the bottle top would allow the alcohol to escape at each occurrence, cumulatively reducing the percentage by a significant amount, but hand sanitizer bottles are typically designed so they don't require that. StuRat (talk) 05:10, 9 January 2017 (UTC)[reply]

Steam locomotive speed

What maximum speed a train hauled by a steam locomotive could attain? --IEditEncyclopedia (talk) 06:09, 9 January 2017 (UTC)[reply]

About 200 km/h (125 mph). See Land_speed_record_for_rail_vehicles#Steam. Notably, the world record holder was going downhill at the time and the engine broke in the process. The level grade record holder is not far behind. Someguy1221 (talk) 06:16, 9 January 2017 (UTC)[reply]

If the "could" is a question about possibility, not historical reality, then I suspect the answer would a lot higher for a purpose-build race machine - I see no particular reason why a train driven by e.g. steam turbine shouldn't be able to beat that. --Stephan Schulz (talk) 08:59, 9 January 2017 (UTC)[reply]

Here is one reason. See Hunting_oscillation. So it could be done but you'd need special rail tracks as well. 196.213.35.146 (talk) 10:18, 9 January 2017 (UTC)[reply]

Yes, but that is not caused by the particular motive force - as the other records show, a conventional train on conventional tracks can go over 300 km/h. --Stephan Schulz (talk) 10:28, 9 January 2017 (UTC)[reply]

The Mallard set a record for steam of 202.58 km/hr (125.88 mph) in July 1938. That record was never broken. Akld guy (talk) 09:19, 9 January 2017 (UTC)[reply]

False precision. The dynamometer-car record was only read in whole miles per hour: that's 126 mph.

Classical steam locomotives (reciprocating engine, direct drive) have a very large reciprocating mass. This makes it very hard to have their wheels turn at more than about 10 revolutions per second. To go fast, they need big wheels; Mallard's driving wheels were 6 ft 8 in (2.032 m) in diameter and making them much bigger would be hard and give poor acceleration.

The speed could be increased by, for example, using a steam turbine and electrical transmission and some of these locomotives were indeed build, but the technology only became mature in the 1930s. By then, some countries, like the UK, still tried to push the speed of steam (building locomotives like the Mallard), while others like Germany focussed on diesel-electric propulsion (Fliegender Hamburger) or, like Italy, electric propulsion (ETR 200). Soon it became obvious that the future of fast trains would be electric (although diesel would play a transitional role) and development of fast steam locomotives stopped. PiusImpavidus (talk) 10:24, 9 January 2017 (UTC)[reply]

Also, while steam trains could reach 126 mph, they could only maintain such speeds for a few minutes before things would begin to fall apart -- in fact, during that record run, the Mallard actually suffered a broken big-end bearing and a hotbox (both due to frictional heating of the parts from overspeeding). Diesel and electric trains, on the other hand, could maintain their maximum speed indefinitely as long as the track was clear -- which meant a higher average speed even if the maximum speed was the same. Add to this better low-end torque with the electric transmission (hence better acceleration) and a lower center of gravity (hence higher speeds around curves) and you can see why fast steam trains didn't see any further development. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 12:50, 9 January 2017 (UTC)[reply]

I remember reading, back in the 1980s when I professionally edited a locomotive-centred publication, that in contrast to Mallard's official record-breaking but somewhat self-destructive run (alluded to by Someguy1221, Akld guy, PiusImpavidus and 2601), contemporary US passenger express locos not infrequently ran at up to 120mph without problems, and could readily have pushed the record beyond that of Mallard had it been desired. I suspect little publicity was sought for these performances because they were probably done unofficially to make up time from late running, and the record was not pursued on either passenger or test runs for fear of frightening off customers. (Sadly, the extensive railway library I built up back them was the property of my employers, not myself, so I have long since lost access to it.) {The poster formerly known as 87.81.230.195} 2.122.62.241 (talk) 23:42, 9 January 2017 (UTC)[reply]

Feynman Lectures. Lecture 6 (6-3, 6-4) [19], Lecture 41 (41-4) [20], Lecture 43 [21]. Probability = 33%

According to the example of Lect. 6 we can calculate the probability of distance after 30 steps with length S_rms=1. The probability to go farther σ = P(D>σ) = $\int _{-\infty }^{-\sigma }p(x)\,dx+\int _{+\sigma }^{+\infty }p(x)\,dx=2\int _{+\sigma }^{+\infty }p(x)\,dx=2\int _{+\sigma }^{+\infty }{\frac {1}{\sigma {\sqrt {2\pi }}}}\,e^{-x^{2}/2\sigma ^{2}}\,dx$ .
For σ=S_rms√30 we have P(D>σ)=0.317.
If the step is fixed as +1 or -1 , then we have the probability = 0.362 JPG xmcd.

According to my previous question [22] if we have e.g. 100 atoms in 100 m³ the probability not to find any atom in 1 m³ = (99/100)¹⁰⁰ = 0.366.

According to Lecture 43 (43-1) the probability that the molecule avoids a collision for a time equal to τ (average time between the collisions) is e⁻¹≈0.37.

Is there any connection between all these probabilities?

Username160611000000 (talk) 11:01, 9 January 2017 (UTC)[reply]

You wrote yourself that one is some value of the error function, another is 0.99^100 and the last is exp(-1). So no.

The closeness of the last two can somewhat be explained by

\lim _{n\to +\infty }(1+a/n)^{n}=\exp(a)

. Tigraan^{Click here to contact me} 16:14, 9 January 2017 (UTC)[reply]

- Thank you very much. Username160611000000 (talk) 18:08, 9 January 2017 (UTC)[reply]

Feynman Lectures. Lecture 43. Ch.43-6 Thermal conductivity [23]

...
The thermal conductivity κ is defined as the ratio of the rate at which thermal energy is carried across a unit surface area, to the temperature gradient:

${\frac {1}{A}}{\frac {dQ}{dt}}=-\kappa {\frac {dT}{dz}}.$ (43.41)

Since the details of the calculations are quite similar to those we have done above in considering molecular diffusion, we shall leave it as an exercise for the reader to show that

$\kappa ={\frac {knlv}{\gamma -1}},$

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

Using arguments of Ch. 43-5 I try next: $J={\tfrac {n_{\text{hot}}\cdot v_{\text{hot}}\Delta T-n_{\text{cold}}\cdot v_{\text{cold}}\Delta T}{\Delta T}}$

If . . $n_{\text{hot}}=n_{\text{cold}}=n$ . . we have $J=n(v_{\text{hot}}-v_{\text{cold}})$

$-(v_{\text{hot}}-v_{\text{cold}})={\tfrac {dv_{a}}{dx}}\Delta x={\tfrac {dv_{a}}{dx}}\cdot 2l$

${\tfrac {d(v_{a})^{2}}{dx}}\sim {\tfrac {dT_{a}}{dx}}$

$m{\tfrac {d(v_{a})^{2}}{dx}}=3k{\tfrac {dT_{a}}{dx}}$

$m{\tfrac {2vdv_{a}}{dx}}=3k{\tfrac {dT}{dx}}\Rightarrow {\tfrac {dv_{a}}{dx}}={\tfrac {dT}{dx}}\cdot {\tfrac {3k}{2mv}}$

$\therefore J=n(v_{\text{hot}}-v_{\text{cold}})=-n{\tfrac {dv_{a}}{dx}}\cdot 2l=-n{\tfrac {dT}{dx}}\cdot {\tfrac {3k\cdot 2l}{2mv}}$
$=-{\tfrac {dT}{dx}}\cdot {\tfrac {3nkl}{mv}}=-{\tfrac {dT}{dx}}\cdot {\tfrac {3nkl{\tfrac {v}{2}}}{mv{\tfrac {v}{2}}}}.$
$J\cdot {\tfrac {mv^{2}}{2}}=-{\tfrac {dT}{dx}}\cdot {\tfrac {3nklv}{2}}$
$J\cdot {\tfrac {mv^{2}}{2}}={\tfrac {dN}{dt}}{\tfrac {1}{A}}\cdot {\tfrac {mv^{2}}{2}}={\tfrac {dQ}{dt}}{\tfrac {1}{A}}$

$\therefore {\tfrac {dQ}{dt}}{\tfrac {1}{A}}=-{\tfrac {dT}{dx}}\cdot {\tfrac {3nklv}{2}}$ .

$(\gamma -1)=2/3$

Is it correct ? I'm not sure that in 1-dimentional case we can write mv²=3kT. For 1 degree of freedom we have 1kT.

Username160611000000 (talk) 18:05, 9 January 2017 (UTC)[reply]

Why are the leaves still red?

In January, a tiny plant in my yard still has red leaves. They look like maple leaves, specifically the Acer pseudoplatanus photo with that article, and there are maple trees across the street. However, full-size trees have pretty much lost their leaves, or at least the ones left on trees have turned brown. This plant, a couple of inches tall, is even red below the leaves (the "trunk"). I never saw that.— Vchimpanzee • talk • contributions • 22:11, 9 January 2017 (UTC)[reply]

Were the leaves green before? Apparently the color leaves turn depends on what was in them when the chlorophyll dies off, apparently red leaves have left over "food" in them while brown leaves are more depleted. Vespine (talk) 22:43, 9 January 2017 (UTC)[reply]

A further possible factor: being so small, the plant may be in a more benign microclimate than the conditions to which nearby full-sized trees are overall subject. The article Deciduous may point to some clues as to why your yard-sheltered plant is privileged.

Re the trunk/stem, I've casually noticed myself that some saplings tend to have thinner bark containing a degree of chlorophyll, as contrasted to more mature specimens of the same species, so the sapling's bark can be expected to emulate the leaves' colour changes. {The poster formerly known as 87.81.230.195} 2.122.62.241 (talk) 23:55, 9 January 2017 (UTC)[reply]

There are a number of maple cultivars that have red leaves year round, see for example the later parts of Acer palmatum article. If it has red leaves year round then it may be either one of those, or a natural mutation. Watch that plant for a few years, and see if the trait was transient or persists. Dr Dima (talk) 03:07, 10 January 2017 (UTC)[reply]

Poinsettias are prized for that behavior. StuRat (talk) 04:21, 10 January 2017 (UTC)[reply]

Where can you drive through a redwood?

I didn't find anything on Wikipedia using the normal methods, but Chaz Henry on KKOV says you can't do it any more. A storm has knocked down that tree. I don't know who Chaz Henry is because he never identifies his employer, but sources for this should be easy to find. However, I don't know what Wikipedia article would require updating.— Vchimpanzee • talk • contributions • 22:13, 9 January 2017 (UTC)[reply]

That would probably be the Pioneer Cabin Tree in Calaveras Big Trees State Park. This tree has been all over the local news in Northern California. For example: Remembering California’s storm-toppled historic Pioneer Cabin Tree (from the San Jose Mercury News, January 8, 2017).

I think I mentioned earlier this weekend about how bad the weather was - it's been really wild out there!

Nimur (talk) 22:53, 9 January 2017 (UTC)[reply]

Interested readers, see also: the Wawona Tree and the rest of the trees on the list of largest giant sequoias; and the Chandelier Tree, which is a close relative, a Coast Redwood. Nimur (talk) 22:56, 9 January 2017 (UTC)[reply]

One thing I haven't seen with the pictures that were published: did the Pioneer Cabin Tree crack at the height of the car tunnel? I'm thinking that digging a tunnel through a sequoia may be cool for a hundred years, but in sequoia terms, it's pretty much a killing blow? Wnt (talk) 00:20, 10 January 2017 (UTC)[reply]

Comparing these two pics, taken from near the same vantage point (note the large block of wood on the right side), it looks like it fell backwards from its burn-marked side and the top part of its roots ripped out. One problem with sequoias is that they don't have a particularly sturdy root system. [24][25] ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:24, 10 January 2017 (UTC)[reply]

There are several drive-thru trees in the Redwood Forest in far Northern California. [26] Killiondude (talk) 01:02, 10 January 2017 (UTC)[reply]

Our article links to Chandelier Tree but mentions it is a "coast redwood not a giant sequoia". (Also mentioned by Nimur above.) Looking at the above list, the species isn't mentioned. A quick search didn't find the species for the other two, so I stopped looking. I get the feeling they're probably coast redwoods though. Nil Einne (talk) 06:08, 10 January 2017 (UTC)[reply]

A simple search finds [27] appears to be the person you're referring to but I'm not sure the relevance of his identity to the question. Nil Einne (talk) 05:11, 10 January 2017 (UTC)[reply]

Engineering question: fit, clearance and tolerance

In reference to something written here (but copied and pasted here), I wonder how to consider this because, in my mind, I've got it backwards:

"When two parts are to be assembled, the relation resulting from the difference between their sizes before assembly is called a fit. A fit may be defined as the degree of tightness and looseness between two mating parts."

The important terms related to the fit are given below:

Clearance

In a fit, this is the difference between the sizes of the hole and the shaft, before assembly, when this difference is positive. The clearance may be maximum clearance and minimum clearance. Minimum clearance in the fit is the difference between the maximum size of the hole and the minimum size of the shaft.

Interference

It is the difference between the sizes of the hole and the shaft before assembly, when the difference is negative. The interference may be maximum or minimum. Maximum interference is arithmetical difference between the minimum size of the hole and the maximum size of the shaft before assembly. Minimum interference is the difference between the maximum size of the hole and the minimum size of the shaft."

I have underlined the part that I don't understand and italicized the corresponding part that I do understand. In terms of what I do understand, interference is when there is what we'd colloquially refer to interference; in other words, item X interferes with item Y. So minimum interference would be a maximum hole and a minimum shaft attempting to pass through that hole. But what I don't understand is why minimum clearance is maximum hole with a minimum shaft attempting to pass -- to be, this seemed to provide the maximum (magnitude of) clearance as 'clearance' is understood colloquially. I suppose it could be a typo, but more likely, I speculate it's merely some mathematical convention of assigning clearance with a negative, and so it's the inverse of what may appear to make sense colloquially -- or perhaps I've just got it more wrong than I think. Thanks to whomever is able to help. DRosenbach ^{(Talk | Contribs)} 23:23, 9 January 2017 (UTC)[reply]

I agree that Minimum clearance in the fit is the difference between the maximum size of the hole and the minimum size of the shaft seems to be a lazy cut and paste. perhaps they just meant maximum. Greglocock (talk) 06:34, 10 January 2017 (UTC)[reply]

January 10