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April 14

How do I know that the municipal water supply is safe?

I always boil water in a kettle, because that's what I've been taught. I think my parents have a habit of doing that, because they used to live in a developing country where parasites were a major concern, and the habit stuck. Also, somehow boiled water tastes better than unboiled tap water. But I've read that in a developed country, there may be toxins, like arsenic, in the water supply. Okay, fine. Am I doomed? Or maybe I am safe as long as my liver is functional? 50.4.236.254 (talk) 02:33, 14 April 2017 (UTC)[reply]

Doomed? No, not unless you've noticed that the rest of your town is suddenly really quiet.

But some municipal water supplies are not as clean as they're supposed to be. Flint Michigan was recently in the news for the Flint_water_crisis.

Where I used to live the water department was required to send everybody in town a letter every year to inform us that the levels of something or the other were very slightly higher than the legal limit.

As a point of interest, many beverages you buy at the store (Soda, bottled water, etc) are often made with tap water. Sometimes lightly filtered for taste, sometimes not. ApLundell (talk) 02:43, 14 April 2017 (UTC)[reply]

And where I live now, the town is required to test the water annually for about a hundred different things, and mail the results to everyone... not just if the results are abnormal, but normal as well. - Nunh-huh 05:15, 14 April 2017 (UTC)[reply]

I once did a lab in school about the water purity. Ultrapure water is used in extremely sensitive lab equipments, but the water is not drinkable. 50.4.236.254 (talk) 02:54, 14 April 2017 (UTC)[reply]

^{[citation needed]} -- I personally drank ultrapure water twice (once because I was very thirsty and had nothing else to drink, once just for the hell of it), and while it tastes very flat, it's quite drinkable. 2601:646:8E01:7E0B:E123:F0BB:BC27:2FB0 (talk) 04:31, 14 April 2017 (UTC)[reply]

I agree with the citation needed. This guy also tried it [1]. Note that video presents the claim ultrapure water is dangerous because it's too pure and therefore risk significant mineral leaching from the body something quite a lot of sources seem to suggest, but I personally find it unlikely this will be a problem. I couldn't find a great source discussion the issue but if you focus on the people with some evidence they know what they're talking about, these discussions come to a similar conclusion. [2] [3] (which links to [4] while dealing with deionised water which may have its own problems but it also dismisses the too pure claim.) This is only a risk if you're drinking quantities of water which are already getting up there in terms of danger. While these are mostly talking about general mineral content, I don't see a reason to assume the loss of minerals from any particular area would be sufficient to to be a concern. Storing the water in a container long term may however be risky depending on the container. (A copper one for example.) Nil Einne (talk) 11:24, 14 April 2017 (UTC)[reply]

Drinking ultrapure water can only leach minerals if that's the majority of what you drink, not just a one time thing. And only then if somehow you're happening to avoid deficiency based on the accidental concentration of a mineral in the drinking water that you aren't getting in food, which is extraordinarily unlikely. That said, it's important to bear in mind that a typical ultrapure system is designed around being reliably ultrapure the vast majority of the time ... rather than being absolutely safe all of the time. There's a risk that someone decided to clean and disinfect the system with something (I know they do that) and by mistake and bad luck now you're getting that in your water, for example. Wnt (talk) 19:32, 14 April 2017 (UTC)[reply]

You have to understand relative risks. The risk of bacteria or parasites in the water supply in a third world country is a serious one, as millions of people die each year from water-borne infectious disease. The risk of arsenic and lead in the water supply in developed nations is extremely low, by comparison. Even when contamination occurs, as in Flint, it's not at a level that's likely to kill anyone (they did have deadly Legionnaires' disease contamination, too, but boiling the water should handle that). Also, water filters can remove many of those toxins, so, if you're concerned, you can use those. StuRat (talk) 03:29, 14 April 2017 (UTC)[reply]

In developed counties there are, at least, controls on what is allowed in the water piped into your home. In developing countries there may well be similar mineral toxins in water: it depends on the local geology, and the route the water has taken between falling as rain and ending up in your home. However, there will probably be no testing of the water. Boiling kills the bugs - but does nothing about the minerals. Most filters won't deal with anything in solution either. Wymspen (talk) 18:05, 14 April 2017 (UTC)[reply]

Well, I think my liver has the job of detoxifying the body of toxins. But if the toxins still manage to seep through, then I'd be doomed. 50.4.236.254 (talk) 15:12, 15 April 2017 (UTC)[reply]

If your liver fails, you're doomed no matter what you drink. Many of the toxins the liver handles are waste products of other bodily functions. You can't avoid "toxins". You MAKE them. ApLundell (talk) 15:26, 15 April 2017 (UTC)[reply]

Fine. Whatever my body can handle is good. I'm still betting on a functional liver. 50.4.236.254 (talk) 16:48, 15 April 2017 (UTC)[reply]

Some other recommendations for safe tap water:

1) Let the water run for a while before you drink it. You can use this water to wash dishes, fill watering cans, etc. Most of the bad stuff in the pipes is washed out this way.

2) Pour water into a covered glass container and put it in the fridge overnight, before drinking. This allows the chlorine compounds to outgas, and the fridge temp prevents things from growing in it after it loses the chlorine.

3) Look at and smell the water before drinking. It may be cloudy at first, especially if there's an aerator on the faucet, but it should be clear and odor-free after step 2. If it's a strange color, cloudy, or smells bad, don't drink it. Note that while some things, like lead, can't be tasted, the same conditions which cause lead pipes to leach also tend to cause iron pipes to rust, and this rust you can see and taste. StuRat (talk) 16:57, 15 April 2017 (UTC)[reply]

I'm sure boiling water on the stove can allow the chlorine to outgas as well. Also, warm water can dissolve compounds better than cool water, so it is possible to dip some plant leaves or a lemon wedge in the water. Though, the ability of a compound to dissolve in water may depend on the compound's own chemical polarity. Oil is nonpolar. It does not mix with water. I think life's always a gamble. 50.4.236.254 (talk) 17:28, 15 April 2017 (UTC)[reply]

Summer ice in Hobart?

Hobart#Climate tells me that January's record low is a few degrees above zero. However, our article on the Tasman Bridge disaster (which occurred in early January) claims that several people died because they were in cars that "hurtled over the edge into the icy river", and this claim (complete with the ice) is in the cited source. Does Hobart really have river ice in summer, even though below-freezing temperatures have never been recorded in January? Hobart's latitude is similar to that of North American cities such as Boston, Niagara Falls, Toronto, and Milwaukee; we never hear of ice in those cities in early July. Nyttend (talk) 03:24, 14 April 2017 (UTC)[reply]

"Icy" can just mean cold. StuRat (talk) 03:31, 14 April 2017 (UTC)[reply]

I suspect it does mean that here, but to really know whether there could be ice on the river, you'd need to check the temperatures at its source (in the Central Highlands of Tasmania), not only at Hobart. --76.71.6.254 (talk) 06:43, 14 April 2017 (UTC)[reply]

No there would not be ice there in summer, and not even in winter. The water there is salt water. It would be well above zero, but feels cold if suddenly immersed. Graeme Bartlett (talk) 12:23, 14 April 2017 (UTC)[reply]

If the picture showing the gap was taken within a short time of the bridge collapse, it's evident there was no ice in the water. But as others have said here, it's entirely possible the water was much colder than the air, and calling it "icy" might be a bit of dramatic license on the part of the author. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:16, 14 April 2017 (UTC)[reply]

The author's point might be that the river is unexpectedly cold because like many rivers it flows from a higher altitude. However, I presently have no idea how much cooler the Central Highlands (Tasmania) would be than the vicinity of Hobart. They say 700 m in River Derwent (Tasmania), which seems significant but well short of a typical snow line. Wnt (talk) 19:37, 14 April 2017 (UTC)[reply]

Actually, I just looked up and saw it can snow in the Central Highlands in summer (December and February) though apparently it is unexpected. The 700m figure for the river was misleading - the February story talked about elevations of 1100 m and above (the river per se is counted as being much lower than the highest peaks of the landscape). So the water might not be much better than ice cold, depending on conditions that day... That said, I just did a little sniffing around and found [5] to look up historical Australian weather data, which gives a table that in the days preceding this accident the minimum temperature at Hobart Airport was >10 C. [6] They also were high in late December 1974. Of course, that's not the mountaintop, but in the extreme weather events Hobart and Launceton were also cold. Wnt (talk) 21:44, 14 April 2017 (UTC)[reply]

Please note that the offending word, together with other hyperbole, has been removed from the article today. Alansplodge (talk) 21:34, 14 April 2017 (UTC)[reply]

Resolved

At what point is something "wild" or "domesticated"?

If a tomato plant is found in a sewer, then is this wild or domesticated? What happens if plants on a farm (blackberries, for example) interbreed with wild blackberries to produce some kind of hybrid? Is the hybrid wild or domesticated? And what about a community who finds a wild avocado tree in the forest and decides to plant the pits and then select for the best ones? 50.4.236.254 (talk) 12:48, 14 April 2017 (UTC)[reply]

Domesticated usually implies that the organism concerned has not only been physically controlled (penned, fenced and confined, etc.) but has had its breeding controlled over enough generations that it has evolved, by artificial selection, inheritable physical differences from its "wild" ancestors. Animals (and plants) actually taken from the wild or with very recent wild ancestors are not domesticated, but tamed: they may (if animals) behave differently from wild exampes of their species (like not attacking people on sight) but retain a wild physiology. Individuals or populations of previously domesticated animals (and plants) may also revert to the wild, evolve in non-human-desired ways, and become feral. There will always be borderline examples where the appropriate definitions may be difficult to decide. {The poster formerly known as 87.81.230.195} 90.217.249.244 (talk) 14:18, 14 April 2017 (UTC)[reply]

Hydrogen vehicles

Hydrogen vehicle#Internal combustion vehicle says the only exhaust product of hydrogen combustion is water vapour. Two questions:

(1) I am correct in assuming that the same is true of hydrogen fuel cells?

(2) Everything I've read about hydrogen cars implies or states that the water vapor emissions are benign. But do we know anything about the effects on local climate if, say, every car in a city is emitting water vapor in those quantities? Would the city's humidity be higher as a result? Would it get more rainfall? Anything else?

Thanks in advance. Loraof (talk) 16:53, 14 April 2017 (UTC)[reply]

2) Note that gasoline engines also theoretically produce just about 100% water vapor, but the reality is that they never burn quite cleanly, so you do get other things mixed in (I also suspect some unburned hydrogen would be released from a hydrogen engine, along with oil vapor, etc.). Therefore, the effects of water vapor released by every car are already known. It's not usually enough to affect the weather, but, in the right conditions (like a traffic jam with no wind and high relative humidity), it can create smog on the roads, which may impair visibility. (If it was pure water vapor, then it would just be fog.) StuRat (talk) 17:02, 14 April 2017 (UTC)[reply]

Okay, but isn't the amount of water vapor ejected per mile much higher for hydrogen vehicles than for gasoline vehicles, so the latter by itself would not give us a good idea of the effects, so the effects would have to be inferred based on meteorological models? Loraof (talk) 18:47, 14 April 2017 (UTC)[reply]

Think of how many gallons are in a gas tank. An equal weight of hydrogen would make a few times more water than that, but no more. (2 H (MW 1) react with 1 O (MW 16), i.e. it produces 9x the weight of water as there was hydrogen) I don't know how much hydrogen is in a hydrogen vehicle, but it is not more than a typical gas tank. Well, you know how many gallons go out of lawn sprinklers on dry days - a lot more than that gas tank. Also: Smog is not fog! That said, I think it is theoretically possible for a bad hydrogen engine to release some hydrogen peroxide; this would release much less energy than water and isn't very stable, but it's conceivable. Breathing enough hydrogen peroxide might be harmful, or it could abuse your hair - I can't imagine that really happening from a real engine but I don't know enough to prove it can't. Wnt (talk) 19:06, 14 April 2017 (UTC)[reply]

I thought my 2 links to smog and fog made it quite clear they were not the same. Also, you need to account for the weight of oxygen pulled from the air in gasoline engines, to do a fair comparison. StuRat (talk) 21:06, 14 April 2017 (UTC)[reply]

I was comparing the weight of water produced to the weight of a typical gas tank (and actually, I omitted the low density). It is true that gasoline ~= -CH2-, so to one significant figure 1 C (12) + 2H (2) + 3O (48) -> CO2 (44) + H2O (18), which shows you get a bit more than 1 gas tank's weight of water out of a gasoline engine, plus a bit over three times its weight of carbon dioxide. But that doesn't affect how much water is produced by the hydrogen engine, unless you want to subtract the tank's worth if it had been a gasoline car and make it a difference. Wnt (talk) 21:39, 14 April 2017 (UTC)[reply]

(Nitpick : The size of the tank is mostly irrelevant. People don't let tank size dictate their consumption. The exhaust-per-mile would be the relevant figure.) ApLundell (talk) 00:58, 15 April 2017 (UTC)[reply]

To answer part 1 of the question: Yes, a hydrogen fuel cell produces water. In fact, IIRC, proton exchange membrane fuel cells were used to provide both electricity and drinking water to astronauts in at least some Gemini missions. --Stephan Schulz (talk) 11:28, 15 April 2017 (UTC)[reply]

Almost all commercially available hydrogen is made from natural gas, so it is not carbon-free at the system level. A pure electric car's carbon use depends on where the electricity comes from. There are two types of hydrogen car: fuel cell and hydrogen IC. Hydrogen IC has some of the same problems as gasoline IC: (NO_xemissions and inefficient while idling) while fuel cells act more like batteries, except for the H₂O output. Gasoline, when used, creates water and carbon dioxide: 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O. It is unclear if the amount of water per joule is much less than for hydrogen. -Arch dude (talk) 03:33, 16 April 2017 (UTC)[reply]

Radio broadcast range and transmitter wattage

Please do not comment here There's a question at https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Miscellaneous#KCTV_.28Korean_Central_TV.29 that addresses the wattage of the transmitter and the range of transmission in terms of the invers square law. Comments regarding its accuracy would be helpful. Thanks. μηδείς (talk) 18:12, 14 April 2017 (UTC)[reply]

This has nothing to do with the question asked there. The question is: Why does the North Korean TV station KCTV only broadcast 8 hours a day? Akld guy (talk) 18:59, 14 April 2017 (UTC)[reply]

She wants a fact check of the claims made there, methinks. A fine use for the ref desk, IMO. Though the organizational aspects may be a bit debatable, one supposes the idea is to keep any criticisms or responses together with the original thread. SemanticMantis (talk) 19:29, 14 April 2017 (UTC)[reply]

The issue at Miscellaneous has been sidetracked into a discussion about radio wave propagation that has nothing to do with the question asked by the OP. Asking readers here to comment there is not going to help the OP. It would have been better to open a question about propagation here and ask readers there to comment here. Akld guy (talk) 20:04, 14 April 2017 (UTC)[reply]

You don't need to comment Akld if you don't think you can help, and I have already been pointed by someone who would not have answered had I not asked here to the proper answer. I had it right in the first place, and someone pointed out the proper article to show that. I can't imagine what else one thinks the ref desks are for, other than getting the OP to the necessary article. This place is not a coliseum, but a collegium. μηδείς (talk) 23:44, 14 April 2017 (UTC)[reply]

Does that mean we are all κολέγιο τελειόφοιτος ? Was never any good at languages because it came across as all Greek to me ; ¬ } Aspro (talk) 00:26, 15 April 2017 (UTC) [reply]

See the article Radio propagation. The Inverse-square law holds exactly for line-of-sight reception in free space. Since North Korea is not in free space, its radio and TV broadcasting is affected by the same phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering as that of every other country. Blooteuth (talk) 00:15, 15 April 2017 (UTC)[reply]

Another Australian weather thing

How were the New South Welshmen and the garrisons in Van Diemen's Land affected by the eruption of Mount Tambora? Since the first settlement of NSW occurred in 1770, presumably there's plenty of primary sourcing for 1810s events (diaries, church records, etc.), and History of Tasmania indicates that the first Tasmanians arrived a few years before the eruption, so I suppose that records might exist from this time period. And what about the Argentines and Chileans, the far southern Brazilians, and the Afrikaner settlements in the Cape Colony? Year Without a Summer, like everything else I ever remember reading, addresses the Northern Hemisphere, but I don't remember encountering anything about the volcano's effects on the Southern Hemisphere summers of 1815-1816 and 1816-1817. Nyttend (talk) 22:22, 14 April 2017 (UTC)[reply]

The first Tasmanians arrived some tens of thousands years before that eruption. --Shirt58 (talk) 03:06, 15 April 2017 (UTC)[reply]

At https://seasia.co/2017/04/08/a-blast-from-the-past-how-indonesian-volcano-changed-the-world there is a map showing the ash cloud (unreliable source) that only shows Western coast of Australia affected, so NSW and VDL are off the hook according to that. Graeme Bartlett (talk) 07:01, 15 April 2017 (UTC)[reply]

At https://www.mdba.gov.au/kid/files/2265-DroughtsInMDBsinceEuropeanSettlement1.pdf it claims weather on the east coast was wet and stormy due to Tambora. Graeme Bartlett (talk) 07:19, 15 April 2017 (UTC)[reply]

April 15

Radio propagation, part 2

Is it possible, in principle, for HF radio transmissions on a sky wave from a transmitter of the same power as that fitted to an Electra 10-E located at Gardner Island to be picked up on the 5th harmonic of the carrier frequency all the way over in St. Petersburg, FL? (Note that I am not asking whether Betty Klenck actually heard what she claimed to have heard, but only whether she could have received such broadcasts in principle.) 2601:646:8E01:7E0B:6D49:6960:EF64:7278 (talk) 04:21, 15 April 2017 (UTC)[reply]

A 15525 kHz signal might propagate that far if there is ionisation. The signal would not absorb too much in daylight, and there was probably daylight over most of the great circle path at the time to reflect down to earth. But you can try to find what is the great circle and what part is daytime, and what is post sunset. The worst time for propagation is around sunrise. The next issue is harmonic. An old transmitter back then could make a harmonic pretty easily, but it would be much weaker. A voice modulated signal would also be much harder to detect, but they probably used AM and a pure carrier might be more detectable. Morse code could also penetrate further. Lack of training is a serious issue for radios from this time, people could not just dial up a digital channel number or frequency. Several knobs would ahve to be optimally set. They probably did not even know exactly what frequency they were on! Graeme Bartlett (talk) 08:05, 15 April 2017 (UTC)[reply]

The great circle path is plotted on http://www.wolframalpha.com/input/?i=great+circle+St.+Petersburg,+Florida+to+Nikumaroro It is only a quater of the Earth and over water, so the whole would be in daylight and more likely possible at that frequency. If you want to explore further find the subspot number for the date, and then with that and date and time you can plot a map of highest useable frequency, and see if 15525 is below that along the path. Graeme Bartlett (talk) 08:14, 15 April 2017 (UTC)[reply]

Right, but the issue is, how much weaker would a 5th harmonic be than the carrier frequency? 2601:646:8E01:7E0B:6D49:6960:EF64:7278 (talk) 09:53, 15 April 2017 (UTC)[reply]

The only way to find that is to take a Measuring receiver (Spectrum analyzer) to a surviving Lockheed Model 10 Electra because the harmonic radiation depends on unspecified characteristics of the transmitter and aerial. This is a lead to a restored plane and here are mentioned other surviving planes e.g. in the National Air and Space Museum, Canada Aviation and Space Museum, New Zealand Museum of Transport and Technology and Science Museum, London. Blooteuth (talk) 13:05, 15 April 2017 (UTC)[reply]

So, no way to know for sure without testing? Thanks! 2601:646:8E01:7E0B:88C9:21D2:79C0:44A3 (talk) 01:13, 16 April 2017 (UTC)[reply]

The OP asks about whether a transmitter "of the same power"...[as the Earhart plane's radio]. So, first of all, let's establish that Earhart's transmitter had an output of fifty watts, as described here at the Tighar site. Akld guy (talk) 23:35, 15 April 2017 (UTC)[reply]

I see no further answers for some time, so I present the following hypothetical explanations. HF antennas on airplanes were grossly inefficient (far too short for the wavelength). Perversely, this meant enhanced performance at higher multiples of the fundamental transmitter frequency. At one of those higher multiples, the length may by chance have been near-optimum. There was normally suppression of the harmonics in transmitters due to antenna matching circuitry designed to optimize the amount of fundamental frequency power transfer to the antenna. Such suppression typically resulted in the 5th harmonic being 40dB down (one ten-thousandth of the power) relative to the power at the operating frequency, meaning that with her 50 watt transmitter there could have been 5 thousandths of a watt (5 mW) of 5th harmonic signal delivered to the antenna. Such low-powered signals from ground stations have been known, under very favorable atmospheric conditions, to span oceans. At great height, such as that of an airplane, with the antenna length happening to favour a harmonic, such a small signal could very well have travelled halfway around the world. So, yes, it is possible that a tiny amount of power and favourable antenna and atmospheric conditions could have resulted in the signal being heard in Florida. There is another explanation altogether, not related to your question: We are accustomed today to privacy in our continent-to-continent communications that use undersea cables and satellite links. "In 1927, radio-telephone communications opened on a 24 hour basis, US-UK. By 1949 there were 70 radio-telephone circuits for all 5 continents." - [information taken from an ITU Telecommunications textbook whose ISBN number I have lost]. If we assume that Earhart's radio signals were picked up at remote receiving stations and relayed via one of those public radio-telephone channels to the US control station, it's possible that the listener in Florida heard the relayed signal rather than the signal from Earhart direct. I apologise for the WP:OR nature of all this. I have a keen interest in 1930s-WW2 military aircraft radio equipment (AN/ARC-5 and SCR-183), am restoring several for use on amateur bands, and have experience in matching them into very short antennas. Akld guy (talk) 05:43, 16 April 2017 (UTC)[reply]

I see. And if the transmitter was at ground level, could the sky wave still have reached Florida? 2601:646:8E01:7E0B:4457:AEC3:D9F:5111 (talk) 06:57, 16 April 2017 (UTC)[reply]

Nothing can be discounted. But all sets of favourable circumstances would have had to come together at the very time when Earhart was lost. In my view, if her plane was on the ground on a remote island in the Pacific: - almost impossible that she was heard on her operating frequencies (on or near 3.105 or 6.210 MHz), highly unlikely that a harmonic of those was heard. For a very good analysis of the technical aspects and shortcomings of her radios, and bungling that may have occurred, see here. Akld guy (talk) 08:56, 16 April 2017 (UTC)[reply]

However there is a suspiscion that she did not know how to tune the antenna, so it might be more like 20dB down instead of 40, if it was tuned to the higher frequency. Graeme Bartlett (talk) 09:06, 16 April 2017 (UTC)[reply]

According to the reference in my first post, the transmitter was located in the aft section of the fuselage. She did not need to (and could not from the cockpit) tune the transmitter for maximum power. The only option she had was to change frequency (by turning a knob in the cockpit connected to the transmitter via a flexible cable like a car's speedo cable). The transmitter was already fixed tuned (before take-off) for each of the operating frequencies for the antenna specified. However, a possibly unauthorized modification of the antenna may have badly affected the pre-set tuning. Akld guy (talk) 09:22, 16 April 2017 (UTC)[reply]

Pressurised carbon dioxide cylinders

This question is about SodaStream, a home carbonation machine which uses cylinders of pressurised carbon dioxide.

Here in New Zealand, the "up to 30L of sparkling water", this is how they advertise them, gas cylinders provided by Sodastream have 270g of carbon dioxide per their own labelling. The "up to 60L of sparkling water" gas cylinders have 400g (not 2x270g=540g). This immediately seemed strange to me. The fact that the masses* in US (or I think much of the world) for the different size cylinders aren't in any way similar was another red flag. There the 130L cylinder has 935g/33oz of CO2, 60L has 410g/14.5oz much more similar to what you would expect and the 130L actually has a little more per volume of water. *Weights if you prefer, the distinction isn't relevant to this question I'm pretty sure.

I tried asking SodaStream about this [7] but the answer I received is I think irrelevant to my question. As far as I see, their reply only relates to the pressure and volume of carbon dioxide in their cylinders but that doesn't help me unless they give exact values for both cylinders in which case it may be possible to figure out an answer. All I care about, as I felt I indicated in my question, is how many bottles of sparking water I'm going to make from one cylinder, assuming I'm pressuring the water to the same level. The reasonable assumption is the 60L cylinders would give close to 2x the amount of sparkling water as a 30L cylinder but it seems likely it's not even close.

I believe this will depend on those factors Sodastream knows (but likely aren't public). If the internal volume of both cylinders is the same (i.e. they just pressurise carbon dioxide more), then there will be the same amount of "wasted" carbon dioxide when the cylinders are used up (carbon dioxide which is under too low pressure to be used for carbonation). Which means you have double with 2 30L cylinders being wasted compared to 1 60L. The 60L cylinder does seem quite a bit bigger but that could be (but is unlikely IMO) just thicker walls if it's under higher pressure, rather than a larger internal volume.

My questions to the RD are ~~1) Am I right SodaStream's answer is largely irrelevant to my question or have I missed something?~~ 2) Since I don't know how long it will take to get a decent answer from SodaStream, does anyone have any idea how likely it is that I will get anything close to 2x 30L with one 60L cylinder assuming the quoted masses of carbon dioxide are correct (and pressurising water to the same level)?

P.S. Can we try and keep this question ontopic, and not digress into SodaStream's reputation and ethics, using paintball or home brew cylinders instead, or the merit of carbonated water or soft drinks. Also although I've effectively linked to my real name, I'd appreciate it if people don't refer to it onwiki.

Nil Einne (talk) 05:18, 15 April 2017 (UTC)[reply]

I removed 1 as thinking about it more, I decided I was definitely correct and also realised the simplest way to respond to SodaStream. Also I guess the key question is how much carbon dioxide is actually wasted. If it only tends to be 30 g (random example), then I don't see how the 60L cylinders can come close. Nil Einne (talk) 10:57, 15 April 2017 (UTC)[reply]

I think the cylinders will be partially filled with liquid carbon dioxide with gaseous CO₂ filling the "void".[8] At 293.15 K (20.00 °C) this will require a pressure of 5,730 kilopascals (56.6 atm).[9] As the cylinder is used up a small amount of what is left of the liquid will evaporate to keep the gaseous space in the cylinder at the same pressure. Only when the liquid is all used up will the pressure drop (very rapidly). There is no point pressurising the cylinder higher because the liquid is just about incompressible and no more will fit in. If the two cylinders are about the same size (are you suggesting that they are?) all I can suppose is that one is roughly half full of liquid and the other is more nearly full. If so pretty much all of the CO₂ will be usable in both cylinders. In the light of this I have no idea of the relevance of the Sodastream reply. This makes me think I am wrong but this is a good place to find out! I think the amount of carbonated water you will be able to get will be very close to proportional to the weight of CO₂ in a cylinder. In the UK 425g CO₂ is supposed to treat "up to 60L".[10] Thincat (talk) 13:54, 15 April 2017 (UTC)[reply]

I now see Sodastream saying the pressure in a cylinder is 57.3 bars (5,730 kPa) at 20 C[11] so this confirms that we are dealing with liquid CO₂. Thincat (talk) 14:12, 15 April 2017 (UTC)[reply]

At 5730 kPa, 20 C, liquid CO₂ is 773.4 kg/m3 so a 1 litre volume (for example) would weigh 773 g; at 101 kPa (1 atmosphere) gaseous CO₂ is 1.84 kg/m3 so a 1 litre volume weighs 1.84 g.[12] That might be a rough guide to how much is "wasted". Thincat (talk) 15:35, 15 April 2017 (UTC)[reply]

Apologies my wording was unclear. I don't think the internal volume is the same, I actually suspect both cylinders start off at a similar level of pressurisation given the size of the "60L" looks like it could easily be double the "30L". However I also can't rule it out. (Of course the internal volume of the "60L" cylinder could be significantly smaller than the "30L" one but that's starting to be an extreme situation and it may not matter anyway.) Nil Einne (talk) 16:17, 15 April 2017 (UTC)[reply]

One obvious missing piece of info is that they don't quantify how carbonated the water will be. Thus, they can honestly say that the two cylinders will carbonate those respective amount of water, to some degree. The marketing people probably decided on the actual claims to make. The "up to" fudge further protects them. StuRat (talk) 14:03, 15 April 2017 (UTC)[reply]

I guess I should have added an additional clarification. I'm well aware their claim is unclear, hence why I took pains to stress "same level of carbonation" in my question to them. But whether or not they have justification due to the weasel wording used is something which is also besides the point of my question. (Such issues will be best dealt with the humanities or misc anyway.) Nil Einne (talk) 16:18, 15 April 2017 (UTC)[reply]

I'm not sure where all the facts here come from, and sometimes you have to double check to see if anything is misinterpreted. I found the sizes here but not the weight values. I found some support for 400 g in random places [13][14]. I could wish for a better source, but so far this is moderately confirmed - the second source says 400 g in 0.605 liter internal volume = 660 kg/m³ which falls right at the highest part of the two phase region at room temperature. Perhaps the two phases help to insulate against unexpected events (sudden dents/crushes)? Now the next question of course is what is carbonated water. This works according to Henry's law with a constant K_H = 29 L atm / mol. If we take 400 g / 60 liters that gives us 6.7 grams of CO2 per liter of soda. (I don't know why this doesn't line up with the carbonated water article's figure of 0.2-1.0%...) Divided by 12+16*2 = 44 gram/mol that is 0.15 moles of CO2. At STP that would take up 22.414 L per mole, per ideal gas law without correction anyway, so that's 3.4 liters of CO2 gas when depressurized. Anyway, in water we take 29 L atm / mol * (0.15 mol) / (1 L) = 4.35 atm. Apparently soda cans or bottles typically hold less than 3 atm of pressure [15]. But, as always, there's a bit of a catch: the CO2 isn't simply dissolving into water, but is in equilibrium with carbonic acid. ~~An acidic soda recipe (and how many aren't?) would presumably drive this reaction more toward the carbonic acid, bringing the CO2, however temporarily, out of the calculation for pressure.~~ That was gibberish, let me try again: CO2 in water is in equilibrium with carbonic acid; the carbonic acid is in equilibrium with bicarbonate and hydrogen ion. A more basic soda recipe (sorry) would take up hydrogen ion and allow carbonate to enter the solution. That said, the recipe shouldn't be all that basic because it would be easier to just put in a bit of acid or acidic buffer to avoid having to dissolve in extra CO2 at the end. FWIW a pure carbonated water would be in an equilibrium [H+][HCO3-]/[H2CO3] = 2.5E-4 M, i.e. the pKa1 is 3.6. So if there's nothing else in the soda and we suppose it's 0.15 M H2CO3, x^2/(0.15 M - x) = 2.5E-4M; x^2 + 2.5E-4M x - 0.15M*2.5E-4M = 0; x= (sqrt(2.5E-4M^2 + 4 * 0.15M*2.5E-4M) - 2.5E-4M)/2 = ... 0.006, which gives pH 2.22. The numbers check out, unless I did the wrong calculation. And it makes sense that pure carbonic acid should be well above the pKa, which is what the pH would be for a half-and-half mix of carbonic acid and carbonate. But this disagrees with this study finding higher pH figures and blaming citric acid, which has a pKa of 3.13. Hmmm... Wnt (talk) 19:17, 15 April 2017 (UTC)[reply]

Thanks for your reply. The weight or mass for NZ and Australian cylinders come from the cylinders and packaging themselves which I've seen and even have photos of. I'm lazy to dig these up but you can see them in these photos from the SodaStream website "30L" [16], "60L" [17].

The US/ROW cylinders are a little more complicated. You can see the "130L" cylinder here [18] [19] a little low resolution but the details can IMO be made out. But you can find third party retailer images that are clearer e.g. [20]. Unfortunately the SodaStream US websites images for the "60L" cylinder that I found don't show the relevant part. But you can find third party images for the "60L" cylinder, e.g. [21] [22] which do show the details. The SodaStream HK website also has the same details "130L" [23], "60L" [24].

Note that as implied by the SodaStream HK website, the cylinders in AU and NZ (possibly South Africa too since the cylinders I get generally mention South Africa, but I'm not sure) are different, at a minimum they have a different attachment. (This comes up when people to want to attach third party cylinders.) I have seen some odd cylinders like [25] which list a weight of 425g in UK/NZ/Australia and 400g in South Africa, but the cylinders I've seen in NZ aren't like that. In any case, while 425g makes a different, it's still not enough to make up for the difference from the "30L" ones by itself. (The "30L" don't seem to be available in the US or the UK or HK.)

Nil Einne (talk) 07:45, 16 April 2017 (UTC)[reply]

BTW, SodaStream devices can only make carbonated water. If you want soft drinks, you need to add syrup after the carbonation process. If you try to carbonate something besides water, I've heard you can get some quite spectaculate results, I think on the order of Mentos+Coke. I've never tried since amongst other things, I don't want to get sugar etc all through the SodaStream parts. Nil Einne (talk) 11:23, 16 April 2017 (UTC)[reply]

From experience, attempting to carbonate anything which has non-dissolved components (e.g. an emulsion or suspension) will result in the whole thing fizzing up spectacularly (and you having to explain to your parents why you are cleaning pineapple juice off the ceiling). Solutions are often OK, so long as they don't have a viscosity significantly different to water. MChesterMC (talk) 13:05, 18 April 2017 (UTC)[reply]

Physics, Overview of Halliday and Resnick

I want to find some clear comparative overview (maybe as a table) of all (or most) textbooks published by Halliday and Resnick (+Walter or Krane). How do they overlap regarding exercises, target readership, content and so on? --Hofhof (talk) 11:22, 15 April 2017 (UTC)[reply]

Here's a great review bibliography: Chicago Undergraduate Physics Bibliography. As its author states, this thorough book review was "written by snotty undergrads..." but the reviews are "useful at least, for their recommendations on what not to read."

More sincerely, just go grab the books and read their respective prefaces. Physics authors almost universally address their audience in the book preface: they outline what you should already know, what you should expect to learn, and how many hours, days, or months you might reasonably expect to spend with their book. For example, since I just cited Krane a few days ago, I have it handy: it has a wonderful front-piece with clearly-marked sections describing the audience, background, emphasis areas, ... "This work began as a collaborative attempt with David Halliday to revise and update the second edition of his classic text... This text is written primarily for an undergraduate audience, but could be used in introductory graduate surveys of nuclear physics as well. It can be used specifically for physics majors as part of a survey of modern physics, but could (with an appropriate selection of material) serve as an introductory course for other areas of nuclear science and technology, including nuclear chemistry, nuclear engineering, radiation biology, and nuclear medicine."

You will not find a more qualified person to explain the contents of such technical books than the book's own author and editor!

If you want a third-party review, you can search the specific author and text at, for example, APS: each APS newsletter usually contains a book review.

So what I'm getting at is, when you reach a certain level of study in physics - or anything else, like chemistry or even postmodernist deconstructive/reconstructive hermeneutics - the most important skill is to learn how to navigate knowledge within that knowledge domain. In complicated scientific fields, there is no better resource than the textbooks themselves; and as a secondary source, review articles in common industry or academic journals (like APS) can help point you toward the right books, papers, and websites. Learning how to use those resources, in itself, is a skill that is probably as important and as difficult as any of the specific mathematical techniques you pick up along the way. One of the greatest fallacies I see, repeated over and over and over again, is the misconception that you can just dive right in to the deep end of advanced physics without spending several years formally building toward it. It's a fallacy that is perpetuated by many of the lesser-quality popular-science writers who are driving their focus toward the community of science-enthusiasts who lack any actual scientific experience. That's just ... ridiculous! It's like asking how to run before you know how to walk. One can not, generally speaking, make headway learning nuclear physics until one has studied regular physics to a great deal of depth. Equally, one cannot read the original writings of Victor Hugo before one learns fluent and proficient use of French. That's how far off the mark we are. It does not matter if we link to the actual explanation in the very book you seek. By the time you are ready for us to cast our light on that explanation, you already know where to find it. As long as you are still lost looking for it, ... we can't help you find it - not even if we point right to it!

Nimur (talk) 17:04, 15 April 2017 (UTC)[reply]

Fantastic answer, thanks. Hofhof (talk) 17:15, 15 April 2017 (UTC)[reply]

Temporarily leaving a profession.

How easy is it to return to a profession like engineering if you temporarily leave it for a year to gain experience of another sector like business project management? 82.132.232.213 (talk) 15:37, 15 April 2017 (UTC)[reply]

Are you asking about a Career Break or a Sabbatical? Aspro (talk) 15:54, 15 April 2017 (UTC)[reply]

not really. Those are leaving to do something completely different. I more meant doing for example a project management role in a large business consultancy before returning to engineering, just to strengthen your general project management and business skills. 82.132.232.213 (talk) 16:02, 15 April 2017 (UTC)[reply]

I don't understand your issues with Aspro's suggestion. What you mean falls perfectly under the definition of sabbatical: " "sabbatical" has come to mean any extended absence in the career of an individual in order to achieve something. In the modern sense, one takes sabbatical typically to fulfill some goal". It's up to you to decide what goals you want to fulfill. Planning with care and getting feedback from your present and prospective employers might be advisable (see [26] for some literature about. --Hofhof (talk) 17:12, 15 April 2017 (UTC)[reply]

Suggestion: Find a place where you can be a working manager on an engineering project. That is, you would manage the project and work on it directly, as an engineer. That way you gain experience in both fields simultaneously. StuRat (talk) 16:10, 15 April 2017 (UTC)[reply]

The effect of taking a one-year break from an engineering profession depends on how much value is placed by employers on up-to-date competence. The best answer could come from someone working in the particular engineering discipline (chemical? electronic? mechanical? other?) if asked "Would it matter if all your experience of developments, components and methods were out of date by a year?". If you seek a job with a new employer, your lack of a recent relevant reference letter may also put you at a disadvantage against competing candidates. Blooteuth (talk) 19:12, 15 April 2017 (UTC)[reply]

Thank you for the answers all. There are many engineering opportunities in the organisation I want to join though in a business management role though. So maybe an internal transfer after a year or so would be easier. 82.132.232.213 (talk) 19:29, 15 April 2017 (UTC)[reply]

In my direct experience, dead easy. Not quite as easy if you want to return to your old job but I know people who have made an art-form of that as well. Perhaps on a simpler level I used to work with a contract drafty who used to work a contract for six months and then leave for a six month skiing holiday. If we had a job for him when he came back, great, if not he worked somewhere else. Greglocock (talk) 00:02, 16 April 2017 (UTC)[reply]

That's even worse. I can't imagine him gaining any applicable skills from skiing holidays to any job. I guess it depends on demand and supply too. 2A02:C7D:B95F:F700:D8F8:ECD8:94E7:FE66 (talk) 00:21, 16 April 2017 (UTC)[reply]

Given the well-documented "leaky pipeline" of women in STEM fields, there is quite a bit written about returning to e.g. engineering after a career break. Yes, engineers give birth too, and with evolving laws regarding maternity leave (and to a lesser extent paternity leave - both those phrases redirect to parental leave), companies have had to devise ways to re-integrate returning workers. The Women's Engineering Society talks about returning to work after children. Here's an article by the founder of Women Returners. The Society of Women Engineers suggests "6 Ways for Engineers to Update Skills after a Career Break". The Institute of Engineering and Technology offers advice on returning to work that doesn't mention parenthood; as is sometimes the case, changes aimed at benefitting one group can have a spill-over positive effect on another. Workers leave their profession for all sorts of reasons; smart employers look beyond the gap on the CV to see the skills the employee offers. Carbon Caryatid (talk) 16:44, 18 April 2017 (UTC)[reply]

Edible disinfectants ?

There's ethanol, but that's a bit hard to take in high enough concentrations to be effective. Any other options ? I'm asking as far as possible inclusion in mouthwash. Many contain hydrogen peroxide, but I'm not convinced that a concentration that would be effective won't cause burning there, either. StuRat (talk) 21:02, 15 April 2017 (UTC)[reply]

In principle, probably most any disinfectant, since the dose makes the poison, though many common ones wouldn't be that great for you to ingest in any sizable amount. Silver salts are one bet. Maybe thymol or lactic acid, as well. --OuroborosCobra (talk) 21:11, 15 April 2017 (UTC)[reply]

Doxycycline. Count Iblis (talk) 22:39, 15 April 2017 (UTC)[reply]

That's an antibiotic, not a disinfectant. Two different things. -Nunh-huh 02:11, 17 April 2017 (UTC)[reply]

Cetylpyridinium_chloride. SemanticMantis (talk) 23:13, 15 April 2017 (UTC)[reply]

And urine [27]. SemanticMantis (talk) 23:21, 15 April 2017 (UTC)[reply]

If the use is primarily as a mouthwash, the list gets quite wide. Chlorhexidine gluconate is a common one, and I find it doesn't have much of a burning sensation. It isn't recommend for long-term use though. --OuroborosCobra (talk) 16:40, 16 April 2017 (UTC)[reply]

Transgender suicide rates

I'm looking for high quality secondary sources on transgender suicide rates. Benjamin (talk) 22:39, 15 April 2017 (UTC)[reply]

Haas et al., "Suicide and Suicide Risk in Lesbian, Gay, Bisexual, and Transgender Populations: Review and Recommendations", Journal of Homosexuality.
Clements-Nolle, Marx & Katz, "Attempted Suicide Among Transgender Persons", Journal of Homosexuality. SpinningSpark 23:24, 15 April 2017 (UTC)[reply]

April 16

DC-3 mountain ops

2 questions: (1) When performing a short-field, hot-and-high takeoff in a DC-3 at (or above) MTOW with a 20-knot tailwind, what is the optimal flap setting? (2) With the optimal flap setting for takeoff, given the following parameters: aircraft weight = MTOW + 1360 lbs., field elevation = 8400 ft., OAT = 2°C, wind = direct tailwind at 20 kts. -- what's the minimum runway length needed? (Question inspired by FSX mission "Crucial Extraction" from Aerosoft's "Flight Tales 2: Adrenaline" mission pack.) 2601:646:8E01:7E0B:88C9:21D2:79C0:44A3 (talk) 01:28, 16 April 2017 (UTC)[reply]

Flaps or no flaps? When you're at high density altitude, this is a very important question! A few weeks ago, me and my copilot spent our evening watching Density Altitude: The Nine Deadly Sins, an hour-long seminar presented by David Hunter, former Principal Scientist for Human Performance at the Office of Aerospace Medicine, Federal Aviation Administration.

"Wrong flap setting" is "deadly sin #8" in Dr. Hunter's talk.

"...There comes a density altitude above which the use of takeoff flaps actually increases ground roll."
"Don't use short field flap settings for high density altitude takeoffs (unless the field is truly short.)
- Short field flap settings offer a better angle, not rate of climb.
- At the typically long high-elevation airports flaps will be a hindrance to reaching V_Y more quickly.

This is a long, and technical, presentation. It's not going to tell you, in direct fashion, whether to use flaps or not to use flaps. It's going to tax your brain for everything it knows about mountain flying, so that you can make the best decision (simulated or real) about what will keep your aircraft safest. At high DA, you're often pushing the edges of the performance envelope of your aircraft. Every optimization along one axis is met by a degradation in some other performance metric. Do you want a slower rate of climb with better angle? Or do you want better margin against the stall with a poor climb gradient and marginal terrain clearance? Would you really take off with a 20kt tail-wind, or would you rather fight with the terrain in the opposite direction? What you don't know will kill you. (This is why - in the real world - we would delay or cancel the flight, even if the departure is "urgent").

To actually answer the quantitative parts: you need real and reliable performance charts for your aircraft - and you need to know how to use 'em! Have you got an E6B? The E6B computer costs less than the computer flight simulator software you're using, and it tells you how to calculate DA; then, you just have to read the rest directly off of your aircraft's performance charts. And yes - the former director of FAA's Aviation Human Factors division recommends hand-calculation using the E6B and the Take-Off Computer. Doing the math by hand, with an analog computer, is slower and less accurate than using a powerful digital electronic software computer; but the analog computer is shown scientifically to help you make a better decision.

Nimur (talk) 06:19, 16 April 2017 (UTC)[reply]

Thanks! In this case, I'm not concerned with terrain clearance -- I'm only concerned with reaching flying speed before running out of runway. And there's something I forgot to tell you about the runway -- it's 4,154 feet long, theoretically asphalt, and sloping on a 3.8% grade -- would the plane be able to take off under these conditions? Also, a related question (you can call it #3): At a gross weight about 1360 lbs. over MTOW (as specified above), is it even remotely possible for a DC-3 to maintain 8500 feet on 1 engine? 2601:646:8E01:7E0B:4457:AEC3:D9F:5111 (talk) 06:41, 16 April 2017 (UTC)[reply]

I'm going to preface this by saying "never fly above max gross..." because that's what the textbooks and the rules say. But if this is a question of physics: it is possible to fly above max gross; it's just significantly less safe. Above max gross weight, normal operations like taxiing, climbing, and even turns and banks, may cause structural failure of the aircraft. If you carefully follow certain rules and procedures, you can do it, safe-and-legal, but it is absolutely not normal. In aviation, when we hear the words "not normal", it is typically bad thing.

Not everyone agrees; Flying Magazine called max gross a "myth"; but what do they know? They're a fun read an an interesting trade-magazine - not a canonical source of correct information about aeronautics. Try asking a flight instructor if you can fly over max! Extra points if you say, "but I read all about it on the internet..."

Throw in the added complexity of multi-engine aircraft, and things get really weird: which engine failed? Was it the critical engine? So, again - these sorts of things come from your aircraft's performance charts - and your DC-3 simulator probably doesn't have really great and accurate charts... so let's default to the safer answer and say "no, the DC-3 can't be safely operated in that fashion." Has anyone ever done it? Well, those aircraft went through the wars...

Nimur (talk) 07:07, 16 April 2017 (UTC)[reply]

Yes, this is a question of physics -- is it possible, under these conditions (disregarding the structural considerations), to take off from the airstrip in question, and then to maintain altitude on one engine (the portside engine, to be exact -- in this mission it's the starboard engine that gets shot out right after takeoff)? And yes, I'm fully aware of the possibility of structural failure above MTOW -- in fact, Amelia Earhart had learned about it the hard way on her first (aborted) world flight attempt. Oh, and just to put this question about overloaded flying to rest: If you get rid of the extra 1360 lbs. and just try to take off at MTOW (the other conditions being as described above), would it be possible to take off within the specified distance and then maintain altitude on one engine? (Yes, I figured out how to prevent overloads in this mission -- once you board as many refugees as you think you can take (21, in this case), just increase power until the copilot shouts "We're leaving, close the f**king door!" (yes, he actually says that), and then the refugees will stop boarding.) 2601:646:8E01:7E0B:4457:AEC3:D9F:5111 (talk) 08:19, 16 April 2017 (UTC)[reply]

Let's build up to this problem: have you done a take-off roll calculation at sea level? And how about at 8400 feet? Next, how does the tail-wind factor in? Next, how does the emergency-checklist read for a single engine failure on takeoff? And how would you adjust for all the extra factors during the emergency?

I sincerely hope you aren't operating your simu-airplane without an appropriate simu-performance-chart! Those calculations are not optional - they are a very important part of flying your airplane! You must have and use those perf charts. I don't fly the DC-3; I don't have its limitations and numbers on hand, but I can say this: every single element in your scenario is urgent enough to warrant choosing not to take off in the first place. In combination, you're asking for (simu-)fatalities. This is not how pilots make decisions. We have seen things, and done things, that make us want those 5x- and 10x- margins.

For example, yesterday I was at sea level at KMRY in a single-engine aircraft. Sea level, and a perfect 12-knot headwind, on a seven thousand foot runway. To save a few bucks driving around on the ground, I opted for - and was cleared for - an intersection takeoff, 28L at K. As I rolled on the runway, I checked and verified three thousand feet of useful runway ahead of me. My aircraft can get off in, say, 600 feet in normal conditions; and with a 12 knot headwind... well, I can estimate 400 feet. So I had only about eight times more runway than I needed. As I rolled on to the runway, with four thousand useful feet already behind me, and eight times more than I needed ahead of me, the thought flickered across my mind: do I "actually actually" have enough runway ahead of me? And a moment of regret - why didn't I just taxi all the way to the end? Of course we took off with no trouble; but that's the kind of safety margin that makes a real pilot twinge. Your simu-scenario added mountains, terrain, hostile antiaircraft fire, overloading, sloping runway, short field, ... I mean, can you add a fogbank, questionable fuel, and an airsick pilot to the scenario for us just to bring the certainty of disaster closer to 100%?

So when you construct a scenario - simulated or otherwise - where you know you don't have the performance you require, you are so far from safe that no reasonable pilot would choose to take off. It would be better to stay on the ground and take your chances with the unfriendly groundlings who shot out that engine.

Nimur (talk) 16:20, 16 April 2017 (UTC)[reply]

I bet this is why FSX is not allowed for real pilot training -- because many of the missions (especially the harder ones) encourage the taking of risks which no pilot should ever take in real life (the "Jet City" mission being the most egregious example -- if you fly over (and under!) Seattle like that in real life, your "reward" would be a revoked pilot license and jail time for public endangerment -- and that's if you survive, which is unlikely!) But to get back to the question, the takeoff run for the DC-3 at sea level is listed in the learning center -- it's 1600 feet on a hard-surface runway with no wind. 2601:646:8E01:7E0B:B80C:1577:D989:3256 (talk) 00:32, 17 April 2017 (UTC)[reply]

Hm, that take-off roll (1600 feet?) sounds a little short, but I don't have a flight manual for DC-3 to verify... you really need a perf chart for the airplane (simulated or otherwise). But based on your questions, what you really need to do is go back to the Airplane Flying Handbook, with special emphasis on chapters:

Chapter 5: Takeoffs
Chapter 12: Transition to Multiengine Airplanes
Chapter 13: Transition to Tailwheel Airplanes
Chapter 17: Emergency Procedures

...and the PHAK, with special emphasis on:

Chapter 11: Performance

Nimur (talk) 23:40, 17 April 2017 (UTC)[reply]

BTW, just so you know, I actually made it off that field and stayed aloft on 1 engine, even with a full load of refugees (which put me 1300+ lbs. over MTOW, as well as made the plane dangerously tail-heavy) -- the key, as you said, was to keep the flaps all the way up. ;-) (And I didn't crash during that mission -- rather, my computer did.) 2601:646:8E01:7E0B:7D48:3AB5:AF2B:A040 (talk) 01:01, 18 April 2017 (UTC)[reply]

Ah, simulators... even when they're legal, it's hard to take them seriously...

Get back to studying your performance-charts, airman!

Nimur (talk) 14:36, 18 April 2017 (UTC)[reply]

Project_engineering

Just read [28]. Why is t that in some projects, project engineer reports to the project manager whilst in other cases, they are level in the structure, each reporting to their team manager who in turn report to the same project director. — Preceding unsigned comment added by 82.132.239.231 (talk) 15:05, 16 April 2017 (UTC)[reply]

Because that's how they want to do it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:42, 16 April 2017 (UTC)[reply]

Exactly. See: The Vertical Structure Vs. the Horizontal Structure in an Organization for more info. Aspro (talk) 18:20, 16 April 2017 (UTC)[reply]

In the organization I worked for, it was because project managers and people managers had different responsibilities: project managers were active engineers, or at least devoted to technical issues, but would not be responsible for things like hiring, performance evaluation, and promotion, which were the responsibility of the "people managers". In a complicated project, a project manager might be organizing some of the activities of several engineers (usually each engineer would have a designated fraction of full time equivalent (FTE = 40hrs/week) dedicated to a project). The project managers might aid the "people managers" in evaluating the people working on his/her projects, but the final say in the evaluation resided with the "people managers". Projects often spread across organizational areas, so some engineers would report to the same "people manager" as the project manager, and some would report to different "people managers". (I wish I could recall the exact title of the people managers; I think they were simply called "managers", or perhaps "engineering managers" to differentiate them from production and maintenance supervisors.)--Wikimedes (talk) 19:06, 16 April 2017 (UTC)[reply]

Doesn't PRINCE2 work on the vertical structure? 2A02:C7D:B95F:F700:9D03:FD57:30DC:BF4F (talk) 21:02, 16 April 2017 (UTC)[reply]

Sexual differentiation delay

According to Live Science, despite inheriting an Y chromosome already during conception, the human male sexual differentiation begins only after about 60 days when testosterone kicks in. Why there's such a delay between inheriting the chromosome and male development? Brandmeister^talk 17:47, 16 April 2017 (UTC)[reply]

Well it's not going to happen when it's a ball of undifferentiated cells. Sagittarian Milky Way (talk) 18:50, 16 April 2017 (UTC)[reply]

That, and also remember that just because you have certain genes in you genome doesn't mean they are expressed immediately. 86.28.195.109 (talk) 07:47, 17 April 2017 (UTC)[reply]

It's that way because it works. That's how evolution operates. Unless there is a definitely "better" way, the old way continues to be used. As to how this evolved, "ontogeny recapitulates phylogeny". -Arch dude (talk) 15:42, 17 April 2017 (UTC)[reply]

No, it doesn't. AndrewWTaylor (talk) 16:27, 17 April 2017 (UTC)[reply]

In a sense, sexual development begins even at a negative age. Looking up SRY, I see its expression begins prior to implantation of the embryo. [29] (I say this is a negative age because an IUD or other device to prevent its implantation is not an abortion, and because pregnancies are often timed from implantation) SRY is the most directly genetic part of a male sexual differentiation program, being on the Y chromosome and driving largely male appearance all by itself.

But your source is not wrong either: sexual development in the morphological sense starts at 60 days because neither a single cell nor a blastocyst has a place to hang a penis from (genital ridge). (Although, to be honest, it seems entirely possible that with just the right stain and a very good eye and a whole lot of human embryos you could spot some difference in morphology in the first few cells, some difference in the cytoskeleton that is simply not presently known... it's just probably not pole-shaped. ;) And of course you can look for Y chromosome and Barr body, but I think philosophically that isn't sexual differentiation because of unusual cases like Klinefelter's syndrome or a mutant SRY gene. That said cases like freemartinism show that sexual differentiation at the early stage is prone to change, much more than it is for transsexuals taking hormones later.) Wnt (talk) 12:23, 18 April 2017 (UTC)[reply]

Magnifying glasses/diopters

Cheap magnifiers with magnification 3.5x or above tend to have a short focal distance of ~12 cm or less which are not practical for many applications such as soldering. I've noticed that some purveyors of reading glasses refer to the diopter rating as magnification so I was wondering whether +7 diopter reading glasses might provide 3.5x magnification with a greater than usual focal distance (ideally 30-40 cm)? Alternatively it's possible to have glasses made online to a prescription - would they be able to do whatever magnification (5x?) with a long focal distance? --78.148.99.149 (talk) 18:57, 16 April 2017 (UTC)[reply]

Dioptre is defined as m⁻¹, which means that +7 dioptre lens has the focal distance of 1/7 m or about 14 cm. This does not seem very different from the mentioned 12 cm focal distance. Ruslik_Zero 19:38, 16 April 2017 (UTC)[reply]

File:Smallest loupe light .jpg

See Magnifying glass#Magnification. The Diopter value of a lens equals the reciprocal of its focal length measured in metres. Its magnification is MP₀ = (0.25 m)Φ + 1, where Φ is the optical power in dioptres, when held close to the eye, or MP = (0.25 m)Φ when close to the object. These assume the viewer sees comfortably at 0.25 m from the eye, but an older person may not manage such a near point.

Single lens magnifiers are limited to 5× or so before significant distortion occurs. A modification that allows 10x to 20x magnification is the Coddington magnifier. The Loupe spectacles with lighting illustrated are useful in dentistry and electronic inspection. Blooteuth (talk) 20:00, 16 April 2017 (UTC)[reply]

Thanks. I've found dentistry ones at 3.5x with 420 mm focal distance but I think they would be overall worse than my current 2.5x lens with ~200 mm focal distance since now the subject is further away, undoing some other magnification (although it is at least more comfortable to use). What about https://www.alie xpress.com/item/BIJIA-Portable-Zoom-Mini-Fishing-Glasses-Telescope-10X-Magnifying-Loupe-Green-Film-Binoculars-For-Outdoor-Concert/32661281596.html these]]? They're 10x but it doesn't say their focal length. It says the exit pupil distance is 0.8 m but I can't figure a way to derive the focal length from that. They're intended for watching football so I'm guessing they won't focus on something as close as 400 mm. Broken link to circumvent stupid spam filter. I'm not trying to sell magnifiers. 78.148.99.149 (talk) 21:17, 16 April 2017 (UTC)[reply]

water temperature of the Columbia River

Where can I find the water temperature of the Columbia River plotted over the course of a year? (Any recent year is fine)

Anywhere along the river is fine, but if possible I'm specifically interested in the section around Portland, Oregon. ECS LIVA Z (talk) 20:41, 16 April 2017 (UTC)[reply]

The USGS has this sort of data on their National Water Information System web site. Constructing a query is a bit complicated, but this URL should give you water-temperature data for 2016 for the Columbia at Dodson. They also have data for a number of other points in Oregon and Washington if you prefer. --76.71.6.254 (talk) 02:30, 17 April 2017 (UTC)[reply]

That's perfect. Thank you so much!! ECS LIVA Z (talk) 08:22, 17 April 2017 (UTC)[reply]

Natural selection and attractiveness - related?

Is the human mating process and what people find attractive related to natural selection? I.e. Can it be said that people who are found to be attractive by more of the population, are more likely to successfully find a mate and reproduce? 2A02:C7D:B95F:F700:9D03:FD57:30DC:BF4F (talk) 21:01, 16 April 2017 (UTC)[reply]

See sexual selection. Sometimes, the interaction between natural selection and sexual selection can have interesting consequences. I remember that there is a type of bird with very long tail feathers. The long feathers are believed to be maladaptive in terms of natural selection, but they are still favored because of sexual selection. 50.4.236.254 (talk) 21:10, 16 April 2017 (UTC)[reply]

Are you thinking about the bird of paradise? 2601:646:8E01:7E0B:B80C:1577:D989:3256 (talk) 00:34, 17 April 2017 (UTC)[reply]

Or peafowl? --Jayron 32 00:57, 17 April 2017 (UTC)[reply]

On the long run, sexual preference is itself subject to natural selection. So, sexual selection acts to prevent medium term drifts toward unfitness due to a temporary change in the natural environment. Count Iblis (talk) 00:35, 17 April 2017 (UTC)[reply]

Yes, sexual attractiveness translates into physical featness and as such successfull reproduction and mating. Large breasts and wide hips in women, for instance, contribute to successfull nursing and childbirth, respectively, while long legs were particularly important in prehistoric times, as it meant faster running speed. Brandmeister^talk 09:37, 17 April 2017 (UTC)[reply]

So, in theory, shouldn't this mean that only the most attractive in society get partners? Yet in reality, almost all humans get a partner. What's happened here? 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 10:46, 17 April 2017 (UTC)[reply]

No, that's not entirely true. In general, the more attractive (whatever biology and evolution and whatnot have determined for that particular population is "attractive") tend to be more likely to find mates, but that doesn't mean that no lesser attractive individual ever finds a mate. Evolution works in trends and generalities over long periods of time, and is not deterministic on the individual level. --Jayron 32 11:03, 17 April 2017 (UTC)[reply]

I'd add that since attractive women and men are more likely to get a partner fast, this forces other mate-seeking people to adapt their preferences and tastes. As the result, when a man, for instance, can't find a tall blonde girl with large breasts for some time (as it often happens), he would eventually adapt and pick an average girl next door. Brandmeister^talk 11:15, 17 April 2017 (UTC)[reply]

Especially if he doesn't find blondes very attractive in the first place. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:21, 17 April 2017 (UTC)[reply]

April 17

Fins

Plz tell me for a heat transfer equation of fins,we have different cases 1.convection from tip. 2.insulated tip 3.infinitely long. plz tell conditions to be met to assume fins to have insulated tip.

SD — Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 04:54, 17 April 2017 (UTC)[reply]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.. --Jayron 32 11:01, 17 April 2017 (UTC)[reply]

I'd like to see a penguin, seal, fish or dolphin with infinitely long fins. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:22, 17 April 2017 (UTC)[reply]

I believe the case with insulated tips implies heat leaves the fin through the two side faces of the fin, but not through the tip. Dolphin (t) 11:59, 17 April 2017 (UTC)[reply]

The article Heat sink has a section about fin efficiency that offers values for convection coefficient. Fin efficiency is defined as the actual heat transferred by the fin, divided by the heat transfer were the fin to have infinite thermal conductivity. However the key value to use in selecting a heat sink is its Thermal resistance defined as temperature rise in degrees Celsius per watt (°C/W). This is tabulated by heat sink manufacturers and the the temperature rise of the device over the ambient air can be calculated by multiplying it by the dissipated power in watts. Note that the thermal couplings of a semiconductor die to its case and of the case to the heatsink each represent thermal resistances in series with the heatsink, and in the latter case can be minimised by a thin layer of Thermal grease. SdrawkcaB99 (talk) 15:33, 17 April 2017 (UTC)[reply]

Governments

Why is it that governments don't have many scientists and engineers? They have nearly all policy specialists and supporting lawyers, economists and statisticians. 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 11:12, 17 April 2017 (UTC)[reply]

Who says they don't? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:20, 17 April 2017 (UTC)[reply]

In the U.K. anyway. I checked their organograms. 2A02:C7D:B8FC:9000:B8C7:87EC:A8:3648 (talk) 12:30, 17 April 2017 (UTC)[reply]

Are you referring to an organization chart? Do such charts list every last employee? And do they include consulting firms? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:33, 17 April 2017 (UTC)[reply]

Because scientists deal in facts, and politicians want to be able to ignore those. The aims of scientists and politicians are often almost diametrically opposed. Having said that there, are/have been scientifically trained heads of state (Angela Merkel, Margeret Thatcher, Elio Di Rupo just in Europe alone), and the current Dutch Interior minister (Ronald Plasterk) was a renowned molecular biologist. Fgf10 (talk) 14:43, 17 April 2017 (UTC)[reply]

There were just 2 scientists in the US Congress, as of 2015: [30]. This is somewhat understandable in the case of Republicans, who often run on an anti-science platform such as denying man-made climate change, supporting teaching "intelligent design" in schools, while opposing teaching evolution, etc. But, in the case of Democrats, more of an explanation is needed (although note that both current scientists are Democrats, as was the one who retired to bring the number down to 2). Running for office often requires the opposite of clear, plain statement of facts. For example, if you tell coal miners their jobs are gone and are never coming back, they won't vote for you. So, scientists tend to avoid politics, or, if they do run, they tend to lose if they try telling voters the truth. StuRat (talk) 14:57, 17 April 2017 (UTC)[reply]

In the U.S., both "pure" science and R&D are mostly contracted to private companies. This includes the companies that run the national labs like ORNL and LLNL, and the scientists and engineers that develop weapons systems. There are two major reasons. First: the political philosophy of "small government" gets translates into "fewer (direct) government employees." Silly. Second: government salaries are controlled via a cumbersome set of rules that make it very difficult to pay scientists and engineers competitively. Contracting to a company avoids this problem. -Arch dude (talk) 15:37, 17 April 2017 (UTC)[reply]

Government run by scientists and engineers is called (broadly) technocracy. Wikipedia's article on technocracy discusses some of the benefits and problems thereof. --Jayron 32 15:39, 17 April 2017 (UTC)[reply]

There are several examples of politicians and cabinet members with science and technology backgrounds. From the technology article linked by Jayron32 above, "...leaders of the Communist Party of China are mostly professional engineers". Margaret Thatcher earned a bachelor's and Angela Merkel a doctorate in physical chemistry, Steven Chu has a Nobel Prize in physics, and Jimmy Carter has a background in submarine nuclear engineering.--Wikimedes (talk) 21:42, 17 April 2017 (UTC)[reply]

Humans have existed for more than 200,000 years, politics has existed in some form for all that time and even before (I've seen a documentary about politics in ape societies). So our brains are adapted to use politics as a method to function in society. But science is a recent invention. While today we may think that in the old days the church repressed the people to keep them away from science, this is not the correct way to think about this issue. Our brains are programmed to respect authorities, so the Church had the respect of the people and they would then side with the Church if that authority would be challenged. Now science is all about being skeptical, statements need to be rigorously proven, it should be possible for anyone to question anything, the answer can never be an argument from authority. This is the complete opposite of how our minds have evolved. While science has made more and more inroads into society in the last few centuries, we're still the same old people who think in an extremely anti-scientific way about most things in life. Count Iblis (talk) 21:27, 17 April 2017 (UTC)[reply]

in my experience, people who cry the loudest how we shouldn't trust our puny brains also swear by wheatgrass juice and oil pulling and such things, and think that Ferguson and Berkeley were the result of active measures by a foreign power, so... Asmrulz (talk) 16:43, 18 April 2017 (UTC)[reply]

Injected drugs coming out in the feces

Recently I was reading about an intravenous drug (Vincristine), and was surprised that the primary mode of elimination (~80%) is apparently via feces [31]. I assume that means that the drug is moving from the blood into the bowel as its main mode of elimination. How common is this? I had pretty much assumed that the elimination of injected/intravenous drugs was either in the urine (via the kidneys) or by being broken down chemically (e.g. in the liver). I can't recall having heard of anything that moves from blood to bowel in any significant degree. Are there natural substances produced in the body (i.e. not artificial drugs) that are also excreted by moving into the bowel? In a circumstance like this, does the contents of the bowel then affect the rate of elimination? Dragons flight (talk) 13:48, 17 April 2017 (UTC)[reply]

The breakdown of hemoglobin involves transport into (and sometimes back out of, if I'm reading Urobilinogen correctly) the intestines (see Hemoglobin#Degradation in vertebrate animals). DMacks (talk) 13:58, 17 April 2017 (UTC)[reply]

I found a paper about this: [32]. It credits biliary excretion, and suggests that loss of liver function might lead to higher levels in the patient. We could use more data on this -- I know that bile salts are excreted in ~~gall~~ (I mean bile) to the intestine and tend to take some hydrophobic crap with them. Indeed the gallstone classically forms from cholesterol being dumped via this route, and vincristine is, at a zero-order approximation, another big complicated molecule with a lot of rings like that. But I'd be lying if I said I understood the mechanism in any meaningful degree. Wnt (talk) 12:37, 18 April 2017 (UTC)[reply]

That is helpful. DMacks link also suggested transport via the bile duct. That makes more sense for large molecules than direct transport from the blood. I was unaware that the bile duct could be used for elimination. Dragons flight (talk) 15:01, 18 April 2017 (UTC)[reply]

As others have said, the two most significant means of elimination are urine and gut. Urobilinogen excreted in urine gives urine its yellow color, while urobilinogen in the gut is converted to stercobilin that gives feces its usual coloration. - Nunh-huh 15:09, 18 April 2017 (UTC)[reply]

Mixing oil and water

Is there any oil that would mix well with water, without making an emulsion?--Hofhof (talk) 19:32, 17 April 2017 (UTC)[reply]

By definition, an oil cannot mix with water. Someguy1221 (talk) 20:11, 17 April 2017 (UTC)[reply]

I would say that if something mixes with water well, it is not an oil. Ruslik_Zero 20:14, 17 April 2017 (UTC)[reply]

This may be of interest, however. Brandmeister^talk 20:36, 17 April 2017 (UTC)[reply]

That got my attention. Specifically, "To test his hunch, Pashley removed almost all the gas from a water-oil mixture by repeatedly freezing and thawing it while pumping off the gases as they evaporated out". I have spent many long hours removing dissolved gasses from superpure water, and have always used [A] a vacuum at the surface, and [B] mechanical agitation. Never tried freezing and thawing. What is the theory behind that? --Guy Macon (talk) 21:07, 17 April 2017 (UTC)[reply]

We have an article about Degasification, including freeze–pump–thaw. If a liquid crystallizes, it often leaves solutes (including gases) physically separate, so then you can pump off those now-gas-phase molecules. That method is pretty standard in some labs, as is (and sometimes "as a step before other methods") sparging with an inert and/or less-reactive gas.DMacks (talk) 21:20, 17 April 2017 (UTC)[reply]

We have an article about Water miscible oil paint. DMacks (talk) 20:45, 17 April 2017 (UTC)[reply]

April 18

Stupid question: What flowers are these?

[33] Thank you. 69.22.242.15 (talk) 00:36, 18 April 2017 (UTC)[reply]

Looks like cherry blossom to me. DuncanHill (talk) 00:38, 18 April 2017 (UTC)[reply]

Pretty sure that is a cherry blossom. Boomer Vial^{Holla! We gonna ball!} 00:46, 18 April 2017 (UTC)[reply]

Definitely cherry - and probably one of the Japanese varieties to get that deep pink. The image isn't clear enough to identify the variety. The only other tree which has similar bright pink blossom is the crab-apple - but that would have leaves as well as blossom. Wymspen (talk) 10:16, 18 April 2017 (UTC)[reply]