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April 9

Chemical Test

How is a chemical test developed and/or discovered.Please explain with an example.117.194.234.95 (talk) 03:22, 9 April 2014 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. StuRat (talk) 04:51, 9 April 2014 (UTC)

I am not a student of school college university.I asked you question that has nothing to do with homework.I disapprove prejudiced notions.I dont think it will be a good thing to go to school/college in thirties.I soloicit your answer to my query and not these malicious conjenctures.117.194.249.163 (talk) 13:32, 9 April 2014 (UTC)

What chemical test did you have in mind? Wikipedia has an article titled Chemical test that discusses many wet chemistry chemical tests. There's a long list of them. If you read articles on any one of them, it may discuss how that test came to be. --Jayron32 14:14, 9 April 2014 (UTC)

I think the OP is thinking about a "chemical test" like the pH paper that you find so often in Chemistry labs. In that case, we may have to look up the history of the pH paper. But it all depends on whatever "chemical test" you're talking about. 140.254.227.100 (talk) 22:02, 9 April 2014 (UTC)

Skin cream gun control study

Hello, maybe you've heard of the study in which participants had to assess the results of a (fake) study about the efficacy of either skin cream or g*n c*ntr*l laws (with exactly same numbers), which purportedly showed that peoples' math reasoning ability declined when the math problem in question had to do with a politicized issue. I'm interested in the (fake) problem itself:

	rash got better	rash got worse
patients who used the cream	223	75
patients who didn't use the cream	107	21

After that the participants had to "indicate whether the experiment shows that using the new cream is likely to make the skin condition better or worse." It says on the internet that it's not enough to compare the numbers, one has to do the ratios. But what ratios? I see two ways of going about solving this:

• Of those who used the cream, 223/(223+75)=75% got better, vs 107/(107+21)=84% of those who didn't => ergo, cream sucks
• Of those whose rash got better, 223/(223+107)=68% used the cream, vs 75/(75+21)=78% of those, whose rash got worse =>cream still sucks

Which way is the correct one and why? (If I'm ever recruited for a similar study:) And is it incidental that in this example they devised, the conclusion is the same either way or is it mathematically inevitable?

Asmrulz (talk) 05:37, 9 April 2014 (UTC)

I'm not an expert, but it seems to me that the 1st method is correct. The 2nd group is your control group, you are comparing the effectiveness of the treatment vs the control group, which can be "no treatment" as in this case, or can be the current best available treatment (especially where withholding treatment all together would be unethical). So yes, put simply with the treatment 75% got better, without it 84% got better, so the treatment actually performed WORSE then no treatment at all. Vespine (talk) 06:02, 9 April 2014 (UTC)

You can only use the second method if you extrapolate the numbers ("normalize"?) to make the population sizes equal. The first group has 298, the second only 128. Multiply the second row by 2.328 and you get 249 and 49. That makes it clearer that using the cream has no particular effect. In fact, it appears that letting the body's own immune system handle it seems to be better than using the cream. But as to whether it "sucks" or not, you would have to do some kind of statistical analysis to see whether the 249 and the 223 are statistically different across the given population. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:25, 9 April 2014 (UTC)

Why the asterisks on "gun control" ? Is it considered an obscene term in your part of the world ? StuRat (talk) 08:33, 9 April 2014 (UTC)

It's from the Jargon file of hacker slang which I read long ago (link) It's funnier this way :) Asmrulz (talk) 10:16, 9 April 2014 (UTC)

The first method where one comparess the ratios of improvement in two unrelated populations is a rational test of the cream. The second method conflates the ratio of interest with the ratio of test and control populations, which is arbitrary, and cannot justify its conclusion. In this data the cream demonstrated less improvement 75% than whatever else (unspecified) other people did that improved 84% of them. The cream really sucks but the lesson here will not be welcomed by g*n r*ghts l*bby*sts with kn**-j*rk th*nk*ng st*ck *n 1791. 84.209.89.214 (talk) 13:08, 9 April 2014 (UTC)

• I agree with others that the first method is the correct one. But let me just add a note that the differences are not actually statistically significant (p = 0.0574 using Fisher's exact test, calculated using this tool, so the conclusion in a published paper would be that the data don't establish that the cream has any effect. Looie496 (talk) 14:02, 9 April 2014 (UTC)

Thanks to all of you for your answers. Asmrulz (talk) 14:43, 9 April 2014 (UTC)

Heat and magnetic fields.

As I understand it, heat destroys magnetism. So why then, does the magnetic field of the earth survive when the core of our planet which is hot enough to create a molten core? — Preceding unsigned comment added by 86.6.96.72 (talk) 09:59, 9 April 2014 (UTC)

Your understanding is wrong. --DHeyward (talk) 10:12, 9 April 2014 (UTC)

Explain?

Heat can stop a magnet being magnetic, this is true. Read the following to understand why we have a magnetic field around the Earth. http://en.wikipedia.org/wiki/Earth's_magnetic_field#Physical_origin 217.158.236.14 (talk) 11:29, 9 April 2014 (UTC)

A Magnetic field is produced by electric charges in motion i.e. Electric current. The way that works was explained by Maxwell in his elegant set of differential equations which hold true at all temperatures that we experience. 84.209.89.214 (talk) 12:09, 9 April 2014 (UTC)

Just to clarify, I am aware of the above and I am not debating it, however it is also true that ferromagnets can lose magnetic properties when heated to above the Curie temperature.217.158.236.14 (talk) 12:23, 9 April 2014 (UTC)

Yes, but that isn't because "heat destroys magnetism". It's because heat alters the crystal structure of the iron so it no longer has ferromagnetism. Different ideas. --Jayron32 12:31, 9 April 2014 (UTC)

Agreed, which is why I said "Heat can stop a magnet being magnetic", and not "destroys magnetism". — Preceding unsigned comment added by 217.158.236.14 (talk) 13:14, 9 April 2014 (UTC)

• To add detail to the answers above: ultimately magnetism arises from the movement of large numbers of electric charges in a synchronized way. In a ferromagnet (an ordinary solid iron magnet), the synchrony comes from the fact that large numbers of atoms are frozen into alignment with each other. If you heat a ferromagnet to near the melting point, the atoms lose their alignment and the magnetic field disappears. But the Earth is not a ferromagnet. Its magnetic field arises from electric currents flowing coherently through the magma on a vastly larger scale. The reason why that happens, incidentally, is not very well understood -- but clearly it does happen. Looie496 (talk) 13:52, 9 April 2014 (UTC)

Vast energies are stored in the Earth's magnetic field and evidence in the Geologic record that it has periodically reversed polarity is evidence that it is part of a resonant system. As yet no simple global model of Earth's resonant modes, that may be linked with resonances in other bodies, has emerged because the short time span of collected data is plagued by Heteroscedasticity of local anomalies. 84.209.89.214 (talk) 16:02, 9 April 2014 (UTC)

(Hey, you seem to be giving some good responses/refs here recently... or at least I think so, but it's hard to keep track of IPs... any chance we can convince you to register? It is less anonymous and more pseudonymous than signing with an IP, but it may actually increase your privacy too :) SemanticMantis (talk) 22:58, 9 April 2014 (UTC)

I'm pretty sure the editor behind the IP has had multiple accounts and are technically WP:block evading. People are just turning a blind eye because they aren't harping on about its/it's and other grammar and spelling issues. However registering another account is still probably not a good idea, instead requesting an unblock under one of their blocked accounts, preferably the main one. Nil Einne (talk) 05:01, 10 April 2014 (UTC)

(Thank you for those kind comments. Nil Einne can identify me easily. "Its" and "it's" mean different things. A registered user pointed that out a while ago.) 84.209.89.214 (talk) 12:52, 10 April 2014 (UTC)

Many factors establish the earth's magnetic field. It's not constant and rotation and heat affect it. If you want an extreme case, look at the sun. It has no iron core. It's created by heat and rotation. It flips N/S polarity every 11 years and often has a weak quadropole during maximum sunspot activity. The resultant magnetic field is very strong at sunspot minima. The earth has a different mechanism, but it's not correct to simply associate heat with the destruction of the magnetic field. There are solid magnetic properties as well as rotating, conducting fluids. See Dynamo theory to see how the Earth's magnetic field is created and changes. A ferromagnetic solid may reflect the magnetic field imprinted on it, but it's not necessarily the force that is responsible for the magnetic field. --DHeyward (talk) 05:42, 10 April 2014 (UTC)

Institutional dependence

Hi there. I am interested in a phenomenon whereas an individual who spends many years in a restrictive environment, e.g. prison, becomes dependent on the institution and develops unhealthy reactions sabotaging normal release process for instance. I am also interested if the phenomenon like this has ever been coded, if there is a corresponding ICD-9 or ICD-10 code describing it. Thank you --AboutFace 22 (talk) 20:01, 9 April 2014 (UTC)

Stockholm syndrome came to my mind. Brandmeister^talk 20:07, 9 April 2014 (UTC)

Oh lordy! I just was about to get back and add that in my understanding the phenomenon I am looking for or the code thereof is NOT the same as Stockholm syndrome. It should be distinct from it. Thanks.--AboutFace 22 (talk) 20:10, 9 April 2014 (UTC)

I think Learned_helplessness is relevant, since it describes the effect that a punitive environment has on individual volition. OldTimeNESter (talk) 20:17, 9 April 2014 (UTC)

So, you are asking about individuals who become institutionalised? 86.146.28.229 (talk) 21:21, 9 April 2014 (UTC)

Thank you. The last two suggestions are quite valuable. I have to think about it, especially the institutional syndrome. --AboutFace 22 (talk) 01:50, 11 April 2014 (UTC)

Quadruple axels and beyond

What actually prevents a figure skater from making quadruple or even quintuple axels and similar feats? And what capabilities should (s)he theoretically have to perform them and similar stuff? Is it just a muscular force of legs during the jump-off, adequate jump height giving more time and a good sense of balance? --93.174.25.12 (talk) 20:04, 9 April 2014 (UTC)

The article on Jumping mentions the force-velocity ratio for muscles, which establishes the biomechanical limits on jumping height. OldTimeNESter (talk) 20:29, 9 April 2014 (UTC)

Basically you have to do it "just right", or you'll be either over or under rotated and will land with the skate blade not pointing in the right direction, and will probably fall. You also have to keep your center of gravity "just so", or you'll land at the wrong angle... and will probably fall. The more spins you have in a given jump, the harder it is to do. But it will happen eventually. The double axel was once considered tough to do. And lots of skaters fall on triple axels. As the commentators said at the Olympics recently, "It's really hard!" But someone will eventually succeed in doing the quad axel (4 1/2 times around) and that will set the bar higher. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:54, 9 April 2014 (UTC)

Maybe we'll see it done some day. But there are limits to the torque a skater can apply to himself, as well as (perhaps softer) limits to the ability to control. I'm confident there's some n for which humanity will never see an n-tuple axel, but what that n is is probably best investigated by watching competitions and waiting, rather than trying to model it from first principles. In other words, I think the answer to your last question is "yes"; it's "just" those three things that would have to improve. Maybe replace "sense of balance" with kinesthetic intelligence. SemanticMantis (talk)

It probably varies per-person, given the above comments. But the basic thing is that you must have enough angular velocity to complete those axels in the time you remain in the air. A quantitative analysis would require the maximum impulse the skater could deliver using the muscles in question, and how quickly (so the time for spinning can be calculated). The axis of rotation should be close to vertical for balance purposes, you do not want any torque components other than the vertical component to deal with (torque is a pseudovector).--Jasper Deng (talk) 07:48, 10 April 2014 (UTC)

One technical point: If you intend "axels" to mean "rotations", note that the jump known as the "Axel" is named for a guy, Axel Paulsen or some such. It's the only one of the jumps that starts facing forward. Hence a single Axel is 1 1/2 revolutions, a double Axel is 2 1/2, and so on. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:07, 11 April 2014 (UTC)

This is purportedly Keegan Messing unsuccessfully attempting a 4A in practice. 70.36.142.114 (talk) 00:02, 13 April 2014 (UTC)

April 10

Nature of carbon atom

Why do carbon atom form bonds tetrahedral in shape? Why do two carbon atoms not form a quadruple bond? 117.242.108.105 (talk) 05:53, 10 April 2014 (UTC)

Only diamonds are tetrahedral, I believe. Graphite is hexagonal and in sheets. The 3 double bonds are actually shared with 6 carbon atoms. Bond order and quantum mechanics are the reason why quadruple bonds aren't common. Basically, the higher the order the less stable so mixtures with lots of carbon will reform into lower order bonds. Acetylene has a triple bond and the amount of energy released when the bond is broken is tremendous. It would be difficult or impossible to have a carbon substance with quadruple bonds, and the diatomic distance associated with it, without it reducing to paired covalent bonds at farther spacings and less potential energy. --DHeyward (talk) 06:40, 10 April 2014 (UTC)

To answer question 1) All atoms that form 4 bonds to 4 different atoms will assume a tetrahedral geometry, because that geometry maximizes the angular distance between electron pairs on the valence level of that atom. Because electron pairs will tend to repel each other, the geometry that is most stable will be the one that maximizes the distance between said pairs of electrons. See VSEPR for more details. The reason why Carbon doesn't form quadruple bonds is pretty complex, you'd need to have some background understanding of molecular orbital theory. You can read a general overview of such bonds at Quadruple bond if you wish. --Jayron32 11:08, 10 April 2014 (UTC)

Dicarbon (C₂) exists, but it doesn't have quadruple bonds as simple valence bond theory would predict. Looking at it with MO theory shows that there are two sets of paired electrons in the sigma system (one bonding and one antibonding) and two sets of pairs in a degenerate pi bonding set. In total the bond order is 2, so we have a double bond instead: and indeed the MO diagram shows two pi bonds and no sigma bonds. Confirmation of this prediction can be seen from B₂, C₂, and N₂ having increasing bond dissociation energy across period 2, indicating single, double, and triple bonds respectively.

In any case, you are not likely to find dicarbon samples lying around, as it is a very strong acid and only persists in dilution or as an adduct. Double sharp (talk) 15:15, 10 April 2014 (UTC)

Jayron's VSEPR bond-counting explanation omits an important detail (though not relevant to 4-bonded carbon specifically): it's not solely the number of bonds, because lone-pairs also count as a "direction". An atom with 4 bonds and a non-bonded pair is the geometry similar to 5 bonds (AX₄E₁) not tetrahedral. Going further, especially into the transition metals, lots of molecules have square planar molecular geometry. DMacks (talk) 15:19, 10 April 2014 (UTC)

Deep water pressure

Why Titanic and other deep water debris is not crushed flat by water pressure?--93.174.25.12 (talk) 07:34, 10 April 2014 (UTC)

It is because the pressure is basically uniform over the entire surface of the object, including the part on the seabed (yes, the part on the seabed gets more force because that force must be the sum of the debris weight in addition to the water weight, but that extra force has always been there regardless of whether there was water), so the forces could only ever act to compress the object. It would be natural to think the metal panels have compressed already, so they will compress no further.--Jasper Deng (talk) 07:43, 10 April 2014 (UTC)

(edit conflict)Because the water is on the inside as well as the outside. The solid pieces of steel are strong enough to withstand very high pressure, though they will compress very slightly so that they have internal stress to match the external pressure. Dbfirs 07:46, 10 April 2014 (UTC)

For clarity, my comment applies to solid objects, not hollow objects which have no internal stress.--Jasper Deng (talk) 08:26, 10 April 2014 (UTC)

Most solid objects don't compress much at those pressures, just like rocks on the sea floor. Styrofoam cups, however, do compress to a small fraction of their original size, under such pressures, because they contain gas bubbles inside each cell. StuRat (talk) 04:20, 12 April 2014 (UTC)

Pretty lakes

Why are supposedly "polluted" lakes always so full off vegetation? It seems to me that unnatural chemicals would stop plants from growing! — Preceding unsigned comment added by 2001:708:110:1004:CACB:B8FF:FE24:8A97 (talk) 08:51, 10 April 2014 (UTC)

"Unnatural" and "natural" aren't very specific words. If the waste in question contains a lot of nitrogen and/or phosphate compounds, then I'm sure it could lead to an algae bloom, for example.--Jasper Deng (talk) 09:04, 10 April 2014 (UTC)

Maybe start with eutrophication. 86.146.28.229 (talk) 09:05, 10 April 2014 (UTC)

Yes, many of the pollutants are "natural", or organic. Sewage spill-over and agricultural runoff are two common sources of such pollution. So, while turds floating in the lake are entirely "natural", and algae just loves it, we find it rather unpleasant. StuRat (talk) 16:14, 10 April 2014 (UTC)

• The growth of algae in lakes is naturally limited by the level of the least abundant limiting resource, which is usually nitrogen. The removal of this limit by adding a little fertilizer has the same effect as removing predators from a system of herbivores like rabbits or deer; a population boom followed by starvation. In this case, the decay of dead algae will consume the oxygen in the water, and kill most of the animals in the water. μηδείς (talk) 17:21, 10 April 2014 (UTC)

See Liebig's law, which expands on the issue of limiting factors. μηδείς (talk) 20:07, 10 April 2014 (UTC)

Underwater "pings" in the Indian Ocean

Recently, searchers have been hearing several pings in the Indian Ocean, as these officials search for that missing airplane, Malaysian Flight 370. I don't understand: why are they not saying "definitely" that the pings are coming from a plane's black box? What other things in the ocean might account for these pings, other than a plane's black box? Are there any other possibilities? What are they? What other items in the ocean might make such a ping? Thanks. Joseph A. Spadaro (talk) 14:36, 10 April 2014 (UTC)

False data, as appears to have been the case in the earlier Chinese reporting, is the most likely alternative. While the particular frequency characteristics of the ping functionally assure that what is being heard is man-made, there's a whole lot of man-made technology clustered around the search area (namely, all of the searchers). It is not inconceivable that something else is generating a similar audio characteristic, even if it's unlikely. Also, from a PR standpoint, it's much easier to walk back a "probably" statement than a "definitely" statement. — Lomn 15:43, 10 April 2014 (UTC)

One report said that whales might make similar sounds. I don't know if it's true, but that's what they said. StuRat (talk) 16:12, 10 April 2014 (UTC)

Whales, dolphins, or other sea life will not make a sound at a single specific frequency with a single specific repetitive interval for a sustained period of time -- something to the effect of 37 kHz for 10 ms every second. Whales might make "similar" sounds in that they make high-frequency sounds and sometimes repeat them, but that's a use of the word "similar" that is completely misleading in terms of the actual science and technology at work. Black box pings are most certainly not natural, and the reported multi-hour contacts are completely inconsistent with sea life as a possible explanation. — Lomn 18:10, 10 April 2014 (UTC)

I've heard (but cannot confirm) that a number of undersea cables have locater beacons attached to them to make them easier to find to repair. Undersea acoustics can do strange things at times, so it's possible that they're picking up long-distance transmission of a cable's beacons. --Carnildo (talk) 01:16, 11 April 2014 (UTC)

The sad thing is, if the terrorists who allegedly disappeared the plane had a chance to get one agent on one ship anywhere in the search pattern, he could have tossed a pinger overboard that produces the exact black box signal, and they'll all spend a month trying to find it. Wnt (talk) 21:30, 12 April 2014 (UTC)

What is the relation between death rates and life expectancy?

"In the nineteenth century twenty-two out of every thousand people died each year, more than 2% of the population– today only 5 out of a thousand people die each year. In the nineteenth century the average lifespan was thirty-six years – today it’s about eighty. The biggest killer in the nineteenth century? Tuberculosis. Also known as consumption, this disease was rampant, believed to be hereditary, and in spite of numerous claims of ways to cure the disease, no cure or effective treatment was available." - From a review of The Remedy on Goodreads by Watchingthewords.

2% of the population is the same as one person out of 50. So if 2% of the population dies every year, then that means that, in any given year, on average, one person out every 50 people will die. If 50 people die every year, then it will take 40 years to kill 1,000 people, which means that your average lifespan is going to be about 40 years. 40 is not that much different from 36, so maybe we are on the right track.

But then we look at today's numbers and we get something that doesn't make any sense. If only 5 people out of 1,000 die every year, then it will 200 years to kill 1,000 people, and nobody lives 200 years.

I suspect there is something wrong with this picture, but I don't know what. I suppose an expanding population could skew the numbers somewhat, but I don't see how they can skew it that much. Pergelator. — Preceding unsigned comment added by 50.43.12.61 (talk) 17:11, 10 April 2014 (UTC)

The current world's population is young, and therefore has low death rate (5 per 1000). It means that it is growing. Your conclusion that "it will [take] 200 years to kill 1,000 people, and nobody lives 200 years" is wrong because you incorrectly assumed that the population is static. Ruslik_Zero 19:45, 10 April 2014 (UTC)

And presumably we will see a much higher death rate when the Baby Boom generation starts to die off in quantity the US, and even more so when all those born before the One Child Policy in China start to die en masse. StuRat (talk) 13:10, 11 April 2014 (UTC)

Why only the US? Baby boomers lurk in lots of un-American places, Stu. -- Jack of Oz ^{[pleasantries]} 20:33, 11 April 2014 (UTC)

The article I linked to only mentions the US, Romania, and Africa, and I'm not sure if the magnitude of those other two is sufficient to warrant a mention. PS: I'm aware that Australia had a baby rabbit boom; did it have one with humans, too, or do you still need to import criminals/prostitutes to supplement your population ? :-) StuRat (talk) 23:41, 11 April 2014 (UTC)

You're not sure if a baby boom across the entire continent of Africa would be of sufficient magnitude to mention, compared to a baby boom in the United States? 85.255.232.229 (talk) 23:46, 11 April 2014 (UTC)

Nope, and the article didn't say it was across all of Africa, either. From the description, it sounded like it excluded the Arab part, and perhaps more. StuRat (talk) 23:49, 11 April 2014 (UTC)

I think you would get more of a world view if you looked at Post–World War II baby boom although even that one is still rather US centric. Richerman (talk) 20:46, 12 April 2014 (UTC)

Death rates from birth are relatively difficult to compare. Really, the best way to look at life expectancy is when a person reaches a certain age and average remaining years. Infant and child mortality dominate stats 50-100 years ago as well as 3rd world countries. But if you look at the CDC tables they report average life remaining at each year attained. Make it to 5 and your remaining life span is nearly the same as when you were born, reflecting higher death rates for young children. Make it to 80 and your remaining life is very nearly the same as it was 50-100 years ago. Whence the huge gains in life expectancy was reducing infant mortality and childhood diseases. Those lucky enough to reach 100 have only seen an improvement of a month or two. Notice how "the oldest person in the world" doesn't appear to be getting any higher. --DHeyward (talk) 04:30, 12 April 2014 (UTC)

Effective normal stress in geotechnical engineering

Normally, effective normal stress is calculated by subtracting the pore water pressure from the normal stress, in natural conditions. However, why is it that in the untrained triaxial compression test, the pore water pressure is negative, meaning it is added to the normal stress to obtain the effective normal stress? Is it because the compressing effect, creates a force which pushes in the opposite direction, thereby adding to the normal stress? 2.221.71.15 (talk) 21:19, 10 April 2014 (UTC)

The pore water pressure in an unconfined sample is negative due to the capillary effect. When a confining pressure is applied the pore water becomes positive, see for instance here. Mikenorton (talk) 22:34, 10 April 2014 (UTC)

April 11

Longest rotational period

Which object that orbits the Sun and does not orbit any other object orbiting the Sun, has the longest rotational period (prograde or retrograde, doesn't matter)? --Atethnekos (Discussion, Contributions) 04:49, 11 April 2014 (UTC)

Longer orbital periods are associated with greater distances from the Sun (see Kepler's second law), so your question is basically asking about the objects that are the furthest from the Sun while still within the Sun's gravitational potential well. I'm not sure which one specific object would be the answer to your question, but I think it'd be something within the Oort cloud. There are long-period comets (which are thought to originate from the Oort cloud) which have orbital periods in the thousands of years. For example, Comet McNaught has an orbital period of about 92,600 years. However, your criterion of an "object that orbits the Sun" is a bit fuzzy, because when you're talking about the objects with the longest orbital periods, that are the most weakly gravitationally bound to the Sun, there's fuzziness as to how long the object has to remain in the vicinity of the Sun before it gets lost as an interstellar comet for it to still fit your definition of an "object that orbits the Sun". Red Act (talk) 05:38, 11 April 2014 (UTC)

The OP asked about rotational period, not orbital period. --140.180.250.141 (talk) 05:57, 11 April 2014 (UTC)

Yes, I seem to have misread the question, so I have retracted my answer. Red Act (talk) 06:17, 11 April 2014 (UTC)

One could say it was redacted! Har! Dismas|^(talk) 15:36, 11 April 2014 (UTC)

Our article on Rotation period includes these figures for major bodies in the Solar System. Extreme rotation periods for some smaller bodies can be found here. Of the bodies known to Wikipedia, it looks like Venus is your answer. RomanSpa (talk) 06:56, 11 April 2014 (UTC)

Since you didn't specify a size, there are an almost infinite number of objects orbiting the Sun directly, when one includes the asteroid belt, Kuiper Belt, and Oort Cloud and allows for sizes down to a pebble. Of all those, I'd expect some have essentially no rotation at all. StuRat (talk) 13:03, 11 April 2014 (UTC)

It's infinite, there are neutral hydrogen atoms that orbit the Sun and they can have a total angular momentum of zero (electron in the 1s state and the electron-proton system in the total spin zero singlet state). Count Iblis (talk) 23:18, 11 April 2014 (UTC)

Probably Mercury (planet) is the correct homework answer as it is tide locked with the sun and Mercurians only get one "day" every 2 "years". (but I didn't check venus) --DHeyward (talk) 04:40, 12 April 2014 (UTC)

Please do so. —Tamfang (talk) 05:41, 12 April 2014 (UTC)

It's conflicting as Venus rotates clockwise. From the article Venus has a longer sidereal day and a shorter solar day than mercury. --DHeyward (talk) 15:31, 12 April 2014 (UTC)

Since the OP used the phrase "rotational period" rather than "solar day", I'm going with Venus, but the OP can make up its own mind. —Tamfang (talk) 05:53, 13 April 2014 (UTC)

Gas pipeline

How heavy must a piece of debris be (assuming it's travelling at the speed of a typical avalanche) to rupture a major aboveground gas pipeline? For example, would a good-sized boulder do the job? How about a snowmobile? Or a typical four-door sedan? Or a 3-ton truck? Thanks in advance! 24.5.122.13 (talk) 06:57, 11 April 2014 (UTC)

I guess we've won the War on Terror if Al Qaida is reduced to this. — Preceding unsigned comment added by 96.227.210.243 (talk) 12:47, 11 April 2014 (UTC)

HAHahaHAHahaHAHahaHAHahaHAHahaHAHaha μηδείς (talk) 22:04, 12 April 2014 (UTC)

Not a question about Al-Qaida, but a research question for a disaster novel. 24.5.122.13 (talk) 23:11, 11 April 2014 (UTC)

The shape and way it hits would make a huge difference. Imagine a block of masonry hitting it. If it hit corner first, it might well poke a hole, while a glancing blow on the side of the block would not. The difference is the pressure exerted at a given point. However, enough total force, even if evenly distributed, could still rip the pipeline off it's supports and rupture it. StuRat (talk) 12:53, 11 April 2014 (UTC)

So, a boulder could do it if it was big enough and/or it hit the "right" way, right? This is just what I hoped to hear -- the rupture of a gas pipeline (which is promptly ignited by a downed 39,000 volt power distribution line, incinerating an automobile with its occupants and threatening to do so to another in which a mother and her daughter are trapped and badly hurt) is an important plot element, and I'd be VERY disappointed if it turned out to be implausible. 24.5.122.13 (talk) 23:11, 11 April 2014 (UTC)

Possible, sure. Make sure a particularly sharp protrusion from the boulder hits the pipeline first. Also, you'd need to explain why they would build a pipeline where there's an obvious avalanche danger. My suggestion, explain it with acoustic lubrication. This is a situation where the sound/vibrations of the landslide hit just the right frequency, providing a type of lubrication that allows the landslide to go much further than predicted. When you see film of such a landslide, it looks like rushing water, due to the greatly reduced friction. To explain it to the readers, the sound frequency makes the boulders vibrate, so they are only in contact with the ground and each other part of the time, significantly lowering the average friction versus if they were inconstant contact. The larger the objects, the lower frequency is needed for this type of resonance, so boulders require quite a low frequency sound. StuRat (talk) 23:30, 11 April 2014 (UTC)

In the Canadian Rockies, there's often no choice but to build stuff despite a known avalanche hazard. A more important question is why that part of the pipeline wasn't built underground -- perhaps it would be to save on construction costs, or maybe it was supposed to be built underground but they decide to turn on the gas first and only then cover the trench because the project is running badly behind schedule? 24.5.122.13 (talk) 23:45, 11 April 2014 (UTC)

It would be nice to actually cite references when stating that something is "possible, sure". Here's a South African report that talks (on page 5) about how impacts are a common cause of pipeline ruptures, although it's talking about underground pipelines. Also note the following sections where it talks about fireballs and such, which may be useful for the novel. Here are US NTSB reports on pipeline incidents, but the table does not classify them by cause, so you might have to read a number of them to see to find ones that are relevant to your scenario. --50.100.193.30 (talk) 00:53, 12 April 2014 (UTC)

Makes it so the avalanche derails a train into the pipeline. The build those things together :). --DHeyward (talk) 03:24, 13 April 2014 (UTC)

You can't have a train without a railroad line (the disaster scene is NOT on the Canadian Pacific or Canadian National) -- but I could try making the avalanche push a truck into the pipeline (which should do the job just as well), and then have the resulting fireball and jet fire incinerate the truck. In fact, this would be PERFECT for my story! 24.5.122.13 (talk) 04:29, 13 April 2014 (UTC)

Bug ID

What is this? Should I be worried that this dropped down onto my desk? -- Zanimum (talk) 12:10, 11 April 2014 (UTC)

Wood louse (Isopoda) suborder, pill bug (Armadillidiidae) family. Very common here. I've never known them to be harmful. In fact, they are kind of fun. Poke them on the back and they will roll up into a little ball like an armadillo, to defend themselves. You can then play marbles with them, until they get tired of it and walk away. :-) StuRat (talk) 12:30, 11 April 2014 (UTC)

A solitary one is not a problem, but; "When large numbers of woodlice are found indoors, perhaps clustered in wall crevices or under skirting boards etc., it is always worth checking for excessive dampness in these places - just in case there is a structural problem with the damp proofing or damp course".[1] Alansplodge (talk) 13:03, 11 April 2014 (UTC)

Right, but they still aren't a problem (other than a cosmetic one), but rather they just indicate that a problem exists. StuRat (talk) 13:56, 11 April 2014 (UTC)

Well, the question was "should I be worried". Referenced answer: "Maybe". Alansplodge (talk) 22:43, 11 April 2014 (UTC)

Please do not worry unduly because it looks like Armadillidium vulgare has survived the fall. Let's not be negative about his lifestyle. 84.209.89.214 (talk) 12:44, 11 April 2014 (UTC)

'Round these parts, we call those roly polys. Justin15w (talk) 14:38, 11 April 2014 (UTC)

I had an interesting experience with one once. I wasn't in the mood to play with it when it crawled into my house, so I flushed it. At the moment it disappeared down the toilet, everything went black and silent, so I thought "Damn, that pill bug must have been God, and now the universe has ended" ... at least until the power came back on a minute later. :-) StuRat (talk) 12:48, 11 April 2014 (UTC)

:) -- Zanimum (talk) 14:44, 11 April 2014 (UTC)

In Kent, according to a former colleague, pill woodlice are known colloquially as "monkey peas",[2] presumably because monkeys are supposed eat them like peas? The origin of this seems to be completely unknown - there are no wild monkeys in the south east of England. Alansplodge (talk) 12:56, 11 April 2014 (UTC)

:) -- Zanimum (talk) 14:44, 11 April 2014 (UTC)

In Norse areas of northern England they were known as "thuslice" /θʊslaɪs/ (originally Thor's lice). Dbfirs 21:16, 11 April 2014 (UTC)

Thanks all! I've seen pillbugs a lot outdoors, never in. I work in a 148-year-old building, so we frequently have surprises. -- Zanimum (talk) 14:44, 11 April 2014 (UTC)

Simple beam calculations

I have a beam with a simple support at one end and a roller support at the other end. The beam has a 30kN load 1m from the left support, a 50kN load 2m from the left and a uniform load 3m from the left, which spans 2m. The overall span of the beam is 6m. I've simplified this to a simply supported beam, which I'm assuming is correct. In order to find the reactions at either end I've done the following. R1+R2=w1+w2+(w3*length of uniform load/2), and for the moments R2*L=w1*x1+w2*x2+w*length of uniform load*distance to centre of uniform load from left of beam. I've basically done this by simplifying the uniform load to a concentrated load acting at the centre of the length of the uniform load. But apparently this is incorrect as my instructor has used W*l instead of w*l/2 to find the contribution of the uniform load to shear force equilibrium, and wl^2/2 instead of wl^2/8 for uniform load contribution to moment equilibrium, which in my opinion treats the uniform load section as a cantilever. Where have I gone wrong in my calculations? Why is that section a cantilever? Clover345 (talk) 13:32, 11 April 2014 (UTC)

We need a diagram. Is this correct (not quite drawn to scale) ?

                          UNIFORM LOAD
         30kN       50kN /            \
          |          |  /              \
          |          | /                \
<-- 1m -->V<-- 1m -->V/<------ 2m ------>\<------ 2m ------> 
============================================================
o                                                          ^

I assumed the uniform load is centered 3m from the left. Also, is the magnitude of the uniform load specified ? StuRat (talk) 13:51, 11 April 2014 (UTC)

The uniform load is centred 4m from the left and it's value is 10kN/m. Also the simple support is at the left and the roller support is at the right. Clover345 (talk) 14:46, 11 April 2014 (UTC)

Like this ?

                                    UNIFORM LOAD
         30kN       50kN           /   10kN/m   \
          |          |            /              \
<-- 1m -->|<-- 1m -->|<-- 1m --> /<----- 2m ----->\ <-- 1m --> 
          V          V          vvvvvvvvvvvvvvvvvvvv
==============================================================
^                                                            o

StuRat (talk) 16:31, 11 April 2014 (UTC)

Ye, that's it exactly. That is a simply supported beam right? According to my instructors calculations that's a cantilever but I can't understand why. Clover345 (talk) 16:48, 11 April 2014 (UTC)

Unfortunately, it's been too many years since I've done such a problem to answer reliably, but now that the Q is clear and we have a diagram, hopefully others can answer. (Your approach of dealing with it as two simple supports seems right to me, too, so either I'm missing something or the instructor made a mistake.) StuRat (talk) 17:08, 11 April 2014 (UTC)

If the uniform load is specified as 10kN/m then its (not spelled "it's") total force is 10k/m times 2m. This is what the instructor means by W*I and the OP has no reason to divide by 2 in the expression for R1+R2 which comes out to 100 kN. The sum of the clockwise moments about the left end is 30 + 50*2 + 10*2*4 kN m = 210 kN m which is in equilibrium with 35 kN force on the support at the right end. That leaves 65 kN force at the left end. The beam is not a cantilever unless it extends (not shown) beyond the right hand support. It's commendable that contributor StuRat shows correct spelling here. 84.209.89.214 (talk) 19:38, 11 April 2014 (UTC)

Thanks but why is this? I thought that in a simple beam with a uniform load, the moment is given by wx/2*(1-x), whilst the shear force is given by w(l/2-x). Clover345 (talk) 20:07, 11 April 2014 (UTC)

This may help. 84.209.89.214 (talk) 21:42, 11 April 2014 (UTC)

Weather/travel

I have heard there is a possibility of a storm on the east coast early next week what is the chance that incoming flights into airports in the northeast will be affected — Preceding unsigned comment added by 75.69.246.118 (talk) 14:55, 11 April 2014 (UTC)

OP geolocates to Massachusetts, so that's probably the coast he's interested in. Rojomoke (talk) 16:24, 11 April 2014 (UTC)

Looking up the weather for Boston, I get rain and winds up to 25 mph on Tuesday, which doesn't seem like enough to cancel flights, to me. If you can be more specific as to the exact arrival date, time and location, we can give a better answer. StuRat (talk) 16:27, 11 April 2014 (UTC)

The OP should call his airline. We don't have some secret knowledge they don't have. μηδείς (talk) 20:11, 11 April 2014 (UTC)

The National Weather Service's area forecast for the Boston region, for April 11, 1745 UTC, includes notification for an AIRMET (AIRMET Sierra) with IFR conditions, mountain obscuration, overcast skies, low ceilings, thunderstorms, severe or greater turbulence, severe ice, low level wind shear, anf IFR conditions. You can check the Terminal Aerodrome Forecast for most major commercial airports to get specific forecast probabilities for specific types of weather. It is at the discretion of the airline whether they ought to delay or cancel flights ahead of time when such weather is forecast. Nimur (talk) 23:41, 11 April 2014 (UTC)

April 12

Please identify yellow flowering plant

Can anyone identify this beautiful yellow-blossomed flowering plant? Thanks. μηδείς (talk) 01:23, 12 April 2014 (UTC)

Hard to tell. Could be an Alstroemeria (Peruvian Lily) or a Daylily or a True Lily. --Jayron32 02:19, 12 April 2014 (UTC)

The image is way too fuzzy for me to have any hope, but the leaves look more dicot-ish than monocot-ish. Looie496 (talk) 02:34, 12 April 2014 (UTC)

Yes, it really does look like a lily, but the flowers remind me of Jimsonweed, the leaves do look dicotish (you can see they don't have parallel veins in the original), and I am fairly sure it is a member of Solanales, if not Solanaceae, and perhaps a Cestrum, whose leaves and size are similar. Not this seems to be one inflorescence from one shoot. The screenshot is from 30:09 of episode 2 season 1 of Boston Legal. The plant looks like a spike cut from a much larger bush. μηδείς (talk) 02:45, 12 April 2014 (UTC)

I left a note on the talk page of @Cullen328:, I seem to have some recollection that he might know something about flowers. --Jayron32 02:59, 12 April 2014 (UTC)

It sure looks like some type of lily to me, but my wife who knows more than me says that the photo is not clear enough to narrow it down beyond that. Very similar flowers are growing by my front door right now, planted over ten years ago by the home builder. A slight correction, Jayron32: You are right that I love flowers and post at least one of my flower photos on Facebook every day, along with its location, as I travel around Northern California on business and pleasure. This is my way of letting my friends know where I travel, and sharing a bit of beauty. But I am not an expert and usually rely on my Facebook friends for help identifying species. Thanks for remembering my interest in flowers, though. Cullen³²⁸ Let's discuss it 03:11, 12 April 2014 (UTC)

It's definitely not a lily. Lilies develop from a banana-shaped bud that splits along three axes, with the entire bud forming one flower, without green sepals. These plants look similar, but the flower is conical, and the base, composed of sepals, remains green, while the flower grows beyond them. The flower is much more like that of Jimson Weed, but yellow. μηδείς (talk) 22:03, 12 April 2014 (UTC)

It looks like an Orienpet hybrid lily, similar to this one but more yellow: http://www.thelilygarden.com/pages_lilies/orienpet_3.html --TammyMoet (talk) 08:37, 13 April 2014 (UTC) Could also be a Lilium hansonii but the flowers aren't open yet so I can't be definite. There's a photo on garden-photos-com.photoshelter.com but it's copyright so I can't link here. --TammyMoet (talk) 08:41, 13 April 2014 (UTC)

Is it true that some Prebiotic fibers could actually make us fatter?

I've heard that some particular types of Prebiotic fibers (whether they'll be Soluble, Insoluble but Fermentable, or Resistant starch), could actually give us the opposite effect and make us fatter, because unlike most of the Prebiotic fibers that supposedly make our Probiotic gut flora differentiate and (basically that's it), these particular aforementioned one's could also resemble the extra effect of breaking into notable amounts of available energy\handable sugars, in the gut, that will then enter the bloodstream directly.

What are the particular types of such "human-fattening prebiotic fibers", if any of them are actually known to Science except from general theoretical thought...? Much thanks!!! — Preceding unsigned comment added by 109.67.164.204 (talk) 08:55, 12 April 2014 (UTC)

See Dietary fiber#Fiber and calories. According to http://www.menshealth.com/mhlists/facts_about_nutritional_fiber/printer.php:

"Fiber is essentially composed of a bundle of sugar molecules. These molecules are held together by chemical bonds that your body has trouble breaking. In fact, your small intestine—can't break down soluble or insoluble fiber; both types just go right through you. That's why some experts say fiber doesn't provide any calories. However, this claim isn't entirely accurate. In your large intestine, soluble fiber's molecules are converted to short-chain fatty acids, which do provide a few calories. A gram of regular carbohydrates has about 4 calories, as does a gram of soluble fiber, according to the FDA. (Insoluble fiber has essentially zero calories.)"

"Fiber's few calories are more than offset by its weight-control benefits. The conclusion of a review published in the journal Nutrition is clear: People who add fiber to their diets lose more weight than those who don't. Fiber requires extra chewing and slows the absorption of nutrients in your gut, so your body is tricked into thinking you've eaten enough, says review author Joanne Slavin, Ph.D., R.D. And some fibers may also stimulate CCK, an appetite-suppressing hormone in the gut."

So note that the benefits of soluble dietary fiber, such as slowing the absorption of sugars and thus preventing blood sugar spikes followed by insulin spikes and sugar crashes, outweigh the negatives. StuRat (talk) 12:41, 12 April 2014 (UTC)

I'm intrigued by the OP's words "could actually give us the opposite effect". Opposite effect to what? HiLo48 (talk) 12:50, 12 April 2014 (UTC)

It is a bit tricky to figure out what they meant, but I took them to mean that fiber is normally good for weight loss because it fills you up and contains no digestible calories. Here the "opposite effect" would be if it causes weight gain because it does contain digestible calories. StuRat (talk) 12:57, 12 April 2014 (UTC)

You're right, that's exactly what I meant... 109.67.164.204 (talk) 15:17, 12 April 2014 (UTC)

Using aggregated data for statistics

If you want to do medical research, one way is to ask for instance GPs to sent all their medical records. This method has obviously huge implications regarding privacy. Even if data like Social Security numbers and names are omitted, sometimes it's not too hard to find out which record is about which patient. Another problem is that the GP doesn't have a guarantee about what the research is used for and by whom.

I'm wondering if it's possible that every GP collects his data (about, say, 2500 patients) and turns it into a file that contains facts like "5% of patients aged 10-15 have diabetes, of which 3% need insulin", etc. So part of aggregating the data takes place at the computer of the GP, and (more) anonymous results are sent to the research institute. Of course, if the practice has only a few people suffering from a particular disease, you might deduct some more information about them, but at least it's better than just sending separate records.

I was told that this method would make some research impossible, or at least very difficult. If the right set of questions can be asked and answered correctly by the system of the GP (like "of all patients using medication A, older then B, how many are also prescribed medication C"), is it true that for some research you actually do need the individual records? Joepnl (talk) 11:16, 12 April 2014 (UTC)

I don't see that approach working. For example, the portion of patients who "need insulin" will vary by doctor, as some may rely more on other methods to control diabetes. StuRat (talk) 12:26, 12 April 2014 (UTC)

The article Medical ethics notes the value placed on the patient-physician privilege. This is upheld because patients might withold sensitive information if unsure whether telling it can have consequences beyond their medical treatment, but it is not an absolute privilege because various laws require physicians to report STD's, gunshot wounds, child abusers and vehicle drivers impaired e.g. by epilepsy. Medical research involving both medical ethics and Research ethics raises questions like the OP's question. Shall results of Human subject research be published for study even if their collection was abusive and unethical (the WW II examples are well known)? Is research without knowing consent of the subjects justifiable? (Ethical questions are raised over Stanley Milgram's 1961 experiment of misleading subjects into applying an increasing scale of shocks to people ostensibly to "improve" them, yet today Wikipedia administrators believe themselves empowered to apply electronic blocks on an identical increasing scale that ends in indefinite dehumanisation of participants.) The problem with the OP's proposed procedure is that a General practitioner is already hard pressed by lack of resources and pharmaceutical company salespeople and has a skill set focussed on giving care to individual patients that is different from being an objective data-collection functionary. The GP might argue in modern terms to have "sworn by Apollo" never to "cut for stone" (take on the role of a surgeon/researcher ?) and "keep secret" (the patient's identity). These considerations detract from the end-to-end transparency, verifiability and accountability that medical research demands. (Readers may be interested to see how voluntary reports on side effects of medicines are collected in Norway, a country with well developed Publicly funded health care. On this site in Norwegian anyone living in the country is invited to report side effects they or others experience from medications. The pink button links to the reporting form; this appears however only for residents.) 84.209.89.214 (talk) 13:12, 12 April 2014 (UTC)

Well, actually the problem is that many GPs in The Netherlands don't seem to realize what kind of data they're sending out for research (or many other purposes). As a tech person, who does know the kind and volume of data leaving the practice without the doctor or patient knowing exactly what's happening, that bothers me. A lot of really important research can't be done without data from their practices, however. So I'm looking for a way that would be good enough for the researchers and at the same time doesn't imply that the most intimate things people share with their doctors can't be traced back to a single patient by them. Joepnl (talk) 13:32, 12 April 2014 (UTC)

Yes, some research couldn't be done this way. You would have trouble doing a longitudinal study for example. Furthermore, if you need to know information like diet, which GPs don't routinely collect, you would not be able to do the research. But the important thing is that this approach would open up a new avenue for research. It would be difficult to get it through ethics committees, so it might have to be handled through private institutions, which are often subject to different ethical processes. IBE (talk) 13:29, 12 April 2014 (UTC)

If you're not already aware of it, you might want to read around the subject of NHS Connecting for Health and the resistance to making this data available to researchers, e.g. the big opt-out. 86.146.28.229 (talk) 14:23, 12 April 2014 (UTC)

• At the level of technical statistics, the problem you face when dealing with aggregated data is heteroscedasticity, also known as inhomogeneous variance. In spite of the tongue-twisting term, that article might be helpful to you. Looie496 (talk) 14:21, 12 April 2014 (UTC)

That's the beginning of the problem. I think whenever you snarf up a bunch of data without looking at it, you're really taking a huge risk of being completely clueless about what it means. For example, suppose you take data from 50 doctors about whether high blood pressure brings a higher risk of diabetes. You might ask some, even most of them whether they test patients for diabetes because they have high blood pressure and they say no, but then somewhere in the pack there are doctors, or doctors who inherited patients from other doctors, who did test their patients specifically because they had high blood pressure, or the patients were otherwise encouraged to get testing, and so of course more diabetics are reported from that group. Actually, I wouldn't trust even one set of researchers writing about data they haven't actually looked at, because it's prone to chicanery. For example, I remember that during a crucial moment in the run-up to the Communications Decency Act a team from Carnegie Mellon tossed out a study claiming that huge amounts of child porn were posted to Usenet. Of course, they couldn't look at the data - that would be illegal - so they used keywords, and counted anything that said "no pubic hair". Problem is, "no pubic hair" was a way of saying "legal in Japan", a country with a grudge against lovely carpets. Several other such howlers were noted by subsequent papers after the bill had been passed (and thank God, struck down by the courts) So there are a lot of reasons why I'm not going to trust a study where the collaborators don't have a way of really drilling down to the original data set. Wnt (talk) 15:26, 12 April 2014 (UTC)

I don't see much problems here if you analyze the data using Bayesian analysis that includes a detailed model of how doctor-patient relations work in practice. By doing the analysis from first principles without making any assumptions, you can get useful information from the raw data. Basically, if you can calculate the raw data corresponding to any given hypothetical real world situation then given the raw data, computing the most likely real world situation is a so-called Inverse problem. Count Iblis (talk) 17:23, 12 April 2014 (UTC)

Unfortunately, an Inverse problem approach to medical research may serve to perpetuate reliance on a bad causation model. For example, in Medieval medicine of Western Europe physicians drew on the Doctrine of signatures superstition which stated that God had provided some form of alleviation for every ill, and that these things, be they animal, vegetable or mineral, carried a signature mark indicating their usefulness. Ideas about the origin and cure of disease based on a world view dominated by factors such as destiny, sin, and astral influences would eventually be superceded by scientific breakthroughs such as vaccines, antibiotics and Germ theory of disease. Enjoy reading Homeopathy and Its Kindred Delusionsa (free on Wikisource) to see that there is still work to do. 84.209.89.214 (talk) 20:30, 12 April 2014 (UTC)

• The article differential privacy and its references might have some info you can use. 70.36.142.114 (talk) 23:13, 12 April 2014 (UTC)

Dynamic load.

How do you find the maximum load, as well as max moment and stress on a cantilever beam if you have the dynamic load factor? I calculated the DLF using FL^3/3EI but I'm lost on where to go from here. — Preceding unsigned comment added by 82.132.236.40 (talk) 12:37, 12 April 2014 (UTC)

If you only have one dynamic load on the beam, it seems to me that the max moment and stress would both occur when that dynamic load is at the maximum. With multiple dynamic loads, the situation is more complex. There the max moment and stress could occur when one of the dynamic loads is at it's max, but this isn't always true, and even if it is, it isn't necessarily the largest dynamic load that's at max at that time.

A computer simulation may be in order in such cases. If the dynamic loads vary independently of each other, you might vary each independently in the simulation and calculate the moment and stress at each time to determine the max for each (again, the maxes may occur at different times). StuRat (talk) 12:50, 12 April 2014 (UTC)

Thank you for your answer but I don't quite understand what you mean. The dynamic load factor is a ratio of the deflection as a result of the dynamic load to the equivalent static load deflection. So from this point, I would probably need to do some sort of energy analysis to find the maximum force but I'm not sure what the correct equation is. — Preceding unsigned comment added by 2.218.65.60 (talk) 14:15, 12 April 2014 (UTC)

There are software packages that are used to calculate the size of beams required for construction projects, such as this one that may be of use. Richerman (talk) 20:27, 12 April 2014 (UTC)

Viagra vs cialis vs levitra

What ones make you last the longest in bed--[[User:A915|A915]] a (talk) 18:26, 12 April 2014 (UTC)

I'm afraid that Wikipedia editors are not allowed to give medical opinions. You'd need to have this discussion with your physician. --Jayron32 18:28, 12 April 2014 (UTC)

The information can be had by comparing what's in the articles. μηδείς (talk) 21:52, 12 April 2014 (UTC)

Cleaning electroporation cuvettes which use conductive polymers

I have some electroporation cuvettes for the purpose of transfecting mRNA/DNA into eukaryotic cells. Reuse is forbidden by the manufacturer but I wondered how an unscrupulous person might be able to clean and reuse it anyway. The electrodes are conductive polymers (they produce fewer toxic ions during the electrolysis which I suppose is inevitable during an electroporation). They would need to be cleaned without trace of anything that went into them. --129.215.47.59 (talk) 13:24, 2 April 2014 (UTC)

Simply rinse them in 70% ethanol a few times, followed by a good soak. Could even store them in the 70%. Before use, rinse in dH2O thoroughly to remove any ethanol traces. Works fine. And most certainly not unscrupulous, just sensible. If I followed manufacturers instructions on everything I use in the lab, I'd be spending three times as much on consumables as I do! Fgf10 (talk) 19:01, 2 April 2014 (UTC)

Thanks. I appreciate the advice. 78.148.110.69 (talk) 12:00, 5 April 2014 (UTC)

Thanks but I'm not sure that rinsing with ethanol would remove all traces of DNA. 129.215.47.59 (talk) 18:30, 12 April 2014 (UTC)

Definitely not. 70% ethanol is what you use to wash salt out of a DNA pellet after centrifugation. Of course, if you're transfecting _the same_ DNA each time that may not be much of a problem. Oh, and check a search engine for stuff like [3][4] -- but for more precise (and recent) results specify your manufacturer name. Wnt (talk) 21:23, 12 April 2014 (UTC)

Do pet shop animals have worms or parasites

Do animals purchased from a pet shop such as petco or petsmart such as rats and mice have worms or parasites or anything else that is transmittable to humans. What is the likelihood of them having it and how easy is it to transfer to humans. --Tarhound21 (talk) 18:41, 12 April 2014 (UTC)

If you want to know what the policies of these companies are with regards to the treatment of animals they sell before they sell them, the best thing to do is to contact them directly. You are highly unlikely to run into anyone on this particular webpage who works for either company. Here is how to contact PetSmart and here is how to contact PetCo. --Jayron32 18:56, 12 April 2014 (UTC)

If you want to know more about zoonoses you can contract from rodents see Zoonoses of House Pets Other Than Dogs, Cats and Birds. Infections from pet rodents are rare but not unknown - allergic reactions are much more likely. Richerman (talk) 19:34, 12 April 2014 (UTC)

• If you're actually going to buy such animals and are concerned, get a consultation with a local vet, and they will gladly prescribe an prophylactic anti-parasitic. In general, pet shop rodents come from lab stock and are intentionally kept disease free by isolation. But there's no guarantee those sexy feral mice aren't seducing the lab ladies, and leaving contaminated droppings. Ask the owner of the pet store where his stock comes from. Also, avoid eating their droppings yourself. μηδείς (talk) 21:58, 12 April 2014 (UTC)

For an immaculate well-bred Mus musculus with good references, choose a Laboratory mouse supplier. 84.209.89.214 (talk) 23:47, 12 April 2014 (UTC)

Really? In the UK no animal laboratory would supply animals to a pet shop and laboratory animal suppliers wouldn't sell their stock to the general public. Richerman (talk) 00:19, 13 April 2014 (UTC)

Yeah, you got us. The pet stores actually bred an entirely new race of ersatz white mice and rats to look like lab animals to fool the public. This guy explains the scam. μηδείς (talk) 01:43, 13 April 2014 (UTC)

Well really it was somewhat the other way round. Actually, I'm surprised that "the mouse woman of Granby" Abbie E.C. Lathrop is still a red link. She really was a pioneer and an unsung American heroine see:[5]. If no-one gets round to it soon (shame on you American women of science!) I may have to write one myself :). Richerman (talk) 09:02, 13 April 2014 (UTC)

April 13

Submarine depth gauge

In the movie "Das Boot," about a Uboat, or in submarines in general, when the depth gauge shows, say 200 meters, what is the reference level in the sub? The bottom or top of the pressure hull, the bottommost point of the nonpressurized fuel tanks under the pressure hull or any projection from the bottom , the center of the sub, the topmost point on the superstructure (sail, radar mast?), or what? On the one hand, the topmost point would make sense, since you want it to be submerged far enough a passing ship doesn't see it or hit it. On the other hand, if you know the water is shallow, you don't want the bottom to hit a rock. From an engineering standpoint, greater depth matters more to the pressurized central portion than to fuel tanks around it which in some cases are at the surrounding pressure and under no particular increased stress at extreme depth. Neither Submarine nor Submarine depth ratings gives an answer to this. If the gauge is calibrated to show how far the bottommost part is below the surface, then how high above that point was the topmost projection of U-96, the basis of Das Boot, when the periscope was down? Edison (talk) 03:39, 13 April 2014 (UTC)

The gauge shows depth to keel -- so, when the sub is surfaced, it shows the sub's draft. 24.5.122.13 (talk) 04:22, 13 April 2014 (UTC)

Canola consumption

From the article intro: Consumption of the oil is not believed to cause harm in humans. Since we know that oils and fats are typically harmful when consumed in large quantities, what is this supposed to mean? Two sources are presented: the second basically says that it doesn't have anything that's actively toxic, and the first is a 404 error. Neither one says that you can't get harmed by consuming canola oil. Nyttend (talk) 03:40, 13 April 2014 (UTC)

In large quantities, EVERYTHING is harmful, even sugar -- so what this statement means is that it doesn't contain anything actively toxic. 24.5.122.13 (talk) 04:24, 13 April 2014 (UTC)

Also, there's acute toxicity, meaning you get sick in short order, versus chronic diseases, which is what too much fat can cause, eventually. StuRat (talk) 06:33, 13 April 2014 (UTC)

Calculus in engineering

Is it true that you don't necessarily need to be good at calculus to do engineering at college? I've heard people say it's not as important as it is in a maths degree.