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April 9

Plutonium and its electrical conductivity

Why does the electrical conductivity of plutonium, in the temperature range of 100 to 400 K, rise with increasing temperature?

This phenomenon is called a "negative temperature coefficient (of resistance)", but no article on Wikipedia I can find explains why this happens, though that link includes some examples. It appears there is more than one reason this can happen. This source lists some possibilities in its introduction. Someguy1221 (talk) 01:00, 9 April 2017 (UTC)

It may be like a semi-conductor - the concentration of charge carries increase with temperature in this range. Ruslik_Zero 08:32, 9 April 2017 (UTC)

"Plutonium Condensed-Matter Physics: A survey of theory and experiment" by A. Michael Boring and James L. Smith, Los Alamos Science Vol.26 2000 p.121 dismisses the Kondo effect as a good explanation and notes that it is a characteristic phenomenon of correlated electron materials, but does not offer an explanation as far as I can see. The phenomenon is even stronger in UBe₁₃, so this may be another avenue of approach.--Wikimedes (talk) 19:11, 10 April 2017 (UTC)

The effects of caffeine and alcohol

Caffeine is a stimulant. Alcohol is a depressant. If a cup of green tea and a cup of alcohol (wine, champagne, beer) are drunk at the same time, then what kind of effect do both have on the body? If a person is mentally depressed, then can he drink some caffeine? Can alcohol be drunk to calm a person with mania? 50.4.236.254 (talk) 02:09, 9 April 2017 (UTC)

Alcohol can be a stimulant or a depressant, depending on the dosage. Note that these terms don't refer to mental depression or mania, but rather physical stimulation and depression, such as heart rate, blood pressure, etc. There's some overlap between them, but they are not identical. StuRat (talk) 02:17, 9 April 2017 (UTC)

Alcoholic drinks have more rapid short-term effects, especially when the drink is carbonated, because alcohol readily passes through cell membranes into the bloodstream and brain. Its immediate effects are decreased anxiety and motor skill, hence the prohibitions on driving. The effects may proceed to euphoria and intoxication. Blooteuth (talk) 11:59, 9 April 2017 (UTC)

• As I have seen it put, if you combine alcohol and caffeine, what you get is a wide awake drunk. At a biological level, the mechanisms of action of alcohol and caffeine are quite different. Some of their high-level effects cancel to some degree, but many do not. Basically the same things apply to the other combinations mentioned in the question. Looie496 (talk) 14:35, 9 April 2017 (UTC)

Are nuts made of cells?

Looking to improve Nut (fruit) with the answer to this question: Are the nuts that we eat made of plant cells, with cell walls and everything, or are they just piles of nutrients hoarded for nearby cells to use? This has inexplicably started to concern me every time I chomp down on one. 8) -- Beland (talk) 10:03, 9 April 2017 (UTC)

The nut is a seed so it must contain living cells if it is to germinate. I would assume that most of the nutrients are stored inside cells rather than between them, but perhaps an expert can confirm this? Dbfirs 10:55, 9 April 2017 (UTC)

Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent (not opening at maturity) seed, such as an acorn or hazelnut. Blooteuth (talk) 11:34, 9 April 2017 (UTC)

Every part of a plant starts as a living cell. Some cells (see Sclerenchyma develop very think and solid cell walls, and the inside of the cell dies - these form the fibres in wood and the shells of nuts. Depending on the age of the nut, some of the living cells from the kernel may also have died, and the fats they stored may have leaked out. The nut you eat probably has a mixture of living cells, dead cells, and some nutrients which have leaked out of cells. Wymspen (talk) 11:38, 9 April 2017 (UTC)

The biology here turns out to be pretty odd. See endosperm, which describes the cellular nature of the bulk of many seeds. Note the endosperm is a different organism than the embryo. Then there is the specific case of coconut water - see here for a cute bit about it. I should look it up properly when I get the chance. I'm reading things about nuclei floating around in a liquid cell - well, syncytium - if I take that right ... my mind boggles. A cell is a very broad concept. ;) Wnt (talk) 20:44, 11 April 2017 (UTC)

I'm not sure I agree with that last statement. Our cell article states "A cell is the smallest unit of life that can replicate independently..." That seems a pretty tight definition to me. DrChrissy ^(talk) 22:21, 11 April 2017 (UTC)

That definition doesn't really work in a lot of cases. For example, most neurons can't replicate, but they are cells. More to the point here, there's the matter of what "replication" is. There are polyploid cells in the liver that will go 2n, 4n, 8n, 16n ... the cells get bigger, but they never form new nuclei. In this case we have the syncytium that forms new nuclei, but not new cell membranes until eventually somehow the nuclei congeal into the coconut meat around the edge. (a bit more about that here; in the coconut water, layers of cytoplasm congeal as "vesicles" around groups of nuclei? this just confuses me so far) I mean, technically my thought is that given there's no membrane between nuclei, the whole watery mass inside the coconut has to be counted as one very multinucleated cell. (this view is supported here) That is ... assuming there is a cell membrane at the edge of the coconut cavity, and not just some kind of extracellular tissue, which I still didn't get around to looking up. If there's no cell membrane even at the outside, is that even cellular tissue? Anyway, it's a broad concept however you look at it. ;) Wnt (talk) 23:08, 11 April 2017 (UTC)

Hmmmmm...I see what you mean. I had a quick look at injured nerves web-pages and they repair, rather than replicate. I take your point - thanks for the input. DrChrissy (talk) 23:30, 11 April 2017 (UTC)

I found this paper demonstrating a clear cellular structure in the coconut meat, after the nuclei form cells. This demonstrates that in general, endosperm at least can be made of fairly typical looking cells ... whatever the developmental process that took it to that point. Wnt (talk) 00:01, 12 April 2017 (UTC)

Will the human population reduce in numbers because of global climate change?

Wikipedia has articles that would be good starting points for this sort of investigation.

• Effects of global warming
• Effects of global warming on humans
• The entire category Category : Effects of Global Warming

These articles defy simple summary, but they may lead you to the answer you're looking for. ApLundell (talk) 18:34, 10 April 2017 (UTC)

April 10

Transgender suicide rates

I'm looking for sources on transgender suicide rates. Benjamin (talk) 03:42, 10 April 2017 (UTC)

[1] — Preceding unsigned comment added by Hofhof (talk • contribs) 11:17, 10 April 2017 (UTC)

Any high quality secondary sources? Benjamin (talk) 11:35, 11 April 2017 (UTC)

UV-vis spectroscopy

I've asked this once before, but nobody answered: In UV-vis spectroscopy, which wavelengths are the best for determination of aqueous Cu²⁺, Al³⁺/AlOH²⁺/Al(OH)₂⁺, and PO₄^3-/HPO₄^2-/H₂PO₄^-? 2601:646:8E01:7E0B:B50C:9D96:7F66:5859 (talk) 05:45, 10 April 2017 (UTC)

I think the UV-vis graph will show you which wavelengths are the best for determination of those aqueous chemicals. The graph will have wavelength at the X-axis and absorbance at the Y-axis. The peak of the curve means that the absorbance reaches a maximum at the corresponding wavelength. In my experience, UV-vis is done through software that is connected to the spectrophotometer machine, and the software will just output the information you want. You just have to set the range of wavelengths. 50.4.236.254 (talk) 12:51, 10 April 2017 (UTC)

I have an old, cheap machine which is not hooked up to any software -- you have to manually set the wavelength on the machine itself, and then it gives you a number for the absorbance. So where can I find the wavelengths I need? 2601:646:8E01:7E0B:E59B:261:F198:38A4 (talk) 00:45, 11 April 2017 (UTC)

In that case, you may have to test each chemical yourself. If you have the chemical samples, then you may put each sample in, one by one, and adjust for wavelength and check the absorbance reading for each wavelength. Then, you plot a curve. Do so for the other chemicals. 50.4.236.254 (talk) 01:18, 11 April 2017 (UTC)

For aqueous copper see https://carnicominstitute.org/wp/the-biggest-crime-of-all-time/?print=print Copper is easily detected in the visual range, with a peak absorption near 750nm and a maximum transmittance in the violet. But the wavelengths move with concentration. So you really need to plot a graph and look at the shape of the whole thing to match features. Your other ions are colourless, so you would have to check UV. Water also absorbs UV, so test some pure water too to see what you get. Our article is at Electromagnetic absorption by water. Water absorbs heavily shorter than 200nm. The metal ions would always be hydrated in water too so no Al³⁺ will be found in isolation in water, it would have about six molecules of water attached. Perhaps these will shift the absorption edge in the UV but I have not come up with any references for this. More normally IR or Raman spectroscopy would be used on the anions. Graeme Bartlett (talk) 02:15, 11 April 2017 (UTC)

Since water is a universal solvent, it can be used as a baseline for the other chemicals in aqueous solution. 50.4.236.254 (talk) 03:29, 11 April 2017 (UTC)

Downsides of fresh beef and natural preservatives/colors/flavors

I know many restaurants are trying to bring in customers by promoting "fresh beef" and "no artificial preservatives/colors/flavors". Though, this means that the food will have an increase in sodium intake, because sodium chloride, for centuries, has always been used as a natural preservative. Does this mean that the fresh beef will have higher content of sodium in order to preserve the beef? What kind of natural preservatives/colors/flavors are harmful in restaurant portion sizes? 50.4.236.254 (talk) 12:43, 10 April 2017 (UTC)

I'm a veggie, so this just ain't my party, but I don't recall restaurants pushing "fresh beef" as a good thing. If anything, high-end beef is sold on how old it is, and the premium product makes a point of it being "aged for 28 days" etc. Some meats (and fish!) are sold by freshness being a great virtue, but not beef.

No comment on salt levels. Andy Dingley (talk) 12:49, 10 April 2017 (UTC)

Interesting. Wendy's keeps promoting "fresh beef" in commercials, and McDonalds is trying to switch to fresh beef to stay competitive. I think that's a trend, because the fast food companies think that using fresh beef will attract more customers. By the way, is "veggie" some kind of vegetarian or a vegan? 50.4.236.254 (talk) 12:57, 10 April 2017 (UTC)

"is "veggie" some kind of vegetarian or a vegan?" Yes. It's a fairly common umbrella term. I happen to be vegetarian, so I eat eggs, dairy, but not fish.

I'm also British, if that makes a difference for which adverts I see. I don't think we have Wendys here, but McD's are busy advertising about the source of their beef, how local and how happy the cows are. In the UK animal welfare is a bigger current issue than simple quality. Although there was a recent McD campaign to try and counter the 'McD's is "all lips and arseholes"' viewpoint that does tend to circulate. Andy Dingley (talk) 13:15, 10 April 2017 (UTC)

I think many Westerners and Indians are lacto-ovo vegetarians. East Asian vegetarians are closer to ovo-vegetarianism (though eggs may be considered a luxury product, so veganism is the default), because of the lack of dairy farming and consumption. Soy milk production is very similar to cow's milk production, and tofu is like cheese. Cheese usually contains a lot of sodium content, while tofu can be flavored with salt or spices. A quick scan of a vegetarian menu in America hints that American vegetarians really like cheese. 50.4.236.254 (talk) 14:20, 10 April 2017 (UTC)

"Fresh" in the McD context, at the moment, is talking about fresh v. frozen. --jpgordon^{𝄢𝄆 𝄐𝄇} 13:17, 10 April 2017 (UTC)

Think some are falling to see the Sales & Marketing angle being used here. Like any good magician they use 'distraction' and misdirection to fool their audiences. 'Fresh' is the current word now. There is growing concern, that a few countries (like for instance the US) are using antibiotics as a growth promoter for their livestock (especially beef) with a total disregarded for the problems that such usage may bring to the final consumer. We are already running out of effective antibiotics and intensive farming methods are making this crisis far worse, by becoming the breeding ground for more antibiotic resistant bacteria. So to stem this negative publicity, the S&M's are promoting the word 'fresh' , 'no artificial preservatives/colors/flavors', as if it also means natural, wholesome and safe. --Aspro (talk) 15:50, 10 April 2017 (UTC)

I believe "fresh" is used as contrast to "frozen", not "aged". Some points:

1) While meat frozen improperly can suffer from freezer burn, if handled properly this shouldn't be an issue.

2) Never-frozen meat is rarely preserved by salting it. While it is possible to do so, the amount if salt required makes the food almost inedible. You need to use small portions of it mixed with bland food, to make it palatable. See salting (food).

3) The salt added to restaurant foods is for flavor and to make you buy high-profit margin beverages.

4) Never-frozen meat does have more of a risk of bacterial contamination, as it spends more time in the temperature danger zone (unless you butcher the animal at the restaurant). Proper cooking should reduce these risks. StuRat (talk) 17:19, 10 April 2017 (UTC)

The commercials specifically state "Fresh, never Frozen." They are using "Fresh" to mean "Not Frozen." It has nothing to do with how old the meat is. In the fine print, it usually states that frozen meat is used for Hawaii and Alaska as meat is usually frozen for long transits. To reinforce the meaning, the commercials show frozen hamburger patties and claim that they don't use those. 209.149.113.5 (talk) 19:18, 10 April 2017 (UTC)

The meat is put in a sterile container and then irradiated. Count Iblis (talk) 19:57, 10 April 2017 (UTC)

So that is a misdirection. Meat, rapidly frozen (before ice crystals can grow and puncture the cells etc.) is the same as freshly slaughtered meat. Frozen or unfrozen... meat can still contain the hormones and anti-biotic encouraged nasties that get pumped into cows. The US are making a song and dance about Europe (under the ]World Trade Organization) not allowing some of their meat products into Europe because of their questionable consumer safety. This is a big issue, because in some countries like the US, if you or your child becomes ill, you simply go off to the doctor and pay what ever is necessary to get your child well again. - if you can afford it. Even if it means paying for very expensive antibiotic more powerful than what the cows were fed - from which the infection may have originated. In many parts of Europe we have better than Obama Health Care . If one is too sick to work, you are unable to pay any tax. Solution, provide cheap and affordable heath care to get you back to work again (and pay tax again). That means removing the cause of one's malady. Banning imported, questionable, American meat is one of them. As for irradiated food , we can buy food (for say mountaineering) that has been gammer'd or betar'd but this not permitted for everyday consumption.--Aspro (talk) 20:41, 10 April 2017 (UTC)

I suppose one can buy free-roaming, organic meat for personal health reasons. Though, those are more expensive than the conventionally grown ones derived from intensive animal farming. But you get what you pay for. If you eat cheap meat, then it has a cheap quality. If you eat organic meat derived from an animal that was raised well with plenty of space, then it is more valuable and healthier, because it is less disease-ridden. It may be more expensive, but the cost should be a reason to eat less meat or reserve meat on special holidays. 50.4.236.254 (talk) 22:59, 10 April 2017 (UTC)

Anyone for pink slime ? StuRat (talk) 02:11, 11 April 2017 (UTC)

Soylent Green may make a good alternative, for those that get turned off by pink stuff.--Aspro (talk) 20:58, 11 April 2017 (UTC)

Once again, there's no intrinsic reason why organic meat is healthier. As for less intensively raised meat, again it's complicated. Less intensively raised meat may reduce bacterial levels but it also depends significantly on the practices and other factors. For example, eating intensively farmed chicken from KFC probably has a far lower risk of infectious diseases than you preparing the chicken yourself, no matter how fancy and non-intensively raised it is. (Eating at KFC may have other health risks, but the point is these don't relate to how the chickens are raised.) Note that while there may be a benefit in reducing the development and spread of some viral diseases, unless you're a farm worker your risk is likely almost negligible. There may be a benefit to the community (and your risk there is higher) but your personal form of meat consumption is basically irrelevant to that, what matters is what everyone else is doing. Even in terms of the use of antibiotics in farm animals, you need to consider the distinction between what your personal risks are, and the effect on the community. Of course, if you aren't selfish, you may want to consider these communal aspects (as well as a bunch of other things) in your decision, just as you may recycle for example, but this is different from suggesting it's going to make a difference to your health where it isn't. Nil Einne (talk) 10:09, 13 April 2017 (UTC)

A lot of the replacement of "artificial" for "natural" is just gibberish to fool the uninformed. A common replacement for nitrite-curing of meat, for instance, is curing the meat instead in beet- or carrot-juice, which chemically accomplishes the same thing, but causes the meat to taste awful. But the food is "healthy", so people are expecting it to taste bad. Someguy1221 (talk) 23:10, 10 April 2017 (UTC)

I found some reference to this here. But what perplexes me about meat curing is that nitrate and nitrite are treated as if they were the same thing. I know nitrates are in beet juice and the soil; since they are so common I think of them as more natural, even if artificially produced. I don't know if there's a natural precedent or longstanding use from the Middle Ages for nitrite, so I wonder more about it... Wnt (talk) 00:11, 12 April 2017 (UTC)

As for natural colors, the downsides are often less of a color range, and some of the ingredients are a bit gross, like the cochineal beetle parts in carmine (red). StuRat (talk) 04:33, 11 April 2017 (UTC)

Is 580°F twice as hot as 60°F? and other weird temperature math

I recognize that saying "120°F is twice as hot as 60°F" doesn't make sense, because the Celsius doubling equivalent of 60°F, ~15°C would get you 30°C, or 86°F.

I understand both Fahrenheit and Celsius have "arbitrary" zero points, and Kelvin uses an *absolute zero*, but converting to Kelvin, then back, doesn't seem right either as it yields bizarre sounding results, like that in the title.

Are there any other units of measurement that have this issue?

Is there a better way to consider the concept of "twice as hot"?

Thanks!

- MacAddct1984 ^{(talk | contribs)} 13:25, 10 April 2017 (UTC)

• For the kinetic theory of gases, which is as good a meaning of temperature as anything, then yes, 580 °F (578 K) is indeed twice as hot as 60 °F (289 K).

I work with lasers, and have worked with plasmas. Where they have "negative" temperatures, on account of being so hot. They produce a condition (for the energy distributions of the atoms within them) of "population inversion". As the word "inversion" might suggest, this is in some, rather arcane, ways comparable to a temperature that would be negative. Andy Dingley (talk) 13:39, 10 April 2017 (UTC)

Heat content also needs to take into account the amount of material (usually mass or mole amounts) and its specific heat capacity rather than just raw temperature; for example a liter of water at some arbitrary temperature (say 25 degrees C) has a LOT more thermal energy than does a liter of air at the same temperature; and a liter of water has more thermal energy than does a milliliter of water. Concepts like enthalpy or internal energy are better for quantifying relationships. Temperature really isn't a "countable" thing in the way that energy would be. Saying something is twice the temperature is almost like saying red is twice the color as blue is... --Jayron32 13:44, 10 April 2017 (UTC)

You're right that converting to Kelvin is the only way that "twice as hot" is literally true, so if you mean anything else you should avoid using the phrase in any context where accuracy is important.

I don't have a cite, but I've noticed that rarely in some contexts "twice as hot" might use room temperature as a baseline. (If you have two overheating electronic components, the one that's 130F might be "twice as hot" as the one that's 100F because what you care about is the heat added by that component, but you don't see that usage often.)

In general, though, I've only commonly heard this expression used in casual conversation as a hyperbole where no actual measurements are implied. ("Texas weather is twice as hot as Maine weather!")

The other part of your question is easier to answer. There aren't too many units of measurements that have non-zero baselines like the common temperature units, but units that are nonlinear have a similar problem. A sound that is "twice as loud" as a 1 decibel sound will not be 2 decibels. An earthquake that is "twice as strong" as a 1 on the richter scale will not be a 2 on the richter scale. Etc.

13:51, 10 April 2017 (UTC)

The decibel (dB) is not a unit of sound level, despite frequent misuse. It is 0.1 times the logarithm of a ratio. A sound Loudness must be expressed in units such as dB SPL (or for perception of single tones dBA) that define what is the 0 dB reference. "Twice as loud" is then by physical definition +3 dB (but the human ear limits the range that can be heard or tolerated.) Blooteuth (talk) 15:05, 10 April 2017 (UTC)

Sure, Decibel SPL. Fair enough. Point is, it's logarithmic, so it doesn't double or halve as one might otherwise expect. ApLundell (talk) 15:21, 10 April 2017 (UTC)

Which, of course, hints at other Decibel-based units that answer the question. The other one you might commonly see is dBm (decibel milliwatt) used to compare radio signal reception. (You're most likely to see this measuring wifi reception.) This is particularly resistant against easy doubling or halving because your wifi reception is almost certainly negative dBm even though obviously a positive amount of power is being detected.ApLundell (talk) 15:31, 10 April 2017 (UTC)

Digital-smart but analog-ignorant engineering has had tragicomic consequence. A company responsible for international emergency communication needed a survey of its radio coverage. A campaign of thousands of field strength measurements was initiated at considerable expense. The measuring instruments indicated values in dBμV (0 dBμV = -60dBmV = -120 dBV). In presenting a "tidy" report to management, someone "smoothed" the raw measurements by taking the arithmetic mean or Average of groups of values. After this, our hero saw no reason to preserve the raw measurements and the entire campaign cost was effectively wasted. Blooteuth (talk) 18:21, 10 April 2017 (UTC)

I would enjoy reading the details of such a spectacular screw-up. Do you have a cite? ApLundell (talk) 18:26, 10 April 2017 (UTC)

Suave mare magno..? I know of two instances of the screw-up but choose not to identify the engineers who have since learned from the experience. Industries where it can happen are a) broadcasting, especially by Geosynchronous satellite where footprint area represents a critical capital investment, and b) the Mobile phones used in Cellular networks display received signal strength indicator bars that are in steps of dB. The only way to calculate a correct average voltage (or power) is by converting values given in dBV (or dBm) to volts (or milliwatts) respectively before averaging them together.

The subject is sensitive to me because I was asked by a company management to invent a technical "justification" for the incorrect adding of decibels that had been programmed into survey equipment already delivered and in use.

Analog-savvy engineers do sometimes add together values in decibel units; this is a correct way of calculating the overall gain of a signal path through a chain of stages with individual gains (positive dB values i.e. amplifiers) and losses (negative dB values). Two-port network develops the theory in full to cover both forward and reverse interactions between stages. Blooteuth (talk) 14:16, 11 April 2017 (UTC)

Musical pitch is also a nonlinear scale. Each one-octave increment is "twice as high" in frequency (two octaves up is four times as high, three octaves is eight times as high). DMacks (talk) 15:40, 10 April 2017 (UTC)

• (ec)Well, it may seem bizarre, but it's the only (?) definition that makes physical sense. In thermodynamics, temperature is (e.g.) a measure for the average kinetic energy of particles of an ideal gas. If you double the temperature measured in Kelvin, you double the kinetic energy of the particles. --Stephan Schulz (talk) 13:51, 10 April 2017 (UTC)

• Any time people don't have a universal concept of the baseline, this situation can occur. If one plane is in level flight at a height of 1000 feet and another is directly above it at 2000 ft, one might say the second is "twice as high". But if they then continue flying straight forward over a 500-foot mountain, it's pretty confusing to say that the second is now "three times as high" as the first, but compared to the ground they are now only 500 ft and 1500 ft respectively. So instead one references sea level rather than ground level for altitude, but that means 2000 ft vs 1000 ft compared to the ground might be much greater than "twice as high" by visual appearance if the ground is high. DMacks (talk) 14:04, 10 April 2017 (UTC)

• Relative to the centre of the Earth, all aircraft are at the same height to within a rounding error. Someguy1221 (talk) 23:13, 10 April 2017 (UTC)

• For some background, see Level of measurement. -- zzuuzz ^(talk) 18:33, 10 April 2017 (UTC)

 

Just a note — the absolute-temperature equivalent of Fahrenheit is the Rankine scale. 60 degrees Fahrenheit equals 519.67 degrees Rankine. Double that is 1039.34 degrees Rankine, which is 579.67 degrees Fahrenheit, the same you got from the Kelvin scale. This is a pretty trivial observation, of course, but I wouldn't want anyone to think that the answer is specific to a particular unit. It's what you get whenever you double the absolute temperature, regardless of the temperature scale you use to do that. --Trovatore (talk) 00:01, 11 April 2017 (UTC)

April 11

Feynman Lectures. Lecture 51. Ch.51-2 Bore in a channel 2 archive

To understand the problem I have simplified the task. Suppose we have a piston in a tube png. A man acts from the right with force = 2N. An unknown force = 1N acts from the left. I write the energy conservation law:
$\sum E_{t=0}=\sum E_{t=1}$
${\text{Work by man}}=E_{\text{kin}}+?$
$F_{\text{man}}\cdot L=0.5m(v_{t=1})^{2}+?$
$2\cdot 0.5=0.5\cdot 1(1)^{2}+?$
$1=0.5+?$
$\therefore \,\,?=0.5J$
"?" is the work done by the piston against unknown force. Is it correct? Username160611000000 (talk) 07:56, 11 April 2017 (UTC)

There are various outcomes for the extra force provided by the man - it can heat the object by friction, or give it kinetic energy by moving it quickly. Of course if the piston is near weightless and frictionless it will take very little effort or time to push it to the final position where it will have very little energy; F=ma means a very large acceleration in that case from the known net 1 N force to the left. (intuitively, he has to run to catch up, which isn't counted - picture you're pushing a cart that you think is heavy with stuff but you realize it's very light stuff) But the mechanical work done is still F s, force times distance, i.e. this super light piston would fly off with incredible speed if the man could duck out of the way and let it go. That's 0.5 meters (using "m" for the mass value also made this rather confusing) times 1 N = 0.5 J work done against the piston. The rest could be trivial or terrible, depending on the piston. Wnt (talk) 23:39, 11 April 2017 (UTC)

In my example piston has a mass = 1 kg and its motion is frictionless. You mean that I should write:

${\text{Work by Resultant}}=E_{{\text{kin}},t=1}$

But according Feynman (Ch. 13 - 3) we can split the total force into components and total work becomes the sum of works by components. The man may not even know whether there is a force from the left. Moreover, the same amount of chemical energy is burned by man's muscles no matter is the force from the left present or not .

Username160611000000 (talk) 06:03, 12 April 2017 (UTC)

Insanely low calories

Looking at this product it says that per 100g it's 84 calories. The whole pack of six is 312g. Rounding the figures that works out about 300 calories per pack. Are you seriously telling me that I can stuff five packets of this stuff a day and still be in a calorie deficit and lose weight?? 68.190.17.93 (talk) 16:52, 11 April 2017 (UTC)

That depends on how much you burn. If I'd eat 5 packets of Quorn a day, I would probably throw up and lose even more weight. Note that the calories are comparable to lean meat - beef filet has 110-120 kcal/100g, filet of pork has slightly less, skinless chicken breast has a bit over 100 kcal/100g. --Stephan Schulz (talk) 17:19, 11 April 2017 (UTC)

• Yes, if that is the only thing you are eating; but 312g/day is not much (euphemism) - [2] says the average 2011 Somalian adult eats more than one kilogram per day, for perspective. Tigraan^{Click here to contact me} 17:31, 11 April 2017 (UTC)

• And note that eating them plain may be unpleasant. Add in sauces, bread, and cheese, and a drink and the calories go way up. This is fairly common situation. Potatoes aren't very high in calories, until you fry them, and add cheese, butter and bacon. StuRat (talk) 18:01, 11 April 2017 (UTC)

• • I eat a low fat diet, so I do need to get my calories from potatoes, rice or pasta. If I eat potatoes for dinner, then I'll eat about 1 kg of potatoes. I think this is what you must do to eat healthy, you must make sure the balance between calorie intake and nutrient intake is right. Count Iblis (talk) 19:47, 11 April 2017 (UTC)

• Other sources of calories are protein and alcohol. So, low fat doesn't need to mean high carb. StuRat (talk) 00:23, 12 April 2017 (UTC)

It says it is rehydrated egg white (see below), which is notably a low calorie, but unsatisfying, food. There are a lot of low calorie foods - green beans, strawberries, mushrooms, spinach for example. Salad pretty much in general, come to think of it. But even a 160-calorie soft pretzel can be pretty satisfying for the calories; it's hard to say what works best. I would be curious whether there is any risk of egg white injury with this one the way this is prepared, though I highly doubt it. Wnt (talk) 20:52, 11 April 2017 (UTC)

It's less than 15% egg white so what's your point? But maybe you just missed that percentage.--TMCk (talk) 00:21, 12 April 2017 (UTC)

@TracyMcClark: Thanks for the correction! Because the first ingredient listed was "Mycoprotein (tm)" and they said the product was Mycoprotein, I thought that was just a brand name rather than an ingredient. I actually mentioned mushrooms were a low calorie food; this is much the same idea. However, according to our article mycoprotein is from Fusarium venenatum grown in vats. (Hmmm, I wonder if this technology was in any way inspired by previous government efforts to weaponize Fusarium oxysporum for spraying on coca crops, or perhaps incidentally other rebel food sources...?) Wnt (talk) 01:12, 12 April 2017 (UTC)

Omnidirectional vs. tight beam broadcast

How do they send radio waves in a tight(er) beam instead of an omnidirectional broadcast? --Hofhof (talk) 17:44, 11 April 2017 (UTC)

The shape of the antenna makes the difference. A parabolic antenna is good for a tight beam directional antenna. Television antenna lists some omnidirectional antennas, such as rabbit ears or a bowtie antenna. There are also multidirection antennas, which broadcast or receive in more than one direction (typically 2 or 4), but not equally well in all directions. StuRat (talk) 17:52, 11 April 2017 (UTC)

• Wikipedia has an article titled Directional antenna which has some information. It also contains links to other articles which may lead you to find even more information on how they work. this article here seems to go into some more technical details on the general differences between omnidirectional and directional antennas. This article has some basic information on common antenna types as well. --Jayron32 19:06, 11 April 2017 (UTC)
• Only the theoretical isotropic antenna is truly omnidirectional, but no such antenna can be built. Simple antennas consisting of one element, such as the half-wave dipole antenna, are usually referred to as omnidirectional, although they do favour radiation (and reception) toward their sides; that is, they are best at angles that are broadside on to the element. By placing more elements at certain harmonically-related distances from the main element, the beam can be narrowed considerably, focusing more of the signal toward (or receiving more from) the intended target. Thus we have the yagi antenna. It has (usually) one reflector element (slightly longer than the main element) spaced close to one-quarter wavelength behind it. This reflects signal back towards the main element, emphasizing the radiation in that direction. By adding one or more shorter director elements in front of the main element at the same spacing, the signal will be focused even more. It's not unusual to obtain up to 10dB front-to-back gain in this way, meaning that 10 times more power is radiated in the forward direction compared to the back direction. A secondary advantage is that interfering signals and noise from the back direction when receiving are suppressed by the same amount. Also see quad antenna for a different type of construction with similar results. Akld guy (talk) 21:56, 11 April 2017 (UTC)

A spherical antenna is an interesting approach to a directional antenna. Unlike a parabolic antenna, it can be aimed without moving the entire thing, but only over a limited range. See Five hundred meter Aperture Spherical Telescope for one example. The rotation of the Earth does most of the aiming, but from there they can fine tune it.StuRat (talk) 00:46, 12 April 2017 (UTC)

The memorable Hairy ball theorem (animation) can explain why an ominidirectional (isotropic) antenna is impossible for coherent linear polarized radiation. The electric (and magnetic) vector fields would be everwhere perpendicular to wave propagation, forming a continuous tangent everywhere on the surface of a sphere around the antenna. But you can't comb flat the hair on a ball, says the theorem. The limitation does not apply to incoherent radiation which can be omnidirectional, e.g. the flash from an explosion or, cosmologists believe, radiation from the Big Bang. The Arecibo Observatory (305 meter) built in the 1960s in Puerto Rico does use a fixed spherical reflector in contrast to the Chinese Five hundred meter Aperture Spherical Telescope whose primary reflector is actually an active surface that emulates a 300 meter parabola. Blooteuth (talk) 12:49, 12 April 2017 (UTC)

What do "weeds" do in any ecosystem?

I know that gardeners want to "improve" the acidic soil by adding garden lime and "improve" alkalinic soil by adding compost. But I have read that weeds may thrive in an acidic environment. In that case, why not just grow weeds in the soil instead? Will there be an advantage if a gardener makes use of the acidic soil and grows edible weeds, like dandelions and nira greens, and if the soil changes, the gardener grows a different set of crops? 50.4.236.254 (talk) 18:28, 11 April 2017 (UTC)

The problem with weeds like dandelions is that they spread to the neighbor's yard who will then be mad at you. There are some people who believe that a natural garden is better, but you need to live away from everyone else or have like-minded neighbors for that to work. As for farmers, there are some crops that can be grown to improve the soil, depending on the issue. StuRat (talk) 18:35, 11 April 2017 (UTC)

There is no biological definition of weed. A weed is simply any plant that the person who is maintaining the garden does not want for whatever reason. People have their own aesthetic reasons for wanting certain plants in their garden or yard, and farms want to maximize the yields of their crops. If we're just restricting ourselves to gardens and yards and land maintained for aesthetic reasons, which you seem to be, it is "the person who maintains the yard doesn't find the weeds as pretty as the other plants". You'll have to ask that person why they don't grow weeds. We can't answer for you, and no reference will provide any meaningful answer. --Jayron32 18:56, 11 April 2017 (UTC)

Okay, fine. What do dandelions and green nira do? 50.4.236.254 (talk) 19:33, 11 April 2017 (UTC)

Whoo. You're asking a complex question. Dandelions etc are very good to eat but a 'gardener' wants to grow a wide range of veg – not just dandelions and acid soil loving nira. What about the other edible weeds like alkaline loving Sanguisorba minor. Should the gardner deny his family of of the joy of those other-weeds?--Aspro (talk) 18:59, 11 April 2017 (UTC)

• Dandelions have one purpose, to make more dandelions, the more the better. Any 'purpose' alloted to them is a human construct that bears no relationship to the their reproduction. The basic purpose of all living things is to reproduce more of its kind. Richard Avery (talk) 07:12, 12 April 2017 (UTC)

Crop rotation is basically the art and science of doing what you suggest. Alternating crops, sometimes including plants like clover specifically just to let them die on the field and be plowed under as Green manure. Of course clover is only a "weed" if you don't want it to grow, but that's a question of semantics.

As for home gardens, Deciding you want the weeds to stick around can be called Natural landscaping. That article discusses some disadvantages of such an approuch, but it doesn't mention the big one StuRat mentions : Neighbors, you neighbors may be very unhappy if you have local plants growing unchecked on your lawn. They may even have legal power to stop you from doing it, depending on local regulations and especially any Homeowner Association you became a member of when you bought the house.

All of this is more complicated than just deciding to eat dandelions, of course, but you knew it wouldn't be that simple. ApLundell (talk) 19:03, 11 April 2017 (UTC)

I think clovers are actually edible. Why don't people bring clovers to market? 50.4.236.254 (talk) 19:35, 11 April 2017 (UTC)

Because people in that locale don't want to eat them. You can't just force people to behave in a certain way because you don't find the way they are behaving explainable beyond "that's what they like/don't like". Lot more things are edible than what people in a particular location choose to spend their money buying to eat. It does no bit of good to bring those things to market if no one will spend money buying them to eat. --Jayron32 19:38, 11 April 2017 (UTC)

APL provides some very good additional perspective. To expand on his excellent reading material APL has provided: As far as HOAs and private property usage in the U.S., many housing developments in the U.S. have covenants attached to the property you are buying; when you purchase a house and its associated land in the U.S., the covenant is attached to the land and requires you, as a homeowner, to maintain your land and dwelling to certain standards. These covenants are a prerequisite of buying the land from the developer, and become attached in perpetuity to the property, since you are not required to buy that property, you are free to not buy land with such covenants attached to it. Why do such lands have such covenants? Because there is a lot of value tied up in Real Estate; as an individual homeowner a substantial portion of your total net worth is tied up in your home. If your neighbor makes it hard for you to sell your house because he doesn't maintain it to a certain standard, that costs you A LOT of money, a prospective buyer may refuse to buy because his yard is in below standard, and that means you have to lower your sale price. Basic economics. So HOAs and covenants exist to protect the investments of everyone who owns property in the development by ensuring that all other owners keep their property up. --Jayron32 19:15, 11 April 2017 (UTC)

Aside: Blanched dandelions don't produce seeds, for to which, spread to your neighbours garden. They (your neighbours) may look upon you as a bit odd at first, until you invite them to taste real home grown produce. Tastes better than anything they can by at the supermarket. Covenants usually restrict nuisance weeds. Before the automobile, land owners had to remove any Jacobaea_vulgaris#Poisonous_effects because of it detrimental effects to horses. Now, nobody takes any notice of this legal requirement and thus it is allowed to grow everywhere. --Aspro (talk) 19:51, 11 April 2017 (UTC)

Fine. Then, the only way to plant stuff is to buy a patch of farmland and live on the farmland in a tent. Though, one probably needs to find fresh water and a way to go to town every now and then. 50.4.236.254 (talk) 19:38, 11 April 2017 (UTC)

Finding a way to go into town should not really be a problem. If you're average, you may well find you have two lower appendages. By moving them back-and-forth you can perambulate at some three mile per hour. Fast enough to get you into town and back home again before nightfall. Make sure your tent is properly water proofed – otherwise you will be bathed in a mist of fine water droplets when it rains. Then, cut turf and built yourself a sod house. A six dollar colt revolver may come in handy too. Oh. And don't be afraid of the natives. They are very friendly, it was Hollywood that portrayed them in a bad light.--Aspro (talk) 20:20, 11 April 2017 (UTC)

I'm pretty sure there is a middle ground between living in a planned community with very strict gardening rules, and living off-the-grid in a tent. ApLundell (talk) 20:38, 11 April 2017 (UTC)

That's quite true. In New England, for example, housing covenants and HOAs are uncommon. I'm sure they may exist in a few places, but they are mostly unknown. --Jayron32 10:51, 12 April 2017 (UTC)

I just remembered I started a Draft:Weeds as soil indicators a while back, meaning to fill out a massive table based on some of the sources there and probably others... and something came up, and it's set there ever since. The history has some semi-relevant material I'd taken out. I was meaning to learn how to read the soil pH by looking at the plants... but there are similar data for garden plants, some of which like more acid pH. Wnt (talk) 23:46, 11 April 2017 (UTC)

In the most basic sense, the "weeds" are the ecosystem, and whatever crops or gardens we grow are just a temporary aberration. StuRat (talk) 00:37, 12 April 2017 (UTC)

Not really. I mean, yes, there are native organisms, but the best "weeds" are invasive species that thrive in disrupted environments, such as gardens and roadsides. There are many weeds which are present nearly anywhere, which is what made them attractive to me as a potential sign to read the soil by. Wnt (talk) 01:14, 12 April 2017 (UTC)

Yes, while dandelion is a common weed in NZ [3] (but not Allium tuberosum AFAIK, some garden shops sell suicides so I assume it isn't considered a risk given NZ's climate), if you look at lists e.g. [4] [5] [6] [7] [8] [9], you'd note stuff of concern can be things like Tradescantia fluminensis, various Hedychium, Solanum mauritianum, Privet. While some of these are perhaps are most concern in native bush or on reserves, I selected examples I've probably dealt with before, and I don't live that near any native bush. Nil Einne (talk) 01:42, 12 April 2017 (UTC)

Salvia are often used in gardens to keep insects at bay. Garlic is a famouse antidot against many sorts of fungi. So "weeds" complement eachother by keeping specific harms in check in their ecosystem. Thats also the key reason why monoculture farming exessively needs so many chemicals. To compensate for the exclusion of weeds that otherwise make mechanical harvesting a challenge, take away a fraction of the plant area and need some direct farmer attention, because some weeds are a also ofcourse a danger to humans. --Kharon (talk) 04:04, 12 April 2017 (UTC)

Beginning of Period R

(Note: the E is not a real E, but an approximation of the C with a horizontal line through it because of its similarity to an E)

We know about periods E, O, S, D, C, P, T, J, K, Pg, N, and Q. Do any scientists have theories on when period R will start?? (The R doesn't stand for anything; it's simply the combination of the fact that it's the next letter after Q and that no other period has that letter as its name.)

The periods can be grouped into ages as follows: E and O are the Age of Trilobites; S and D are the Age of Fishes; C and P are the Age of Amphibians; T, J, and K are the Age of Reptiles; Pg and N are the Age of Mammals; and Q is the Age of Humans. (Most of the known dinosaurs lived during periods J and K.) Do any scientists have any theories on either when period R will start or what life on earth will be like during period R?? Georgia guy (talk) 21:08, 11 April 2017 (UTC)

Technological singularity in less than 25 years. --Digrpat (talk) 22:14, 11 April 2017 (UTC)

According to Stephen J. Gould, those "Age of XXX" labels are very misleading and shouldn't be used. However the division into periods is mostly based on when mass extinctions occur. Since the sixth mass extinction is currently in progress, the next period probably is starting right now. CodeTalker (talk) 22:53, 11 April 2017 (UTC)

The relevant term is Anthropocene, but I couldn't find a cite for an abbreviation. The use of "A" seems obvious, but I can't tell you it's fact. Also note that it is still not that universally accepted. Wnt (talk) 23:52, 11 April 2017 (UTC)

At least partly because homocene isn't inclusive and would confuse many creationists? Sagittarian Milky Way (talk) 00:30, 12 April 2017 (UTC)

It might confuse evolutionists also, since Homo has been around much longer than the very late proposed start dates. I have to admit some skepticism because really the whole Holocene has been shaped by human activity, say the extinction of Megatherium. A variant of this is given in the "early anthropocene" version of events. There's a case to be made that the Holocene is just too short to chop off yet. Wnt (talk) 01:23, 12 April 2017 (UTC)

The term Homogenocene is also used for the same concept, the book 1493: Uncovering the New World Columbus Created uses that term when discussing the ecological changes associated with globalization. --Jayron32 10:47, 12 April 2017 (UTC)

April 12

If a person eats an apple seed, then will an apple seedling grow inside him?

What about a watermelon seed or an orange seed or a cherry pit? If an apple, watermelon, orange, or cherry is part of a person's last meal, then will the seed grow inside the person's dead body? 50.4.236.254 (talk) 00:12, 12 April 2017 (UTC)

The digestive system is a rather hostile place for seeds, and they normally would only spend a day or two in there anyway. I suppose a dead person might make it possible for the seed to grow a bit, if it made it past the acidic environment intact, but it would probably die before it made it out. Tree roots have grown into coffins and taken the shape of a corpse, as they grew through it and absorbed it. StuRat (talk) 00:15, 12 April 2017 (UTC)

Many seeds are designed to be defecated alive which is why they're placed at the center of delicious fruits. You're the seed's taxicab. Sagittarian Milky Way (talk) 00:25, 12 April 2017 (UTC)

A main problem there is that the seed basically contains cotyledons (two since apples are a eudicot). The seed splits open and delicate seed leaves come out on a short stalk. Depending on the size of the seed they may have stored energy resources to fall back on, but to grow out through a significant amount of flesh, perhaps clothing, let alone a coffin seems like too much to ask. The seed can certainly survive a short bath in acid, as pointed out above, so if the body is left on the surface it is possible that scavengers tear it apart and the seed drops on fertile ground. Wnt (talk) 01:28, 12 April 2017 (UTC)

A slight tangent, tomato seeds can certainly make it through the human gut and remain viable, as can be seen on railway tracks and in sewage plants. An example here. DuncanHill (talk) 01:32, 12 April 2017 (UTC)

A somewhat famous example would be Surtsey#Human impact Nil Einne (talk) 10:22, 12 April 2017 (UTC)

What nobody has clarified is that germination requires a variety of cues, most of which are not met inside the human digestive tract. SemanticMantis (talk) 19:18, 12 April 2017 (UTC)

I'm not sure this is the case of this scenario. The OP wants to know what if the person dies with the seed in the stomach, would the body decompose and leave a viable seed behind? At a first glance this look realistic to me. Seeds are resilient. Hofhof (talk) 22:51, 12 April 2017 (UTC)

It appears that placing apple seeds in a very cold environment (a fridge) for a prolonged period of time is required for them to germinate (e.g. (http://www.instructables.com/id/Growing-Apple-trees-from-seed/]). Basic plant biology is that, once germinated, light is required for growth to continue. So, I think the answer depends on several questions about the body and how it is treated after death. DrChrissy ^(talk) 23:41, 12 April 2017 (UTC)

Windows in highrise buildings

So, as I sit here with the sun going down over Anaheim, on the eleventh floor of a hotel, my windows are cracking and spluttering and creaking with the sun moving into obscuration. Are there any examples of high-rise buildings whose windows simply smashed with the temperature differentials, or did they get it right, straight off the bat, when making such shiny buildings? The Rambling Man (talk) 02:18, 12 April 2017 (UTC)

Breaking windows is nothing. A Twin Towers-ish sized building was built such that sub-hurricane wind would blow it over like a tree being cut down and this wasn't discovered till some undergraduate told the structural engineer. Its city was hours away from hurricane evacuation and repairs were only half done, the police had a plan to evacuate a mile wide circle of the New York City CBD so the building and any debris didn't fall on people and the existence of the poor design was kind of covered up for 20 years cause the hurricane veered away. Sagittarian Milky Way (talk) 07:56, 12 April 2017 (UTC)

The Hancock building in Boston springs to mind. 200_Clarendon_Street#Engineering_flaws. It famously had many of its windows replaced with plywood while engineers tried to figure out the problem.

Sadly, the Spontaneous glass breakage article does not have a list of notable historical examples. ApLundell (talk) 02:33, 12 April 2017 (UTC)

Indeed, nor does it have single reference. But thanks for your reply. The Rambling Man (talk) 02:49, 12 April 2017 (UTC)

Generally according to the Coefficient of thermal expansion (Glass 8.5, Iron or Steel 11.1, Concrete 12, Aluminum 23) neither the glass nor the height are cause but glass is the most brittle of the common building materials. So these tension brakes in glass are the result but the cause lies in the construction/design of the glass or window frames which are usually made of or themselves framed up in the other mentioned materials. In any good construction there are always spare spaces or gaps to cope with the differences of termal material expansions. So the closest conclusion likely is a bad construction/design. --Kharon (talk) 03:29, 12 April 2017 (UTC)

Yes, but that doesn't answer my question. The Rambling Man (talk) 03:34, 12 April 2017 (UTC)

It's very unlikely that a window pane would "simply smash" due to temperature difference. Sure, it might crack, probably at one corner, but shatter? No. Plenty of examples of high-rise panes falling around the world because of high winds, but we never know whether they cracked due to high temp before falling because the evidence is destroyed on impact. All googleable crack links that I've found are associated with high winds. Of course, any cracks that appear in panes are unlikely to be publicized, because of confidentiality clauses. They're not as publicly conspicuous as panes that actually fall. Akld guy (talk) 05:52, 12 April 2017 (UTC)

I'm not sure, but I remember reading something about the Seagram Building's windows breaking over time because of thermal expansion-related stresses (which is probably why it has two-colored (black and orange) glass now instead of the original all-black glass). 2601:646:8E01:7E0B:89D0:8453:4885:B526 (talk) 06:49, 12 April 2017 (UTC)

It's perhaps helpful to first get an idea of what we're talking about. [10] which seems to be from an expert suggests that failures due to thermal stress are normall called thermal? stress cracks. It does however suggest that care needs to be taken in diagnosis since cracks arising from thermal stresses after edge damage may look the same. [11] suggests (I think, didn't read that well, it's a very long story full of heart string elements) that a fallen window fragment from the CNA Center#History that killed someone was a result of stress cracking and failed remedial work. One thing does sources sort of suggest as does [12], is that actually determing the precise reason for failure can get complicated, particularly once lawyers get involved. Nil Einne (talk) 10:17, 12 April 2017 (UTC)

• This seems related to the current questions. --Jayron32 10:44, 12 April 2017 (UTC)

Thanks all. I'll look forward to tonight's sunset and another orchestra of bangs, cracks and pings, and not get too stressed about it! The Rambling Man (talk) 14:42, 12 April 2017 (UTC)

Anecdote: ever since we replaced the windows in our house with double-pane windows, they audibly make such noises at morning and evening. Our previous cheap single-pane windows didn't. I presume the double-pane construction amplifies the noises from thermal contraction/expansion, with the gas-filled cavity between the panes acting as a resonator. The hotel windows are likely double-pane, since places like hotels care about energy savings since it costs them a lot of money. If you don't have double-pane windows at home, you're presumably not used to the noises. --47.138.161.183 (talk) 05:23, 13 April 2017 (UTC)

How many trees need to be planted in order to reverse global climate change?

Yeah, I know carbon dioxide is a greenhouse gas. But trees need it to photosynthesize. So, how many trees and other types of flora need to be planted in order to reverse global climate change? Is it possible to fill up an entire city with lots and lots of indoor plants, with plants in every room and in every story? Can ballparks and farms and schoolyards become thick, dense forests? 50.4.236.254 (talk) 03:59, 12 April 2017 (UTC)

No, and for two reasons. First, there is an excess of about a trillion tonnes of carbon dioxide in the atmosphere as a result of industry [13]. Such a quantity contains a similar amount of carbon to the entire biomass of all living eukaryotes on the Earth (see Biomass (ecology) and be careful converting the numbers, as this article considers the mass of carbon alone, whereas my first link is talking about carbon dioxide). So you would have to plant so many trees you'd double the biomass of the planet, which is a pretty tall order. Second reason, though, is that trees only cause a net reduction of carbon dioxide in the atmosphere when they are growing. In a thriving ecosystem, plants are born, consume CO2, grow, and then die. When they die, their decomposition results in much of that carbon simply being returned to the atmosphere, unless it gets sequestered. You'd eventually reach the Earth's capacity for plants, and then would be helpless to get rid of any new carbon dioxide being released to the atmosphere from fossil fuels. Now, if your plan was to grow an absurd number of trees, then cut them down and store them in such a way that their carbon never re-entered the carbon cycle, that would theoretically work. As you can read at the sequestration article I linked, this is something people have been thinking about for a very long time. Someguy1221 (talk) 04:08, 12 April 2017 (UTC)

But fossil fuels will eventually be depleted. So, will that put a limit in the amount of carbon dioxide in the atmosphere? 50.4.236.254 (talk) 04:17, 12 April 2017 (UTC)

It depends (as always ;-). Putting on my theoretical logician's hat, yes, the amount of carbon and oxygen on Earth and in its future light cone is finite (assuming current models of the universe), so there is an upper limit on the CO2 in the atmosphere (and there are other such theoretical arguments - if you add too much CO2, the Earth will turn into a black hole), but these are not very relevant, because the upper limits are gross overestimates of what humans (as a species) are likely to experience. Going back to human time scales, this paper in Nature Climate Change claims that five trillion tonnes of carbon ("5 exagram") is an accepted lower estimate for economically feasible reserves. Burning those under a "business as usual" scenario might lead to a temperature increase of about 10K by 2300. I'm not a climate scientist, but if they say 5egC is an accepted lower bound, the real value might be within one order of magnitude, so maybe 50egC. That would set a an upper bound under realistic assumptions. Now, going back into insufferable "knows-it-all"-mode, most of the carbon on (as opposed to in) Earth is ultimately released from carbon-bearing rocks, and that process continues. So even if we burn all current fossil fuels, over geologic periods, more may form, and I think that in the long run (many many millions of years) the amount of carbon available on and near the surface will very slowly increase. --Stephan Schulz (talk) 07:39, 12 April 2017 (UTC)

I read a 40 year old tree may arrogate roughly 1 ton of carbon dioxide. So we would have to plant 1 trillion trees, according Someguy1221's reference about the exess of carbon dioxide. Its most likely less because, as these trees produce an exess of oxygene, our atmosphere would expand and thus in some part get lost into space in addition to changing the mixture by filling it up with oxygene.

Unfortunately there is not enough suitable land on earth to grow that many additional(!!) trees and it is needed for farming at the same time. Also even if it would be achievable to plant that many trees, it would take 40 years to let them grow enough to bind all the exess co2 into biomass (wood) and ofcourse we would have to stop burning stuff aka produce more and more CO2, which already seems impossible to get done on this planet, nomatter it seems to be the easier part of such a plan. --Kharon (talk) 10:48, 12 April 2017 (UTC)

(1) as these trees produce an [excess] of [oxygen], our atmosphere would expand and thus in some part get lost - but they also "destroy" some carbon dioxide, so the net effect on the total atmospheric volume that gets out in space is not as obvious as your reasoning makes it seem. (2) there is not enough suitable land on earth to grow [1 trillion] [additional] trees - need some numbers on that: assuming 1 to 100 m^2 are needed for each tree, the area is 10^12 to 10^14 m^2. Earth physical characteristics tables says the emerged landmass on Earth is 149.10^12 m^2, so an argument about the area is not sufficient. Of course, it will only happen if we assume away economics (humans suddenly transformed into a slave species of treeplanters) and physics (humans irrigate the whole Sahara and design a giant greenhouse for Antartica), so it is not going to happen.

Feynman Lectures. Lecture 52. Ch.52-4, Ch.52-5, Ch.52-6 Reflection symmetry

...

Now we have agreed to represent the mirror rotation by the same rule, it is a “vector” which, on reflection, does not change about as the polar vector does, but is reversed relative to the polar vectors and to the geometry of the space; such a vector is called an axial vector.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

...

Now if the law of reflection symmetry is right in physics, then it must be true that the equations must be so designed that if we change the sign of each axial vector and each cross-product of vectors, which would be what corresponds to reflection, nothing will happen.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

I don't understand why does Feynman in reflected world use right-hand screw rule but not left-hand screw (e.g. Fig. 52–3). And why do both the result and the vector product change sign in reflected world? It contradicts first statement. Username160611000000 (talk) 10:56, 12 April 2017 (UTC)

Are humans only concerned about climate change because they know they will be affected negatively?

While it is true that many species of flora and fauna are dying, other species seem to be thriving... just not in a way that would be favorable to humans. Many bacterial species may be completely harmless for the average human with a healthy immune system, but they can easily attack an immunocompromised human, the very young, the very old, and the unborn of pregnant women. Plants that humans don't want are interpreted as "weeds", and animals that humans don't want are interpreted as "pests", and those must be exterminated or removed from the food supply. But plants, animals, and bacteria can become resistant to the chemical treatments, so a new chemical must be developed. In the end, isn't nature winning, and humans are always struggling to keep alive and their populations up? 50.4.236.254 (talk) 13:09, 12 April 2017 (UTC)

There are lots of organizations around for conserving plants and animals that some people would consider pests. So the answer to you is no. Try thinking for yourself of things against something you think as well as things which confirm it, well anyway try doing that if you aren't interested in going into religion or politics ;-). Dmcq (talk) 13:55, 12 April 2017 (UTC)

But wouldn't elimination of the entire human species be the ultimate way of conservation of other species? 50.4.236.254 (talk) 14:02, 12 April 2017 (UTC)

Only ones that can survive in the new climate. In the past, sudden climate changes have resulted in all kinds of extinctions. Every schoolchild knows about the Cretaceous–Paleogene_extinction_event that killed all of the dinosaurs (but happily, not all the birds.), but there have been others. The Permian–Triassic extinction event was pretty devastating. With the benefit of hind-site we can say these were all "good" because they set into motion the events that eventually birthed our species, but from the perspective of the species that were killed, or the species that might have evolved from them but never got the chances, it was a disaster of the highest possible order. ApLundell (talk) 14:36, 12 April 2017 (UTC)

Even if that is true, it's irrelevant. You seem to be thinking people can only have one goal and must do everything possible to achieve it. In reality plenty of people may have many different genuine goals and these can sometimes come into conflict. There are plenty of people who may genuinely support conservation. The vast majority of them by far, for a variety of reasons, don't support the elimination of the human species. A larger but still small number may support a drastic reduction of the human population numbers (in a completely voluntary fashion). More commonly conflict comes in other ways. For example, when is the development of land or the mining of resources acceptable despite a negative effect on conservation. Or predator-human interactions. There is perhaps legitimate question over whether people have a tendency to push others to conserve but then fail to do so themselves (particularly in the developing-developed world context). And also even where people do conserve, how reasonable it is to demand others conserve at the possible expense of their development when you've already developed at the expense of conservation. But an argument people need to support the elimination of the human species if they are genuine about conservation doesn't tend to get much traction. Nil Einne (talk) 09:51, 13 April 2017 (UTC)

"Only"? No. But that's a big part of it. Effects_of_global_warming_on_humans could be pretty devastating to our civilization. ApLundell (talk) 14:36, 12 April 2017 (UTC)

So, climate change is only devastating to species who are adapted in the former environment and rewarding to species who are adapted in the new environment, especially in the environment devoid of the previous species, including humans, which means how "good" or "bad" something is depends on what point-of-view you are looking at. So, if humans don't do any sort of "environmental protection", then they will be essentially living in their own filth and die. Bad for humans, great for the microbes or anything that can live at the expense of humanity. 50.4.236.254 (talk) 15:15, 12 April 2017 (UTC)

Sure, if you want to look at the "big picture".

If you want to look at the really big picture, Earth life in general is doomed unless a spacefaring species comes along in the next five billion years. (Sun#Life phases)

ApLundell (talk) 16:12, 12 April 2017 (UTC)

We might only be a hundred years from being able to terraform planets around other suns and put humans there using robots for the spacefaring, we already have most of the required basic technology. People doing spacefaring though would take a lot more work. Dmcq (talk) 20:31, 12 April 2017 (UTC)

I guess that's kind of my point. This is veering into soapboxing and theorizing, but briefly, if the question is "does it matter to other Earth life if humanity goes extinct?", then I think part of the answer is that deap-space spacefaring is required for super-long-term survival. It's tough to say if humanity is earth life's best chance of that, or if something better might develop after we're gone. Five billion years is a long time. Perhaps it's vanity to think our extinction means no more spaceships.

ApLundell (talk) 21:41, 12 April 2017 (UTC)

We'll be able to do that soon enough anyway. What people will do is another question though. And I suppose it is life, but that view of life is like a child bashing things to make noise compared to music. The glory of life on earth is being pushed into pitiful enclaves on the edge of our civilization. Dmcq (talk) 09:16, 13 April 2017 (UTC)

Clams, Oysters, Pearls in Freshwater ??

Are there any types of clam or oyster that lives in freshwater, and can pearls from such living organisms appear in freshwater? Most likely not, I should think...

Well, I found one, at least. The Freshwater Mollusc — Preceding unsigned comment added by 84.211.184.66 (talk) 15:04, 12 April 2017 (UTC)

84.211.184.66 (talk) 14:59, 12 April 2017 (UTC)

In the U.S., one of the largest cultured pearl regions is Tennessee where the Megalonaias nervosa or "Washboard Mussel" is farmed for pearl cultivation. See here for example. Wikipedia has articles on Cultured freshwater pearls. The Freshwater pearl mussel is a different species as well. --Jayron32 16:06, 12 April 2017 (UTC)

Thanks, Jayron. Much appreciated. 84.211.184.66 (talk) 16:27, 12 April 2017 (UTC)

Distance estimate to the outside objects in driverless cars

I wonder how they do it? Do they use lasers or what? It seems lasers are ill suited for this. I also wonder if they measure the distance or estimate the distance. There is a difference. Any ideas? Thanks, - --AboutFace 22 (talk) 15:00, 12 April 2017 (UTC)

Many techniques exist; the most famous robot cars use LIDAR and other sensors, and then use complicated software algorithms to combine data (sensor fusion) and make high-level planning decisions.

Here's a great review of Stanley, the original 2005 automobile robot. They used a LIDAR to create a point cloud model of the surroundings, and had a special algorithm to estimate obstacle positions from point cloud data. They also used cameras and RADARs. That technology is decades old - newer cars use lots of other hardware and software methods - but you might as well start with the basics...

Nimur (talk) 15:35, 12 April 2017 (UTC)

• Another link: [14] (see in particular the section behind "goal #2"). Tigraan^{Click here to contact me} 16:43, 12 April 2017 (UTC)

Thank you. Helpful. --AboutFace 22 (talk) 20:22, 12 April 2017 (UTC)

This story shows an animation which illustrates the information a Google self-driving car has about other road users - a world build up from the information fusion of its various sensors. It's a pretty rich picture - certainly better than the mental model a person would have of the same situation. The animation also shows the limits of the technology - look at the vehicles in the opposite lane: as they pass through the intersection, where they are densely occluded by other vehicles, the Google car has difficulty tracking the individual cars, so they flicker about. One goal self-driving vehicle makers have for the future is "swarming", where a given vehicle can also use sensor information from other vehicles to built its unified world view. -- Finlay McWalter··–·Talk 13:33, 13 April 2017 (UTC)

Could future fossil fuels be dying now?

Where might these plants be? (sentients would have to not harvest them while they're still peat or pre-oil, dismantle the Earth in a technological singularity or otherwise disturb them for millions of years) Sagittarian Milky Way (talk) 17:15, 12 April 2017 (UTC)

Oil mostly comes from water based microorganisms. So presumably they're still in the ocean doing whatever they do. Petroleum#Formation

Coal is a tricker question. It's believed to come from forests and land-based plants that become buried. Coal#Formation

But when we think about the time frames involved I don't think we're necessarily talking about a continual process. Perhaps a small forest gets buried every couple centuries. ApLundell (talk) 17:53, 12 April 2017 (UTC)

• Modern geologists would all broadly agree the answer to the question is an unqualified "yes". Starting with James Hutton and Charles Lyell in the early 1800s, the principle of uniformitarianism has been a central tenet of geology for almost 2 centuries; the notion that processes that are going on now have been going on in broadly the same manner for a few billion years, and will continue to happen under roughly the same mechanisms for the forseeable future. We have no reason to suppose that the principles of geology are expected to change in the future, or have stopped working. --Jayron32 18:28, 12 April 2017 (UTC)

So there's no currently non-existing requirement like oil needs calcite seas to form or only certain configurations of continents can cause current microorganisms to be crushed into oil or anything like that? Sagittarian Milky Way (talk) 22:42, 12 April 2017 (UTC)

Right, fossil fuels are forming even as we speak -- only very slowly! 2601:646:8E01:7E0B:4C74:BE2F:701E:8F7E (talk) 04:40, 13 April 2017 (UTC)

The cycles that led to the formation of fossil fuels in the past are expected to repeat in the future as well. Uniformitarianism isn't an expectation that the earth remain identical, merely that for any arbitrarily long time period, there is no reason to presume any past process would not have similar conditions in the future which could recreate it. --Jayron32 14:54, 13 April 2017 (UTC)

Coal is the exception here. Coal formed on Earth after the first trees evolved. It took a very long time before microbes evolved the capability to break down wood from dead trees. Huge amounts of dead trees from the Carboniferous era were converted to coal as a result. Count Iblis (talk) 19:47, 12 April 2017 (UTC)

Actually, coal formed under anaerobic conditions which would preclude microbial decomposition even today -- so coal could still form today under the right conditions, just not on such a yuge scale. 2601:646:8E01:7E0B:4C74:BE2F:701E:8F7E (talk) 04:40, 13 April 2017 (UTC)

What was the soil profile like at the end of the Carboniferous? Dead trees merging into lignite or something over hundreds of meters? Sagittarian Milky Way (talk) 20:52, 12 April 2017 (UTC)

A paradise for all those people who today pollute the air with their wood stoves. Count Iblis (talk) 21:11, 12 April 2017 (UTC)

Unless we get to something like the world of Soylent Green where nothing and nobody will have the chance to become a fossil. ;-) Dmcq (talk) 20:14, 12 April 2017 (UTC)

Peat is itself a fuel, and was used as such long before lignite or coal were perceived as resources. I am less clear on whether dried sphagnum moss (before becoming compacted) was or is used as a fuel in any significant amount. [15] There are indeed ecological issues - peat moss bogs straddle the line between a renewable ecosystem and a fossil fuel. [16] Wnt (talk) 11:33, 13 April 2017 (UTC)

It's all about supply rate compared to extraction rate. Sustainability essentially means that the extraction rate is at or below the supply rate. Oil is renewable if you're willing to wait 65 million* years for the next batch (*made up). Timber is renewable if you're willing to wait a few decades. Peat is formed more slowly than trees grow. Most of it formed around 4,000-8,000 years ago, but some is much older. We have lots of info on how many board feet we can sustainably harvest from a Loblolly pine plantation, but I am not aware of any comparable work for peat (or oil!). There is a decent amount of research in to accurately dating peat deposits [17], and so presumably there are some people working on establishing site-based estimates of supply rate. This [18] Slate article has a fairly credible person saying that we'll run out of peat in a bout 2k years if use stays constant, but would never run out if peat were only used for Scotch production. Of course, use is not constant, and in fact more peat is used each year, as its use as fuel [19] becomes more attractive. SemanticMantis (talk) 16:10, 13 April 2017 (UTC)

April 13

Feynman Lectures. Lecture 52. Ch.52-7

...

There are a lot of other features that were predicted. For example, it turns out that the spin, the angular momentum, of the cobalt nucleus before disintegration is 5 units of ℏ, and after disintegration it is 4 units. The electron carries spin angular momentum, and there is also a neutrino involved. It is easy to see from this that the electron must carry its spin angular momentum aligned along its direction of motion, the neutrino likewise. So it looks as though the electron is spinning to the left, and that was also checked. In fact, it was checked right here at Caltech by Boehm and Wapstra, that the electrons spin mostly to the left. (There were some other experiments that gave the opposite answer, but they were wrong!)

The next problem, of course, was to find the law of the failure of parity conservation. What is the rule that tells us how strong the failure is going to be? The rule is this: it occurs only in these very slow reactions, called weak decays, and when it occurs, the rule is that the particles which carry spin, like the electron, neutrino, and so on, come out with a spin tending to the left. That is a lopsided rule; it connects a polar vector velocity and an axial vector angular momentum, and says that the angular momentum is more likely to be opposite to the velocity than along it.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

I have a question about the spin and the magnetic field vector. First, according to the description of the experiment the cobalt-60 nuclei were put in upward magnetic field causing the nuclei to line up and orient their spin vector upward also (rotation to the right png) . Nucleus is positive charged object, when it rotates this produces the small circle currents and magnetic field. Before the decay, nucleus spin = 5. After decay, the nucleus spin = 4. Electron spin = 1/2, neutrino spin = 1/2. Total angular momentum must be 5, so electron must rotate to the right also. If it rotates to the right it acquires magnetic field directed downward, because of negative current. What happens next (will electron repel by external field or will it perform the spin flip)? How did Feynman get electrons rotating to the left? Username160611000000 (talk) 19:47, 12 April 2018 (UTC)

Feynman is glossing over a lot of very difficult quantum mechanical physics, because the audience for this lecture had not yet studied it.

You get the spin of the electron by applying the angular momentum operator to the wave function for the system. This is not an easy task and it is not conducive to a short-form explanation.

@Nimur: Feynman writes It is easy to see from this that the electron must carry its spin angular momentum aligned along its direction of motion, the neutrino likewise. If it is easy, I think it can be explained using classical mechanics (with some warnings). Here [20] is written Particles with spin can possess a magnetic dipole moment, just like a rotating electrically charged body in classical electrodynamics. Username160611000000 (talk) 03:29, 13 April 2017 (UTC)

There is always a well-known solution to every human problem — neat, plausible, and wrong. - H. L. Mencken Tigraan^{Click here to contact me} 11:46, 13 April 2017 (UTC)

Here's a link to Griffiths' Quantum Mechanics text book. If you buy it online, pay special attention to the author's advice about retailers who sell older versions, and to his published errata.

One typically will use Griffiths' book after completing several years of advanced study of quantum mechanics at and beyond the university level.

Nimur (talk) 20:44, 12 April 2017 (UTC)

Thank you for the suggestion, but I have neither money nor time for other textbooks. Feynman Lectures contain quantum mechanics. I like Lectures and I will continue to read them.Username160611000000 (talk) 03:29, 13 April 2017 (UTC)

As for what happens next, unless you have a large apparatus or very strong field, the electron exits the external field essentially unchanged because it is moving at near-relativistic speeds. Cobalt-60 decay liberates 0.3 MeV in its most common beta mode, and a significant chunk of that goes into accelerating the electron. To the extent that it does interact with the field, the electric charge and high velocity is more important than the magnetic moment in determining the change in the motion of the electron in the magnetic field. The spin flip timescale will depend on details of the magnetic fields but anything from roughly < 1 ns to 10s of microseconds could occur depending on the nature of the apparatus (strength of field, shape of field, static/pulsed/oscillating, etc.). Dragons flight (talk) 14:02, 13 April 2017 (UTC)

Krane, Introductory Nuclear Physics, works this example problem for the cobalt beta decay and studies the apparent parity violation. Just as Feynman says, this is an easy problem - it's in an introductory textbook. The worked math is several pages long and is preceded by three hundred pages of preparatory material. Nimur (talk) 14:20, 13 April 2017 (UTC)

Somebody ripped off somebody here: the Feyman lectures go through the exact same examples - including the Wu experiment that Krane cites precisely (Phys. Rev. 105, 1413, 1957), and the Martian handshake analogy that Krane cites precisely (The Ambidextrous Universe, 1964), and attributes to Martin Gardner. So - the "Feynman lecture" appears to be the contents of Krane, Chapter 9, only presented in a sloppier and less physically-accurate fashion and without citing sources. Have I mentioned before that the "Feynman Lectures" were not actually written by Feynman, but were in fact "published essentially because an international publisher issued an ultimatum intending to republish those copyrighted works without permission"? Oh, I did mention that, and I even cited sources! Nimur (talk) 14:31, 13 April 2017 (UTC)

Cats and dogs

Which breeds of dogs are the most cat-friendly (or maybe I should say "cat-tolerant" -- I don't think any of them are actually cat-friendly in the strict sense) and which are the most cat-unfriendly? And on this scale, where do bulldogs fit in? 2601:646:8E01:7E0B:4C74:BE2F:701E:8F7E (talk) 06:34, 13 April 2017 (UTC)

Anecdotally, my golden retriever thinks cats essentially are dogs. She is interested in them and does her normal "play with me" motions that she uses when approaching a new dog. Cats generally respond with a range of indifference, fear, or aggression, and mostly just want her to leave them alone. At least in her case, I would say she is quite friendly towards cats, though we've yet to meet a cat that is interested in being friendly with her. [And I keep worrying that she is going to approach the wrong cat some day and get her face scratched up]. So, depending on what you are looking for, it may depend not only on the type and personality of the dog but also how dog-friendly (or dog-tolerant) the cat happens to be. I doubt there are any absolutes when it comes to this, as it will depend both the personalities of the particular animals and their life experiences. A dog/cat that has had negative experiences with other cat/dog is unlikely to be friendly to a new one, so if possible it is probably better to introduce a new animal when it is young and do so gradually under controlled conditions. For example, start by having them in separate areas where they can see each other but not interact. After a while, when they are calm with that situation, gradually increase the contact in ways that aim to be as unthreatening and calm as possible. Dragons flight (talk) 13:28, 13 April 2017 (UTC)

Google "cat friendly dogs" and you'll find lots of info. Richerman (talk) 14:32, 13 April 2017 (UTC)

You might choose a small breed of dog, that way they will have a "balance of power", so the dog won't attack, partially out of fear of reprisals. Raising them together since puppies/kittens is a good way to establish a bond. Of course, they need to be the same age to do this. StuRat (talk) 15:41, 13 April 2017 (UTC)

Dog breeds that have neotenic traits such as floppy ears, curly tails, piebald coloration, shortened vertebra, large eyes, rounded forehead, large ears, and shortened muzzle, as exemplified by Cavalier King Charles Spaniel may be perceived by a cat as unaggressive. Terriers, sighthounds and herding breeds are most likely to initiate a confrontation. Click for advice on introducing dogs to cats. Cats operate with triple choice fight-or-flee-or-pointedly ignore agendas that are incrutable. Scratches to the face are the deterrance to any dog from a wary mother cat with kittens; a serious attack by a cat will be from ambush (usually unsuccesful and often aborted) to grasp and hold the dog by the neck. Blooteuth (talk) 16:50, 13 April 2017 (UTC)

Laser pointer reflected light harmful to eyes in close proximity?

At a community workshop I sometimes use is a laser cutter and it has what appears to be a red laser pointer used to indicate the location of cuts (the cutting laser is infra-red and can't be seen). I was staring intently at the red dot produced by the laser pointer and a fellow workshop member told me to avoid damaging my eyes by limiting my time spent looking closely at this red dot. In my opinion he misunderstands one of the warning labels talking about scattered radiation which I think is a reference to the 40 W IR laser and does not apply to the red indicator. Obviously a laser pointer used in a presentation presents less harm because the meters of distance mean large dissipation. I'd say that if the manufacturer used a laser pointer harmful to eyes in close proximity they designed a stupid indicator system. --129.215.47.59 (talk) 14:09, 13 April 2017 (UTC)

Jeez. Don't people care about themselves. Are there written instructions for its use? Are you wearing the proper protective goggles for the machine? Dmcq (talk) 14:56, 13 April 2017 (UTC)

There are no goggles; the machine has a lifting cover which is placed down when cutting so the IR laser is not an issue. My question is about the visible laser indicator. --129.215.47.59 (talk) 16:08, 13 April 2017 (UTC)

It depends on the Laser safety#Classification of the red indicator laser. I checked a few saws with laser guides, and they were all Class IIIa (<5 mW maximum). DMacks (talk) 15:05, 13 April 2017 (UTC)

Rather than have us speculate irresponsibly about a system we have never seen, it would be better to tell us precisely what class laser is used and/or what warning labels are present. This information should be present on the device and its accompanying documentation. Dragons flight (talk) 15:28, 13 April 2017 (UTC)

I've sent an e-mail to the manufacturer of the machine to ask them about it. 129.215.47.59 (talk) 16:07, 13 April 2017 (UTC)

I would say it could cause eye damage, so why risk it ? Avoid looking directly at it for extended periods. (If you look at a white object right after you will probably see a green dot.) Does anybody make goggles with a darkened spot in the center, just for this case (it could even specifically block only red) ? StuRat (talk) 15:35, 13 April 2017 (UTC)

It's not like I'm looking at it to have a good time! It's kind of necessary when trying to line up material to be cut. I guess a pair of any old sunglasses will at least reduce the amount of radiation experienced. I'd rather the manufacturer simply distributed machines with indicator lasers set to an appropriate intensity (I just told them so in an e-mail). --129.215.47.59 (talk) 16:07, 13 April 2017 (UTC)

Maybe you can tape some red plastic sheets to your safety goggle to reduce the amount of red getting through, without impairing your view of the work area. Or, if you do just use regular dark glasses, be sure to increase the general light level. StuRat (talk) 17:23, 13 April 2017 (UTC)

Adhara (second brightest star of Canis Major)

1. Why's it so obscure in the US and presumably Europe for something magnitude 1.50 and only -28°58'?

2. What's the millennium when it straddles the 1st magnitude/2nd magnitude border? Sagittarian Milky Way (talk) 15:13, 13 April 2017 (UTC)