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May 22

Brush for painting walls

What kind of brush was used before the invention of the Paint roller and what was it's name? In Romania, the paint roller was not used before the fall of communism (1990). The painters used a big and thick brush called bidinea - the word comes from the Turkish badana. It looked pretty much like an American Wall-paper brush. I wonder if Wikipedias in other languages have an article for this item. —  Ark25  (talk) 01:05, 22 May 2017 (UTC)

Paintbrush#Decorators' brushes has some information, and a picture. Rojomoke (talk) 04:01, 22 May 2017 (UTC)

I still use them (for better coverage on rough surfaces), but just call them large paintbrushes. Dbfirs 08:52, 22 May 2017 (UTC)

• They're still used today, made much the same as they always were. A wallpaper paste brush is easier to find and very close in style (if of the traditional style).

Masonry walls are alkaline, which will damage many paints. So "wall paint" has historically been alkaline itself, either "whitewash" or "distemper" (a very thin lime wash). This was applied with a distemper brush, a large brush itself resistant to alkali, so it was tied together mechanically, rather than the bristles glued in. Owing to their size (often 6" wide) they were usually a hollow core, i.e. the bristles were placed on two sides of a wooden centre, with two wood sides nailed or riveted on (rivets stay tight longer in wood that's being continually wetted). As these crude washes will never give a particularly smooth finish, they never needed a very high quality brush.

The manufacture of paint brushes isn't a simple "one style makes all", and some large or specialised brushes get very expensive. Japanese paper-making brushes can be a few hundred $ each, mostly because they're so rare and are handmade. French oval varnish brushes became unavailable a few years ago, when the last machine that made the ferrules was sold. Andy Dingley (talk) 10:43, 22 May 2017 (UTC)

Here's one type of distemper brush, a WWII ex-RAF one: https://hatchfive.wordpress.com/2015/06/

This one is (as described above) mechanically bound, by the bristles being string-tied bundles. As such bundles are always round (or slightly oval), a wide brush is made by putting pairs of bundles onto the handle. Andy Dingley (talk) 21:46, 23 May 2017 (UTC)

Thanks for all the answers. —  Ark25  (talk) 15:18, 24 May 2017 (UTC)

See here for some examples of various brushes. Iapetus (talk) 17:07, 24 May 2017 (UTC)

Eliminating infectious diseases by bioengineering large numbers of brainless humans with weakened immune systems?

As pointed out here:

"How do the principles of virulence help to explain the enigma of invertebrate immunity? One answer is that invertebrates don’t need an acquired immune system because they never had it. The parasitic agents of invertebrates have not coevolved with acquired immunity so their virulence is calibrated to the coevolved innate immune system. The proposal here is that contrary to widely held views of practicing immunologists, the immune system is not evolutionarily selected to prevent infection in an absolute sense. Rather, it is selected to make one individual slightly more resistant or at least different than others of the same or related species. The adversary of any individual is not really the world of parasites, they are truly undefeatable, it is his or her neighbor. A zebra doesn’t have to outrun the lion, just the slowest member of the herd."

This then suggest that we could benefit from creating vast numbers of biological systems that can be infected by the same microbes that infect us, but with weaker immune systems. On the long run this would cause the microbes to evolve to infect these systems instead of us. Or you could say that since the relevant competition is between us, we put ourselves collectively in the winning position by creating a large number of losers. This will then work because we're then going to keep the losers alive artificially. For ethical reasons one would then be led to creating brainless humans, or just large volumes of human tissues that can be kept artificially alive in some way. Count Iblis (talk) 01:30, 22 May 2017 (UTC)

No, this logic is flawed. It would only work if regular humans no longer interacted with each other, but only with the brainless easy prey-humans, in which case you don't even need them, just keep the regular humans isolated from each other. Anywhere a large pool of regular humans existed, microbes would still evolve to take advantage of them. Those microbes have no way of "knowing" that easier prey exist elsewhere, and no way to get there, in any case, so they will continue to evolve to take advantage of their current hosts. StuRat (talk) 01:36, 22 May 2017 (UTC)

I don't think StuRat's argument is valid, so long as the prey-humans have enough contact with real humans to transmit disease to them. The prey-humans would fulfill a role broadly similar to that of plants in crop refuges, which someone should probably blueify. See eg [1] and [2]. Adrian J. Hunter^{(talk•contribs)} 10:58, 22 May 2017 (UTC)

As some day it may happen that a victim must be found, I've got a little list... The OP's biological application of Chamberlain's Appeasement method against microbes should ensure "Health For Our Time", what could possibly go wrong? But it really doesn't matter whom you put upon the list, For they'd none of 'em be missed. SdrawkcaB99 (talk) 11:06, 22 May 2017 (UTC)

I can think of a more practical context for a related idea in the context of antiviral drugs for influenza. Drugs like oseltamivir can result in resistance, the prevalence of which is limited by the larger number of people who don't have immediate resort to a doctor to wave the magic pen unlocking their access to the drug, who presumably serve as a sort of susceptible reserve population like the GMO-free band around a Roundup Ready cornfield. Stockpiling antiviral medications for pandemic influenza implies such decisions with the limited stockpiles. But I haven't actually looked into what has been worked out about all this scientifically... Wnt (talk) 14:01, 22 May 2017 (UTC)

Thinking a bit more about this.... According to the article one would explain the fact that young people rarely get diseases like pneumonia while it's not unusual for old people to get it, not by saying that young people we have such good immune systems but because old people bring down the average that the microbes have adapted to. If immunity in old people were to decline less, then infectious diseases would occur at similar rates as they do now but it would be more evenly divided between old and younger people. One may then postulate that the aging process could have been an outcome of natural selection. Not only would biology not have come up with a fix for the aging processes, it may actually have fine tuned it in such a way as to steer away diseases from the young in an optimal way. Count Iblis (talk) 01:02, 23 May 2017 (UTC)

Why epinephrine is discriminated from nor-epinephrine and dopamine by the definition of hormone?

Why epinephrine is discriminated from nor-epinephrine and dopamine by the definition of hormone? I've read the talk on the article "list of hormones" and I saw that the same answerer there, made two different comments... in one he said: "The catecholamines such as epinephrine, etc. are classified as neurotransmitters, not hormones." and later after someone comment on his answer he said "Epinephrine has significant distant effects from the adrenal glands where it is synthesized and therefore it is legitimately classified an hormone... The rest of the catecholamines such norepinephrine appear to act primarily as neurotransmitters and therefore have not been added to the table.". and I really didn't understand his discrimination between epinephrine, norepinephrine and dopamine. I would like to understand it. 93.126.88.30 (talk) 12:44, 22 May 2017 (UTC)

Neurons send neurotransmitters at the synapse between the axon terminals and dendrites. Hormones may use the circulatory system or the extracellular fluids to deliver signals, near and far. Sometimes, the boundary between a hormone and neurotransmitter is not very clear. 140.254.70.33 (talk) 13:24, 22 May 2017 (UTC)

Epinephrine and the other catecholamines are all made by neuroendocrine cells. The difference in whether a specific catecholamine is described as a neurotransmitter or a hormone is its primary function.

Quoting from our article neuroendocrine cell,

"Neuroendocrine cells are cells that receive neuronal input (neurotransmitters released by nerve cells or neurosecretory cells) and, as a consequence of this input, release message molecules (hormones) to the blood."

Neurotransmitters provoke the production of hormones - they are the body's signal to produce hormones and drive organs and other groups of cells into action. However, both general classes of biomolecules can act centrally on the brain and also in the neuroendocrine system distributed throughout the body. The extent to which this happens wasn't always understood when molecules were being classified as one or the other. "Neurotransmitters" tend to have a much shorter duration of action in the body than "hormones", which is probably what the author of that article was getting at. loupgarous (talk) 23:30, 23 May 2017 (UTC)

Histamine is considered as hormone or not?

Histamine is considered as hormone or not? In our article here (histamine) as well as in the list of hormones- no mention about its definition as hormone but on other places it's considered as an hormone as well. Wikipedia normally doesn't take a side but just share with the readers the different opinions objectively. For example in this encyclopedia it's considered as an hormone.93.126.88.30 (talk) 12:43, 22 May 2017 (UTC)

If you look up hormone, there are two problematic aspects to the definition the article gives: hormones are secreted by glands, and they are transported by the circulatory system. This is a typical definition but in biology definitions tend to creep. Are individual immune cells secreting histamine from wherever part of a "gland"? Well, is a gland defined by a visible morphology, or is anything that secretes a hormone a gland, making the definition tautological? Then there is the circulatory system aspect. Localized inflammatory reaction does involve the circulatory system. But I think usually when people think of a "real hormone", they mean something that you can take out a vial of blood from whatever site is most convenient to measure it, even if the nurse has to pull out a junkie's penis hunting for a suitable vein. But histamine's effect is, by design, local, and the overall blood level, if there is one, likely doesn't represent the intensity of its effect where it matters. There are some relevant concepts that come up if you look at endocrine, exocrine, paracrine, apocrine etc. Wnt (talk) 14:11, 22 May 2017 (UTC)

Thank you for your answer, but unfortunately I really don't understand why acting of substance on cells near to secreting cell (this is the definition of paracrine hormone) or acting on the secreting cell it self (this is the definition of aoutocrine hormone) avoid this substance to be called an hormone.

Regarding to the question: "Are individual immune cells secreting histamine from wherever part of a "gland"? Well, is a gland defined by a visible morphology, or is anything that secretes a hormone a gland, making the definition tautological?" before we discuss about this question we have to agree firstly what hormone is and to know what the definition of gland is. And as we know glands can be exocrine and endocrine while according to what I've been told today, just those who secreted by the endocrine are considered hormones. Then not any gland secretes hormones... 93.126.88.30 (talk) 17:20, 25 May 2017 (UTC)

Based on encyclopedia.com's ridiculous article about homeopathy I wouldn't trust it for anything.

I agree with Wnt that a hormone, as I understand the term, is a molecule that works by endocrine signalling, meaning it's transported throughout the body rather than acting locally (paracrine signalling). Histamine's best-known effects are local. But histamine has many effects, some of them apparently systemic (eg), so perhaps it acts as a true hormone in addition to its better-known effects. Also, even peer-reviewed articles sometimes speak of "paracrine hormones" (pubmed), so there's inconsistency (or at least sloppiness) in how people use the term "hormone". Adrian J. Hunter^{(talk•contribs)} 14:25, 22 May 2017 (UTC)

How can gunpowder propel something over Mach 1?

If it doesn't burn faster than the speed of sound? Sagittarian Milky Way (talk) 15:32, 22 May 2017 (UTC)

Newton's second law. --Jayron32 15:35, 22 May 2017 (UTC)

• I think the question is misguided. Gunpowder does indeed burn "slowly", i.e. it makes no detonation, but that defines how fast the combustion front can move, which has no direct relation to the speed of a projectile. The latter is propelled, not by the combustion front itself, but by the heated gases trapped (e.g. in a gun's rifling), hence Jayron32's taciturn answer.

However, there is still a nontrivial question: as the projectile accelerates and reaches the speed of sound, the heated gases are no longer at pressure equilibrium. Said otherwise, the projectile will "outrun" the pressure that is trying to accelerate it, and hence the acceleration should stop at the speed of sound (actually, a bit slower). But then it is the speed of sound in the heated gases, higher than at room temperature (the projectile will move in the air). Tigraan^{Click here to contact me} 15:45, 22 May 2017 (UTC)

Oh right. Duh. Sagittarian Milky Way (talk) 16:05, 22 May 2017 (UTC)

The important thing is that there is no law of conservation of velocity, but there is a law of conservation of momentum... --Jayron32 16:19, 22 May 2017 (UTC)

There is no law on how many percent of the momentum goes to the bullet, though. If a rifle's illegally sawed off to a 2 millimeter barrel the bullet will not leave as fast. Sagittarian Milky Way (talk) 16:55, 22 May 2017 (UTC)

Again, I have no idea how to respond when you write such confusing statements and non-sequiturs. It makes it difficult to help you find answers to your questions. --Jayron32 17:01, 22 May 2017 (UTC)

What he wrote is pretty straightforward - if we suppose that the expanding gas were to stop at a certain velocity, then the bullet would carry only a fraction of the momentum and the remainder would stay with the gas as it leaves the gun later on. Really, F=ma seems more of a non sequitur since the whole issue is whether the gas can keep up with the bullet to apply any force to it past a certain point.

On second thought, I find myself wondering as I think about that is whether "speed of sound" is relevant to the expanding gasses in the gun barrel. I mean yes, it can limit the speed of disturbances in air, but those gasses aren't moving through air, they are the medium. If the gun barrel were perfectly smooth, then we can think of the gas right behind the bullet as stationary in its own frame of reference! Maybe what we need to be looking at is how a bullet or any other kind of fast-moving piston can move down a bore faster than the speed of sound in the air in that bore. How does the air get out of the way faster than the speed of sound? (It's time for me to look up shock wave and start from scratch, because I don't know this!) Wnt (talk) 18:18, 22 May 2017 (UTC)

Air is highly compressible, so can just compress until the end of the barrel is reached, then move to the sides and decompress. Of course, this will create a bang. StuRat (talk) 19:19, 22 May 2017 (UTC)

Which bang is known as the bullet crack. It is also called a bullet bow shockwave; but in article one thing I do not get is when and where a witness will not be able to hear the cracking sound produced by the bullet. --Askedonty (talk) 19:38, 22 May 2017 (UTC)

Infact is seems Mach 6-9 is typical for explosions. See article Detonation velocity. --Kharon (talk) 17:02, 22 May 2017 (UTC)

@Kharon: Not all explosions are detonations. See also high explosive, which gunpowder is not. Tigraan^{Click here to contact me} 09:35, 23 May 2017 (UTC)

The essential item in this discussion is the law of conservation of momentum. Confined in the gun barrel, the pressure behind the bullet as the gunpowder (smokeless powder, for high-velocity rounds, actually) charge imparts momentum to the bullet from the expanding gases, which at the point the bullet leaves the bore of the gun barrel is what propels the bullet forward. A mathematical summation of the forces acting on that bullet would show the cumulative force on that bullet over the amount of time it takes for the gases to push the bullet out of the barrel, plus the wavefront of the escaping gases pushing the bullet afterward.

The difficulty the OP had was imagining the bullet being pushed by an unconfined wavefront of expanding gases, outside the barrel, when most of the velocity and momentum imparted to the bullet are transferred during a time interval when the bullet is being pushed through the barrel, some of the gases's energy is dissipated as heat from friction between the barrel bore, the lands of the rifling, and the bullet, heat from the powder's combustion inside the barrel but mostly the linear transfer of energy from the expanding gases against the barrel and the bullet.

As the bullet "gives" and the barrel doesn't, most of that pressure moves and accelerates the bullet for that fraction of a second it's in the barrel to make it travel faster than sound. The momentum imparted to the bullet's mass is where most of the force of the exploding powder and its violently expanding gases goes while the bullet is in the barrel.

Since it is imparted over a period of time, more of that momentum's pushing the bullet away from the explosion than it would be if the bullet were just placed at the edge of a charge of gunpowder detonated outside a gun barrel - the barrel "focuses" the momentum mostly toward the bullet, so it moves faster than the molecules of the expanding gas. loupgarous (talk) 00:13, 24 May 2017 (UTC)

Even more impressive is that there are various mixes of smokeless powder that have different burn rates. The amount of powder a case can hold, the size and weight of the bullet, along with the pressure rating and length of barrel are engineered to provide the best ballistics possible. A gurn rate that quickly reaches maximum pressure and a burn rate that sustains that pressure as the bullet allows the volume to expand provides the best return. --DHeyward (talk) 08:31, 24 May 2017 (UTC)

What kind of voltage regulator is this?

The voltage regulator article discusses many different kinds of voltage regulator. What [kind of regulator is this] so that I can read about that one specifically? Does it turn all the unwanted energy to heat? So 1 A @ 5 V from a 12 V supply would give 7 W heat? Thanks! ----Seans Potato Business 22:25, 22 May 2017 (UTC)

The the specs say it includes "thermal shut-down control" does imply that it's converting excess energy into heat. (I find that they rarely say so outright, as this is obviously an inefficient and non-ideal way to do things.) StuRat (talk) 23:06, 22 May 2017 (UTC)

I think the way to approach this question is to begin with simple conservation of energy, as we do when first considering power transformers, gear trains etc. If the output is 1 A at 5 V, that is a power of 5 W. Assuming simple conservation of electrical energy, the input would be 12 V and 5/12 A (or 0.417 A). Power transformers and gear trains operate with a certain amount of the input energy leaving the system as unwanted heat, and it would be the same with this voltage regulator. Assuming 20% of the input energy is lost to heating of the surroundings leads to the conclusion that the input current will be 1.2 times 0.417 A (or 0.5 A). Input power will be 6 W and output power will be 5 W, so energy will be lost to heating of the surroundings at the rate of 1 W. Dolphin (t) 23:35, 22 May 2017 (UTC)

(edit conflict)::See 78xx. User:StuRat is correct in that the 78xx series dissipates excess power as heat, but his reasoning is a bit off. For example, switching regulators (which do not work by dissipating excess power as heat) often include thermal shutdown capability. Note any voltage regulator that is less than 100% efficient will dissipate some energy as heat and therefore may be susceptible to thermal overload. Physics being what it is, all regulators are less than 100% efficient. Shock Brigade Harvester Boris (talk) 00:55, 23 May 2017 (UTC)

I'm rather surprised that overheating is a concern for those. Of course, some heat will be generated by other methods, but it seems far less likely to be more than the device can handle, not being on the same order of that from a device where 100% of the unused energy goes to heat. StuRat (talk) 01:06, 23 May 2017 (UTC)

Clicking on the datasheet option and looking at the block diagram, it's apparent (if you're used to looking at this sort of thing) that the series pass element is Q17 and R11 and most of the waste heat will be dissipated in these two elements. So for output of 5 V and 1 A, about 7 W will be dissipated in Q17 & R11. A small amount of power will be dissipated in the rest of the regulator. Jc3s5h (talk) 00:26, 23 May 2017 (UTC)

The device is a linear series regulator and is mentioned here. Jc3s5h has answered correctly; the small amount of power additional to the 7W dissipated in Q17 & R11 is (I_d x 12) W where I_d is the quiescent current to ground, about .004 to .006 A according to the data sheet. Dolphin's answer incorrectly supposes conservation of energy but the device is only 41.5% efficient and wastes 58.6% of input energy as heat. Thermal protection is provided in case someone fails to provide the Heat sink that the device needs. Blooteuth (talk) 01:18, 23 May 2017 (UTC)

You are looking for a 7805 linear voltage regulator in TO-220 package. The 1.5 amperes may be the shortcut peak current. The 78xx series have some special variants like 78L05 or 78S05. Theres a 100 mA variant in TO-92 package. There are 2 and 3 ampere variants avail. Note: Never clamp linear regulators in parallel. Such circuits cause output voltages on the input voltage level and oscillating output similar to a noise amplifier or function generator. Indeed the heat is the power drop in the regulator device 7 W = (12 - 5 V) * 1 A. This are 7 watts heat spread over a necessary heat sink. This series usually require 3 volts more input than output to generate a proper output voltage level. A socalled low drop regulator needs less volts to operate properly. The maximum input voltage is 37 volts. When the heat drop exceeds its maximum, have another circuit before to generate 8 volts for the 5 volts regulator. Depending on the application, a stepdown converter, also called buck converter which is a switching mode voltage regulator. It might be more energy efficient, but for some applications too noisy on the output. For this issue, have the linear regulator behind the buck converter. Switching mode voltage regulators can reach an energy efficiency up to 97 %. Another example are Class-D amplifiers, using an audio input as reference voltage. German Wikipedia has an overview of switching mode voltage regulators, see de:Schaltregler. Most linear regulators have 3 pins. A switching mode regulator needs an extra input pin to sense the output. Depending on the type a voltage divider can be installed there to make the circuit generate another output voltage. --Hans Haase (有问题吗) 17:39, 23 May 2017 (UTC)

Dolphin's answer is completely wrong, and StuRat's is not helpful. Series regulators of the LM-7812 and LM-7805 type (which is the type the OP asked about) regulate the output voltage by wasting the excess. If you connect an LM-7805 to a 12 volt DC source, it will provide a regulated 5V output. Very little energy will be dissipated in the device when no load is placed on the output, since the device consumes only a few milliamps itself. When connected to a 12 volt supply and 1 Amp is being drawn by the load, the device is dropping 7 volts @ 1 Amp, which is indeed 7 Watts, answering the OP's question. The data sheet in the link does not mention the device's power dissipation, but these devices are typically rated at 5W, and at 7W it should therefore be mounted on a suitable heatsink. The alternative is to drop the input supply to 10V, when 5W will be dissipated. I don't recommend going lower, as these devices have a threshold of about 2.5 volts above their stated output, and operation becomes erratic when the supply drops below that threshold. Akld guy (talk) 20:40, 23 May 2017 (UTC)

The words of the datasheet "If adequate heat sinking is provided..." require the designer to do a proper thermal calculation. For the TO-220 package, Table 2 Thermal Data indicates we need a heatsink with thermal resistance no more than R_thj-amb - R_thj-case = 50 - 5 = 45 °C/W. If the ambient temperature is 25° then we must not dissipate more than (150 - 25)/50 = 2.5 W because 150° is the absolute maximum junction temperature. Our need to dissipate 7W therefore demands a bigger heatsink, certainly one with no higher thermal resistance than 12.86 °C/W. However a responsible engineer would not settle for a design on the edge of self destruction and would lay in a healthy safety margin against eventualities such as increased ambient temperature and poor ventilation. His options include choosing a bigger heatsink with lower thermal resistance, choosing the 2-bolt TO-3 package for better heatsinking and reducing the device dissipation with an external dropping resistor as shown in the datasheet Fig. 32. (If the load happens to be a 5 ohm resistance and the supply is exactly 12V then a 7 ohm Resistor could substitute for the whole regulator.) Blooteuth (talk) 01:06, 24 May 2017 (UTC)

Using a 7 ohms resistor does not support the full load of the whole circuit. As some linear regulators need 3 extra volts for the internal circuit, it is possible to use a 4 ohms resistor when the 12 volts are stable. The other idea is using a 7809 or 7808 to supply the 5 volts regulator, sharing the thermal load. --Hans Haase (有问题吗) 11:03, 24 May 2017 (UTC)

@Hans Haase I don't think you have noticed that I only mentioned the 7 ohm resistor as a theoretical substitute (replacement) for the whole regulator. Of course it would not regulate the output voltage. Blooteuth (talk) 21:49, 24 May 2017 (UTC)

Yes, thanks! Indeed, 1 ampere output at 12 volts input, the 7805 temporary behaves like 7 ohms resistor. The right way for thermal calculations assuming a normal operation, but just bear in mind other factors of real use like stable output and shortcut scenario, I pointed on. --Hans Haase (有问题吗) 09:44, 25 May 2017 (UTC)

May 23

Chemistry - Chloro-amphetamine

Hello, If "Chloro-amphetamine" as well as any of its ortho/meta/para-substitutions are to be called "the CA group". Chemistry speaking, will it also include the chemical "DOC"(2,5-Dimethoxy-4-chloroamphetamine)?

Thanks for the help and sorry for my grammer, Dave. — Preceding unsigned comment added by 79.181.165.55 (talk) 09:32, 23 May 2017 (UTC)

I did a quick web search and saw a paper using the term here. Actually the term is "4-CA group", for 4-chlorinated amphetamine derivatives. Two examples they give there are 4-chloro-N-methylamphetamine (CMA) and 4-chloro-amphetamine (4-CA). Arguably, 2,5-Dimethoxy-4-chloroamphetamine is also a 4-chlorinated amphetamine, therefore chemically (since that's what you ask) part of the 4-CA group.

That said, putting oxygens on the back end of an amphetamine may chemically be a substitution, but practically, oxygenation is the relevant difference between derivatives of the amino acids phenylalanine, tyrosine, and L-DOPA. It's not that neat to explain here since (like other 4-CA group) it has a chlorine where tyrosine and DOPA have a hydroxyl, and an oxygen at a 2-position that doesn't come up much in nature that I can recall. The archetypal contrast where the aromatic ring is concerned is between meth and MDMA; it can make a difference. Anyway, all this sort of chemical logic is questionable under the best of circumstances - every compound is pretty much its own experiment, and there's no actual guarantee that what happens from a new one will make much sense a priori, not unless you have a structure for every possible catecholamine receptor and can model them all simultaneously, and I doubt if that would work either. Wnt (talk) 18:39, 23 May 2017 (UTC)

Sugar in baked beans

Apparently baked beans make people fart because the sugar in them are not digestible by humans. Does that mean even though a can of baked beans lists it as having 20g of sugar none of that sugar actually enters the blood stream and is all used up by bacteria producing gas in the large intestine? Or do the nutritional values on food packaging only list sugars that can be digested? — Preceding unsigned comment added by 59.44.40.209 (talk) 13:13, 23 May 2017 (UTC)

It is not the added sugar, which is in the form of sucrose, glucose, or fructose; all of which are highly digestible. There are different sugars in the beans, specifically sugars such as stachyose and raffinose, which make it to your intestines and make you fart. These sugars are in the beans themselves, and can make you fart even in applications that don't involve added sugar, such as chili. --Jayron32 13:16, 23 May 2017 (UTC)

I remember watching a food-related documentary, Michael Pollan's In Defense of Food, and one section mentions that the indigestible sugars known as dietary fiber are food for the bacteria, which then secrete gaseous waste products, which make you expel flatulence. 140.254.70.33 (talk) 15:13, 23 May 2017 (UTC)

Not exactly the same thing, while both dietary fiber and sugars are both carbohydrates, "sugars" are usually taken to be relatively small, either mono-, di-, or tri- saccharides, fiber is a very long-chained polysaccharide. Dietary fiber could also be the source of gas, depending on a person's intestinal flora. --Jayron32 18:46, 23 May 2017 (UTC)

So, the term "sugar" refers to relatively simple sugars (mono-, di-, and tri- saccharides), while "fiber" refers to big, indigestible polysaccharides. Also, some sugars can be indigestible. And dietary fiber itself can be a source of gas. This reminds me of an instance when I used the term "benign cancer" and "malignant cancer", and the instructor corrected me that all cancers are malignant, while tumor can be benign or malignant. So, cancer is a subset of tumor. Ay, picky wording. 140.254.70.33 (talk) 13:45, 24 May 2017 (UTC)

As to whether those sugars are included on the label, there may not be a universal answer. It may depend on the actual methods and devices used, such as a calorimeters. According to [3], there's only 1 g of "sugar" in a 177 g sample, so I have to think they are excluding most of the indigestible sugars. StuRat (talk) 16:15, 23 May 2017 (UTC)

"Beans (legumes) cause gas because they contain a type of sugar which is indigestible by our bodies. It’s called oligosaccharide. It’s a large molecule that is different from other sugars in the way our body handles it. It is not absorbed and broken down in the small intestine". WHY DO BEANS MAKE US GASSY AND HOW TO PREVENT IT It's not the same as dietary fibre, although beans have plenty of that. Alansplodge (talk) 11:39, 24 May 2017 (UTC)

Acidity and preservatives

Often, recipes instruct newbie cooks that lemon juice can prevent the discoloration of the avocado or apple. The fruit is still edible, but the ugliness of the color will probably be less appetizing. In regards to acids and bases, can vinegar and very dilute hydrochloric acid work just as well? How acidic does the acid have to be to avoid burning or dissolving the esophagus? What about bases? Can bases be used to preserve foods too? Instead of lemon juice, what happens if sodium bicarbonate is coated on food? 140.254.70.33 (talk) 14:59, 23 May 2017 (UTC)

I would avoid using HCl, since, as a major constituent of stomach acid, it smells "like vomit" to most people. StuRat (talk) 15:43, 23 May 2017 (UTC)

I highly doubt that. HCl ... well, you shouldn't smell it, but it just has a sharp acid smell. People scrub concrete with moderately dilute solutions of it. And when you mix it into anything that is a weak base that can be neutralized, like a food, it will just be chloride ions and a more protonated something. Many of the pills people take contain HCl to turn drugs to the hydrochloride for isolation; recreational alkaloids like cocaine and morphine also use it. Wnt (talk) 18:43, 23 May 2017 (UTC)

For many who have vomited, or been near somebody else who has, that smell is distinctive, especially when mixed with food, and will trigger unpleasant memories. StuRat (talk) 19:49, 23 May 2017 (UTC)

That's probably so because the limbic system, which contains the hippocampus and amygdala, is so close to the olfactory nerve. The sense of smell is a good danger detector. 140.254.70.33 (talk) 20:57, 23 May 2017 (UTC)

The horrible smell is due to butyric acid. When dairy-product fat breaks up in digestion to yield free fatty acids, you get that substance. HCl has a different smell. Graeme Bartlett (talk) 11:31, 24 May 2017 (UTC)

"Can bases be used to preserve foods too?" - yes, see Food_preservation#Lye. SemanticMantis (talk) 16:44, 23 May 2017 (UTC)

Note that the example of a browning apple isn't bacterial decomposition, but rather oxidation. I don't know if bases would prevent that. We need a chemist (and I don't mean a pharmacist, for any BrE speakers). StuRat (talk) 16:48, 23 May 2017 (UTC)

I just did a web search and found [4]. This looks well written and plausible. Polyphenol oxidase is indeed the cause of browning - note that polyphenols are a plant compound fairly analogous to melanin - perhaps even homologous, over some vast evolutionary distance, but I don't know any way to prove that. Plants use polyphenols like insects use melanization, to make a pigment and simultaneously protect against infection. Oh, anyway, note that it gives primary credit to ascorbic acid, though bringing the enzyme out of its optimal pH range also helps. Vitamin C is an archetypal antioxidant, and all these polyphenol/melanin processes involve taking aromatic compounds and reacting them with so much oxygen that they turn into a hyper chemically active mess (compare the reactivity of phenol, quinone, etc.) that congeals into an extended polymer. Wnt (talk) 18:46, 23 May 2017 (UTC)

Vitamin E does it also, with the side effect of making you not want to eat the apple slice afterwards. shoy (reactions) 19:23, 24 May 2017 (UTC)

Honey contains a small protein that inhibits polyphenol oxidase.doi:10.1021/jf00100a002 Cyanide is also a decent inhibitor (sequesters the copper cofactor), but probably gives an objectionable result if you're aiming for food. Well, unless you're tired of your dinner guests whining about how bad your cooking is. DMacks (talk) 03:39, 26 May 2017 (UTC)

Or you're Alan Turing. —Tamfang (talk) 07:52, 26 May 2017 (UTC)

• Food preparations with lye and other similar bases include lutefisk and nixtamalized maize. --Jayron32 18:50, 23 May 2017 (UTC)

History of Allergy Testing in the 20th Century

Can anyone point me in the direction of information about the history of allergy testing. I've looked over Radioallergosorbent test, which was a little bit helpful but not quite enough. Specifically, I'm seeking to verify the feasibly of an allergy test for meats (chicken, lamb, etc.) that was conducted in the late 1950's-early 1960's. What sort of allergy testing technology existed in that time period for food allergies? Thanks! Helene O'Troy - Et In Arcadia Ego Sum (talk) 15:19, 23 May 2017 (UTC)

You really don't need any technology. Just feed the person a tiny sample of the item, and see if they react. If not, give them slightly more, until you get to a normal dosage (meal). If they still show no reaction, then they aren't allergic to that item. The "give them a tiny amount" part might need to be even tinier amounts in ancient times, though, due to a lack of medical ways to respond to an allergic reaction. StuRat (talk) 15:46, 23 May 2017 (UTC)

This does make sense. However, I'm trying to verify a story about someone "getting a test when I was a teenager" that resulted in a positive allergy to lamb meat. I'm looking for information about what a doctor's procedure would have been in this situation. Helene O'Troy - Et In Arcadia Ego Sum (talk) 16:01, 23 May 2017 (UTC)

Try searching for variants on allergen restriction or elimination diet. There were published diet schedules that eliminated possible allergens in a systematic way. I remember seeing one of these a long time ago and, oddly, in the diet schedule I read through, lamb was one of the last things to be eliminated as it was regarded as having low allergenic potential. Odd the things one's brain saves away for a rainy day. 2001:8B0:1625:41F:0:0:0:36 (talk) 23:37, 23 May 2017 (UTC)

There a skin test method where samples of the substances in question are adhered to the skin with something like the "dot" bandages, remain there for some time, and any skin reaction is seen as a sign of an allergy. However, I'm not sure this method would catch all food allergies and reactions, such as lactose intolerance. Skin tests, including pricking the skin, have been around since the 1860's, so a century before your inquiry: [5]. Note that an allergy to lamb is sufficiently rare that they wouldn't be likely to test for it proactively, but only to verify the problem once somebody becomes ill after eating lamb. (Personally, if eating item X made me sick, I wouldn't bother with tests to verify this fact, I'd just avoid eating it again.) StuRat (talk) 16:21, 23 May 2017 (UTC)

This is reviewed at skin allergy test. I've heard more argument than usual about the accuracy of these tests, but without doing a lot of research I'm not prepared to summarize it in a neutral way. Wnt (talk) 18:24, 23 May 2017 (UTC)

Feynman Lectures. Exercises PDF. Exercise 4-14 JPG1JPG2

. . .

...

4-14. Smooth, identical logs are piled in a stake truck. The truck is forced off the highway and comes to rest on an even keel letgthwise but with the bed at an angle Θ with the horizontal. As the truck is unloaded, the romoval of the log shown dotted leaves the remaining three in a condition where they are just ready to slide, that is, if Θ were any smaller, the logs would fall down. Find Θ.

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

...

We number the logs, as shown in the figure. Consider such a virtual movement of logs, in which the log 3 is moved up the body, as a result of which the log 2 fails between the logs 1 and 3. Let the center of the log 3 be displaced a short distance BB '= Δx. The center of the log 2 will then take the position of C ', and we may assume that the log 2 first moves perpendicular to the body by a distance CK = Δy, and then to the right parallel to the body by a distance KC' - LL '= (AB'-AB) / 2 = Δx / 2. With such movements, the center of the log 3 will rise upward by a distance Δh₃ = Δx sin Θ, and the center of the log 2 will drop down by Δh₂ = Δy cos Θ - (Δx / 2) sin Θ. But the change in the potential energy of the logs with such displacements must be zero, whence Δh₂ = Δh₃ (here it is taken into account that the masses of all logs are the same). Substituting for Δh₂ and Δh₃ their values, we obtain
Δy cos Θ - (Δx / 2) sin Θ = Δx / 2
or
tan Θ = (2Δy)/(3Δx)

We compute Δy. It follows from the right-angled triangles ACL and AC'L 'that CL = R√3 , and $C'L'={\sqrt {(2R)^{2}-[R+(\Delta x/2)]^{2}}}\approx {\sqrt {3R^{2}-R\Delta x}}=R{\sqrt {3}}{\sqrt {1-(\Delta x/3R)}}\approx R{\sqrt {3}}(1-\Delta x/6R)$ .We neglected, as in the previous problem, the terms of the type Δx₂, as we extracted the square root, we used the approximate formula ${\sqrt {1+x}}\approx 1+(1/2)x$, which is valid for x << 1. Thus, Δy = CL - C'L' = Δx/2√3 , and tan Θ = 1/3√3, Θ = 11°.

—  MEPhI , Solutions (Google Translate)

There is second solution from MEPhI (earlier date of publication) which says that upper and rightmost logs must replace each other heights to keep potential energy the same before and after the falling . So Θ = 30 °.
I have made some drawing https://s.sender.mobi/u/image/2017/5/23/lUnPk5ylV/-.PNG
From it, it is clear that angle Θ = 15 °.

It is obvious that the 2nd MEPhI solution is wrong, but I can't find a mistake in the 1st one. Why then doesn't my answer coincide?

Username160611000000 (talk) 19:55, 23 May 2017 (UTC)

The potential energy solution is what came to mind immediately for me, but there's a catch. If the logs fall you have three logs lined up on the bottom (i.e. the dotted log in the diagram is real). If we arbitrarily define the center of the corner log as 0 potential energy, then the one next to it has PE = D sin theta * M, where D is the diameter of a log and M is the mass. But that's present in both configurations and we need speak no more of it. The dotted log has PE = 2DM sin theta by the same logic. The top log looking to fall has energy DM sin (theta + 60) = DM sin theta cos 60 + DM cos theta sin 60 = 2DM sin theta at equal potential energy. Given cos 60 = 1/2 and sin 60 = sqrt(3)/2 then DM sin theta * (2-(1/2) = sqrt(3)/2 DM cos theta, or tan theta = sqrt(3)/(2(3/2)) = 1/sqrt(3), so theta = 30. It's a great solution, except for one catch, which is that the logs don't actually have to reach their potential energy minimum without jiggling (which is why wise physicists do not climb up into crashed logging trucks to admire the beauty of their equations). Wnt (talk) 20:52, 23 May 2017 (UTC)

(edit conflict) Looking at your drawing, I think your method would be correct if log B and log D moved equal distances, i.e. if moving B 0.1 mm parallel to AB would move D also 0.1 mm along DC. However, I don't think that's the case, but log D would slide slower than B would. - Lindert (talk) 21:28, 23 May 2017 (UTC)

Yep. According drawing if the log D goes 1 unit along its trajectory the log B goes √3 units along its trajectory. So we must choose Θ such that √3 Sin(Θ) = 1 Sin(30 - Θ). Username160611000000 (talk) 04:52, 24 May 2017 (UTC)

Have any planes, ships or train cars had cables to increase stiffness or strength?

Older airliners were aluminum cause steel's too heavy so would steel-cable reinforced aluminum have been viable? Or one of those strong polymer cables/wires like Kevlar? Sagittarian Milky Way (talk) 20:30, 23 May 2017 (UTC)

• Old biplanes and triplanes relied on cables to hold them together, including Snoopy's favorite, the Sopwith Camel.

• Older ships used cables to secure some structures. See rigging for sailboat examples. Here's a later steamship example: [6] (you may need to zoom in to make out all the cables). The German battleship Bismarck also had some support cables: [7].

• I haven't found any pure locomotive examples, but I can imagine a system that needs to raise and lower components off a rail car using cables. Locomotive-based weapons systems come to mind, but I haven't found any of them using cables to do this, yet. A train car with it's own crane is a case I did find: [8], but I'm not sure if that's what you're looking for. StuRat (talk) 20:36, 23 May 2017 (UTC)

• Many ancient Egyptian ships were stiffened by one or more cables (though neither steel nor polymer) running lengthwise above the deck, at least according to Björn Landström's interpretation. He shows them used e.g. in a ship from the time of Sahure (3000 BCE), and in ships built 1500 years later by Hatshepsut (likely not in person ;-), both in sea-going ships for an expedition to Punt, and in giant Nile ships used in the transport of obelisks. Egypt never had good timber, so they had to assemble ships from small pieces - ok for compressive loads, but horrible for tensile loads. --Stephan Schulz (talk) 21:37, 23 May 2017 (UTC)

Our article says that ancient Greek triremes were stiffened with cables called hypozomata which "would act as a stretched tendon straight down the middle of the hull, and would have prevented hogging". CodeTalker (talk) 01:13, 24 May 2017 (UTC)

You may be interested in learning about the principles of tensegrity. Most of the examples thus far are in that vein. I think you may be thinking more in terms of reinforcement like reinforced concrete or ripstop nylon. I don't think I've ever heard of aluminum being reinforced with steel cable in that manner, though I too would be curious to see if anything like that has been tried. SemanticMantis (talk) 01:57, 24 May 2017 (UTC)

• And some newer aircraft such as the Boeing 787 Dreamliner make extensive use of composite materials, which use things like Kevlar or carbon fiber in a plastic matrix. -Arch dude (talk) 04:50, 24 May 2017 (UTC)

Thor Heyerdahl built two ships from papyrus, called Ra and Ra II, hoping to prove that the ancient Egyptians could have sailed to the Americas. When the first one fell to pieces, he added "a tether that acted like a spring to keep the stern high in the water while allowing for flexibility". Rojomoke (talk) 04:47, 24 May 2017 (UTC)

I read the Kontiki book half a century ago, but I think his early 1940's rafts were built of a balsa wood and with a bamboo deck.lashed together with hemp. (If all else fails, smoke the rope). . Later he made rafts of the reeds from which papyrus was made. Edison (talk) 05:15, 24 May 2017 (UTC)

Small quibble: Kon-Tiki was 1947, in part using WW2 surplus equipment, and with some of the participants being ex-WW2 fighters. In the early 1940s, much of the world had different priorities.The Ra expeditions were in 1969 and 1970, and while one might argue either way, I think the boats would be offended to be called rafts ;-). --Stephan Schulz (talk) 06:44, 24 May 2017 (UTC)

Our Kon-Tiki expedition article says it "was a 1947 journey by raft" the definition being, I think, that a boat has a hull with sides ans gunwales, whereas a raft is just a floating platform. Alansplodge (talk) 08:53, 24 May 2017 (UTC)

Apologies, I see you refereing to the Ra boats. Alansplodge (talk) 08:55, 24 May 2017 (UTC)

No harm done ;-). Yes, I was referring to Ra and Ra II. One might argue even in their case, because they still float due to the buoyant material they are made from, not due to a watertight hull. But they certainly look boaty.. --Stephan Schulz (talk) 14:55, 24 May 2017 (UTC)

Many modern ultralight aircraft use cables extensively as part of the structure. Roger (Dodger67) (talk) 07:17, 24 May 2017 (UTC)

Paragliding is the closest I can think of. The shape of the wing is held in tension. Parasaiing and parachutes work the same way. Some older aircraft I beieve had cables from the wing to the fuselage to make sure the force of lift didn't rip the wings off. --DHeyward (talk) 08:12, 24 May 2017 (UTC)

Zeppelin's are usually full with such construction choices. Its not used in modern aircraft design anymore, except in ultralight's. --Kharon (talk) 09:45, 24 May 2017 (UTC)

The rigidity of a Zeppelin rigid airships came from an aluminium frame; however, wooden framed airships such as the Schütte-Lanz and Spiess models were far more reliant on steel cable bracing, but had been discarded in favour of the Zeppelin system by the end of WWI. Modern airships, such as the Airlander 10 or Skyship 600 are either non-rigid, being entirely shaped by he internal gas pressure, or semi-rigid, using internal pressure and a hull formed by synthetic materials. Alansplodge (talk) 11:52, 24 May 2017 (UTC)

Zeppelin frames only work with cables in between like a bicycle wheel needs spokes. --Kharon (talk) 18:39, 24 May 2017 (UTC)

You're quite right, I found this description of the LZ 129 Hindenburg, the ultimate development of the Zeppelin method: "The fifteen main rings of the hull are arranged one behind the other at intervals of 49 feet, thus dividing the hull into sixteen sections, each of which contains a gas-bag. Between every two main rings are two auxiliary rings, all rings being in the form of a polygon of thirty-six sides. The longitudinal members are attached to the corners of the rings, the main rings having truss frame members on the circumference, braced centrally by wires, the intermediate rings having plain triangular members but with no bracing". Alansplodge (talk) 19:11, 24 May 2017 (UTC)

May 24

Decentralized electric networks

Are electric networks of low volts always being decentralized?--109.252.29.219 (talk) 11:00, 24 May 2017 (UTC)

Can low volts to create centralized electric networks?--109.252.29.219 (talk) 11:07, 24 May 2017 (UTC)

I think you're asking if there are any large scale low voltage networks. See Electric power transmission. Not at the moment - energy is saved by transmitting electricity at a high voltage. The voltage is stepped up at the generators and stepped down using transformers near the point of use. So high voltage AC is how electricity is transmitted nowadays. High-voltage direct current is also used for some long distance links. There are plans I believe though to transmit power using low voltage DC in superconducting networks. This sort of thing would be a very large project for sending power between countries for instance. Dmcq (talk) 11:12, 24 May 2017 (UTC)

Thanks a lot. Are low volts of renewable energy not powerful to create centralized electric networks?--109.252.29.219 (talk) 12:23, 24 May 2017 (UTC)

Are being plans to use optical resonance in optical fiber to transfer electricity of low volts for long distances?--109.252.29.219 (talk) 12:36, 24 May 2017 (UTC)

Volts is not the same as power or energy. A meal for instance gives a certain amount of energy. A person cycling has a maximum amount of power they can produce per hour and using the energy in one meal could probably produce it for a few hours. The gears on his bicycle produce either high speed with low force or low speed with high force. A transformer is like that - it can produce high voltage electricity with a low current or a low voltage with a high current for the same power.

Renewable energy is not a particular amount of energy. An installation producing renewable energy could be large or small. If it is small it produces only a small amount of power and if it is large it produces a lot. A transformer can transform the voltage and does not care what the source is.

No there are no plans to send power down optical cables. Why should anyone try to do that when there are perfectly good electricity power lines around? Dmcq (talk) 13:03, 24 May 2017 (UTC)

There are a few cases where it is useful to transmit power by Optical fiber using a photovoltaic cell to convert the light into electricity. While inefficient, it is a way to avoid having a metallic conductor near MRI machines, which produce strong magnetic fields. Other examples are for powering electronics in high-powered antenna elements and measurement devices used in high-voltage transmission equipment. Blooteuth (talk) 16:34, 24 May 2017 (UTC)

Is it true that low volts always carry low power and low Ampere’s force?--109.252.29.219 (talk) 14:18, 24 May 2017 (UTC)

Because the low dynamics - low kinetics will not be high dynamics, isn't it?--109.252.29.219 (talk) 14:29, 24 May 2017 (UTC)

As for me the volts and the Ampere's force are always directly proportional to the power.--109.252.29.219 (talk) 14:50, 24 May 2017 (UTC)

Agree that the potential kinetics of power cannot be more potential kinetics of volts or potential kinetics of Ampere’s force.--109.252.29.219 (talk) 16:11, 24 May 2017 (UTC)

Is it true...? No. Electric power is the product of Voltage and current which are separate, measurable variables. The supply for an electric arc welder is an example of a low voltage producing a very high current, and therefore delivering a high power. The Weller Soldering gun also delivers substantial heating power using a low-voltage high-current transformer winding. Blooteuth (talk) 16:48, 24 May 2017 (UTC)

Much thanks. The kinetics of power always closer to the kinetics of volts or kinetics of Ampere’s force?--109.252.29.219 (talk) 18:37, 24 May 2017 (UTC)

Please read the first 3 articles that I linked to in my answer. It is not necessary to learn Ampère's force law to understand electric power, voltage and current. Blooteuth (talk) 21:39, 24 May 2017 (UTC)

The lower the voltage is, the higher is the current for same energy transfer. This increases lost on conductors and connectors. High current needs thick wires. This means more conductive material is needed. Taking a closer look inside a computer, modern CPUs have operating voltages far below two volts. The buck converter, generating this low voltage for the 12 volts power supply is located on the motherboard due voltage drop on connectors and lines. When the CPU operating voltage drop at any time, the CPU goes into brownout, causing malfunction and discontinuing the program flow. Cheaper and older computer failures are caused by this. Starting the engine of a car, the 12 volts from battery are not 12 volts anymore when the starter motor drives the engine. Lower light from bulbs appear at this time. Using a bigger battery helps a litte, but the lead in the starter battery is no super conductor. An other example is, increasing the length of wires computer power supplies by plugging a number of Y-cables or Y-adapters can increase the resistance of the wires to the point, where shortcuts are not detected anymore, causing burning the wires and starting a fire. In the Low Voltage Directive, also taken most likely for American standards, prevention of similar damages are regulated. There are technologies like smart grid and high-voltage direct current, to interconnect low(er) voltage power grids. --Hans Haase (有问题吗) 09:32, 25 May 2017 (UTC)

Thank you. According to the Law of conservation of energy, the low dynamics - low kinetics will not be high dynamics – high kinetics.--109.252.29.219 (talk) 09:35, 25 May 2017 (UTC)

Electric field at plane of non-conducting uniformly charged thin disk

Will field at plane of a disk excluding the disk itself be zero? Here basis of above conclusion is that the field lines will originate perpendicularly to the plane, and from both faces therefore they will never be able to reach plane of disk at finite distance.

From above the potential at edge will also be zero, if a test charge is bought from infinity through the path passing through plane to the edge, which is obviously not true.

Therefore, tell me where I'm wrong and please provide the field line distribution due to the disk. — Preceding unsigned comment added by Tejasvi Singh Tomar (talk • contribs) 14:22, 24 May 2017 (UTC)

An Electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Let's distinguish between these cases.

   +  +  +  +  +  +                 +  +  +  +  +  +   
 + OOOOOOOOOOOOOOOO +               OOOOOOOOOOOOOOOO 
   +  +  +  +  +  +                 -  -  -  -  -  -   

      CASE "A"                          CASE "B"

Case A is a uniformly charged disk which may be conductor or insulator. Electric field lines emanate to infinity from every "+" point including the edge. The density of the lines correlates with the strength of the force. At a large distance their density is the same so the force is the same for a point in the plane of the disk as any other. One may also sketch the shapes of Equipotential surfaces which in 2-D are sausage-shaped close to the disk and circular far from the disk.

Case B is a differentially charged insulator disk. Electric field lines emanate from every "+" point then bend towards and pass through the plane of the disk at 90 degrees, then continue bending to meet the "-" on the other side. There is an equipotential surface of zero potential throughout the plane of the disk so in this case it is true that no work is needed to bring a charge from infinity to the edge of the disk. Blooteuth (talk) 16:21, 24 May 2017 (UTC)

If the disk is finite, the answer is no. The field in the plane of the disk will not be zero and the field lines in the plane will be parallel to it. Ruslik_Zero 14:43, 25 May 2017 (UTC)

Table salt

Are all table salts made of sodium chloride? Or is sodium chloride the principal ingredient, mixed with other compounds for nutrition, either naturally or artificially? If hydrochloric acid and sodium hydroxide make water and table salt, then can that be placed in soup and still be safe to drink? 140.254.70.33 (talk) 16:54, 24 May 2017 (UTC)

From Salt#Edible_salt: Salt is used in many cuisines around the world, and is often found in salt shakers on diners' eating tables for their personal use on food. Salt is also an ingredient in many manufactured foodstuffs. Table salt is a refined salt containing about 97 to 99 percent sodium chloride.[35][36][37] Usually, anticaking agents such as sodium aluminosilicate or magnesium carbonate are added to make it free-flowing. Iodized salt, containing potassium iodide, is widely available. Additional info follows regarding more specialized salts such as fortified (which has various other additives), sea salt (which contains other salts), Himalayan salt (which has additional content), etc. Iapetus (talk) 17:13, 24 May 2017 (UTC)

[Edit Conflict] Searching for Table salt on Wikipedia would have redirected you to Salt#Edible salt, which should mostly answer your first two questions.

I will leave the last question for others with greater chemical knowledge to address (with the caveat that the formulae described in introductory chemistry textbooks are often idealised, and ignore all sorts of minor side reactions that can produce other products in lesser quantities). I would ask, however, why anyone would want to go to the additional bother of obtaining these reagents and performing the reaction, as table salt itself is in the modern world plentifully available and cheap? {The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 17:15, 24 May 2017 (UTC)

Chemical equations suggest that the equations go back and forth. But that depends on the speed of the reverse reaction. HCl and NaOH are both strong acid and base, respectively. So, they are supposed to dissolve completely. In that case, the H+ and OH- will bind and may form more water molecules. And the Na+ and Cl- will bind and may form salt, which dissolves in water. I wonder if the finished product will taste like salt water. 140.254.70.33 (talk) 17:32, 24 May 2017 (UTC)

You'd better be damned sure you're exact on your amounts. If you're off by 1 part in a thousand in either direction, your solution will taste shockingly sour or soapy. The behavior of a neutralization reaction is quite sensitive near the equivalence point. --Jayron32 17:35, 24 May 2017 (UTC)

Will adding a buffer help? What kind of buffer is non-toxic? Can one use pig blood purchased from a grocery store? 140.254.70.33 (talk) 17:55, 24 May 2017 (UTC)

If you're making black pudding. --Jayron32 19:58, 24 May 2017 (UTC)

Also, while you can make NaCl + H2O from HCl and NaOH, you'd better premix it outside your soup, otherwise either or both reagents will react with soup stuff (tm) causing probably undesirable results. But we did the basic experiment in chemistry class - you use a titration pipette and a indicator strip to get close to neutral. Our teacher made us taste the result (salty, as expected). But he also had us make nitroglycerin and managed to put a permanent stain on the ceiling of the lab with a piece of metallic potassium causing an unexpectedly vigorous reaction. And we got to distill (bad) wine into (worse) brandy, with surprisingly low yield... --Stephan Schulz (talk) 17:51, 24 May 2017 (UTC)

The proposed in-soup reaction is

HCl_(aq) + Na(OH)_(aq) → H₂O + NaCl_(aq)

In this reaction both the sodium and chloride ions are spectators as the neutralization reaction,

H⁺ + OH⁻ → H₂O

does not involve them, but since it is exothermic it will help keep the soup warm. Blooteuth (talk) 19:28, 24 May 2017 (UTC)

I wouldn't try it unless you knew that your starting chemicals were food grade. Industrial chemicals can have some nasty impurities. shoy (reactions) 19:26, 24 May 2017 (UTC)

Table salt consisting of mainly potassium salts also exists. But note that salt in the way we use it is poisonous, had we not used salt since thousands of years then the FDA would never have approved its use in foods, not even a fraction of a gram of it. It would only have been used as drug to deal with water poisoning and perhaps some complications due to using diuretics. Count Iblis (talk) 22:25, 24 May 2017 (UTC)

I think deer are known to lick the underwear of unsuspecting campers for salt content. I think some animals lick rocks for salt. Are you suggesting that humans should lick rocks for salt? Or are you suggesting that humans should get sodium elsewhere - celery or pig's blood? 140.254.70.33 (talk) 22:42, 24 May 2017 (UTC)

Iblis has idiosyncratic beliefs about diet and nutrition, which he will gladly attempt to "prove" by cherry-picking source (mostly pseudoscience) to prove. You can safely ignore anything he has to say on the matter, and instead refer to well established sources. --Jayron32 22:44, 24 May 2017 (UTC)

We do need a fair amount of salt. That could come from seafood, or we can add salt to other foods. This is a reasonable thing to do, so long as we keep the amounts reasonable. For a rough rule-of-thumb, the average person needs about 2000-2500 mg of sodium a day (there's debate on this, but this is the figure I will use) and about that many kilocalories, so foods should have roughly the same mg of sodium as kcals. Some may be a bit more, some a bit less, but if most of your food has many times as many mg of sodium as kcals, then that's too much. StuRat (talk) 23:04, 24 May 2017 (UTC)

That 2000-2500 mg is the upper limit above which you can already easily detect symptoms in healthy people, the recommendation is to not go above that, but somehow this has become a proxy for the RDA. Count Iblis (talk) 23:31, 24 May 2017 (UTC)

I cited a well established source (International journal of epidemiology published by Oxford Academic). So, while we do need salt, it's just about 50 milligrams per day even if you sweat a lot (if you only get 50 mg of salt a day your sweat won't contain much salt anymore). Animals in the wild have to do with what they can eat in the wild, and they may from time get a bit short on salt. These animals typically weigh a lot more than we do and they have not added any table salt in their food since they were born. The consequences of the "normal" amount of salt in our diet is that instead of a blood pressure of 100/60 that most Yanomami Indians have, we have blood pressures of 120/80 and instead of sticking to 100/60 well into old age like the Yanomami Indians do, the systolic blood pressure rises to 140, 160 and doctors will say that this is just the normal increase due to old age, leading to the "normal" consequences like heart attacks and strokes.

The recommendations by the IoM take into account the fact that it's difficult to give up bad habits, they make that explicitly clear and come up with advice on how to reduce salt intake. But you can't take such high end advice as a substitute for the hard facts in the scientific literature. It's similar to the difference between what was known about smoking in the late 19th century and the medical advice at that time,

see here: "In the mid- to late-19th century, doctors determined that lip and tongue cancer rates were higher among smokers of pipes and cigars. Despite this link, major medical journals mocked those who opposed smoking. The Lancet, the leading journal of the time and still one of the most important medical journals in the world, wrote in 1879, “We have no sympathy with prejudices against … tobacco, used under proper restriction as to the time and amount of the consumption. ... A cigar when the mood and the circumstances are propitious [is] not only to be tolerated, but approved.” Moderation, not abstinence, was the order of the day." Count Iblis (talk) 23:18, 24 May 2017 (UTC)

I have to agree that the FDA, given the chance today, would not approve salt. The hip culinary crowd would make backyard stills to produce tasty illicit meat jerkies. Elite police squads would be formed to sniff these out with dogs, and the producers would start smuggling bags of the white powder. On TV you would read about multimillion dollar salt busts as cops stood proudly over the bags of captured material. Certain desert areas would be fenced off and mined, sea coasts would be wastelands patrolled by thugs with guns defending their turf from rival gangs. Occasional resorts for rich people, standing out among the crime, would feature kids swimming in the ocean, but if watchful lifeguards caught them swallowing they would get hauled off to jail for five years at a time. Meanwhile the TV shows would glorify the lifestyle of the salt eater and the massive cartels, with big stakes in the studios, would ensure that a salt cartel never really is defeated in any action movie, and whoever gets tempted to rob their precious white resources would always be suitably punished. None of this is even slightly more insane than the world we know. [User:Wnt|Wnt]] (talk) 11:30, 25 May 2017 (UTC)

@Wnt Condiment on a good story. Blooteuth (talk) 17:20, 25 May 2017 (UTC)

Oh, no, that's not the same thing. The situation in colonial India, pre-Gandhi, is what you get after the progressive "legalize, regulate, tax [and monopolize]" crowd finally, after many decades, realize their dream... Wnt (talk) 23:39, 25 May 2017 (UTC)

But given that it's allowed, a better strategy may be to create an anti-salt movement like the anti-gluten, anti-GM etc. movements. Count Iblis (talk) 00:27, 26 May 2017 (UTC)

does tb has cure?

does tb has cure? — Preceding unsigned comment added by 31.4.137.4 (talk) 21:00, 24 May 2017 (UTC)

If you mean Tuberculosis, then no. Mycobacterium tuberculosis is constantly evolving. There are Multiple-Drug Resistant Tuberculosis, as well as XDR Tuberculosis (extreme drug resistance). There is prevention, though. 140.254.70.33 (talk) 21:09, 24 May 2017 (UTC)

(edit conflict)

Tuberculosis is typically treated with a combination of antibiotics. However, this does not necessarily cure the disease as it tends to be very resistant to antibiotics.

See Tuberculosis#Management for more information.

ApLundell (talk) 21:11, 24 May 2017 (UTC)

There is also TB vaccine for prevention. 140.254.70.33 (talk) 21:21, 24 May 2017 (UTC)

The pessimism here seems exaggerated. While some very low cure rates have been cited, apparently considering everyone who is given a couple of pills, DOTS (Directly Observed Treatment, Short-Course) has been found to work roughly 60% of the time. Note that a Cochrane review [9] finds that the cure rate for people taking pills on their own is not actually significantly lower than that. And of course the failure of a single short-course treatment with a certain set of drugs doesn't guarantee that some other existing treatment won't kill the mycobacteria. Really, there aren't many bacterial infections where a course of antibiotics is guaranteed to work. Wnt (talk) 11:18, 25 May 2017 (UTC)

May 25

Can sea water be purified and made into fresh water?

There is more water than land on this planet, Earth. And yet, some people complain that there is not enough fresh water. Now, I know sea water is not drinkable. But, water can be purified by various ways - reverse osmosis, distillation, de-ionization, filtration. And water can be collected from the rain. Earth is a very watery planet. Humans already collect sea salt from the sea. Why not the water as well? 50.4.236.254 (talk) 01:23, 25 May 2017 (UTC)

1) It takes a lot of energy and/or expensive facilities to desalinate the water.

2) It takes money and infrastructure to distribute that water inland.

Collectively, the result is that rich nations can do this, but not poor nations. As for collecting rain, they do this, but it doesn't always rain in all places. Large cisterns are needed to survive multi-year droughts, and those aren't always practical. Then the flooding carries soil inland, where it can nourish plants there. StuRat (talk) 01:25, 25 May 2017 (UTC)

As for collecting rain, the problem is that it falls over a large area. So in many places the most efficient way to collect it is to let the water flow naturally into or over the ground until it reaches a river, which can then be dammed to create a reservoir. This is done in many places. (Added later: Obviously there are also many places where it won't work. For example, maybe the terrain is the wrong shape for the water to flow to a suitable location for a reservoir, or maybe the climate is so arid that the water evaporates before it can be collected.) --69.159.60.50 (talk) 21:55, 25 May 2017 (UTC)

Desalination of seawater / ocean water is actually pursued on a large scale in places where electric power is available but fresh water is scarce. Our desalination article describes the technological approaches used; in a nutshell, they are distillation and reverse osmosis, both of which the OP has already mentioned in the question. Here's a good list of Desalination facilities. --Dr Dima (talk) 03:06, 25 May 2017 (UTC)

There are two problems with water supply. One is that in some areas there just isn't enough to do everything that the people want to do with it. If they are rich enough, desalination is an option - though it is usually cheaper to pipe it in from further away. In other areas, there is plenty of water - but it isn't safe for people to drink. That is the real problem today - because it kills large numbers. Wymspen (talk) 14:08, 25 May 2017 (UTC)

• Reverse osmosis requires a pressure differential of about 50 psi, which we supply using pumps driven by electricity. But this pressure is equivalent to about 150 feet of rise. That means that desalinated seawater delivered to a town 150 feet above sea level is twice as expensive as that delivered to a town at sea level. So San Diego California may be able to use desalinisation but Reno cannot, even ignoring the cost of the pipeline. -Arch dude (talk) 15:41, 25 May 2017 (UTC)

Water purification is Wikipedia's article about large scale, municipal water purification. The article Desalination describes methods for extracting potable water from sea water. Blooteuth (talk) 16:37, 25 May 2017 (UTC)

You can extract pure water straight out of the atmosphere. The theoretically minimum energy required is then the Gibbs energy difference between the water vapor at the actual relative humidity r and at 100% relative humidity, which is -N k T Log(r) where N is the number of water molecules and T the ambient temperature. Count Iblis (talk) 22:04, 25 May 2017 (UTC)

Soil formation on the bank of the Nile river

Some time ago, I asked on the Humanities desk about the Fertile Crescent. The responders seemed more focused on rejecting the claim that the Fertile Crescent is a desert, even though I looked at the provided pictures and saw desert land. One person pointed out that the bank of the Nile river has soil and flooding, probably due to the seasonal tides, so it allows plant colonization. But, that still leaves a mystery for me. How can the Nile river bank be fertile while a sandy beach seems so barren? How is the soil formed in the first place, thereby allowing plant colonization on land? 50.4.236.254 (talk) 01:32, 25 May 2017 (UTC)

Plants have a lot to do with it. Many plants can't take salt-water, so don't grow on ocean beaches. Also, the major waves and tides on ocean beaches are rough on plants. But river banks tend to be more gentle, allowing plants to grow roots there, which then retain the soil which would otherwise wash downstream. StuRat (talk) 01:54, 25 May 2017 (UTC)

If you want some additional reading on the Nile, Wikipedia has an article titled Flooding of the Nile which is sadly a bit brief, but hints at some importance including the deposition of silt from upstream sources, an important source of nutrients. The Wikipedia article titled Ancient Egyptian agriculture has more information. This brief article from the Smithsonian Institution also discusses the importance of the nutrient-rich silt carried by the Nile from volcanic sources further south. This article at Britannica discusses the Nile Valley soil formation in more details. this book hints at the importance of fresh alluvium from the Nile inundations. This article is a rather detailed survey of modern Egyptian agriculture, with a focus on the soils of Egypt. If you really wanted to get detailed on the soil science this paper looks like a good launching point. I hope some of that reading helps explain things. --Jayron32 03:41, 25 May 2017 (UTC)

This makes me happy. :) 50.4.236.254 (talk) 04:27, 25 May 2017 (UTC)

How did the common people come to define "organic" to mean "without pesticides"?

There was one time when I asked my chemistry instructor about the meaning of the term, "organic". He said, "comes from life". I didn't get it, because then I wondered whether my fruits and vegetables in my refrigerator and on my table were "organic". They came from life, so I figured they must be organic. Later, I found out that "organic" meant "without pesticides". How did the common people come up with this definition? In terms of agriculture, if a large conventional farm borrows "organic" farming practices for better environmental management and increased yield, then has the farm suddenly changed into an "organic farm"? And in terms of pesticides, are large herbivores (deer, rabbits) considered "pests" too? The farm basically grows a lot of food intended for human consumption. But, given that the plants occupy a significant amount of land, and that the plants are edible, it stands to reason that hungry deer and rabbits and field mice would happily munch on the plants, reducing yield. Also, these large pests are vertebrate mammals, so they may be very phylogenetically related to humans, making it harder to treat by pesticide poisoning. I mean, they may be killed, but if a poison intends to kill them, the poison can also kill humans due to the shared biology. 50.4.236.254 (talk) 04:54, 25 May 2017 (UTC)

Organic in the broader biological sense and organic in the Organic food culture sense are not related. It's like how when real doctors use the word "medicine," it's a very different word from when homeopaths use the term. You can read more about the disadvantages of organic farming in our article on the subject. Ian.thomson (talk) 05:01, 25 May 2017 (UTC)

There's a significant flaw in that article: the word "recent". First it's undefined, a weasel-word. Second, this concept has been around for well over 50 years. It was referenced in a Stan Freberg recording called The United States of America Volume One: The Early Years - a satirical history recorded in 1961, in which he has an Indian trying to persuade Columbus to eat some "organically grown vegetables." The casual use of that term indicates it was well-established by 1961. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:26, 25 May 2017 (UTC)

EO says the meaning "free from pesticides and fertilizers" dates to at least 1942.[10] ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:28, 25 May 2017 (UTC)

Organic does not mean without pesticides. See Organic farming#Pesticides. Pesticides used in organic farming can have additional safety concerns, as it is prohibited to process them from their "natural" state to be safer. 91.155.195.247 (talk) 05:06, 25 May 2017 (UTC)

• It is important to note that words, in different contexts, can have different meanings, and that is OK, and completely normal and how all languages, including English, works. So, in the context of Chemistry, organic means "chemistry of carbon"[11] and in the context of farming, it means "grown without the use of man-made chemicals or GMOs".[12] Some people get pissy about this, and I don't know why, because they can happily carry other words in their brains that have different meanings in different contexts. "Organic" is not special nor difficult in this regard. --Jayron32 12:47, 25 May 2017 (UTC)

Chemists worry about chemophobia, I think. shoy (reactions) 13:27, 25 May 2017 (UTC)

• Look at the history through the Soil Association. This goes back to WWII, their first certification for organic farms was in the mid '60s. Andy Dingley (talk) 13:17, 25 May 2017 (UTC)

• According to our organic food article, this usage was originated by Lord Northbourne in a 1939 book, based on his conception of "the farm as organism". Looie496 (talk) 13:54, 25 May 2017 (UTC)

• Think of "organic" as meaning "100% organic". So, if even a tiny portion of the chemical residue on the skin was made in a lab, that's not "organic". However, there are organic pesticides, like vinegar: [13]. Lab-produced pesticides have a history of being dangerous to people, however, with Round-up being the latest.

• Large herbivores can be kept out by non-chemical means, like fences, or dogs to chase birds away. StuRat (talk) 14:47, 25 May 2017 (UTC)

Thank you for giving me an opportunity to shit on a common chemophobic claim: "organic" pesticides can be toxic as well. See pyrethrin for example. Someguy1221 (talk) 06:48, 26 May 2017 (UTC)

That " as meaning "100% organic"" claim is sheer OR, matching neither the chemists' definition, nor the Soil Association's. Andy Dingley (talk) 15:55, 25 May 2017 (UTC)

This isn't about how chemists define organic, it's about how food consumers do. StuRat (talk) 16:23, 25 May 2017 (UTC)

The US Food and Drug Administration has a set of standards that define what can be labeled "organic" in the United States[14]. These standards have nothing to do with whether the product was treated with a substance "made in a lab". And yes, some synthetic pesticides are allowed on organically labeled food, as well as a variety of non-synthetic pesticides, some of which are quite dangerous to humans and/or damaging to the environment, such as boron, copper sulphate, and rotenone.[15] CodeTalker (talk) 22:12, 25 May 2017 (UTC)

The OP's question may be more suitable for the Languages reference desk. The chemistry teacher's answer "organic means comes from life" can be challenged in the case of Urea, an organic compound now synthesized from inorganic starting material. The common people did not come up with a definition of "organic" to be used as a marketing category for farm products that often carry a premium price or are less superficially attractive; this usage is agenda driven, see this outline. To be marketable as a Pesticide, a product ideally harms only small pests that cause harm and elicit no sympathy. For control of animals larger than an insect with which one might feel empathy, a humane person may prefer to employ an Animal repellent instead of a lethal biological agent that is predictably destructive to humans, their pets and the enviranment. Blooteuth (talk) 15:16, 25 May 2017 (UTC)

The OED has literally dozens of different senses of the word organic, many of them obsolete, but the OP might be interested in the definition for chemistry (first cite 1822): " Originally: relating to or designating compounds which exist naturally as constituents of living organisms or are formed from such substances (all of which contain carbon and hydrogen). Later: of, relating to, or designating any compounds of carbon (other than certain simple compounds such as oxides, carbides, carbonates, etc.), whether of biological or non-biological origin", and for farming (first cite 1942): " Of a method of farming or gardening: using no chemical fertilizers, pesticides, or other artificial chemicals. Also designating a farmer or gardener utilizing such a method, or a farm on which the method is employed.". Dbfirs 05:52, 26 May 2017 (UTC)

"Organic" refers to running the farm as an organism, where crops are rotated and animals are part of the system: cows help refresh fallow soil, chickens get rid of weeds and bugs, pigs dispose of waste. It is in contrast to specialized farming, where only one crop or animal is raised, hence the need for artificial fertilizers and pesticides. Organic standards limit the use of pesticides, which is one of the reasons people buy them, but not why they are called organic. TFD (talk) 06:27, 26 May 2017 (UTC)

Human size and power of blows, strikes, kicks

Is there an optimal average size for maximum striking power? The rationale is that although you'll need mass, maybe from a certain mass on your speed start going down. Would then someone be stronger but lighter due to this higher speed? --Hofhof (talk) 10:41, 25 May 2017 (UTC)

The evidence from boxing and shot-putting would I say indicate otherwise. Anyway do you really think anyone could stand up to being whacked by the tail of a whale? I guess there is a limit eventually but it must be pretty huge. Dmcq (talk) 11:33, 25 May 2017 (UTC)

Yes, but for the tail of a whale the rule still applies. Maybe other animals are much faster, even if less massive, and can hit harder. Many other factors also apply, starting by the fact that claws would be much more damaging than the smooth skin of a whale.

Where's the evidence from boxing and shot-putting? Has this been analyzed scientifically? AFAIK, the athletes are massive, but no one is like 400 pounds, which would prove my point. Hofhof (talk) 11:41, 25 May 2017 (UTC)

Sorry I didn't know you were trying to prove a point. Dmcq (talk) 12:20, 25 May 2017 (UTC)

I mean, it's a hypothesis, it can be refuted, or not. — Preceding unsigned comment added by Hofhof (talk • contribs) 13:41, 25 May 2017 (UTC)

We have had 400 pound wrestlers, even up to 800 (Happy Humphrey): [16]. However, if we move up to 1000 pounds, you have a point. The limits may be more due to them dealing with their own weight, than the relative effect of blows. At 1000 lbs the human body may be seriously injured by falls, and just moving around takes a huge effort. Of course, that's because the design of the human body doesn't support that type of weight well. Larger animals can manage that weight just fine. When fighting a much larger wrestler, the strategy should be to hit and run, and don't allow them to hit you or get hold of you. Just let them tire themselves out chasing you. StuRat (talk) 14:54, 25 May 2017 (UTC)

16 Psyche on earth

If 16 Psyche, the metal asteroid, was somehow to be gently brought to earth (not a giant crash), would the mass be enough to disturb the earth's orbit? What changes in position and duration would occur? -- SGBailey (talk) 13:54, 25 May 2017 (UTC)

• If we assume that the asteroid magically teleports onto the Sahara without any immediate change to the Earth's rotational motion except the added mass, none because mass does not matter for orbits (also, 16 Psyche has a negligible mass compared to the Sun's). On a fundamental level, this is linked with the equivalence principle (saying that the "mass" used for inertia in Newton's second law and for gravity in the gravitation law).

However, if the asteroid is somehow towed towards Earth, surely while it is in transit close to Earth it would attract it and hence modify its orbit. By how much would depend of how long the towing takes etc., though I would guess "not much". Tigraan^{Click here to contact me} 14:28, 25 May 2017 (UTC)

• Agreed. The Earth's mass is some 200,000 times more, so any effect would be minimal. StuRat (talk) 15:01, 25 May 2017 (UTC)

From our archives, I dug out: August 2012, "What If..."

“ We get this question a lot. If I may quote myself, from March of 2012, when I quoted myself from a similar question in September of 2011: (I have taken some liberties to modify the quote to increase relevance to the current question):

"The answer to this type of physics question always depends: how would [the asteroid magically transport to a position near Earth]? If you can specify that, we can follow through with the consequences by solving the equations of motion for the Earth-Moon[-Asteroid] system.

For example, if you hypothesize that a giant comet large and fast enough to change the [asteroid's orbital position] impacted [16 Psyche], .... well, we would need to calculate the effect that such a large comet has on the orbits of Earth and everything else in the solar system, too. We could solve that problem by setting up an n-body problem to model the solar system, including Earth, Moon, Sun, and other planets; and we would use perturbation theory to study how sensitively the system reacts when we add in a new comet on a course to impact the [asteroid]. The results are difficult to compute, but this can be done in a reasonable amount of time with a reasonable amount of effort.

...

On the other hand, if you just want to make something up, "just imagine" that the [asteroid] magically changes its [orbit], all bets are off. We can't meaningfully speculate what consequences follow when one law of physics breaks "because of magic." Anything could happen. Everything we know about the way the [asteroid] orbit couples into the Earth's rotation depends on the rules of physics as we currently understand them.

”

So - does that answer your question? Anything. Anything could happen.

You cannot magically transport mass from one point to another - in any circumstance, let alone in orbital mechanics. It takes a change in energy and momentum to change an orbit - even if the final position has no net motion relative to Earth, and even if the relative velocity exactly equals zero at the moment of contact with Earth. You have to do something to cause the energy and momentum of the asteroid to change; how you do so must be in compliance with these conservation laws, and how you do so would profoundly alter the outcome. The ensemble set of these conservation laws, ostensibly, constitute the single absolute most important-est and most inalienable part of our understanding of our physical universe. If you try to bend them for the purposes of the hypothetical, all you get is the principle of explosion - it is absolutely meaningless to proceed from a logical falsehood.

To put the absurdity of the original question in to terms that you might be able to explain to your kids: "Imagine that you knocked a brick off of the top of the roof of a very tall building, and the brick dropped down towards the ground. But, instead of falling down really fast and impacting the ground, the brick just remained stationary and rested on the ground and didn't move. (Not a giant crash). When it hits the ground, does the brick shatter on impact?" Yes? No? Use your imagination! The question asks about a situation that doesn't even make sense!

Nimur (talk) 15:06, 25 May 2017 (UTC)

If Asteroid mining ever becomes feasible, 16 Psyche is believed to contain 1.7×10¹⁹ kg of nickel–iron, which could supply the world production requirement for several million years. Planetary Resources and Deep Space Industries are companies that are attracting investors to their plans for asteroid exploitation though this speculative list of target asteroids does not include 16 Psyche. The proposal of towing that 200 km (120 mi) diameter body to a gentle (!) touchdown on Earth is so daunting that we can only consider an exploitation scenario where manageable amounts of ore are first extracted and processed on the asteroid before they are shipped to Earth. Long before change to Earth's orbit becomes evident, this activity would have political repercussions on Earth (now addressed by the UN Office for Outer Space Affairs) and likely alter the trajectories of other asteroids with unforseeable consequences. Blooteuth (talk) 16:23, 25 May 2017 (UTC)

I remember when you first posted that, Nimur. I liked it then and I like it now, but please note that the OP said nothing about magic; they only suggested that its landing be non-catastrophic, which brings up any number of real world possibilities that enable controlled descent (albeit difficult given the proposal). Matt Deres (talk) 16:29, 25 May 2017 (UTC)

Indeed - and if he were to precisely explain the mechanism of mass transference - by describing a collision, or explaining a rocket-powered scheme to change the trajectory of the planet - I would be very happy to start pointing to real and useful resources that would help explain the outcome! One of my favorite books is To Rise From Earth: An Easy-To-Understand Guide to Spaceflight, and it shows the reader how to set up the basic problems in orbital mechanics. That book is written for a technically-inclined, but non-rocket-scientist, audience.

I'm sort of keen on running the math myself to figure out how much energy you'd have to expend if you attached rockets and conducted a Hohmann-transfer for the entire asteroid. I'm sort of curious whether we're in the ballpark of the order of magnitudes achievable with chemical rockets, or if we'd really need to dive into deep science-fiction to make it happen.

Nimur (talk) 22:16, 25 May 2017 (UTC)

Even if by some Non-Magical Magic the 200 km sized object was to land on Earth with zero relative velocity, it would not stay still. Rather, it would collapse under its own weight: the max mountain height on Earth is on order of 10 km, because taller objects produce pressures at their base which exceed the pressure of elasto-plastic transition in the material. Two things will happen: (a) the object will collapse and spread out as a pancake, and (b) the continental crust will deform and sink and/or flow outwards from the location of the touchdown. This is a Bad Thing. Dr Dima (talk) 17:27, 25 May 2017 (UTC) Also of note, the continental crust average density is 2.7 g/cm3, about a third of the typical Fe-Ni alloy density. There is therefore a distinct possibility that some (or all) of the Psyche material will end up sinking straight into the Earth mantle and towards the core. Oops. Dr Dima (talk) 17:55, 25 May 2017 (UTC)

Agree that isn't good, nevertheless, for two-body problems Kepler's third law assumes M>>m, where here M is the Sun's mass and m is the Earth's mass, and this assumption holds true when 16 Psyche's mass is added as well. However, more precise and accurate models do not make that assumption such that both M and m affect their orbital period and separation. Solar mass M_☉ is about 332946 M_E (Earth mass) (I've a textbook that says about 300,000 times so StuRat is not too far off the mark above). Currently, our article on the Sun shows that we know the Sun's mass to within about one M_E, hence any simulations of this are not going to be able to include mass changes smaller than that. Still, I am certain that with conservation of angular momentum we can determine how much the year is shortened by some tiny amount even if it's not measurable. This is because bringing in an object from beyond the Earth's orbit increases it's angular speed (much like a skater spins faster when they pull their hands in) and so the interior orbital periods are shorter consequently and that any accretion of mass on Earth simply increases its gravitational acceleration towards the Earth's and Sun's common barycenter and that brings about a faster and tighter orbit (thereby conserving momentum too). This imaginary barycenter is the system's mass center which has to move closer to the Earth as their mass imbalance is reduced. Conservation of angular momentum for a mass m on a string of length r requires that mr^2T be some constant where T is the orbital period. Thus given this constant the new radius is r=sqrt(constant/mT) where m is the new mass and T the new period which is the parameter we want to solve for by eliminating r using the equation for two orbiting bodies (I already linked to it). To further simplify that work, note that we have to include the mass and momentum of the asteroid body as it nears us. So the net mass m cancels and we really only have r=sqrt(constant/T) for the constant (Tr^2). Also, one must assume a greater precision than we have for the Sun's mass (by appending a spherical cow of zeros beyond the current precision that we have) to get different mass totals, but we are not interested in their absolute values anyway, only the magnitude of relative change that occurs for these parameters. Disclaimer: @SGBailey: I'm not a physicist, but I did take this stuff in high school and college like decades ago... thus some of the things I learned have stuck with me more than others, but I hope this helps more thoroughly answer your question. -Modocc (talk) 21:47, 25 May 2017 (UTC)

@Dr Dima: I agree what you say is true, but ... well, a while ago I asked about mantle hotspots and learned that ordinary granite is a rheid. So I realize now to take some of these terms about plastic flow with a grain of... caution. When you say that the asteroid would collapse and cause the crust to buckle, are you talking about a geological timescale, or something more dramatic? Wnt (talk) 23:46, 25 May 2017 (UTC)

@Wnt: This is not really an appropriate place for original research, and I don't have solid literature to cite because the whole scenario is obviously hypothetical. However, since pressure wave travels at least with a speed of sound, the material near the point of contact between Psyche and Earth will start to yield within seconds if not faster. The whole of Psyche will then proceed in a nearly free fall for at least a while, until the pressure force produced by compression and heating of both crust and asteroid material will sufficiently exceed the Psyche weight to decelerate and stop the Psyche fall. This will be followed by a rebound, etc. I think. Dr Dima (talk) 01:27, 26 May 2017 (UTC) (To be clear, when I say "Psyche weight" and "Psyche fall" I don't at all imply that it will behave as a solid. Rather, it will behave more like a blob of liquid, given the pressure values produced). Dr Dima (talk) 01:32, 26 May 2017 (UTC)

BTW, here's another way to look at it. at 100 km above the surface of the Earth (which would be the initial position of Psyche's center of mass, as well as its equatorial plane), a potential energy of 1 kg of iron is mgh = 1 kg * 10 m/s2 * 100000 m = 1e6 Joules. This energy has to go somehwere as the iron falls down to Earth. Heat capacity of iron at room temperature is 444 J / kg K, and latent heat of fusion (melting) is about 1e5 J/kg; so assuming half the energy (5e5 J per 1 kg) goes into heating the iron and half goes into heating air and crust material, the temperature of the Psyche material will, on average, rise by over 1000 K. It will not all melt, but some of it will actually melt, and the rest will be rather unpleasantly hot for a while :) --Dr Dima (talk) 02:41, 26 May 2017 (UTC)

Can hormones be secreted by the endocrine system only?

or it's possible to secrete hormones by another way in the body17:10, 25 May 2017 (UTC) — Preceding unsigned comment added by 93.126.88.30 (talk)

Wikipedia is your friend. Please read endocrine system, juxtacrine signaling, paracrine signaling, autocrine signaling, neurotransmission, and neuromodulation. These articles address the many specific aspects of your question. --Dr Dima (talk) 17:43, 25 May 2017 (UTC)

Solar and lunar eclipse in Toronto

When was the last time that the City of Toronto observed the lunar and solar eclipses? Donmust90 (talk) 23:40, 25 May 2017 (UTC)Donmust90Donmust90 (talk) 23:40, 25 May 2017 (UTC)

You can work this out yourself by researching at Lists of solar eclipses and Lists of lunar eclipses. --Jayron32 00:39, 26 May 2017 (UTC)

Technically "never" as lunar and solar eclipses never happen at the same time. They are typically two weeks apart. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:47, 26 May 2017 (UTC)

At least! —Tamfang (talk) 08:07, 26 May 2017 (UTC)

May 26

Mammals that sexually mature later than humans?

What mammals reach sexual maturity later than human beings? I'm counting both the ability to sire/bear offspring and also having reached more or less adult size.Naraht (talk) 02:03, 26 May 2017 (UTC)

The elephant, for one. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 26 May 2017 (UTC)

Great White Sharks may be the latest, possibly as late as 26ish. --Jayron32 02:54, 26 May 2017 (UTC)

Except they're not mammals. But if that's the latest reproductive age of any creature, that puts a boundary around it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:00, 26 May 2017 (UTC)

I don't think elephants is the correct answer. The elephant article does not mention when they achieve sexual maturity but mentions musth, which is not the same thing. Unfortunately I am at work and our connection is very slow so I can view Google results and Wikipedia but not much else. So Google provided the following results when I put in Mammals that sexually mature later than humans and that seems to indicate that humans are the latest. The partial result for the Quora site looks interesting. Then using Google to ask Sexual maturity elephants gives interesting results with this looking good. But exactly CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 07:32, 26 May 2017 (UTC)

Exocrine system + endocrine system =?

What is the name for endocrine system + exocrine system? In another language that my friend speaks they are called "secretion system" but in English the term secretion system is different and it is about proteins in Gram-negative bacteria. 93.126.88.30 (talk) 08:08, 26 May 2017 (UTC)