Wikipedia:Reference desk/Archives/Science/2016 February 3

= February 3 =

Movement of the North Ecliptic Pole
Hello, again!

I've been reading about the North Celestial Pole, and how it currently tilts about 24 degrees to the ecliptic. During the 25,776-year cycle of precession, it wanders through various stars including Polaris (its current location), Alpha Draconis, Vega, and Deneb. The North Ecliptic Pole, in turn, is tilted by about 60 degrees—relative to the North Galactic Pole—and currently points to the neck of Draco.

I cannot help but wonder, though: Does it also have its own cycle of movement and wander through various parts of the night sky? If so, then how long does it take through complete one circling of the sky, and at what point (in the distant future) will our descendants see it again in the neck of Draco?

Pine (talk) 04:53, 3 February 2016 (UTC)
 * Unless I'm mis-remembering my high school physics class, the answer would be that same 25,776 years. ←Baseball Bugs What's up, Doc? carrots→ 05:04, 3 February 2016 (UTC)


 * You're misunderstanding the question. This is asking about the motion of the ecliptic itself, with reference to things outside the solar system.  That's called precession of the ecliptic, or formerly planetary precession, as distinct from the cycle about 26,000 yaers, which is precession of the equator or formerly precession of the equinoxes.  The article axial precession describes both motions, though it mostly talks about the larger one.  It says that precession of the ecliptic operates about 500 times more slowly, and links to a paper that gives the rate as 0.096865 arcseconds/year, which works out to one cycle about every 13,380,000 years. Of course that's enough time for the constellations themselves to have changed appreciably, so "the neck of Draco" may well no longer exist. --76.69.45.64 (talk) 10:07, 3 February 2016 (UTC)
 * Just to be clear, that precession is about Jupiter's axis, not the North Galactic Pole. So the Earth's orbit gets inclined to a very slight degree this way and that relative to Jupiter.  But it doesn't change direction relative to the galaxy as a whole.  If it did so (and if other planets did the same) then the orbits in the solar system would be all over the place, not aligned in a plane.  But the galaxy doesn't seem to put a whole lot of differential pull on the planets ... maybe it's just too big, too far away with too little tide, too chaotic a force to have that effect. Wnt (talk) 19:30, 4 February 2016 (UTC)
 * What does Jupiter's axis have anything to do with this? The invariant plane of the solar system (Jupiter's orbit plane plus some small wobbles from Saturn and random detritus like Earth and Neptune) would make more sense. The galactic tide is a real thing but it affects the Oort cloud which is much bigger than the known planets' orbits and has much weaker bonds to this solar system. And since the solar system orbits a quarter turn once every 50-60 million years, wouldn't there be nothing to turn it around and the ecliptic poles would point towards the same distant quasars? Then the center of the galaxy should appear to move relative to the NEP and SEP. The Andromeda Galaxy and any other galaxies not on the galactic pole would also move in and out of the hemisphere centered on the galactic center over time since the direction of the galactic center switches sides once every 100-125 million years. Sagittarian Milky Way (talk) 20:16, 4 February 2016 (UTC)
 * Yeah, I really should have double checked my language that time. By "Jupiter's axis" I was thinking of a direction perpendicular to the plane of its orbit, not its spin axis.  And by "relative to the Galaxy as a whole", well, shoot, I was thinking of the rest of the universe as a whole.  All in all, not one of my better responses! Wnt (talk) 02:48, 5 February 2016 (UTC)

Basic physics problem
Suppose I have a rigid, uniform rod in space, and apply a force at one of the ends of the rod perpendicular to the rod's length. What are the equations of motion describing the rod's motion? It seems like an easy question, but I'm not sure what happens.--Leon (talk) 08:52, 3 February 2016 (UTC)
 * The key to this is that in the absence of any other forces, the object's centre of mass is its pivot. The rod will move through space so that its centre of mass accelerates according to $$F = ma$$, and it will rotate about its centre of mass according to the equivalent law for rotation $$\tau = I \alpha$$ (where $$\tau$$ is the torque (in this case, that's just force times distance from the pivot), $$I$$ is moment of inertia (for a rod of mass m and length L, $$I = \frac{m L^2}{12} \,\!$$), and $$\alpha$$ is angular acceleration). Smurrayinchester 10:06, 3 February 2016 (UTC)
 * (By the way, the precise answer depends on how you apply that force. The most plausible one would be to have a rocket engine attached at one end, in which case the rod should start tracing a complex spiral shape as the direction of the force vector changes constantly. Although I can't derive the exact equations right now, I believe that the rod's motion should (on average) tend in the direction of the initial impulse - because the rod is constantly turning faster and faster, the rocket engine will spend longer pointing in the initial direction than in the opposite direction, and therefore there will be net acceleration in that direction.) Smurrayinchester 14:28, 3 February 2016 (UTC)

Accelerating around a curve in a car
I have been told more than once that it is advisable to decelerate on approach to a bend in the road, and accelerate whilst going round the bend. Why is this advisable, and what are the implications of not doing it?--Leon (talk) 08:54, 3 February 2016 (UTC)


 * If you try to brake and turn at the same time, you're asking the tires to transmit more force than if you do one at a time. If you don't slow down, you may realize on entry to the curve that you're going too fast to be able to turn sharply enough.  If you then try to brake while steering around the curve, you may not be able to do it.  So it helps to slow down first.  Once you are on the curve, if you realize you've slowed more than you need to, it's safe to accelerate gradually. --76.69.45.64 (talk) 10:14, 3 February 2016 (UTC)
 * It's worth considering the g-force involved in changing direction or speed of a car. The momentum will keep it going in a straight line while you try to turn, so whenever you change direction you're fighting centrifugal force and losing traction on the tires in the direction you're turning. Weight also transfers between the front and the back of the vehicle depending on how hard you brake or accelerate, also affecting traction. If you combine both braking while turning you're effectively throwing momentum and centrifugal force together (and therefore the weight of the car onto one point), and at the same time losing grip everywhere else. So it makes sense to brake before a bend (you're just transferring the weight of the car forward.
 * You shouldn't actually accelerate through a bend but keep the accelerator/gas pedal down just enough to maintain a constant speed, to keep the weight of the car balanced. Accelerating through a bend too much would cause oversteer, which is something I have experienced several times as a younger driver and is pretty terrifying. Mike Dhu (talk) 11:56, 3 February 2016 (UTC)
 * On accelerating through a corner it only creates overstear if you have a rear wheel drive car, front wheel drive cars create understeer while accelerating round a corner, which is a lot more predictable and easier to correct than oversteer. However if you catch the backend just right with oversteer it's a lot more fun (but probable best not done on a public road). Dja1979 (talk) 17:31, 3 February 2016 (UTC)
 * Ah yes, thanks for correcting that point. My brain wasn't in gear when I mentioned oversteer :-) Mike Dhu (talk) 20:33, 4 February 2016 (UTC)
 * The answers people gave before are correct, but they don't explain wny we have to be told this more than once. As we drive, we get an intuitive sense for how to steer a car, and we handle that pretty well, just like we manage to stay upright in a bicycle without being told its physics.
 * The reason why decelerating before a curve needs to be hammered in is that the situation contains a fatal trap. Roads are not homogeneous; you may lose traction unexpectedly. You may go through curves 999 times just fine not decelerating until you reach the curve, but that only gives you a wrong sense of safety. If you slip when you're in the curve, it's too late to counteract, you'll just fly out of the curve. By braking on the approach to the bend you give yourself a safety buffer. &mdash; Sebastian 17:47, 3 February 2016 (UTC)


 * Certainly you should try to separate out braking from turning. The tires only have so much traction - and if you share it between cornering and braking, both will be less successful.  When you enter a corner and start steering - and only then find that you're going to start skidding because you were going too fast - then applying the brakes to kill your speed will just make it even more likely that the car won't steer without skidding...which is how people get into trouble.   So if you need to slow down in order to get around the corner without skidding, then braking before you start steering into the turn is by far the safest thing to do.


 * But there is a lot of subtlety to this - for example, tapping the brakes tilts the car slightly forward - which shifts more of the weight onto the front wheels. More weight on the wheels gives them more traction - so you can steer more aggressively.  But most of the advice depends heavily on whether you have front, rear or four-wheel drive.  Things have changed with modern cars that have cornering control electronics - my car tries to correct oversteer and understeer by applying the brakes automatically on just two wheels on one side of the car - this actually helps the steering to keep it pointing in the direction you demand...so braking supplements steering. But the brake pedal only lets you brake with all four wheels at once - and only the cars' computer can help you there! SteveBaker (talk) 22:11, 3 February 2016 (UTC)


 * This will happen. -- Hans Haase (有问题吗) 02:33, 5 February 2016 (UTC)


 * Braking when approaching a curve makes sense, but I'd wait to accelerate until past the bend. Of course, elevation differences and the exact shape of the curve also matter.  (Some badly designed curves have a sharp "kink" in the middle and relatively little bend before and after.)  Also, rear wheel drive vehicles tend to fishtail if you accelerate in a bend. StuRat (talk) 05:39, 5 February 2016 (UTC)


 * The advice given in the original question is good, and for public roads is sufficient. However for optimum speed you should be braking almost to the apex,and more importantly accelerating out of the apex. The intention is to fully exploit the friction circle of the tires. Braking while turning is called trail braking and is rather difficult to do well. For some reason accelerating out of a corner just comes naturally to many drivers. Greglocock (talk) 16:33, 6 February 2016 (UTC)

Haber process clarification
the article about the Haber process: Under "The Process" is written: This conversion is typically conducted at [....] 150–250 bar and between 400–500 °C And a little further down: [...] the ammonia synthesis loop operates at pressures ranging from [....] 60–180 bar Unless I missed something there is a contradiction here. Could someone clarify? 92.111.189.56 (talk) 08:30, 3 February 2016 (UTC)
 * It also waffles on whether the source-of-hydrogen is part of the process itself of a separate process that is just often coupled for pipelining/efficiency reasons. A diagram of the Catalytic cycle, not just a numbered list of steps, would also help clarify the inputs, outputs, and key stages where various pressure and other factors matter most. DMacks (talk) 14:14, 3 February 2016 (UTC)


 * This source says it varies by plant, but that using 200 atm ~= 203 bar is a good reference point. Assuming different manufactures do use different pressures at the same part of the cycle, and perhaps different pressures throughout the cycle at the same plant, then this would explain why there are a range of numbers in our article, because it was likely assembled using many different sources, each quoting their own pressures. SemanticMantis (talk) 16:03, 3 February 2016 (UTC)
 * SemanticMantis brings up some good points. Just to run with this, the Haber Process is a classic teaching reaction for demonstrating Le Chatelier's principle: equilibrium is shifted towards producing excess ammonia at high pressures and high temperatures.  However, the optimum temperature and pressure by which one does the Haber process reaction is really a chemical engineering problem rather than a chemistry problem.  In the absence of engineering concerns, the mathematics for optimizing the reaction is some fairly trivial mathematics involving things like Gibbs free energy and the equilibrium constant and yada yada yada.  However, none of those chemistry concerns take into account the chemical engineering concerns over things like thermal control of reaction vessels, materials cost analyses, maintenance of large-scale production facilities, etc.  After all, (just to invent numbers for a hypothetical situation) if one finds that the optimum temperature is one hot enough to liquify steel, or if the optimum pressure would require a vessel which costs too much to manufacture, those factors need to be taken into account when choosing a practical rather than mathematical optimum conditions.  And those practical concerns will vary somewhat depending on the specific design of your manufacturing plant.  Since, as SemanticMantis notes, our article has those figures cited to completely different sources, which are likely based on completely different engineering concerns, that's why the values don't agree.  -- Jayron 32 16:19, 3 February 2016 (UTC)

mosquito
mosquito transmit a lot of diseases but dont contract it themselves. is there any disease that actually infects and kill mosquitos? or is the only way to kill them is with a good squash by my hand? — Preceding unsigned comment added by Money is tight (talk • contribs) 10:14, 3 February 2016 (UTC)
 * Bacillus thuringiensis has been shown to infect and kill mosquitoes. I'd start there with your research.  -- Jayron 32 10:44, 3 February 2016 (UTC)
 * I hope http://www.ncbi.nlm.nih.gov/pubmed/16184014 is still true. 50.203.182.130 (talk) 13:32, 3 February 2016 (UTC)
 * That's not really directly about the disease causing bacteria directly; that's about the insertion of genes from the BTI bacteria (a strain of Bacillus thuringiensis) into the genomes of plants so they produce the toxin that kills mosquitoes rather than the use of the bacteria itself. It's sort of tangentially related to the discussion, but Bacillus thuringiensis is a disease causing bacteria as sought by the OP.  -- Jayron 32 13:35, 3 February 2016 (UTC)
 * True. I wonder how they figure out how much Bti butterflies and bees usually encounter. 50.203.182.130 (talk) 13:43, 3 February 2016 (UTC)
 * The linked Wikipedia article on the bacteria specifically notes this. See Bacillus thuringiensis. -- Jayron 32 16:06, 3 February 2016 (UTC)


 * Biological pest control is our general article. Yes, lots of people have been working on lots of ways to kill mosquitoes, for quite some time. The challenge is largely to kill enough to be effective, while minimizing effects to non-targeted species. Wolbachia can infect and shorten mosquito lifespan, some strains by up to 50% . While you were probably thinking of viruses and bacteria, some types of Entomopathogenic fungus are also being investigated as a means of mosquito control . Here I posted several other refs related to biocontrol of mosquitoes, notably Sterile_insect_techniques are potentially very powerful but also come with large ethical and legal considerations. SemanticMantis (talk) 14:53, 3 February 2016 (UTC)

The mosquitos absolutely do contract the diseases they spread - they could not spread them otherwise. The typical route of transmission is for the mosquito to acquire an infection from its first bite victim, become infected, and then transfer the infection to subsequent bite victims. It's not that the mosquitos do not contract the infection, it's rather that the infection is not terribly harmful to the mosquito. Someguy1221 (talk) 21:36, 3 February 2016 (UTC)

Meiosis occurs in all our cells of the body or just in the sexual cells?
93.126.95.68 (talk) 14:36, 3 February 2016 (UTC)

This division is specific to the germ cells. See Meiosis. 94.193.78.90 (talk) 14:45, 3 February 2016 (UTC)


 * Yes. When other cells divide it is by a process called mitosis. Looie496 (talk) 17:10, 3 February 2016 (UTC)

When someone is hearing voices, whythese tend to be destructive?
When someone suffers from schizophrenia, why do the voices (correct me if I am wrong) tend to be destructive or command self-destruction? Couldn't someone have a kind voice in his head? --Llaanngg (talk) 16:13, 3 February 2016 (UTC)


 * Auditory hallucinations are not identical to paranoid schizophrenia or other severe mental illnesses. This may be a case where popular-psychology has led you astray from scientific understanding of these conditions.  Nimur (talk) 16:21, 3 February 2016 (UTC)


 * The reasons you believe this to be true are likely some combination of confirmation bias (i.e. you only are aware of examples where the voices tell people to do bad things; other situations aren't reported, or you aren't aware of them) and pop psychology (the media and fiction tends to focus only on the interesting stories, and ignores the real facts of these phenomena). As noted by Nimur, this is not how these phenomena work, and it's best to not believe your premise to be true, because it isn't.  -- Jayron 32 16:24, 3 February 2016 (UTC)


 * I don't think the answers above are very helpful. I can't cite specific research studies, but there is certainly a near-universal belief among clinicians that the voices that people with paranoid schizophrenia hear are overwhelmingly negative in tone.  Unfortunately the mechanisms that underlie paranoid schizophrenia are very poorly understood, and the cause of those voices is a mystery.  There is a pretty strong case that people who "hear voices" are really hearing their own thoughts and perceiving them as external voices, but even if that is accepted there is still the mystery of why people with schizophrenia show such a tendency toward negative thinking. Looie496 (talk) 17:08, 3 February 2016 (UTC)


 * Further, there is no evidence of hearing voices other than self-reporting. It is well documented that self-reporting is not accurate. 209.149.115.90 (talk) 17:16, 3 February 2016 (UTC)


 * "I can't cite specific studies" = "something I think I heard once". If you can't share any further reading to support your claims, one must default to the null hypothesis which I have done above.  In order to refute the null hypothesis, one must cite some evidence, n'est ce pas?  -- Jayron 32 17:23, 3 February 2016 (UTC)
 * Here's a specific study on the nature of auditory hallucinations . Here's another that makes comparisons between  patients with schizophrenia, patients with a dissociative disorder, and nonpatient voice-hearers. It says in the abstract that The subjects in the nonpatient group, unlike those in the patient groups, perceived their voices as predominantly positive: they were not alarmed or upset by their voices and felt in control of the experience.
 * Neither of those two studies is freely accessible. This one is . It's a review of coping strategies (why cope if you like the voices?) and table 2 summarized 14 other studies, which presumably each give more detail on their methods and the nature of hallucinations. Better refs can be likely be found, but I think these support Looie's claim to my satisfaction. I'll add that the quote above both supports the notion that patients diagnosed with schizophrenia tend to have negative hallucinations, while people who have auditory hallucinations for other reasons indeed do often have positive associations, i.e. something like a nice voice in their head. SemanticMantis (talk) 17:49, 3 February 2016 (UTC)
 * This study analyzes the fMRI activity showing the same area being activated when the patient "hears" imaginary voices and when the patient hears real voices. The activity in both cases matches. An abstract can be found here: . --Scicurious (talk) 23:50, 3 February 2016 (UTC)


 * Here's one answer http://www.maps.org/research-archive/psychedelicreview/n11/n11063dus.pdf "Hallucinations as the World of Spirits" Wilson van Dusen 1971. Van Dusen has two further books related to topic. GangofOne (talk) 21:53, 3 February 2016 (UTC)
 * Wilson van Dusen believed that Schizophrenia was caused by demonic possession (he called them spirits, big diff). He shouldn't really be cited for any scientific facts or theories. Someguy1221 (talk) 22:02, 3 February 2016 (UTC)
 * He was a clinician. He has data. GangofOne (talk) 22:24, 3 February 2016 (UTC)
 * Just because van Dusen was formally educated as a psychiatrist or had data is not enough. You could still be a charlatan. Trying to explain evil thoughts or OP's mentioned angry voices as the work of demons is not really a scientific explanation nor adds anything valuable to understanding schizophrenia. --Scicurious (talk) 23:39, 3 February 2016 (UTC)
 * Your preconceptions preclude you from any benefit from Van Dusen's clinical experiences. If psychology really were a science, might be you right, but psychology at this stage of history hardly knows anything fundamental. GangofOne (talk) 04:11, 4 February 2016 (UTC)
 * Demonic possession is not falsifiable and thus outside of the realm of science. That some of van Dusen's data could be used by later scientists to draw more reasonable conclusions is irrelevant.  That van Dusen happened to get something right doesn't mean he's done anything worthwhile.  Even a blind dog can piss on a tree once in a while.  -- Jayron 32 15:53, 4 February 2016 (UTC)
 * To put it a different way, whether or not psychology is a science, demonic possession definitely isn't. Since this is the science desk, if you believe psychology is not a science, then you should provide something which is a science instead, not something which is also not a science. That's like saying "there are too many racists in the world, so I'll be sexist". Nil Einne (talk) 17:36, 4 February 2016 (UTC)
 * Maybe, but the joke is that memetics is often presented as science. It's cool, it's atheist, and it assumes that intellectual entities stored inside living human brain tissue are incapable of thought, planning, and malice.  I suppose Occam's razor delivers different strokes for different folks -- to me, burdening the concept of a demon with these extra restrictions seems like the more complex hypothesis, but there are lots of people who go such things (e.g. the idea that if there's life on other planets it must be very primitive, because it's less complicated to propose something really limited than to propose something with unknown potential).  Admittedly we are most unlikely to get anywhere here, but one of the few advantages of the surveillance society is that, in theory, its techniques could be used to look for the anomalous coordination of evil impulses without identifiable conscious communication between the actors. Wnt (talk) 19:13, 4 February 2016 (UTC)
 * Memetics may be different things for different people. For some it is a theory. For me, it seems to be more of a hypothesis (that could be tested) or an epistemological framework, than a science. Whatever we consider it to be, it won't change anything about this discussion.
 * I don't know what you mean by "the concept of a demon" which is being "burdened." If it is something like a unicorn, then this is the wrong desk. But you seem to be treating it like a real thing. Feel free to provide any hint of information about its existence. It is also difficult to guess what you mean by "intellectual entities stored inside living human brain tissue", but you are free to disclose any evidence about these too.  In the same way, you are free to search for behavioral patterns in big data. Do not expect that people integrate your "evil entities coordination theory" into any aspect related to consciousness.Scicurious (talk) 21:25, 4 February 2016 (UTC)


 * I think you're all taking the concept of a "meme" too far. A meme (as originally conceived by Richard Dawkins) is just an idea or a concept - like (for example) the false idea that vaccinations cause autism.  This idea was in nobody's heads at all until some fraudster in the UK came up with it.  He published a scientific paper which claimed to have proved the connection (it was fraudulant) and thereby passed this meme onto other people, and those who were already concerned that modern medicine might be a bit dubious leaped on the idea and started telling other people.  The "meme" had started to spread far beyond the scientific community - like an infection it was passed between people and grew exponentially, just like a viral or bacterial infection.  Along the way, the meme mutated into a claim about a specific mercury-based preservative in vaccines being the culprit.  This meme had mutated - and because the idea was now much more specific - perhaps more plausible - people who didn't have a propensity to dislike modern medicine, but who knew just enough about how mercury can affect the brain started to become infected by the meme...even though science had by now proven that the idea it contained was entirely false.  The meme had evolved to spread to a wider audience...and it continues to evolve and spread...just like a disease organism.  The idea that these things are somehow alive or represent some physical embodiment within the brain is not a part of the original concept of a meme.  Memes can cross-breed with each other - sometimes two ideas will be conflated into a single new meme.  Urban legends make great memes - and in each re-telling, people will add small details to make them sound more interesting...and the meme gradually becomes more virulent.  Darwinian evolution clearly apply to ideas like this (it's no accident we talk about them "going viral") - ideas replicate, they mutate, and ideas that are appealing to the most minds will crowd out versions that aren't so attractive to people - so the classic "survival of the fittest" applies to them.  This doesn't suggest that memes are "alive" or "intelligent" or anything like that.  You can think of tunes that "get stuck in your head" as being memes - and those can be spread too. SteveBaker (talk) 19:56, 5 February 2016 (UTC)
 * you're assuming the idea evolves solely according to the way that makes it most likely to be believed. But what if it is doing more than that?  To take your example, maybe some parents who have this idea have some subconscious resentment of all that squalling and all those dirty diapers, and so the meme goes from being "you should worry about vaccination" to "you must not vaccinate ... even if normally you would take some risk to protect your child from another risk... because if it catches a nice quick childhood disease you might not have to worry about it any longer"?  And so the meme might evolve a meanness that is not intrinsic to itself, or to what those holding it consciously believe, because there's this reservoir of subconscious threat constantly tweaking its memetic code in a directed fashion, sort of like how a trinucleotide repeat expands to cause disease out of its own molecular agenda, not due to a selective pressure to do so.  But in this case that directing force may be actually conscious.  I'm not saying I can prove that's true but I am surely not convinced it's false. Wnt (talk) 02:59, 6 February 2016 (UTC)


 * All I mean is, if "memes" exist, is there any evidence that they don't think, don't feel, don't have aspirations of their own? They're physically part of brain encoding, so why shouldn't they?  But if they do, how are they different from demons? Wnt (talk) 21:41, 4 February 2016 (UTC)


 * We don't need evidence of non-existence and can hardly provide it. I am not denying that lots of things exists and are unknown to me. However, if you believe in some sort of brain demons, coordinating evil impulses, people will ask how you came to this conclusion. Notice that in memetics "memes" are defined, and the whole hypothesis is open for debate. --Scicurious (talk) 22:43, 4 February 2016 (UTC)


 * "People suffering from schizophrenia may hear 'voices' – auditory hallucinations – differently depending on their cultural context, according to new Stanford research. In the United States, the voices are harsher, and in Africa and India, more benign, said Tanya Luhrmann, a Stanford professor of anthropology and first author of the article in the British Journal of Psychiatry.". Modocc (talk) 22:39, 4 February 2016 (UTC)
 * Simon McCarthy-Jones's 2012 book Hearing Voices: The Histories, Causes and Meanings of Auditory Verbal Hallucinations Cambridge (2012) is freely available at archive.org. Evidence for the phenomenon other than self-reporting goes back to Louis Gould in 1948 at least.John Z (talk) 19:33, 6 February 2016 (UTC)

How much does time vary from one day to the next for sunrise and sunset?
I notice that the times listed (in my local newspaper) for sunset change a little each day. So, today it might be 5:06 PM. Tomorrow it might be 5:07 PM. And so forth. Same with sunrise. My question is: is that change a constant number or does it vary for some reason or another? In other words, is the change from day-to-day always an exact constant (like, for example, 1.63 minutes, or whatever)? Or will that value vary from day to day? Thanks. Joseph A. Spadaro (talk) 17:59, 3 February 2016 (UTC)
 * No, the rate of change varies throughout the year: slowest near the solstices and fastest near the equinoxes. A plot of the rate of change, IIRC, forms a sine curve, as does a plot of the actual sunset and sundown times. Hopefully someone will be able to give a quantitatively precise reply. הסרפד  (call me Hasirpad) 18:18, 3 February 2016 (UTC)
 * Such a reply would require knowing the latitude and what century you're in. And the point of no change is usually not the exact solstice because of the equation of time. This is actually extremely important at low enough latitudes and completely swamps the influence of the seasons on which date the sunset stops changing, though the actual magnitude of the change is small there (no more than half hour variation at the equator compared to hours higher up) Sagittarian Milky Way (talk) 18:40, 3 February 2016 (UTC)


 * Why does the century matter? Or is that a typo for "country"?  I am in the USA.  Thanks. Joseph A. Spadaro (talk) 19:13, 3 February 2016 (UTC)


 * It matters for the quantitative reply that הסרפד mentioned or if you're interested in the reasons but not if you just want to know if it's constant or not and don't care about the number of minutes if it isn't a constant. Sagittarian Milky Way (talk) 20:34, 3 February 2016 (UTC)


 * Sure, it varies, but we can give a general graph that shows day length at various latitudes. OP should look at the graphics here . For any non-zero latitude, the derivative of the day length gives the rate of change of day length, which gives the total amount that the sunrise/sunsets have moved. Since the day length is roughly sinusoidal, the derivative will also be sinusoidal, and this is why day length changes the least when the days are the longest and shortest, near the solstices. Further refinements are possible, but I think this is what the OP wants to know about. SemanticMantis (talk) 18:50, 3 February 2016 (UTC)
 * This doesn't look very sinusoidal. Note that the times when sunset change at 3°N is zero are February/March border, May, August, and November and there's four of them instead of two (and none are solstice months). Earliest sunrise is in November there and latest sunset is February below c. 1.5-2°N or so. It's true that the equation of time is swamped by the seasons by mid-latitudes though the sine-ish wave pstill looks pretty crooked if graphed. At 40°N the 2 weeks separating the day of zero sunset change from the winter solstice is the bigger difference. The sunset is only a couple minutes earlier than at the winter solstice though so it's pretty minor. If the OP wants to know the time of zero change to some accuracy though the latitude and whether he wants his lifetime or a historical era is still important because of the equation of time. At 50°N the time of zero sunset change is about 10 days before the solstice and at 60°N it's more like 6. Source: the Astronomical Calendar 2015 by Guy Ottewell. Sagittarian Milky Way (talk) 20:34, 3 February 2016 (UTC)
 * The (Sunrise_equation and Sunset equation) are trigonometric. Their behavior is close enough to a sine wave (at least between the tropics and the arctic/antarctic circles of latitude) and a to make some vague generalizations:
 * The rate of change will be low around the solstices. The name solstice refers the the relatively static sun angle; and
 * The rate of change will be near its greatest around the equinoxes.
 * Because the Earth's orbit is an ellipse, the earliest and latest sunrises and sunsets do not fall at the solstices exactly. (See Analemma.) BiologicalMe (talk) 19:14, 3 February 2016 (UTC)
 * So that is why it's hard to notice at the OP's latitude (he is a Northeasterner I believe). The small analemma offset of at most a quarter hour gets added to the perfect sine wave sunset times and that already varies by 6 times as much (also, at this point in history the largest offsets in the analemma are small by geological standards and aren't near the times of latest and earliest sunset which make them harder to notice (especially near your time zone's official longitude)). Sagittarian Milky Way (talk) 21:09, 3 February 2016 (UTC)

Back to the issue of "century". So if I asked this question in the 20th century, I would get a different reply/result than if I had asked in the 21st century? I still don't follow this idea? Joseph A. Spadaro (talk) 17:23, 4 February 2016 (UTC)
 * User:Joseph A. Spadaro, Nothing changed between 1999 and 2001. Or at least nothing much. The name of the year is unimportant, but the time period that we want to forecast is. If you only want to look at why the amount of time that a time of sunrise changes each day will change and not be constant, all you have to consider is the axial tilt and a given latitude. That explains why the change in sunrise time is different each day, and can tell you roughly when the fastest and slowest change days are. But that's a simplified picture. If the Earth had no tilt and had a perfectly circular orbit, there would be no change in sunrise or sunset ever. If you want to know what time the sun will rise, and how big the change is, next year at this location on this date, it will be pretty much the same as the time it rose today at this location, in large part because the Gregorian calendar is fairly advanced, and it's designed to keep e.g. March as a spring month in the Northeastern USA (and we add leap days and such to keep it that way).
 * But the obliquity of the ecliptic and Orbital_eccentricity of Earth conspire to make things a little more complicated. This is explained at Equation_of_time, and note also the animated pictures that show the two main components forming the analemma. I think what SMW is referring to (confusingly, and perhaps unnecessarily, IMO) is that the equation of time itself slowly changes! We have scant coverage of this at Equation_clock. The earth slowly slows down, the tilt may change a bit, etc., etc., and eventually we'll fall into the sun or it will engulf us, whatever. But none of that matters unless you want to make ultra-precise predictions for a very long time in the future, even for 2216, I don't think you have to account for changes in the equation of time to get the time of sunrise correct within a minute. This is really all about mathematical models. All models are wrong, some models are less wrong. Sometimes a simple model is better if you just want to get the gist, sometimes you need to get very complicated if you want very high accuracy and precision over long time scales. Anyway, I think what I wrote is basically correct, I'm sure User:Sagittarian Milky Way can correct me if I made some error of concept or terminology. Hope that helps, SemanticMantis (talk) 20:42, 4 February 2016 (UTC)
 * I guess it is perhaps unnecessary. The OP did say X.XX minutes though. I found a nice graph of the change. Sagittarian Milky Way (talk) 01:15, 5 February 2016 (UTC)
 * The Equation of time (linked above) gives details of the reason for the change over centuries.   D b f i r s   20:25, 4 February 2016 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 19:11, 5 February 2016 (UTC)

What is the formula for conversion of testosterone nmol/L to testosterone ng/dL?
What is the formula if I want to convert a value from nmol/L to ng/dL? If it matters, I am looking at values from this page: Reference ranges for blood tests. Thanks. Joseph A. Spadaro (talk) 18:08, 3 February 2016 (UTC)
 * To convert moles to grams, you need to know the molar mass for each substance. The formula is:
 * $$C [ng/dL] = 10 * M * c [nmol/L]$$,
 * where C is the concentration, M is the molar mass, and c is the molarity. For a sodium ion, for instance, it's around 22 (the atomic weight of sodium), which is why in the table, 145 mmol/L corresponds to 330 mg/dL. Smurrayinchester 18:22, 3 February 2016 (UTC)


 * If you look on that page (Reference ranges for blood tests), there is a chart under the "Sorted by concentration" section. In that chart, they list "Testosterone" (both for males under age 50 and over age 50).  The units are listed as nmol/L in that chart.  But, I want to convert them to ng/dL.  What would be the formula to do so?  Thanks.  (I see that some conversions have already been down at the bottom of that article.  But I still need/want the actual formula.)  Thanks. Joseph A. Spadaro (talk) 19:20, 3 February 2016 (UTC)
 * In the InfoBox for Testosterone, the atomic mass is stated as 288.42. Therefore you divide the nmol/litre by 288.42 to get ng/dL. LongHairedFop (talk) 19:39, 3 February 2016 (UTC)


 * Thanks. The above formula has five variables.  Three of them are:  capital "C", lower case "c", and capital "M".  For testosterone, what are the values for those three variables?  The above formula also has the two other variables (nmol/L and ng/dL), which are the values that I know/have.  Thanks.   Joseph A. Spadaro (talk) 20:57, 3 February 2016 (UTC)
 * The square-brackets denote the units for the preceding variable. For example, this formula would be read "the value of C in ng/dL equals...". The idea of concentration is just "how much of one thing in a mixture of things", so the value depends on how you measure the thing and the total of things. DMacks (talk) 21:34, 3 February 2016 (UTC)
 * Yes, sorry, that made it a bit confusing. I just put the units in there for clarity because you have litres on one side, but decilitres on the other, so you need an extra factor of ten for the conversion. Smurrayinchester 10:37, 4 February 2016 (UTC)


 * I am still confused. Is the correct formula: number of "ng/dL" = 10 * M * number of "nmol/L"?  Or is it "divide the nmol/litre by 288.42 to get ng/dL", as someone stated above?  They both seem like very different formulas?   Joseph A. Spadaro (talk) 17:19, 4 February 2016 (UTC)
 * In general, numbers in physics formulas should always have units. Alright, there are fans of natural units, a lot of them nowadays, but they give me a headache - dimensional analysis is crucial IMHO, and even when a number doesn't have regular units (like the cycles in Hz i.e. "cycles/second") sometimes it helps to keep track of them anyway.  Anyway, the brackets suggest that if you put a variable in, it should have those units already attached.  (I'm not sure how standard a usage this is; it might have been better to make this explanation off to the side...)  If you start with a number in nmol/L, you need to multiply by another number in ng/nmol to get a number in ng/L.  Note ng/nmol = g/mol = "molar mass".  In general, most simple formulas like this should practically work themselves, in that you know what units you have, what units you have to get, and what ratios of units are equal to 1 - as M number of nanograms is for one nanomole of a certain chemical. Wnt (talk) 19:24, 4 February 2016 (UTC)

Thanks. Joseph A. Spadaro (talk) 19:11, 5 February 2016 (UTC)

List of quad style Drones

 * 1) The first ever made (concept/prototype/original), at what year?
 * 2) The evolution of each/it?
 * 3) Latest one including the CES Shows 'Single Human Carier' one?

Apostle (talk) 18:56, 3 February 2016 (UTC)


 * For 1, see Quadcopter, see also here . The word "drone" is an unfortunate choice for a thing little flying machine that may or may not be controlled by a human. Perhaps that's why we don't have an article on it under that name. Of course "drone" can mean a drone_(bee), or Bagpipes, but for flying machines the term is hopelessly ill-defined. We do have articles on unmanned aerial vehicle, as well as radio-controlled aircraft and autonomous vehicle. So you'd get better search results if you use those better terms. SemanticMantis (talk) 19:37, 3 February 2016 (UTC)
 * Thanks SM . I'll read through after the 15 or 20th of this month; low on kbs...
 * I'm particularly concerned about "point no:1" (I believe you stated and summarised clearly) and "point no:3". "Point no:3": From what I recall, they are apparently 100,000 per unit, and a request for a legislation will be put through for China...
 * Apostle (talk) 20:55, 4 February 2016 (UTC)

In case of atrial fibrillation does a part of the atrial pulses passes to the ventricles?
In atrial fibrillation occur a hundreds of pulses in the atrium, but my question is if some of them pass through the AV node to the ventricles or what happens is that a escape rhythm enter instead of the sinus pulses and send pulses to the ventricles? I've read the article here (atrial fibrillation) and I didn't see answer.93.126.95.68 (talk) 20:47, 3 February 2016 (UTC)


 * Quoting from the pertinent part of our article on atrial fibrillation:
 * "Although the electrical impulses of AF occur at a high rate, most of them do not result in a heart beat. A heart beat results when an electrical impulse from the atria passes through the atrioventricular (AV) node to the ventricles and causes them to contract. During AF, if all of the impulses from the atria passed through the AV node, there would be severe ventricular tachycardia, resulting in severe reduction of cardiac output. This dangerous situation is prevented by the AV node since its limited conduction velocity reduces the rate at which impulses reach the ventricles during AF."


 * By definition, atrial fibrillation is fibrillation of the atrial myocardium. The A-V node specifically acts as a frequency filter; its neurons don't conduct rapidly enough to allow fibrillatory waves from the atrial myocardium through to cause fibrillation of the ventricular myocardium. loupgarous (talk) 21:45, 3 February 2016 (UTC)
 * They are not "neurons". They are special muscle cells. Ruslik_ Zero 20:34, 4 February 2016 (UTC)

PEG-PVA excipient ("binder" et al. for Active Pharmaceutical Ingredients primarily for oral route preparations) article in sorry stub state
Anyone care to tackle it? A very good source (albeit, singular; but itself referred by numerous sources which could be directly sourced themselves) is the latest issue of American Pharmaceutical Review (specific article to be found in full online @ this link). Anybody into pharmacology + chemistry care to discern what information is pertinent and transclude it? I'd be very grateful, as this is not my area of expertise (but however, an area of avid interest). Nagelfar (talk) 20:47, 3 February 2016 (UTC)


 * That particular source isn't a very usable source in and of itself to expand the stub article PEG-PVA, being a primary article describing the author's own research, especially as the author works for BASF, the manufacturer of "Kollicoat IR" brand PEG-PVA excipient. Apart from that BASF-affiliated source, there's another source not mentioning PEG-PVA at all, apparently cited as a source of the definition of the word "excipient". In its present state, the article ought to be a candidate for speedy deletion according to WP:PROMOTION.


 * A Google search for "PEG-PVA excipient" turns up numerous other articles on PEG-PVA, only one of which, "Scientific Opinion on the safety of polyvinyl alcohol-polyethylene glycol graft-co-polymer as a food additive", EFSA Panel on Food additives and Nutrient Sources added to Food, European Food Safety Authority (EFSA) wasn't written by someone working at BASF.


 * Until we see at least one review of the relevant literature on PEG-PVA by someone not affiliated with BASF, its manufacturer, I'd be inclined to not add anything but that European Food Safety Authority study. (None of the Google Books entries covering excipients that turned up in the Google search actually talks about PEG-PVA.)  That would still leave it a stub.  The BASF workers' papers which make up rest of the Web-available literature on PEG-PVA at this point are primary sources, and can't be most of the sources for this article, in my humble opinion. loupgarous (talk) 02:01, 4 February 2016 (UTC)

"Sexual cells are cells which able to reproduce a new generation."
If I would define sexual cell as "Sexual cells are cells which able to reproduce a new generation.", would it consider right? It's not clear to me because also the somatic cells can reproduce a new generation. no? 93.126.95.68 (talk) 22:39, 3 February 2016 (UTC)
 * It would be "Sex cells", a synonym for germ cells, not "sexual". It also would help to clarify that the new generation is organisms. Somatic cells can undergo mitosis to produce more somatic cells within the organism, but they do not yield new organisms, by definition. BiologicalMe (talk) 22:49, 3 February 2016 (UTC)
 * Ish. Mitosis of somatic cells can lead to reproduction in some cases, which is typically called fragmentation in animals and vegetative reproduction in plants. Someguy1221 (talk) 00:06, 4 February 2016 (UTC)
 * Yes, I would suggest the OP read meiosis and mitosis. "Sex cells" and "reproduce" are not the technical words used by biologists. μηδείς (talk) 03:03, 4 February 2016 (UTC)


 * Alternation_of_generations_simpler.svg you want to get a broader picture, consider alternation of generations. In humans, we think of adults, who use gametes to make new humans. But for mosses and other life-forms, the gametophytes have a whole life of their own. Note the ferns you see don't have sex, but their little gametophytes do. Put simply, a mature fern makes spores, and those spores don't directly make another fern, but they make something else that can make gametes, and those gametes can fuse to make a mature fern. Since a spore forms from mitosis, it does not come from or participate in any sexual process. However, it is the thing that starts a new generation. SemanticMantis (talk) 17:23, 4 February 2016 (UTC)