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October 13

Do T3 and T4 hormones play role in regulation of the body temperature?

I know that they play role in stimulation of the metabolism rate, growth and development and brain maturation during fetal development. but my question is on the regulation of the body temperature. (I can understand that the metabolism rate relates in such way or another to the temperature) 93.126.88.30 (talk) 00:26, 13 October 2016 (UTC)

I had high hopes for the article Thermoregulation in humans, but it doesn't seem to go into that kind of detail. I didn't watch this video here: [1]. But the title has some potential to be useful. --Jayron32 02:00, 13 October 2016 (UTC)

Unfortunately there's no information there. but thank you for your motivation to help. 93.126.88.30 (talk) 17:44, 13 October 2016 (UTC)

Are follicles the structural units for all types of glands or just thyroid gland?

I am reading about the thyroid gland now and the book states: "Thyroid tissue is composed of follicles, which are structural units of the gland". It's not clear if it refers to any gland or to the thyroid only. According to what I read here (follicular cell) it seems to be in thyroid glands only, but I'm not sure about it. 93.126.88.30 (talk) 01:17, 13 October 2016 (UTC)

Have a look at Endocrine gland, all of them are linked and have a "structure" section. While I admit it's a little ambiguous, I think using "the gland" in the sentence indicates reference to the object, in this case "Thyroid", not "glands" in general. If instead follicular tissue was the substance all glands are made out of, the sentence would make a lot less sense. Vespine (talk) 01:26, 13 October 2016 (UTC)

Just analyzing the sentence, "units of the gland" means a specific gland, to me, while "units of a gland" or better yet "any gland", would have the more general meaning. StuRat (talk) 14:19, 13 October 2016 (UTC)

Google's dictionary says a follicle is "a small secretory cavity, sac, or gland, in particular." NOAD's definition is identical. Arnold's Glossary of anatomy [2] has a similarly broad definition, as does Wiktionary [3]. Our own article Follicle_(anatomy) gives the broad sense too. Ovary has follicles. Peyer's_patch is described as a follicle. Lymphatic_system says there are lymphoid follicles in tonsils.

These links show that the term 'follicle' has a general anatomical usage, and it is clear that glands other than thyroid have sub structures called follicles. I would not assert, based on this evidence, that all glands have substructures described as follicles. SemanticMantis (talk) 15:46, 13 October 2016 (UTC)

Anatomical usage is basically descriptive Latin. wikt:follicle from wikt:folliculus, a small wikt:follis. In common Late Latin, a follicle is a little sac, like the scrotum; in anatomy, the term has since been applied at the end of a microscope. Wnt (talk) 15:59, 13 October 2016 (UTC)

Just looked at this again and tried some random searches. "Mammary follicle", "Harderian follicle", "parotid follicle" basically strike out. "Pituitary follicle" and "prostatic follicle" hit on stuff. "Sebaceous follicle" is the gland. "Salivary follicle" hits really old literature, comparative anatomy. I'm not sure though how much difference is biological and how much is cultural, basically random chance of who uses what term (also Harderian is pretty obscure, but "lacrimal follicle" picks up only junk hits also). It would take a long time to think this one through properly. Wnt (talk) 22:28, 13 October 2016 (UTC)

That is consistent with some of my research as well. Another tack is to search each article in List of glands of the human_body to see which use the term. I noted a few that did, many that did not. It's hard to rule out linguistic/cultural trends in science. I don't think we have any actual physiologists or anatomists in the house, but I'd be happy to be proven wrong on that. SemanticMantis (talk) 14:28, 14 October 2016 (UTC)

Mortality during pregnancy

What happens when a pregnant woman dies during the middle of her pregnancy? What happens when a married man dies during the middle of his wife's pregnancy? GeoffreyT2000 (talk, contribs) 16:48, 13 October 2016 (UTC)

"What happens?" is very broad. Can you specify what aspects you are interested in? Life insurance may come into play in either scenario. Maternal death is our article about women who die during pregnancy. SemanticMantis (talk) 17:10, 13 October 2016 (UTC)

See en ventre sa mere for the legal implications in common-law jurisdictions of the second case. Tevildo (talk) 18:11, 13 October 2016 (UTC)

There is also Posthumous birth although it includes cases where the father isn't married to the mother, sometimes not even alive during conception. And in rare cases of the first, there is Coffin birth. Nil Einne (talk) 07:02, 14 October 2016 (UTC)

October 14

How long would electrons take to stop accelerating if homes used DC?

Drift velocity not field propagation velocity. Is this why AC has less resistive losses? (the electrons not getting that "fast" in 1/200th 1/100th or 1/240th 1/120th of a second) Sagittarian Milky Way (talk) 00:54, 14 October 2016 (UTC)

No, the average time between collisions is orders of magnitude shorter than the switching time of AC current. Dragons flight (talk) 01:27, 14 October 2016 (UTC)

So since the voltage hardly changes in the short time between the first and second collision after the current's on does that mean both collisions are about same speed, at least for the average electron? (luck at dodging atom centers and quantum mechanics and all that) Sagittarian Milky Way (talk) 02:09, 14 October 2016 (UTC)

As I understand it, the advantage of AC for long-distance transmission is that you can use a higher voltage; therefore you don't need as high a current to transmit the same power. (Power = voltage times current, but resistive power loss = resistance times the square of current).

So you may ask, why can you use a higher voltage? Well, theoretically, you could use just as high a voltage for DC transmission, but then what are you going to do when you want to power a house? Stepping down DC voltage is complicated and costly. For AC it's easy; you just use a transformer. --Trovatore (talk) 01:34, 14 October 2016 (UTC)

Ah, I did not know your penultimate sentence. I always guessed AC was to keep drift velocities down and they didn't exceed 60Hz to avoid needing gears for the generator. Sagittarian Milky Way (talk) 02:27, 14 October 2016 (UTC)

Also some further info can be found in HVDC converter. Vespine (talk) 04:11, 14 October 2016 (UTC)

See also War of Currents for the history of AC vs DC mains electricity. Tevildo (talk) 07:10, 14 October 2016 (UTC)

• Is this why AC has less resistive losses? No. Shameless self-promotion of a section I wrote: Electric_power_transmission#Advantage_of_high-voltage_power_transmission

If you are interested in those questions, you might also want to give a look at the skin effect, which is the reason why power cables everywhere have the same diameter (well, High-voltage cables are larger, but the extra section is not made of copper). Tigraan^{Click here to contact me} 07:40, 14 October 2016 (UTC)

The Drift velocity of electrons in wires is typically 1570 km/s (related to the Fermi energy concept in quantum mechanics). Please compare the values in bold as they relate to the OP's question. As derived in detail in the linked article[4]:

- 1A DC flowing in a small copper wire changes the electron velocity by 0.000 023 m/s. It's probable that the majority of electrons in a switch when it left the factory never move out of it throughout the life of the switch.

- Going from DC to AC means the change direction reverses 120 (US) or 100 (Europe) a second. Here the original electrons certainly never leave the switch or indeed any metallic conductors.

This may make it clear that electrons never "stop accelerating" and our use of them for electric power distribution has almost negligible effect on their individual paths.

Virtually all electronic equipment in the home, including the computer or phone you are using, uses DC supplies. Homes could be (have been) supplied by DC mains but AC distribution is universally preferred because of its advantages of low-cost voltage conversion by transformers, the possibility to balance generators and loads in a network by phase control, and other minor advantages in avoiding corrosion at connections between dissimilar metals, arc quenching and avoiding permanent magnetization.

The saving in cable weight by using a high voltage (low current) for long-distance distribution applies to both DC and AC. However AC conductors need more insulation to handle 41% higher peak voltage than DC for the same power level. The choice of AC frequency is a compromise between contradictory requirements.

Lower frequency	Higher frequency
More reliable rotating generators and converters	Smaller transformers for a given power  :-)
Negligible skin effect	Skin effect reduces effective cross section of conductors
Negligible power factor loss	Power factor effects require correction and over-dimensioning of generators and network components to handle extra reactive current
Negligible impact of cable capacitance	Cable capacitance hinders long-distance power transmission
Tolerable audio hum from transformers or interference from mains wiring to audio equipment	Increasingly noticeable noise from transformers (see Magnetostriction) and potential for man-made EMI

The main results of standardization are:

• Home distribution in Europe and Asia: 50 Hz
• Home distribution in USA: 60Hz
• Aircraft on-board power distribution: 400 Hz (for low weight)
• New long-distance high-power lines: DC (as new HVDC conversion equipment becomes economical). AllBestFaith (talk) 17:42, 14 October 2016 (UTC)

Magnetostriction, incidentally. Worth a redirect as a likely misspelling? Tevildo (talk) 18:28, 14 October 2016 (UTC)

Thank you for the correction. AllBestFaith (talk) 19:36, 14 October 2016 (UTC)

@AllBestFaith: Oh crap, nevermind. I should have read what you wrote... Wnt (talk) 20:44, 14 October 2016 (UTC)

• Add to the above table the fact that low-frequency AC produces visible flicker with some types of lighting. Some people can see flicker even with 50-60 Hz, I believe, but with the lower frequencies hat used to be used in some places it was more common. --69.159.61.230 (talk) 06:42, 16 October 2016 (UTC)

That is true if the power waveform is sinusoidal but not necessarily so if a trapezoidal waveform were chosen. AllBestFaith (talk) 13:52, 16 October 2016 (UTC)

• I think the common misconception as "electricity is the flow of electrons" is what is at heart of the misunderstandings here. Such misunderstandings come from MANY common misunderstanding of electrons as little, discretely identifiable little hard balls of negative change, bouncing around like ping pong balls. I'm not sure that level of misunderstanding is capable of being rectified in this scope of this discussion, so let's ignore it, and use the "little balls" model (wrong as it is) to show that even if we were to assume it correct, electricity is still not the movement of electrons. Electricity is the flow of energy through an electric field. Not a single one of the electrons actually has to carry the energy individually from one place to another. Even if we think of electrons (quite wrongly, but lets keep it for now) as little rigid balls; those little rigid balls don't travel down a wire as though they were marbles being rolled down a tube. Direct current is NOT all of the balls rolling down the tube in one direction, and alternating current is NOT all the little balls shaking back and forth, though some simplified models try to show it that way. Instead we should think about electrical energy being passed through a medium in the same manner that energy gets passed though the stationary ball in the roquet move in the game of croquet. See this video if you're unfamiliar. Notice how the red ball doesn't go anywhere and yet is able to transmit a bunch of energy to the blue ball. Electricity is like that: the electrons don't go anywhere in either AC or DC. They just "pass the energy" down the chain. Of course, that's still a very wrong way to think of electrons and electricity, but it's right enough to get us to reach the correct conclusion that electrons don't move. --Jayron32 18:49, 14 October 2016 (UTC)

  I think you're overstating this a bit, Jayron. Direct current in particular does involve flow of charge, and you can't have flow of charge without movement of charge carriers. If you take a line carrying one ampere, and pick an arbitrary point, one second later, there will be approximately six quintillion electrons to the right of that point, that were to the left of the point when you started. (That's a net figure; there could be electrons to the left of the point that were to the right when you started, but they count negatively.) --Trovatore (talk) 22:26, 14 October 2016 (UTC)

  Yes, you're probably right there; but the issue is that when we consider electrons as isolatable, individual particles with a clear identity, it introduces all sorts of problems with how physics works. Your statement also isn't strictly correct; it would imply a "hole" with six quintillion less electrons to the left of that point. Instead, what we know is that the electrons to the left of that point have lower potential energy than the ones to the right of that point. The problem is, you can't say that any specific 6 quintillion electrons actually moved; like if you painted them red and followed them with a little microscope. Electrons are not individually identifiable. To say that some arbitrary number of electrons moved implies you could say which ones moved and which ones didn't. It's not even a limit of our measuring capabilities, like we know that they are moving, but we just can't build a device capable of tracking them. We literally couldn't track them because the physics says we can't, per Heisenberg and all that jazz. Certain aspects of electron behavior imply movement and motion and mobility, so we have concepts like electron spin and electron mobility; the mathematical predictions of such concepts bears out fine, but considering electrons as discrete balls that can spin and travel around freely creates problems as well; if electrons were discrete balls, then we wouldn't have the contradictions of the double slit experiment and the like. --Jayron32 00:09, 15 October 2016 (UTC)

  Well, so we need to keep two aspects of the question separate, those being the classical picture, and the quantum weirdness.
  For the classical picture, the point about the "hole" is addressed by the fact that what we really have is a circuit. It's like a big hula hoop with sand inside, the sand being the electrons. For AC, the sand is sloshing back and forth, and energy is transmitted via the sloshing. For DC, the sand is moving in a consistent direction around the hoop, and that is how it transmits energy. Complications being that the energy is not transmitted via the kinetic energy of the particles, but rather via their interaction with the EM field; and that the particles are individually moving much faster than their collective drift.
  Now when you get to quantum weirdness, what you can do is think of each of the possible classical descriptions as being a single Feynman diagram, and then you take the path integral over all of them. --Trovatore (talk) 00:22, 15 October 2016 (UTC)

  Yes, but the problem is that "classical picture" doesn't represent what happens, because the classical picture makes too many inaccurate predictions about the behavior of electrons. Electrons as grains of sand we could track if we wanted to, but just can't be bothered to is still not the same thing as saying that electrons are not actually discretely identifiable particles. If one is taking a VERY long birds-eye view of electricity, the classical description works fine as a lie-to-children for broad behavior like Ohm's law. Once we start getting down to the small picture, however, and looking at what is going on with those electrons, the classical model is woefully inadequate. --Jayron32 00:48, 15 October 2016 (UTC)

  It's inadequate, but not on the question of whether electrons transmit energy by moving. They do transmit energy by moving. --Trovatore (talk) 01:03, 15 October 2016 (UTC)

  Which electrons moved? That's the problem. Saying "the electrons move" leads to the question "which ones moved and which ones stayed put?" Which is why we need the reminder that we can't identify individual electrons as such, and then say electrons move. We can say both "charge moves down the wire" and we can say "electrons carry the negative charge". The problem comes from the chain of thinking that says "this electron here moves over there..." as though that were a question that were even answerable. I agree with you that I was way too overzealous in speaking in absolutely, but the problem is that we really need to unask the question. QM causes such confusing leaps of logic, because our brains operate in a classical world. The same problem exists with considering electron spin. Electrons clearly behave as though they have spin; and yet if electrons are true point particles, then we have the geometric paradox that a point can't spin. Being able to work in quantum mechanics requires one to carry physical contradictions happily in one's brain. I guess I would have done best here to listen to David Mermin. "Shut up and calculate". --Jayron32 01:36, 15 October 2016 (UTC)

  We can do a little better than shutting up and calculating: the wavefunction of all the electrons in the system will have an observable momentum (directed around the circuit appropriately) even if the electron probability density is everywhere constant (in time). I'm not sure, however, if you can say, in a quantum-mechanically-correct way, what the drift speed of the electrons is (and thus how many are moving). --Tardis (talk) 15:21, 16 October 2016 (UTC)

Going back to the question "how long", this is determined by the inductance of the conductors. The current will not stop instantaneously, instead it will have some tendency to keep flowing into whatever load is on the wires. Our article will be hard to understand, but what you would have with a powerline, is a pair of parallel wires. You can expect that the current will stop on the order of several nanoseconds. If your try to stop it too fast, a high voltage will appear across what ever you try to stop it with, so for example flicking a switch or pulling out a plug may make a spark. Graeme Bartlett (talk) 22:53, 14 October 2016 (UTC)

This is correct and is a consequence of the fact that utility power transmission lines are not impedance matched transmission lines. An ideal matched line has uniformly distributed inductance and capacitance that together give it a characteristic impedance. It can successfully deliver a wideband waveform such as an abrupt on/off pulse to a load that has the same impedance. Near-ideal matched lines and loads are used throughout electronic circuits that handle high frequencies. The exactness of their match can be measured by TDR technique and expressed in SWR values at frequncies of interest. Matched power feeding is essential for, say, a radio Transmitter antenna but would be very impractical for utility power distribution. AllBestFaith (talk) 12:57, 15 October 2016 (UTC)

If we treat this as a high school level exercise where we pretend that Ohm's law is valid on any time scale (it only starts to be valid for time scales that are a bit larger than the typical collision time), we can argue as follows. Ohm's law says that the relation between the current and the drop in voltage $\Delta V$ across a piece of wire of resistance R is $\Delta V=IR$. The resistance R can be written as $R=\rho L/A$ where $\rho$ is the resistivity of the wire, L the length and A the cross-section. The current can be written as $I=-Anev$ where $n$ is the free electron number density, v the (average) velocity, and e the magnitude of the electron charge. We can then write the electric field E in the wire, given as the voltage drop divided by the length, as:

$E=-\rho nev$

The force exerted on an electron due to the applied voltage is thus given by:

$F=-eE=\rho ne^{2}v$

This is for a steady state situation where the electrons are moving at some constant average velocity. This means that the total force exerted in the electrons is zero, therefore there exists a friction force that is equal in magnitude but opposite in sign as the force due to the applied voltage. This friction force is thus given by:

$F_{f}=-\rho ne^{2}v$

it is caused by collisions of the electron with lattice vibrations and other electrons. If we suddenly cut the voltage, the friction force will still be there, slowing down the current. Newton's second law yields:

${\frac {dv}{dt}}=-{\frac {\rho ne^{2}}{m}}v$

where m is the electron mass. The current will thus decay on a time scale of

$\tau ={\frac {m}{\rho ne^{2}}}$

This is of the order of $10^{-14}s$ for copper, which is similar to the collision time. So, it will take somewhat longer than this time scale for the current to dissipate. Count Iblis (talk) 01:06, 17 October 2016 (UTC)

The Hydraulic analogy is sometimes used to help students grasp electronic processes (by letting fluid pumps / pipes / pressure / fluid flow / fluid volume / pipe constriction / rubber diaphragm stand in for electric generators / wires / voltage / current / charge / resistor / capacitor respectively) in an intuitive way but is clumsy when it represents an inductor. The exercise above interestingly gives a result that implies that the inertia of the electron mass gives every current flow in wire an inductor-like behaviour. The article Electric current explains the rôle of electrons as the charge carriers in metals. The suggested model of solid unmoving croquet balls is incompatible with modern understanding of the free-moving delocalized Valence electrons throughout the metal, that distinguish it from an insulator that has only bound electrons. AllBestFaith (talk) 18:59, 17 October 2016 (UTC)

The science behind how "Metanium" cream works

Please could you explain to me how the ingredients in "Metanium" cream actually treat nappy rash. According to this website the cream contains;

Titanium dioxide 20.0% w/w
Titanium peroxide 5.0% w/w
Titanium salicylate 3.0% w/w
Dimethicone 350
Light liquid paraffin
Tincture of benzoin
White soft paraffin

I am only interested in the scientific understanding of how the ingredients in this cream treat nappy rash. I believe this question is acceptable on the Reference Desk and does not contravene the medical advice prohibition because I am not asking for any diagnosis or treatment plan. To make absolutely clear, I do not have nappy rash and I am not asking this question in relation to any specific case of nappy rash that has ever existed. This is purely a scientific question.

ありがとう — Preceding unsigned comment added by 2A01:430:D:0:2CC:B0FF:FE9B:CC73 (talk) 12:57, 14 October 2016 (UTC)

Irritant diaper dermatitis#Treatments has some information. DMacks (talk) 13:08, 14 October 2016 (UTC)

"A review of the pathophysiology, prevention and treatment of irritant diaper dermatitis" [5] - seems to be a very comprehensive and relatively recent review, including titanium dioxide ointment treatments like the one you mentioned, mechanisms, and many further refs. It is unfortunately paywalled, I can provide a copy to interested readers upon request. Here [6] is a less comprehensive but freely accessible overview of topical agents in neonates. SemanticMantis (talk) 14:20, 14 October 2016 (UTC)

We currently redirect titanium peroxide to titanium oxide, but this seems invalid, as it apparently contains a true peroxide group. Actually, the combination of this peroxide + the organic chemicals in this mixture leaves me a little bit surprised it doesn't go boom... Wnt (talk) 15:57, 14 October 2016 (UTC)

10% benzoyl peroxide hasn't blown me up yet. The article says it can be explosive in pure form, but apparently diluting and mixing it with a base makes it safe, or else it presumably wouldn't be sold in every drugstore. I can definitely vouch for its bleaching effect though! Even a little bit of residue is great at bleaching all your towels. --47.138.165.200 (talk) 09:52, 15 October 2016 (UTC)

What's larger, follicle cell or parafollicle cell?

it's not clear to me if the follicle itself is cell or something which composed of many epithelial cells 93.126.88.30 (talk) 19:27, 14 October 2016 (UTC)

A follicle can be a single cell, a group of cells, or even a subpart of a cell. A follicle just means "little pocket", and the term can refer to any number of structures, its basically a description of a shape, not of a specific type of structure or functional part. --Jayron32 19:58, 14 October 2016 (UTC)

October 15

Would the world be in a worse state if we still relied on horse and cart?

Economically, environmentally etcetera? JoshMuirWikipedia (talk) 02:39, 15 October 2016 (UTC)

The use of cars is not allowed by any Old and New Order Amish who consider the rules of their church, particularly regarding rural life, manual labor and humility, to be consonant with a better world obedient to God's will. AllBestFaith (talk) 15:13, 15 October 2016 (UTC)

Sort of a general theme of economics is that making it cheaper for people to do something they already want to do allows them to spend more money on other things. This spurs demand, which spurs hiring, which increases the money available to buy things, which... so on and so forth. It's hard to say precisely how much economic damage would be caused by such a drastic change, but you could imagine a massive collapse of various businesses (caused by the vastly increased cost of travel) would cost jobs, incomes, tax revenues, charitable contributions, and government expenditures on lots of worthwhile things. So, potentially huge. As for environmental issues, horses are pretty awful for the environment, despite being "all natural" (well, so is oil). See for instance the great horse manure crisis of 1894. Someguy1221 (talk) 02:54, 15 October 2016 (UTC)

(edit conflict) Read this and this and this for some background on the environmental question. We of course cannot answer questions of opinion such as "better" or "worse". But those articles should help you become more informed so as to reach your own conclusions. Also consider that the transportation of people and goods by horses is of a smaller scale than other transportation methods, such as rail, air, and road vehicles. This article covers the amount of goods moved through one country (the United States) by road transport. One can drive across the U.S. in 3-4 days by automobile. According to this a horse can travel only about 100 miles in 24 hours under optimal conditions; it would take well over a month to cross the U.S. like that. Also according to This a horse can at best carry 300-400 pounds for at most 8 hours per day. You can extrapolate from these calculations what it would take to move goods around the U.S. solely by horse. Again, "worse" is for you to decide without us telling you. But I've probably given you enough references to make your own comparisons regarding economic differences between using horses vs. trucks for transporting goods; this also ignores rail and air contributions as well.--Jayron32 02:56, 15 October 2016 (UTC)

(edit conflict)I take that to mean you're excluding steam engines. Checking Google maps, it's roughly 1400 miles (2250 km) from Florida to Wisconsin. A horse and buggy gets maybe 6 miles/9.5 km per hour. A single horse with a rider might be able to travel 60-100 km (or 37-62 miles) during a maybe 12 hour period. Horses have to eat, sleep, and even get additional rest even when not sleeping; cars and trucks just need to refuel. It's not unreasonable to assume that a horse pulling a cart with cargo might only be able to safely travel six hours. Even if you had stations for switching off horses and drivers every six hours (and had the swap down to a science), it'd still take about five days to ship oranges from Florida to Wisconsin. That would be too expensive for (at most) a couple dozen crates of oranges though. So, most non-canned, non-pickled foods would have to be grown locally, which would increase malnutrition (if not outright starvation).

The Mississippi river flows about 1.2 miles per hour, and north to south, so it wouldn't help with oranges. Indeed, it would be useless for anything that can't wait a couple of months (assuming you're sailing and rowing as much as possible). An enterprising Wisconsin cheese manufacturer might use the ride to age his wax-sealed cheese, cutting down on production time. Otherwise, the river is useless without steam engines.

And it's about 1850 km (or about 1150 miles) from Valencia to London, which includes at least 33.3 km (20.7 mi) of sailing. It took about a week to sail from Tunis to Genoa, which (per Google maps) is just under 900 km (roughly 550 miles). So, premodern sailors could get about 125 km/75 miles per day on a good day. If the crew rotates shifts and the weather is good, they should be able to pull 5 km/3 miles per hour, making the English Channel a six or seven hour crossing at best (two days at worst). Again, assuming you have stations to switch horses and drivers every six hours, have the sailing crew rotate, and everything's down to a science, it's still just over a week to get a crate of oranges from Valencia to England.

Since uncut oranges can last just over a fortnight, the 1975 series Survivors might have been exaggerating when one of the characters surmised that none of their children would ever taste an orange; but it would certainly be an exotic, decadent, foreign luxury.

And those are the best case scenarios. Realistically, the land travel would probably take two to four times as long. Ian.thomson (talk) 03:55, 15 October 2016 (UTC)

No need for malnutrition. If you can't get your vitamin C from oranges, just eat apples instead. Vitamin pills might be a good idea, too. StuRat (talk) 17:20, 15 October 2016 (UTC)

We know how to travel upriver without steam power. It is slower than downstream but not impossible. Just ask any voyageur. Rmhermen (talk) 04:04, 15 October 2016 (UTC)

I knew about rowing, but figured that it'd be unfeasible over the couple thousand miles involved except for very light travelers (like Huck and Jim). The voyageur article's description of the dangers would (under modern legal conditions) render land travel preferable to that. That said, there were indeed trading posts up the Mississippi, though I expect they'd still have to restrict the goods to something more portable than crates of oranges. Though there does appear to have been plans for (if not actual use of) animal-driven paddle boats after all, so maybe not. No idea what the speed would be. Ian.thomson (talk) 05:20, 15 October 2016 (UTC)

If there were real canals, then animals could pull heavy boats. This used to happen in the Netherlands. Rivers would be too shallow on the edge and not have a track on the side for the horse/ox. One person would be needed to steer the boat, and another to make the animal pull. Graeme Bartlett (talk) 11:36, 15 October 2016 (UTC)

You might find this account of the 1894 great horse manure crisis in London of some interest - http://www.historic-uk.com/HistoryUK/HistoryofBritain/Great-Horse-Manure-Crisis-of-1894/ Wymspen (talk) 11:39, 15 October 2016 (UTC)

Bubbles on puddles

Why is it that when bubbles form on the surface of puddles during rain, this is considered a sign that the rain will continue? My personal hypothesis is that this indicates that dissolved air is coming out of the water, which is a sign that barometric pressure is still falling (and therefore that the low-pressure system bringing the rain is still on the way in) -- am I on to something here? 2601:646:8E01:7E0B:ADC2:429C:883B:48A1 (talk) 10:11, 15 October 2016 (UTC)

What is the basis of your first sentence? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:38, 15 October 2016 (UTC)

Yes, without commenting on the factuality either way, I can't say I've ever heard the expression. During a rainfall you're unlikely to see many bubbles just because the water in the puddles would be in constant motion. Or are you talking about during gaps in the rainfall? There are a number of factors that would influence the presence of bubbles, including pockets of air in the soil itself. Matt Deres (talk) 13:04, 15 October 2016 (UTC)

I think surface tension traps air under a canopy of water until the bubble bursts due to its own inherent instability. I think the formation of the bubble results from the impact of the raindrop on the surface of the puddle, displacing some water and momentarily trapping some air. Bus stop (talk) 15:32, 15 October 2016 (UTC)

Searching for bubbles puddles rain I find half a dozen totally non-reliable sources saying this is a genuine old wives' tale, right up there with the thing about red sky in the morning. As such, well, it has a fair chance of being true. Wnt (talk) 18:08, 15 October 2016 (UTC)

Feynman Lectures. Lecture 31. Sec. 31–2 The field due to the material [7]

I have understood everything except one phrase: "the driven motion of the electrons produced an extra wave which travels to the right (that is what the factor e^iω(t−z/c) says)"

I don't understand why does factor e^iω(t−z/c) say the wave travels to the right. Why not to the left (as we know that waves are source-symmetrical)? In the case of Sec. 31-2 the position z=0 is the glass plate (not the source S). So to use the shifts of the graphs E(t) and E(r) as proof we should assume where source is situated and in what direction the wave goes. But direction is what we have to prove. Besides it is written in Table 31–1 that z is perpendicular distance from the plate (so positive no matter in what point field is measured: to the left or to the right of the plate).

I understand that if the graph of E(t) is like this, then the graph of E(z) is like this in accordance with Fig. 29–2 and Fig. 29–3 and in accordance with rules of graph transformation (like with y=f(x) and y=f(-x)).

Can somebody explain how does factor e^iω(t−z/c) (or Cos[ω(t−z/c)]) prove that direction of wave is rightward? I feel the answer must be simple, but I reached a deadlock. Username160611000000 (talk) 11:51, 15 October 2016 (UTC)

• If the wave from accelerated electrons of the plate would be moving to the left then the factor would become e^iω(t+z/c). Is it correct? Username160611000000 (talk) 15:59, 15 October 2016 (UTC)

You're right that "waves are source-symmetrical" in that the general solution to the wave equation is symmetric. Particular solutions need not be; $e^{i\omega (t-z/c)}$ describes a right-moving wave because its surfaces of constant phase are $t-z/c=a$ for arbitrary a, or $z=c(t-a)=z_{0}+ct$ with a rephrased $z_{0}=-ca$. --Tardis (talk) 15:00, 16 October 2016 (UTC)

Magnesium sulphate and mineral water

Our article on Magnesium sulphate says "It is naturally present in some mineral waters" with a citation needed tag. Is it possible to state this? I know that magnesium ions and sulphate ions could be present in some mineral waters (those in the town of Bath, for example) - but it seems to me that, unless those are the only salt ions present, then the compound itself can't be said to be present. Is this correct?--Phil Holmes (talk) 12:05, 15 October 2016 (UTC)

IUPAC changed the spelling of sulphur/sulphate to sulfur/sulfate in 1980.
Sleigh (talk) 12:13, 15 October 2016 (UTC)

IUPAC has no authority whatsoever over the English language. (Given that they prefer the atrocious "aluminium", it's a good thing they don't.) --Trovatore (talk) 21:57, 15 October 2016 (UTC)

My English dictionary still says sulphur, so that's good enough for me. But can you answer my question?--Phil Holmes (talk) 12:41, 15 October 2016 (UTC)

@Sleigh: it was actually 1990[8]. DMacks (talk) 21:27, 15 October 2016 (UTC)

There are certainly quite a few Br⁻ anions in the sea, but we don't have much of a problem saying that there is common salt (NaCl) in it, right? Same principle. Double sharp (talk) 12:51, 15 October 2016 (UTC)

By extension, if the water has unusually high levels of both magnesium and sulfate but not of other ions, one could say "it has high levels of magnesium sulfate" because there's not any other obvious way it could have only these two being high. And likewise if there are lots of ions but those two are present in a 1:1 ratio and no other ion levels provide the correct ratio for this substance one could deconvolute the components. But you're right, that if you toss certain amounts of MgSO₄ into certain amounts of ocean water, you can't tell after the fact whether you added MgSO₄ to water containing NaCl vs adding MgCl₂ into water containing Na₂SO₄. DMacks (talk) 21:21, 15 October 2016 (UTC)

Mission to Europa

In April 2016 issue of Astronomy, a popular magazine, there is a feature article: "FINALLY. The historic journey to Europa." Europa is a Jupiter satellite of course. They say on page 25 that it will be a flyby mission with 45 revolutions around the moon only because the craft will eventually be destroyed by a powerful electron wind emanating from Jupiter. My questions are: (1) If there is a stable wind of electrons that means that Jupiter must be strongly positively charged and that charge must keep increasing. Is it what's happening? The second question is: (2) "What is the origin of those electrons? Thanks, --AboutFace 22 (talk) 16:32, 15 October 2016 (UTC)

We have an article about the mission at Europa Multiple-Flyby Mission (not sure it needs italicizing, but it is in the article) which leads to Magnetosphere of Jupiter, a featured article all about the topic of your question. Give those a look and come on back if there's anything that's still unclear. Matt Deres (talk) 16:36, 15 October 2016 (UTC)

I've put a note on the article talk page about the italics. The name is apparently rather controversial. Tevildo (talk) 14:16, 16 October 2016 (UTC)

(ec)Could it be that electrons move away from Jupiter at that location, but move towards Jupiter at other locations, in an equal amount, guiding by the Jovian magnetic field ? The other possibility is that the electron wind is in orbit, neither leaving nor hitting the planet. The actual answer may be a bit of both. (Hopefully Matt's links answer these follow-up Q's.) StuRat (talk) 16:42, 15 October 2016 (UTC)

The electrons are trapped in the same way as they trapped in Earth's radiation belts: they gyrate around the magnetic field lines while cyclically moving along the lines up and down out the equatorial plane. The word "wind" is a misnomer. Ruslik_Zero 18:55, 15 October 2016 (UTC)

Loudspeaker's size and weigh

Does a good loudspeaker, one that has deep basses and precise high frequencies, have to be heavy and bulky?--Llaanngg (talk) 17:00, 15 October 2016 (UTC)

As far as the bass goes, yes. To reproduce the lowest bass frequencies at a reasonable volume you have to move a lot of air, which means a cone with a large diameter and a long excursion, and the box itself has to be large and rigid. You can lighten it a bit with neodymium magnets and using plywood instead of heavier particle board, but that only helps some.

One good way around this is to use high-quality headphones. I highly recommend the Audio-technica ATH-M50. --Guy Macon (talk) 17:21, 15 October 2016 (UTC)

There are expensive systems that have good bass and small size, such as this one from Bose: [9]. But, there are limits, which is why built-in speakers on even high-end flat-screen TVs often sound horrid. The solution, if you don't need much volume, is a good 2.1 plug-in speaker system (right, left, and subwoofer speakers), which can give you decent bass for like $30. StuRat (talk) 17:24, 15 October 2016 (UTC)

• No, but it has to be stiff. Unless you have a supply of unobtainium, the necessary stiffness has usually been achieved (as this is the cheapest way) by using materials that are heavy and bulky. In a few cases, esoteric materials (mostly carbon fibre composites) have been used to produce lightweight bass speakers - often as horns (although most horns are used as mid-range drivers, large horns can handle bass). Bose speaker systems have tried this, using cheap injection moulded plastics and marketing. WP used to have a lot more on Bose, but it was deleted during one of the religious wars. So it goes.

A bass speaker will still have to be large though.

Headphones are a little different. The frequency response of eardrums are themselves limited, so much of the low frequency comes from bone conduction. This allows headphones to achieve a useful bass performance, despite the limits of their small drivers. Andy Dingley (talk) 19:15, 15 October 2016 (UTC)

Wait, unobtainium is a term? I routinely use (the French version of) unfoundablium, and thought I was pretty witty to be the first to come up with the term. Tigraan^{Click here to contact me} 17:48, 16 October 2016 (UTC)

It was the goal in the sci-fi Avatar (2009 film). StuRat (talk) 22:51, 16 October 2016 (UTC)

"Unobtainium, n. A substance having the exact high test properties required for a piece of hardware or other item of use, but not obtainable either because it theoretically cannot exist or because technology is insufficiently advanced to produce it. Humorous or ironical." -- Interim Glossary, Aero-Space Terms, 1958, Air University of the US Air Force. --Guy Macon (talk) 00:32, 17 October 2016 (UTC)

Blood tests

When you look at your blood test results, which is the specific blood test that would indicate concerns for high cholesterol? Which is the specific blood test that would indicate concerns for diabetes? And are these specific tests usually included in the CBC (Complete Blood Count)? Or are they ordered specially and individually? Thanks. Joseph A. Spadaro (talk) 19:19, 15 October 2016 (UTC)

Cholesterol is tested using a Lipid profile. Diabetes is tested for by using Glycated hemoglobin levels. Neither is included in a Complete blood count, and will be requested specifically. Of course, to discuss the results of a particular blood test, or if you're worried about your health, you should consult an appropriate professional. Tevildo (talk) 19:49, 15 October 2016 (UTC)

At least in the U.S., they generally only order a glycated hemoglobin test if you have elevated glucose levels. Glucose level is part of the basic metabolic panel, which in turn seems to be part of the standard tests most doctors order. To the original poster, if you are having tests ordered for yourself, your doctor or other practitioner will probably answer any questions you might have. --47.138.165.200 (talk) 03:52, 16 October 2016 (UTC)

Thanks. I have had many CBC's in the past. I wanted to know if I would find anything in there. I guess the answer is "no", then? Joseph A. Spadaro (talk) 15:04, 16 October 2016 (UTC)

We do have an article on the complete blood count. The CBC contains tests about hematologic parameters—the cells in the blood, including red blood cells, white blood cells, and platelets, and reveals information about their number and morphology. It doesn't include tests of blood chemistry, like glucose or cholesterol.

It's fairly standard screening in the U.S. for an initial evaluation of a patient to include both a CBC and tests of blood chemistry. Though they are thus often ordered at the same time (under the theory of "we have to draw his blood anyway, why not get two tubes in one stick instead of doing them separately") they test different things. - Nunh-huh 20:31, 16 October 2016 (UTC)

Yes, thanks. I had assumed that a CBC was more encompassing than it apparently is. In my mind, the term "Complete Blood Count" always translated as "the generic blood tests that a doctor always orders about the most basic items". I guess I was wrong about that. Joseph A. Spadaro (talk) 03:14, 17 October 2016 (UTC)

How do you *spill* methyl mercaptan?

The L.A. Times just published an enraging story about a community (Eight Mile, Alabama) reported to have endured 8 years of stench affecting 1300 people from 500 gallons of spilled methyl mercaptan.

What's confusing me is that methyl mercaptan is a gas sold in pressurized cylinders. How do you spill it, and why didn't it rapidly volatilize?

This is somewhat interesting since I see that a cylinder of methyl mercaptan seems to go for $200-$300 [10], so for $10,000 a person could have fifty of them and (perhaps) build a "dirty bomb" that apparently can leave an entire community seeking long term evacuation. Wnt (talk) 20:31, 15 October 2016 (UTC)

Under pressure higher boiling point gases will liquefy. When spilt as a liquid, it would boil and cool down more. Perhaps there are also traces of less volatile mercaptans contaminating the original gas. These could stay around longer. Also methyl mercaptan could have reacted with ambient substances to make other longer lasting smelly sulfur compounds. One cylinder would disrupt a shopping centre but we don't want too many WP:BEANS.Graeme Bartlett (talk) 20:51, 15 October 2016 (UTC)

Also after reading the article, it claims to be in ground water. It could be stored underground for quite a while. Bacteria should be able to dispose of it if they can get oxygen. Face masks as seen in the protest will do nothing to stop the odor. Graeme Bartlett (talk) 21:00, 15 October 2016 (UTC)

From the article Wnt linked, I found Mobile Gas' FAQ website, explaining that their investigation discovered a line used to carry odorant was damaged by lightning. So there was a continuous source of new chemical flowing through that line - and leaking - over a potentially long period of time. The facts about total quantity and duration, it seems, are subject to some dispute - hence the scandalous story as reported by the Los Angeles Times' reporters.

The website of Mobile Gas links to the State of Alabama's document archive, which contains even more information on the history and facts of the incident as they are known to the state government.

To follow up on Wnt's other concerns: most sources conclude that methyl mercaptan isn't harmful in the very low doses that one normally expects to encounter - but this material safety data sheet published by Chevron Phillips does list toxicity hazards as part of the full safety information for the chemical. In sufficient quantities, this chemical - like almost any other - transgresses beyond nuisance to become a real hazard. Once again, because there is some dispute about quantities and durations of exposure, the community and the company seem to disagree about whether the case in Eight Mile, Alabama, was a mere nuisance or a true health-hazard.

But the same is true of many hazards: if a malicious group wanted to create nuisance or hazard, they could do so with many hazardous items that are freely available in the United States. On the spectrum of things to worry about, I'd say methyl mercaptan "dirty bombs" are low on the priorities list. Emergency responders would probably be able to handle such an event by following "normal" HAZMAT emergency procedures. I'm inclined to link again to caltrops - if an anarchic and malicious person wanted to harm a community, they could do tremendous damage using only a few dollars of parts and no special skills; this doesn't diminish the threat of "unique" chemical attacks, but it does demonstrate that difficulty-of-execution is not the primary barrier that prevents such antisocial behavior.

Nimur (talk) 20:54, 15 October 2016 (UTC)

Thanks for pointing out that link! I should feel guilty for not checking that link when I read the article, but I think the author should feel more guilty for not checking it when she wrote the article. It says "Mobile Gas purchases its mercaptan from a vendor whose product contains a combination of tert-Butyl mercaptan and Methyl ethyl sulfide." I still have to look these up, but tert-butyl sounds heavy and more liquid and stickier.... yeah, we have an article! The methyl boils at 6 C, but the tert-butyl boils at 62-65 C. So indeed it can be spilled as a liquid and can take much longer to evaporate. I see prices as low as allegedly $600 a metric ton, if I believe Alibaba -- then again, I'm not sure I believe anyone here. I mean, the simplest answer to the riddle of the stench is that somebody is lying about how much was leaked out of that line by several orders of magnitude... Wnt (talk) 03:21, 16 October 2016 (UTC)

The same way you spill helium: Really fast. Sagittarian Milky Way (talk) 03:43, 16 October 2016 (UTC)

To support Nimur's point [11] mentions cleanup of an accidental spill using soapy potassium permanganate soloution. It doesn't mention it lasting long term after that. Of course intentional contamination over a wide area may be more difficult. Still I'm not sure if the Eight Mile case is a good example since it sounds like there has been a lot of controversy over precisely what has happened and what's been done [12]. Note also that our Stink bomb article mentions US and Israeli law enforcement agencies and militaries developing devices for riot control and area denial weapons. It seems unlikely that they don't have a fair idea of the capabilities of weapons using these and far more hard to obtain chemicals. Perhaps Butyl isocyanide (admittedly also a fairly toxic compound) which is available here [13] but only in lab quantities. (But I haven't looked at industrial chemical suppliers.) The first source quotes a 1937 experience:

Butyl isocyanide proved to be so disagreeable to manipulate that none of its physical constants except boiling point were determined. Even when a hood with an extra forced draft was used, the odor pervaded the laboratory and adjoining rooms, deadening the sense of smell and producing in the operator, and in others, severe headaches and nausea which usually persisted for several days.

Nil Einne (talk) 07:05, 16 October 2016 (UTC)

Selenium and tellurium compounds might give these a run for the money, taking advantage of the periodically increasing stink down group VIB. Double sharp (talk) 07:41, 16 October 2016 (UTC)

A chemist of my acquaintance was contracted to make the flavouring for spring onion flavour crisps (scallion flavor potato chips). After making a batch he reported to his boss that it was a simple enough synthesis, and would generally have been worthwhile as a product. However the risk wasn't worth it - the chemical is such a powerful smell (like mercaptans) that if they'd ever spilled any, the clean-up would have been so difficult that it would have overwhelmed any profit they might ever have made from it. Andy Dingley (talk) 09:03, 16 October 2016 (UTC)

October 16

Radioactivity sucker

Is there such a device that can suck all the radioactivity out of something radio active. I just saw it on a science film?--86.187.171.5 (talk) 01:25, 16 October 2016 (UTC)

What was the name of the film? Ian.thomson (talk) 01:27, 16 October 2016 (UTC)

Usually you would have to do something like isotope separation. The time when you might be able to "suck" is when you remove radon, which is a gas. See radon mitigation. Nuclear reprocessing can be used if the radioactive substance is a different chemical element. Graeme Bartlett (talk) 02:01, 16 October 2016 (UTC)

Are you by any chance talking about X the Unknown, the article of which you edited prior to posting this question? If so, well, it's a science fiction film. There's a reason it's called that. --47.138.165.200 (talk) 03:58, 16 October 2016 (UTC)

Please keep in mind that not everything in a work of science-fiction is necessarily fiction, so it's legitimate to ask the question. However, I think Graeme has answered it already: basically, no, there isn't. --69.159.61.230 (talk) 06:47, 16 October 2016 (UTC)

• No. But most bulky things aren't themselves radioactive, they're contaminated with particles of something else that is. For soil around large nuclear accidents in particular, there has been success with methods as simple as cabbage growing. These absorb the contaminant metals and grow radioactive brassicas, which contain more of the contaminant (as a ratio) than the soil did, thus help to reduce the contamination in the soil. The vegetables can be picked and disposed of in one place.

If the base material is a liquid, with a contaminant dispersed in it, then separation techniques like chelation can help in a similar way. Andy Dingley (talk) 08:58, 16 October 2016 (UTC)

The sizes of hot particles encountered will vary by means of distribution (and with distance from the source). Particles from a fire, such as that at Chernobyl, entering the global environment, are of the order of 1 μm (ref), which is the same range as ordinary combustion-product contaminants (see the chart in the particulates article). Concomitantly the number of such particles will be in the billions, and only some wholesale process like Andy's brassicas (yay, another reason not to eat cauliflower) will address the issue. But where the particles are large (and distributed by a means like water, or just being ejected by an event like an explosion) there may be few enough (and each particle large enough) to make individual detection and removal practical. This is the case for the effluent from the Dounreay facility in Scotland. It may have shed 5,000 particles, each the size of a grain of sand, into the local marine environment(ref). Those particles, hundreds of times bigger than the aerosolised contaminants from Chernobyl or Fukushima, seem to be staying mostly in the environs of the Dounreay plant. SEPA routinely searches the local beaches for particles, and if it finds one it individually removes it - they've done this about 200 times so far. I imagine (but I can't find sources) that the areas around major disasters like Chernobyl will have a ring of such particles - outside the visible debris area, but with larger (and thus much more dangerous) particles than the airborne ones - and presumably watercourses will have carried these kind of particles away, better than the wind could have done. -- Finlay McWalter··–·Talk 12:55, 16 October 2016 (UTC)

Radioactivity is the continuous process of atoms emitting particles and energy as they decay, see Radioactive decay. It is impossible to predict when a particular atom will decay. One can only characterize a material by its Half-life which is the time for 50% of any large number of its atoms to decay. Materials are known with half-lives ranging from years to fractions of a second for unstable isotopes made in the laboratory, but there is no device that can change the half-life of a given material. An important use of a known half-life is in dating once-living carbon-containing remains by their relative content of carbon-14 whose half-life is 5,730 years. The answer to the OP is that there is no such device for a given material, but there are many ways and devices to carry out Decontamination which includes the physical removal of radioactive substance(s) by methods and devices as basic as a Vacuum cleaner. AllBestFaith (talk) 13:25, 16 October 2016 (UTC)

Isn't it possible to increase the radioactivity of a given sample of radioactive material e.g. by subjecting it to a neutron source or, with some materials, a Neutron moderator? Fission rate is controlled and adjusted in nuclear power plants and bombs. Could an object be made less radioactive in the future by encouraging fission in it now? Preferably so we don't create transuranics or other nastiness.

There is a fictional thing called nuclear damper but that is science fiction. 91.155.195.247 (talk) 14:27, 16 October 2016 (UTC)

See Nuclear_transmutation#Artificial_transmutation_of_nuclear_waste. Fgf10 (talk) 16:22, 16 October 2016 (UTC)

I see this bird in Catford

| Does anyone know what species this bird is? Sorry if it's grainy, but hopefully you can identify it as that's the only photo of that bird I have on my computer._ CyanoTex (talk) 12:02, 16 October 2016 (UTC)

RSPB bird identifier suggests (with me guessing some of the info) a Wryneck [14], but with other possibilities including a starling. -- Finlay McWalter··–·Talk 12:28, 16 October 2016 (UTC)

*| Hmm. I'll see if I can get a more polished picture when the weekend's over. Description: Small bird when next to a pigeon. Black and yellow (more like a golden shade) color scheme. Beak looks more or less medium sized and perhaps of medium thickness._ CyanoTex (talk) 13:35, 16 October 2016 (UTC)

Almost certainly a Common starling (the wryneck is much smaller than a pigeon). See, in particular File:Sturnus vulgaris no.JPG. Tevildo (talk) 14:09, 16 October 2016 (UTC)

I do a bit of bird watching here in the UK. I think it is either a Song thrush or a Mistle thrush. Note the breast patterning. DrChrissy ^(talk) 15:18, 16 October 2016 (UTC)

I still think a starling is more likely - the thrush has a pale breast with dark spots, while a starling (and the OP's bird) has a dark breast with pale spots. A photo of the bird's head would probably be decisive. Tevildo (talk) 15:47, 16 October 2016 (UTC)

The OP describes it as "black and yellow" - that would be a very unusual starling as they are black, sometimes with spots (hence the name "starling"). DrChrissy ^(talk) 16:08, 16 October 2016 (UTC)

I concur that a Common starling is quite likely. At this time of year they are moulting (I was greatly puzzled when I first saw one close up in this state), and additionally the juveniles look somewhat different to the adults – see the first photo in the Description section of the article (already linked above), bearing in mind that there can be some individual variation. {the poster formerly known as 87.81.230.195} 90.197.27.88 (talk) 17:10, 16 October 2016 (UTC)

I doubt it is a wryneck - according to our article, their toes are in the manner of woodpeckers', with two pointing backwards. Common starling is possible, but most are darker and shinier than that. Matt Deres (talk) 13:21, 16 October 2016 (UTC) (restoring comment deleted by CyanoTex). Matt Deres (talk) 19:13, 16 October 2016 (UTC)

* | It is a common starling! Huh. Thanks, Reference Desk._ CyanoTex (talk) 20:51, 16 October 2016 (UTC)

• In October? It's a starling. Andy Dingley (talk) 02:35, 17 October 2016 (UTC)

I'd like to see a bit of explanation there. I mean, I think of starlings as glossy, scruffy, purplish or greenish even, while this seems softer. Its underside is practically a zebra stripe, as much white as black, and it even seems like there's a sort of a whitish band across the back. I understand an immature starling is browner, but usually very visibly speckled white on black though yes some are lighter. Can people comment on subspecies or point to some similar images for reference? Wnt (talk) 11:08, 17 October 2016 (UTC)

Cf. this one. N.b. the brown-edged, black secondaries. "There is more genetic variation between common starling populations than between nominate common starling and spotless starling". As explained at common starling, there is *tons* of genetic variation here, and subspecies are far from being unequivocally defined. Keep in mind we're not only talking juvenile/mature changes and subspecies changes in plumage, we're also right in the middle of molting time, and that creates a lot of varied looks too. Sure, it could in principle perhaps be a funny-looking example of some other bird. But OP shows us a photo that looks much like one of the most common urban birds in the world, and it's probably that. SemanticMantis (talk) 15:12, 17 October 2016 (UTC)

Perhaps it is a leucistic individual. That could explain the white band on the neck. DrChrissy ^(talk) 17:29, 17 October 2016 (UTC)

The image is blurry, but from what I can make out, there appears simply to be three exposed white feathers, with black ones underneath these,y because this bird's head feathers are raised on account of it preening feathers on its chest. --Modocc (talk) 17:50, 17 October 2016 (UTC)

What are the grid fins on Shenzhou for?

Soyuz, with grid fins for the launch abort system
(Photo from the grid fin article)

These photos: https://twitter.com/AJ_FI/status/787725451238207488

seem to show Grid fin not covered in the Shenzhou (spacecraft) articles.

What are they for? Hcobb (talk) 19:15, 16 October 2016 (UTC)

They've been a feature of Soyuz since the 1960s(?), although were covered by fairings until the mid 1970s (removed to lose unnecessary weight). They're part of the launch abort system. Andy Dingley (talk) 19:54, 16 October 2016 (UTC)

Are there more species which go on two legs permanently like human being?

I'm not talking about kenguru which is not really goes on two legs only as human being does. The same thing about bears. 93.126.88.30 (talk) 19:38, 16 October 2016 (UTC)

See our article on bipedalism. ---Sluzzelin talk 19:42, 16 October 2016 (UTC)

E/c Birds. We have an article on Bipedalism. DrChrissy ^(talk) 19:43, 16 October 2016 (UTC)

Sasquatch--Aspro (talk) 20:05, 16 October 2016 (UTC)

I'd like to know from the OP why they think Kangaroos do not move on two legs are you talking about the gait, i.e kangaroos hop whereas humans walk? DrChrissy ^(talk) 20:17, 16 October 2016 (UTC)

ok, actually I meant to ask about mammals rather than birds. Kengero use a lot in their frontal legs. 176.100.5.242 (talk) 21:09, 16 October 2016 (UTC)

If you look at articles on kangaroos, they almost all classify them as bipedal. Don't forget, humans sometimes crawl using our front limbs, especially as children. DrChrissy ^(talk) 21:13, 16 October 2016 (UTC)

I believe the general view is that kangaroos are bipedal while moving fast (by hopping), but pentapedal when grazing or moving slow. See our articles (including Macropodidae and Tripod stance) and [15] Nil Einne (talk) 01:55, 17 October 2016 (UTC)

That's got me thinking (and yes, before anybody else says it – I know I should refrain from this bad habit). Apollo lunanoughts could put on foot in front of the other when walking slow but to move quickly, they found hopping was better -due to the inflexibility of an inflated space suit. Now: although they weighed only 1/6 of what they would have done on Earth, their 'mass' was the same and so was the mass of the very heavy life-support system which was on their backs. Look at the mass distribution on a 'roo and compare it with a lunanought. Looks to me about the same. Harrison Schmitt seemed to spend a lot of his time quadrupedal ( I am of that certain age when I was able to watch hours of telecasts live from de moon) Apollo 17 EVAs 10 (Schmitt falls again) . His actions are more like a slow motion rendition, of a holiday-maker in Cornwall, with a heavy backpack of tent and camping gear, looking for where he dropped his spectacles after drinking too much scrumpy. --Aspro (talk) 18:03, 17 October 2016 (UTC)

Hopping in low gravity gets around the problem of low friction between the bottom of the foot and the ground. It isn't simply due to the heavy and/or inflexible suit. You can think of walking in low gravity to be similar to walking on ice. Because you fall slowly, it is easier to hop, avoiding a slip, and then quickly adjust your stance when you land. I doubt that Kangaroos have any issues with ground friction. 209.149.113.4 (talk) 18:10, 17 October 2016 (UTC)

October 17

Medical, hydrocell

Hydrocell,its origin and treatment — Preceding unsigned comment added by 116.68.82.248 (talk) 07:03, 17 October 2016 (UTC)

Do you mean hydrocele? If so, please read that article and let us know if you have specific questions. Rojomoke (talk) 07:27, 17 October 2016 (UTC)