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November 28

Chemical potential

I have had some trouble applying our article on chemical potential or similar sources to actually figure the amount of energy in a chemical potential. For example, in the section on deviation from ideality, the chemical potential is said to depend on ln(x), where x is the mol fraction of solute, yet the graph depicts it intersecting with the y axis. So to be clear, suppose great alien overlords hand me a liter of absolutely pure water at STP, and in a mad act of defiance I add x moles of NaCl to it, perhaps hoping for an infinitely large explosion. What's the real formula and/or data for the amount of energy released? Wnt (talk) 14:35, 28 November 2018 (UTC)[reply]

Have you read our article, Enthalpy change of solution? Nimur (talk) 15:33, 28 November 2018 (UTC)[reply]

Per Nimur, the enthalpy change of solution is really what you are looking for. The chemical potential concept is really a generalized measure of free energy, and is a fairly esoteric way to get at the energy changes of a reaction. Specific enthalpy relations are usually much more useful, such as enthalpy of reaction, enthalpy of solution, etc. --Jayron 32 16:24, 28 November 2018 (UTC)[reply]

Well, the problem with the enthalpy change of solution article is that it applies only at infinite dilution (or in that approximation). I mean yes, it says the energy released isn't infinite, but I still don't know how to go from a concentration difference to energy release. I was reminded of this issue by the question above about ion excretion: I wanted to say "you can't purify all the copper out of your urine, because it takes a lot of energy to do that" but I don't actually know that's true. I mean, chemical potential runs the mitochondrial ATP production and costs of desalination and countless other things, and I don't have a grip on how to do the math about it. Wnt (talk) 12:51, 29 November 2018 (UTC)[reply]

It's calculated from a partial differential equation of energy with respect to number of particles. Which energy term you use (and which variables are left to float) are based on which application you want. The article on chemical potential has the equations for calculating it with respect to internal energy, enthalpy, Gibbs free energy, or Helmholtz free energy. At this point, you've exhausted my calculus knowledge, and if you've exhausted your own, I'm not sure what else to do. The reason it's so messy is that chemical potential is basically potential energy between the different particles in a system, and depends solely on 1) the average strength of one of those interactions and 2) the number of those particles, and of course it varies nonlinearly (that is a 4 particle system does not have a value double that of a 2 particle system), and also varies with respect to other factors like temperature, pressure, etc. and ALSO we're not dealing with 2 or 4 particles, but things on the scale of Avogadro's number of particles.

Chemical potential calculations are not usually done from first principles to produce direct single numerical calculations. Usually, you do that calculus to derive a specific equation that would be applicable to your system, and then simplify or approximate the equation to get something close enough for your purposes (i.e. the Ideal Gas Law, the Enthalpy of solution, the specific heat equations can, IIRC, all be derived from first principles starting at Chemical Potential. At least, I remember having to do stuff like that when I took physical chemistry, back in 1996-1997, and I'm pretty sure I forgot it by about 1998. The point I'm trying to make is, you can do it, but you probably don't want to because someone already did the hard part and has a simple plug-and-chug equation you can just use. --Jayron 32 16:10, 29 November 2018 (UTC)[reply]

Cure of hemiparesis

What is the state of research on treatment of hemiparesis by stem cell therapy or surgery.if a person has congenital left hemiparesis since say over 33 years and if he can walk,run and even move things and leading a normal life like completing education and doing job is it possible is it possible that with current trends of research he will get complete cure by medication/surgery/stem cell therapy/neurogenesis in his lifetime.Is research progressing in this direction that he will get a complete cure in his or lifetime with state of research in 2018.I have asked inadvertently in other section of this forum,extremely sorry because Google Scholar is incomprehensible to me so I take this opportunity to know from any of you who is knowledgeable in this field may please be kind enough to shed some light on this neglected topic.Wrogh456 (talk) 16:39, 28 November 2018 (UTC)[reply]

Hemiparesis is a symptom of various conditions rather than a disease unto itself, and depending on the nature of the disease which caused it may affect the treatments of it. here you can see some various sources depending on the condition, some for stroke, some for cerebral palsy. That would be a good start for your research. --Jayron 32 16:45, 28 November 2018 (UTC)[reply]

November 29

Tremors and fasciculation

What is the difference between a tremor and a fasciculation? Is it just that a fasciculation happens randomly, while a tremor happens rhythmically and repeatedly? 208.95.51.53 (talk) 18:36, 29 November 2018 (UTC)[reply]

Not exactly. It has nothing to do with the rhythmic nature of it; the defining feature of a tremor is the "twitching movements of one or more body parts" (as quoting the article on tremor. That is, in a tremor, an entire body part (like arm, leg, etc.) will shake subtly back and forth. A fasciculation is a "small, local, involuntary muscle contraction and relaxation which may be visible under the skin" (quoting the article fasciculation) that is, the defining feature is it's small, localized nature: some tiny part of a muscle (like a little patch of your quadriceps or something) will twitch a little bit. It doesn't shake your whole leg back and forth like a tremor does; it's just a tiny little pulse on a small patch of muscle. I hope that helps. --Jayron 32 15:59, 30 November 2018 (UTC)[reply]

Lake Vostok

What is the island in Lake Vostok? The article says "In 2005 an island was found in the central part of the lake.[25]" and the reference only says "He added that current efforts to investigate the lake had revealed an island located in the central part of the lake." Is there actually air stuck in there too and land is sticking out of water into it, or is the lake donut shaped with an ice pillar in the middle, or were the scientists talking about something third? 78.0.203.173 (talk) 23:11, 29 November 2018 (UTC)[reply]

This article also mentions islands. They are not sticking up into air, instead they are are just sticking up through water into ice. Figure 1 there shows something nearly an island sticking up from the bedrock. Graeme Bartlett (talk) 10:52, 30 November 2018 (UTC)[reply]

November 30

Question on Adaption

At the cellular level, how do adaptions occur if the organisms which perpetuate these adaptions do not possess the ability to know or percieve the external pressures that they are adapting to? The evolution of feathers for insulation in dinosaurs is one example. What is actually going on down there? How is the cold and the dangers presented by it being reacted to in such an efficient way, as if genes had a mind of their own? déhanchements (talk) 03:29, 30 November 2018 (UTC)[reply]

Gene-centered view of evolution may help. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:16, 30 November 2018 (UTC)[reply]

It doesn't happen in an efficent way. Mutations (which is a more relevant article) happen randomly; the useful ones help the organism survive and so are the ones we see spread through the fossil record; the detrimental ones lead to a quicker death. Henry ^Flower

Not necessarily just living and dying. A mutation that tripled the organisms overall success at reproduction would spread even if it halved the organisms expected lifespan. Conversely, a mutation that increased lifespan while decreasing overall reproductive success would probably not spread. --Khajidha (talk) 16:45, 1 December 2018 (UTC)[reply]

Microscopic bugs, in color

You know those teensy bugs we see in shades of grey with electron microscopes? Are they colourful like a lady bug or emerald ash borer? Anna Frodesiak (talk) 06:52, 30 November 2018 (UTC)[reply]

When I have seen these tardigrades they are usually pretty colourless and transparent, or slightly yellowish—which may be due to what they ate! Graeme Bartlett (talk) 08:26, 30 November 2018 (UTC)[reply]

Hi Graeme. Ooooooh, transparent or yellowish, eh? Well, what about those mites and all those other creepy-crawlies we see walking about? I'm kind of guessing they're pretty blind, so might not need colour. I'm not a good guesser, though. Anna Frodesiak (talk) 08:41, 30 November 2018 (UTC)[reply]

Well mites I have seen are dark, green or red. I imagine they come in all sorts of colours to camouflage against what they live on. The dust mite looks white in the pictures. Graeme Bartlett (talk) 10:44, 30 November 2018 (UTC)[reply]

The dust mites have pink feet, like shrimp. Is that real colour? And do they need colour? Can tiny predators see? Anna Frodesiak (talk) 11:12, 30 November 2018 (UTC)[reply]

There were some awesome tardigrades in Ant-Man and the Wasp, but, you know, WP:FILMSCI. Gråbergs Gråa Sång (talk) 10:56, 30 November 2018 (UTC)[reply]

[1] says

Tardigrades are often white, or colourless and more or less transparent; some are brown, yellow, orange, pink, red or green. The body colour can reflect the pigmentation of the body cuticle itself, or can be due to the gut contents showing through the colourless body wall.

Nil Einne (talk) 12:02, 30 November 2018 (UTC)[reply]

A similar statement is made in the abstract here [2] although weirdly I can't see where it's made in the article. According to [3] and [4], Ramazzottius varieornatus is one example of a pink tardigrade, at least along its back. Nil Einne (talk) 12:14, 30 November 2018 (UTC)[reply]

Thank you, all! :) Anna Frodesiak (talk) 17:28, 1 December 2018 (UTC)[reply]

Eyebrows

Anna Frodesiak (talk) 11:13, 30 November 2018 (UTC)[reply]

Demodex folliculorum and Demodex brevis Graeme Bartlett (talk) 12:16, 30 November 2018 (UTC)[reply]

Gross! Hey, I found a pic for brevis at commons. Yay!....and gross! Anna Frodesiak (talk) 23:18, 30 November 2018 (UTC)[reply]

Plants that produce sound

Which plants are known for producing sound? Poplars come to mind, though I do not know if any particular species is "louder" than others. I suppose a lot of grasses rustle in the wind too. Surtsicna (talk) 14:17, 30 November 2018 (UTC)[reply]

It depends what you mean by producing sound. Practically any plant will rustle if it's big enough and there's enough wind. There are a large number of plants with exploding seed pods. See [5].--Shantavira|^{feed me} 15:01, 30 November 2018 (UTC)[reply]

Monica Gagliano, a plant physiologist at the University of Western Australia claims that corn seedlings emit a 220 Hz purr[6]. The leaves of pine trees and Douglas firs occasionally make a pop sound as they clear an Air embolism from their Xylem (water transport tissue). Lois Wardell of Arapahoe SciTech in Tucson and geophysicist Charlotte Rowe detect "squawks" from Saguaro cactus that may signal "I'm cold" or "I'm really thirsty".[7]. Gagliano notes Shamans' claims to learn from plant sounds and speculates that plants may communicate by sound vibrations even though they lack structures resembling a mouth or ears. DroneB (talk) 15:22, 30 November 2018 (UTC)[reply]

I mean producing sound that is clearly audible and pleasant to humans. Poplars rustle under the slightest wind, practically even when we cannot feel the wind. Perhaps I should emphasize that I am asking about plants that are notable for the sound they produce or commonly associated with it. Surtsicna (talk) 15:36, 30 November 2018 (UTC)[reply]

The Wind in the Willows (although to be fair, willows and poplars are both cousins in the Salicaceae family). Alansplodge (talk) 16:33, 30 November 2018 (UTC)[reply]

Screaming Trees? Martinevans123 (talk) 16:36, 30 November 2018 (UTC)[reply]

If you search for "creaking trees" on YouTube there are pages of results, many of which claim to be "relaxing". I'm not sure that any tree species creaks more than any other. Alansplodge (talk) 16:46, 30 November 2018 (UTC)[reply]

I had my doubts about hearing corn grow on a still night, until I did a consulting job in Indiana and stood next to a cornfield on a windless night. --Guy Macon (talk) 17:28, 30 November 2018 (UTC)[reply]

By corn do you mean maize? DuncanHill (talk) 23:31, 30 November 2018 (UTC)[reply]

The word "corn" in the context of a trip to the U.S. state of Indiana has zero ambiguity. Stop being pedantic. If I had told a story about a trip to Hertfordshire, I would have used UK English. --Guy Macon (talk) 23:46, 30 November 2018 (UTC)[reply]

Christ, someone got out of bed the wrong side! DuncanHill (talk) 23:51, 30 November 2018 (UTC)[reply]

Yeah, stop being so pedantic, Duncan, ya doofus. It'll soon be Christmas. Martinevans123 (talk) 23:55, 30 November 2018 (UTC)[reply]

And this page is off my watchlist. You can do the reverting and asking for page protection. Not worth bothering with any more. DuncanHill (talk) 00:00, 1 December 2018 (UTC)[reply]

Wow. Yeah looks like he meant maze. But glad you've managed to escape. Martinevans123 (talk) 00:07, 1 December 2018 (UTC)[reply]

I don't know how pleasant one might consider it, but some plants, such as witch-hazel, release their seeds with an audible popping sound. See Dehiscence (botany). And I just noticed that Shantavira alredy mentioned this above. Deor (talk) 19:26, 30 November 2018 (UTC)[reply]

Well don't tell the trees Deor, 'cause the trees don't need to know. Martinevans123 (talk) 20:59, 30 November 2018 (UTC) [reply]

I wonder if Surtsicna is referring to aspens (Populus tremuloides, Populus tremula)? They are known for their constantly fluttering leaves. Apparently P. tremula is sometimes known in Welsh as coed tafod merched, 'the tree of the woman's tongue'. (Source: Broadleaves by the Forestry Commission, 1985, p56, isbn 0-11-710039-0). PaleCloudedWhite (talk) 22:03, 30 November 2018 (UTC)[reply]

To illustrate what others have said about popping seedpods, this video, although not RS, might be of interest. PaleCloudedWhite (talk) 22:15, 30 November 2018 (UTC)[reply]

Oi Paley. Even in parts of Berkshire and in Manx also, it seems. Martinevans123 (talk) 23:38, 30 November 2018 (UTC)[reply]

"Manx for that". PaleCloudedWhite (talk) 09:21, 1 December 2018 (UTC)[reply]

Yes, I meant the entire Populus genus. Surtsicna (talk) 23:46, 30 November 2018 (UTC)[reply]

A different method of noise production occurs in bladderworts (Utricularia spp.), though whether this is pleasant, rather than just interesting, is debatable. "If you ever remove a bladderwort plant from the water, you may be surprised to find audible crackling noises as the bladders get triggered shut".[8] PaleCloudedWhite (talk) 09:17, 1 December 2018 (UTC)[reply]

Rhubarb can be heard 'squeaking' as it grows ("the farmer, Janet Oldroyd-Hume, said that if you stood quietly you could hear the rhubarb grow: the gentle pop of a bulb, the creaking of a stem"[9] "it's really true that you can hear it eerily creaking or squeaking in the darkness as it pushes its way through the soil!"[10] PaleCloudedWhite (talk) 10:23, 1 December 2018 (UTC)[reply]

True story. Here's rhubarb (without any Custard): [11]. Martinevans123 (talk) 15:49, 1 December 2018 (UTC)[reply]

Memorizing constants/values for exams in college?

I assume no one can be expected to know in an exam that e = 2.7182818284590452353602874713527. But how far should we go? In the case of Pi, is using a value of 3.14 enough? Is rounding 9.80665 m/s2 to 9.8 or even 10 a safe approximation? Doroletho (talk) 18:16, 30 November 2018 (UTC)[reply]

In my day, examination questions used to state what approximation to take for such constants, or more often asked for exact answers in terms of e, pi or g. Are modern children expected to learn any of these? Are there many exams these days where calculators are not allowed? (I do recall a question on a JMB Physics special paper that I sat in the days of slide rules. No constants were given, and the question just asked "Estimate the heat loss from a typical house in Manchester in the middle of winter". I just happened to know the relevant coefficients of thermal conductivity, so I went to town on that question.) Dbfirs 18:27, 30 November 2018 (UTC)[reply]

Whether or not a teacher or professor expects you to memorize values like this depends entirely on how much of an asshole they are, with there being a direct assholery-to-memorization relationship. For the most part, these values can be looked up if needed to greater than 2-3 digits, and even so, most major exams have reference tables with values of common constants, etc. For example, here is the reference tables for the NY Regents exams, here is the one used for the Advanced Placement Physics exam, etc. Most major standardized tests just give you such information. If you're expected to memorize anything, 2-3 digits will suffice. I've never heard of a job where a person was required to memorize numbers in real life. If they need the value, you can google it and get it to whatever accuracy you want. Pi = 3.14 works for any multiple choice test (heck, for most multiple choice tests, 3 works fine, since usually only 1 of the 4-5 answers is usually close enough). When I teach physics, I tell students, for multiple choice questions, just use 10 for gravity. It gets close enough. --Jayron 32 19:31, 30 November 2018 (UTC)[reply]

The constants and conversion factors in the APP sheet are all wrongly stated as exact numerical values. Ways to show that values are rounded include replacing = by ≈ (almost equal sign), ellipsis ... to show trailing digits or a footnote such as "to 3 significant figures". It quotes the Speed of light, 3.00x10⁸ m/s "effective 2015" when in reality since 1983 the speed of light in vacuum has by definition been exactly 299,792,458 m/s. One hopes Jayron's students find out that "just use 10" gravity has units m/s² of acceleration. DroneB (talk) 00:26, 1 December 2018 (UTC)[reply]

Didn't some of the New York tests mention 22/7 or was that just my teacher? Sagittarian Milky Way (talk) 20:48, 30 November 2018 (UTC)[reply]

Sagittarian Milky Way: 22/7 is an excellent approximation for Pi, the ratio of circumference to diameter of a circle. Dolphin (t) 01:24, 1 December 2018 (UTC)[reply]

It's close for such a small denominator (better than 314/100) which locks out the other small denominators from being closer and algebra prefers fractions so no wonder teachers tell you about it. The next fractions that are closer are apparently 179/57 then 201/64 which aren't that much lower error than 22/7. Sagittarian Milky Way (talk) 02:02, 1 December 2018 (UTC)[reply]

355/113 is much more notable. Not only does it repeat odd digits in a notable way, but it's within 1/3,000,000 of the true value. --76.69.46.228 (talk) 19:16, 3 December 2018 (UTC)[reply]

I think it is useful to know the most important constants to 1-3 significant digits (3.14, 2.7, 9.81, 6e23, 22.4 are the ones that come to my mind) to be able to do Fermi approximations, to get an idea of the scale of a problem. But I'd never ask student to memorize theses numbers - that's what paper (or silicon) is for. --Stephan Schulz (talk) 21:12, 30 November 2018 (UTC)[reply]

It will vary according to the examining body, who should make clear their requirements in advance. For example, for my A Levels some boards allowed the use of log books which included a variety of physical constants, and formulae, others did not allow their, use and one needed to memorise some constants to a given number of significant figures. This was set out in the syllabus and taught to us by our lecturers. I would advise the OP to ask their lecturers what the requirements are for their various courses and exams. DuncanHill (talk) 21:17, 30 November 2018 (UTC)[reply]

Rounding g to 10 m/s/s is probably a bit slack. In real engineering work I use 9.81 m s-2. In the absence of any specific guidance you should get a clue from the number of significant figures in the problem that is set. Incidentally at my uni we had standard data books that we used in exams, chock full of exciting numbers like e and g and steam tables and material properties and so on. Greglocock (talk) 22:30, 30 November 2018 (UTC)[reply]

One of the most useful lessons to learn in physics at High School is that we are deluding ourselves if we think our answers deserve any more than three significant figures - see False precision. (I failed to learn that lesson until a couple of years after High School!) Consequently, no teacher should encourage students to memorise any physical constant to more than three significant figures. e is 2.72 and pi is 3.14. This will help students realize that if more significant figures are required, human memory is not sufficiently reliable and a written source should be consulted. Dolphin (t) 00:48, 1 December 2018 (UTC)[reply]

I was spending first ~6 months of 7th grade memorizing pi for fun and didn't find out I remembered wrong till high school (3.14159265358979326, not 3.1415926535897936) Sagittarian Milky Way (talk) 02:32, 1 December 2018 (UTC)[reply]

And you'd still be wrong. ...8979323846 :) DMacks (talk) 17:15, 1 December 2018 (UTC)[reply]

According to the Old Testament (1 Kings, 1:27), π = 3. Some highly educated friends (PhD, Princeton) tell me that said manuscript is divinely inspired and inerrant.

I have, in my infancy, decided that it is ancient fake news, but not everybody agrees.

My theory , however, is falsyfiable. π has been around since the well known π-thagororas - a rational and polydigital mathematician - invented it. Of course, π possibly was a much overrated thinker when compared to the stable geniuses of the current era. --Cookatoo.ergo.ZooM (talk) 17:14, 1 December 2018 (UTC)[reply]

The Greek letter

π

was originally an abbreviation of the Greek word for periphery (περιφέρεια) and later in 1706 for perimeter (perimetros περίμετρος) , but not for Pythagoras (Πυθαγορας). DroneB (talk) 23:47, 1 December 2018 (UTC)[reply]

The correct verse is 1 Kings 7:23. What it says is that the circumference all around the brim was 30 cubits with a (not-mentioned) diameter of 9.55 cubits. In addition, there was apparently a flat ledge extending out from the brim that was supported by "knops" (ornamental knobs). It appears that the ledge's outer diameter was 10 cubits with a (not-mentioned) circumference of 31.4 cubits. To illustrate, any overfilling would result in contents flowing over the brim onto the 0.45 cubit wide ledge. Akld guy (talk) 18:53, 1 December 2018 (UTC)[reply]

There is nothing in the text saying anything about protruding knops. However, all the measurements in that verse (and the rest of the description of the temple) are given as whole cubits, and it is possible to have a circle with dimensions that when rounded to the nearest whole number give a diameter of 10 units and a circumference of 30 units. He made the Sea of cast metal, circular in shape, measuring ten cubits from rim to rim and five cubits high. It took a line of thirty cubits[o] to measure around it. Iapetus (talk) 10:44, 3 December 2018 (UTC)[reply]

I didn't say anything about the knops protruding, and it's impossible to tell from your reply whether you understood what I said. Let me say it again. There was a circular sea (like a bowl or wok) that had a stated circumference around its rim of 30 cubits. We assume therefore that the diameter was 9.55 cubits. From verse 7:24, we can deduce that a horizontal ledge extended out from the rim, all the way around. This ledge had a stated (outer) diameter of 10 cubits, and it was supported by knops attached underneath to the sea all the way around. Therefore there is no discrepancy in trying to relate the 10 cubit diameter to the circumference of 30 cubits. They are referring to two different things, the inner circumference of the ledge (30) and its outer diameter (10). If you compute the difference, you find that the ledge was about 0.45 cubits wide (10-9.55). Akld guy (talk) 19:17, 3 December 2018 (UTC)[reply]

How has this discussion, including both fact and folly ideas, gone this far without mentioning the Indiana Pi Bill? DMacks (talk) 17:18, 1 December 2018 (UTC)[reply]

For e, I was told ~10 years ago the absolutely stupid mnemonic that it is 2.7 followed by twice Leon Tolstoi's year of birth (1828). It is absolutely stupid because chances are you never knew Tolstoi's year of birth or forgot it, yet because of the way my brain is wired I remembered both that e=2.718281828 and Tolstoi's DOB. (Neither fact has been of any use so far.) Tigraan^{Click here to contact me} 18:55, 1 December 2018 (UTC)[reply]

My teacher said square root of 3, Washington's birth year. Sagittarian Milky Way (talk) 20:05, 1 December 2018 (UTC)[reply]

My (physical) mailing address at one time included the nearest integer to 1200/ln(2), a factor useful for Cent (music) notation. —Tamfang (talk) 10:14, 3 December 2018 (UTC)[reply]

About 4.7*10^(30) hydrogen atoms will fit on a perfect circle with the radius of the galaxy, so if we get pi right to within a fractional error of less than 2*10^(-31), we can compute the radius of such a circle as measured by the number of hydrogen atoms one can put on it as an exact integer. An absolute error of 6*10^(-31) would then suffice, that level of accuracy was obtained for the first time by Ludolph van Ceulen in the late 16th century. Count Iblis (talk) 20:01, 1 December 2018 (UTC)[reply]

When Tigraan said "twice Leon Tolstoi's year of birth (1828)" I was puzzled until I realised that he meant "write 1828 twice". 62.49.80.34 (talk) 09:12, 3 December 2018 (UTC)[reply]

Chemical education.

So recently someone told me that all Bronsted-Lowry acid/bases are a type of Lewis acid/bases. So all proton transfer reactions have an electron-transfer reaction but not all electric-transfer reactions have a proton-transfer reaction. Does anyone disagree with this? If it were up to me, I'd think it'd make more sense to put the Lewis acid/base chapters with the oxidation-reduction transfers, rather than with the Bronsted-Lowry acid/base chapters, and if it were also up to me, teach Gen Chem students about Lewis acid/bases before Bronsted-Lowry acid/bases. I think there's this big book by Linus Pauling in 1970 that services as a general model as to how Gen Chem textbooks are written, so somewhere along the line, Lewis acid-bases are not taught with oxidizing/reducers.

From the guy who previous asked "Is it a contradiction to be a strong Lewis acid (receive electrons) and a strong reducing agent (loses electrons) at the same time? And is it a contradiction to be a strong Lewis base (loses electrons) and a strong oxidizing agent (causes others to lose electrons) at the same time?" which can be found here https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2018_January_17#Chemistry_question. Thanks. 67.175.224.138 (talk) 21:06, 30 November 2018 (UTC).[reply]

Yes, all B-L acid/base reactions can be also expressed as a Lewis acid/base reaction. With Lewis reactions, I'm not a fan of the "donor" or "transfer" language, as it doesn't really capture the situation as well as other terminology. Lewis acid-base reactions are bond-formation reactions whereby an atom that has a lone pair of electrons forms a new bond (via that lone pair) with an atom that has an empty orbital. This bond is sometimes called a coordinate covalent bond, to distinguish it from other 2-electron covalent bonds whereby each atom on either side of the bond contributed one electron to the bond. The electrons aren't donated or transferred per se (as that would imply they left their original atom) but instead simply form a new 2-electron bond with the Lewis acid atom. A B-L acid/base reaction is a great example of this, as the B-L base forms a new bond with the H⁺ ion using this exact mechanism. That's why B-L bases are also Lewis bases. Since, however, Lewis bases can form bonds to other atoms besides hydrogen, it's a broader category than B-L bases. --Jayron 32 11:57, 3 December 2018 (UTC)[reply]

December 2

Article about voltage variation?

Would the topic be worth an article? Or is there some article already covering it? Anyway, what voltge variation can you expect when the official voltage is something like 220-240? What causes it? And what nuisances does it cause to move out of range? Doroletho (talk) 00:12, 2 December 2018 (UTC)[reply]

Have a look at Mains electricity and Electric power quality and also Dynamic voltage restoration. Dolphin (t) 00:58, 2 December 2018 (UTC)[reply]

Be careful that there are (at least!) three quite different problems encountered here: spikes, brownouts, blackouts. Spikes are short but large voltage transients - often quite high voltages. They are caused by switching transients in the network, lightning induction, and others. Brownouts are longer periods when the voltage is out of range, usually lower. They're much less trouble for modern electronic equipment than they used to be. Blackouts are a loss of all power, either seconds (the network switching) or maybe hours. Andy Dingley (talk) 12:15, 3 December 2018 (UTC)[reply]

December 3

gravity on other bodies: confirmed?

The surface gravity of the Moon, Mars etc. was calculated long before anything landed there, but has any lander bothered to measure it? For example, did any Apollo crew measure the period of a pendulum? —Tamfang (talk) 08:29, 3 December 2018 (UTC)[reply]

I wonder how successful the moon landing would have been if there was a significant error in their estimate of g? Greglocock (talk) 08:42, 3 December 2018 (UTC)[reply]

Gravimeters using special springs rather than pendulums were invented in the 1930's by Lucien LaCoste. We have been measuring the effects on local gravity of Mascons on the Moon since 1968 from spacecraft and probes orbiting it (a recent mission is described here), and such measurements have been made on Mars as well. I don't know if gravitometers have been carried on specific landers, but doubtless someone else will be able to enlarge on this. {The poster formerly known as 87.81.230.195} 90.202.210.56 (talk) 10:02, 3 December 2018 (UTC)[reply]

Wikipedia has an article titled Gravity of Mars which includes both earth-based estimates from observations, and measurements made by probes, landers, etc. as early as Mariner 9. There are several other probes and landers which made measurements listed in the article as well. --Jayron 32 11:51, 3 December 2018 (UTC)[reply]

Yes, confirmed by measurements of tides the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of Earth as long ago as the 2nd century BC by the Babylonian astronomer, Seleucus of Seleucia who was the first to link tides to the lunar attraction. DroneB (talk) 15:06, 3 December 2018 (UTC)[reply]

This answer does not appear to address the OP's question in any way. {The poster formerly known as 87.81.230.195} 90.202.210.56 (talk) 11:21, 4 December 2018 (UTC)[reply]

Regrettably, the Lunar Surface Gravimeter, carried to the Taurus Littrow valley on the Moon's surface by the astronauts of the Apollo 17 mission, "failed" due to a manufacturing defect. No useful science data was collected by that instrument, but it would have yielded highly-accurate and time-varying measurements of lunar surface gravity, if it had worked correctly.

This instrument was not a pendulum, but was a mass-spring instrument similar to the Lacoste-Romberg gravity meters commonly used by geoscientists on Earth.

If you're interested in its operational details, here is a 1972 training hand-out prepared to familiarize Earthling scientists with the instrument package so they could analyze its data in "post-production."

Needless to say, there have been plenty of other, less-accurate--but-still-pretty-accurate measurements of Moon's gravitational field - mostly from orbital instruments and orbital-mechanics calculations relating to orbital navigation. For example, Apollo 15 released its "Sub-Satellite, which accurately measured Moon's gravity from orbit.

Nimur (talk) 17:17, 3 December 2018 (UTC)[reply]

Fate of dead bacteria.

So I think this planet is being filled with dead bacteria and is not as reversible. Do bacteria eat dead bacteria? If not, then hence my conclusion. When you pour concentrated bleach on your floors, that kills living bacteria (and therefore takes away it's smell, which is an accomplishment). When the janitor mops the bleached floor, he moves dead bacteria around, and only some of it getting into the janitor's bucket via the mop which is eventually poured into the sewers. I also heard some dead bacteria end up being broken further down into proteins, carbs, and nucleic acids. (It's not like you can use a gigantic vacuum cleaner and vacuum it all up.). And matter can't be destroyed. Now for the dead bacteria that goes into sewers: it is also safe to drink water with dead bacteria - say, after boiling it to 165 F and cooling it back down. We cook meat and then eat the meat with the now-dead bacteria. My toxicology textbook says fecal matter is about 30-42% weight originating from bacteria. And some dead bacteria is shower-rinsed, so that along with toilet, all goes to a sewer system. So what about in the treatment plant in the 2ndary treatment, where the bacteria eat the sewage - is that were bacteria eat some dead bacteria? Notes: the cell wall of bacteria is peptidoglycan - article says peptidoglycan makes up 90% of weight of Gram-positive bacteria and 10% of weight of Gram-negative bacteria, so this planet is also being filled with peptidoglycan molecules too, which I guess can be broken down. Thanks. 67.175.224.138 (talk) 17:19, 3 December 2018 (UTC).[reply]

Sorry, your question is a bit scrambled; so I'm having trouble following it. Best as I can make out, your question is what is the harmfulness of bacteria already dead compared to living bacteria. Many bacteria are only harmful while they are alive, but there ARE some bacteria that leave residual toxins which do not decompose, and could harm you even if the original bacteria are dead. The most famous example I can think of is Clostridium botulinum, which produces Botulinum toxin. The toxin can cause Botulism even if the original bacteria is dead; though the toxin is denatured by cooking above a certain temperature, and/or treatment with some kinds of disinfectant chemicals. I hope that at least partially answers your question. --Jayron 32 17:35, 3 December 2018 (UTC)[reply]

Yea I think there's 2 types of toxins you're talking about: endospores and exotoxins. 2 main types of endospores come from Gram-positive bacteria are from the aerobic Bacillus and the anaerobic Clostridium. Then exotoxins are proteins released by both Gram-positive and negative bacteria. E. coli, Vibrio, Shiegella, all release them. Examples of diseases caused by bacterial exotoxins include anthrax, botulism, tetanus, and cholera. Does anyone know if it's safe to eat dead exotoxins? Now there is a 3rd category but it is not a spore, this 1 being endotoxins, which is a piece of outermembrane of Gram-negative bacteria. 67.175.224.138 (talk) 15:47, 4 December 2018 (UTC).[reply]

What do you mean by "dead"? If a toxin has been properly chemically altered, it isn't that toxin anymore. For example, bleach is a good general-purpose oxidizer that massively disrupts most organic molecules, many toxins are effectively destroyed by bleach, others by heat, etc. These are not "dead", they were never "alive", but it is more accurate to say they have been chemically altered into new substances that aren't harmful anymore. --Jayron 32 16:10, 4 December 2018 (UTC)[reply]

Note also that chlorine bleach is quite good at reacting with organic substances and converting them to carbon dioxide. But also you will be eating tiny amounts of bacteria live and dead all the time without harm. Many small animals also eat bacteria, these would include mites and worms in terrestrial environments. In water many things eat bacteria, eg protozoa and filter feeders. One result of rotting down organic matter is compost or humus which will be rich in dead bacteria. Accumulation of dead bacteria is reversible, and almost everything produced by living organisms is consumed by another living organism. Graeme Bartlett (talk) 21:37, 3 December 2018 (UTC)[reply]

Dead bacteria are part of the organic component of soil, where they are consumed/absorbed and broken down by living organisms including bacteria, plants, fungi and animals.-gadfium 22:17, 3 December 2018 (UTC)[reply]

Plants dominate the total biomass, bacteria come second, so most of the dead bacteria are recycled as plants. Count Iblis (talk) 04:50, 4 December 2018 (UTC)[reply]

Your gut and skin are entire ecosystems filled with things that live, reproduce, and die. Everywhere on Earth where life can exist is filled to the brim with bacteria and other microbes. We are just one part of a living, breathing, biosphere. Every glass of water you've ever drank had bacteria in it, whether from the container, the air, or the pipes. "Recycling" organic molecules is pretty much what organisms do, and indeed, most dead bacteria are "eaten" by other bacteria. Without bacteria decomposing the remains of organisms, we would be buried in waste almost overnight.

On a specific note about bleach: bleach gets rid of many odors by oxidizing the chemicals that smell. Killing microbes is only tangentially related, in that, obviously, if bacteria are producing odoriferous compounds, killing them will stop them from making more. These smells are most often thiols produced by bacteria breaking down sulfur compounds; a widespread example is hydrogen sulfide, which has the distinctive "rotten egg" smell. --47.146.63.87 (talk) 08:56, 4 December 2018 (UTC)[reply]

So you think dead bacteria for the most part smell the same as living bacteria? The analogy I use here is washing feet, because overtime feet smells due to the increased presence of anaerobic bacteria, rinsing feet with water rinses off some of them. 67.175.224.138 (talk) 15:47, 4 December 2018 (UTC).[reply]

Bacteria don't really "smell". When you smell something, you're detecting molecules that are binding with olfactory receptors in your nose. Generally these are volatile molecules, like the aforementioned hydrogen sulfide. Bacteria aren't molecules; your nose doesn't have smell receptors for bacteria. Bacteria can release compounds into the environment that you can then smell, but, to me, that isn't the same thing. If your feet smell, it's not that bacteria from your feet are wafting into the air and into your nose. The bacteria adhere to your skin. What you're smelling are volatile odor compounds produced by the bacteria as they digest your sebum, sweat, and dead skin. --47.146.63.87 (talk) 20:06, 4 December 2018 (UTC)[reply]

Where can I find US TV reception maps from before the analog shutdown?

Google is overgrown with sites giving post-2009 maps. Sagittarian Milky Way (talk) 21:41, 3 December 2018 (UTC)[reply]

What do space engineers/planners say is the best approach for the immediate future, and is manned exploration part of it?

Background(as I perceive it): Humans went to the Moon, but then Moon exploration fizzled, maybe because of the lack of payoffs that needed to be both obvious and huge, so enthusiasm went down. Then we decided to focus on manned space stations orbiting Earth, closer to home, and thus (we hoped) more practical, and economic. But my perception, and also my perception of the perceptions of the taxpaying public, is that space stations haven't had many payoffs scientifically or economically either-we just do it for the sake of international comity and the fun of putting "athletes" up there. Now the discussion is on should we do a manned mission to Mars and/or put colonies(akin to manned space stations, in a way) on the Moon, but much as I would like those, the arguments in favor don't seem to be any different than the arguments for the first manned trips to the Moon or the space stations-it seems to be mainly arguments for how inspiring it would be. And I don't want us to have another fizzling of enthusiasm...Meanwhile, my other perception is that NASA and other nations' space agencies and private companies have been doing and are doing a great deal of worthwhile scientific, profitable, and military stuff up there with unmanned machinery.-so Q1.] Is anything really reachable with current tech out there that humans with current life support and propulsion systems could learn from or make profitable?(vs what unmanned machines/robots could do)? Q2.] If not, should we focus on unmanned exploration? Just for now, or forever? Q3.] Will manned exploration ever be no more difficult than Columbus's admittedly difficult journey to the Americas? Because going to the Americas made money and led to scientific advances.(Would fission or fusion rockets be enough to make that happen, or do we need something totally new?) What I would like is for my perceptions to change by getting information from you that space experts think there's a quadrillion bucks to be made out there on the Moon, and that going to Mars isn't crazy, and not purely inspirational in motive. Links would also be appreciated! ThanksRich (talk) 21:56, 3 December 2018 (UTC)[reply]

I've linked this 2015 speech several times: Astronomy Talk: America’s Space Program – NASA’s Roadmap To Tomorrow’s Missions, in which former NASA Administrator Charles Bolden candidly describes, well, NASA's roadmap. Dr. Bolden is a scientist, astronaut, pilot, and an expert in spaceflight policy; he directly addressed almost all of the questions posed here during that invited talk at the Keck Observatory.

Since that time, we've had a change of president, which has also meant a change in space policy.

If you want something slightly more recent, here's the 2017 Space Policy Directive from December 2017; and here's Space Policy Directive #2 from May 2018; and here's Space Policy Directive #3 from June 2018.

...And here's another interview with Charlie Bolden from summer 2017 - after he stepped down - in which he can speak with even more candor about spaceflight and its future.

Nimur (talk) 00:59, 4 December 2018 (UTC)[reply]

If the Soviets got lucky enough to do JFKs goal first America would've tried to do something harder. Sagittarian Milky Way (talk) 17:26, 4 December 2018 (UTC)[reply]

...Probably not... If you want some context for the history of JFK's announcement, here's a very wonderful 1979 documentary, The other side of the moon, presented by historian James Burke who covered the Apollo Program for BBC. President Kennedy's bold public statements announcing our moon aspirations were the result of many years of diligent behind-the-scenes research. Unlike more recent presidents, Kennedy did not make his remarks "off the cuff." His advisors did a lot of homework to make sure the President did not make a statement that would be later proven impossible - because in the early 1960s, Presidents of the United States refrained from loose talk and foolish statements. Nimur (talk) 03:04, 5 December 2018 (UTC)[reply]

December 4

Fire in zero g

I have read something about a fire on the Mir space station recently which made me curious if there are any videos or the like showing how a fire burning in a zero g environment looks like and how it behaves? I would assume it would look somewhat spherical due to the oxygen being consumed evenly all around it, or am i mistaken there? Were there any controlled experiments conducted involving open flames somewhere, like on the ISS for example? Are there differences in heat, oxygen consumption and so on between a fire on earth and a zero g environment? 37.138.77.85 (talk) 02:50, 4 December 2018 (UTC)[reply]

From NTRS: Technical Report TR R-246, Flammability in Zero-Gravity Environment (1966).

NTRS is probably the best resource to continue searching for more research on this kind of topic.

Nimur (talk) 04:09, 4 December 2018 (UTC)[reply]

~~They have not conducted open flame tests on ISS~~, but you may be interested in the Saffire project where they ignited a few fires onboard unmanned cargo ships that had already completed their deliveries. ApLundell (talk) 04:14, 4 December 2018 (UTC)[reply]

NASA released a video of open flame tests on ISS. [ https://www.youtube.com/watch?v=BxxqCLxxY3M ]. --Guy Macon (talk) 05:26, 4 December 2018 (UTC)[reply]

They also started fire in water: [ https://www.youtube.com/watch?v=TysrIYJOlpk ] --Guy Macon (talk) 05:33, 4 December 2018 (UTC)[reply]

Cheers for the links. Looks very interesting and the mention of the 'invisible' heptane fire in the video is also very curious. And it looks rather pretty too (when it actually does burn visibly lol). 85.16.227.219 (talk) 14:06, 4 December 2018 (UTC)[reply]

Gravity waves - what turns into energy?

I know when two neutron stars collide, they can lose mass and generate gravity waves. What is happening at the atomic level? What goes away? Tdjewell (talk) 17:49, 4 December 2018 (UTC)[reply]

We have the article Stellar collision that reports the gravitational wave event GW170817. The neutron star merger event is thought to result in a kilonova, characterized by a short gamma ray burst followed by a longer optical "afterglow" powered by the radioactive decay of heavy r-process nuclei. See also Gravitational wave and Neutron star merger. DroneB (talk) 01:56, 5 December 2018 (UTC)[reply]

Battery eliminator for smartphones?

Moved to Wikipedia:Reference desk/Computing § Battery eliminator for smartphones?

– 47.146.63.87 (talk) 05:44, 5 December 2018 (UTC)[reply]

And why did you do that? It is an engineering problem, not a bit twiddling one. Greglocock (talk) 08:16, 5 December 2018 (UTC)[reply]

December 5

Celestial bodies named after congresspeople?

Is this list complete? Are there potentially any others than listed? Thanks Abeg92contribs 03:42, 5 December 2018 (UTC)[reply]

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 == [[Battery eliminator]] for smartphones? ==
 {{moved discussion to|1=Wikipedia:Reference desk/Computing#Battery eliminator for smartphones?|2=[[Special:Contributions/47.146.63.87|47.146.63.87]] ([[User talk:47.146.63.87|talk]]) 05:44, 5 December 2018 (UTC)}}
+:And why did you do that? It is an engineering problem, not a bit twiddling one. [[User:Greglocock|Greglocock]] ([[User talk:Greglocock|talk]]) 08:16, 5 December 2018 (UTC)
 = December 5 =

Wikipedia:Reference desk/Science: Difference between revisions