Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

December 2

RMWI?

Hello, as a part of my grade 11 chemistry assignment, we have to write a report on the arsenic levels in chicken, and how much of it is consumed in a sample of ten people. One of the questions it deals with is to find the "Recommended Maximum Weekly Intake (RMWI) for each person." Now, the only thing we were given was the toxicological reference value (TRV) of chicken being 0.024µg As/kg BW per day, and so we had to research the RMWI ourselves. This link gives the formula:

${\frac {TRV\times BW\times 7}{CF}}$ , where
TRV = toxicological reference value (µg/kg body weight/day)
BW = body weight (kg)
CF = concentration in food.

I tried the equation, using the TRV value given (0.024 µg/kg) and the weight of a sample person (68kg), but I do not have the concentration in food, nor could I find it online. Does anyone have any idea of what this concentration could be, or if there is a better formula available? Thanks. 50.101.203.177 (talk) 00:19, 2 December 2013 (UTC)[reply]

I'm not absolutely sure, but I think your 0.024 ug/kg is the 'concentration in food' where the people are concerned, and what you still need to get is the reference value for how much arsenic a person can consume in ug/kg body weight/day.... nay, wait a minute, the figure you gave is an intake per day for the chicken, hmmm. Are you sure about that? Which are you calculating this for - what maximum intake of ?grain? is needed to keep the chicken meat below a specific arsenic concentration, or what the maximum intake of chicken is to keep the level of arsenic in the humans below a certain level (and if so what level?) Wnt (talk) 01:49, 2 December 2013 (UTC)[reply]

Quick reality check: [1] [2] [3] has people talking about 0.6 to 3 micrograms of arsenic per kg of chicken, with the organic people crowing and cackling about the lower level in their product because they don't use roxarsone. Jeesh, the commercial folks should take a page from the laetrile salesmen and call it "vitamin As" :) Anyway, I have to recognize you are giving me a ug/kg/day figure then, not a ug/kg figure. I think there's something missing in the definition of this problem. Wnt (talk) 01:54, 2 December 2013 (UTC)[reply]

Oh, and according to [4] the dosage of roxarsone is "22.7 to 45.4 g roxarsone/ton feed"; assuming a metric ton (1000 kg) for now, that is 22.7 to 45.4 mg/kg of roxarsone, which is 75/263 arsenic... hmmm, that seems waaay higher than the figure given. Even the organic chickens ought to be getting much more. Hmmm, I should return here and see if I slipped up. Wnt (talk) 02:00, 2 December 2013 (UTC)[reply]

I'm guessing the CF in this case would refer to arsenic concentration in chicken meat, and the TRV to maximum arsenic intake from chicken alone (considering that other foods and drinks may also contain As). In that case you still need the arsenic concentration in chicken meat; the FDA limit is 500 ppb or 500 ug/kg (and 2000 ppb for chicken liver). But that's huge in comparison with 0.024 microgram/kg BW /day, it gives you an RMWI of only 22.8 gram for someone weighing 68 kg. This study from 2006 lists arsenic content in chicken meat from several suppliers. In uncooked chicken the maximum found was 21.2 ppb, In fast food chicken the Church's chicken thighs contained 46.5 ppb. The 21.2 would result in an RMWI of 530 grams for the same person. So it all depends on which value you take for CF... Ssscienccce (talk) 16:27, 2 December 2013 (UTC)[reply]

California coastal oak balls

I am going nuts. Every year I see the acorns on the ground & I see them in the trees. However, I also see these perfectly round balls on the ground & for the life of me I can't find any in the tree. Where do they come from? Are they formed from the acorn top left in the tree? Many thanks! — Preceding unsigned comment added by 24.23.237.218 (talk) 01:37, 2 December 2013 (UTC)[reply]

They are probably some type of oak gall. μηδείς (talk) 02:47, 2 December 2013 (UTC)[reply]

Maybe, but it would be helpful to have a picture. Looie496 (talk) 16:39, 2 December 2013 (UTC)[reply]

A Sex Change (Dramatically) Changing One's Sexuality?

Is it possible for a sex change (especially the hormone replacement therapy, et cetera) to (dramatically) change one's sexuality (such as previously being completely or predominantly attracted to females and then becoming completely or predominantly attracted to males)? Also, if so, then how frequently does such a (dramatic) change in one's sexuality occur in such cases? Thank you very much. Futurist110 (talk) 05:18, 2 December 2013 (UTC)[reply]

Yes, I have seen a documentary (I'll look for it) where female to male post-transexuals have changed orientation. This article suggests heterosexual males who have transitioned to females become attracted to males at a significant rate (6 out of 20). μηδείς (talk) 05:37, 2 December 2013 (UTC)[reply]

This article suggests that 40% of presumably female-attracted female to male transexuals become attracted to gay men to some extent within 10 years of transitioning. μηδείς (talk) 05:41, 2 December 2013 (UTC)[reply]

It must depend on the person's will to change. There is probably a placebo effect. The effect of hormone therapy vis-a-vis sexual attraction may reduce with age. The reason why I don't believe that hormone therapy inherently changes sexual preference is that a standard and commonly used treatment for men with prostate cancer for 40 years has been hormonal therapy (there are other treatments - eg surgery) as prostate cancer is hormone dependent. The hormone dosage is sufficient to stimulate breast growth, and in some cases the breasts can be quite prominent. A workmate of mine aquired breasts about size 42C - looked at little odd on a 6 foot 3 inch muscular man. But such men do not change partner preference. There is usually some loss of libido. If the man has difficulty getting an erection (say due to circulatory issues or diabetes), the hormone treatment may kill it off completely, but they are still men and they still want real females. There is of course no way that other sex change procedures (eg cosmetic surgery) can change one's preference. 58.169.252.71 (talk) 10:16, 2 December 2013 (UTC)[reply]

Hormone replacement therapy is more than just estrogen pills. A trans woman who has not had reassignment surgery or an orchiectomy will still produce testosterone, which is why she would also be on spirolactone or some other androgen antagonist. If she elects for one of those surgeries, then her body will no longer produce testosterone at all. Her estrogen dose would also be designed to raise her bodie's estrogen level to one similar to other women. Progesterone is also commonly used to encourage some of the physical feminization. This means you can't just compare the medical effects of estrogen for prostate cancer to those for HRT. The majority of trans people I know have had confusion about their orientation in the past, likely due to gender issues, and then settle on something as they figure themselves out during transition. In my case I went from thinking i was straight man to a bi man, then realizing I was a woman and for a while identifying primarily as a lesbian right in the middle of the hard parts of the realization and early transition, then back to being a bi woman as things settled down, and that was all pre-HRT. I would describe those shifts (except for maybe straight to bi) as real, and they had nothing to do with transition related medical procedures - it was all personal development as I learned more about who I am. Hormones and other procedures end up having a profound mental effect on trans people, so even if there isn't a direct medical link, I can understand the personal development that comes along with finally having a body that matches one's gender identity leading to changes in orientation. Katie R (talk) 12:47, 2 December 2013 (UTC)[reply]

This doesn't sound treatment-wise much different to hormone therapy for prostate cancer. Such treatment includes drugs to stop testosterone production (it won't stop it completely, but then neither will sex change therapy, in any case some testosterone is present in natural females) plus optionally an estrogen or estrogen analogue course. Other androgen receptor blocking drugs are also used in some cases. It sounds from your post that rather than the hormone treatment driving a change in partner preference and persona, it just made it mentally easier to achieve an orientation you wanted or subconsciously had built in anyway. In contrast, men with prostate cancer don't want to change partner preference or their own sex persona, and are not a feminine person trying to get out, so they don't change, regardless of the treatment. All the best for your future though Katie. 58.169.252.71 (talk) 15:28, 2 December 2013 (UTC)[reply]

That's interesting to know - I've heard the estrogen side mentioned several times, but not the anti-androgens, but I've never really looked into prostate cancer treatment. It just happens to come up in discussions of HRT sometimes. But yes, aside from pointing out what I thought was different in the treatments, the main point I was trying to make was that there is a lot going on on the mental side of things, and even if a specific procedure doesn't have a direct medical link to orientation changes it can still trigger the change as a part of the personal development going on at the same time. I think we agree there - I just wanted to explain to the OP how those sorts of changes can happen during transition regardless of the specific medical procedures involved, because it sounded like he might be interested in orientation changes in general, even though he mentioned medical procedures in the question. Katie R (talk) 16:12, 2 December 2013 (UTC)[reply]

Here's part one of at least on of the documentaries of which I was thinking above: http://www.youtube.com/watch?v=-c9ZnpMppHQ. μηδείς (talk) 02:05, 3 December 2013 (UTC)[reply]

If you watch part 3/4 of this documentary, the men and women discuss for a bit the statistics and their personal experience with orientation changes after to the physical changes. It is very interesting that heterosexual men tend, if they change, to become heterosexual women, while lesbian females often become gay males. μηδείς (talk) 01:45, 4 December 2013 (UTC)[reply]

Thank you very much for all of this information. I will definitely check out all of it in a little bit. Sorry for the late reply, but I was pretty busy with school-related things in the last couple of days. Futurist110 (talk) 16:57, 6 December 2013 (UTC)[reply]

Autonomous vehicle

Has any autonomous vehicle, other than spacecraft, circumnavigated the world? --140.180.255.56 (talk) 08:07, 2 December 2013 (UTC)[reply]

There is nothing listed at List of circumnavigations but it looks as though such a feat is now theoretically possible [5].--Shantavira|^{feed me} 12:28, 2 December 2013 (UTC)[reply]

Yes, and I can think of 3 different ways: airplane (although here fuel might run short), helium or hydrogen balloon, and boat. A land vehicle would also be possible, if not for the fact that the trip would be interrupted by oceans. StuRat (talk) 12:41, 2 December 2013 (UTC)[reply]

You can think of 3 ways, but have any of them ever been done? --Bowlhover (talk) 22:07, 2 December 2013 (UTC)[reply]

There is a team working on a robotic, solar powered boat that will, or has done this. I remember reading about it some time ago. 217.158.236.14 (talk) 13:36, 2 December 2013 (UTC)[reply]

Doubt it has happened yet, some google results about the idea itself (forums etc), but nothing on it having been achieved. Shouldn't be too hard for a balloon or airship, specially if you make it buoyancy neutral at some fixed height. Judging by the global wind patterns all you need then is launch it with the trade winds. Ssscienccce (talk) 16:49, 2 December 2013 (UTC)[reply]

This has actually been done by a superpressure balloon (a type of stratospheric weather balloon), but I forgot the name of the reference. 24.23.196.85 (talk) 00:32, 3 December 2013 (UTC)[reply]

From Aerobot#The Mars aerobot effort:

The French had already conducted extensive experiments with solar Montgolfieres, performing over 30 flights from the late 1970s into the early 1990s. The Montgolfieres flew at an altitude of 35 kilometers, where the atmosphere was as thin and cold as it would be on Mars, and one spent 69 days aloft, circling the Earth twice.

but I agree with Dismas below that this wouldn't meet the requirement of being being autonomous. -- ToE 13:32, 4 December 2013 (UTC)[reply]

I am not sure what you mean by autonomous, but Steve Fossett flew around the world in a balloon. μηδείς (talk) 21:26, 2 December 2013 (UTC)[reply]

He means an unmanned vehicle that isn't remotely controlled. See for example autonomous underwater vehicle or autonomous car Ssscienccce (talk) 22:39, 2 December 2013 (UTC)[reply]

There has been discussions of using a novel wave-powered craft to do this - without the need to carry fuel, and with simple satellite navigation, it seems plausible that a very small craft could make the trip. That would make it a fairly cheap device (by the standards of other circumnavigation efforts) - but there are no reported successes as yet. Liquid Robotics have a device called "Wave Glider" that is a semi-submersible powered by waves and solar cells. The craft is around 7 feet long and looks like a surf-board with solar panels on the top. The Wave glider has successfully travelled 9,000 miles on a year-long autonomous mission as a part of the "PacX" challenge to cross the pacific and holds the current Guinness world record for autonomous travel. The accepted minimum distance for a "circumnavigation" is 24,800 miles (40,000km) - so this craft has managed more than a third of that and there is no reason to assume that it couldn't complete the entire journey if so desired. The Suntory Mermaid II (manned trimaran) demonstrates that even a 3 tonne vessel can be propelled by wave-power alone at between 1 and 2 knots - so even if a much larger vessel is required, this is clearly "do-able". But at a speed of 1 to 2 knots - covering the required 40,000 km will take at least 11,000 hours and probably more like 22,000 hours (30 months!). That means that the reliability of the craft - especially in extreme conditions - becomes a critical matter. Having something that can survive the worst weather conditions continuously for two or more years at sea is not such a simple problem to solve I suspect!

Since we have had successful non-stop circumnavigations in an aircraft (Virgin Atlantic GlobalFlyer), it ought to be possible to program a drone-pilot to make the same trip in a similar craft (the necessary additional computers, cameras and batteries being lighter than the pilot and engineer from the manned trip) - but since there isn't really a compelling record to be broken, I doubt people are working towards doing that. SteveBaker (talk) 00:12, 3 December 2013 (UTC)[reply]

As far as surviving bad weather at sea, I suggest a boat that can detect bad weather and submerge to a safe depth until it passes. StuRat (talk) 08:04, 3 December 2013 (UTC)[reply]

You are probably not going to have an autonomous vehicle transiting the canals (what, with robotic line handlers in Panama?), so it would circumnavigate via the great capes, and what passes for good weather in the southern ocean is bad weather elsewhere. Boats there expect to sail during typical gale force winds, and only heave to or tow warps or drogues during stronger storms. Insolation is limited, what with the high latitude and cloud cover, so I suspect that a Wave Glider could cross the Pacific back and forth a dozen times easier than it could circumnavigate via the great capes. Generating electrical power from wind turbines or towed water generators is very practical at those latitudes, and would mesh well with solar generation used is the low winds of the equatorial Atlantic, so it shouldn't be too difficult to build an autonomous sailboat which powers its own sail controls from these sources, but, as others have mentioned, reliability would be the big issue. You need a design which can go for many months in all types of conditions without human assistance unjamming caught lines, replacing chaffed and broken ones, and stitching up torn sails. -- ToE 13:32, 4 December 2013 (UTC)[reply]

I wouldn't discount the possibility of one of these devices making it through the Panama and Suez canals. The machine is capable of navigating via predetermined GPS waypoints - so all it would take would be some arrangement where it would call ahead to request the canal locks being operated for it. But since it's only about the size of a surfboard, it could probably be programmed to sneak into the locks with some larger ship.

Even if it had to go past the capes, because it has no fuel issues, it could loiter until the weather was optimal to do the trip...so now the question is whether the best weather at the cape is worse than the worst weather it successfully managed during an entire year in the Pacific. SteveBaker (talk) 00:45, 5 December 2013 (UTC)[reply]

How about an autonomous, parasitic boat, called the Remora, which suctions onto the hull of ships to go where it wants. Perhaps it could read the ship's transponders and look up the shipping records via satellite to figure out which ship is going where it wants to go. StuRat (talk) 09:23, 6 December 2013 (UTC)[reply]

Speaking to the idea of releasing a balloon into the trade winds, that doesn't seem like it would fit the OP's requirement of the vehicle being autonomous. "Autonomous", in every case I've seen, at least implies that the thing has some sort of control over its own workings. A balloon simply set adrift on the winds has no way of making any changes to altitude, speed, or heading. Dismas|^(talk) 05:13, 3 December 2013 (UTC)[reply]

That's a good point, but how much would it have to do to qualify ? If it just monitors it's progress and then releases gas to descend when it reaches the target, would that qualify ? (I bet it would need to do more than that, though, like change altitude to avoid weather, get into the proper wind currents, etc.) StuRat (talk) 08:01, 3 December 2013 (UTC)[reply]

Certainly you could imagine a vehicle that can inflate or deflate a balloon to control altitude being described as "autonomous" - but only if it does so in order to achieve some degree of control over the flight path. It could perhaps be informed of the wind speeds at different altitudes at its location and autonomously control altitude in order to control direction. However, the amount of information available to it about wind speed versus direction over the entire earth might be problematic...so then you'd have to imagine it either measuring that information with some kind of doppler-effect thing - or perhaps moving up and down to experimentally discover the best height to be at. This seems like a fairly challenging problem - so I doubt that this kind of gadget would be the first autonomous circumnavigation. My bet is definitely on the Liquid Robotics boat - it's already travelled 9,000 miles and since it doesn't require fuel, there is no particular reason to assume that it couldn't go the whole distance...although reliability issues over a 2 to 3 year voyage, and some lack of desire on behalf of the owner to actually make the attempt might prevent it from being the first to do this. SteveBaker (talk) 15:13, 3 December 2013 (UTC)[reply]

I would think "navigate" would be a factor whether a human program or artificial intelligence (animals wouldn't count). Dropping a bottle with a message into the ocean might traverse the globe but it has no navigational ability. Ferdinand Magellan and Juan Sebastián Elcano made navigation decisions to circumnavigate the globe. Similarly, simply tracking a whale wouldn't count either. --DHeyward (talk) 09:21, 4 December 2013 (UTC)[reply]

December 3

Skin color and auto accidents

According to a report by the Centers for Disease Control and Prevention, the death rate for American pedestrians in auto accidents, 2001-2010, was much higher for blacks than for whites. This report was the only solid source I could find that's at all relevant to skin color, so I'll have to ask for help finding something that interprets the data. Is anyone aware of studies that directly address the effect of skin color on rates of auto-pedestrian collisions? I was left wondering about skin color itself while walking along a street after nightfall this evening: I'm left wondering if my light-skinned face and hands are more visible to a driver than they would be if my skin were dark. Since statistically average white and black Americans differ in much more than just skin color, we obviously can't say that the different death rates are purely the result of drivers seeing white pedestrians more easily than black pedestrians. Has anyone done a study that seeks to control for all other factors (e.g. controlling for percentages of people of each race walking in places without sidewalks, walking at night, walking while drunk, etc.), leaving only the visibility of the skin as a variable? Lest this be misinterpreted: I'm not fishing for anything, nor suggesting anything about common black culture versus common white culture; I would ask the same question if common concepts of race relied primarily on eye color and ignored skin color entirely. It's purely a question of the relationship between melanin and optics. Nyttend (talk) 02:14, 3 December 2013 (UTC)[reply]

Seriously? (Are you from the Alps? Methinks thou dost protest too much.) Blacks in the US are overrepresented as part of the urban population, where car-pedestrian impacts are most common. μηδείς (talk) 03:43, 3 December 2013 (UTC)[reply]

I think you'd definitely need a controlled study under strictly defined conditions to rule out all of the confounding variables such as differences in fashion. I don't think you can take actual incidents and control every factor like that, because for example how would you categorize every garment every person was wearing? (I know there are definitely some colors that are more popular with people of a particular race in a given area) Wnt (talk) 03:39, 3 December 2013 (UTC)[reply]

<sigh> Recite ten times: "Correlation does not imply causation" (then read our fine article: Correlation does not imply causation).

It is true in the US that (for example) on the average, (per Racial wage gap in the United States) black people only have 65% of the income of an average American. So perhaps the truth is really: "Poor people have a higher death rate than the middle classes in pedestrian auto accidents". Perhaps they live in neighborhoods with worse street lighting and the real news is "People who live in well-lit neighborhoods have a lower death rate in pedestrian auto accidents"...which takes us from a socially divisive message to a socially useful one that says "We should improve street lighting in the poorer parts of America"....or not. We don't know because the science wasn't done right.

For all scientific studies, you absolutely must employ at least one control group - and for this study, you'd need MANY control groups before jumping to any kind of conclusion whatever. So in this case, one would want to control for income by (say) comparing the death rates for people of different skin colors in identical income groups - and who live in identical parts of the city, etc, etc.

Jumping straight to the conclusion that skin color is the "cause" is a very, very bad idea when all you have is a single "correlation".

So this study (as it stands) is entirely useless and may safely be filed away under the heading of "unqualified data" until we see some halfway reasonable study about why pedestrian accidents happen.

SteveBaker (talk) 03:40, 3 December 2013 (UTC)[reply]

Have you read any of the study, or even the question, before denouncing the study as "entirely useless"? The study makes absolutely no claim about why black people have more accidents. It simply lists accident rates by race, gender, urbanization level, age, and other factors, and doesn't even put any emphasis on race.

If you read the question, you'd know the OP asked "Since statistically average white and black Americans differ in much more than just skin color, we obviously can't say that the different death rates are purely the result of drivers seeing white pedestrians more easily than black pedestrians. Has anyone done a study that seeks to control for all other factors..." He's asking precisely for a controlled study. --Bowlhover (talk) 04:36, 3 December 2013 (UTC)[reply]

The first thing missing that I see is a comparison to other accidental death rates and non-accidental death rates. Considering that it's only 13% of vehicle related deaths, the next study I would look at is wheher vehicle/vehicle accidental deaths are correlated in the same way as pedestrian/vehicle deaths (that seems surprisingly missing). Those studies should be available broken down by the same categories. The next question is whether pedestrian/auto deaths are a significant cause of accidental death in each group or is it in the noise (this is particularly egregious omission as it appears to be raising alarm bells for an aging population - death rates increase by age but do other accidental death rates, such as falling, increase faster? We don't know.) . Accidental death rates by cause are available as well. As a whole, the study starts with auto accidents being overall #1 cause (but not pedestrian/auto) of accidental deaths. Then makes a scary number for elderly pedestrian death rates but fails to rank it for the elderly group. That's pretty poor. Also, as it states, the study doesn't control for alcohol but uses cause of death on death certificates. "Vehicular assault" is not accidental and may vary by geography as to whether it's accidental or not. The study clearly indicates that there is a correlation to urbanization and that within those areas, the other factors correlate to each other. "Approximately three fourths of all pedestrian deaths in 2010 occurred in urban areas (3). Higher pedestrian death rates in urban areas are, at least in part, a result of more concentrated vehicle and pedestrian activity in these areas. The current study found that for many age groups and racial/ethnic populations, patterns in pedestrian death rates by level of urbanization were similar to those for overall pedestrian death rates" which seems to mean that for 3/4ths of all pedestrian deaths, race/ethnicity was not a factor and the differences appear when non-metro areas are factored in. --DHeyward (talk) 14:06, 3 December 2013 (UTC)[reply]

My first thought was the same as Medeis, i.e. it could have to do with being relatively more clustered into urban as opposed to rural populations. In the latter, you almost have to try to get hit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:51, 3 December 2013 (UTC)[reply]

One might also check whether the death rate mentioned covers deaths in pedestrian–car collisions only or also caused by such collisions, and then consider the time and quality of medical service available to those injured. --CiaPan (talk) 06:36, 3 December 2013 (UTC)[reply]

Some thoughts:

1) As stated before, blacks tends to live in high density communities where car-pedestrian accidents are more common.

2) Also, blacks who live in such places are less likely to own a car, so more likely to be a pedestrian.

3) I have noticed, however, that there seems to be a black cultural habit of walking down the middle of the street, versus on the sidewalks. This seems to be particularly true of male teens. I even posted a question about that once on the Ref Desk.

4) I've also noticed a total lack of reflective clothing, although I suppose being able to hide from those who wish to do you harm, like the police, in some cases, might explain this. StuRat (talk) 07:53, 3 December 2013 (UTC)[reply]

The intro states that the highest death rates are native americans and those > 75 y/o. There needs to be lots of controls before assigning causative vs. correlative. In addition, there is no analysis of whether the differences are statistically significant. The study starts off with about 33,000 vehicle deaths and then states about 13% are pedestrian related. The biggest glaring hole that I see is that it fails to compare accidental deaths of pedestrians against other accidental deaths (i.e. trips/falls, drowning, etc). It's pretty bold to say that the aging population may suffer more pedestrian/auto deaths if it's dwarfed by trip/fall deaths or auto/auto deaths. Even though as a whole, auto/auto deaths are the leading cause of accidental death (and it doesn't even state whether they consider alcohol related deaths to be accidental or vehicular assault), the study doesn't seem to break down whether pedestrian/auto deaths are, as a whole, significant. Nor does it break down each group and identify whether pedestrian/auto deaths as a cause of accidental death is higher or lower than other causes. It's number 1 overall but even though it's a higher death rate for > 75 y/o's, it could be the 5th highest cause of accidental death for > 75 and trending lower as the cause of accidental death even while the rate goes up. There's a lot of inferences made that don't seem to have a rigorous mathematical underpinning of sampling statistics and correlations. --DHeyward (talk) 13:29, 3 December 2013 (UTC)[reply]

For people wearing dark clothing at night, against a dark background, it would make a difference for the distance at which one is first noticed. Weber's law and Ricco's law would be relevant. Weber's ratio seems to have the best correlation with detection distance according to this. Skin reflectance for different populations: African (Black) 5 - 10%, African (Pigmy) 10 - 15%, Indian (India) 15 - 30%, Iranian 20 - 40%, European 35 - 60%, source: Jablonski, N.G. and Chaplin, G., The evolution of human skin coloration. J Hum Evol 2000; 39: 57-106, quoted on a photography forum. Pictures like this or this suggest that when dressed in dark non-reflective clothing at night, the skin would be the most (or only) visible feature. In those circumstances white people would be detected at a greater distance than black people. And (available) time to react depends on detection distance. Same would apply to blond versus black hair when seen from the back. That doesn't mean of course that the difference in death rates are caused by skin color, we don't even know when these accidents happen, but the idea that skin color can affect visibility and therefore the risk at night seems quite reasonable. I doubt however that anyone has studied this, might be controversial... Ssscienccce (talk) 14:08, 3 December 2013 (UTC)[reply]

Just because something is controversial doesn't mean it hasn't been statistically studied. For example, the U.S. Army and the Marine Corps have determined beyond a reasonable doubt that these skin colors are the most difficult to see. Sort of a pixelated grayish green with brown and olive patches to break up the outlines... these patterns are not arbitrary; they are the result of a century of statistical testing on human perception. I'm sure we can find hundreds of papers listing variations on those experiments. In some cases, bright high-contrast colors and geometric shapes are more difficult to see. In any case, I think we can thoroughly discredit the idea that visibility due to skin coloration is the determining factor in automobile-pedestrian collisions. The studies that Nyttend actually linked to implore further research into other sociological factors to provide new explanatory variables. Nimur (talk) 14:21, 3 December 2013 (UTC)[reply]

More than once while driving at night, I've nearly hit white guys wearing dark clothes and not paying sufficient attention to traffic. Skin color isn't much of an issue, as you only see a small portion of their bodies. It's the clothing that's the problem. That's what a study should look at. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:13, 3 December 2013 (UTC)[reply]

I meant studies specifically looking at pedestrians being killed due to low visibility of their skin color: inadequate street lighting will be more prevalent in poor neighborhoods, so a study telling them their skin color is "to blame" might seem a bit cynical... Ssscienccce (talk) 16:58, 3 December 2013 (UTC)[reply]

That's another "obvious" claim with no basis in reality. The most well lit neighbourhoods I have ever lived in were black and Latino neighbourhoods in NYC and urban areas of New Jersey with low income residents. The most poorly lit were upper middle-class ones in rural-suburban South Jersey and at the Jersey shore. μηδείς (talk) 03:16, 4 December 2013 (UTC)[reply]

And I'm saying that for a given person, there's a lot more clothing visible than skin. So clothing is more likely to be a determining factor. Obviously, if a black person is wearing dark clothing, their odds of being seen are liable to decrease. But I'm also telling you, from experience, that a white person wearing dark clothes is also difficult to see. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:49, 3 December 2013 (UTC)[reply]

I was responding to Nimur, not you. And of course clothing is much more important, that's why every autumn we see safety campaigns with people dressed like glowstick adverts on tv. I didn't say white persons in black clothes are easy to see at night, I'm saying that skin color will make a difference in visibility level in some situations. I didn't say anything about it's relative importance. Ssscienccce (talk) 22:12, 3 December 2013 (UTC)[reply]

And that's why I always get off the street when a car comes along, even though my skin is light, since most of my cold-weather clothes are dark. Since rural and suburban residents are more white than urban residents, I figured that the sidewalk factor might be a big issue: most streets in urban settings are accompanied by sidewalks, unlike many streets/roads in suburban and rural settings, and many of those suburban or rural thoroughfares are lit only by the moon and the stars, so place of walking and quality/quantity of street lighting aren't purely a problem for the urban resident. For example, I know a woman whose father was killed while running along a Kansas farm road in the 1970s, because of factors other than visibility; of course that incident might only be anecdotal, but non-visibility factors such as simple inattentiveness would definitely need to be controlled for the kind of study I was envisioning. Nyttend (talk) 01:15, 4 December 2013 (UTC)[reply]

How can we characterize the quality of OECD data on working hours vs productivity?

Recently on the Humanities Reference Desk, this relation between hours worked per year and productivity from an article in The Economist was called "low quality." While there do appear to be bifurcated strands along the same trend, I am not sure I would call such a correlogram particularly low quality. What do Science reference deskers say? EllenCT (talk) 08:28, 3 December 2013 (UTC)[reply]

The Economist article linked to this paper that found the same result from a totally different data set. The paper formally reviews their data collection and processing, including the statistical significance of their conclusion. It seems that we can't realistically attack this correlation by attributing it to poor data, nor to poor methodology, nor to statistical insignificance. A complete run-down of the statistics in that paper rule out several confounding factors, and make a strong case for the significance of the correlation (which they term the "elasticity" of hours worked versus compensation rate). From a purely statistical point of view we can confidently say that this correlation is strong, it is significant, and it emerges from multiple different data sets. So, if we want to maintain a scientifically valid standpoint, we should seek a causal explanation for the data.

The authors provide four plausible causal hypotheses, and because they are behavioral economists, they have a preference for a behavioral explanation: the workers are choosing to end their days early when they earn well; they have a fixed income target. I am more inclined to believe their liquidity-constraint hypothesis, based on my personal experiences; but the authors provide compelling counter-evidence by showing that high-capital laborers exhibit the same behavior as low-capital laborers.

I think the most critical point might be that productivity, as defined by the OECD and most other economists strictly refers to economic productivity: activity that has monetary value. That may differ from your intuitive notions about productivity. The next time you pull long hours at school or at your job, you might be working very hard, and you might even be making progress toward some end goal. But consider, for a while, whether your activity is productivity as an economist sees it: are you measurably increasing the GDP ?

Nimur (talk) 13:44, 3 December 2013 (UTC)[reply]

In that topic someone said "the data quality is likely to be poor", claiming that in his industry the nominal number of hours was 1620 while the actual number was about 3000. According to OECD Measures of Total Hours Worked, "in many countries actual hours are derived from establishment surveys for production and non supervisory workers in employee jobs and from labour force surveys (LFS) for self-employed, managers and supervisory workers, farm workers and public sector employment. Hours lost due to sickness are estimated from the number of days not worked from social security registers and/or health surveys..."

Germany recently revised its system to better account for workers with few hours, France is now excluding short rests and work breaks from the total (which is contrary to the guidelines)...

Labour force surveys seem to overestimate the number of hours worked and underestimate the hours not worked due to holiday, vacation, sickness, maternity leave etc.. the difference with establishment-based surveys was 1 to 3% (in France, Germany, Netherlands and Switzerland). 3% won't make much of a difference to the graph.

The data may not be totally accurate, but it's likely the best data available. Ssscienccce (talk) 20:23, 3 December 2013 (UTC)[reply]

2011 Tōhoku earthquake and tsunami.

Was it the largest in Japan? The 869 Sanriku earthquake was believed to could have been around 9.0. Applies to Japan. --78.156.109.166 (talk) 10:20, 3 December 2013 (UTC)[reply]

The earthquake was the largest in the vicinity of Japan since recording began. It's impossible to say whether there were larger quakes earlier. Note though that the Tohoku quake had its epicenter well offshore. The shaking on the mainland lasted for a long time but was not all that intense. There have been many quakes that caused more intense shaking at points on the mainland, and more severe shaking-related damage. The damage from the Tohoku quake was mainly due to the tsunami rather than the shaking. Looie496 (talk) 17:07, 3 December 2013 (UTC)[reply]

How much damage/casualties from the quake? --78.156.109.166 (talk) 19:52, 4 December 2013 (UTC)[reply]

Studies of the 869 Jogan Sanriku earthquake suggest that it was similar in scale to the 2011 event[6][7]. The amount of inundation was found to be similar, the earlier tsunami's extent was underestimated as it became clear that the sandy tsunami deposit from the 2004 tsunami did not represent the full amount of inundation - mud and silt went significantly further. Taking that in to account it looks like the 869 event may have reached 9.0 magnitude, or even larger. Mikenorton (talk) 23:36, 4 December 2013 (UTC)[reply]

Sex determination by the father?

Do "normal healthy" human males produce 2 kinds of sperm, one kind that results in male children and another kind that results in female children? (option A)

Or do "normal healthy" human males produce 1 kind of sperm that can result in either male or female children, depending on something else? (option B)

If the answer is A, are there conditions in which some men only produce one kind or the other? In other words, are there some men who can only have sons or only have daughters?

If the answer is B, what are the main things that determine whether child is male or female?

Thank you, CBHA (talk) 18:09, 3 December 2013 (UTC)\[reply]

The father is the sex-determinant of the child. It has to do with whether a given sperm cell has the X-chromosome or the Y-chromosome. And of course there are gazillions of sperm cells in a given "batch". I'm sure there is a great deal of info here. Try gamete for a start, and see where it leads. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:47, 3 December 2013 (UTC)[reply]

For the most part, "the sex-determinant of the child" is not so much the father, as it is random chance. Yes, the winning sperm is the one that determines the child's sex, but the father as such has very little influence over which sperm "wins". --Trovatore (talk) 21:16, 3 December 2013 (UTC)[reply]

Sure it's random, for the most part. I didn't say the father had a choice. But he's still the biological determinant of the child, as opposed to the mother, who isn't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:19, 4 December 2013 (UTC)[reply]

Well, no, sorry, that's wrong. The father is not the biological determiner of the child's sex. Which kind of sperm happens to win, that's the determiner, but not the father. --Trovatore (talk) 07:49, 4 December 2013 (UTC)[reply]

The problem is a linguistic one. That is, 'determines' means different things to different people. To many it sounds like a synonym for "chooses", as in "I will determine which movie we see". In that interpretation of the word, the father does not "determine" the sex of the offspring. StuRat (talk) 09:47, 4 December 2013 (UTC)[reply]

In biology class, they always told us, "the father determines the sex of the offspring". I'll rely on what my biology teacher said, and what internet sources say,[8] as opposed to nitpicking over the meaning of the word "determine". Maybe Il Trovatore would prefer to say that the source of the sex of the offspring is the father's sperm. But it's ultimately the same thing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:25, 4 December 2013 (UTC)[reply]

Well, science is about being precise, and a scientific statement that can be taken two ways doesn't seem at all precise to me. StuRat (talk) 08:04, 5 December 2013 (UTC)[reply]

The sex of the child was once thought to somehow be determined by the mother. Once they discovered chromosomes, they realized it was determined by the father. Maybe they didn't feel like talking about gametes in public, so saying the sex of the child was determined by the father was sufficient. Or maybe they just didn't want to present the whole story every time. How precise does it need to be? It's determined by whichever sperm cell happens to get to the nucleus of the ovum first. And then you get into more and more details. Do you want a lecture? Or do you want to know which parent is the source of the sex of the child? It reminds me of the story about the kid who comes to the parent and asks, "What is sex?" So the parent goes into a long, graphic description of the reproduction process. The young'un, looking like a deer in headlights, finally says, "I have this paper to fill out, and it says, 'Sex __' What should I put there?" ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:37, 5 December 2013 (UTC)[reply]

The fact that the child's sex is determined by which sperm wins does not imply that it's determined by the father. In fact, it doesn't even imply that it's not determined by the mother (or more precisely by the environment of the mother's reproductive tract). If Shettles was right, then the pH of the mother's reproductive tract is actually a major contribution to determining the sex of the child.

Now, I gather that Shettles' theories are no longer in favor. Maybe they're even considered to have been refuted; I'm not an expert and I wouldn't know. But it is certainly not as simple as saying the sex is "determined by the father". --Trovatore (talk) 01:54, 7 December 2013 (UTC)[reply]

(EC) As described in the Spermatozoon article, human males produce two kinds of sperm cells: some contain a Y chromosome, which will produce a boy, and some contain an X chromosome, which will produce a girl. I can't find any condition that results in a man only producing one of the two types of sperm cells. But see Human sex ratio#Factors affecting sex ratio in humans. Red Act (talk) 18:52, 3 December 2013 (UTC)[reply]

Males have two sex chromosomes, an X and a Y. Sperm cells are the result of meiosis, a process involving cell division, where one cell will get the Y chromosome and the other the X chromosome. These cells split again to create four sperm cells, two with X and two with Y. So a man should produce the same number of X and Y sperms. Ssscienccce (talk) 19:28, 3 December 2013 (UTC)[reply]

One thing I looked into is whether an aneuploidy involving a lack of an X chromosome could produce a man who could only father boys. However, according to Aneuploidy#Types, having no X chromosome is lethal. Red Act (talk) 20:47, 3 December 2013 (UTC)[reply]

Thank you all. Followup question - are there "factors" in the female (chemistry for example) which differentially affect sperm? Ie, that make it more likely that a particular woman would have male children or female children even though the sperm she received had a 1-1 sex ratio? CBHA (talk) 22:08, 3 December 2013 (UTC)[reply]

There was a brief splash made back in the Seventies or so (update: actually Sixties) when some researcher claimed he had a method of making a boy or girl more likely, depending on parent preference, based on the pH of the woman's system. He claimed that an acidic environment was hostile to all sperm, but that the X sperm were tougher and more likely to survive it, so an acidic environment favored girls and an alkaline environment boys (because the ratio is not in fact 1–1; it's actually about 2–1 in favor of Y sperm, if I remember correctly). Here it is: Shettles method. It appears that it is not now considered to work. --Trovatore (talk) 22:14, 3 December 2013 (UTC)[reply]

And see also Sex selection. The only preimplantation methods which are known to work I'm aware of, and mentioned in our article, are those which involve artificial insemination or in vitro fertilisation. in other words, any method which is supposed to use sexual intercourse for conception has no evidence of working. Note that while controversial, there is a fair amount of interest in sex selection particularly male selection in certain cultures, so there is some degree of research. So for many popular methods, there's a fair chance the is something which has shown the method may not work (or alternatively it may be there's good reason to think it won't work even without research). (You can of course use post conception selection with sex but that's even more controversial and doesn't seem to be what the OP is getting at.)

And there any plenty of supposed natural methods [9] [10], many even more junky than Wheelan or Shettles [11].

Incidentally the sperm sorting methods could provide a clue as to what could potentially work. However the methods known to work and even some that don't appear to [12] are not the sort of thing you can expect to emulate. Of course as with most things, this sort of research gets confusing. As per the prior link, there's some evidence sorting via the Ericsson method doesn't actual achieve any sort of specific sex sperm enrichment, but there's also some evidence (as per our article) it produces a non expected sex ratio at birth. (Sperm sorting is also of strong generally uncontroversial interest for use in non human mammals. While there's no guarantee these methods will cross over and methods which may work in humans may not work for other mammals particularly somewhat more distantly related ones like cows but it's another area of research or relevance.)

P.S. For completeness I should mention I believe there is some evidence the sex ratio varies depending on the health of the mother [13]. This could be pre implantation or post implantation or both. I think most think it's more likely to be predominantly post implantation (with at least some degree perhaps even most being non concious factors). But even if there is some degree of pre implantation causation, I don't think many would seriously suggest starving the mother for a minor change in the sex ratio.

Nil Einne (talk) 23:02, 3 December 2013 (UTC)[reply]

Maybe. See Maternal influence on sex determination. Red Act (talk) 23:20, 3 December 2013 (UTC)[reply]

There is related information at http://www.boygirldiet.com/index.htm.

—Wavelength (talk) 23:26, 3 December 2013 (UTC)[reply]

Very interesting, though I'm not sure that's a WP:RS, let alone authoritative. I make no judgment, just flagging for propriety :) SemanticMantis (talk) 00:41, 4 December 2013 (UTC)[reply]

To answer the original question, there are chromosomal karyotypes that result varying chromosomal counts. See Klinefelter syndrome for description of the most common anomaly. I don't know how often that karyotype produces viable sperm or what the M/F ratio might be. --DHeyward (talk) 09:36, 4 December 2013 (UTC)[reply]

Best breeding age for human females

After what age does the offspring become likely to be genetically bad? At what age should the femaile be impregnated and by what age male to insure the child is genetically fit? — Preceding unsigned comment added by 74.14.28.186 (talk) 21:15, 3 December 2013 (UTC)[reply]

It's a sliding scale for the probability of Down's syndrome, for example. But even young, healthy mothers frequently have miscarriages. There may be an optimal age range for carrying children, but there are no guarantees. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:22, 4 December 2013 (UTC)[reply]

Your heading only says "Best breeding age" while your question only refers to genetics. As Teenage pregnancy says, there are other problems with young mothers. I suspect (don't know) that if we only look at genetics then younger is generally better. Other health factors are more important when you for example go from 20 to 13, so I don't recommend the latter. PrimeHunter (talk) 01:08, 4 December 2013 (UTC)[reply]

Biologically, 20 is best, assuming the female is fully mature. The range of 20-34 is considered best because of fertility, and the older the mother the more financially stable and mentally mature. This is all over the place if one simply googles the question. Of course the answer now also works depending on one's state of mind. μηδείς (talk) 05:14, 5 December 2013 (UTC)[reply]

In a sense this isn't a scientific question. Evolution clearly has an impregnate early, impregnate often agenda; 'barefoot and pregnant' was, after all, the human condition for a very long time. A risk of death, even for the mother, was balanced against the gain of offspring. In evolutionary terms the "what if the child is genetically unfit" worry just doesn't exist - either it survives (victory!) or it doesn't, which in cold arithmetic is no loss. Now a person with modern sensibilities can say that the chance of having a healthy child is not worth a certain chance of one with Down Syndrome, but if so... when is it ever worth it? If you truly take a 'do no harm' approach then pregnancy is right out, Shaker style. So the balance you seek is a compromise between philosophies, a value judgment you make at an arbitrary rate of exchange. We might show you incidence graphs of various conditions (I'm sure there must be one in Down syndrome) but you have to make your own decision. Wnt (talk) 14:51, 5 December 2013 (UTC)[reply]

Constrictor snakes' skin

We've all seen the discussions of the ways by which constrictor snakes are sometimes able to swallow large prey, e.g. the goat or deer pictured here. But what about their skin? How does the skin stretch to facilitate a temporarily far larger snake? How doesn't it just tear in pieces and kill the snake by blood loss? Force an adult human into children's clothing and you'll up with little bits of torn cloth; since the snakes eat much too fast for the skin simply to grow big enough to accommodate the large prey, I don't see the difference. After all, a hungry constrictor snake doesn't have massive amounts of extra skin, which one might initially imagine as the expansion mechanism. Nyttend (talk) 23:17, 3 December 2013 (UTC)[reply]

Here's a start, it's all about the collagen structures. Here's a paper "Mechanical behaviour of snake skin", that says

“

... Analysis of the loading curves revealed substantial variation in loads and maximum stiffnesses among samples from different dorsoventral regions within an individual and among homologous samples from different species. Skin thickness varied by a factor of more than five, but this only partially accounts for the differences in the force per width of sample at a given extension. Qualitative differences in the dermal collagen fibres are implied by the shapes of the loading curves and the terminal elastic modulus which varied from about 15 to 585 MN/m2. ... The size of the scales within a skin sample was not a reliable predictor of the loading behaviour of the sample. Correlations between the mechanical behaviour of skin and specializations in locomotion and associated musculature are discussed

”

[14](emphasis mine). As usual, just ask me (or at WP:REX) if anyone needs access to the full paper. My understanding is that comparing snake skin to human, with respect to ductility and elasticity (two different kinds of "stretchiness") is (somewhat) analogous to comparing different weaves or knits of the same fiber -- they can have vastly different mechanical properties, even though they are (mostly) made of the same stuff. E.g. most cotton sweaters can stretch much more than cotton T-shirts, even though they are both made of cotton. Things like gauge of the yarn, and pattern of weave, have a huge effect! SemanticMantis (talk) 00:34, 4 December 2013 (UTC)[reply]

Keep in mind that the scales we see are not the skin itself, but overlapping (for the most part) and embedded in it. The skin itself resembles chicken skin. If a snake swallows a large meal, the scales go from overlapping to widely separated.

Using the clothing analogy, we could design clothes that could expand that much, using elastic, pleats, etc. StuRat (talk) 10:23, 4 December 2013 (UTC)[reply]

December 4

Lagrange's equilateral triangle solution

I've tried googling but with no luck- what are the conditions on the initial velocities / masses for Lagrange's equilateral triangle solution to the three body problem? 68.0.144.214 (talk) 00:05, 4 December 2013 (UTC)[reply]

Lagrange points L4 and L5 - those which are described by an equilateral triangle whose base is the line between n₁ and n₂ - have no constraint on mass of n₃. In the rotating frame of reference, there is no net velocity; equivalently; the velocity of the L4 and L5 points is the orbital velocity of n₂ about n₁. If you're looking for Lagrange's actual mathematics, you can find the link in our article on Lagrangian point: Essai sur le Problème des Trois Corps. Lagrange's notation is actually almost identical to the sort of modern differential equations I used in university - so his work is a lot easier to read than, say, that of Isaac Newton - except, of course, that you need to be fluent in French. He sets up the equations for constant angular offset in Article XLII ("Page 308" in the PDF file); and also in Article XXV: Ainsi les Corps B et C ne feront que tourner autour du Corps A avec vitesse angulaire constante et égale à

{\sqrt {\frac {A+B+C}{r^{3}}}}

. Granted, this is a little bit more obtuse than stating "L4" and "L5" outright, as you will find in a modern physics book; but if you really get the points, you probably don't need to enumerate the points. Nimur (talk) 01:33, 4 December 2013 (UTC)[reply]

Awesome answer, thanks Nimur! SemanticMantis (talk) 02:25, 4 December 2013 (UTC)[reply]

Hm, ok. Are there configurations with non-zero velocity that maintain the equilateral triangle while the distance between the three bodies changes? 68.0.144.214 (talk) 03:41, 4 December 2013 (UTC)[reply]

Not quite, but the horseshoe orbit is an almost stable orbit around L4 or L5 that has a non-zero relative angular velocity between the second and third bodies: as the angular distance varies, the leg lengths of the triangle also vary and are not equilateral. It is not possible to thus maintain an equilateral triangle: varying the velocity changes the distance between n₂ and n₃ - that implies that you are varying all the leg lengths; that would change the orbital radius of the second body, but not in a stable way. The radial period can not be resonantly locked with the orbital period of n₂ and n₃: as you set up your scenario, they have different velocities! The resulting behavior would be a non-stable orbit and proceed in a chaotic way. The system would rapidly decay into unstable motion. You can develop an intuition about the metastability of these orbits; there are actually very few stable 3-body configurations, even in an ideal system. Nimur (talk) 04:03, 4 December 2013 (UTC)[reply]

Here is a page with equilateral examples where the distance changes. Case 7 shows that the bodies can maintain an equilateral triangle while moving in elliptical orbits when the masses are different. The last paragraph focuses on your question and has a journal article citation that sounds like it will get into the math. Katie R (talk) 12:47, 6 December 2013 (UTC)[reply]

Twins

Do identical twins (or triplets, etc.) have DNA that is exactly identical? Or is it somehow different? Also, do identical twins (or triplets, etc.) have distinct fingerprints or identical fingerprints? Thanks. Joseph A. Spadaro (talk) 05:38, 4 December 2013 (UTC)[reply]

Identical DNA. Identical fingerprints. HiLo48 (talk) 06:25, 4 December 2013 (UTC)[reply]

No, they do not. The process that creates fingerprints is not determined by genetics. Even identical twins have distinguishable fingerprints. See http://www.straightdope.com/columns/read/1277/do-identical-twins-have-different-fingerprints for reference. Someguy1221 (talk) 06:30, 4 December 2013 (UTC)[reply]

No they don't. See Fingerprint. It's rather disturbing that a reference desk answer with no citation would contradict a WP article. Identical twins do not have identical fingerprints. If HiLo48 has a source that contradicts the article s/he should update it. If s/he doesn't, s/he shouldn't guess. --DHeyward (talk) 06:36, 4 December 2013 (UTC)[reply]

Sorry. No source. Just mistaken confidence in my knowledge. HiLo48 (talk) 07:12, 4 December 2013 (UTC)[reply]

It's also not true that twins have identical DNA. In fact, due to mutation, a random pair of twins probably don't. See [15], which found that the average pair of twins have 359 genetic differences that occurred early in development. (Mutations that occur late in development would only be shared by a small fraction of the twin's cells.) --Bowlhover (talk) 07:43, 4 December 2013 (UTC)[reply]

However, that's a very small portion of the total, so, if your evil identical twin kills somebody, and they compare his DNA from the murder scene with your own, they might very well declare it a match, unless you can prove you have an identical twin and they then do more detailed DNA testing. StuRat (talk) 10:18, 4 December 2013 (UTC)[reply]

Identical twins are considered to be natural clones of each other, but as noted above, during gestation their genetics diverge a bit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:22, 4 December 2013 (UTC)[reply]

stingless bees finding their hive

Note this curious detail in an article today on our local stingless bees in the Sydney Morning Herald"

"They can find their way back to the hive if it is moved less than a metre or more than a kilometre, but anything in between means some bees will never find their way home."

http://www.smh.com.au/environment/animals/no-sting-in-this-tale-of-homely-bees-20131203-2yoq7.html

I am trying to figure out how that could possibly be. (Note, downside of our indigenous stingless bees - a hive produces half a kilo of honey each year.)

From same article:

"For most Australians the only connection they have with insects is from the wrong end of a spray can."

Is this arse-about? If there is a "right end" of a spray can, surely it is at the end where you push the button, not the end which where the target of the spray is.

banned user

The following discussion has been closed. Please do not modify it.

Whether it is arse-about depends on your point of view. But the article seems to be rubbish anyway. Given the methods bees use to get back to the hive (they sense the polarisation of light from the sky to get general direction, and then use landmarks to localise on the hive), it is reasonable to expect bees to be tricked by moving the hive perhaps a few metres, but unreasonable to expect them to somehow recover their ability to find the hive if it is moved a larger distance. I have kept bees myself, and have found that moving the hives a few metres is not a problem - however I had 4 hives in a group in an open area at least 20 metres form any tree or structure. So they had to 1) find their way back to the clear area, and 2) pick which of the 4 hives is theirs. Quite a few Australians have more contact with insects than as something to spray at. Red Back spiders, very poisonous, infest toilets, garden sheds, and other structures that have a fair bit of ventilation to outside air. Squirting them with flyspray can make them struggle about as though drunk, and then they recover. I squirt them with CRC - that imobilises and suffocates them. And CRC is nowhere near as harmful to humans as poisons designed for spiders. Many Australians live in old suburbs in old houses built with wooden floors (houses built in the last 40 years or so mostly are brick with concrete floors and are easy to keep cockroach-free). These tend to be infested with cockroaches, which require treatment by a pest exterminating company (while you stay in a hotel for a few nights, or get it done before you move in) to really get rid of. Then there are wasps that crawl into your can of beer or soft drink while you are not looking. In areas close to fresh water, mosquitoes are a nuisance - anit-mosquito burners & candles are best for them. 1.122.59.94 (talk) 06:59, 4 December 2013 (UTC)[reply]

Without commenting on whether the statement is correct, I could propose a reason why that might not be able to find the hive after a moderate move. It could be that they have two distinct detection methods, one short-range and one long-range. The short-range method would be used normally, while the long-range method might be used to find the hive if it needed to be moved in an emergency (perhaps a fire), where presumably they would move it a good distance. What could this long-range location system be ? Perhaps smell ? In this case, if they were too close to the old hive, it's smell might overpower the scent of the new hive, since it seems more familiar, so they would need to move outside the range where they could smell the old hive to detect the new one. StuRat (talk) 10:14, 4 December 2013 (UTC)[reply]

The only interpretation I can think of that seems to make sense is that if you move a hive, with the bees inside(!), to another location nearby, once a bee comes across a place she "knows" she will take the route home she remembers best, which is the one to the old location. That can't happen if you move the hive far enough so the old and new foraging areas don't overlap; the old memories can't override the new route she learned. I guess for small displacements the hive could be found by accident and the bees would take the new route eventually, but the number of bees lost would increase with distance; and likewise when the areas overlap only slightly, you'd only lose the ones who happen to wander into the old territory. Ssscienccce (talk) 12:36, 4 December 2013 (UTC)[reply]

I think you're more or less right. See [16] which while not an RS, says something similar. If you move more than a metre but less than 500 metres or so, their homing instinct will bring them back to the old location so they will never find the hive (during previous foraging, they would have learnt the old routes to return). If you move more than 500 metres or whatever, this is further than they ever normally forage so they will I guess learn the new foraging routes (having no old routes as reference) and generally return to the new location. This must be referring to bees inside the hive, bees outside will still I presume return to the old location. Nil Einne (talk) 19:44, 4 December 2013 (UTC)[reply]

At the risk of being accused of being pedantic, Red Back spiders are not one of the insects come into contact with. Bazza (talk) 13:09, 4 December 2013 (UTC)[reply]

I don't understand that comment, but in any case let me give a pointer to our Redback spider article. Looie496 (talk) 15:46, 4 December 2013 (UTC)[reply]

I think despite the extremely confusing indenting and location, Bazza is replying to our resident banned Perth engineer with many names, and pointing out that Red back spiders are arthropods but not generally considered insects. Therefore not one of the insects Australians or anyone else ever come in to contact with, whether on the wrong/right end of fly spray or in some other fashion. Nil Einne (talk) 19:48, 4 December 2013 (UTC)[reply]

OP myles325a back live. Well, if Bazza is being a pedant about what constitutes an insect, he has shot himself in the nuts by then expressing this in English that is as meaningless as a spilt bowl of alphabet soup.

I am also a little mystified as to why one of the most impressive answers here is by someone who has been banned for some reason. He SOUNDS sensible, he SOUNDS learned, he SOUNDS like a responsible and proactive member of the Bunyip aristocracy, and yet he is persona non grata. Hmmmm....

But thanks to all respondents. Yes, the answer appears to be along the lines that moving the hive a small distance may lead to the bees following their usual paths and getting lost. Moved 500 metres or so (the article cited suggests) will obviate this problem. Myles325a (talk) 07:47, 5 December 2013 (UTC)[reply]

Skin wearing thin during writing

I'm left handed and when I write for an extended period of time, the skin of my middle finger which interfaces with the pen seems to wear thin and it becomes uncomfortable to write. Does this happen to everyone or do most people get calluses? Is it related to left-handedness (I guess I'm pushing the pen rather than pulling it)? It's not really a medical problem so I couldn't justify wasting my (NHS) GP's time but I might ask next time I'm there, not that I'd expect he could prescribe anything or even have anything insightful to say. I remember it bothered me at school but I just assumed everyone was the same. ----Seans Potato Business 12:20, 4 December 2013 (UTC)[reply]

My suggestion would be a pen with a soft grip. This can be more comfortable. Also, I think larger diameter pens might be better. Perhaps the larger diameter pen distributes pressure over a larger area of interface between pen and fingers resulting in lower pressure per square unit of contact. Bus stop (talk) 12:32, 4 December 2013 (UTC)[reply]

Those would be my suggestions as well. I know the phenomenon, although it was a long time ago. Also, adding some kind of anti-slip material would likely lower the amount of force you're using to hold the pen: This study suggests that a lower-level neural mechanism adapts the force used by each finger to the surface condition under that finger, a sort of anti-slip strategy. When lifting an object by a handle that had a different surface for every digit, each finger applied the amount of pressure and force that assured a stable grip on that specific surface. So it's likely that people unconsciously apply more pressure when holding a pen that is smooth and relatively "slippery". Ssscienccce (talk) 13:55, 4 December 2013 (UTC)[reply]

Don't know if there's a medical term for it, people get calluses from writing and blisters from more intensive friction/irritation. I think it's somewhere in between the two, too much friction/rubbing/pressure/irritation for a callus, to little for a blister... Ssscienccce (talk) 14:14, 4 December 2013 (UTC)[reply]

As another data point, I'm left-handed, but I've never had this problem - so it's evidently not a universal thing. SteveBaker (talk) 00:30, 5 December 2013 (UTC)[reply]

I used to get a blister on the last knuckle of my middle finger from grade school to freshman year college every september after summer vacation was over. The solution was growing an inelegant callus there by halloween. I still have the ghost of a callus, although I have been typing now since the 80's. (μηδείς (talk) 05:06, 5 December 2013 (UTC))[reply]

(No idea who posted the above unsigned) I write with my right hand and also use to get a callus/blister on my middle finger when I was in school. IIRC it was mildly uncomfortable sometimes but it didn't really bother me much, more just something I noticed. Nil Einne (talk) 04:13, 5 December 2013 (UTC)[reply]

T'was me. Or t'were I. In any case, the callus was never a problem until one year I tore it. That's godawful. μηδείς (talk) 05:06, 5 December 2013 (UTC)[reply]

PS, I was lectured that I got the callus because I held the stylus rubbing against the knuckle, rather than between the knuckle and nail. It all seemed like barely veiled sadism from my elders at the time. μηδείς (talk) 05:10, 5 December 2013 (UTC)[reply]

Given I have the ghost of a callus between the knuckle and the nail, it also seems like complete rubbish. I get the same problem as the OP on the few occasions I have to write a large amount by hand now, but it tends to work itself out eventually, and the slight arthritis in my fingers tends to kick in before it gets uncofotable in any single session. I'm right handed. MChesterMC (talk) 09:40, 5 December 2013 (UTC)[reply]

BTW, why do you need to write so much by hand ? Can't some of this writing be done on computer ? Are you somebody famous who has to sign a lot of autographs ? StuRat (talk) 07:59, 5 December 2013 (UTC)[reply]

I consider my writer's callus a mark of honor! There are plenty of situations other than autographs where people need or want to hand write things, for example I hand-write all my notes in seminars, meetings etc. (then scan them into evernote) since I haven't been able to find a software package or markup language that allows me the flexibility I have with my own notetaking on paper. This involves custom symbols, sometimes invented on the fly, sections of mind-maps interspersed with lists, diagrams and longer sections of prose and extensive use of arrows to link concepts together, with the shape of the arrow and the style of the arrowhead conveying various meanings. There's still plenty of reason to work with pen and paper (besides, a pen never runs out of battery). Equisetum (talk | contributions) 11:40, 5 December 2013 (UTC)[reply]

I still occasionally write things by hand, such as keeping score during card games, making a grocery or "To Do" list, etc. It's just doing so much manual writing that it damages the hand which seems odd to me. When I first felt any pain, I'd switch to computer. StuRat (talk) 09:01, 6 December 2013 (UTC)[reply]

Well, as a left-hander who used to have a terrible hand position when writing (because I was taught, badly, by right-handers who didn't take the time to understand the fundamental asymmetry between right handed and left handed writing) I can attest to the fact that it doesn't take very much manual writing at all to cause pain - half a page would do it for me, admittedly not because of a wearing down of the skin, but certainly the pressure of the pen on my middle finger and the position of my wrist would both be markedly uncomfortable after that point. This caused problems both with the legibility and speed of my writing, which was a bit of an issue for exams in high school. Fortunately this was entirely correctable (at least in my case) by adopting a relaxed, neutral wrist position and switching to a pen which requires very little pressure to write with. It took my a couple of years to fully change my writing position, but I've had no issues since then. Curiously the thing that helped most was learning to write with a fountain pen, which I was always told was impossible or at least very difficult for a left-hander (this notion is complete bollocks). I also made a mockery of the practice of handwriting analysis, since the change of hand position radically changed my handwriting without, presumably, completely changing my personality (unless the proponents of such analysis have cause and effect mixed up, hmm.. that reminds me of retrophrenology).. Equisetum (talk | contributions) 10:26, 6 December 2013 (UTC)[reply]

I'm a PhD student and we have to keep paper logbooks. It's an institute-wide policy and there's no option for using a computer except perhaps if I type everything up and print and stick it into the book, signing the corners. 78.148.106.99 (talk) 10:34, 6 December 2013 (UTC)[reply]

For the OP - what sort of pen do you use, and how do you hold your hand when you write? I am also left-handed and found I had much the same problem when I was using a ballpoint pen due to the pressure required to write with one. Once I changed my hand position to be below the line I am writing (to alleviate smudging issues), and switched to using rollerball or fountain pens which require much less pressure, the problem more or less resolved itself (I still have a small residual callus, but it is never painful). Equisetum (talk | contributions) 11:40, 5 December 2013 (UTC)[reply]

I use a ballpoint. I'll try a rollerball. 78.148.106.99 (talk) 10:34, 6 December 2013 (UTC)[reply]

As you're a PhD student (me too!) one thing to be careful of is the water/alcohol/organic solvent resistance of the ink in a rollerball, and also its longevity, which isn't great in some brands - some institutes actually mandate the use of a ballpoint because of these issues. One good option would be the Uniball Jetstream range [17] , as these have a supposedly very water, solvent and fade resistant pigment ink which was designed to prevent even deliberate erasure, for example in cheque fraud (they even resist acetone!), and are also very smooth flowing and fast drying. They also look quite like a standard ballpoint on the page, so you should be fine claiming they are a ballpoint if necessary. I don't use them myself anymore, as I have fallen in love with the Pilot G-Tec C4, but I did use them for two years during my undergrad and was very happy with them. Remember to consciously loosen your grip and reduce the pressure you apply to the page with them - it can take a bit of getting used to if you only use ballpoints. Hope this helps. Equisetum (talk | contributions) 13:25, 6 December 2013 (UTC)[reply]

Huh, apparently it's not just the Jetstream that has that highly resistant pigment ink - take your pick from any of these [18]. Or do as I would, and buy one of each! - I think I once counted that I had 55 different models of pen in my stationary drawer. Equisetum (talk | contributions) 13:34, 6 December 2013 (UTC)[reply]

Will light inhibit dark dependent flowering once it's begun?

I have some poinsettias I deadheaded, grew outside over the summer, and rebloomed from last year by bringing them in as the season darkened, around Oct 1. One of them is in "full bloom" (it doesn't have actual flowers yet, but the bracts have changed color richly.

If I bring the poinsettia into an environment where it's on show, but gets low and irregular artificial light when it's dark outside, will this inhibit further blooming? Thanks. μηδείς (talk) 20:58, 4 December 2013 (UTC)[reply]

Don't know about poinsettias, but for the orchids in my experience the answer is usually "no, it won't inhibit the blooming". Many orchid species and hybrids initiate a flower spike in response to a shorter day / longer night. Changing the conditions (temperature, humidity) abruptly may cause them to abort the flower spike, but changing the light/dark periods alone will usually has no effect at that point. Some orchids even tend to bloom right after they've been shipped by mail: 2-3 days in a dark box do the trick. --Dr Dima (talk) 22:11, 4 December 2013 (UTC)[reply]

Great. I never had noticed any of the flowers abort under long-light conditions. μηδείς (talk) 22:18, 4 December 2013 (UTC)[reply]

I agree with Dr Dima, but I'm not sure if I agree with his reasoning (which is essentially that the plant's bloom trajectory is started, and won't easily be knocked off course). Here's my issue: is bract color changing actually hormonally linked to blooming? Conceivably, the bract-turning could respond to one cue, while the true infloresence responds to others. Despite that, I think you'll be fine, esp. since "normal" levels of indoor evening light are essentially worth zero to most plants, in terms of both photosynthesis and photoperiod. Finally, this is exactly how the plants are often sold commerically, showy bracts, few if any true buds. Congrats on your successful mission! SemanticMantis (talk) 17:53, 5 December 2013 (UTC)[reply]

Yes, I am going to move the one I have in mind to the front window out of the unused room I have it in now. It will rarely get light after 6pm anyway. It's a white poinsettia that was actually thrown in the trash during the last freezing weather last March. I rescued it and it survived with a stunted growth habit, and now some very nice bracts. I'll have to see if I can upload a picture. μηδείς (talk) 18:30, 5 December 2013 (UTC)[reply]

This rings a bell. I'm more interested with preventing my lettuces bolting at the end of season due the the change in day length and ensuring a good harvest of very late cropping tomatoes around Christmas - than flowers (whereas the wife, is more interested in stopping me bolting down the pub as the evenings draw in). Yet yes, even with flowers, temperature and light is everything. Poinsettia Cultural Characteristics . Although it is not quite vegetable, I'd like to know if anybody knows how I can get some haggis to ripen for the new year – about February 2014 would by nice?--Aspro (talk) 22:58, 4 December 2013 (UTC)[reply]

December 5

AGRIS vs AGROVOC thesaurus

In the context accessing Agricultural library resources.Both AGRIS and the AGROVOC thesaurus are used, yet they are not "compatible". A comment from an expert or person involved is welcome. --Connection (talk) 09:21, 5 December 2013 (UTC)[reply]

This page is for asking specific questions. If you are having no luck on the AGRIS talk page, I suggest you take this to Wikipedia:WikiProject Agriculture. You may need to wait some time for a response.--Shantavira|^{feed me} 13:44, 5 December 2013 (UTC)[reply]

Why whenever I seek cooperation I find people harrassing me!? I need this to develop my own Library database, the purpose is how to integrate both. My mistake I took it first to the AGRIS talk page!--Connection (talk) 07:28, 6 December 2013 (UTC)[reply]

Maybe I completely misunderstand the problem, but as far as I can see, AGRIS uses a (hierarchical) category system, see the list here. It has a number of main categories, one of which is "Natural Resources (P)". In that category there are subcategories like "Nature conservation and land resources (P01)", "Soil erosion, conservation and reclamation (P36)".. (see here, choose Classification scheme= AGRIS/.. category=natural resources P )

Every article would be put in one (or more?) of these categories. (not sure if more than one is allowed).

AGROVOC is a thesaurus, containing relevant (agriculture related) terms, together with relationships between the terms, like "related", "narrower", "broader" term; RT, NT, BT; which is basically also a hierarchical structure, BT at higher level, NT at lower, RT at same level. For example "Natural resources" has as BT "Resources", as RTs "resource management", "Resource conservation", "Wilderness areas", "production possibilities", "Biological production" ... as NTs "Nonrenewable resources", "agricultural resources", "marine resources", "energy resources" ...

There are about 130 categories in AGRIS, but tens of thousands of AGROVOC terms.

A category "Seed production (F03)" tells you very little about the content, in contrast to a list of agrovoc terms: wild plants, microsatellites, Helianthus, plant genetics, Interspecific hybridization, phenotypes, Plant breeding, Meiosis.

Some examples of articles from the same category, irrigation, which is the subject category F Plant production > F06 Irrigation.

This article has as Agrovoc terms: greenhouses, irrigation schemes, pot plants, growing media, experimentation, indigenous knowledge, research
This one has: Machinery industry, Russian Federation, Pipes, Trickle irrigation, Sweet peppers, Irrigation, Water conservation costs, Farm equipment
Another: Calcareous soils. Flax, Irrigation frequencies, Micronutrients application, Flax fiber yield.

While some categories in AGRIS have identical names as AGROVOC terms, they have nothing to do with each other, and you should not look for compatibility or similarity in structure between the two. There is a short, fixed list of categories, and an almost endless list of possible index terms, to which new terms are added every day. Ssscienccce (talk) 21:13, 7 December 2013 (UTC)[reply]

Surface gravitation of "kissing" spheres?

Suppose two earth-sized spheres were just touching eachother (ignore for a moment the fact that they would be compelled to merge). What would the surface gravitation be like? That is, if you were to walk around between them, what would it be like on different points on their surfaces? I imagine the gravity at the point that they touch would be almost zero, wouldn't it (and if they had atmospheres the gasses would most likely be stripped away and drift off from this point)? Any ideas? -70.112.97.77 (talk) 15:43, 5 December 2013 (UTC)[reply]

You can calculate the gravitational potential using Gauss's law for gravity. This is actually a very easy calculation, because you have assumed fixed, rigid, non-moving spheres; so each sphere can be trivially treated as a point-mass. Nimur (talk) 16:42, 5 December 2013 (UTC)[reply]

Are you also assuming the spheres are not orbiting about their barycenter? If they are, the tidal acceleration of the distal faces will be huge, flinging much of the mass into space, regardless of a gravity somewhat under two gees. μηδείς (talk) 17:48, 5 December 2013 (UTC)[reply]

Please see Roche lobe. For a pair of non-rigid planets or stars, a configuration in which each one fills out its respective Roche lobe is, in principle, stable. They will both be tear-shaped, touching at the pointed ends. You may also want to see Rocheworld and Last Exile for works of fiction that explore this theme. --Dr Dima (talk) 19:27, 5 December 2013 (UTC)[reply]

Supposing they're made out of scrith, equal mass and radius, and touching, it is as Nimur says just the gravity toward two point masses. If you are off a little bit (dy) from the merge point, then the inward force is going to be 2g sin (dy/(r+dy)) (r/r+dy)^2. For this small dy, sin (dy/(r+dy)) ~= dy/(r+dy), so this is 2g dy r^2 /(r + dy)^3. So if your planets are 6000 km diameter and you stray 10 km, the gravity pulling you back to the center is 1/300 normal gravity. At that point, there will be a sqrt(6000^2 + 10^2 = 36000100) = 6000.00833 -> minus 6000 and * 2 = 16.6 meter gap between the two planets. Your gravity to the center of one planet will be off by the square of the distance, i.e. 36000100/36000000 or 2.78 x 10^-6, which is doubled because you're that much further from the other, or about 1/400000 normal gravity. So regardless of the surface you stood on you'd still feel you were being drawn more or less straight "down" to the kissing point rather than at any angle toward the nearer planet. Unless I fouled up, which is not unlikely on this one! (note, however, that mascons coulod really throw everything off; see that article for how much unrequited gravity one might apply) Wnt (talk) 20:21, 5 December 2013 (UTC)[reply]

If they are made out of scrith, you'll be dead before you ever see the kzin that kills you. μηδείς (talk) 20:39, 5 December 2013 (UTC)[reply]

So .. if J get it right, .. one could, near the center, hop between the two halves of that double planet .. floating, always sure to land somewhere near the center region again? --217.84.69.206 (talk) 20:01, 6 December 2013 (UTC)[reply]

The planets wouldn't quite be touching if you could stand at the center, but if I suppose they had, say, the 16.6 meter gap I mentioned, then gravity toward either would be about 1/400000 of normal gravity as described above. So you'd have a really hard time noticing that you weren't completely weightless. I should also note that the "centrifugal force" that normally reduces gravity would enhance it in this case (because away from the center of a mutually rotating system is toward the surface) but it would be reduced by an equivalent amount as the gravity because you're so close to the center point. Wnt (talk) 05:54, 7 December 2013 (UTC)[reply]

Interesting. Thanks for the answers everyone! -70.112.97.77 (talk) 03:20, 6 December 2013 (UTC)[reply]

The atmosphere would not float off at that point, instead it would be the place of maximum pressure. The point is like the center of the Earth. If that was hollow there would be no gravity, but there still is pressure from all around. Graeme Bartlett (talk) 20:13, 6 December 2013 (UTC)[reply]

Oh my, there's a challenger math problem for the audience! To calculate the air pressure you need to figure out the volume of the space between the touching planets, how much air (assuming normal Earth atmospheres to start) there is to fill it, what the weight of the column of air is (remember, it's weightless at the bottom!). Yikes. I don't even have a sense of whether the pressure would be less or more than 1 atm, given these contrary factors. This should definitely be worth the extra credit points in the AP Calculus class, I guarantee it. :) Wnt (talk) 05:58, 7 December 2013 (UTC)[reply]

Fiddling about with some bad Python just now (no guarantees!) I came up with the figure that you'd need at least 17 planets worth of air to have normal atmospheric pressure at the center, with the atmosphere extending outward 771 km! What's weird (tell me if I messed up) is to think that the "column of air" is a wedge; an entire equator-full of air rests upon a single tiny crevice at the center. (While many things are doubtless wrong with this simulation, at least it gave the same result with 1 meter and 2 meter step sizes)

import math
radius = 6371000 # using average radius; we're ignoring rotation anyway though...
heightstep = 2 # meter
totalmass = 5e18 #kilograms of air in the atmosphere
density = 28.8 / 22.4 # grams per liter at STP = kilograms per cubic meter
# density = density * 1000 # grams per cubic meter rather than cubic decimeter
# density = density / 1000 # kilograms , not grams
g = 9.806665 # newtons = kg m / s ^ 2 per kg
atm = 101325 # newtons per meter squared

def slice(pressure, height):
    # height is perpendicular to the line linking the two planets, outward from the center
    # cleavage is parallel to the line linking the two planets
    # circumference is AROUND the line linking the two planets
    circumference = height * 2 * math.pi
    cleavage = (radius*radius + height*height)**0.5 - radius
    rgrav = g * (radius/(radius + cleavage))**2 # gravity toward one planet's center
    cgrav = 2 * rgrav * math.sin(height/radius) # gravity toward common center
    slicevolume = circumference * cleavage * heightstep
    slicepressure = cgrav * heightstep * (pressure/atm) * density
    slicemass = slicevolume * pressure * density
    # print (circumference, cleavage, slicevolume, slicemass)
    sliceweight = cgrav * slicemass
    # slicepressure = cgrav * slicemass / (circumference * cleavage) # force per unit area
    nextpressure = pressure - slicepressure # counting down...
    pass
    return nextpressure, slicemass

pressure = atm
masscount = 0
height = 0
while (pressure > 1):
    height = height + heightstep
    pressure, massinc = slice(pressure, height)
    masscount += massinc
    if (height % 1000 == 0):
        print (pressure, massinc, masscount, height)

Wnt (talk) 14:07, 7 December 2013 (UTC)[reply]

Masochistic pigeons

I passed two pigeons in a fountain, sitting in cold tap water, on a cold-looking "full-contact stone" (unlike say large-grained concrete or something, which is probably not a "full-contact stone" for pigeons), on a sunless day, in 55F weather, and not drinking. Why would they do that? 12.196.0.56 (talk) 16:35, 5 December 2013 (UTC)[reply]

For the two pigeons in question. They do not experience having their feet in cold water, the same way as a I and you would (assuming your a Homo sapien too) . As always... Wikipedia has an article about the why: Rete_mirabile#Birds--Aspro (talk) 16:56, 5 December 2013 (UTC)[reply]

If I understand correctly, birds in general are not cold-sensitive in their feet or talons, as if the process "fools" their brains into thinking the temperature is just fine? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:07, 5 December 2013 (UTC)[reply]

Define "just fine". The birds do not sense the cold as uncomfortable, full stop. Birds also also unable to feel the pain of capsaicin. It doesn't mean the birds are being fooled. There's no "fooling" going on, which would imply that whatever is different-from-human is suboptimal. Birds don't feel cold the way humans feel cold, but there's no "fooling" and there's no "fine". WHat is normal for birds is not normal for humans, and visa versa, without placing normative value on either birdness or humanness. --Jayron32 17:13, 5 December 2013 (UTC)[reply]

OK, I think I get it now. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:53, 5 December 2013 (UTC)[reply]

Here is a bit more on why birds feet don't freeze. [19] Of course Tom Lehrer and his girlfeind also found another way alleviating any and all, of the pigeons sufferings[20]. ♬Two pigeons in the fountain, which one will the strychnine bless?♪--Aspro (talk) 17:47, 5 December 2013 (UTC)[reply]

Don't forget it takes two masochistic pigeons to tango. :) Wnt (talk) 20:03, 5 December 2013 (UTC)[reply]

But they were sitting, not standing, and about the entire the bottom of the birds were in the water. 12.196.0.56 (talk) 19:02, 5 December 2013 (UTC)[reply]

Maybe they like cold temperatures, the way that some people do. 24.23.196.85 (talk) 02:47, 6 December 2013 (UTC)[reply]

Did you observe them before that ? Maybe they were just engaged in some athletic flying, overheated, and are now using the cold water to cool off.

Another theory, perhaps they have some type of parasite (do they get fleas ?), and the cold water stops them from biting. StuRat (talk) 08:56, 6 December 2013 (UTC)[reply]

Could they just have been bathing? I'm not sure about pigeons, but I've seen gulls happily splashing around in water when it can't be much above freezing out. Also, birds tend to run hot. In the region of 40-44 degrees C, if I remember correctly. I'm not sure how that would affect a bird's perception of the cold. It may even be literally impossible to know for certain how a bird perceives anything. --Kurt Shaped Box (talk) 15:23, 6 December 2013 (UTC)[reply]

Where would anybody get the impression that 55 degrees is cold weather? The pigeons don't have bare underparts unless they have a brood patch. μηδείς (talk) 21:41, 6 December 2013 (UTC)[reply]

Best skin color etc.

What combination of human race-like traits would be best adapted to New York City? It wouldn't be Finnish or dark African for example, evolution would select against that without sunscreen and Vitamin D in milk. I suspect the people Henry Hudson met would be close but given the migration history maybe they didn't reach equilibrium yet? I can still see some "Mongoloidism" in Amazonians and Polynesians and Mongolia is like 40 degrees below zero. Heck, even some of India's women have a trace of Chineseism. No racist, Indian women are goddesses to me. Of course hunter-gatherers and postindustrials have different degrees of sunlight and weather exposure and typical clothing coverage, and the heat island effect has caused 5 to 10 degrees of unglobal warming. Even the paradaisical wilderness with a few small farms found by Europeans is artificial. The Native Americans burned or cut meadowless forest into their own image. (for hunting) 12.196.0.56 (talk) 18:43, 5 December 2013 (UTC)[reply]

A very difficult question indeed. I would be tempted to pull out a painting of the Manhattan tribe and be done; but we know that their ancestors travelled very widely indeed - Africa, Asia, Europe, Siberia, Alaska. What you would want to evolve optimally is a reaction norm - a set of responses to different environments, anywhere a New Yorker might want to travel (but where might that be, and where would he evolve to want to?). Tanning in some conditions and not others. Wearing clothing, perhaps, according to the ever changing climate, from Ice Age to heat island to runaway manmade greenhouse, though the latter tends to defeat adaptation. How do you evolve to constant migration, changing fashion, changing environment? The clear thing is that we haven't yet - there isn't time - but perhaps some photogray mechanism awaits in the future. But to choose a single color? It is an impossible calculation. What evolution does when it encounters the impossible is to try a lot of different options, with genetic variation, keeping genes around so that it is always ready. There's no predicting nor accounting for what happens in the end, it just does, I guess. Wnt (talk) 19:58, 5 December 2013 (UTC)[reply]

"Chineseism"? It's a stretch even to pretend there's a question here. The Lenape Indians inhabited the area before the Europeans came. Eskimos are darker than Poles, and New York City is at the same latitude as Istanbul. There's no way to answer this. μηδείς (talk) 20:36, 5 December 2013 (UTC)[reply]

Just because you don't have the answer doesn't meant that there isn't one. I'd find an ethnic group at the same latitude (N or S of the equator), and same elevation, which has been isolated for a very long time, and that should be the "ideal shade". However, note that modern inventions like sunblock and vitamin pills alter the calculations considerably, so you'd need to assume those were not available. StuRat (talk) 08:51, 6 December 2013 (UTC)[reply]

You've quite missed the point. Cultural habits like clothing and diet override any attempt at a simple equation of lattitude and color. I assume you understand that Eskimo live far to the north of the Polish, for example, yet are far darker than them on average. This is not a question about a spherical cow. And I would still like to know wtf "chineseism" is. μηδείς (talk) 18:38, 6 December 2013 (UTC)[reply]

Snow and ice reflect UV light. Inuit snow goggles were worn to protect against snow blindness. But those wouldn't protect the skin, so... Ssscienccce (talk) 01:56, 7 December 2013 (UTC)[reply]

My understanding is that the Eskimo are thought to have remained dark because they get plenty of Vitamin D from their diet. Lack of that vitamin is supposed to be what drives the selection pressure towards lighter skin. --Trovatore (talk) 07:02, 7 December 2013 (UTC)[reply]

Yes, that's correct, Trovatore. μηδείς (talk) 17:31, 7 December 2013 (UTC)[reply]

That's also an option, maybe a more likely one, I'm not even sure if there would have been enough time to get their current skin color if they first had evolved white skin. Selection pressure due to Vit D deficiency could be significant, due to excessive UV not so much, at least not in the arctic where people cover most of their skin. Unless eye color and risk of cataract is significant, not exactly my area of expertise... Ssscienccce (talk) 10:00, 7 December 2013 (UTC)[reply]

Can I point out our article Human skin color to you? Skin color is rapidly selected for, the differences between Europeans and Chinese have happened within the last 50 thousand years. Dmcq (talk) 09:17, 6 December 2013 (UTC)[reply]

The first answer above says "What evolution does when it encounters the impossible is to try a lot of different options, with genetic variation, keeping genes around so that it is always ready." This is ascribing a purpose to evolution which is something it doesn't have. Random genetic mutations are produced all the time - whatever the situation. Some are beneficial and some are a hindrance. The beneficial ones tend to propagate and the non-beneficial ones tend to die out. Evolution is totally without purpose and works by natural selection. Richerman (talk) 15:01, 6 December 2013 (UTC)[reply]

2011 Tōhoku earthquake and tsunami.

How much damage/casualties from the quake? --78.156.109.166 (talk) 19:53, 5 December 2013 (UTC)[reply]

You can look this up at 2011 Tōhoku earthquake and tsunami.--Shantavira|^{feed me} 20:01, 5 December 2013 (UTC)[reply]

I mean from the quake alone, not the tsunami. --78.156.109.166 (talk) 15:29, 6 December 2013 (UTC)[reply]

In the article: "Of the total confirmed victims, 14,308 drowned, 667 were crushed to death or died from internal injuries, and 145 perished from burns." If we assume that no one drowned from the quake itself (i.e. before the tsunami) than the upper limit would be about 900 deaths from the quake. However, it is likely that some of the crush injuries and fires were also triggered by tsunami effects, so the true total for the quake alone is probably smaller. Dragons flight (talk) 21:36, 6 December 2013 (UTC)[reply]

December 6

Why do peanuts make me thirsty ?

Note that I eat unsalted Spanish peanuts. I suspect it's the liner between the meat and the shell that does it, but want to confirm this and also know the mechanism.

Thanks, StuRat (talk) 08:45, 6 December 2013 (UTC)[reply]

Are you saying you eat the paper? μηδείς (talk) 18:33, 6 December 2013 (UTC)[reply]

The Spanish peanut's brown skin contains bitter astringent tannins, per http://naldc.nal.usda.gov/download/CAT83783188/PDF. -Modocc (talk) 20:36, 6 December 2013 (UTC)[reply]

Do you mean you become more thirsty that your companions that have consumed an equal amount of the same nuts, at the same sitting, or are you asking -why do you become thirsty? As you already know and appreciate, we can not give medical advice so I am hovering between the simple answer and go discus this with your qualified practitioner.--Aspro (talk) 20:53, 6 December 2013 (UTC)[reply]

Eating pretty much anything makes me thirsty. Hard to figure why Stu would find it unusual. But as you say, if he's got genuine concerns, he should go to a doctor and tell him what's up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:00, 6 December 2013 (UTC)[reply]

Jeez, I doubt Stu has or asked about a medical issue. Anyway, see the article on astringency that I linked to. Wild persimmons are my favorite, since they are quite sweet when ripe, but will make your mouth feel dry. Peanut skins can do this too. -Modocc (talk) 22:10, 6 December 2013 (UTC)[reply]

So can the increased blood sugar level of a diabetic. Aspro's reticence is justified. If Stu wants to tell us he doesn't get thirsty when eats the same amount sans papers we can absolve him. μηδείς (talk) 22:21, 6 December 2013 (UTC)[reply]

I would think, on the face of it, that Stu does mean he gets more thirsty eating peanuts than other foods. But you guys are free to, you know... --Modocc (talk) 22:37, 6 December 2013 (UTC)[reply]

It kind of reminds me of the old, fake medical warning: "Do you suffer from loss of appetite after a heavy meal?" ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:13, 6 December 2013 (UTC)[reply]

1) Yes, I eat the "paper", because in Spanish peanuts, unlike other types, it adheres to the meat and is therefore difficult to remove. And yes, they make me more thirsty than I would have expected, based on the quantity and lack of added salt.

2) The astringent property makes sense.

3) I don't see foods making people thirsty as a "medical problem". On the contrary, if there is a way to encourage people to drink more water, without increasing their salt intake, then this sounds like a good idea to me.

4) Note that not all foods make people thirsty. Foods which contain lots of water, like fruit, for example, may not. StuRat (talk) 09:49, 7 December 2013 (UTC)[reply]

Point 3 (see above). As I said, I'm am not going to get into a medical debate. Some medical conditions often only first surface to the practitioners awareness, after the the recognition of symptoms, that have temporal connection, that appear to be linked with the consumption a large hand-full of 'protein' rich peanuts alone -(i.e., without any other food types being consumed at the same time to slow digestion down). Peanuts are very rich protein source, compared to most other food types. Protein toxicity. Early detection, helps to prevent further damage by the adoption of dietary changes. By the way, if your over 45, you can save a load of money on GP visits, by checking your kidney function monthly, with over the counter Albustix Reagent Strips for Urinalysis, Tests for Protein available from your local drug store. Your Quack will use the same product but will charge an arm and a leg for the privilege.--Aspro (talk) 17:11, 7 December 2013 (UTC)[reply]

Yes, I don't think Stu's question invokes Kainaw's criteria. But increased thirst is indeed a symptom of various medical conditions. μηδείς (talk) 17:30, 7 December 2013 (UTC)[reply]

Technique for avoiding nodding off

I was reading something about an engineer nodding off and causing a train crash,^[21] and it reminded me of what a mystery "daytime sleep" really is to me. It's one thing to go to sleep at night for hours, but how to explain routine sleepiness at classes, seminars, or (what matters) while driving, that strikes when there's no exceptional circumstance like staying up all night or jet lag, which seems like one single moment of unconsciousness can be enough to end it? (I've heard this called highway hypnosis but our article doesn't use the phrase that way) Especially, I was wondering whether the technique I've come to use myself works for other people, or is an example of any higher principle: specifically, I practice answering some question or other somebody might ask at a job interview. (Some crazy social test like "what's the most difficult thing you've ever done", explaining some past project, etc.) It seems crazy, but I've found that speaking just two or three sentences to rehearse such an answer - at times when no such interview was upcoming to which stress could be attributed - seems to absolutely, utterly, completely banish routine highway sleepiness, from the point of thinking about pulling off the side of the interstate to avoid falling asleep in the next minute, to not even feeling like sleep is an option. It feels about a hundred times more effective than loudly singing, hyperventilating, rolling the windows all the way down, or blaring music on the radio. (However, finding a political talk show on the radio can also be effective, depending on the topic) Is there some systematic explanation for this? Wnt (talk) 09:01, 6 December 2013 (UTC)[reply]

Sure. This sleepiness is probably an evolutionary response to boredom. That is, when there's nothing much to do, you might as well sleep, so you will be well rested when there is something that needs doing. Cats take this to an extreme.

Unfortunately, in the modern world, there are situations which are both boring and potentially dangerous, like driving. We are not well adapted to those situations. Thinking means you are busy doing something your body assumes must be useful, so it holds off on sleep until a better time. StuRat (talk) 09:15, 6 December 2013 (UTC)[reply]

Wouldn't there have been situations like that for thousands of years? Walking miles to a spring to collect water, looking for berries, even fishing in a place where you could be attacked by wild animals. -- Q Chris (talk) 11:04, 6 December 2013 (UTC)[reply]

Walking and searching both require using the brain, so you would stay awake there. Fishing could indeed induce drowsiness, at least once you have the line in the water and are just waiting for a bite. Fly fishing, on the other hand, where you cast continuously, would not. Guard duty is another notorious problem, whether in ancient times, while watching for enemy soldiers and wolves, or in modern times when watching CCTV monitors for signs of trouble. StuRat (talk) 09:18, 7 December 2013 (UTC)[reply]

The term for sleepiness is Somnolence, and while the Wikipedia article is a bit stubby, there;s plenty of resources out there that seriously study this subject. --Jayron32 15:21, 6 December 2013 (UTC)[reply]

PubMed redirects somnolence to sleep, but searching with the term in quotes and adding in microsleep does get me up to 10% or more relevant papers. Some interesting connections with the immune system, actually. Which makes me suspicious the glymphatic system could be involved (it sure feels like there's a pressure change involved when nodding off, doesn't it?) but I didn't find anything about that. Hmmm... curiously, I don't see any mention of my particular method of practicing responses on various lists of ideas I see online. [22] I still wonder if it would work for other people as well as it seems to for me. Wnt (talk) 06:05, 7 December 2013 (UTC)[reply]

Simulating incorrect vision?

My friend has perfect eyesight. I have pretty bad short sightedness. If my friend looks through my glasses does he get a good approximation of what I see, since it's sort of... overcorrecting the correction the lenses provide? If not, is there any way you could simulate this, with special lenses? 81.138.15.171 (talk) 10:58, 6 December 2013 (UTC)[reply]

To accurately simulate it you would need a lense which is the opposite. If you may have a -2 diopter concave lens (for example) your friend would have to wear a +2 diopter convex lens to get the same effect. If you give him your lenses to wear you are simulating farsightedness. Small degrees of farsightedness don't impact as much as nearsightedness, it is easier to hold a book slightly further away than it is to get close to distant objects! -- Q Chris (talk) 11:12, 6 December 2013 (UTC)[reply]

I would recommend against that kind of tomfoolery, as anecdotal experience tells me that it can be literally painful to look through lenses that are starkly different from your own (be they natural or artificial). ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:58, 6 December 2013 (UTC)[reply]

It would have to be the opposite correction, as Q Chris explains. I don't know whether that's reliable way to simulate it. Accommodation may determine the result. It could also depend on what you want to simulate, with your case (near-sightedness) more likely to give the right result than trying the same for far-sightedness, because you want to take away part of the range, and we all have the same fixed limit for our upper range (no one ever needs to focus beyond "infinity"), but there's no equivalent lower limit where a further range would become useless: if you could focus on objects 2 cm from your eye, you'd never need a magnifying glass. So we would expect people with normal vision to have the same "far limit", and giving them glasses with a positive curvature would reduce their field of vision in a predictable way.

But that's just an assumption, to know if the result is at all accurate I would compare both your vision without glasses and his vision wearing the opposite glasses with an online simulator like this or a clip of such a simulation. And these by themselves give him already a good idea of what you see, without the need for glasses. If you google for myopia simulation you'll probably find more of them. Another option (if you want to try out the glasses idea) would be a simple eye chart to see if his vision is as bad as yours. Ssscienccce (talk) 14:17, 7 December 2013 (UTC)[reply]

Follow up to "Surface gravitation of "kissing" spheres"

Imagine two non-rotating black holes rushing past each other on a non-collision path. They both have a spherical event horizon when they are far away from each other. Based on the same Roche Lobe mentioned earlier, the event horizons ought to become non-spherical as they approach. The way I figure it, the event horizons should recede from each other. That should let you have access to a part of space-time previously inaccessible. Is that correct? Does it let you peek into the outer bit of a black hole, or does space on our side of the black hole stretch, or what? Tdjewell (talk) 13:32, 6 December 2013 (UTC)[reply]

Hmmmm, black holes aren't really known for a generous refund policy. Bear in mind that "orbits" near a black hole tend to end in sorrow - even a neutron star is surrounded by a photon sphere. Gravity and acceleration are more or less the same thing, and if acceleration isn't going to get you out, neither is gravity. Wnt (talk) 16:31, 6 December 2013 (UTC)[reply]

Binary black hole is this sort of situation. The black holes will not remain spheres in this situation, they will extend towards each other, (not recede) and may form a connecting tube, followed by merge. Any point beyond the event horizon will stay there, that is what event horizons are, the point of no return. If you can return, then it is not an event horizon. Graeme Bartlett (talk) 19:52, 6 December 2013 (UTC)[reply]

If the OP doesn't mind asking, and just from my own curiosity, what was the reasoning behind thinking they would recede from each other? μηδείς (talk) 02:16, 7 December 2013 (UTC)[reply]

I assumed the net gravitation towards one black hole would be offset by the other, so what used to be the event horizon would move closer to the black hole, because now you could escape because of the other black hole puling the other way. 96.241.147.59 (talk) 14:28, 7 December 2013 (UTC)[reply]

The important simplified measure is the gravitational potential, rather than the force. If the negative potential is greater than the mass energy in the object, then it would be past the point of no return. Graeme Bartlett (talk) 19:52, 7 December 2013 (UTC)[reply]

Do humans' body size increase gradually in recent thousands of years?

I just recalled a newspaper article says that humans' body size did increase, one evidence given is that modern adult can barely fit in a medieval armor. Is that true?--chao xian de lun zi (talk) 14:23, 6 December 2013 (UTC)[reply]

See the Wikipedia article titled Human height. You can also answer your question by typing "History of human height" or other similar searches into Google. --Jayron32 15:11, 6 December 2013 (UTC)[reply]

It's worth noting that our article, reflecting the present state of the literature, treats the subject without consideration of the role of the inheritance of acquired characteristics (transgenerational epigenetic inheritance). This is hinted at as a possibility, however, in recent reviews ([23]) because so many of the factors involved are circulating hormones that could affect epigenetic marks on genes within the gonads. As a result, though properly written, our article probably misses the most important mechanisms. Wnt (talk) 16:47, 6 December 2013 (UTC)[reply]

That is a design feature, not a flaw. Rmhermen (talk) 17:32, 6 December 2013 (UTC)[reply]

Historically, nutrition has been the limiting factor in potential size at maturity. People from the same ethnic group, transported to an affluent nation, tend to outgrow those who stay in an impoverished homeland. This blog has some useful references. Human height mentions changes in growth trends in relation to nutrition as well, with significant increase in height before 1950 and stagnation since then. μηδείς (talk) 22:18, 6 December 2013 (UTC)[reply]

Is it dangerous to eat raw eggs?

Is it dangerous to eat raw eggs? --78.156.109.166 (talk) 20:37, 6 December 2013 (UTC)[reply]

Danger is a relative concept. Per Raw_egg#Contamination, 1/30,000 eggs are contaminated with Salmonella. μηδείς (talk) 20:43, 6 December 2013 (UTC)[reply]

It doesn't seem to bother the average weasel. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:55, 6 December 2013 (UTC)[reply]

Saying they are dangerous can be detrimental as well. Just ask Edwina Curry, she lost her post as junior health minister and broke up with John Major after mentioning salmonella! Ssscienccce (talk) 14:30, 7 December 2013 (UTC)[reply]

The other health risk (for consumers of vast quantities of raw egg) is biotin deficiency due to the presence of avidin in raw eggs. Cooking the eggs would denature the protein and render it inactive. - Nunh-huh 01:49, 7 December 2013 (UTC)[reply]

As the page lined by Medeis mentions, some eggs may be produced by vaccinated hens to reduce or eliminate the possibility they contain Salmonella. Some markets also sell pasteurized eggs, which will kill Salmonella without hardening the egg if the pasteurization was done correctly. Someguy1221 (talk) 01:59, 7 December 2013 (UTC)[reply]

μηδείς: Had a bad stomache recently and I often eat 'em raw. Someguy1221: Yea, already saw that. But why do they vaccinate if most bought raw eggs (at least in Denmark) has text that reads: Must be cooked to 75°C, else use pasteurized eggs? --78.156.109.166 (talk) 20:32, 7 December 2013 (UTC)[reply]

Self-healing cutting mats

Many cutting mats seem to claim to be "self-healing". I bought a cheap cutting mat on ebay and, unsurprisingly, it doesn't self-heal like the manufacturer claims. Does any mat? How? --78.148.106.99 (talk) 21:12, 6 December 2013 (UTC)[reply]

A simple internet search for 'self healing cutting mat' or I suspect any similar term will find our article Self-healing material as well as this non RS [24] which has some useful info in the comments and also links to [25] with again some useful comments. As well as a number of videos, most of them fairly adverty, but some have some useful info, e.g. [26] identifies [27] as one material used although I think arguably doesn't really meet our article's definition of self healing. Whether it meets yours I can't say as it was undefined although I assume you weren't expecting the mat to rejoin if cut in half (to be honest I don't think many of these mats will meet my definition either). Related searches will find more research on self healing materials (not necessarily for mats) such as this recent one [28]. Nil Einne (talk) 23:50, 6 December 2013 (UTC)[reply]

"Bridge" rectifier

I know what a rectifier is but I don't know why I sometimes see the word "bridge" applied. What is the word bridge doing there? Are there more than one type of single-phase full-wave rectifier of the which the one using four diodes is only one? --78.148.106.99 (talk) 23:34, 6 December 2013 (UTC)[reply]

Correct. There are bridge circuits that are not rectifiers; and there are rectifier circuits that are not bridges; and there are variants of both that use diodes (and others that use no diodes). When a circuit satisfies all criteria - built from diodes in a bridge configuration for the purposes of rectifying a signal, then it is a "diode bridge rectifier." Nimur (talk) 00:15, 7 December 2013 (UTC)[reply]

Geography question: which GNIS code should we use?

(Full details at Talk:Buena Park, California)

There are two different GNIS codes and altitudes for the city of Buena Park, CA:

~~https://geonames.usgs.gov/pls/gnispublic/f?p=132:2:533393829700819::NO:RP::~~
https://geonames.usgs.gov/pls/gnispublic/ (type 2409932 into the Feature ID box)
Feature Name: City of Buena Park
ID: 2409932
Class: Civil
Ele(ft): 72

~~https://geonames.usgs.gov/pls/gnispublic/f?p=132:2:533393829700819::NO:RP::~~
https://geonames.usgs.gov/pls/gnispublic/ (type 1652676 into the Feature ID box)

Feature Name: Buena Park
ID: 1652676
Class: Populated Place
Ele(ft): 75

So, which should we use? --Guy Macon (talk) 23:37, 6 December 2013 (UTC)[reply]

Your two links are identical... --Jayron32 02:53, 7 December 2013 (UTC)[reply]

This is Buena Park (second entry) :https://geonames.usgs.gov/pls/gnispublic/f?p=132:3:533393829700819::NO:3:P3_FID,P3_TITLE:1652676%2CBuena%20Park --Auric talk 03:09, 7 December 2013 (UTC)[reply]

Wait a minute, are we splitting hairs over 3 feet? The distance between your belt buckle and your head? Pick one and go with it. If someone else complains, tell them to find something greater injustice in the world, because this problem is pretty low on the "stuff that one needs to waste bits on the Wikipedia server" about... --Jayron32 03:12, 7 December 2013 (UTC)[reply]

Stating the elevation of an entire 10 square mile city to a precision of better than 10 feet is kinda stupid anyway. Suppose someone dumped a pile of dirt on the spot where the measurement is taken on one day and removed it again the next? Suppose they measured the elevation at City Hall, then built a new one after levelling the site or something....should we say that the entire city changed elevation? I'm quite sure there is much more than three feet of vertical elevation variation across the city! Personally, from a scientific/mathematical perspective I would change the article to say 70 feet in order to avoid implying more precision than is realistically possible!

If I had to guess as to why you're seeing two different numbers then I'd go with the guy who answered this question on "The straight dope" - which is that there isn't a standard way for people to describe the elevation of a city...and often it's just someone eyeballing it from a contour line on an outdated map. He found two different sources for the elevation of Denver that differed by 20 feet - and our article on Denver (wisely) specifies a range of elevations rather than a single number.

Truly - this is a waste of time. If you really want to improve the article, find a photograph of the place to stick in there - given the current state of the article, that would do more to improve it than almost anything else!

SteveBaker (talk) 06:41, 7 December 2013 (UTC)[reply]

The URL thing is weird. I thought that I had made a simple cut and paste error, but it turns out that the GNIS site gives you two different pages with two different GNIS numbers using the exact same URL. I fixed it by replacing the URLs with instructions on how to do the queries.

As for the importance of the elevation, those who think that getting it right is not important are welcome to not respond and move on to a question that they deem important. Some of us care about getting even small things right. See Talk:Slackware#ANNOUNCE: Slackware Linux Distribution 1.00 for one example. There is room in Wikipedia for both types of editor.

As for the speculation about eyeballing contour lines on outdated maps, the dataset GNIS uses is the USGS National Elevation Dataset. as it says at http://ned.usgs.gov/ , "The NED is a seamless dataset with the best available raster elevation data of the conterminous United States, Alaska, Hawaii, and territorial islands. The NED is updated on a nominal two month cycle to integrate newly available, improved elevation source data. The NED is derived from diverse source data that are processed to a common coordinate system and unit of vertical measure". Yes, modern cartography can indeed determine the average elevation of a city in the continental US within a meter. LIDAR is good enough to get you within a half meter or so.

Of course this being Wikipedia, what matters is what is sourced. In general, when we run into contradictory sources, we don't arbitrarily decide that the difference is unimportant and randomly pick one source.

I appreciate your time, but I am going to try another forum. Perhaps Wikipedia:WikiProject Maps. --Guy Macon (talk) 08:00, 7 December 2013 (UTC)[reply]

December 7

Recoil force and momentum

When a gun fires, the recoil it produces is equal and opposite to the momentum of the projectile. But since recoil is a force, why isn't recoil calculated using force? ScienceApe (talk) 03:11, 7 December 2013 (UTC)[reply]

Recoil, at least as defined by our recoil article, is not a force -- it is the result of a force. Looie496 (talk) 04:12, 7 December 2013 (UTC)[reply]

The law of physics that most easily applies here is "Conservation of linear momentum". The gun and bullet are initially stationary and have zero momentum. When you pull the trigger, the bullet goes one way and the the gun the other way. Because the directions of their motions are opposite, the total momentum still adds up to zero and the conservation law applies...and naively, you can say that the mass of the bullet multiplied by the muzzle velocity is equal to the recoil velocity of the gun times the mass of the gun. This isn't quite true - as I'll explain in a moment.

Doing the calculations using Newtons' law (that every action has an equal and opposite reaction_ is also applicable at the instant that the gun fires - but force causes acceleration and it's a complicated calculation because the bullet is exposed to the forces of the expanding gasses over some amount of time and you'd have to integrate that continually varying force curve to calculate the final velocity of bullet and gun. That's a perfectly valid calculation to do - but it's complicated and relies on knowing a heck of a lot about gunpowder, bullets, barrels and so forth. Using conservation of momentum is much simpler - and gets you the answer in one step without having to know whether the gun is powered with gunpowder, a big spring, compressed air or an elastic band! You could use Newton's law to arrive at the same answer - but it would be painful to crunch the numbers.

Of course, in the case of any real gun, simply calculating the momentum of gun and bullet won't get you the correct result because the gasses that expand and leave the barrel also have momentum. So the recoil of the gun will actually be a little more than you'd predict from the mass and velocity of the bullet alone. Note that firing a blank round (where there is no bullet) still produces a recoil due to the expanding gasses.

So the actual FORCE of the recoil will depend on the nature of the gun. The force might start off as a huge force and gradually reduce - or it might be a continuous smaller force depending on ugly details of the propellant's chemical reaction - it's certainly a complicated matter and cannot possibly be stated as a single number "The force of the recoil is X" because you can only say "The force of the recoil Y milliseconds after the trigger is pulled is X".

However, the VELOCITY of the recoil by the time the bullet has left the barrel (and neglecting friction, etc) is simply stated as a single number and easily calculated.

SteveBaker (talk) 04:41, 7 December 2013 (UTC)[reply]

To put that more simply, or at least more sillily, suppose you have a witty bitty gun - in fact, it is the same weight as the bullet and has the same cross-section/frictional force in the air. What happens if you fire it? Well, if it is capable of firing the bullet properly, it will go back at the same speed as the bullet, teaching the shooter a valuable but perhaps final lesson in physics. On the other hand, suppose you shoot the bullet out of a monstrous solid gold illuminated blunderbuss that weighs two hundred pounds. Then the force of the recoil will be no more than the force felt by the guy standing behind the person you shoot when he gets hit by the bullet, provided it doesn't go through. Of course the total force felt over time is still F delta t, the change in momentum. You can change how much you get at any given moment, much as you can change the force you feel when moving something by using a lever. Wnt (talk) 06:20, 7 December 2013 (UTC)[reply]

NASA's recent picture of Saturn

NASA recently released an image of Saturn they put together from images recorded by the Cassini probe. You can see the picture here: http://apod.nasa.gov/apod/ap131113.html It's a lovely picture, but there are some features here that I do not understand. Our viewpoint is from the dark side of Saturn looking back towards the sun, which is obscured by the planet.

1. Why is the face of the planet not just completely black? Some people have suggested that it is being illuminated by light being reflected from the rings. I find it hard to believe that there would be enough light reflected from the portions of the rings that are in sunlight to illuminate the entire face of the planet, much less produce an image that could be recorded by our spacecraft.

2. The black band: there is a narrow white band encircling the face of the planet. It is interrupted in some places, but it is basically a circle. Around the upper half of this white ring there is a wider black band of varying width, but it is generally several times wider than the white ring. I presume the white ring is sunlight being refracted through the atmosphere, but what is the black band?

I'm beginning to think this is just a publicity shot put together by the marketing department and has no bearing on reality. 50.43.12.61 (talk) 05:12, 7 December 2013 (UTC)[reply]

See ringshine. The Moon illuminates Earth, and while the particles surrounding Saturn are much smaller, the Sun never penetrates the interior of a rock - only their surface area matters.

The black band mystifies me also, now that you point it out - good question! I'm tempted to speculate about refraction, but I'd be blowing smoke. Wnt (talk) 06:11, 7 December 2013 (UTC)[reply]

Everything there seems consistent with NASA's caption.

The rings glow from transmitted and reflected light - except where they are in the shadow of the planet. The planet softly glows in reflected light where it lies close to the glowing sections of the ring (which is exactly what NASA say in their caption, I don't think they'd lie about such a thing!).

The shadowed parts of the ring are occluding that dim light and making black bars across the planet. Bear in mind that the sensors on this spacecraft are quite sensitive - and they may have left the shutter open for a long time in order to capture enough light to form an image. So it really doesn't matter that this twice-reflected sunlight is very dim...the camera could easily capture it if it took the photo over many hours.

Bear in mind that the sun isn't a zero-sized dot...so it actually illuminates slightly more than a hemisphere of the planet...that, along with atmospheric scattering easily explains the bright white line...which is also occluded by the thicker sections of the rings.

The black region is harder to explain. Personally, I suspect that it's an artifact of the motion of the spacecraft while the picture was taken. Cassini is in a polar orbit around Saturn - so it's entirely plausible that it's moving in the vertical direction of the photograph. There is no other explanation that I could imagine for why the black bar would appear at the top of the planet and not the bottom.

The existence of such an imaging artifact strongly suggests that NASA did not in fact heavily doctor the photo because they could easily have removed it had they wanted to.

SteveBaker (talk) 06:16, 7 December 2013 (UTC)[reply]

I doubt it's an artifact - think of how high-res Cassini images can be! And it was stitched together from hundreds of individual shots. [29] Nay, we're still stumped! Wnt (talk) 06:24, 7 December 2013 (UTC)[reply]

No, that's EXACTLY my point. Because it's stitched together from a lot of images, the spacecraft must have moved between shots. Certainly you can process the image to align the photos together to minimise this effect, but in order to do that, you are (in effect) picking a particular point of view from which you're assembling the composite. But there are guaranteed to be parts of the sky that are visible from that chosen point of view that were never present in any of the images...and because we know that the craft was moving vertically - it makes perfect sense that this produces a section of the image at the top edge of the planet for which no data is available. Rather than falsify this data, NASA leaves it blank. SteveBaker (talk) 06:49, 7 December 2013 (UTC)[reply]

OK, I got it. I thought about this backwards on my own, but this set me back on the right path. The thing is, the rings that you see blocking the light on the rear side of Saturn are between Cassini and the planet, on the far side from the Sun. Also on that side: Saturn's shadow. Now Saturn's shadow is going to be about the same size as Saturn (a little smaller for totality, a little bigger for penumbra) but Cassini is closer to the farside part of the rings than it is to Saturn. So from its perspective the shadowed part of the rings will look a little bigger than Saturn itself. Wnt (talk) 06:34, 7 December 2013 (UTC)[reply]

That makes no sense. SteveBaker (talk) 06:49, 7 December 2013 (UTC)[reply]

Well, look at the source I cited, #4 on the picture. That is the black ring you mean, right? (It's substantially larger in that photo because the sun is less perfectly aligned with the planet and probe) Wnt (talk) 12:18, 7 December 2013 (UTC)[reply]

It looks to me like there are dark rings which absorb light from Saturn. And, as far as the light-colored rings reflecting enough light, consider that we can see them from Earth with a minimal telescope, so they must be reflecting lots of light to be visible at that distance. StuRat (talk) 09:32, 7 December 2013 (UTC)[reply]

Does the fact that Saturn is a gas giant, i.e. not solid, have a bearing on why we see the black ring? --TammyMoet (talk) 13:32, 7 December 2013 (UTC)[reply]

TammyMoet, I think not. The artifact you see as a black ring is more probably a local contrast artifact, because what we are looking at here is a high dynamic range photograph whose parameters would blow the minds of most earthly photographers. The tone mapping algorithm in that area is being asked to combine imagery where adjacent pixels have photopic intensities that correspond to thousands of times - several dozens of bits, or hundreds of decibels - of dynamic range. Even NASA's greatest imaging experts cannot realistically create an algorithm that does so with zero artifacts.

A few months ago, when Cassini turned to photograph us for NASA's "Wave At Saturn" public relations program, I wrote a very lengthy article on Cassini's imaging system that I distributed to my friends and coworkers. I will dig into my archives and extract a few pieces that may be relevant to today's discussion. Nimur (talk) 16:30, 7 December 2013 (UTC)[reply]

Excerpted from my summary, and based on these resources:

"Cassini's narrow-angle camera is a 1-megapixel 1024x1024) CCD with 12-micron radiation-hardened pixels, manufactured by Loral Corp. It shoots through an f/10.5 2-meter Cassegrain-style Ritchy-Chretian mirror. Each of the 24 individual color filters are captured sequentially with an optical filter wheel. Q.E. ranges from 10% to 40% across visible wavelengths. The pixel well is 120,000 electrons per pixel, with optional 2x2 and 4x4 analog binning. Pixels are sampled at 12-bits. Sensor read-out takes a minimum of 12 seconds. For transmission to Earth, pixels are optionally gamma-adjusted and truncated to 8-bits; and optionally transmitted in JPEG form."

"...Saturn is blocking the sun; and each exposure will probably last several minutes, depending on the AE algorithm, so the total photograph will take several hours."

For a horrifying glimpse at the mathematical constraints, read: A Modern Tour of Image Filtering, which was published in IEEE Signal Processing Magazine a few months ago. The difficulty in astrophotographs is that the contrast is so incredibly high, any stable algorithm must clip or blur. This is state of the art. You probably won't find better HDR algorithms outside of the Jet Propulsion Lab that could produce a nicer image with less artifact. (Though, I encourage any enthusiasts to download Hugin (software) and try!) Alternately, we could have a digital artist go in and "fill" the dark circle - but at that point, our output image is no longer rendered from real data. Nimur (talk) 17:13, 7 December 2013 (UTC)[reply]

This is partly true in the sense that the photo is clearly normalized so that the dim farside can be compared directly to the illuminated rings. But the black band itself is not an artifact. It's the shadow of Saturn on the ring behind it. Which looks bigger than Saturn itself because it's closer to the probe. Wnt (talk) 21:46, 7 December 2013 (UTC)[reply]

Wnt, the entire dark side of the planet is in "the shadow!" The dark ring is an artifact. It is rendered darker, but that is not an accurate representation of the number of photons from that area. If it were physically darker than the unilluminated side of Saturn, that would mean the penumbra is more shadowed than the umbra, which is not physical. That dark region rendered to a lower pixel value than some of its neighbors, even though it corresponds to a region that had more photons. Sounds like an image artifact to me!

Cassini FAQs from JPL: "The camera measures light from an object at each point in an image and assigns it a number from zero to 4095 depending on its brightness. Sometimes the scientist can't afford to send this amount of data for each pixel because of the amount of storage it takes. The camera has the ability to convert this range of values to those from zero to 255. The camera does this according to a preset table of values designed by the scientists. This table devotes many of the 256 levels for less bright things and less levels for brighter pixels. Part of calibrating an image on the ground is to reverse this table and get back pixels in the range of zero to 4095. Because you're looking at the raw data, images sent back in this mode will have dimmer things look brighter compared to the brighter parts of the image than in images not in this mode...The ideal use of this mode is for image scenes that are dark with almost all of the pixel values less than 255. If the scene is simple with gradual increases in brightness, then even if the original values get over 255 and go dark again, the scientists can figure out what the real value was. If the scene is very complicated or the original values are much brighter than 255, the image can have many bright and dark transitions with strange contours. In this case, the image will look very bizarre but not have much scientific value."

This dark region is an artifact, in the sense that the rendered image not have a monotonic tone map. You can experiment with this yourself: play with some images in GIMP, for example. Grab some photographs with really high contrast. Set up a nonmonotonic luminosity curve. Watch what it does to dark regions, bright regions, and high-contrast edges. Nimur (talk) 23:19, 7 December 2013 (UTC)[reply]

Hamiltonian

How does one calculate the Hamiltonian of a system? Hamiltonian (quantum mechanics) lists a lot of special cases. How are these derived, in general? 150.203.188.53 (talk) 09:27, 7 December 2013 (UTC)[reply]

They are derived by calculating the Hamiltonian in terms of generalized orthogonal coordinates. The machinery of the mathematics is very straightforward, albeit quite lengthy to write: the Hamiltonian is just kinetic plus potential energy; and to solve the dynamics, calculate the differential of the Lagrangian with respect to the differential of the generalized coordinates with respect to time; and subtract that from the same, premultiplied by the generalized velocities. What is this doing ? It's constructing a general representation of action, because according to physicists like LaGrange and Hamilton, minimization of action is a more fundamental statement that encapsulated conservation of energy and conservation of momentum.

The hard part, though, is not the mathematics: it is the transformation of a real physical system into some generalized form that is actually valid. When you look at an automobile, your gut instinct is to desrcribe it in cartesian coordinates. It has an x,y,z position. If you're an advanced physics student, you actually append a general velocity for x,y,z that is represented independently from the position, because you care more about the phase space of the car's momentum than you do about the time derivative.

But if you're a very advanced student of physics and engineering, you recognize that this is insufficient. You need to postfix your coordinate vector with new coordinates describing, say, the angular position of each of the wheels. You need coordinates to represent harmonic modes of vibration of the sheet metal. You need to write coordinates for how much potential energy is in the crumple zone. You need to write everything that can store mechanical potential energy in the car, so that you can express the kinetics of the car in all cases. And, you must make those coordinates orthogonal so that you are can explicitly solve for mechanical coupling. Now you need an applied mathematician to help you write those vectors! You'll probably need a lot of matrix algebra to verify that your representation is valid. Most of all, you have to know which physical action is important enough to write down in your coordinate vector.

In the quantum case, you have to do all of the above, and satisfy additional constraints - some of your vectors do not satisfy regular mathematical relations, because they are physically quantized. You have to replace basic operations like addition and subtraction with physical operators, so that you ensure the system remains mathematically quantized.

Once you have represented the system in those coordinates, your math is trivial: plug and chug, as they say. The formula is splattered throughought every physics textbook and most of our articles on the topic,; and soon it will be burned indelibly into your brain. It's just a shorthand way of writing out some vector math. If you take a simple quantum mechanics class, you'll solve the Hydrogen atom, and somebody will tell you "use these four quantum numbers." If you proceed to the more general case, nobody will tell you which quantum numbers you need - and just like the car example, you have to know. Nimur (talk) 16:10, 7 December 2013 (UTC)[reply]

Life cycle of frog

Could you please tell me about the life cycle of a frog?Mominjawad13579 (talk) 10:21, 7 December 2013 (UTC)[reply]

See Frog#Life_cycle, and come back and ask us if you have any specific questions. Rojomoke (talk) 10:47, 7 December 2013 (UTC)[reply]

An orbit that any point on the planet gets the same amount of radiation

Hi,
I would like to ask if there is an orbit, that when you sum up the amount of radiation in each point on the planet you get the same result.Exx8 (talk) 15:51, 7 December 2013 (UTC)[reply]

Radiation from the sun around which the planet orbits I assume? if you talk about the amount received during a complete orbit, then you may get close to the same value, I think, when the axis of rotation of the planet lies in the orbital plane and the orbit is circular. Could be I'm forgetting something obvious due to sleep deprivation, but apart from small parallax differences (because the poles stay on the orbital plane, the rest of the planet goes above and under it, so the mean distance from the sun would be somewhat larger plus a small difference in the angle of incoming radiation), the total amount of incoming radiation should be the same everywhere. I think... Ssscienccce (talk) 21:38, 7 December 2013 (UTC)[reply]

I will Survive!!!!

This abdominal cavity foam is really a weird way to stabilize a patient with blunt trauma.

I wonder if there are actual stories of persons, whether in a battle field or in the wild, who suffered very serious internal bleeding blunt trauma, managed to survive by crawling or hiking a long way to rescue. -- Toytoy (talk) 16:31, 7 December 2013 (UTC)[reply]

ROFL - I thought the stuff in the video looked like polyurethane foam spray insulation that I've seen put around the inside of a garage. And... it is! Folks, don't try this at home... but maybe you could... :) Wnt (talk) 21:43, 7 December 2013 (UTC)[reply]

Let me guess, they didn't (nor will they) bother to test the Ecuadorian fungus Pestalotiopsis, or it's enzymes for the ability to consume the polyurethane in the wound after the injury has stabilized, even in the "animal" trials. Nor did they bother to see how the polyurethane would interact with anything that actually regenerates the damaged tissue. Dirty deeds done cheep. CensoredScribe

List of experiments preformed in space

Is their a convenient list you can browse which compiles all the experiments preformed by all the worlds space agencies currently? I had a few I was interested in; like whether the conditions of a burning building have been approximated on a space station (I know that fire+space station=extremely dangerous) I was also wondering whether someone has already investigated the effects of space on Saprophytic fungi and Black carbon, either alone or mixed together. CensoredScribe (talk) 17:30, 7 December 2013 (UTC)[reply]

Here's NASA's list anyway. Clarityfiend (talk) 23:52, 7 December 2013 (UTC)[reply]

Thank you for that list Clarityfiend; I don't suppose there is a similar one from the Russian space agency Roscosmos, formerly RASA? I'd be interested in if they've taken that radiotrophic chernobyl mold into space yet. CensoredScribe (talk) 00:41, 8 December 2013 (UTC)[reply]

Tsunamis from non-earthquakes.

How often do tsunamis come from other sources than earthquakes? --78.156.109.166 (talk) 20:07, 7 December 2013 (UTC)[reply]

The article Tsunami lists various ways they can be triggered. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:22, 7 December 2013 (UTC)[reply]

Mahuika crater is one - possible - example. --Cookatoo.ergo.ZooM (talk) 23:26, 7 December 2013 (UTC)[reply]

Presumably the impact causing the Chicxulub crater would have triggered a significant tsunami. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:37, 7 December 2013 (UTC)[reply]

Ulysses butterfly

If the Ulysses butterfly is only found in Australia, New Guinea and the Solomons according to the article, then how did two of them wind up being photographed in Vienna as the main page picture says? 24.23.196.85 (talk) 02:10, 8 December 2013 (UTC)[reply]