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May 5

Earth tidal heating

If Earth is in interstellar space, and the Moon is orbiting it in a circular distance d, then what d will allow tidal heating to maintain a temperature of 15 degrees Celsius or 59 degrees Fahrenheit?

What if Earth is orbiting Jupiter in a circular orbit?

Are seasons possible?32ieww (talk) 02:24, 5 May 2017 (UTC)

There is a way of working out the answer, but I'm not going to do the heavy lifting for you. Work out the radiated heat energy from the earth using the Boltzman equation, at 288 K, then you'll know how much power we need to suck out of the moon to get that, then do the orbital mechanics on the moon. At the moment we get about 3.7TW from the moon. I'd guess the power extracted is proportional to the tidal velocities cubed. The rest is easy. No, no seasons Greglocock (talk) 05:25, 5 May 2017 (UTC)

Well, seasons are possible if you allow the moon to have an ellipsoidal orbit, with the tide level hence tidal heating being higher when the moon is closer. I probably need to add that "the Sun is closer to the Earth in summer" is an incorrect explanation for seasons, which can easily be proven false if you remember that "summer" and "winter" are not simultaneous in the northern and southern hemispheres. Tigraan 08:37, 5 May 2017 (UTC)

Hmmm, actually it is not obvious how tidal heating depends with tidal height. Surely it is nondecreasing, but maybe it increases sufficiently slowly that the main effect is the period of the tides. The formula for the satellite tidal heating found at tidal heating does not involve height... Tigraan 08:50, 5 May 2017 (UTC)

As in surface temperature.32ieww (talk) 02:52, 9 May 2017 (UTC)

• You might want to ask at the Math Desk, @32ieww: if you need help with the heavy lifting. μηδείς (talk) 00:20, 6 May 2017 (UTC)

What weights are involved?32ieww (talk) 02:52, 9 May 2017 (UTC)

Comments:

1) Maintain that temp where ? In the atmosphere ? That's a tall order considering the atmosphere is almost entirely heated by the Sun, at present. Tidal forces sufficient to warm the atmosphere to that degree might well tear the Earth and/or Moon apart.

2) Radioactive decay also is a major source of heat in the interior of the planet.

3) As for seasons, you could have a highly eccentric orbit for the Moon, which would cause higher tidal heating when it was near. Of course, at the small distances needed to warm the Earth that much, the Moon's orbit wouldn't last a year, or even a month. StuRat (talk) 01:10, 6 May 2017 (UTC)

Why we cannot see crescent of Venus

for more explanation , we know that nearest object after moon to earth , is Venus and as it is bigger than mars and near to sun , so we might be able to see its crescent . --Akbarmohammadzade (talk) 15:39, 5 May 2017 (UTC)

We can see the phases of Venus, though it's usually too small to see with the naked eye, unlike the moon which is much larger. Misplaced Pages has an article titled phases of Venus, which describes it more fully. --Jayron32 15:41, 5 May 2017 (UTC)

Back when I had a telescope, I saw the crescent of Venus many times. It occurs when Venus is closer to us. Although a crescent, its highly reflective atmosphere makes it very bright. As Venus approaches the far side of the sun it becomes more "full" but also appears smaller, of course. ←Baseball Bugs carrots→ 16:25, 5 May 2017 (UTC)

You should see Venus from Mercury. There it can be full without being far away and so reaches magnitude -7.7 which is as bright as a crescent Moon on Earth. Venus gets to a see a Full Earth, which is bigger and more impressive. Sagittarian Milky Way (talk) 07:36, 6 May 2017 (UTC)

That's OR, @Baseball Bugs: and you know it! μηδείς (talk) 00:11, 6 May 2017 (UTC)

So is the OP's claim that crescent Venus can't be seen. And by an amazing coincidence, my recollection of seeing the crescent through a telescope matches the photo you posted! ←Baseball Bugs carrots→ 01:01, 6 May 2017 (UTC)

My interpretation of the OP's question is not that they think Venus doesn't exhibit a crescent telescopically, but that we ought to be able to see it with the naked eye, but seemingly can't.

In fact, it is just possible under some circumstances to see the crescent with the naked eye, as hinted at by Jayron above. From the Phases of Venus article Jayron linked, in the Naked eye observations section:

"The extreme crescent phase of Venus can be seen without a telescope by those with exceptionally acute eyesight, at the limit of human perception. The angular resolution of the naked eye is about 1 minute of arc. The apparent disk of Venus' extreme crescent measures between 60.2 and 66 seconds of arc, depending on the distance from Earth. Nevertheless it is possible for observers with extremely acute eyesight to see a crescent Venus under ideal atmospheric circumstances."

{The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 09:44, 6 May 2017 (UTC)

Could be. Maybe the OP will come back here and clarify. ←Baseball Bugs carrots→ 11:10, 6 May 2017 (UTC)

May 6

Acrylic Adhesive

Is "Acrylic Adhesive" considered a subclass of Epoxy adhesives or is it a different category altogether?

Colloquially, people refer to pretty much all binary adhesives as "epoxy glue" so I'm a little confused as to its exact classification. ECS LIVA Z (talk) 06:58, 6 May 2017 (UTC)

Technically, "epoxy" relates to epoxide group, whereas "acrylic" relates to Polymethyl methacrylate (emphasis added). - 107.15.152.93 (talk) 08:16, 6 May 2017 (UTC)

When acrylic is polymerized by combining it with an epoxy resin, it is a type of epoxy adhesive. For example, In "Handbook of Thermoset Plastics", by Sidney H. Goodman (Editor) p.76, acrylic is shown forming a copolymer with a bisphenol A epoxy resin. I don't know if this is always how acrylic adhesives work, or even if this is how the product linked by the OP works.--Wikimedes (talk) 09:07, 6 May 2017 (UTC)

Two sources that would probably directly answer your question are "Adhesive Chemistry, Developments and Trends", Editors: Lieng-Huang Lee (Ed.) and the chapter "The Chemistry of Structural Adhesives: Epoxy, Urethane, and Acrylic Adhesives", by Denis J. Zalucha, Kirk J. Abbey in "Kent and Riegel’s Handbook of Industrial Chemistry and Biotechnology".--Wikimedes (talk) 09:15, 6 May 2017 (UTC)

How can I swing

How can I swing in a swing by moving my feet? Why does it not cancel out when I swing my feet? — Preceding unsigned comment added by 85.76.112.192 (talk) 07:42, 6 May 2017 (UTC)

@85.76.112.192: You're acting to move your upper body backwards, even though (instantaneously), your center of mass still remains where it previously was. This moves the swing backwards, and in turn, the swing no longer perfectly balances the force of gravity, so there is now a net force on you by gravity. Keeping your body rigid from then on makes gravity (literally) do the rest of the work.

Another way to look at it is that although your net momentum initially remains zero, you did do nonzero work on yourself when you swung your feet, part of which was converted to gravitational potential energy. Swinging your feet more at the right time (so that you approximately act as a driven harmonic oscillator) introduces more energy to the system, which leads to a bigger amplitude.--Jasper Deng (talk) 08:02, 6 May 2017 (UTC)

I think if the pivot on a swing went to your center of mass, you would theoretically not be able to swing. But it goes of course to the seat, and your legs are something extra, so you can shift the center of mass back and forth relative to the seat and the chain, gradually acquiring a lateral momentum (which gets converted to lateral displacement and potential energy with each swing peak). Wnt (talk) 12:05, 6 May 2017 (UTC)

@Wnt: You could not swing without gravity: by Newton's first law, if you don't have that net force, you're not going to get moving. So it's not you giving yourself momentum, but, as I said, giving yourself gravitational potential energy so gravity can give you kinetic energy.--Jasper Deng (talk) 21:31, 6 May 2017 (UTC)

@Jasper Deng: I think you could swing without gravity if you had, say, a fairly stiff, elastic rod in place of the chain. I think it would work nearly the same way - by sticking your legs out you still put the center of gravity further from the pivot. The difference would be that in this scenario it is not the center of gravity being pulled toward the lowest end of its arc, but the rod that would get displaced as you rearrange yourself about the center, and then applies a force to move the center of gravity away from it. Wnt (talk) 11:52, 7 May 2017 (UTC)

Speaking in the language of math this is called a parametric resonance. By moving your feet you changes your moment of inertia. Under some conditions these changes cause a runaway acceleration of the motion. Ruslik_Zero 12:18, 6 May 2017 (UTC)

Landlocked fish

What is a landlocked fish, and do we have an article about the landlocked-ness condition in fish? The Alosinae article notes that many species in this subfamily are "anadromous or even landlocked", but the link goes to Landlocked, which discusses landlocked countries and has no hatnotes except one to Landlocked parcel, a matter of property law. Nyttend (talk) 10:57, 6 May 2017 (UTC)

For a definition see here. Ruslik_Zero 12:00, 6 May 2017 (UTC)

There's a little more at Alosa. The idea is, most of this group of fish is capable of tolerating salt water and is free to ply the oceans at some point. I take it from the text that some are limited to fresh water by adaptation, but fish can also be restricted by geography, even recent human activity like dams. That said, I'd take accounts of geographical restriction with a grain of salt, because rivers are far more variable on a scale of thousands of years or more than they appear to us. Wnt (talk) 12:00, 6 May 2017 (UTC)

It's fair to say that the fish at Crater Lake are landlocked. ←Baseball Bugs carrots→ 13:11, 6 May 2017 (UTC)

The article lead says the fish were stocked from the 1880's to the 1940's. The crocodiles, however, are native. μηδείς (talk) 23:28, 6 May 2017 (UTC)

• This question came up when I took Limnology. Most such fish when not stocked intentionally are spread by flooding, changes in land-level (landslides and elevation change since the ice age) or river-courses, and even hurricanes and tornadoes. μηδείς (talk) 15:07, 6 May 2017 (UTC)

Looking further, there is speculation that fish eggs can be blown by the wind or carried by waterfowl. And remember that give timescales of thousands of years, floods, rains, and puddle hopping (see Snakehead (fish) can allow travel quite some distance. μηδείς (talk) 19:27, 6 May 2017 (UTC)

This discussion group has some tangential studies, but is largely critical of the bird and wind explanations. Yet if monkeys rafted across the nascent Atlantic given enough time, I think they are looking at a snapshot, rather than a span of millenia. μηδείς (talk) 19:42, 6 May 2017 (UTC)

An example might be the gwyniad, a fish native to one lake in Wales and thought to have been there since the last ice age. Alansplodge (talk) 18:21, 7 May 2017 (UTC)

Given the fish is Welsh, it probably actually came to Wales around 600BC Brittonic_languages#History_and_origins. μηδείς (talk) 05:00, 8 May 2017 (UTC)

Feynman Lectures. Exercises Google OCR. Exercise 1-5 JPG

...

Can you explain why there are no crystals which have the shape of a regular pentagon? (Triangles, squares, and hexagons are common in crystal forms)

—  R. B. Leighton , Feynman Lectures on Physics. Exercises

...

Let us consider a part of the face of the crystal. The arrangement of the atoms in the crystal is such that each atom is surrounded by a certain arrangement of other atoms. This means that atoms of one kind are located at the so-called equivalent points, that is, points whose surroundings are exactly the same. The minimum distance between the equivalent points a is called the lattice period. In Fig. equivalent points are the points 0, 1, 2, 3. The nearest equivalent points form a flat figure - a "cell" (in the figure it is a rhomb with vertices at the points 0, 1, 2, 3), and if we consider the entire crystal, and Not its face, it is a three-dimensional figure. When forming a crystal, more and more cells are growing, so the shape of the crystal face depends on the geometric shape of the cell. Of course, the rate of growth of the crystal in different directions is different, so that the outer faces of the crystal are not simply a repetition of the shape of the cell. But it is quite clear that the angles between the sides of the crystal face are equal to the angles between the sides of the cell, so to answer the question posed in the problem it suffices to indicate that there can not exist cells in the form of a regular pentagon.
We give the proof by contradiction. Let the crystal cell be a regular pentagon, and let O and A be equivalent points (Figure 2). Obviously, the point E should be equivalent (if an equivalent point is placed at a distance a from 0 when moving to the right, then there must be an equivalent point and when moving to the left by the same distance). Other equivalent points can be constructed by rotating the segment OA through the angle 2π / 5 = 72°. After the first turn we get point B, and after the second point C. But the distance EC <a, which contradicts the original assumption (the distance between equivalent points is not less than a). Thus, the face of the crystal can not be a regular pentagon. It can be shown rigorously that an analogous construction is consistent only if the crystal cells are in the form of a regular triangle, a quadrangle (square), and a hexagon.

—  MEPhI , Solutions (Google Translate)

I have read Wallpaper group and Crystallographic restriction theorem but I still need more explanations.
First, how are the triangle crystal faces possible with rhombic cells? Username160611000000 (talk) 15:22, 6 May 2017 (UTC)

Roughly speaking, if a crystal with a rhombohedral unit cell grows more slowly in the body diagonal direction than in the direction of the faces of the rhombohedron, then growth will not be fast enough to reach a vertex and a face will form instead. Since 3 faces of the rhombohedral cell meet at a vertex, the new face resulting from slow growth will intersect with 3 faces, forming 3 edges, and thus the new face is a triangle.--Wikimedes (talk) 18:45, 6 May 2017 (UTC)

Ok. But in such case the shape of a crystal is irregular, and I thought Feynman spoke about the triangular prism.

Second question. Why is the translation necessary? Why atoms can't be situated like this: png

Username160611000000 (talk) 20:56, 6 May 2017 (UTC)

I can't visualize how a rhombohedron can truncate to a triangular prism, but that may be due to inadequate visualization abilities on my part, or it may be that growth is more complicated than different rates in 2 directions. Maybe I'll take a look at Feynman's discussion of it later.

I'll take your second question in 2 parts. First answer is that translational symmetry is not necessary, just common and useful. Amorphous solids (glass) and Quasicrystals exist. Because of the lack of translation, quasicrystals can even have 5-fold symmetry; see the picture of a Ho-Mg-Zn dodecahedral crystal in Quasicrystal#Materials science. Second, there are proofs that 5-fold symmetry and periodic translation are incompatible. Solid State Theory by Walter A. Harrison pp.11-12 has one proof (which I honestly don't find convincing). Since the two types of symmetry are incompatible, there is probably a deviation from ideal symmetry in the drawing that is is too small to be distinguishable. If you want to dig deeply into symmetry of solids, I recommend the MIT online course "Symmetry, Structure, and Tensor Properties of Materials" .--Wikimedes (talk) 23:08, 6 May 2017 (UTC)

The idea of a crystal structure is (roughly) that you have equivalent points equivalently spaced. (Understanding what that means or why it must be seems like by far the hardest part of the proof, and the part omitted in our article; I don't claim to have a good explanation or understanding there. I mean, mathematicians have a hard time proving you can't pack 13 spheres around a sphere but they can talk about all possible crystals? How?). Anyway, if you have two lines of points, and look at two points in the bottom line relative to the top one, you can form triangles:

.X
X.X

Or squares:

X.X
X.X

Or hexagons:

X...X
.X.X.

Or straight lines only (180 degree symmetry):

X.X.X.X

Or no particular symmetry. Note in the last two cases there are lines of X's near each other but they don't relate to each other the same way as within a line, so it's a grid with different distances (rectangles). This proof applies in two dimensions only, but another argument that seems hard to prove is that you can only rotate in two dimensions in three dimensions and so it has to work the same way there. (What I'm describing is the trigonometric proof - the math there is that the two X's on the end (or the top X in the triangle) are 0, 1, 2, or 3 units apart only; there are no intermediate values, and that limits the angles to things with sines a multiple of 1/2. (they say cosines; I think they measured a different angle than I'm thinking of but it should work out the same) Wnt (talk) 12:05, 7 May 2017 (UTC)

Nice. That's the gist of a proof I came up with that finally convinced me (I doubt I was the first). To formalize a bit: Let the distance between the Xs on the bottom row be the minimum symmetry translation. Rotate each X up by the same symmetry angle, using the other X as a pivot point. The distance between the new Xs thus generated must be multiples of the minimum symmetry translation, and the only possible multiples are 0 (60 degree rotation), 1 (90 degree rotation), 2 (120 degree rotation) and 3 (180 degree rotation), which are nicely drawn by Wnt. One could think of the trivial case of 0 degrees as multiplying the original translation by -1.--Wikimedes (talk) 19:18, 7 May 2017 (UTC)

The Crystallographic_restriction_theorem#Short_trigonometry_proof is absolutely unclear. First, you cannot rotate the row clockwise and counterclockwise simultaneously, because 2π ≠ 4(2π/n) + 2k(2π/n) (the left angle must be filled 2k times, so n must be even). Second, this image PNG shows there is no row, but only the ray. Again author uses an unproven translation...Username160611000000 (talk) 06:28, 8 May 2017 (UTC)

I don't understand your first concern. If a rotation clockwise by 2π/n is a symmetry operation, then a rotation counterclockwise by 2π/n is also a symmetry operation (I can explain this if this is the problem). I don't see it as simultaneous rotations, rather the 2 rotations are done consecutively to show where 2 more lattice points must be, and that these 2 new lattice points must be on a line parallel to the original line.

Suppose n=15 and angle = 24°. By two rotations you fill some part of the complete angle (red). But the rest of the angle you should fill also (green). As you can see pngdwg you cannot do that without overlap. Username160611000000 (talk) 05:49, 9 May 2017 (UTC)

I can now see why your diagram showing 5 fold symmetry has no lattice translations. If you start from a point and take the distance and direction (or the opposite direction) to an adjacent point and repeat it, it doesn't always lead to another point. In particular, translating across the drawn lines or center point is where the translations no longer lead to another point (and therefore are not really lattice translations). (A 5-fold rotation that links 5 equivalent sectors, each of which has lattice translations, is interesting, but it is a different thing from having periodically repeating 5-fold axes.)

(I can't see the .dwg files). --Wikimedes (talk) 20:48, 8 May 2017 (UTC)

All-day use of CPAP Continuous positive airway pressure devices.

I am curious if there any scholarly studies for long-term "all-day" (except for meals, and the obvious) use of a CPAP device.

Normal use is while sleeping, and it is common advice to have new patients start using it an hour before sleep to get used to the device. One comment I saw on a blog by someone who signed as a doctor said that a person doing this might have a problem different from sleep apnea, such as a deviated septum or sinusitis. But I am just interested in peer-reviewed research in general, not necessarily to treat some other medical issue. Thanks.

(BTW, I actually had to google google scholar to find it. It seems "Alphabet" is deprecating its use. μηδείς (talk) 19:20, 6 May 2017 (UTC)

Medeis, do you have access to an academic library, or is Google Scholar your best route? Are you familiar with using MeSH, or is basic keyword-searching the best route with which you're familiar? Online resources from the National Library of Medicine include a way to browse the MeSH thesaurus, and using it, I found a subject heading for "continuous positive airway pressure"; see . They don't provide much in tree navigation, although the NT and BT relationships are given (narrower term and broader term, like wiki subcategory and parent category relationships) if you click the "MeSH Tree Structures" tab. My point if you have access to some sort of academic library, or if your public library is big and impressive (do I remember rightly that you're in New York City and can use NYPL? They probably have more academic resources than virtually any other US public library), talk with the reference department about what databases they have that support MeSH searches, and then use these subject headings. You can also use PubMed for free from anywhere, since it searches the MEDLINE database that (if I remember rightly) is open access. And finally, let me know if I can help; my library has plenty of medical literature (we have to, since we have a medical school), so I may be able to find helpful information that you can't access, especially if you don't have access to an academic library. I can't share copies of publications directly (contractual restrictions by most vendors), but print articles are available for ILL (and many vendors permit ILL for e-articles), so if we identify articles that you'd like, you can get articles this way. PS, scholar.google.com is an easy way to access Google Scholar. Nyttend (talk) 11:31, 7 May 2017 (UTC)

I have direct access two two large university libraries, but not the medical libraries for borrowing purposes as I am not a physician or medical student.

I would point out that CPAP means constant in the sense of moment-to-moment, from breath to breath, not 24 hours. A CPAP is like a much less invasive measure than intubation, tracheo(s)tomy, or using a respirator. The devices are prescribed to use when you are asleep, since they blow air into the nostrils to keep the airway from being blocked during apnea, although new users are often advised to put them on early to get used to them. When you are awake they are not necessary, as you overcome any issue by voluntary control.

My question is, is there any study of their use or harmfulness with long-term use during wakefulness. This does happen, as insurance coverage requires a minimum number of hours of use during the month, and sickness like vomitting or diarrhea can make this impractical for several days--in which case the rental company suggests wearing the device while awake--but that is a monetary motivation, and others do, according to blogs, wear the devices constantly. Given this "off-label" usage is known to the medical community, I am curious if any studies have been published on it.

As for the NYPL, its glory days are long gone. The last time I was to the main branch I was disgusted by its physical upkeep, dearth of adult non-fiction on any serious level, and unhelpfulness of the staff. MY NYC neighborhood branch has children's books, romance novels, and broken computers. Since I don't drive in NYC, and I have a NJ license, I order materials online or by the phone through my elderly parents' local branch library, part of a large consortium, and I pick them up when I visit weekends. I regularly get academic books and foreign films from Princeton and Rutgers via ILL, for example, delivered weekly.

Unfortunately they charge to print out journal articles, and I have gotten charged $5-$15 for articles, sight unseen, that had perhaps one page of relevant material. Hence my wish to use online sources, if you can help. Frankly, any relevant material is going to be in the abstract, as I am not looking for complex data or mechanisms. Thanks. μηδείς (talk) 13:26, 7 May 2017 (UTC)

Let me see what I can find. I'm surprised about you being required to print out the journal articles — aside from the occasional situation where the original is photocopied and they mail the photocopies (so you'd just keep the printouts), all the article ILLs I've encountered are fulfilled either by emailing the customer the document or uploading the document to a secure server and emailing the customer the login credentials. But maybe that's one of those things that's handled differently in public libraries? Nyttend (talk) 00:34, 8 May 2017 (UTC)

Medeis, I found one item almost immediately. This is OCLC 923522573, Atlas of Procedures in Neonatology from academic publisher Wolters Kluwer, speaking of using this device in infants with breathing problems. Were you looking for adult use, or is this related to your interests? I can get you a little sketch of the respiratory section, but as it's only available in e, you won't be able to ILL the whole thing. Do you have access to the digital resources of those two large libraries? If so, check to see if they have it. This title's held by such institutions as the CUNY Graduate Center, the Borough of Manhattan Community College, and the New York Academy of Medicine; those are the first few results I'm getting, but I can't find more results because whenever I set my location to New York, it resets the location to my actual location after I read the first page of results. Nyttend (talk) 00:45, 8 May 2017 (UTC)

PS, I was wrong. At least the University of Virginia holds this title in print, so it will be ILL-able if an institution is willing to send it. Nyttend (talk) 01:18, 8 May 2017 (UTC)

I started using a CPAP this year when I had bariatric surgery; I love it. For it to be covered by insurance, I have to use it at least 4 hours a day, at least 21 days a month. But I have other intermittent conditions that can make this difficult for a week at a time. Then my breathing tube was ripped when the devicee fell off the table.

The saleswoman told me I could just wear it while awake to log hours. I do have a pending appointment with the pulmonologist, but they are hard to schedule and will not answer questions over the phone. I did myself find a doctor on a blog who said that such use long-term could weaken the tone of the "lung muscles" (diaphragm?) My intention is to continue with the prescribed protocol. Had I found anything published one way or the other I would have made other arrangements to see the doctor and ask them about that material.

As for the printouts, I assume the local librarian thought I wanted hard copies, and then just presented them. I did find out a list of databases and journals I can get on line, but they don't provide specialized keyed services like you mentioned. Thanks for help with the research.

Well, seeing that you've been around since 2010, I don't think you're neonatal anymore (although if your account's been compromised by a neonate, your case will definitely warrant appearance in the journal Child Development, and I'll happily skip the {{Compromised account}} in order to get more data for the research article), so I can see what else I can find on adult use. Nyttend (talk) 01:51, 8 May 2017 (UTC)

As an aside, Sci-Hub does some excellent interlibrary loans... I'm not going to touch the question myself because a) this is veering too far into medical advice I'm not qualified to give, b) CPAP strikes me as a ridiculous medieval contraption, and c) a decade or two back when I experienced some sleep apnea symptoms I noticed that the position matching where my throat felt sore, partially blocking the airway, was not a stable one to hold voluntarily (it either stopped up tight or went wide open with any straying of attention); after a semiconscious tete-a-tete with the part of my mind handling the sleeping arrangements I got the answer back that it felt more comfortable to do that, at which point I realized my breathing muscles felt a need to be stretched that was causing the response. It seemed like some occasional very deep inhalations to stretch out my lungs were enough to keep this at bay, though of course I don't know if the apnea symptoms would have been a onetime aberration anyway. I wonder if there's any scientific data available to prove or disprove that hypothesis. Wnt (talk) 02:27, 8 May 2017 (UTC)

Most of what I'm seeing in PubMed (again, you can search that for free, and it supports the use of MeSH) that's relevant is talking about its use in patients with cardiac problems. For a couple of examples, see https://www.ncbi.nlm.nih.gov/pubmed/16840396 from Chest (quote from the article: "CPAP was applied through a tight-fitting nasal mask breathing at pressure of 8 cm H2O with the mouth closed for a 30-min period every morning while awake and in the sitting position.", so yes they're looking at this issue) and https://www.ncbi.nlm.nih.gov/pubmed/24026964 from Sleep and Breathing (article title: "Acute haemodynamic effects of continuous positive airway pressure in awake patients with heart failure"), but then I've looked over only a comparatively small percentage of the results. I have access to most of these articles; if you find a useful-looking abstract, let me know and I can check the article for you. Nyttend (talk) 02:30, 8 May 2017 (UTC)

Well, I considered the medical advice aspect before posting, but I am not asking anyone here for a diagnosis, prognosis, or personal treatment advice, just literature on the off-label use of a medical device, which doesn't go beyond User:Kainaw/Kainaw's criterion. I have gone from a 45 to a 31 BMI in two years but have chronic GI issues, yet no other life-threatening issues like heart failure, so I consider the issue under control.

Had there been ten peer-reviewed studies saying one thing or another about such use I might insist on an emergency consult. I am happy to wait, and again appreciate the help. I actually see my general practitioner tomorrow, and will bring it up--I wanted to be prepared if there was alarming literature one way or the other. Thanks again, all, for the help.

BTW, my sister's 10-year-old device is indeed the size of a dorm fridge and has a face mask that looks like the facehugger from Aliens. Mine is the size of a shoebox, half that if I remove the heating and humidifying unit, and I can read and watch TV or use my laptop with it quite comfortably. This is pretty much standard and not so much a mediaeval torture device nowadays. Also, I cannot hear it, and like that I can sleep under the sheets and have my air pumped in.

Maybe they'll soon be considered luxury items? μηδείς (talk) 03:17, 8 May 2017 (UTC)

Sorry, you're right this wasn't medical advice - I misread/misthought that time. Wnt (talk) 12:58, 8 May 2017 (UTC)

No need to apologize, @Wnt: the comment was in good faith, and the concern occurred to me after all. μηδείς (talk) 17:27, 8 May 2017 (UTC)

What's the point of non-specialized scientific magazines?

Why are non-specialized science magazines, like Nature and Science, so highly regarded? What's the purpose of publishing in the same place an article about the Mayas, about HIV research, or astrophysics? What education would someone need to understand it? --Dikipewia (talk) 19:27, 6 May 2017 (UTC)

These are very old and prestigious publications (read their articles--you should have linked to them) which existed long before there was enough demand for and copy written for more specialized journals. Chanel and Tiffany are dead, but not their brands.μηδείς (talk) 19:45, 6 May 2017 (UTC)

Anyone who needs to be given links to articles on the journals is unlikely to be able to give a helpful answer. Medeis' answer is relevant to the extent that the factors affecting journal ranking are to an extent self-reinforcing: prestigious journals attract good work, so remain prestigious. Henry 22:01, 6 May 2017 (UTC)

Pre-Columbian era archeologists, HIV epidemiologists and Astrophysics experts are as likely as anyone else to be interested enough in each other's works to read about them in the journals Nature and Science. The links give more information. Blooteuth (talk) 22:08, 6 May 2017 (UTC)

Briefly, the concept for these journals is that they publish the peer-reviewed work of scientific specialists, but only when the importance of that work is sufficient to interest non-specialists. A work published in such a broad journal meets the criteria that it has impact outside of its original field. For example, "Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public." "Science continues to publish the very best in research across the sciences, with articles that consistently rank among the most cited in the world."

Nobody forces anyone to regard these journals highly. Many scientists do regard these journals highly, because many scientists respect the editorial choices that these journals make.

Nimur (talk) 23:12, 6 May 2017 (UTC)

I would think the very variety of these magazines contributes to their usefulness and popularity. And since the OP's question is "what's the purpose" - I would say the purpose is to educate a broader segment of society than a highly specialized journal would. ←Baseball Bugs carrots→ 23:18, 6 May 2017 (UTC)

My sister is a biologist, her husband a physicist. I was going to get them a subscription to Nature until I found out I could get them a lifetime subscription to National Geographic (which would interest teir kids) for 2/3 the price of a year of Nature. μηδείς (talk) 23:24, 6 May 2017 (UTC)

The annual rate I'm paying for NG works out to about 3.25 per issue, which is extraordinarily cheap for the quality of the publication. ←Baseball Bugs carrots→ 23:31, 6 May 2017 (UTC)

"What education would someone need to understand it" Bear in mind that much of the market for these journals, like for most journals, is academic libraries. Not many people aside from academics and students have any interest in reading academic journals, whether prominent ones like Science and Nature, or lesser-known ones like the Journal of Tribology and the Sixteenth Century Journal, and the people who do have interest in them typically don't need most of the articles in an issue, so instead we subscribe to the journals our students and faculty need, and many/most of our users (especially in the case of electronic journals) access them on the article level, rather than using the whole thing in one or a few sittings. Nyttend (talk) 11:12, 7 May 2017 (UTC)

It is a disease of conspicuous consumption (cf. sexual display, Fisherian runaway, handicap principle), where people are assured career advancement by doing something that doesn't make sense - like spurning open access publishing for a predatory commercial empire. Wnt (talk) 12:51, 7 May 2017 (UTC)

Under the open access concept, at what point in the process do authors make money for their efforts? ←Baseball Bugs carrots→ 20:45, 8 May 2017 (UTC)

Probably around the time when they stop paying page charges for publishing their work in the non-open access journals! Seriously, it is common for authors to pay for the honor of being published in high profile locations, and rare for authors to get any payment publishing science articles anywhere, and even when they do, we're talking something like $50 split three ways, I mean, nothing like a capitalist incentive.

There is, to be sure, a genuine problem with open access journals, but it's not that: the problem is that they still are expected to be gatekeepers of content, even though their business model now encourages accepting as many articles as possible. This conflict of interest leads to some very low quality open access journals.

Properly done, the archivist of content should charge neither author nor reader, but obtain funding directly from the sources from which their authors and readers currently budget it - governments and charitable foundations. These funders should expect archivists only to maintain content availability with good technical parameters, and not even look at the content. The "journal" should be replaced by an entity distinct from the archivist, which consists essentially of a list of recommended reading material, plus various add-on features; this too can be funded by the source agencies, but because there is more subjectivity (which can be problematic, and makes top-down rating schemes dangerous) it may be best for the funders to direct their readers to each take a small portion of their funding and direct it to such "journals" according to choice. But the costs for these "journals" would be minimal, as they would not host content and originate essentially in pleasant discourses among scientists about current research. Wnt (talk) 21:50, 8 May 2017 (UTC)

electric train whining noise

When electric trains start there's that annoying whining noise. I've never really thought about the exact source of that noise until I saw this youtube video.

So where exactly is that noise coming from? Is it from the traction motor, or the power electronics that drives the motor? Or is it 50/50? ECS LIVA Z (talk) 22:49, 6 May 2017 (UTC)

c. 2002 the New York City subway train starting whine was a sequence of three musical pitches (in tune) that then wavered between two of the notes before choosing one (which was the normal electric whine - changing proportionally to changes in throttle and speed and so on). Some time after the trains stopped making the 3 notes. Explain that! Sagittarian Milky Way (talk) 23:20, 6 May 2017 (UTC)

Are you asking about model trains or full sized ones ? StuRat (talk) 00:31, 7 May 2017 (UTC)

Full sized ones. ECS LIVA Z (talk) 20:11, 7 May 2017 (UTC)

The noise comes from the motor. Its simply a very small byproduct (vibration) of the way magnetic fields are applied inside the motor. You only hear these sounds because electrical motors typically handle surprisingly high powers, compared to their size and additionally, very contrary to combustion engines or turbines, you usually find little to non constructiv measures to silence them. --Kharon (talk) 04:37, 7 May 2017 (UTC)

Electric trains usually have a service life of about 40 to 50 years (there are exceptions lasting less than 10 or more than 80 years), so at any point in time on any network you'll find trains of several different generations, using different technologies. Universal motors running on DC with series resistors or choppers, or on AC using tap changers, or 3-phase AC from power electronics running induction motors or synchronous motors, you can find them all on modern railway systems and they sound different, and that's even ignoring the noise that comes from different coolers and compressors. Trains older than 35 years don't have power electronics and often have a loud whining noise, in frequency proportional to speed, which definitely comes from the traction motors. The three musical pitches mentioned above seem typical for the power electronics for induction motors of the 1990s. PiusImpavidus (talk) 10:19, 7 May 2017 (UTC)

To add a bit to this (great) answer: Electric motor control is surprisingly difficult, especially with AC induction motors. In order to make the motor as efficient as possible, you need to carefully match the speed of the motor to the needed torque output - drive the motor too fast or too slow, and you just waste lots of power. If the train has a variable-frequency drive, the drive will adjust the motor speed as it accelerates, changing the frequency of the sound the motor produces. Some variable frequency drives increase the frequency in steps, which produces the arpeggio effect that Sagittarian Milky Way describes, while others do it more smoothly for a glissando. The Siemens EuroSprinter is an especially beautiful version - its motors plays a musical scale as it departs. Smurrayinchester 08:28, 8 May 2017 (UTC)

The power electronics described in previous posts is the source of the frequency spectrum, but it reaches your ears because the transformer's, and possibly the motor's, soft iron suffers from the Magnetostriction effect. GilHamiltonTheArm (talk) 11:09, 8 May 2017 (UTC)

Mass, acceleration, gravitational field, and electric field.

Why is there a difference between gravitational field and electric field, regarding whether ? Is this difference - a direct result of the equations only - without any further explanation, or there is a deeper explanation for this difference? BTW, I know Einstein assumed the equivalence between all kinds of mass, so this equivalence can explain the difference between gravitational field and electric field (regarding whether the body's mass influences its acceleration), but I wonder if there are other explanations for this difference. HOTmag (talk) 22:50, 6 May 2017 (UTC)

Take a look at Hierarchy problem which may be a bit technical! Graeme Bartlett (talk) 00:26, 7 May 2017 (UTC)

I'm looking for intuitive explanations, rather than for technical ones - as those hidden in the Newtonian equations already mentioned in my previous post. Additionally, Hierarchy problem discusses the relationship between the weak force and gravity, but does not discuss the influence of the body's mass on its acceleration - which is what I've been asking about. HOTmag (talk) 07:17, 7 May 2017 (UTC)

Gravity is caused by energy, not mass. A body at a distance from a large mass has potential energy (relative to that other mass), and the gravitational force it experiences is based on its proper mass and its potential energy - both added. The same with acceleration - it must accelerate both the proper mass and the potential energy. As it falls the gravitational force does not change even though its "mass" goes up, because as the mass goes up, the potential energy goes down, and there is no net change. In an electric field though, the strength of the force of the field is not affected by the potential energy. So the field must accelerate both the charged particles, and the potential energy, without the gain the potential energy gives to gravity. Ariel. (talk) 08:06, 7 May 2017 (UTC)

In what way does gravity depend on potential energy? I know only of the inverse square law for distance. Dbfirs 08:13, 7 May 2017 (UTC)

I can't see how the potential energy has anything to do with my original question. Please notice that I'm asking - not about one body - whose (relativistic) mass goes up as far as the body continues to fall in a gravitational field, but rather about two different bodies - which have different sizes of mass - and which are located (e.g.) at the same distance from a star that makes them accelerate towards it. Both of them have the same acceleration (don't they?) - so it is not affected by the different sizes of their masses (e.g. when located at the same distance from the star), even though their acceleration would be affected by the different sizes of their masses - if they were located in an electric field - e.g. at the same distance from an electric charge (assuming they have electric charge as well). HOTmag (talk) 09:03, 7 May 2017 (UTC)

The force of gravity is proportional to mass, but the electrostatic force is proportional to charge. Is this what you mean? Dbfirs 10:24, 7 May 2017 (UTC)

I'm not talking about forces but rather about acceleration. The body's acceleration - caused by an electrostatic field - is affected by the body's mass, whereas the body's acceleration - caused by a gravitational field - is not. What makes this difference between the electrostatic field and the gravitational field? From Newton's viewpoint, this difference is a technical result of his equations only (i.e. this is - as you said - only because "the force of gravity is proportional to mass but the electrostatic force is proportional to charge "), so that no further insight is expected for explaining this difference. However, from Einstein's viewpoint, this difference can only be explained by the equivalence between the gravitational mass and the inertial mass. Now I wonder if there are other insights for explaining this difference (because in my view - the equivalence between the gravitational mass and the inertial mass - is not intuitive at all). HOTmag (talk) 10:48, 7 May 2017 (UTC)

(edit conflict)If the charge is proportional to the mass, then the accelerations will be identical, nothing to do with some special property of gravity in Newtonian mechanics. See below for the inertial/gravitational mass equivalence. Dbfirs 11:00, 7 May 2017 (UTC)

See below my response. HOTmag (talk) 11:27, 7 May 2017 (UTC)

(edit conflict) The acceleration of a particle in a given electric field depends on the ratio of charge to inertial mass, the acceleration of a particle in a gravitational field depends on the ratio of gravitational mass to inertial mass. We have observed that this latter ratio is a constant. We have chosen this constant to be 1 and use the same units for both. Einstein took advantage of this observation by formulating a theory of gravity that no longer treats gravity as a force. Why this ratio is constant we cannot say, but if the general theory of relativity be true, it must be constant. Physics only tells us how, what the laws of nature look like, never why they look like that. That's a question best left to philosophers. PiusImpavidus (talk) 10:57, 7 May 2017 (UTC)

My question, about why the electrostatic field and the gravitational field behave differently - regarding whether the body's (inertial) mass influences its acceleration (when the body is in the field), is another way to ask why - the ratio between the gravitational mass and the inertial mass - is constant. I've preferred to ask this question - in my words (about the difference between the electrostatic field and the gravitational field) - rather than in your words (about why the ratio between the gravitational mass and the inertial mass is constant), because when this question is presented in my words - then it becomes less mathematical (about ratios and constants) and more intuitive (about a crucial difference between fields rather than a technical one). HOTmag (talk) 11:27, 7 May 2017 (UTC)

... but if you phrase it in terms on Newtonian forces, then there is no difference between the behaviour of the two fields. Dbfirs 12:14, 7 May 2017 (UTC)

Correct, and that's why I've phrased it in terms of acceleration (rather than in terms of forces), thus showing the difference (that can't be noticed in terms of forces). Please notice that acceleration is a universal concept that describes a universal feature affected by both gravity and electricity, as opposed to other features like electrostatic charge or electrostatic force. HOTmag (talk) 12:19, 7 May 2017 (UTC)

I suppose that Unified field theory might, at some time in the future, provide a good answer to your question, but to "old Newtonians" such as myself, the question doesn't need an answer, so I'll leave it to someone else to continue the discussion. Dbfirs 14:36, 7 May 2017 (UTC)

Calories in Sucralose

I'm a bit confused and I hope you can help me. The Sucralose article states that Sucralose is "noncaloric" and has zero calories. However every Sucralose product I have searched for shows it as having almost as many calories as regular sugar. For example, Sucralose at 376kcal per 100g Vs. regular sugar at 400kcal per 100g. What am I missing here? — Preceding unsigned comment added by 90.109.27.35 (talk) 23:39, 6 May 2017 (UTC)

Those are blends of sugars and Sucralose (better for baking). Yours in the link is mostly maltodextrin (with the same calories as sucrose) and is only 1% Sucralose. Also, since it's much sweeter, you use less, so get fewer calories that way. Note that the same link that lists 376 kcals per 100 g of Sucralose only lists 2 kcals per serving, while the sugar lists 20 kcal per serving.

Of course, with any discussion of artificial sweeteners I should mention that they haven't been shown to help with weight loss. You do better to learn to live without sweeteners. StuRat (talk) 00:19, 7 May 2017 (UTC)

To say it another way, the main bulking agents in most "zero-calorie", "sugar-free" artificial sweeteners (in packets, and many other forms) - are uhhhh, sugars. So such packets have, not zero, but about a third the calories of a packet of sugar - because they weigh about a third as much, with about a third the sugar. See, e.g. our Splenda- "Splenda products have a slightly lower caloric content than sugar." One can have some difficulty finding truly zero-calorie, sugar-free products, as the labelling can be misleading.John Z (talk) 02:07, 8 May 2017 (UTC)

You can buy pure sucralose (check Amazon), but you can't substitute it in recipes like the blends. The amount of sucralose you would be using to replace the sugar (the packages I have seen include a 1/32 teaspoon scoop) is so small that it will throw off your recipe. Sucralose is much sweeter than sugar by weight. shoy (reactions) 12:45, 9 May 2017 (UTC)

May 7

Antidepressants

I'm looking for sources on antidepressants causing the side effect of emotional numbness. Benjamin (talk) 10:12, 7 May 2017 (UTC)

"Antidepressants" encompass a huge spectrum of very different drugs and medications. Our article links to several review articles, including Review of maintenance trials for major depressive disorder.... Papers like that one go over lots of research on a wide variety of clinically-prescribed drugs. If you're interested only in a specific category - say, the SSRI family of drugs, our article points to many references on that topic. If you need help connecting a brand-name medicine to the research articles about that drug, let us know. Nimur (talk) 12:15, 7 May 2017 (UTC)

I don't see anything in that article about emotional numbness. Benjamin (talk) 12:33, 7 May 2017 (UTC)

There are lots of things you won't find in that specific article; it is a review of many different research studies across many different drugs. Evidently, the authors did not feel, based on their literature survey, that the symptom you named was relevant or prominent enough to mention. Sometimes, reading a review article is good to give you perspective: it doesn't mean that you won't find the detail you seek - perhaps some specialist has studied that specific detail in other work - but perhaps the detail is not so important that it merits mention in a broad summary of the state-of-the-art knowledge about the entire field.

Here is another, perhaps more accessible, resource: SSRIs, from the Mayo Clinic. This website, operated by the Mayo Clinic, describes SSRI drugs that are commonly prescribed for depression and other clinical purposes. Many side effects are listed, but "emotional numbness" is not one of them - nor is it listed by any similar name in "medical-ese," such as reduced affect display, (let alone paresthesias).

This doesn't mean it couldn't happen - it does not mean it's never been studied - but it's all providing evidence for a pretty solid case that you're describing an out-of-the-ordinary side-effect, as opposed to a well-known side-effect.

Here is the forty-four page FDA-approved drug label sheet for Zoloft, one popular brand-name for one type of SSRI. On CAPS, (a standardized battery of tests used to measure, among other items, "avoidance/numbing" - this is a specific clinical term for a type of emotional disorder commonly comorbid with post traumatic stress disorder), the correctly-administered drug "was shown to be significantly more effective than placebo on change from baseline to endpoint on the CAPS." This means, in plain English, that the drug statistically reduces the effect you are describing.

These drugs are powerful and complex. They can be helpful or harmful. They should be taken only in consultation with a professional. If you have questions specific to your conditions, whether you take medications or not, you should consult a medical professional.

Nimur (talk) 12:46, 7 May 2017 (UTC)

I found this and this, though note that they're specific to SSRIs. Incidentally, searching for antidepressants emotional numbness gives you a lot of extremely questionable pseudoscientific stuff that you have to be careful to pick through. Matt Deres (talk) 13:12, 7 May 2017 (UTC)

Indeed, a search engine will find content that matches your search query, regardless of the quality of that content. This is one reason that I specifically disrecommend the use of a search engine, and try to promote methodological survey of actual scientific references... Despite the speed with which a modern search engine delivers content, I find that it is typically significantly slower at delivering information when I compare it to more traditional methods of information-gathering. I would go farther to say that search engines, compared to traditional research methods, are many orders of magnitude faster at delivering data; yet simultaneously, search engines are many more orders of magnitude slower at delivering knowledge. Nimur (talk) 13:29, 7 May 2017 (UTC)

Why is it that when I talk to people about their personal experience with side effects of antidepressants, they often mention emotional numbness, but I never see it mentioned as an official side effect of the medication? Benjamin (talk) 16:52, 7 May 2017 (UTC)

Because "emotional numbness" is not a side effect. I've talked to many people who are on antidepressants and nobody ever mentioned it. --AboutFace 22 (talk) 17:15, 7 May 2017 (UTC)

Antidepressants are supposed to put the user into a calm state of mind. Maybe the OP is confusing calmness with numbness? ←Baseball Bugs carrots→ 18:00, 7 May 2017 (UTC)

• I've seen lots of anecdotes about people who discontinued SSRIs due to emotional numbness. And Matt Deres' two links above show that "emotional blunting" or "emotional indifference" is a side effect. Loraof (talk) 19:54, 7 May 2017 (UTC)

All antidepressants are also antianxiety drugs, they make people less anxious. Perhaps this is mistaken for emotional numbness? --AboutFace 22 (talk) 23:38, 7 May 2017 (UTC)

I'd highly qualify that. After 9/11 my doctor first tried versions of zoloft and prozac. They had no effect on my anxiety and insomnia, they just made me jittery during the day and falling asleep even harder. μηδείς (talk) 01:21, 9 May 2017 (UTC)

I have no idea what emotional numbness is. But I should note that anhedonia is a symptom of depression. Question: Is it plausible that SSRIs treat some other symptoms of depression but are not as effective against anhedonia? Oh... and I see now our article says that sexual anhedonia can be a symptom of SSRIs. (I really haven't looked into this, was just thinking out loud...) Wnt (talk) 01:00, 10 May 2017 (UTC)

Letters on a pill

What do they use to write on this pill? Is there any black ink that's safe for ingestion (I think it's black)? --Dikipewia (talk) 18:43, 7 May 2017 (UTC)

There are certainly black dyes that can safely be eaten - you can get black icing paste for decorating cakes. It is E151 (Brilliant Black) or E153 (Carbon Black, or Vegetable Carbon). Wymspen (talk) 21:42, 7 May 2017 (UTC)

Does completely charcoalized vegetable lose that horrible burnt taste? Sagittarian Milky Way (talk) 22:31, 7 May 2017 (UTC)

Plain charcoal (as in Activated carbon) has no taste and is widely used for medical purposes, but also for the filtration of water (or vodka). --Stephan Schulz (talk) 23:26, 7 May 2017 (UTC)

Thanks, I have never put charcoal in my mouth so wasn't sure. Sagittarian Milky Way (talk) 23:38, 7 May 2017 (UTC)

A warning: Don't put charcoal in your mouth that's intended for bbq's. It's not the same as charcoal intended for filtration use. It may be coated with toxic chemicals and fuel. StuRat (talk) 02:32, 8 May 2017 (UTC)

"... coated with toxic chemicals" How? Why? Richard Avery (talk) 07:21, 8 May 2017 (UTC)

In some markets, some brands of charcoal for BBQ purposes are pre-soaked in liquid hydrocarbons (think charcoal lighter fluid), to make them easier to light. The theory is that the fluid will fully evaporate and burn off before you put the dead cow on top of the fire. But that does not apply if you eat it ;-). In general, charcoal for medical use is carefully prepared to avoid contamination, and I would not recommend to just pick any from a bag of BBQ supplies. --Stephan Schulz (talk) 08:26, 8 May 2017 (UTC)

These for example. --Jayron32 14:47, 8 May 2017 (UTC)

And, as Stephen Schultz' link says, it's "harmful or fatal if swallowed". StuRat (talk) 22:40, 8 May 2017 (UTC)

Liquorice candy is typically black. ←Baseball Bugs carrots→ 20:39, 8 May 2017 (UTC)

Many commercial black food dyes are a mixture of red, blue, and yellow/green dye with cocoa powder. Perfectly edible and very black. Someguy1221 (talk) 22:46, 8 May 2017 (UTC)

I don't consider liquorice edible, but that's a matter of taste, not toxins. ←Baseball Bugs carrots→ 03:36, 9 May 2017 (UTC)

"Eww ! This tastes like anise !" StuRat (talk) 15:42, 9 May 2017 (UTC)

May 8

Astronomy / Calendar : Thirteen Groups of (Almost) Eight

What possible astronomical meaning or calendrical interpretation, if any, can be assigned to a structure containing thirteen groups of eight objects (of which two such groups might be slightly smaller, containing only six or seven objects each) ? Of course, one probable explanation would be the number of seven-day weeks in two years; however, the civilization which build the structure is known to have had a six day week, hence the dilemma. — 82.79.178.230 (talk) 08:13, 8 May 2017 (UTC)

Your question sounds like you're confusing astronomy (a discipline of physics, a body of knowledge based on application of the scientific method to elucidate knowledge about the universe) and astrology, which is bullshit. --Jayron32 14:45, 8 May 2017 (UTC)

Nothing of the sort. There is an ancient Carpathian sanctuary, consisting of four concentric circles. The meaning of the second and fourth circles are quite easily discernible; that of the first and third, not so much. There is also a smaller round sanctuary nearby, similar in structure (and, presumably, also in meaning) with the outer circle of the former. — 82.79.178.230 (talk) 20:57, 8 May 2017 (UTC)

Historically, most ancient civilizations conflated what we now call astronomy with what we now call astrology, and associated it/these with calendrical matters, so in a historical context the question is perfectly respectable. {The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 17:12, 8 May 2017 (UTC)

13 Venus year equals 8 Earth year. Sagittarian Milky Way (talk) 14:54, 8 May 2017 (UTC)

And at least one ancient culture has been shown to have been aware of this correspondence – see Observations and explorations of Venus, Section 1.6 Maya. Is the 6-day week civilization in question the Akan? {The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 17:00, 8 May 2017 (UTC)

No, it is Eastern European. — 82.79.178.230 (talk) 22:21, 8 May 2017 (UTC)

The lunar month is somewhere around 28 days, depending on how you measure it (see article for details). That puts about 13 in a year. StuRat (talk) 15:43, 8 May 2017 (UTC)

See pages 28 and 29 of this book: . There is a list of numbers in the left hand column (i.e. on the pages for March and April - the note at the bottom of March (continued at the bottom of April) tells you what they are). Eight of these numbers generally appear in any thirteen - day period - moreover any number is 8 larger than the one above it (the numbers are not allowed to exceed 19 so you may have to add 19 to the second number to appreciate this). 195.147.104.148 (talk) 21:15, 9 May 2017 (UTC)

Whom to trust?

Magnetism

Since magnetism is electromagnetism, what is the wavelength and frequency of the photons around e.g. two bar magnets next to each other? Th4n3r (talk) 12:24, 8 May 2017 (UTC)

I'm not familiar with the most advanced theories of sub-atomic physics, which have all kinds of strange particles not usually mentioned in introductory university physics courses (with a target audience of science and engineering students). If we confine ourselves to electromagnetism as explained by Maxwell's equations, just because there are electric and magnetic fields, there isn't any electromagnetic radiation unless the electric and magnetic fields are changing. So in the situation you describe, supposing the bar magnets are static, there aren't any photons. Jc3s5h (talk) 12:42, 8 May 2017 (UTC)

This is a field of physics known as Quantum electrodynamics (QED). The math involved here is way over my head, but your question can be answered by QED. --Jayron32 14:39, 8 May 2017 (UTC)

Without going into very difficult mathematics, we can give you this answer: the magnetic field around a bar magnet is, essentially, static - it does not change with time. So it is in steady state, which corresponds to zero frequency; hence, infinite wavelength. This is why the photon model is not very useful when we describe steady-state ferromagnetism: if you want to describe a static magnetic field and you choose to write it down with the math that describes photons, you have to deal with a lot of zeros and infinities in inconvenient places.

It might frustrate you to see a real scientist talk to you about photons with wavelength-infinity. But, in photon physics, there are a lot of non-intuitive things you'll have to wrap your mind around. Here is a brief anecdote that may help you to accept that this answer is actually correct and valid: in answering this question, I pulled out my copy of Griffiths' Electrodynamics.... After spending 500 pages building up the details of mathematical treatments for electromagnetism, the author introduces the photon in the very last chapter, by presenting a conundrum about conservation of momentum; and, in answering, he writes: "personally, I would regard this argument as a joke, were it not for the fact that at least one massless particle is known to exist in nature: the photon."

So - don't get too hung up on the conundrum: you can have wavelength-infinity waves, and you can even think of them as particles: they're just not behaving in a very particle-like way. They are not moving, they are not conveying energy and momentum. If you write the math very carefully, these conclusions follow directly.

Nimur (talk) 14:54, 8 May 2017 (UTC)

Making sense out of North Korea's assassination plot suggestion

I don't doubt the North Koreans make stuff up or that they're nuts... nonetheless, killing Kim Jung Il sounds like a capital idea to most Americans. And I generally go by the rule of thumb that almost every nasty thing either side says about the other in any war is true, and this is a nasty thing. So can we make sense out of it? Now obviously it would help if someone can track down the original Korean and translate this without the "crazy" filter setting (I mean, I suspect it's pretty nuts in that language but I bet the BBC translators were hamming it up) but here is what I have to work with now:

The remarkable claim here is that it is a radioactive substance and a biochemical substance. This implies a level of sophistication in the attack comparable to something like a targeted cancer therapy that brings a radioactive isotope to a specific (cancer) cell to kill it. The North Koreans have obviously thought up the notion of finding some cell type to target (what???) that is a lot less dispensable than a cancer cell. Whether they have thought that up by interrogating a U.S. agent or have purely invented it in their own laboratories to use on us, it is still of interest.

Anyway, some topic of interest here: is there any record of people considering "targeted assassination therapy", and what would they target? Is there something that is easier to inhale and get into a bloodstream than an antibody that they could link to the radioactive isotope? Or would they just be hoping to make a lot of shrapnel and something would hit, or do they have a way to make inhaled antibody cross from lung to bloodstream? There are so many options here I don't even know where to begin - that's obviously a really vague source text. What can we think of? Wnt (talk) 14:05, 8 May 2017 (UTC)

Oh, my --- I just looked up Kim Hak-Song on PubMed and found several results, including this cancer therapy targeting paper. (other results - I have no idea whether that is the same person - the address for author information was in South Korea (and also is in the latest publication even though NCBI somehow left it out, sorry) If the North Koreans are writing a novel here, they certainly did their background research. Wnt (talk) 14:40, 8 May 2017 (UTC)

Possible relevance: "repebody" molecules that are bacterially produced antibodies with multiple leucine-rich repeat modules -- earlier paper by Kim. IF the North Koreans can be taken at their word, one of these might currently be under selection by someone working with the CIA to recognize a target on critical cells. (It is quite possible that the researcher involved is unaware he is helping to build a weapon). This patent covers repebody inhalation, but it might be purely boilerplate. Ditto this one, which also talks about inhaled aerosols. Actually, it looks like the repebody term is almost unique to this researcher, and is based on an understanding of the lamprey immune system - it can benefit, however, from rational design using LRRs from known human proteins. It's introduced here - when I get time I'll try to understand how it actually works. This seems like an interesting, multi-purpose technology. Wnt (talk) 15:03, 8 May 2017 (UTC)

• Going back the the OP's question. Doubt if there is any plot to assassinate Kim Jung. It would not achieve anything, because in this type of regimen there is always someone else that can step in. So, there is no chance of creating a 'power vacuum' which could destabilize the regimen. Things would just carry on as normal. Secondly, the DPRK are not nuts. The 'family' are brought up learning gamesmanship. They are very astute and very ruthless towards anyone who descents. Third: biochemical substances and nano poisonous substance may be metaphors. Most NK's are peasants. The DPRK is able to maintain control with the help of small middle-class elite. Being well educated they are naturaly very curious about the outside World to which they have no Internet nor any other access. Therefore: Nano poisonous substances may refer to some plans which include simple things like launching balloon from South Korea to drop pen-dives and DVD's on the middle-class city in NK just across the river. The data in them could even included copies of WP. The NK finder may well feel too frighted to tell their friends at first -as to what the have discovery and read – but then one must take into account human nature. If the drops of data are intensive enough, some will realize from normal conversational topics, that their friends have also read these drops, and a bond of mutual understanding and trust forms as they discus what they have learnt. A similar thing is thought to have helped to destabilize the former Soviet Union. The privileged elite, could get not only Betamax video machines but films. Glimpsing the outside World made them discontented with the then Soviet regimen. Result was that the regimen lost the 'blind' support of the elite and the rest is now history. Kim Jung was born in Russia and he may be using the metaphor biochemical substances to refer to the elite of the former Soviet Union which turned on their suppressors once they eyes had been opened. Unfortunate, the military elite of all or most counties like a blitzkrieg. They just want to storm in, leaving long term problems in their wake, rather than taking the gently, gently approach. Those that forget history are doomed to relive it. This is not an issue to be left up to the politicians in the 21st Century – it can lead to an ever more dangerous situations, which as ever, the politicians & military will make a mess of – if left to them. We (the World) need to become (or already are) the biochemical substances to bomb any repressive regimen with Nano liberating substances. Aspro (talk) 00:12, 9 May 2017 (UTC)

Does the Milky Way rotate around anything?

For a haywire SF plot, I'm stepping through rotational frames of reference and summing up angular velocities relative to a given gravitational center (Earth rotation, Earth orbit, orbit of solar system around galaxy center...). Now I'm trying to figure out whether I can go one farther and add an angular velocity for the movement of the Milky Way. However, IIUC, there is no indication of actual rotation of the Milky Way around, e.g., the gravitational center of the Local Group, or anything at larger scales. Once we leave the galaxy, movements are linear and/or omnidirectional (Hubble flow, microwave background). Is that correct? --Elmidae (talk · contribs) 15:17, 8 May 2017 (UTC)

See: Supermassive black hole — 107.15.152.93 (talk) 15:25, 8 May 2017 (UTC)

That contributes to rotation within the galaxy, while the OP was asking about rotation of galaxies relative to each other. StuRat (talk) 15:28, 8 May 2017 (UTC)

Note also rotation vs. revolution; this is actually about the latter. Wnt (talk) 01:08, 9 May 2017 (UTC)

I always learned that the movements on those scales - larger than the local group - were virial (thermal). Nowadays, every cosmologist you talk to has a different idea - there is less consensus than there was many years ago. I would attribute that development to the rise of powerful computers that can simulate general relativity - so lots of people can try out various theories and make predictions that are consistent with observational data. Nimur (talk) 15:26, 8 May 2017 (UTC)

That some galaxies move towards each other and eventually collide, rather than moving away, to me suggests there are eddies in the large-scale movements of galaxies. This also implies rotation within those currents. However, at human timescales, I'm not sure if those can be measured. That is, the time for a significant change in direction to occur may be longer than we have been measuring. StuRat (talk) 15:27, 8 May 2017 (UTC)

See the Local Group and the Great Attractor. Most bodies in motion towards each other tend to be off center and hence have some rotational component (think of the Theia hypothesis but the space scale may be so vast we have not had time to observe it directly. μηδείς (talk) 17:22, 8 May 2017 (UTC)

"Eddies" and "currents" are deceptive terms in this context, as galaxies are not (so far as we know) embedded within any fluid that could apply external positive pressures to them – force fields such as gravity are not fluids and do not have eddies and currents in this sense (despite Eddy currents!).

It is however fairly trivial that in a gravitationally bound group of galaxies such as the Local Group, all members must be orbiting the group's common barycentre, just as is the case with larger Galaxy clusters, and heirarchically upwards with Superclusters. (One also needs to take account of the dark matter associated with the galaxies individually and perhaps the Group as a whole.) However, orbits are not just circular, they are elliptical and can be of any eccentricity, even approaching linearity. Moreover, on the huge duration scales involved in movements of galaxies, it would be very difficult for us to observe any curvature of their orbits directly – we can only take effectively instantaneous measurements of their velocities, which will appear linear until we take more measurements over many millions of years.

The Milky Way and the Andromeda Galaxy are currently nearing each other and are clearly gravitationally bound; all other members of the Local Group are by comparison much less massive, and most if not all of them will likely also be bound (though interactions could conceivably cause some satellite galaxies, globular clusters or individual stars to exceed escape velocity). {The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 17:45, 8 May 2017 (UTC)

Re: "galaxies are not (so far as we know) embedded within any fluid that could apply external positive pressures to them". See dark fluid for one possible theory that proposes just that. StuRat (talk) 22:02, 8 May 2017 (UTC)

If by "one possible theory" you mean "one dude with a crazy idea" (he's basically the only sources for that poorly cited article). --Jayron32 00:45, 9 May 2017 (UTC)

I found a 1999 article about the Sun's motion relative to the Local Group here. It says the Sun is moving at 300 km/s "relative to all LG members" and gives a heading in Galactic coordinates that I should admit I don't necessarily understand. There is discussion about a local standard of rest that refers to the barycenter of the Local Group and/or the point where cosmic background radiation is equally shifted from all directions, but I didn't follow what they did there. I assume someone reasonably skilled in the art is supposed to know the Sun's motion relative to the Milky Way and can mentally delete that from its Local Group motion... in any case, there must be updated numbers if you search for what cites that. But the bottom line is that the Local Group is defined by mutual gravitation and is relevant. As opposed to the situation with Great Attractor, where they start talking about "peculiar motions" because everything is being pulled apart by expanding space! There really is a scale beyond which there are no orbits; it's just bigger than the Local Group. Wnt (talk) 01:30, 9 May 2017 (UTC)

Alright, thanks guys. This strikes me as "it's complicated, but for practical purposes there is no orbiting motion with readily discernable characteristics". That should be enough to not make me break my intended Level 4 position on the SF Mohs Scale :) --Elmidae (talk · contribs) 08:01, 9 May 2017 (UTC)

@Elmidae: That wasn't the message I meant to send with my comment about the paper above. It actually did define a region based on the distance where the gravity from the Local Group can retain galaxies within a region ... I think. So AFAICT the Milky Way is orbiting ... it's just that the nature of the "center" in a group of galaxies, when there are a few stray galaxies mixed in that aren't expected to be gravitationally bound but nonetheless affect the whole, and all the data is incomplete anyway, is a little iffy. Wnt (talk) 16:15, 9 May 2017 (UTC)

Appreciate it! And if I was writing an article or a paper, I'd have to dive into that. But really, fact-checking for an SF story is equal parts mining for ideas and ass-covering. As long as I'm not committing a blatant faux-pas here ("Everyone knows that the Milky Way orbits the Manichaean Gap!") and not overlooking some obvious cool feature to exploit, I'm good. - Leaning far enough out of the window in some other aspects, admittedly %) --Elmidae (talk · contribs) 17:05, 9 May 2017 (UTC)

Blackest black fabric that is reasonable to achieve?

I want a black backdrop for making some project videos for YouTube and photographers seem to recommend velvet but it seems to me that even velvet can have some sheen and reflect light, appearing grey. Would it make sense to buy a fabric and then attempt to dye it further? It's possible that all the locations in the fibres that can be occupied by the dye are already occupied. I know photographers can make a white background look black in a suitable environment but that's not possible in the confinement of my living room. How to make a surface not reflect visible light and absorb more? --78.148.99.149 (talk) 16:26, 8 May 2017 (UTC)

Maybe get ahold of some super black? Or maybe use a more solid background, such as a piece of plywood painted in matte or flat black? Just some ideas. --Jayron32 16:42, 8 May 2017 (UTC)

Velvet is the right idea, but most velvets are designed to shine, so they're made from a fabric with fibres that are individually shiny. It doesn't usually look grey, more of a pearlescent sheen mixing black and quite light shades. A cotton velvet might do it, or even a moleskin. With a budget, you can simply buy backcloth fabrics that are made to be an invisible black. In the fabric shop though, you're probably looking at dull non-sheen cottons, rather than velvets. Once you're far enough away to not see the weave, it matters less what the fabric is. Andy Dingley (talk) 17:05, 8 May 2017 (UTC)

Velvet also shines more when seen at an angle. You can get a small piece and experiment before you buy enough for an entire set. μηδείς (talk) 17:16, 8 May 2017 (UTC)

Some photographers use the lining from blackout curtains. This may require 2 layers if the weave is more open than you wanted. DrChrissy 17:49, 8 May 2017 (UTC)

The lining of my blackout curtains seems to be a shiny silver color. It is opaque but not at all nonreflective. CodeTalker (talk) 21:50, 8 May 2017 (UTC)

When I've done black backdrops for photographs (IANAPP so take this advice with what it is worth), I've just used off-the-shelf black linen sheets from a big box store, something like thus. No idea if that serves your purposes or not. You may want to actually go to the store to look at it rather than order online to see if it meets your needs. --Jayron32 17:52, 8 May 2017 (UTC)

Want the ultimate non-reflective coating (price is no object)? See: Vantablack & — Preceding unsigned comment added by 107.15.152.93 (talk) 21:12, 8 May 2017 (UTC)

The professionals simply use a green or blue screen aka "colour-separation overlay" for such purposes. --Kharon (talk) 02:37, 9 May 2017 (UTC)

The OP does not explain the purpose of the black backdrop. An analog video signal can never represent absolute black, it has only a systematic "black level" that is limited by Signal-to-noise ratio and Lens flare. Chroma key as Kharon says is an effective way to replace a background with any desired color (or a background image) but depends on having en evenly lit rear wall in a uniform color that does not occur in the main subject. A Test card of physical, not digitally generated type, for TV cameras was made by Marconi to calibrate a wide range of brightness; the black segment of the grey scale was actually a porthole to a black velvet lined box constructed behind the card. Blooteuth (talk) 11:34, 9 May 2017 (UTC)

Personality types.

This article explores an interesting concept that people can broadly be put into 4 different categories. However, can it be argued that this is too broad even for managing relationships in the workplace? Because this could differ based on different cultures (whether organisational, related to a specific profession) or even depending on a person's mood or period of their life. In addition, I can think of many personality types which don't fit into these 4 categories. For example, where would you put the competitive type who likes to play strategic mind games with others, often prevalent in macho organisations? 2A02:C7D:B953:4700:4F9:B85D:C8AB:CF4F (talk) 17:31, 8 May 2017 (UTC)

Misplaced Pages has an article on Personality. Perhaps you would like to look a that first and then come back with a more specific query. Dmcq (talk) 17:36, 8 May 2017 (UTC)

Alfred Adler would have strongly disagree with such rough categories while Sigmund Freud always seemed to like (intellectually) sorting individuals into just a few big boxes. The resulting two main- and some other, newer, different "schools of Psychology" are the base for Science till today. So if you would ask your question at two different (real) Experts you likely would end up with 3 opinions nevertheless. --Kharon (talk) 02:26, 9 May 2017 (UTC)

Jung said 16 types. Five factor model would say 32 black or white types and more gray types. Sagittarian Milky Way (talk) 02:57, 9 May 2017 (UTC)

US energy efficiency drop

In both 2011 and 2016, US used approximately 97 quads of primary energy. In 2011, 41.7 quads went into energy services, a 43% efficiency. While in 2016 only 30.8 quads went into energy services, resulting in an efficiency of only 32%.

With all the talk about electric cars and energy conservation, I expected a slight improvement in overall energy efficiency. But this is a eleven percentage points drop in energy efficiency. In just five years! What's going on here? ECS LIVA Z (talk) 18:37, 8 May 2017 (UTC)

The change to energy-efficient light bulbs in homes may be a big factor, if not the biggest. ref - Akld guy (talk) 20:07, 8 May 2017 (UTC)

So energy efficiency should be going up then, right? I'm asking why instead it's dropping like a rock. ECS LIVA Z (talk) 20:11, 8 May 2017 (UTC)

I don't know the answer, but I notice that the biggest difference between those two charts seems to be the efficiency of the "industrial" block.

Perhaps something changed there. (Obvious question : Is this a real effect, or a change in how those numbers are reported?)ApLundell (talk) 21:37, 8 May 2017 (UTC)

• You do realize that electric cars are highly inefficient. The batteries are hugely expensive, the charging networks the same, and the electricity still comes from burning hydrocarbons. This is simply hid from the end-use consumer, since he doesn't see the huge subsidies the car makers get and the coal plants and transmission wires losing energy to heat as they carry the wattage of huge distances. But think of how efficient they are at virtue signalling!

The description under the charts points out that these numbers are estimated. Also such "global" numbers actually reflect the efficiency of the energy market, not of the technology used. However energy services are generally becoming less efficient (economically!) because a service network always needed to be balanced, or more specifically power supply always needs to be regulated according the power demand, and since the socalled renewable energy production produces energy independent of demand and unpredictable, yet has (politically given) priority to be used, the conventional electric power production is shut off more frequent the more renewable energy takes its increasing share of the total. This is one possible but not necessary the main reason for these numbers. Another could simply be that, besides renewable, the main production switches to whatever natural resource is the cheapest. Given the changes on the market for crude oil, gas and coal this can change these numbers too. And last not least allot of energy is "wasted" because it needs to be transfered. Even the advanced 800 kilovolt High-voltage direct current lines have a loss rate of 4%/1000km. Ofcourse local low voltage nets have a much higher loss rate and on top this all adds up in total. --Kharon (talk) 01:44, 9 May 2017 (UTC)

Fixed your link. --76.71.6.254 (talk) 05:30, 9 May 2017 (UTC)

Looking at the flowcharts, it's clear that electricity wastage is less of a factor - the rejected energy directly from electricity generation goes down, and the rise in rejected energy from industry is greater than the input to industry from the electricity generation. So a large chunk of the efficiency drop off is probably due to the direct industrial uses of natural gas and petroleum. For residential use, the change in efficiency might be related to electricity wastage, but that's a smaller contribution to the total waste.

Reading the notes gives a better picture - the 2016 flowchart is calculated assuming 65% energy efficiency for residential and commercial, and 40% for industrial (based on the DOE's estimate of manufacturing in 2017). For 2011, those three sectors are calculated assuming 80% efficiency. So the efficiency on the chart has gone down because the estimated efficiencies used to calculate it have been changed - and to see the reasons for that, you'd need to find which DOE report the revised estimates are based on. MChesterMC (talk) 09:38, 9 May 2017 (UTC)

• As MChesterMC says, it's really a bookkeeping issue. The primary inputs to the users are easily measured while the user efficiency is estimated, not measured. For sure, LEDs use roughly 1/10 the power of incandescents for the same amount of light, but was electricity wasted by incandescent bulbs counted as "rejected" or not? -Arch dude (talk) 19:45, 9 May 2017 (UTC)

Agree with MChester - note that it says the estimates were "updated" in 2017, and the 2016 estimates were all 4/5 or 1/4, which means they were probably really handwavey numbers. So I'm not sure anything actually changed at all, and if it did, it probably changed over much more than one year, and if it did, it might be something like that light bulb case mentioned. Wnt (talk) 01:07, 10 May 2017 (UTC)

• Do we use electricity to produce gasoline from CO2 or hydrocarbons to produce electricity? μηδείς (talk) 01:18, 10 May 2017 (UTC)

Animals swallowing live prey

I saw a video of an African Bullfrog swallowing a mouse whole without chewing or anything. The mouse was still alive without even a scratch as it was swallowed. How come the mouse can't attack the insides of the Bullfrog and escape? Isn't swallowing live prey that can attack your insides very dangerous? How long would the mouse be alive down there and what would be the cause of its death?--83.136.45.50 (talk) 21:50, 8 May 2017 (UTC)

I once drowned a mouse, and it took 12 seconds for it to stop moving. (I wasn't trying to be cruel, but it was caught in a glue trap and this seemed to be the quickest way to stop it's pain.) But I've wondered myself why animals which are prey to such animals that swallow them whole don't evolve a defense against being swallowed whole, like porcupine spikes, pointed in all directions. StuRat (talk) 22:19, 8 May 2017 (UTC)

Put the mouse in a plastic bad and step on its head. Death in under a second, and then discard the bag. Drowning is much crueler, μηδείς (talk) 23:04, 8 May 2017 (UTC)

I was right by the sink, and it would have taken longer to get a plastic bag. StuRat (talk) 23:31, 8 May 2017 (UTC)

In small apartments in NY it's common practice to hang the day's small plastic shopping bag from the doorknob for use as a teporary trash depositso it can be taken out to the building's garbage when next you leave. In any case, I would discount the stuck time from the equation as irrelevant, and prefer One hour and 12 seconds of being glued, then an instant, imperceptible death, to an hour of being glued then 12 seconds of being drownt. μηδείς (talk) 01:14, 9 May 2017 (UTC)

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