Wikipedia:Reference desk/Archives/Science/2017 May 6

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May 6

Acrylic Adhesive

Is "Acrylic Adhesive"[1] 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.) [2] and the chapter "The Chemistry of Structural Adhesives: Epoxy, Urethane, and Acrylic Adhesives",[3] 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). [When the center of mass is displaced in any direction, the swing can lower it by moving to put it directly under the pivot. Since gravity pulls down and the chain pulls in, the net force does precisely that] 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. [4] 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.[5] ←Baseball Bugs ^{What's up, Doc?} 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. [6] 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" [7].--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 [8]. 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^Flower 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 ^{What's up, Doc?} 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 ^{What's up, Doc?} 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 ^{What's up, Doc?} 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[9]. 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 [just] 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)